U.S. patent application number 12/594997 was filed with the patent office on 2011-08-18 for pulverized coal burning boiler.
This patent application is currently assigned to Babcock-Hitachi Kabushiki Kaisha. Invention is credited to Seishi Miyake, Noriyuki Ohyatsu, Hitoshi Okimura, Katsumi Shimohira, Hidehisa Yoshizako.
Application Number | 20110197831 12/594997 |
Document ID | / |
Family ID | 39925510 |
Filed Date | 2011-08-18 |
United States Patent
Application |
20110197831 |
Kind Code |
A1 |
Ohyatsu; Noriyuki ; et
al. |
August 18, 2011 |
Pulverized Coal Burning Boiler
Abstract
A pulverized coal burning boiler is provided, which reduces an
air-excess ratio thereby to reduce the emission of unburned
contents such as CO. The pulverized coal burning boiler includes a
pulverized coal feed measuring device for measuring the feeding
rates of the pulverized coal to be conveyed through coal feeding
pipes, individually, and a control device for calculating the
burning air feeding rates to match the pulverized coal feeding
rates thereby to send a control command signal to burning air feed
adjusting device, so that a burner air ratio set by a burner air
ratio setting device may be kept on the basis of both the
pulverized coal feeding rate, which is measured by the pulverized
coal feed measuring device, and the burning air feeding rate, which
is measured by the burning air feeding rate measuring device and
fed to a pulverized coal burner connected to the coal feeding
pipes.
Inventors: |
Ohyatsu; Noriyuki;
(Kure-shi, JP) ; Yoshizako; Hidehisa; (Kure-shi,
JP) ; Shimohira; Katsumi; (Kure-shi, JP) ;
Okimura; Hitoshi; (Kure-shi, JP) ; Miyake;
Seishi; (Kure-shi, JP) |
Assignee: |
Babcock-Hitachi Kabushiki
Kaisha
Chiyoda-ku, Tokyo
JP
|
Family ID: |
39925510 |
Appl. No.: |
12/594997 |
Filed: |
April 11, 2008 |
PCT Filed: |
April 11, 2008 |
PCT NO: |
PCT/JP2008/057184 |
371 Date: |
March 25, 2010 |
Current U.S.
Class: |
122/6R ;
110/186 |
Current CPC
Class: |
G01F 1/712 20130101;
G01F 1/666 20130101; G01P 5/22 20130101; F23N 1/022 20130101; F22B
35/00 20130101; G01F 1/74 20130101; F23N 2241/10 20200101; F23D
1/00 20130101; G01F 1/7046 20130101; F23N 2239/02 20200101 |
Class at
Publication: |
122/6.R ;
110/186 |
International
Class: |
F22B 33/00 20060101
F22B033/00; F23N 5/00 20060101 F23N005/00; F23K 1/00 20060101
F23K001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 13, 2007 |
JP |
2007-105973 |
Claims
1. A pulverized coal burning boiler comprising: milling means which
generate pulverized coal by milling supplied coal; coal feeding
pipes which are arranged in such a manner that a plurality of coal
feeding pipes are connected to one milling means and through which
the pulverized coal is airflow-conveyed by primary air; pulverized
coal burners which are connected to front end sides of the coal
feeding pipes respectively and which have pulverized coal nozzles
disposed so as to face into a furnace; combustion air supply means
which supply combustion air other than the primary air to the
pulverized coal burners individually; combustion air supply amount
measuring means which measure the supply amounts of the combustion
air supplied by the combustion air supply means individually;
combustion air supply amount adjusting means which adjust the
supply amounts of the combustion air; and burner air ratio setting
means which set burner air ratios; wherein pulverized coal milled
and generated by the milling means is distributed to the coal
feeding pipes, jetted from the pulverized coal nozzles into the
furnace and burned under supply of the combustion air; the
pulverized coal burning boiler characterized in that there are
provided: pulverized coal supply amount measuring means which
individually measure the supply amounts of pulverized coal conveyed
through the coal feeding pipes respectively; and air supply amount
control means which calculate the supply amounts of combustion air
corresponding to the supply amounts of pulverized coal based on the
supply amounts of pulverized coal measured by the pulverized coal
supply amount measuring means and the supply amounts of combustion
air supplied to the pulverized coal burners connected to the coal
feeding pipes and measured by the combustion air supply amount
measuring means and send control command signals to the combustion
air supply amount adjusting means so that burner air ratios set by
the burner air ratio setting means can be kept.
2. A pulverized coal burning boiler according to claim 1,
characterized in that the pulverized coal supply amount measuring
means are attached to the coal feeding pipes of pulverized coal
burners or pulverized coal burner groups high in unburned component
reducing effect in the pulverized coal burners so that the supply
amounts of combustion air are adjusted individually.
3. A pulverized coal burning boiler according to claim 1,
characterized in that the pulverized coal burners are disposed as
several stages for the furnace and the pulverized coal supply
amount measuring means are attached to the coal feeding pipes of
the pulverized coal burners except the pulverized coal burners
disposed on the lower stage so that the supply amounts of
combustion air are adjusted individually.
4. A pulverized coal burning boiler according to claim 1,
characterized in that the pulverized coal burners are disposed as
several stages for the furnace and the pulverized coal supply
amount measuring means are attached to the coal feeding pipes of
the pulverized coal burners disposed on at least the uppermost
stage so that the supply amounts of combustion air are adjusted
individually.
5. A pulverized coal burning boiler according to claim 1,
characterized in that a plurality of the pulverized coal burners
are disposed side by side to form a burner stage, a plurality of
after air ports are disposed side by side on a downstream side of
the burner stage in an exhaust gas flow direction, the amount of
combustion air supplied to at least one of the pulverized coal
burners is adjusted, and the amount of combustion air supplied to
an after air port near to flame formed by the pulverized coal
burner is adjusted.
6. A pulverized coal burning boiler according to claim 5,
characterized in that the plurality of pulverized coal burners and
the plurality of after air ports are disposed so as to be separated
into a vessel front and a vessel back of a furnace, when the amount
of combustion air supplied to the pulverized coal burners disposed
in the vessel front is adjusted, the amount of combustion air
supplied to the after air ports disposed in the vessel back is
adjusted, and when the amount of combustion air supplied to the
pulverized coal burners disposed in the vessel back is adjusted,
the amount of combustion air supplied to the after air ports
disposed in the vessel front is adjusted.
7. A pulverized coal burning boiler according to claim 1,
characterized in that a plurality of after air ports are
dispersively disposed on a downstream side of the pulverized coal
burners in an exhaust gas flow direction, concentration
distribution detection means for detecting a distribution of oxygen
concentrations or CO concentrations in exhaust gas is provided in a
flue on a downstream side of the after air ports in an exhaust gas
flow direction, and while the amount of combustion air supplied to
the pulverized coal burners is adjusted, the amount of combustion
air supplied to the after air ports corresponding to a low oxygen
concentration or high CO concentration region detected by the
concentration distribution detection means is increased.
8. A pulverized coal burning boiler according to claim 5,
characterized in that the pulverized coal burners are disposed as a
plurality of stages for a furnace, the pulverized coal burners to
adjust the supply amount of combustion air are pulverized coal
burners disposed on the uppermost stage.
9. A pulverized coal burning boiler according to claim 1,
characterized in that each of the pulverized coal supply amount
measuring means has a microwave resonance pipe through which a
mixed fluid of the pulverized coal and primary air circulates, and
a microwave transmitter and a microwave receiver which are disposed
in the microwave resonance pipe so as to be at a predetermined
distance from each other along a direction of a flow of the mixed
fluid, and the microwave transmitter transmits microwaves to the
microwave receiver to measure a resonance frequency of the
microwave resonance pipe to thereby measure the supply amount of
the pulverized coal based on the resonance frequency.
10. A pulverized coal burning boiler according to claim 9,
characterized in that a part of each of the coal feeding pipes is
used as the microwave resonance pipe.
11. A pulverized coal burning boiler according to claim 9,
characterized in that the microwave transmitter and the microwave
receiver protrude into the microwave resonance pipe, and a knocking
member is disposed on an upstream side of the microwave transmitter
in the microwave resonance pipe to unravel a flow of the pulverized
coal condensed like a string in the microwave resonance pipe.
12. A pulverized coal burning boiler according to claim 1,
characterized in that the pulverized coal supply amount measuring
means has a first charge sensor and a second charge sensor which
are disposed in each of the coal feeding pipes so as to be at a
predetermined distance from each other along an axial direction of
the coal feeding pipe, and movement of electrostatic charges
resulting from passage of pulverized coal in the coal feeding pipe
is measured by the two charge sensors so that the supply amount of
pulverized coal is measured based on the movement of electrostatic
charges measured by the two charge sensors.
13. A pulverized coal burning boiler according to claim 12,
characterized in that the first charge sensor and the second charge
sensor are circular and fluid guiding means is provided on an
upstream side of the charge sensors to collect pulverized coal and
pour the collected pulverized coal into a central portion side of
the coal feeding pipe to thereby reduce the amount of pulverized
coal passing through an inner circumferential side of the charge
sensors.
14. A pulverized coal burning boiler provided with a first reheater
system and a second reheater system disposed side by side so that
supplied steam circulates while forked into the first and second
reheater systems, characterized in that there are provided:
reheating steam distributing amount adjusting means which adjust
the amounts of steam distributed to the first and second reheater
systems; reheater outlet steam temperature measuring means which
measure reheater outlet steam temperatures of the first and second
reheater systems; and reheating steam distributing amount control
means which send control command signals to the reheating steam
distributing amount adjusting means to eliminate the temperature
difference based on a deviation between the reheater outlet steam
temperatures measured by the reheater outlet steam temperature
measuring means.
15. A pulverized coal burning boiler comprising: milling means
which generate pulverized coal by milling supplied coal; coal
feeding pipes which are arranged in such a manner that a plurality
of coal feeding pipes are connected to one milling means and
through which the pulverized coal is airflow-conveyed by primary
air; pulverized coal burners which are connected to front end sides
of the coal feeding pipes respectively and which have pulverized
coal nozzles disposed so as to face into a furnace; combustion air
supply means which supply combustion air other than the primary air
to the pulverized coal burners individually; combustion air supply
amount measuring means which measure the supply amounts of the
combustion air supplied by the combustion air supply means
individually; combustion air supply amount adjusting means which
adjust the supply amounts of the combustion air; burner air ratio
setting means which set burner air ratios; and a reheater which has
a first reheater system and a second reheater system disposed side
by side; wherein pulverized coal milled and generated by the
milling means is distributed to the coal feeding pipes, jetted from
the pulverized coal nozzles into the furnace and burned under
supply of the combustion air; and steam from a high-pressure
turbine is heated by the reheater and supplied to middle-pressure
and low-pressure turbines; the pulverized coal burning boiler
characterized in that there are provided: pulverized coal supply
amount measuring means which individually measure the supply
amounts of pulverized coal conveyed through the coal feeding pipes
respectively; air supply amount control means which calculate the
supply amounts of combustion air corresponding to the supply
amounts of pulverized coal based on the supply amounts of
pulverized coal measured by the pulverized coal supply amount
measuring means and the supply amounts of combustion air supplied
to the pulverized coal burners connected to the coal feeding pipes
and measured by the combustion air supply amount measuring means
and send control command signals to the combustion air supply
amount adjusting means so that burner air ratios set by the burner
air ratio setting means can be kept; reheating steam distributing
amount adjusting means which adjust the amounts of steam
distributed to the first and second reheater systems; reheater
outlet steam temperature measuring means which measure reheater
outlet steam temperatures of the first and second reheater systems;
and reheating steam distributing amount control means which send
control command signals to the reheating steam distributing amount
adjusting means to eliminate the temperature difference based on a
deviation between the reheater outlet steam temperatures measured
by the reheater outlet steam temperature measuring means.
16. A pulverized coal burning boiler according to claim 14,
characterized in that there is provided pulverized coal supply
amount deviation calculating means which calculates a deviation
between the amount of pulverized coal supplied to pulverized coal
burners of a group heating the first reheater system and the amount
of pulverized coal supplied to pulverized coal burners of a group
heating the second reheater system, and control command signals are
output from the reheating steam distributing amount control means
to the reheating steam distributing amount adjusting means based on
the deviation between the reheater outlet steam temperatures
measured by the reheater outlet steam temperature measuring means
and the deviation between the supply amounts of pulverized coal
calculated by the pulverized coal supply amount deviation
calculating means.
17. A pulverized coal burning boiler according to claim 14,
characterized in that there are provided: reheating steam
temperature deviation prediction means which has reheating steam
temperature deviation prediction models and which predicts a
reheating steam temperature deviation based on information exerting
influence on the reheating steam temperatures; and correction means
which obtain correction signals for correcting control command
signals output from the reheating steam distributing amount control
means based on the reheating steam temperature deviation value
predicted by the reheating steam temperature deviation prediction
means.
18. A pulverized coal burning boiler according to claim 17,
characterized in that the information exerting influence on the
reheating steam temperatures contains at least one piece of
information selected from the group consisting of the supply amount
of pulverized coal, the supply amount of water, the flow rate of
spray, and the power generator output.
19. A pulverized coal burning boiler provided with a first
superheater system and a second superheater system disposed side by
side so that supplied steam circulates while forked into the first
and second superheater systems, characterized in that there are
provided: superheating steam distributing amount adjusting means
which adjust the amounts of steam distributed to the first and
second superheater systems; superheater outlet steam temperature
measuring means which measure superheater outlet steam temperatures
of the first and second superheater systems; and superheating steam
distributing amount control means which send control command
signals to the superheating steam distributing amount adjusting
means to eliminate the temperature difference based on a deviation
between the superheater outlet steam temperatures measured by the
superheater outlet steam temperature measuring means.
20. A pulverized coal burning boiler comprising: milling means
which generate pulverized coal by milling supplied coal; coal
feeding pipes which are arranged in such a manner that a plurality
of coal feeding pipes are connected to one milling means and
through which the pulverized coal is airflow-conveyed by primary
air; pulverized coal burners which are connected to front end sides
of the coal feeding pipes respectively and which have pulverized
coal nozzles disposed so as to face into a furnace; combustion air
supply means which supply combustion air other than the primary air
to the pulverized coal burners individually; combustion air supply
amount measuring means which measure the supply amounts of the
combustion air supplied by the combustion air supply means
individually; combustion air supply amount adjusting means which
adjust the supply amounts of the combustion air; burner air ratio
setting means which set burner air ratios; and a superheater which
has a first superheater system and a second superheater system
disposed side by side; wherein pulverized coal milled and generated
by the milling means is distributed to the coal feeding pipes,
jetted from the pulverized coal nozzles into the furnace and burned
under supply of the combustion air; and steam is superheated by the
superheater and supplied to a high-pressure turbine; the pulverized
coal burning boiler characterized in that there are provided:
pulverized coal supply amount measuring means which individually
measure the supply amounts of pulverized coal conveyed through the
coal feeding pipes respectively; air supply amount control means
which calculate the supply amounts of combustion air corresponding
to the supply amounts of pulverized coal based on the supply
amounts of pulverized coal measured by the pulverized coal supply
amount measuring means and the supply amounts of combustion air
supplied to the pulverized coal burners connected to the coal
feeding pipes and measured by the combustion air supply amount
measuring means and send control command signals to the combustion
air supply amount adjusting means so that burner air ratios set by
the burner air ratio setting means can be kept; superheating steam
distributing amount adjusting means which adjust the amounts of
steam distributed to the first and second superheater systems;
superheater outlet steam temperature measuring means which measure
superheater outlet steam temperatures of the first and second
superheater systems; and superheating steam distributing amount
control means which send control command signals to the
superheating steam distributing amount adjusting means to eliminate
the temperature difference based on a deviation between the
superheater outlet steam temperatures measured by the superheater
outlet steam temperature measuring means.
21. A pulverized coal burning boiler according to claim 19,
characterized in that there is provided pulverized coal supply
amount deviation calculating means which calculates a deviation
between the amount of pulverized coal supplied to pulverized coal
burners of a group heating the first superheater system and the
amount of pulverized coal supplied to pulverized coal burners of a
group heating the second superheater system, and control command
signals are output from the superheating steam distributing amount
control means to the superheating steam distributing amount
adjusting means based on the deviation between the superheater
output steam temperatures measured by the superheater outlet steam
temperature measuring means and the deviation between the supply
amounts of pulverized coal calculated by the pulverized coal supply
amount deviation calculating means.
22. A pulverized coal burning boiler according to claim 19,
characterized in that there are provided: superheating steam
temperature deviation prediction means which has superheating steam
temperature deviation prediction models and which predicts a
superheating steam temperature deviation based on information
exerting influence on the superheating steam temperatures; and
correction means which obtain correction signals for correcting
control command signals output from the superheating steam
distributing amount control means based on the superheating steam
temperature deviation value predicted by the superheating steam
temperature deviation prediction means.
23. A pulverized coal burning boiler according to claim 22,
characterized in that the information exerting influence on the
superheating steam temperatures contains at least one piece of
information selected from the group consisting of the supply amount
of pulverized coal, the supply amount of water, the flow rate of
spray, and the power generator output.
24. A pulverized coal burning boiler according to claim 15,
characterized in that there is provided pulverized coal supply
amount deviation calculating means which calculates a deviation
between the amount of pulverized coal supplied to pulverized coal
burners of a group heating the first reheater system and the amount
of pulverized coal supplied to pulverized coal burners of a group
heating the second reheater system, and control command signals are
output from the reheating steam distributing amount control means
to the reheating steam distributing amount adjusting means based on
the deviation between the reheater outlet steam temperatures
measured by the reheater outlet steam temperature measuring means
and the deviation between the supply amounts of pulverized coal
calculated by the pulverized coal supply amount deviation
calculating means.
25. A pulverized coal burning boiler according to claim 15,
characterized in that there are provided: reheating steam
temperature deviation prediction means which has reheating steam
temperature deviation prediction models and which predicts a
reheating steam temperature deviation based on information exerting
influence on the reheating steam temperatures; and correction means
which obtain correction signals for correcting control command
signals output from the reheating steam distributing amount control
means based on the reheating steam temperature deviation value
predicted by the reheating steam temperature deviation prediction
means.
26. A pulverized coal burning boiler according to claim 20,
characterized in that there is provided pulverized coal supply
amount deviation calculating means which calculates a deviation
between the amount of pulverized coal supplied to pulverized coal
burners of a group heating the first superheater system and the
amount of pulverized coal supplied to pulverized coal burners of a
group heating the second superheater system, and control command
signals are output from the superheating steam distributing amount
control means to the superheating steam distributing amount
adjusting means based on the deviation between the superheater
output steam temperatures measured by the superheater outlet steam
temperature measuring means and the deviation between the supply
amounts of pulverized coal calculated by the pulverized coal supply
amount deviation calculating means.
27. A pulverized coal burning boiler according to claim 20,
characterized in that there are provided: superheating steam
temperature deviation prediction means which has superheating steam
temperature deviation prediction models and which predicts a
superheating steam temperature deviation based on information
exerting influence on the superheating steam temperatures; and
correction means which obtain correction signals for correcting
control command signals output from the superheating steam
distributing amount control means based on the superheating steam
temperature deviation value predicted by the superheating steam
temperature deviation prediction means.
Description
TECHNICAL FIELD
[0001] The present invention relates to a pulverized coal burning
boiler such as a power generation boiler apparatus and particularly
to a pulverized coal burning boiler in which a plurality of coal
feeding pipes are connected to a single milling means such as a
roller mill so that pulverized coal generated by the milling means
is distributed to the plurality of coal feeding pipes, fed to
individual pulverized coal burners and burned.
BACKGROUND ART
(Background Art 1)
[0002] Conventionally, a pulverized coal burning boiler uses a
two-stage burning method in which air with a smaller ratio than a
theoretical air ratio is imported by a burner and low NOx
combustion is performed in a reducing atmosphere in order to reduce
the amount of emergence of NOx and then additional air is imported
from an after airport (hereinafter abbreviated as AAP) as a
post-stage in order to burn unburned contents such as CO.
[0003] To achieve complete burning at a furnace outlet finally, the
amount of air imported into a combustion device as a whole is
imported so excessively as to be about 1.2 which is more than the
theoretical air ratio of 1.0.
[0004] In recent years, there has been an increasing demand for
combustion at a ratio as close to the theoretical air ratio of 1.0
as possible, i.e. at a low excess air ratio for the purpose of
reducing the amount of combustion gas to thereby attain reduction
in size of a furnace and an exhaust gas processing device, etc.
following the furnace, reduction in various kinds of fan motive
utilities, etc.
[0005] With respect to the background art 1, for example, Patent
Documents 1 to 3 can be listed.
(Background Art 2)
[0006] FIGS. 36 and 37 are views for explaining a variable pressure
once-through type pulverized coal burning boiler according to the
background art. As shown in FIG. 36, in this type pulverized coal
burning boiler according to the background art, multi-stage
multi-column pulverized coal burners 702 are disposed for a furnace
701 so that pulverized coal and combustion air are jetted from the
pulverized coal burners 702 into the furnace and burned. To reduce
production of NOx, this combustion device uses a two-stage
combustion method in which a smaller amount of combustion air than
the theoretical air amount is imported by the pulverized coal
burners 702, low NOx combustion is performed in a reducing
atmosphere and then additional air is imported from AAPs 703 as a
post-stage to burn an unburned component such as CO.
[0007] The amount of this additional air is supplied so that the
total amount of air containing the amount of air supplied from the
pulverized coal burners 702 exceeds the theoretical air amount.
This is for the purpose of compensating for local shortage of air
caused by uneven supply of pulverized coal to the pulverized coal
burners 702 or the purpose of compensating for imperfect mixing of
exhaust gas from the pulverized coal burners 702 and air imported
from the AAPs 703 as will be described later.
[0008] Accordingly, as the excess ratio of the total air amount to
the theoretical air amount, that is, the excess air ratio
increases, the concentration of CO in exhaust gas decreases but
thermal loss due to exhaust gas increases to cause lowering of
boiler efficiency. For this reason, the excess air ratio is
generally set to be about 20-30%. Incidentally, there may be a
pulverized coal burning boiler using a so-called single-stage
combustion method in which all air is supplied from pulverized coal
burners without provision of any AAP.
[0009] Raw coal is milled by milling means so that pulverized coal
is generated and supplied to the respective pulverized coal burners
702. Although the amounts of pulverized coal supplied to the
respective pulverized coal burners 702 are adjusted to be equal at
the time of trial operation, a deviation may be generated between
the supply amounts of pulverized coal in vessel left and right
because it is difficult to adjust the amounts of pulverized coal
uniformly based on all loads and the supply amounts of pulverized
coal may be unbalanced in accordance with aging. The deviation
between the supply amounts of pulverized coal in vessel left and
right causes a deviation between combustion gas temperatures in the
furnace. As a result, a deviation is generated between steam
temperatures in the vessel left and right.
[0010] As shown in FIG. 36, in the pulverized coal burning boiler
according to the background art, when suspension type secondary
repeaters are disposed in a flue in reheating steam temperature
control, a vessel left side primary reheater 710 is connected to a
vessel right side secondary reheater 713 and a vessel right side
primary reheater 711 is connected to a vessel left side secondary
reheater 712 to thereby reduce the deviation between steam
temperatures in the vessel left and right.
[0011] FIG. 37 is a characteristic graph showing an example of
reheating steam temperature (ROT) deviations based on deviations
between the supply amounts of fuel (pulverized coal). In FIG. 37,
the solid line shows a state of the vessel left side and the broken
line shows a state of the vessel right side. As shown in FIG. 37,
when a deviation is generated between the supply amounts of
pulverized coal in the vessel left and right at time A for a
certain reason, a deviation is generated in a gas temperature
distribution, a deviation is lately generated in a reheater metal
temperature distribution and a deviation is further lately
generated between reheating steam temperatures (ROTs) in the vessel
left and right at time B. If there is no countermeasure, the
deviation remains forever as shown in FIG. 37.
[0012] In Japan, the reheating steam temperature generally must not
be increased by 8.degree. C. or higher from a designated steam
condition. Accordingly, in the state in which the higher one is
5.degree. C. higher and the lower one is -5.degree. C. lower than
the steam condition, tolerance on control is only 3.degree. C., as
shown in FIG. 37. Because the limit of 8.degree. C. is provided for
the purpose of protecting materials, repeater inlet sprays start
immediately when not an average but either of reheating steam
temperatures in the vessel left and right is going to be 8.degree.
C. higher.
(Background Art 3)
[0013] JP-A-6-101806 (Patent Document 4) has described that a
deviation between reheating steam temperatures is reduced when the
apertures of gas distributing dampers disposed in the rear of a
furnace are adjusted to apply biases to the vessel left and right.
FIG. 38 is a view showing arrangement of the gas distributing
dampers in a flue based on this proposal.
[0014] As shown in FIG. 38, a partition wall 801a is provided in
the center between the vessel left and right, and a partition wall
801b is provided so as to be perpendicular to the partition wall
801a. Gas distributing dampers 718, 719, 720 and 721 are disposed
in respective space portions partitioned by the partition walls
801a and 801b and a casing 802. The apertures of the gas
distributing dampers 718 to 721 can be adjusted individually.
(Background Art 4)
[0015] JP-A-9-21505 (Patent Document 5) has described that a
connection pipe 902 connecting the inlet and outlet of a primary
reheater 901 is provided and a steam flow rate adjusting valve 903
inserted in an intermediate portion of the connection pipe 902 is
operated based on a temperature difference between the vessel left
and right systems to adjust the flow rates of steam in the vessel
left and right to thereby reduce the deviation between reheating
steam temperatures, as shown in FIG. 39.
[0016] In FIG. 39, the reference numeral 904 designates a secondary
reheater; 905, a primary reheater inlet connection pipe; 906, a
reheater inlet spray connection pipe; 907, a reheater inlet spray;
908, a reheater inlet spray adjusting valve; 909, a secondary
reheater inlet connection pipe; and 910, a reheater outlet
connection pipe.
(Background Art 5)
[0017] As shown in FIG. 36, in main steam temperature control, a
vessel left side secondary superheater 706 is connected to a vessel
right side tertiary superheater 709 and a vessel right side
secondary superheater 707 is connected to a vessel left side
tertiary superheater 708 to thereby reduce a deviation between left
and right steam temperatures.
[0018] Alternatively, the amounts of spray water in superheater
inlet sprays 723 and 724 shown in FIG. 36 are biased in the vessel
left and right to thereby reduce a deviation between main steam
temperatures.
[0019] In FIG. 36, the reference numeral 704 designates a vessel
left side primary superheater; 705, a vessel right side primary
superheater; 714, a header; 715 drawn by the arrowed thick line,
various kinds of steam piping; and 722, a primary repeater inlet
spray.
[0020] FIG. 40 is a characteristic graph showing an example of
superheating steam temperature (SOT) deviations based on deviations
between the supply amounts of fuel (pulverized coal). As shown in
FIG. 40, when a deviation is generated between the supply amounts
of pulverized coal in the vessel left and right at time A for a
certain reason, a deviation is generated in a gas temperature
distribution, a deviation is lately generated in a superheater
metal temperature distribution and a deviation is further lately
generated between superheating steam temperatures (SOTs) in the
vessel left and right at time C. [0021] Patent Document 1:
JP-A-8-270931 [0022] Patent Document 2: JP-A-4-222315 [0023] Patent
Document 3: JP-A-60-221616 [0024] Patent Document 4: JP-A-6-101806
[0025] Patent Document 5: JP-A-9-21505
DISCLOSURE OF THE INVENTION
Problems that the Invention is to Solve
(Problem 1)
[0026] As described in (Background Art 1), combustion at a low
excess air ratio has a demerit that the supply amount of combustion
air decreases greatly and production of an unburned component such
as CO increases in comparison with the related art.
[0027] A pulverized coal burning method for reducing the amount of
produced NOx has been disclosed in the Patent Document 1.
Specifically, combustion of pulverized coal by an in-flame
denitration type pulverized coal burner which forms a reducing
flame region short of oxygen takes a point of view that the
concentration of NOx in exhaust gas is largely affected by the
temperature of the reducing flame region or the air ratio of the
reducing flame region.
[0028] Configuration is made so that a light extractor is attached
to the pulverized coal burner, light of flame in the reducing flame
region formed by the burner is detected by the light extractor, the
detection signal is led to an emission spectrometer, the intensity
of emitted light is detected, the temperature of the reducing flame
region or the air ratio of the reducing flame region is calculated,
and the amount of pulverized coal or the amount of air supplied to
the burner is controlled based on a result of the calculation.
[0029] This pulverized coal burning method is effective in reducing
NOx but brings a state short of oxygen as a whole. As a result,
there is a problem that production of an unburned component such as
CO increases.
(Problem 2)
[0030] In a structure (see FIG. 36) in which the vessel left side
primary reheater 710 is connected to the vessel right side
secondary reheater 713 and the vessel right side primary reheater
711 is connected to the vessel left side secondary reheater 712 as
described in (Background Art 2), the deviation between the
reheating steam temperatures in the vessel left and right is apt to
be reduced but quantitative control cannot be performed so that the
deviation between the reheating steam temperatures cannot be
eliminated surely. Therefore, there is a problem of
reliability.
(Problem 3)
[0031] In the method in which the deviation between the reheating
steam temperatures in the vessel left and right is eliminated by
the gas distributing dampers described in (Background Art 3), the
gas distributing dampers 718 to 721 are disposed in the respective
space portions partitioned as shown in FIG. 38. For example, assume
now that the vessel left reheater side gas distributing damper 720
is opened and the vessel right reheater side gas distributing
damper 721 is closed to increase the reheating steam temperature on
the vessel left reheater side and decrease the reheating steam
temperature on the vessel right reheater side. Then, the flow rate
of gas on the reheater side increases on the vessel left side and
decreases on the vessel right side, whereas the flow rate of gas on
the superheater side decreases on the vessel left side and
increases on the vessel right side. This is because the flow rates
of gas interfere with one another to be balanced at the place where
all pressure losses from the inlets of the rear heat-transfer
surfaces to the gas distributing dampers 718 to 721 are
equalized.
[0032] Because the gas distributing dampers 718 to 721 are
mechanically slow in operating velocity and a metal thermal
capacity is interposed in each of the gas distributing dampers 718
to 721, for example, gas distributing damper reheating steam
temperature characteristic exhibits a wasteful time of 1-5 minutes
and a time constant of about 3-10 minutes. Finally, because of the
interference and the response delay of the gas distributing dampers
718 to 721, response of the gas distributing dampers 718 to 721 to
the reheating steam temperature and the main steam temperature is
further worsened so that there is a possibility that the deviation
between the vessel left and right steam temperatures cannot be
eliminated by the gas distributing dampers 718 to 721. In this
case, a superheater spray which has a wasteful time of 30 seconds
to 2 minutes and a time constant of 2-5 minutes, that is, has
rapider response than the gas distributing dampers 718 to 721 is
started to keep the steam temperature condition.
[0033] To use the reheater spray is to cool superheated steam with
spray water. This causes lowering of efficiency of the combustion
device. Moreover, when the number of times of importing compressed
water into a connection pipe in which superheated steam circulates
increases, the spray is damaged by thermal shock so that the
lifetime of the spay is shortened.
(Problem 4)
[0034] In the method (see FIG. 39) in which the connection pipe 902
connecting the inlet and outlet of the primary reheater 901 is
provided so that the flow rates of steam in the vessel left and
right systems are adjusted as described in (Background Art 4), the
amount of absorbed heat is reduced because any primary reheater
needs to be bypassed to adjust the flow rates. For this reason, the
heat-transfer area needs to increase in accordance with reduction
of the amount of absorbed heat to bring increase in device size and
increase in construction cost. Moreover, because the reheater
outlet steam temperature in a primary reheater in which the flow
rate of steam is reduced is too high, a reheat spray is started.
Accordingly, lowering of efficiency of the combustion device and
damage of the spray by thermal shock occur so that the lifetime of
the spray is shortened.
(Problem 5)
[0035] In the structure (see FIG. 36) in which the vessel left side
secondary superheater 706 is connected to the vessel right side
tertiary superheater 709 and the vessel right side secondary
superheater 707 is connected to the vessel left side tertiary
superheater 708 as described in (Background Art 5), the deviation
between the steam temperatures in the vessel left and right is apt
to be reduced but quantitative control cannot be performed. For
this reason, the deviation between the steam temperatures cannot be
eliminated surely, so that there is a problem of reliability.
[0036] In the method in which the amounts of spray water put into
the secondary superheater inlet spray 723 and the tertiary
superheater inlet spray 724 are biased in the vessel left and right
as shown in FIG. 36, a function of adjusting the superheating steam
temperatures in the vessel left and right is added to the sprays
723 and 724 besides the function of controlling the superheating
steam temperatures. For this reason, increase in the amount of
superheater inlet spray is unavoidable. Accordingly, there is a
demerit such as lowering of efficiency of the combustion device,
reduction in controllable range, etc.
[0037] A first object of the invention is to provide a pulverized
coal burning boiler in which production of an unburned component
such as CO is reduced in a pulverized coal burning boiler having a
reduced excess air ratio.
[0038] A second object of the invention is to provide a pulverized
coal burning boiler which is so highly efficient that a deviation
between steam temperatures in the vessel left and right can be
reduced.
Means for Solving the Problems
[0039] A first means of the invention to achieve the first object
is a pulverized coal burning boiler including:
[0040] milling means such as vertical roller mills which generate
pulverized coal by milling supplied coal;
[0041] coal feeding pipes which are arranged in such a manner that
a plurality of coal feeding pipes are connected to one milling
means and through which the pulverized coal is airflow-conveyed by
primary air;
[0042] pulverized coal burners which are connected to front end
sides of the coal feeding pipes respectively and which have
pulverized coal nozzles disposed so as to face into a furnace;
[0043] combustion air supply means which supply combustion air
other than the primary air to the pulverized coal burners
individually;
[0044] combustion air supply amount measuring means which measure
the supply amounts of the combustion air supplied by the combustion
air supply means individually;
[0045] combustion air supply amount adjusting means which adjust
the supply amounts of the combustion air; and
[0046] burner air ratio setting means which set burner air
ratios;
[0047] wherein pulverized coal milled and generated by the milling
means is distributed to the coal feeding pipes, jetted from the
pulverized coal nozzles into the furnace and burned under supply of
the combustion air;
[0048] the pulverized coal burning boiler characterized in that
there are provided:
[0049] pulverized coal supply amount measuring means which
individually measure the supply amounts of pulverized coal conveyed
through the coal feeding pipes respectively; and
[0050] air supply amount control means which calculate the supply
amounts of combustion air corresponding to the supply amounts of
pulverized coal based on the supply amounts of pulverized coal
measured by the pulverized coal supply amount measuring means and
the supply amounts of combustion air supplied to the pulverized
coal burners connected to the coal feeding pipes and measured by
the combustion air supply amount measuring means and send control
command signals to the combustion air supply amount adjusting means
so that burner air ratios set by the burner air ratio setting means
can be kept.
[0051] According to a second means of the invention, the pulverized
coal burning boiler defined in the first means is characterized in
that the pulverized coal supply amount measuring means are attached
to the coal feeding pipes of pulverized coal burners or pulverized
coal burner groups high in unburned component reducing effect in
the pulverized coal burners so that the supply amounts of
combustion air are adjusted individually.
[0052] According to a third means of the invention, the pulverized
coal burning boiler defined in the first means is characterized in
that the pulverized coal burners are disposed as several stages for
the furnace and the pulverized coal supply amount measuring means
are attached to the coal feeding pipes of the pulverized coal
burners except the pulverized coal burners disposed on the lower
stage so that the supply amounts of combustion air are adjusted
individually.
[0053] According to a fourth means of the invention, the pulverized
coal burning boiler defined in the first means is characterized in
that the pulverized coal burners are disposed as several stages for
the furnace and the pulverized coal supply amount measuring means
are attached to the coal feeding pipes of the pulverized coal
burners disposed on at least the uppermost stage so that the supply
amounts of combustion air are adjusted individually.
[0054] According to a fifth means of the invention, the pulverized
coal burning boiler defined in the first means is characterized in
that a plurality of the pulverized coal burners are disposed side
by side to form a burner stage, a plurality of after air ports are
disposed side by side on a downstream side of the burner stage in
an exhaust gas flow direction,
[0055] the amount of combustion air supplied to at least one of the
pulverized coal burners is adjusted, and
[0056] the amount of combustion air supplied to an after air port
near to flame formed by the pulverized coal burner is adjusted.
[0057] According to a sixth means of the invention, the pulverized
coal burning boiler defined in the fifth means is characterized in
that the plurality of pulverized coal burners and the plurality of
after air ports are disposed so as to be separated into a vessel
front and a vessel back of a furnace,
[0058] when the amount of combustion air supplied to the pulverized
coal burners disposed in the vessel front is adjusted, the amount
of combustion air supplied to the after air ports disposed in the
vessel back is adjusted, and
[0059] when the amount of combustion air supplied to the pulverized
coal burners disposed in the vessel back is adjusted, the amount of
combustion air supplied to the after air ports disposed in the
vessel front is adjusted.
[0060] According to a seventh means of the invention, the
pulverized coal burning boiler defined in the first means is
characterized in that a plurality of after air ports are
dispersively disposed on a downstream side of the pulverized coal
burners in an exhaust gas flow direction, concentration
distribution detection means such as a concentration measuring
meter for detecting a distribution of oxygen concentrations or CO
concentrations in exhaust gas is provided in a flue on a downstream
side of the after air ports in an exhaust gas flow direction,
and
[0061] while the amount of combustion air supplied to the
pulverized coal burners is adjusted, the amount of combustion air
supplied to the after air ports corresponding to a low oxygen
concentration or high CO concentration region detected by the
concentration distribution detection means is increased.
[0062] According to an eighth means of the invention, the
pulverized coal burning boiler defined in any one of the fifth to
seventh means is characterized in that the pulverized coal burners
are disposed as a plurality of stages for a furnace, the pulverized
coal burners to adjust the supply amount of combustion air are
pulverized coal burners disposed on the uppermost stage.
[0063] According to a ninth means of the invention, the pulverized
coal burning boiler defined in the first means is characterized in
that each of the pulverized coal supply amount measuring means has
a microwave resonance pipe through which a mixed fluid of the
pulverized coal and primary air circulates, and a microwave
transmitter and a microwave receiver which are disposed in the
microwave resonance pipe so as to be at a predetermined distance
from each other along a direction of a flow of the mixed fluid,
and
[0064] the microwave transmitter transmits microwaves to the
microwave receiver to measure a resonance frequency of the
microwave resonance pipe to thereby measure the supply amount of
the pulverized coal based on the resonance frequency.
[0065] According to a tenth means of the invention, the pulverized
coal burning boiler defined in the ninth means is characterized in
that a part of each of the coal feeding pipes is used as the
microwave resonance pipe.
[0066] According to an eleventh means of the invention, the
pulverized coal burning boiler defined in the ninth or tenth means
is characterized in that the microwave transmitter and the
microwave receiver protrude into the microwave resonance pipe, and
a knocking member such as fluid guiding means which will be
described later is disposed on an upstream side of the microwave
transmitter in the microwave resonance pipe to unravel a flow of
the pulverized coal condensed like a string in the microwave
resonance pipe.
[0067] According to a twelfth means of the invention, the
pulverized coal burning boiler defined in the first means is
characterized in that the pulverized coal supply amount measuring
means has a first charge sensor and a second charge sensor which
are disposed in each of the coal feeding pipes so as to be at a
predetermined distance from each other along an axial direction of
the coal feeding pipe, and
[0068] movement of electrostatic charges resulting from passage of
pulverized coal in the coal feeding pipe is measured by the two
charge sensors so that the supply amount of pulverized coal is
measured based on the movement of electrostatic charges measured by
the two charge sensors.
[0069] According to a thirteenth means of the invention, the
pulverized coal burning boiler defined in the twelfth means is
characterized in that the first charge sensor and the second charge
sensor are circular and fluid guiding means is provided on an
upstream side of the charge sensors to collect pulverized coal and
pour the collected pulverized coal into a central portion side of
the coal feeding pipe to thereby reduce the amount of pulverized
coal passing through an inner circumferential side of the charge
sensors.
[0070] A fourteenth means of the invention to achieve the second
object is a pulverized coal burning boiler provided with a first
reheater system and a second reheater system disposed side by side
so that supplied steam circulates while forked into the first and
second reheater systems, characterized in that there are
provided:
[0071] reheating steam distributing amount adjusting means which
adjust the amounts of steam distributed to the first and second
reheater systems;
[0072] reheater outlet steam temperature measuring means which
measure reheater outlet steam temperatures of the first and second
reheater systems; and
[0073] reheating steam distributing amount control means which send
control command signals to the reheating steam distributing amount
adjusting means to eliminate the temperature difference based on a
deviation between the reheater outlet steam temperatures measured
by the reheater outlet steam temperature measuring means.
[0074] A fifteenth means of the invention to achieve the second
object is a pulverized coal burning boiler including:
[0075] milling means which generate pulverized coal by milling
supplied coal;
[0076] coal feeding pipes which are arranged in such a manner that
a plurality of coal feeding pipes are connected to one milling
means and through which the pulverized coal is airflow-conveyed by
primary air;
[0077] pulverized coal burners which are connected to front end
sides of the coal feeding pipes respectively and which have
pulverized coal nozzles disposed so as to face into a furnace;
[0078] combustion air supply means which supply combustion air
other than the primary air to the pulverized coal burners
individually;
[0079] combustion air supply amount measuring means which measure
the supply amounts of the combustion air supplied by the combustion
air supply means individually;
[0080] combustion air supply amount adjusting means which adjust
the supply amounts of the combustion air;
[0081] burner air ratio setting means which set burner air ratios;
and
[0082] a reheater which has a first reheater system and a second
reheater system disposed side by side;
[0083] wherein pulverized coal milled and generated by the milling
means is distributed to the coal feeding pipes, jetted from the
pulverized coal nozzles into the furnace and burned under supply of
the combustion air; and
[0084] steam from a high-pressure turbine is heated by the reheater
and supplied to middle-pressure and low-pressure turbines;
[0085] the pulverized coal burning boiler characterized in that
there are provided:
[0086] pulverized coal supply amount measuring means which
individually measure the supply amounts of pulverized coal conveyed
through the coal feeding pipes respectively;
[0087] air supply amount control means which calculate the supply
amounts of combustion air corresponding to the supply amounts of
pulverized coal based on the supply amounts of pulverized coal
measured by the pulverized coal supply amount measuring means and
the supply amounts of combustion air supplied to the pulverized
coal burners connected to the coal feeding pipes and measured by
the combustion air supply amount measuring means and send control
command signals to the combustion air supply amount adjusting means
so that burner air ratios set by the burner air ratio setting means
can be kept;
[0088] reheating steam distributing amount adjusting means which
adjust the amounts of steam distributed to the first and second
reheater systems;
[0089] reheater outlet steam temperature measuring means which
measure reheater outlet steam temperatures of the first and second
reheater systems; and
[0090] reheating steam distributing amount control means which send
control command signals to the reheating steam distributing amount
adjusting means to eliminate the temperature difference based on a
deviation between the reheater outlet steam temperatures measured
by the reheater outlet steam temperature measuring means.
[0091] According to a sixteenth means of the invention, the
pulverized coal burning boiler defined in the fourteenth or
fifteenth means is characterized in that there is provided
pulverized coal supply amount deviation calculating means which
calculates a deviation between the amount of pulverized coal
supplied to pulverized coal burners of a group heating the first
reheater system and the amount of pulverized coal supplied to
pulverized coal burners of a group heating the second reheater
system, and
[0092] control command signals are output from the reheating steam
distributing amount control means to the reheating steam
distributing amount adjusting means based on the deviation between
the reheater outlet steam temperatures measured by the reheater
outlet steam temperature measuring means and the deviation between
the supply amounts of pulverized coal calculated by the pulverized
coal supply amount deviation calculating means.
[0093] According to a seventeenth means of the invention, the
pulverized coal burning boiler defined in the fourteenth or
fifteenth means is characterized in that there are provided:
[0094] reheating steam temperature deviation prediction means which
has reheating steam temperature deviation prediction models and
which predicts a reheating steam temperature deviation based on
information exerting influence on the reheating steam temperatures;
and
[0095] correction means which obtain correction signals for
correcting control command signals output from the reheating steam
distributing amount control means based on the reheating steam
temperature deviation value predicted by the reheating steam
temperature deviation prediction means.
[0096] According to an eighteenth means of the invention, the
pulverized coal burning boiler defined in the seventeenth means is
characterized in that the information exerting influence on the
reheating steam temperatures contains at least one piece of
information selected from the group consisting of the supply amount
of pulverized coal, the supply amount of water, the flow rate of
spray, and the power generator output.
[0097] A nineteenth means of the invention to achieve the second
object is a pulverized coal burning boiler provided with a first
superheater system and a second superheater system disposed side by
side so that supplied steam circulates while forked into the first
and second superheater systems, characterized in that there are
provided:
[0098] superheating steam distributing amount adjusting means which
adjust the amounts of steam distributed to the first and second
superheater systems;
[0099] superheater outlet steam temperature measuring means which
measure superheater outlet steam temperatures of the first and
second superheater systems; and
[0100] superheating steam distributing amount control means which
send control command signals to the superheating steam distributing
amount adjusting means to eliminate the temperature difference
based on a deviation between the superheater outlet steam
temperatures measured by the superheater outlet steam temperature
measuring means.
[0101] A twentieth means of the invention to achieve the second
object is a pulverized coal burning boiler including:
[0102] milling means which generate pulverized coal by milling
supplied coal;
[0103] coal feeding pipes which are arranged in such a manner that
a plurality of coal feeding pipes are connected to one milling
means and through which the pulverized coal is airflow-conveyed by
primary air;
[0104] pulverized coal burners which are connected to front end
sides of the coal feeding pipes respectively and which have
pulverized coal nozzles disposed so as to face into a furnace;
[0105] combustion air supply means which supply combustion air
other than the primary air to the pulverized coal burners
individually;
[0106] combustion air supply amount measuring means which measure
the supply amounts of the combustion air supplied by the combustion
air supply means individually;
[0107] combustion air supply amount adjusting means which adjust
the supply amounts of the combustion air;
[0108] burner air ratio setting means which set burner air ratios;
and
[0109] a superheater which has a first superheater system and a
second superheater system disposed side by side;
[0110] wherein pulverized coal milled and generated by the milling
means is distributed to the coal feeding pipes, jetted from the
pulverized coal nozzles into the furnace and burned under supply of
the combustion air; and
[0111] steam is superheated by the superheater and supplied to a
high-pressure turbine;
[0112] the pulverized coal burning boiler characterized in that
there are provided:
[0113] pulverized coal supply amount measuring means which
individually measure the supply amounts of pulverized coal conveyed
through the coal feeding pipes respectively; air supply amount
control means which calculate the supply amounts of combustion air
corresponding to the supply amounts of pulverized coal based on the
supply amounts of pulverized coal measured by the pulverized coal
supply amount measuring means and the supply amounts of combustion
air supplied to the pulverized coal burners connected to the coal
feeding pipes and measured by the combustion air supply amount
measuring means and send control command signals to the combustion
air supply amount adjusting means so that burner air ratios set by
the burner air ratio setting means can be kept;
[0114] superheating steam distributing amount adjusting means which
adjust the amounts of steam distributed to the first and second
superheater systems;
[0115] superheater outlet steam temperature measuring means which
measure superheater outlet steam temperatures of the first and
second superheater systems; and
[0116] superheating steam distributing amount control means which
send control command signals to the superheating steam distributing
amount adjusting means to eliminate the temperature difference
based on a deviation between the superheater outlet steam
temperatures measured by the superheater outlet steam temperature
measuring means.
[0117] According to a twenty-first means of the invention, the
pulverized coal burning boiler defined in the nineteenth or
twentieth means is characterized in that there is provided
pulverized coal supply amount deviation calculating means which
calculates a deviation between the amount of pulverized coal
supplied to pulverized coal burners of a group heating the first
superheater system and the amount of pulverized coal supplied to
pulverized coal burners of a group heating the second superheater
system, and
[0118] control command signals are output from the superheating
steam distributing amount control means to the superheating steam
distributing amount adjusting means based on the deviation between
the superheater output steam temperatures measured by the
superheater outlet steam temperature measuring means and the
deviation between the supply amounts of pulverized coal calculated
by the pulverized coal supply amount deviation calculating
means.
[0119] According to a twenty-second means of the invention, the
pulverized coal burning boiler defined in the nineteenth or
twentieth means is characterized in that there are provided:
[0120] superheating steam temperature deviation prediction means
which has superheating steam temperature deviation prediction
models and which predicts a superheating steam temperature
deviation based on information exerting influence on the
superheating steam temperatures; and
[0121] correction means which obtain correction signals for
correcting control command signals output from the superheating
steam distributing amount control means based on the superheating
steam temperature deviation value predicted by the superheating
steam temperature deviation prediction means.
[0122] According to a twenty-third means of the invention, the
pulverized coal burning boiler defined in the twenty-second means
is characterized in that the information exerting influence on the
superheating steam temperatures contains at least one piece of
information selected from the group consisting of the supply amount
of pulverized coal, the supply amount of water, the flow rate of
spray, and the power generator output.
EFFECT OF THE INVENTION
[0123] The first means of the invention is configured as described
above. Because the flow rates of pulverized coal conveyed through
the coal feeding pipes are measured individually so that the supply
amounts of combustion air corresponding to the supply amounts of
pulverized coal can be calculated and supplied so that burner air
ratios set in advance can be kept, production of an unburned
component such as CO can be reduced effectively even in the
pulverized coal burning boiler in which the excess air ratio is
reduced, for example, to 1.1.
[0124] The fourteenth, fifteenth, nineteenth and twentieth means of
the invention are configured as described above. Because the steam
temperature deviation is detected to adjust the flow rates of
steam, the steam temperature deviation can be reduced to zero to
attain improvement in efficiency.
BEST MODE FOR CARRYING OUT THE INVENTION
[0125] Specific contents of the invention will be described below
with reference to the drawings.
(1) Configuration of Pulverized Coal Burning Combustion System
[0126] FIG. 23 is a schematic configuration view showing an example
of a pulverized coal burning combustion system.
[0127] As shown in FIG. 23, air A fed in by an air forcing blower 1
is bifurcated to primary air A1 and secondary air A2, and the
primary air A1 is bifurcated to air directly fed as cold air to a
vertical roller mill 3 by a primary air forcing blower 2 and air
heated by an exhaust gas type air preheater 4 and fed as hot air to
the vertical roller mill 3. The cold air and the hot air are mixed
and adjusted to form mixed air of a suitable temperature to be
supplied to the roller mill 3.
[0128] After raw coal 5 is put into a coal banker 6, the raw coal 5
is supplied to the vertical roller mill 3 by a coal supply 7 and
milled. Pulverized coal milled and generated while dried with the
primary air A1 is conveyed by the primary air A1, jetted from
pulverized coal nozzles 8 into a pulverized coal burning boiler 9
and ignited/burned. The secondary air A2 is heated by a steam type
air preheater 10 and the exhaust gas type air preheater 4, fed to a
wind box 11 and after air ports (AAP) 65 and subjected to
combustion in the pulverized coal burning boiler 9.
[0129] A system for exhaust gas generated by the combustion of the
pulverized coal is formed so that dust is removed by a dust
collector 12, NOx is reduced by a denitrator 13, the exhaust gas is
sucked by an induced blower 14 via the exhaust gas type air
preheater 4, a sulfur content is removed by a desulfurizer 15, and
the exhaust gas is released from a chimney 16 into the atmospheric
air.
[0130] Although this example shows the case where the dust
collector 12, the denitrator 13 and the exhaust gas type air
preheater 4 are disposed in this order from an upstream side in a
direction of a flow of the exhaust gas, there may be, for example,
the case where the denitrator 13, the exhaust gas type air
preheater 4 and the dust collector 12 are disposed in this
order.
(2) Configuration of Vertical Roller Mill 3
[0131] FIG. 24 is a schematic configuration view showing an example
of the vertical roller mill 3.
[0132] As shown in FIG. 24, the vertical roller mill 3 mainly
includes a milling portion 21, a classifying portion 22, a milling
portion driving portion 23, a classifying portion driving portion
24, and a distributing portion 25.
[0133] The milling portion 21 includes a housing 26, a milling
table 27, milling rollers 28 rolled on the milling table 27, and a
throat 29 which is a primary air inlet provided in an outer
circumference of the milling table 27.
[0134] The classifying portion 22 includes the housing 26, a
cyclone type stationary classifier 30 disposed in the inside of the
housing 26, and a rotary classifier 31 disposed in the inside of
the stationary classifier 30. The stationary classifier 30 has a
fixed fin 32, and a recovery cone 33 provided so as to be connected
to a lower end of the fixed fin 32. The rotary classifier 31 has a
rotary shaft 34, and a rotary vane 35 supported to the rotary shaft
34.
[0135] The milling portion driving portion 23 includes a milling
portion motor 36 for driving the milling table 27 to rotate, a
pedestal 37 on which the milling table 27 is mounted rotatably,
pressure frames 38 and brackets 39 for supporting the milling
rollers 28, a rod 40, a pressure cylinder 41 for adjusting
pressurizing force of each milling roller 28 acting on the milling
table 27, etc.
[0136] The classifying portion driving portion 24 has a classifier
motor 42, an output of which is transmitted to the rotary shaft 34
of the classifying portion 22 through gears. The distributing
portion 25 is provided in an upper portion of the vertical roller
mill 3 and has one distributing chamber 47 to which coal feeding
pipes 43 are connected. In this embodiment, about 4-6 coal feeding
pipes 43 are connected. However, only one coal feeding pipe 43 is
drawn in FIG. 24 for the sake of simplification of the drawing.
[0137] Raw coal 5 supplied by a coal supply pipe 44 drops down into
a central portion of the milling table 27 rotating, moves to an
outer circumferential side by centrifugal force generated with
rotation of the milling table 27 and is clamped between the milling
table 27 and each milling roller 28 so as to be milled.
[0138] The milled coal grains further move to the outer
circumference, become confluent with primary air 45 heated to
150.degree. C.-300.degree. C. led into a milling chamber from the
throat 29 provided in the outer circumference of the milling table
27, and are blown up while dried. The blown-up grains are
primary-classified according to weight, so that rough coal grains
drop down and return to the milling portion 21.
[0139] Small coal grains which have reached the classifying portion
22 are classified (secondary-classified) into pulverized coal not
larger than a predetermined grain size and roughly-powdered coal
larger than the predetermined grain size by the stationary
classifier 30 and the rotary classifier 31. The roughly-powdered
coal drops along the inner wall of the recovery cone 33 so that the
roughly-powdered coal will be milled again. On the other hand, a
mixed fluid 46 of pulverized coal not larger than the predetermined
grain size and primary air is fed into the distributing chamber 47.
In the distributing chamber 47, the mixed fluid 46 is distributed
into the coal feeding pipes 43 and conveyed to the pulverized coal
nozzles 8 through the coal feeding pipes 43 respectively.
[0140] Incidentally, a small number of coal feeding pipes (e.g.
about 1-4 pipes) may be connected to the mill so that each of the
coal feeding pipes branches halfway and leads to two or more
burners. The description "coal feeding pipes connected for one
milling means" in Claim 1 includes such a form.
[0141] Fine-powdered coal flowmeters 51 are attached to
intermediate portions of the coal feeding pipes 43 respectively.
The configuration and measuring theory of each pulverized coal
flowmeter 51 will be described below.
(3) Configuration and Measuring Theory of Pulverized Coal Flowmeter
51
[0142] The pulverized coal flowmeter 51 used in this embodiment is
classified into a microwave type flowmeter and an electrostatic
charge type flowmeter.
[0143] FIG. 25 is a schematic configuration view of a microwave
type pulverized coal flowmeter 51a. The flowmeter 51a uses the coal
feeding pipe 43 as a microwave resonance pipe (waveguide) and has a
microwave transmitter 52 and a microwave receiver 53 which are
disposed opposite to each other with a predetermined distance in
the inside of the coal feeding pipe 43.
[0144] Although the transmitter 52 transmits microwaves to the
receiver 53, the resonance frequency of the coal feeding pipe 43
(microwave resonance pipe) varies according to dielectric constant
.di-elect cons.r in the inside of the pipe. The dielectric constant
.di-elect cons.r of air is 1 whereas the dielectric constant
.di-elect cons.r of coal is about 4. Frequency characteristic in
the case where the coal feeding pipe 43 is empty and frequency
characteristic in the case where the mixed fluid 46 of pulverized
coal and primary air flows in the coal feeding pipe 43 can be
measured based on the difference between the dielectric constants,
so that the flow rate of pulverized coal flowing in the coal
feeding pipe 43 can be calculated based on the difference between
resonance frequencies.
[0145] FIG. 26 is a schematic configuration view of an
electrostatic charge type pulverized coal flowmeter 51b. The
flowmeter 51b has two charge sensors 54a and 54b which catch static
electricity generated by collision of pulverized coal and a flow
path wall while the pulverized coal passes through the coal feeding
pipe 43. The flowmeter 51b uses the fact that the amount of
electric charges varies according to the concentration of
pulverized coal. Movement of electrostatic charges with passage of
pulverized coal through the coal feeding pipe 43 is detected by the
two charge sensors 54a and 54b, so that the flow rate of pulverized
coal can be measured.
[0146] As shown in FIG. 26, the first charge sensor 54a and the
second charge sensor 54b are disposed in an intermediate portion of
the coal feeding pipe 43 with a predetermined distance L along the
axial direction of the pipe.
[0147] First, a concentration .rho. of pulverized coal passing
through the coal feeding pipe 43 is obtained by the charge sensors
54a and 54b. Then, a passage time .tau. of pulverized coal from the
first charge sensor 54a to the second charge sensor 54b is
obtained. The passage time .tau. can be measured based on a time
difference between a fluctuating phenomenon (specific waveform
portion) detected when pulverized coal passes through the first
charge sensor 54a and a fluctuating phenomenon (the same specific
waveform portion) detected when pulverized coal passes through the
second charge sensor 54b. Then, the flow velocity V of pulverized
coal is calculated based on the relational expression V=L/.tau..
Then, the flow rate Q of pulverized coal can be calculated based on
the relational expression Q=.rho..times.V.times.S in which .rho. is
the concentration of pulverized coal, V is the flow velocity of
pulverized coal, and S is the flow sectional area of the coal
feeding pipe 43.
[0148] Incidentally, as shown in FIG. 26, each of the charge
sensors 54a and 54b is circular and has an inner diameter
substantially equal to the inner diameter of the coal feeding pipe
43 so that the charge sensors 54a and 54b are prevented as
sufficiently as possible from being worn away by pulverized
coal.
[0149] The flow rate of pulverized coal distributed from the mill
to each burner always varies according to the amount of coal
supplied to the mill, the deviation on distribution, etc.
Incidentally, in the background art, the amount of air supplied to
each burner and each downstream-side AAP could not be controlled in
real time because there was no means for measuring the flow rate of
pulverized coal directly. Therefore, it was necessary to supply
excessive air to the furnace combustion region as a whole for
complete combustion of unburned parts such as CO, so that it was
impossible to obtain combustion at a low excess air ratio as
described above.
[0150] When the pulverized coal flowmeter 51 is used, the flow rate
of pulverized coal distributed from the mill to each burner can be
measured accurately. Accordingly, the amount of air supplied to
each burner and each AAP can be adjusted/controlled precisely in
accordance with the measured flow rate of pulverized coal, so that
combustion can be made at an air ratio as close to the theoretical
air ratio of 1.0 as possible, that is, at a low excess air
ratio.
(4) First Embodiment
[0151] FIG. 1 is a schematic plan configuration view of a
pulverized coal burning boiler according to a first embodiment.
[0152] In this embodiment, for example, four pulverized coal
burners 61a to 61d are disposed in vessel front of the pulverized
coal burning boiler 9 while four pulverized coal burners 61e to 61h
are disposed in vessel back thereof so as to be opposite to the
four pulverized coal burners 61a and 61d respectively. Two mills 3
are disposed in vessel front and in vessel back, respectively. Four
coal feeding pipes 43a to 43d extended from the vessel front mill
3a are connected to the pulverized coal burners 61a to 61d
respectively while four coal feeding pipes 43e to 43h extended from
the vessel back mill 3b are connected to the pulverized coal
burners 61e to 61h respectively.
[0153] Pulverized coal flowmeters 51a to 51h are attached to the
coal feeding pipes 43a to 43h respectively so that the flow rates
of pulverized coal passing through the coal feeding pipes 43 can be
measured individually.
[0154] FIG. 2 is a schematic configuration view of a pulverized
coal burner 61. As shown in FIG. 2, a pulverized coal nozzle 8 is
disposed in the central portion of the pulverized coal burner 61. A
combustion air supply path 63 for supplying combustion air
(secondary air and tertiary air) 62 other than primary air is
provided in an outer circumferential portion of the pulverized coal
nozzle 8 individually in accordance with each burner 61. Combustion
air supply amount adjusting means 64 (see FIG. 4), for example, of
a dumper type or a slide type for adjusting the amount of supplied
combustion air 62 is provided in an intermediate portion of the
combustion air supply path 63. As shown in FIG. 2, while the mixed
fluid 46 of pulverized coal and primary air is jetted from the
pulverized coal nozzle 8 into the furnace, combustion air 62 of a
low excess air ratio is supplied from the combustion air supply
path 63 to thereby ignite and burn pulverized coal.
[0155] Although this embodiment has been described in the case
where the combustion air 62 is supplied to the outer circumference
of the pulverized coal nozzle 8, the invention is not limited
thereto as long as the combustion air 62 can be supplied so that
pulverized coal jetted from the pulverized coal nozzle 8 into the
furnace can be burned.
[0156] FIG. 3 is a graph showing an example of deviations from an
average flow rate in the case where pulverized coal obtained by
supplying raw coal at a rate of X(t/h) to one mill 3 and milling
the raw coal in the mill 3 is distributed to coal feeding pipes 43a
to 43d so that the flow rates of pulverized coal are measured by
pulverized coal flowmeters 51a to 51d respectively.
[0157] In this graph, 0% deviation means detection of pulverized
coal at the average flow rate (X/4 in this example). This example
shows that pulverized coal at flow rates lower than the average
flow rate is conveyed to the coal feeding pipes 43a and 43b while
pulverized coal at flow rates higher than the average flow rate is
conveyed to the coal feeding pipes 43c and 43d. For example, the
deviation of the measured value is caused by a pressure loss
difference based on the pipe length difference between the coal
feeding pipes 43, the structure of the mill, etc. It is confirmed
that the deviation varies according to the operating condition of
the mill such as the rotational velocity of the rotary
classifier.
[0158] In this embodiment, a deviation state of the flow rate of
pulverized coal conveyed by each coal feeding pipe 43 is detected,
the amount of supplied combustion air corresponding to the amount
of supplied pulverized coal is calculated based on the deviation
individually for each burner so that the air ratio set by the
burner air ratio setting means can be kept, and a control signal is
transmitted to each combustion air supply amount adjusting means 64
to thereby adjust the amount of combustion air supplied to each
burner 61 individually.
[0159] FIG. 4 is a view for explaining a combustion air supply
amount control system therefor. A right half of FIG. 4 is a view
showing an example of arrangement of pulverized coal burners 61 and
AAPs 65 on their downstream sides in the pulverized coal burning
boiler 9. Each of vessel front and vessel back is separated into
burner stages so that a large number of pulverized coal burners 61
are arranged side by side in accordance with each burner stage.
AAPs 65 are provided separately in both vessel front and vessel
back so that the AAPs 65 are arranged side by side correspondingly
to the respective pulverized coal burners 61.
[0160] A left half of FIG. 4 is a view showing a combustion air
supply amount control system for the pulverized coal burners 61.
The amounts of pulverized coal distributed and supplied from the
mill 3 to the respective burners 61a and 61b as described above are
measured individually by the pulverized coal flowmeters 51a and
51b, so that measured values thereof are input to a control circuit
66.
[0161] On the other hand, combustion air supply amount adjusting
means 64a and 64b and air flowmeters 67a and 67b are attached
individually to intermediate portions of combustion air supply
paths 63a and 63b provided correspondingly to the burners 61a and
61b respectively. Measured values of the amounts of air supplied to
the burners 61a and 61b and measured individually by the air
flowmeters 67a and 67b are also input to the control circuit 66.
There is a mechanism that the control circuit 66 outputs combustion
air supply amount control signals 68a and 68b to the combustion air
supply amount adjusting means 64a and 64b individually.
[0162] FIG. 5 is a block diagram showing an example of
configuration of the control circuit 66. Values measured by the
pulverized coal flowmeters 51a and 51b are input to the control
circuit 66, so that deviation values from the average flow rate in
the respective coal feeding pipes 43a and 43b are obtained by an
adder 69 and dividers 70.
[0163] A supplied coal amount 71, a burner air ratio 72, a
theoretical air amount 73, combustion air amounts 74a and 74b for
the respective burners, etc. are input to the control circuit 66 in
advance. In this embodiment, the burner air ratio 72 is set at 0.8
and the AAP air ratio is set at 0.3. Accordingly, the air ratio of
the whole boiler is a low excess air ratio of 1.1.
[0164] Combustion air supply amounts corresponding to the
pulverized coal supply amounts are calculated and output as
combustion air amount command values 68a and 68b based on the
various set values and the deviation values of the pulverized coal
amounts in the respective coal feeding pipes 43a and 43b so that
the aforementioned burner air ratio can be kept. Various
multipliers 76, subtracters 77, etc. in the control circuit 66 are
used as means for calculating the command values 68a and 68b.
Limiting items of correction amount limiters 75a and 75b provided
on the output end side of the control circuit 66 are upper and
lower limits of absolute values, change widths, and change
ratios.
[0165] When the combustion air supply amounts corresponding to the
pulverized coal supply amounts in the respective coal feeding pipes
are controlled individually as described above, a CO reducing
effect is large in combustion at a low excess air ratio.
(5) Second Embodiment
[0166] FIG. 6 is a schematic configuration view of a pulverized
coal burning boiler according to a second embodiment.
[0167] As shown in FIG. 6, mills 3a to 3c are disposed. The mills
3a, 3b and 3c are connected to upper-stage, middle-stage and
lower-stage burners 61 respectively so that pulverized coal is
supplied thereto.
[0168] FIG. 7 is a view showing results of an experiment performed
for specifying a burner stage large in CO reducing effect. This
experiment was performed by use of a combustion analysis model
having six burners in each burner stage.
[0169] The amount of CO produced when pulverized coal (fuel) was
equally distributed to burners in each burner stage was measured
and regarded as a reference value (1.00) (see left columns in FIG.
7). A relative value of the amount of CO produced when deviation
was given to the fuel supply amount so that the sum of deviation
values (see FIG. 3) from the average flow rate of the six burners
became 20% was shown in each central column in FIG. 7. As shown in
the central columns in FIG. 7, the amount of CO produced in the
lower-stage burners little increased in spite of more or less
deviation of the fuel supply amount whereas the amount of CO
produced in the upper and middle stages increased by about 40% or
more when there was deviation of the fuel supply amount.
Especially, the increase in the amount of CO produced in the
upper-stage burners was remarkable.
[0170] Then, the pulverized coal flowmeters 51 were attached to the
coal feeding pipes 43 connected to the burners 61 respectively and
the combustion air amount was adjusted as described in the first
embodiment. Results thereof were shown in right columns in FIG. 7.
As is obvious from the results in the right columns in FIG. 7, the
CO reducing effect in the upper and middle stages is large,
especially the effect in the upper-stage burners is remarkable.
[0171] Therefore, this embodiment is configured so that the
pulverized coal flowmeters 51, the control circuit 66, etc. are not
attached to the lower stage but the pulverized coal flowmeters 51,
the control circuit 66, etc. are attached to the upper and middle
stages having a CO reducing effect, especially, to at least the
upper stage to adjust the combustion air amount.
[0172] Although this embodiment has been described in the case
where whether the pulverized coal flowmeters 51 and the control
circuit 66 are attached or not is determined in accordance with
each burner stage, the magnitudes of the CO reducing effect in all
burners may be grasped in advance by an experiment or the like so
that the pulverized coal flowmeters 51 and the control circuit 66
can be selectively attached to burners having a CO reducing
effect.
(6) Third Embodiment A third embodiment will be described below. In
the electrostatic charge type pulverized coal flowmeter 51b shown
in FIG. 26, the concentration .rho. of pulverized coal passing
through the coal feeding pipe 43 and the flow velocity V of the
pulverized coal can be obtained as described above. Accordingly,
the flow rate of primary air carrying pulverized coal can be
calculated based on the concentration .rho. and flow velocity V of
the pulverized coal, the circulation sectional area S of the coal
feeding pipe 43 and the temperature correction value. As the flow
velocity V becomes higher, the flow rate of primary air, that is,
the flow rate of primary air supplied to the burner 61
increases.
[0173] Therefore, this embodiment is configured so that the flow
rate of primary air is calculated and the amount of supplied
combustion air 62 is adjusted in consideration of the flow rate of
primary air, for example, by means of reducing the amount of
supplied combustion air 62 when the flow rate of primary air is
high. Incidentally, calculation of the flow rate of primary air and
adjustment of the amount of supplied combustion air 62 based on the
calculation result are performed by the control circuit 66.
[0174] This embodiment is particularly effective for a coal type
such as subbituminous coal low in theoretical air amount because
the rate of the amount of primary air in the coal type is higher
than that in another coal type such as bituminous coal. The
theoretical air amount of bituminous coal is 7.0 m.sup.3N/kg
whereas the theoretical air amount of subbituminous coal is 5.5
m.sup.3N/kg which is small.
(7) Fourth Embodiment
[0175] FIG. 8 is a schematic configuration view of a pulverized
coal burning boiler according to a fourth embodiment. FIG. 8(a) is
a view showing the correspondence relation between pulverized coal
burners 61 and AAPs 65. FIG. 8(b) is a view showing the arrangement
of pulverized coal burners 61. FIG. 8(c) is a view showing the
arrangement of AAPs 65.
[0176] In this embodiment, as shown in FIG. 8(b), pulverized coal
burners 61a to 61d in vessel front are disposed opposite to
pulverized coal burners 61e to 61h in vessel back on a plane. As
shown in FIG. 8(c), AAPs 65a to 65d in vessel front are disposed
opposite to AAPs 65e to 65h in vessel back on a plane. As shown in
FIG. 8(a), the AAPs 65 are disposed just above the pulverized coal
burners 61 respectively.
[0177] A burner combustion air amount adjustable range in each of
the pulverized coal burners 61a to 61h is limited in advance from
view of burner design. In this embodiment, the adjustable range is
limited to 10% of the rating burner combustion air amount.
[0178] For example, when the air amount needs to increase by 13% of
the rating air amount as a result of calculation based on the
output of the pulverized coal flowmeter 51c shown in FIG. 8(b),
configuration is made so that the amount of burner combustion air
supplied to the pulverized coal burner 61c increases by 10% and the
amount of AAP air supplied to the AAP 65g on the opposite side
increases by the remaining 3%.
[0179] FIG. 9 is a view showing the CO reducing effect in this
embodiment. In this experimental example, a fuel deviation of +20%
is detected in the pulverized coal burner 61c in the vessel-front
upper stage. On this occasion, the CO relative value is 1.53 (see
the upper stage in FIG. 7). Accordingly, when the amount of burner
combustion air supplied to the pulverized coal burner 61c increased
by 10%, the relative value of CO decreased to 0.75 (see the right
of the upper stage in FIG. 9) so that the amount of CO could be
reduced by 25% from the reference value.
[0180] The amount of AAP air needs to cover the remaining 10%. The
CO reducing effect in the case where the amount of air supplied to
the vessel-front AAP 65c just above the pulverized coal burner 61c
was increased by 10% and the CO reducing effect in the case where
the amount of air supplied to the vessel-back AAP 65g on the side
opposite to the pulverized coal burner 61c was increased by 10%
were examined. When the amount of air supplied to the vessel-front
AAP 65c was increased, there was little effect (see the left of the
lower stage in FIG. 9). On the other hand, when the amount of air
supplied to the vessel-back AAP 65g was increased, a further CO
reducing effect was obtained, so that the amount of CO could be
overall reduced by 37% from the reference value (see the right of
the lower stage in FIG. 9).
(8) Fifth Embodiment
[0181] FIG. 10 is a view showing the correspondence relation
between pulverized coal burners 61 and AAPs 65 in a pulverized coal
burning boiler according to a fifth embodiment.
[0182] In this embodiment, the number of AAPs 65 is larger than the
number of pulverized coal burners 61, so that each pulverized coal
burner 61 is disposed just below a midpoint between two AAPs 65.
For example, when the amount of air supplied to the vessel-front
pulverized coal burner 61b is increased, the amount of air supplied
to the vessel-back AAPs 65g and 65h substantially opposite to the
pulverized coal burner 61b, that is, nearest to flame formed by the
pulverized coal burner 61b is increased while divided into two
equal parts for the vessel-back AAPs 65g and 65h. Configuration is
made so that when the amount of air supplied to the vessel-front
pulverized coal burner 61c is increased, air is increased while
divided into two equal parts for the vessel-back AAPs 65h and 65i
substantially opposite to the pulverized coal burner 61c.
(9) Sixth Embodiment
[0183] FIG. 11 is a schematic configuration view of a pulverized
coal burning boiler according to a sixth embodiment. An economizer
79 is disposed on an outlet side of a furnace 78. An oxygen
densitometer (or a CO densitometer) 80 for measuring the
concentration of oxygen (or the concentration of CO) in exhaust gas
is provided on a downstream side of the economizer 79. A dumper
type supply amount adjuster 84 is attached individually to an
intermediate portion of each supply path of AAP air 83 supplied to
each AAP 65.
[0184] A plurality of detection ends 81 (four in this embodiment)
of the oxygen densitometer 80 are disposed in a widthwise direction
X (see FIG. 12) of a flue 82. The detection ends 81 can be moved
vertically so that the position of each detection end 81 can be
switched to a plurality of stages (three stages in this embodiment)
in a vertical direction Y (see FIG. 12) of the flue 82.
[0185] FIG. 12 shows measuring points in the flue 82. An oxygen
concentration or CO concentration distribution state of the
economizer outlet can be grasped by the measuring points. The
measuring points substantially correspond to the positions of the
AAPs 65 (vessel front, vessel back, vessel right and vessel left),
respectively.
[0186] In this embodiment, the total amount of AAP air supplied to
all the AAPs 65 is determined to be constant. For example, when the
concentration of oxygen measured at the measuring point
.circleincircle. is lower than that measured at any other measuring
point or when the concentration of CO measured at the measuring
point .circleincircle. is higher than that measured at any other
measuring point, a command signal is output from the control
portion to increase the amount of AAP air on the vessel front and
vessel left side.
[0187] Although this embodiment has been described in the case
where the total amount of AAP air supplied to all the AAPs 65 is
determined to be constant and then the amounts of AAP air supplied
to the AAPs 65 respectively are determined, the total amount of AAP
air may be not determined to be constant so that the amount of air
supplied to an AAP corresponding to the region where a low oxygen
concentration or a high CO concentration is detected can be
increased simply. Accordingly, in this case, the total amount of
AAP air is increased by the amount.
[0188] According to these embodiments, the amount of AAP air can be
accurately distributed to a region high in unburned gas
concentration.
[0189] Incidentally, also in the fifth and sixth embodiments, the
amount of burner combustion air is adjusted in accordance with the
flow rate of pulverized coal but the amount of air not covered is
supplemented as AAP air.
(10) Seventh Embodiment
[0190] FIG. 13 is a view for explaining correction of coal supply
amount data according to a seventh embodiment. As described above,
raw coal 5 input to the coal banker 6 passes through the coal
supply 7 and is milled by the mill 3, so that pulverized coal
distributed to each coal feeding pipe 43 is measured by the
pulverized coal flowmeter 51. At the time of measurement, coal
supply amount data 85 from the coal supply 7 is output to the
pulverized coal flowmeter 51 (control circuit 66). However, coal
staying time in the mill 3 is generally from 45 seconds to 60
seconds, so that there is actually a time lag until pulverized coal
passes through the flowmeter 51.
[0191] Therefore, this embodiment is configured so that the coal
supply amount data 85 is multiplied by a correction coefficient in
consideration of the staying time in the mill so that the corrected
coal supply amount data 85 is output to the pulverized coal
flowmeter 51 (control circuit 66).
[0192] According to this embodiment, the detection accuracy of the
pulverized coal flowmeter 51 can be improved. This embodiment is
suitable for a system in which the absolute amounts of pulverized
coal passing through the respective coal feeding pipes 43 are
measured by the pulverized coal flowmeters 51 so that deviations
between the respective coal feeding pipes 43 are calculated based
on the absolute amounts.
(11) Eighth Embodiment
[0193] FIG. 14 is a view for explaining correction of the flow rate
of pulverized coal according to an eighth embodiment. In this
embodiment, the flow rate of pulverized coal is corrected based on
the percentage of moisture contained in raw coal, the coal supply
amount, the amount of primary air supplied to the mill and the
temperature difference between the inlet and outlet of the
mill.
[0194] FIG. 15 is a characteristic graph showing the relation
between the moisture increasing rate in coal having 3% by weight of
moisture and the dielectric constant increasing rate of the coal.
As shown in FIG. 15, in the pulverized coal flowmeter 51 which
measures the flow rate of pulverized coal based on the dielectric
constant as described above, because a difference is generated
between dielectric constants when the percentage of moisture in
coal changes, the percentage of moisture contained in pulverized
coal passing through the pulverized coal flowmeter 51 is estimated
to correct the output of the flowmeter 51 so that the accuracy of
the measured value can be improved.
[0195] Therefore, in this embodiment, as shown in FIG. 14, a mill
inlet air thermometer 86 and a mill outlet air thermometer 87 are
attached to the inlet and outlet of the mill 3, respectively, so
that a mill inlet air temperature T1 and a mill outlet air
temperature T2 of primary air A1 supplied to the mill 3 are
measured and a temperature difference .DELTA.T (=T1-T2) between the
inlet and outlet of the mill 3 is calculated based on the
temperatures T1 and T2.
[0196] The percentage C of moisture contained in raw coal varies
according to the coal type. The percentage C of moisture according
to the coal type can be stored in a storage portion (not shown) of
the control circuit 66 in advance by analysis or the like. The
amount Q of coal supplied to the mill 3 can be obtained based on
the rotational speed of the coal supply 7. The flow rate A of
primary air A1 supplied to the mill 3 can be obtained based on the
rotational speed of the forcing blower 1.
[0197] The estimated value of the amount of evaporation of moisture
in coal milled in the mill 3 is calculated based on these data in
accordance with the following relational expression:
Moisture Evaporation Amount Estimated Value=f(C,Q,A,.DELTA.T)
in which f is a correction coefficient.
[0198] The percentage of moisture contained in pulverized coal
passing through the pulverized coal flowmeter 51 is estimated based
on the thus calculated estimated value of the moisture evaporation
amount to thereby correct the output of the pulverized coal
flowmeter 51 so that detection accuracy can be improved.
(12) Ninth Embodiment
[0199] FIG. 16 is a schematic configuration view showing a ninth
embodiment. FIGS. 17 and 18 are views for explaining the function
of fluid guiding means used in this embodiment. FIG. 17 is a
sectional view. FIG. 18 is a side view of the fluid guiding means
from an upstream side.
[0200] In this embodiment, fluid guiding means 88 made of an
abrasion-resistant material or coated with an abrasion-resistant
material is disposed on an upstream side of the pulverized coal
flowmeter 51 in order to improve accuracy of the pulverized coal
flowmeter 51 and prevent abrasion due to pulverized coal.
Specifically as shown in FIGS. 17 and 18, the fluid guiding means
88 includes a separation plate 89 disposed in a substantially
central position of the inside of the coal feeding pipe 43 so as to
extend along a flow direction of the mixed fluid 46, and a turning
plate 90 provided in a leading end portion of the separation plate
89. The side shape of the turning plate 90 is substantially so
semicircular as to correspond to an aperture of the coal feeding
pipe 43. As shown in FIG. 17, the turning plate 90 can turn around
a turning shaft 91 in directions of the arrows.
[0201] When the group of pulverized coal flows in the coal feeding
pipe 43, pulverized coal is not distributed substantially equally
in the pipe but becomes in most cases a flow condensed like an
irregularly bent string. The uneven flow has a bad influence on
detection accuracy of the pulverized coal flowmeter 51.
[0202] In this embodiment, a microwave type pulverized coal
flowmeter 51a having a transmitter 52 and a receiver 53 is disposed
in an intermediate portion of the coal feeding pipe 43. Because the
transmitter 52 and the receiver 53 are inserted into the coal
feeding pipe 43, the transmitter 52 and the receiver 53 are worn
out by collision with pulverized coal.
[0203] Therefore, in this embodiment, the turning plate 90 is
raised as shown in FIGS. 17 and 18 to unravel the flow of
pulverized coal condensed like a string by collision with the
turning plate 90 to distribute pulverized coal uniformly to thereby
attain improvement of detection accuracy.
[0204] Moreover, the concentration of pulverized coal flowing on
the transmitter 52 side and on the receiver 53 side is reduced by
the turning plate 90 so as not to hinder measurement to thereby
suppress abrasion of the transmitter 52 and the receiver 53.
(13) Tenth Embodiment
[0205] FIGS. 19 and 20 are views for explaining the function of
fluid guiding means used in a tenth embodiment. FIG. 19 is a
sectional view. FIG. 20 is a side view of the fluid guiding means
from an upstream side. The fluid guiding means 88 according to this
embodiment has a reduced diameter portion 92, and taper faces 93
and 93 provided in front and back of the reduced diameter portion
92.
[0206] FIGS. 21 and 22 are views showing a modification of this
embodiment. FIG. 21 is a sectional view. FIG. 22 is a side view of
the fluid guiding means from an upstream side. The fluid guiding
means 88 according to the modification has a trumpet-shaped member
94 tapered gradually from an upstream side to a downstream
side.
[0207] As shown in FIGS. 19 and 21, a pulverized coal flowmeter 51b
having a first charge sensor 54a and a second charge sensor 54b is
disposed on a downstream side of the fluid guiding means 88. The
charge sensors 54a and 54b are made of circular bodies. Inner
circumferential surfaces of the charge sensors 54a and 54b are
substantially on the same level with the inner circumferential
surface of the coal feeding pipe 43.
[0208] Pulverized coal in the mixed fluid 46 conveyed by the coal
feeding pipe 43 is collected to the central portion side of the
coal feeding pipe 43 by the reduced diameter portion 92 or the
trumpet-shaped member 94. Accordingly, the amount of pulverized
coal passing through the inner circumferential surface side of the
charge sensors 54a and 54b is reduced so that abrasion of the
charge sensors 54a and 54b due to pulverized coal can be
suppressed.
(14) Eleventh Embodiment
[0209] FIG. 27 is a flow path system view of a reheater in a boiler
according to an eleventh embodiment. A reheater 100 disposed in a
flue on a downstream side of an exhaust gas flow in a furnace
includes a primary reheater portion 101 and a secondary reheater
portion 102 from view of arrangement and configuration of members.
The reheater 100 includes a first reheater system 103 on a vessel
left side and a second reheater system 104 on a vessel right side
from view of steam flow path system. The first reheater system 103
and the second reheater system 104 are provided side by side.
[0210] In this embodiment, the first reheater system 103 has a
primary reheater inlet header 105a, a primary reheater 106a, a
primary reheater outlet header 107a, a secondary reheater inlet
header 108a, a secondary reheater 109a, and a secondary reheater
outlet header 110a. The second reheater system 104 has a primary
reheater inlet header 105b, a primary reheater 106b, a primary
reheater outlet header 107b, a secondary reheater inlet header
108b, a secondary reheater 109b, and a secondary reheater outlet
header 110b.
[0211] In this embodiment, a first reheating steam distributing
valve 111 and a second reheating steam distributing valve 112 are
disposed on the inlet side of the first reheater system 103 and the
second reheater system 104. A first reheater steam thermometer 113
and a second reheater steam thermometer 114 are disposed on the
outlet side of the first reheater system 103 and the second
reheater system 104.
[0212] Steam supplied from a high-pressure turbine (not shown) is
forked into two flow paths via one reheater spray 115. The forked
steam is heated while passing through the first and second reheater
systems 103 and 104 from the first and second reheating steam
distributing valves 111 and 112 respectively, so that the reheated
steam is fed from the secondary reheater outlet headers 110a and
110b to middle/low-pressure turbines.
[0213] Although this embodiment is configured so that the
distributing valves 111 and 112 are provided in the first and
second reheater systems 103 and 104 respectively to thereby adjust
the flow rates of distributed steam, a distributing valve may be
provided in one reheater system so that the flow rates of steam
distributed to the first and second reheater systems can be
adjusted by operation of the distributing valves.
[0214] A method of adjusting apertures of the distributing valves
111 and 112 will be described below. First, the reheater outlet
steam temperatures 116 and 117 of vessel left and right, that is,
of the first and second reheater systems 103 and 104 are measured
by the reheater steam thermometers 113 and 114, so that the
measured signals are input to a subtracter 118 to obtain a
deviation value 119. The signal of the deviation value 119 is input
to a PI controller 120, so that aperture adjusting signals 121 and
122 for eliminating the deviation value 119 are output from the PI
controller 120 to the distributing valves 111 and 112 respectively.
On this occasion, an operation reverse in phase to the distributing
valve 111 is performed on the distributing valve 112 through an
inverter ("-1") 123.
[0215] FIG. 28 is a characteristic graph showing an example of
time-lapse changes of the flow rate of fuel (flow rate of
pulverized coal), the aperture of the distributing valve, the flow
rate of steam and the reheater outlet steam temperature (ROT) in
this embodiment.
[0216] As shown in FIG. 28, when a deviation is generated between
the amounts of fuel supplied to the burners at time A for a certain
reason, a deviation is generated between ROTs of the first and
second reheater systems 103 and 104 at time B later than the time
A. This deviation is detected by the reheater steam thermometers
113 and 114 to perform an operation of opening the aperture of the
distributing valve (e.g. distributing valve 111) of a system high
in ROT based on the aperture adjusting signal 121 and contrariwise
throttling the aperture of the distributing valve (e.g.
distributing valve 112) of a system low in ROT based on the
aperture adjusting signal 122 at time C. Accordingly, the flow rate
of steam distributed to the system high in ROT, that is, having an
increased thermal load increases and the flow rate of steam
distributed to the system low in ROT, that is, having a decreased
thermal load decreases, so that the deviation between ROTs of the
first and second reheater systems 103 and 104 is eliminated.
[0217] Although the example has been described in the case where
both the apertures of the distributing valves 111 and 112 are
adjusted, the same effect can be expected in the case where only
the aperture of the distributing valve (e.g. distributing valve
112) on an ROT reduced side, that is, on a side required to reduce
the flow rate of distributed steam is throttled.
[0218] Although the embodiment has been described in the case where
the distributing valves 111 and 112 are disposed on the inlet side
of the first and second reheater systems 103 and 104 respectively,
a resistor such as an orifice may be provided in place of one
distributing valve (e.g. distributing valve 111) so that the flow
rates of steam distributed to the first and second reheater systems
103 and 104 can be adjusted when only the aperture of the other
distributing valve (e.g. distributing valve 112) is adjusted.
[0219] Because ROTs of the first and second reheater systems 103
and 104 are averaged when the maximum temperature limit of ROT is a
reference steam condition plus 8.degree. C. or lower, there is a
function of keeping tolerance at 8.degree. C. Accordingly, the
number of times for starting the reheater spray 115 can be reduced
against disturbance due to the load change in the combustion
device, stopping of the mill, the start of a soot blower, etc., so
that improvement in boiler efficiency and improvement in life of
the reheater spray 115 can be attained.
(15) Twelfth Embodiment
[0220] FIG. 29 is a flow path system view of a reheater in a boiler
according to a twelfth embodiment of the invention.
[0221] An attempt to reduce the excess air ratio to about 10% has
been made in order to attain further reduction of NOx and
improvement of boiler efficiency in recent years. In the excess air
ratio of 10%, there is a possibility that CO will be produced
because of local shortage of air even when the amounts of
pulverized coal supplied to the burners are slightly uneven. To
cope with this, a method of individually measuring the amounts of
pulverized coal supplied to the respective burners to thereby
dynamically adjust combustion air supplied to the respective
burners, that is, individual burner air ratio control has been
proposed in the first to tenth embodiments, etc.
[0222] In a pulverized coal burning boiler using the individual
burner air ratio control, there is a possibility that the deviation
between combustion gas temperatures in vessel left and right may
become large compared with a pulverized coal burning boiler in
which combustion air is equally supplied to the respective burners.
In the background art, because air was equally supplied to the
vessel left and right, imperfect combustion due to shortage of air
occurred in a place where much pulverized coal was supplied so that
the deviation between thermal loads in the vessel left and right
was suppressed compared with the deviation between the amounts of
pulverized coal. However, when just enough air is given to
pulverized coal supplied to the vessel left and right with a
deviation as in the individual burner air ratio control, the
deviation between the amounts of supplied pulverized coal appears
directly as a deviation between thermal loads in the vessel left
and right.
[0223] For example, assume that pulverized coal 15% larger than the
average value of the supply amounts is supplied to the vessel right
side, that is, pulverized coal 15% smaller than the average value
is supplied to the vessel left side in a pulverized coal burning
boiler operated at an excess air ratio of 10%. On the other hand,
because air is equally supplied to all after air ports, the
deviation between the amounts of pulverized coal supplied to the
vessel left and right exceeds supplied air tolerance to cause
imperfect combustion. For this reason, though fuel (pulverized
coal) 15% larger is supplied to the vessel right side, increase in
thermal load is reduced to 10%. However, in the pulverized coal
burning boiler using the individual burner air ratio control,
because air just fit to the deviation between the amounts of
supplied pulverized coal is supplied, 15% increase in thermal load
equal to the deviation between the amounts of supplied pulverized
coal appears in the aforementioned example. The increase in thermal
load has a direct influence on the amount of heat exchange in a
heat exchanger to bring a deviation between steam temperatures.
This embodiment aims at this respect.
[0224] In the pulverized coal burning boiler, the deviation between
the amounts of pulverized coal supplied to the respective burners
appears as a deviation between ROTs with a time lag as described
above. This is because a heat exchanger having a large number of
heat-transfer pipes has a response delay corresponding to change in
gas temperature caused by its metal heat capacity. The time
constant sometimes reaches tens of seconds to several minutes.
[0225] In this embodiment, like the first embodiment etc., the
supply amounts of combustion air corresponding to the supply
amounts of pulverized coal are calculated based on the flow rates
of pulverized coal measured by the pulverized coal flowmeters 51a
to 51h and the supply amounts of combustion air measured by the air
flowmeters 67a to 67h and control command signals are sent to
combustion air supply amount adjusting means 64a to 64h so that the
burner air ratio set by the burner air ratio setting means can be
kept.
[0226] As shown in FIG. 1, the pulverized coal flowmeters 51a to
51h are attached to the coal feeding pipes 43a to 43h connecting
the roller mills 3a and 3b and the respective pulverized coal
burners 61a to 61h so that the amounts of pulverized coal passing
through the coal feeding pipes 43 can be measured individually.
[0227] The flows of exhaust gas produced by combustion in the
respective pulverized coal burners 61a to 61h are substantially
directly poured into flues without large disorder and give heat to
the repeater 100.
[0228] Accordingly, in this embodiment, from the relation between
FIGS. 1 and 29, the first reheater system 103 disposed on the
vessel left side is heated by exhaust gas produced from the
pulverized coal burners 61c, 61d, 61g and 61h disposed on the
vessel left side, whereas the second reheater system 104 disposed
on the vessel right side is heated by exhaust gas produced from the
pulverized coal burners 61a, 61b, 61e and 61f.
[0229] In this embodiment, in addition to the aforementioned
combustion air supply amount individual control, measured values of
the flow rates of pulverized coal from the pulverized coal
flowmeters 51a to 51h are input to a vessel left/right fuel supply
amount calculator 124 as shown in FIG. 29. The vessel left/right
fuel supply amount calculator 124 calculates the flow rate of
pulverized coal supplied to the vessel left side pulverized coal
burners 61c, 61d, 61g and 61h and the flow rate of pulverized coal
supplied to the vessel right side pulverized coal burners 61a, 61b,
61e and 61f. The former is obtained as the sum of the pulverized
coal flowmeters 51c, 51d, 51g and 51h whereas the latter is
obtained as the sum of the pulverized coal flowmeters 51a, 61b, 51e
and 51f.
[0230] A vessel left/right fuel supply amount calculated value 125
calculated thus is input to a bias calculator 126. The bias
calculator 126 obtains a deviation between the flow rate of
pulverized coal supplied to the vessel left side pulverized coal
burners 61c, 61d, 61g and 61h and the flow rate of pulverized coal
supplied to the vessel right side pulverized coal burners 61a, 61b,
61e and 61f and calculates bias values 127 and 128 for the aperture
adjusting signals 121 and 122 as the PI feedback control signals
based on the pulverized coal flow rate deviation value.
Incidentally, optimum patterns for the size of the bias (the shape
of the feed-forward component) are obtained by dynamic
characteristic calculation in advance and the patterns are adjusted
at the time of trial operation.
[0231] The calculated bias values 127 and 128 are added to the
aperture adjusting signals 121 and 122 by adders 129 and 130
respectively to obtain aperture adjusting signals 131 and 131 in
consideration of deviations of the flow rate of pulverized coal to
thereby adjust the apertures of the distributing valves 111 and
112.
[0232] FIG. 30 is a characteristic graph showing an example of
time-lapse changes of the flow rate of fuel (flow rate of
pulverized coal), the aperture of the distributing valve, the flow
rate of steam and ROT in this embodiment.
[0233] As shown in FIG. 30, unbalance (deviation) between the flow
rates of fuel (flow rates of pulverized coal) causing the deviation
between the vessel left and right repeater outlet steam
temperatures is detected early at time D and the apertures of
distributing valves 104a and 104b are adjusted since the time D
based on the unbalance (as represented by the hatched portion in
FIG. 30) so that feed-forward control can be made. Accordingly, the
deviation between the vessel left and right ROTs can be reduced, so
that improvement of boiler controllability can be attained.
(16) Thirteenth Embodiment
[0234] According to the twelfth embodiment, there is a possibility
that the feed-forward component may be so intensive that the
temperature reduction is too large or too small in accordance with
the occasion because the feed-forward component has a substantially
fixed shape.
[0235] For example, as shown in FIG. 36, superheaters 706 to 709
are disposed on upstream sides of reheaters 710 to 713 in an
exhaust gas flow direction. Sprays 723 and 724 are mainly used in
accordance with the transitional temperature change of superheating
steam. The sprays 723 and 724 operate to change the amounts of heat
exchange of the superheaters 706 to 709 and have influence on the
inlet gas temperatures of the reheaters 710 to 713. Accordingly,
when the bias of the flow rate of reheating steam is determined
only based ion the change of the flow rate of fuel (flow rate of
pulverized coal) as in the twelfth embodiment, excess and
deficiency may occur due to the effect of the sprays 723 and
724.
[0236] This embodiment is accomplished in consideration of this
respect. FIG. 31 is a flow path system view of a repeater in a
boiler according to the thirteenth embodiment.
[0237] In this embodiment, various kinds of reheating steam
temperature deviation prediction models 133 for predicting
reheating steam temperature deviations based on pieces of
information exerting influence on the reheating steam temperature,
such as the amount of supplied fuel, the flow rate of boiler
supplied water, the amount of superheater inlet spray, the output
of a power generator, etc. are prepared so that the reheating steam
temperature deviation prediction models 133 are stored in a storage
portion (not shown) of reheating steam temperature deviation
prediction means 134.
[0238] The amount of supplied fuel 135, the flow rate of boiler
supplied water 136, the amount of superheater inlet spray 137 and
the power generator output 138 in the pulverized coal burning
boiler currently operating are input to the reheating steam
temperature deviation prediction means 134, so that a predicted
reheating steam temperature deviation value 139 is obtained by
referring to these input values and the reheating steam temperature
deviation prediction models 133.
[0239] The predicted reheating steam temperature deviation value
139 is input to reheating steam distributing valve aperture
correction means 140. The reheating steam distributing valve
aperture correction means 140 generates distributing valve aperture
correction signals 141 and 142 based on the predicted reheating
steam temperature deviation value 139. The distributing valve
aperture correction signals 141 and 142 are added to the aperture
adjusting signals 121 and 122 by adders 143 and 144 respectively,
so that the apertures of the reheating steam distributing valves
111 and 112 are adjusted based on the corrected aperture adjusting
signals 145 and 146 respectively.
[0240] FIG. 32 is a characteristic graph showing an example of
time-lapse changes of the flow rate of fuel (flow rate of
pulverized coal), the aperture of the distributing valve, the flow
rate of steam and ROT in this embodiment.
[0241] In this embodiment, the apertures of the distributing valves
104a and 104b are adjusted at time D (as represented by the hatched
portion in FIG. 32) based on the vessel left and right ROT
deviations in consideration of pieces of information exerting
influence on the reheating steam temperature, such as the amount of
supplied fuel, the flow rate of boiler supplied water, the amount
of superheater inlet spray, the power generator output, etc.
Because feed-forward control can be performed in this manner,
further reduction in the vessel left and right ROT deviations can
be obtained so that further improvement in boiler controllability
can be attained.
(17) Fourteenth Embodiment
[0242] In a superheater, when a bias between the vessel left and
right is applied to the input amount of superheater spray, the
deviation between the vessel left and right superheating steam
temperatures can be reduced. However, when the deviation between
the vessel left and right superheating steam temperatures is high,
it is necessary to increase the flow rate of spray because
tolerance of steam temperature control as the original purpose of
the superheater spray is reduced, and control follow-up
characteristic is worsened because spray control is complicated. As
a result, increase in the flow rate of spray means increase in the
amount of bypassing the heat-transfer surface halfway, so that
boiler efficiency is lowered.
[0243] In this embodiment, the flow rates of steam in the vessel
left and right of the superheater are adjusted to eliminate the
deviation between the vessel left and right main steam
temperatures.
[0244] FIG. 33 is a flow path system view of a superheater in a
boiler according to the fourteenth embodiment.
[0245] A superheater 200 disposed from an upper portion of a
furnace into a flue on a downstream side in an exhaust gas flow
direction thereof includes a primary superheater portion 201 and a
secondary superheater portion 202 from view of arrangement and
configuration of members. The superheater 200 includes a first
superheater system 204 on the vessel left side and a second
superheater system 205 on the vessel right side from view of steam
flow path systems. The first superheater system 204 and the second
superheater system 205 are arranged side by side.
[0246] In this embodiment, the first superheater system 204 has a
primary superheater inlet header 206a, a primary superheater 207a,
a primary superheater outlet header 208a, a secondary superheater
inlet header 209a, a secondary superheater 210a, a secondary
superheater outlet header 211a, a tertiary superheater inlet header
212a, a tertiary superheater 213a, and a tertiary superheater
outlet header 214a. The second superheater system 205 has a primary
superheater inlet header 206b, a primary superheater 207b, a
primary superheater outlet header 208b, a secondary superheater
inlet header 209b, a secondary superheater 210b, a secondary
superheater outlet header 211b, a tertiary superheater inlet header
212b, a tertiary superheater 213b, and a tertiary superheater
outlet header 214b.
[0247] In this embodiment, a first superheating steam distributing
valve 215 and a second superheating steam distributing valve 216
are disposed on the inlet side of the first superheater system 204
and the second superheater system 205. A first superheater steam
thermometer 217 and a second superheater steam thermometer 218 are
disposed on the outlet side of the first superheater system 204 and
the second superheater system 205.
[0248] In the first superheater system 204, a secondary superheater
inlet spray 219a is attached to a connection pipe which connects
the primary superheater outlet header 208a and the secondary
superheater inlet header 209a. A tertiary superheater inlet spray
220a is attached to a connection pipe which connects the secondary
superheater outlet header 211a and the tertiary superheater inlet
header 212a. In the second superheater system 205, a secondary
superheater inlet spray 219b is attached to a connection pipe which
connects the primary superheater outlet header 208b and the
secondary superheater inlet header 209b. A tertiary superheater
inlet spray 220b is attached to a connection pipe which connects
the secondary superheater outlet header 211b and the tertiary
superheater inlet header 212b.
[0249] Steam supplied from a cage (not shown) is forked into two
flow paths via outlet headers 221a and 221b. The forked steam is
superheated while passing through the first and second superheater
systems 204 and 205 from the first and second superheating steam
distributing valves 215 and 216 respectively, so that the
superheated steam is fed from the tertiary superheater outlet
headers 214a and 214b to high-pressure turbines.
[0250] A method of adjusting the apertures of the distributing
valves 215 and 216 will be described below. First, superheater
outlet steam temperatures 222 and 223 of vessel left and right,
that is, of the first and second superheater systems 204 and 205
are measured by the superheater steam thermometers 217 and 218, so
that the measured signals are input to a subtracter 224 to obtain a
deviation value 225. The signal of the deviation value 225 is input
to a PI controller 226, so that aperture adjusting signals 227 and
228 for eliminating the deviation value 225 are output from the PI
controller 226 to the distributing valves 215 and 216 respectively.
On this occasion, an operation reverse in phase to the distributing
valve 215 is performed on the distributing valve 216 through an
inverter ("-1") 229.
[0251] When a deviation is generated between the amounts of fuel
supplied to the burners for a certain reason, a deviation is lately
generated between superheater outlet steam temperatures (SOTs) 222
and 223 of the first and second superheater systems 204 and 205.
This deviation is detected by the superheater steam thermometers
217 and 218 to perform an operation of opening the aperture of the
distributing valve (e.g. distributing valve 215) of a system high
in SOT based on the aperture adjusting signal 227 and contrariwise
throttling the aperture of the distributing valve (e.g.
distributing valve 216) of a system low in SOT based on the
aperture adjusting signal 228. Accordingly, the flow rate of steam
distributed to the system high in SOT, that is, having an increased
thermal load increases and the flow rate of steam distributed to
the system low in SOT, that is, having a decreased thermal load
decreases, so that the deviation between SOTs of the first and
second superheater systems 204 and 205 is eliminated.
[0252] Although FIG. 28 is a characteristic graph showing an
example of time-lapse changes of the flow rate of fuel, the
aperture of the distributing valve, the flow rate of steam and the
reheater outlet steam temperature (ROT) in the eleventh embodiment,
the fourteenth embodiment behaves as if the reheater outlet steam
temperature (ROT) in FIG. 28 were replaced by the superheater
outlet steam temperature (SOT).
(18) Fifteenth Embodiment
[0253] FIG. 34 is a flow path system view of a superheater in a
boiler according to a fifteenth embodiment.
[0254] As shown in FIG. 34, measured values of the flow rates of
pulverized coal from the pulverized coal flowmeters 51a to 51h are
input to a vessel left/right fuel supply amount calculator 230. The
vessel left/right fuel supply amount calculator 230 calculates the
flow rate of pulverized coal supplied to the vessel left side
pulverized coal burners 61c, 61d, 61g and 61h and the flow rate of
pulverized coal supplied to the vessel right side pulverized coal
burners 61a, 61b, 61e and 61f. The former is obtained as the sum of
the pulverized coal flowmeters 51c, 51d, 51g and 51h whereas the
latter is obtained as the sum of the pulverized coal flowmeters
51a, 61b, 51e and 51f.
[0255] A vessel left/right fuel supply amount calculated value 231
calculated thus is input to a bias calculator 232. The bias
calculator 232 obtains a deviation between the flow rate of
pulverized coal supplied to the vessel left side pulverized coal
burners 61c, 61d, 61g and 61h and the flow rate of pulverized coal
supplied to the vessel right side pulverized coal burners 61a, 61b,
61e and 61f and calculates bias values 233 and 234 for the aperture
adjusting signals 227 and 228 as the PI feedback control signals
based on the pulverized coal flow rate deviation value.
Incidentally, optimum patterns for the size of the bias (the shape
of the feed-forward component) are obtained by dynamic
characteristic calculation in advance and the patterns are adjusted
at the time of trial operation.
[0256] The calculated bias values 233 and 234 are added to the
aperture adjusting signals 227 and 228 by adders 235 and 236
respectively to obtain aperture adjusting signals 237 and 238 in
consideration of deviations of the flow rate of pulverized coal to
thereby adjust the apertures of the distributing valves 215 and
216.
[0257] Although FIG. 30 is a characteristic graph showing an
example of time-lapse changes of the flow rate of fuel, the
aperture of the distributing valve, the flow rate of steam and the
reheater outlet steam temperature (ROT) in the twelfth embodiment,
the fifteenth embodiment behaves as if the reheater outlet steam
temperature (ROT) in FIG. 30 were replaced by the superheater
outlet steam temperature (SOT).
(19) Sixteenth Embodiment
[0258] FIG. 35 is a flow path system view of a superheater in a
boiler according to a sixteenth embodiment.
[0259] In this embodiment, various kinds of superheating steam
temperature deviation prediction models 240 for predicting
superheating steam temperature deviations based on pieces of
information exerting influence on the superheating steam
temperature, such as the amount of supplied fuel, the flow rate of
boiler supplied water, the amount of superheater inlet spray, the
power generator output, etc. are prepared so that the superheating
steam temperature deviation prediction models 240 are stored in a
storage portion (not shown) of superheating steam temperature
deviation prediction means 241.
[0260] The amount of supplied fuel 242, the flow rate of boiler
supplied water 243, the amount of superheater inlet spray 244 and
the power generator output 245 in the pulverized coal burning
boiler currently operating are input to the superheating steam
temperature deviation prediction means 241, so that a predicted
superheating steam temperature deviation value 246 is obtained by
referring to these input values and the superheating steam
temperature deviation prediction models 240.
[0261] The predicted superheating steam temperature deviation value
246 is input to superheating steam distributing valve aperture
correction means 247. The superheating steam distributing valve
aperture correction means 247 generates distributing valve aperture
correction signals 248 and 249 based on the predicted superheating
steam temperature deviation value 246. The distributing valve
aperture correction signals 248 and 249 are added to the aperture
adjusting signals 227 and 228 by adders 250 and 251 respectively,
so that the apertures of the superheating steam distributing valves
215 and 216 are adjusted based on corrected aperture adjusting
signals 252 and 253 respectively.
[0262] Although FIG. 32 is a characteristic graph showing an
example of time-lapse changes of the flow rate of fuel, the
aperture of the distributing valve, the flow rate of steam and the
reheater outlet steam temperature (ROT) in the thirteenth
embodiment, the sixteenth embodiment behaves as if the reheater
outlet steam temperature (ROT) in FIG. 32 were replaced by the
superheater outlet steam temperature (SOT).
[0263] Although the embodiment has been described in the case where
steam distributing valve control for reheater systems and steam
distributing valve control for superheater systems are performed
separately, steam distributing valve control for reheater systems
and superheater systems can be performed in only one pulverized
coal burning boiler.
[0264] Specific effects of the invention are as follows.
(1) With respect to the problem that the deviation between reheater
vessel left and right steam temperatures cannot be eliminated
thoroughly by the background-art method of exchanging reheater
vessel left and right systems, the effect of reducing the steam
temperature deviation to zero is obtained according to this
invention because the flow rates of steam are adjusted while the
deviation between the reheater vessel left and right steam
temperatures is viewed. (2) With respect to the problem that
response is delayed due to the influence of interference and the
operating velocity of a gas damper in the background-art method
using the gas damper for adjusting the deviation between reheater
vessel left and right steam temperatures, the effect of quickening
the response characteristic is obtained according to this invention
because adjustment of the flow rates of steam supplied to the
reheater vessel left and right does not interfere with the
superheater and the flow rates of steam supplied to the superheater
vessel left and right does not likewise interfere with the
reheater. (3) With respect to the problem that lowering of
efficiency due to bypassing, increase in the heat-transfer surface
and sudden increase in temperature in the bypassed heat-transfer
surface occur in the background-art method in which a connection
pipe for connecting the inlet and outlet of the primary reheater is
provided to adjust the flow rates of steam in the vessel left and
right systems, the problem of lowering of efficiency, increase in
the heat-transfer surface and sudden increase in temperature of the
bypassed heat-transfer surface does not occur in this invention
because bypassing can be avoided when the balance between the flow
rates of steam supplied to the repeater vessel left and right is
changed. (4) With respect to the problem that the deviation between
superheater vessel left and right steam temperatures cannot be
eliminated thoroughly by the background-art method of exchanging
superheater vessel left and right systems, the effect of reducing
the steam temperature deviation to zero is obtained according to
this invention because the flow rates of steam are adjusted while
the deviation between the superheater vessel left and right steam
temperatures is viewed.
[0265] With respect to the problem that the flow rate of spray
increases in the background-art method of applying a bias to the
flow rate of superheating spray between the vessel left and right,
the effect of reducing the flow rate of spray is obtained according
to this invention because the deviation between the superheater
vessel left and right steam temperatures is adjusted only based on
the flow rate of steam led into the superheater so that the spray
is used only for adjusting the temperature of superheating
steam.
BRIEF DESCRIPTION OF THE DRAWINGS
[0266] FIG. 1 A schematic plan configuration view of a pulverized
coal burning boiler according to a first embodiment of the
invention.
[0267] FIG. 2 A schematic configuration view of a pulverized coal
burner used in the pulverized coal burning boiler according to the
first embodiment.
[0268] FIG. 3 A graph showing an example of deviations from an
average flow rate in the case where pulverized coal is distributed
to four coal feeding pipes and the flow rates of pulverized coal
are measured by pulverized coal flowmeters respectively.
[0269] FIG. 4 A view for explaining a combustion air supply amount
control system according to the first embodiment of the
invention.
[0270] FIG. 5 A block diagram showing a control circuit used in the
combustion air supply amount control system.
[0271] FIG. 6 A schematic configuration view of a pulverized coal
burning boiler according to a second embodiment of the
invention.
[0272] FIG. 7 A view showing results of an experiment performed for
specifying a burner stage large in CO reducing effect.
[0273] FIG. 8 A schematic configuration view of a pulverized coal
burning boiler according to a third embodiment of the invention.
FIG. 8(a) is a view showing the correspondence relation between
pulverized coal burners and AAPs. FIG. 8(b) is a view showing the
arrangement of pulverized coal burners. FIG. 8(c) is a view showing
the arrangement of AAPs.
[0274] FIG. 9 A view showing the CO reducing effect in the third
embodiment.
[0275] FIG. 10 A view showing the correspondence relation between
pulverized coal burners and AAPs in a pulverized coal burning
boiler according to a fifth embodiment of the invention.
[0276] FIG. 11 A schematic configuration view of a pulverized coal
burning boiler according to a sixth embodiment of the
invention.
[0277] FIG. 12 A view showing measuring points in a flue in the
sixth embodiment.
[0278] FIG. 13 A view for explaining correction of coal supply
amount data according to a seventh embodiment of the invention.
[0279] FIG. 14 A view for explaining correction of the flow rate of
pulverized coal according to an eighth embodiment of the
invention.
[0280] FIG. 15 A characteristic graph showing the relation between
the moisture increasing rate in coal and the dielectric constant
increasing rate of the coal.
[0281] FIG. 16 A schematic configuration view showing a ninth
embodiment of the invention.
[0282] FIG. 17 A sectional view for explaining the function of
fluid guiding means used in this embodiment.
[0283] FIG. 18 A side view of the fluid guiding means from an
upstream side.
[0284] FIG. 19 A sectional view for explaining the function of
fluid guiding means used in a tenth embodiment of the
invention.
[0285] FIG. 20 A side view of the fluid guiding means from an
upstream side.
[0286] FIG. 21 A sectional view for explaining the function of
fluid guiding means used in a modification of the tenth embodiment
of the invention.
[0287] FIG. 22 A side view of the fluid guiding means from an
upstream side.
[0288] FIG. 23 A schematic configuration view of a pulverized coal
burning combustion system according to an embodiment of the
invention.
[0289] FIG. 24 A schematic configuration view of a vertical roller
mill used in an embodiment of the invention.
[0290] FIG. 25 A schematic configuration view of a microwave type
pulverized coal flowmeter used in an embodiment of the
invention.
[0291] FIG. 26 A schematic configuration view of an electrostatic
charge type pulverized coal flowmeter used in an embodiment of the
invention.
[0292] FIG. 27 A flow path system view of a reheater in a boiler
according to an eleventh embodiment of the invention.
[0293] FIG. 28 A characteristic graph showing an example of
time-lapse changes of the flow rate of fuel, the aperture of the
distributing valve, the flow rate of steam and the reheater outlet
steam temperature (ROT) in this embodiment.
[0294] FIG. 29 A flow path system view of a reheater in a boiler
according to a twelfth embodiment of the invention.
[0295] FIG. 30 A characteristic graph showing an example of
time-lapse changes of the flow rate of fuel, the aperture of the
distributing valve, the flow rate of steam and the reheater outlet
steam temperature (ROT) in this embodiment.
[0296] FIG. 31 A flow path system view of a reheater in a boiler
according to a thirteenth embodiment of the invention.
[0297] FIG. 32 A characteristic graph showing an example of
time-lapse changes of the flow rate of fuel, the aperture of the
distributing valve, the flow rate of steam and the reheater outlet
steam temperature (ROT) in this embodiment.
[0298] FIG. 33 A flow path system view of a superheater in a boiler
according to a fourteenth embodiment of the invention.
[0299] FIG. 34 A flow path system view of a superheater in a boiler
according to a fifteenth embodiment of the invention.
[0300] FIG. 35 A flow path system view of a superheater in a boiler
according to a sixteenth embodiment of the invention.
[0301] FIG. 36 A view for explaining a variable pressure
once-through type pulverized coal burning boiler according to the
background art.
[0302] FIG. 37 A characteristic graph showing an example of
deviation of reheating steam temperature (ROT) based on deviation
of the amount of supplied fuel in the pulverized coal burning
boiler.
[0303] FIG. 38 A view showing arrangement of gas distributing
dampers in a fuel based on a proposal according to the background
art.
[0304] FIG. 39 A view showing a reheating steam system in a boiler
proposed according to the background art.
[0305] FIG. 40 A characteristic graph showing an example of
deviation of superheating steam temperature (SOT) based on
deviation of the amount of supplied fuel in a pulverized coal
burning boiler according to the background art.
DESCRIPTION OF THE REFERENCE NUMERALS AND SIGNS
[0306] 1: forcing blower, 2: primary air forcing blower, 3:
vertical roller mill, 4: exhaust gas type air preheater, 5: raw
coal, 6: coal banker, 7: coal supply, 8: pulverized coal nozzle, 9:
pulverized coal burning boiler, 10: steam type air preheater, 11:
wind box, 12: dust collector, 13: denitrater, 14: induced blower,
15: desulfurizer, 21: milling portion, 22: classifying portion, 23:
milling portion driving portion, 24: classifying portion driving
portion, 25: distributing portion, 43: coal feeding pipe, 44: coal
supply pipe, 45: primary air, 46: mixed fluid, 47: distributing
chamber, 51: pulverized coal flowmeter, 51a: microwave type
pulverized coal flowmeter, 51b: electrostatic charge type
pulverized coal flowmeter, 52: microwave transmitter, 53: microwave
receiver, 54a: first charge sensor, 54b: second charge sensor, 61:
pulverized coal burner, 62: combustion air, 63: combustion air
supply path, 64: combustion air supply amount adjusting means, 65:
AAP, 66: control circuit, 67: air flowmeter, 68: combustion air
amount control command value, 69: adder, 70: divider, 71: coal
supply amount, 72: burner air ratio, 73: theoretical air amount,
74: combustion air amount, 75: correction amount limiter, 76:
multiplier, 77: subtracter, 78: furnace, 79: economizer, 80: oxygen
concentration measuring meter, 81: detection end, 82: flue, 83: AAP
air, 84: supply amount adjuster, 85: coal supply amount data, 86:
mill inlet thermometer, 87: mill outlet thermometer, 88: fluid
guiding means, 89: separation plate, 90: turning plate, 91: turning
shaft, 92: reduced-diameter portion, 93: taper face, 94:
trumpet-shaped member, A: air, A1: primary air, A2: secondary
air.
[0307] 100: reheater, 101: primary reheater portion, 102: secondary
reheater portion, 103: first reheater system, 104: second reheater
system, 105: primary reheater inlet header, 106: primary reheater,
107: primary reheater outlet header, 108: secondary reheater inlet
header, 109: secondary reheater, 110: secondary reheater outlet
header, 111: first reheating steam distributing valve, 112: second
reheating steam distributing valve, 113: first reheating steam
thermometer, 114: second reheating steam thermometer, 115: reheater
spray, 116: first reheater outlet steam temperature, 117: second
reheater outlet steam temperature, 118: subtracter, 119: deviation
value, 120: PI controller, 121, 122: aperture adjusting signal,
123: inverter, 124: vessel left/right fuel supply amount
calculator, 125: vessel left/right fuel supply amount calculated
value, 126: bias calculator, 127, 128: bias calculated value, 129,
130: adder, 131, 132: aperture adjusting signal, 133: reheating
steam temperature deviation prediction model, 134: reheating steam
temperature deviation prediction means, 135: fuel supply amount,
136, boiler water supply amount, 137: superheater inlet spray
amount, 138: power generator output, 139: predictive reheating
steam deviation value, 140: reheating steam distributing valve
aperture correction means, 141, 142: distributing valve aperture
correction signal, 143, 144: adder, 200: superheater, 201: primary
superheater portion, 202: secondary superheater portion, 203:
tertiary superheater portion, 204: first superheater system, 205:
second superheater system, 206: primary superheater inlet header,
207: primary superheater, 208: primary superheater outlet header,
209: secondary superheader inlet header, 210: secondary
superheater, 211: secondary superheater outlet header, 212:
tertiary superheater inlet header, 213: tertiary superheater, 214:
tertiary superheater outlet header, 215: first superheating steam
distributing valve, 216: second superheating steam distributing
valve, 217: first superheating steam thermometer, 218: second
superheating steam thermometer, 219: secondary superheater inlet
spray, 220: tertiary superheater inlet spray, 221: outlet header,
222, 223: superheater outlet steam temperature, 224: subtracter,
225: deviation value, 226: PI controller, 227, 228: aperture
adjusting signal, 229: inverter, 230: vessel left/right fuel supply
amount calculator, 231: vessel left/right fuel supply amount
calculated value, 232: bias calculator, 233, 234: bias calculated
value, 235, 236: adder, 237, 238: aperture adjusting signal, 240:
superheating steam temperature deviation prediction model, 241:
superheating steam temperature deviation prediction means, 242:
fuel supply amount, 243: boiler water supply amount, 244:
superheater inlet spray amount, 245: power generator output, 246:
predictive superheating steam deviation value, 247: superheating
steam distributing valve aperture correction means, 248, 249:
distributing valve aperture correction signal, 250, 251: adder,
252, 253: aperture adjusting signal.
* * * * *