U.S. patent application number 13/262391 was filed with the patent office on 2012-05-17 for method and assembly for improving the dynamic behavior of a coal-fired power plant.
Invention is credited to Hellmuth Brueggemann, Olivier Drenik, Michael Heim, Haider Mirza.
Application Number | 20120122042 13/262391 |
Document ID | / |
Family ID | 42333293 |
Filed Date | 2012-05-17 |
United States Patent
Application |
20120122042 |
Kind Code |
A1 |
Brueggemann; Hellmuth ; et
al. |
May 17, 2012 |
METHOD AND ASSEMBLY FOR IMPROVING THE DYNAMIC BEHAVIOR OF A
COAL-FIRED POWER PLANT
Abstract
The invention relates to a method for improving the dynamic
behavior of a coal-fired power plant for primary and/or secondary
requirements of the power grid operator with respect to the current
output into the grid, wherein the power plant has a nominal output
(RC) and is operated by way of firing, wherein upon an increase in
the primary and/or secondary requirements of the power grid
operator with respect to the current output into the grid the coal
dust volume that is supplied is raised with respect to the present
actual output, and wherein upon a decrease in the primary and/or
secondary requirements of the power grid operator with respect to
the current output into the grid the coal dust volume that is
supplied is lowered with respect to the present actual output and
is stored, and to an assembly for carrying out the method.
Inventors: |
Brueggemann; Hellmuth;
(Esslingen, DE) ; Drenik; Olivier; (Belfort,
FR) ; Heim; Michael; (Horb, DE) ; Mirza;
Haider; (Stuttgart, DE) |
Family ID: |
42333293 |
Appl. No.: |
13/262391 |
Filed: |
March 19, 2010 |
PCT Filed: |
March 19, 2010 |
PCT NO: |
PCT/DE2010/000323 |
371 Date: |
November 11, 2011 |
Current U.S.
Class: |
431/12 ; 110/105;
110/222; 110/347; 431/18 |
Current CPC
Class: |
F23K 2203/105 20130101;
F23D 1/00 20130101; F23C 6/02 20130101; F23K 2201/1006 20130101;
F23N 1/00 20130101; F23K 2203/103 20130101; F23K 3/02 20130101;
F23K 1/00 20130101; F23C 6/047 20130101 |
Class at
Publication: |
431/12 ; 110/347;
110/105; 110/222; 431/18 |
International
Class: |
F23N 1/00 20060101
F23N001/00; F23K 3/02 20060101 F23K003/02; F23K 3/00 20060101
F23K003/00; F23D 1/00 20060101 F23D001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 3, 2009 |
DE |
10 2009 016 191.0 |
Claims
1. A method for improving the dynamic behavior of a coal-fired
power plant for primary and/or secondary requirements of the power
grid operator with respect to the current output into the grid,
wherein the power plant has a nominal output (RC) and is operated
with a furnace comprising at least one firing box for the firing of
the fuel, at least two coal grinding plants for the grinding of the
fuel having a direct fuel system, wherein at least one of these
coal grinding plants comprises an additional indirect firing system
and the coal dust is indirectly fed to the firing box via the
indirect firing system having at least one silo and apportioning
organs and the further coal grinding plant(s) directly feeds the
coal dust to the firing box via the direct firing system, and
wherein upon an increase of the primary and/or secondary
requirements of the power grid operator with respect to the current
output into the grid the coal dust quantity indirectly fed in via
silo and apportioning organs compared with the present actual
output or compared with the coal dust quantity fed in through each
of the coal grinding plant(s) is increased and in the process coal
dust stocked in the silo is withdrawn and introduced into the
firing box, and wherein upon a reduction of the primary and/or
secondary requirements of the power grid operator with respect to
the current output into the grid the coal dust quantity indirectly
fed in via silo and apportioning organs is reduced compared with
the present actual output or compared with the coal dust quantity
fed in through each of the coal grinding plant(s) is reduced and in
the process coal dust excessively produced by the grinding plant
stored in the silo.
2. The method as claimed in claim 1, characterized in that the silo
has a storage volume (V.sub.Sp) and in normal operation of the
indirect firing system with regard to volume is filled to about
half with coal dust for stocking and use upon an increase of the
primary and/or secondary requirements of the power grid operator
with respect to the power output into the grid and the remaining
storage volume is used for receiving and storing the excess
produced coal dust upon reduction of the primary and/or secondary
requirements of the power grid operator with respect to the current
output into the grid.
3. The method as claimed in claim 1, characterized in that the
increase or reduction of the indirectly fed-in coal dust quantity
is effected through controlled increase or reduction of the
throughput rate of the apportioning organs.
4. The method as claimed in claim 1, characterized in that upon an
increase or a reduction of the indirectly fed-in coal dust quantity
the volumetric flow of the conveying gas blower is increased or
reduced in a controlled manner.
5. The method as claimed in claim 3, characterized in that the
increase or the reduction of the throughput rate of the
apportioning organs and/or the increase or reduction of the
volumetric flow of the conveying gas blower is brought about by the
block output control of the coal-fired power plant influenced by
the requirements of the power grid.
6. The method as claimed in claim 1, characterized in that the
primary requirement is triggered through a remote-controlled
signal.
7. The method as claimed in claim 1, characterized in that the
secondary requirement is triggered through a remote-controlled
signal.
8. The method as claimed in claim 1, characterized in that the
secondary requirement is triggered through written or oral
instruction to the operating personnel of the power plant.
9. An assembly for improving the dynamic behavior of a coal-fired
power plant for primary and/or secondary requirements of the power
grid operator with respect to the current output into the grid,
wherein the power plant has a nominal output (RC) and is designed
with a furnace (1) which substantially comprises at least one
firing box for the firing of the fuel, at least two coal grinding
plants (2.1, 2.2) for the grinding of the fuel comprising a direct
firing system, wherein at least one of these coal grinding plants
(2.1, 2.2) comprises an additional indirect firing system and the
coal dust can be indirectly fed to the firing box via the indirect
firing system having at least one silo (5) and apportioning organs
(10) and with the further coal grinding plant(s) (2.1, 2.2) the
firing box can be directly fed with coal dust via the direct firing
system, and wherein upon an increase of the primary and/or
secondary requirements of the power grid operator with respect to
the current output into the grid the coal dust quantity that can be
indirectly fed in via silo (5) and apportioning organs (10)
compared to the present actual output or compared to the coal dust
quantity that can be fed in by the coal grinding plant(s) (2.1,
2.2) in each case can be increased and in the process coal dust
stocked in the silo (5) can be withdrawn and introduced into the
firing box and wherein upon a reduction of the primary and/or
secondary requirements of the power grid operator with respect to
the current output into the grid the coal dust quantity that can be
indirectly fed in via silo (5) and apportioning organs (10)
compared with the present actual output or compared with the coal
dust quantity that can be fed in through the coal grinding plant(s)
(2.1, 2.2) in each case can be reduced and in the process excess
coal dust produced by the grinding plant (2.1, 2.2) can be stored
in the silo (5).
Description
[0001] Method and assembly for improving the dynamic behavior of a
coal-fired power plant for primary and/or secondary requirements of
the power grid operator with respect to the current output into the
grid.
[0002] The invention relates to a method and assembly for improving
the dynamic behavior of a coal-fired power plant for primary and/or
secondary requirements of the power grid operator with respect to
current output into the grid.
[0003] Keeping the alternating voltage frequency in power grids
constant constitutes an important objective. Deviations from the
predetermined frequency can result in the failure of consumers
connected to the grid and consequential damages resulting from such
failure.
[0004] Deviations from the predetermined grid frequency value
mainly occur when the power requirement on the power plants
connected to the power grid suddenly changes because for instance a
power plant is disconnected from the grid because of an accident or
a large consumer is connected to the grid or because the grid
configuration or grid distribution changes. In order to keep the
grid frequency constant at the predetermined value or within a
certain tolerance range it has to be ensured, within the scope of
the so-called primary control or primary control output, that the
generated power and the grid load remain balanced and as much
electric power is always generated as is consumed by the grid load
when operating with a predetermined grid frequency. In doing so,
the primary control is additionally supported by the secondary
control or secondary control output, which following the balancing
of a sudden change of the consumed or the generated power through
the primary control offsets quasi-stationary deviations both of the
frequency as well as of the transfer power.
[0005] In order to be able to counteract deviations from the
predetermined grid frequency value in the shortest time, some
national grid operators stipulate in their standards conditions or
targets under which this has to be accomplished. Thus, the British
Grid Operator National Grid Electricity Transmission plc for
example through its document "The Grid Code", Issue 3, prescribes
that in the event of a frequency deviation a power plant linked to
the power grid, for example at an operating mode of 65% of its
nominal output the power plant output within the scope of the
primary control or the primary requirements is increased by 10% of
its nominal output, within 10 seconds, thus counteracting the
frequency deviation. This, in terms of time, very rapid and with
respect to the power output very large change makes major demands
on the power plant, particularly on a coal-fired power plant.
[0006] As a rule, large coal-fired power plants are designed with
coal dust furnaces, with which the coal ground in the coal grinding
plant can be directly fed to the firing box of the power plant via
coal dust lines (so-called "direct" coal dust furnaces). The
condition of the fuel is one of the main factors for good
combustion, a sound efficiency, low emissions and little that is
uncombusted in the ash in order to be able to utilize this
by-product. For coal conditioning, the coal grinding plant or coal
mill has to be in a stationary heat and mass flow equilibrium,
which results in load changes on the coal dust furnace and thus on
the power plant itself being able to be carried out only slowly and
thus a delay time occurring when load changes are carried out or
are required.
[0007] The delay time of the coal mill with changing fuel quantity
or charge is a substantial part of the overall plant delay time.
The delay time of the coal mill can be long depending on the raw
coal conditioning process (dependent on fineness, moisture,
hardness of the raw coal and the mill loading) and therefore has a
detrimental effect on the delay time of the overall plant.
[0008] The object of the invention now is to create a method for
improving the dynamic behavior of a coal-fired power plant for
primary and/or secondary requirements of the power grid operator
with respect to the current output into the grid, with which the
delay time of the coal dust furnace of the power plant is reduced
so that the power plant meets the targets or conditions of
respective national operators of power grids. It is, moreover, an
object of the invention to create an assembly for improving the
dynamic behavior of a coal-fired power plant for primary and/or
secondary requirements of the power grid operator with respect to
the current output into the grid.
[0009] The object mentioned above is solved through the totality of
the features of Patent Claim 1 with respect to the method and
through the totality of the features of Patent Claim 9 with respect
to the assembly.
[0010] Advantageous configurations of the invention can be taken
from the subclaims.
[0011] Through the solution according to the invention a method and
an assembly for improving the dynamic behavior of a coal-fired
power plant for primary and/or secondary requirements of the power
grid operator with respect to the current output into the grid is
created, which has or have the following advantages: [0012]
Creation of the possibility for power plant operators to obtain the
required permits for building and operating power plants in
agreement with the prescribed national grid frequency requirements.
[0013] Through the sale of primary control reserve, the power plant
operator is enabled to operate the plant more economically or
achieve higher profits. [0014] The manufacturer or supplier of such
power plants is enabled to offer or sell these power plants on
world-wide markets, e.g. UK, Ireland, France, China, India,
Singapore etc.
[0015] An advantageous embodiment of the invention provides that
the silo having a storage volume V.sub.Sp in normal operation of
the indirect firing system is filled, in terms of volume,
approximately half with coal dust for storage and use upon increase
of the primary and/or secondary requirements of the power grid
operator with respect to the current output into the grid and the
remaining storage volume is used for receiving and storing the
excess-produced coal dust upon reduction of the primary and/or
secondary requirements of the power grid operator with respect to
the current output into the grid.
[0016] In an advantageous configuration of the invention, the
increase or reduction of the indirectly fed-in coal dust quantity
is effected through a controlled increase or reduction of the
throughput rate of the apportioning organs. Thus, the needs or the
dynamic behavior of the coal-fired power plant can be accurately
taken into account.
[0017] An advantageous configuration provides increasing or
reducing the volumetric flow of the conveying gas blower in a
controlled manner upon an increase or a reduction of the indirectly
fed-in coal dust quantity. Thus, the smooth input of the coal dust
in the firing box is maintained.
[0018] It is advantageous that the increase or the reduction of the
throughput rate of the apportioning organs and/or the increase or
the reduction of the volumetric flow of the conveying gas blower is
brought about by the block output control of the coal-fired power
plant influenced by the requirements of the power grid. Through
this measure it is ensured that in the event of a frequency change
or a requirement in the power grid an influencing signal of the
grid control is directly sent to the block output control of the
coal-fired power plant and its furnace and a countermeasure without
loss of time is thus initiated in order to optimize the dynamic
behavior of the power plant.
[0019] In an advantageous embodiment of the invention, the primary
requirement or the primary control is triggered through a
remote-controlled signal. In a further advantageous embodiment of
the invention the secondary requirement or the secondary control is
likewise triggered through a remote-controlled signal.
[0020] The secondary requirement or the secondary control can be
additionally triggered through written or oral instruction to the
operating personnel of the power plant.
[0021] In the following, exemplary embodiments of the invention are
explained in more detail by means of the drawings and the
description.
[0022] FIG. 1 shows an extract from the British Electricity Grid
Regulations (Grid Code (UK)), wherein the extract shows the minimum
requirement profile of the frequency dependency for a 0.5 Hz
frequency change from the target frequency (minimum frequency
response requirement profile for a 0.5 Hz frequency change from
target frequency),
[0023] FIG. 2 shows an extract from the British Power Grid
Regulations (Grid Code (UK)), wherein the extract shows the
interpretation of the primary and secondary control or primary and
secondary requirement (interpretation of primary and secondary
response values),
[0024] FIG. 3 shows, represented schematically, an assembly for
improving the dynamic behavior of a coal-fired power plant for
primary and/or secondary requirements of the power grid operator
for the current output into the grid, wherein the coal grinding
plant including coal dust lines of the furnace of the power plant
are shown,
[0025] FIG. 4 shows, represented schematically, the relation of an
output increase as a function of time and of the firing method.
[0026] In an electrical energy supply system (power grid) the
generated power has to be constantly in equilibrium with the
consumer power. Changes to the consumer load or power plant fault
impair this equilibrium and cause frequency deviations in the grid,
to which the machines involved in the primary control or the
primary requirement, react. Because of its control behavior, the
primary control or the equivalent primary requirement guarantees
the restoration of the equilibrium between generated and consumed
power within a few seconds, while the frequency is held within the
permissible limit values. In the power grid, there are
quasi-stationary deviations (with respect to the target values)
both of the frequency .DELTA. f as well as the transfer power
.DELTA. Pi between the individual control zones following the
balancing of a sudden change of the consumed or generated power
through the primary control or the primary requirement. In this
connection, the secondary control or secondary requirement becomes
functional whose objective it is to return the frequency to its
target value and the transfer outputs to the agreed values and thus
to have the entire activated primary control output again available
as reserve.
[0027] FIG. 1 shows the interpretation of the primary and secondary
control or primary and secondary control output or primary and
secondary requirement (interpretation of primary and secondary
response values) of the British Power Grid Regulations (Grid Code
UK) that has to occur upon a frequency deviation (frequency change)
of -0.5 Hz from the target frequency of the power grid. The diagram
of FIG. 1 shows that a power plant connected to the power grid
according to the primary control P has to react within a time span
T.sub.Sp of 10 seconds with a plant response and thus increase the
power plant output. The amount of the output increase within this
time span T.sub.Sp is dependent on the load range with which the
power plant happens to be operated at the time of the drop in
frequency. The British Power Grid Regulations determine for example
with a fixed required minimum load (minimum generation) of 65% of
the nominal output (RC) (registered capacity) of the power plant
that with this part load the power plant output has to be increased
within the 10 seconds by 10% (percentage A.sub.p) of the nominal
output or capacity RC of the power plant (see FIG. 2). According to
FIG. 2 (the abscissa shows the load range (in percent of the RC) of
the power plant, the ordinate shows the primary or secondary
control ranges (in percent of the RC)) the increase by 10% of the
rated capacity RC of the power plant has to be guaranteed between
the part load range of 65 to 80% of the nominal power plant output
RC. Between the part load range of 80 to 100% of the nominal power
plant output RC the power increase decreases linearly from 10% to
0.
[0028] In the event of the frequency being exceeded or a reduction
of the primary and/or secondary requirements of the power grid
operator with respect to the current output into the grid it is
provided according to FIG. 2 to lower the power plant output in the
part load range between 95% and 70% of the rated power of the power
plant by 10% of the rated power RC of the power plant within the 10
seconds. Between the part load ranges of 70% to 65% of the nominal
power plant output RC the output reduction decreases linearly from
10% to approximately 6.5 and between 100% and the part load range
of 95%, the power reduction increases linearly from approximately
5% to 10%. FIG. 2 additionally shows the minimum load (minimum
generation MG) of the power plant required by the British Power
Grid, which is at 65% of the nominal power plant output.
[0029] FIG. 3 exemplarily shows how these requirements raised by
the British Power Grid Regulations can be satisfied. To this end,
the furnace 1 of the power plant according to the invention which
is not shown is exemplarily designed with four coal grinding plants
2.1, 2.2, 2.3, 2.4, all of which directly fire the firing box of
the power plant which is not shown (direct firing system), wherein
at least one of the coal grinding plants 2.1, 2.2, 2.3, 2.4 is
designed in such a manner that it can be used to fire the firing
box indirectly (indirect firing system) instead of directly, i.e.
that at least one of the coal grinding plants 2.1, 2.2, 2.3, 2.4 in
addition to the direct firing system is additionally designed with
an indirect firing system.
[0030] Directly fired or a direct firing system means to say that
the coal reduced in the coal grinding plant or coal mill 2.1, 2.2,
2.3, 2.4 is directly fed to the firing box by means of a carrier
gas or support air via coal dust lines 3.1, 3.2, 3.3, 3.4 and fired
therein. Here, according to FIG. 3, a burner level each can be
serviced by each coal grinding plant 2.1, 2.2, 2.3, 2.4 and the
coal dust lines 3.1, 3.2, 3.3, 3.4 originating from the respective
coal grinding plants 2.1, 2.2, 2.3, 2.4 each service the burners
which are not shown in the respective corners or side walls of the
generally rectangular firing boxes of the coal-fired power
plant.
[0031] Indirectly fired or an indirect firing system means to say
that the coal reduced or ground in the coal grinding plant or coal
mill 2.1, 2.2, 2.3, 2.4 is discharged via coal dust lines 3.1, 3.2,
3.3, 3.4 and initially conducted in the direction of the firing
box, but then, via a coal dust switch 6 each arranged in the coal
dust line 3.1, 3.2, 3.3, 3.4 and via storage lines 7.1, 7.2, 7.3,
7.4 is fed to a separator 4 common to all storage lines. In the
separator 4, the coal dust is separated from the carrier gas or
support air and via a connecting line 8 fed to a silo 5 and stored
therein. Via feed lines 9.1, 9.2, 9.3, 9.4 and regulated
apportioning organs 10 arranged in these feed lines the coal dust
can be extracted from the silo 5 and via a charging device 15 each
and a further coal dust switch 13 fed to the coal dust lines 3.1,
3.2, 3.3, 3.4 downstream of the first coal dust switches 6 in order
to be conveyed into the firing box by these. For conveying the coal
dust extracted from the silo 5 into the firing box the charging
devices 15 arranged in the feed lines 9.1, 9.2, 9.3, 9.4 downstream
of the apportioning organs 10 are supplied with a conveying gas,
for example air, via a conveying gas line 11, which air is supplied
by a conveying gas blower 12. The charging device 15 can for
example be an injector, a feeder shoe, a dust pump or the like.
[0032] The carrier gas or support air separated in the separator 4
is discharged via a carrier gas discharge line 14 and fed into the
atmosphere, while it is one more time cleaned before that in a dust
separating system. Instead of into the atmosphere, the carrier gas
can also be conducted into the firing box or the smoke gas drafts
of the coal-fired power plant connected downstream of the firing
box and freed of dust in the existing dust separating system (e.g.
e-filter, hose filter of the like) of the power plant system.
[0033] Deviating from FIG. 3, each of the storage lines 7.1, 7.2,
7.3, 7.4 can each have its own separator 4 and its own silo 5
connected downstream, from which the respective feed lines 9.1,
9.2, 9.3, 9.4 then originate.
[0034] In normal operation of the power plant, the coal grinding
plants 2.1, 2.2, 2.3 of the furnace 1 according to FIG. 3 work in
such a manner that the coal dust ground therein is directly fed to
the firing box for firing via the respective carbon dust lines 3.1,
3.2, 3.3, 3.4. In the case of the coal grinding plant 2.4, which
exemplarily (instead of the grinding plant 2.4, it can also be any
other grinding plant) is designed with an indirect firing system in
addition to the direct firing system, the respective coal dust
switches 6 and 13 arranged in the coal dust lines 3.1, 3.2, 3.3,
3.4 are each set in such a manner that the coal dust ground in the
coal grinding plant 2.4 is not directly fed to the firing box, but
to the firing box by way of the silo 5. To this end, the
apportioning organs 10 arranged in the feed lines 9.1, 9.2, 9.3,
9.4 and charging devices 15 are in operation and conveying gas is
provided to the charging devices 15 through the conveying gas line
11 and the conveying gas blower 12. In the charging devices 15, the
conveying gas picks up the respective coal dust apportioned by the
apportioning organs 10 and conveys it into the firing box. The
operation of the grinding plant 2.4 is such that as a rule, at the
start of the operation, the grinding output of the grinding plant
2.4 compared with the grinding output of the grinding plants 2.1,
2.2, 2.3 or compared with the current requirement of the grinding
output of the grinding plant 2.4 or compared with the present
actual output of the grinding plant 2.4 is increased in order to
half fill the volume of the silo 5 having a storage volume V.sub.Sp
with the excess offer of ground fuel. Following completed filling
of the silo 5 the grinding output of the grinding plant 2.4 is
adapted to those of the grinding plant 2.1, 2.2, 2.3 or the current
requirement of the grinding output of the grinding plant 2.4. With
the exception of the filling operation of the silo 5, the discharge
or conveying output of the apportioning organs 10 corresponds to
the quantity-based grinding output of the grinding plant 2.4, i.e.
after the filling operation, the quantity of coal dust as produced
by the grinding plant 2.4 is discharged from the silo 5 and
conveyed into the silo 5, while minute losses in the separator 4
are taken into account.
[0035] In the case of a frequency change or a frequency drop or a
frequency undershot by for example 0.5 Hz of the power grid the
block output control of the coal-fired power plant is influenced
via the grid control of the power grid or its primary and/or
secondary requirements of the power grid operator with respect to
the current output into the grid, which substantially increases the
quantity of the coal dust discharged by the apportioning organs 10
from the silo 5 and indirectly fed to the firing box relative to
the present actual output or relative to the coal dust quantities
in each case supplied by the coal grinding plants 2.1, 2.2, 2.3.
During this, the coal dust stored and stocked in the silo 5 for
these purposes can be introduced into the firing box for firing in
a very short time and thereby, on the part of the furnace, a
substantial contribution can be made for improving the dynamic
behavior of the coal-fired power plant. The present actual output
designates the output or the part load with which the coal-fired
power plant is currently operated and on which the fuel quantity
fed in to the firing box and thus also the respective throughput
rate of the individual coal grinding plants 2.1, 2.2, 2.3, 2.4 is
dependent.
[0036] In the event of a frequency being exceeded for example by
0.5 Hz of the power grid the block output control of the coal-fired
power plant is influenced via the grid control of the power grid or
its primary and/or secondary requirements of the power grid
operator with respect to the current output into the grid, which
substantially reduces the quantity of the coal dust discharged by
the apportioning organs 10 from the silo 5 and indirectly fed to
the combustion chamber compared with the present actual output or
compared with the coal dust quantities supplied in each case by the
coal grinding plants 2.1, 2.2, 2.3 and thus, as with the increase
of the coal dust quantity, a substantial contribution is made by
the furnace to the improvement of the dynamic behavior of the
coal-fired power plant. Here, coal dust provided by the grinding
plant 2.4 during this process and which is not necessary, i.e.
excess, is buffer-stored in the silo 5.
[0037] For realizing the improvement of the dynamic behavior of a
coal-fired power plant the silo 5 connected downstream of the coal
grinding plant 2.4 is dimensioned and designed with a receiving
capacity or a storage volume V.sub.Sp for the coal dust to be
stored. However, additional coal grinding plants of the exemplary
four coal grinding plants 2.1, 2.2, 2.3, 2.4 in FIG. 3 can each be
designed with an indirect firing system and thus with a silo 5 for
the storage of coal dust. If for example two, three or all four
coal grinding plants 2.1, 2.2, 2.3, 2.4 are additionally designed
with an indirect furnace or an indirect firing system the entire
storage volume or the receiving capacity V.sub.Sp of coal dust can
be divided over the existing number of silos 5 or the storage
volume V.sub.Sp increased through the increased number of silos 5.
Through the additional design of a plurality of grinding plants
with indirect firing system and thus increased coal dust storage
capacity in the silos 5 the dynamics of the fuel apportioning of
the coal-fired power plant can be further improved if required.
Through this improvement of the dynamics of the fuel the primary
and secondary reserve of the coal-fired power plant can also be
improved or increased.
[0038] The storage volume V.sub.Sp of the silo 5 is dimensioned in
such a manner that upon normal operation, i.e. with stationary
state, the storage volume V.sub.Sp of the silo 5 is filled to about
half and thereby has stored sufficient coal dust in order to be
able to introduce an increased coal dust quantity into the firing
box in the event of a frequency drop or a primary and/or secondary
requirement of the power grid operator with respect to the current
output into the grid, i.e. of an instationary state, in order to
improve the dynamic behavior of the power plant. On the other hand,
the silo 5 still has to have sufficient storage capacity in order
to be able to introduce a reduced coal dust quantity into the
firing box in the event of a frequency being exceeded or a primary
and/or secondary requirement of the power grid operator with
respect to the current output into the grid, i.e. in turn of an
instationary state, and thereby receive or store the excess coal
dust quantity produced by the grinding plant 2.4 during the
instationary state in the silo 5.
[0039] In addition to the silo or the silos 5 the apportioning
organs 10, the charging devices 15 and the coal dust lines (feeding
lines 9.1, 9.2, 9.3, 9.4 and coal dust lines 3.1, 3.2, 3.3, 3.4)
can be suitably designed dimensionally downstream of the silo or of
the silos 5 as far as to the firing box in order to be able to
conduct and feed to the firing box the required fuel quantities in
the short time required. The conveying gas or support air required
for this purpose is supplied in a controlled manner through the
conveying gas line 11 and by means of the conveying gas blower
12.
[0040] FIG. 4 schematically shows the dynamic behavior of a direct
and an indirect furnace or of a direct as well as an indirect
firing system of a coal-fired power plant. While the increase of
the boiler output from L.sub.0 to L.sub.1 with the direct furnace
starting out from t.sub.0 takes the time t.sub.2, the increase of
the same boiler output with the indirect furnace starting out from
t.sub.0 only requires the time t.sub.1 and thus comes substantially
closer to an ideal, rapid increase within a time t.sub.0 (step
response). Through the method according to the invention or the
assembly according to the invention of designing at least one of
the coal grinding plants 2.1, 2.2, 2.3, 2.4 in addition to the
direct furnace with an indirect furnace and operating said furnace
as indirect furnace and upon a frequency change in the power grid
or a primary and/or secondary requirement of the power grid
operator with respect to the current output into the grid of
increasing or reducing the quantity of the coal dust discharged
from the silo 5 and indirectly fed to the firing box compared with
the indirectly supplied coal dust quantity upon stable grid
frequency, the dynamic behavior of the furnace according to FIG. 4
and thus also the plant response behavior, i.e. the dynamic
behavior of the coal-fired power plant can be substantially
improved. The increase of the boiler output from L.sub.0 to L.sub.1
constitutes a percentage A.sub.p of the nominal power plant output
RC, for example an increase by 10% of the nominal power plant
output RC.
[0041] In the event of a maintenance or a failure of an
apportioning organ 10 or of a charging device 15 of the indirect
firing system on the coal grinding plant 2.4 the operation of the
coal grinding plant 2.4 as direct firing system can be continued in
that the coal dust switches 6 and 13 are reset and the coal dust
through the coal dust lines 3.1, 3.2, 3.3, 3.4 is directly fed to
the firing box and the silo 5 as well as the apportioning organs 10
and the charging device 15 are thus bypassed. If further coal
grinding plants 2.1, 2.2, 2.3 are additionally designed with an
indirect firing system, one or a plurality of coal grinding plants
can be reset by means of resetting of the coal dust switches 6 and
13 to the operation as indirect firing system and thus temporarily
replace the indirect firing system of the coal grinding plant 2.4
currently undergoing maintenance.
[0042] Obviously, with the method according to the invention or the
assembly according to the invention regarding the primary and
secondary control or the primary and secondary requirement and from
this the plant response behavior or with respect to the improved
dynamic behavior of a coal-fired power plant not only the
exemplarily mentioned British Power Grid Regulations and their
requirements can be maintained or satisfied, but also further
national or international regulations requiring a rapid or improved
dynamic behavior of the coal-fired power plant. To this end, if
required, merely the storage volume V.sub.Sp of the silo or silos 5
and the throughput rates of the apportioning organs 10 and/or of
the charging devices 15 and/or of the conveying gas blower 12 have
to be adapted to the regulations.
LIST OF REFERENCE NUMBERS
[0043] 1 Furnace [0044] 2.1 Coal grinding plant [0045] 2.2 Coal
grinding plant [0046] 2.3 Coal grinding plant [0047] 2.2 Coal
grinding plant [0048] 3.1 Coal dust line [0049] 3.2 Coal dust line
[0050] 3.3 Coal dust line [0051] 3.4 Coal dust line [0052] 4
Separator [0053] 5 Silo [0054] 6 Coal dust switch [0055] 7.1
Storage line [0056] 7.2 Storage line [0057] 7.3 Storage line [0058]
7.4 Storage line [0059] 8 Connecting line [0060] 9.1 Feed line
[0061] 9.2 Feed line [0062] 9.3 Feed line [0063] 9.4 Feed line
[0064] 10 Apportioning organ [0065] 11 Conveying gas line [0066] 12
Conveying gas blower [0067] 13 Coal dust switch [0068] 14 Carrier
gas discharge line [0069] 15 Charging device
* * * * *