U.S. patent application number 11/160616 was filed with the patent office on 2007-01-04 for method and system for controlling coal flow.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. Invention is credited to Philippe Gauthier, Neil Colin Widmer.
Application Number | 20070000416 11/160616 |
Document ID | / |
Family ID | 37588001 |
Filed Date | 2007-01-04 |
United States Patent
Application |
20070000416 |
Kind Code |
A1 |
Widmer; Neil Colin ; et
al. |
January 4, 2007 |
Method and System for controlling coal flow
Abstract
A system for controlling coal flow in a coal-fired boiler
including: a coal flow damper in operable communication with a
burner pipe; a coal flow sensor in operable communication with the
burner pipe which generates a coal flow signal; and a fuel trim
controller in operable communication with the coal flow damper, the
fuel trim controller controlling the coal flow damper responsive to
the coal flow signal.
Inventors: |
Widmer; Neil Colin; (San
Clemente, CA) ; Gauthier; Philippe; (Fullerton,
CA) |
Correspondence
Address: |
CANTOR COLBURN, LLP
55 GRIFFIN ROAD SOUTH
BLOOMFIELD
CT
06002
US
|
Assignee: |
GENERAL ELECTRIC COMPANY
1 River Road
Schenectady
NY
|
Family ID: |
37588001 |
Appl. No.: |
11/160616 |
Filed: |
June 30, 2005 |
Current U.S.
Class: |
110/342 ;
110/186 |
Current CPC
Class: |
F23N 2241/10 20200101;
F23N 1/002 20130101; F23N 2239/02 20200101; F23N 2235/12 20200101;
F23K 2203/105 20130101; F23N 5/184 20130101; F23K 3/00 20130101;
F23K 2203/104 20130101; F23N 2237/02 20200101 |
Class at
Publication: |
110/342 ;
110/186 |
International
Class: |
F23B 90/00 20060101
F23B090/00; F23N 5/18 20060101 F23N005/18 |
Claims
1. A system for controlling coal flow in a coal-fired boiler
comprising: a coal flow damper in operable communication with a
burner pipe; a coal flow sensor in operable communication with said
burner pipe, which generates a coal flow signal; and a fuel trim
controller in operable communication with said coal flow damper,
said fuel trim controller controlling said coal flow damper
responsive to said coal flow signal.
2. The system of claim 1 wherein said fuel trim controller
comprises a physics-based mill circuit coal flow model capable of
predicting changes in burner coal flow velocity as a result of coal
flow damper adjustments wherein said fuel trim controller maintains
a specific coal flow velocity range in said burner pipe.
3. The system of claim 1 wherein said coal flow damper comprises a
flow restrictor and an actuator in operable communication with said
flow restrictor.
4. The system of claim 3 wherein said fuel trim controller adjusts
a position of said flow restrictor with said actuator.
5. The system of claim 4 wherein said fuel trim controller
autonomously adjusts a position of said flow restrictor with said
actuator responsive to said coal flow signal.
6. The system of claim 1 wherein said fuel trim controller
autonomously controls said coal flow damper responsive to said coal
flow signal.
7. The system of claim 6 wherein said fuel trim controller
maintains a predetermined coal flow rate set by a user.
8. The system of claim 6 wherein said fuel trim controller
maintains a prescribed coal flow biasing among a plurality of
burner pipes.
9. The system of claim 8 wherein said fuel trim controller is
capable of storing preferred bias set points for different
operating conditions of the coal-fired boiler.
10. A method for controlling coal flow in a coal-fired boiler
comprising: sensing a coal flow in a burner pipe; generating a coal
flow signal indicative of said coal flow in said burner pipe; and
adjusting said coal flow in said burner pipe responsive to said
coal flow signal.
11. The method of claim 10 wherein a fuel trim controller controls
said coal flow damper responsive to said coal flow signal.
12. The method of claim 10 wherein said coal flow damper comprises
a flow restrictor and an actuator affixed to said flow
restrictor.
13. The method of claim 12 wherein said adjusting said coal flow in
a burner pipe with a burner coal flow damper is achieved by
controlling a position of said flow restrictor with said
actuator.
14. The method of claim 10 wherein said adjusting said coal flow in
said burner pipe reduces at least one of the following: a NO.sub.x
emission; a FEGT; or a unburned carbon on fly ash.
15. The method of claim 10 wherein said adjusting said coal flow in
said burner pipe improves spatial combustion.
16. A system for controlling coal flow in a coal-fired boiler
comprising: means for sensing a coal flow in a burner pipe; means
for adjusting the coal flow in said burner pipe responsive to the
coal flow in said burner pipe.
17. The system of claim 16 further comprising means for maintaining
a prescribed coal flow bias among a plurality of burner pipes for
the coal-fired boiler.
18. The system of claim 16 further comprising means for
automatically balancing coal flow among a plurality of burner pipes
for the coal-fired boiler.
19. The system of claim 16 further wherein said means for adjusting
the coal flow in a burner pipe responsive to the coal flow in a
burner pipe improves spatial combustion.
20. The system of claim 16 further wherein said means for adjusting
the coal flow in a burner pipe responsive to the coal flow in a
burner pipe reduces at least one of the following: a NO.sub.x
emission; a FEGT; or a unburned carbon on fly ash.
Description
BACKGROUND
[0001] The present disclosure relates generally to a method and
system for controlling coal flow, and more particularly to
controlling the coal flow to the burners in a coal fired boiler in
order to optimize boiler operations.
[0002] Coal fired boilers utilize pulverizers to grind coal to a
desired fineness so that it may be used as fuel for the boilers.
Typically, raw coal is fed through a central coal inlet at a top of
the pulverizer and falls by gravity to a grinding area. Once
pulverized, the coal is transported upwards, using air as the
transport medium. The pulverized coal passes through classifier
vanes within the pulverizer. These classifier vanes may vary in
structure, but are intended to establish a swirling flow within a
"rejects" cone to prevent coarse coal particles from flowing into a
discharge turret of the pulverizer. The centrifugal force set up in
the "rejects" cone forces coarse coal particles to drop back down
into the grinding area until the desired fineness is met. Once the
coal is ground finely enough to pass through the classifier, it
enters the discharge turret. From the discharge turret the
pulverized coal is distributed among multiple pulverized coal
outlet pipes and into respective fuel conduits where it is carried
to the burners. Each coal pulverizer is an independent system and
delivers the pulverized coal to a group of burners.
[0003] Poor balance of pulverized coal distribution between burner
pipes is commonly experienced in boilers. This imbalance results
from, inter alia, system resistance of each individual fuel
conduit, physical differences inside the pulverizer, and coal
fineness. Unbalanced and generally random varying distribution of
coal among the burner pipes adversely affects unit performance and
leads to decreased combustion efficiency, increased unburned carbon
in fly ash, increased potential for fuel line plugging and burner
damage, increased potential for furnace slagging, and irregular
heat release within the combustion chamber. In addition, it is
critical for low NO.sub.x. (Nitric Oxides) firing systems to
precisely control air-to-fuel ratios in the burner zones to achieve
low levels of NO.sub.x formation.
[0004] For an understanding of the degree of imbalance and
accompanying issues commonly experienced reference is made to FIG.
1. FIG. 1 illustrates an example of the coal flow distribution
under typical, or baseline, conditions for a plant comprising five
mills with five burner pipes each. FIG. 1 shows significant coal
flow imbalances between the burner pipes. Data from a number of
plants show even worse coal flow balance with coal flow deviations
of more than thirty percent.
BRIEF DESCRIPTION
[0005] Disclosed herein is a system for controlling coal flow in a
coal-fired boiler including: a coal flow damper in operable
communication with a burner pipe; a coal flow sensor in operable
communication with the burner, pipe which generates a coal flow
signal; and a fuel trim controller in operable communication with
the coal flow damper, the fuel trim controller controlling the coal
flow damper responsive to the coal flow signal.
[0006] Also disclosed herein is a method for controlling coal flow
in a coal-fired boiler including: sensing a coal flow in a burner
pipe; generating a coal flow signal indicative of the coal flow in
the burner pipe; and adjusting the coal flow in the burner pipe
responsive to the coal flow signal.
[0007] Further disclosed herein is a system for controlling coal
flow in a coal-fired boiler comprising: means for sensing a coal
flow in a burner pipe and means for adjusting the coal flow in a
burner pipe responsive to the coal flow in the burner pipe.
[0008] Other systems, methods, and/or computer program products
according to exemplary embodiments will be or become apparent to
one with skill in the art upon review of the following drawings and
detailed description. It is intended that all such additional
systems, methods, and/or computer program products be included
within this description, be within the scope of the present
invention, and be protected by the accompanying claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Referring to the exemplary drawings wherein like elements
are numbered alike in the accompanying Figures:
[0010] FIG. 1 illustrates an example of the coal flow distribution
under baseline conditions for a plant including 5 mills each with
five burner pipes;
[0011] FIG. 2 illustrates an exemplary embodiment of a coal flow
control system;
[0012] FIG. 3 illustrates an exemplary embodiment of a coal flow
damper;
[0013] FIG. 4 illustrates another exemplary embodiment of a coal
flow control system;
[0014] FIG. 5 illustrates an example of the coal flow distribution
for one mill at a plant operating under baseline conditions, under
manual coal flow balancing, and under automatic coal flow
balancing;
[0015] FIG. 6 illustrates an example of targeted coal flow
biasing;
[0016] FIG. 7 illustrates another example of targeted coal flow
biasing;
[0017] FIG. 8 illustrates the impact of the coal flow biasing
capability on FEGT (Furnace Exit Gas Temperature); and
[0018] FIG. 9 illustrates the impact of the coal flow biasing
capability on NOx emissions.
DETAILED DESCRIPTION
[0019] In coal fired boilers, balanced coal flow among burners is
traditionally an important factor for combustion optimization. In
order to effectively optimize furnace combustion performance, coal
flow to each individual burner must be closely controlled. Coal
flow control can be accomplished automatically and continuously
through the use of a coal flow control system. Referring to FIG. 2,
an exemplary embodiment of the coal flow control system is shown
generally at 10. A coal flow sensor 14 measures the coal flow in a
burner pipe and communicates a coal flow signal, indicative of coal
flow in the burner pipe, to a fuel trim controller 16. A coal flow
damper 12 controls the coal flow in the burner pipe and receives
command signals from the fuel trim controller 16. The coal flow
damper 12 is discussed in more detail hereinafter with reference to
FIG. 3. The fuel trim controller 16 receives the coal flow signal
from the coal flow sensor 14 and input signals from a controller,
indicative of a desired coal flow in a burner pipe. The fuel trim
controller 16 calculates a desired change in coal flow in the
burner pipe responsive to the coal flow signal and the input
signal. The desired change in coal flow is communicated to the coal
flow damper 12, which responsively alters the coal flow in the
burner pipe.
[0020] Continuing with FIG. 2, the coal flow sensor 14 is used to
measure the mass flow of coal in the burner pipe, which in this
embodiment is determined from the concentration of coal and the
velocity of coal. In an exemplary embodiment, attenuation of
low-power, low-frequency microwaves between a transmitting and
receiving sensor are used to quantify coal concentration.
Additionally, in this embodiment the velocity of the coal flow is
measured by a cross correlation method, which consists of measuring
the time for a coal density signal to travel from one sensor to
another. It is preferable to install the coal flow sensors 14 in
vertical up-flow pipe runs because horizontal pipe runs may impact
the measurement reference conditions if "coal layout", i.e.
accumulation of coal particles in the pipe, occurs. Additionally,
the coal flow sensors 14 should be installed in sufficient straight
pipe runs to minimize flow disturbances. For example, for pipe
sizes up to eighteen inches, the total straight, undisturbed coal
flow distance should be a minimum of seven pipe diameters.
[0021] Turning now to FIG. 3, an exemplary embodiment of a coal
flow damper 12 is illustrated. The coal flow damper 12 includes a
box, which encloses a flow restrictor 20. The flow restrictor 20
forms an adjustable orifice 22, which controls the coal flow
through the burner pipe. The flow restrictor 20 may have a ceramic
coating, such as a highly abrasion resistant alumina-ceramic
coating, to prevent corrosion and increase the useful life of the
flow restrictor 20. The flow restrictor 20 may be a manually
adjusted flow restrictor 24 or an actuator 30 may control the
position of the flow restrictor 20. The position of the flow
restrictor 20 may be adjusted as needed during operation to
maintain proper coal flow through the burner pipe. As the flow
restrictor 20 reduces the area of the adjustable orifice 22 a
pressure drop is induced, which changes the coal flow in the burner
pipe. The actuator can be controlled manually or automatically when
coupled with the fuel trim controller 16. The damper 12 also
includes an air purge line (e.g., side of the flow restrictor 20)
to prevent coal deposits in a flow restrictor guides. In an
exemplary embodiment, a threaded adjusting rod 24 allows the flow
restrictor 20 to be manually positioned. In an exemplary
embodiment, there are two adjustable flow restrictors 20 in the
coal flow damper 12. One flow restrictor 20 may be actuated for
continuous trimming adjustment while another flow restrictor 20 may
be used for extending control range and approximately centering the
orifice.
[0022] Turning now to FIG. 4, an alternative exemplary embodiment
of the coal flow control system 10 is depicted. The coal flow
control system 10 includes three coal flow dampers 12, three coal
flow sensors 14, the fuel trim controller 16, a coal flow
measurement system 26, and a controller HMI (Human Machine
Interface) 28. The coal flow measurement system 26 receives sensor
signals, indicative of the coal flow in the burner pipe, from the
coal flow sensors 14 and calculates the coal flow in each of the
burner pipes. The coal flow measurement system 26 communicates the
coal flow in each burner pipe to the fuel trim controller
responsive to the sensor signals. The fuel trim controller 16 uses
algorithms and diagnostics to determine adjustments to the coal
flow damper 12 responsive to the command signals from the coal flow
measurement system 26 and input signals received from the
controller HMI 28. The fuel trim controller 16 may include design
features and alarm functions that enable a remote tuning option.
Additionally, the fuel trim controller 16 may include several
unique capabilities such as an automatic balancing mode, a
prescribed coal flow biasing mode, a redundant coal flow damper 12
constraint system, or an operational and safety alarm. The coal
flow control system 10 provides improved coal flow distribution to
a coal fired burner and is able to maintain the improved coal flow
distribution over a wide range of mill operating loads.
Additionally, the coal flow control system 10 can provide rapid and
continuous coal flow adjustments for tighter control of boiler
combustion performance.
[0023] The fuel trim controller 16 may be operated in either a
manual or automatic mode. The manual operating mode of the fuel
trim controller 16 allows a controller to set and hold the position
of the coal flow damper 12. The automatic operating mode, allows
the fuel trim controller 16 to adjust the position of the coal flow
dampers 12 automatically to maintain desired coal flow
distribution. To maintain reliable damper operation, the fuel trim
controller 16 includes an adjustable purge system to prevent coal
deposits in the damper flow restrictor guides. The purge system is
operated at least once before adjusting the coal flow damper 12 and
intermittently (operator adjustable). The fuel trim controller 16
may have an automatic balancing mode that can be used to balance
coal flow distribution. The fuel trim controller 16 may also have a
prescribed fuel biasing mode capability that allows lateral coal
flow biasing between burners of a mill which in turn allows the
operator to use the controller HMI 28 to set prescribed coal flow
biases for each pipe to overcome flow field anomalies, local
fouling and slagging, local corrosion, local flame impingement,
off-centered fireballs, spatial combustion performance (reducing CO
and carbon in ash) and economizer O2 stratification. The
stand-alone operating mode of the fuel trim controller 16 can
maintain a set coal flow or it may be readily integrated with a
boiler optimizer control system to automatically adjust coal flow
distribution targets as a function of boiler operating conditions.
The -fuel trim controller 16 operational and safety alarms detect
low coal flow velocities in the pipes and improper positioning of
the coal flow damper 12.
[0024] Additionally, the fuel trim controller 16 may include a
physics-based mill circuit coal flow model to predict burner coal
flow velocity as a safety constraint to coal flow damper 12
adjustments. This velocity prediction ensures that the coal flow
damper 12 adjustments do not cause coal flow velocity to fall below
a configurable minimum velocity and above a configurable maximum
velocity. Adjustment of one of the coal flow dampers 12 can affect
coal flow in other burners within that mill. The physics-based mill
circuit coal flow model evaluates planned adjustments to the coal
flow damper 12 to ensure that the minimum and maximum predicted
coal flow velocities are not violated.
[0025] Continuing with FIG. 4, the coal flow control system 10
includes methods to assess the measurement capability of the coal
flow sensors 14. Additionally, a targeted performance band can be
set by the coal flow control system 10 to minimize coal flow damper
12 adjustments in response to small fluctuations in sensor signals
transmitted by the coal flow sensor 14 that may result from sensor
noise or coal flow pulsations. This technique involves operating
the mill at constant load for a period of time and recording data
from the coal flow sensors 14. After an acceptable probability of
making a false adjustment is determined, i.e. 95% or two standard
deviations, the coal flow measurement average and upper and lower
limits that fall within the acceptable probability may be
calculated. These values are entered into the fuel trim controller
16 to provide the pass band, such that when coal flow is between
the target flow minus the lower limit and the target flow plus the
upper limits, no adjustments are made to the coal flow damper 12.
The fuel trim controller 16 may also include the ability to adapt
by continuously evaluating the upper and lower limit and adjusting
these values. This adaptive feature can be used to account for
changes in mill performance or coal flow sensor 14 health over
time. Another method that may be used to reduce the probability of
making an unnecessary adjustment to the coal flow damper 12, is to
use a rolling average of the coal flow sensor 14 sensor
signals.
[0026] FIG. 5 illustrates the coal flow for one mill at a plant for
typical coal distribution (e.g., as-found), manual coal flow
balancing, and automatic coal flow balancing. The typical coal
distribution performance illustrates the initial coal flow bias for
this boiler with one pipe having a -25% bias. The manual operating
mode of the coal flow control flow system 10 was effective at
achieving +/-10% coal flow deviation. The automatic operating mode
of the coal flow control system 10 was able to further improve coal
flow balance consistently to within +/-5%. The automatic operating
mode of the coal flow control system 10 is also capable of
achieving these balanced conditions at various mill load
conditions, which is not possible with manual tuning.
[0027] In terms of prescribed coal flow biasing, FIGS. 6 and 7
illustrate the ability of the coal flow control system 10 to
achieve targeted coal flow biases; the targeted bias and the actual
bias are illustrated for two different prescribed bias conditions.
FIG. 6 illustrates a bias condition of redistributing an additional
10% of the coal flow from the left side to the right side of the
furnace. FIG. 7 illustrates another bias condition where an
additional 10% of the coal flow is directed to the center burner
and 5% to the two burners next to the center burner. In both
examples a successful operation of the control system is shown, in
which the system was able to consistently achieve the targeted coal
flows within +/-5% deviation.
[0028] Turning now to FIG. 8, the impact of the coal flow biasing
capability on the FEGT (Furnace Exit Gas Temperature) distribution
is illustrated. The baseline coal distribution condition
corresponds to a typical (e.g. as-found) coal flow distribution.
The balanced coal distribution condition consists of distributing
the coal flow evenly between the pipes. The optimized coal
distribution condition refers to a prescribed bias of coal flow.
The results showed that the FEGT on the west side of the furnace
was reduced from 2520.degree. F. for the baseline (e.g. as found)
coal distribution condition to 2460.degree. F. for the optimized
coal distribution condition; this is a 60.degree. F. reduction in
FEGT. In addition the west to east FEGT difference was reduced from
110.degree. F. baseline coal distribution to just 30.degree. F. for
the optimized coal distribution condition and average FEGT was
reduced 20.degree. F. FIG. 9 illustrates the impact of the coal
flow biasing capability on the NO.sub.x emissions. The results
showed that the NO.sub.x was reduced by 8% when operating at the
optimized coal distribution. Additionally, the coal flow biasing
may result in a reduction in a unburned carbon on fly ash and
improved spatial combustion.
[0029] While the invention has been described with reference to
exemplary embodiments, it will be understood by those skilled in
the art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the invention. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention not be limited to the
particular embodiment disclosed as the best or only mode
contemplated for carrying out this invention, but that the
invention will include all embodiments falling within the scope of
the appended claims. Moreover, the use of the terms first, second,
etc. do not denote any order or importance, but rather the terms
first, second, etc. are used to distinguish one element from
another. Furthermore, the use of the terms a, an, etc. do not
denote a limitation of quantity, but rather denote the presence of
at least one of the referenced item.
* * * * *