U.S. patent application number 12/482837 was filed with the patent office on 2010-12-16 for solids flow meter for integrated boiler control system.
This patent application is currently assigned to ALSTOM Technology Ltd. Invention is credited to Randal M. Racine, Michael C. Tanca.
Application Number | 20100316964 12/482837 |
Document ID | / |
Family ID | 42199696 |
Filed Date | 2010-12-16 |
United States Patent
Application |
20100316964 |
Kind Code |
A1 |
Racine; Randal M. ; et
al. |
December 16, 2010 |
SOLIDS FLOW METER FOR INTEGRATED BOILER CONTROL SYSTEM
Abstract
A combustion control system [100] for a combustion system [7]
having a plurality of fuel pipes [5]. The combustion control system
[100] including a plurality of flow meters [10], a controller [8],
fuel flow controls [11] and secondary air controls [61,62,72]. Each
meter [10] is adapted to monitor flow of fuel within a respective
one of the fuel pipes [5] by sensing a pressure field within the
fuel pipe [5]. A controller [8] receives the flow information from
each of the flow meters [10], to evaluate performance of the
combustion system [7]. Controller [8] also providing control
information for controlling the flow of secondary air dampers
[61,62,71] into the combustion system [7], and optionally
controlling the flow of fuel in each fuel pipe [5].
Inventors: |
Racine; Randal M.;
(Westfield, MA) ; Tanca; Michael C.; (Tariffville,
CT) |
Correspondence
Address: |
ALSTOM Power Inc.
200 Great Pond Drive, P.O. Box 500
WINDSOR
CT
06095
US
|
Assignee: |
ALSTOM Technology Ltd
Baden
CH
|
Family ID: |
42199696 |
Appl. No.: |
12/482837 |
Filed: |
June 11, 2009 |
Current U.S.
Class: |
431/12 ; 110/186;
431/89; 431/90 |
Current CPC
Class: |
F23N 2237/16 20200101;
F23N 3/002 20130101; F23N 2005/185 20130101; F23N 5/184 20130101;
F23K 3/02 20130101 |
Class at
Publication: |
431/12 ; 431/89;
431/90; 110/186 |
International
Class: |
F23N 1/02 20060101
F23N001/02; F23N 5/18 20060101 F23N005/18 |
Claims
1. A combustion control system [100] for a furnace [7] comprising a
plurality of fuel pipes, the system comprising: a plurality of flow
meters [10], each meter [10] adapted for monitoring a flow of fuel
within a respective one of the fuel pipes [5] by sensing a pressure
field within the fuel pipe [5]; and a controller [8] for receiving
flow information from each of the flow meters [10], evaluating
performance of the furnace [7], and providing control information
for controlling secondary air flow into said furnace [7].
2. The combustion control system [100] as in claim 1, further
comprising at least one secondary air flow control [61,62,71 ] for
receiving the control information and controlling the secondary air
flowing into said furnace [7].
3. The combustion control system [100] as in claim 1, wherein the
controller [8] comprises fuel characterization data for qualifying
the flow information.
4. The combustion control system [100] as in claim 1, wherein the
controller [8] comprises an input for receiving operational
information comprising at least one of temperature information and
flue gas composition information.
5. The combustion control system [100] as in claim 1, further
comprising machine executable instructions stored on
machine-readable media, the instructions comprising instructions
for: estimating fuel flow information; and adjusting at least one
secondary air flow control according to the fuel flow
information.
6. The combustion control system [100] as in claim 5, further
comprising instructions for at least one of: initiating the
estimating; and shutting down the flow meter.
7. The combustion control system [100] as in claim 5, further
comprising instructions for controlling secondary air flow
according to operational information.
8. The combustion control system [100] as in claim 1, wherein the
flow meter [10] is adapted for monitoring a multi-phase flow.
9. The combustion control system [100] as in claim 1, wherein the
flow meter [10] comprises clamping features for clamping to the
fuel pipe [5].
10. The combustion control system [100] as in claim 1, wherein the
plurality of sound-based sensors [10] is disposed at predetermined
axial locations along the fuel pipe [5].
11. A method [20] for controlling operation of a combustion system
[7], the method comprising: obtaining fuel flow information [22]
from at least one fuel tube [5] from a flow meter [10], each flow
meter [10] comprising a sensor for sensing information regarding a
pressure field within a respective fuel pipe [5] carrying the flow
of fuel to the nozzle [6];and adjusting at least one air flow
control [61,62,71] according to the fuel flow information.
12. The method [20] as in claim 11, wherein the step of adjusting
comprises the steps of: calculating the optimal air flow for the
fuel flow information obtained; converting the calculated optimal
air flow to an approximate damper opening setting; and adjusting at
least one damper to the approximate damper opening setting.
13. The method [20] as in claim 11, wherein at least one of the
obtaining [21] and the adjusting [23] is performed on a real-time
basis.
14. The method [20] as in claim 11, further comprising referencing
characterization data to refine an estimate of the flow
information.
15. The method [20] as in claim 11, wherein controlling the flow of
fuel comprises controlling a flow of coal from a pulverizer
[2].
16. The method [20] as in claim 11, wherein the adjusting is
performed to improve an efficiency of the combustion system
[7].
17. The method [20] as in claim 11, wherein the adjusting is
performed to limit formation of pollutants by the combustion system
[7].
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to coal-fired combustion systems, and
more particularly to more efficient coal-fired combustion systems
that accurately measure fuel flow and adjust secondary air flow
based upon the measured fuel flow.
[0003] 2. Description of the Related Art
[0004] In various coal-fired combustion systems, such as a boiler
or furnace, a pulverizer is used to feed pulverized coal to the
combustion system through a number of fuel pipes. Typically, the
flow rate of coal through the fuel pipes cannot be accurately
measured with intrusive flow meters due to the erosive environment
within the coal pipe. Periodic measurements are used to adjust
riffle distributors to provide approximately the same fuel flow
through each fuel feed lines, balancing the lines.
[0005] Fuel line imbalance can cause improper air/fuel ratio and
improper combustion in various portions of the combustion system.
This affects carbon loss and can lead to production of undesired
emissions such as carbon monoxide (CO), various nitrogen compounds
(NOx), as well as various volatile organic compounds and others.
Such emissions can cause a plant to be out of emissions compliance
or run inefficiently.
[0006] Thus, what are needed are methods and apparatus for accurate
measurement of fuel flow for improved control over combustion
systems, leading to improved efficiency and reduced emissions.
BRIEF SUMMARY OF THE INVENTION
[0007] The present invention may be embodied as a combustion
control system [100] for a furnace [7] comprising a plurality of
fuel pipes, the system comprising:
[0008] a plurality of flow meters [10], each meter [10] adapted for
monitoring a flow of fuel within a respective one of the fuel pipes
[5] by sensing a pressure field within the fuel pipe [5]; and
[0009] a controller [8] for receiving flow information from each of
the flow meters [10], evaluating performance of the furnace [7],
and providing control information for controlling secondary air
flow into said furnace [7].
[0010] At least one secondary air flow control [61,62,71] receives
the control information and controls the secondary air flowing into
said furnace [7] creating more efficient combustion and reduced
emissions.
[0011] The present invention may also be embodied as a method [20]
for controlling operation of a combustion system [7], the method
comprising:
[0012] obtaining fuel flow information [22] from at least one fuel
tube [5] from a flow meter [10], each flow meter [10] comprising a
sensor for sensing information regarding a pressure field within a
respective fuel pipe [5] carrying the flow of fuel to the nozzle
[6]; and
[0013] adjusting at least one air flow control [61,62,71] according
to the fuel flow information.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The subject matter which is regarded as the invention is
particularly pointed out and distinctly claimed in the claims at
the conclusion of the specification. The foregoing and other
features and advantages of the invention are apparent from the
following detailed description taken in conjunction with the
accompanying drawings in which:
[0015] FIG. 1 depicts aspects of one embodiment of a combustion
system according to the present invention;
[0016] FIG. 2 is a partially cut-away perspective view of fuel
nozzles, air nozzles and dampers, as they would appear within the
wall of furnace.
[0017] FIG. 3 is an enlarged perspective view of a sold fuel nozzle
and an air nozzle of FIG. 2; and
[0018] FIG. 4 depicts aspects of a method for using the flow
meter.
DETAILED DESCRIPTION OF THE INVENTION
[0019] Disclosed methods and apparatus providing for accurate
measurement of fuel flow. The measurements provide for improved
control over combustion systems, such as a boiler combustion
system, leading to improved efficiency. In general, the teachings
herein make use of at least one low-frequency, ultrasonic,
non-intrusive solids flow meter. The at least one flow meter may be
disposed in a variety of locations, and as an example, may be used
to measure flow to each windbox within a boiler combustion
system.
[0020] In FIG. 1, the combustion system shown includes a pulverizer
2 that provides pulverized sold fuel. The solid fuel particles are
entrained in a flow of air through a fuel line 3 to a splitter
4.
[0021] The pulverized solid fuel is passed through a plurality of
fuel pipes 5. The splitter 4 may be a riffling distributor that
adjusts the flow through each of the fuel pipes 5.
[0022] The fuel then flows through a plurality of fuel nozzles 60.
The fuel nozzles 60 are disposed on an interior wall 9 of a furnace
7. The pulverized solid fuel is burned in furnace 7.
[0023] The combustion control system 100 employs at least one flow
meter 10. Each of the flow meters 10 generally senses a pressure
field within a fuel pipe 5 (or similar component). Exemplary
technology for the flow meter 10 may include low frequency,
ultrasonic and/or solids monitoring technologies.
[0024] Additionally, a fan 14 provides air through dampers 61, 71
and into furnace 7.
[0025] Further shown in FIG. 1 is a plurality of flow controls 11.
The flow controls 11 may be riffle distributors such as those
described in U.S. Pat. No. 7,017,501 Issued Mar. 28, 2006 to
Jeffrey Mann entitled "Rifle Distributor for a Fossil Fuel Fired
Combustion Arrangement".
[0026] The flow controls 11 provide for limited control flow of
fuel flow to the plurality of nozzles 6, and thus work in
combination with other components of the combustion control system
100. However, additional control is required to provide more
efficient combustion.
[0027] Additional air is provided by a fan 14 "secondary air". This
secondary air is provided through dampers 61, 71 and into the
furnace to adjust the fuel/air mixture for efficient
combustion.
[0028] Each of the flow meters 10 provides measurement data (also
referred to as "flow information") of fuel flow through each of the
fuel tubes 5. In one embodiment, the flow measurement data is sent
to a controller 8. The controller 8 then determines appropriate
adjustments to flow of fuel and secondary air and sends commands
for manipulation of each of the respective flow controls 11 and
dampers 61, 71. The flow controls 11 and dampers 61, 71 include
apparatus as necessary for at local and/or remote operation.
[0029] The controller 8 may include apparatus as deemed appropriate
for receiving flow measurement data and controlling flow. For
example, the controller 8 may include a personal computer (PC)
equipped with additional electronics (such as analog to digital
converters, and other such additional equipment). The controller 8
may be a shared use unit, such as in the case of a PC, and may
generally be realized simply as software (i.e., machine executable
instructions stored on machine readable media). In other
embodiments, the controller 8 may be a dedicated unit, such as a
realized by implementation of a local unit installed proximate to
at least one of the flow meters 10 and the flow controls 11. In
such latter embodiments, the controller 8 may be realized in the
form of a low cost dedicated processor supported by a dedicated
power supply, machine executable instructions stored on machine
readable media, such as in read-only-memory, and other such
components.
[0030] Of course, the controller 8 may have a variety of inputs for
evaluating and controlling performance of the combustion system.
That is, the controller 8 may receive operational information as
inputs. Exemplary operational information includes such parameters
as temperature, constituents of effluent (such as a concentration
of NO.sub.x) and other such parameters. In general, each input
parameter provides the controller 8 with information needed for
controlling the flow of secondary air into the furnace to result in
improved efficiency of the combustion system.
[0031] In addition, the controller 8 may include fuel
characterization data. Characterization data may be useful for
qualify aspects of measurements. For example, the characterization
data may include information such as density and/or particle size
of a particular fuel type. Accordingly, characterization data may
be useful, particularly in combination with operational data (such
as flow rates) to refine measurement data produced by the flow
meters 10.
[0032] It should be recognized that the example of FIG. 1 is merely
illustrative. For example, flow meters 10 may be deployed at least
one of before and after flow controls 11 and/or any splitter(s) 4.
Flow controls 11 may be omitted, or at least partially omitted.
Certain components such as the flow control 11, the flow meter 10,
the controller 8 and the splitter 4 may be incorporated into a
single unitary structure (i.e., for a single component).
[0033] In general, each flow meter 10 is a low frequency,
ultrasonic, non-intrusive solids flow meter 10. The flow meter 10
may be used anywhere deemed appropriate in the combustion system to
more accurately measure flow of fuel to a combustion delivery
device, such as the plurality of nozzles 6. With the measurement
data, combustion controls systems can tune the furnace 7 for
desired purposes (such as improved efficiency and/or reductions in
solid and gaseous emissions).
[0034] In some embodiments, the flow meter(s) 10 are used in
conjunction with flow controls 11 such as local air dampers 61, 71.
Through flow measurement and appropriate control of the air dampers
within windboxes near the coal nozzles, the local stoichiometry can
be evenly maintained within the furnace. The local stoichiometry
within the furnace 7 can also be measured with the flow meter(s) 10
being located anywhere downstream of the windboxes in the flue gas
stream, including within the furnace, a stack, a heat exchanger, a
gas clean-up system, and other such components. Locating the flow
meters downstream provides for further enhancements to control.
[0035] One exemplary flow meter 10 is a device produced by CIDRA
Corporation of Wallingford Conn., and offered under the tradename
"SONARTRAC." This device exhibits array processing techniques to
"listen" to, and interpret pressure fields generated by turbulent
pipe flows. The flow meter provides accurate, reliable,
non-intrusive and robust flow measurement for a wide range of
single phase and multiphase flows. The device may be clamped on to
an existing fuel pipe 5 or fuel line 3, thus eliminating process
disruptions associated with installing other types of flow meters,
such as integrated devices.
[0036] Exemplary flow meters 10 include those disclosed in U.S.
Pat. No. 7,330,797, entitled "Apparatus And Method For Measuring
Settlement Of Solids In A Multiphase Flow" and incorporated herein
in its entirety by reference. This patent discloses a method and
apparatus for measuring a parameter of a flow passing through a
pipe is provided, wherein the apparatus includes at least two
spatial array of sensors disposed at different axial locations
along the pipe, wherein each of the sensors provide a signal
indicative of unsteady pressure created by convection with the flow
within the pipe at a corresponding axial location of the pipe. The
apparatus also includes a signal processor configured to determine
the flow rate at the circumference location of each sensor array in
response to the respective measured unsteady pressures. The signal
processor compares the velocity of the flow at each respective
location and provides a signal indicative the presence of solids
settled at the bottom of the pipe and/or the level of the settled
solids in the pipe, in response to an uncharacteristic increase in
the velocity of a lower portion of the flow in comparison to the
velocity measured above the lower portion of the flow.
[0037] Other exemplary flow meters 10 include those disclosed in
U.S. Pat. No. 7,295,933, entitled "Configurable Multi-Function Flow
Measurement Apparatus Having An Array Of Sensors" and incorporated
herein in its entirety by reference. This patent discloses a
configurable multi-function flow measurement apparatus is provided
that can selectably function to measure the speed of sound
propagating through a fluid flowing within a pipe and/or to measure
pressures disturbances (e.g. eddies) moving with a fluid to
determine respective parameters of the flow propagating through a
pipe and detects the health of an industrial process. The
configurable flow measurement device can also be selectable to
function as a system diagnostic meter that provides a diagnostic
signal indicative of the health of the industrial process, namely
health of pumps, valves, motors and other devices in an industrial
flow loop. The apparatus includes a sensing device that includes an
array of strained-based or pressure sensors used to measure the
acoustic and convective pressure variations in the flow to
determine desired parameters. In response to a remote or local
configuration signal, a control logic selects the desired function
of the flow measurement apparatus.
[0038] Further examples of flow meters 10 include those disclosed
in U.S. Pat. No. 7,322,245, entitled "Apparatus And Method For
Measuring A Fluid Flowing In A Pipe Using Acoustic Pressures" and
incorporated herein in its entirety by reference. This patent
discloses apparatus for sensing applications where at least one
parameter of at least one fluid in a pipe is measured using a
spatial array of acoustic pressure sensors placed at predetermined
axial locations x.sub.1, x.sub.2, x.sub.3 along the pipe. The
pressure sensors provide acoustic pressure signals P.sub.1(t),
P.sub.2(t), P.sub.3(t) on lines, which are provided to signal
processing logic which determines the speed of sound a.sub.mix of
the fluid (or mixture) in the pipe using acoustic spatial array
signal processing techniques with the direction of propagation of
the acoustic signals along the longitudinal axis of the pipe.
Numerous spatial array-processing techniques may be employed to
determine the speed of sound a.sub.mix.The speed of sound a.sub.mix
is provided to the logic, which calculates the percent composition
of the mixture (e.g., water fraction, or any other parameter of the
mixture) or fluid, which is related to the sound speed a.sub.mix.
The logic may also determine the Mach number M.sub.x of the fluid.
The acoustic pressure signals P.sub.1(t), P.sub.2(t), P.sub.3(t)
measured are lower frequency (and longer wavelength) signals than
those used for ultrasonic flow meters, and generally tolerant to
in-homogeneities in the flow. No external source is required and
thus may operate using passive listening. The apparatus will work
with arbitrary sensor spacing and with as few as two sensors if
certain information is known about the acoustic properties of the
system.
[0039] FIG. 2 is a partially cut-away perspective view of fuel
nozzles 60, air nozzles 80 and dampers 61, 71 as they would appear
within the wall of furnace (9, 7 of FIG. 1). The plurality of solid
fuel nozzles 64 typically receive pulverized coal entrained in a
stream of primary air that passes through a primary outlet of solid
fuel nozzles 64 into the furnace.
[0040] Optionally, there may be liquid fuel nozzles 63 which burns
a combustible liquid (such as oil) fed through a liquid fuel pipe
69.
[0041] There is also additional air for combustion, referred to as
"secondary air" that is provided to the furnace through separate
outlets in both the solid fuel nozzles 64, and liquid fuel nozzles
63. These are shown in greater detail in FIG. 3.
[0042] Also show here are the boiler tubes 12 that carry water, are
heated and produce steam.
[0043] FIG. 3 is an enlarged perspective view of a sold fuel nozzle
60 and an air nozzle 70 of FIG. 2. Pulverized coal is entrained in
a stream of primary air and passes through fuel pipe 5 (show in
phantom) and out of primary outlet 67 of solid fuel nozzle 60.
[0044] In this embodiment, secondary air is provided through an
upper fuel nozzle damper 61 passes through a partition of duct 65
and to upper secondary outlets 66 of solid fuel nozzle 60. Also,
secondary air enters through lower fuel nozzle damper 62, through a
separate partition of duct 65 and out of lower secondary outlets 68
of solid fuel nozzle 60.
[0045] Similarly, secondary air enters through air nozzle damper
71, through a duct 75 and out of an air nozzle 70 into the furnace
for combustion.
[0046] All dampers are shown in a closed position in FIG. 3,
however, they are controllable to open and close, or be adjusted to
any position between these positions under the control of
controller (8 of FIG. 1). Standard electric motors and known
electronics may be used to implement the actuation of the dampers.
This effectively controls the amount of secondary air being
provided to the furnace thereby adjusting the combustion
characteristics.
[0047] As stated above, each fuel pipe 5 is independently
monitored, and each damper is independently adjusted. The
adjustments are based upon the flow measured for each fuel pipe 5.
This therefore, allows for independent monitoring and adjustment of
each fuel nozzle 60 to provide a more accurate and cleaner
combustion.
[0048] Referring now to FIG. 4, there is shown an exemplary
flowchart depicting a method for adjustment of operation of the
system using the flow meter 10. In FIG. 4, a process for
controlling flow 20 is initiated, such as by the controller 8. The
process begins by initializing the equipment for operation in step
21.
[0049] In step 22, fuel flow is measured in each of the fuel pipes
5.
[0050] Optionally, in step 23, the flow controls 11 may be
adjusted. These may be performed on every pass through this
flowchart, or less often. Similarly, if step 23 is performed,
another fuel flow measurement similar to that of step 22 is
performed.
[0051] In step 25, the amount which the fuel flow for a specific
fuel pipe 5 being measured differs from the other fuel pipes 5 is
determined. It is then calculated how much extra air, or reduced
air is required to cause combustion from the measured fuel pipe 5
to become optimal. This is determined by employing optimal
stoichiometry calculations.
[0052] In step 26, the additional or reduced air flow calculated is
converted to one or more damper settings.
[0053] In step 27, the calculation unit (8 of FIG. 1) sets one or
more dampers to the calculated damper settings (or as close as
possible to the calculated damper settings.)
[0054] In step 28 it is determined if the operation of the furnace
is to be completed. If so, processing continues at step 29 and the
system is shut down.
[0055] If not, then processing continues at step 22.
[0056] Generally, the process for controlling flow 20 continues
unabated until shutdown 29 of the combustion system 100.
[0057] It should be recognized that the teachings herein provide a
number of advantages. That is, as fuel, generally from a plurality
of pulverizers 2 is fed through a series of fuel splitters 4 to
split into various pipes 5, inherent inconsistencies result. For
example, the pipe splitters 4 may be inherently inaccurate in
splitting the coal within the piping 5 and result in uneven
distribution of fuel to the nozzles 6 within the furnace 7. This
maldistribution of fuel results in different localized
stoichiometries that may not be optimal for proper furnace
operation.
[0058] Particular features provided include continuous measurement
of fuel to the furnace for each fuel nozzle, thus providing
improved furnace combustion and emissions control; an integrated
control system may be realized which accepts a local fuel feed
measurement signal and changes furnace operations, such as
secondary air damper settings, to improve performance; a
non-intrusive, solids flow meter which accurately measures the fuel
rate without flow meter erosion can be integrated with a furnace
controls system; a non-intrusive, solids flow meter which
accurately measures a primary air flow through each fuel pipe is
provided, and permits for close control of an air-to-coal ratio
which minimizes NO.sub.x formation at a tip of the fuel nozzle; a
non-intrusive, solids flow meter which accurately measures particle
size distributions to the furnace provides for better controls over
furnace combustion and emissions; and measurement of the flow of
coal to individual fuel nozzles may be performed with a high
accuracy.
[0059] One skilled in the art will recognize that the teachings
herein may be employed with a variety of pulverizers 2 as well as a
variety of furnaces 7 (i.e., combustion chambers). More
specifically, the use of flow meters 10 is generally limited only
by the sensitivity and other such parameters of a given flow meter
10 for monitoring of a specific flow. In that regard, particular
flow meters 10 may be selected to account for, or be particularly
sensitive to parameters including: flow rate, pipe diameter, piping
wall thickness, materials used in the piping, size of particulate
matter in the fuel, phase, including multi-phase flow, moisture
content and other such properties.
[0060] Further, the flow meters 10 may be provided as part of a
retrofit to existing combustion systems. For example, the flow
meters 10 may be mounted onto existing piping 5 and integrated with
existing controllers 8. Accordingly, a system making use of the
teachings herein may also include computer software (i.e., machine
readable instructions stored on machine readable media). The
software may be used as a supplement to existing controller
software (and/or firmware) or as an independent package.
[0061] The computer readable medium, may include any type of media,
such as for example, magnetic storage, optical storage,
magneto-optical storage, ROM, RAM, CD ROM, flash or any other
computer readable medium, now known or unknown, that when executed
cause a computer to implement the method of the present invention.
These instructions may provide for equipment operation, control,
data collection and analysis and other functions deemed relevant by
a user.
[0062] Further, the kit may include all other necessary components
as may be needed for successful installation and operation. Example
of other components include, without limitation, electrical wiring,
power supplies, motor and/or manually operated valves, computer
interfaces, user displays, assorted circuitry, assorted housings,
relays, transformers, and other such components.
[0063] 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 mode contemplated for
carrying out this invention, but that the invention will include
all embodiments falling within the scope of the appended
claims.
* * * * *