U.S. patent application number 11/301657 was filed with the patent office on 2007-06-14 for pulse detonation particulate agglomerator.
This patent application is currently assigned to United Technologies Corporation. Invention is credited to Blake C. Chenevert.
Application Number | 20070131151 11/301657 |
Document ID | / |
Family ID | 37831817 |
Filed Date | 2007-06-14 |
United States Patent
Application |
20070131151 |
Kind Code |
A1 |
Chenevert; Blake C. |
June 14, 2007 |
Pulse detonation particulate agglomerator
Abstract
The burning of fuel (e.g., coal) generates an exhaust flow
containing particles. The flow is passed through a pulsed
combustion agglomerator. The agglomerator is cyclically operated by
introducing a fuel and oxidizer charge to at least one conduit,
initiating combustion of the charge. The combustion generates a
shock wave to which the flow is exposed causing partial
agglomeration of the particles. The flow is passed through a
particle removal system and exhausted.
Inventors: |
Chenevert; Blake C.;
(Redmond, WA) |
Correspondence
Address: |
BACHMAN & LAPOINTE, P.C. (P&W)
900 CHAPEL STREET
SUITE 1201
NEW HAVEN
CT
06510-2802
US
|
Assignee: |
United Technologies
Corporation
|
Family ID: |
37831817 |
Appl. No.: |
11/301657 |
Filed: |
December 12, 2005 |
Current U.S.
Class: |
110/342 |
Current CPC
Class: |
B01D 51/08 20130101 |
Class at
Publication: |
110/342 |
International
Class: |
F23B 90/00 20060101
F23B090/00 |
Claims
1. An apparatus comprising: a combustor; an exhaust flowpath
extending from the combustor a particulate removal device along the
exhaust flowpath; and a pulsed-combustion particle agglomeration
system along the exhaust flowpath between the furnace and the
removal device and comprising: a source of fuel and oxidizer; a
plurality of combustion conduits coupled to the source to receive
charges of said fuel and oxidizer; and a plurality of igniters
coupled to the combustion conduits to ignite the charges.
2. The apparatus of claim 1 wherein: the combustor is a
coal-burning furnace.
3. The apparatus of claim 2 further comprising: pendant boiler
tubes receiving heat from combustion of the coal to heat steam in
the tubes, the system being downstream of the tubes along the
exhaust flowpath.
4. The apparatus of claim 3 further comprising: an economizer in
the exhaust flowpath; and an air heater in the exhaust flowpath,
the pulsed-combustion particle agglomeration system being between
the economizer and the air heater.
5. The apparatus of claim 2 further comprising: a plurality of
pulverizers delivering pulverized coal to the furnace.
6. The apparatus of claim 1 wherein: said combustion conduits have
outlets aimed transverse to a downstream direction of the
flowpath.
7. The apparatus of claim 1 wherein: at least four of said
combustion conduits are positioned at essentially a common
streamwise location along the exhaust flowpath.
8. The apparatus of claim 1 further comprising: a smokestack
forming an outlet of the flowpath to atmosphere.
9. The apparatus of claim 1 wherein the source comprises: a first
source of said fuel, said fuel consisting in majority part, by
mass, of fuel selected from the group consisting of hydrogen,
hydrocarbon fuels, and their mixtures; and a second source of said
oxidizer, said oxidizer consisting essentially of air.
10. The apparatus of claim 1 wherein: said combustion conduits are
configured to operate at a cycle frequency of at least 1.5 Hz.
11. The apparatus of claim 1 wherein: there are at least six of
said combustion conduits.
12. The apparatus of claim 1 wherein: there are at least four of
said combustion conduits positioned in two out-of-phase groups.
13. The apparatus of claim 1 wherein: said combustion conduits have
lengths of 0.5-4 m and cross-sectional areas of 5-150 cm.sup.2.
14. An apparatus comprising: a combustor; an exhaust flowpath
extending from the combustor; a particulate removal device along
the exhaust flowpath; and pulsed-combustion means for encouraging
particle agglomeration along the exhaust flowpath between the
combustor and the removal device.
15. The apparatus of claim 14 wherein the combustor is a fossil
fuel-burning furnace;
16. The apparatus of claim 14 being a boiler system
17. A method for operating a plant comprising: burning a plant fuel
and generating a flow containing particles; passing the flow
through a pulsed detonation particulate agglomerator including
cyclically: introducing a fuel and oxidizer charge to at least one
conduit; initiating combustion of the charge; and exposing the coal
combustion products flow to shock waves generated by the pulsed
detonation combustion causing agglomeration of the particles;
passing the flow through a particulate removal system; and
exhausting the flow.
18. The method of claim 17 wherein: the plant fuel is selected from
the group consisting of coal, fuel oil, hydrocarbon gas biomass,
trash, and combinations thereof.
19. The method of claim 17 further comprising: recirculating a
portion of the flow.
20. The method of claim 17 wherein: the exposing comprises passing
the flow past and exposing said flow to said shock waves from a
plurality of said conduits.
21. The method of claim 17 wherein: the exposing comprises passing
the flow between opposed outlets of one or more pairs of said
conduits.
22. The method of claim 17 wherein: the agglomeration enhances mass
extraction by the particulate removal system.
23. The method of claim 17 wherein: the charge comprises hydrogen
as a by weight majority of the fuel.
24. The method of claim 17 wherein: the at least one conduit is
operated with an air purge before each charge introduction.
25. The method of claim 17 wherein: the at least one conduit is
operated at a cycle frequency of at least 1.5 Hz.
Description
BACKGROUND OF THE INVENTION
[0001] The invention relates to coal-fired industrial equipment.
More particularly, the invention relates to the control of
particulate emissions from coal-fired industrial equipment such as
pulverized coal-fired utility boilers.
[0002] Particulate emissions from coal-fired industrial equipment
have plagued industry for centuries. Among well developed
technologies for removing particulate are bag houses, cyclonic
separators, and electrostatic precipitators. One area of recent
attention is acoustic agglomeration. U.S. Pat. No. 6,749,666 of
Meegan, Jr. identifies use of a modulated acoustic field to induce
particulate agglomeration. A device is used to generate a modulated
acoustic field of a desired sound pressure level and frequency. The
sound waves cause small particulate to agglomerate to form larger
particulate that is easier to capture with conventional
equipment.
SUMMARY OF THE INVENTION
[0003] The burning of fuel (e.g., coal) in industrial equipment
generates an exhaust flow containing airborne particulate. The flow
is passed through a pulsed detonation particulate agglomerator. The
agglomerator is cyclically operated by introducing a fuel and
oxidizer charge to at least one conduit and initiating combustion
of the charge. The combustion generates a shock wave to which the
flow is exposed causing agglomeration of the particulate. The flow
is processed through conventional particulate removal equipment and
exhausted.
[0004] The details of one or more embodiments of the invention are
set forth in the accompanying drawings and the description below.
Other features, objects, and advantages of the invention will be
apparent from the description and drawings, and from the
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 is a partially schematic view of a coal-fired boiler
system.
[0006] FIG. 2 is a transverse sectional view of a particulate
agglomeration system of the boiler system of FIG. 1.
[0007] FIG. 3 is a longitudinal sectional view of the particulate
agglomeration system of FIG. 2.
[0008] FIG. 4 is a schematic view of particulate before
agglomeration.
[0009] FIG. 5 is a view of particulate during agglomeration.
[0010] FIG. 6 is a view of particulate after agglomeration.
[0011] Like reference numbers and designations in the various
drawings indicate like elements.
DETAILED DESCRIPTION
[0012] FIG. 1 shows a schematic view of a pulverized coal-fired
electric power plant 20. The exemplary plant may be an electrical
power plant having a steam generator 22 providing steam to a steam
turbine electrical generator unit 24. Along a combustion flowpath,
the steam generator 22 has an upstream radiant (furnace) zone 26
followed by a downstream convective (backpass) zone 28. The steam
generator 22 receives input flows of coal 30, air 32, and water
34.
[0013] The coal 30 passes through a pulverizer system 40. The air
flow 32 passes through an air heater 50 (discussed below) at a
downstream end of the backpass 28. The backpass heat exchangers may
comprise vertical/streamwise or horizontal/transverse tube arrays.
The air enters the furnace 42 as a preheated flow 52 partially
including entrained pulverized coal 44. The furnace serves as a
combustor combusting the coal and air mixture. A combustion flow 54
passes downstream along the combustion flowpath.
[0014] The water flow 34 enters the convective zone 28 where it is
preheated in an economizer 56 before entering the vertical walls
(water walls-typically vertically extending tube arrays) 58 of the
furnace 42. Heat exchange from the combustion products 54 boils the
water to produce steam. Downstream along both the gas/combustion
products flowpath and water/steam flowpath, the steam is
superheated to high temperature and, in turn, delivered to a high
pressure turbine 60. Exemplary superheating occurs in a two-stage
process, first in a primary superheater 62 across the convective
zone upstream of the economizer 56 and then in a pendant secondary
superheater 64 on the radiant zone. In the radiant zone 26, flow is
primarily upward and, in the convective zone, primarily downward.
The two zones are separated by a bull nose 66 adjacent the pendant
heat exchanger(s).
[0015] Steam from the high pressure turbine 60 continues along the
water/steam flowpath and returns to the boiler to be reheated.
Exemplary reheating is in a two-stage process, with a primary
reheating (e.g., in a heat exchanger 70 across the convective zone
between the primary superheater 62 and economizer 56) and a
secondary reheating (e.g., in a pendant reheater 72 spanning the
radiant and convective zones). Thereafter, the re-heated steam is
delivered to an intermediate pressure turbine 80.
[0016] Steam exiting the intermediate pressure turbine 80 is
directed to a low pressure turbine 82. Steam (and optionally water)
exiting low pressure turbine 82 may proceed to a condenser 84 for
correction and processing (e.g., to return as the stream 34).
Energy extracted by the turbines drives an electrical generator 90
to produce electrical power.
[0017] After heating the water in the backpass region, the flow 54
heats the incoming air in the air heater 50 and then may proceed to
a pollution control system 100. The exemplary system 100 includes
an upstream chemical scrubber 102 and a downstream particulate
removal device 104 (e.g., a bag house or electrostatic
precipitator). Thereafter, the combustion products may pass through
a stack 110 for discharge to atmosphere.
[0018] As so-far described, the system is illustrative of just one
of a variety of plant configurations to which the present invention
may be applied. According to the present invention, one or more
particulate agglomeration systems 120 may be located along the
air/combustion products flowpath. The system(s) 120 may
advantageously be located within the backpass region, within the
pollution control system 100, or in between those two.
[0019] FIG. 2 shows an exemplary agglomeration system 120
positioned along the combustion products flowpath away from boiler
tubes or other heat exchange elements. The exemplary system 120
includes a plurality of pulsed combustion devices 122. Each device
122 has a conduit 124 having an outlet 126 at one end in
communication with the interior 128 of the flue duct 130. The
conduit 124 may include one or more inlets for receiving fuel and
oxidizer. FIG. 2 shows exemplary fuel and oxidizer lines 140 and
142 coupled to common fuel and oxidizer sources 144 and 146. The
exemplary devices 122 further include control modules 150 which may
be connected to a central control system 152. Additional structural
and operational details may be similar to those of pulsed
combustion cleaning apparatus such as shown in US Pregrant Patent
Publications 2005-0112516 and US 2005-0199743, the disclosures of
which are incorporated by reference herein as if set forth at
length. Unlike the cleaning apparatus, operation as a particulate
agglomeration apparatus would be essentially continuous rather than
intermittent.
[0020] The exemplary duct 130 is rectangular in transverse section.
Along each of the two longer sides is an associated group 160 and
162 of the devices 122. FIG. 3 shows the two groups at a common
streamwise position along the duct 130. Other configurations are
possible.
[0021] The control system 152 may operate the devices 122 to
repeatedly combust charges of the fuel and oxidizer. Exemplary
combustion includes detonation producing associated shock waves
170. FIG. 2 shows the two groups 160 and 162 as being out of phase
to maximize effective coverage.
[0022] As the shock waves propagate through the flue gas, they
induce particle agglomeration, reducing the number density of
smaller particulate and thereby increasing the effectiveness of
downstream particulate removal equipment 104. FIGS. 4-6 show the
effect of pressure waves on particle distribution. FIG. 4 shows an
exemplary distribution including relatively large and relatively
small particles, prior to arrival of the shock wave. As the wave
passes, smaller particles are preferentially accelerated (FIG. 5)
due to their low mass to cross-sectional area ratio. This may cause
these particles to collide with relatively large particles or other
relatively small particles. Some of these collisions result in
agglomeration of particles, thereby forming yet larger
particles.
[0023] The formation of larger particles may be by any of several
mechanisms. It may include purely mechanical bonding of solid
particles to each other (e.g., by the interlinking of the irregular
surfaces of adjacent particles). It may include liquid-solid
bonding (e.g., where a liquid droplet sticks to a solid particle
such as by surface tension/wetting). It may include liquid-liquid
bonding (e.g., where the droplets merge to relax surface tension
and, optionally, internally mix to form a uniform structure).
[0024] FIG. 6 shows a resultant distribution wherein characteristic
particle size has been substantially increased by the above
mechanisms and will facilitate removal in the pollution control
system 100.
[0025] The exemplary devices 122 may be fired simultaneously (e.g.,
repetitively and without interruption while the furnace is in
operation or sequentially). A given cycle will induce particulate
agglomeration within a slug of the flue gas passing through the
system 120. The cycle timing may be selected to just allow a slug
refresh or allow only a partial refresh. Exemplary timing is in
excess of 1 Hz, more particularly in the 1.5-10 or 2-6 Hz ranges.
Alternatively, there may be groups of devices 122 at multiple
streamwise positions along the combustion flowpath (either adjacent
positions or positions separated by other components). The timing
of the firing of the groups at different streamwise positions could
be selected so that a given slug is exposed to at least one set of
shock waves from such devices. For example, this may be required if
needed refresh times of the devices 122 exceed the desired cycle
interval for a single streamwise location. Alternatively such high
device minimum refresh times might be accommodated by replacing the
individual devices with pairs or clusters wherein the individual
devices of each pair or cluster are sequentially fired.
[0026] Particular physical and operational parameters will depend
on the desired characteristics of emissions control. For
coal-powered plants, this may partially be influenced by the nature
of the particular coal being burned. For example, it may be
desirable to remove particulate in general, on the one hand while,
on the other hand, it may be desirable to remove particulate as a
tool to remove one or more specific chemicals in the particulate.
For example, some contaminants such as mercury tend to adsorb onto
or amalgamate with other particles (e.g., fly ash). Specific
adsorption (mass of pollutant adsorbed relative to particle mass)
will be highest on smaller particles which have higher specific
surface areas. It may be desirable to position the system 120
relatively downstream to maximize the available time for such
adsorption. This may be balanced against effectiveness of
agglomeration. Agglomeration effectiveness might be higher upstream
where particulate is warmer and, therefore, more likely to be
softer, if not actually liquid. The wave intensity may be optimized
in view of the desired removal, to have sufficient strength to
cause desired agglomeration, while not being so strong as to cause
undesired breakup of existing particulate. Exemplary intensity is
at least about 0.3 pounds per square inch differential (PSID) or
160 db overpressure at extent of range (e.g., at an opposite duct
surface (e.g., about 2.5-5 m away) and/or at a location where the
peak overpressure from another conduit is equal). Intensity at the
conduit outlet will tend to be higher.
[0027] One or more embodiments of the present invention have been
described. Nevertheless, it will be understood that various
modifications may be made without departing from the spirit and
scope of the invention. For example, when implemented in a
reengineering or upgrade of an existing system configuration or
system, details of the existing configuration may influence details
of any particular implementation. Although illustrated with respect
to a coal-burning plant, the invention applies to other heat
transfer facilities that produce particulate. Some prime examples
would be trash incinerators and biomass/wood burners. Trash
incinerators may be particularly relevant due to the possible
capture of a variety of toxic trace elements. Accordingly, other
embodiments are within the scope of the following claims.
* * * * *