U.S. patent application number 13/653636 was filed with the patent office on 2014-04-17 for in-bed solids control valve with improved reliability.
This patent application is currently assigned to BABCOCK & WILCOX POWER GENERATION GROUP, INC.. The applicant listed for this patent is BABCOCK & WILCOX POWER GENERATION GROUP, INC.. Invention is credited to KIPLIN C. ALEXANDER, THOMAS J. FLYNN, SHENGTENG HU, DAVID L. KRAFT, MIKHAIL MARYAMCHIK.
Application Number | 20140102342 13/653636 |
Document ID | / |
Family ID | 50474199 |
Filed Date | 2014-04-17 |
United States Patent
Application |
20140102342 |
Kind Code |
A1 |
MARYAMCHIK; MIKHAIL ; et
al. |
April 17, 2014 |
IN-BED SOLIDS CONTROL VALVE WITH IMPROVED RELIABILITY
Abstract
A non-mechanical valve arrangement for use with circulating
fluidized bed (CFB) boilers has a CFB reaction chamber and a
bubbling fluidized bed (BFB) within an enclosure in the lower
portion of the CFB reaction chamber, the BFB containing an in-bed
heat exchanger (IBHX). Solids flowing from the BFB enclosure to the
CFB reaction chamber may be controlled using one or more
non-mechanical valves. Each non-mechanical valve is independently
controlled using independently controlled fluidizing means. The
non-mechanical valve has collectors to collect solids backsifting
into the fluidizing means of the valve. Agglomerates are removed
which could block the valve. Channel walls parallel to the
direction of solids flow through the valve opening may be provided
to reduce external interference with local fluidization to maintain
the proper functionality of the non-mechanical valve.
Inventors: |
MARYAMCHIK; MIKHAIL;
(FAIRLAWN, OH) ; KRAFT; DAVID L.; (MASSILLON,
OH) ; ALEXANDER; KIPLIN C.; (WADSWORTH, OH) ;
FLYNN; THOMAS J.; (NORTH CANTON, OH) ; HU;
SHENGTENG; (COPLEY, OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BABCOCK & WILCOX POWER GENERATION GROUP, INC. |
Barberton |
OH |
US |
|
|
Assignee: |
BABCOCK & WILCOX POWER
GENERATION GROUP, INC.
Barberton
OH
|
Family ID: |
50474199 |
Appl. No.: |
13/653636 |
Filed: |
October 17, 2012 |
Current U.S.
Class: |
110/245 ;
110/104R; 122/4D; 165/104.16; 431/12 |
Current CPC
Class: |
F23C 2900/10008
20130101; F23C 10/10 20130101; F23C 10/30 20130101; F23C 2206/102
20130101; F23C 10/26 20130101; F22B 31/0038 20130101; F23C 2206/103
20130101; F23C 10/04 20130101 |
Class at
Publication: |
110/245 ;
122/4.D; 110/104.R; 165/104.16; 431/12 |
International
Class: |
F23C 10/02 20060101
F23C010/02; F22B 31/00 20060101 F22B031/00; F23C 10/24 20060101
F23C010/24; F23C 10/10 20060101 F23C010/10; F23C 10/18 20060101
F23C010/18 |
Claims
1. A circulating fluidized bed boiler comprising: a circulating
fluidized bed boiler reaction chamber comprising side walls and a
distribution grid defining a floor at a lower end of the
circulating fluidized bed boiler reaction chamber, the distribution
grid being adapted for providing fluidizing gas into the
circulating fluidized bed boiler reaction chamber; a bubbling
fluidized bed located within a lower portion of the circulating
fluidized bed boiler reaction chamber and being bound by enclosure
walls and by the floor of the circulating fluidized bed boiler
reaction chamber; at least one controllable in-bed heat exchanger,
the in-bed heat exchanger occupying part of the circulating
fluidized bed boiler reaction chamber floor and being within the
enclosure walls of the bubbling fluidized bed; at least one
non-mechanical valve designed to permit the control of solids
discharge from the bubbling fluidized bed into the circulating
fluidized bed boiler reaction chamber, the valve comprising at
least one opening in the enclosure wall of the bubbling fluidized
bed, and including at least one independently controlled fluidizing
means located at least at one of upstream and downstream of the
opening; the at least one independently controlled fluidizing means
each being connected to corresponding fluidizing medium supply
means, the independently controlled fluidizing means being adapted
for controlling a flow rate of solids from the bubbling fluidized
bed to the circulating fluidized bed boiler reaction chamber, the
independently controlled fluidizing means being controlled
separately from the distribution grid; the independently controlled
fluidizing means and the fluidizing medium supply means being at
least one of connected to and comprising collectors, the collectors
being adapted for collecting solids in the event of backsifting of
solids into the fluidizing means such that the collected solids do
not obstruct the supply of fluidizing medium; valves for sealing at
least one of the collectors, the fluidizing means, and the
fluidizing medium supply means, to allow removal of backsifted
solids from the collectors during operation of the circulating
fluidized bed furnace; the non-mechanical valve further comprising
at least one solids removal means, being adapted for removal of
agglomerates, located at least one of upstream and downstream of
said at least one opening in the bubbling fluidized bed enclosure
wall; the removal means each being connected to at least one screw
cooler adapted for sealing against furnace pressure, for
controlling solids discharge rate through the removal means, and
for cooling discharged solids and agglomerates; the bubbling
fluidized bed enclosure wall comprising a plurality of channel
walls adjacent to one or more openings in the bubbling fluidized
bed enclosure wall, the walls projecting generally away from the
enclosure wall into at least one of the circulating fluidized bed
and the bubbling fluidized bed, the channel walls being adapted to
reduce lateral movement of solids in one or more directions
perpendicular to the direction of solids discharge from the
bubbling fluidized bed to the circulating fluidized bed.
2. A circulating fluidized bed boiler comprising: a circulating
fluidized bed boiler reaction chamber comprising side walls and a
distribution grid for providing fluidizing gas into the circulating
fluidized bed boiler reaction chamber; a bubbling fluidized bed in
a compartment including at least one enclosure wall; at least one
controllable in-bed heat exchanger, the in-bed heat exchanger being
located within the compartment comprising the bubbling fluidized
bed; at least one non-mechanical valve adapted to control solids
discharge from the bubbling fluidized bed into the circulating
fluidized bed boiler reaction chamber, the valve comprising at
least one opening in the enclosure wall, and including at least one
independently controlled fluidizing means located at least at one
of upstream and downstream of the opening; the independently
controlled fluidizing means each being connected to fluidizing
medium supply means, the independently controlled fluidizing means
being adapted for controlling a flow rate of solids from the
bubbling fluidized bed to the circulating fluidized bed boiler
reaction chamber, the independently controlled fluidizing means
being controlled separately from the distribution grid; and
collectors linked to the one or more independently controlled
fluidizing means, the collectors being adapted for collecting
solids in the event of backsifting of solids into the fluidizing
means such that the collected solids do not obstruct a supply of
fluidizing medium.
3. The circulating fluidized bed boiler of claim 2, wherein the
non-mechanical valve further comprises: one or more solids removal
means, the solids removal means being adapted to provide a passage
for removal of agglomerates, and being located at least one of
upstream and downstream of said at least one opening in the
bubbling fluidized bed enclosure wall.
4. The circulating fluidized bed boiler of claim 3, wherein the
bubbling fluidized bed is located within a lower portion of the
circulating fluidized bed boiler reaction chamber, wherein the
bubbling fluidized bed is bound by enclosure walls and by the floor
of the circulating fluidized bed boiler reaction chamber; and
wherein the in-bed heat exchanger occupies part of the circulating
fluidized bed boiler reaction chamber floor and is within the
enclosure walls of the bubbling fluidized bed.
5. The circulating fluidized bed boiler of claim 3, wherein the
removal means are sealed against furnace pressure.
6. The circulating fluidized bed boiler of claim 3, further
comprising: one or more screw coolers, each being connected to the
one or more solids removal means and being adapted for cooling
discharged solids and for sealing against furnace pressure.
7. The circulating fluidized bed boiler of claim 2, further
comprising: means for sealing at least one of the collectors, the
fluidizing means, and the fluidizing medium supply sources, to
allow removal of backsifted solids from the collectors during
operation of the circulating fluidized bed boiler.
8. The circulating fluidized bed boiler of claim 2, further
comprising: a plurality of channel walls projecting generally away
from the enclosure wall into at least one of the circulating
fluidized bed and the bubbling fluidized bed, the channel walls
being adapted to reduce lateral movement of solids in one or more
directions perpendicular to the direction of solids discharge from
the bubbling fluidized bed.
9. The circulating fluidized bed boiler of claim 8, wherein at
least one opening is complemented by a channel wall on each side of
the opening and wherein said walls both protrude into at least one
of the bubbling fluidized bed and the circulating fluidized bed by
a distance of at least one half the width of the opening.
10. The circulating fluidized bed boiler of claim 9, further
comprising: one or more bridging surfaces linking the tops of a
plurality of channel walls, the bridging surfaces being adapted to
reduce vertical movement of bed material near at least one opening
in the enclosure wall.
11. The circulating fluidized bed boiler of claim 3, further
comprising: independently controlled fluidizing means located at
least at one of upstream and downstream of each solids removal
means.
12. The circulating fluidized bed boiler of claim 2, further
comprising: one or more rotary valves each connected to at least
one collector for removal of backsifted solids from the collectors
during operation of the circulating fluidized bed boiler
furnace.
13. The circulating fluidized bed boiler of claim 2, wherein the
openings in the bubbling fluidized bed enclosure wall comprise
passages having depth to height ratios of 1.4 or greater, and
wherein the openings are adapted to substantially prevent solids
flow through the openings in the absence of fluidization by one or
more independently controlled fluidizing means.
14. The circulating fluidized bed boiler of claim 2, wherein the
openings are adapted to substantially prevent solids flow out of
the bubbling fluidized bed compartment in the absence of
fluidization by one or more independently controlled fluidizing
means.
15. The circulating fluidized bed boiler of claim 2, wherein one or
more openings comprise a pipe.
16. The circulating fluidized bed boiler of claim 2, further
comprising: a plurality of channel walls projecting on each side of
one or more openings in the bubbling fluidized bed enclosure wall,
the channel walls projecting away from the enclosure wall into at
least one of the circulating fluidized bed and the bubbling
fluidized bed, the channel walls being adapted to reduce lateral
movement of solids in one or more directions perpendicular to the
direction of solids discharge from the bubbling fluidized bed; and
bridging surfaces linking the tops of a plurality of channel walls
and adapted to reduce vertical movement of bed material near at
least one opening in the enclosure wall; wherein the channel walls
and bridging surfaces are adapted to collectively extend the
effective length of one or more openings in the enclosure wall; and
wherein the one or more openings, together with their respective
channel walls and bridging surfaces, are collectively adapted to
substantially prevent solids flow out of the bubbling fluidized bed
compartment in the absence of fluidization by one or more
independently controlled fluidizing means adjacent to those
openings.
17. The circulating fluidized bed boiler of claim 2, wherein the
bubbling fluidized bed enclosure comprises tubes cooled by at least
one of water and steam.
18. The circulating fluidized bed boiler of claim 2, wherein the
bubbling fluidized bed is located within a lower portion of the
circulating fluidized bed boiler reaction chamber, wherein the
bubbling fluidized bed is bound by enclosure walls and by the floor
of the circulating fluidized bed boiler reaction chamber; and
wherein the in-bed heat exchanger occupies part of the circulating
fluidized bed boiler reaction chamber floor and is within the
enclosure walls of the bubbling fluidized bed.
19. The circulating fluidized bed boiler of claim 2, wherein the
enclosure wall comprises at least two non-mechanical valves, each
valve being adapted to independently control solids discharge from
the bubbling fluidized bed into the circulating fluidized bed
boiler reaction chamber, and wherein each valve comprises at least
one independently controlled fluidizing means located at least one
of upstream and downstream of its respective opening.
20. The circulating fluidized bed boiler of claim 19, the boiler
having a partially-opened condition wherein at least one
non-mechanical valve is in a closed state while at least one other
non-mechanical valve is in an open state; wherein said
partially-opened state is characterized by at least one
independently controlled fluidizing means of the closed
non-mechanical valve being in a non-fluidizing state; and wherein
said partially-opened state is characterized by at least one
independently controlled fluidizing means of the open
non-mechanical valve being in a fluidizing state.
21. The circulating fluidized bed boiler of claim 2, wherein at
least one opening comprises a channel with a depth to height ratio
of not less than 1.0.
22. The circulating fluidized bed boiler of claim 2, wherein at
least one opening comprises a channel with a depth to height ratio
of not less than 1.4.
23. The circulating fluidized bed boiler of claim 2, wherein at
least one opening is defined by materials comprising one or a
combination of ceramic, firebrick, and refractory covered
tubes.
24. The circulating fluidized bed boiler of claim 2, wherein each
independently controlled fluidizing means is connected to a
fluidizing medium source by a path which passes through a
collector, the fluidizing medium being supplied through the
collector at an elevation above a maximum level of backsifted
solids collected by the collector.
25. The circulating fluidized bed boiler of claim 2, comprising at
least one source of fluidizing medium adapted to provide fluidizing
medium having reduced oxygen content to at least one independently
controlled fluidizing means.
26. The circulating fluidized bed boiler of claim 2, comprising at
least one source of fluidizing medium adapted to provide fluidizing
medium having an oxygen content not exceeding 15% by volume to at
least one independently controlled fluidizing means.
27. The circulating fluidized bed boiler of claim 2, comprising at
least one source of fluidizing medium adapted to provide fluidizing
medium having an oxygen content not exceeding 12% by volume to at
least one independently controlled fluidizing means.
28. The circulating fluidized bed boiler of claim 2, comprising at
least one source of fluidizing medium adapted to provide fluidizing
medium having an oxygen content not exceeding 9% by volume to at
least one independently controlled fluidizing means.
29. The circulating fluidized bed boiler of claim 2, comprising at
least one source of fluidizing medium adapted to provide fluidizing
medium having an oxygen content not exceeding 6% by volume to at
least one independently controlled fluidizing means.
30. A non-mechanical valve arrangement for selectively controlling
a flow of particulate solids between two compartments wherein at
least one of said compartments comprises a fluidized bed, the
non-mechanical valve arrangement comprising: an enclosure wall
separating the two compartments; an opening in the enclosure wall
linking the two compartments; independently controlled fluidizing
means located at least one of upstream and downstream of the
opening, the independently controlled fluidizing means being
connected to fluidizing medium supply means and being adapted for
selectively controlling the flow of particulate solids through the
opening; one or more collectors connected to the independently
controlled fluidizing means, the collectors being adapted for
collecting any solids entering the fluidizing means such that the
collected solids do not obstruct the supply of fluidizing medium to
the fluidizing means; and one or more independently controlled
solids removal means located at least one of upstream and
downstream of the opening, the removal means being adapted for
removal of solids and agglomerates.
31. The non-mechanical valve arrangement of claim 30, the
non-mechanical valve arrangement further comprising: A plurality of
channel walls projecting away from the enclosure wall into at least
one compartment comprising a fluidized bed, wherein one or more
channel walls are adjacent to the opening, and wherein the channel
walls are adapted for reducing lateral movement of solids in at
least one direction perpendicular to the direction of solids flow
through the non-mechanical valve.
32. The non-mechanical valve arrangement of claim 30, wherein a
plurality of independently controlled fluidizing means are provided
in at least one row, each row being parallel to a wall comprising a
non-mechanical valve, wherein the independently controlled
fluidizing means in each row can be turned on and off as a
group.
33. A method for preventing agglomeration of solids in the
circulating fluidized bed boiler of claim 2 when one or more
non-mechanical valves are in a closed state, the closed state being
characterized by the independently controlled fluidizing means of
the closed valves not emitting fluidizing medium, the method
comprising periodically emitting fluidizing medium from at least
one independently controlled fluidizing means of each valve for not
less than 10% of a span when said valves are in the closed
state.
34. A method for preventing agglomeration of solids in the
circulating fluidized bed boiler of claim 2 when one or more
non-mechanical valves are in a closed state, the closed state being
characterized by the independently controlled fluidizing means of
the closed valves not emitting fluidizing medium, the method
comprising periodically emitting fluidizing medium from at least
one independently controlled fluidizing means of each valve for not
less than 5% of a span when said valves are in the closed
state.
35. A method for preventing agglomeration of solids in the
circulating fluidized bed boiler of claim 2 when one or more
non-mechanical valves are in a closed state, the closed state being
characterized by the independently controlled fluidizing means of
the closed valves not emitting fluidizing medium, the method
comprising periodically emitting fluidizing medium from at least
one independently controlled fluidizing means of each valve for not
less than 2% of a span when said valves are in the closed
state.
36. A method for preventing agglomeration of solids in the
circulating fluidized bed boiler of claim 2 when one or more
non-mechanical valves are in a closed state, the closed state being
characterized by the independently controlled fluidizing means of
the closed valves not emitting fluidizing medium, the method
comprising periodically emitting fluidizing medium from at least
one independently controlled fluidizing means of each valve no less
than every five minutes.
Description
BACKGROUND
[0001] The present invention relates generally to the field of
circulating fluidized bed (CFB) reactors and boilers such as those
used in electric power generation facilities and industrial
facilities. It particularly relates to CFB reactor arrangements
containing both a CFB and one or more bubbling fluidized bed(s)
(BFB's) feeding materials into a lower portion of the CFB reactor
enclosure, and to non-mechanical valves for controlling solids
flowing between slow bubbling bed region(s) and highly-fluidized
CFB regions.
[0002] Reactors and boilers can use CFB's and BFB's together in
various arrangements. For example, U.S. Pat. No. 5,533,471 teaches
placing the slow BFB below and to the side of the bottom of the
faster moving CFB chamber. In U.S. Pat. No. 5,526,775, the slow BFB
is above and to the side of the fast CFB. U.S. Pat. No. 5,190,451,
to Goldbach, illustrates a CFB chamber having a heat exchanger
immersed within a fluidized bed at the lower end of the chamber.
U.S. Pat. No. 5,184,671 to Alliston et al. teaches a heat exchanger
having multiple fluidized bed regions. The present invention can be
adapted for use with these or other arrangements.
[0003] The present invention also relates to valves for regulating
the movement of solids, including solid fuel, between BFB's and
CFB's. It relates, in particular, to non-mechanical valves to
control the flow of granular solids between fluidized beds by
regulating local fluidization at an opening in a wall between
enclosures. As a general principal, such valves "open" by
sufficiently aerating the area immediately around an opening
between the enclosures so that the particles are "fluidized" and
flow through the opening in a manner similar to a liquid. The
valves "close" by stopping or slowing fluidization around the same
openings so that the particles no longer behave and flow similarly
to a liquid.
[0004] For example, U.S. Pat. No. 6,532,905 to Belin et al.
describes a CFB boiler with a controllable in-bed heat exchanger
(IBHX). The boiler comprises both a CFB furnace and a
separately-controllable BFB heat exchanger located inside of the
CFB furnace. Heat transfer in the BFB's heat exchanger is
controlled by controlling the rate of solids discharged from the
lower part of the BFB into the larger CFB furnace. The discharge
control may be accomplished using at least one non-mechanical valve
between the CFB and the BFB. The non-mechanical valve may be
operated by controlling flow rate of fluidizing gas in the vicinity
of the valve. Reducing or completely shutting off fluidizing gas
flow to the controlling fluidizing means (typically, bubble caps)
hampers local fluidization and, as a result, slows or stops solids
movement through the non-mechanical valve, thus allowing the
control of the solids discharged from the BFB to the CFB (see, for
example, Published Patent Application US 2011/0073049 A1).
[0005] One problem with the prior art non-mechanical valve of Belin
et al. is that solid bed material may fall into the fluidizing
means (e.g., bubble caps), particularly when the fluidizing gas
flow is shut off to limit the flow of solids through the valve. The
problem can be particularly severe for idle fluidizing means that
are adjacent to active fluidizing means. This can block the
fluidizing gas flow once it is turned back on, and can hinder
further use of the non-mechanical valve.
[0006] Another problem of reducing the flow rate of the fluidizing
gas in the vicinity of the non-mechanical valve is bed material
agglomeration. Turning off the fluidizing gas reduces local bed
mixing. As bed solids combustion continues, there may be an
increase in the local bed temperature that can lead to solid
material agglomeration. Agglomeration may also happen elsewhere in
the boiler, with the agglomerates eventually moving towards the
non-mechanical valve along with the flow of other solids in the
system. Such agglomerates, whether forming or accumulating in the
vicinity of the valves, can eventually plug the valve and hinder
its operation.
[0007] Yet another problem with operating a CFB boiler including a
BFB is that the vigorous fluidization of the CFB furnace can
interfere with local fluidization in the vicinity of the
non-mechanical valve. This can interfere with control of solids
flow from the BFB into the CFB through the valve which relies, at
least in part, on controlling fluidization.
BRIEF DESCRIPTION
[0008] The present invention provides an improved non-mechanical
valve assembly which can be used with prior art fluidized bed
boilers including, but not limited to, the CFB boiler taught by
U.S. Pat. No. 6,532,905 to Belin et al. comprising a BFB linked to
a CFB. As mentioned, non-mechanical valves can be used to control
the flow of granular solids between enclosures by regulating local
fluidization at an opening in a wall between the enclosures.
Typically, such valves "open" by injecting fluidizing gas into the
area immediately around an opening between the two enclosures so
that the solid particles there are "fluidized", i.e., behaving in a
manner similar to a liquid. The solid particles flow through the
opening in the wall when they are fluidized. The valves "close" by
stopping or slowing gas injection, thereby ending fluidization
around the openings. Absent fluidization, the solid particles no
longer behave or flow like a liquid, and thus no longer flow
through the opening in the wall, or else move through at a much
lower rate.
[0009] The present invention eliminates problems associated with
temporarily closing non-mechanical valves by reducing or stopping
the flow of fluidizing medium. The problem of solid material
backsifting into the fluidization means when fluidizing gas flow is
turned off, and thereby causing their blockage, is solved by
providing collectors. These collectors are typically placed below
the fluidization means, so that solids backsifting into the
fluidization means will fall into the collectors and be stored
below a level where they can impede the flow of the fluidizing gas.
The solids are periodically or continuously removed from the
collectors to keep their level sufficiently low. In a preferred
embodiment, the collectors can be emptied during boiler operation
without interrupting the flow of fluidizing medium, ideally without
breaking any seal that would allow escape of fluidizing medium.
[0010] Removal means are also provided in the valve arrangement for
removing agglomerates from the solids flow based, for example, on
their larger size and greater weight. As a result, the probability
of large agglomerates sticking in and blocking valves is reduced.
In a preferred embodiment, the removal means are sealed against
furnace pressure, the rate of solids removal out of the system is
controlled, and the removed material is cooled.
[0011] The present invention also alleviates interference between
the intense fluidization of the CFB furnace and the
fluidization-controlled non-mechanical valve between the CFB and
the BFB. Walls projecting into the BFB and/or CFB from the BFB
enclosure wall form channels or tunnels, which block lateral solids
movement near the valve openings. These walls shield the opening
between the CFB and the BFB from the most extreme effects of the
CFB solids churning, and thus improve control over local
fluidization and the function of the non-mechanical valves.
[0012] In a preferred embodiment, there is little or no solids flow
through the non-mechanical valve, i.e. the valve is "closed," when
local fluidization by independently controlled fluidizing means is
turned off. The invention teaches how to design passages between
BFB's and CFB's that substantially block particle flow in the
manner of an L-valve. All of the improvements of the invention can
be applied to a range of non-mechanical valves regulating granular
material flow between different compartments using local
fluidization, particularly where at least one of the compartments
contains a fluidized bed.
[0013] Accordingly, one aspect of the present invention is drawn to
a circulating fluidized bed boiler comprising: a circulating
fluidized bed boiler reaction chamber comprising side walls and a
distribution grid defining a floor at a lower end of the
circulating fluidized bed boiler reaction chamber, the distribution
grid being adapted for providing fluidizing gas into the
circulating fluidized bed boiler reaction chamber; a bubbling
fluidized bed located within a lower portion of the circulating
fluidized bed boiler reaction chamber and being bound by enclosure
walls and by the floor of the circulating fluidized bed boiler
reaction chamber; at least one controllable in-bed heat exchanger,
the in-bed heat exchanger occupying part of the circulating
fluidized bed boiler reaction chamber floor and being within the
enclosure walls of the bubbling fluidized bed; at least one
non-mechanical valve designed to permit the control of solids
discharge from the bubbling fluidized bed into the circulating
fluidized bed boiler reaction chamber, the valve comprising at
least one opening in the enclosure wall of the bubbling fluidized
bed, and including at least one independently controlled fluidizing
means located at least at one of upstream and downstream of the
opening; the at least one independently controlled fluidizing means
each being connected to corresponding fluidizing medium supply
means, the independently controlled fluidizing means being adapted
for controlling a flow rate of solids from the bubbling fluidized
bed to the circulating fluidized bed boiler reaction chamber, the
independently controlled fluidizing means being controlled
separately from the distribution grid; the independently controlled
fluidizing means and the fluidizing medium supply means being at
least one of connected to and comprising collectors, the collectors
being adapted for collecting solids in the event of backsifting of
solids into the fluidizing means such that the collected solids do
not obstruct the supply of fluidizing medium; valves for sealing at
least one of the collectors, the fluidizing means, and the
fluidizing medium supply means, to allow removal of backsifted
solids from the collectors during operation of the circulating
fluidized bed furnace; the non-mechanical valve further comprising
at least one solids removal means, being adapted for removal of
agglomerates, located at least one of upstream and downstream of
said at least one opening in the bubbling fluidized bed enclosure
wall; the removal means each being connected to at least one screw
cooler adapted for sealing against furnace pressure, for
controlling solids discharge rate through the removal means, and
for cooling discharged solids and agglomerates; the bubbling
fluidized bed enclosure wall comprising a plurality of channel
walls adjacent to one or more openings in the bubbling fluidized
bed enclosure wall, the walls projecting generally away from the
enclosure wall into at least one of the circulating fluidized bed
and the bubbling fluidized bed, the channel walls being adapted to
reduce lateral movement of solids in one or more directions
perpendicular to the direction of solids discharge from the
bubbling fluidized bed to the circulating fluidized bed.
[0014] Yet another aspect of the present invention is drawn to a
circulating fluidized bed boiler comprising: a circulating
fluidized bed boiler reaction chamber comprising side walls and a
distribution grid for providing fluidizing gas into the circulating
fluidized bed boiler reaction chamber; a bubbling fluidized bed in
a compartment including at least one enclosure wall; at least one
controllable in-bed heat exchanger, the in-bed heat exchanger being
located within the compartment comprising the bubbling fluidized
bed; at least one non-mechanical valve adapted to control solids
discharge from the bubbling fluidized bed into the circulating
fluidized bed boiler reaction chamber, the valve comprising at
least one opening in the enclosure wall, and including at least one
independently controlled fluidizing means located at least at one
of upstream and downstream of the opening; the independently
controlled fluidizing means each being connected to fluidizing
medium supply means, the independently controlled fluidizing means
being adapted for controlling a flow rate of solids from the
bubbling fluidized bed to the circulating fluidized bed boiler
reaction chamber, the independently controlled fluidizing means
being controlled separately from the distribution grid; and
collectors linked to the one or more independently controlled
fluidizing means, the collectors being adapted for collecting
solids in the event of backsifting of solids into the fluidizing
means such that the collected solids do not obstruct a supply of
fluidizing medium.
[0015] Yet another aspect of the present invention drawn to a
non-mechanical valve arrangement for selectively controlling a flow
of particulate solids between two compartments wherein at least one
of said compartments comprises a fluidized bed, the non-mechanical
valve arrangement comprising: an enclosure wall separating the two
compartments; an opening in the enclosure wall linking the two
compartments; independently controlled fluidizing means located at
least one of upstream and downstream of the opening, the
independently controlled fluidizing means being connected to
fluidizing medium supply means and being adapted for selectively
controlling the flow of particulate solids through the opening; one
or more collectors connected to the independently controlled
fluidizing means, the collectors being adapted for collecting any
solids entering the fluidizing means such that the collected solids
do not obstruct the supply of fluidizing medium to the fluidizing
means; and one or more independently controlled solids removal
means located at least one of upstream and downstream of the
opening, the removal means being adapted for removal of solids and
agglomerates.
[0016] These and other non-limiting aspects and/or objects of the
disclosure are more particularly described below.
[0017] The various features of novelty which characterize the
invention are pointed out with particularity in the claims annexed
to and forming a part of this disclosure. For a better
understanding of the invention, its operating advantages, and
specific objects attained by its uses, reference is made to the
accompanying drawings and descriptive matter in which a preferred
embodiment of the invention is illustrated.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] In the drawings:
[0019] FIG. 1 is a schematic partial side elevational view of a CFB
boiler which comprises a CFB furnace or reaction chamber, a
particle separator, a BFB containing an IBHX, and a non-mechanical
valve separating the CFB furnace from the BFB;
[0020] FIG. 2, taken along sectional view 2-2 of FIG. 1, is a
sectional plan view of the CFB boiler, CFB furnace, BFB, and
IBHX;
[0021] FIG. 3 is an enlarged partial side sectional view of a
non-mechanical valve of the invention separating the BFB and the
CFB furnace;
[0022] FIG. 4 is an enlarged partial side sectional view of an
alternative embodiment of the non-mechanical valve of the invention
separating the BFB and the CFB furnace;
[0023] FIG. 5A is a partial top perspective view of an enclosure
wall between the BFB and the CFB, the wall including non-mechanical
valves and channel walls protruding away from the enclosure wall,
part of the enclosure wall being removed for improved
visibility;
[0024] FIG. 5B is an enlarged view of a portion of the enclosure
wall of FIG. 5A where part of the wall covering is removed to show
pipes inside the wall;
[0025] FIG. 6 is a partial top perspective view of an alternative
arrangement of openings in the enclosure wall between the BFB and
the CFB, and of channel walls protruding away from the enclosure
wall, part of the wall being removed for improved visibility;
[0026] FIG. 7 is a partial top perspective view of openings in
another enclosure wall between the BFB and the CFB, and of channel
walls connected by a top bridging surface protruding away from the
enclosure wall, part of the wall being removed for improved
visibility; and
[0027] FIGS. 8A and 8B are sectional side elevational views of two
embodiments of non-mechanical valve arrangements comprising
channels, the channels having dimensions adapted to shut down
solids flow through them in the absence of fluidization.
DETAILED DESCRIPTION
[0028] A more complete understanding of the processes and
apparatuses disclosed herein can be obtained by reference to the
accompanying drawings. These figures are merely schematic
representations based on convenience and the ease of demonstrating
the existing art and/or the present development, and are,
therefore, not intended to indicate relative size and dimensions of
the assemblies or components thereof.
[0029] Although specific terms are used in the following
description for the sake of clarity, these terms are intended to
refer only to the particular structure of the embodiments selected
for illustration in the drawings, and are not intended to define or
limit the scope of the disclosure. In the drawings and the
following description below, it is to be understood that like
numeric designations refer to components of like function.
[0030] The modifier "about" used in connection with a quantity is
inclusive of the stated value and has the meaning dictated by the
context (for example, it includes at least the degree of error
associated with the measurement of the particular quantity). When
used with a specific value, it should also be considered as
disclosing that value. For example, the term "about 2" also
discloses the value "2" and the range "from about 2 to about 4"
also discloses the range "from 2 to 4."
[0031] As is known to those skilled in the art, heat transfer
surfaces which convey steam-water mixtures are commonly referred to
as evaporative boiler surfaces; heat transfer surfaces which convey
steam therethrough are commonly referred to as superheating (or
reheating, depending upon the associated steam turbine
configuration) surfaces. Regardless of the type of heating surface,
the sizes of the tubes, their material, diameter, wall thickness,
number, and arrangement are based upon temperature and pressure for
service, according to applicable boiler design codes, such as the
American Society of Mechanical Engineers (ASME) Boiler and Pressure
Vessel Code, Section I, or equivalent other codes as required by
law.
[0032] To the extent that explanations of certain terminology or
principles of the heat exchanger, boiler, and/or steam generator
arts may be necessary to understand the present disclosure, and for
a more complete discussion of CFB boilers, or of the design of
modern utility and industrial boilers, the reader is referred to
the reader is referred to Steam/its generation and use, 41st
Edition, Kitto and Stultz, Eds., Copyright .COPYRGT. 2005, The
Babcock & Wilcox Company, Barberton, Ohio, U.S.A., Lib. of
Congress No. 92-74123, the text of which is hereby incorporated by
reference as though fully set forth herein.
[0033] The present invention solves several problems encountered
with non-mechanical, fluidizing-medium controlled valves of the
prior art. In a particularly preferred embodiment described herein
to demonstrate the invention, an improved non-mechanical valve is
used with a CFB boiler comprising both a CFB reaction chamber and a
BFB with IBHX located within the reaction chamber.
[0034] Referring now to the drawings, where like reference numerals
designate the same or similar elements throughout the drawings,
FIGS. 1 and 2 show a preferred CFB boiler system comprising a CFB
reaction chamber or furnace 1 and implementing the present
invention. The furnace includes walls 2, and an in-bed heat
exchanger (IBHX) 3 immersed in a BFB 4 located within the reaction
chamber 1. The heating surface of the IBHX 3, which absorbs heat
from the BFB 4, may be a superheater, a reheater, an economizer, or
combinations of similar heating surfaces which are known to those
skilled in the art. The IBHX heating surface is typically comprised
of tubes or pipes 31 which convey a heat transfer medium
therethrough, such as water, a two-phase mix of water and steam, or
steam.
[0035] The CFB may be comprised of solids made up of fuel 5, the
ash of the fuel 5, sorbent 6 and, in some cases, external inert
material 7 fed through at least one of the walls 2 of the furnace.
Many other possible solid components are known to those of skill in
the art. The CFB is fluidized by injection of the primary air 8
and/or by other gases. The fluidizing air is preferably supplied
through a distribution grid 9 which may comprise a part of the
furnace floor, and which typically comprises bubble caps.
[0036] Some solids 15 are entrained upward by gases resulting from
the fuel combustion and eventually reach a particle separator 16
near the furnace exit. While some of the solids 17 pass the
separator, the bulk of the solids 18 are captured and recycled back
to the furnace. Part of the captured solids 18, along with other
solids 19 falling out of the upflow solids stream 15 driven by
gravity will enter the BFB 4.
[0037] The BFB 4 is fluidized by fluidizing medium 25 fed through a
distribution grid 26, which may comprise part of the furnace floor.
This will generally be a separate grid from the distribution grid
9, which fluidizes the CFB. As is well known to those skilled in
the art, the most common design of a distribution grid would be an
array of bubble caps fed from a corresponding source of fluidizing
medium. A bubble cap is comprised of a bubble cap proper and a
supply pipe, typically referred to as the stem, which interconnects
the fluidizing medium with the fluidized bed. Fluidizing gas is
conveyed upwardly along the stem into the bubble cap, from which it
is distributed to the fluidized bed via a plurality of outlet
holes. Jets of fluidizing gas exiting from the outlet holes
penetrate into the CFB or BFB fluidizing particulate solids in the
area around each bubble cap.
[0038] Means for removing solids from the CFB and BFB (27 and 28,
correspondingly) are preferably provided in the pertinent areas of
the floor.
[0039] The BFB 4 is separated from the CFB by an enclosure wall 30
comprising one or more non-mechanical valves 40. The rate of solid
recycle 35 back to the CFB through one or more non-mechanical
valves 40 is controlled by controlling one or more streams of the
fluidizing medium 45 and 46. The streams of fluidizing medium are
preferably provided through one or more independently controlled
fluidizing means 86, 87, 94, 95, which are located upstream
(towards the BFB) and/or downstream (towards the CFB) of the
opening(s) 85 in the enclosure wall 30 (FIGS. 3-4).
[0040] Gas flow to the vicinity of the non-mechanical valve
promotes solids discharge from the lower part of the BFB 4 into the
CFB 1. Independent control of these flow rates, e.g., turning them
on and off in alternate cycles, allows for smoothing the solids
discharge rate. Particular fluidizing medium control patterns
(frequency of cycling, length of a cycle, etc.) depend on
properties of the bed material and boiler operation requirements
and should be established during boiler commissioning.
[0041] The fluidizing gas streams 45, 46 are preferably controlled
independently of the CFB distribution grid 9 and the BFB
distribution grid 26, and may be controllable independently of each
other, but are most preferably regulated in accordance with each
other in operation. As used in the claims, the term "independently
controlled fluidizing means" always refers to fluidizing means
which are capable of being controlled independently of the
distribution grids 9, 26, and preferably, but not necessarily,
independent of other independently controlled fluidizing means in
the same row or in different rows. In one preferred embodiment,
independently controlled fluidizing means are provided in from one
to six rows on each of one or both sides of a enclosure wall 30,
each row comprising a plurality of bubble caps. In a most preferred
embodiment the fluidizing means in each row are controlled together
as a row, but each row can be controlled separately from any other
rows and separately from the distribution grids 9, 26. Typically,
each row will be parallel to a enclosure wall 30, the wall having
one or several openings 85. Thus, controlling the fluidization of
each row may affect more than one valve 40 if the row is near more
than one opening 85. Embodiments where each valve is controlled
separately, and where fluidizing means are not controlled as a row,
are also possible, however.
[0042] Persons of skill in the art will appreciate that the
non-mechanical valves 40 can include wall openings 85,
independently controlled fluidizing means 86, 87, 94, 95, solids
removal means 60, and other components in a wide variety of
configurations. FIG. 5A shows an embodiment similar to the example
of FIG. 3. In FIGS. 3 and 5A there are solids removal means 60, 61
immediately on both sides of each opening 85. Outside of each
solids removal means 60, 61 is a single row of independently
controlled fluidizing means 86, 87. The bubble caps beyond the
single row of independently controlled fluidizing means make up the
BFB and CFB distribution grids 26 and 9, correspondingly. FIG. 6
shows an embodiment similar to the example of FIG. 4. Each side of
the enclosure wall 30 has a single row of independently controlled
fluidizing means 94, 95, followed by a solids removal means 60, 61,
followed by one more row of independently controlled fluidizing
means 86, 87 in the example of FIG. 4, and two more rows in the
example of FIG. 6. FIG. 7 shows another alternative where not all
of the independently controlled fluidizing means are provided in
complete rows. Two independently controlled fluidizing means bubble
caps are provided immediately on each side of each opening 85,
although the rows nearest the openings are not continuous between
the openings 85 of the valves 40.
[0043] The independently controlled fluidizing means 86, 87, 94, 95
are typically bubble caps, but other embodiments are possible. The
independently controlled fluidizing means may comprise the same
type of bubble caps as found in the distribution grids 9, 26, or
they may take different forms.
[0044] The enclosure wall 30 is preferably made of tubes or pipes
50 that are cooled by water or steam. The tubes are usually
protected from erosion and corrosion by a protective layer,
commonly formed by a refractory held by studs welded to the tubes.
The tubes may be horizontal as shown in FIG. 5B, vertical, or in
other arrangements. FIGS. 3 and 4 show sectional views of pipes 50
within an enclosure wall 30. FIG. 2 shows an example tube 50 within
a enclosure wall 30 from above. The tubes may optionally extend
into channel walls 100 and bridge surfaces 105 when present.
[0045] In a preferred embodiment, secondary air 70 or another gas
is supplied through nozzles 75. The nozzles 75 are typically
located on the opposite walls 2 of the CFB furnace somewhat above
the floor of the furnace.
[0046] FIG. 3 shows a blowup of the area around and including a
preferred embodiment of a non-mechanical valve 40. The valve
comprises an opening 85 in the enclosure wall 30, and independently
controlled fluidizing means 86 and 87, located upstream and
downstream of the opening 85 respectively. These fluidizing means
can be implemented as a number of bubble caps connected to
corresponding sources 47 and 48 of fluidizing medium, 45 and 46,
respectively. Each fluidizing means, i.e. 86 or 87, can be
comprised of several groups of bubble caps, each group being
supplied with fluidizing medium from its own corresponding source
47 or 48 with the flow rate being controlled for each group
independently. Such a group can be arranged as a row of bubble caps
parallel to the enclosure wall 30 containing the opening 85. It is
possible that only one means (either upstream or downstream of the
opening 85) is employed, and the other one is not present in some
designs. It is possible to have multiple openings 85 having either
separate or shared fluidizing means 86, 87 so that all of the
openings 85 might be controllable only as a group, or each opening
85 may be separately controllable.
[0047] As is well known to those skilled in the art, the most
common embodiment of a distribution grid, such as 9 for CFB or 26
for BFB, would be an array of bubble caps fed from a corresponding
source of the fluidizing medium, i.e. 8 for CFB and 25 for BFB. To
prevent erosion of the bubble caps (or other fluidizing means) in
the vicinity of the opening 85 by the solids flow through the
opening, the tops of the bubble caps should not be higher than the
bottom of the opening.
[0048] The non-mechanical valve 40 is preferably equipped with
solids removal means 60 and 61. The removal means 60 and 61 are
adapted to allow passage for removal of agglomerates that can be
formed at, or transported to, the vicinity of the opening, and
selectively remove agglomerates from the other solids based, for
example, on their greater size and weight. Solids removal means 60
and 61 are preferably located both upstream and downstream of the
opening 85, but their positions and quantity can vary. For example,
solids removal means might only be provided on one side of each
wall opening, and there may or may not be fluidizing means between
the removal means and the nearest wall opening. Preferably, the
solids removal means 60 and 61 are separately controlled.
Preferably, the removal means 60 and 61 are sealed against furnace
pressure, and to control solids discharge. This can be accomplished
using screw coolers 88 and 89 that are also adapted to cool
discharged solids, or by other means known to those skilled in the
art.
[0049] Independently controlled fluidizing means 86, 87,94, 95 are
preferably connected to corresponding collectors 92 and 93.
Fluidizing medium 45 and 46 is preferably supplied to the upper
parts of the collectors 92 and 93, respectively, from where it is
distributed to corresponding fluidizing means. If backsifting takes
place, such as when the fluidizing medium is turned off, any solids
falling into the fluidizing means 86 and 87 should end up in the
collectors 92 and 93. The level of accumulated solids in the
collectors 92 and 93 should be maintained below the elevation of
the supply of the fluidizing medium 45 and 46 so that backsifted
solids do not affect operation of the fluidizing means 86 and
87.
[0050] Alternatively, the means 92 and 93 for collecting backsifted
solids may be further separated from the path of the fluidizing
medium 45, 46 to the corresponding fluidizing means. For example,
the FIG. 4 shows an embodiment where fluidizing medium 45 and 46 is
provided to the midpoint of tubes that lead upward to fluidizing
means 94 and 95 respectively and downward to areas where solids can
collect well away from the path of the fluidizing medium. Persons
of skill in the art will be capable of devising various means for
collecting or trapping backsifted solids without blocking
fluidizing medium using this concept. Embodiments where fluidizing
medium does not pass through the collectors 92 and 93 may be
desirable in some applications.
[0051] In preferred embodiments the collectors 92, 93 can be
emptied while the furnace is operating, and without turning off the
fluidizing medium 45, 46 pressure to any fluidizing means. Sealing
off the collectors 92 and 93 while removing the backsifted solids
can be accomplished by rotary valves 96 and 97 or by other means
known to those skilled in the art. For example, a rotary valve
could be used to remove backsifted solids from the bottom of a
collector, while the collector remains pressurized, without opening
a direct path for the escape of fluidizing medium. Alternatively,
the collectors themselves could be temporarily sealed off from the
fluidizing medium pressure during emptying. It is preferable if the
fluidizing medium streams 45 and 46 can be maintained while the
collectors 92 and 93 are emptied to prevent backsifting of
additional solids during emptying, and to allow uninterrupted
operation of the boiler system.
[0052] The independently controlled fluidizing means 86, 87, 94, 95
can be located on either one or both sides of the solids removal
means 60 and 61. The latter arrangement is exemplified in FIG. 4.
There may be more than one fluidizing means or multiple rows of
fluidizing means on each side of each opening 85. For example, FIG.
6 shows an embodiment having three rows of independently controlled
fluidizing means 86, 87, 94, 95 on each side of each opening 85.
Fluidizing means and removal means may be effectively used in a
variety of arrangements, and the invention is not limited to the
illustrative embodiments shown in FIGS. 3-7.
[0053] Each fluidizing means 86 and 87, or each part of each
fluidizing means (such as when a fluidizing means comprises
multiple bubble caps), may be supplied with fluidizing medium 45
and 46 either individually or via shared sources of fluidizing
medium 47 and 48 shared with other units. Similarly, solids
collection means 92 and 93 may or may not be shared.
[0054] Arrangements where different fluidizing media may be
selectively supplied to each fluidizing means--such as regular air
or reduced oxygen air--may be used.
[0055] The applicants have found that the considerable turbulence
of CFB's can interfere with fluidization in the vicinity of
adjacent non-mechanical valves. This can affect the ability of such
non-mechanical valves to regulate solids discharge rate, for
example, from a BFB into a CFB furnace.
[0056] The applicants have discovered that controllability of
solids discharge rate can be improved by creating channels parallel
to the direction of the solids discharge. Such channels allow
unobstructed solids movement through the opening, but suppress bed
movement in other directions. These channels can be formed, for
example, by walls 100 on the sides of opening 85. Each wall
protrudes away from the enclosure wall 30 into at least one of the
CFB and/or the BFB, preferably by a distance of at least one half
of the width of the opening. The channel walls suppress lateral bed
material movement in directions perpendicular to that of the solids
discharge from the BFB to the CFB. See FIGS. 5A, 6 and 7 for
non-limiting examples of wall 100 arrangements and placements
relative to the openings 85. The tops of the walls 100 above the
opening(s) can also be bridged by a surface 105 for restricting the
vertical movement of the bed material near the opening 85. A bridge
surface 105 can reduce vertical bed material movement which is also
perpendicular to the direction of the solids discharge from the BFB
into the CFB furnace. The bridge surfaces 105 protrude into at
least one of the CFB and the BFB, preferably protruding at least as
far as the walls 100 protrude (FIG. 7). This aspect of the
invention--using walls 100 parallel to the solids flow direction to
limit perpendicular motion--can be applied to a variety of
interfaces which comprise fluidized solids on one or both
sides.
[0057] Similar to other parts of the enclosure wall 30, the walls
100 and bridge surfaces 105 may comprise tubes 50 cooled by water
or steam, and are preferably covered with refractory, firebrick or
a similar substance.
[0058] The size, shape and length of the opening 85 can play a role
in controlling the flow of granular solids from the BFB side of the
enclosure wall 30 to the CFB furnace 1 side. In a preferred
embodiment, solids will not flow substantially from the BFB side
though the opening 85 to the CFB side of the enclosure wall 30
unless the solids are at least somewhat fluidized. Preferably,
steady flow through the opening 85 can be restored using
fluidization means 86, 87, 94, 95.
[0059] The area inside the enclosure wall 30 which may be a BFB
under fluidization conditions, in combination with a properly
dimensioned opening 85, can together function as an L-valve for
regulating the flow of granular solids through the opening. As is
known to those skilled in the art, L-valves allow reliable control
of the rate of solids flow, including complete flow shutdown.
[0060] The L-valve geometry required for flow rate control depends
on the properties of the solids, in particular, the solids' angle
of repose. While most common bed material produced in CFB
combustion has an angle of repose in the 35-40.degree. range, in
atypical cases the angle of repose may fall in the range of
30-45.degree.. Given an angle of repose in the 35-40.degree. range,
the minimal depth-to-height ratio (horizontal:vertical ratio) of
the channel 85 required for solids flow shutdown is about 1.4-1.2
for most common cases. The ratio may be as high as 1.7 or as low as
1.0 in unusual cases. See FIGS. 8A and 8B. The angle of repose of
the solids, such as fuel ash, that a given CFB boiler is designed
to accommodate can be used to calculate desirable channel 85
dimensions depending on, for example, whether or not it is
desirable for solids to flow through the opening 85 in the absence
of fluidization.
[0061] The walls 100 and bridging surfaces 105 discussed above may,
optionally, be designed to function as part of an L-valve in
addition to regulating lateral fluidization movement.
[0062] In addition to the embodiments using walls 100, 105
described above, channels can be formed in other ways, e.g., by
using the thickness of the enclosure wall 30, by forming opening 85
with pipe 110, and other means which will be apparent to one of
skill in the art. Two examples are illustrated in FIG. 8. The
components of the channels, such as walls 100, bridging surfaces
105, or pipes 110, can be made of various materials able to
withstand conditions of a CFB furnace: ceramic, firebrick,
refractory covered tubes, etc. and a combination of thereof, e.g.
refractory covered tubes and ceramic parts.
[0063] Solids discharge through one or more non-mechanical valves
40 can be stopped by stopping fluidization by the pertinent
independently controlled fluidizing means 86, 87, 94, 95. This,
however, may cause agglomeration of solids in the
temporarily-stagnated bed in the vicinity of the shut down valve.
This is particularly true when continued combustion causes
localized temperature increase. Since formation of agglomerates is
usually a slow process, it can be prevented by periodic
fluidization of the stagnated bed. Such a fluidization can be brief
relative to the duration of the idle period to minimize its effect
on overall discharge rate, but of sufficient duration to break-up
and prevent incipient agglomerates. For example, the areas adjacent
to the wall openings or other regions might be fluidized for short
periods spaced by longer periods of non-fluidization.
[0064] As discussed, local reductions in fluidization can result in
local heat buildup due to continued combustion, leading to the
formation of agglomerates. Thus, it is sometimes desirable to
reduce the local heat release rate in areas of the bed where mixing
may (at least temporarily) be reduced, such as the vicinity of the
opening 85, to decrease the chances of forming agglomerates there.
A reduction of the heat release rate around an opening 85 may be
accomplished by using a fluidizing medium 45 and 46 with reduced
content of oxygen, e.g. flue gas. Depending on the makeup of the
fuel, the ash, and other solids, reducing oxygen content in the
fluidizing medium down to 15% may be sufficient for preventing
agglomeration. In other cases, its oxygen content should be reduced
to 12%, or even as low as 9% or 6% to achieve adequate cooling. Low
oxygen medium may be used in combination with the intermittent
fluidization technique to prevent agglomerates.
[0065] It will be understood by persons of skill in the art that
the improved non-mechanical valves of the present
invention--comprising agglomerate removal means 60 and 61,
backsifted solids collection means 92 and 93 connected to the
fluidizing means 86, 87, 94, 95, perpendicular channel walls 100
and 105, valve openings having specific depth to height ratios,
and/or other disclosed improvements--can be used in a variety of
boilers and other devices comprising fluidized beds known in the
art. Non-limiting examples are described in the patents identified
in the Background section above, as well as in texts such as
Steam/its generation and use, 41st Edition, Kitto and Stultz, Eds.,
Copyright .COPYRGT. 2005, The Babcock & Wilcox Company,
Barberton, Ohio, U.S.A., pp. 17-1-17-15. Lib. of Congress No.
92-74123.
[0066] The present disclosure has been described with reference to
exemplary embodiments. Obviously, modifications and alterations
will occur to others upon reading and understanding the preceding
detailed description. It is intended that the present disclosure be
construed as including all such modifications and alterations
insofar as they come within the scope of the appended claims or the
equivalents thereof.
[0067] While specific embodiments of the present invention have
been shown and described in detail to illustrate the application
and principles of the invention, it will be understood that it is
not intended that the present invention be limited thereto and that
the invention may be embodied otherwise without departing from such
principles. In some embodiments of the invention, certain features
of the invention may sometimes be used to advantage without a
corresponding use of the other features. Accordingly, all such
changes and embodiments properly fall within the scope of the
following claims.
* * * * *