U.S. patent application number 13/960384 was filed with the patent office on 2014-04-24 for system and method for controlling scale build-up in a wfgd.
The applicant listed for this patent is Babcock & Wilcox Power Generation Group, Inc.. Invention is credited to Daniel B Johnson.
Application Number | 20140112834 13/960384 |
Document ID | / |
Family ID | 50485515 |
Filed Date | 2014-04-24 |
United States Patent
Application |
20140112834 |
Kind Code |
A1 |
Johnson; Daniel B |
April 24, 2014 |
SYSTEM AND METHOD FOR CONTROLLING SCALE BUILD-UP IN A WFGD
Abstract
The present invention relates generally to the cleaning of a
flue gas and, in one embodiment, to a device, system and method
that mitigates and/or prevents slurry deposition at the flue inlet
to a wet flue gas desulfurization (WFGD) unit in order to keep the
inlet dry and minimize deposition (e.g., deposition scale) at the
flue inlet to the WFGD tower. In one embodiment, a wet flue gas
desulfurization (WFGD) unit, system and/or method according to the
present invention comprises, among other features, a scale
prevention system comprising a plenum air device and/or forced-air
box located proximate the inlet transition zone. In another
embodiment, a wet flue gas desulfurization (WFGD) unit, system
and/or method according to the present invention comprises, among
other features, a scale prevention system comprising at least one
chill plate located proximate the inlet transition zone.
Inventors: |
Johnson; Daniel B; (Orland
Park, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Babcock & Wilcox Power Generation Group, Inc. |
Barberton |
OH |
US |
|
|
Family ID: |
50485515 |
Appl. No.: |
13/960384 |
Filed: |
August 6, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61717133 |
Oct 23, 2012 |
|
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|
Current U.S.
Class: |
422/173 ;
422/168 |
Current CPC
Class: |
F01N 3/04 20130101; F23J
2215/20 20130101; F23J 2219/80 20130101; F23J 15/003 20130101; F23J
15/04 20130101; F01N 3/05 20130101; B01D 53/80 20130101; F23J
2217/50 20130101; B01D 2258/0283 20130101; B01D 53/504
20130101 |
Class at
Publication: |
422/173 ;
422/168 |
International
Class: |
F01N 3/05 20060101
F01N003/05 |
Claims
1. A scale prevention system for a wet flue gas desulfurization
unit, the system comprising: a flue structure, wherein the flue
structure is connected to a flue inlet of a wet flue gas
desulfurization unit; at least two air nozzles, each air nozzle
having a respective air supply line, wherein the at least two air
nozzles are positioned on the interior of the flue structure so as
to provide air coverage across the horizontal width of a flue inlet
to the wet flue gas desulfurization unit; and at least one inlet
awning designed to deflect a slurry from the wet flue gas
desulfurization unit, the at least one inlet awning being position
above the flue inlet to the wet flue gas desulfurization unit.
2. The system of claim 1, wherein the flue structure has a
rectangular or square cross-sectional shape and the at least two
air nozzles are positioned on opposite interior walls of the
flue.
3. The system of claim 2, wherein the at least two air nozzles are
positioned on opposite vertical interior walls of the flue.
4. The system of claim 1, wherein the at least two air nozzles
receive temperature controlled air that is within a range of about
-25.degree. F. to about +25.degree. F. of the wet flue gas
desulfurization unit slurry temperature.
5. A scale prevention system for a wet flue gas desulfurization
unit, the system comprising: a flue structure, wherein the flue
structure is connected to a flue inlet of a wet flue gas
desulfurization unit and the flue structure has a cross-sectional
shape selected from a rectangle or a square; at least two air
nozzles, each air nozzle having a respective air supply line,
wherein at least one air nozzle is positioned on each opposite
vertical interior wall of the flue structure so as to provide air
coverage across the horizontal width of a flue inlet to the wet
flue gas desulfurization unit; and at least two lateral air
nozzles, each lateral air nozzle having a respective air supply
line, wherein each lateral air nozzle is positioned internally of
each of the at least two air nozzles and are positioned at the top
edge of the flue inlet to the wet flue gas desulfurization unit so
as to provide air coverage across the horizontal width of the flue
inlet to the wet flue gas desulfurization unit.
6. The system of claim 5, wherein the at least two lateral air
nozzles are separated by a baffle plate.
7. The system of claim 5, wherein the system further comprises at
least one inlet awning designed to deflect a slurry from the wet
flue gas desulfurization unit, the at least one inlet awning being
position above the flue inlet to the wet flue gas desulfurization
unit.
8. The system of claim 5 wherein the at least two air nozzles
receive temperature controlled air that is within a range of about
-25.degree. F. to about +25.degree. F. of the wet flue gas
desulfurization unit slurry temperature.
9. A scale prevention system for a wet flue gas desulfurization
unit, the system comprising: a flue structure, wherein the flue
structure is connected to a flue inlet of a wet flue gas
desulfurization unit; and at least two chill plates, each chill
plate having a respective supply line, wherein the at least two
chill plates are positioned on the interior of the flue structure
so as to provide temperature control across the horizontal width of
a flue inlet to the wet flue gas desulfurization unit.
10. The system of claim 9, wherein each chill plate receives
temperature controlled gas.
11. The system of claim 9, wherein each chill plate receives
temperature controlled liquid.
12. The system of claim 9, wherein the at least two chill plates
receive a temperature controlled gas that is within a range of
about -25.degree. F. to about +25.degree. F. of the wet flue gas
desulfurization unit slurry temperature.
13. The system of claim 9, wherein the at least two chill plates
receive a temperature controlled liquid that is within a range of
about -25.degree. F. to about +25.degree. F. of the wet flue gas
desulfurization unit slurry temperature.
14. The system of claim 9, wherein the system further comprises at
least one inlet awning designed to deflect a slurry from the wet
flue gas desulfurization unit, the at least one inlet awning being
position above the flue inlet to the wet flue gas desulfurization
unit.
15. The system of claim 9, wherein the flue structure has a
rectangular or square cross-sectional shape and at least one chill
plate is positioned on each of the opposite vertical interior walls
of the flue structure.
16. The system of claim 9, wherein the flue structure has a
cross-sectional shape selected from a rectangle or a square and at
least one chill plate is positioned on each of the opposite bottom
interior corners of the flue structure.
17. A scale prevention system for a wet flue gas desulfurization
unit, the system comprising: a flue structure, wherein the flue
structure is connected to a flue inlet of a wet flue gas
desulfurization unit; at least two air nozzles, each air nozzle
having a respective air supply line; and at least two chill plates,
each chill plate having a respective supply line, wherein the
combination of the at least two air nozzles and the at least two
chill plates are positioned on the interior of the flue structure
so as to provide temperature control across the horizontal width of
a flue inlet to the wet flue gas desulfurization unit.
18. The system of claim 17, wherein the system further comprises at
least one inlet awning designed to deflect a slurry from the wet
flue gas desulfurization unit, the at least one inlet awning being
position above the flue inlet to the wet flue gas desulfurization
unit.
19. The system of claim 17, wherein the flue structure has a
rectangular or square cross-sectional shape and the at least two
air nozzles are positioned on opposite vertical interior walls of
the flue.
20. The system of claim 17, wherein the flue structure has a
rectangular or square cross-sectional shape and at least one chill
plate is positioned on each of the opposite vertical interior walls
of the flue structure.
21. The system of claim 17, wherein the flue structure has a
cross-sectional shape selected from a rectangle or a square and at
least one chill plate is positioned on each of the opposite bottom
interior corners of the flue structure.
22. The system of claim 17, wherein the at least two air nozzles
receive temperature controlled air that is within a range of about
-25.degree. F. to about +25.degree. F. of the wet flue gas
desulfurization unit slurry temperature.
23. The system of claim 17, wherein the at least two chill plates
receive a temperature controlled gas that is within a range of
about -25.degree. F. to about +25.degree. F. of the wet flue gas
desulfurization unit slurry temperature.
24. The system of claim 17, wherein the at least two chill plates
receive a temperature controlled liquid that is within a range of
about -25.degree. F. to about +25.degree. F. of the wet flue gas
desulfurization unit slurry temperature.
25. A scale prevention system for a wet flue gas desulfurization
unit, the system comprising: a flue structure, wherein the flue
structure is connected to a flue inlet of a wet flue gas
desulfurization unit; at least two air nozzles, each air nozzle
having a respective air supply line, wherein at least one air
nozzle is positioned on each opposite vertical interior wall of the
flue; at least two lateral air nozzles, each lateral air nozzle
having a respective air supply line, wherein each lateral air
nozzle is positioned internally of each of the at least two air
nozzles and are positioned at the top edge of the flue inlet to the
wet flue gas desulfurization unit; and at least two chill plates,
each chill plate having a respective supply line, wherein the at
least two chill plates are positioned on the interior of the flue,
wherein the combination of the at least two air nozzles, the at
least two lateral air nozzles and the at least two chill plates are
positioned on the internal surfaces of the flue structure so as to
provide temperature control across the horizontal width of a flue
inlet to the wet flue gas desulfurization unit.
26. The system of claim 25, wherein the at least two lateral air
nozzles are separated by a baffle plate.
27. The system of claim 25, wherein the system further comprises at
least one inlet awning designed to deflect a slurry from the wet
flue gas desulfurization unit, the at least one inlet awning being
position above the flue inlet to the wet flue gas desulfurization
unit.
28. The system of claim 25, wherein the flue structure has a
rectangular or square cross-sectional shape and the at least two
air nozzles are positioned on opposite vertical interior walls of
the flue.
29. The system of claim 25, wherein the at least two lateral air
nozzles are separated by a baffle plate.
30. The system of claim 25, wherein the flue structure has a
rectangular or square cross-sectional shape and at least one chill
plate is positioned on each of the opposite vertical interior walls
of the flue structure.
31. The system of claim 25, wherein the flue structure has a
cross-sectional shape selected from a rectangle or a square and at
least one chill plate is positioned on each of the opposite bottom
interior corners of the flue structure.
32. The system of claim 25, wherein the at least two air nozzles
receive temperature controlled air that is within a range of about
-25.degree. F. to about +25.degree. F. of the wet flue gas
desulfurization unit slurry temperature.
33. The system of claim 25, wherein the at least two chill plates
receive a temperature controlled gas that is within a range of
about -25.degree. F. to about +25.degree. F. of the wet flue gas
desulfurization unit slurry temperature.
34. The system of claim 25, wherein the at least two chill plates
receive a temperature controlled liquid that is within a range of
about -25.degree. F. to about +25.degree. F. of the wet flue gas
desulfurization unit slurry temperature.
Description
RELATED APPLICATION DATA
[0001] This patent application claims priority to U.S. Provisional
Patent Application No. 61/717,133 filed Oct. 23, 2012 and titled
"System and Method for Controlling Scale Build-Up in a WFGD." The
complete text of this application is hereby incorporated by
reference as though fully set forth herein in its entirety.
FIELD AND BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to the cleaning of a
flue gas and, in one embodiment, to a device, system and method
that mitigates and/or prevents slurry deposition at the flue inlet
to a wet flue gas desulfurization (WFGD) unit in order to keep the
inlet dry and minimize deposition (e.g., deposition scale) at the
flue inlet to the WFGD tower. In one embodiment, a wet flue gas
desulfurization (WFGD) unit, system and/or method according to the
present invention comprises, among other features, a scale
prevention system comprising a plenum air device and/or forced-air
box located proximate the inlet transition zone. In another
embodiment, a wet flue gas desulfurization (WFGD) unit, system
and/or method according to the present invention comprises, among
other features, a scale prevention system comprising at least one
chill plate located proximate the inlet transition zone. In still
another embodiment, a wet flue gas desulfurization (WFGD) unit,
system and/or method according to the present invention comprises,
among other features, a scale prevention system comprising a plenum
air device and/or forced-air box and at least one chill plate,
where both devices are located proximate the inlet transition
zone.
[0004] 2. Description of the Related Art
[0005] FIG. 1 is an illustration of a typical wet flue gas
desulfurization (WFGD) unit and the various parts and features
contained therein. As illustrated in FIG. 1, the SO.sub.2-laden
flue gas that enters via the inlet shown in FIG. 1 in various WFGD
towers comes into contact with the slurry utilized in the WFGD
tower. Due to the hot flue gas entering the tower, the flue gas
temperature and the gas flow path around the inlet can cause the
slurry to deposit on the walls/roof of the inlet nozzle. The slurry
can then "flash-dry" onto this surface thereby leaving one or more
deposits extremely hard scale. This scale has the potential to
break off in-service during tower load swings and plant outages
thereby causing one or more pieces of hard and abrasive material to
fall into the WFGD tank and make its way through the process
streams.
[0006] While not wishing to be bound to any one theory, it is
believed that the formation of the scale starts in the two lower
corners of the WFGD inlet with the lowest gas flow, and thus, the
highest possibility of stagnation and highest potential of liquid
to gas in the inlet. One non-limiting theory is that in the
specific case of tile-lined WFGD towers allow for more adhesion of
the scale due to the porous nature of the grout and/or tile
utilized therein. This allows for large pieces of scale to form and
shed at one time.
[0007] Given this, one potential solution to the above problem is
disclosed in U.S. Pat. No. 5,403,523 where a deflection system is
utilized to maintain a cleaner WFGD inlet. Given this, an exemplary
prior art solution is illustrated in FIGS. 2 through 5.
[0008] Turning to Figures, FIG. 1 is an overall view of an
exemplary wet flue gas desulfurization (WFGD) unit, while FIG. 2 is
a cross-sectional illustration of a portion of a known wet flue gas
desulfurization (WFGD) system 10, wherein a wet scrubber module 12
having a cylindrical housing 14 receives a flue gas 16 at a
transition between an inlet flue 18 and the housing. Inlet flue 18
typically approaches cylindrical housing 14 at a downward angle
ranging from 0.degree. to 90.degree. from the horizontal. Inlet
flue 18 is typically rectangular in cross-section, having a width W
that is approximately 2.5 times greater than its height H (i.e., an
aspect ratio of width to height W/H of approximately 2.5). At
locations 20, 22 near an intersection of upper and lower surfaces
24, 26, respectively of inlet flue 18 and cylindrical housing 14,
inlet flue 18 is mitered so that it intersects and attaches to
cylindrical housing 14 at a 90.degree. angle; i.e., inlet flue 18
is substantially perpendicular to cylindrical housing 14. This
perpendicular orientation simplifies the transition, structural
design and fabrication of the wet scrubber module 12. Prior to
inlet flue 18, other portions (not shown) of the flue system
upstream of inlet flue 18 may include cross-section transitions,
elbows, fans, and/or other hydraulic devices to supply the flue gas
16 to the inlet flue 18.
[0009] As illustrated in FIGS. 3A and 3B, within the cylindrical
housing 14, an inlet awning 28 is used to direct part of the hot
flue gas 16, typically provided to the wet scrubber module 12 at a
temperature of approximately 300.degree. F., downwardly at a
45.degree. angle with respect to horizontal. Liquid slurry 30 that
is sprayed within the wet scrubber module 12 and/or which drains
from packing, trays, or other surfaces within the wet scrubber
module 12, flows downwardly onto an upper surface 32 of the inlet
awning 28. A weir plate 34 located above a tip 36 of the inlet
awning 28 provides a gap 38 through which liquid slurry 30 passes,
and thus regulates and improves the uniformity of a liquid slurry
curtain 40 that is discharged down into the hot flue gas stream 16.
As the hot flue gas 16 enters the wet scrubber module 12, it is
quenched and humidified by the liquid slurry curtain 40,
evaporating a fraction of the water present in the liquid slurry
curtain 40.
[0010] In the absence of an inlet awning 28, a thin liquid film of
liquid slurry 30 flowing downwardly along the walls of the wet
scrubber module 12 contacts the hot flue gas 16. However, the
amount of water present in the thin liquid film of slurry 30
falling across the inlet opening to the wet scrubber module 12 is
not sufficient to completely quench and humidify the hot flue gas
16. The inlet awning 28 collects all the liquid slurry 30 that
falls on top of it and channels the liquid slurry 30 to the gap 38
to form the thick liquid slurry curtain 40. This larger amount of
water diverted by the inlet awning 28 and forming the liquid slurry
curtain 40 exceeds what is needed for complete and instantaneous
quenching and humidification of the hot flue gas 16. This complete
and sudden quench and humidification reduces the wet/dry interface
and the possibility of solid deposition.
[0011] In the absence of an inlet awning 28, if the liquid slurry
30 and hot flue gas 16 combination contacts any surface of the
inlet flue 18 or housing 14, solid deposits will form as the liquid
slurry 30 evaporates. Solids form at the wet/dry interface because
the water present is not sufficient to continuously and fully
humidify the incoming gas. These solid deposits build up over time,
which requires the wet scrubber module 12 to be shut down so that
maintenance personnel can enter the wet scrubber module 12 and
remove the deposits. Shut down of a wet scrubber module 12 requires
that either spare wet scrubber modules 12 be available to clean the
flue gas 16, that the boiler load is reduced so that the amount of
flue gas produced does not exceed the capacity of the remaining
on-line wet scrubber modules 12, or that there is a discharge of
partially or untreated flue gas 16 directly into the atmosphere.
All of these alternatives are undesirable and not accepted by the
industry. It is thus preferable to maintain the wet/dry interface
of the liquid slurry 30 with the hot flue gas 16 away from these
surfaces, and the inlet awning 28 accomplishes this result by
creating the liquid slurry curtain 40. The liquid slurry curtain 40
is maintained away from these surfaces because the inlet awning 28
extends downwardly and into the cylindrical housing 14 of wet
scrubber module 12. The liquid slurry curtain 40 also provides more
water than required for humidification.
[0012] As shown in FIGS. 4 and 5, at the side ends 42 of the inlet
awning 28, sidewalls 44 extend from the inlet awning 28 into the
housing 14 and downwardly to a point below the lower surface 26 of
inlet flue 18. These sidewalls 44 prevent liquid slurry 30 from
flowing off the side ends 42 of the inlet awning 28 or along an
inner surface 46 of the housing 14 from entering inlet flue 18.
These sidewalls 44 are necessary to maintain an acceptable wet/dry
interface away from these surfaces to avoid the deposition problems
discussed earlier. In addition, the inlet awning 28 is provided
with stiffeners 48 which, in conjunction with the sidewalls 44,
further distribute the slurry flow 30 evenly about these
surfaces.
[0013] Hydraulic testing of the known inlet flue 18 and inlet
awning 28 devices described above revealed a significant flue gas
side total pressure drop. High flue gas side pressure drops require
increased fan pressure capability, resulting in increased fan and
motor capacity and increased operating costs for the life of the
unit. This is very undesirable because even a 1.0 inch H.sub.2O gas
side pressure drop can be assessed at values which can reach one
million dollars. Therefore, reducing the flue gas side pressure
drop in the wet scrubber equipment is an effective way to reduce
costs. However, such reductions must still be achieved in a manner
which prevents unwanted deposition of dried slurry material at the
transition interface and/or zone.
[0014] Given the above, a need exists in the art for a device,
system and/or method by which to reduce the amount of slurry
material that deposits in the transition interface and/or zone
where the flue gas inlet meets the WFGD tower.
SUMMARY OF THE INVENTION
[0015] The present invention relates generally to the cleaning of a
flue gas and, in one embodiment, to a device, system and method
that mitigates and/or prevents slurry deposition at the flue inlet
to a wet flue gas desulfurization (WFGD) unit in order to keep the
inlet dry and minimize deposition (e.g., deposition scale) at the
flue inlet to the WFGD tower. In one embodiment, a wet flue gas
desulfurization (WFGD) unit, system and/or method according to the
present invention comprises, among other features, a scale
prevention system comprising a plenum air device and/or forced-air
box located proximate the inlet transition zone. In another
embodiment, a wet flue gas desulfurization (WFGD) unit, system
and/or method according to the present invention comprises, among
other features, a scale prevention system comprising at least one
chill plate located proximate the inlet transition zone. In still
another embodiment, a wet flue gas desulfurization (WFGD) unit,
system and/or method according to the present invention comprises,
among other features, a scale prevention system comprising a plenum
air device and/or forced-air box and at least one chill plate,
where both devices are located proximate the inlet transition
zone.
[0016] Accordingly, one aspect of the present invention is drawn to
a scale prevention system for a wet flue gas desulfurization unit
(WFGD), the system comprising: a flue structure, wherein the flue
structure is connected to the inlet of an wet flue gas
desulfurization unit; at least two air nozzles, each air nozzle
having a respective air supply line, wherein the at least two air
nozzles are positioned on the interior of the flue so as to provide
air coverage across the horizontal width of the flue inlet to the
wet flue gas desulfurization unit; and at least one inlet awning
designed to deflect a slurry from the wet flue gas desulfurization
unit, the at least one inlet awning being position above the flue
inlet to the wet flue gas desulfurization unit.
[0017] In yet another aspect of the present invention, there is
provided a scale prevention system for a wet flue gas
desulfurization unit (WFGD), the system comprising: a flue
structure, wherein the flue structure is connected to the inlet of
an wet flue gas desulfurization unit; at least two air nozzles,
each air nozzle having a respective air supply line, wherein at
least one air nozzle is positioned on each opposite vertical
interior wall of the flue so as to provide air coverage across the
horizontal width of the flue inlet to the wet flue gas
desulfurization unit; and at least two lateral air nozzles, each
lateral air nozzle having a respective air supply line, wherein
each lateral air nozzle is positioned internally of each of the at
least two air nozzles and are positioned at the top edge of the
flue inlet to the wet flue gas desulfurization unit so as to
provide air coverage across the horizontal width of the flue inlet
to the wet flue gas desulfurization unit.
[0018] In yet another aspect of the present invention, there is
provided a scale prevention system for a wet flue gas
desulfurization unit (WFGD), the system comprising: a flue
structure, wherein the flue structure is connected to the inlet of
an wet flue gas desulfurization unit; and at least two chill
plates, each chill plate having a respective supply line, wherein
the at least two chill plates are positioned on the interior of the
flue so as to provide temperature control across the horizontal
width of the flue inlet to the wet flue gas desulfurization
unit.
[0019] 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 benefits attained by its uses, reference is made to the
accompanying drawings and descriptive matter in which exemplary
embodiments of the invention are illustrated.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is an illustration of a typical wet flue gas
desulfurization (WFGD) unit;
[0021] FIG. 2 is a cross-sectional illustration of the wet flue gas
desulfurization (WFGD) unit of FIG. 1;
[0022] FIG. 3A is a sectional side view of the transition between
the inlet flue and the wet scrubber module of FIG. 2;
[0023] FIG. 3B is a sectional view illustrating a portion of FIG.
3A;
[0024] FIG. 4 is sectional plan view taken in the direction of the
4-4 arrows of FIG. 2;
[0025] FIG. 5 is a sectional side view illustrating a side wall for
the inlet awning of FIG. 2;
[0026] FIG. 6 is an illustration of one embodiment of a scale
prevention system for a WFGD flue inlet;
[0027] FIG. 7 is a cross-sectional illustration of the scale
prevention system of FIG. 6;
[0028] FIG. 8 is an illustration of another embodiment of a scale
prevention system for a WFGD flue inlet;
[0029] FIG. 9 is a cross-sectional illustration of the scale
prevention system of FIG. 8;
[0030] FIG. 10 is an illustration of still another embodiment of a
scale prevention system for a WFGD flue inlet;
[0031] FIG. 11 is a cross-sectional illustration of the scale
prevention system of FIG. 10;
[0032] FIG. 12 is a cross-sectional illustration of still another
embodiment of a scale prevention system for a WFGD flue inlet;
[0033] FIG. 13 is a cross-sectional illustration of still another
embodiment of a scale prevention system for a WFGD flue inlet;
and
[0034] FIG. 14 is a cross-sectional illustration of still another
embodiment of a scale prevention system for a WFGD flue inlet.
DESCRIPTION OF THE INVENTION
[0035] The present invention relates generally to the cleaning of a
flue gas and, in one embodiment, to a device, system and method
that mitigates and/or prevents slurry deposition at the flue inlet
to a wet flue gas desulfurization (WFGD) unit in order to keep the
inlet dry and minimize deposition (e.g., deposition scale) at the
flue inlet to the WFGD tower. In one embodiment, a wet flue gas
desulfurization (WFGD) unit, system and/or method according to the
present invention comprises, among other features, a scale
prevention system comprising a plenum air device and/or forced-air
box located proximate the inlet transition zone. In another
embodiment, a wet flue gas desulfurization (WFGD) unit, system
and/or method according to the present invention comprises, among
other features, a scale prevention system comprising at least one
chill plate located proximate the inlet transition zone. In still
another embodiment, a wet flue gas desulfurization (WFGD) unit,
system and/or method according to the present invention comprises,
among other features, a scale prevention system comprising a plenum
air device and/or forced-air box and at least one chill plate,
where both devices are located proximate the inlet transition
zone.
[0036] As used herein, "inlet transition zone" is defined to mean
the area in the WFGD inlet and/or tower where the temperature
gradient is changing from "hot" to "cold" and/or the flue gas is
experiencing a change in the amount of water saturation in the flue
gas due to contact of the flue gas with the slurry from the WFGD.
As would be apparent to those of skill in the art, the "inlet
transition zone" is not located in one specific area. Rather, the
"inlet transition zone" varies from one WFGD unit to another, or
can even vary within the same WFGD depending upon operating
conditions.
[0037] Regarding the air utilized in the various scale mitigation
and/or prevention systems of the present invention, the air
supplied to the various air lines and/or piping of any one or more
embodiments of the present invention can be supplied from
temperature controlled air from any suitable source (e.g., from any
suitable air pump, compressor, etc.), or can be supplied from any
surplus oxidation air that might be available from the oxidation
air being supplied to the WFGD. In another embodiment, the air
supplied to the various air lines and/or piping of any one or more
embodiments of the present invention can be supplied from any
combination of temperature controlled air from any suitable source
(e.g., from any suitable air pump, compressor, etc.) and any
surplus oxidation air that might be available from the oxidation
air being supplied to the WFGD.
[0038] Furthermore, the temperature of the air supplied to the
various air lines and/or piping of any one or more embodiments of
the present invention should be within a range of about -25.degree.
F. to about +25.degree. F. of the WFGD slurry temperature. In
another embodiment, the temperature of the air supplied to the
various air lines and/or piping of any one or more embodiments of
the present invention should be within a range of about -20.degree.
F. to about +20.degree. F., or about -15.degree. F. to about
+15.degree. F., or about -10.degree. F. to about +10.degree. F., or
about -5.degree. F. to about +5.degree. F., or even about
-2.5.degree. F. to about +2.5.degree. F. of the WFGD slurry
temperature. Here, as well as elsewhere in the specification and
claims, individual range values and/or limits can be combined to
form additional non-disclosed ranges.
[0039] Turning to the Figures, FIG. 6 illustrates one embodiment of
an inlet scale mitigation and/or prevention system (hereinafter
solely referred to as a "scale prevention system" for the sake of
brevity). In the embodiment of FIG. 6, a scale prevention system
100 is disclosed. As illustrated in FIG. 6, flue 102 is shown as
entering the tower portion 104 of a WFGD unit. It should be noted
that although the tower portion 104 of the WFGD is shown as having
a circular cross-sectional shape, the present invention is not
limited thereto. Accordingly, any geometric shape can be utilized
for the tower portion 104 of a WFGD unit. Turning to the remaining
portions of scale prevention system 100, flue 102 is formed so as
to have at least one expansion joint 106 that traverses the width
of flue 102. Additionally, scale prevention system 100 also
includes left and right air lines and/or piping 108 that supply air
to left and right side clean-out nozzles 110. Side clean-out
nozzles 110 direct clean-out air supplied via each clean-out
nozzle's respective air line and/or piping 108 in the same general
direction as the flue gas flow direction (denoted by arrow 112). In
some embodiments, scale prevention system 100 can further include
an inlet awning and/or sidewalls like those disclosed and discussed
in FIG. 5 so as to provide additional coverage and/or protection to
the top and/or side portions of flue 102 so as to prevent WFGD
slurry "raining" down from above and then entering flue 102.
Accordingly, the combination of left and right air lines and/or
piping 108, left and right side clean-out nozzles 110 and, if so
present, inlet awning and/or sidewalls (see FIG. 5) act together to
prevent WFGD slurry from entering into flue 102 and causing scale
to build-up on the WFGD-end of flue 102.
[0040] FIG. 7 is a cross-sectional illustration of the open end of
flue 102 as it enters the tower portion 104 of the WFGD
illustrating the orientation of left and right clean-out nozzles
110. In another embodiment, if so desired an inlet awning and/or
sidewalls according to the embodiment of FIG. 5 can be placed over
the top and side edges of flue 102 (above the upper edges of left
and right clean-out nozzles 110) to provide further protection
against the WFGD slurry "raining" down from above and then entering
flue 102. In still another embodiment, left and right clean-out
nozzles 110 can be any desired height so long as left and right
clean-out nozzles start at the bottom edge of flue 102 and proceed
substantially vertically up toward the top edge of flue 102.
[0041] Turning to FIG. 8, FIG. 8 illustrates another embodiment of
a scale prevention system 200. As illustrated in FIG. 8, flue 202
is shown as entering the tower portion 204 of a WFGD unit. It
should be noted that although the tower portion 204 of the WFGD is
shown as having a circular cross-sectional shape, the present
invention is not limited thereto. Accordingly, any geometric shape
can be utilized for the tower portion 204 of a WFGD unit. Turning
to the remaining portions of scale prevention system 200, flue 202
is formed so as to have at least one expansion joint 206 that
traverses the width of flue 202. In another embodiment, the
expansion joint can have one or more expansion joint drip zones
and/or drains 232 represented by the left and right rectangular
shapes. In one embodiment, expansion joint drip zones and/or drains
232 are located on the underside of the expansion joint section of
flue 202. Additionally, scale prevention system 200 also includes
left and right air lines and/or piping 234 that supply air to left
and right side clean-out nozzles 236 as well as lateral clean-out
nozzles 238. Lateral clean out nozzles 238 are located toward the
center line of flue 202 and are separated by baffle plate 240.
[0042] In one embodiment, lateral clean-out nozzles 238 and baffle
plate 240 are located along the bottom edge of flue 202 as it
enters into tower 204. In another embodiment, lateral clean-out
nozzles 238 and baffle plate 240 are located along the top edge of
flue 202 as it enters into tower 204. For the purposes of the
present invention, the bottom edge of flue 202 is located closest
to the bottom of tower 204. Baffle plate 240 is placed between
lateral clean-out nozzles 238 in order to create multiple air zones
due to the presence of at least two lateral clean-out nozzles. In
one embodiment, the existence of baffle plate 240 permits each of
the left and right lateral clean-out nozzles 238 to be operated
independently of one another thereby permitting customized control
of the air provided to the left and right portions of flue 202 as
it enters tower 204. In another embodiment, left and right
clean-out nozzles 238 can be operated in tandem rather than
independently.
[0043] Given the above, the combination of side clean-out nozzles
236 and lateral clean-out nozzles 238 direct clean-out air supplied
via each clean-out nozzle's respective air line and/or piping 234
in the same general direction as the flue gas flow direction
(denoted by arrow 212). In another embodiment, although not
illustrated, scale prevention system 200 can further include an
inlet awning and/or sidewalls that cover/surround the top and/or
side portions of flue 202 so as to prevent WFGD slurry "raining"
down from above and then entering flue 202. Accordingly, the
combination of left and right air lines and/or piping 234, left and
right side clean-out nozzles 236, left and right lateral clean-out
nozzles 238, and baffle plate 240 act together to prevent WFGD
slurry from entering into flue 202 and causing scale to build-up on
the WFGD-end of flue 202.
[0044] FIG. 9 is a cross-sectional illustration of the open end of
flue 202 as it enters the tower portion 204 of the WFGD
illustrating the orientation of left and right clean-out nozzles
236, left and right lateral clean-out nozzles 238, and baffle plate
240. In another embodiment, if so desired an inlet awning and/or
sidewalls can be placed over/around the top and/or side edges of
flue 202 (above left and right lateral clean-out nozzles 238 and
baffle plate 240) to provide further protection against the WFGD
slurry "raining" down from above and then entering flue 202.
[0045] Turning to FIG. 10, FIG. 10 illustrates another embodiment
of a scale prevention system 300. As illustrated in FIG. 10, flue
302 is shown as entering the tower portion 304 of a WFGD unit. It
should be noted that although the tower portion 304 of the WFGD is
shown as having a circular cross-sectional shape, the present
invention is not limited thereto. Accordingly, any geometric shape
can be utilized for the tower portion 304 of a WFGD unit. Turning
to the remaining portions of scale prevention system 300, flue 302
is formed so as to have at least one expansion joint 306 that
traverses the width of flue 302. In another embodiment, the
expansion joint can have one or more expansion joint drains (not
shown) located on the underside of the expansion joint section of
flue 302. Additionally, scale prevention system 300 also includes
left and right lines and/or piping 320 that supply temperature
controlled air and/or temperature controlled liquid to left and
right chill plates 322. The combination of left and right lines
and/or piping 320 and left and right chill plates 322 seek to
reduce the temperature at the inlet of WFGD tower 304 so as to
mitigate and/or prevent scale build-up due to a large temperature
change between the flue gas entering the WFGD and the WFGD's slurry
that is "raining" down from above. It should be noted that in
another embodiment of the present invention the embodiment of FIG.
10 can be combined with either of the embodiments of FIG. 6 or FIG.
8.
[0046] In still another embodiment, although not illustrated, scale
prevention system 300 can further include an inlet awning and/or
sidewalls that cover/surround the top and/or side portions of flue
302 so as to prevent WFGD slurry "raining" down from above and then
entering flue 302.
[0047] FIG. 11 is a cross-sectional illustration of the open end of
flue 302 as it enters the tower portion 304 of the WFGD
illustrating the orientation of left and right chill plates 322. In
another embodiment, if so desired an inlet awning can be placed
over the top edge of flue 302 to provide further protection against
the WFGD slurry "raining" down from above and then entering flue
302.
[0048] Turning to FIGS. 12 through 14, FIGS. 12 through 14 are
cross-sectional illustrations of various alternative embodiments of
the present invention. In the embodiment of FIG. 12, a flue 402 and
partial WFGD tower 404 are illustrated. As shown in the embodiment
of FIG. 12, the scale prevention system disclosed therein contains
both left and right side clean-out nozzles 236 and left and right
chill plates 322. In the embodiment of FIG. 13, the scale
prevention system disclosed therein contains left and right
clean-out nozzles 236, left and right lateral clean-out nozzles
238, baffle plate 240, and left and right chill plates 322 located
as shown at the end of flue 502 as it enters tower 504. In the
embodiment of FIG. 14, the scale prevention system disclosed
therein contains left and right clean-out nozzles 236, left and
right lateral clean-out nozzles 238, baffle plate 240, and left and
right chill plates 322, with the left and right clean-out nozzles
236 being located vertically above the respective left and right
chill plates 322 located as shown at the end of flue 602 as it
enters tower 604. In still another embodiment, although not
illustrated, any of the embodiments of FIGS. 12 through 14 can
further include an inlet awning and/or sidewalls that
cover/surround the top and/or side portions of flue 402/502/602 so
as to prevent WFGD slurry "raining" down from above and then
entering flue 402/502/602.
[0049] It should be noted that the size, height and/or width of any
of the nozzles, chill plates and/or baffle plates of the present
invention can be varied as needed and/or desired. Accordingly, the
present invention is not limited to just one geometric shape,
layout, and or design orientation. Furthermore, the various
nozzles, chill plates, and/or baffle plates can be operated in
combination, various sub-combinations, or even each item
independently.
[0050] While not wishing to be bound to any one advantage, or set
of advantages, a scale prevention system according to the present
invention prevents scale from forming and then falling into the
WFGD tank. Alternatively, if scale forms the scale that forms is
smaller in size and is able to broken-up into smaller pieces by the
agitators and pump (absorber recycle pumps and/or bleed pumps).
Given this, in the bleed pump stream, the scale pieces are able to
be pumped into the primary hydroclones. The one or more systems of
the present invention prevent larger scale pieces from forming and
thereby prevents such scale pieces from entering into the one or
more hydroclones were such pieces are not able to be removed in the
underflow stream. This reduces plugging of the one or more
hydroclones and thus reduces the frequency of maintenance
intervals.
[0051] The present invention is also advantageous over those
systems that utilize some type of water-based system to prevent
scale formation at the tower end of a flue entering a WFGD. Such
water-based systems are subject to a number of drawbacks including,
but not limited to, undesirable variations in the WFGD tower
water/aqueous balance, corrosion at the tower end of the flue
entering the WFGD; and/or water supply problems that might actually
end up causing an increase in scale formation.
[0052] Another potential advantage attributable to the present
invention is the reduction in scale size and frequency reduces the
amount and size of scale pieces that are forced through the
Absorber Recycle (AR) pumps. This has the potential of reducing the
amount of abrasive particles in the pump stream. Furthermore, scale
pieces are typically pushed into the AR headers and into the slurry
nozzles in the upper portion of the towers. These nozzles have
small openings and if enough scale pieces become wedged together,
there is a high likelihood of plugging AR nozzles and/or headers.
Such plugging leads to a drop in SO.sub.2 removal as well as the
risk of lower limestone utilization by the system. Accordingly, the
one or more embodiments of the present invention can reduce the
severity and/or occurrence of this phenomena thereby resulting in
better SO.sub.2 removal rates as well as less damage to the one or
more AR nozzles.
[0053] Given the above, the embodiments of the present invention
utilize two different principles to reduce the amount of scale that
forms at the flue inlet of a WFGD. The embodiments of FIGS. 6
through 8 utilize pressurized and/or forced air via various nozzles
and/or a plenum structure to keep the inlet area clean by two
means: (i) by higher pressure air forcing any slurry and/or eddy
current gas flow out of the inlet and into the tower; and (ii) by
supplying air that serves to create an insulating zone between the
hot flue gas and cooler slurry. In one embodiment, the air supplied
to the flue inlet can be humidified down to an acceptable
temperature. This colder plenum should be kept at a temperature
equal to or less than the operating temperature of the WFGD fluid
in order to prevent the slurry from flash-drying to the plenum and
forming scale.
[0054] In still another embodiment, the air source for the various
embodiments of the present invention is provided from the WFGD's
oxidation air flow into the tower, then an added benefit is
realized in that WFGD sites are designed and are operating with
(due to tower loading turn-down) excess oxidation air. This excess
oxidation air leads to adverse chemistry effects in some plants
including but not limited to: (a) strong oxidizer formation with
downstream impacts; (b) tower corrosion from manganese deposition
forming a galvanic bridge to drive fluoride induced under-deposit
corrosion; (c) adverse selenium speciation; and (d) mercury
reemission. Accordingly, the use of such excess oxidation air can
help to reduce, mitigate and/or eliminate one or more of the above
noted negative effects.
[0055] The embodiments of FIGS. 9 and 10 that utilize left and
right chill plates, with or without the use of
pressurized/oxidation air, can decrease the formation of the scale
at the flue inlet to the WFGD. The chill plates help to maintain a
cooler inlet surface which helps to prevent the thermal shock the
slurry experiences at the flue inlet. This thermal shock can lead
to the "flash drying" that is linked to scale formation at the flue
inlet. The chill plates also permit the use flowing liquid/or gas
at a predetermined temperature so as to keep the contact surface of
the inlet at a lower temperature than the flue gas inlet
temperature.
[0056] 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.
* * * * *