U.S. patent number 3,741,235 [Application Number 05/214,009] was granted by the patent office on 1973-06-26 for washing and purging apparatus for liquid seals.
This patent grant is currently assigned to Combustion Engineering, Inc.. Invention is credited to Alwin W. Ambrose, Joseph W. Parker, III.
United States Patent |
3,741,235 |
Ambrose , et al. |
June 26, 1973 |
WASHING AND PURGING APPARATUS FOR LIQUID SEALS
Abstract
A washing and purging system for a liquid seal in the flue gas
bypass duct of a steam generating facility having an air pollution
control system. A series of nozzles positioned within the seal
provide a continuous turnover of liquid and are also periodically
used to flush accumulated particulate matter from the seal.
Disposal of excess liquid from the seal is accomplished through the
use of an overflow weir which also serves to skim off surface
contaminant particles before they can settle to the bottom of the
seal.
Inventors: |
Ambrose; Alwin W. (Enfield,
CT), Parker, III; Joseph W. (West Simsbury, CT) |
Assignee: |
Combustion Engineering, Inc.
(Windsor, CT)
|
Family
ID: |
22797422 |
Appl.
No.: |
05/214,009 |
Filed: |
December 30, 1971 |
Current U.S.
Class: |
137/238; 55/355;
134/104.4; 134/166R; 137/247.25; 137/253 |
Current CPC
Class: |
F16K
13/10 (20130101); Y10T 137/4658 (20150401); Y10T
137/4516 (20150401); Y10T 137/4245 (20150401) |
Current International
Class: |
F16K
13/00 (20060101); F16K 13/10 (20060101); F16k
011/02 () |
Field of
Search: |
;134/104,166R
;137/251,252,253,254,238,247.25 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Weakley; Harold W.
Claims
What is claimed is:
1. In combination with a liquid seal for preventing the flow of a
contaminated hot gas through a conduit, the seal having a first
duct means communicating with a gas supply conduit and defining a
first plenum chamber, a second duct means communicating with a gas
exhaust conduit and defining a second plenum chamber, said first
and second duct means cooperating to define a generally horizontal
passageway interconnecting said first and second plenum chambers at
the lower ends thereof and means for admitting a liquid into said
seal to a level completely immersing said passageway, the
improvement which comprises:
a. an inclined generally rectangular plate forming the bottom of
said interconnecting passageway;
b. drain means disposed in the lower portion of said duct means
adjacent the lower end of said inclined bottom plate, said drain
being selectively operable to an open or closed position to drain
liquid from or retain liquid in said seal respectively;
c. at least one series of nozzles positioned adjacent the upper
side of said inclined plate, a portion of the nozzles in each of
said series being angularly directed toward the opening in said
drain means whereby liquid ejected from said nozzles is directed
toward said drain opening;
d. means for selectively supplying a liquid to said nozzles at a
flow rate sufficient to maintain the normal liquid level in said
seal when said drain means is in an open position; whereby when
said liquid seal is filled to its normal level, said drain means is
actuated to an open position, and said nozzle supply means is
operating, a sluicing operation is performed on the inclined bottom
plate of said liquid seal without requiring the gas tight seal to
be broken.
2. The apparatus of claim 1 wherein each drain means has at least
one series of nozzles associated exclusively therewith.
3. The apparatus of claim 1 wherein the number of nozzles per unit
area of inclined plate becomes increasingly greater as the lower
end of said inclined plate is approached.
4. The apparatus of claim 1 including the following additional
elements:
a. an overflow collector attached to said first duct means and
having an overflow discharge opening in the lower end thereof;
b. liquid discharge means communicating with said overflow
discharge opening to carry overflow liquid to an appropriate
disposal point exterior of said seal;
c. liquid overflow means defining a generally horizontal upper edge
for communicating the interior of said seal adjacent the desired
liquid level to the interior of said overflow collector; and
d. means for continuously replenishing the liquid in the seal when
the seal is provided with a gas sealing body of liquid.
5. The apparatus of claim 4 wherein said means for continuously
replenishing the liquid in the seal comprises at least one of said
nozzles, said nozzle being adapted to selectively provide
continuous liquid flow to said seal.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to liquid seals and more particularly to a
washing and purging arrangement for a liquid seal.
2. Description of the Prior Art
One major source of air pollution is the particulate matter (fly
ash) and obnoxious gaseous contaminants, such as SO.sub.2, which
are emitted in the flue gas of coal-fired utility boilers used in
electric power generating facilities. One approach to removing
these contaminants from the gases has been through the use of a gas
cleaner having a wet scrubber.
Typically in such a system dust and fume laden gases exit the
boiler through an air preheater and continue through ducts to the
scrubber where the washing and cleaning of the gas is accomplished.
The clean gas then exits from the scrubber and continues through
additional ductwork and a booster fan to the stack where it is
emitted to the atmosphere.
Many coal-fired steam generating furnaces have the ability to burn
fuels other than coal such as low sulfur oil or gas. Such auxiliary
fuels do not produce the high level of contaminants and particulate
matter which result from the burning of coal and thus permit the
boiler units to be operated without the scrubber units on the line.
This is accomplished by providing a bypass duct around the scrubber
which provides a path directly to the booster fan and the
stack.
Because of the very strict governmental air pollution requirements
regulating permissible amounts of SO.sub.2 and particular matter
emission, water seals are often provided in the bypass ducts of
such systems to assure that contaminated gas does not leak through
the bypass to the atmosphere when the scrubber is in operation.
One type of liquid seal commonly used in this application is
similar to the U-type trap frequently used in sink drains. With
such an arrangement a number of problems have been encountered as a
result of interactions between dead pocket gases and water which
occurs at the inlet plenum water surface of the seal. One such
problem is corrosion of the metal walls of the seal caused by an
intolerable acid condition of the seal water. This acid condition
comes about as a result of corrosive materials in the gases
condensing from the gas on the water surface and subsequently being
absorbed into the water. Another problem encountered is that of
large accumulations of particulate contaminants in the bottom of
the seal. This comes about due to particles in the gas contacting
and adhering to the water surface and eventually settling to the
bottom of the seal. In order to remove such deposits it has been
necessary to periodically drain the liquid from the seal and remove
them by hand.
SUMMARY OF THE INVENTION
The herein provided invention involves a washing and purging system
for a water seal located in a hot gas bypass duct. A series of
nozzles is located in the bottom of the seal. Overflow weirs,
communicating with overflow discharge means, are provided at the
desired liquid level of the seal. During normal operation a
constant supply of relatively alkaline water is introduced into the
seal by less than the full complement of nozzles. This water
effects a continuous purge of the seal water and provides a
three-fold advantage: (1) the pH of the seal water is kept at a
non-corrosive level, (2) potential loss of the water seal due to
water evaporation or level control malfunction is eliminated, and
(3) excess water passing from the seal over the overflow weir takes
with it surface particulate contaminants before they can
settle.
A periodic cleaning operation is performed to remove accumulated
particulate matter from the bottom of the seal. This is achieved by
activating the entire complement of nozzles and opening the drain
connection provided in the bottom of the seal. The seal bottom is
inclined with the drain connection at the lower end thereof and the
nozzles are so arranged to effect a sluicing operation to guide the
accumulated matter through the drains. A distinct advantage of this
cleaning operation is that it may be carried out without requiring
the water seal to be broken.
Other objects and advantages of the invention will become apparent
upon reading the following detailed description and upon reference
to the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic side elevational view, partly in section, of
an air pollution control system having a wet scrubber bypass duct
water seal which has the washing and purging features of this
invention;
FIG. 2 is an enlarged view, partly in section, of the water seal of
FIG. 1;
FIG. 3 is a sectional view taken on lines 3--3 of FIG. 2;
FIG. 4 is a sectional view taken on lines 4--4 of FIG. 2; and
FIG. 5 is a partial view, similar to FIG. 3, showing one end of a
seal having an overflow collector in accordance with a further
embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring first to FIG. 1, there is illustrated a steam generating
boiler 10 having a pollution control system including wet scrubber
12 for cleansing flue gases prior to passage to the atmosphere. A
flue gas scrubber bypass 14 having a water seal 16 is provided to
circumvent the scrubber when desired. Under normal circumstances,
i.e., when the scrubber is in use, contaminated flue gases produced
in the furnace 18 pass into an appropriate duct 20 through an air
preheater 22 and into an inlet duct 24 to the wet scrubber 12. The
inlet duct 24 has a damper 26 arrangement located therein for
selectively opening and closing the duct to the passage of flue
gases. Gases passing into the wet scrubber 12 are cleansed of
gaseous and particulate contaminants in a well-known manner not
forming a part of this invention.
The cleansed flue gases pass from the scrubber 12 through a
scrubber outlet duct 28. Located in the outlet duct 28 is a stack
gas reheater 30 to minimize steam plume formation and a damper
assembly 34 for selectively controlling the passage of gases
therethrough. Communicating with the outlet duct 28 is an
appropriate exit duct 36 which in turn communicates with the inlet
of induced draft fan 38. The fan 38 creates a sufficient pressure
differential to insure positive passage of the gases through the
ductwork and scrubber into the stack 40 for passage to the
atmosphere.
The flue gas scrubber bypass 14 includes a first conduit 42
communicating with the scrubber inlet duct 24 upstream of the
scrubber inlet damper arrangement 26. A second conduit 44
communicates at one end with the first conduit 42 and at the other
end with the scrubber outlet duct 28 at a location downstream of
the outlet damper 34. The passage of gases from the first conduit
42 to the second conduit 44 is selectively controlled by the level
of water in the water seal 16.
As best shown in FIG. 2 the water seal 16 includes a first plenum
chamber 46 and a second plenum chamber 48 communicating with the
first conduit 42 and the second conduit 44, respectively. The
plenum chambers 46, 48 are fabricated from appropriate ducting
material and have a common bottom plate 50 which is angularly
disposed from the horizontal. The plenum chambers 46, 48 are
separated by a vertical baffle plate 52 originating at the junction
of the upper walls of the first and second bypass conduits 42, 44
and terminating at a level spaced from the inclined bottom 50 to
define a horizontal passageway interconnecting the two chambers.
Located in the lower end of the ducting forming the front of the
seal are two drain connections 54, 56 which are selectively
operable to opened and closed position by means of conventional
valve arrangements 58, 60.
As best shown in FIGS. 3 and 4, underlying the inclined seal bottom
50 is a network of water pipes 67 communicating through valve
arrangements, which will be subsequently further described, to a
water supply 64 and adapted to distribute water to a plurality of
water nozzles, 66a-f, 68a-f, extending through the bottom plate and
which are directed substantially parallel to the bottom and toward
the drain connections 54, 56 adjacent the lower end of the bottom.
In the preferred embodiment, best illustrated in FIG. 4, a separate
series of nozzles is associated with each drain connection. The
nozzles are so arranged that the number of nozzles per unit area of
the bottom plate becomes increasingly greater as the lower end of
the plate is approached. Further in accordance with the invention a
portion of the nozzles in each series are disposed in pairs 66c-f,
68c-f laterally offset on opposite sides of and angularly directed
toward their associated drain connections.
Referring back to FIG. 3 the valve arrangement interconnecting the
water supply 64 and the nozzles 66, 68 comprises a main shutoff
valve 70 and a flush valve 72. The shutoff valve 70 directly
controls the water supply to one pair of replenishing nozzles 66c,
68c in each series and to the flush valve 72 which in turn controls
the supply to the piping 67 communicating with the remainder of the
nozzles.
There are located on the interior walls at opposite ends of the
first plenum chamber 46 overflow collectors 74 having open upper
ends defining generally horizontal upper edges 76. These collectors
are positioned so that their upper edges 76 are substantially
coincident with the desired normal water level of the seal when it
is filled to provide a gas tight seal. Openings 78 are provided in
the seal walls for communicating the interior of each collector 74,
at the lower end thereof, to discharge pipes 80 extending to the
exterior of the seal. The discharge pipes 80 in turn communicate
with appropriate conduits 82 which terminate, at a point below the
level of the water in the seal, in settling tank or pond 84 of a
size capable of handling the overflow liquid. The pond 84 serves as
a second liquid seal to insure that atmospheric air is not drawn
into plenum 46 through the discharge conduits 82. Such an
occurrence would otherwise be probable because the pressure within
plenum 46 is less than atmospheric, due to the sucking action of
the fan 38.
When the furnace 18 of the steam generating boiler 10 shown in FIG.
1 is burning a low sulfur auxiliary fuel such as gas it is not
necessary to pass the products of combustion gases through the wet
scrubber 12. Under such circumstances there is no water in the
water seal and the scrubber inlet damper 26 and the scrubber outlet
damper 34 are placed in a closed position. All flue gases thus pass
through the first bypass conduit 42 into the first plenum 46 under
the baffle 52 to the second plenum 48 and through the second bypass
conduit 44 to the exit duct 36 and ultimately from the stack 40 to
the atmosphere.
Under normal circumstances, however, the furnace burns a fuel such
as coal which yields a highly contaminated product of combustion
gases which must be passed through the scrubber 12 before being
released to the atmosphere. During such operation the scrubber
dampers 26, 34 are opened and the water seal 16 in the bypass 14 is
filled to insure that no contaminated gases are permitted to bypass
the scrubber 12. Filling of the water seal is accomplished by
opening both the main supply valve 70 and the flush valve 72, water
is thus caused to flow into the seal through the full complement of
nozzles 66a-f, 68a-f. When the lower edge of the baffle plate 52 is
completely immersed in water the seal is effective to prevent the
passage of flue gases therethrough.
When the water level in the seal reaches the horizontal upper edge
76 of the overflow collectors the flush valve 72 is moved to its
closed position. Only the replenishing nozzles 66c, 68c, located
generally midway along the length of the inclined bottom, are now
feeding water into the seal. These nozzles 66c, 68c are supplied
with water continuously whenever the seal is in use. The water fed
into the seal by these nozzles serves two primary purposes. The
first is to provide a replenishing of the water in the seal at a
rate sufficient to avoid the creation of corrosive conditions in
the seal. This is accomplished by making the supply water of a
sufficiently alkaline nature to maintain the body of water in the
seal in a substantially neutral condition. The second primary
purpose of the supply of water is to maintain a continuous flow of
water over the upper edges 76 of the overflow collectors 74. This
constant overflow results in a skimming off of the surface water in
the seal. There is contained in this surface water a high
concentration of particulate matter from the gas in the inlet
plenum of the seal which has contacted and adhered to the water
surface but has not yet settled to the bottom of the seal. By
skimming off this surface water this particulate matter is thereby
removed.
Despite the skimming off of a large portion of the particulate
matter adhering to the water surface, with time, an undesirable
amount of such particles settle to the bottom of the seal. These
accumulated particles are periodically removed from the seal,
without requiring the seal to be broken, by opening the flush valve
72 and opening the drain connections 54, 56 adjacent the lower end
of the inclined bottom 50. The positions of the nozzles 66a-f,
68a-f in the bottom, all of which are now injecting water along the
bottom, serve to encourage the passage of the accumulated particles
from the seal through the drain connections 54, 56. The water
supply 64 and nozzles 66, 68 and the drain connections 54, 56 are
appropriately sized so that the normal level of liquid in the seal
is maintained during this cleaning or sluicing operation. When it
is determined that the seal is sufficiently clean, the drain
connections and the flush valve are closed and normal seal
operation is resumed.
Referring to FIG. 5, an additional embodiment of an overflow
collector is shown. A horizontal slot 86 is provided in the seal
wall, the lower edge thereof being substantially coincident with
the desired normal liquid level. A fully enclosed overflow
collector 88 is attached to the outside wall of the seal to
completely surround the horizontal slot 86. The collector 88 has a
discharge pipe 90, similar to that of the preferred embodiment,
attached to an opening in the lower end thereof for carrying off
water which has passed into the collector through the slot.
While the invention has been described in conjunction with specific
embodiments thereof, it is to be understood that such showings are
merely illustrative and that changes may be made without departing
from the spirit and scope of the invention as claimed.
* * * * *