Gas and liquid contact apparatus – Contact devices – Wet baffle
Reexamination Certificate
1997-11-26
2003-04-22
Bushey, C. Scott (Department: 1724)
Gas and liquid contact apparatus
Contact devices
Wet baffle
C261S117000, C096S297000, C096S326000
Reexamination Certificate
active
06550751
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to gas-liquid contactors used in the removal of particulate matter and acidic gases from utility and industrial combustion gases. More particularly, this invention is directed to an open spray absorber having a spray tower that is equipped with an internal structure that enhances the efficiency of the contactor by reintroducing into the gas flowing through the tower any liquid that has cohered to the tower walls.
BACKGROUND OF THE INVENTION
Gas-liquid contactors are widely used to remove substances such as gases and particulate matter from combustion or flue gases produced by utility and industrial plants. Often of particular concern are sulfur dioxide (SO
2
) and other acidic gases produced by the combustion of fossil fuels and various industrial operations. Such gases are known to be hazardous to the environment, and therefore their emission into the atmosphere is closely regulated by clean air statutes. The method by which acidic gases are removed from flue gases while flowing through a spray tower or other type of gas-liquid contactor is known as wet flue gas desulfurization (FGD).
The cleansing action produced by a gas-liquid contactor is generally derived from flowing the flue gas upwardly through a tower countercurrently to a descending liquid, which contacts the flue gas and absorbs the acidic gases and particulate matter. Wet flue gas desulfurization processes typically involve the use of calcium-based slurries or sodium-based or ammonia-based solutions. As used herein, a slurry is a mixture of solids and liquid in which the solids content can be any desired level, including the extreme condition in which the slurry is termed a moist solid. Examples of calcium-based slurries are limestone (calcium carbonate; CaCO
3
) slurries and hydrated lime (calcium hydroxide; Ca(OH)
2
) slurries formed by action of water on lime (calcium oxide; CaO). Such slurries react with the acidic gases to form slurries of sulfate and sulfite salts that can be collected for disposal or recycling. Intimate contact between the alkaline slurry and acidic gases present in the flue gases, such as sulfur dioxide, hydrogen chloride (HCl) and hydrogen fluoride (HF), result in the absorption of the gases by the slurry. Thereafter, the slurry can be accumulated in a tank.
A spray tower
10
is represented schematically in vertical and horizontal cross-section in
FIGS. 1 and 2
, respectively, for a gas-liquid contactor known as an open spray absorber. The tower
10
is generally an upright tubular-shaped structure having a wall
14
that defines a vertical passage. An inlet duct
12
serves to introduce combustion gases into the tower
10
. Above the inlet duct
12
are multiple banks of spray nozzles
16
that each introduces a spray
18
of a cleansing liquid, such as one of the above-noted slurries or solutions, into the passage formed by the wall
14
. The number of banks of nozzles
16
provided will vary in accordance with the requirements of a given application. Intimate contact between the spray
18
and the flue gases rising through the tower
10
results in a cleansing action, by which the liquid and the entrapped or reacted gases are collected at the bottom of the tower
10
in a tank (not shown). The cleansed gases that continue to rise through the tower
10
then typically pass through a mist eliminator (not shown), and thereafter are either heated or passed directly to the atmosphere.
The liquid introduced by the nozzles
16
is typically in the form of fine droplets, typically in the range of about 0.5 to 5 millimeters in diameter. As is evident from
FIGS. 1 and 2
, the spray
18
produced by a nozzle
16
within one bank overlaps the spray
18
from adjacent nozzles
16
of the same bank. The spray
18
from each nozzle
16
also overlaps the spray
18
emitted by nozzles
16
of lower banks as the spray
18
flows downwardly through the tower
10
under the influence of gravity. From
FIG. 1
, it can be seen that, even with multiple banks of nozzles
16
, a true uniform slurry distribution in the tower
10
is not achieved due to wall effects. The sprays
18
from the nozzles
16
nearest the wall
14
impinge on the wall
14
, such that the liquid flows downwardly on the surface of the wall
14
without contributing effectively to acid gas and particulate removal. Consequently, the spray concentration or density in an annular-shaped outer region
22
of the passage, shown generally as being between the outermost nozzles
16
and the wall
14
, is lower than that in the central region
20
of the tower
10
. Lower spray density in the outer region
22
results in low resistance to gas flow, such that the flue gases flow upward at relatively high velocities along the wall
14
of the tower
10
. The combination of low spray concentration and higher gas velocity near the wall
14
results in a low liquid-to-gas ratio (L/G), high flue gas penetration, and a reduced absorber efficiency.
In view of the above, it can be appreciated that the efficiency of gas-liquid contactors of the type shown in
FIGS. 1 and 2
are reduced by a nonuniform distribution of liquid within the spray tower, and that enhanced efficiencies could be achieved if a more uniform distribution were achieved or otherwise compensated for.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a more efficient gas-liquid contactor for the removal of acidic gases and/or particulate matter from flue gases produced by utility and industrial facilities.
It is a further object of this invention that such a contactor is configured to redistribute liquid within the contactor in order to achieve enhanced absorption and removal of gases and particulate matter from flue gases.
It is another object of this invention that such a contactor is configured to reduce gas penetration along the walls of the contactor in order to achieve enhanced absorption and removal of gases and particulate matter from flue gases.
The present invention provides a gas-liquid contactor for removing gases and particulate matter from flue gases produced by processing operations of the type carried out in utility and industrial plants. The contactor is generally an open spray absorber having a spray tower whose walls form a passage within the tower. Flue gases are introduced into the tower through an inlet from which the flue gases flow vertically upward or downward through the passage. Disposed within the passage are heads for introducing a liquid into the passage such that the liquid contacts the flue gases. As used herein, the term “liquid” encompasses any of the slurries and solutions employed in the industry with gas-liquid contactors. A portion of the liquid introduced by the heads contacts the wall of the tower, such that the portion of the liquid flows downwardly along the wall. Finally, the tower is equipped with a deflecting device disposed on or near the wall for deflecting the portion of the liquid away from the wall, and thereafter reintroducing the portion of the liquid into the passage so as to contact the gases flowing through the passage. The deflecting device is also preferably configured to obstruct the flow of gases along the wall in order to reduce gas penetration at the wall and divert the gases toward the center of the passage where more efficient contact with the liquid is made. In a preferred embodiment, the deflecting device reintroduces the portion of the liquid deflected from the wall as droplets into the passage to promote the absorption efficiency of the reintroduced liquid.
From the above, it can be seen that a significant advantage of this invention is that the deflecting device serves to reintroduce into the gas stream any portion of the liquid adhering to the walls of the tower—liquid which otherwise would not contribute effectively to removal of gases and particulate matter from the flue gases. By also obstructing the flow of flue gases along the wall of the tower, the deflecting device greatly improves the liquid/gas ratio near the wall. As a result, gas
Brown Gregory Norman
Gal Eli
Gansley Raymond Raulfs
Mengel Michael Lyn
Bushey C. Scott
Hartman Domenica N. S.
Hartman Gary M.
Hartman & Hartman P.C.
Marsulex Environmental Technologies Corp.
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