Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Carbon dioxide or hydrogen sulfide component
Reexamination Certificate
1998-05-11
2001-05-22
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Carbon dioxide or hydrogen sulfide component
C423S232000, C423S242100, C423S243060, C422S168000
Reexamination Certificate
active
06235256
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a process for scrubbing acidic gases, in particular SO
2
, HCl and H
2
S from flue gas by means of alkaline or earth-alkaline suspensions, lime stone and/or dolomite, in which the flue gases are scrubbed in several stages with a suspension and/or solution broken down into droplets and a device to carry out the process. As seen in the direction of flue gas flow, the flue gas is first directed through a spraying or scrubbing tower in the first scrubbing stage in an opposite direction to the flow of liquid droplets being sprayed through nozzles and in a second scrubbing stage in the same direction as the spray of liquid droplets. In the second stage, the flue gas is directed through one or more narrowing channels having throats in a direction opposite to the force of gravity, i.e., vertically upward, into an acceleration segment of the channels defined between the inlet of the channels and the narrowest point of the throat. In this manner, the scrubbing liquid in the form of droplets before the acceleration segment formed by the throats, or at the beginning of same.
BACKGROUND OF THE INVENTION
DE 43 31 415 A1 discloses a process for the treatment of gases in two scrubbing steps, whereby the scrubbing liquid drops in both steps as an substantially evenly distributed rain and is separated from the gas stream.
From AT-PS 333 588, it is known to scrub SO
2
out of SO
2
-containing flue gases by means of an earth alkali slurry in two stages and to reconstitute usable bisulfite, whereby great pressure loss occurs because of the multiple deflection of the flue gas. The energy expenditure for the transfer pumping of scrubbing fluid together with the absorption solution as well as for the spraying of the scrubbing fluid in the different scrubbers is considerable. This applies in particular if a product to be dumped is to be produced.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to eliminate this disadvantage and to achieve inexpensive separation of acidic flue gas components by using the least expensive absorption means such as lime stone and/or dolomite, in particular following power station steam producers, whereby the used absorption solution can be dumped without any problems if necessary.
The process according to the invention is characterized in that the droplets are deflected by 180° in the direction of gravitational force in a first demister, i.e. a mist precipitator, after the step with a reaction zone lying between a throat and an inlet of a channel into the first demister, using preferably a ratio of <5 lm
3
in nearly parallel and concentric channels and are then conveyed to a second demister.
In additional embodiments of the process in accordance with the invention, the channel has a variable cross-section and an acceleration section is defined between an inlet of the channel and a narrowest cross-section of the channel (i.e., the throat), the liquid droplets being sprayed in a vertically upward direction into the channel and the flue gas being directed to flow vertically upward. The channel and the first demister are ideally constructed such that the velocity of the flue gas in the acceleration section of the channel is less than about 23 m/s, the velocity of the flue gas in the reaction zone between the channel and the first demister is less than about 18 m/s, and a ratio of the velocity of the flue gas in the reaction zone to the velocity of the flue gas in the acceleration section is about 0.7. The channel is formed between a pair of walls, the reaction zone being defined between the walls after the channel, and the pair of walls are formed such that the droplets are deflected away from the portion of the walls defining the reaction zone. The velocity of the flue gas may be increased in the first demister as the flue gas is turned around in the channels in the first demister. As the droplets in the second stage, a suspension containing lime stone or dolomite dust having a high residual carbon value may be used such that the residual carbon content in the second stage is greater than the residual carbon content in the first stage, the density of the lime stone or dolomite being greater than about 50 g/l. The suspension is removed after interacting with the flue gas from the spray tower and at least part of the sulfite of the removed suspension is oxidized into sulphate.
In other embodiments, the droplets are collected after interacting with the flue gas, i.e., after scrubbing the same, in a settling basin situated at a bottom of the spray tower, and sulfite in the suspension in the settling basin is oxidized by directing at least one of air and flue gas into the settling basin of the spray tower. After the droplets are collected, after interacting with the flue gas, the solution collected in the basin may be subjected to a scrubbing for magnesium hydroxide or heavy metal catalysts. Alternatively, the droplets may be collected after interacting with the flue gas in an oxidation tank, sulfites in the suspension in the oxidation tank oxidized by directing at least one of air and flue gas into the oxidation tank, and a level of suspension
11
in the oxidation tank maintained substantially equal to a level at which the spray nozzles associated with the second stage are situated.
The device according to the invention to carry out the process is characterized in that a wet scrubber with downstream two-level demister is provided, and in particular installed on the scrubbing tower, after a scrubbing tower for the atomization of a scrubbing fluid, whereby a carbon-containing suspension is used as the scrubbing liquid for the absorption of the acidic gas components, and in that the device is provided with parallel and concentric channels for the deflection of the droplets by 180° in the direction of the gravitational force and in that a suspension container in form of an oxidation tank is provided next to the scrubbing tower, its liquid surface being provided approximately at the level of the spray nozzles of the wet scrubber and in that the wet scrubber is provided with throats for the acceleration of the flue gases in a direction contrary to the direction of gravitational force, with constriction of the gas flow from 0 -50%, preferably 20% and in that the spray nozzles of the wet scrubbers are located under the throats, whereby the spray nozzles of the wet scrubber and the device for atomization of the scrubbing liquid are installed in the scrubbing tower in such manner that the liquid droplets in the wet scrubber are introduced in the direction of gas flow and in the direction opposite to gas flow in the scrubbing tower and in that the throats are made in form of pocket-shaped catch grooves with a tear edge.
In additional embodiments of the arrangement in accordance with the invention, the channels in the scrubber are pocket-shaped and comprises a tear edge. Guide plates may be arranged to define the channels in the first demister, an uppermost one of the guide plates including a V-shaped central groove with an opening angle of greater than about 90° such that the guide plates form an angle a with a horizontal plane in the reaction zone that is less than about 45°. A settling basin may be arranged at a bottom of the scrubbing tower for receiving droplets after interacting with the flue gas, an outlet coupled to the settling basin for removing the suspension from the settling basin, and a dewatering device is coupled to the outlet for receiving the removed suspension.
A basic embodiment of the invention relates to a spray tower including means for directing flue gases containing acidic gases, such as SO
2
, HCl and H
2
S, in a flow path, and means for spraying liquid droplets of alkaline or earth-alkaline absorbents, lime stone and/or dolomite into the flow path of the flue gases to react with the acidic gases and thereby scrub the flue gases. The improvement is a demister arranged at a location after the liquid droplets have been sprayed by the spray means into the flow path of the flue gases and
Chybin Dieter
Glasner Alfred
Lang Diethard
Obwaller Georg
Austrian Energy & Environment SCP/Waagner-Biro GmbH
Griffin Steven P.
Medina Marikel
Steinberg & Raskin, P.C.
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