CA1168025A - Process for removal of pollutants from waste gas emissions - Google Patents
Process for removal of pollutants from waste gas emissionsInfo
- Publication number
- CA1168025A CA1168025A CA000357471A CA357471A CA1168025A CA 1168025 A CA1168025 A CA 1168025A CA 000357471 A CA000357471 A CA 000357471A CA 357471 A CA357471 A CA 357471A CA 1168025 A CA1168025 A CA 1168025A
- Authority
- CA
- Canada
- Prior art keywords
- scrubber
- chlorine
- process according
- gas
- flue gas
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/46—Removing components of defined structure
- B01D53/60—Simultaneously removing sulfur oxides and nitrogen oxides
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Health & Medical Sciences (AREA)
- Biomedical Technology (AREA)
- Environmental & Geological Engineering (AREA)
- Analytical Chemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Treating Waste Gases (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
The use of chlorine injected in a gaseous or liquid form into a hot (greater than 100° C) gas stream for the purpose of oxidizing objectionable components of the gas, such as, but not restricted to, NO, when the oxidized form of these gases is more readily removed from the gas stream. The gas stream-chlorine mixture is left to react for a time not less than that needed to result in a significant amount of reaction to occur. A significant amount of reaction shall be defined as that amount of reaction that results in a 10% increase in absorption of an objectionable component in the following gas absorption stage over what would be absorbed without previously using the method of this invention, or an amount of increased absorption of less than 10% if the increase of absorption is sufficient to make the addition of the method of this invention economically worthwhile.
The use of chlorine injected in a gaseous or liquid form into a hot (greater than 100° C) gas stream for the purpose of oxidizing objectionable components of the gas, such as, but not restricted to, NO, when the oxidized form of these gases is more readily removed from the gas stream. The gas stream-chlorine mixture is left to react for a time not less than that needed to result in a significant amount of reaction to occur. A significant amount of reaction shall be defined as that amount of reaction that results in a 10% increase in absorption of an objectionable component in the following gas absorption stage over what would be absorbed without previously using the method of this invention, or an amount of increased absorption of less than 10% if the increase of absorption is sufficient to make the addition of the method of this invention economically worthwhile.
Description
8~125 _ackground of the Invention The present invention relates to the removal of objectionable components from a moving gas stream, and the principal embodiment is expected to be the removal of sulphur dioxide, SO2, nitrogen oxides, NOx, from -~lue gases from industrial and utllity sources.
Other embodiments include the removal of toxic metallic vapors such as mercury, and other oxidizable gas components as well as halogens, and acidic and basic components from industrial effluents. The invention may also be used for purification and sterilization of air for applications wherever clean air is required such as hospitals or clean rooms, and also for deodorization purposes.
Sulphur dioxides and nitrogen oxides are produced in very large quantities daily from the burning of fossil fuels, and after oxidation in the atmosphere, are returned to the ground in what is cal.led "acid rain". The higher levels of acidity in the rainfall downwind of large 52 and NOx sources in the form of large industrial areas has a large environmental impact in many parts of the world. The fish of many lakes and streams in these areas have vanished, either as a direct kill, or from a break in their food chain. Agricultural production in some areas has decreased due to a leaching out of nutrients from the soil. Many other long term effects are still under investigation and all effects are causing much concern.
The major sources of SO2 and NOx produced by man derive from the burning of coal and petroleum products. All fossil fuels containg sulphur, and the most popular grades of fuel are the low sulphur varieties, since 1n the burning of sulphur containing fuels the sulphur present forms SO2 with the 1~68~ZS
associated environmental problems. Nitrogen oxides are produced in the burning process principally from the nitrogen in the air, and may be controlled to an extent by manipulation of the burning conditions. Some NOx is nonetheless produced even in the best practical situations, Due to the present uncertainties affecting the world petroleu~
supplies, and the limited supply in any case, other energy sources are being sought to fuel the worlds energy needs, which are continually increasing. One readily available energy that is not being fully utilized at present is coal, and much of this coal that is not being exploited is unused due to environmental concerns as the coal has an unacceptably high sulphur content. It has been estimated that 95% of the sulphur in coal forms SO2 on burning. ~
Over the last few decades , much interest has been shown in the removal os SO2 from flue gases and many systems for S2 removal from flue gases have been developed. Many large power plants have been fitted with some form of SO2 removal system to date.
- la -, ~-~8~:)25 The efficiency of these desulphurization attempts is in general insufficient to prevent large scale environmental damage. In a report to the Air Pollution Control Association in 1978, William H. Megonnel of the National Association of Electric Companies in an article entitled "Efficiency and Reliability of Sulphur Dioxide Scrubbers" examines the systems in operation ln utilities at that time. Of the thirty-two utilities classed as operational at that time, virtually all used some variation on a carbonate or alkaline scrubbing process, involving a collection of S02 as calcium sulfite;ùltimately. In the remaining example, the Wellman-Lord,Allied Chemical system was used involvingS02 recovery and reduction to sulphur at 90% efficiency. The primary deficiency of these system is the unacceptable removal efficiency obtained in operation, an average of around 75~ in the examples quoted. As North America is forced , due to economic and political reasons, to switch more and more to coal, including high sulphur coal, as an energy source, this removal efficiency demonstrated is insufficient to prevent large scale environmental damage.
In the large majority of S02 removal systems in use, the acidic nature o a water solution of S02 is used to trap the S02 in the form of a sulfite or bisulfite by reaction with a basic material such as calcium oxide or hydroxide, or by reaction with a carbonate such as limestone or dolomite. In some cases, the sulfite produced is oxidized with atmospheric oxygen to an lnsoluble sulfate. Although in laboratory scale and small pilot scale operations these systems show great promise, it appears that on a large scale, in which non-optimum conditions are constantly occurring, the efficiencies seen on a small, 1`, ' 1~80Z~
wellconrolled scale do not seem easily obtainable. One primary cause of this difficulty seems to be the reversibility of the reaction used to fix the S02 M2S3 ~~ S2 ~ H20 ~--~ 2MHS03 (1) The reversibility of the reaction, which forces the use of a countercurrent scrubber arrangement, leads to a situation where very careful control of gas flow rate vs S02 concentration is needed or else the S02 absorption efficiency becomes poor.
Other major problems encountered in the operation of these cleanup processes include large problems with scaling and erosion. Much of the work done to date on this kind of system involves only improvements of various kinds to aleviate the considerable difficulties involved in the operation of these systems.
Other research has been carried out on various dry processes, catalytic processes, and processes involving additions to the fuel, but to date little practical use ahs been made of these other processes, although the disadvantages of the carbonate or hydroxide scrubbing processes described earlier are causing great interest in alternate cleanup processes.
- 2a -.
, - ~6~3~Z~
Nitrogen oxides have been removed with varying success by a very large ~umber of methods on a laboratory scale, often in very uneconomical ways using expensive reagents. Methods used include dry catalytic reduction or oxidationl wet scrubbing with baslc solutions or amines, and aqueous scrubbing with oxidizing solutions. The methods used for nitrogen oxides removal are very diverse, and it appears that relatively few processes have been put into practical use, with the emphasis having been on the removal of S02 , which is generally present in larger quantities and is much more easily removed by conventional methods.
:
Generally the wet scrubbing methods, especially the methods using aqueous oxidizing solutions , are the only systems readily useable for the simultaneous removal of NOx and S02 .
zs SU~ARY OF TflE INVENTION
. _ The inven-tion is directed to providing a method Eor the removal of oxidizable components from a gas stream such as, ~ut not limited to, flue gas, into a scrubbing solution. This is done by using the scrubber effluent solutions to regenerate the oxidizing agent for reuse in the process. An economy is obtained by removal of the o~idlzing agent from the effluent solutions beEore disposal.
Acidic and basic components are removed from the lQ gas stream due to the chemical composition and pH of the scrubbing solutions used to accomplish the first object.
Similarly, halogens are removed from the gas stream.
The process may be built on any scale from that needed for cleaning -the flue gas from an industrial size utility to a very small unit capable of handling a gas stream line only a few inches in diameter, in a commercially reasonable installation.
The process also removes objec-tionable levels of particulates from -the gas stream if desired.
;8~25 The process for gas stream cleanup is designed to oxidize objectionable components of the gas and so render them non-volatile or more readily absorbed. This oxidation will occur either in the gas phase or in solution in the scrubbers. The process can be used to remove or reduce the amount presentof the following: S02, NOx, H2S, ammonia, and mercury and other metallic vapours, although it will be evident to anyone skilled in the art that this is by no means a complete list of readily oxidizable compounds which may be removed from gas streams by this invention. Because of the pH or chemical compositions of the scrubber solutions used in the process, the process will remove almost any acidic or basic compounds as well as halogens from the gas stream~ The principal embodiment of the invention is the cleanup of industrial effluents such as flue gases, and other embodiments include more economical deod-orization systems, and also sterilization of air.
The process in a brief summary consists of the following:
a). injection of chlorine into the hot gas, which is then left to react for a time determined by the dimensions of the pipe used and the gas flow rate.
b). a water quench to cool the gas.
c). gas absorption in a packed scrubber.
d). chlorine absorption in a counter-current packed scrubber, and return of the effluent solution containing chlorine to earlier stages of the system.
e). final removal of chorine in a counter-current packed scrubber with a solution of a carbonate, bicarbonate, or hydroxide, or packed with a solid carbonate, or using a lime or limestone slurry or similar. This effluent solution is mixed with an acid solution for the regeneration of chlorine, ~^ - 5 -1~8$2S
which is returned to earlier stages of the process.
f)~ demisting of the gas stream , followed by disposal of the gas.
When particulate removal is desired, either a dry electro-static precipitator can be used before the chlorine injection, or else a high energy venturi or similar scrubber may be used between the quench and first packed scrubberO Chlorine is removed from the effluent solutions before disposal by bubbling uslng some of the gas stream.
This summary is only indicative of the many different config-urations of the system, which can be altered somewhat at almost every stage in order to fit the system into a certain situation.
Stages a) and b) for example are omitted when the gas stream temperature is less than 100 degrees C, and chlorine is added .into stage c). above.
- 5a -~`.,, 1~6~25 Brief Description of the Drawings . _ .
Figure 1 illus-trates an embodiment of the process for use as a flue gas cleanup system as would be used by an electrical utility or similar large scale user.
Figure 2 illustrates an embodiment of the process for use in smaller scale applications.
These two embodiments are only indicative of the many different forms the process may take.
DETAILED DESCRIPTION OF THE INVENTION
. . .
The process for gas stream cleanup is designed to oxidize objectionable components of the gas and in doing so to render them non-volatile or much more readily absorbed. This oxidation will occur either in the gas phase or in solution in the scrubbers. The process can be used to remove or reduce the amount present of the following: S02, NOx, H2S, ammonia, mercury and other metallic vapors, although it will be evident to anyone skilled in the art that this is by no means a complete list of readily oxidizable compounds which may be removed from gas streams. Because of the pH or chemical compositions of the scrubber solutions used in the process, the process will remove almost any acidic or basic compounds as well as halogens from the gas stream.
The process for gas stream cleanup consists of one option from each o~ eight sections, and as such gives many hundreds oE reasonable systems derived from the process.
The first section of the process consists of either a dry electrostatic precipitator of standard design operated at the gas stream temperature, or else no precipitator. The function of the precipitator , if used, is the removal of particulate matter from the gas stream, as would be found in the use of this process as a flue gas cleanup system. A high energy wet scrubber can be used later in the process as an alternative particulate removal device , if desired~ Particle collection may be omitted as desired.
~6~l~%S
The second stage of the process conslsts of a section of chemically inert pipe or similar, with or without baffles, into which chlorine is added in one or more of the following ways:
1) gaseous chlorine
Other embodiments include the removal of toxic metallic vapors such as mercury, and other oxidizable gas components as well as halogens, and acidic and basic components from industrial effluents. The invention may also be used for purification and sterilization of air for applications wherever clean air is required such as hospitals or clean rooms, and also for deodorization purposes.
Sulphur dioxides and nitrogen oxides are produced in very large quantities daily from the burning of fossil fuels, and after oxidation in the atmosphere, are returned to the ground in what is cal.led "acid rain". The higher levels of acidity in the rainfall downwind of large 52 and NOx sources in the form of large industrial areas has a large environmental impact in many parts of the world. The fish of many lakes and streams in these areas have vanished, either as a direct kill, or from a break in their food chain. Agricultural production in some areas has decreased due to a leaching out of nutrients from the soil. Many other long term effects are still under investigation and all effects are causing much concern.
The major sources of SO2 and NOx produced by man derive from the burning of coal and petroleum products. All fossil fuels containg sulphur, and the most popular grades of fuel are the low sulphur varieties, since 1n the burning of sulphur containing fuels the sulphur present forms SO2 with the 1~68~ZS
associated environmental problems. Nitrogen oxides are produced in the burning process principally from the nitrogen in the air, and may be controlled to an extent by manipulation of the burning conditions. Some NOx is nonetheless produced even in the best practical situations, Due to the present uncertainties affecting the world petroleu~
supplies, and the limited supply in any case, other energy sources are being sought to fuel the worlds energy needs, which are continually increasing. One readily available energy that is not being fully utilized at present is coal, and much of this coal that is not being exploited is unused due to environmental concerns as the coal has an unacceptably high sulphur content. It has been estimated that 95% of the sulphur in coal forms SO2 on burning. ~
Over the last few decades , much interest has been shown in the removal os SO2 from flue gases and many systems for S2 removal from flue gases have been developed. Many large power plants have been fitted with some form of SO2 removal system to date.
- la -, ~-~8~:)25 The efficiency of these desulphurization attempts is in general insufficient to prevent large scale environmental damage. In a report to the Air Pollution Control Association in 1978, William H. Megonnel of the National Association of Electric Companies in an article entitled "Efficiency and Reliability of Sulphur Dioxide Scrubbers" examines the systems in operation ln utilities at that time. Of the thirty-two utilities classed as operational at that time, virtually all used some variation on a carbonate or alkaline scrubbing process, involving a collection of S02 as calcium sulfite;ùltimately. In the remaining example, the Wellman-Lord,Allied Chemical system was used involvingS02 recovery and reduction to sulphur at 90% efficiency. The primary deficiency of these system is the unacceptable removal efficiency obtained in operation, an average of around 75~ in the examples quoted. As North America is forced , due to economic and political reasons, to switch more and more to coal, including high sulphur coal, as an energy source, this removal efficiency demonstrated is insufficient to prevent large scale environmental damage.
In the large majority of S02 removal systems in use, the acidic nature o a water solution of S02 is used to trap the S02 in the form of a sulfite or bisulfite by reaction with a basic material such as calcium oxide or hydroxide, or by reaction with a carbonate such as limestone or dolomite. In some cases, the sulfite produced is oxidized with atmospheric oxygen to an lnsoluble sulfate. Although in laboratory scale and small pilot scale operations these systems show great promise, it appears that on a large scale, in which non-optimum conditions are constantly occurring, the efficiencies seen on a small, 1`, ' 1~80Z~
wellconrolled scale do not seem easily obtainable. One primary cause of this difficulty seems to be the reversibility of the reaction used to fix the S02 M2S3 ~~ S2 ~ H20 ~--~ 2MHS03 (1) The reversibility of the reaction, which forces the use of a countercurrent scrubber arrangement, leads to a situation where very careful control of gas flow rate vs S02 concentration is needed or else the S02 absorption efficiency becomes poor.
Other major problems encountered in the operation of these cleanup processes include large problems with scaling and erosion. Much of the work done to date on this kind of system involves only improvements of various kinds to aleviate the considerable difficulties involved in the operation of these systems.
Other research has been carried out on various dry processes, catalytic processes, and processes involving additions to the fuel, but to date little practical use ahs been made of these other processes, although the disadvantages of the carbonate or hydroxide scrubbing processes described earlier are causing great interest in alternate cleanup processes.
- 2a -.
, - ~6~3~Z~
Nitrogen oxides have been removed with varying success by a very large ~umber of methods on a laboratory scale, often in very uneconomical ways using expensive reagents. Methods used include dry catalytic reduction or oxidationl wet scrubbing with baslc solutions or amines, and aqueous scrubbing with oxidizing solutions. The methods used for nitrogen oxides removal are very diverse, and it appears that relatively few processes have been put into practical use, with the emphasis having been on the removal of S02 , which is generally present in larger quantities and is much more easily removed by conventional methods.
:
Generally the wet scrubbing methods, especially the methods using aqueous oxidizing solutions , are the only systems readily useable for the simultaneous removal of NOx and S02 .
zs SU~ARY OF TflE INVENTION
. _ The inven-tion is directed to providing a method Eor the removal of oxidizable components from a gas stream such as, ~ut not limited to, flue gas, into a scrubbing solution. This is done by using the scrubber effluent solutions to regenerate the oxidizing agent for reuse in the process. An economy is obtained by removal of the o~idlzing agent from the effluent solutions beEore disposal.
Acidic and basic components are removed from the lQ gas stream due to the chemical composition and pH of the scrubbing solutions used to accomplish the first object.
Similarly, halogens are removed from the gas stream.
The process may be built on any scale from that needed for cleaning -the flue gas from an industrial size utility to a very small unit capable of handling a gas stream line only a few inches in diameter, in a commercially reasonable installation.
The process also removes objec-tionable levels of particulates from -the gas stream if desired.
;8~25 The process for gas stream cleanup is designed to oxidize objectionable components of the gas and so render them non-volatile or more readily absorbed. This oxidation will occur either in the gas phase or in solution in the scrubbers. The process can be used to remove or reduce the amount presentof the following: S02, NOx, H2S, ammonia, and mercury and other metallic vapours, although it will be evident to anyone skilled in the art that this is by no means a complete list of readily oxidizable compounds which may be removed from gas streams by this invention. Because of the pH or chemical compositions of the scrubber solutions used in the process, the process will remove almost any acidic or basic compounds as well as halogens from the gas stream~ The principal embodiment of the invention is the cleanup of industrial effluents such as flue gases, and other embodiments include more economical deod-orization systems, and also sterilization of air.
The process in a brief summary consists of the following:
a). injection of chlorine into the hot gas, which is then left to react for a time determined by the dimensions of the pipe used and the gas flow rate.
b). a water quench to cool the gas.
c). gas absorption in a packed scrubber.
d). chlorine absorption in a counter-current packed scrubber, and return of the effluent solution containing chlorine to earlier stages of the system.
e). final removal of chorine in a counter-current packed scrubber with a solution of a carbonate, bicarbonate, or hydroxide, or packed with a solid carbonate, or using a lime or limestone slurry or similar. This effluent solution is mixed with an acid solution for the regeneration of chlorine, ~^ - 5 -1~8$2S
which is returned to earlier stages of the process.
f)~ demisting of the gas stream , followed by disposal of the gas.
When particulate removal is desired, either a dry electro-static precipitator can be used before the chlorine injection, or else a high energy venturi or similar scrubber may be used between the quench and first packed scrubberO Chlorine is removed from the effluent solutions before disposal by bubbling uslng some of the gas stream.
This summary is only indicative of the many different config-urations of the system, which can be altered somewhat at almost every stage in order to fit the system into a certain situation.
Stages a) and b) for example are omitted when the gas stream temperature is less than 100 degrees C, and chlorine is added .into stage c). above.
- 5a -~`.,, 1~6~25 Brief Description of the Drawings . _ .
Figure 1 illus-trates an embodiment of the process for use as a flue gas cleanup system as would be used by an electrical utility or similar large scale user.
Figure 2 illustrates an embodiment of the process for use in smaller scale applications.
These two embodiments are only indicative of the many different forms the process may take.
DETAILED DESCRIPTION OF THE INVENTION
. . .
The process for gas stream cleanup is designed to oxidize objectionable components of the gas and in doing so to render them non-volatile or much more readily absorbed. This oxidation will occur either in the gas phase or in solution in the scrubbers. The process can be used to remove or reduce the amount present of the following: S02, NOx, H2S, ammonia, mercury and other metallic vapors, although it will be evident to anyone skilled in the art that this is by no means a complete list of readily oxidizable compounds which may be removed from gas streams. Because of the pH or chemical compositions of the scrubber solutions used in the process, the process will remove almost any acidic or basic compounds as well as halogens from the gas stream.
The process for gas stream cleanup consists of one option from each o~ eight sections, and as such gives many hundreds oE reasonable systems derived from the process.
The first section of the process consists of either a dry electrostatic precipitator of standard design operated at the gas stream temperature, or else no precipitator. The function of the precipitator , if used, is the removal of particulate matter from the gas stream, as would be found in the use of this process as a flue gas cleanup system. A high energy wet scrubber can be used later in the process as an alternative particulate removal device , if desired~ Particle collection may be omitted as desired.
~6~l~%S
The second stage of the process conslsts of a section of chemically inert pipe or similar, with or without baffles, into which chlorine is added in one or more of the following ways:
1) gaseous chlorine
2) liquid chlorine
3) a mixture of chlorine gas and air, inert gas or flue gas, which may also contain hydrochloric and/or nitric acid.
4) a water solution of chlorine.
5) recycled process solution containing chlorine, and which may also contain hydrochloric and/or nitric acid.
The chlorine added into the gas stream is for the gaseous oxidation of objectionable components to form compounds more readily absorbed in the following scrubbers. The temperature and/or the water vapour concentration may be adjusted at this time by the addition of one or more of:
1) liquid water 2) a water solution of chorine.
3) recycled process solution containing chlorine, and which amy also contain hydrochloric and/or nitric acid.
although the addition of the water solutions of 2) or 3) may not be necessary for the control of water vapour concentration and/or temperature since these solutions may be used rather for the chlorine addition with no concern ~ .~
-., ~
for other parameters.
The chlorine being added into this section may come from one of three sources. The chlorine added as a gas , liquid or as a water solution is from the chlorine cylinder used as the process chlorine source, and one or more of these is preferred. the chlorine mi~ed with air, inert gas or flue gas derives from using gas or warm gas to recover chlorine from the process effluent solutions by bubbling. The recycled process solution containing chlorlne is the ef1uent solution of the sixth stage of the process. The chlorine sources other than the cylinder are intended for the return of chlorine to the earliest stage of the process for reuse of unreacted chlorine.
It is anticipated that this stage of the process will be used only if the gas stream is 100 C or higher in temperature. If the objectionable components in the gas stream are sufficiently well absorbed in the following stages of the process without prior oxidation, this stage of the process may be omitted.
zs In this stage the gas stream - chlorine mixture is left to react for a time not less than that needed to result in a 10%
increase in absorption of an objectionable component over that which would be absorbed with this section omitted, or less than 10% if this is economically useful. In the case of flue gas cleanup the component of interest is nitric oxide, NO, principally, which due to its low solubility is difficu~t to remove from gases in wet scrubbers. Sulphur dioxide is sufficiently soluble that this stage should prove unnecessary for adequate absorption.
The third section of the process is an optional water quench for cooling the flue gas before entering the wet scrubber stages.
Water or recycled process solution is added as a spray, with the recycled process solution again coming from the chlorine reclaiming scrubber as in stage 2. Gaseous chlorine may be added in this stage.
The fourth stage of the processis a high energy particle scrubber of standard design and is used when particulate removal is desired and no electrostatic precipitator is used in stage 1. Thls scrubber is ideally a high pressure venturi or venturi with applied high intensity ionisation. This scrubber will also collect some of the gas stream components, especially some SO2 in the presence of chlorine.
The scrubber water solution is ideally recirculated in order to obtain as high a concentration of acid as possible in the solution. The feedwater used in this scrubber may come from the water mains or may be recycled process solutions from later stages of the process. Dissolved chlorine in the effluent sGlution may by bubbling be blown out using air, an inert gas --.. .
~l6~:s25 or flue gas and added to the second stage of the process. This givesa greater economy in the use of chlorine without increasing the complexity of the system unduly., especially if hot flue gas is used. Chlorine may be added into this scrubber from the cylinder, either as a gas or into the scrubbing solution.
The fifth stage of the process involves a gas absorbing scrubber of standard design, ideally a packed scrubber such as a crossflow scrubber, but almost any scrubber of standard design may be used, with the suitability being principally determined by the gas contact time with the scrubbing solution.
Chlorine may be added to this scrubber either in gaseous form or by dissolving in the scrubber feedwater. If it was chosen to add no chlorine earlier in the system, chlorine will be added to this stage in the process from the chlorine cylinder~ Addition of chlorine as agas may be either into the gas stream going into the scrubber, or into the interior of the scrubber. The scrubbing solution in this stage derives from the same sources, is reciculated similarly to and may be dechlorinated in the same fashion as that in the fourth stage of the system, and if desirable, may be mixed with the solution of the fourth stage.
- lOa _ ~i8~
The primary function of this stage of the process is the absorption of the objectionable components into solution, followed by the rapid, irreversible oxidation of these components to form either non-vol.atile compounds , such as sulphuric acid or else highly soluble volatile compounds such as nitric acid.
The size and type of this type of scrubber is determined by the demands of each situation, and and installation having to deal only with S02 , as an example , will need only a relatively simple scrubber due to the relatively high solubility of S02, whereas an installation handling a large amount of NOx will need longer residence time scrubber with high liquid contact due to the lower solubility of nitrogen oxide.
The sixth stage of the process , which may be omitted or abbreviated if economy in the us~ hlorine is not a major consideration, is a gas absorbing scrubber of standard design, ideally a packed scrubber such as a crossflow absorber or a coutercurrent packed scrubber.Recirculation of the scrubbing liquid in this absorber is kept to a minimum and is recirc-ulated to an earlier section of this absorber in the case of a cross flow absorber. The purpose of this absorber is to recover chlorine and acid vapours from the gas exiting the /.
previous ahsorber, for return o the chlorine to earlier sections of the overall process. The effluent solution of this scrubber may be used as some or all of the feedwater in st~ges 2 through 5.
The size and type of scrubber used in this stage is determined by the chlorine collection efficiency desired in this scrubber.
The reci.rculation of the scrubbing solution may be accompanied by dechlorinating the effluent solution as in stage ~ and 5 , otherwise the recirculation of the solution is llmited by the dissolved chlorine in the effluent solution from the scrubber.
~168~5 The seventh section of the process is ideally a calcium carbonate or dolomite packed countercurrent scrubber for the removal of chlorine from the gas stream and for the return of the chlorine to previous stages of the system. A packed scrubber may also be used with a recirculating solution of a soluble carbonate, or bicarbonate, or else a soluble hydroxide such as sodium hydroxide or calcium hydroxide from slaked lime. A scrubbing slurry of an alkaline earth carbonate may also be used. In the case of using solutions or slurries of carbonates, bicarbonates or hydroxides, however, some caution must be exercised since the scrubber effluent solution is mixed with acid effluents from previous stages for the regeneration of chlorine and the residual carbonate, bicarbonate or hydroxide must be taken into consideration in the mixing.
The chlorine reacts in the seventh section with the carbonate bicarbonate or hydroxide to produce either a hypochlorite or hypochlorous acid, HOC1. Upon mixing with the effluent solutions from previous scrubbers, which are high in acidity, especially with hypchloric acid and sulphuric acid, any hypochlorite is converted to HOC1 , and iithe presence of HCl , the chlorine dissolution and disproportionation equi;ibrium results in the regeneration of free chlorine.
- lla -iL lLti8(3;~5 Both HOCl and chlorine are the active oxidizing agents in the previous sections. The solution from this section may be added directly to the recirculating solutions in the earlier scrubbers, or may be added to some of the solution from these sections separately under controlled conditions.
If the solution Erom this section of the process contains calcium ions, from a CaC03 , dolomite, slaked lime or slaked calcined dolomite scrubber, steps must be taken to filter out the CaS04 precipitated during the acidification with the HCl and H2S04 mixture. A controlled amount of excess ~I2S04 is used ideally,in order ^to minimize the total dissolved calcium in the solution to prevent scaling in the scrubbers from occurring. The minimum dissolved calcium is achieved when the volume ratio of the calcium and sulfate containing solutions are as below, where the concentrations are the calcium and sulfate concentrations in the two solutions before mixing:
1 volume calcium TO 2 Calcium + 1 volume of sulfate containing solution concentration containing sol.
_ , ., Sulfate concentration This minimum total dissolved calcium is desireable to avoid a high calcium concentration in the recycled solutions which could precipitate calcium sulfate inside the scrubbers and at the points of highest sulfate concentration.
If the solution from this seventh section of the process contains any appreciable amount of dissolved hydroxide, carbonate or bicarbonate, the mixing with previous stage solutions must be carried out very carefully, due to the release of heat or C02, which poses no serious problems if taken into consideration.
- ~ - 12 -~8~D2~
The evolved C02, if any , is vented into the process no later than the input of stage 7 and preferrably earlier, since the evolution of C02 will tend to carry acid vapours and dissolved chlorine out of the mixture.
The acidified effluent of this stage of the process may be dechlorinated as in stage 4 or 5 , and the mixture of chlorine and air, inert gas or flue gas added to the second stage of the process.
The eiyhth and final stage of the process consists of a demisting stage of standard design. A packed bed demister is preferred, but any demister of reasonable efficiency may be used. This stage may be combined with the previous by making a packed scrubber and introducing the scrubbing liquid at a point below the top surface of the packing, and using the packing above the liquid introduction level as a demlster.
The effluent gas from the system is routed to a stack for disposal.
- 12a -Process Chemical Reactions ~ he hot gas phase reactions with chlorine in the process have been investiga-ted in the literature, and are yenerally well known, but only as reactions of the pure gases. The reaction rates in the gas stream are expected to be accelerated by the presence of the other gases, moisture and flue dust surfaces. The equilibrium C12 + H2O = 2HCl ~ 2 2 may increase the oxidizing power of the gas mix-ture, as this equilibrium orms a hiyhly oxidizing medium, possibly due to the production of atomic oxygen or hydroxyl radicals at high tenlperatures. It appears that this unusual characteristic of this mixture has never been investigated since the report in a Russian journallin ].939. No investi-~ations into the mechanis.ms of this reaction have been discovered, al~houyh the thexmodynamic constants are known as the revers~ reaction is the basi.s for the Deacon process for the manu:Eacture of chlorille from HCl and oxygen.
~1o~her method for increasiny the free radical concentration in the gas is the rapid vaporiæation of a solution of chlorine in water, to produce gaseous HOCl, which decomposes to give hydroxy and chlorine radicals, as in reaction la. This vaporization HOCl (gas) - - ~ HO + Cl (la~
is done very rapidly using a fine spray into the hot gas ; in order to evaporate the solution before the equilibrium of equation 13 can shift to give chlorine gas instead of HOCl gas.
1. A.P. Kreshkov, J. Chem. Ind. (U.S.S.R.) 16, No. 4-5, 38-41 (1939) Abstracted in Chemical Abstracts 33, no. 77293 .
' ~6~25 The principal reactions expected as forming some contribu-tion to the gas phase reaction are SO + O ` SO (2) NO + O ~ N02 (3) and similar radical reactions S2 ~~ C12 = SO2C1 2 12 H20 ~ SO3 ~ 2HCl (5) 2NO + C12 = 2NOCl (6) 2NO2 + C12 = 2NO2Cl (7) N02Cl + NO ~ N02 ~ NOCl (8) NOC1 -~ 1/2 2 > NO2 + 1/2 C12 (9) Hg (gas) ~ C12 ~--~HgC12 very fast (10) Metal vapor - chlorine reactions in general are expected to be practically instantaneous and comple-te. Mercury out~
put in the gas stream from this process is expected to be well below acceptable levels.
1'he water phase reactions in this process are very rapid and complete. The ~ollowing reactions are expected.
1~6~ 5 SO3 + H2O ---~ H2SO4 (11) S2 + H2O ~- H2S 3 (12) C12 + H2O ~--~ EICl + HOCl (13) 2N2 + H2O ~ HNO2 + HNO3 slow (14) 2NO + H2O -~ HNO3 ---3 3HNO2 (15) NO2 + 2HCl ---, NOC1 + H2O + ~CL2 (16) NO + NO2 + H2O ~~ 7 2~N2 (17) 2MO -~ 3HCl + HNO3 ---~ 3NOCl + 2H20 (18) NOC1 + H2O ---7 HNO + HCl (l9) NOC1 + C12 + ~2 ~~ ~ HNO3 (20) NO2Cl + H2O ---~ HNO + HCl (21) S2C12 + 2H2 ~ H2 4 (22) H2SO3 ~ HOCl ---~ H SO + HCl (23) HSO32 ~ HOCl ---~ HSO + HCl (24) SO3 + HOC1 ---~ SO + HCl (25) HNO2 ~ HOCl ---~ HNO3 + HCl (26) NO2 ~ HOCl ~ NO3 + HCl (27) NH3 -~ H+ ---~ NH4+Xida-t---onNo- (28) In th~ chlorine removal scrubber, the chlorine and acid vapors are removed from the gas stream. The preferred method is the use of a packed tower of calcium carbonate, dolomite or a similar solid, insoluble and reactive carbonate. This has the advantage of simplicity of design and a relatively low cost.
Other scrubber sy,stems which may be used are countercurrent packed scrubbers or simila-r using a scrubbing solution containing a soluble carbonate, bicarbonate or a h~droxide or a scrubber using a slurry of an insoluble carbonate or slaked lime or calcined dolomite or similar.
, ~8~2S
The effluent of these scrubbers, upon acidification, can be used as feedwater in other sections of the process, after filtering if necessary. The oxidizing power of the chlorine is not lost in this chlorine removal scrubber, but remains in the form of hypochlorlte or hypochlorous acid and upon acidif-ication, chlorine is regenerated as in the equilibrium in equation 13 , and may be returned to the earlier stages of the process.
e - lSa -~ ~6~Z5 The reactions in the chlorine removal scrubber are as follows:
C12 + H20 = HCl + HOCl HOCl or HCl + M2C03 ~ MOCl or MCl + H20 + CO2 HOCl or HCl + 2MOH ~ MOC1 or MCL + 2H20 HOCl or HC1 + 2MHCO3 ~ MOC1 or MC1 + 2H20 + 2C02 The presence of hypochlorite or hypochlorous acid in the re-circulated scrubbing liquid results in an oxidising condition in this scrubber. This results in a contribution to the removal of objectionable components in the gas stream by reactions similar to those of the water phase reactions mentioned earlier.
The e~fluent from the chlorine removal scrubber is mixed with effluent from earlier in the process, containing hydrochloric, sulfuric and nitric acids. The effluent highest in sulphuric acid concentration ls preferred. This acidification regenerates chlorine and precipitates calcium sulfate as in the following e~uations~
CaClOCl + H2S04 ~ Ca~S04(s) -~ HCl + HOCl HCl + HOCl ~ C12 + H20 , , 8~S
` Legend of Large Flue Gas System Illustrated in Figure 1 1. Firebox 2. Stack 3. Addition of Chlorine, etc. followed by the hot section.
4. Quench 5. Venturi and associated cyclone and fan
The chlorine added into the gas stream is for the gaseous oxidation of objectionable components to form compounds more readily absorbed in the following scrubbers. The temperature and/or the water vapour concentration may be adjusted at this time by the addition of one or more of:
1) liquid water 2) a water solution of chorine.
3) recycled process solution containing chlorine, and which amy also contain hydrochloric and/or nitric acid.
although the addition of the water solutions of 2) or 3) may not be necessary for the control of water vapour concentration and/or temperature since these solutions may be used rather for the chlorine addition with no concern ~ .~
-., ~
for other parameters.
The chlorine being added into this section may come from one of three sources. The chlorine added as a gas , liquid or as a water solution is from the chlorine cylinder used as the process chlorine source, and one or more of these is preferred. the chlorine mi~ed with air, inert gas or flue gas derives from using gas or warm gas to recover chlorine from the process effluent solutions by bubbling. The recycled process solution containing chlorlne is the ef1uent solution of the sixth stage of the process. The chlorine sources other than the cylinder are intended for the return of chlorine to the earliest stage of the process for reuse of unreacted chlorine.
It is anticipated that this stage of the process will be used only if the gas stream is 100 C or higher in temperature. If the objectionable components in the gas stream are sufficiently well absorbed in the following stages of the process without prior oxidation, this stage of the process may be omitted.
zs In this stage the gas stream - chlorine mixture is left to react for a time not less than that needed to result in a 10%
increase in absorption of an objectionable component over that which would be absorbed with this section omitted, or less than 10% if this is economically useful. In the case of flue gas cleanup the component of interest is nitric oxide, NO, principally, which due to its low solubility is difficu~t to remove from gases in wet scrubbers. Sulphur dioxide is sufficiently soluble that this stage should prove unnecessary for adequate absorption.
The third section of the process is an optional water quench for cooling the flue gas before entering the wet scrubber stages.
Water or recycled process solution is added as a spray, with the recycled process solution again coming from the chlorine reclaiming scrubber as in stage 2. Gaseous chlorine may be added in this stage.
The fourth stage of the processis a high energy particle scrubber of standard design and is used when particulate removal is desired and no electrostatic precipitator is used in stage 1. Thls scrubber is ideally a high pressure venturi or venturi with applied high intensity ionisation. This scrubber will also collect some of the gas stream components, especially some SO2 in the presence of chlorine.
The scrubber water solution is ideally recirculated in order to obtain as high a concentration of acid as possible in the solution. The feedwater used in this scrubber may come from the water mains or may be recycled process solutions from later stages of the process. Dissolved chlorine in the effluent sGlution may by bubbling be blown out using air, an inert gas --.. .
~l6~:s25 or flue gas and added to the second stage of the process. This givesa greater economy in the use of chlorine without increasing the complexity of the system unduly., especially if hot flue gas is used. Chlorine may be added into this scrubber from the cylinder, either as a gas or into the scrubbing solution.
The fifth stage of the process involves a gas absorbing scrubber of standard design, ideally a packed scrubber such as a crossflow scrubber, but almost any scrubber of standard design may be used, with the suitability being principally determined by the gas contact time with the scrubbing solution.
Chlorine may be added to this scrubber either in gaseous form or by dissolving in the scrubber feedwater. If it was chosen to add no chlorine earlier in the system, chlorine will be added to this stage in the process from the chlorine cylinder~ Addition of chlorine as agas may be either into the gas stream going into the scrubber, or into the interior of the scrubber. The scrubbing solution in this stage derives from the same sources, is reciculated similarly to and may be dechlorinated in the same fashion as that in the fourth stage of the system, and if desirable, may be mixed with the solution of the fourth stage.
- lOa _ ~i8~
The primary function of this stage of the process is the absorption of the objectionable components into solution, followed by the rapid, irreversible oxidation of these components to form either non-vol.atile compounds , such as sulphuric acid or else highly soluble volatile compounds such as nitric acid.
The size and type of this type of scrubber is determined by the demands of each situation, and and installation having to deal only with S02 , as an example , will need only a relatively simple scrubber due to the relatively high solubility of S02, whereas an installation handling a large amount of NOx will need longer residence time scrubber with high liquid contact due to the lower solubility of nitrogen oxide.
The sixth stage of the process , which may be omitted or abbreviated if economy in the us~ hlorine is not a major consideration, is a gas absorbing scrubber of standard design, ideally a packed scrubber such as a crossflow absorber or a coutercurrent packed scrubber.Recirculation of the scrubbing liquid in this absorber is kept to a minimum and is recirc-ulated to an earlier section of this absorber in the case of a cross flow absorber. The purpose of this absorber is to recover chlorine and acid vapours from the gas exiting the /.
previous ahsorber, for return o the chlorine to earlier sections of the overall process. The effluent solution of this scrubber may be used as some or all of the feedwater in st~ges 2 through 5.
The size and type of scrubber used in this stage is determined by the chlorine collection efficiency desired in this scrubber.
The reci.rculation of the scrubbing solution may be accompanied by dechlorinating the effluent solution as in stage ~ and 5 , otherwise the recirculation of the solution is llmited by the dissolved chlorine in the effluent solution from the scrubber.
~168~5 The seventh section of the process is ideally a calcium carbonate or dolomite packed countercurrent scrubber for the removal of chlorine from the gas stream and for the return of the chlorine to previous stages of the system. A packed scrubber may also be used with a recirculating solution of a soluble carbonate, or bicarbonate, or else a soluble hydroxide such as sodium hydroxide or calcium hydroxide from slaked lime. A scrubbing slurry of an alkaline earth carbonate may also be used. In the case of using solutions or slurries of carbonates, bicarbonates or hydroxides, however, some caution must be exercised since the scrubber effluent solution is mixed with acid effluents from previous stages for the regeneration of chlorine and the residual carbonate, bicarbonate or hydroxide must be taken into consideration in the mixing.
The chlorine reacts in the seventh section with the carbonate bicarbonate or hydroxide to produce either a hypochlorite or hypochlorous acid, HOC1. Upon mixing with the effluent solutions from previous scrubbers, which are high in acidity, especially with hypchloric acid and sulphuric acid, any hypochlorite is converted to HOC1 , and iithe presence of HCl , the chlorine dissolution and disproportionation equi;ibrium results in the regeneration of free chlorine.
- lla -iL lLti8(3;~5 Both HOCl and chlorine are the active oxidizing agents in the previous sections. The solution from this section may be added directly to the recirculating solutions in the earlier scrubbers, or may be added to some of the solution from these sections separately under controlled conditions.
If the solution Erom this section of the process contains calcium ions, from a CaC03 , dolomite, slaked lime or slaked calcined dolomite scrubber, steps must be taken to filter out the CaS04 precipitated during the acidification with the HCl and H2S04 mixture. A controlled amount of excess ~I2S04 is used ideally,in order ^to minimize the total dissolved calcium in the solution to prevent scaling in the scrubbers from occurring. The minimum dissolved calcium is achieved when the volume ratio of the calcium and sulfate containing solutions are as below, where the concentrations are the calcium and sulfate concentrations in the two solutions before mixing:
1 volume calcium TO 2 Calcium + 1 volume of sulfate containing solution concentration containing sol.
_ , ., Sulfate concentration This minimum total dissolved calcium is desireable to avoid a high calcium concentration in the recycled solutions which could precipitate calcium sulfate inside the scrubbers and at the points of highest sulfate concentration.
If the solution from this seventh section of the process contains any appreciable amount of dissolved hydroxide, carbonate or bicarbonate, the mixing with previous stage solutions must be carried out very carefully, due to the release of heat or C02, which poses no serious problems if taken into consideration.
- ~ - 12 -~8~D2~
The evolved C02, if any , is vented into the process no later than the input of stage 7 and preferrably earlier, since the evolution of C02 will tend to carry acid vapours and dissolved chlorine out of the mixture.
The acidified effluent of this stage of the process may be dechlorinated as in stage 4 or 5 , and the mixture of chlorine and air, inert gas or flue gas added to the second stage of the process.
The eiyhth and final stage of the process consists of a demisting stage of standard design. A packed bed demister is preferred, but any demister of reasonable efficiency may be used. This stage may be combined with the previous by making a packed scrubber and introducing the scrubbing liquid at a point below the top surface of the packing, and using the packing above the liquid introduction level as a demlster.
The effluent gas from the system is routed to a stack for disposal.
- 12a -Process Chemical Reactions ~ he hot gas phase reactions with chlorine in the process have been investiga-ted in the literature, and are yenerally well known, but only as reactions of the pure gases. The reaction rates in the gas stream are expected to be accelerated by the presence of the other gases, moisture and flue dust surfaces. The equilibrium C12 + H2O = 2HCl ~ 2 2 may increase the oxidizing power of the gas mix-ture, as this equilibrium orms a hiyhly oxidizing medium, possibly due to the production of atomic oxygen or hydroxyl radicals at high tenlperatures. It appears that this unusual characteristic of this mixture has never been investigated since the report in a Russian journallin ].939. No investi-~ations into the mechanis.ms of this reaction have been discovered, al~houyh the thexmodynamic constants are known as the revers~ reaction is the basi.s for the Deacon process for the manu:Eacture of chlorille from HCl and oxygen.
~1o~her method for increasiny the free radical concentration in the gas is the rapid vaporiæation of a solution of chlorine in water, to produce gaseous HOCl, which decomposes to give hydroxy and chlorine radicals, as in reaction la. This vaporization HOCl (gas) - - ~ HO + Cl (la~
is done very rapidly using a fine spray into the hot gas ; in order to evaporate the solution before the equilibrium of equation 13 can shift to give chlorine gas instead of HOCl gas.
1. A.P. Kreshkov, J. Chem. Ind. (U.S.S.R.) 16, No. 4-5, 38-41 (1939) Abstracted in Chemical Abstracts 33, no. 77293 .
' ~6~25 The principal reactions expected as forming some contribu-tion to the gas phase reaction are SO + O ` SO (2) NO + O ~ N02 (3) and similar radical reactions S2 ~~ C12 = SO2C1 2 12 H20 ~ SO3 ~ 2HCl (5) 2NO + C12 = 2NOCl (6) 2NO2 + C12 = 2NO2Cl (7) N02Cl + NO ~ N02 ~ NOCl (8) NOC1 -~ 1/2 2 > NO2 + 1/2 C12 (9) Hg (gas) ~ C12 ~--~HgC12 very fast (10) Metal vapor - chlorine reactions in general are expected to be practically instantaneous and comple-te. Mercury out~
put in the gas stream from this process is expected to be well below acceptable levels.
1'he water phase reactions in this process are very rapid and complete. The ~ollowing reactions are expected.
1~6~ 5 SO3 + H2O ---~ H2SO4 (11) S2 + H2O ~- H2S 3 (12) C12 + H2O ~--~ EICl + HOCl (13) 2N2 + H2O ~ HNO2 + HNO3 slow (14) 2NO + H2O -~ HNO3 ---3 3HNO2 (15) NO2 + 2HCl ---, NOC1 + H2O + ~CL2 (16) NO + NO2 + H2O ~~ 7 2~N2 (17) 2MO -~ 3HCl + HNO3 ---~ 3NOCl + 2H20 (18) NOC1 + H2O ---7 HNO + HCl (l9) NOC1 + C12 + ~2 ~~ ~ HNO3 (20) NO2Cl + H2O ---~ HNO + HCl (21) S2C12 + 2H2 ~ H2 4 (22) H2SO3 ~ HOCl ---~ H SO + HCl (23) HSO32 ~ HOCl ---~ HSO + HCl (24) SO3 + HOC1 ---~ SO + HCl (25) HNO2 ~ HOCl ---~ HNO3 + HCl (26) NO2 ~ HOCl ~ NO3 + HCl (27) NH3 -~ H+ ---~ NH4+Xida-t---onNo- (28) In th~ chlorine removal scrubber, the chlorine and acid vapors are removed from the gas stream. The preferred method is the use of a packed tower of calcium carbonate, dolomite or a similar solid, insoluble and reactive carbonate. This has the advantage of simplicity of design and a relatively low cost.
Other scrubber sy,stems which may be used are countercurrent packed scrubbers or simila-r using a scrubbing solution containing a soluble carbonate, bicarbonate or a h~droxide or a scrubber using a slurry of an insoluble carbonate or slaked lime or calcined dolomite or similar.
, ~8~2S
The effluent of these scrubbers, upon acidification, can be used as feedwater in other sections of the process, after filtering if necessary. The oxidizing power of the chlorine is not lost in this chlorine removal scrubber, but remains in the form of hypochlorlte or hypochlorous acid and upon acidif-ication, chlorine is regenerated as in the equilibrium in equation 13 , and may be returned to the earlier stages of the process.
e - lSa -~ ~6~Z5 The reactions in the chlorine removal scrubber are as follows:
C12 + H20 = HCl + HOCl HOCl or HCl + M2C03 ~ MOCl or MCl + H20 + CO2 HOCl or HCl + 2MOH ~ MOC1 or MCL + 2H20 HOCl or HC1 + 2MHCO3 ~ MOC1 or MC1 + 2H20 + 2C02 The presence of hypochlorite or hypochlorous acid in the re-circulated scrubbing liquid results in an oxidising condition in this scrubber. This results in a contribution to the removal of objectionable components in the gas stream by reactions similar to those of the water phase reactions mentioned earlier.
The e~fluent from the chlorine removal scrubber is mixed with effluent from earlier in the process, containing hydrochloric, sulfuric and nitric acids. The effluent highest in sulphuric acid concentration ls preferred. This acidification regenerates chlorine and precipitates calcium sulfate as in the following e~uations~
CaClOCl + H2S04 ~ Ca~S04(s) -~ HCl + HOCl HCl + HOCl ~ C12 + H20 , , 8~S
` Legend of Large Flue Gas System Illustrated in Figure 1 1. Firebox 2. Stack 3. Addition of Chlorine, etc. followed by the hot section.
4. Quench 5. Venturi and associated cyclone and fan
6. Crossflow gas absorher
7. Crossflow Chlorine absorber
8. CaCO3 to~er ; 9. Cooling Tower 10. Stack reh2~t 11. Flue dust settling and filtration 12. ~ludge washer 13. Collection and silt settllng tank 14. Acid mixing 15. CaSO4 settling and filtration.
16. Chlorine gas removal 17. Chlorine gas removal 18. Demisting 19. CaCo3 addition chute 20 Acid holding tank A. Water Mains B. Chlorine reclaim scrubber effluent C. Venturi cyclone effluent D. Filtered venturi effluent ~.Dechlorinated D and F
E Sludge wash solution H. Dechlorinated B
F. Chlorine scrubber effluent J. Acidified and filtered CaCO3 column effluent.
K. Acid byproduct output.
s Description of Large Flue Gas System The embodiment of figure 1 is an example of a large scale system for the removal of S02 and NOx from flue gas. For handling very large flow rates, parallel units are used at each stage where appropriate, which also gives flexibility in handling varying flow rates, as well as allow,ing the removal of a particular unit from use for servicing without forcing a shutdown of the entire system.
After the firebox 1, the flue gas first enters the hot reaction section 3 where gaseous chlorine is added into the gas. Immediately prior to the chlorine addition, some of the flue gas is diverted to the chlorine sparge sections 16 and 17 where dissolved chlorine is removed from various system solutions by bubbling the hot flue gas through the solutions.
The flue gas now containing chlorine is reunited with the flue gas stream at the point of chlori.ne addition 3. Also at this point effluent solution B from the chlorine reclaim scrubber 7 is added. The flue gas and chlorine mixture passes through the hot reaction section for a time determined by the dimensions of the piping used. The gas then enters a quench 4 of solution B fromthe chlorine reclaim scrubber 7 and recycled quench and venturi solution D for cooling before entering the venturi scrubber 5 for particle removal. The effluent solutions from the quench 4 and venturi scrubber 5 are combined and filtered 11 and the separated flue dust is washed with water from the mains A, mixed 12 with a small amount of limestone or dolomite for residual acid removal, and filtered before disposal.
~68~32S
The wash solution E is used as feedwater for the venturi 5 and first crossflow scrubber6. The filtered effluent solution D
from the venturi scrubber 5 i5 reci~culated to the venturi. A
portion of the filtered solution D is diverted to the flue gas bubbling section 17 for removal of dissolved chlorine followed by disposal to a holding tank 20.
After the venturi scrubber the flue gas enters the first crossflow scrubber 6, which is operated with all of the sections using the same scrubbing liquid source. The effluent solution F from this scrubber is treated in the same fashion as the solution from the venturi scrubber , except with no filtering.
The dechlorinated effluent solution G that is diverted for disposal is placed in holding tank 20.
The flue gas now enters the second crossflow scrubber 7, the chlorine reclaim scrubber, which is operated in a counter-current manner for removal of the majority of chlorine from the gas stream. The effluent solution B from this scrubber is used as feedwater ~or the hot gas section 3, the quench 4, the venturi scrubber 5, and the first crossflow scrubber 6. Any excess solution to these needs is dechlorinated ln the flue gas bubbling section 17 and returned to the chlorine reclaim scrubber 7 for reuse. The feedwater for this scrubber is taken from the water mains A.
The flue gas then enters a scrubber 8 packed with crushed limestone for chlorine removal from the gas stream. The feedwater for this scrubber is taken from the water mains.
- 18a ~-s The effluent solution from this scrubber is filtered 13 to remove unreactive solids such as silica, and rec~cled to the top of the scrubber 8. Some of this solution diverted and mixed 14 with a controlled amount of effluent solution D from the venturi scrubber ro regenerate chlorine. This mixture is filtered 15 to remove calcium sulfate, which is washed in a similar fashion to the treatment of the flue - 18b-~P~8~32~i dust in 12, and then disposed of. The filtered solution is dechlorinated in the flue gas bubbling section 16 and then is used as feedwater J ln the ven-turi 5 and first crossflow scrubber 6.
A cooling -tower 9 is shown in the figure and is used to cool the effluents from the quench 4 and the venturi 5 if necessary. A water cooled heat exchanger is immersed in the tank holding the effluent and the water is circulated to the tower 9 or similar for cooling.
Description of Small Flue Gas System Figure 2 is a diagram of an apparatus for use in a small scale flue gas cleanup system. Flue gas leaving the firebox 1 passes upward through 2 which is a heat exchange section for heating the cleaned effluent gases inside pipe 21 prior to release.
The hot flue gas continues through 3, which contains an air radiating cooling section 4 and is drawn by a blower 5, which forces the gas through the entire system.
The gas then passes through a water cooled condenser 6 which condenses moisture out of the flue gas and brings the gas temperature below 100 C. The moisture is collected in 7 and stored in tank 8, which contains a water cooled heat exchanger for cooling the temperatures to near ambient temperatures.
The condenser and associated components may be omitted in a flue gas system for a low water content flue gas. The condensed water is used for process water and is suplemented with mains water where necessary.
I'he flue gas then enters 9, and is sprayed with the circulating chlorine and acid solution for both temperature reduction and the introduction of chlorine to the incoming flue gas.
The flue gas, at a temperature of 50 to 60 c, then enters the counterflow packed scrubber 10 for reaction of objectionable components with gaseous and dissolved chlorine. Chlorine gas from the cylinders enters the system at 22, within the body of the scrubber. The temperature of the gas entering the scrubber and the gas flow rate are used in the bottom half of the scrubber to partially dechlorinate the effluent solution and to push the chlorine back up into the scrubber.
i ' 8~ZS
The partially dechlorinated effluent solution from both 9 and 10 are collected in tank 11 containing a water cooled heat exchanger for cooling the effluent. A small amount of hot flue gas is bubbled through the solution to remove more free chlorine from the effluent solution. The effluent is taken off continually with a surface siphon to storage tank 12, from which the acid can be shipped for use.
The flue gas, after addition of chlorine at 22, passes up column 10. The^flow of solution down the column gradually removes chlorine from the gas stream. The gas then enters column 13, another packed column, which continues the chlorine removal and also simultaneously continues the oxidation of gas components using available chlorine. The circulating solution in 13 is supplied from either the water mains or from tank 8 and is recirculated from tank 11. After passing through the column 13, the solution is collected in tank 14 and from there is circulated to the top of column 10.
The chlorine in the system is thus concentrated in column 10.
In the top of column 13 is a small demisting section 23 for the removal of acid droplets from the gas stream.
The flue gas is then fed to the bottom of column 15, which is a counter flow column packed with chunks of calcium carbonate, for the removal of acid and chlorine from the gas.
The ciculating solution in column 15 is collected in tank 17 and recirculated to the top of the column. Additional water is provided from the water mains or from tank 8. Insoluble silt is separated at the bottom of 17 and the excess solution is siphoned off to tank 18 for acidification with a controlled amount of solution from tank 11. The calcium sulphate formed is separated by filtration or centrifuging - 20a ~
~6~3~1Z~
in 19 , and is disposed of after subsequent washing and mixing with a small amount of ground calcium carbonate.
The solution leaving 19 contains regenerated chlorine and is added to the solution ~sed in sections 9 and 10.
- 20 b -.
The flue gas then passes through a demisting section 16, and is conducted into the heated stack line 21. The updraft due to the heating of the gas helps drive the gas through the system and eases the blower requirements in the system.
A cooling tower of standard design 20 is shown in the figure and is used to cool the circulating water in the heat exchangers in tanks 8 and 11 and in the condenser 6. The heat radiated from from the system at 4 and 20 may be used for heating or for powering the system fans if desired.
All sections of the sy.stem are of standard design. The only special requirement is corrosion resistance, which means that the packed columns, tanks, pumps, valves and flue lines are to be constructed of suitable palstics. Hot flue lines prior to chlorine addition may be made of conventional materials.
External to the system is a washing apparatus for the purpose of cleaning the s.ilt from 17 and the calcium sulfate from 19;`.
The s~ids are washed with clean water and mixed with a small amount of ground calcium carbonate to remove residual acid before disposal. If the washing and mixing process is performed on site, the acidic solution effluent may be used as system feedwater.
~' .
, - ~3 6~
The appatatus of figure 2 differs from that of figure 1 in a number of ways, re~lecting the versitility of the process.
This apparatus uses no hot chlorine treatment and no attempt is made to collect particulates , as this particular embodiment is intended primarily for use in oil well and refinery flares which have no particulate problems but which have a problem principally with S02. As these flares have a high temperature, high water vapour flue gas, both heat and water vapour recovery are practical, reducing or eliminating need for building heat-ing in winter and for water forsystem operation from an outside source. This small system uses simple , vertical scrubbers made from plastic pipe for economy rather than more complex scrubbers. Unlike the system of figure l the effluent solids from this system are not cleaned as a part of the treatment but are cleaned externally.
As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modificati-ns are possible in the practice of this lnvention without departing from the spirit or scope thereof. Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.
- 21a -
16. Chlorine gas removal 17. Chlorine gas removal 18. Demisting 19. CaCo3 addition chute 20 Acid holding tank A. Water Mains B. Chlorine reclaim scrubber effluent C. Venturi cyclone effluent D. Filtered venturi effluent ~.Dechlorinated D and F
E Sludge wash solution H. Dechlorinated B
F. Chlorine scrubber effluent J. Acidified and filtered CaCO3 column effluent.
K. Acid byproduct output.
s Description of Large Flue Gas System The embodiment of figure 1 is an example of a large scale system for the removal of S02 and NOx from flue gas. For handling very large flow rates, parallel units are used at each stage where appropriate, which also gives flexibility in handling varying flow rates, as well as allow,ing the removal of a particular unit from use for servicing without forcing a shutdown of the entire system.
After the firebox 1, the flue gas first enters the hot reaction section 3 where gaseous chlorine is added into the gas. Immediately prior to the chlorine addition, some of the flue gas is diverted to the chlorine sparge sections 16 and 17 where dissolved chlorine is removed from various system solutions by bubbling the hot flue gas through the solutions.
The flue gas now containing chlorine is reunited with the flue gas stream at the point of chlori.ne addition 3. Also at this point effluent solution B from the chlorine reclaim scrubber 7 is added. The flue gas and chlorine mixture passes through the hot reaction section for a time determined by the dimensions of the piping used. The gas then enters a quench 4 of solution B fromthe chlorine reclaim scrubber 7 and recycled quench and venturi solution D for cooling before entering the venturi scrubber 5 for particle removal. The effluent solutions from the quench 4 and venturi scrubber 5 are combined and filtered 11 and the separated flue dust is washed with water from the mains A, mixed 12 with a small amount of limestone or dolomite for residual acid removal, and filtered before disposal.
~68~32S
The wash solution E is used as feedwater for the venturi 5 and first crossflow scrubber6. The filtered effluent solution D
from the venturi scrubber 5 i5 reci~culated to the venturi. A
portion of the filtered solution D is diverted to the flue gas bubbling section 17 for removal of dissolved chlorine followed by disposal to a holding tank 20.
After the venturi scrubber the flue gas enters the first crossflow scrubber 6, which is operated with all of the sections using the same scrubbing liquid source. The effluent solution F from this scrubber is treated in the same fashion as the solution from the venturi scrubber , except with no filtering.
The dechlorinated effluent solution G that is diverted for disposal is placed in holding tank 20.
The flue gas now enters the second crossflow scrubber 7, the chlorine reclaim scrubber, which is operated in a counter-current manner for removal of the majority of chlorine from the gas stream. The effluent solution B from this scrubber is used as feedwater ~or the hot gas section 3, the quench 4, the venturi scrubber 5, and the first crossflow scrubber 6. Any excess solution to these needs is dechlorinated ln the flue gas bubbling section 17 and returned to the chlorine reclaim scrubber 7 for reuse. The feedwater for this scrubber is taken from the water mains A.
The flue gas then enters a scrubber 8 packed with crushed limestone for chlorine removal from the gas stream. The feedwater for this scrubber is taken from the water mains.
- 18a ~-s The effluent solution from this scrubber is filtered 13 to remove unreactive solids such as silica, and rec~cled to the top of the scrubber 8. Some of this solution diverted and mixed 14 with a controlled amount of effluent solution D from the venturi scrubber ro regenerate chlorine. This mixture is filtered 15 to remove calcium sulfate, which is washed in a similar fashion to the treatment of the flue - 18b-~P~8~32~i dust in 12, and then disposed of. The filtered solution is dechlorinated in the flue gas bubbling section 16 and then is used as feedwater J ln the ven-turi 5 and first crossflow scrubber 6.
A cooling -tower 9 is shown in the figure and is used to cool the effluents from the quench 4 and the venturi 5 if necessary. A water cooled heat exchanger is immersed in the tank holding the effluent and the water is circulated to the tower 9 or similar for cooling.
Description of Small Flue Gas System Figure 2 is a diagram of an apparatus for use in a small scale flue gas cleanup system. Flue gas leaving the firebox 1 passes upward through 2 which is a heat exchange section for heating the cleaned effluent gases inside pipe 21 prior to release.
The hot flue gas continues through 3, which contains an air radiating cooling section 4 and is drawn by a blower 5, which forces the gas through the entire system.
The gas then passes through a water cooled condenser 6 which condenses moisture out of the flue gas and brings the gas temperature below 100 C. The moisture is collected in 7 and stored in tank 8, which contains a water cooled heat exchanger for cooling the temperatures to near ambient temperatures.
The condenser and associated components may be omitted in a flue gas system for a low water content flue gas. The condensed water is used for process water and is suplemented with mains water where necessary.
I'he flue gas then enters 9, and is sprayed with the circulating chlorine and acid solution for both temperature reduction and the introduction of chlorine to the incoming flue gas.
The flue gas, at a temperature of 50 to 60 c, then enters the counterflow packed scrubber 10 for reaction of objectionable components with gaseous and dissolved chlorine. Chlorine gas from the cylinders enters the system at 22, within the body of the scrubber. The temperature of the gas entering the scrubber and the gas flow rate are used in the bottom half of the scrubber to partially dechlorinate the effluent solution and to push the chlorine back up into the scrubber.
i ' 8~ZS
The partially dechlorinated effluent solution from both 9 and 10 are collected in tank 11 containing a water cooled heat exchanger for cooling the effluent. A small amount of hot flue gas is bubbled through the solution to remove more free chlorine from the effluent solution. The effluent is taken off continually with a surface siphon to storage tank 12, from which the acid can be shipped for use.
The flue gas, after addition of chlorine at 22, passes up column 10. The^flow of solution down the column gradually removes chlorine from the gas stream. The gas then enters column 13, another packed column, which continues the chlorine removal and also simultaneously continues the oxidation of gas components using available chlorine. The circulating solution in 13 is supplied from either the water mains or from tank 8 and is recirculated from tank 11. After passing through the column 13, the solution is collected in tank 14 and from there is circulated to the top of column 10.
The chlorine in the system is thus concentrated in column 10.
In the top of column 13 is a small demisting section 23 for the removal of acid droplets from the gas stream.
The flue gas is then fed to the bottom of column 15, which is a counter flow column packed with chunks of calcium carbonate, for the removal of acid and chlorine from the gas.
The ciculating solution in column 15 is collected in tank 17 and recirculated to the top of the column. Additional water is provided from the water mains or from tank 8. Insoluble silt is separated at the bottom of 17 and the excess solution is siphoned off to tank 18 for acidification with a controlled amount of solution from tank 11. The calcium sulphate formed is separated by filtration or centrifuging - 20a ~
~6~3~1Z~
in 19 , and is disposed of after subsequent washing and mixing with a small amount of ground calcium carbonate.
The solution leaving 19 contains regenerated chlorine and is added to the solution ~sed in sections 9 and 10.
- 20 b -.
The flue gas then passes through a demisting section 16, and is conducted into the heated stack line 21. The updraft due to the heating of the gas helps drive the gas through the system and eases the blower requirements in the system.
A cooling tower of standard design 20 is shown in the figure and is used to cool the circulating water in the heat exchangers in tanks 8 and 11 and in the condenser 6. The heat radiated from from the system at 4 and 20 may be used for heating or for powering the system fans if desired.
All sections of the sy.stem are of standard design. The only special requirement is corrosion resistance, which means that the packed columns, tanks, pumps, valves and flue lines are to be constructed of suitable palstics. Hot flue lines prior to chlorine addition may be made of conventional materials.
External to the system is a washing apparatus for the purpose of cleaning the s.ilt from 17 and the calcium sulfate from 19;`.
The s~ids are washed with clean water and mixed with a small amount of ground calcium carbonate to remove residual acid before disposal. If the washing and mixing process is performed on site, the acidic solution effluent may be used as system feedwater.
~' .
, - ~3 6~
The appatatus of figure 2 differs from that of figure 1 in a number of ways, re~lecting the versitility of the process.
This apparatus uses no hot chlorine treatment and no attempt is made to collect particulates , as this particular embodiment is intended primarily for use in oil well and refinery flares which have no particulate problems but which have a problem principally with S02. As these flares have a high temperature, high water vapour flue gas, both heat and water vapour recovery are practical, reducing or eliminating need for building heat-ing in winter and for water forsystem operation from an outside source. This small system uses simple , vertical scrubbers made from plastic pipe for economy rather than more complex scrubbers. Unlike the system of figure l the effluent solids from this system are not cleaned as a part of the treatment but are cleaned externally.
As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modificati-ns are possible in the practice of this lnvention without departing from the spirit or scope thereof. Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.
- 21a -
Claims (24)
1. A method of purifying a hot flue gas stream involving the oxidation and removal of sulfur oxides, nitrogen oxides, and other oxidizable components from the hot flue gas stream comprising treating the hot flue gas stream in the following sequential manner:
(a) injecting chlorine into the hot flue gas stream;
(b) quenching the hot gas stream with a cooling quench of water;
(c) passing the quenched stream through a first gas absorbing scrubber;
(d) passing the stream from the first scrubber through a second gas absorbing scrubber; and (e) passing the stream from the second scrubber through a chlorine removing scrubber.
(a) injecting chlorine into the hot flue gas stream;
(b) quenching the hot gas stream with a cooling quench of water;
(c) passing the quenched stream through a first gas absorbing scrubber;
(d) passing the stream from the first scrubber through a second gas absorbing scrubber; and (e) passing the stream from the second scrubber through a chlorine removing scrubber.
2. A process according to Claim 1 wherein the hot flue gas stream is passed through a dry electrostatic precipitator before being injected with chlorine.
3. A process according to Claim 1 wherein the hot flue gas stream is injected with chlorine in combination with other gas treating chemicals.
4. A process according to Claim 1 wherein the quench solution is water containing dissolved hydrochloric acid or nitric acid.
- Page 1 of Claims -
- Page 1 of Claims -
5. A process according to Claim 1 wherein the quenched hot gas stream is passed through a high energy scrubber for particle removal before being passed through the first gas absorbing scrubber.
6. A process according to Claim 1 wherein the stream after it passes through the chlorine removing scrubber is passed through a demister.
7. A process according to Claim 5 wherein the high energy scrubber is a high pressure venturi type.
8. A process according to Claim 5 wherein the scrubbing liquid from the high energy scrubber is recirculated to a relatively high acid concentration.
9. A process according to Claim 1, 2 or 3 wherein the scrubbing liquid used in the scrubbers has therein added dissolved chlorine.
10. A process according to Claim 1 wherein the first scrubber is a packed scrubber.
11. A process according to Claim 1, 2 or 3 wherein gaseous chlorine is added to the input or interior of the first scrubber.
12. A process according to Claim 1, 2 or 3 wherein the scrubbing water solution from the first scrubber is recirculated to a relatively high acid concentration.
13. A process according to Claim 1, 2 or 3 wherein the scrubbing liquid for the first scrubber has therein added dissolved chlorine.
14. A process according to Claim 1, 2 or 3 wherein the second gas absorbing scrubber is a packed scrubber.
15. A process according to Claim 1, 2 or 3 wherein recirculation of the second scrubber solution is kept to a minimum to maximize the absorption of chlorine.
- Page 2 of Claims -
- Page 2 of Claims -
16. A process according to Claim 1, 2 or 3 wherein dissolved chlorine in acidized effluent generated in the process is blown out of solution using air, inert gas or flue gas and the resulting mixture is added in step (a).
17. A process according to Claim 1 for use in the removal of oxidizable components from a cool, non-flue gas source for purposes of deodorization and sterilization of air, wherein steps (a) and (b) are omitted, and the gas is cool.
18. A process according to Claim 1, 2 or 3 wherein the temperature of the hot flue gas stream to be treated is greater than 100°C.
19. A process according to Claim 1 wherein one or more of the components selected from the following group of components is injected into the gas stream in addition to the chlorine:
(a) air;
(b) an inert gas;
(c) a mixture of air, or inert gas, or flue gas, and chlorine;
(d) a mixture of air, or inert gas, or flue gas, chlorine, with hydrochloric and/or nitric acid vapors;
(e) liquid water;
(f) a water solution of chlorine containing hydrochloric and/or nitric acid; and (g) a water solution of hydrochloric and/or nitric acid.
(a) air;
(b) an inert gas;
(c) a mixture of air, or inert gas, or flue gas, and chlorine;
(d) a mixture of air, or inert gas, or flue gas, chlorine, with hydrochloric and/or nitric acid vapors;
(e) liquid water;
(f) a water solution of chlorine containing hydrochloric and/or nitric acid; and (g) a water solution of hydrochloric and/or nitric acid.
20. A process according to Claim 1 wherein the chlorine moving scrubber incorporates alkaline earth - Page 3 of Claims -carbonate and an acid solution is added to water effluent from the scrubber to regenerate chlorine and hypochlorous acid.
21. A process according to Claim 1 wherein the chlorine removing scrubber incorporates calcium carbonate, dolomite, or a mixture thereof.
22. A process according to Claim 1 wherein the chlorine removing scrubber incorporates sodium carbonate, sodium bicarbonate, or a mixture thereof.
23. A process according to Claim 1 wherein the chlorine removing scrubber incorporates sodium hydroxide or calcium hydroxide, or a mixture thereof.
24. A process according to Claim 1 wherein the chlorine removing scrubber incorporates a slurry of slaked lime, slaked calcined dolomite, or slaked calcined alkaline earth metal carbonate.
- Page 4 of Claims -
- Page 4 of Claims -
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000357471A CA1168025A (en) | 1980-08-01 | 1980-08-01 | Process for removal of pollutants from waste gas emissions |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000357471A CA1168025A (en) | 1980-08-01 | 1980-08-01 | Process for removal of pollutants from waste gas emissions |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1168025A true CA1168025A (en) | 1984-05-29 |
Family
ID=4117554
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000357471A Expired CA1168025A (en) | 1980-08-01 | 1980-08-01 | Process for removal of pollutants from waste gas emissions |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1168025A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0220075A2 (en) * | 1985-10-18 | 1987-04-29 | Isca Management Limited | Process for removal of pollutants from waste gas emissions |
| DE3925984A1 (en) * | 1989-08-05 | 1991-02-07 | Metallgesellschaft Ag | Hot waste gas desulphurisation - by cooling, reaction with chlorine in static mixer and absorption |
| DE4304193C1 (en) * | 1993-02-12 | 1994-05-05 | Noell Gmbh | Process to wash acid components out of waste gases - by absorption with washing fluid passed briefly through two packed vessels through which smoke rises |
-
1980
- 1980-08-01 CA CA000357471A patent/CA1168025A/en not_active Expired
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0220075A2 (en) * | 1985-10-18 | 1987-04-29 | Isca Management Limited | Process for removal of pollutants from waste gas emissions |
| EP0220075A3 (en) * | 1985-10-18 | 1988-10-05 | Isca Management Limited | Process for removal of pollutants from waste gas emissions |
| DE3925984A1 (en) * | 1989-08-05 | 1991-02-07 | Metallgesellschaft Ag | Hot waste gas desulphurisation - by cooling, reaction with chlorine in static mixer and absorption |
| DE4304193C1 (en) * | 1993-02-12 | 1994-05-05 | Noell Gmbh | Process to wash acid components out of waste gases - by absorption with washing fluid passed briefly through two packed vessels through which smoke rises |
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