CA2030042C - Apparatus to remove acid gases from a flue gas - Google Patents
Apparatus to remove acid gases from a flue gas Download PDFInfo
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- CA2030042C CA2030042C CA 2030042 CA2030042A CA2030042C CA 2030042 C CA2030042 C CA 2030042C CA 2030042 CA2030042 CA 2030042 CA 2030042 A CA2030042 A CA 2030042A CA 2030042 C CA2030042 C CA 2030042C
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- gas
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- inlet
- reaction tower
- gases
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- 239000007789 gas Substances 0.000 title claims abstract description 88
- 239000003546 flue gas Substances 0.000 title claims abstract description 16
- 239000002253 acid Substances 0.000 title claims abstract description 15
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 title claims abstract description 13
- 238000006243 chemical reaction Methods 0.000 claims abstract description 48
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims abstract description 28
- 230000003647 oxidation Effects 0.000 claims abstract description 23
- 238000007254 oxidation reaction Methods 0.000 claims abstract description 23
- 150000007514 bases Chemical class 0.000 claims abstract description 21
- RAHZWNYVWXNFOC-UHFFFAOYSA-N Sulphur dioxide Chemical compound O=S=O RAHZWNYVWXNFOC-UHFFFAOYSA-N 0.000 claims abstract description 20
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 14
- 238000000034 method Methods 0.000 claims abstract description 13
- 239000007788 liquid Substances 0.000 claims abstract description 12
- 230000001590 oxidative effect Effects 0.000 claims abstract description 11
- 235000010269 sulphur dioxide Nutrition 0.000 claims abstract description 10
- 239000004291 sulphur dioxide Substances 0.000 claims abstract description 10
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 claims abstract description 7
- 239000005864 Sulphur Substances 0.000 claims abstract description 7
- 238000005201 scrubbing Methods 0.000 claims abstract description 5
- 239000007787 solid Substances 0.000 claims description 12
- 150000001875 compounds Chemical class 0.000 claims description 11
- 230000007935 neutral effect Effects 0.000 claims description 6
- 150000003839 salts Chemical class 0.000 claims description 5
- AXCZMVOFGPJBDE-UHFFFAOYSA-L calcium dihydroxide Chemical compound [OH-].[OH-].[Ca+2] AXCZMVOFGPJBDE-UHFFFAOYSA-L 0.000 claims description 4
- 239000000920 calcium hydroxide Substances 0.000 claims description 4
- 229910001861 calcium hydroxide Inorganic materials 0.000 claims description 4
- 239000002002 slurry Substances 0.000 claims description 3
- 239000000725 suspension Substances 0.000 claims description 2
- 238000001816 cooling Methods 0.000 claims 1
- 238000004064 recycling Methods 0.000 claims 1
- ZCCIPPOKBCJFDN-UHFFFAOYSA-N calcium nitrate Chemical compound [Ca+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O ZCCIPPOKBCJFDN-UHFFFAOYSA-N 0.000 description 12
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 description 8
- AKEJUJNQAAGONA-UHFFFAOYSA-N sulfur trioxide Chemical compound O=S(=O)=O AKEJUJNQAAGONA-UHFFFAOYSA-N 0.000 description 8
- 238000004519 manufacturing process Methods 0.000 description 7
- OSGAYBCDTDRGGQ-UHFFFAOYSA-L calcium sulfate Chemical compound [Ca+2].[O-]S([O-])(=O)=O OSGAYBCDTDRGGQ-UHFFFAOYSA-L 0.000 description 6
- MWUXSHHQAYIFBG-UHFFFAOYSA-N nitrogen oxide Inorganic materials O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 6
- 238000003916 acid precipitation Methods 0.000 description 5
- 239000003595 mist Substances 0.000 description 4
- 235000011132 calcium sulphate Nutrition 0.000 description 3
- 239000003337 fertilizer Substances 0.000 description 3
- 229910052602 gypsum Inorganic materials 0.000 description 3
- 239000010440 gypsum Substances 0.000 description 3
- 230000008569 process Effects 0.000 description 3
- 239000000779 smoke Substances 0.000 description 3
- IOVCWXUNBOPUCH-UHFFFAOYSA-M Nitrite anion Chemical compound [O-]N=O IOVCWXUNBOPUCH-UHFFFAOYSA-M 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- 150000007513 acids Chemical class 0.000 description 2
- 239000001175 calcium sulphate Substances 0.000 description 2
- 230000007613 environmental effect Effects 0.000 description 2
- 239000001117 sulphuric acid Substances 0.000 description 2
- 235000011149 sulphuric acid Nutrition 0.000 description 2
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 230000003197 catalytic effect Effects 0.000 description 1
- 239000007795 chemical reaction product Substances 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 150000004683 dihydrates Chemical class 0.000 description 1
- 238000002845 discoloration Methods 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
- 239000012286 potassium permanganate Substances 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 239000010935 stainless steel Substances 0.000 description 1
- XTQHKBHJIVJGKJ-UHFFFAOYSA-N sulfur monoxide Chemical class S=O XTQHKBHJIVJGKJ-UHFFFAOYSA-N 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
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- Treating Waste Gases (AREA)
Abstract
Apparatus and method to remove acid gases from a flue gas containing sulphur dioxide and oxides of nitrogen. The apparatus includes a heat exchanger to reduce incoming flue gas temperatures. An oxidation chamber receives gases from the heat exchanger and oxidises the oxide of sulphur and nitrogen in the flue gases to the highest valency state. A reaction tower receives gases from the oxidizing chamber. The reaction tower includes a reaction surface. There is a first inlet for gas adjacent the base of the reaction tower and a second inlet for a basic compound in the reaction tower, above the first inlet. This arrangement allows counter-current flow of the gas and the basic compound to enable scrubbing of the gas. There is an outlet for scrubbed gases and an outlet for liquids at the tower base.
Description
APPARATUS TO REMOVE ACID GASES FROM A FLUE GAS
This invention relates to wn apparatus to remove acid gases from a flue gas containing sulphur dioxide and oxides of nitrogen.
Acid rain is now considered a problem throughout the world. In the north eastern United States, in eastern Canada, particularly southern Ontario, and in virtually all of western Europe, the production of acid rain is a major problem, affecting the environment through poor air quality, acid lakes and the killing of the vegetation, particularly trees, by acid.
In the main, the problem stems from sulphur dioxide production in smoke stacks. Sulphur dioxide is subsequently oxidised in the atmosphere to sulphur trioxide, which forms sulphuric acid on dissolving in water. The oxides of nitrogen also are a factor in producing nitric acid in the atmosphere but the problem is less pronounced.
There have been large numbers of suggestions to curb acid rain. In general, international agreements are required because the smoke stacks put gases into the atmosphere at substantial heights and the acid gases are then moved in the atmosphere over considerable distances.
For example, Canada has complained to the United States concerning acid rain and, in Europe, Britain is blamed by several Scandinavian countries for acid rain in those countries.
No effective solution is yet widely available and there is clearly a demand for a solution to this problem.
The present invention provides an apparatus that is simple to operate and to make and uses relatively simple chemical reactions to curb acidity at the point of production, that is prior to emission of the exhaust gases into the atmosphere through smoke stacks.
Accordingly, in its broadest aspect, the present invention provides an apparatus to remove acid gases from a flue gas containing sulphur dioxide and oxides of nitrogen, the apparatus consisting essentially of, in sequence:
a heat exchanger to reduce flue gas temperatures;
an oxidation chamber to receive gases from the heat exchanger and to oxidize the oxides of sulphur and nitrogen in the flue gases to the highest valency state, said oxidation chamber comprising a plurality of corrugated sheets to increase internal surface area;
a reaction tower to receive gases from the oxidizing chamber;
a first pump prior to the oxidation chamber and a second pump prior to the reaction tower to assist gas flow in the apparatus;
means within the reaction tower to define a reaction surface;
said reaction tower including a first inlet for gas adjacent its base;
a second inlet for a basic compound in the reaction tower, above the first inlet, to allow counter current flow of the gas and the basic compound to scrub the gas;
an outlet for scrubbed gases;
the reaction tower including a conduit extending from the top of the reaction tower to the outlet for scrubbed gases, adjacent the tower base, whereby gas passed up the tower to be scrubbed then down the conduit to the outlet for scrubbed gases;
the second inlet being a pipe surrounding the conduit;
a third inlet surrounding the conduit to allow introduction of an oxidizing compound to ensure complete oxidation of gasses in the tower;
-2a -a pipe to recycle gas from the base of the tower to a fourth inlet in the tower whereby a second scrubbing of the gas may be carried out;
means to cool the recycled gas in the pipe, and an outlet for liquids at the tower base;
the outlet for liquids communicating with a liquid/-solid separator to separate solution and slurry solids.
In a further aspect, the invention provides a method of removing an acid gas from a flue gas containing a sulphur dioxide and oxides of nitrogen, the method comprising:
reducing the flue gas temperature in a heat exchanger to a temperature of about 65°C.;
oxidizing the gas from the heat exchanger in an oxidation chamber containing a plurality of corrugated sheets to increase the internal surface area, the gas being oxidized in the oxidation chamber so that the oxides of sulphur and nitrogen are in their highest valency states;
conducting the gas from the oxidation chamber to a reaction tower and introducing the gas into the reaction tower through a first inlet, adjacent the base of the reaction tower;
introducing a solution of a basic compound into the reaction tower through a second inlet, above the first inlet, and allowing the solution of the basic compound to flow counter-current to the gas to neutralize the acid components in the gas to produce a neutralized gas;
directing the neutralized gas into a conduit extending from the top of the reaction tower to an outlet for neutralized gas adjacent the base of the tower whereby gas passes up the tower, acid compounds are neutralized by a counter-current flow of the basic compound, then pass down the conduit to the outlet;
collecting a suspension comprising a solution of neutral, soluble salts and neutral insoluble salts, at the base of the reaction tower; and 2b separating the solids from the liquid in a liquid/solid separator.
The invention is illustrated in the drawing which is diagram of an apparatus according to the present invention.
'c The drawing shows, diagrammatically, a filter house containing conventional filter bags (not shown) in which solids are removed from an exhaust gas that enters through inlet 12. The gas is then fed through a heat 5 exchanger 14 where heat is extracted. Typically the temperature reduction is from about 250°C to about 65°C.
The gas is then pumped by blower 16 to an oxidation chamber 18 where the sulphur oxides and nitrogen oxides in the gas are oxidized to their highest valency state.
10 For example, the predominant oxide of sulphur in the exhaust gas will be sulphur dioxide but sulphur trioxide is a much more reactive gas and in the oxidation chamber 18 the sulphur dioxide will be oxidized to sulphur trioxide by a mechanism involving nitrogen oxides.
Typically the oxidizing chamber will include a plurality of corrugated sheets 20 to increase the internal surface area. The sheets may be of stainless steel or of lead. In any event a catalytic oxidation of the oxides of nitrogen and sulphur, particularly the latter, to the highest valency state takes place.
Gases from the oxidation chamber 18 are pumped by pump 22 to a reaction tower 24 where they may be reacted to substantially eliminate the environmentally unacceptable compounds.
The reaction tower 24 has a base 25 and a first inlet 26 for gas adjacent base 25. There are means within the reaction tower 24 to define a reaction surface. For example, the reaction tower 24 may be packed with tile or with Raschig rings or, indeed, any chemically inert material that simply functions to increase surface area and thus the area at which reactions can take place. The reaction tower 24 includes a second inlet 28 for a basic compound, above the first r...
This invention relates to wn apparatus to remove acid gases from a flue gas containing sulphur dioxide and oxides of nitrogen.
Acid rain is now considered a problem throughout the world. In the north eastern United States, in eastern Canada, particularly southern Ontario, and in virtually all of western Europe, the production of acid rain is a major problem, affecting the environment through poor air quality, acid lakes and the killing of the vegetation, particularly trees, by acid.
In the main, the problem stems from sulphur dioxide production in smoke stacks. Sulphur dioxide is subsequently oxidised in the atmosphere to sulphur trioxide, which forms sulphuric acid on dissolving in water. The oxides of nitrogen also are a factor in producing nitric acid in the atmosphere but the problem is less pronounced.
There have been large numbers of suggestions to curb acid rain. In general, international agreements are required because the smoke stacks put gases into the atmosphere at substantial heights and the acid gases are then moved in the atmosphere over considerable distances.
For example, Canada has complained to the United States concerning acid rain and, in Europe, Britain is blamed by several Scandinavian countries for acid rain in those countries.
No effective solution is yet widely available and there is clearly a demand for a solution to this problem.
The present invention provides an apparatus that is simple to operate and to make and uses relatively simple chemical reactions to curb acidity at the point of production, that is prior to emission of the exhaust gases into the atmosphere through smoke stacks.
Accordingly, in its broadest aspect, the present invention provides an apparatus to remove acid gases from a flue gas containing sulphur dioxide and oxides of nitrogen, the apparatus consisting essentially of, in sequence:
a heat exchanger to reduce flue gas temperatures;
an oxidation chamber to receive gases from the heat exchanger and to oxidize the oxides of sulphur and nitrogen in the flue gases to the highest valency state, said oxidation chamber comprising a plurality of corrugated sheets to increase internal surface area;
a reaction tower to receive gases from the oxidizing chamber;
a first pump prior to the oxidation chamber and a second pump prior to the reaction tower to assist gas flow in the apparatus;
means within the reaction tower to define a reaction surface;
said reaction tower including a first inlet for gas adjacent its base;
a second inlet for a basic compound in the reaction tower, above the first inlet, to allow counter current flow of the gas and the basic compound to scrub the gas;
an outlet for scrubbed gases;
the reaction tower including a conduit extending from the top of the reaction tower to the outlet for scrubbed gases, adjacent the tower base, whereby gas passed up the tower to be scrubbed then down the conduit to the outlet for scrubbed gases;
the second inlet being a pipe surrounding the conduit;
a third inlet surrounding the conduit to allow introduction of an oxidizing compound to ensure complete oxidation of gasses in the tower;
-2a -a pipe to recycle gas from the base of the tower to a fourth inlet in the tower whereby a second scrubbing of the gas may be carried out;
means to cool the recycled gas in the pipe, and an outlet for liquids at the tower base;
the outlet for liquids communicating with a liquid/-solid separator to separate solution and slurry solids.
In a further aspect, the invention provides a method of removing an acid gas from a flue gas containing a sulphur dioxide and oxides of nitrogen, the method comprising:
reducing the flue gas temperature in a heat exchanger to a temperature of about 65°C.;
oxidizing the gas from the heat exchanger in an oxidation chamber containing a plurality of corrugated sheets to increase the internal surface area, the gas being oxidized in the oxidation chamber so that the oxides of sulphur and nitrogen are in their highest valency states;
conducting the gas from the oxidation chamber to a reaction tower and introducing the gas into the reaction tower through a first inlet, adjacent the base of the reaction tower;
introducing a solution of a basic compound into the reaction tower through a second inlet, above the first inlet, and allowing the solution of the basic compound to flow counter-current to the gas to neutralize the acid components in the gas to produce a neutralized gas;
directing the neutralized gas into a conduit extending from the top of the reaction tower to an outlet for neutralized gas adjacent the base of the tower whereby gas passes up the tower, acid compounds are neutralized by a counter-current flow of the basic compound, then pass down the conduit to the outlet;
collecting a suspension comprising a solution of neutral, soluble salts and neutral insoluble salts, at the base of the reaction tower; and 2b separating the solids from the liquid in a liquid/solid separator.
The invention is illustrated in the drawing which is diagram of an apparatus according to the present invention.
'c The drawing shows, diagrammatically, a filter house containing conventional filter bags (not shown) in which solids are removed from an exhaust gas that enters through inlet 12. The gas is then fed through a heat 5 exchanger 14 where heat is extracted. Typically the temperature reduction is from about 250°C to about 65°C.
The gas is then pumped by blower 16 to an oxidation chamber 18 where the sulphur oxides and nitrogen oxides in the gas are oxidized to their highest valency state.
10 For example, the predominant oxide of sulphur in the exhaust gas will be sulphur dioxide but sulphur trioxide is a much more reactive gas and in the oxidation chamber 18 the sulphur dioxide will be oxidized to sulphur trioxide by a mechanism involving nitrogen oxides.
Typically the oxidizing chamber will include a plurality of corrugated sheets 20 to increase the internal surface area. The sheets may be of stainless steel or of lead. In any event a catalytic oxidation of the oxides of nitrogen and sulphur, particularly the latter, to the highest valency state takes place.
Gases from the oxidation chamber 18 are pumped by pump 22 to a reaction tower 24 where they may be reacted to substantially eliminate the environmentally unacceptable compounds.
The reaction tower 24 has a base 25 and a first inlet 26 for gas adjacent base 25. There are means within the reaction tower 24 to define a reaction surface. For example, the reaction tower 24 may be packed with tile or with Raschig rings or, indeed, any chemically inert material that simply functions to increase surface area and thus the area at which reactions can take place. The reaction tower 24 includes a second inlet 28 for a basic compound, above the first r...
inlet 26. This allows a basic compound to flow counter-current to the gas flow and the basic compound therefore scrubs the gas by reacting with the acidic compounds in the gas to produce neutral salts. In a particularly preferred embodiment the basic compound is calcium hydroxide which produces calcium nitrate by reaction with the oxides of nitrogen and calcium sulfate by reaction with sulphuric acid produced from sulphur trioxide. Both these compounds are chemically neutral and, in particular, are of environmental value as a fertilizer in the case of calcium nitrate and as a means of producing wall board in the case of the dihydrate of calcium sulphate, also known as gypsum.
There is an outlet 30 for scrubbed gases. In the illustrated embodiment the reaction tower 24 includes a conduit 32 extending from the top of the reactor tower to the second outlet 30, adjacent the tower base. Gases pass up the tower 24 to be scrubbed then down the conduit 32 to the outlet 30. In this arrangement the basic compound, for example calcium hydroxide, is dripped or sprayed through an inlet pipe 34 surrounding the conduit 32 and receiving the basic compound from inlet 28.
In the illustrated embodiment an inlet 36 for an oxidizing compound is shown. The inlet 36 feeds to an annulus 38 surrounding the conduit 32. The oxidizing compound ensures complete oxidation of gases that may not have been oxidized completely in the oxidation chamber 18. In a preferred embodiment a solution of hydrogen peroxide may be used.
There is a further inlet 40, above the inlet 28 for the basic compound, where additional basic compound may be fed to annulus 42, if required.
s _5 _ There is a mist eliminator 44 within the tower. In the illustrated embodiment the mist eliminator 44 is a disc surrounding the upper end of the conduit 32 and having a large number of perforations. It is desirable to avoid mist production in the process. Mist is itself an environmental hazard that reduces air quality.
The base 25 of the reaction tower 24 receives the reaction products produced in the tower and communicates with a liquid/solid separator 46 that separates the solution and slurry solids. The solution, a solution of calcium nitrate in the preferred embodiment, is fed to a tank 48 and the solids, typically insoluble calcium sulphate, are fed to a vessel 50.
The illustrated embodiment includes pipe 52 to recycle gas from the base 25 of the tower 24 to an inlet 54 in the tower to ensure that complete scrubbing of the gas may be carried out. The pipe 52 includes a pump 56 and also a heat exchanger 58 to cool the recycled gas.
The extraction of heat from industrial processes is always desirable. It may facilitate the reaction, but it is also a desirable source of heat which, otherwise, would simply be vented to the atmosphere. Inlet 54 communicates with an annulus through which recycled gas is fed back into tower 24.
The apparatus may be extensively monitored. It is envisaged that the calcium nitrate may be used directly as a fertilizer and sold to the public in the form in which it is received in the tank 48. To this end, it is desirable to monitor constantly the specific gravity of the calcium nitrate solution. The pH of the process should also be monitored to ensure proper gypsum production.
The necessity of adding hydrogen peroxide may be detected by testing the oxidation potential of the contents of the reaction chamber 24. For example if nitrite is present then contact with potassium permanganate solution will show the presence of nitrite by discoloration of the permanganate solution. In those circumstances, hydrogen peroxide, or additional hydrogen peroxide, can be fed through inlet annulus 38.
The present invention thus provides an apparatus that can be added to existing plants at relatively minor cost. The apparatus is effective in removing the vast majority of acidic compounds from exhaust gases, which is in itself desirable, but the process has the additional advantage of producing industrially useful compounds.
Calcium nitrate is a valuable fertilizer; gypsum is a valuable industrial compound, useful in the production of wall board.
Although the forgoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it will be readily apparent to those of ordinary skill in the art in light of the teachings of this invention that certain changes and modifications may be made thereto without departing from the spirit or scope of the appended claims.
-..
There is an outlet 30 for scrubbed gases. In the illustrated embodiment the reaction tower 24 includes a conduit 32 extending from the top of the reactor tower to the second outlet 30, adjacent the tower base. Gases pass up the tower 24 to be scrubbed then down the conduit 32 to the outlet 30. In this arrangement the basic compound, for example calcium hydroxide, is dripped or sprayed through an inlet pipe 34 surrounding the conduit 32 and receiving the basic compound from inlet 28.
In the illustrated embodiment an inlet 36 for an oxidizing compound is shown. The inlet 36 feeds to an annulus 38 surrounding the conduit 32. The oxidizing compound ensures complete oxidation of gases that may not have been oxidized completely in the oxidation chamber 18. In a preferred embodiment a solution of hydrogen peroxide may be used.
There is a further inlet 40, above the inlet 28 for the basic compound, where additional basic compound may be fed to annulus 42, if required.
s _5 _ There is a mist eliminator 44 within the tower. In the illustrated embodiment the mist eliminator 44 is a disc surrounding the upper end of the conduit 32 and having a large number of perforations. It is desirable to avoid mist production in the process. Mist is itself an environmental hazard that reduces air quality.
The base 25 of the reaction tower 24 receives the reaction products produced in the tower and communicates with a liquid/solid separator 46 that separates the solution and slurry solids. The solution, a solution of calcium nitrate in the preferred embodiment, is fed to a tank 48 and the solids, typically insoluble calcium sulphate, are fed to a vessel 50.
The illustrated embodiment includes pipe 52 to recycle gas from the base 25 of the tower 24 to an inlet 54 in the tower to ensure that complete scrubbing of the gas may be carried out. The pipe 52 includes a pump 56 and also a heat exchanger 58 to cool the recycled gas.
The extraction of heat from industrial processes is always desirable. It may facilitate the reaction, but it is also a desirable source of heat which, otherwise, would simply be vented to the atmosphere. Inlet 54 communicates with an annulus through which recycled gas is fed back into tower 24.
The apparatus may be extensively monitored. It is envisaged that the calcium nitrate may be used directly as a fertilizer and sold to the public in the form in which it is received in the tank 48. To this end, it is desirable to monitor constantly the specific gravity of the calcium nitrate solution. The pH of the process should also be monitored to ensure proper gypsum production.
The necessity of adding hydrogen peroxide may be detected by testing the oxidation potential of the contents of the reaction chamber 24. For example if nitrite is present then contact with potassium permanganate solution will show the presence of nitrite by discoloration of the permanganate solution. In those circumstances, hydrogen peroxide, or additional hydrogen peroxide, can be fed through inlet annulus 38.
The present invention thus provides an apparatus that can be added to existing plants at relatively minor cost. The apparatus is effective in removing the vast majority of acidic compounds from exhaust gases, which is in itself desirable, but the process has the additional advantage of producing industrially useful compounds.
Calcium nitrate is a valuable fertilizer; gypsum is a valuable industrial compound, useful in the production of wall board.
Although the forgoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it will be readily apparent to those of ordinary skill in the art in light of the teachings of this invention that certain changes and modifications may be made thereto without departing from the spirit or scope of the appended claims.
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Claims (8)
1. Apparatus to remove acid gases from a flue gas containing sulphur dioxide and oxides of nitrogen, the apparatus consisting essentially of, in sequence:
a heat exchanger to reduce flue gas temperatures;
an oxidation chamber to receive gases from the heat exchanger and to oxidize the oxides of sulphur and nitrogen in the flue gases to the highest valency state, said oxidation chamber comprising a plurality of corrugated sheets to increase internal surface area;
a reaction tower to receive gases from the oxidizing chamber;
a first pump prior to the oxidation chamber and a second pump prior to the reaction tower to assist gas flow in the apparatus;
means within the reaction tower to define a reaction surface;
said reaction tower including a first inlet for gas adjacent its base;
a second inlet for a basic compound in the reaction tower, above the first inlet, to allow counter current flow of the gas and the basic compound to scrub the gas;
an outlet for scrubbed gases;
the reaction tower including a conduit extending from the top of the reaction tower to the outlet for scrubbed gases, adjacent the tower base, whereby gas passes up the tower to be scrubbed then down the conduit to the outlet for scrubbed gases;
the second inlet being a pipe surrounding the conduit;
a third inlet surrounding the conduit to allow introduction of an oxidizing compound to ensure complete oxidation of gases in the tower;
a pipe to recycle gas from the base of the tower to a fourth inlet in the tower whereby a second scrubbing of the gas may be carried out;
means to cool the recycled gas in the pipe, and an outlet for liquids at the tower base;
the outlet for liquids communicating with a liquid/solid separator to separate solution and slurry solids.
a heat exchanger to reduce flue gas temperatures;
an oxidation chamber to receive gases from the heat exchanger and to oxidize the oxides of sulphur and nitrogen in the flue gases to the highest valency state, said oxidation chamber comprising a plurality of corrugated sheets to increase internal surface area;
a reaction tower to receive gases from the oxidizing chamber;
a first pump prior to the oxidation chamber and a second pump prior to the reaction tower to assist gas flow in the apparatus;
means within the reaction tower to define a reaction surface;
said reaction tower including a first inlet for gas adjacent its base;
a second inlet for a basic compound in the reaction tower, above the first inlet, to allow counter current flow of the gas and the basic compound to scrub the gas;
an outlet for scrubbed gases;
the reaction tower including a conduit extending from the top of the reaction tower to the outlet for scrubbed gases, adjacent the tower base, whereby gas passes up the tower to be scrubbed then down the conduit to the outlet for scrubbed gases;
the second inlet being a pipe surrounding the conduit;
a third inlet surrounding the conduit to allow introduction of an oxidizing compound to ensure complete oxidation of gases in the tower;
a pipe to recycle gas from the base of the tower to a fourth inlet in the tower whereby a second scrubbing of the gas may be carried out;
means to cool the recycled gas in the pipe, and an outlet for liquids at the tower base;
the outlet for liquids communicating with a liquid/solid separator to separate solution and slurry solids.
2. Apparatus as claimed in claim 1 including a pump in the pipe to the fourth inlet to facilitate flow of the recycled gas.
3. A method of removing an acid gas from a flue gas containing a sulphur dioxide and oxides of nitrogen, the method comprising:
reducing the flue gas temperature in a heat exchanger to a temperature of about 65°C.;
oxidizing the gas from the heat exchanger in an oxidation chamber containing a plurality of corrugated sheets to increase the internal surface area, the gas being oxidized in the oxidation chamber so that the oxides of sulphur and nitrogen are in their highest valency states;
conducting the gas from the oxidation chamber to a reaction tower and introducing the gas into the reaction tower through a first inlet, adjacent the base of the reaction tower;
introducing a solution of a basic compound into the reaction tower through a second inlet, above the first inlet, and allowing the solution of the basic compound to flow counter-current to the gas to neutralize the acid components in the gas to produce a neutralized gas;
directing the neutralized gas into a conduit extending from the top of the reaction tower to an outlet for neutralized gas adjacent the base of the tower whereby gas passes up the tower, acid compounds are -8a-neutralized by a counter-current flow of the basic compound, then pass down the conduit to the outlet;
collecting a suspension comprising a solution of neutral, soluble salts and neutral insoluble salts, at the base of the reaction tower; and separating the solids from the liquid in a liquid/solid separator.
reducing the flue gas temperature in a heat exchanger to a temperature of about 65°C.;
oxidizing the gas from the heat exchanger in an oxidation chamber containing a plurality of corrugated sheets to increase the internal surface area, the gas being oxidized in the oxidation chamber so that the oxides of sulphur and nitrogen are in their highest valency states;
conducting the gas from the oxidation chamber to a reaction tower and introducing the gas into the reaction tower through a first inlet, adjacent the base of the reaction tower;
introducing a solution of a basic compound into the reaction tower through a second inlet, above the first inlet, and allowing the solution of the basic compound to flow counter-current to the gas to neutralize the acid components in the gas to produce a neutralized gas;
directing the neutralized gas into a conduit extending from the top of the reaction tower to an outlet for neutralized gas adjacent the base of the tower whereby gas passes up the tower, acid compounds are -8a-neutralized by a counter-current flow of the basic compound, then pass down the conduit to the outlet;
collecting a suspension comprising a solution of neutral, soluble salts and neutral insoluble salts, at the base of the reaction tower; and separating the solids from the liquid in a liquid/solid separator.
4. A method as claimed in claim 3 in which the basic compound comprises calcium hydroxide.
5. A method as claimed in claim 4 in which the calcium hydroxide is dripped or sprayed through a second inlet that surrounds the conduit.
6. A method as claimed in claim 3 including introducing an oxidizing compound into the reaction tower to ensure complete oxidation of gas in the tower.
7. A method as claimed in claim 3 including recycling the gas from the base of the tower to an inlet in the tower whereby a second scrubbing of the gas is carried out.
8. A method as claimed in claim 7 including cooling the recycled gas being recycled from the base of the tower to said inlet.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2030042 CA2030042C (en) | 1990-11-15 | 1990-11-15 | Apparatus to remove acid gases from a flue gas |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2030042 CA2030042C (en) | 1990-11-15 | 1990-11-15 | Apparatus to remove acid gases from a flue gas |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2030042A1 CA2030042A1 (en) | 1992-05-16 |
| CA2030042C true CA2030042C (en) | 2000-02-08 |
Family
ID=4146439
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2030042 Expired - Fee Related CA2030042C (en) | 1990-11-15 | 1990-11-15 | Apparatus to remove acid gases from a flue gas |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2030042C (en) |
-
1990
- 1990-11-15 CA CA 2030042 patent/CA2030042C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| CA2030042A1 (en) | 1992-05-16 |
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| MKLA | Lapsed |