CA2196531A1 - Method and equipment for recovery and treatment of sulphur dioxide contained in exhaust gases - Google Patents
Method and equipment for recovery and treatment of sulphur dioxide contained in exhaust gasesInfo
- Publication number
- CA2196531A1 CA2196531A1 CA002196531A CA2196531A CA2196531A1 CA 2196531 A1 CA2196531 A1 CA 2196531A1 CA 002196531 A CA002196531 A CA 002196531A CA 2196531 A CA2196531 A CA 2196531A CA 2196531 A1 CA2196531 A1 CA 2196531A1
- Authority
- CA
- Canada
- Prior art keywords
- liquid container
- sulphur dioxide
- sulphuric acid
- equipment
- separate
- 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.)
- Abandoned
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B17/00—Sulfur; Compounds thereof
- C01B17/69—Sulfur trioxide; Sulfuric acid
- C01B17/74—Preparation
- C01B17/76—Preparation by contact processes
- C01B17/775—Liquid phase contacting processes or wet catalysis processes
-
- 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
- B01D53/48—Sulfur compounds
- B01D53/50—Sulfur oxides
- B01D53/507—Sulfur oxides by treating the gases with other liquids
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Organic Chemistry (AREA)
- Biomedical Technology (AREA)
- Health & Medical Sciences (AREA)
- Inorganic Chemistry (AREA)
- Environmental & Geological Engineering (AREA)
- Analytical Chemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Treating Waste Gases (AREA)
- Gas Separation By Absorption (AREA)
Abstract
The invention concerns a method and an equipment (10) for recovery and treatment of sulphur dioxide (SO2) contained in exhaust gases. In the method, the flue gases are passed as a flow (13) into the washer part (11), and the sulphur dioxide (SO2) contained in the flue gases is dissolved into the washing liquid passed into the washer part (11). The mixture that contains sulphur dioxide (SO2) and that has been dissolved into the washing liquid is passed along a flow line (17) into a liquid container (12). The mixture that is placed in the liquid container (12) and that contains sulphur dioxide (SO2) is oxidized at a pressure of free choice, by means of a gas, preferably air, that is placed in the liquid container (12) and that contains oxygen (O2), into sulphur trioxide (SO3), which forms sulphuric acid (H2SO4) together with the water present in the liquid container (12).
Description
21 9653l Met_od and e~lui~ cnt for recovery and tre~tm~nt of sulphur dioxide contained in exhaust gases The invention concellls a method for recovery and treatment of sulphur dioxide contained in exhaust gases.
10 Further, the invention concerns an eql~irm~nt for recovery and treatment of sulphur dioxide contained in exhausl ~ases.
Cleaning of exhaust gases, such as, for example, flue gases, has been considered to be high~y important for a long time. Initially, ~ y~, were made to recover the dust 15 contained in flue gases only, but at present, it is stip~ t~d by law that especially large qll~ntities of e~h~lJst gases must also be cleaned in respect of their gas content.
In particular the sulphur dioxide co..l~i..F~ in flue gases has been restricted to certain emission limits. The emission lirnits are staggered so that little amounts of exhaust gases are allowed to contain SOlllC~. hdt more sulphur than, for example, large power-20 plant gas emissions, in which hull~leds of tholls~n~c of cubic metres of gas per hourcan be co~-r~ d. In the case of smaller ~mollnts of 1JU1 Ig, i.e. lower emissions, the emissions of sulphur dioxide have been limited by means of fuels of lower contents of sulphur, in which case sep~te removal of sulphur is, as a rule, not at all n~cess~ry. The costs of inve~.. f ll of the devices used for cle~ning of flue gases 25 are high, and their operation also produces e~pel~,es.
The commonest device for cle~ning of flue gases is an electric filter, which usually removes the dust from flue gases to a s~i~ffirienr extent, but which allows freepassage for the gaseous components of the flue gases. Thus, if the lirnits of sulphur 30 emissions stipulated by law are to be reached by means of an electric filter, it is n~ceSs~ to use a fuel subst~nti~lly free from sulphur.
w0 96/04202 2 1 9 6 5 3 1 PCT/FIgS/00410 In the removal of sulphur dioxide, primarily three dirf~cl~L processes are employed, which are the dry, semi-dry and wet separation processes.
The neutralizing agent needed in the dry-separation process, as a rule caustic-lime/limestone powder, is fed either directly into the combustion or to among the hot flue gases. By adding a suitable proportion of moisture to the exhaust gases that are departing, the temperature of the flue gases is lowered, whereby the sulphur dioxide (SO2) and the moisture and the caustic lime react with each other and forrn calcium sulphite powder (CaSO3), which is then sepa,d~ed by means of dry filtering. In this 10 way, besides the dust in the flue gases, also the sulphur dioxide can be elimin~tçd It is a drawback of this prior-art process that the particle size of the neutralizing agent used must be fine, and the material must also be sufficiently pure in order that the neutralization should be s~ ntly efficient. It is a further drawback of the process that the co,~ulllption of the neutralizing agent is by orders higher than what 1~ would be required by the stoichiometric need (stoichiom~try means the molar ratios of calcium to sulphur). This is why, in the future, the dry-separation process will not be a viable solution from the point of view of nature.
In the semi-dry sepal~ion process, most commonly, milk of lime is atomized into 20 the flue gases as the neutralizing agent. The supply of milk of lime must be large enough so that the sulphur dioxide can be neutralized reliably and, at the same time, the tcl~ ule of the flue gases be lowered s~lrr~ iPl,lly for dry filtering. The result of this process is a dry powder which co~t~inc~ besides the solids contained in the flue gases, also calcium sulphite that has been formed. True enough, part of the25 calcium sulphite may be oxidized to calcium s~lph~t~, i.e. gypsum, but the main part of the product of neutralization consists of c~ m sulphite powder.
The drawbacks of the semi-dry separation process are, in principle, the same as those of the dry se~a,~tion process, i.e; disy~wlionately high con~u,~tion of pure 30 neutralizing agent, but additionally also the fact that the calcium sulphite (CaS03) formed as a powder is a material that has no co",~l~s~ion ~llell~ . This results from the "hairinessi' of calcium sulphite, i.e. calcium sl~lphitç consists of pin-covered wos6/04202 2 1 9 6~31 PCT/~195100410 granules which cannot be colllpiessed into a compact mix. Thus, the use of the calcium sulphite formed, for example, as filling soil for foundations of bnil~ing~ or roads is out of the question. In principle, the calcium sulphite formed is a material suitable for skiing pistes only. Nor do e*.e~ . carried out by means of stabiliz-5 ation with cement provide an a lPqll~t-f~, rh~ lly stable solution, because, for example, the oxygen content in ground water oxidizes the calcium sulphite to calcium sulphate. This is why the c~lrillm slllphit~ ought to be oxidized by heating at about 1000~C to ~yl~ulll, i.e. c~lrillm sulphate. This is, however, so e~c~ ethat the solution is not econn,..i~lly reasonable. On the basis of the above, the semi-10 dry process of sepaldlion is also a solution unacceptable from the point of view ofnature for removal of sulphur.
From the point of view of nature, the best process known so far for removal of sulphur is the so-called wet-wdshing process, in which the fluelcombustion gases are 15 washed with a neutralizing washing liquid. In such a case, the sulphur dioxide dissolves from the flue gases into the wil~l~ing liquid and makes the washing liquid acid. The acid washing liquid is then neutralized by means of a suitable rhf.oir~l, most commonly with limf stonf (CaC03) or milk of lime, i.e. calcium hydroxide (Ca(OH)2). The details of C&llyillg out the wet-washing process, however, involve 20 a few fliffirlllti~s. First, the r~lrillm bi~llphit~ (CaHS03) fornied in the neutralizing stage must be oxidized to c~lcinm slllph~te. This reaction must take place within a relatively precise pH-range, which ullposes high l~ uil~l~.e,lL~, besides on the pH-meter, also on the metering of the neutralizing agent. These ~iffirlllties together make the wet-sep~dLion process rather tliffirult to carry out and to monitor. If these 25 circllm~t~nres have been taken into account sufficiently well, the final product that is obtained is even good gypsum, for which there is use, for example, as raw-material for the gypsum hldu~ and also as filling soil, because ~y~ùlll is slakyand is co...p~d well with a good co~ lession ~ . At the same time, the slaky ~y~ulll is chPmic~lly stable. A drawback of the wet-sepdld~ion process is the 30 high investm~nt cost, and the operation of the process also causes e~ cllses. This is why the wet-s~ara~ion process has been used primarily for large flue-gas qll~ntiti~s w096/04202 2 1 9 6 5 3 1 - Pcr/F~S/00410 and at large plants, in which the washing of the flue gases must be sufficientlyeff;rient among other things, in respect of sulphur.
The object of the present invention is to provide a method and an equipment in S which the numerous d,a~l,acks present in the prior-art solutions are avoided.
The method in accordance with the invention is characterized in that a) the flue gases are passed as a flow into the washer part, and the sulphur dioxide (SO2) contained in the flue gases is dissolved into the washing liquid passed into the washer part, b) the ~ Ul~ that contains sulphur dioxide (S02) and that has been dissolved into the washing liquid is passed along a flow line into a liquid contai,~l, and c) the ,ll,~lu,~ that is placed in the liquid colllaill~- and that contains sulphur dioxide (SO2) is oxidized at a p,~u,e of free choice, by means of a gas, preferably air, that is placed in the liquid container and that contains oxygen (~2)~ into sulphur trioxide (SO3), which forrns sulphuric acid (H2SO4) together with the water present in the liquid co~ r.
The eq~ in accordallce with the invention is chala~t~l,~d in that the equip-ment inr~ les 25 a) a washer part, into which the flue gases are passed along a first flow line and the washing liquid along a second flow line and/or along a third flow line, in which con,~e~;~ion the sulphur dioxide contained in the flue gases is dissolved into the washing liquid that has been passed into the washer part, 30 b) a fourth flow line for passing the ~ ulc that has been dissolved into the washing liquid and that contains sulphur dioxide (SO2) from the washer part into the liquid container, and wo 96/W202 2 1 9 6 5 3 1 Pcr/Fls5loo4lo -c) a liquid container, in which the mixture that contains sulphur dioxide is oxidized at a ples~u,e of free choice, by means of a gas, preferably air, that is placed in the liquid container and that contains oxy~en (~2)~ into sulphur trioxide (SO3), which forms sulphuric acid (H2S04) together with the water S present in the liquid container.
In the present invention, it has been realized to oxidize the sulphur dioxide inconnection with the washing directly into sulphuric acid. In the method and equip-ment in accoldal~ce with the present invention, the sulphur dioxide contained in the 10 flue gases is dissolved into the w~-sllillg liquid, which is oxygenated/aerated inten-sively, whereby the sulphur dioxide dissolved in the washing liquid is oxidized into sulphur trioxide (SO2 + 'hO2 -~ SO3), which, together with the water present in the washing liquid, forms sulphuric acid (H2SO4), which again dissolves sulphur dioxide (SO2) into itself, for example 35 grams of S02 per kilogram of H2SO4 15 50 % at a te.ll~cl~lule of 50~C, i.e. an almost equal amount as co.l.paled with the amount dissolved into pure water: 40 grams of SO2 per kilogram of H2O at 50~C, and, dissolved in oxidizing conditions, the sulphur dioxide is again oxidized into sulphur trioxide and from it further into sulphuric acid.
20 The invention is in no way critical in respect of the washing-liquid system that is used. Washing liquid can be passed into the washer part either from the liquid cont~inPr in which sulphuric acid is formed or from a separate washing-liquid duct or from both.
25 By means of the method and e4uil,...en~ in accol-lance with the present invention, a number of si~nifir~nt advantages are obtained colllpdl~d with the processes of separation known from the prior art. In the method and equipment of the present invention, it is ~ cess~.y to use a number of control units, a measuring detector or coll~ of neutralizing agents by whose means the dissolved sulphur dioxide 30 can be neutralized, a deposit, removal of deposit, filt~l~n~, conveyors, or various t~. According to a ~cfelled embodiment of the invention, it is sufficient to regulate a suitable supply of additional liquid so that the order of m~gnit~l~e of the wo 96/04202 PCr/FIs5/oo4lo ~mollnt of the washing liquid that flows out, i.e. the sulphuric acid, corresponds to the desired conce~ liOn of sulphuric acid. The pumps and pipe systems with theirw~.l~ing-liquid co~ remain clean and free from any blocking in the event of pH variations, which blocking tends to occur frequently in neutralization with lime 5 if the pH is not within the desired limits out of some reason.
In the process of the present invention, the tre~tmPnt of the acid Il~ u~e that flows out may be either concel,l,dtion or neutralization witn a suitable lirne, which lime is now, however, of secondar importance and can be even impure lime. Thus, the 10 result is a chemical product of reasonably low cost, concentrated sulphuric acid, or ~y~sulll that is suitable for filling soil and raw-material. In any case, the neutraliz-ation taking place in the process of the present invention is directly stoichiometric witnout any extra col~.u~ )Lion of neutralizing agent. These advantages of the invention collc~.~ond to neutralization and sulphur-removal acceptable to nature. At 15 the same time, the invention proves that sulphuric acid can also be produced without lead chdlllbe.s. or V205 catalysts.
The invention will be described in detail with refe,ence to a solution of principle of the invention illustrated in the figure in the accompanying drawing, the invention 20 being, however, not supposed to be co,~,l~ed to said embodiment alone.
In the figure in the drawing, the c.~ in accordance with the invention is denoted generally with tne lefelcl~ce numeral 10. The flue gases that contain sulphur dioxide are passed into the washer part 1 i as a flow 13. At the same time, into the 25 washer part 11, washing liquid is passed, for example, from a circulation water pump 15, which sucks washing liquid out of the washing-liquid container 12. If nlocess~ry~ into the washer part 11, additional washing liquid, such as additional water, can be passed along the flow line 16 as a washing liquid of its own, which replaces any amount of washing liquid that may evapolate and the acid solution that 30 flows out along the dischalge line 22. In the washing-liquid container 12, there is a stirrer shaft 18, at whose end tnere is a stirrer-disperser 19, in which case the air/oxygen mixture which is fed out of the feed line 20, preferably, for example, wo 96/W202 2 1 9 6 5 3 1 PCI~ /00410 through the hollow stirrer shaft 18 is passed and dispersed by means of the stirrer/dl~perser 19 into the washillg liquid present in the washing-liquid container 12, whereby the sulphur dioxide dissolved in the washing liquid is oxidized intosulphur trioxide. A motor 21 is fitted to rotate the stirrer shaft 18. From the washer S part 11, the w~hing liquid into which the sulphur dioxide dissolved from the flue gases has becen dissolved flows along the flow line 17 into the washing-liquid CO~ h~cl 12. The circulation water pump 15 is preferably such that it sucks the air that flows along the flow line 23. Owing to this, additional air is supplied into the oxygenous liquid in the washing-liquid/water cGlllailKr, which air is dissolved into 10 the washing liquid in the flow duct 14 after the circulation water pump 15 under ,r~s~ule, preferably of an order of about 1...10 bar, before the liquid enters into the washer part 11. Owing to thisj the liquid that flows into the washer part 11 is highly oxygenous and, at the same time, takes care of the chc~ e that the sulphur dioxide that has been dissolved into the wa~hing liquid, the liquid that contains 15 sulphuric acid and water, is oxidized under pl~ul~ ever more completely into sulphur trioxide.
Thus, in the plcÇ~llcd embodiment of the process and equipment of the present invention, oxidization of sulphur dioxide takes place both in the flow duct/pipe 14 20 placed after the circulation water pump 15 and passing into the washer part 11, in the washer part 11, and in the ~ g-liquid co~ 12. It should be noted that, in the washing-liquid con~ r 12, oX~ 7~tion takes place with the aid of the addition of air/oxygen supplied along the feed line 20 and with the aid of the stirrer 18 and the stirrer/di~l~er 19 just at a very low positive pl~,s~ule. The bottom part 25 of the washing-liquid coll~h~r 12 is provided with a removal of deposit 24 for the removal of the deposit that arises as a result of solid matter tnat may be contained in the flue gases and as a result of precipitati~ reslllting from probable oxidization.
The process of oxidi_ation in acco--lance with the present invention can also be30 carried out in a number of dirf~ ways and by means of dirr. ,en~ solutions ofequipment, but an ecse~ l feature is oxidization of the sulphur dioxide in tne liquid/water, at a pressure which can be chosen freely in principle, in the washing-w096/04202 2 1 9 6 5 3 1 Pcr~gs/oo~lo liquid container 12, and the ultimate oxidization under pressure in the pipe/duct 14after the circulation water pump 15. The addition of air/oxygen can also be carried out in a way differing from the embodirnent shown in the figure in the drawing, but even then the final result is the desired one. The supply of air/oxygen into theS circulation water pump 15 or into the pressurized flow duct or pipe 14 after the pump can be carried out in a number of different ways, but the major part or even all of the sulphur dioxide is oxidized in the ~l~cs~u~i2ed state 14. The washing-liquid container 12 is kept rich in oxygen jusI otherwise. Thus, the process of the present invention is elastic and simple.
Regarding its co~ ulion and principle of operation, the washer part 11 may be a washer part known from the prior art. It is the essential idea that the sulphur dioxide is dissolved into the washing liquid as completely as possible, which liquid contains a substantial amount of sulphuric acid, as a result of conce~ tion, according to the 15 basic realization of the invendon. A suitable concenll~lion of acid is, for example, a 50 % sulphuric acid, which is taken out as the flow 22, this concentration being the capacity of dissoludon of sulphur dioxide by sulphuric acid and being almostequal to the co~ olldi,lg capacity of dissolulion of sulphur dioxide by pure water.
20 As the oxi~li7ing gas passed along the line 20, it is possible to use air or air enriched with oxygen, but also pure oxygen gas can be used. The latter mode is just an expensive mode of oxi-li7ing.
Above, a solution of principle of the invention is described, and it is obvious to a 25 person skilled in the art that llullltlous modifications can be made to said solution within the scope of the inventive idea stated in the accompanying patent claims.
10 Further, the invention concerns an eql~irm~nt for recovery and treatment of sulphur dioxide contained in exhausl ~ases.
Cleaning of exhaust gases, such as, for example, flue gases, has been considered to be high~y important for a long time. Initially, ~ y~, were made to recover the dust 15 contained in flue gases only, but at present, it is stip~ t~d by law that especially large qll~ntities of e~h~lJst gases must also be cleaned in respect of their gas content.
In particular the sulphur dioxide co..l~i..F~ in flue gases has been restricted to certain emission limits. The emission lirnits are staggered so that little amounts of exhaust gases are allowed to contain SOlllC~. hdt more sulphur than, for example, large power-20 plant gas emissions, in which hull~leds of tholls~n~c of cubic metres of gas per hourcan be co~-r~ d. In the case of smaller ~mollnts of 1JU1 Ig, i.e. lower emissions, the emissions of sulphur dioxide have been limited by means of fuels of lower contents of sulphur, in which case sep~te removal of sulphur is, as a rule, not at all n~cess~ry. The costs of inve~.. f ll of the devices used for cle~ning of flue gases 25 are high, and their operation also produces e~pel~,es.
The commonest device for cle~ning of flue gases is an electric filter, which usually removes the dust from flue gases to a s~i~ffirienr extent, but which allows freepassage for the gaseous components of the flue gases. Thus, if the lirnits of sulphur 30 emissions stipulated by law are to be reached by means of an electric filter, it is n~ceSs~ to use a fuel subst~nti~lly free from sulphur.
w0 96/04202 2 1 9 6 5 3 1 PCT/FIgS/00410 In the removal of sulphur dioxide, primarily three dirf~cl~L processes are employed, which are the dry, semi-dry and wet separation processes.
The neutralizing agent needed in the dry-separation process, as a rule caustic-lime/limestone powder, is fed either directly into the combustion or to among the hot flue gases. By adding a suitable proportion of moisture to the exhaust gases that are departing, the temperature of the flue gases is lowered, whereby the sulphur dioxide (SO2) and the moisture and the caustic lime react with each other and forrn calcium sulphite powder (CaSO3), which is then sepa,d~ed by means of dry filtering. In this 10 way, besides the dust in the flue gases, also the sulphur dioxide can be elimin~tçd It is a drawback of this prior-art process that the particle size of the neutralizing agent used must be fine, and the material must also be sufficiently pure in order that the neutralization should be s~ ntly efficient. It is a further drawback of the process that the co,~ulllption of the neutralizing agent is by orders higher than what 1~ would be required by the stoichiometric need (stoichiom~try means the molar ratios of calcium to sulphur). This is why, in the future, the dry-separation process will not be a viable solution from the point of view of nature.
In the semi-dry sepal~ion process, most commonly, milk of lime is atomized into 20 the flue gases as the neutralizing agent. The supply of milk of lime must be large enough so that the sulphur dioxide can be neutralized reliably and, at the same time, the tcl~ ule of the flue gases be lowered s~lrr~ iPl,lly for dry filtering. The result of this process is a dry powder which co~t~inc~ besides the solids contained in the flue gases, also calcium sulphite that has been formed. True enough, part of the25 calcium sulphite may be oxidized to calcium s~lph~t~, i.e. gypsum, but the main part of the product of neutralization consists of c~ m sulphite powder.
The drawbacks of the semi-dry separation process are, in principle, the same as those of the dry se~a,~tion process, i.e; disy~wlionately high con~u,~tion of pure 30 neutralizing agent, but additionally also the fact that the calcium sulphite (CaS03) formed as a powder is a material that has no co",~l~s~ion ~llell~ . This results from the "hairinessi' of calcium sulphite, i.e. calcium sl~lphitç consists of pin-covered wos6/04202 2 1 9 6~31 PCT/~195100410 granules which cannot be colllpiessed into a compact mix. Thus, the use of the calcium sulphite formed, for example, as filling soil for foundations of bnil~ing~ or roads is out of the question. In principle, the calcium sulphite formed is a material suitable for skiing pistes only. Nor do e*.e~ . carried out by means of stabiliz-5 ation with cement provide an a lPqll~t-f~, rh~ lly stable solution, because, for example, the oxygen content in ground water oxidizes the calcium sulphite to calcium sulphate. This is why the c~lrillm slllphit~ ought to be oxidized by heating at about 1000~C to ~yl~ulll, i.e. c~lrillm sulphate. This is, however, so e~c~ ethat the solution is not econn,..i~lly reasonable. On the basis of the above, the semi-10 dry process of sepaldlion is also a solution unacceptable from the point of view ofnature for removal of sulphur.
From the point of view of nature, the best process known so far for removal of sulphur is the so-called wet-wdshing process, in which the fluelcombustion gases are 15 washed with a neutralizing washing liquid. In such a case, the sulphur dioxide dissolves from the flue gases into the wil~l~ing liquid and makes the washing liquid acid. The acid washing liquid is then neutralized by means of a suitable rhf.oir~l, most commonly with limf stonf (CaC03) or milk of lime, i.e. calcium hydroxide (Ca(OH)2). The details of C&llyillg out the wet-washing process, however, involve 20 a few fliffirlllti~s. First, the r~lrillm bi~llphit~ (CaHS03) fornied in the neutralizing stage must be oxidized to c~lcinm slllph~te. This reaction must take place within a relatively precise pH-range, which ullposes high l~ uil~l~.e,lL~, besides on the pH-meter, also on the metering of the neutralizing agent. These ~iffirlllties together make the wet-sep~dLion process rather tliffirult to carry out and to monitor. If these 25 circllm~t~nres have been taken into account sufficiently well, the final product that is obtained is even good gypsum, for which there is use, for example, as raw-material for the gypsum hldu~ and also as filling soil, because ~y~ùlll is slakyand is co...p~d well with a good co~ lession ~ . At the same time, the slaky ~y~ulll is chPmic~lly stable. A drawback of the wet-sepdld~ion process is the 30 high investm~nt cost, and the operation of the process also causes e~ cllses. This is why the wet-s~ara~ion process has been used primarily for large flue-gas qll~ntiti~s w096/04202 2 1 9 6 5 3 1 - Pcr/F~S/00410 and at large plants, in which the washing of the flue gases must be sufficientlyeff;rient among other things, in respect of sulphur.
The object of the present invention is to provide a method and an equipment in S which the numerous d,a~l,acks present in the prior-art solutions are avoided.
The method in accordance with the invention is characterized in that a) the flue gases are passed as a flow into the washer part, and the sulphur dioxide (SO2) contained in the flue gases is dissolved into the washing liquid passed into the washer part, b) the ~ Ul~ that contains sulphur dioxide (S02) and that has been dissolved into the washing liquid is passed along a flow line into a liquid contai,~l, and c) the ,ll,~lu,~ that is placed in the liquid colllaill~- and that contains sulphur dioxide (SO2) is oxidized at a p,~u,e of free choice, by means of a gas, preferably air, that is placed in the liquid container and that contains oxygen (~2)~ into sulphur trioxide (SO3), which forrns sulphuric acid (H2SO4) together with the water present in the liquid co~ r.
The eq~ in accordallce with the invention is chala~t~l,~d in that the equip-ment inr~ les 25 a) a washer part, into which the flue gases are passed along a first flow line and the washing liquid along a second flow line and/or along a third flow line, in which con,~e~;~ion the sulphur dioxide contained in the flue gases is dissolved into the washing liquid that has been passed into the washer part, 30 b) a fourth flow line for passing the ~ ulc that has been dissolved into the washing liquid and that contains sulphur dioxide (SO2) from the washer part into the liquid container, and wo 96/W202 2 1 9 6 5 3 1 Pcr/Fls5loo4lo -c) a liquid container, in which the mixture that contains sulphur dioxide is oxidized at a ples~u,e of free choice, by means of a gas, preferably air, that is placed in the liquid container and that contains oxy~en (~2)~ into sulphur trioxide (SO3), which forms sulphuric acid (H2S04) together with the water S present in the liquid container.
In the present invention, it has been realized to oxidize the sulphur dioxide inconnection with the washing directly into sulphuric acid. In the method and equip-ment in accoldal~ce with the present invention, the sulphur dioxide contained in the 10 flue gases is dissolved into the w~-sllillg liquid, which is oxygenated/aerated inten-sively, whereby the sulphur dioxide dissolved in the washing liquid is oxidized into sulphur trioxide (SO2 + 'hO2 -~ SO3), which, together with the water present in the washing liquid, forms sulphuric acid (H2SO4), which again dissolves sulphur dioxide (SO2) into itself, for example 35 grams of S02 per kilogram of H2SO4 15 50 % at a te.ll~cl~lule of 50~C, i.e. an almost equal amount as co.l.paled with the amount dissolved into pure water: 40 grams of SO2 per kilogram of H2O at 50~C, and, dissolved in oxidizing conditions, the sulphur dioxide is again oxidized into sulphur trioxide and from it further into sulphuric acid.
20 The invention is in no way critical in respect of the washing-liquid system that is used. Washing liquid can be passed into the washer part either from the liquid cont~inPr in which sulphuric acid is formed or from a separate washing-liquid duct or from both.
25 By means of the method and e4uil,...en~ in accol-lance with the present invention, a number of si~nifir~nt advantages are obtained colllpdl~d with the processes of separation known from the prior art. In the method and equipment of the present invention, it is ~ cess~.y to use a number of control units, a measuring detector or coll~ of neutralizing agents by whose means the dissolved sulphur dioxide 30 can be neutralized, a deposit, removal of deposit, filt~l~n~, conveyors, or various t~. According to a ~cfelled embodiment of the invention, it is sufficient to regulate a suitable supply of additional liquid so that the order of m~gnit~l~e of the wo 96/04202 PCr/FIs5/oo4lo ~mollnt of the washing liquid that flows out, i.e. the sulphuric acid, corresponds to the desired conce~ liOn of sulphuric acid. The pumps and pipe systems with theirw~.l~ing-liquid co~ remain clean and free from any blocking in the event of pH variations, which blocking tends to occur frequently in neutralization with lime 5 if the pH is not within the desired limits out of some reason.
In the process of the present invention, the tre~tmPnt of the acid Il~ u~e that flows out may be either concel,l,dtion or neutralization witn a suitable lirne, which lime is now, however, of secondar importance and can be even impure lime. Thus, the 10 result is a chemical product of reasonably low cost, concentrated sulphuric acid, or ~y~sulll that is suitable for filling soil and raw-material. In any case, the neutraliz-ation taking place in the process of the present invention is directly stoichiometric witnout any extra col~.u~ )Lion of neutralizing agent. These advantages of the invention collc~.~ond to neutralization and sulphur-removal acceptable to nature. At 15 the same time, the invention proves that sulphuric acid can also be produced without lead chdlllbe.s. or V205 catalysts.
The invention will be described in detail with refe,ence to a solution of principle of the invention illustrated in the figure in the accompanying drawing, the invention 20 being, however, not supposed to be co,~,l~ed to said embodiment alone.
In the figure in the drawing, the c.~ in accordance with the invention is denoted generally with tne lefelcl~ce numeral 10. The flue gases that contain sulphur dioxide are passed into the washer part 1 i as a flow 13. At the same time, into the 25 washer part 11, washing liquid is passed, for example, from a circulation water pump 15, which sucks washing liquid out of the washing-liquid container 12. If nlocess~ry~ into the washer part 11, additional washing liquid, such as additional water, can be passed along the flow line 16 as a washing liquid of its own, which replaces any amount of washing liquid that may evapolate and the acid solution that 30 flows out along the dischalge line 22. In the washing-liquid container 12, there is a stirrer shaft 18, at whose end tnere is a stirrer-disperser 19, in which case the air/oxygen mixture which is fed out of the feed line 20, preferably, for example, wo 96/W202 2 1 9 6 5 3 1 PCI~ /00410 through the hollow stirrer shaft 18 is passed and dispersed by means of the stirrer/dl~perser 19 into the washillg liquid present in the washing-liquid container 12, whereby the sulphur dioxide dissolved in the washing liquid is oxidized intosulphur trioxide. A motor 21 is fitted to rotate the stirrer shaft 18. From the washer S part 11, the w~hing liquid into which the sulphur dioxide dissolved from the flue gases has becen dissolved flows along the flow line 17 into the washing-liquid CO~ h~cl 12. The circulation water pump 15 is preferably such that it sucks the air that flows along the flow line 23. Owing to this, additional air is supplied into the oxygenous liquid in the washing-liquid/water cGlllailKr, which air is dissolved into 10 the washing liquid in the flow duct 14 after the circulation water pump 15 under ,r~s~ule, preferably of an order of about 1...10 bar, before the liquid enters into the washer part 11. Owing to thisj the liquid that flows into the washer part 11 is highly oxygenous and, at the same time, takes care of the chc~ e that the sulphur dioxide that has been dissolved into the wa~hing liquid, the liquid that contains 15 sulphuric acid and water, is oxidized under pl~ul~ ever more completely into sulphur trioxide.
Thus, in the plcÇ~llcd embodiment of the process and equipment of the present invention, oxidization of sulphur dioxide takes place both in the flow duct/pipe 14 20 placed after the circulation water pump 15 and passing into the washer part 11, in the washer part 11, and in the ~ g-liquid co~ 12. It should be noted that, in the washing-liquid con~ r 12, oX~ 7~tion takes place with the aid of the addition of air/oxygen supplied along the feed line 20 and with the aid of the stirrer 18 and the stirrer/di~l~er 19 just at a very low positive pl~,s~ule. The bottom part 25 of the washing-liquid coll~h~r 12 is provided with a removal of deposit 24 for the removal of the deposit that arises as a result of solid matter tnat may be contained in the flue gases and as a result of precipitati~ reslllting from probable oxidization.
The process of oxidi_ation in acco--lance with the present invention can also be30 carried out in a number of dirf~ ways and by means of dirr. ,en~ solutions ofequipment, but an ecse~ l feature is oxidization of the sulphur dioxide in tne liquid/water, at a pressure which can be chosen freely in principle, in the washing-w096/04202 2 1 9 6 5 3 1 Pcr~gs/oo~lo liquid container 12, and the ultimate oxidization under pressure in the pipe/duct 14after the circulation water pump 15. The addition of air/oxygen can also be carried out in a way differing from the embodirnent shown in the figure in the drawing, but even then the final result is the desired one. The supply of air/oxygen into theS circulation water pump 15 or into the pressurized flow duct or pipe 14 after the pump can be carried out in a number of different ways, but the major part or even all of the sulphur dioxide is oxidized in the ~l~cs~u~i2ed state 14. The washing-liquid container 12 is kept rich in oxygen jusI otherwise. Thus, the process of the present invention is elastic and simple.
Regarding its co~ ulion and principle of operation, the washer part 11 may be a washer part known from the prior art. It is the essential idea that the sulphur dioxide is dissolved into the washing liquid as completely as possible, which liquid contains a substantial amount of sulphuric acid, as a result of conce~ tion, according to the 15 basic realization of the invendon. A suitable concenll~lion of acid is, for example, a 50 % sulphuric acid, which is taken out as the flow 22, this concentration being the capacity of dissoludon of sulphur dioxide by sulphuric acid and being almostequal to the co~ olldi,lg capacity of dissolulion of sulphur dioxide by pure water.
20 As the oxi~li7ing gas passed along the line 20, it is possible to use air or air enriched with oxygen, but also pure oxygen gas can be used. The latter mode is just an expensive mode of oxi-li7ing.
Above, a solution of principle of the invention is described, and it is obvious to a 25 person skilled in the art that llullltlous modifications can be made to said solution within the scope of the inventive idea stated in the accompanying patent claims.
Claims (16)
1. A method for recovery and treatment of sulphur dioxide (SO2) contained in exhaust gases, in which method sulphur dioxide (SO2) is dissolved in a washing liquid and a mixture containing sulphur dioxide (SO2) is oxidized into sulphur trioxide (SO3), which forms sulphuric acid (H2SO4) together with water, characterized in that a) the flue gases are passed as a flow (13) into a separate washer part (11), and the sulphur dioxide (SO2) contained in the flue gases is dissolved into the washing liquid passed into the separate washer part (11), b) the mixture that contains sulphur dioxide (SO2) and that has been dissolved into the washing liquid is passed along a flow line (17) into a separate liquid container (12), and c) the mixture that is placed in the separate liquid container (12) and that contains sulphur dioxide (SO2) is oxidized at a pressure of free choice, by means of a gas, preferably air, that is placed in the separate liquid container (12) and that contains oxygen (O2), into sulphur trioxide (SO3), which forms sulphuric acid (H2SO4) together with the water present in the separate liquid container (12), and the sulphuric acid (H2SO4) is allowed to be concentrated to a desired H2SO4-concentration in the separate liquid container (12).
2. A method as claimed in claim 1, characterized in that the sulphuric acid (H2SO4) is allowed to be concentrated preferably to a concentration of at least 50 %, before the solution of sulphuric acid is taken out.
3. A method as claimed in claim 1 or 2, characterized in that additional washingliquid / additional water is fed along the line (16) into the washer part (11) to replace any amount of washing liquid that may evaporate and to replace the H2SO4-containing solution that is removed.
4. A method as claimed in any of the claims 1 to 3, characterized in that additional oxidization is carried out under pressure in the flow duct / flow line (14) passing into the washer part (11).
5. A method as claimed in claim 4, characterized in that the circulation water pump (15) is fitted to suck air / oxygen-rich gas into the flow duct / flow line (14) that passes into the washer part (11).
6. A method as claimed in any of the claims 1 to 5, characterized in that sulphuric acid is removed from the liquid container (12) along a discharge line (22).
7. A method as claimed in any of the claims 1 to 5, characterized in that sulphuric acid is removed from the flow duct / flow line (14) that passes into the washer part (11).
8. A method as claimed in any of the claims 1 to 7, characterized in that oxygen-containing gas is passed into the liquid container (12).
9. An equipment (10) for recovery and treatment of sulphur dioxide (SO2) contained in exhaust gases, in which method sulphur dioxide (SO2) is dissolved in a washing liquid and a mixture containing sulphur dioxide (SO2) is oxidized into sulphur trioxide (SO3), which forms sulphuric acid (H2SO4) together with water, characterized in that the equipment (10) includes a) a separate washer part (11), into which the flue gases are passed along a first flow line (13) and the washing liquid along a second flow line (14) and/or along a third flow line (16), in which connection the sulphur dioxide (SO2) contained in the flue gases is dissolved into the washing liquid that has been passed into the separate washer part (11), b) a fourth flow line (17) for passing the mixture that has been dissolved into the washing liquid and that contains sulphur dioxide (SO2) from the separate washer part (11) into a separate liquid container (12), and c) the separate liquid container (12), in which the mixture that contains sulphur dioxide (SO2) is oxidized at a pressure of free choice, by means of a gas, preferably air, that is placed in the separate liquid container (12) and that contains oxygen (O2), into sulphur trioxide (SO3), which forms sulphuric acid (H2SO4) together with the water present in the separate liquid container (12), the sulphuric acid (H2SO4) being allowed to be concentrated to a desired H2SO4-concentration in the separate liquid container (12).
10. An equipment as claimed in claim 9, characterized in that the liquid container (12) is provided with a duct (20) for the feed of gas that contains oxygen.
11. An equipment as claimed in claim 9 or 10, characterized in that the equipment (10) includes a circulation water pump (15), which is fitted to suck washing liquid out of the liquid container (12) and to pass the washing liquid along the second flow line (14) under pressure into the washer part (11).
12. An equipment as claimed in claim 11, characterized in that the circulation water pump (15) communicates with a flow line (23) that contains air / oxygen-rich gas, the circulation water pump (15) being fitted to suck the air / the oxygen-rich gas into the second flow line (14) passing into the washer part (11).
13. An equipment as claimed in any of the claims 9 to 12, characterized in that the liquid container (12) is provided with a duct (22) for the discharge of the sulphuric acid.
14. An equipment as claimed in any of the claims 9 to 13, characterized in that the liquid container (12) is provided with a stirrer shaft (18), at whose end there is a stirrer-disperser (19).
15. An equipment as claimed in claim 14, characterized in that the stirrer shaft(18) is hollow, the oxygen-containing gas being fitted to flow from a feed duct (20) through the hollow stirrer shaft (18) to the stirrer disperser (19).
16. An equipment as claimed in any of the claims 9 to 15, characterized in that in the lower part of the liquid container (12), there is a duct (24) for the removal of deposit.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FI943589 | 1994-08-02 | ||
| FI943589A FI943589L (en) | 1994-08-02 | 1994-08-02 | Scrubbing of exhaust gas sulfur dioxide into sulfuric acid |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2196531A1 true CA2196531A1 (en) | 1996-02-15 |
Family
ID=8541153
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002196531A Abandoned CA2196531A1 (en) | 1994-08-02 | 1995-08-01 | Method and equipment for recovery and treatment of sulphur dioxide contained in exhaust gases |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0796221A1 (en) |
| AU (1) | AU3079395A (en) |
| CA (1) | CA2196531A1 (en) |
| FI (1) | FI943589L (en) |
| WO (1) | WO1996004202A1 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5851265A (en) * | 1996-09-03 | 1998-12-22 | Monsanto Company | Selective removal and recovery of sulfur dioxide from effluent gases using organic phosphorous solvents |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1577365A (en) * | 1976-02-28 | 1980-10-22 | Chiyoda Chem Eng Construct Co | Gas-liquid contacting method and apparatus |
| FR2668386B1 (en) * | 1990-10-29 | 1994-10-14 | Socrematic | PROCESS FOR TREATING WASTE GASES CONTAINING SULFUR DIOXIDE. |
| FI90397C (en) * | 1992-04-21 | 1994-02-10 | Wiser Oy | Method and apparatus for treating liquids |
-
1994
- 1994-08-02 FI FI943589A patent/FI943589L/en unknown
-
1995
- 1995-08-01 CA CA002196531A patent/CA2196531A1/en not_active Abandoned
- 1995-08-01 WO PCT/FI1995/000410 patent/WO1996004202A1/en not_active Ceased
- 1995-08-01 AU AU30793/95A patent/AU3079395A/en not_active Abandoned
- 1995-08-01 EP EP95944007A patent/EP0796221A1/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| FI943589A7 (en) | 1996-02-03 |
| WO1996004202A1 (en) | 1996-02-15 |
| AU3079395A (en) | 1996-03-04 |
| EP0796221A1 (en) | 1997-09-24 |
| FI943589L (en) | 1996-02-03 |
| FI943589A0 (en) | 1994-08-02 |
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Legal Events
| Date | Code | Title | Description |
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| FZDE | Discontinued |