CA2094150A1 - Process for purifying flue gases with a high chloride content - Google Patents
Process for purifying flue gases with a high chloride contentInfo
- Publication number
- CA2094150A1 CA2094150A1 CA002094150A CA2094150A CA2094150A1 CA 2094150 A1 CA2094150 A1 CA 2094150A1 CA 002094150 A CA002094150 A CA 002094150A CA 2094150 A CA2094150 A CA 2094150A CA 2094150 A1 CA2094150 A1 CA 2094150A1
- Authority
- CA
- Canada
- Prior art keywords
- washing
- stage
- solution
- subsequent
- process according
- 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
Links
- 239000003546 flue gas Substances 0.000 title claims abstract description 27
- 238000000034 method Methods 0.000 title claims abstract description 23
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 title claims abstract description 7
- 238000005406 washing Methods 0.000 claims abstract description 57
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims abstract description 33
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 15
- 238000004056 waste incineration Methods 0.000 claims abstract description 6
- 239000002253 acid Substances 0.000 claims abstract description 5
- 238000010521 absorption reaction Methods 0.000 claims abstract description 4
- 239000012266 salt solution Substances 0.000 claims abstract description 4
- 239000000243 solution Substances 0.000 claims description 37
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 claims description 36
- 235000002639 sodium chloride Nutrition 0.000 claims description 29
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 claims description 26
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 claims description 23
- 150000003839 salts Chemical class 0.000 claims description 15
- 239000011780 sodium chloride Substances 0.000 claims description 14
- 239000012670 alkaline solution Substances 0.000 claims description 9
- 230000002378 acidificating effect Effects 0.000 claims description 8
- AXCZMVOFGPJBDE-UHFFFAOYSA-L calcium dihydroxide Chemical compound [OH-].[OH-].[Ca+2] AXCZMVOFGPJBDE-UHFFFAOYSA-L 0.000 claims description 8
- 239000000920 calcium hydroxide Substances 0.000 claims description 8
- 229910001861 calcium hydroxide Inorganic materials 0.000 claims description 8
- 239000002699 waste material Substances 0.000 claims description 7
- VSCWAEJMTAWNJL-UHFFFAOYSA-K aluminium trichloride Chemical compound Cl[Al](Cl)Cl VSCWAEJMTAWNJL-UHFFFAOYSA-K 0.000 claims description 6
- 238000006386 neutralization reaction Methods 0.000 claims description 6
- 239000003595 mist Substances 0.000 claims description 4
- 239000007787 solid Substances 0.000 claims description 4
- 239000003610 charcoal Substances 0.000 claims description 3
- 238000001816 cooling Methods 0.000 claims description 3
- 238000004821 distillation Methods 0.000 claims description 3
- IRPGOXJVTQTAAN-UHFFFAOYSA-N 2,2,3,3,3-pentafluoropropanal Chemical compound FC(F)(F)C(F)(F)C=O IRPGOXJVTQTAAN-UHFFFAOYSA-N 0.000 claims description 2
- KLZUFWVZNOTSEM-UHFFFAOYSA-K Aluminum fluoride Inorganic materials F[Al](F)F KLZUFWVZNOTSEM-UHFFFAOYSA-K 0.000 claims description 2
- 230000003009 desulfurizing effect Effects 0.000 claims description 2
- 239000000306 component Substances 0.000 claims 2
- 230000008030 elimination Effects 0.000 claims 1
- 238000003379 elimination reaction Methods 0.000 claims 1
- 229910000041 hydrogen chloride Inorganic materials 0.000 abstract description 18
- IXCSERBJSXMMFS-UHFFFAOYSA-N hydrogen chloride Substances Cl.Cl IXCSERBJSXMMFS-UHFFFAOYSA-N 0.000 abstract description 18
- 229910001385 heavy metal Inorganic materials 0.000 abstract description 8
- 238000010791 quenching Methods 0.000 abstract description 3
- 230000000171 quenching effect Effects 0.000 abstract description 3
- 239000007789 gas Substances 0.000 abstract description 2
- 239000010791 domestic waste Substances 0.000 abstract 1
- 239000003500 flue dust Substances 0.000 abstract 1
- 239000012535 impurity Substances 0.000 abstract 1
- UXVMQQNJUSDDNG-UHFFFAOYSA-L Calcium chloride Chemical compound [Cl-].[Cl-].[Ca+2] UXVMQQNJUSDDNG-UHFFFAOYSA-L 0.000 description 6
- 239000001110 calcium chloride Substances 0.000 description 6
- 229910001628 calcium chloride Inorganic materials 0.000 description 6
- 235000011148 calcium chloride Nutrition 0.000 description 6
- 235000011116 calcium hydroxide Nutrition 0.000 description 5
- 229940095643 calcium hydroxide Drugs 0.000 description 5
- KRHYYFGTRYWZRS-UHFFFAOYSA-M Fluoride anion Chemical compound [F-] KRHYYFGTRYWZRS-UHFFFAOYSA-M 0.000 description 4
- 238000001704 evaporation Methods 0.000 description 4
- 230000008020 evaporation Effects 0.000 description 4
- 238000000746 purification Methods 0.000 description 4
- 239000000126 substance Substances 0.000 description 4
- 239000002351 wastewater Substances 0.000 description 4
- 150000003841 chloride salts Chemical class 0.000 description 3
- 238000005868 electrolysis reaction Methods 0.000 description 3
- 239000010881 fly ash Substances 0.000 description 3
- 238000001556 precipitation Methods 0.000 description 3
- 239000000047 product Substances 0.000 description 3
- 239000000725 suspension Substances 0.000 description 3
- 239000000356 contaminant Substances 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 239000000428 dust Substances 0.000 description 2
- 150000002222 fluorine compounds Chemical class 0.000 description 2
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 1
- 239000003513 alkali Substances 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- KGBXLFKZBHKPEV-UHFFFAOYSA-N boric acid Chemical compound OB(O)O KGBXLFKZBHKPEV-UHFFFAOYSA-N 0.000 description 1
- 239000004327 boric acid Substances 0.000 description 1
- 239000006227 byproduct Substances 0.000 description 1
- 230000004087 circulation Effects 0.000 description 1
- 230000001276 controlling effect Effects 0.000 description 1
- 230000000875 corresponding effect Effects 0.000 description 1
- 238000005137 deposition process Methods 0.000 description 1
- 230000003292 diminished effect Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000000706 filtrate Substances 0.000 description 1
- 150000004673 fluoride salts Chemical class 0.000 description 1
- 150000004679 hydroxides Chemical class 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 150000002894 organic compounds Chemical class 0.000 description 1
- 238000001953 recrystallisation Methods 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 229910052708 sodium Inorganic materials 0.000 description 1
- 239000011734 sodium Substances 0.000 description 1
- 238000011282 treatment Methods 0.000 description 1
- 239000002912 waste gas Substances 0.000 description 1
- 238000004065 wastewater treatment Methods 0.000 description 1
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
-
- 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
- B01D53/68—Halogens or halogen compounds
-
- 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
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
- Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
Landscapes
- 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)
- Sealing Material Composition (AREA)
Abstract
2094150 9206771 PCTABS00011 Described is a process for purifying flue gases with a high chloride content, in particular gases from domestic-waste and special waste incineration plants, by multi-stage absorption of the impurities, the strongly acid components of the flue gases, such as HCl and HF, being scrubbed out first with water and/or lye and the less acid components, such as SO2 and NOx, being removed afterwards. The invention calls for flue dust, heavy metals and HF
to be separated out by quenching with water, while hydrogen chloride is converted, in at least two subsequent washing stages, into salt solutions.
to be separated out by quenching with water, while hydrogen chloride is converted, in at least two subsequent washing stages, into salt solutions.
Description
:- 2 0 ~ 0 KH
PR~CESS FOR PURIFYING FLUE GA~ HAVTN~ HI~H CHLORIDE CONTENT
The present invention relates to a process for purifying flue gas having high chloride content, and more specifically of flue gas from waste and special waste incineration plants by a multi-stage absorption of con-taminats, wherein initially, strongly acidic components of the flue gas such as HCl and HF are removed by washing with water and/or alkaline solutions, and in subsequent stages the less acidic flue gas components such as SO2 and NOx are removed.
In the purification of flue gases, HCl and HF play a big part, besides SO2 and NOx, and especially so if the flue gas is derived from a waste incineration plant. Depending on composition of the waste subjected to incineration, the HCl content of the flue gas may amount to even more than 10 g/m3.
As a rule, such high ~Cl contents require particular treat-ment in flue gas purification plants. Today, this is effected primarily by introducing a stage of HCl removal preceding the stage of SO2 removal. Here, HCl removal frequently is effected with simultaneous quenching of the flue gas, with alkaline chemicals being already added in most of the casesO
Furthermore, in such quenching, a ma~or part of residual dust remaining in the flue gas is deposited.
The solution or suspension obtained during the deposition process and mostly still being acidic due to hydrochloric acid generally contains the major part of heavy metals contained in the flue gas. This hydrochloric acid solution or suspension mostly is subjected to waste water treatment. Upon addition of alkali or alkaline earth car-.: .. ~, . : ~ : .
:; . , , ,. : . : , ~ : : , . . . : .
20941~
bonates or hydroxides, neutralization along with precipita-tion of heav~v metals occurs. Subsequent to filtrating the suspension, the filtrate usually is fed into a preclarifier or is evaporated, with the residue being conveyed to a disposal site. When entering the preclarifier, the waste water in most of the cases still contains considerable amounts of soluble salts as well as certain residual contents of heavy metal.
If it is intended to recover utilizable salts such as common salt or calcium chloride from these residues, an efficient and expensive procedure of waste water re-pxocess-ing must generally be carried out prior to evaporation and, depending on the circumstances, the crystal mass precipitated during evaporation must be subjected to one or more recrys-tallization steps which involves a high apparative and energetic input while, nevertheless, degrees of purity for the salts as demanded in practice cannot be guaranteed.
It is an object of the present invention to further improve the process for purifying flue gas having a high chloride content, in particular, flue gas from a waste and special waste incineration plant, and render it simpler and safer, with maximum possible amounts of re-usable products and only small amounts of waste material loading waste water or disposal site being formed. More particularly, it is an object of the invention to conduct the removal of the strongly acidic components such as HCl and HF ~rom the flue gas in a manner such that re-usable substances are recoverPd thexefrom with low costs and in reliable fashion. The process is based on such processes where in a pre-stage, strongly acidic components of the flue gas such as HCl and HF are washed out with water initially containing up to 20 g/l of HCl, and in subsequent stages the less acidic components of the flue gas such as SO2 and NOX are removed.
: - .: : .................. , . : ~ . . .
: .- ;: ,. .... ..
20941~0 ~ ,.
Said object can be attained in a surprisingly simple way by pre-washing with water in a quencher pre-stage, then washing once more with water in at least one subsequent washing stage, and then washing once more with water in at least one further subsequent washing stage at pH values of < 3, preferably at pH values of < 1 with neutralization using alkaline solutions, preferably sodium hydroxide solution or calcium hydroxide, and only then desulfurizing and denitriz-ing in the usual fashion, with the washing solution from the first washing stage(s) being re-fed into the quencher, and the washing solution neutralized with alkaline solution being eliminated from the process on exceeding the desired maximum concentrations o~ salts.
Surprisingly, it has turned out that according to the invention, in the quencher stage and in at least one of the su~sequen~ washing stages using water, virtually the entire amount of heavy metals and fluoride - except for r~sidual flue ash - is deposited so that in the subsequent washing stage(s) using sodium hydroxide solution or calcium hydrox-ide, sodium chloride or calcium chloride is obtained with high purity. The quencher bottom, in addition to heavy metals and possibly fluoride, consists of hydrochloric acid cor-responding to the equilibrium partial pressure of hydrogen chloride in the flue gas. Once this equilibrium concentration is reached, the flue gas again contains the original HCl concentration after the quencher stage.
By adding aluminum chloride to the first washing solution after the quencher stage, it is possible to deposit sparingly soluble aluminum fluoride which may be utilized separately.
In the subsequent washing stages with neutralization using alkaline solutions such as sodium hydroxidP solution or calcium hydroxide, the HCl gas is removed from the flue gas almost completely, without substantial removal of SO2 and NOx .. : ,,: ,. .: . :: :~
- : . -. .. i , . : :
PR~CESS FOR PURIFYING FLUE GA~ HAVTN~ HI~H CHLORIDE CONTENT
The present invention relates to a process for purifying flue gas having high chloride content, and more specifically of flue gas from waste and special waste incineration plants by a multi-stage absorption of con-taminats, wherein initially, strongly acidic components of the flue gas such as HCl and HF are removed by washing with water and/or alkaline solutions, and in subsequent stages the less acidic flue gas components such as SO2 and NOx are removed.
In the purification of flue gases, HCl and HF play a big part, besides SO2 and NOx, and especially so if the flue gas is derived from a waste incineration plant. Depending on composition of the waste subjected to incineration, the HCl content of the flue gas may amount to even more than 10 g/m3.
As a rule, such high ~Cl contents require particular treat-ment in flue gas purification plants. Today, this is effected primarily by introducing a stage of HCl removal preceding the stage of SO2 removal. Here, HCl removal frequently is effected with simultaneous quenching of the flue gas, with alkaline chemicals being already added in most of the casesO
Furthermore, in such quenching, a ma~or part of residual dust remaining in the flue gas is deposited.
The solution or suspension obtained during the deposition process and mostly still being acidic due to hydrochloric acid generally contains the major part of heavy metals contained in the flue gas. This hydrochloric acid solution or suspension mostly is subjected to waste water treatment. Upon addition of alkali or alkaline earth car-.: .. ~, . : ~ : .
:; . , , ,. : . : , ~ : : , . . . : .
20941~
bonates or hydroxides, neutralization along with precipita-tion of heav~v metals occurs. Subsequent to filtrating the suspension, the filtrate usually is fed into a preclarifier or is evaporated, with the residue being conveyed to a disposal site. When entering the preclarifier, the waste water in most of the cases still contains considerable amounts of soluble salts as well as certain residual contents of heavy metal.
If it is intended to recover utilizable salts such as common salt or calcium chloride from these residues, an efficient and expensive procedure of waste water re-pxocess-ing must generally be carried out prior to evaporation and, depending on the circumstances, the crystal mass precipitated during evaporation must be subjected to one or more recrys-tallization steps which involves a high apparative and energetic input while, nevertheless, degrees of purity for the salts as demanded in practice cannot be guaranteed.
It is an object of the present invention to further improve the process for purifying flue gas having a high chloride content, in particular, flue gas from a waste and special waste incineration plant, and render it simpler and safer, with maximum possible amounts of re-usable products and only small amounts of waste material loading waste water or disposal site being formed. More particularly, it is an object of the invention to conduct the removal of the strongly acidic components such as HCl and HF ~rom the flue gas in a manner such that re-usable substances are recoverPd thexefrom with low costs and in reliable fashion. The process is based on such processes where in a pre-stage, strongly acidic components of the flue gas such as HCl and HF are washed out with water initially containing up to 20 g/l of HCl, and in subsequent stages the less acidic components of the flue gas such as SO2 and NOX are removed.
: - .: : .................. , . : ~ . . .
: .- ;: ,. .... ..
20941~0 ~ ,.
Said object can be attained in a surprisingly simple way by pre-washing with water in a quencher pre-stage, then washing once more with water in at least one subsequent washing stage, and then washing once more with water in at least one further subsequent washing stage at pH values of < 3, preferably at pH values of < 1 with neutralization using alkaline solutions, preferably sodium hydroxide solution or calcium hydroxide, and only then desulfurizing and denitriz-ing in the usual fashion, with the washing solution from the first washing stage(s) being re-fed into the quencher, and the washing solution neutralized with alkaline solution being eliminated from the process on exceeding the desired maximum concentrations o~ salts.
Surprisingly, it has turned out that according to the invention, in the quencher stage and in at least one of the su~sequen~ washing stages using water, virtually the entire amount of heavy metals and fluoride - except for r~sidual flue ash - is deposited so that in the subsequent washing stage(s) using sodium hydroxide solution or calcium hydrox-ide, sodium chloride or calcium chloride is obtained with high purity. The quencher bottom, in addition to heavy metals and possibly fluoride, consists of hydrochloric acid cor-responding to the equilibrium partial pressure of hydrogen chloride in the flue gas. Once this equilibrium concentration is reached, the flue gas again contains the original HCl concentration after the quencher stage.
By adding aluminum chloride to the first washing solution after the quencher stage, it is possible to deposit sparingly soluble aluminum fluoride which may be utilized separately.
In the subsequent washing stages with neutralization using alkaline solutions such as sodium hydroxidP solution or calcium hydroxide, the HCl gas is removed from the flue gas almost completely, without substantial removal of SO2 and NOx .. : ,,: ,. .: . :: :~
- : . -. .. i , . : :
2~150 i. .
occurring. Decisively important is the pH value which is maintained in all the washing stages at < 3, preferabl~ < 1.
Addition of alkaline solutions such as sodium hydroxide solution or of calcium hydroxide is always done in only such extent as is necessary to neutralize absorbed HCl. Thus, conveniently, controlling the addition of each alkaline solution is effected via pH values of the washing solutions.
The absorption capacity of the washing solutions for HCl is diminished with increasing concentrations or dissolved salts such as sodium chloride or calcium chloride. Thus, according to the invention, 2 washing stages with neutraliza-tion are provided. While in the first washing stage con-centrating the salt solutions up to a desired maximum value is effected, the second and optionally further washing stages serve to more completely remove HCl from the flue gas.
Conveniently, eliminating the washing solutions from each washing stage is done according to thP concentrations of sal~s. Most simply, these can be measured via conductivity or density. In principle, it would also be possible to determine the overall chloride content, but with hitherto known methods, this is much more costly.
At last, an amazingly pure and almost neutralized sodium chloride solution is eliminated from the first washing stage with neutralization using sodium hydroxide solution.
Purity and concentration of these sodium chloride solutions are so high that it is possible to employ them in the electrolysis of alkaline chloride salts with relatively lo~
effort. ~iXewise, the removed calcium chloride is amazingly pure and may be used like any other pure calcium chloride~ If desired, the salt solutions may also be evaporated to dryness and thus, solid salts may be recovered. Production of pure solid sodium chloride has proven especially advantageous.
In particular, having relatively high contents of HF, it has proven convenient to add a water soluble fluoride-209~
: .
binding substance to the first washing stage subsequent tothe quencher stage. As the fluoride-binding substance, aluminum chloride but optionally also calcium chloride or boric acid are possible above all. Thus, residual entrained flue ash, heavy metals and above all, precipitated fluorides are eliminated from the first washing solution. If desired, the quencher bottom may also be subjected to separation and processing in order to recover further utilizable products.
Most simply, this is done by fractionated precipitation using calcium hydroxide or sodium hydroxide solution, for instance.
If high fluoride concentrations are present, the precipitated fluoride salts and fluoride compounds may also be removed and recycled.
- It has turned out that in spite of the expense ofhaving several separate washing stages and circulations of washing solutions and seeming greater initially, it is much more lower in cost and simpler to remove the contaminants that are removable beforehand such as flue ash, heavy metals, HF, and HCl and convert them to utilizable products instead of removing them together and attempting later to re&over useful fractions again.
The process of the invention operates especially efficient when entrainment between washing stages is prevent-ed by mist eliminators. By installing mist eliminators it is possible to reduce entrainment from one washing stage to the next from about 10% to about 2-3%. Instead of having several washing stages and the expense associated therewith, mist eliminators permit to have fewer washing stages and never-theless, to achieve the same effects.
According to another variant of khe process of the invention, hydrochloric acid is removed by distillation from one of the acid washing stages following the quencher, the condensate i~; purified over active charcoal and neutralized 2~9~:L ~ a using sodium hydroxide solution with cooling to give a sodium chloride solution of at least 100 g, preferably 150 to 250 g NaCl/l. It has turned out that with this variant of the process as well, residual dust, heavy metals and organic contaminants are predominantly concentrated in the bottom of the distillation, and that residues of organic compounds passing over with the hydrochloric acid vapors may be removed by an active charcoal adsorber. On neutrali~ing the thus obtained hydrochloric acid with sodium hydroxide solution with cooling, sodium chloride solutions or - on evaporation to giva the salt - solid salts are obtained with such purity that it is possible to further use them as high grade saline or pure salts. According to the invention, the expense for pur~fying the salts is less than in conventional purification of the salts, in particular of sodium chloride by stepwise evaporation and precipitation of the crystal mass.
At the same time, purification of the waste gases can be achieved better, safer and more economical in this ~ashion, with less formation of waste water and waste material which loads the disposal sites.
For example, the process of the invention may be employed in close vicinity to a plant for electrolysis of alkaline chloride salts where most frequently, chlorinated waste material is formed as well which is intended to be disposed in the special waste incineration. ~ikewise/ sodium hydroxide solution needed to neutralize the hydrogen chloride is directly available. Without major expense, the recovered sodium chloride solution may be re-fed to the electrolysis of alkaline chloride salts so that virtually, all the by products of such a plant may be recovered and recycled.
;` :
.- , .. , ,. ..:- ~... .
.
- , : : :: : .~- . . ... : :
, ~ ,. :: ::: . .
occurring. Decisively important is the pH value which is maintained in all the washing stages at < 3, preferabl~ < 1.
Addition of alkaline solutions such as sodium hydroxide solution or of calcium hydroxide is always done in only such extent as is necessary to neutralize absorbed HCl. Thus, conveniently, controlling the addition of each alkaline solution is effected via pH values of the washing solutions.
The absorption capacity of the washing solutions for HCl is diminished with increasing concentrations or dissolved salts such as sodium chloride or calcium chloride. Thus, according to the invention, 2 washing stages with neutraliza-tion are provided. While in the first washing stage con-centrating the salt solutions up to a desired maximum value is effected, the second and optionally further washing stages serve to more completely remove HCl from the flue gas.
Conveniently, eliminating the washing solutions from each washing stage is done according to thP concentrations of sal~s. Most simply, these can be measured via conductivity or density. In principle, it would also be possible to determine the overall chloride content, but with hitherto known methods, this is much more costly.
At last, an amazingly pure and almost neutralized sodium chloride solution is eliminated from the first washing stage with neutralization using sodium hydroxide solution.
Purity and concentration of these sodium chloride solutions are so high that it is possible to employ them in the electrolysis of alkaline chloride salts with relatively lo~
effort. ~iXewise, the removed calcium chloride is amazingly pure and may be used like any other pure calcium chloride~ If desired, the salt solutions may also be evaporated to dryness and thus, solid salts may be recovered. Production of pure solid sodium chloride has proven especially advantageous.
In particular, having relatively high contents of HF, it has proven convenient to add a water soluble fluoride-209~
: .
binding substance to the first washing stage subsequent tothe quencher stage. As the fluoride-binding substance, aluminum chloride but optionally also calcium chloride or boric acid are possible above all. Thus, residual entrained flue ash, heavy metals and above all, precipitated fluorides are eliminated from the first washing solution. If desired, the quencher bottom may also be subjected to separation and processing in order to recover further utilizable products.
Most simply, this is done by fractionated precipitation using calcium hydroxide or sodium hydroxide solution, for instance.
If high fluoride concentrations are present, the precipitated fluoride salts and fluoride compounds may also be removed and recycled.
- It has turned out that in spite of the expense ofhaving several separate washing stages and circulations of washing solutions and seeming greater initially, it is much more lower in cost and simpler to remove the contaminants that are removable beforehand such as flue ash, heavy metals, HF, and HCl and convert them to utilizable products instead of removing them together and attempting later to re&over useful fractions again.
The process of the invention operates especially efficient when entrainment between washing stages is prevent-ed by mist eliminators. By installing mist eliminators it is possible to reduce entrainment from one washing stage to the next from about 10% to about 2-3%. Instead of having several washing stages and the expense associated therewith, mist eliminators permit to have fewer washing stages and never-theless, to achieve the same effects.
According to another variant of khe process of the invention, hydrochloric acid is removed by distillation from one of the acid washing stages following the quencher, the condensate i~; purified over active charcoal and neutralized 2~9~:L ~ a using sodium hydroxide solution with cooling to give a sodium chloride solution of at least 100 g, preferably 150 to 250 g NaCl/l. It has turned out that with this variant of the process as well, residual dust, heavy metals and organic contaminants are predominantly concentrated in the bottom of the distillation, and that residues of organic compounds passing over with the hydrochloric acid vapors may be removed by an active charcoal adsorber. On neutrali~ing the thus obtained hydrochloric acid with sodium hydroxide solution with cooling, sodium chloride solutions or - on evaporation to giva the salt - solid salts are obtained with such purity that it is possible to further use them as high grade saline or pure salts. According to the invention, the expense for pur~fying the salts is less than in conventional purification of the salts, in particular of sodium chloride by stepwise evaporation and precipitation of the crystal mass.
At the same time, purification of the waste gases can be achieved better, safer and more economical in this ~ashion, with less formation of waste water and waste material which loads the disposal sites.
For example, the process of the invention may be employed in close vicinity to a plant for electrolysis of alkaline chloride salts where most frequently, chlorinated waste material is formed as well which is intended to be disposed in the special waste incineration. ~ikewise/ sodium hydroxide solution needed to neutralize the hydrogen chloride is directly available. Without major expense, the recovered sodium chloride solution may be re-fed to the electrolysis of alkaline chloride salts so that virtually, all the by products of such a plant may be recovered and recycled.
;` :
.- , .. , ,. ..:- ~... .
.
- , : : :: : .~- . . ... : :
, ~ ,. :: ::: . .
Claims (9)
1. A process for purifying flue gas having high chloride content, and more specifically of flue gas from waste and special waste incineration plants by a multi-stage absorption of contaminats, wherein initially, strongly acidic components of the flue gas such as HCl and HF are washed out with water and/or alkaline solutions, and in subsequent stages the less acidic flue gas com-ponents such as SO2 and NOX are removed, characterized in that in a quencher pre-stage, pre-washing with water is effected, then washing once more with water in at least one subsequent washing stage, and then washing once more with water in at least one further subsequent washing stage at pH values of < 3, preferably at pH values of < 1 with neutralization using alkaline solutions, preferably sodium hydroxide solution or calcium hydroxide, and only then desulfurizing and denitrizing in the usual fashion, with the washing solution from the first washing stage(s) being re-fed into the quencher, and the washing solution neutralized with alkaline solution being eliminated from the process on exceeding the desired maximum con-centrations of salts.
2. The process according to claim 1, characterized in that entrainment between washing stages is prevented by mist eliminators.
3. The process according to claim 1 or 2, charac-terized in that subsequent to the quencher stage, washing with water is effected in at least two washing stages, and the washing solution of each subsequent washing stage is partially transferred to the preceding washing stage on exceeding a pre-set maximum concentration of acid.
4. Process according to one of claims 1 to 3, characterized in that in the first washing solution subsequent to the quencher stage, aluminum chloride is added and the precipitated aluminum fluoride is removed prior to re-feeding into the quencher stage.
5. Process according to one of claims 1 to 4, characterized in that subsequent to the water washing stages, the washing solutions are neutralized in at least two washing stages using sodium hydroxide solution or calcium hydroxide and the washing solution of each subsequent washing stage is partially transferred to the preceding washing stage on exceeding a pre-set maximum concentration of salts.
Process according to one of claims 1 to 5, characterized in that addition of sodium hydroxide solution or calcium hydroxide to each washing solution is controlled via pH values.
7. Process according to one of claims 1 to 4, characterized in that the elimination of salt-containing washing solutions from each washing stage is controlled via conductivity.
8. Process according to one of claims 1 to 4, characterized in that hydrochloric acid is removed by distillation from one of the acid washing stages following the quencher, the condensate is purified over active charcoal and neutralized using sodium hydroxide solution with cooling to give a sodium chloride solution of at least 100 g, preferably 150 to 250 g NaCl/1.
9. Process according to one of claims 7 or 8, characterized in that the salt solutions are subsequently evaporated to give solid salt.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP4032945.3 | 1990-10-17 | ||
| DE4032945A DE4032945C1 (en) | 1990-10-17 | 1990-10-17 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2094150A1 true CA2094150A1 (en) | 1992-04-18 |
Family
ID=6416471
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002094150A Abandoned CA2094150A1 (en) | 1990-10-17 | 1991-10-08 | Process for purifying flue gases with a high chloride content |
Country Status (7)
| Country | Link |
|---|---|
| EP (1) | EP0553146B1 (en) |
| KR (1) | KR100215088B1 (en) |
| AT (1) | ATE122258T1 (en) |
| CA (1) | CA2094150A1 (en) |
| DE (2) | DE4032945C1 (en) |
| ES (1) | ES2072018T3 (en) |
| WO (1) | WO1992006771A1 (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE4304191A1 (en) * | 1993-02-12 | 1994-08-18 | Noell Gmbh | Process for scrubbing acidic gas components out of flue gases by absorption |
| DE4447583A1 (en) * | 1994-09-05 | 1996-04-18 | Uhde Gmbh | Removing harmful pollutants from combustion waste gases and recovering |
| DE19519532C2 (en) * | 1995-05-27 | 1998-07-16 | Metallgesellschaft Ag | Process for the separation of mercury from combustion gases |
| EP0778067B1 (en) * | 1995-12-06 | 2001-08-22 | Lurgi Lentjes Bischoff GmbH | Apparatus for purifying smokes containing acid compounds of different concentration acid process for operating the apparatus |
| FR2750416B1 (en) * | 1996-06-28 | 1998-08-14 | Lab Sa | PROCESS FOR TREATING THE PURGES OF A WET SYSTEM FOR THE PREPARATION OF A NEW REAGENT |
| DE102006016963B3 (en) * | 2006-04-11 | 2007-10-04 | Forschungszentrum Karlsruhe Gmbh | Method for reducing nitrogen oxides and halogenated organic compounds in a waste gas in a combustion installation comprises removing fly ash using a dust separator, removing hydrochloric acid in a first scrubber and further processing |
| CN102416288B (en) * | 2011-12-06 | 2015-01-07 | 中南大学 | Method for separating and recovering valuable metal chloride and hydrogen chloride from high-temperature chloridizing metallurgy flue gas |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4147756A (en) * | 1976-04-09 | 1979-04-03 | Envirotech Corporation | Combustion gas scrubbing system |
| DE2735566A1 (en) * | 1977-08-06 | 1979-02-22 | Metallgesellschaft Ag | METHOD FOR REMOVING FLUOROUS COMPOUNDS AND SULFUR DIOXIDE FROM EXHAUST GASES |
| DE2939744A1 (en) * | 1979-10-01 | 1981-04-02 | Saarberg-Fernwärme GmbH, 6600 Saarbrücken | Flue gas treatment to remove fly ash and sulphur oxide(s) - with pre:wash to remove fluorine and chlorine cpds. and residual fly ash allowing pure gypsum recovery |
| DE3139991A1 (en) * | 1981-10-08 | 1983-04-28 | Hölter, Heinz, Dipl.-Ing., 4390 Gladbeck | Limestone scrubbing for scrubbing waste gases, preferably from coal power stations |
| EP0169997B1 (en) * | 1984-07-28 | 1991-09-18 | Kernforschungszentrum Karlsruhe Gmbh | Process for purifying smoke |
| DE3521205A1 (en) * | 1985-06-13 | 1986-12-18 | Gottfried Bischoff Bau kompl. Gasreinigungs- und Wasserrückkühlanlagen GmbH & Co KG, 4300 Essen | Plant for purifying industrial exhaust gases |
| DE3611886A1 (en) * | 1986-04-09 | 1987-10-22 | Hoechst Ag | Process for removing hydrogen chloride and chlorine from combustion gases with recovery of hydrochloric acid |
| ES2042115T5 (en) * | 1989-04-17 | 1996-03-01 | Krc Umwelttechnik Gmbh | PROCEDURE FOR EXHAUST GAS DEPURATION WITH HIGH CHLORIDE CONTENT. |
-
1990
- 1990-10-17 DE DE4032945A patent/DE4032945C1/de not_active Expired - Fee Related
-
1991
- 1991-10-08 AT AT91917707T patent/ATE122258T1/en not_active IP Right Cessation
- 1991-10-08 CA CA002094150A patent/CA2094150A1/en not_active Abandoned
- 1991-10-08 KR KR1019930701138A patent/KR100215088B1/en not_active IP Right Cessation
- 1991-10-08 DE DE59105472T patent/DE59105472D1/en not_active Expired - Fee Related
- 1991-10-08 EP EP91917707A patent/EP0553146B1/en not_active Expired - Lifetime
- 1991-10-08 WO PCT/EP1991/001910 patent/WO1992006771A1/en active IP Right Grant
- 1991-10-08 ES ES91917707T patent/ES2072018T3/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| EP0553146A1 (en) | 1993-08-04 |
| WO1992006771A1 (en) | 1992-04-30 |
| EP0553146B1 (en) | 1995-05-10 |
| ES2072018T3 (en) | 1995-07-01 |
| KR930702061A (en) | 1993-09-08 |
| DE4032945C1 (en) | 1992-01-30 |
| DE59105472D1 (en) | 1995-06-14 |
| ATE122258T1 (en) | 1995-05-15 |
| KR100215088B1 (en) | 1999-08-16 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued |