CA2086778A1 - Process for the reduction of nitrogen oxides in exhaust gases - Google Patents
Process for the reduction of nitrogen oxides in exhaust gasesInfo
- Publication number
- CA2086778A1 CA2086778A1 CA 2086778 CA2086778A CA2086778A1 CA 2086778 A1 CA2086778 A1 CA 2086778A1 CA 2086778 CA2086778 CA 2086778 CA 2086778 A CA2086778 A CA 2086778A CA 2086778 A1 CA2086778 A1 CA 2086778A1
- Authority
- CA
- Canada
- Prior art keywords
- starting substance
- exhaust gas
- hnco
- substance
- carbamate
- 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
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/46—Removing components of defined structure
- B01D53/54—Nitrogen compounds
- B01D53/56—Nitrogen oxides
Abstract
ABSTRACT OF THE DISCLOSURE
In the process for the reduction of nitrogen oxides in exhaust gases, the exhaust gas is brought into contact with NCO free radicals which are formed by thermal dissociation of isocyanic acid (HNCO). In this case, a starting substance present in the molten form below about 100°C, preferably a carbamate, is used.
Compared with the hitherto used solid starting substances, this is easier to handle and also does not produce deposits in the exhaust gas channel (l).
(Figure 1)
In the process for the reduction of nitrogen oxides in exhaust gases, the exhaust gas is brought into contact with NCO free radicals which are formed by thermal dissociation of isocyanic acid (HNCO). In this case, a starting substance present in the molten form below about 100°C, preferably a carbamate, is used.
Compared with the hitherto used solid starting substances, this is easier to handle and also does not produce deposits in the exhaust gas channel (l).
(Figure 1)
Description
2~3~778 TITLE OF THE INVENTION
PROCESS FOR THE REDIJCTION OF NITROGEN OXIDES IN EXHAllST
GASES
BACKGROUND OF THE INVENTION
Field of the invention The invention relate~ to a process for the reduction of nitrogen oxides in exhaust gases, in which process the exhaust gas is brought into contact with NCO free radicals, which are formed by thermal dissociation of isocyanic acid (HNCO).
Discussion of backqround Apart from many other processes, the so-called RAPRENOX process has attained a cer~ain importance in the denitration of exhaust gases. In this process - it was described ~or the first time in US Patent 4,731,231 - the NCO free radical is used for NOX rednction. The free radicals are obtained from isocyanic acid HNCO by cleavage of the H atom. HNCO in turn is obtained in this process by thermal decompositio~ ~of cyanuric acid or oligomers of HNCO. Cyanuric acid in the solld state forms, at temperatures of 300 to 400~ and above, by sublimation a gaseous/vapor-form intermediate, which then reacts at temperatures above 500C ~ln the exhaust gas to form isocyanic acid (HNCO). Other known processes use urea (H2NCONH2) as starting s~bstance. A
common characteris~ic of the known processes is the use of a solid starting substance, which is con~erted into the gas phase by sublimation.
Apart from the fact that obtaining HNCO.in this manner is expensive in terms of apparatus, the known processes require relatively high temperatures and have the disadvantage that by-products which are difficult ''." , ' ' ~
~ . ~ - ., ' :., .. ',, ~ : . .,: ` ' to handle are formed, which are deposited at cold points in the evaporator device.
SU~MARY OF THE INVENTION
Accordingly, one object of the invention is to provide a novel process for the reduction of nitrogen oxides, which likewise operates with the free radical NCO, but in which the isocyanic acid can be prepared at relatively low temperature ~nd thus is also much simpler to carry out.
This object is achieved according to the . invention in that the starting substance used is a substance which occurs in the molten state below 100C
and is highly evaporative rom the liquid phase, which substance acts directly or after pretreatment on the exhaust gas.
The advantage of the invention is to be seen in particular in that already at temperatures above about 200C, the thermal decomposition of the starting substance is produced and thus HNCO is produced at a substantially lower temperature and sLmpler than in the known RAPRENOX process. The starting substance is very simple to handle. No deposits result in the exhaust gas channel.
,` Exemplary embodiments of the in~vention and the ~; advantages achieved therewith are described below in more detail with reference to the drawing BRIEF DESCRIPTION OF THE DRAWING
;. ~
A more complete appreciation o~ the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection ` with the accompanying drawings, wherein:
.. . .
Figure 1 depicts a schematic representation of the exhaust gas channel of a thermal power station;
Figure 2 is a diagram which depicts the : decomposition of methyl carbamate in relation to the S temperature.
DESCRIPTION OF THE PREFERRED ENBODIMENTS
Referring now to the drawing, a first pipe 2 `10 opens into the exhaust gas p~pe 1 of a thermal power station, for example a gas turbine, which first pipe leads to a first treatment chamber 3. This in turn is connected via a second pipe 4 to a second treatment chamber 5. The second treatment cham~er S is partially filled with the starting substance 6, in ~his case methyl carbamate. It is heated to a temperature of about 80C and is therefore partly in the liquid state and partly in the vapor form.
The vapor produced enters via the pipe 4 into the ~optional) first treatment chamber 3. A gas stream, for example air or nitrogen, can be introduced at the same time into the second treatment chamber 5 via a third pipe 7. The additional gas stream dilutes the vapor and accelerates its flow out of the second treatment chamber 5. ~
Further events depend on whether the (optional) treatment chamber is present and on which conditions prevail there, or whether the vapor-form methyl carbamate is fed or admixed directly t~o the exhau~t gas.
In the latter case, the thermal dë~omposition of the vapor-form methyl carbamate proce~ds with formation of HNCO and the decomposition of the HNCO
proceeds with formation of NCO free radicals, which finally effect the reduction of the nitrogen oxide, in the exhaust ga~. The decomposition of the vapor-form methyl carbamate and the formation of HNCO in relation to temperature i8 illustrated by the diagram :: ' ' " , ~ .. ,:
. ~ ..
i i - , , , , . . .. . . . .. .
,.. ' ::
' , I' 2~8~778 represented in Figure 2. The residence time of the vapor-form methyl carbamate at the temperature plotted on the abscissa was in each case in the order of magnitude of a few tenths of a second. It can be clearly seen that the formation of HNCO begins even at relatively low temperatures. These temperatures are considerably below those temperatures which are required for the formation of HNCO from cyanuric acid (above 500C) or from urea.
If the optional treatm~nt chamber 3 is present, and if a sufficiently high temperature corresponding to the diagram in Figure 2 prevails there, the vapor-form methyl carbamate is decomposed in the first treatment chamber 3 into HNCO and other decomposition products.
The HNCO then passes, with the other decomposition products of the methyl carbamate and, possibly with the gas stream additionally added via pipe 7, through pipe 2 into the exhaust gas pipe 1, where it is mixed with the exhaust gas and ~hen, when the exhaust gas temperature is sufficiently high, NCO free radicals are formed, which then react wi~h the nitrogen oxides in a known manner.
The heating of the first treatment chamber 3 or the heat supply to this can be achieved by a separate 2S heat source, possibly with exploitation~of the (exhaust gas) heat from the power station. .~
However, it is alternatively possible to set the temperature in the first treatment chamber 3 high enough so that even in the latter the HNCO is already decomposed at least in part into atomic hydrogen and NCO free radicals. Temperatures of above ~600C are necessary for this. The subsequent direct introduction of NCO free radicals permits the reduction of nitrogen oxide at lower exhaust gas temperatures than hitherto, since these free radicals do not have to be first formed in the exhaust gas, which would firstly require a sufficiently high temperature in the exhaust gas and ~3~778 would secondly require a certain period of time for the free radical formation.
The production of NCO free radicals from HNCO
prior to entry into the exhaust gas can also be carried ~ 5 out by other physical and/or chemical pretreatment, such as for example pho~olytic and/or catalytic pretreatment and/or by irradiation with infrared light, `electron beams, radio waves etc. In Figure 1, for example, pretreatment with W light is depicted, in which the absorption of W ~ight quanta effects`the cleavage of an H atom from the HNCO.
Because of th~ short live~ of the NCO free radicals, the pipe 2 between the exhaust gas channel 1 and the pretreatment chamber must not be very long.
15In addition to the methyl carbamate mentioned in the exemplary embodiment, a series of other starting subs~ances can be considered, mainly generally oxygen-containing hydrocarbons having at least one nitrogen function, aliphatically substituted carbamates, in addition to the mentioned methyl carbamate, ethyl - carbamate, tertiary butyl carbamate. Oxyurea or hydroxyurea, hydrazinates or esters thereof, preferably hydrazinecarboxylic acid or hydrazinecarboxylic esters, oxamic acid or oxamide and semicarbazones are also used as starting substance. ~
Obviou31y, numerous modif~ications and variations of the present in~ention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein. i~
:, , , -;- . :
~, ' - , , ,' . "
: : .
'' " ~, ,: .:. , ,
PROCESS FOR THE REDIJCTION OF NITROGEN OXIDES IN EXHAllST
GASES
BACKGROUND OF THE INVENTION
Field of the invention The invention relate~ to a process for the reduction of nitrogen oxides in exhaust gases, in which process the exhaust gas is brought into contact with NCO free radicals, which are formed by thermal dissociation of isocyanic acid (HNCO).
Discussion of backqround Apart from many other processes, the so-called RAPRENOX process has attained a cer~ain importance in the denitration of exhaust gases. In this process - it was described ~or the first time in US Patent 4,731,231 - the NCO free radical is used for NOX rednction. The free radicals are obtained from isocyanic acid HNCO by cleavage of the H atom. HNCO in turn is obtained in this process by thermal decompositio~ ~of cyanuric acid or oligomers of HNCO. Cyanuric acid in the solld state forms, at temperatures of 300 to 400~ and above, by sublimation a gaseous/vapor-form intermediate, which then reacts at temperatures above 500C ~ln the exhaust gas to form isocyanic acid (HNCO). Other known processes use urea (H2NCONH2) as starting s~bstance. A
common characteris~ic of the known processes is the use of a solid starting substance, which is con~erted into the gas phase by sublimation.
Apart from the fact that obtaining HNCO.in this manner is expensive in terms of apparatus, the known processes require relatively high temperatures and have the disadvantage that by-products which are difficult ''." , ' ' ~
~ . ~ - ., ' :., .. ',, ~ : . .,: ` ' to handle are formed, which are deposited at cold points in the evaporator device.
SU~MARY OF THE INVENTION
Accordingly, one object of the invention is to provide a novel process for the reduction of nitrogen oxides, which likewise operates with the free radical NCO, but in which the isocyanic acid can be prepared at relatively low temperature ~nd thus is also much simpler to carry out.
This object is achieved according to the . invention in that the starting substance used is a substance which occurs in the molten state below 100C
and is highly evaporative rom the liquid phase, which substance acts directly or after pretreatment on the exhaust gas.
The advantage of the invention is to be seen in particular in that already at temperatures above about 200C, the thermal decomposition of the starting substance is produced and thus HNCO is produced at a substantially lower temperature and sLmpler than in the known RAPRENOX process. The starting substance is very simple to handle. No deposits result in the exhaust gas channel.
,` Exemplary embodiments of the in~vention and the ~; advantages achieved therewith are described below in more detail with reference to the drawing BRIEF DESCRIPTION OF THE DRAWING
;. ~
A more complete appreciation o~ the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection ` with the accompanying drawings, wherein:
.. . .
Figure 1 depicts a schematic representation of the exhaust gas channel of a thermal power station;
Figure 2 is a diagram which depicts the : decomposition of methyl carbamate in relation to the S temperature.
DESCRIPTION OF THE PREFERRED ENBODIMENTS
Referring now to the drawing, a first pipe 2 `10 opens into the exhaust gas p~pe 1 of a thermal power station, for example a gas turbine, which first pipe leads to a first treatment chamber 3. This in turn is connected via a second pipe 4 to a second treatment chamber 5. The second treatment cham~er S is partially filled with the starting substance 6, in ~his case methyl carbamate. It is heated to a temperature of about 80C and is therefore partly in the liquid state and partly in the vapor form.
The vapor produced enters via the pipe 4 into the ~optional) first treatment chamber 3. A gas stream, for example air or nitrogen, can be introduced at the same time into the second treatment chamber 5 via a third pipe 7. The additional gas stream dilutes the vapor and accelerates its flow out of the second treatment chamber 5. ~
Further events depend on whether the (optional) treatment chamber is present and on which conditions prevail there, or whether the vapor-form methyl carbamate is fed or admixed directly t~o the exhau~t gas.
In the latter case, the thermal dë~omposition of the vapor-form methyl carbamate proce~ds with formation of HNCO and the decomposition of the HNCO
proceeds with formation of NCO free radicals, which finally effect the reduction of the nitrogen oxide, in the exhaust ga~. The decomposition of the vapor-form methyl carbamate and the formation of HNCO in relation to temperature i8 illustrated by the diagram :: ' ' " , ~ .. ,:
. ~ ..
i i - , , , , . . .. . . . .. .
,.. ' ::
' , I' 2~8~778 represented in Figure 2. The residence time of the vapor-form methyl carbamate at the temperature plotted on the abscissa was in each case in the order of magnitude of a few tenths of a second. It can be clearly seen that the formation of HNCO begins even at relatively low temperatures. These temperatures are considerably below those temperatures which are required for the formation of HNCO from cyanuric acid (above 500C) or from urea.
If the optional treatm~nt chamber 3 is present, and if a sufficiently high temperature corresponding to the diagram in Figure 2 prevails there, the vapor-form methyl carbamate is decomposed in the first treatment chamber 3 into HNCO and other decomposition products.
The HNCO then passes, with the other decomposition products of the methyl carbamate and, possibly with the gas stream additionally added via pipe 7, through pipe 2 into the exhaust gas pipe 1, where it is mixed with the exhaust gas and ~hen, when the exhaust gas temperature is sufficiently high, NCO free radicals are formed, which then react wi~h the nitrogen oxides in a known manner.
The heating of the first treatment chamber 3 or the heat supply to this can be achieved by a separate 2S heat source, possibly with exploitation~of the (exhaust gas) heat from the power station. .~
However, it is alternatively possible to set the temperature in the first treatment chamber 3 high enough so that even in the latter the HNCO is already decomposed at least in part into atomic hydrogen and NCO free radicals. Temperatures of above ~600C are necessary for this. The subsequent direct introduction of NCO free radicals permits the reduction of nitrogen oxide at lower exhaust gas temperatures than hitherto, since these free radicals do not have to be first formed in the exhaust gas, which would firstly require a sufficiently high temperature in the exhaust gas and ~3~778 would secondly require a certain period of time for the free radical formation.
The production of NCO free radicals from HNCO
prior to entry into the exhaust gas can also be carried ~ 5 out by other physical and/or chemical pretreatment, such as for example pho~olytic and/or catalytic pretreatment and/or by irradiation with infrared light, `electron beams, radio waves etc. In Figure 1, for example, pretreatment with W light is depicted, in which the absorption of W ~ight quanta effects`the cleavage of an H atom from the HNCO.
Because of th~ short live~ of the NCO free radicals, the pipe 2 between the exhaust gas channel 1 and the pretreatment chamber must not be very long.
15In addition to the methyl carbamate mentioned in the exemplary embodiment, a series of other starting subs~ances can be considered, mainly generally oxygen-containing hydrocarbons having at least one nitrogen function, aliphatically substituted carbamates, in addition to the mentioned methyl carbamate, ethyl - carbamate, tertiary butyl carbamate. Oxyurea or hydroxyurea, hydrazinates or esters thereof, preferably hydrazinecarboxylic acid or hydrazinecarboxylic esters, oxamic acid or oxamide and semicarbazones are also used as starting substance. ~
Obviou31y, numerous modif~ications and variations of the present in~ention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein. i~
:, , , -;- . :
~, ' - , , ,' . "
: : .
'' " ~, ,: .:. , ,
Claims (9)
1. A process for the reduction of nitrogen oxides in exhaust gases, in which the exhaust gas is brought into contact with NCO free radicals, which are formed by thermal dissociation of isocyanic acid (HNCO), which comprises using as starting substance a substance which occurs in the molten state below 100°C and is highly evaporative from the liquid phase, which substance acts directly, or after pretreatment, on the exhaust gas.
2. The process as claimed in claim 1, wherein oxygen-containing hydrocarbons having at least one nitrogen function are used as the starting substance.
3. The process as claimed in claim 2, wherein the starting substance used is an aliphatically substituted carbamate, in particular methyl carbamate, ethyl carbamate or tertiary butyl carbamate.
4. The process as claimed in claim 1, wherein the starting substance used is oxyurea or hydroxyurea.
5. The process as claimed in claim 1, wherein hydrazinates or esters thereof, preferably hydrazine-carboxylic acid or hydrazinecarboxylic esters, are used as the starting substance.
6. The process as claimed in claim 1, wherein the starting substance used is oxamic acid or oxamide.
7. The process as claimed in claim 1, wherein semicarbazones are used as the starting substance.
8. The process as claimed in one of claims I to 7, wherein the starting substance is chemically and/or physically pretreated for cleavage of the H atom from the HNCO molecule.
9. The process as claimed in claim 8, wherein the pretreatment is carried out in a thermal, catalytic and/or photolytic manner.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19924206024 DE4206024A1 (en) | 1992-02-27 | 1992-02-27 | METHOD FOR REDUCING STICKOXYDES IN EXHAUST GASES |
| DEP4206024.9 | 1992-02-27 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2086778A1 true CA2086778A1 (en) | 1993-08-28 |
Family
ID=6452714
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2086778 Abandoned CA2086778A1 (en) | 1992-02-27 | 1993-01-06 | Process for the reduction of nitrogen oxides in exhaust gases |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0558809A1 (en) |
| JP (1) | JPH06277449A (en) |
| CA (1) | CA2086778A1 (en) |
| DE (1) | DE4206024A1 (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2001523165A (en) * | 1997-12-12 | 2001-11-20 | エフエーファウ・モトーレンテヒニク・ゲゼルシャフト・ミト・ベシュレンクテル・ハフツング・ウント・コンパニー・コマンディトゲゼルシャフト | Method for reducing nitrogen oxides in exhaust gas containing oxygen, especially exhaust gas of an internal combustion engine |
| DE102006047019A1 (en) | 2006-10-02 | 2008-04-03 | Emitec Gesellschaft Für Emissionstechnologie Mbh | Exhaust gas system's reduction agent containing gas flow providing method for internal combustion engine, involves adding reduction agent containing gas flow to exhaust gas of internal combustion engine |
| JP7150257B2 (en) * | 2018-04-10 | 2022-10-11 | 国立大学法人茨城大学 | Isocyanic acid production method, production device, built-in kit and gas generator |
| CN114060123A (en) * | 2020-08-07 | 2022-02-18 | 长城汽车股份有限公司 | Urea nozzle, automobile and anti-crystallization method |
Family Cites Families (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1259298B (en) * | 1964-08-29 | 1968-01-25 | Hamburger Gaswerke Gmbh | Process for removing nitrogen oxides from gases by catalytic reduction thereof to nitrogen |
| JPS52117869A (en) * | 1976-03-31 | 1977-10-03 | Onoda Cement Co Ltd | Method for decreasing nitrogen oxides contained in combustion exhaust gas |
| AU585670B2 (en) * | 1985-10-04 | 1989-06-22 | Fuel Tech. Inc. | Reduction of nitrogen- and carbon-based pollutants through the use of urea solutions |
| US4844878A (en) * | 1985-10-04 | 1989-07-04 | Fuel Tech, Inc. | Process for the reduction of nitrogen oxides in an effluent |
| US4886650A (en) * | 1986-05-05 | 1989-12-12 | Robert Perry | No reduction using sublimation of cyanuric acid |
| US4731231A (en) * | 1986-05-05 | 1988-03-15 | Robert A. Perry | NO reduction using sublimation of cyanuric acid |
| US4803059A (en) * | 1987-04-15 | 1989-02-07 | Fuel Tech, Inc. | Process for the reduction of nitrogen oxides in an effluent using a hydroxy amino hydrocarbon |
| US4851201A (en) * | 1987-04-16 | 1989-07-25 | Energy And Environmental Research Corporation | Methods of removing NOx and SOx emissions from combustion systems using nitrogenous compounds |
| DE4003515A1 (en) * | 1990-02-06 | 1991-08-08 | Bayer Ag | METHOD FOR REDUCING NITROGEN OXIDS CONTAINED IN EXHAUST GAS |
| US4985219A (en) * | 1990-02-14 | 1991-01-15 | Research-Cottrell, Inc. | Removal of nitrogen oxides from waste gases |
| WO1992004966A1 (en) * | 1990-09-14 | 1992-04-02 | Cummins Power Generation, Inc. | Surface stabilized sources of isocyanic acid |
| US5087431A (en) * | 1990-09-20 | 1992-02-11 | Molecular Technology Corporation | Catalytic decomposition of cyanuric acid and use of product to reduce nitrogen oxide emissions |
-
1992
- 1992-02-27 DE DE19924206024 patent/DE4206024A1/en not_active Withdrawn
- 1992-12-03 EP EP92120596A patent/EP0558809A1/en not_active Withdrawn
-
1993
- 1993-01-06 CA CA 2086778 patent/CA2086778A1/en not_active Abandoned
- 1993-02-24 JP JP5034996A patent/JPH06277449A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| DE4206024A1 (en) | 1993-09-02 |
| EP0558809A1 (en) | 1993-09-08 |
| JPH06277449A (en) | 1994-10-04 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Dead |