DE3442927A1 - EXHAUST GAS TREATMENT METHOD - Google Patents

Description

The present invention relates to an exhaust gas treatment method for reducing the concentration of pollutants, a process for retrofitting existing thermal and / or catalytic exhaust gas treatment processes as well as an exhaust gas treatment system.

Thermal post-combustion (TNV) is a process for the oxidative breakdown of pollutants in exhaust gas. known.

A series of fundamental studies on TNV of pollutants shows that in the majority of Use cases the design of the TNV system according to the oxidation conditions the intermediate products (secondary pollutants), primarily carbon monoxide (CO) and correspondingly high operating temperatures well above 750 * C are required.

Especially for pollutants of emission class III of the technical instructions for keeping the air clean in the following called TALuft - the permissible residual concentrations of the primary pollutants (300 mg / m ³ ) (standard m ³ ) can already be reached at temperatures between 500 and 600 "C, while a CO residual concentration of a maximum of 100 mg / m ^3, which is to be regarded as permissible, can only be achieved above 800 ^° C.

To remove secondary pollutants, the exhaust gas must thus treated at significantly higher temperatures than this for the removal of the primary pollutants in itself 'would be necessary. This necessity makes conventional exhaust gas treatment both technical and from an economic point of view much more expensive than being due to the actual cause needed.

If exhaust gas is to be treated in a TMV system, the organic nitrogen compounds and / or hydrogen cyanide contains, additional problems arise due to the formation of further secondary pollutants.

As disturbing secondary pollutants are in particular Nitrogen oxides (NO,) to mention at high temperatures are preferably formed, partly from elemental nitrogen already present in the exhaust gas.

When treating org. Exhaust gas containing N-compounds occurs as a further, dangerous secondary pollutant Hydrogen cyanide. Unless hydrogen cyanide is in resulting gas flow escapes, it becomes more or less NO in the course of conventional exhaust gas treatment processes, converted so that also from hydrogen cyanide - be it as Primary or secondary pollutant - NO «is formed.

Because of the opposing effects - primary or secondary pollutant removal Er3t at high temperatures, but there increasing NO "formation" - the TNV is not for Treatment of exhaust gas suitable that contains organic nitrogen compounds and / or hydrogen cyanide.

Another known method for the oxidative breakdown of pollutants in exhaust gas is catalytic post-combustion (KNV), which generally allows working at lower temperatures than the TNV. With treatment of exhaust gas containing organic nitrogen compounds and / or

'S ■

Contains hydrogen cyanide, but the same difficulties arise as with TNV: at relatively low temperatures the primary pollutant emission cannot be reduced sufficiently, at temperatures that allow the primary pollutant emission to be reduced, on the other hand, nitrogen oxides (NO _x ). The KNV is therefore not suitable for this application either.

The task was therefore to provide an exhaust gas treatment process that would reduce pollutant emissions Allowed to limit the permissible range and to treat organic nitrogen compounds and / or exhaust gas containing hydrogen cyanide is suitable.

A special task was to fix existing TNV and / or KNV systems by simple measures to improve in the stated sense.

The stated object is achieved by the method characterized in the claims.

The exhaust gas treatment method according to the invention represents a multi-stage process.

In a first stage, pollutant-containing gas is in oxidizing, thermally and / or catalytically treated in a manner known per se.

In the case of thermal treatment, this first stage works at temperatures of 400 to 1000 "C,

in the case of the catalytic treatment at temperatures of 280 to 600 ^° C. and in the case of a combined thermal and catalytic treatment in the thermal part at 400 to 600 ° C. and in the catalytic part at 280 to 600 ° C. 35

The gas flow resulting from the first stage, which in the conventional process is already the clean gas represents, is according to the invention in a further stage

3 A 42 9

(KSR stage) catalytically treated with addition of ammonia.

The addition of ammonia can be done directly in the next stage or in the first and the next Level connecting line take place.

In a preferred variant, the addition of ammonia is regulated according to the content of nitrogen oxides (NO _x ) in the gas flow resulting from the first stage. Corresponding measuring and regulating devices known per se are provided for this variant. For example, a partial flow can be branched off from the resulting gas flow _{for continuous NO x determination, in which the NO x} content is continuously determined by chemiluminescence analysis and this measured value is used to control the ammonia dosage.

It has been found to be advantageous to dose 0.3 to 3, preferably 0.5 to 2, parts by volume of ammonia per part by volume of nitrogen oxide (NO _x). In the case of high NO ₂ proportions in the NO _x, the ammonia additive to be dosed will be more in the upper part of the specified range, while in the case of high NO proportions in the NO _x , a value from the lower range can be selected.

In the further stage, temperatures of 130 to 320.degree. C., in particular 150 to 250.degree. C., are preferably used.

As catalysts for the oxidizing, first treatment stage as well as for the further stage come per se known oxidation catalysts are used. These can be in all known forms, e.g. as fabrics, nets or Screens or bulk unformed or shaped particles can be used. Preferably come on porous supports Fixed catalysts are used, the carrier preferably in bead form, as an extrudate or in honeycomb

perform is trained. The active component of the catalyst is based on noble metal, preferably noble metal Platinum group and / or vanadium. A catalyst is preferred which contains platinum and / or palladium as a noble metal. Such catalysts are commercially available.

Exhaust gases can hit the method according to the invention are treated, the organic nitrogen compounds and / or contain hydrogen cyanide as primary pollutant, In addition, other carbon or hydrogen can optionally be used and / or pollutants containing oxygen may be present in the exhaust gas. In particular, there are single or multiple of the following organic nitrogen compounds in question:

- primary, secondary, tertiary aliphatic amines with Alkyl radicals of in particular 1 to 6 carbon atoms such as mono-, di-, tri-methyl-, -ethyl, -n-propyl-, -n-butylamine. Mono-, di-isopropyl-, -iso butyl-, -sec-butylamine. tert. Butylamine

Cycloalkylamines such as cyclohexylamine, M-methyl-, N, N-dimethyl-cyclohexylamine, Dicyclohexylamine

Di- and polyamines such as mono-, di-, triethylenediamine 25

cyclic amines such as piperidine, morpholine. N-methyl-, N-EthyImorpholine

aromatic amines such as aniline, toluidines, xylidines, aminophenols, benzylamines

Nitriles, in particular aliphatic nitriles such as aceto-, propio-, butyronitrile, acrylonitrile, methacrylonitrile
35

Nitro compounds, e.g. aliphatic nitro compounds such as nitromethane, -athane, -propane or e.g. aroma-

Λ-

table nitro compounds such as nitrobenzene, nitrotoluenes

nitrogen-containing heterocycles such as pyridine, pyrrole 5

Amide derivatives. like 2.B. N, N-dimethylformamide.

Partial oxidation results from primary pollutants and / or secondary pollutants through degradation reactions such as formaldehyde or acetaldehyde, especially carbon monoxide, Nitrogen oxides CNO,), ammonia, hydrogen cyanide. The method according to the invention allows in particular to effectively limit the content of secondary pollutants.

The basic circuit diagram of a system according to the invention is shown in FIG. The exhaust gas to be cleaned is passed through a line (1) via a heat exchanger (2) to a first Exhaust gas treatment stage (3) fed. This exhaust treatment stage (3) can be thermal, catalytic

20 or a combined thermal (3a) and catalytic (3bJ be exhaust gas treatment.

If the first treatment stage is a purely thermal stage (TNV), the exhaust gas in chamber C3a) is below

IS exposed to external energy, cleaned in an oxidizing manner. For this purpose, fuel, for example (propane / air mixture), is preferably supplied via line (4) and burned together with the exhaust gas in an open flame. The resulting gas stream containing primary and secondary pollutants arrives

! 0 via line (5) to heat exchanger (2) and from there via Line (5a) to the further treatment stage.

The first stage of treatment is purely catalytic Stage (KNV), the exhaust gas is fed via line (la) to the catalytic stage (3b), in which a catalytic converter (6) is arranged and hung from there via line (7) to the further treatment stage.

• 3.

The first stage, a combined thermal / catalytic stage, is preferred Level (TNV / KNV). In this case, the one resulting from the thermal stage (3a) arrives Gas flow either via line (5) or directly via line (4a) to the catalytic stage (3b). That catalytic aftertreated gas (resulting gas) is fed via line (7 / 7a) to the further stage (8), which is connected to a Catalyst (9) is provided. Alternatively, the resulting gas stream can pass a heat exchanger via line (7 / 7b)

(2) are fed. Ammonia is metered into stage (8) via line (11). However, it is also possible to use ammonia to be metered into line (7a) or (7b). The stream of clean gas emerging from stage (8) is discharged via line (12) fed to the exhaust chimney (not shown). That the The clean gas leaving the second stage (8) can alternatively be fed to the heat exchanger via line (12a) if the heat content is high enough (10) and used for the additional recovery of waste heat, e.g. via superheated steam pipe (13) will.

With the method according to the invention, essential Achieve advantages over known processes:

Elimination of organically bound nitrogen-containing primary pollutants and / or hydrogen cyanide from exhaust air flows with reduced nitrogen oxide (NO.) emissions

Elimination of nitrogen-containing intermediate products that arise as secondary pollutants in conventional exhaust air purification processes
30th

Avoidance of nitrogen oxide (NO _x ) formation from atmospheric nitrogen when using the TNV / KNV combination by lowering the combustion temperatures

simple adaptation of existing thermal and / or catalytic exhaust air incineration systems to changed legal requirements by adding a further Βο-handling step e
5

the reduction of nitrogen oxides (NO,) in the exhaust gas is not due to atmospheric oxygen in the exhaust gas disturbed.

The following examples are intended to illustrate the invention Describe the procedure in more detail without restricting its scope.

The results shown in Tables 1 and 2 were obtained on a system, the first treatment stage a combined thermal / catalytic stage CTNV / KNV). The exhaust gas was according to Fig. 1 via line (la) the directly fired combustion chamber (3a) and from there via line (4a) to the catalytic stage (3b). Of the resulting gas stream was passed through line (7 / 7b) for heat recovery via heat exchanger (2) and the KSR stage (8) supplied. A commercial catalyst was used both in the KNV stage (3a) and in the KSR stage (S) available oxidation catalyst based on PIatin used (KNV: catalyst KCO-WK-2203T, KSR: catalyst KCO-1934-K / M. Manufacturer: Fa. Kali-Chemie AG) used.

To analyze the gas mixtures, samples were taken before and after the individual process stages.

In Tables 1 and 2, the respective pollutant concentration (in percent by volume) is dependent on the Temperature (T measured in * C at the exit of the combustion chamber). The composition is based on the carbon bound in the primary pollutant (carbon balance) or Nitrogen (N balance).

Other abbreviations given have the following meanings:

S = pollutant, C-ZP = nitrogen-free organic intermediate products, V = molar ratio NH ₃ / NO _x , c = concentration of primary pollutant, D = throughput.

From the results given, the decrease in primary or Secondary pollutant when using the invention Procedure clearly visible. 10

Corresponding experiments with hydrogen cyanide, 2-Mitro toluene and acrylonitrile as primary pollutants resulted in ver equally good results.

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Table 2:

Aniline as the primary pollutant

a) C-balance sheet

S. TNV CO I HCN
j CO ₂ S. TNV + KNV HCN CO ₂ I TNV + KNV + KSR
I. COIHCNICo ₂ I.
I. 59 C-ZP 11th I ο 20th 19th C-ZP I CO
I. 0 81 IS IC-ZP
ι ι 0 I 0 I 92 420 I. 45 10 29 I ι 20th 10 0 I.
10 0 90 I 8 I 0 480 I. 25th 5 50 I ι 24 10 0 10 0 90 I I 550 I. 17th 0 45 I 4 34 5 0 to 0 95 I I 600 I. 0 0 10 I I

b) N-balance

S. TNV NH ₃ NO » N ₂ S. TNV + KN \ r NO » IN ₂ TNV + KNV + KSF < N ₂ 59 I HCN 0 21 17th 19th | HCN
j INH ₃ 70 I 11 S | HCN NH ₃ NO _x 71 420 45 I.
I 3 3 45 3 10 I o I.
I o 90 I o 8 I 0 0 21 480 25th I 4 14th 55 0 10 I o I o 90 I o I. 550 17th I 6 7th 55 0 5 I o I o 95 I o I. 600 I 21 I ο I o I.

c = 220 ppm, D = 78 Nm ³ / h, V = 2.5

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Claims (11)

Claims 1. Procedure 2 for reducing the concentration of pollutants in exhaust gas through oxidizing, thermal and / or catalytic treatment, characterized in that when using organic nitrogen compounds and / or exhaust gas containing hydrogen cyanide following the oxidizing, thermal and / or catalytic treatment stage the resulting gas stream in a further stage Treated catalytically with the addition of ammonia. 2. The method according to claim 1, characterized in that one in the oxidizing, thermal treatment stage works at temperatures from 400 to 1000 ° C. 3. The method according to any one of the preceding claims, characterized in that in the oxidizing, catalytic treatment stage at temperatures of 280 20 to 600'C works. 4. The method according to any one of the preceding claims, characterized in that one in the oxidizing, thermal treatment stage at temperatures of 400 to 600 * C and in the oxidizing catalytic treatment stage operates at 280 to 600 ° C. 5. The method according to any one of the preceding claims, characterized in that in the further stage at temperatures of 130 to 320 ° C., preferably 150 to 250 ° C., works. 6. The method according to any one of the preceding claims, characterized in that the addition of ammonia is _{regulated according to the content of nitrogen oxides (NO x} ) in the resulting gas stream.
5 7. The method according to claim 6, characterized in that per part by volume of nitrogen oxides 0.3 to 3, preferably 0.5 to 2 parts by volume of ammonia are metered in. 8. The method according to any one of the preceding claims, characterized in that one in the oxidizing, catalytic treatment stage and / or in the further stage a catalyst based on noble metal, preferably Noble metal of the platinum group and / or vanadium is used. 9. The method according to claim 8, characterized in that a catalyst is used which, as a noble metal, Contains platinum and / or palladium. 10. Process for retrofitting existing thermal and / or catalytic exhaust gas treatment systems, for Treatment of exhaust gas containing organic nitrogen compounds and / or contains hydrogen cyanide, characterized in that that the resulting gas stream is treated catalytically in a further stage with the addition of ammonia. 11. exhaust gas treatment system for performing a method according to any one of claims 1 to 9, containing an oxidizing, thermal and / or catalytic treatment stage and a further stage in which the resulting Gas stream is treated catalytically with the addition of ammonia.