JPS61197024A - Method and apparatus for lowering concentration of harmful substance in waste gas - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a waste gas treatment method for reducing the concentration of hazardous substances, a method for retrofitting existing thermal and/or catalytic waste gas treatment methods. Regarding equipment.

BACKGROUND OF THE INVENTION As a method for oxidative decomposition of harmful substances in waste gas, the thermal post-incineration (TNV) method is known.

From a series of basic studies for the TNV treatment of hazardous substances, in many applications the TN'v device can be used to treat intermediate products (
It has become clear that secondary hazardous substances), in particular carbon oxides (CO), should be installed after oxidizing conditions, thus requiring operating temperatures significantly higher than 750°C.

Especially for hazardous substances of emission class ■ in the industrial specifications for air purification (TA total air listed below), the permissible residual concentration (600 m9 / Nm') of - grade hazardous substances is already within the range of 500 to 600℃. The maximum CO residual concentration to be tolerated is 1001n9/m' at 800°C.
This can be achieved only after the above.

Therefore, in order to eliminate secondary hazardous substances, the waste gas must be treated at significantly higher temperatures than is necessary to eliminate the primary hazardous substances themselves. This requirement makes conventional waste gas treatment significantly more expensive from a technical and economic point of view than was deemed necessary on original grounds.

If waste gases containing organic nitrogen compounds and/or hydrogen cyanide are to be treated in TNV installations, additional problems arise due to the formation of other secondary hazardous substances.

Poisonous substances include in particular nitrogen oxides, which, especially at high temperatures, are formed partly from the elemental sulfur already present in the waste gas.

When treating waste gases containing organic nitrogen compounds, hydrogen cyanide is produced as another dangerous secondary pollutant. Unless hydrogen cyanide is discharged into the resulting gas stream, it will be converted to NOx to a greater or lesser degree in the normal waste gas treatment process, and therefore no hydrogen cyanide can be used as a secondary or secondary hazardous substance. , a NO hole is formed.

Primary or secondary hazardous substance removal takes place only at high temperatures; however, due to the contradictory effect of increased Nox production at high temperatures, TNv treats waste gases containing organic nitrogen compounds and/or hydrogen cyanide. It's not appropriate for that purpose.

Another method for the oxidative decomposition of hazardous substances in waste gases is post-catalytic combustion (KNV), which can generally be operated at lower temperatures than TNV. However, the same difficulties as TNV arise when treating waste gases containing organic nitrogen compounds and/or hydrogen cyanide. At relatively low temperatures, it is not possible to sufficiently reduce the release of secondary harmful substances, whereas at temperatures that can reduce the release of primary harmful substances, more and more nitrogen oxides are formed. . Therefore, KNv is also unsuitable for this application.

Problem to be Solved by the Invention Accordingly, there is provided a waste gas treatment method which makes it possible to limit harmful substance emissions to an acceptable range and which is suitable for treating waste gases containing organic nitrogen compounds and/or hydrogen cyanide. A particular problem arose was to modify existing TNT and/or KNV equipment for this purpose by simple means.

Means for Solving the Problem The invention provides a method for reducing the concentration of harmful substances in waste gas by oxidative, thermal and/or catalytic treatment, in which waste gas containing organic nitrogen compounds and/or hydrogen cyanide is treated. When gases are used, the solution is to catalytically treat the gas stream obtained following the oxidative, thermal and/or catalytic treatment step in a further step with addition of ammonia.

The waste gas treatment method according to the invention is a multi-stage method.

In the first step, the gas containing harmful substances is treated oxidatively, thermally and/or catalytically by a method known per se.

In this case, in the case of thermal treatment, this first step
At a temperature of 1000 °C, 280-6 in case of contact treatment
In the case of a combination of thermal and catalytic treatment, the thermal treatment is carried out at a temperature of 400-600°C and the catalytic treatment at a temperature of 280-600°C.

According to the invention, the gas stream obtained from the first step, which is already a pure gas in the conventional process, is subjected to another process a (KSR
catalytic treatment using ammonia in step).

In this case, the ammonia can be added directly to the further step or to the conductor connecting the first and further step.

In one advantageous variant, the addition of ammonia is controlled in accordance with the content of nitrogen oxides (Nox) in the gas stream obtained from the first step. For this variant, corresponding measuring and control devices known per se may be provided. For example, branching off a substream from the gas stream obtained for continuous No2 measurement, in which the NOx content is continuously measured by chemiluminescent analysis and the measured value is used to control the ammonia metering. be able to.

, Nitrogen oxide (Nox) 0 ammonia per part by volume
．． It has proven advantageous to meter in 3 to 3, preferably 0.5 to 2 parts by volume. At this time, N in Nox
If the proportion of O2 is increased, the ammonia addition amount to be metered lies in the upper part of the range, whereas if the proportion of NO in the NO treatment is increased, values in the lower range can be chosen rather.

In another step, 130-320°C, especially 150-250°C
It is advantageous to operate at a temperature of .degree.

Oxidation catalysts known per se can be used as catalysts for the first oxidative treatment step as well as for the further steps. These catalysts can be used in all known forms, for example as fabrics, nets or sieves or as bulk and unshaped or shaped particles. It is advantageous to use catalysts fixed on porous supports, in which case the supports are advantageously constructed in the form of pearls, as extrudates or in the form of honeycombs. The active components of the catalyst are based on noble metals, preferably platinum noble metals and/or vanadium. Preference is given to catalysts containing platinum and/or palladium as noble metals. Such catalysts are commercially available.

By applying the method of the present invention, it is possible to treat waste gas containing organic nitrogen compounds and/or hydrogen cyanide as secondary harmful substances. In addition, other carbon-, hydrogen- and/or oxygen-containing harmful substances may optionally be present in the waste gas. This applies in particular to one or more of the following organic nitrogen compounds: 1) primary, secondary, in particular having 1 to 6 carbon atoms;
Tertiary aliphatic aminos such as 7-no, di-trimethyl-1-ethyl-1-n-propyl-1-n-butylamine, mono-, di-isozorobyl-1-isobutyl-1
-S-butylamine, -t-butylamine, 2) cycloalkylamines such as cyclohexylamine, N-methyl-1N, N-dimethyl-cyclohexylamine, dicyclohexylamine, 3) di- and polyamines such as mono-, di-, triethylenediamine, 4) 5) Aromatic amines such as aniline, toluidine, xylidine, aminophenol, benzylamine, 6) Nitriles, especially aliphatic nitriles such as aceto-, propio- , butyronitrile, acrylonitrile, methacrylnitrile, 7) nitro compounds such as aliphatic nitro compounds such as evanitromethane, -ethane, -propane or aromatic nitro compounds such as nitrobenzene, nitrotoluene, 8) nitrogen-containing heterocyclic compounds such as pyridine, pyrrole, 9) amide derivatives such as N,N-dimethylformamide.

Secondary harmful substances, such as formaldehyde or acetaldehyde, in particular carbon oxides, nitrogen oxides (NOx), ammonia, hydrogen cyanide, are formed from the primary harmful substances by partial oxidation and/or decomposition reactions. The method according to the invention makes it possible in particular to effectively limit the content of secondary harmful substances.

Example The invention will now be explained with reference to the illustrated embodiment.

FIG. 1 shows a basic diagram of the device according to the invention. Nll! The waste gas to be treated is fed via a conduit 1 via a heat exchanger 2 to a first waste gas treatment stage 3 . This waste gas treatment step 3 can be thermal, catalytic or a combination of thermal 3
a and catalytic 3b waste gas treatment.

If the first treatment step is a purely thermal step (TNV), the waste gas is purified oxidatively in the chamber 3a under the action of foreign energies. For this purpose, it is advantageous to supply a fuel, for example a propane/air mixture, via line 4 and combust it together with the waste gas in an open flame. - The resulting gas stream, which contains primary and secondary harmful substances, passes via line 5 to heat exchanger 2 and from there via line 5a to a further processing step.

If the first treatment stage is a pure catalytic stage (KNV), the waste gas is fed via line 1a to a catalytic stage 313 in which a catalyst 6 is arranged and from there via line f7 to a further treatment. Reach the process.

The first step is a combined thermal/catalytic step (Tuff/K
NV). In this case, the gas flow obtained from the thermal step 3a is routed via conduit 5 or via conduit f4
contact step 3b is reached directly via a. The post-contact treated gas (produced gas) is fed via line f7/7a to a further stage 8 with a catalyst 9. Optionally, the product gas stream can be fed to the heat exchanger 2 via the conductor i 7 / 7 b. Ammonia is metered into step 8 via line 11. Of course, ammonia is
It is also possible to meter 7a or 7b. The pure gas stream resulting from step 8 is fed via conduit 12 to waste gas, not shown. The pure gas leaving the second stage 8 is optionally fed to the heat exchanger 10 via the conductor f12a if the heat content is sufficiently high and is additionally used for waste heat utilization, for example via the hot steam conduit f13. be done.

Effects of the Invention With the method of the invention, significant advantages can be achieved compared to known methods.

1) Nitrogen oxide (NO) emissions can be reduced to remove organically bound nitrogen-containing primary hazardous substances and/or hydrogen cyanide from the waste air stream.

2) Nitrogen-containing intermediate products produced as secondary harmful substances in conventional waste air purification methods can be removed.

6) Nitrogen oxide (NO) formation from air nitrogen is avoided when using the NVAMY combination by lowering the combustion temperature.

4) Existing thermal and/or catalytic waste gas combustion equipment can be easily adapted to changing legal standards by joining another process step.

5) The reduction of nitrogen oxides (NoX) in the waste gas is not hindered by the atmospheric oxygen present in the waste gas.

However, the examples are not intended to limit the present invention (the results shown in Figures 1 and 2 below 1° indicate that the first treatment step is combined and the thermothermal/catalytic process (TNV/KNV )
This was obtained using a device that

According to FIG. 1, the waste gas is fed directly via line f1a to the combustion chamber 3a for combustion and from there via line f4a to the contact stage 3b. The generated gas flow is guided [7/7
t) was conducted via heat exchanger 2 for heat recovery and then fed to stage 8R. As a catalyst, a commercially available platinum-based oxidation catalyst (KNV: catalyst KCO-WK-220ST) was used in KNv step 3a as well as in KBR step 8.
5KSR: Catalyst KCO-1934-/M% Manufacturer:
Currie Chemie AG) was used.

Samples were taken before and after the individual treatment steps in order to analyze the gas mixture.

Tables 1 and 2 show the respective pollutant ffa degrees in relation to the temperature (T=measured in °C at the outlet of the combustion chamber). In this case, the composition is based on carbon (C-balance) or nitrogen (N-balance) bound within the primary harmful substance.

Other abbreviations have the following meanings: 2S=hazardous substance C-ZP=nitrogen-free mechanical intermediate product V"' NH3
/NoX% k ratio (! ==-Next hazardous substance OS degree=
From the results listed in the throughput table, a reduction in primary or secondary right-handed substances using the method of the invention is clearly recognized.

Corresponding experiments using hydrogen cyanide, 2-nitrotoluene and acrylonitrile as primary hazardous substances gave correspondingly good results.

[Brief explanation of drawings]

FIG. 1 is a basic system diagram of the device according to the invention.

Claims (1)

[Claims] 1. In a method for reducing the concentration of harmful substances in waste gas by oxidation, heat and/or catalytic treatment, when waste gas containing organic nitrogen compounds and/or hydrogen cyanide is used, oxidation A process for reducing the concentration of harmful substances in waste gas, characterized in that, following a thermal and/or catalytic treatment step, the gas stream obtained is catalytically treated with the addition of ammonia in another step. . 2. The method according to claim 1, wherein the oxidation heat treatment step is carried out at a temperature of 400 to 1000°C. 3. The method according to claim 1 or 2, wherein the oxidation contact treatment step is carried out at a temperature of 280 to 600°C. 4. The method according to any one of claims 1 to 3, wherein the oxidation heat treatment step is carried out at a temperature of 400 to 600°C and the oxidation contact treatment step is carried out at a temperature of 280 to 600°C. 5. Any one of claims 1 to 4, which operates at a temperature of 130 to 320°C in another step.
The method described in section. 6. The process as claimed in claim 1, wherein the addition of ammonia is adjusted accordingly to the content of nitrogen oxides (NOx) in the gas stream produced. 7. The method according to claim 6, wherein 0.3 to 3 parts by volume of ammonia are metered in per part by volume of nitrogen oxide. 8. Process according to any one of claims 1 to 7, characterized in that catalysts based on noble metals and/or vanadium are used in the oxidative catalytic treatment step and/or subsequent steps. 9. The method according to claim 8, which uses a catalyst containing platinum and/or palladium as the noble metal. 10. In a process for retrofitting existing thermal and/or catalytic waste gas treatment equipment to treat waste gases containing organic nitrogen compounds and/or hydrogen cyanide, the resulting gas stream is converted into ammonia in another step. A method for retrofitting existing thermal and/or catalytic waste gas treatment equipment, characterized in that the treatment is carried out catalytically by adding. 11. In an apparatus carrying out a method for reducing the concentration of harmful substances in waste gas by oxidative, thermal and/or catalytic treatment, the oxidative, thermal and/or catalytic treatment step and the resulting gas stream are treated with ammonia. A device for reducing the concentration of harmful substances in waste gas, characterized in that it consists of another step of addition and catalytic treatment.