Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Organic component
Patent
1988-06-02
1989-10-31
Heller, Gregory A.
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Organic component
423247, B01J 800, C10H 2300, C01B 3118
Patent
active
048775924
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE ART
The invention relates to the techniques of cleaning industrial and ventilation gases discharged into the atmosphere and has specific reference to the methods of catalytic cleaning of exhaust gases from organics and carbon monoxide. Resolving the problem of protecting the atmosphere from toxic air pollutants, it may be of utility in the catalytic cleaning of exhaust gases in various industries.
PRIOR ART
There are known a number of methods of cleaning exhaust gases, which resort either to the adsorption or absorption of the toxic matter by a solid or liquid sorbent or to converting this matter into harmless substances. In most cases the conversion of toxic organics and carbon monoxide into safe compounds is accomplishes through the agency of deep oxidation. Deep oxidation involves oxidation of toxic matter to carbon dioxide and water vapours. The oxidation is performed in a bed of granular catalysts at a temperature which is higher than that at which the reaction of oxidation begins (250.degree.-450.degree. C.). Since most of the exhaust gases have a temperature of 100.degree. C. or even less, they must be heated to the temperature at which the reaction would begin. To that end, the exhaust gases can be either mixed with hot flue gases or heated up by the cleaned exhaust in a heat exchanger.
Nowadays, most catalytic cleaning plants employ a combined method of heating. The sequence of events in this case is as follows. The exhaust gas to be cleaned is fed into a heat exchanger where it is heated due to a heat transfer with the cleaned gas before this is exhausted. Further heating up is effected by adding to the gas which is being cleaned some hot flue gases produced by burning fuel. The hot gas at a temperature enabling the reactions of oxidation of the toxic pollutants to take place is passed through a bed of catalyst where its temperature increases due to the fact that these reactions are exothermic ones. The gas cleaned on the catalytic bed is passed through a shell-and-tube heat exchanger where it heats up the incoming gas which is being cleaned and then is exhausted into the atmosphere (cf. "Termicheskie Metody Obezvrezhivaniya Otkhodov", Khimiya, 1975, Leningrad, pp. 111-118).
This method requires bulky and complicated heat-exchanging equipment for its implementation and is costly, for extra fuel is needed for heating up the gas which is being cleaned. The burning of extra fuel is practically avoidable only if the total amount of the organics in the incoming gas is over 4 or 5 g/m.sup.3. If this content is less than 4 g/m.sup.3, the heating up of the incoming gas by a hot flue gas produced by burning fuel is indispensable and leads to the formation of toxic oxides of nitrogen. Generously surfaced heat exchangers seem to be an alternative to burning extra fuel but the heat losses into the atmosphere significantly increase in this case. The known method is also difficult to adapt to processing gases with a pollutant cotent varying with time. The answer can be found by introducing automatic control of the process of burning extra fuel.
In an attempt to overcome these disadvantages, a number of other methods have been suggested based on non-steady process of cleaning discharge gases from toxic pollutants. They have been realized by passing the gas to be cleaned through a bed of catalyst a number of times in succession, reversing each time the direction of gas flow (SU,A, No. 849594).
The cleaning of gases by the non-steady process renders the catalytic reactors less metal-intensive by a factor of 2 to 5 and eliminates the need in fuel if the pollutant content of the gas cleaned is over 1 g/m.sup.3. Gases in varying amounts and of varying composition can be effectively processed by virtue of a significant heat capacity of the catalytic reactor.
The cleaning process by the non-steady method is accomplished as follows. A bed of catalyst interposed between two layers of inert material is heated up to a given temperature (250.degree.-500.degree. C.) together with the inert material. The gas
REFERENCES:
patent: 4366668 (1983-01-01), Madgavkar et al.
patent: 4410499 (1983-10-01), Aiken et al.
Bugdan Evgeny S.
Chumachenko Viktor A.
Matros Jury S.
Noskov Alexandr S.
Zudilina Ljudmila J.
Heller Gregory A.
Institut Kataliza Sibirskogo Otdelenia Akademii Nauk SSSR
Spetsialnoe Konstruktorsko-Technologicheskoe Bjuro Katalizatorov
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