Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture
Patent
1985-03-19
1986-06-17
Doll, John
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
55181, 55390, 422177, 423219, 423230, 423239, 423240, 423241, 423244, 423245, B01D 3900, B01D 5300, B01J 800
Patent
active
045955751
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for the continuous purification of waste gases by chemisorption and adsorption of the gaseous pollutants to activated carbon and desorption of these pollutants or of their reaction products.
In the literature, a distinction is made between dry and wet or wet-catalytic processes for adsorptive waste gas purification. The dry processes operate above the dew point of the waste gases, but in case the adsorbent is recycled, they require either thermal desorption or, after extraction with a liquid extraction agent, drying. The wet or wet-catalytic processes, on the contrary, operate below the dew point of the waste gases, so that the usually water vapor-saturated clean gases must be heated up. This is often regarded as a disadvantage, but it can be remedied by means of a heat exchanger between hot waste gas and clean gas. The desorption of the pollutants occurs by extraction or washing of the adsorbent.
As an example of a dry process for the continuous purification of waste gases with activated carbon there may be cited the flue gas desulfurization process of Bergbau-Forschung (Mining Research) (Chemische Industrie, August 1975, pages 437 to 461). A traveling bed reactor is used as adsorber here. The laden activated carbon is mixed in the desorber with heated sand and regenerated at a temperature between 500.degree. and 650.degree. C. Thereby a SO.sub.2 -rich gas is obtained, which can be processed to sulfur or sulfuric acid. Since in the continually renewed filter bed also solids particles are being separated, an additional dust separation is not required. A disadvantage, however, is the high cost of instrumentation and energy of the regeneration plant required for the process. Besides, depending on the hardness of the activated carbon used, considerable abrasion must be expected, which must be compensated by continuous replenishment of fresh activated carbon.
As an example of a wet-catalytic process for the continuous purification of waste gases with activated carbon the Lurgi SULFACID process (Lurgi Newsletter T 1260/11.77) may be cited. The process is also used for the separation of sulfur dioxide from waste gases. Here the crude gas is passed through a fixed bed of activated carbon at a temperature of 50.degree. to 80.degree. C. In the presence of water and oxygen, the sulfur dioxide in the activated carbon is transformed into sulfuric acid, which is washed out periodically with water in counter-current. To obtain a uniform purification of the waste gases, only a segment of the fixed bed is sprayed with water each time. Due to the water film surrounding the activated carbon grains, the adsorption capacity of this segment is reduced. However, there is little danger of sulfur dioxide irruption, as the flow resistance is increased at the same time. To reduce the thickness of the water film and thereby to increase the rate of adsorption, the washed activated carbon is dried with the unsaturated crude gas.
It must be regarded as a disadvantage that because of the long drying time to attainment of the maximum adsorption capacity of the dry activated carbon, a height of the fixed bed is necessary which is much greater than would be necessary for adsorption to unladen activated carbon. Furthermore, the fixed bed with periodic desorption is not very suitable for dust-containing crude gases because the dust settles between the activated carbon grains and is not flushed away by the laminar flow of the water film. It is proposed, therefore, to wash the crude gases before entrance into the fixed bed with the thin acid occurring in the process and thereby to increase the concentration thereof. Thus, however, a saturated crude gas would be obtained which is unable to dry the washed fixed bed segment. As an advantage must be seen the low cost of instrumentation and energy in this process.
It is the object of the invention to develop a wet or wet-catalytic process for the continuous purification of waste gases with activated carbon which does not have the described disadvantages.
This prob
REFERENCES:
patent: 4344920 (1982-08-01), Isserlis
patent: 4366085 (1982-12-01), Ikegami et al.
patent: 4521390 (1985-06-01), Mouille et al.
Kempfert Joachim R.
Oeste Franz D.
Doll John
Freeman Lori S.
Rutgerswerke Aktiengesellschaft
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