Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture
Patent
1997-05-16
1998-09-22
Straub, Gary P.
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
42324308, 4232451, 423555, 422168, 422187, 422234, B01D 5334, B01J 800
Patent
active
058110666
DESCRIPTION:
BRIEF SUMMARY
This application is a national stage filing under 35 U.S.C. 371 of PCT/EP95/04440 filed 13 Nov. 1995.
BACKGROUND OF THE INVENTION
The invention relates to a method and a device for scrubbing flue gases of furnaces, whereby the flue gases are subjected to wet scrubbing with addition of activated carbon particles.
In refuse incinerators it is known from practice to reduce to a large extent the heavy metal contents of the flue gases with a series of wet scrubbing steps. Problems may occur in regard to mercury. A respective scrubbing process is therefore needed in order to comply with government regulations. They require at the time that the mercury contents be no greater than 50 .mu.g/m.sup.3. For heavy metal scrubbing, an activated carbon filter is provided upstream of the smoke stack which functions as a solid bed or fluid bed device. The required volume especially for a solid bed device is considerable. Furthermore, a comparatively high pressure loss occurs. Overall, a considerable investment and operating expenditure. Finally, a fire hazard, which should not be overlooked, is present. Furthermore, it is to be anticipated that in the future the allowable maximum contents of heavy metals, especially mercury, will be lowered.
For power plant furnaces the conditions are somewhat different. The flue gases generated here, when using German coal, contain mercury in an amount of 10 to 15 .mu.g/m.sup.3. At this time, there are no government regulations. However, in the future it is be counted on that these requirements will be tightened.
Active carbon filters can comply with these requirements only with the aforementioned disadvantages, whereby it must be taken into consideration that for refuse incinerators the produced amount of flue gases is comparatively small. The conditions are much more unfavorable for power plant furnaces which produce many times more flue gases. A filter would have to be dimensioned such that, in practice, it could not be tolerable with respect to the required space as well as with respect to the amount of pressure loss and the resulting costs.
The known method of the aforementioned kind (DE 41 23 258) provides a solution in that the activated carbon particles introduced into the wet scrubbing process reduce the heavy metal contents to such a great extent that heavy metals are no longer detectable in the flue gases exiting from the wet scrubbing process. This does not require an additional method step and requires only a minimal amount of expenditure with regard to the device technology. With respect to pressure loss, there are also no considerable disadvantages. Furthermore, an additional advantage is that the activated carbon particles, under the conditions of wet scrubbing, are able to not only bind heavy metals but also organic compounds such as dioxins and furanes.
The required amount of activated carbon particles is relatively small. However, it was found that it is desirable to lower the amount of adsorption medium even more because activated carbon is a relatively expensive material.
It is an object of the invention to reduce for scrubbing of flue gases the amount of activated carbon particles.
SUMMARY OF THE INVENTION
As a solution to this object the method of the present invention is characterized in that the activated carbon particles are separated from the suspension resulting from wet scrubbing and are recirculated into the wet scrubbing process whereby a portion the particles is branched off and thermally desorbed before recirculation.
The inventive method of scrubbing flue gases comprises the steps of: scrubbing; thermally desorbing the first portion of the activated carbon; portion of the activated carbon; step a).
The method may further include the step of adjusting the treatment conditions for step a) to a pH of 6 by adding at least one pH-adjusting compound selected from the group consisting of slaked lime and limestone.
Step b) may include segregating gypsum and heavy metal-containing particles from the suspension by flotation.
Step b) may further include partial
REFERENCES:
patent: 5618508 (1997-04-01), Suchenwirth et al.
Neumann Marion
Winkler Hermann
Steag Aktiengesellschaft
Straub Gary P.
Vanoy Timothy C.
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