Sorbent for the dry cleaning of waste gases charged with mercury and process for the production thereof

#The invention concerns a sorbent for the dry cleaning of waste gases charged with mercury, comprising at least one adsorptively acting constituent in the form of activated carbons, activated cokes, zeolites or the like, and powder elementary sulfur.

#The use of sulfur-bearing substances or indeed the use of elementary sulfur for the separation of elementary mercury from waste gases from thermal processes such as for example from waste gases of refuse incinerators or from metallurgical or secondary-metallurgical procedures is basically known.

#It is known for example from DE 199 36 930 A1, for the separation of metallic mercury from hot pyrolysis gases from waste substances, for mercury-binding substances to be introduced into the pyrolysis gas, which afford solid mercury compounds. They are separated off at fine dust filters. DE 199 36 930 refers to sulfur, sulfur-doped activated carbons, hearth furnace cokes, bentonites, zeolites, trasses and/or brick dusts as well as substances which give off sulfur such as sodium thiosulfate, sulfuric acid and hydrochloric acid, as mercury-binding substances.

#FIG. 1: FIG 1 shows the variation in respect of time of the Hg exit concentration from the adsorber, the uppermost graph showing the variation in concentration of the pure process dust (EOS1996). The graph therebeneath shows the variation in concentration of the sulfur-doped coke sample. The graphs shown therebelow illustrate the variations in concentration of the sulfur-doped coke dust sample to which process dust of the composition shown in Table 3 was added in a ratio of 50:50. The adsorber temperature was 120 ° C. in that case.

#The following Example describes the mode of operation of a sorbent which is distinguished from the sorbent according to the invention in that the ratio of the median values, that is provided in accordance with the invention, was not observed.

#2 kg of brown coal coke of a grain size<4 mm was comminuted with 0.105 kg of sulfur pellets (about 6 mm) corresponding to 5 percent by mass of sulfur in a drum mill (20 kg grinding body, 70 rpm) for a period of 100 minutes and in so doing was mixed. The grain size distribution of the mixture, the saturation loading with 1, 3-dichlorobenzene at 20° C. and the loading with elementary mercury were measured in a fixed bed adsorber. The measurement conditions in respect of Hg adsorption were as follows: entry concentration of the elementary mercury 980 μg/m3; adsorber temperature 90° C.; vacuum gas speed 1.7 cm/s; carrier gas with 14% by volume of oxygen, 0.4% by volume of water vapor and the balance nitrogen. The sample in powder form was introduced into the adsorber in the form of 3 individual layers each of 0.5 g, separated by glass wool felts. The sandwich structure of the adsorption layer ensures a uniform flow of the sample in powder form therethrough.

#A d50 value of 7 μm for the sulfur-doped coke dust was determined after comminution in the drum mill by means of a laser granulometer (Helos, from Sympatec). The mean loading with mercury was 255 μg/g after 12 hours. The mercury was 90.6% removed from the gas flow. The loading with 1,3-dichlorobenzene was reduced from 18.4 percent by mass for the untreated hearth furnace coke to 11.2 percent by mass for the sulfur-doped coke sample (reduction by 39% in relative terms), which is to be attributed to the blockage of micropores which occurred by the loading in the mill.