Fig. 3-8 Removal efficiency of nitrogen and sulfur obtained from the pilot plant tests The removal efficiency strongly depends on the nitrogen oxide concentration in the fuel gas: The lower the concentration, the higher the efficiency. The removal efficiency of sulfur, on the other hand, is increased with decreasing temperature. By choosing adequate irradiation conditions, we reached the pre-set goal: removal efficiency of 80 % for nitrogen and more than 94 % for sulfur, with 8.3 kGy.

Fig. 3-9 Pilot plant for exhaust gas treatment installed in a coal-fired power station

Flue gases from a coal-burning boiler contain such substances as nitrogen/sulfur oxides that may cause acid rain. A municipal waste incinerator, moreover, exhausts hydrogen chloride and organic chlorine compounds as a result of the burning of plastics. Exhaust gases from paint-coating works may contain volatile organic compounds. We have studied radiation chemical reactions caused by ionization or excitation of a main component of flue gas, in most cases nitrogen, to find out an adequate method of removing existing toxic substances; for example, the addition of ammonia to obtain fertilizer, ammonium sulfate/nitrate, from coal-fired exhaust gas, and the addition of lime (CaO)-water to obtain powdered calcium salt in the case of municipal waste gas. Pilot-scale tests of this technology have been carried out by joint research groups including an electric power company and a city government to get further information from the technical and economical point of view. Technology transfer to other countries is also expected.

Reference O. Tokunaga et al., Application of Electron Beam Irradiation (4) Treatment of pollutants by electron beam irradiation, Radioisot. 43, p.781-790 (1994).

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