Pollutant adsorption during activated carbon and steam regeneration in technical columns (experiments, modelling): Part 2. Influence of process parameters during steam regeneration of activated carbon beds on pollutant exit concentration

Abstract

Experiments in activated carbon columns of technical scale with upstream adsorption and downstream steam regeneration showed that pollutant exit concentration of waste gas can be markedly decreased if the upper zone of the fixed bed is preheated to ⩾120 °C before desorption and, additionally, if the bed is desorbed with superheated steam with a temperature ⩾150 °C. With this improved steam regeneration technique a decrease in pollutant exit concentration is achieved: for example, from 20 to 3 mg m −3 toluene. An increase in adsorption time before pollutant breakthrough from 12 to 19 h is also noted. During regeneration of a cold bed of activated carbon with saturated steam the particles will become wetted with condensate outside and adsorbed steam inside. These water condensation/adsorption effects are markedly reduced by preheating the particles to temperatures so far above that of steam condensation that steam adsorption is prevented too. Additionally the regeneration steam is superheated so that the temperature drop caused by heat of pollutant desorption is not so great that steam adsorption occurs. The whole desorption-adsorption cycle in a technical scale bed, including the effects of Steam condensation/ adsorption, flux and suction of condensate, hetero-azeotropic pollutant distillation and evaporation of condensate was modelled. Radial maldistribution effects (discussed in part 1 of this paper, Chem. Eng. Proc., 32 (1993) 359) have not been taken into account here. The calculated flux rates of pollutant in the gas mixture leaving the bed during desorption and the pollutant breakthrough curves at the following adsorption step correlate quite well with experimental results.