Behavior of lead compounds during municipal solid waste incineration

Abstract

In order to depress the concentration of heavy metals in the bottom ash in the incinerator, the behavior of lead compounds during simulated municipal solid waste (MSW) incineration was investigated, using an electrically heated drop tube furnace. In the experiments, special type of fish food was chosen as the simulated waste, which was burned alone and also blended with pure lead compounds, such as PbO, PbCl 2 and PbSO 4. For the simulated waste blending with PbO, test with addition of HCl gas into the combustion air was also conducted. The furnace temperature and combustion air stoichiometry were varied from 873 to 1273 K and 0.5 to 1.2, respectively. Ash particles were isokinetically sampled at the furnace exit by a water-cooled sampling probe, at the tip of which N 2 gas was injected to quench the combustion gas and particles. Those particles were then separated by a low pressure impactor with 13 stages. The results show that the tendency of the lead enrichment in the fine particles less than 1 μm depends on the melting temperatures of the lead compounds. Of the three lead compounds, PbCl 2 is enriched the most into the fine particles, and PbSO 4 is the most difficult at the low-temperatures examined. However, when HCl gas was mixed with the combustion air, more Pb is enriched in fine particles even at low temperatures. The low combustion air stoichiometry enhances formation of a large amount of fine particles containing high concentrations of lead. The mechanism of Pb enrichment in the coarse particles is controlled by the surface reaction of vapor of Pb compounds with the ash particles. Two-stage incinerator including a first-stage gasification zone with higher temperature and lower stoichiometric air ratio, is preferable to shift the Pb enrichment from bottom ash into fly ash during waste incineration.