Migration Of Cr、Hg And Pb In Coal And Biomass Co-gasification

This paper investigate the migration behavior of some heavy metals, include chromium, lead and mercury in the gasification process, and the factors affecting their migration. The main contents and conclusions of this paper are as follows:(1)The laboratory-scale high frequency heat gasifier is used to investigate the migration behavior of heavy metals (Cr, Pb, Hg) during biomass/coal co-pyrolysis and co-gasification. The temperature investigated is900℃～1300℃. The content of heavy metals in the samples is not the main factors which affect the volatilization behavior. The volatilization behavior is relevant to the heavy metals’ chemical speciation in the samples. Chromium tends to exist as the stable residue state in the pyrolysis coke, so at high temperature, chromium is not easily to volatilize. When the adding ratio of leather sludge is40wt%, the volatilization of chromium is biggest, because the ash melting point is1400℃, there is much more pores in the slag, its surface is loose and it is conducive to the volatilization of chromium.(2) Ontario method is used to investigate themorphological distribution of mercury in gas. Mercury exists mainly in elemental mercury in the gas, and when the temperature raises, the content of the elemental mercury in the gas decreases. When the content of chlorine increases, the percentage of oxidation state mercury will increase.(3) The fly ash collected from four-nozzle thermal mode platform were investigated, to study the ability of adsorpting heavy metals. Thefly ash collected from gasification reaction zone has the best ability to adsorp heavy metals, it is related to mineral composition and the melting substance on the surface of the fly ash.(4) The toxic leaching experiment is carried out, using the fixed-bed to make the low-temperature gasification slag. The content of chromium in the leaching solution is too low to cause harm to the environment. The chromium’s valence in the slag is analyzed by using XPS. Chromium exists mainly in the lower valence state when in a reducing atmosphere, but in an oxidizing atmosphere, chromium exists not only in lower valence state, but also in high valence, which is toxic.