Transformation Behavior Of As/Cd/Pb/Zn During Coal Pyrolysis And Gasification

Coal is expected to keep its important position as a major world energy source for along term. Coal also plays a particularly vital role in power generation. Therefore,environmental pollution problems caused by the utilization of coal are needed urgently tobe solved, especially heavy metal pollution caused by the release of trace element. Coalgasification is an economic, efficient, clean way to make use of coal. Nowadays, clean coaltechnology exampled by IGCC has developed rapidly. Most of the rare researches on traceelement during coal gasification are in normal temperature and pressure. In order toeffectively control the release of harmful trace elements in coal gasification process, it isnecessary to improve the basis theory for pollution prevention and controlling. In this paper,the release and enrichment of trace elements and morphological transformation during hightemperature and high pressure coal pyrolysis and gasification were studied systematically.Three kinds of typical coal: XM, XWJ, NCP and four typical trace elements: As, Cd,Pb, Zn were selected as experimental samples. High temperature and high pressurepyrolysis experiments were done using high temperature tube furnace and PTGA. Theresult showed that the release rate of As, Cd, Pb, Zn increased with increasing pyrolysistemperature; The effect of coal type on the release of trace element depended on theoccurrence of trace element in coal; The transformations of minerals in coal influenced therelease behevior of trace element. The release rate of Cd, Pb, Zn decreased with increasingpressure, but the release rate of As increased.High temperature CO2gasification and steam gasification experiments were doneusing high temperature tube furnance. The result showed that the atmosphere during CO2and steam gasification all improved the release rate of trace elements, the improvementeffect of steam gasification was stronger. The effect of coal type on the release of traceelement depended on the chemical specialization of trace element in coal.Finally, software of chemical thermodynamic calculation was used to predict thespeciation distribution of trace element during pyrolysis and gasification. In contrast withthe speciation distribution of trace element during pyrolysis, CO2promoted thetransformation of As(s) to AsO(g), As(g), AsH(g), steam promoted the transformation of As(s) to AsH(g),AsH2(g),AsH3(g). Atmosphere had little effect on the transform path of Cd,but CO2and steam promoted the release of Cd(g) at lower temperature. Pb released in theform of PbCl4(g) at low temperature, atmosphere also had little effect on the transform pathof Pb, but CO2and steam promoted the release of Pb(g) and PbCl(g) at lower temperature.CO2and steam promoted the transformation of ZnS to ZnO, thus promoting the release ofZn(g) at lower temperature.