HotSpot: High temperature behaviour of potentially toxic and corrosive trace elements in thermal gasification systems

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The thermochemical conversion of carbonic fuels causes the emission of significant amount of trace elements, e.g. heavy metals, arsenic, which can be toxic. In the plant the trace elements can cause corrosion of heat exchangers and turbines, poisoning of catalysts, inactivation of membranes, and in general the efficiency of downstream parts of the plant can decrease, e.g. sequestration of CO2, production of methane and liquid fuels, basic chemicals and fertilisers. Advanced, highly efficient power plant processes, e.g. the integrated gasification combined cycle which can use biomass, derived fuels and coal, need a proper gas cleaning. During the last decades scientific research lead to significant reduction of several air pollutants from the power plants, e.g. SOx, NOx. However, the transformation behaviour of trace elements has not been exhaustively investigated, especially for gasification conditions.The planned study aims the determination of release mechanisms of trace elements As, Pb, Sn, and V, their gas phase chemistry and their condensation behaviour which is the fundament for effective hot gas cleaning. Specific thermodynamic data will be determined as a function of important process parameters of gasifiers (temperature, steam content) and significant trace gases (H2S and HCl). The data will be implemented into a model. The first important methodical focus is the quantification of the influence of the parameters under investigation at gasification conditions. This is important for the modelling, because it put emphasis on the value of the influencing factor. The obtained results will broaden the data base of modelling significantly, because mainly combustion phenomena have been investigated in the past.The second important focus is the determination of gas phase species directly in the hot gas using Molecular Beam Mass Spectrometry. The online determination of significant gas phase species will be done for the first time worldwide in this thematic context. It allows to proof theoretical transformation mechanisms by detection of important gas phase species and to modify mechanisms (if necessary) and/or to propose new mechanisms.Finally, the study aims to build up a thermodynamic model of release and condensation of a selected number of trace elements. The model shall be able to describe and explain the transformation behaviour in its essential characteristics and to predict the behaviour for modified process parameters.Further studies can a) include a broader number of significant trace elements, e.g. quicksilver, cadmium, and/or b) focus on process parameters of relevant applications, e.g. for the cement industry or hazardous waste treatment.