Influence of H2O, HCl and H2S on the release and condensation of trace metals in gasification

High temperature coal utilization processes such as gasification emit hazardous traces of heavy metals into the atmosphere, impacting the environment, human health and causing technological problems in gasification plants. These trace metals present in parts per million levels in coal give rise to several tons of these pollutants in the environment per year. Therefore, the development of cleaner and more efficient techniques in next generation coal power plants is essential. A promising coal utilization process is the Integrated Gasification Combined Cycle (IGCC) with integrated hot gas purification and CO2 separation. An increased efficiency and a decreased amount of heavy metal species can be accomplished through hot fuel gas cleaning. However, in order to develop clean up techniques that reduce or remove heavy metal traces, it is necessary to understand their behaviour during the gasification process. Some studies have already determined that the chlorine, sulphur and moisture content of fuels have a significant influence on the behaviour of some trace metals. Hereby, the influence of steam, HCl and H2S on the release and condensation of Zn, Cd, Pb, As, Sn and V was experimentally investigated. The condensation behaviour (temperature and speciation) of the heavy metal vapours was investigated in a heated flow channel reactor housed in a furnace with a gas cooling zone. Experiments on the release of the inorganic vapours were carried out in a heated flow channel reactor coupled to a molecular beam mass spectrometer (MBMS) in order to analyse the gas in-situ. The results of the experimental investigation were compared with “Scheil-Gulliver Cooling” calculations performed by FactSage 6.3. Furthermore, thermodynamic pseudo-equilibrium calculations were carried out to predict the condensation behaviour of the heavy metals under the influence of super-cooling and chemical reaction control. A better understanding of the gasification process and a new insight into the optimization of the process to reduce the trace metal emissions was achieved