Optimum gasification process for coal wastes utilization in Tanzania

This thesis focuses on developing an optimum gasification process for eco-friendly utilization of coal wastes. Challenges to the safe utilization of coal wastes are low volumetric energy density, heterogeneous solid fuels, and high ash and trace metals contents which become problematic in direct gasification due to toxic formation. Multi-metal as well as single-metal interactions were investigated to provide an insight of formation of toxic species in a wide range of temperature environments and in-situ mitigation of their pollutions during the gasification process. Emphasis was also placed on the study of the use of inorganic sorbents to adsorb heavy metal emissions from gasified metal contained in coal wastes using computer code, MALT, and compared with experimental results, in which alumino-silicate sorbents such as kaolinite and alumina due to their strong chemical bond with the metals were found to chemically bind airborne metal emissions. The optimal gasification parameters and heat transfer in Fluidized Bed Gasifier (FBG) was modelled using Computational Fluid Dynamics software (CFD-FLUENT) followed by experimental gasification of the fuel in a laboratory-scale test rig model gasifier in order to elucidate the effects of kaolinite on effective chemisorptions of toxic and corrosive trace elements producing syngas consisting mainly of CO, H2 and CH4 at 8500 C. Coal wastes gasification chemistry, process modelling, gasifier design and operation and product gas cleaning were performed in the invented gasifier test facility model.