In-situ generation of electricity from fossil fuels

The aim of this report was to investigate the possibility of using in-situ gasification (for coal) and combustion (for oil and gas) of the three fossil fuels to generate electric power and sequester the CO2 produced in underground formation. This study was motivated by the need to mitigate CO2 into the atmosphere which has been linked to climate change but also by the need to increase the profitability of hydrocarbon. This increase in profitability is based on the reduction of the need for surface storage, treatment and pumping equipment. Three cases were studied: in-situ generation of electricity from coal gasification using the gasification product syngas, in-situ generation of electricity from oil combustion, and in-situ generation of electricity from gas combustion. The combustion was coupled to a downhole power generation system followed by sequestration of combustion gases in a zone above the hydrocarbon reservoir. The resulting process thus injects only air into the underground formation and retrieves only electric power from the formation. The mathematical models used were the gasification model (for coal gasification), an eductor model, a turbine-generator model, and a CO2 sequestration model. Aspen HYSYS, MATLAB, and Excel were employed for the simulations. The results of the simulation and the models were compared to verify the agreement between the Aspen simulation and models provided by literature. Using the sequestration zone model, the curves of the CO2 layer over the brine were developed as well as the curves showing pressure increase at the injection point with time for each case. Based on the results obtained it was shown that in-situ generation of electricity from coal gasification was not viable option due to very small net power output of 0.423 MW. The turbine-generator model provided a negative net power output for coal gasification with a value of -0.643 MW. On the other hand, in-situ generation of electricity from combustion of oil and gas provided a positive power outputs, 5.934 MW and 3.691 MW respectively using Aspen Hysys. The net power generation value using Aspen simulation was found to be very close to the values obtained using mathematical model in the case of gas combustion. However in the case of the oil combustion the mathematical model provided a much larger net power output of 8.375 MW. the overall efficiency for coal was found to be 16.23 %. While oil and gas process had energy efficiencies of 40.03 % and 35.23 % respectively. It was therefore recommended that further research be conducted focusing on in-situ generation of electricity from combustion of oil and gas and the design of an adequate underground turbine-generator set.