The Possibility of using Flared Gas to Generate Electricity using Combined Power Cycle

Abstract

This work evaluated the possibility of generating electricity from flared gases through the application of combined power cycle (Organic Rankine and Brayton circle) which was simulated using Aspen Hysys. The data for the stimulation was obtained from literature in terms of the process plant operating conditions. The results obtained from the simulation were presented in terms of material balance, energy balance, costing, sensitivity analysis and exergy analysis, which is otherwise known as energy availability. The major equipment in the plants were: pump, heat exchanger, compressor, combustion chamber (conversion reactor), and an expender modeled as a gas and steam turbine respectively in Aspen Hysys simulation. The condenser was modeled as a cooler. The material and balance results were in agreement with the principles of conservation of mass and energy for a stead state process. The costing of the plant in terms of total capital cost, total operating cost, total utility cost, equipment cost and total installation cost were: $16,762,100.00, $70,661,490.00, $4,745,230.00, $11,323,700.00 and $12,359,400.00 correspondingly. The sensitivity analysis results revealed that efficiency of the gas turbine increase with an increase in exhaust gas pressure (kPa), signifying that the efficiency increased from 81.5% to 85% when the exhaust gas pressure was raised from 100 kPa to 500 kPa. The efficiency of the steam turbine increased from 72.6% to 74.2% when the outlet pressure was raised from 100 kPa to 900 kPa. Finally, the exergy result for gas turbine in terms of total exergy inlet and outlet are 14187 kW and 3710 kW respectively. This indicates an exergy efficiency of 26.15% or 10,477 kW exergy destruction. Similarly, the exergy result for steam turbine in terms of total exergy inlet and outlet are 1,856 kW and 1,357 kW respectively. This indicates an exergy efficiency of 73.12% or 498kW exergy destruction