Thermodynamic and economic analyses of power generation from gas turbine exhaust

Abstract

This paper presents the development of a thermodynamic model of natural gas production processes on the offshore platform by applying Organic Rankine Cycle (ORC) technology to the plant. This research considered the thermodynamic performance and economic feasibility of using ORC for electricity production from exhaust gas generated by gas turbine engines which were used as prime movers to drive natural gas compressors. According to the Process & Instrumentation Diagram (P&ID), the process of recovering waste heat from Booster Compression and Sales Gas Compression and Export modules from the entire gas production processes of the plant has been modeled in DWSIM program which is an open-source chemical process simulation. The simulation result showed that the exhaust gas had a temperature at 527 ^oC at Booster Compression and 504 ^oC at Sale Gas Compression and Export. The ORC was designed as a simple cycle with no degree of superheating and subcooling due to limited area of the offshore platforms. We have selected the most suitable working fluid for ORC in order to get the highest turbine power and efficiency. From the simulation, Toluene was identified as the most suitable working fluid which provided the highest turbine power and efficiency at 1.9 MW and 24.33%, respectively. So, the installation of 4 cycles of ORC for offshore platform will get total energy at 7.6 MW. To demonstrate the commercial feasibility of this project, a detailed economic analysis has been performed. The results showed that the ORC technology has the net present value (NPV) is 40.141 million Baht, the payback period (PB) is around 16.49 years, the internal rate of return (IRR) is 8.18% per year (from the minimum attractive rate of return or MARR at 8% per year) and the benefit cost ratio (B/C ratio) is 1.10. All indicators show economically favorable results, thus, indicating that this research is economically feasible and worth for the investment.