Performance Evaluation of Double-flash Geothermal Power Plant at Dieng Using Second Law of Thermodynamics

Abstract

A Single-flash system has been adopted for power generation in the Dieng geothermal power plant, Indonesia, which produces 22 MW of electricity despite of its installed capacity of 60 MW. To achieve optimum energy utilization, a modification of the plant to double-flash system is examined and evaluated by energy and exergy analysis using actual and designed data of the plant. The Engineering Equation Solver (EES) is used to simulate a double flash system on the basis of the plant model. The results of a proposed design indicated that the total maximum net power output of the plant is obtained to be 34.76 MW from high pressure turbine (HPT) and low pressure turbine (LPT). The steam is supplied from five production wells with available exergy evaluated at the well head to be 84.98 MW. The separator pressure for HPT is given as 9.87 bar based on actual data of the plant while that for LPT is 1.43 bar based on the optimal design. Two gas ejectors are operated for extracting non-condensable gases and are driven by steam. The total steam mass flow rates used for these ejectors are 5.207 kg/s. The energy and exergy efficiencies of the overall power plant are calculated to be 40.90 %.