The Assessment of steam above ground system of Unit-1 and Unit-2 Ulubelu geothermal field, Indonesia, after 5 years of operation

Abstract

This study assesses the Steam Above Ground System (SAGS) of Unit-1 and Unit-2 in Ulubelu geothermal field in Indonesia after 5 years of operation. After this period of operation, there are changes in operation parameters such as pressure, temperature and flow from production wells due to the decline of the geothermal resource. It has effects not only on the SAGS performance, i.e. pressure drop, fluid velocity, equipment efficiency etc., but also potential silica scaling in the reinjection line. In addition, there is a reduction in the operating life of SAGS, especially regarding the pipes and the separator that need to be monitored and evaluated. This study focuses on pressure drop analysis of the two-phase flow of steam and brine, separator performance analysis, Silica Scaling Index (SSI) analysis in the reinjection line, wall thickness evaluation and estimation of turbine chamber pressure by Stodola’s law. All of the calculations were done using Engineering Equation Solver (EES), comparing and evaluating both the design and the present condition. The assessment result shows that at present conditions, the SAGS performance decreases with the decrease of operation parameters. It is characterized by some operation parameters that are below allowable conditions, such as pressure and temperature at interface point, silica saturation index and steam quality at separator outlet. Based on those conditions, some optimization scenarios are recommended to be applied in order to improve the SAGS performance.