Geothermal Power Plant Retrofit to Optimize Generation: A Case Study from Salak Unit 4/5/6

Abstract

Star Energy Geothermal (SEG) is Indonesia's largest geothermal energy company that manages and operates geothermal power plants situated at Darajat (DRJ), Wayang Windu (WW) and Salak (SLK) with a combined capacity of 886 MW. The SLK geothermal power plants are located in Sukabumi regency, West Java province, comprises three units (SLK1/2/3) 60 MW each and three units (SLK4/5/6) 67 MW each. SEG supplies geothermal steam to SLK1/2/3 those are operated by a PLN subsidiary company, while SLK4/5/6 are operated by SEG. In order to maintain safe and reliable operation as well as to optimize plant performance, SEG conducted a comprehensive study aimed at retrofitting these SLK4/5/6 units by replacing and upgrading the steam turbine rotor and stator. Several project constraints were applied, including no additional steam mass flow rate, no major upgrades to main equipment and the Balance of Plant (BOP), no significant civil or structural modifications, and no additional steam wells related to this project. Under these constraints, the retrofit project for SLK4/5/6 is expected to yield an additional power generation increase of 2.4 MW for each unit, resulting in a total increase of 7.2 MW across the three units. The scope of the retrofit for SLK4/5/6 is primarily focused on modifying the turbine blades to enhance the isentropic efficiency parameter, while keeping other parameters unchanged. Referring to the turbine work formula, turbine output is influenced by parameters such as steam mass flow rate (ṁ), delta enthalpy (h1-h2), and isentropic efficiency (ƞt). Notably, parameters like steam mass flow rate (ṁ), inlet enthalpy (h1), and outlet enthalpy (h2) remain unaltered as no additional steam mass flow or steam pressure change is required for this retrofit plan. The expected improvement in the parameter of isentropic efficiency (ƞt) is anticipated to rise from the current average of 79.2% to 81.5% through the turbine blade modification, employing a new three-dimensional (3D) design as opposed to the existing two-dimensional (2D) design.