Implementation of a Digital Control System for Inlet Condenser Valve Positioning to Enhance the Reliability of the Salak Geothermal Power Plant

From 2017 to 2019, the Inlet Condenser Valve positioning system of Unit 2 at the Salak geothermal power plant experienced significant control system failures, which hindered the valve's ability to regulate the flow of cooling water into the condenser. This malfunction, caused by the system's inability to respond to set point commands from the DCS (Distributed Control System), necessitated manual operation via a chain block. Consequently, the startup recovery process was disrupted, leading to delays averaging over 10 hours, reducing the Equivalent Availability Factor (EAF) and compromising the power plant's reliability due to frequent trips. This research aimed to enhance the reliability and efficiency of the Unit 2 system by overhauling the control system, transitioning from analog to digital control for more precise valve positioning. The upgraded system, now managed through a PC interface using Nexus MPC software, retained PID (Proportional Integral Derivative) control algorithms. Data processing via Excel enabled accurate response time assessments, while PID tuning was derived empirically from open-loop responses and finetuned through field testing. The analysis demonstrated superior digital control performance, achieving a valve opening response time of 16.5 seconds with a minimal error of 0.02%. The implementation led to a 0.0029% per hour improvement in EAF, with recovery times reduced by 1.6 hours, generating a financial benefit of Rp 115,796,250. Furthermore, the revamped inlet condenser valve control system successfully prevented forced outages twice in 2023, underscoring the enhanced reliability of the equipment and the overall power plant unit.