Session: 21-02 Combined and Renewable Cycle Operation

Submission Number: 179288

A Thermodynamic Study on Steam Turbine Floor Pressure Modification for Performance Enhancement in Combined Cycle Power Plants 

In combined cycle power plants, the operational mode of the steam turbine is a critical factor influencing overall plant efficiency, operational flexibility, and system stability. During standard operation with multiple gas turbines supplying thermal energy to the heat recovery steam generators (HRSGs), the steam turbine typically functions in sliding pressure mode, wherein the main steam pressure adjusts dynamically in response to variations in gas turbine load and exhaust conditions. Conversely, under single gas turbine operation in a multi-shaft configuration, the resulting reduction and fluctuation in steam generation from a single HRSG necessitate transitioning the steam turbine to a fixed pressure mode to maintain stable and reliable performance

This paper presents a comprehensive study on enhancing heat rate performance at an ACWA Power combined cycle power plant operating in a 1-1-1 configuration under fixed pressure mode. The improvement strategy centers on optimizing steam pressure set points across the high-pressure and intermediate-pressure stages of the steam turbine. A thermodynamic model was initially developed to simulate various pressure combinations, enabling detailed analysis of their impact on plant performance. The findings indicate that increasing the HP main steam pressure by 2 bar while decreasing the IP steam pressure by 2 bar results in a heat rate improvement of approximately 25–30 kJ/kWh at the block level. Key performance indicators, including steam flow rates, turbine power output, isentropic efficiencies, and exhaust temperatures, were closely monitored to assess the effects of pressure adjustments. The results demonstrate a net increase in steam turbine output by 1–1.5 MW, primarily attributed to improved expansion in the HP stage of the steam turbine, despite a slight reduction in IP turbine output. Overall, the study supports the viability of steam pressure optimization as a cost-effective and technically sound approach to improving plant efficiency.

Presenting Author: Yahya Zafar ACWA Power

Presenting Author Biography: Associate Performance Manager at ACWA Power’s Monitoring & Prediction Centre, where he oversees performance monitoring, efficiency enhancement, and reliability for large‑scale assets, including combined‑cycle, thermal, and CSP plants. With over 9 years of experience, his expertise spans early fault detection using AI/ML and APR, rigorous RCAs, and the development of plant-level digital twins for what-if analysis and optimization. He has led the deployment of GE Operational Performance Management (OPM), Asset Performance Management (APM), and EtaPro solutions across multiple sites; created thermodynamic models in Ebsilon and GateCycle; and supported guarantee and capacity tests with a focus on contractual compliance. Yahya’s research includes several ASME GT2025 papers on HRSG performance assessment, compressor isentropic‑efficiency impacts of water‑wash frequency, and seawater‑flow effects on LP steam‑turbine efficiency and exhaust moisture, as well as a U.S. patent application on gas‑turbine inlet heating using stack‑exhaust heat. He holds a B.Sc. in Chemical Engineering.

Authors:

Yahya Zafar ACWA Power
Muhammad Adnan Saroosh ACWA Power
Jalal Hunain Zia ACWA Power
Tariq Nada ACWA Power
Muhammad Azhar Janjua ACWA Power