Effect of Seawater Flow on Low-Pressure Steam Turbine Isentropic Efficiency and Exhaust Moisture Content

Abstract Adequate seawater (SW) flow or cooling water flow through the condenser in a thermal power plant is a critical factor in maintaining the isentropic efficiency of the LP steam turbine, condenser pressure and moisture content at the turbine exhaust. At one of ACWA Power’s thermal sites, deviations from the design seawater flow rates were identified during operation, as compared to the original equipment manufacturers HMBs. The site was operating three pumps on two blocks instead of the required four pumps, two on each block due to the constraints in the SW pit level. An investigation was conducted using thermodynamic modeling software to assess the impact of reduced SW flow on the LP turbine’s performance and condenser pressure. The analysis indicated that the LP turbine’s isentropic efficiency and condenser pressure and exhaust moisture content were deviating from the design reference due to the inadequate SW flow. To validate these findings, actual plant data was analyzed. It was observed that when sufficient SW flow was restored, moisture content, condenser pressure and isentropic efficiency returned to the expected levels with the improvement of around 40–45 KJ/KWh in steam cycle heat rate.