Numerical Study of the Effect of Damper Opening Angle and Flue Gas Temperature on Temperature Distribution in Heat Recovery Steam Generator (HRSG)

Abstract Combined Cycle Gas Turbine (CCGT) utilises the hot flue gas from the gas turbine to produce steam in the Heat Recovery Steam Generator (HRSG). The steam from the HRSG is then used to generate electricity in the steam turbine. At PLTGU Tanjung Uncang Batam, the exhaust gas temperature when the damper is open must be below 400°C. However, the turbine gas with an initial load of 5 MW has an exhaust gas temperature of 560°C - 580°C. It is necessary to remove the turbine gas load or Full Speed No Load (FSNL) to reduce the inlet temperature of the turbine gas. The analysis was conducted using Computational Fluid Dynamics (CFD) with ANSYS Fluent 2020 software. The variations used are the diverter damper angle values of 51°, 68°, and 90° combined with inlet temperatures of 400°C and 580°C. HRSG simulation results, velocity, and temperature contours show that the flue gas is not evenly distributed. The turbine flue gas is only spread along 4 - 12 m. Apart from that, from the results of calculations based on operation conditions, at a flue gas temperature of 580°C, the steam flow rate affects the tube wall temperature. Analysis shows that at a steam flow rate of 0.0576 t/h, the tube wall temperature can increase to 541.84°C, which causes the material strength limit to decrease significantly to 143.94 MPa. The ideal steam flow rate is 2.484 t/h, at which the material strength limits remain almost the same as the current operating conditions (400°C). Thus, if the steam flow rate is 2.484 t/h, which is safe for the tube temperature, there is potential for cost savings. Savings from using demineralized water reach IDR 24,708,240 per start up process.