Combined Cycle Power Plant with Multi pressure Steam

Combined Cycle Power Plant with Multi pressure Steam M. Asad jan Ibni Amin M. Tariq M. Arshad Kaleem ullah

Introduction • It is a cycle which reduces the temperature of the gas leaving the heat recovery boiler and results in increased efficiency of the plant as a whole. Dual pressure cycle consist of heat recovery boiler with two steam circuits. High pressure circuit and lower pressure circuit.

STATISTICS Steam Cycle Pressure =1300 psi(90 bar) Saturation temperature =575 F Feed water into HRB=264 F Gas temperature leaving HRB=300 to 400 F So some of energy leaving with that gas can be utilized in a multi pressure steam cycle.

Cycle Power Plant Efficiency Steam cycle Single pressure Dual pressure Net efficiency 60 (%) 58 56 54 52 50 48 46 960°C — 50 bar 460°C 1000°C — 60 bar 485°C 1050°C — 75 bar 510°C 1120°C — 80 bar 520°C Tripple pressure with reheat 1160°C — 100 bar 520°C 1230°C 1190°C 130°C 200°C 110 bar 550°C 540°C 1250°C 1230°C 200°C 130°C 160 bar 125 bar 580°C 565°C 1983/84 1987/88 1990/91 1992/93 1994/95 1996/97 1998/99 2001 2005/06 Year of commissioning Turbine inlet temp. (ISO) Fuel preheating Life steam pressure Life steam temperature

Efficiency Improvements due to Increasing the Number of Pressure Stages Temperature curves in a heat recovery steam generator Temperature [°C] 600 500 1 -pressure process 2 -pressure process 3 -pressure process Efficiency increase D h net [%-points] 125 bar/565 °C 28 bar/565 °C 4 bar/235 °C 3 125 bar/565 °C 29 bar/320 °C 5 bar/200 °C Exhaust gas 400 2 80 bar/540 °C 5 bar/210 °C 300 2. 8 100 0 2. 1 1 200 1. 6 65 bar/540 °C Transfered heat 0 54. 1% 1 -pressure 2 -pressure 3 -pressure without with reheat

Quick Start up Increases Plant Utilisation Factor . . . Start-up after 8 h Shut-down Typical plant start-up Plant Load [MW] Plant start-up with improved equipment GT at full load/ Bypass System closed ≈ 40 min ≈ 90 min Time