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Table 3-5: Improvement in cycle efficiency with higher steam parametersInlet pressure Inlet temperatures Efficiency increase(kg/cm 2 ) (°C) (% points)170 537 537 Base (500 MW)170 537 565 0.75247 565 565 1.31247 565 593 1.64247 600 600 1.96After supplying more than 950 subcritical boilers, BHEL is currently adopting advancedsteam cycles to improve the environmental and economic performance in India’s powergeneration. BHEL offers Indian power utilities "Once Through" supercritical technologylicensed from Alstom, France. Figure 3-2 depicts the basics of supercritical technology.Figure 3-2: Supercritical technologySC steam generatorBoiler steam pressureabove the critical point35Critical point221 bar, 374 deg. CTemperatureT421 6EntropyS1-2 Feed water pumping process2-3 Heat addition in the feedwater heaters & boiler3-4 Expansion in high-pressureturbine4-5 Reheating in boiler5-6 Expansion in IP 7 LP turbine6-1 Heat injection in condenserFor improving the cycle efficiency, higher pressure, higher SHO/RHO temperature andhigher feed water temperature have been adopted. Drum has been eliminated, verticalseparator with start-up recirculation system used for loads below 40 per cent boilermaximum continuous rating (BMCR), and two-stage SH and two-stage RH adopted.Pollution control systems typically comprise selective catalytic reduction for 85 percent NOx reduction, low-NOx burner for 50 per cent NOx reduction, flue gas desulphurizationfor more than 90 per cent reduction in SO 2, and dust collection equipmentthat meets the current standard. BHEL developed a Bypass Over Fire Air (BOFA)system to reduce NOx emission by about 40 per cent (Figure 3-3).90