Evolution of Power Cycle Efficiency and Heat Rate

 Evolution of Boiler technology is directly related to metallurgical evolution of boiler tube materials. Power generation through fossil fuel firing system is operated on modified Rankine cycle. The cycle efficiency  increases with increase in operating pressure and temperature. Main limiting factor for increasing temperature is metallurgy of the boiler tube. The sub critical, low super critical, super critical and ultra super critical technology are evolved with increasing pressure and temperature of the cycle.

 The main parameters of the above cycle are as follows:

	Unit size	Main Steam Pressure	Main Steam Temperature	Reheat Steam Temperature
Sub-critical	500 MW	166 bar	538°C	538°C
Low supercritical	660 MW	247 bar	538°C	565°C
Ultra supercritical	800 MW	270 bar	565°C	593°C
Advanced supercritical	1000 MW	295 bar	600°C	600°C

Higher  Boiler operating pressure and temperature means :

§Higher cycle efficiency and Heat Rate

§Lower green house gas emission

§Lower fuel , auxiliary power and water consumption

§Lower unit cost of generation

Below figure denotes clearly how the efficiency of the power plant in Germany gradually improved over the years with improvement in boiler technology. This clearly shows from 1970 to 2010 plant efficiency is increased from 14% to 50%.

Efficiency Vs Year in Germany Power Plant Improvement of Heat Rate vs Improvement in cycle pressure and temperature The below fig shows if we increase the pressure and temperure to 30MPa ,650deg.C from 18.5Mpa, 535 Deg.C then heat rate will increase upto 12% for double reheat system.    Trend in efficiency improvement in Indian Power Sector  In 1978 Steam Pr and temp was 130ata and 537Deg.C gradually changed to 280ata and 600/620Deg.C. So, heat rate improved by more than 14% as per below fig.