Energy and exergy analysis and optimization of Kalina cycle coupled with a coal fired steam power plant

This paper provides a computer simulation of a Kalina cycle coupled with a coal fired steam power plant with the aim of examining the possibility of exploiting low-temperature heat of exhaust gases for conversion into electricity. The numerical model described here has also been used to find the optimum operating conditions for the Kalina cycle. The effect of key parameters namely ammonia mass fraction in the mixture and ammonia turbine inlet pressure on the cycle performance has been investigated. Results indicate that for a given turbine inlet pressure, there is an optimum value of ammonia fraction that yields the maximum cycle efficiency. Increasing the turbine inlet pressure increases the maximum cycle efficiency further corresponding to a much richer ammonia–water mixture. With a moderate pressure of 4000 kPa at ammonia turbine inlet and an ammonia fraction of 0.8, when the exhaust gas temperature is reduced from existing 407.3 K to 363.15 K, the bottoming cycle efficiency reaches a maximum value of 12.95% and a net bottoming cycle output of 605.48 kW is obtained thereby increasing the overall energy efficiency of the plant by 0.277% and the overall exergy efficiency by 0.255%. In the Kalina cycle, maximum exergy destruction was found in the evaporator.