2 Heat recovery steam cycle Report A

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Course of Energy Conversion A 2014/2015 Prof. G. Valenti _________________________________________________ 2nd project Heat Recovery Steam Cycle • Index: 1. Introduction; 2. Correction to gas turbine outlet temperature 3. Considerations on the evaporation temperature optimization 4. Optimization of the evaporation temperature with constant steam turbine isoentropic efficiency 5. Optimization of the evaporation temperature with steam turbine isoentropic efficiency corrected on the basis of the outlet steam fraction 1. Introduction In this project we will design a heat recovery steam cycle with one evaporation level with a configuration as it follows. This is not the best configuration for a combined cycle from a thermodynamical point of view: bottoming steam cycle are characterized by more evaporation level at different pressure in order to minimize the dissipation of thermodynamical potential of the exhaust gas in the heat exchanges. Roughly speaking a cycle with two levels instead of one can cut down stack losses from 21% to 10%. However this is an easy configuration useful to analyze the performance variation at different temperature evaporation. 2. New gas turbine outlet temperature The installation of a heat recovery steam generator involves a pressure loss of 3000 Pa on the exhaust gas flow. According to this fact the turbine won’t expand the gas until 104 325 Pa instead of ambient condition assumed as 101 325 Pa. Assuming the exhaust gases as perfect gas enthalpy and entropy can be defined as follows:
ℎ =  

=  
 − ∗
Hence: ℎ = ℎ +   
   At To=25 °C the ho=0. ,  =  +   
   − ∗ 
  Where Cp is a fourth order polynomial coefficients:  =  +    +   +    +   We have to consider now the following…