Comparative analysis and evaluation of reciprocating engines and gas turbines used in cogeneration systems up to 50 MW

The objective in this paper is to create a tool for developers of CHP systems that could select the right gas turbine or reciprocating engines. A parametric study was conducted at 38 commercial turbines and 44 reciprocating engines of a set of data base of the manufacturers specifications, in a power range of 0.03 MW to 50 MW. The brands studied were: Hitachi, Kawasaki, Mitsubishi, Rolls-Royce, Solar Turbines and Siemens for gas turbine. For reciprocating engine: 2G Energy, Cummins, Caterpillar, General Electric, Guascor and Rolls Royce. The evaluation method was performed from conventional mathematical-thermodynamic models to determine the coefficient of derating of each engine as a function of the environmental temperature and pressure. The Q/E ratio and the available heat for cogeneration were studied as function of the power and thermal and electrical efficiencies. The simulations were performed with commercial software (TermoGraf and Excel). The load factor was not considered. For the cases of gas turbines, it was found that the generated power was reduced in average 5.5 % for each 500 m. above sea level and 1.7 % for each 5 °C of ambient temperature. The available heat has a second-order polynomial behavior. For the reciprocating engine, the coefficient of derating as a function of the environmental temperature has the same behavior of that of gas turbines. The generate power was reduced in average 5.5 % for each 500 m. above sea level and 0.85 % for each 5°C of ambient temperature. The Q/E ratio for the set of gas turbine fluctuates between 2 and 5 which corresponds to balanced consumption user. For the reciprocating engine set the Q/E ratio was between 0.5 and 2.5, which are mostly for electrical requirements and not for thermal ones.