Cogeneration represents one of the main ways for increasing the efficiency of
primary energy use. This paper deals with a theoretical analysis of cogeneration
plants equipped with various back-pressure turbines type R. These plants are studied
during their operation with conventional method (water injection) and the suggested
method (sliding live steam temperature) to regulate steam temperature supplied to the
industrial consumers. A computer program had been written to work under MathCad
software to simulate cogeneration plant with each back-pressure turbine under design
and off design conditions. The performance of the different schemes is analysed in
view of the first and second laws. In this analysis entropy method (second law) in
addition to more conventional energy analysis (first law), are employed to evaluate
overall and component efficiencies, fuel consumption and to identify the
thermodynamic losses. The results show that, using the suggested method leads to
increase the overall efficiency of the cogeneration plant for all types of back-pressure
turbine and can reduce the fuel consumption. Finally, the results show that increasing
back-pressure leads to improve the performance of cogeneration plant regardless of
the method used.