Abstract
We present an analysis of two different cogeneration schemes. A comparison is made with a conventional plant of separate units for producing process heat and power. Use of the first and second laws quantifies the irreversible losses. In the cogeneration schemes, the required process heat is obtained either from a boiler and a back-pressure turbine or from a combined-cycle gas turbine. The effects of the process pressure and heat-to-power ratio on performance are presented. The performance of the different schemes is analysed in view of the first- and second-law efficiencies, cogeneration efficiency and irreversibility rates for the different components in each plant. The irreversible losses occur mostly in the boiler and combustion chamber and are greatly reduced in a gas-turbine cogeneration unit.