Author(s)

A. KHALIQ, S. AHMED

Abstract

The depletion of non-renewable energy sources and its high cost, along with global warming related problems, have led engineers to re-assess more efficient and eco-friendly energy utilization. The objective of this paper is to determine the magnitude of fuel exergy saving and CO2 emission reduction from combined heat and power plants in comparison to separate heating and power generation plants. The energy and exergy efficiencies have been defined for different types of energy plants. The efficiency of the cogeneration unit and the CO2 emissions of the power plant are the two major factors that determine the amount of reduction in CO2 emission. The expression for fuel exergy saving through cogeneration is also developed in terms of the second-law efficiency of cogeneration plants and the second-law efficiencies of separate heating and power generation plants. The exergy saving is determined for various kinds of cogeneration arrangements. From the results of the study, it is observed that maximum exergy will be saved in internal combustion based cogeneration plants and minimum exergy will be saved through extraction-condensing steam turbine based cogeneration. Results also show a similar trend for CO2 emission reductions. It is observed that with the increase in efficiency of the power plant and cogeneration, the CO2 emission decreases. A reduction in CO2 emission ranges of 20%–25% is possible depending on the conditions. The proposed methodology may be quite useful in the selection and comparison of combined energy production systems in terms of CO2 reduction, within the framework of the Kyoto Protocol on climate changes.

Keywords

cogeneration, CO2 emission reductions, fuel-exergy savings, sustainable development.