Cogeneration: Energy Efficiency of Competing Technologies

Abstract

The article proposes a methodology for carrying out a comparative analysis of the energy efficiency of combined (cogeneration) and separate arrangements for electricity and heat generation, which takes into account the operating characteristics of different cogeneration unit classes [steam turbine units (STU), gas turbine units (GTU), and combined cycle units (CCU)], as well as the regional climatic conditions of their operation. By using the developed calculation tool, it is possible to determine key indicators such as relative annual fuel saving, coefficient of fuel utilization (CFU), and capacity factor (CF). The study was carried out for a wide range of the capacities of gas units (10–230 MW) and for a coal fired STU (100 MW) with taking into account the characteristics of regional power systems at the places of possible use of cogeneration units. It is shown that cogeneration is an efficient method for saving fuel and reducing greenhouse gas emissions under the currently existing conditions, and with the expected improvement in the efficiency of separate electricity and heat generation. Currently, the use of GTUs and STUs for cogeneration purposes can save 19–37% of fuel, and that of CCUs, up to 28–44% depending on the regional and climatic conditions. Even if we take a hypothetical case of achieving average annual efficiency equal to 55% in the separate arrangement of electricity and heat generation at fossil fueled power plants, the fuel saving due to cogeneration still remains positive, although it will decrease to make from 1 to 11% in the case of using steam turbine and gas turbine units, and 6–19% in the case of using combined cycle units. It has been determined that the best prospects for use will be for cogeneration units featuring high electricity generation efficiency, also during operation at partial loads, and also with a wide thermal power adjustment range. The obtained conclusions and developed techniques can be used for substantiating the choice of technologies in designing and modernizing combined heat and power plants, and in elaborating programs for development of thermal power facilities in regions with different climatic conditions.