Increasing the efficiency and economy of a cogeneration power plant with an air turbine

Abstract

The use of renewable fuel and energy resources as fuel makes it possible to reduce the cost of a unit of electrical and thermal energy, reduce the load on the main energy system of the state, and improve the overall environmental impact on the environment. When using a pyrolysis pre-furnace, it is possible to use as a primary fuel: waste wood, pellets, sunflower husks, buckwheat, etc., and the use of an air turbine avoids contamination of its working surface. The aim of the work is to increase the efficiency and economy of a cogeneration power plant with an air turbine, which includes the following main elements: a fuel bunker, a pyrolysis pre-furnace, a combustion chamber-mixer, an air heater, a compressor, an air turbine, electric generator, water heater, smoke exhauster and chimney. To achieve this aim, three options for the scheme of a cogeneration plant with an air turbine with an electric power of 300 kW and with and without different connection variants of a water heater are considered and analyzed in terms of energy and economic indicators. A thermodynamic analysis of the circuit solutions of a cogeneration plant and their comparison in terms of capital costs for the creation of the plant showed that with almost the same cost for the main elements, compared with the circuit where the water is heated by air after the turbine and with the circuit where there is no water heater, the circuit of a cogeneration plant with water heating by flue gas has the highest overall efficiency. This scheme was chosen as rational. As a result of replacing the source fuel with the heat of the air turbine exhaust, the overall efficiency of the cogeneration plant according to this scheme is 73.9 %, and the electrical efficiency is 36.2 %, which corresponds to the level of a gas turbine plant according to the Brayton cycle with regeneration of the working fluid heat, at a moderate value of the degree of air compression in the compressor πk=3. The latter causes the low specific capital cost of the main equipment of the cogeneration plant – 134.6 USD/kW (excluding inflation). Keywords: pyrolysis pre-furnace, air turbine, thermodynamic analysis, capital costs, overall efficiency, electrical efficiency.