BINARY ELECTRICAL GENERATING INSTALLATION FOR UTILIZATION HEAT OF BOILER FLUE GASES
Authors: Shubenko Oleksandr , Senetskyi Oleksandr , Babak Mikola 
Published: October 2023

The work is devoted to the development of modern thermal schemes for the production of electrical energy while utilizing the heat of flue gases from boilers of power units. On the example of a typical district boiler house, the parameters and potential of heat discharged into the atmosphere with the flue gases of boilers are investigated, and it is determined that they are sufficient to generate electrical energy by implementing the so-called organic Rankine cycles. To utilize the heat of exhaust gases with a temperature of 280 °С at a flow rate of 10 kg/s, a three-loop power generating plant similar to those used in geothermal energy was studied. In the process of conducting research related to solving the problem, the thermal scheme was improved. A number of turbine working bodies that meet the necessary requirements are analyzed and the most suitable ones are recommended. Taking into account the characteristics of the heat source, in order to determine the rational configuration of the circuit, 50 calculations of thermal circuits of power plants on different working fluids were performed. The research results showed that the efficiency (electrical efficiency) and power of the turbine cycle are determined by the waste heat potential, the thermodynamic properties of the working fluid, the structural and parametric characteristics of the circuit. Among the studied indicators, the best indicators are: electrical efficiency of 20,6 %, a "useful" electrical power of 357 kW at a flue gas temperature of 131 °C was a three-circuit utilization plant with working bodies Water / R-245fa / R-245fa. The variant of the circuit with working fluids Water / R-600a / R-600a lost ~ 8 kW of electric power to the best variant, but was recognized as more promising, since R-600a (isopropane) Freon has consumer advantages over R-245fa. Computational studies of the binary thermal scheme of the power plant were also carried out, which showed that it is rational to use Water for the 1st circuit, R-600a for the 2nd circuit. This solution made it possible to obtain the calculated "useful" electric power of the energy complex ~ 290,8 kW (1st circuit ~ 129 kW, 2nd circuit ~ 161,8 kW). The loss of the binary scheme in terms of "useful" electric power to the promising version of the three-loop scheme is compensated by a significant simplification of the thermal scheme and, as a result, significantly lower capital costs. The specific mass of the proposed heat exchange equipment of the installation with a binary thermal scheme is ~ 150 kg/kW. Taking into account the properties of the working fluids, a preliminary study of the structures of the turbines of the 1st (Water) and 2nd (R-600a) circuits was carried out. For the 1st circuit, it is proposed to use a 6-stage axial turbine, for the 2nd – a single-stage radial. The geometric characteristics of the flow parts of turbines are determined by calculation. A preliminary simplified assessment of a simple payback period indicates good prospects for the implementation of the proposed energy-saving installation.