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Session: Poster session
Session starts: Tuesday 13 October, 13:30

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Osamu Furuya ()
Eiichi Sakaue ()

Abstract:
Ironworks have various furnaces and have been exhausting waste heats of various temperatures. Though waste heats of more than 250℃ have already been utilized for electricity and heat recuperations, that of lower than 200℃ have not been effectively utilized yet. For 40 years, electric power generation system using organic working fluid has been commercialized for the geothermal hot water of lower than 200℃ in geothermal power plants. But due to environmental problems of organic working fluids, electric power generation system using organic working fluid has not been applied in the lower waste heats. Organic working fluid’s problems for commercial application are toxicity, flammability, ozone depletion and global warming potential (GWP). Recently, in respect of climate change, low GWP working fluids have been paid attention and developed. Some are being released into market. The low GWP working fluids are more degradable in high atmosphere and have shorter lifetime than existing organic working fluid such as R134a and R245fa and less flammability than flammable working fluid such as pentane, butane, propane due to its molecule structure. In this study, to design ORC system using low GWP working for waste heat of lower temperature, various kinds of thermal properties of those low GWP have been evaluated using publicized reliable database, for the first step. Also other properties such as stability, productivity and economics are evaluated to find out effective low GWP working fluids. As the second step, power generation efficiency for waste gas of lower than 200℃ using low GWP working fluids such as R1234ze(E) and R1233zd(E) was evaluated compared with conventional ones. Various power generation system types are evaluated such as subcritical Rankine cycle, supercritical Rankine cycle and recuperated Rankine cycle, based on depending on critical temperature of working fluids and turbine outlet gas superheated temperature. Evaluations also take into accounts following factors, such as turbine efficiency, working fluid pump efficiency, generator efficiency, pinch-point temperature difference and pressure loss of heat recovery heat exchanger, condenser, recuperator, and pipe pressure loss. Since, expected power generation output is more than 1MW, and turbine inlet pressure is more than 1MPa, multi-stage axial is picked up as turbine type. As the result, power generation gross efficiency and net efficiency are estimated and heat exchangers scales are determined by basic designation.