Design of heat exchangers used in waste heat source ORC system

In this study, the design and modelling of heat exchangers for an ORC system that will use the flue gas heat released into the atmosphere from the annealing furnaces for plastic shaping of the product in iron-steel industry has been carried out. It is assumed that water is used as energy carrier fluid between ORC and flue gas and cooling media in the condenser. R245fa was selected as the working fluid in ORC. A heat exchanger constructed by circular finned tubes with circular cross section is designed and modelled for heat exchange in flue gas. AKU type shell and tube heat exchanger is designed and modelled as evaporator. Both water entering and working fluid leaving the evaporator are accepted in saturated vapor phase. Heat exchanger type selected for condenser is shell and tube BEM type heat exchanger. In the condenser model, it is assumed that the working fluid R245fa enters the heat exchanger as superheated steam and exits as subcooled. Heat transfer surface areas of designed circular finned tube heat exchangers, AKU type evaporator and BEM type condenser are 244,8m2-51,6m2-95,4m2 , respectively. Performances of heat exchangers in different working conditions are evaluated and results are given. Analysis showed that 1567 kW of energy was recovered at a mass flow rate of 6.89 kg/s and a flue gas temperature of 380°C.