Utilisation of bleed steam from power plant to increase saturation temperature in organic Rankine cycle

In the paper presented is a novel concept to utilize the heat from the turbine bleed to improve the quality of working fluid vapour in the organic Rankine cycle (ORC), which contributes to the increase of ORC efficiency and the overall efficiency of the combined system of the power plant and ORC plant. Calculations have been accomplished for the case when available is waste heat as a flow rate of hot water at a temperature of 90 ◦C, which is used for preliminary heating of working fluid in ORC cycle. That hot water is obtained as a result of conversion of exhaust gases from power plant to the energy of hot water. Then the working fluid in ORC is further heated by the bleed steam to reach 120 ◦C. Such vapour is subsequently directed to the turbine. Possible working fluids were examined, namely R134a, silicone oils MM and MDM, toluene, and ethanol. Only under conditions of 120 ◦C/40 ◦C the silicone oil MM showed the best performance, in all other cases the ethanol proved to be best performing fluid of all. Results are compared with the ‘stand alone’ ORC module showing its superiority.