Research On Low Temperature Heat Driven Small Scale Organic Rankine Cycle

In China, the industrial energy consumption is about 70% of the total energy consumption, and a lot of low temperature waste heat emission to the environment in the industrial process. Many studies are aimed on gaining electricity from the low temperature heat resource. The organic rankine cycle(ORC) is a quite promising technology in waste heat recovery.The biology, solar energy, geothermal and waste heat is four main heat resources. The selection of work fluid for the ORC system for different heat resources is still in discussion. Eight work fluid sincluding R134a, R245fa, R407c, RC318, R22, R123, water and R11 are discussed in this paper. Thermodynamic models for the ORC system are established based on the software EES. The results prove that when the inlet temperature and evaporate pressure are changed, the average efficiency increased with the boil point temperature of the work fluid. Also, R245fa is selected as the most suitable work fluid for temperature lower than 100℃.According to theoretical results, a test rig of ORC system is established with 100℃heat source and 1 kW expansion power as inputs. The heat source temperature below 150℃is available in the test rig, also the water and oil flowrate could be changed. In the end, the thermodynamic parameters and performance of components is tested.Before evaluated R245fa, R134a, R22 and R32 performance, the test of generator with different load is carried out to check if there is any influence to the cycle. The R245fa shows the best performance with 8.48% of efficiency and 11℃of subheat temperature. On the contrary, the R32 shows the worst performance with 1.6% of efficiency and 2514 kPa evaporate pressure, which is non economy.Then three variable conditions are demonstrated, including the oil temperature, oil flowrate and the pump displacement. The results shows that when the heat temperature increase, the R245fa efficiency is higher than that of R134a, and the expand has higher performance in R245fa system ; when the work fluid mass flowrate raise, the outpower is higher; when the oil flow rate is added, only the RPM of expand go up and there is no influence on other parameters.Four improvement are proposed to optimize the organic rankine cycle. The IHE and regeneration cycles are researched with exergy flow topology graph. And the results showed that R245fa cycle efficiency increased from 8.89% to 10%, the exergy efficiency of evaporator and system improved from 63.8% to 72.41% and from 66.89% to 72.98% respectively.