Energy Efficiency Analysis Of Organic Rankine Cycle System For Low-temperature Waste Heat Power Generation

Organic Rankine Cycle can convert low-grade heat into high-grade electricity, with using low boiling point organics as the working fluid. It has advantages of compact structure, easy maintenance and good load adaptability etc. In this paper, experimental test research and energy efficiency analysis on the self-designed Organic Rankine Cycle waste heat power generation system were carried out, with the heat source about 100~130℃, together with simulation analysis on the schemes. The main content is as follows:(1)Energy efficiency analysis model of Organic Rankine Cycle waste heat power generation system was built based on the first and the second laws of thermodynamic, using the way of exergy equilibrium to build. The influences of different operating conditions on the performance of ORC system was simulated and analyzed using the thermodynamic model built in Aspen plus. The results show that the evaporating temperature, environment temperature and isoentropic efficiency of radial inflow turbine are beneficial to the increase of the performance of ORC system, on the contrary, condenser temperature and undercooling are harmful; The superheat of expander nearly has no influence.(2)Waste heat power generation experimental system was designed and built,using R123 as working fluid and radial inflow turbine as expander with the heat source being thermal oil. Experimental test research and analyses on major equipment is carried out. The results indicate that the rotational speed, output power, irreversible loss and isentropic efficiency increase with the increasing inlet temperature of radial inflow turbine; the heat transfer, thermal efficiency and exergy efficiency of evaporator increase with the increasing oil inlet temperature, while the opposite influence is with the lower evaporator’s irreversible loss. Evaporator exergy loss is the biggest. The higher condenser pressure is, the higher condenser’s irreversible loss and the lower exergy efficiency is, and condenser’s irreversible loss is the second high compared with evaporator; Hydraulic diaphragm type pump has a good performance with no leakage and low irreversible loss which fits for low temperature waste heat power generation system.(3)Experimental test research on the system shows that: with the increase of oil inlet temperature, the output power, thermal efficiency and exergy efficiency of system get higher, the total irreversible loss get lower, and the total irreversible loss decrease with the increasing evaporating pressure; The heat transfer temperature difference loss of evaporator and condenser and leakage loss of expander are the main parts of system.(4)Three structure optimize measures were proposed and thermodynamic analysis model was built based on experimental research, which are system with recuperator, system with regenerative extraction and system with reheater respectively. Simulation and analysis on three cycles in Aspen plus are worked out finally. The results indicate that the thermal efficiency and exergy efficiency the ORC system with regenerator, regenerative extraction and reheater are 3.64% and 9.11%, 2.83% and 3.66%, 3.17% and 2.08% higher than of the basic ORCs respectively, with the constant source temperature and evaporating temperature 88 ℃. So the performance of system with recuperator is the best structure optimize measure.