The Research Of Low Temperature Waste Heat Recovery Of Coal-fired Power Plant Based On Organic Rankine Cycle

Nowadays，coal has become the main energy and the most importmant industrialraw material to support the economy of our nation.In China,the electricity generated bycoal-fired power plant accounts for77%of the total quantity. Therefore，in perspectiveof the energy utilization,it is important to make full use of the low-grade heat andimprove the total thermal efficiency of the whole plant. Because of its simple structure,high thermal efficiency, and simibility to run in terms of the recovery of lowtemperature waste heat, the Organic Rankine Cycle （ORC） has attracted wideattention of scholars worldly.In view of the characteristics of low temperature flue gas and the water released bycoal-fired power plant, the thermodynamic model and economic model of the ORCsystem under constraint condition have been established.The present research usesEngineering Equation Solver （EES） software to caculate the thermal properties oforganic working fluid and simulate the cycle model. The impact of the pinch pointtemperature difference （PPTD） and the outlet temperature of heat resource on thethermal efficiency, the net power output and the exergy efficiency has been discussedand analyzed.Results indicate that:First, for a fixed heat source inlet temperature,the net power output of ORCincreses then decreases with respect to the evaperation temperature,and there exists amaximal net power output.In terms of low grade heat recovery,ORC has an obviousadvantage compared to water.Secondly, in terms of the flue gas waste heat recovery cycle, for a given heatsource and PPTD,a parabola relationship between the net power output of each workingfluid achieves.R245fa has the best thermal performance.Howerever, the net poweroutput and thermal efficiency descends with the increasing of PPTD at a fixed outlettemperature of heat source.When the exhaust gas temperature is reduced from existing407.3K to363.15K,the thermal efficiency of ORC reaches a maximum value of10.86%and a net power output of16.1kW.Thirdly, For the wet slag water heat recovery system,the system efficiency and netpower output increase with the increasing of the potential heat of working fluid.Ethanolis considered as the most suitable wor king fluid due to its the maximum net output（187.627kW） and thermal efficiency. When the evaporating temperature is fixed, the system net power output, exergy efficiency power consumption of pumps and mass flowrate of working fluid increase as the outlet temperature of source decreases while thethermal efficiency keeps almost unchanged. For a fixed outlet temperature of the heatsource, the net system output power, thermal efficiency, exergy efficiency show a risingtrend with the increase of evaporating temperature, the irreversibility and the mass flowrate indicate an opposite trend. For the recovery of the latent heat makes a majorproportion of the waste heat recovery systems, the working fluids with high latent heatare recommended.