Performance Of Thermal Power System For Waste Heat Recovery In Large Power Plant

With the increasingly perilous situation of the international energy,the change of internal energy structures and urgent requirement of energy conservation and emission reduction,the large power plant energy must carry on the in-depth study of energy conservation and emission reduction to improve the efficiency of energy utilization and to reduce the discharge of the pollutant,which gratify the national requirements and maintain its competitiveness in the electricity market.Nowadays,the thermal efficiency of 1000 MW ultra-supercritical condensing power plant is 47.82%.And the remaining heat is output into the environment directly as the form of a great variety of waste heat.However,the efficiency of national energy utilization of nationa requirement is 80%or more.According to the second law of thermodynamics,the main loss of power plant is triggered by temperature difference of the boiler.And,according to the first law of thermodynamics,the main loss of power plant appears in the condenser.Therefore,the waste heat recovery of boiler and condenser in the power plant can improve the energy efficiency of the power station.By taking the waste heat recovery of the power plant as the research object,this paper studies the system of waste heat recovery of the ORC-flue gas and circulating cooling water system based on thermal performance of phase change material.Then the paper discusses thermal performance and economic performance of power plant units caused by the system of waste heat recovery of the ORC-flue gas and circulating cooling water system.The study found that the two systems have theoretical significance and engineering value.Aiming at the problem of high exhaust temperature power plant unit,the system of waste heat recovery of flue gas based on ORC is proposed and analyzed.First mathematical model is developed,after that the influence of working medium type,vaporization temperature,pinch point temperature difference of the evaporator and pressure ratio on the ORC system.The results illustrate that the influences of various factors are taken into account;the system of waste heat recovery of flue gas based on ORC has the best performance when R123 is used as working medium.Based on the above research,the calculation model of the screw expander is proposed,and the performance of the screw expander is analyzed.Finally,thermal performance and economic performance of the thermal recovery system of ORC flue gas was discussed compared to low-temperature economizer.The results reveal that thermal performance and economic performance of the thermal recovery system of ORC flue gas are better than that of the low-temperature economizer.In order to resolve the problem of significant amounts of energy loss in cold end and the quality of waste heat,particularly for recirculating cooling water system in steam-electric plants,this paper proposed a new type of energy saving methods based on flow and heat transfer characteristics of phase change material slurry.The particles of phase change material were added to the condenser to reduce the volume flow and pump power.Combined with a closed loop cooling system,the relationship between mass concentration of the phase change material particle and the thermal physical properties of fluid,water saving and energy saving were analyzed in detail.Results show that the proposed method reduces the condenser pressure,circulating cooling water and pump power when inlet temperature of the circulating cooling water are between 15?23 ?.The potential interest of water saving and energy saving of new method to the condenser is obvious.This method do not directly Convert the waste heat in the condenser into electrical energy.However,phase change material is used to reduce the circulating pump power consumption,thereby to reduce the auxiliary power consumption rate and to reduce coal consumption rate of power supply.