Analysis Of The Water-heat Combined Supply System Based On Waste Heat Utilization Of Nuclear Power Units

In recent years,China's nuclear power construction has entered a period of rapid development,especially the construction of millions of nuclear power units in the northern coast has been fully launched.However,a large amount of waste heat from exhaust steam will be generated during the operation of nuclear power units,which will eventually be directly discharged into the sea through circulating cooling seawater,resulting in a serious waste of energy.How to use the waste heat of nuclear power units to prepare high-temperature hot water for heating and seawater desalination,and realize heating and water supply at the same time,has important practical significance for simultaneously solving the two major livelihood problems of urban clean heating and fresh water demand.Therefore,based on the principle of the water-heat combined supply,the seawater reverse osmosis(SWRO)technology and the district heating technology with co-generation based on absorption heat exchange(Co-ah)were organically combined and integrated,and a water-heat combined supply system based on waste heat utilization of nuclear power units has been proposed in this thesis.The research work has been carried out in the following aspects: waste heat utilization in water-heat cogeneration link,operation characteristics under all working conditions and hydraulic working conditions of hydrothermal co-transmission pipeline network.Based on the safety mechanism of waste heat utilization of large nuclear power units,the relationship between the minimum cooling flow,maximum extraction-condensation ratio and exhaust pressure is analyzed.Compared with conventional thermal power heating and wet cooling units,the minimum cooling flow of nuclear power units is larger,and the maximum extraction-condensation ratio is smaller.Increasing exhaust steam pressure requires a larger increase in exhaust steam volume.Co-ah systems are constructed based on nuclear power and thermal power units,and the waste heat recovery performance of the Co-ah systems has been studied.The analysis results show that the waste heat recovery rate is lower,which has a greater impact on power generation.Therefore,an optimized operation scheme of condenser circulating water system is proposed to reduce the influence of waste heat utilization on power generation and further improve the waste heat recovery rate.A water-heat combined system based on the waste heat utilization of nuclear power units has been proposed,which is composed of water-heat cogeneration,hydrothermal cotransmission,and hydrothermal separation.The double back pressure operation of the condenser can meet the requirements of seawater desalination and Co-ah system respectively,and improve energy utilization efficiency.Water-heat cogeneration link is composed of multistage cascade heating processes,which can effectively reduce the irreversible loss of heat exchange links.The double pipe form is adopted for the hydrothermal co-transmission pipe network to solve the imbalance between heating water supply and water supply,and save the investment and power consumption of the water transmission system.Aiming at each component of the water-heat cogeneration,a variable working condition calculation model has been established.The simulation results show that the circulating seawater temperature and water supply ratio have little effect on the heating performance coefficient and heating load of the absorption heat pump,but have a great effect on the energy consumption of seawater reverse osmosis.Compared with the traditional heating and water supply systems,the water-heat cogeneration has obvious advantages in reducing energy consumption for heating and water making.Based on the calculation model of quality regulation of heat supply,the variation law of water temperature and heating load under all working conditions of water-heat combined supply system has been studied.The analysis shows that with the increase of outdoor temperature,the heating load of extraction steam and extraction-condensation ratio decrease,the heat load of waste heat of exhaust steam with high back pressure increases,and the power generation decreases.Then,aiming at the influence of heating and water-making on power generation,the evaluation index of traditional heating equivalent electricity is modified to evaluate the energy efficiency of the water-heat combined supply system under all working conditions.The results show that the comprehensive energy efficiency decreases with the increase of outdoor temperature,but it is significantly higher than that of the district heating system with cogeneration.According to the load forecasting model of water supply network,the urban water consumption is predicted.The results show that the urban water consumption varies greatly,and there is always a difference between the urban water consumption and the fresh water supply.The mathematical calculation model of hydraulic condition is established for the hydrothermal co-transmission network,including the calculation model of working characteristics of circulating water pump and regulating valve.Among them,the regulating valve resistance characteristic model is derived on the basis of the ideal flow characteristic,and has high prediction accuracy.The calculation program is written in C++ programming language,and the hydraulic calculation software of the hydrothermal co-transmission pipeline network has been developed.The comparison results with the actual operation data of heating network show that the predicted value meets the requirements of engineering accuracy.Combined with the hydraulic calculation results of the hydrothermal co-transmission pipeline network,the hydraulic working conditions are analyzed,and it is found that the return water pressure line becomes more gentle with the decrease of the return ratio.Taking the waste heat utilization project of nuclear power plants in Weihai City as an example,this thesis carries out engineering practice research,and analyzes and demonstrates its energy conservation,environmental and economy protection.It has significant energy-saving benefits,outstanding environmental protection benefits and good economic benefits,and has high popularization and engineering application value.