Energy Transport In Crude Oil Heating System With Solar Thermal Storage

Keeping crude oil temperature is the key to ensure safe and economic operation of floating roof oil tank.Boiler heating is a common method for maintaining temperature in crude oil reserves,but this method consumes a lot of energy and emits a lot of greenhouse gases,which directly affects the benefits of crude oil reserves.According to the characteristics of crude oil temperature maintenance and energy use,clean and low-carbon solar energy is used as the heat source for crude oil temperature maintenance,and phase change material(PCM)with high heat storage density is applied to stabilize the dynamic fluctuation of energy supply and demand side,and the crude oil heating technology with solar thermal storage is proposed.However,in this regard,there are some problems,such as flow and heat transfer of fluid in each subsystem and energy transport characteristics of the whole system are unclear.Therefore,it is necessary to analyze the turbulent flow and heat transfer of crude oil in the large space floating roof oil tank,the phase change heat storage and the flow heat transfer of PCM with non-uniform energy boundary in a limited space.On this basis,a long-term energy transport model of the crude oil heating system with solar thermal storage is established,and the long-term dynamic operation characteristics of the system are studied.The main research contents and results are as follows:(1)The turbulent flow and heat transfer model of crude oil in floating roof oil tank considering the influence of crude oil physical properties is established,and the large eddy simulation method is used to calculate the flow and heat transfer process of crude oil in the tank,and influence of finned heating tube bundle on crude oil temperature,flow filed and heat flux of tank boundaries is analyzed.The results show that the average temperature and temperature uniformity of crude oil are improved due to the increase of the heat exchange area between the crude oil and the heating tube bundle.Compared to the heating tube bundle without fins,the maximum average temperature and temperature uniformity of crude oil are increased by 1.90°C and 5.19%respectively when the fin length is 200 mm.The number of fins has a weak effect on the heat transfer process of crude oil in the tank,and the temperature uniformity of crude oil is increased by 3.04%when the fin number is 4.The relationship among the heat flux at the boundary of the floating roof oil tank is tank top>tank wall>tank bottom,and corresponding proportions are 44%-45%,37%-38%and 16%-17%,respectively.(2)The effect of expanding the heat transfer area and improving the heat transfer performance of PCM on strengthening the comprehensive performance of the shell-and-tube latent heat thermal energy storage unit is investigated,and a two-dimensional transient"conduction-convection-phase change"multi-dimensional heat transfer model of shell-and-tube latent heat thermal energy storage unit is established,and the influence of fin parameters and nanoparticle parameters on the heat transfer is analyzed.The results show that compared to equal-length fins,incremental unequal-length fins can increase the melting rate and total heat storage by 6.17%and 1.21%,respectively.Increasing the total length of the unequal fins can effectively improve the heat transfer performance and heat storage of the PCM.Adding high thermal conductivity hybrid nanoparticles,the sensible heat storage and heat storage rate of PCM are improved,but it is not conducive to the latent heat storage and average heat storage density.Compared to the mono Nano-PCM,the average melting rate of binary and ternary Nano-PCM is increased by 2.30%and 5.20%,and the average heat storage rate is increased by 0.60%and 1.70%,respectively.(3)The effect of PCM on the thermal performance of the evacuated tube solar collector is studied,and a three-dimensional heat transfer model of the evacuated tube solar collector with PCM is established,and effects of density,specific heat,thermal conductivity,latent heat,and melting temperature of PCM on thermal performance of evacuated tube solar collector are investigated.The results show that with increasing PCM density,specific heat and latent heat,the HTF peak outlet temperature and effective heat collection decrease,but the effective heat collection time and temperature delay time increase.With the increase of the melting temperature of PCM,the effective heat collection first increases and then decreases,while the effective heat collection time decreases.The application of PCM into evacuated tube solar collector in different regions has different requirements for PCM thermophysical parameters.The enhanced thermal performance is not obvious in Daqing when the density,thermal conductivity,specific heat and latent heat of PCM exceed 1700kg/m~3,1 W/(m·K),4 k J/(kg·K),and 247.50 k J/kg,respectively.(4)The long-term energy transport model of the crude oil heating system with solar thermal storage is established,and the operating characteristics of the system and the influencing mechanism of parameters are studied.The results show that under the condition of combined heating of evacuated tube solar collector,phase change heat storage tank and auxiliary heat source,the system can achieve stable operation by means of the controller,and the average temperature of crude oil is higher than the design temperature(40°C)and the average temperature of PCM is higher than the phase transition temperature(45°C)accountes for 74.9%and 50.96%of the whole year,respectively,and the maximum heat supply proportion of the phase change heat storage tank and the evacuated tube solar collector accountes for 34.16%and 67.07%,respectively.With the increase of crude oil reserves,the time lag for the crude oil to reach the design temperature,and the total annual heat loss of the floating roof oil tank increases,and the heat supply proportion of the phase change heat storage tank and the evacuated tube solar collector decreases.Compared to the 3.5 kg/s heat transfer fluid flow rate,the annual total heat loss at 7 kg/s and 14 kg/s heat transfer fluid flow rate increases by 5.69%and 5.28%,and the heat supply proportion of phase change heat storage tank increases by 1.78%and 3.66%,respectively.The initial temperature of crude oil increases,and the time for crude oil to reach the design temperature is earlier,and the heat loss of the floating roof oil tank increases due to the large temperature difference between crude oil and environment.Compared to the 24°C initial temperature of crude oil,the heat supply proportion of evacuated tube solar collector and phase change heat storage tank at the40°C initial temperature of crude oil increases by 1.11%and 0.94%,respectively.