| The oil shale in-situ recovery requires huge thermal energy.In order to reduce fossil energy consumption and reduce the production cost(PC)of oil shale recovery,an oil shale in-situ recovery system with solar intermittent heating is proposed,and the system and operation strategy are designed and optimized.In terms of system modeling,to improve the simulation accuracy and speed of temperature distribution,an improved oil shale recovery model and grid division method are proposed.By comparing the temperature distribution and oil production with different heating modes(solar intermittent heating mode and continuous heating mode by natural gas or natural gas-assisted solar energy),it’s found that oil shale in-situ recovery by intermittent solar heating is feasible.During system design optimization,in order to reduce the oil shale production cost(PC),the value of solar multiple(SM),thermal energy storage(TES)capacity and the distance between the steam injection well and the production well(Dw)are optimized.The economics of different heating modes is also studied.The result shows that,when the SM is 2.5,TES capacity is 16 h,and Dw is 20 m,the PC of oil shale in-situ recovery with solar intermittent heating mode is the lowest,which is 306 $/t and is even lower than that with continuous heating mode by natural gas and natural gas-assisted solar energy.Besides,the sensitivity analysis of PC to solar field investment costs and Dw shows that,the cost of O&M has the biggest effect on the PC,Dw has the minimal effect on the PC.Analyzing the influence of loan interest rate on PC under different heating modes,it is found that the system under the solar intermittent heating mode can bear a higher loan interest rate,which is 3.57%.In terms of system operation and parameter optimization,the heat consumption of the system under different heating modes are compared,and the method of pinch analysis is used to study the utilization of system waste heat and the optimization of initial steam parameters.It is found that there is a small difference in the proportions of the system heat consumption under intermittent heating and continuous heating.The waste heat loss of exhaust steam accounts for the largest proportion(about 76%),and other heat losses(pipe heat loss.formation heat dissipation)account for the smallest propoition(less than 2%).By recovering the exhaust heat to heat the feed water,the thermal efficiency of the system can be increased by more than 4%.The optimal steam pressure is 35.5MPa and the temperature is 525℃.Finally.the oil shale recovery system has been improved.Considering the pressure-bearing capacity of the formation,the initial steam parameters are increased from 9MPa.550℃ to 15.3MPa,550℃.Under intermittent heating,the ratio of oil shale heat consumption to total heat injection increases from 20.3%to 33.5%.After the waste heat recycling,the ratio of oil shale heat consumption to total heat injection increased to 38.4%,PC decreased to 174.7$/t,and the highest loan interest rate that the system can bear is 12.5%.The thermal efficiency and economy of the system are greatly improved. |
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