Development Of Ice-Valve Coring Drilling Tool By Vapor Compression Refrigeration For Loose Sandstone-type Uranium Deposits

Electric power industry is one of the industries with high carbon emission and large consumption of fossil fuels.Nuclear power will play a crucial role in achieving the carbon peaking and carbon neutrality goals.Uranium is an important raw material in nuclear power production.The geological conditions of the target strata of the in-situ leachable sandstone-type uranium deposit are complex,loose and fragile,Poor or no cementation,the core is easy to fall off,and core recovery percentage is low.In view of the above problems,this paper combines theoretical analysis,laboratory experiment and outdoor test to develop the ice-valve coring drilling tool by vapor compression refrigeration for loose sandstone-type uranium deposits.The main research contents and conclusions are as follows:(1)The drilling tool built-in miniature compression refrigeration system prototype machine was designed and built based on the theory of vapor compression refrigeration system and the working condition of hole bottom.Combined with the structure of the ice valve tube and its application condition,performance test platform of drilling tool built-in miniature compression refrigeration system was developed,and the influence of the refrigerant charging amount on the system performance was studied.The results show that the refrigerant charging amount of the refrigeration system has an optimal value of 55 g,which makes the COP,refrigeration capacity and thermodynamical perfectness of the system tend to be the highest overall.Under the optimal charging condition,the peak refrigeration capacity reaches 181 W,COP reaches 2.13,and thermodynamical perfectness reaches 0.372.With the sample temperature decreasing the refrigeration capacity,COP,thermodynamical perfectness and other performance parameters have a stable zone and a decreasing zone.In the stable area,the above performance indicators decreased slightly;In the decline zone,the above performance indicators decline rapidly.The refrigeration capacity of the system is most sensitive to the amount of refrigerant charged and sample temperature,while the thermodynamical perfectness is least sensitive to the amount of refrigerant charged.(2)The influence of suction pipe insulation on the performance of the refrigeration system was studied by using the performance test platform of drilling tool built-in miniature compression refrigeration system.Results show that the suction pipe insulation can reduce the suction superheat of the compressor,and improve the COP and thermodynamical perfectness of the system.The COP,thermodynamical perfectness and refrigeration capacity of the system were increased by 15.2%,13.6%and 3.15% in the whole sample temperature range,respectively.The suction pipe insulation reduces the energy consumption of the system,improves the energy conversion rate of the refrigeration system,and makes the system close to the ideal refrigeration cycle.(3)Based on the performance test platform of drilling tool built-in miniature compression refrigeration system the influence of condensing circulating water parameters on the performance of the refrigeration system was studied.The sample temperature is controlled at 8℃ and the circulating water flow is 4L/min.When the circulating water temperature range is increased within 20～32℃,the input power of the compressor increases approximately linearly,the COP of the system decreases,and the refrigeration capacity and thermodynamical perfectness first increase and then decrease.The optimum temperature of circulating water was determined to be 24 ℃,the corresponding peak refrigeration capacity was 169.3W,and the peak thermodynamical perfectness was 0.381.When the sample temperature is 8℃ and the circulating water temperature is 24℃,the thermodynamical perfectness is basically unchanged when the circulating water flow increases within the range of 2～8L/min,the input power of the compressor decreases approximately linearly,and the refrigeration capacity and COP increase first and then decrease.The optimal flow rate of circulating water was determined to be 4L/min,the peak refrigeration capacity was 169.3W,and COP reached the peak value of 2.21.For this system,the optimal circulating water temperature is 24℃and the optimal flow rate is 4L/min.(4)Performance test platform for simulating hole bottom conditions was developed,and the formation process and formation time of the ice-sand valve were studied.In the process of forming the ice-sand valve,the temperature at the center point of the sample can be divided into three stages: pre-cooling zone,phase transition zone and postfreezing zone.When the sample center temperature drops to-5℃,the ice-sand valve is formed.In the freezing process,there is serious cold loss at the transition connection between the ice valve tube and the core tube,resulting in a long time for the formation of the ice-sand valve.The thermal insulation joint made of PEEK material between the ice valve tube and the core tube can shorten the formation time of the ice-sand valve by4 min.The aerogel insulation layer thickness of 3mm can meet the heat insulation requirements.The effect of sample type on the formation time of ice-sand valve is not obvious,and the formation time of ice-sand valve increases by about 1min when the initial sample temperature increases by 2℃.The bearing capacity of the ice-sand valve formed by siltstone,medium-coarse-grained sandstone and conglomerate samples is up to 1.1ton,1.2ton and 1.08 ton respectively,and the sample size has little influence on the bearing capacity.The bearing capacity fully meets the requirement of supporting core weight(24kg)at the maximum core length,and the safety factor is high.(5)The battery,electronic components and circuit components after epoxy resin filling can meet the requirements of 8.4MPa hole bottom pressure,and have twice the safety factor.The outdoor test results of the drilling tool show that the refrigeration system works well,and can meet the requirements of rapid in-situ formation of ice-sand valve at the bottom of the hole,and the drilling tool is stable and reliable.With 25 min as the safe freezing time at the bottom,the core recovery reaches 90%,which can meet the requirements of high quality coring of sandstone-type uranium deposits.