【作者】 张金宝；

【导师】 赵大军；

【作者基本信息】 吉林大学 ， 地质工程， 2014， 博士

【摘要】 世界油页岩资源丰富，全世界已有37个国家发现油页岩矿床100多个，将储量折算成页岩油可达4100亿吨以上，是目前世界天然原油探明可采储量的3倍，油页岩开发前景广阔，作为一种重要的替代能源引起各国家的高度重视。我国油页岩资源丰富，已查明的储量折算成页岩油达500.49亿吨，在常规油气资源供给不足时，非常规油气资源——油页岩将会成为重要的油气补充，并且有望成为常规油气的替代品。油页岩原位加热开采时，需要在开采区域周围建立地下冷冻墙，以隔绝地下水对开采区域的影响并防止开采油气的泄露。常规的人工冻结方法是使用制冷机组制冷盐水溶液冻结，这需要消耗大量的电能，而我国东北地区油页岩储量丰富，且冬季温度低、时间长，自然低温冷源丰富。针对这些情况，本文建立了油页岩原位开采地下冷冻墙联合制冷系统实验平台，通过利用冬季自然风冷制冷冻结，联合制冷冻结以及单独利用制冷机组制冷冻结三种运行模式的实验，研究地下冷冻墙的制冷效果以及联合制冷的经济性，主要包括以下方面：首先，分析地层热物性对地下冻结传热的影响，建立单排冻结管地下冻结传热的数值模型，利用ANSYS分析软件，对不同制冷工况下冻结温度场进行了理论分析，得出低温冷冻液的温度和流量对地下温度场的影响规律。模拟结果表明，越低的冷冻液温度和越高的流量将使冻结圈的交圈时间越短，但是交圈时间与冷冻液温度和流量之间存在最优组合，采用最优组合不仅可以有效减少冻结交圈时间，还能大幅降低运行和设备投资成本，本文给出了合理的冷冻液温度及冷冻液流量。其次，针对东北地区的气候特点，结合模拟分析结果，建立了能同时满足单独利用风冷机组冻结、制冷机组和风冷机组联合制冷冻结、制冷机组制冷冻结的多功能油页岩原位开采地下冷冻墙实验平台。单独利用风冷机组制冷时间为720h，冻结管影响半径1m范围内地下土层平均降温幅度为4℃，降温前期温度下降较快，随着环境温度的逐步升高，降温速率逐渐放缓；从风冷机组运行数据分析，当环境温度低于-10℃时，风冷机组制冷效果较好，其出口温度可达-5℃左右，随着环境温度的降低，制冷功率将进一步加大，当环境温度为-20℃时，其制冷功率为-10℃时的两倍。利用联合制冷系统进行制冷时间为360h，采用交替制冷运行模式，当环境温度为-10℃以下时利用风冷机组制冷，当环境温度升高到-10℃以上时利用制冷机组制冷，实验表明，当环境温度低于-10°C时，风冷机组的制冷功率达20kW左右，基本满足冻结孔的冷冻需求；地下温度场的降温速率较为稳定，整体降温速率与单独使用风冷机组冻结时基本一致。单独利用制冷机组进行制冷时间为1980h，制冷机组制冷功率随环境温度的升高而有所下降，气温每升高10℃，制冷功率下降10%左右，同时制冷液温度也有所上升，制冷液平均温度由-18.5℃升高到-13.5℃，制冷功率平均为42.5kW；地下温度下降曲线整体呈下凹状，相邻冻结孔中间土体温度下降最快，冻结圈内侧土体温度下降速度略快于冻结圈外侧相应位置，土体进入冻结前温度下降较快，进入冻结后温度下降趋势放缓，至冻结结束，已冻土体直径达1.0m以上，相邻冻结孔中间土体也已下降至0℃以下，进入冻结状态。通过实验得出的地下温度场变化与模拟结果进行对比分析，现场实测的温度下降随时间的变化曲线与数值模拟曲线发展趋势完全一致，数值差别较小；风冷和联合制冷期间，模拟与实验温差最大不超过15%，平均温差为8.2%；制冷机组冻结期间，模拟与实验温差最大不超过10%，平均温差为6.4%；验证了数值模拟结果的可靠性。最后，以本实验台为例，对采用联合制冷系统冻结与常规人工冻结进行了经济性对比分析，结果表明在寒冷地区采用联合制冷系统进行冻结比常规人工冻结方法每年可以节省运行成本20%以上，风冷机组的成本投资可在3~4年甚至更短时间内收回。通过HDPE同轴套管换热器与钢质套管换热器进行成本分析对比，结果表明：在相同冻结情况下，HDPE同轴套管换热器成本约为钢质套管换热器成本的30.9％，且HDPE同轴套管换热器在施工成本、施工速度及施工便捷性上更具优势。综上可知，在油页岩原位开采中，可充分利用自然界低温冷源，采用联合制冷方案以减少电能消耗，降低制冷成本；同时也减少了氨、氟利昂等制冷机组的使用，从而保护了环境，推动油页岩原位开采技术的进一步发展。更多还原

【Abstract】 Oil shale resources of the world are rich, the Oil shale deposits more than100have beendiscovered by37countries around the world. If they are converted into reserves of shale oil,the weight of shale oil could reach more than410billion tons, and it’s three times thanrecoverable reserves of the world natural crude oil. Many countries have paid close attentionto develop the oil shale because of the broad development prospects and important alternativeenergy. China is rich in oil shale resources, if the identified reserves are converted into shaleoil, the weight could reach50.049billion tons, oil shale and gas will be an importantcomplement and be expected to be a substitute, when the supply of conventional oil and gasresources are insufficient.The underground water sealing and frozen wall need to be build in the mining area, whencarried out in situ heating of oil shale mining. The method of conventional artificial freezingis to use refrigeration brine solution and refrigeration units, it need to consume a lot ofelectrical energy. But, the northeast of China have rich oil shale reserves, and cold naturalsource because of low temperature in long winter. For these cases, the experimental platformof underground mining of oil shale in situ freeze wall joint refrigeration system wasestablished in this paper. By using three kinds of experimental operation mode including thenatural air-cooled refrigeration in winter, joint freezing and separate refrigeration unit coolingto study the effects of the frozen underground wall and the economic analysis of the jointfreezing, including the following aspects:First of all, the numerical model of underground freezing and heat transfer using singlerow frozen pipes was established based on the analysis of the impact of the underground heaton underground freezing and heat transfer. Freezing temperature fields under different coolingconditions were analyzed using ANSYS analysis software, and the influence law of cryogeniccoolant temperature and flow rate on underground temperature field was obtained. The simulation results show that the lower coolant temperature and the higher traffic would resultin the shorter cross lap time of freeze lap, but there are optimal combination between the crosslap time and the coolant temperature and flow. The cross lap time of freeze lap and theinvestment costs of operation and equipment could be both effectively reduced. The rationalcoolant temperature and coolant flow were provided in this paper.Secondly, considering northeast climate characteristics of China and combined withsimulation results, the multifunctional experimental platform of the underground frozen wallfor mining of oil shale in situ, it could meet separate refrigeration unit, the joint freeze ofrefrigeration units and air-cooled refrigeration unit, and refrigeration unit cooling freeze,simultaneously. The freezing time of separate refrigeration unit was720h, the averagecooling extent in1m radius range of soil under the mainland was4℃effected by the frozenpipes, the temperature drop rapidly in the pre-cooling, the cooling rate was slow graduallywith the gradual increase in ambient temperature. By analysis on the operating data ofair-cooled refrigeration unit, it showed that the cooling effect was better when the ambienttemperature was below-10℃, and its outlet temperature was about-5℃. The coolingpower would further increased with the decrease of the ambient temperature. Cooling powerwas twice than it was at-10℃when the ambient temperature was-20℃. The freezing timeof joint refrigeration system was360h, the results of alternate cooling operation mode thatusing air-cooled refrigeration unit to freeze when the ambient temperature was below-10℃and using refrigeration unit to freeze when the ambient temperature risen to above-10℃showed that the cooling power of air-cooled refrigeration unit was about20kW, it couldbasically meet the needs of frozen for freeze holes, when the ambient temperature was below-10℃. The cooling rate of underground temperature field was relatively stable, and the overallcooling rate was consistent with using alone air-cooled unit to freeze.The freezing time ofseparate refrigeration units was1980h, the cooling power of refrigeration units decreasedwith the rise of ambient temperature. The temperature increased by10℃, the cooling powerwould be down about10%, at the same time,the cooling fluid temperature also increasedfrom-18.5℃to-13.5℃and the average cooling power was42.5kW. The drop curve ofunderground temperature was concave, the soil temperature between adjacent intermediate freeze hole declined fastest and the soil temperature inside the freeze ring decreased slightlyfaster outside the corresponding position. The soil temperature before frozen decreasedrapidly and the temperature declined slowly after frozen until the frozen end. The diameterof permafrost body was above1.0m, and the soil temperature between adjacent intermediatefreeze hole has dropped to below0℃and reached frozen state.The curve which showed the decline of temperature measured in field dropped changedwith time was consistent with the curve of numerical simulation, by comparative analysis onthe changes in ground temperature field and the simulation results. When using air-cooledrefrigeration and Joint refrigeration, the maximum temperature difference between simulationand experiment didn’t exceed15%and the average temperature difference was8.2%. Whenusing refrigeration units, the maximum temperature difference between simulation andexperiment didn’t exceed10%and the average temperature difference was6.4%, these dataverified the reliability of numerical simulation.Finally, the results showed that in cold areas, using joint refrigeration system to freezecompared with conventional and artificial freezing could save operating costs more than20%yearly and the cost of investment in air-cooled units would be available to recover in3to4years or shorter time, by comparative analysis of economic on Joint refrigeration system andconventional and artificial freezing. The result showed that the cost of the HDPE coaxial tubeheat exchanger was30.9percent of the cost of steel tube heat exchanger in the same frozen,and the HDPE coaxial tube heat exchanger had advantages in construction costs, constructionspeed and construction.convenience, by the cost comparison analysis on HDPE and steelcoaxial tube heat exchanger and steel tube heat exchanger.TO sum up, the cold natural source could be underutilized in high temperature in-situ oilshale mining. The energy consumption, ammonia and freon released by refrigeration unitswas reduced by using joint refrigeration system. Not only reduces the cost, but also to protectthe environment, so as to promote technology in situ oil shale mining for further development.更多还原