Research On The Comprehensive Evaluation Of Shallow Geothermal Energy Resource In Yinchuan

With the rapid development of Chinese economy,the energy situation is becoming more and more serious,which derives an increasing requirement for energy-saving and emission reduction.Shallow geothermal,as a very important novel clean energy,is much meaningful for building a resource-saving and environment-friendly society when it is exploited.The resource can not only be used as a new energy instead of coal,but also have good social benefits for reducing a large amount of pollution gas into the atmosphere.In recent years,a huge portion of carbon dioxide emissions has made temperatures keep rising and triggered a series of environmental problems.Especially in winter in Northern China,fog and haze frequently appears in the northern city due to massive utilization of fossil energy such as coal.As the capital city of Ningxia Hui Autonomous Region,the air quality in Yinchuan is declining in recent years with the urban development.Light and moderate pollution in atmospheric environment has appeared based on monitoring data from relevant departments in Yinchuan.In this paper,the suitability partition of shallow geothermal energy was conducted and the heat capacity,power of heat transfer,exploitation potential,economic and environment benefit of shallow geothermal energy are also evaluated in the 555km² area in Yinchuan city,based on the investigation of the hydrogeological conditions,geothermal geological conditions and the development and utilization of shallow geothermal energy.After that,an existing ground-source heat pump project was selected to monitor the temperature and heat pump energy consumption in the period of cooling and heating,the ground temperature changes around the buried pipe was analyzed and the energy efficiency coefficient,the coal saving and the emission reduction effect of the heat pump was evaluated finally.In this paper,the methods including field investigation,data collection and compilation,sample data analysis,field tests and data monitoring are used to evaluate the shallow geothermal resource in Yinchuan city comprehensively.Conclusions are summarized as follows:?1?In-situ thermal conductivity tests and thermos-physical properties tests of rock-soil samples in Yinchuan city are carried in several regions to analyze the geothermal conditions and temperature field features in the depth of 200m.The initial temperature is 13.77?.The average heat transfer coefficient is approximately 2.11 W/?m.k?.The amount of formation heat absorption and heat release is about 61.84W/m and 25.22 W/m.?2?The suitability partition of the shallow geothermal energy is conducted based on hydrogeological conditions and thermal parameters in the study area.The general suitable area of groundwater heat pump is 232.42km²,and non-suitable area is about 210.70km²;the suitable area of ground-coupled heat pump is about 114.22km²,and general suitable area is about 328.91km².?3?The total heat capacity in 200m depth is 2.46×10¹⁴KJ/?by calculation using volumetric approach in the range of 555 km²,the heat capacity per area is consistent with the average value of the capital cities in China.The heat capacity in 100m depth was partitioned into three zones according to visualization result of heat capacity distribution,and the total heat capacity is 1.231×10¹⁴KJ/?by calculation.?4?The distribution of shallow geothermal energy in space was analyzed.The heat power of two ways of geothermal utilization including the groundwater source heat pump and ground-coupled heat pump was analyzed,results shown that ground-coupled heat pump is better than groundwater heat pump in terms of resource amount.Considering the combination of two ways of utilization,the comprehensive heat transfer power was evaluated and the result falls in the middle of the above two ways.?5?The available geothermal amount was analyzed based on the results of resource analysis of shallow geothermal energy.The total available amounts of ground water source heat pump and the ground-coupled heat pump is 9.11 x 10⁶GJ and 5.59×10⁷GJ per year,with the economic benefits of 107 million yuan and 695 million yuan respectively.The total available amount of comprehensive utilization of above two ways is 4.14×10⁷GJ per year,with the economic benefit of 484 million yuan per year.?6?The emission reduction was evaluated with the utilization rate of 35%of shallow geothermal energy,the results confirm the apparent improvement of environment when utilizing shallow geothermal energy.The utilization of groundwater source heat pump can reduce the carbon dioxide emission by 4.33×10⁵ t/a,saving environmental management fee of 50 million yuan per year.The utilization of ground-source heat pump can reduce the carbon dioxide emission by 2.83×10⁶t/a,saving environmental management fee of 334 million yuan per year.The comprehensive utilization of shallow geothermal energy can reduce the carbon dioxide emissions by 1.97×10⁶t/a,saving environmental management fee of 233million yuan per year.?7?It is found that in the process of ground-source heat transfer,there are some differences in the influence of the surrounding formation temperature in vertical direction due to the stratigraphic characteristics in Yinchuan area.With the operation of the heat pump project,the strata temperature variation in the strong seepage layer is greater than that in other layers,and the temperature influential distance of heat transfer hole in the layer is 5m,which is relatively farther than that in other layers with 3m.The formation temperature is basically constant after the heat pump project in the long-term cooling and heating,and slight heat accumulation phenomenon appeared in certain depth of the formation.After running for 10years,the project can still meet the building refrigeration and heating needs.Therefore,ground-source heat pump project can be selected as the primary technology to utilize the shallow geothermal energy.