(1. Tianjin Geothermal Exploration and Development Design Institute; 2. Tianjin Municipal Bureau of Land Resources and Housing Management)
With the continuous acceleration of economic construction in Tianjin, the demand for energy is increasing day by day. Shallow geothermal energy, as a new field of geothermal development, its development and utilization will certainly play a positive role in alleviating the shortage of energy supply and demand in Tianjin. Based on the analysis of existing research data, it is considered that Tianjin area is rich in shallow geothermal energy reserves and has broad prospects for development and utilization.
1 preface
Geothermal resources belong to renewable energy. According to historical records, China has been developing and utilizing geothermal resources for more than 2,000 years, and it is one of the countries that used geothermal resources earlier in the world. China began to explore and develop geothermal resources in the 1970s, and the development and utilization have developed rapidly, involving power generation, heating, medical treatment, bathing and industrial and agricultural production, and achieved remarkable economic, social and environmental benefits. Especially since the 1990s, driven by the demand of market economy and the continuous development of utilization technology, the development and utilization of geothermal resources have developed more vigorously and the application scope has become increasingly extensive. With the increasing shortage of conventional energy, the development and utilization of renewable energy such as geothermal energy has attracted worldwide attention. People's Republic of China (PRC) Renewable Energy Law came into effect on June 65438+1 October1,2006, which listed the development and utilization of renewable energy as a priority area of energy.
Shallow geothermal energy is a part of geothermal resources, which refers to low-temperature geothermal resources contained in shallow rock and groundwater. In the past 30 years, limited to the use of technical level, only pay attention to the development of deep high-temperature geothermal energy. Due to the high cost and high risk of drilling deep wells, the demand for geothermal energy is increasing. With the continuous emergence of new technologies for development and utilization, people begin to pay attention to shallow geothermal resources with low temperature potential and find that there are also huge energy resources here. In recent years, shallow geothermal energy utilization technology has been very mature and widely used in developed countries such as Europe and America. In China, it is still in its infancy, shallow geothermal energy has not been systematically explored and evaluated, and the development and utilization technology needs to be improved. Therefore, the document No.288 [2005] of the Ministry of Land and Resources regards the investigation, evaluation, development and utilization of shallow geothermal energy as one of the key geothermal energy work recently developed by the Ministry of Land and Resources.
At present, the shortage of energy supply has become a prominent contradiction restricting Tianjin's economic and social development. Geothermal exploration, development and utilization began in the 1970s, and geothermal energy has become an important supplementary energy source in Tianjin, which has alleviated the shortage of energy supply and demand to some extent. However, with the shortage of high-grade geothermal resources caused by large-scale development and utilization, it is urgent to find new resources. Therefore, shallow geothermal energy will become the focus of geothermal development and utilization in the next few years. The exploration and development of shallow geothermal energy in Tianjin is basically blank, and this part of geothermal resources has great potential. Therefore, accelerating the exploration and development of shallow geothermal energy resources will certainly play a positive role in alleviating the tension between energy supply and demand in Tianjin.
2 Characteristics of shallow geothermal field in Tianjin Plain
Figure 1 Isogram of Shallow Geothermal Gradient in Tianjin Area
Tianjin is dominated by plains, accounting for 93.7% of the city's total area. The Cenozoic loose strata with thick sediments in the plain area have large thickness, high specific heat capacity and low thermal conductivity, while the heat flow value in Tianjin area is relatively large and there is much heat, which lays a foundation for the development and utilization of shallow geothermal energy.
The uppermost part of the earth's crust is called thermocline, which receives the most solar radiation energy. It is characterized by changing with the season of solar radiation, morning and evening, and sunny and rainy changes. In summer and at noon, its top can be higher than 30℃, and the downward temperature gradually decreases; The maximum temperature can be lower than 0℃ in the early morning of winter, and the downward temperature will gradually increase. The change in sunny days is greater than that in rainy days. Below the temperate zone is the constant temperature layer, which refers to the zone where the ground temperature remains relatively constant all the year round within a certain depth range. Tianjin constant temperature zone has a depth of 30m and a temperature of 65438 03.5℃. Then there is the geothermal warming zone, that is, the temperature rises downward at a certain rate. This rate, also known as geothermal gradient, is measured in degrees per1200m. In the geothermal exploration in Tianjin, the geothermal gradient greater than 3.5℃/ 100m is called geothermal anomaly. According to the temperature data of geothermal exploration in Tianjin, the geothermal anomaly area of 10 can be circled (see figure 1), with a geothermal gradient of 4.5 ~ 8.8℃/ 100 m and an area of 2328km2. The geothermal gradient in other areas is generally 2.0 ~ 3.5℃/ 100 m, and the shallow geothermal energy depth in China is 200m at present. According to the geothermal calculation formula of a certain depth (see formula 1), the temperature at the depth of 200m in Tianjin Plain is 2 1 ~ 28℃, and the non-geothermal abnormal area is With the improvement of technical and economic conditions and the increase of utilization depth, more geothermal energy will be available.
Shallow geothermal energy: proceedings of the national on-site experience exchange meeting on geothermal (shallow geothermal energy) development and utilization
Where: t is the temperature for calculating the depth (℃); D 1 is the calculated depth (m); Gi is the average geothermal gradient of caprock (℃/100m); D2 is the buried depth of the constant temperature layer (m); T0 is the isothermal layer temperature (℃).
3 Tianjin shallow groundwater resources
Cenozoic loose sediments are widely distributed in the southern plain of Tianjin, and the Quaternary and Tertiary aquifers can be divided into five layers. The first water-bearing formation is equivalent to Holocene and Upper Pleistocene (Q4+3), and the bottom boundary depth is generally above 70m. The second water-bearing formation is equivalent to the Middle Pleistocene (Q2), and its bottom boundary depth is 180 ~ 220m. The third water-bearing formation is roughly equivalent to the upper member of the Lower Pleistocene (), with a bottom boundary depth of 290 ~ 3 10m, and the fourth water-bearing formation is equivalent to the lower member of the Lower Pleistocene. The uplift area also includes some Neogene water-bearing strata (), and the bottom boundary depth is 370 ~ 430m. The fifth water-bearing formation is Neogene water-bearing formation (N2), and the buried depth of the bottom boundary is 520 ~ 560m. The first aquifer belongs to shallow groundwater.
Ⅱ-ⅴ water-bearing formation belongs to deep groundwater (Table 1). According to the results of a new round of groundwater resources evaluation in Tianjin, the natural groundwater resources of the five-layer aquifer group are18.13×108m3/a. According to the analysis of hydrogeological conditions and repeated demonstration of water resources, Tianjin has groundwater resources that have been replenished stably for many years, and the sustainable water resources are (7 ~ 8 )×/kloc-.
According to the temperature measurement data of nearly 100 shallow wells with a depth of about 200m in Tianjin Plain in the past, the water temperature is 65438 07 ~ 28℃, and the water and gas in five aquifers have become huge energy reservoirs because of little temperature change. With the maturity of low-temperature utilization technology, the time is ripe for large-scale development and utilization of this part of energy.
4 shallow geothermal energy utilization technology
Heat pump is an advanced heat energy utilization and energy-saving equipment, which can effectively utilize the low-temperature heat energy contained in air, water and soil. It has the advantages of environmental protection, stability, high efficiency, energy saving, space saving, low maintenance, low operating cost and little environmental pollution. In recent years, in the direct utilization of geothermal energy in the world, the application of heat pump to develop shallow geothermal energy is at the forefront, and its installed capacity and utilization energy increase by more than 20% every year. By 2005, 65,438+300,000 heat pumps have been installed in 33 countries around the world, with a total installed capacity of 15723MWt. At present, shallow geothermal utilization technology has been very mature in developed countries such as Europe and America, and has been widely used. The development and utilization of shallow geothermal energy in China started late. In 1990s, the shallow geothermal energy development and utilization technology of ground source heat pump system began to be researched and popularized, and it was widely popularized in China in 2000. In June 2005, the Ministry of Construction of People's Republic of China (PRC) and the General Administration of Quality Supervision, Inspection and Quarantine jointly issued the Technical Specification for Ground Source Heat Pump System Engineering to guide the construction of heat pump system engineering.
Table 1 Division of Quaternary and Some Neogene Aquifer Groups in Tianjin Plain and Hydrogeological Characteristics of Each Group
Tianjin is rich in shallow geothermal energy resources, and social development and people's living standards are constantly improving. At present, many projects in Tianjin have adopted ground source heat pump system to solve the heating and cooling problems, such as Meijiang Community, Haibin Avenue in Development Zone, Data Archives of National Security Bureau and Hua Kai Commercial Plaza in Tanggu. It provides reference for the development and utilization of shallow geothermal energy in Tianjin. Therefore, the technical and resource conditions for developing shallow geothermal energy by using heat pump in Tianjin are basically available, and the development prospect is very promising. Under the current severe energy situation, it is of great practical significance to actively promote heat pump technology and develop shallow geothermal energy on a large scale.
refer to
[1] Tianjin Geothermal Exploration and Development Design Institute. General survey of geothermal field in Wang Lan Zhuang, Tianjin. 1987
[2] Tianjin Geothermal Exploration and Development Design Institute. Tianjin thermal storage engineering research institute. 2005
Chen Moxiang et al. Geothermal in North China. Science Press, 1988.
Duan, Wang, Xing Guifa. Groundwater resources and its sustainable utilization in Tianjin. Hydrogeology Engineering Geology, 2004
[5] Zheng Kebang. Present situation of exploitation and utilization of shallow geothermal energy in the world and its development prospect in China. Textbook of 2006 National Ground Source Heat Pump Technology Training Course