CHENG Wanqing1 LIN Jianwang1 HAN Jinshu2 WANG Kun2 LIU Yang1
(1. Tianjin Geothermal Exploration and Development Design Institute; 2. Tianjin Municipal Bureau of Land Resources and Housing Administration)
Abstract: The accelerated pace of Tianjin's economic construction, the increasing demand for energy, the development and utilization of shallow geothermal energy as a new field of geothermal development will certainly play a positive role in easing the tense situation of energy supply and demand in Tianjin. The development and utilization of shallow geothermal energy, as a new field of geothermal energy development, will certainly play a positive role in alleviating the tension between energy supply and demand in Tianjin. Through the analysis of existing research data, that the Tianjin area is rich in shallow geothermal energy reserves, the development and utilization of broad prospects.
1 Preface
Geothermal resources belong to renewable energy, according to historical records, China's development and utilization of geothermal has been more than 2,000 years of history, is the world's use of geothermal resources in one of the earlier countries. Since the 1970s, China began to explore and develop geothermal resources, the development and utilization of its rapid development, the use of areas involved in power generation, heating, medical, bathing, and industrial and agricultural production, etc., and has achieved significant economic, social and environmental benefits. Especially since the 1990s, driven by the market economic demand and the continuous development of utilization technology, the development and utilization of geothermal resources has been more vigorous development, with an increasingly wide range of applications. With the increasing lack of conventional energy, geothermal energy and other renewable energy development and utilization of the world's attention. 2006 January 1, the People's Republic of China Renewable Energy Law, the development and utilization of renewable energy as a priority area of energy.
Shallow geothermal energy is part of geothermal resources, referring to the low-temperature geothermal resources embedded in shallow rock and soil bodies and groundwater. In the past 30 years, limited to the level of utilization technology, only focusing on the development of deep high-temperature level geothermal energy. Due to the high cost and risk of drilling deep wells and the increasing demand for geothermal heat, with the emergence of new technologies for development and utilization, people began to pay attention to the shallow low-temperature geothermal resources, and found that there is also a huge amount of energy stored here. In recent years, shallow geothermal energy utilization technology in Europe and the United States and other developed countries has been very mature and widely used. In our country, it is in the initial stage, and the systematic investigation and evaluation of shallow geothermal energy has not yet been carried out, and the development and utilization technology needs to be improved. Therefore, the land resources development [2005] No. 288 will be shallow geothermal energy survey and evaluation and development and utilization of the pilot program as the Ministry of Land and Resources will be exploited in the near future, one of the geothermal key work.
Currently, the lack of energy supply has become an outstanding contradiction that restricts the economic and social development of Tianjin. Since the 1970s, geothermal exploration and development and utilization, geothermal has become an important supplemental energy in Tianjin, to a certain extent, to alleviate the situation of energy supply and demand tension. However, with the insufficient supply of high-grade geothermal resources caused by large-scale development and utilization, there is an urgent need to find new resources, therefore, shallow geothermal energy has become the focus of geothermal development and utilization in the next few years. Shallow geothermal energy exploration and development in Tianjin basically still belongs to the blank, and this part of the geothermal resources have great potential, therefore, increase the acceleration of shallow geothermal energy resources exploration, development efforts will play a positive role in alleviating the tense situation of energy supply and demand in Tianjin.
2 Characteristics of shallow geothermal field in the plain area of Tianjin
Figure 1 Contour map of shallow geothermal temperature gradient in Tianjin
Tianjin is dominated by the plain, which accounts for about 93.7% of the total area of the city. The plain area deposits thicker Cenozoic loose strata, due to the large thickness, high specific heat capacity, low heat conduction coefficient, and the relatively large value of heat flow in Tianjin area, therefore, endowed with a large amount of heat, which lays the basic conditions for the development and utilization of shallow geothermal energy.
The uppermost part of the earth's crust is called the variable temperature layer, which is the place that receives the most solar radiation energy, characterized by the temperature with the size of solar radiation, seasonal, morning and evening, and rain and shine changes. In summer, its top can be higher than 30℃ at noon, and the temperature gradually decreases downward; in winter, the top can be lower than 0℃ in the early morning, and the temperature gradually increases downward. The variation is greater on sunny days than on rainy days. Below the variable temperature zone is the constant temperature layer, which refers to a certain depth range of the internal temperature remains relatively constant all year round, and the depth of the constant temperature zone in Tianjin area is 30m, and the temperature is 13.5°C. The geothermal warming zone is further below the zone. Then under the geothermal warming zone, that is, with a certain rate of downward warming. This rate is also known as the ground temperature gradient, how many degrees per 100m increase as a unit. In tianjin geothermal survey work will be more than 3.5 ℃ / 100m temperature gradient called geothermal anomaly. According to the Tianjin geothermal exploration work in the temperature measurement data can be circled 10 geothermal anomaly area (see Figure 1), the temperature gradient in 4.5 ~ 8.8 ℃ / 100m, an area of 2328km2. other areas of the temperature gradient is generally in the range of 2.0 ~ 3.5 ℃ / 100m. China's current depth of the development and utilization of shallow geothermal energy in the depth of 200m, in accordance with the depth of a certain formula for calculating the temperature of the calculation (see formula 1) : The temperature at a depth of 200m in the Tianjin plain area is 21～28℃ in the geothermal anomaly area and 17～19℃ in the non-geothermal anomaly area. With the improvement of technical and economic conditions, the utilization depth is increasing, then the available geothermal energy will be more.
Shallow geothermal energy: Proceedings of the National Geothermal (Shallow Geothermal Energy) Development and Utilization of Field Experience Exchange Meeting
In the formula: T is the temperature of the calculated depth (℃); D1 is the calculated depth (m); Gi is the average geothermal temperature gradient of the cover layer (℃/100m); D2 is the depth of burial of the thermostat layer (m); T0 is the temperature of the thermostat layer (℃).
3 Shallow groundwater resources in Tianjin
The loose sediments of the Cenozoic era are widely distributed in the plain area in the southern part of Tianjin, and the aquifers of the Quaternary System and the Neoproterozoic System can be divided into five layers. The Ⅰ water-bearing group is equivalent to the Holocene and Upper Pleistocene (Q4+3), and the depth of the bottom boundary is generally more than 70 meters. The Ⅱ water-bearing group is equivalent to the middle Pleistocene (Q2), the depth of the bottom boundary is 180～220 m. The Ⅲ water-bearing group is equivalent to the upper part of the Lower Pleistocene ( ), the depth of the bottom boundary is 290～310 m. The Ⅳ water-bearing group is equivalent to the lower part of the Lower Pleistocene, and in the uplift area, there are also part of the Neoproterozoic water-bearing group ( ), the depth of the bottom boundary is 370～430 m. The Ⅴ water-bearing group is the Neoproterozoic water-bearing group (N2), the depth of the bottom boundary is 520～560 m. depth of 520-560m. Ⅰ water-bearing group belongs to shallow groundwater.
The Ⅱ-V water-bearing group is deep groundwater (Table 1). According to the results of a new round of evaluation of groundwater resources in Tianjin, the natural resources of groundwater in the five water-bearing groups are 18.13×108m3/a, and according to the analysis of hydrogeological conditions and the repeated demonstration of water resources, there are many years of stable recharge of underground water resources in Tianjin, and the water resources that can be utilized in a sustainable way are (7-8)×108m3/a.
Based on the previous geothermal survey work in Tianjin, the depth of nearly 100 eyes in the Pingyuan District is 560m. Pingyuan District, nearly a hundred depth of about 200m shallow well temperature measurement data, water temperature in 17 ~ 28 ℃, because of its temperature change is not large, these five aquifers occupy the part of the water and gas, it becomes a huge energy bank, with the maturity of low temperature utilization technology, the scale of the development and utilization of this part of the energy is ripe for the time.
4 shallow geothermal energy utilization technology
Heat pump is an advanced heat utilization and energy saving equipment, can effectively use the air, water and soil in the hidden low-temperature heat energy, which has the advantages of environmental protection, stability, high efficiency and energy saving, save space, low maintenance, low operating costs and reduce environmental pollution. In recent years, in the direct utilization of geothermal energy in the world, the application of heat pumps to develop shallow geothermal energy has taken the lead, and its installed capacity and utilization of energy are growing at a rate of more than 20% per annum, and up to 2005, 1.3 million heat pumps have been installed in 33 countries around the world, with a total installed capacity of 15,723 MWt. At present, the technology of utilizing the shallow geothermal temperature in developed countries such as Europe and the United States has matured well and has been extensively application. China's development and utilization of shallow geothermal energy started late, the 1990s began to study and promote the development and utilization of shallow geothermal energy technology of ground source heat pump system, and has been widely promoted in the country since 2000.In November 2005, the Chinese People's Republic of China *** and the Ministry of Construction and the State General Administration of Quality Supervision, Inspection and Quarantine jointly issued the "Ground Source Heat Pump System Engineering Technical Specification" to guide the heat pump system engineering construction.
Table 1 Division of Aquifer Groups of the Quaternary System and Some Neoproterozoic System in the Plain Area of Tianjin City and Hydrogeological Characteristics of Each Group
Tianjin is quite rich in shallow geothermal energy resources, and with the social development and the continuous improvement of the people's living standard, there are several projects in Tianjin that are utilizing the ground-source heat pump system to solve the problems of heating and cooling such as the Meijiang Residential Area, the Development Area Seaside Boulevard, the National Security Bureau, the Data Archive, the Tanggu Kaiju Heat Pump System, the National Security Bureau, and the National Security Bureau. Data Archives, Tanggu Kaihua Commercial Plaza, etc., which provides a reference for the development and utilization of shallow geothermal energy in Tianjin. Therefore, the development of shallow geothermal energy in Tianjin using heat pump technology and resource conditions are basically available, the development prospects are very favorable. And in the current energy situation is very serious, actively promote heat pump technology, scale development of shallow geothermal energy, has important practical significance.
References
[1] Tianjin Geothermal Exploration and Development Design Institute. Census of Wang Lanzhuang Geothermal Field, Tianjin, 1987
[2] Tianjin Geothermal Exploration and Development Design Institute. Tianjin Thermal Reservoir Engineering Research. 2005
[3] Chen Moxiang et al. North China Geothermal. Science Press, 1988
[4] Duan Yonghou, Wang Jiabing, Wang Yabin, Xing Guifa. Groundwater resources and sustainable utilization in Tianjin. Hydrogeology and Engineering Geology, 2004
[5] K.Y. Zheng. Development and utilization of shallow geothermal energy in the world and the development prospect in China. Textbook of National Geothermal Heat Pump Technology Training Course. 2006
.