(Guangzhou Institute of Energy, Chinese Academy of Sciences)
Abstract: This paper introduces an absorption refrigeration technology for developing medium and low temperature geothermal resources-hot water two-stage lithium bromide absorption refrigeration technology. The test data show that when the heat source temperature is 63 ~ 65℃, the coefficient of performance of the refrigerator can still be stabilized at 0.38 ~ 0.42. Compared with the original electric compression refrigeration air conditioning system, geothermal refrigeration air conditioning system can save about 62% electricity. The payback period of the whole system is less than 4 years, which has high practical value and market prospect.
1 Introduction
Geothermal energy is a clean and renewable energy. It has the advantages of high heat flux, easy collection and transportation, stable parameters (flow rate and temperature) and convenient use. Geothermal is not only a mineral resource, but also a valuable tourist resource and water resource, which has become a hot spot for development and utilization in various places.
The utilization of low-temperature geothermal resources in China has achieved good results in some areas, such as Beijing and Tianjin using geothermal water for heating in winter [1 2], which has produced good results in reducing the use of fossil fuels and improving the atmospheric environment of the two cities. However, compared with some developed countries abroad, there is a certain gap in the total amount and utilization level of geothermal energy in China. Except for the high temperature resources used for power generation, most of the medium and low temperature geothermal resources are still used in a simple and primitive way. Especially, when many tourist hotels near hot spots use 70 ~ 90℃ geothermal water, they often rely on natural cooling to lower the temperature below 50℃ for bathing and physical therapy, which wastes a lot of heat energy.
In recent years, many tourist resorts have been built around geothermal hotspots in Guangdong, and investors have devoted great interest to the rational development and utilization of geothermal resources. Combined with the demand of tourist resorts, two-stage lithium bromide absorption chillers [3, 4, 5] with hot water are adopted to make full use of geothermal resources above 70℃ to provide refrigeration and air conditioning for buildings. The geothermal water (60℃) can be used for drying, bathing and breeding of agricultural and sideline products in turn, which realizes the cascade comprehensive utilization of geothermal resources and promotes the development of local tourism and agricultural economy.
Refrigeration principle of hot water two-stage lithium bromide absorption refrigerator
The two-stage lithium bromide absorption refrigeration cycle system consists of evaporator, low-pressure absorber, high-pressure absorber, low-pressure generator, high-pressure generator, condenser, low-pressure solution heat exchanger, high-pressure solution heat exchanger, solution circulating pump and refrigerant pump, as shown in figure 1.
The refrigeration process can be divided into three processes: ① refrigerant circulation (indicated by solid line); (2) low-pressure stage solution circulation (dotted line); (3) High pressure stage solution circulation (dotted line). The low-pressure refrigerant vapor from evaporator E is absorbed by the solution in low-pressure absorber Al, evaporated in low-pressure generator Gl through low-pressure stage solution circulation, absorbed by the solution in high-pressure absorber Ah, evaporated in high-pressure generator gh through high-pressure stage solution circulation, dissipated in condenser K, cooled and depressurized through throttle valve (U-tube), and entered evaporator E to provide air conditioning cooling load for buildings.
Figure 1 Schematic diagram of two-stage lithium bromide absorption refrigeration
Compared with the traditional single-stage absorption refrigerator, the two-stage absorption refrigerator is equipped with a high-pressure absorber and a low-pressure generator, in order to obtain chilled water with the same low temperature under the same environmental conditions when the local hot water temperature is low.
3 coefficient of performance of two-stage lithium bromide absorption chiller for hot water
The refrigeration capacity of the two-stage lithium bromide absorption refrigerator is Qo, and the heat absorbed by the high-pressure generator and the low-pressure generator from geothermal water is Qhg and Qlg, so the performance coefficient of the refrigerator is:
Shallow geothermal energy: proceedings of the national on-site experience exchange meeting on geothermal (shallow geothermal energy) development and utilization
As can be seen from the above formula, in the two-stage lithium bromide absorption refrigerator, the generator inputs two parts of heat to get one part of cold energy, so the actual performance coefficient COP of the two-stage lithium bromide absorption refrigerator is about 0.4.
4 engineering application examples
In 2002, Guangzhou Energy Research Institute of Chinese Academy of Sciences built the first practical geothermal refrigeration and air conditioning system in China, and put it into operation that year. The system was built in Wuhua Hot Mine Mud Villa, Meizhou City, Guangdong Province. Geothermal water of about 70℃ is used as heat source to produce 9℃ chilled water, which is used for air conditioning in cafes and lounges of hot mud villas.
4. 1 composition of geothermal refrigeration and air conditioning system
The system mainly consists of a hot water type two-stage lithium bromide absorption refrigerator, a chilled water circulating pump, a deep well pump, a geothermal water circulating pump, a plate heat exchanger, a hot water circulating pump, a cooling water circulating pump, a cooling tower, a control box, a connecting pipeline and air conditioning terminal equipment. The system is shown in Figure 2. The outlet water temperature of the hot well used in this system is 70 ~ 75℃, the inlet water of the heat exchanger is 20m3/h, and the flow rate of chilled water generated by the system is 15.2m3/h, which is sent to the fan coil units of the lounge and the coffee shop to provide air conditioning, of which the flow rate of chilled water in the lounge is 4.7m3/h, and that in the coffee shop is 10.5m3/h, and two.
Fig. 2 100kW geothermal refrigeration and air conditioning system
4.2 Main system parameters
The main parameters of geothermal refrigeration system are shown in table 1:
Table 1 Main parameters of geothermal refrigeration system
4.3 System Test Data Analysis
Hot water, cooling water and frozen water are three kinds of media that the absorption refrigerator exchanges with the outside world, and the parameters of these three media directly affect the refrigeration capacity of the refrigerator. In order to study the operating conditions of two-stage absorption refrigerator driven by low-temperature geothermal hot water for air conditioning, the system was tested and analyzed in detail.
As can be seen from Figure 3, the heat source temperature of the refrigerator is basically stable at 63 ~ 65℃, and its stability determines the stability of the output chilled water temperature and performance coefficient of the refrigerator. Although the geothermal temperature is low, the coefficient of performance of the refrigerator remains at 0.38 ~ 0.42.
Fig. 3 Operation curve of geothermal refrigeration air conditioner
4.4 System Economic Analysis
The comparison between the geothermal refrigeration air conditioning system and the original air conditioning system is shown in Table 2 below. Compared with the original air-conditioning system, the geothermal refrigeration air-conditioning system reduces the input power by 27.35kW per year and saves the electricity fee by 5,565,438 yuan, which has good energy-saving characteristics. The one-time investment of geothermal refrigeration and air conditioning system needs to be increased by 265,438+10,000 yuan. If the annual air conditioning time is 7 months, the additional investment of geothermal refrigeration and air conditioning system can be recovered in less than 4 years.
Table 2 Economic Analysis of Geothermal Refrigeration and Air Conditioning System
5 conclusion
A remarkable feature of geothermal resources in China is its abundance and uneven distribution. Most of them are distributed in some remote areas, such as rural areas, and have not been well used in the past. With the development of rural urbanization, it is of great significance to rationally develop geothermal energy, a unique natural resource, and develop tourism, aquaculture and other related industries for revitalizing rural economy, driving farmers to become rich and accelerating the construction of a well-off society in rural areas.
The hot water type two-stage lithium bromide absorption refrigeration technology effectively utilizes the medium and low temperature geothermal resources (70 ~ 90℃) and becomes a very important link in the process of cascade comprehensive utilization of geothermal resources. With the construction of tourist resorts near hot spots, this technology will be well applied.
refer to
Liu, thanks. Develop the geothermal industry with the characteristics of China's capital. Beijing Geology 1995, (2): 1 ~ 5
[2] Wang Zuwei. Present situation and development countermeasures of geothermal resources in Tianjin. Research on Land and Natural Resources, 2000, (3): 50 ~ 5 1
[3] Xia Wenhui, Ma Weibin et al. A new type of low-temperature hot water refrigerator. Refrigeration, 1996, (2): 1 ~ 6.
Ma Weibin, Xia Wenhui, et al. Application of hot water lithium bromide two-stage absorption refrigerator in industry. Refrigeration, 1998, (4): 37 ~ 40.
[5] Ma W B, Deng S M. Low theoretical analysis? Temperature heat source drive two? Lithium bromide /H2O absorption refrigeration system. Journal of Refrigeration, Vol. 19, No.2.