Domestic and foreign geothermal power generation technology development status and trend

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In the process of exploitation and utilization of middle and low temperature geothermal resources, dual-working fluid cycle and Karina cycle technology have broad prospects for development.

10.A schematic diagram showing the basic concept of a low-temperature  geothermal binary ORC system for electrical power  generation.

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Foreign ORC generator set product information

The Karina cycle is a new thermal cycle, which is different from the conventional Rankine cycle. The mixture of ammonia and water is used as the working medium, and the boiling point of the mixed working medium is changed with the change of the ratio of ammonia to water. When the heat source parameter changes, only the ratio of ammonia and water needs to be adjusted to achieve the best circulation effect. The temperature rise curve of the working medium is closer to the temperature drop curve of the heat source, so as to reduce the heat transfer temperature difference as much as possible, reduce the entropy increase of the system during the heat transfer process, and improve the cycle efficiency. Because of this remarkable feature of the Karina cycle, it has been widely used in the field of medium and low temperature geothermal power generation. The current industrial application shows that the cycle efficiency of the Karina cycle power generation technology is 20% ~ 50% higher than that of the Rankine cycle. However, due to the use of liquid ammonia as the circulating working medium, there are high requirements for the sealing of the system, and the storage and use of working medium will have a certain impact on the environment. Attention should be paid to strengthening the environmental assessment work in the construction process of the power station.

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The Kalina power cycle technology introduced from the United States is the main means for Shenghe Company to make breakthroughs in solar thermal power generation, geothermal power generation, cement waste heat power generation, float glass, iron and steel industry, thermal power plant to improve cycle efficiency, coke industry and ferroalloy furnace waste heat power generation and waste heat utilization. This technology could significantly increase the efficiency of Rankine cycles currently used in conventional thermal power generation and waste heat generation systems. This technology using ammonia water as the circulating working medium is derived from the conventional Rankine cycle and has great particularity.

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2. Exploitation of middle-deep geothermal resources and dry hot rock resources

In addition, after the large-scale development of shallow geothermal energy, middle-deep geothermal resources and dry hot rock resources will become new resources of geothermal power generation technology. In the next step of the development of geothermal power generation technology, attention should be paid to the exploitation of middle-deep geothermal resources and dry hot rock resources.

enhanced geothermal systems (EGS) are emerging for the development and utilization of hot dry rock (HDR) thermal energy 3 ~ 10 km deep underground. Enhanced geothermal power generation technology, by injecting water back into groundwater, To create new geothermal resources, geothermal resources can be obtained at higher temperatures, which can reach 175 ~ 225 ° C. Generally, dual-cycle power generation is used to maintain the pressure of geothermal water and reduce the energy consumption of recharge.

14. Fenton EGS in the United States, SoultzEGS in France, Rosemanowes EGS in the United Kingdom, Hijiori EGS in Japan, Cooper EGS in Australia, etc., after 40 years of field test and research, Technical achievements have been made in drilling exploration, hydraulic fracturing, artificial heat storage and heat recovery cycle. In the field of dry hot rock, China's initial investment is small, mainly funded academic exchanges, exploration and research, and has not formed a national level of dry hot rock technology research and development base and equipment conditions.

3. Development trend of geothermal power generation technology

However, the new combined cycle power generation technology is the development direction of geothermal power generation technology. The cycle efficiency of single steam Rankine cycle power generation technology is low, only less than 20%; The discharge temperature of tail water is relatively high, generally above 100℃, and the utilization of geothermal energy is insufficient. The dual-working fluid cycle and Karina cycle power generation technology systems are more complex, involving two sets of working fluid systems, but the cycle efficiency is high, and the tailwater discharge temperature can be reduced to below 60℃. In the future geothermal power generation technology, the way of combined cycle can be adopted. In the high temperature stage of geothermal water, the expansion type steam power generation system is used to utilize the high temperature part of geothermal energy. When the temperature of geothermal water cannot meet the operating conditions of expansion power generation, the dual-working medium cycle or Karina cycle technology is adopted to make full use of the low temperature part of geothermal energy and maximize the efficiency of geothermal power generation cycle. Based on the expansion system, the Kizildere geothermal power station in Turkey jointly uses the dual-working mass cycle technology to carry out the research of the test unit, the maximum power reaches 18.238kW, the cycle efficiency reaches 38.58%, and the performance of the combined cycle power generation system is stable.