New energy generation method: geothermal power generation - geothermal energy

Geothermal energy comes from a large amount of heat generated by the decay of natural radioactive isotopes such as uranium, thorium and potassium in the Earth's interior, which is transferred to the surface through carriers such as volcanic eruptions, hot springs and groundwater. The heat energy transported to the surface from inside the earth is equivalent to 28 billion tons of standard coal every year, because of its large reserves, wide distribution, clean environmental protection, stability and reliability and many other advantages and has been widely used, at present, more than 88 countries and regions in the world use geothermal energy for power generation and heating. In 2020, China proposed for the first time to achieve "carbon peak" in 2030 and "carbon neutrality" in 2060, and clean energy is an indispensable part of achieving this goal.

Hydrothermal geothermal resources in China are equivalent to 1.25 trillion tons of standard coal, and the annual recoverable resources are equivalent to 1.865 billion tons of standard coal, which can be divided into convective hydrothermal system, conductive hydrothermal system and conduction-convective composite hydrothermal system according to heat transfer mode, and can be divided into high-temperature geothermal (150 ° C) and medium-low temperature geothermal (<150 ° C) according to temperature. Hydrothermal medium and low temperature geothermal resources are mainly distributed in the North China Plain, Songliao Basin, Sichuan Basin, Jiaodong Peninsula, Liaodong Peninsula and other regions, with an annual mining capacity equivalent to 1.85 billion tons of standard coal, mainly used for heating, tourism, industrial drying and so on. High-temperature hydrothermal geothermal energy is mainly distributed in the southwest of China, such as South Tibet, west Yunnan and west Sichuan, with an annual mining capacity equivalent to 18 million tons of standard coal, which is mainly used for power generation and industrial utilization.

Dry hot rock refers to the high-temperature rock mass with no or little water content at a depth of 3 ~ 10km from the surface, which is mainly metamorphic or crystalline rock with low porosity and poor fracture permeability. Therefore, geothermal reservoirs need to be formed by artificial fracturing to be exploited and utilized. The temperature range is 150℃ ~ 650℃. The basic resources of dry hot rock buried less than 10,000 m in China can be equivalent to 856 trillion tons of standard coal, mainly distributed in Xizang, Yunnan, Guangdong, Fujian and other regions.

New energy generation method: geothermal power generation - geothermal energy

The flash evaporation electric system, also known as the vacuum expansion power generation system, transforms the ground hot water under low pressure from liquid to gas by using the principle of different boiling points of water under different pressures. The working process is shown in Figure 2(a). The steam and water mixture with a certain pressure extracted from the geothermal well is transported to the flash evaporator through the pipeline for pressure reduction and expansion; the expanded water is pumped underground through the pipeline; the expanded steam is dehumidified by the dehumidifier and then sent to the steam turbine through the pipeline to do work; the exhaust gas discharged from the steam turbine is condensed by the condenser and then transported to the recharge well and pumped underground. According to the different times of geothermal water passing through the flash evaporator, it can be divided into single-stage flash system and two-stage flash system. The two-stage flash system is an improvement based on the single-stage flash system, and its working principle is shown in Figure 2(b). The expanded water is sent to the flash evaporator again for secondary flash expansion, and the steam generated by expansion is sent to the low pressure end of the turbine to continue generating power.

New energy generation method: geothermal power generation - geothermal energy

Flash evaporation power system is the most commonly used power generation system for geothermal power generation. When the power generation system is in normal operation, the separated brine contains some high concentration of dissolved minerals, which will cause serious water pollution if it is mixed with the surface or groundwater. The concentration of waste brine in the two-stage flash evaporation power station is generally higher than that in the single-stage flash power station. In order to prevent water pollution, the wastewater needs to be recharged, which can effectively restore the fluid in the reservoir and maintain the pressure of the reservoir. The single-stage flash evaporation electric system is simple in structure and easy to manufacture, but the conversion efficiency is low. The equipment of the two-stage flash evaporation system is complex, but the conversion efficiency can be increased by 20% to 30% compared with the single-stage flash evaporation system under the same heat source condition. The use of single-stage or two-stage flash evaporation system depends on the characteristics of geothermal resources, the economy of geothermal power station and the loss of equipment.