New energy generation method: geothermal power generation - geothermal energy

Dry steam power generation system

Dry steam power generation system is a power generation system in which the geothermal fluid extracted from the ground is dominated by dry steam. Its working principle is shown in Figure 3. First, dry steam extracted from geothermal Wells is filtered out of solid particles with large diameter through a purification separator, and then sent to the turbine for power generation. Finally, the exhaust steam from the turbine is pumped back underground through the condenser and cooling tower, and the equipment used is the same as that of conventional thermal power plants. The power generation system is mainly aimed at dry steam geothermal fields with high parameters, and has the advantages of safety and reliability, little impact on the environment, and is generally suitable for high temperature geothermal energy. Comparing Figure 2 and Figure 3, it can be seen that the dry steam power generation system is very similar to the flash evaporation power system. The difference is that the dry steam power generation system uses a purification separator instead of a flash evaporator. The power generation process only uses steam and does not produce any mineral-containing brine, so the impact on the environment is lower than that of the flash evaporation power system. Currently, there are 63 dry-steam geothermal power plants in the world, mainly in countries such as the United States, Italy and Japan, accounting for about 22% of the world's total installed geothermal capacity.

New energy generation method: geothermal power generation - geothermal energy

Dual fluid power generation system

The dual-working medium cycle power generation system uses low-boiling organic working medium as the circulating working medium, and geothermal water does not directly participate in the thermal cycle. According to the different circulating working medium, it can be divided into organic Rankine cycle (ORC) and Kalina power generation system. ORC power generation system is the use of low boiling point organic working substances, such as halogenated hydrocarbons (CFCs), hydrochlorofluorocarbons (HCFCS), hydrofluorocarbons (HFCs), alkane (HCs), organic oxides and cyclic organic compounds. The working principle is shown in Figure 4. The low-boiling organic working medium exchanges heat with geothermal fluid through the heat exchanger to complete preheating and evaporation, and then generates power through the steam turbine, and finally returns to the heat exchanger through the working medium pump after condensation by the condenser to complete the cycle. The low boiling point organic working medium is mostly flammable and explosive, which requires higher sealing of equipment.

Kalina cycle uses ammonia mixture as the circulating working medium. At a lower temperature, ammonia gas will evaporate out and the components of the ammonia mixture in the circulating solution will change, resulting ina change in the boiling point temperature. The mixture of ammonia and water is exchanged with geothermal water in the evaporator, the gas-liquid mixture is generated and then enters the separator for gas-liquid separation. The separated saturated ammonia vapor is sent to the steam turbine to expand and do work to drive the generator to generate electricity. The separated ammonia water is sent to the regenerator to recover the heat. The exhaust gas discharged from the steam turbine is sent to the condenser to condense into ammonia, which is then sent to the evaporator through the working medium pump for re-circulation.

The dual-medium power generation system is widely used in geothermal power generation, and has the advantages of compact equipment, small turbine size and low operating cost. When the temperature of the local thermal reservoir is low, the use of flash evaporation electric system has large investment and low efficiency, and the dual-medium power generation system can not only use the geothermal fluid of 85 ° C ~ 170 ° C, but also in the cycle process, because there is no direct contact between the geothermal fluid and the power production equipment, it can effectively prevent the corrosion and scale of the power generation equipment. The power generation system can make use of low-grade energy of low-temperature geothermal resources, promote steam turbine to do power generation, and make reasonable use of low-temperature geothermal resources.

New energy generation method: geothermal power generation - geothermal energy

Enhanced geothermal system

Enhanced Geothermal Systems (EGS) refer to the construction of artificial geothermal reservoirs through hydraulic fracturing and other technical means to build cracks in the rock to form a heat exchange space between the rock and the fluid, which is generally used in hot and dry rock geothermal resources. The process of EGS power generation is to build artificial heat storage by pressurizing cold water through water injection Wells. Cold water penetrates cracks in rock strata and contacts with high-temperature rock mass to absorb heat. Then hot water or water vapor is extracted to the ground by production Wells and heat is exchanged through heat exchangers. Hot and dry rock resources are abundant in China, but only stay in the exploration and development stage at present. In May 2015, China Geological Survey organized the implementation of China's first dry hot rock scientific drilling in Zhangzhou, Fujian, which marked the official start of China's national dry hot rock practice. In 2017, the hydrogeological team of the Hebei Coal Geology Bureau implemented a dry hot rock pre-survey project, drilling a well 4000 m deep at 110℃. Subsequently, China successfully drilled 236℃ hot dry rock at a depth of 3,705 meters in Gonghe Basin, Qinghai Province, and is expected to successfully build one to two hot dry rock demonstration projects in 2035 to achieve power generation from hot dry rock. In June 2021, the key technology research and demonstration project of dry hot rock development in Matouying Uplift Area of Tangshan City, Hebei Province, realized the experimental power generation of dry hot rock, which is the first time to realize the experimental power generation of dry hot rock in China.