2025-01-14
We often hear about thermal power plants, wind power, solar power, and rarely about geothermal power. Actually, geothermal power generation is already a very mature form of resource utilization. So today we're going to talk about geothermal power.
The newly appearing geothermal power generation uses hot water or steam underground as power source. Its underlying mechanism is very similar to the conversion energy of thermal power, hence the theory in a like manner, drawing its basic essence from the conceptions. Geothermal energy is the kind of renewable heat within deep grounds stemming from the Earth's interior partial melting and radioactivity matter decay.
Groundwater circulates deep down, and magma invades the earth's crust, bringing heat from deep underground to the surface. Geothermal power generate electricity is the conversion of underground heat into mechanical energy, and then the mechanical energy into electricity. For example, water is injected into rock formations by hydraulic or blasting fragmentation to produce hot water vapor, which pulls out of the ground to turn turbines and generate electricity. In this process, a part of the unused steam or waste gas is reduced to water by condenser treatment and pumped back into the ground to achieve circulation.
Steam geothermal power generation
Primary steam method:
Generate electricity directly from dry saturated or slightly superheated steam in the ground, or from steam separated from a mixture of steam and water. For instance, the Geysers geothermal Field in the United States uses this approach, which is the largest steam-based geothermal field in the world, comprising several large geothermal generators that supply the surrounding area with electricity continuously.
Secondary steam process:
One is not to directly use the dirty natural steam, instead to let it vaporize the clean water through the heat exchanger, and then use the clean steam to generate electricity; The other is that through the reduction of pressure, the high temperature hot water separated from the first steam water is expanded to produce secondary steam (its pressure is still higher than the local atmospheric pressure), and the primary steam is led into the turbine for generating electricity. The Waira base in New Zealand has a very hot field and some units adopt the method of secondary steam, which raises the energy utilization efficiency and reduces equipment corrosion effectively.
Hot water geothermal power generate electricity:
Flash system: The vacuum pump is used to reduce the pressure of the underground hot water entering the expansion vessel, re-boiling the unsaturated underground hot water for power generation with temperature lower than 100 ° C, then separating the steam and water, draining the water, and injecting the steam into the turbine for work. The Radero geothermal field in Italy was one of the early adopters of flash systems and hosts the world's first geothermal power station. Over the years, the field has developed to optimize flash technology in order to maintain a stable power generation capacity.
Two-media or two-working-medium power generation system: chloroethane, n-butane, isobutane, freon are used as the media to generate power. Through a heat exchanger, the underground hot water heats up the media with low boiling points to vaporize quickly, and then the produced gas is used to enter the generator for doing work. After that, the working medium, after work, is discharged from the turbine into the condenser, in which the cooling system cools it and it is condensed into liquid working medium again for recycling. Therefore, partial geothermal plants were done on a small-scale with Japan adopting an approach by implementing an intermediary working medium methodology where localized and decentralized resources were utilized maximally and would supplement such a place with remote access power.
There exists, further combined cycle geothermal power which is a culmination of the preceding type described-geothermal steam, which converts this natural product into electric generation. And similarly, geothermal water-based power.
Clean energy: Geothermal energy is pollution-free clean energy, and heat energy can be renewable if the heat extraction rate does not exceed the rate of replenishment. In the whole life cycle, the average CO2 emission potential of geothermal power generate electricity is lower than that of wind power generation and photovoltaic power generation.
Cost advantage: Generally, no fuel is used, and the cost of power generation is lower than hydropower, thermal power, and nuclear power in most cases. The utilization time of equipment is long and usually has a construction investment lower than hydropower stations.
Stable power generation: it is not affected by rainfall and seasonal changes. With annual utilization hours of more than 8,000, the generated power can be compared to nuclear power but is much higher compared to wind power and photovoltaic power; hence, it can provide a steady supply to the grid.
High energy utilization coefficient: the unit utilization rate (capacity factor) of geothermal power generate electricity is above 0.7, about 5 times that of photovoltaic power generation and 4 times that of wind power generation.
At present, China's geothermal power generation is mainly concentrated in Xizang Yangbajing geothermal field, which is the largest geothermal power station in China. Yangbajing Geothermal Power Station was built in 1977, and its installed capacity has been continuously expanding, making an important contribution to the power supply of Tibet. In addition, there are also some small-scale geothermal power generation projects in Yunnan, Sichuan and other places in the trial or small-scale operation stage.
However, there are still many challenges facing the geothermal power industry in China. In terms of technology, although some conventional geothermal power generation technologies have been mastered, there is still a gap with the international advanced level for the development of deep geothermal resources, dry hot rock power generation, and other key technologies. For instance, the current exploration degree for China's geothermal resource as a whole is rather at the lower end, so its knowledge of resource distribution and reserve is not deep enough. In respect of resource development, large-scale developments or utilisations are rather restricted. Policy Support: The geothermal power generation, with regard to policy support, although some policies have been promulgated by the state to promote the development of renewable energy, there is no perfect special support policy for geothermal power generation, lacking a long-term stable incentive mechanism.
Resource exploration is difficult: geothermal energy is hidden in the ground and cannot be seen or touched, and the exploration of the reserves, types and distribution of geothermal resources requires a lot of capital and technology, and there is uncertainty.
High development costs: Early development costs are high, including drilling, equipment installation and other expenses, and development cycles are long and unpredictable.
Technological problems: Although there is a variety of mature technologies, for some special geothermal resources, such as the power generation from dry hot rock, there is still some degree of technological difficulty and is still in the critical stage.
Environmental impact: Although the overall impact on the environment is slight, geothermal fluids are generally rich in calcium silicate, calcium sulfate, calcium carbonate and dissolved oxygen and other substances, so that the scaling and corrosion may be caused, improper treatment can affect the environment and equipment.
Tags:
