Geothermal power generation is actually an energy conversion process that converts underground thermal energy into mechanical energy and then converts mechanical energy into electrical energy, or geothermal power generation. The geothermal resources currently being developed are mainly steam-type and hot-water type. Therefore, geothermal power generation is also divided into two categories.
Geothermal steam power generation has two kinds of steam method and secondary steam method. The primary steam process directly utilizes dry-saturated (or slightly superheated) steam in the ground, or uses steam separated from the steam and water mixture to generate electricity. The secondary steam method has two meanings. One is that it does not directly use the relatively dirty natural steam (primary steam), but allows it to vaporize the clean water through the heat exchanger and then use the clean steam (secondary steam) to generate electricity. The second meaning is that the high-temperature hot water separated from the first soda water is decompressed and expanded to produce secondary steam, the pressure is still higher than the local atmospheric pressure, and the primary steam enters the steam turbine to generate electricity.
The water in geothermal water cannot be directly sent to the steam turbine for work according to the conventional power generation method. It must be input into the steam turbine for work in the steam state. At present, there are two methods for unsaturated underground hot water power generation with temperatures below 100 °C: one is the decompression expansion method. Using a vacuuming device, the underground hot water entering the expansion vessel is decompressed and decompressed to generate a volume expansion steam lower than the local atmospheric pressure, and then the steam and water are separated, drained, and the steam is charged into the steam turbine for work. This system is called a "flash system." ". The specific volume of the low-pressure steam is large, so that the single-machine capacity of the gas turbine is greatly limited. But it is safer during the operation. The other is to use low-boiling substances such as ethyl chloride, n-butane, isobutane and Freon as intermediates for power generation. Underground hot water is heated by heat exchangers to rapidly vaporize low-boiling substances. The generated gas enters the generator to work, and the working fluid after the work is discharged from the steam turbine into the condenser, and is cooled by the cooling system, and then re-condensed into a liquid working medium and recycled. This method is called the “intermediate working methodâ€, and this system is called “dual flow system†or “dual working systemâ€. This kind of power generation method is less safe. If the power system is slightly leaked, the accident will easily occur after the working medium escapes.
In the mid-1990s, Israel's Ormat Corporation combined the above-mentioned geothermal steam power generation and geothermal water power generation systems into one, and designed a new geothermal power generation system named as a combined cycle. Some countries in the world are installed and running, and the effect is very good.
The biggest advantage of the combined cycle geothermal power generation system is that it can be applied to high-temperature geothermal fluids (including hot brines) of more than 150 °C, and the fluid after one generation of power generation enters duplex again under the condition of not lower than 120 °C. The power generation system performs secondary work. This is to make full use of the thermal energy of the geothermal fluid. It not only improves the efficiency of power generation, but also re-uses the tail water discharged from the previous generation, which greatly saves resources.
Geothermal technology: The best way to use high-temperature geothermal resources is geothermal power generation. Geothermal energy of 200~400 °C can be directly used to generate electricity.
Steam geothermal power generation
The dry steam in the steam field is directly introduced into the steam turbine generator set. However, the cuttings and water droplets contained in the steam should be separated before being introduced into the generator set. This type of power generation is the simplest, but dry steam geothermal resources are very limited, and exist in deeper strata, which is difficult to mine, so its development is limited. There are mainly two types of power generation systems, back pressure type and condensing type.
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