Geothermal is hot water, steam, and gases containing chemicals, which are formed by accumulated heat at various depths of the earth’s crust. Geothermal energy means that the utilization of these geothermal resources and the energy they generate directly or indirectly.
“Geo” means “from the earth,” and “thermal” means “heat,” so this type of energy is available under the earth.
How does Geothermal Energy Work?
As a result of the application of various research techniques, geothermal energy is easier than ever, by drillings under appropriate geological conditions. This geothermal fluid is separated into water-vapour phases by a decrease in pressure.
The separated steam is sent to the geothermal power plants and converted into electrical energy, and the wastewater used in other heating systems or underground. It is more efficient for electricity generation if wet steam, steam percentage, and enthalpy are high.
The dry steam obtained from the depths of the earth’s crust is directly transmitted to the geothermal power plants and converted into electrical energy. The most suitable geothermal sources for electricity generation are high temperature and high enthalpy dry steam systems. Their temperature ranges from 250ºC to 380ºC. Vapour with very little humidity is called dry steam.
3 Important Geothermal Power Plant Types
Depending on the phase of the extracted geothermal fluid, we use various cycles for electricity generation. The turbine uses steam to convert an energy source to mechanical energy. The power plants divide into three according to whether the vapour is directly from the reservoirs or the fluid used is different. Because the boiling point of the double fluid used is lower, we can use in partially low-temperature reservoirs. (Experts recommend that the lowest temperature in the reserves is above 150 ° C).
In this case, heat exchangers provide heat transfer between the first fluid and the binary fluid
- Dry Steam
- Flash Steam
- Binary Cycle
The simplest of all geothermal power plant types dry steam plants. In principle, such power plants in regions with saturated or superheated geothermal steam available. Saturated or superheated geothermal in the world geothermal areas with liquid is quite limited. Vapour, dry steam or light from geothermal source direct steam turbine under hot steam conditions we can generate electricity by sending it to the generator group.
Examples of resources with these features in the world, we can give In Italy – Larderello and US – The Geysers Resources.
The straightforward and most economical geothermal cycle is dry steam cycle without condensate which extracted from a geothermal well. After passing through a turbine, the system throws the steam into the atmosphere. Since the turbine outlet is directly open to the atmosphere, steam leaves the turbine at atmospheric pressure. The advantage of the cycle is that the condenser is not construction and operation costs to condenser plants is less than that.
The waste of this cycle as a result of the geothermal steam directly into the atmosphere disposal of the environment causes pollution.
It is not common for the geothermal fluid removed from the ground to be fully in the vapour phase. The extracted geothermal fluid is usually a saturated liquid-vapour mixture. In these cases, if the percentage of vapour is high enough, the steam is separated from the liquid, and the system conveys the fluid into the turbine, and then inject the liquid underground.
We use vapour steam cycles where the percentage of steam is low or when the geothermal fluid is entirely in the liquid phase. The system carries out the spraying process in a place called the spray pool according to the operating principle of the throttling valves. After spraying, the system sends biphasic fluid to a separator. The vaporizer and the liquid are separated from each other by various methods.
Cyclone separators use the high-density difference between steam and liquid, vapour with fluid as a result of centrifugal movement. This type of separators can produce steam with dryness of up to 99.9%.
At low temperature (usually less than 170 ° C) and liquid-weighted geothermal sources, we use an electric cycle in the production of a second cycle. In this cycle, the turbine flow through the turbine is not a geothermal vapour. It is a fluid called a secondary fluid, and its boiling temperature is much lower than the boiling temperature of the water. In this cycle, the geothermal fluid forms the heat source of the period.
Isobutane, isopentane, pentane, and R114 are secondary fluids. We commonly use them in geothermal secondary cycle power plants. At the end of 1985, the total capacity of the geothermal power plants on Earth was around 4763MW (Megawatt).
Thanks to the geothermal power plants, humanity reached 72890 MW of electricity production in 2000. This data indicates that geothermal energy will become a significant source of power in the future and will replace conventional fossil energy sources.