Components of a Geothermal Plant

The sun and the Earth’s inner core are the two greatest energy sources on the planet. Utilising theses two forms of energy to produce electricity is going to be one method to fight global warming. One is a perpetual source of energy and other other a gigantic energy store. Why should we look for other sources?

Even though the current geothermal power generation is minuscule 0.3 % of world generation, it holds a promising future. What, then, are the main components of a geothermal powerplant? How does it compare with conventional power plants?

The most important part of any geothermal plant is the source of steam. Steam from the underground thermal reservoirs, 1000 to 2000 m deep, raises to the surface though bore holes drilled through the stones, rocks, and other layers. This is similar to a production well of an oil rig. Each location has one or many wells with the output connected to a header. Headers and pipes connect the wellheads to the power plant. Depending on the nature of the geothermal reserve, the wells may be located as far as 10 to 14 kilometers from the power plant.

Depending on the source, the steam from the wells can be either dry or moist. Wet steam passes through moisture separators where the water separates. The water or the brine then goes for reinjection back to the underground reservoir through reinjection wells.

The steam then goes to the turbine.

A properly located well can be a continuous energy source for many years.

The turbines in geothermal power plants have special requirements. The steam can be corrosive due to many Non Condensable Gases (NCG) including Hydrogen Sulphide. This requires special materials and corrosion protection for the turbine components. Special coatings protect the rotor, blades, and nozzles from corrosion.

The generation and transmission side of geothermal power plants is similar to conventional power plants.

As in conventional power plants, the steam condenses at a vacuum at the turbine exi,t so the work done by unit mass of steam is high. Most of the plants use direct contact condensers that use the condensed water itself as the cooling media.

Cooling towers cool the hot condensate for use in the condensers and for plant cooling.

The excess condensate and the brine from the separators returns back to the underground thermal reservoirs. Reinjection wells similar to the steam production wells are located in appropriate places. Some reservoirs can give outputs for years without re-injection.

Some plants reinject municipal waste water from nearby cities deep into the wells.

The steam contains Non-condensable gases including Hydrogen Sulphide which separates in the condenser. Steam ejectors suck out these gases so that the vacuum is maintained in the condenser.

Depending on the Hydrogen Sulphide content special H2S removal systems are used.

These are the key components of a geothermal power plant.