Content of PetroWiki is intended for personal use only and to supplement, not replace, engineering judgment. SPE disclaims any and all liability for your use of such content. The heat of the earth, usually from produced natural steam, heat recovered from circulated water or direct heat-to-energy conversion (on-going research).
The type of energy conversion system used to produce electrical power from a geothermal resource depends on the type and quality (temperature) of the resource. Vapor-dominated resources use conversion systems where the produced steam is expanded directly through a turbine. Liquid-dominated resources use either flash-steam or binary systems, with the binary conversion system predominately used with the lower temperature resources. When the geothermal resource produces a saturated or superheated vapor, the steam is collected from the production wells and sent to a conventional steam turbine (see Figure 1). Before the steam enters the turbine, appropriate measures are taken to remove any solid debris from the steam flow, as well as corrosive substances contained in the process stream (typically removed with water washing).
Biofuels are an alternative to fossil fuels that are produced from fats derived from living organisms. One source of biofuel that is being explored more thoroughly in recent years is microalgae. It can bloom in places where salty water, excessive sun exposure, and lack of vital nutrients inhibit growth of other crops. But the higher the concentration of algae cells, the lower the ability to absorb light. In heterotrophic conditions, the algae can use sugars, organic acids, and other organic carbons as carbon sources, replacing the need for light.