Explaining Geothermal Cycles

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Geothermal energy has become more and more popular globally due to its sustainability and economic stand point. Geothermal power plants run on a variety of temperatures and utilize hydrothermal resources (water/steam and heat) from below the earth surface to generate electricity for people’s daily consumption. Resources can come from dry steam or hot water wells.

There are three kinds of Geothermal cycle for power plants: binary cycle, dry steam and flash steam. Binary cycle power plants use the heat transfer from geothermal hot water to secondary fluids with a low boiling point at the lower end of standard geothermal temperature (225 to 360 F). This heat will cause the secondary fluid to bubble and turn into steam in the heat exchanger, which is then used to turn the turbine. Since water and secondary fluids are kept apart in the cycle, air emission is minimized.

Dry steam is the first geothermal power plant to ever exist from a natural rupture of steam, though considerably uncommon since it demands sustainable underground heat sources to work. The steam used as a working fluid will be piped directly from the underground geothermal reservoirs to turn a turbine and generate electricity.

Flash steam is the most common type of geothermal application, using a underground high-pressure hot water reservoir with a minimum temperature of 360 F, converting it to steam as it moves up to the surface from change in pressure. After steam gets separated from water, it drives the turbines to produce electricity. As the steam cools down and condenses to water, fluid then will be injected back to the reservoir to be reused.

Each one of these system designs comes with its own advantages and disadvantages. For example, binary cycle allows low temperature geothermal sources to be used thus can be used in more wide spread applications. This kind of cycle also does not release geothermal fluid into the system, thus the technology is more environmentally friendly. On the other hand flash steam power plant gives you the advantage of sustainability as well as cost effectiveness in the long run, though it’s rather geographically sensitive. Dry steam application is hard to implement due to the rather rare natural resource used to be able to implement such a cycle, though it generates less of a footprint and require simpler technology which results to lower initial cost. The better application is really dependent on the designer’s needs and goals.

References:

http://large.stanford.edu/courses/2011/ph240/yan2/

http://me1065.wikidot.com/flash-steam-geothermal-power-plants

https://www.nrel.gov/workingwithus/re-geo-elec-production.html

http://energy.gov/eere/geothermal/how-geothermal-power-plant-works-simple

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