Gas Detectors for Geothermal Power Generation Facilities

Geothermal Power Generation

Geothermal power plants derive their energy from heat deep within the earth’s core. Power plants use steam produced from geothermal reservoirs to generate electricity. There are three geothermal power plant technologies being used to convert hydrothermal fluids to electricity—dry steam, flash steam, and binary cycle. The type of conversion used depends on the state of the fluid (steam or water) and its temperature.

Dry Steam Power Plant

Dry steam plants use hydrothermal fluids that are primarily steam. The steam travels directly to a turbine, which drives a generator that produces electricity. The steam eliminates the need to burn fossil fuels to run the turbine (also eliminating the need to transport and store fuels). These plants emit only excess steam and very minor amounts of gases.

Flash Steam Power Plant

Flash steam plants are the most common type of geothermal power generation plants in operation today. Fluid at temperatures greater than 360°F (182°C) is pumped under high pressure into a tank at the surface held at a much lower pressure, causing some of the fluid to rapidly vaporize, or "flash." This flashing vapor then drives a turbine, which drives a generator. Any liquid remaining in the tank can be flashed again in a second tank to extract even more energy.

Binary Cycle Power Plant

Binary cycle geothermal power generation plants differ from Dry Steam and Flash Steam systems in that the water or steam from the geothermal reservoir does not come in contact with the turbine/generator units. Low to moderately heated (below 400°F) geothermal fluid and a secondary ("binary") fluid with a much lower boiling point that water pass through a heat exchanger. Heat from the geothermal fluid causes the secondary fluid to flash to vapor then driving the turbines and subsequently, the generators.

Gas & Flame Hazards in Geothermal Power Generation

While the source for geothermal power is clean and the by-products are limited, the process does have its hazards. In dry steam and flash steam processes deep wells have the potential to draw a mixture of gases, notably carbon dioxide (CO2), hydrogen sulfide (H2S), methane (CH4), and ammonia (NH3). If these gases are released within the facility or accumulate they could cause significant harm to facility workers.
Within the binary cycle process the second substance [hence the name binary] with a lower boiling point than water is added to the geo-heated steam, is commonly dissolved pentane. Due to the low boiling point this additive flashes to a vapor. Since a fuel, oxygen, and ignition source are present the potential for an explosion exists.

Solutions for Geothermal Power Generation Hazards

Installation of reliable fixed gas detection helps ensure a safe production environment. Fixed gas detectors with the appropriate sensor should be installed in all production and control room areas where workers are present as each of the potential gases hazards could cause harm to plant workers. Where methane or pentane gases are potentially present high-performance combustible gas detectors should be installed along with electro-optical flame detection.