Jun 17, 2014

Level Control Applications for Geothermal Power

Geothermal reservoirs located deep underground provide powerful sources of heat energy. Drilling a geothermal well to a reservoir brings hot water and steam to the surface, where it is valued as a source of renewable energy. The three principal uses of geothermal power are electricity generation, geothermal heating and geothermal heat pumps. In these systems, there is a wide range of applications that require reliable level measurement and control for efficiency and safety.

GEOTHERMAL POWER GENERATION
Geothermal electricity can be produced at dry steam plants, flash steam plants and binary cycle plants. Dry steam plants use steam piped directly from a geothermal reservoir. Flash steam plants take high-pressure hot water and convert it to steam. As the water rises, the pressure is reduced and the water flashes to steam. Binary cycle plants take heat from the geothermal water and transfer it to an organic fluid (a butane or pentane hydrocarbon) with a low boiling point in a high-pressure heat exchanger known as a vaporizer. The heat transfer causes the second (or “binary”) liquid to turn to steam.

Geothermal heating is the direct use of geothermal heat for space and process heating applications. Industrial applications include zinc and gold mining, desalination, milk pasteurization and food dehydration.

Geothermal heat pumps use the Earth’s constant temperatures to heat and cool buildings by transferring and removing heat into buildings according to seasonal needs.

GEOTHERMAL LEVEL APPLICATIONS
1. STEAM/BRINE SEPARATOR: To achieve better conditions for turbine operation, a reservoir’s steam and brine (salt water) is separated into streams where the brine water and particulate matter settle out and the steam vapors rise. The steam collects at the top of the separator where it is removed. Liquid level control modulates the amount of water that is drawn off.
Recommended Continuous Level Technologies: Guided Wave Radar, Displacer Controller
Recommended Point Level Technologies: External Cage Float, Thermal Dispersion

2. DEGASSER TANK: Geothermal hot water is often routed through a degasser – a large insulated tank equipped to remove organic gases and provide displacement with air or nitrogen. Degassing operations provide treatment by way of carbon adsorption, thermal/catalytic oxidization, combustion, vacuum induction or by a series of condensers.
Recommended Continuous Level Technologies: Guided Wave Radar, Displacer Controller
Recommended Point Level Technologies: External Cage Float, Thermal Dispersion

3. WATER STORAGE TANK: Water tanks include those for heated water, cooling water, and wastewater. Direct heat use applications require heated water storage. Spent geothermal fluids with high concentrations of chemicals are stored prior to treatment and reinjection into the reservoir. Hot water can be cooled in special storage tanks to avoid modifying the ecosystem of natural bodies of water prior to reinjection.
Recommended Continuous Level Technologies: Guided Wave Radar, Displacer Controller, Pulse Burst Radar (Through Air), Ultrasonic
Recommended Point Level Technologies: Float Actuated, Ultrasonic

4. FLASH TANK: Hot water from the geothermal well enters a flash tank where the reduced pressure causes the water to boil rapidly, or “flash” into vapor. Water that remains liquid in the tank is returned to the groundwater pump to be forced down into the reservoir again. The vapor from the flash tank drives the steam turbine.
Recommended Continuous Level Technologies: Guided Wave Radar
Recommended Point Level Technologies: Displacer Switch, Thermal Dispersion

VAPORIZER: In these special heat exchangers, the geothermal fluid heats and vaporizes a secondary “binary” fluid, which is typically an organic liquid with a low boiling point. The organic vapor drives the turbine. The level of water in the tank must be monitored.
Recommended Continuous Level Technologies: Guided Wave Radar, Displacer Controller
Recommended Point Level Technologies: External Cage Float, Ultrasonic

Download our Level and Flow instruments for Renewable Energy Brochure.