Low-Temperature Geothermal Power Generation with HVAC Hardware

Halley K. Dickey
UTC Power, Redlands, CA

Demand is growing for affordable, domestic renewable energy sources. Geothermal power systems are one of the few renewable energy sources that can generate power at full capacity all the time, in contrast to solar, wind, and hydro, which are subject to variations in availability of input; sun, wind, and water level.

Geothermal energy from oil & gas resources is renewable because it utilizes the almost unlimited heat generated by the Earth's core. The hot water taken out of the earth can be re-injected, making it a renewable sustainable energy source, and can be extracted without burning fossil fuels such as coal, gas, or oil, making it a non-fossil fueled, zero-combustion, zero emission energy source.

UTC has developed an power cycle utilizing an refrigerant instead of water or steam. Being refrigerant based, commercial off-the-shelf air-conditioning and refrigeration equipment can be simply used for the system.

The turbine is nearly identical to a standard centrifugal vapor compressor used in water-cooled chillers. The shell and tube heat exchangers; used for the vaporizer and condenser, are nearly identical to heat exchangers found on a standard water chiller. The combination of equipment and supply chain synergy has created an extremely cost effective geothermal power plant.

Closed-cycle plants, like PureCycle, using geothermal or co-produced fluids, can generate 225 kW of electrical power, and essentially release no emissions:
- The PureCycle system can operate on a range of resource temperatures from 165°F (74°C) to 300°F (149°C).
- UTC Power’s PureCycle geothermal systems, have achieved ~99% availability in the field.
- The PureCycle geothermal system enables oil & gas wells deemed unproductive to become viable energy resources.
- Modular skid mounted packages can be sized and deployed according to need, reducing onsite installation.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas