Case study - Green Machine uses biomass to put power back on the grid


Courtesy of ElectraTherm

St. Helena Island, South Carolina
Gross Power Output: up to 43kWe
Thermal Heat Input: 200 - 500kWt
Hot Water Input Range: 160 - 235°F
Hot Water Flow: 150 GPM    
Cold Water Input: 68°F
Cold Water Flow: 150 GPM

In fall 2010, American Capital Resources Company installed ElectraTherm’s heat-to-power Green Machine, for generating power from its ornamental tree farm located on St. Helena Island, South Carolina. There, solid wood waste is high-temperature combusted and the heat is converted to clean electricity. The power generated is exported to SCANA CorpoYouTube_SC[1].jpgration’s subsidiary, South Carolina Electric and Gas (SCE&G) via a transformer connected to the grid. American Capital Resources Company (ACR) engaged the local utility early on to utilize net metering to promote clean energy generation. This is the only biomass renewable generator on SCE&G’s net metering program. The project has been so successful, SCANA even produced a video highlighting the development, available in the link above.

“[ACR] sells the energy [it] generates back to us. We put it back on our system and distribute it to our network. And we’re paying for that energy,” said Casey Logan, SCE&G Power Quality Engineer.

Biomass power generation from non-fractionalized virgin solid waste wood marks the first in the United States to use refrigerant-based distributed power generation from recovered heat. This is also the first U.S. biomass application of ElectraTherm’s Organic Rankine Cycle (ORC) technology powered by its patented Twin Screw Expander.

ACR purchased the hydronic boiler and integrated the ORC with it after seeing the extensive amount of waste wood in South Carolina resulting from routine timbering/logging operations as well as from arborists and land clearing processes.  ACR realized that trillions of BTUs were being wasted for lack of a better alternative.

The hydronic unit connects to ElectraTherm’s Green Machine to leverage the heat from the hot water to generate clean electricity.  Unlike other forms of renewable energy, such as solar thermal and wind, biomass can be run continuously: 24 hours a day – 7 days a week.

ElectraTherm’s Green Machine uses a closed-loop ORC to create pressure by boiling a working fluid into a gas. The gas expands and turns a twin screw expander, the power block, which drives a generator to produce electricity. The machine is robust and has low maintenance requirements using automated controls, much of which can be performed off site through remote monitoring.

While ElectraTherm generally sizes an air cooled condenser for projects to serve as the cooling source for the working fluid, ACR utilizes the geothermal cooling properties of the Earth by extracting 68°F aquifer water year-round before returning it via an injection well to serve the same purpose, thus eliminating the additional capital. Additionally, ACR looks to expand upon this project by adding a CHP (Combined Heat & Power) component. It has plans for heating an adjacent greenhouse that will use the rejected heat from condensing to provide 100°F water for winter vegetable growing.

ACR expects many more similar projects in areas with ample wood waste, especially in South Carolina and other states that reward clean energy applications with subsidies and incentives. In many circumstances, the waste wood is considered a nuisance and sent to landfills at an expense, literally paying to waste this abundant resource.

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