Organic Rankine Cycle
This project is a collaborative research effort among ACEP, Tanana Chiefs Conference, and Alaska Power and Telephone.
One of the most promising technologies for decreasing fuel usage of diesel-powered electric generators in rural Alaska communities is Organic Rankine Cycle (ORC) engines.
These heat-to-power generating systems capture excess heat fromlow-quality heat sources (such as diesel engine jacket water, biomass boilers, and geothermal sources) to generate between 30 and 65 kilowatts of emission-free electricity. In the case of rural Alaska villages, heat from the diesel generators in the local power plant can be captured from the jacket water and utilized in ORC engines to boost overall power plant efficiency. ORC technology has been used for decades on large, industrial power applications, but smaller units compatible with rural Alaska power plants are still in the development stage.
ACEP researchers conducted an initial analysis of small ORC units available on the market. The GreenMachine unit from ElectraTherm was an ideal candidate for testing because it was close to a commercial release and the company was interested in testing the device in the harsh Alaskan environment. The Green Machine was also selected with rural Alaska villages in mind because the operation and maintenance steps are actions that a village diesel generator operator would be familiar with.
The Green Machine ORC unit was installed at the UAF power plant in November-December 2011. The unit was run for 600 hours under conditions designed to simulate the operating conditions of a typical village diesel generator.
Laboratory testing under controlled conditions showed that the ORC unit can consistently generate a gross power of 50kW and a net power of 47.1 kW under the conditions of sufficient temperature and flow rate of the heating source and cooling source.
Current Testing Underway
After the Green Machine proved promising in a controlled laboratory environment, the next step was to test under real-world conditions of a rural village power plant. ElectraTherm was also interested in the performance data that ACEP would collect during the device’s field deployment.
Tok was selected in partnership with its utility, Alaska Power and Telephone (AP&T), which manages several power plants statewide. The Green Machine was installed at AP&T’s Tok power plant, in the summer of 2013. AP&T agreed to contribute its expertise and trained man-power at the test site.
The Green Machine as installed, utilizing waste heat from the Tok diesel cooling system, has the potential to generate over 200,000 kWhrs per year, saving over $60,000 per year in fuel. The fuel savings are directly reflected in the Energy Charge component of the Tok power bills. While the energy generated by the Green Machine is only 2% of the total, it provides direct benefit to the Tok rate payers, utilizing energy that would otherwise be lost.
If the Green Machine performs as well in Tok as it has at the UAF power plant, it will be clear that the Green Machine, and possibly other small-scale ORC systems, are feasible for use in other Alaska power plants.
Photo 1: This project was conducted at the UAF campus heat and power plant by removing excess steam from the campus heating loop. Courtesy of Todd Paris, UAF.
Photo 2: ACEP researcher Vamshi Avadhanula describes his work on the Green Machine laboratory testing. Courtesy of Todd Paris, UAF.
Photo 3: The Green Machine was installed at the Tok Power Plant and is producing power. Courtesy of Alaska Power & Telephone.