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“Green machine” installed at Austria biogas plant

US firm’s machine boosts electricity production at Austrian biogas plant

ElectraTherm, a renewable energy company based in Reno, Nevada, has installed its first Green Machine in Austria at a biogas power generation facility to increase electrical production at the site without adding fuel or emissions. The site at Inning, Austria produces biogas through anaerobic digestion to fire a 500kWe GE Jenbacher 312, generating electricity to sell to the grid while using heat to dry crops during harvest.

With the addition of the Green Machine, excess engine heat will now be used to generate additional electricity, Electratherm said. “This is the first known application where an Organic Rankine Cycle (ORC) is incorporated into a biogas facility to supplement the efficient use of renewable energy,” the firm added.

The Green Machine generates distributed power from waste heat, and patent pending technology offers “unprecedented efficiency and flexibility” for biogas power plants with anaerobic digesters. Hot water enters the Green Machine at 190°F (88°C), where it heats a working fluid into a pressurised vapor, using ORC technology.

The high pressure vapor expands through ElectraTherm’s twin screw power block, spinning an electric generator and creating up to 65kWe. “For the size engine and available waste heat at this site the power generated averages at 32kWe,” the US firm said. Since its commissioning in September 2011, the machine has operated for approximately 3,000 hours.

The Jenbacher 312 engine is equipped with an exhaust gas heat exchanger designed to combine both the heat available in the exhaust and the heat available in the jacket water into a single heat stream. The waste heat from the engine is used to heat the anaerobic digestion process, as well as dry maize after harvest. The excess heat not needed to optimise the anaerobic digestion process and the seasonal grain drying is used by the Green Machine to free electricity 24/7 as required.

Karl Leisch, president of WTI and project developer noted the power generated by the ElectraTherm unit also meets feed-in tariff requirements by the utility, which can pay up to EUR 0.185/kWe. “The value of the Green Machine provides a significant revenue stream for 20 years,” he said.