A biogas-generation facility in Austria has been running an ElectraTherm “green machine” since the fall of 2011 to increase electrical production without adding fuel or emissions.
The site produces biogas (methane)
through anaerobic digestion to fire a 500kWe GE Jenbacher 312, which generates
electricity to sell to the grid and uses the waste heat to dry crops during
harvest. Reno, Nev.-based ElectraTherm says this is the first known application
where an organic Rankine cycle (ORC) is incorporated into a biogas facility to
supplement efficient use of renewable energy.
The Electratherm unit generates
distributed power from waste heat. Hot water enters the unit at 190°F (88°C)
where it heats a working fluid into a pressurized vapor using ORC technology.
The high pressure vapor expands through a twin-screw power block, spinning an
electric generator and creating up to 65kWe. For the size engine and available
waste heat at the Austrian site, the power generated averages 32kWe. Since its
commissioning in September 2011, the machine has operated approximately 3,000
The production process requires heating
of the anaerobic digester tanks, which keeps the bacteria at the appropriate
temperature for effective biomass decomposition to create methane. The system
recovers as much waste heat as possible to sustain the anaerobic digestion
process as well as produce both fuel- and emission-free electricity.
The Jenbacher 312 engine has an
exhaust-gas heat exchanger to combine into a single stream both the heat
available in the exhaust and the heat available in the jacket water. The
engine’s waste heat then heats the anaerobic digestion process and dries maize
after harvest. The excess heat not used for anaerobic digestion or seasonal
grain drying is used to produce fossil fuel-free electricity 24 hours a day,
seven days a week, as needed.
The power generated by the green machine
meets the utility’s European feed-in tariff requirements, paying up to
approximately 24 cents per kWe, says Karl Leisch, project developer.
'Green Machine' Turns Engine Heat into Electricity
May 30, 2012