Biogas Waste Heat to Power in Austria

Application: Engine Waste Heat Recovery
Power Output: 32 kWe
Thermal Input : 450 kWth

Hot Water Temperature:  93°C
Hot water Flow Rate: 8 l/s

ElectraTherm installed its first ORC heat recovery system, the Power+ Generator, in Austria at a biogas power generation facility to produce additional electricity from biogas waste heat without additional fuel or emissions. The system produces biogas through anaerobic digestion to fire a 500kWe GE Jenbacher 312, generating electricity to sell to the grid and heat crops during harvest. With the inclusion of the Power+, excess engine heat will now be employed to generate additional electricity. This is the first application to our knowledge where an Organic Rankine Cycle (ORC) is incorporated into a biogas facility to supplement this impressive and efficient use of renewable energy.

ElectraTherm’s Power+ generates distributed power from waste heat. Hot water enters the Power+ at 190°F (88°C), where it heats a working fluid into pressurized vapor, using ORC technology. The high pressure vapor expands through ElectraTherm’s patented twin screw power block, spinning an electric generator and creating up to 32kWe. The vapor is cooled by water from a liquid radiator and condensed back into a liquid, then it is pumped to the evaporator to repeat the process.

 

The anaerobic digestion process begins by gathering and piling maize from nearby corn fields. Whole corn plants are ground, stored and then loaded into a self-feeding hopper. From the hopper, the maize biomass is pumped to the digester, where methane is produced through mesophilic anaerobic digestion. The methane in turn fuels the engine. Approximately 200 Hectares of corn are required annually for producing 500kWe from the Jenbacher engine.

“In addition to increasing plant efficiency, the power generated by the Power+ Generator meets feed-in tariff requirements by utility, which can pay up to 18.5 Euro cents per kWe,” says Karl Leisch, President of WTI and Project Developer. “The value of the Power+ Generator provides a significant revenue stream for 20 years.”

The anaerobic digestion process requires heating of the anaerobic digester tanks, to keep the bacteria at the appropriate temperature to effectively decompose the biomass to create methane (biogas). The system is designed to recover as much waste heat as possible to sustain the anaerobic digestion process as well as produce fuel free, emission free electricity using the ElectraTherm Power+.

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 sustain the anaerobic digestion process and the seasonal grain drying is utilized by the Power+ to produce fossil-fuel free electricity 24/7 as required.

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