Case study - Heat-to-power application using a Dreyer & Bosse CHP power unit with an internal combustion engine


Courtesy of ElectraTherm

Location: Trechwitz, Germany
Site Gross Power Output Range 500kWe + 30-35kWe from ElectraTherm ORC
Thermal Heat Input Range:  375-450kWt
Hot Water Input Range:  90-95°C (118-203°F)
Hot Water Flow Range:  39 m3/hour (172 GPM)
Ambient Temperature: 0-15°C (32-59°F)
Date Commissioned: Q2 2012

ElectraTherm installed a Green Machine in Germany at a biogas power generation facility to produce additional electricity without additional fuel or emissions. The site is producing biogas through anaerobic digestion to fire an 800kWe Dreyer & Bosse CHP with an MWM internal combustion engine that generates electricity to sell to the grid. The current output of the engine is 500kWe due to gas volume available, but with the inclusion of the Green Machine, excess engine heat will now be used to generate approximately 7% more electricity. This is the first application in Germany where an Organic Rankine Cycle (ORC) is incorporated into a biogas facility meeting the 60% thermal requirements to qualify for Germany’s EEG 2012 bonus feed-in tariff rate. The Dreyer & Bosse CHP together with the Green Machine allows the entire site’s electrical production to qualify for the higher rate which equates to a very attractive payback period. 


“Germany’s 2012 feed-in tariff rate rewards biogas facilities that utilize 60% of the thermal heat load in their processes,” said Markus Heyde, Project Manager for Etalon. “Adding the Green Machine to this site helped us reach the 60% requirement, and the incentive enables an attractive payback.”

ElectraTherm’s Green Machine generates distributed power from waste heat. Hot water enters the Green Machine at 90-95°C, where it heats a working fluid into a pressurized vapor. The high pressure vapor expands through ElectraTherm’s patented twin screw power block, spinning an electric generator rated for 30-65kWe output. After turning the twin screw expander, the vapor is condensed back into a liquid through the use of an external air cooled condenser. After condensing, the working fluid flows back to the evaporator to repeat the process.

The anaerobic digestion process at this site uses a maize and manure mix as the “fuel” for the anaerobic digestion process. The maize and manure are loaded into a self-feeding hopper. From the hopper, the resulting biomass is pumped to the digester, where methane is produced through anaerobic digestion.The raw methane is monitored and filtered by Dreyer & Bosse equipment ie., gas cooler and charcoal filter to remove impurities which can then  safely  fuel the engine for long term reliability.

The Dreyer & Bosse CHP 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 CHP is used to heat the anaerobic digestion process, and excess heat not needed to sustain the anaerobic digestion process is utilized by the Green Machine to produce fossil-fuel free electricity 24/7.

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