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Where there’s muck…

In the village of Trechwitz, in rural Germany, an ORC unit is harvesting waste heat from a biogas plant that runs on the 45 tonnes of manure and slurry processed daily. RAC reports

The development of modern biogas plants in the region around Trechwitz, near Potsdam, started a few years ago, when father and son farmers Hergen and Timo Wessels looked to specify a biogas plant for their own farm.

Upon discovering there was no technology to match their plans, they developed their own concept for the needs of their farm.

The first plant completed by was in 2008, at Timo Wessels’ farm, but the concept proved so successful that the Wessels diversified their agricultural business into design, operation and maintenance of biogas plants.

The plant in Trechwitz was built to capitalise on the manure and slurry generated by a number of agricultural operations in and around the village.

Among these operations are the Wessels’ own cow barns, a riding stable and a chicken farm. “Every day, we process 45 tonnes of manure and slurry,” says facility manager Radko Doldzhev. “We generate about 500 kWh of power per hour. Since the plant has a total capacity of 800 kWh, there is still potential to generate more electricity.”

What makes this biogas plant distinctive is its use of Organic Rankine Cycle technology. From the beginning, Timo Wessels put a strong focus on operating the plant with maximum energy efficiency.

In co-operation with Potsdam-based energy consultant Etalon and US ORC specialist ElectraTherm, they put into operation a whole new concept of an ORC plant.

ORC denotes the process of driving steam turbines with a working fluid other than steam.

This process is used to generate electricity with the help of combined heat and power generation, eg in biogas plants.

ElectraTherm has designed a compact ORC unit called the Green Machine, which is able to generate electricity from low-temperature waste heat by using an organic working fluid (R245fa), using its proprietary technology.

ElectraTherm uses low-temperature waste heat (77 – 116 deg C) to produce pressurised vapour from the working fluid.

As the vapour expands, it drives a twin screw power block, which spins an electric generator to produce fuel-free, emission-free electricity.

The inclusion of the Green Machine ORC can increase engine electrical efficiency up to 8 per cent and uses heat that would otherwise go to waste, the company says.

Green Machines are sized up to 110 kW based on customer needs, and are available as turnkey packages.

ElectraTherm says its ORC technology also works well with satellite combined heat and power (CHP), district heating systems and geothermal applications.

New opportunities

ElectraTherm vice-president of sales Rob Emrich says: “The small-scale ORC market is still fairly new and this project is an excellent demonstration of our proven technology.

This plant is one of 41 that is equipped with a Green Machine to date.”

On top of the machine room, there are two dry coolers from Güntner’s GFH series, comprising one unit with a single fan, serving as the oil-mixture cooler, and a unit with four fans serving as the emergency cooler.

Before the Green Machine was installed, the entire waste heat of the motor was dissipated into the ambient air by the four-fan dry cooler, but now the waste heat is used to generate electrical energy, so this emergency cooler is only used during maintenance work on the block heating station.

The working fluid used in the ORC process of the Green Machine is being cooled by a Güntner series GVD condenser, developed especially for the energy industry.

This V-shape coil condenser has a very small footprint compared to its power density and can be adapted to any application due to its modular design, the manufacturer says.

There are eight basic models with a high flexibility of fin and tube geometries and a large variety of heat exchanger coils, allowing for the design of the optimally suited unit.

The units are delivered by truck ready for operation, so that no installation of individual components on site is necessary.

The plant in Trechwitz has been running to design specs since its commissioning. Last year, the plant was retrofitted and the Green Machine equipped with a sound-attenuated enclosure reducing the sound pressure level to 71.6 dB (A).

ElectraTherm has extended its product line to offer 35 kW, 65 kW and 110 kW options, available as standalone units or in series.

For each capacity, Güntner offers the corresponding GVD cooler with the appropriate nominal capacity.  

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