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Smart dry digestion plant

A new dry digestion plant is being built in Kirchberg, Hunsrück around 40 km west of the German city of Mainz and will process around 15,000 metric tons of source-separated organic waste a year.

The municipal operating company, Rhein-Hunsrück Entsorgung (RHE), has awarded the contract to build the facility to a consortium consisting of Swiss cleantech company Hitachi Zosen Inova (HZI) and the German construction and composting technology specialist Eggersmann.

Eggersmann will be in charge of the conveying equipment, construction, and biological drying system, while HZI will supply its Kompogas technology, the digestate separation and storage components, as well as the combined heat and power units. The HZI/Eggersmann bidding consortium has won the pan-European public tender on the strength of the most cost-efficient solution.

The new facility will already be the second Kompogas installation in the Rhein-Hunsrück area. The first went into operation back in 1997.

“The old Kompogas plant has been operated by a private operation company and has given us exceptional service over the last 20 years, doing a great deal to assure reliable waste disposal in our region,” explained RHE managing director thomas Lorenz.

Design for greater efficiency
The plant has various technically sophisticated features: The organic waste delivered to the plant will first be prepared in a special separation process before being fed into the digester for anaerobic digestion, and subsequently sieved again. This procedure will maximise the quality of the 10,000 or so metric tons of liquid digestate produced for use as high-grade fertiliser in agriculture.

The digestion process will yield around 1.85 million Nm3 of biogas annually, which will be used to generate 4.26 million kWh of electricity. Another special feature of the Kirchberg plant will be two cogeneration units configured to generate electricity as it is needed:

While one of the units will assure a constant supply of heat and electricity to the plant, the other will only switched in during the day if electricity grid demand is particularly high. The waste heat from the cogeneration units will also be fed into an ORC turbine to generate additional electricity, further boosting the overall efficiency of the plant.