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  Description of a Cofermentation Biogas Plant  
  To improve economy of biogas plants some owners decide not to digest manure alone but to take other organic substances - so-called coferments - as well. Typical coferments are fats, market wastes, spice residues, residues from food industry and many similar substances. The operator of the cofermentation biogas plant increases his earnings in two ways: first, just by taking the coferments from the person who wants to dispose them and second, through higher biogas production.  
       
  Cofermentation biogas plants are generally (much) larger then farm-scale biogas plants. Sometimes they still conform to the agricultural standards but most often to the industrial ones. In Germany many large-scale cofermentation biogas plants have been constructed at a location central to several (large) farms. All these surrounding farms deliver their manure to the plant. Additionally coferments are delivered. The standard ratio is about 3:1 to 2:1 for manure and coferments. top
       
  Agricultural standard cofermentation biogas plant  
  Cofermation Biogas Plant  
       
  The manure from all the surrounding farms is delivered by trucks or pumped to the cofermentation biogas plant. The coferments are delivered by truck. These trucks are unloaded in sumps which are normally closed to reduce odour emissions and opened only for adding the coferments. For further reduction of odours sometimes all deliveries are made within a closed hall. At first the coferments are ground, hygienized and mixed with manure. Hygienisation is most often performed at 70° C for one hour with a maximum particle size of 1 cm. The homogenisation with manure is performed in a mixing tank with strong agitators.  
       
  After this pretreatment all the organics are pumped into the digester. Normally large tanks are constructed out of coated steel. Coatings are either enamel or epoxy. Most tanks are bolted together. Standard digestion volumes of cofermentation biogas plants range from 500 m³ to several thousand m³. Mixing is sometimes done by a centrally located mixer on top of the roof, sometimes by submersible stirrers.  
       
  The biogas produced is used in gas or diesel gas engines. Power can be several MW. Large-scale cofermentation biogas plants have emergency flares in case the engine(s) is (are) not in operation and biogas has to be burnt. The gas system may include a blower, condensate trap, desulfurisation and so on. Everything is controlled by a gas system control unit.  
       
  Digested manure is pumped into a standard manure storage tank. An ever-increasing number of these tanks are covered with a roof to collect as much biogas as possible. Although the gas production inside manure storage tank is not large, it is worthwhile to collect it. Some of the roof incorporate biogas storage membranes.  
       
  All large-scale cofermentation biogas plants are controlled by an overall process control system. There are many devices for measurement and safety purposes. At night everything is run automatically, during the day there are operators on site - especially for repair and maintanance reasons and for taking the coferments and manure.  
       
  Large-scale cofermentation biogas plants are constructed for one reason only: to make a profit. Therefore, the plant must operate day and night. The investment costs may be as high as several million Euros. Depending on the input substrates the pretreatment has to be engineered and constructed. Indeed, depending on the input substrate and the pretreatment, the hydraulic retention time may vary. This has direct impact on the digester volume. Therefore, a lot of expert information is needed to construct such a large-scale cofermentation biogas plant. Krieg & Fischer offers this knowhow. top
       
  Please take a look at some Krieg & Fischer cofermentation biogas plant references  
   
       
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