The drying of digestates is a conclusive heat utilization concept at biomass plants. Due to the sales of the heat in combination with a bonus, the efficiency of biomass plants increases.
In addition, digestate drying can be the solution for nutrient problems in areas with high livestock production or with agglomerations of biogas plants. The use of excess organic nutrients can take place due to the low-cost transport of the concentrated substrates to plants and regions with needs for nutrients.
An additional positive side effect is the reduction of the investment volume due to reduction of the final storage capacities.
Digestate drying/digestate processing makes a crucial contribution towards an optimal utilisation of the chances that are given for agriculture and the environment due to Renewable Energies.
The dryers have been developed particularly for manure and digestate drying, as well as the drying of related products. The plant length is 12 – 26m, the width is approx. 4 – 6m; in addition, several dryers can be installed on top of each other.
They are horizontal belt dryers with a circular belt made of two inverse layers of perforated steel sheet sections, which ensures an optimal air passage.
Waste heat is suitable for drying air, which develops in the BHKW during the conversion of biogas into electricity. The belt, or rather the steel sheets are moved by chain drive. The transport speed is variable. The throughput of the continually operating dryer depends on the input material, the desired drying goal and the available heat, among other things. With the surplus heat waste of a biogas plant with a capacity of 500kW, a water equivalent of 4,000 – 6,000m³ can be evaporated annually.
In order to achieve an optimal drying result, the goods fed into the dryer must be drip-free. For this reason, part of the already dried digestate is added to the liquid digestate from the biogas fermenter before it is applied to the drying plates.
The goods to be dried pass through the belt dryer twice in opposite directions before a defined quantity of the dried goods with a dry matter content of 80-85% reach the product storage.
The end product has the structure of loose bulk material and can be directly used as fertiliser or can be further refined. For example, by pressing or granulating, a homogeneous granulate with a grain diameter of 4 – 5 mm is formed.
The automatically controlled exhaust air decontamination system guarantees a reliable compliance with the limits of TA Luft.
