Production of biomethane from biogenic residues
Demonstration plant to be built in Goldenstedt, Lower Saxony
The company New Power Pack, the German research centre Forschungszentrum Jülich, Fraunhofer UMSICHT and the transmission system operator OGE have teamed up for the research project BiRG (BioReststoffGas) to build a demonstration plan with capacity of 300 kg/h that will produce approx. 100 m3/h of synthesis gas to test the production of biomethane using biogenic residues. Alongside trialling a demonstration plant capable of continuous load conditions, the team also plans to develop alternative process conditions and variants for a wide selection of possible raw materials and raw material combinations. The plant is scheduled to go into operation in Goldenstedt in the first quarter of 2022.
The research project has three aims: Firstly, the biomethane is to be utilised for energy, for which it will be fed into the existing gas pipeline network and replace fossil-based natural gas. Secondly, the sole by-product resulting from the pyrolysis process is biochar. Biochar is a sought-after raw material, since the nutrients it contains boost soil fertility. In addition, it remains in the soil for a long time and, acting as a carbon store, has a negative carbon balance. Biochar is therefore used for the purpose of soil improvement. Thirdly, the project partners plan to develop an on-site solution for recycling biogenic residues for municipalities and agricultural enterprises as an alternative to the previous costly disposal method of shipping the residues into regions with nutrient-poor soils.
Biogenic residues as base material
In Germany, large quantities of biogenic residues accumulate every year from agriculture, municipalities and industry. These include sewage sludge, fermentation residues from biogas plants, liquid manure or even chicken droppings, straw, nutshells, and horse and turkey dung. The use and spreading of the first three abovementioned residues on agricultural land contribute to nitrate pollution of groundwater and are now subject to restrictions is most regions. Disposal is an expensive undertaking for local agricultural and industrial businesses and for municipalities.
An on-site solution is therefore required for local utilisation as an alternative to expensive transportation to regions whose soils lack nitrogen and other nutrients. This is where the energetic use of biogenic residues for generation of renewable energies comes in.
Operating principle of the demonstration plant
The biogenic residues are converted into biomethane through a pyrolysis process, a purification stage for the resulting raw gas, a water gas shift reactor and methanation. In the pyrolysis stage, the conversion of the biogenic residues into raw gas and biochar takes place at very high temperatures. Part of the raw gas is recycled and used to fuel the pyrolysis. In the purification stage and the water gas shift reactor, the raw gas is prepared in such a way that single-cell microorganisms, so-called archaea, convert carbon dioxide and hydrogen into methane in the microbial methanation process with the addition of hydrogen.