Low-Cost Biogas Upgrading Technology
As demand for pipeline and vehicle-quality biomethane increases, so does the need for cost-efficient, scalable biogas upgrading technologies suitable for anaerobic digestion facilities with low biogas flows, such as those on farms in North America. Now the Swedish Institute of Agricultural and Environmental Engineering (JTI) think they have found the solution.
For this research, JTI installed their mobile pilot-scale 5m3 anaerobic digester (pictured), a desorption column and wood-ash filter at a commercial on-farm anaerobic digestion facility in Sweden. The pilot-scale digester was operated with an organic loading rate of 2.6kgVS/m3/day and a hydraulic retention time of 25 days. Biogas production from the pilot-scale digester was 1.08m3biogas/m3/day.
After the pilot-scale digester reached stable performance, in-situ methane enrichment was initiated by recirculating digester sludge from the pilot-scale digester through the desorption column. The desorption gas (outdoor air) was injected at the bottom of the column. After reaching stable conditions indicated by gas composition, the pilot-scale digester’s biogas outlet was coupled to the wood-ash filter (up-flow). The combined desorption column and wood-ash filter system was operated for approximately three weeks.
The in-situ methane enrichment process increased methane concentration of the biogas from 60% to 81%, while removing 72% carbon dioxide. The process also reduced hydrogen sulfide concentration by an average of 83%. Inclusion of the wood-ash filter removed additional carbon dioxide and hydrogen sulfide from the biogas, increasing methane concentration to 97% (the remaining balance being mainly nitrogen and water). Methane loss during this process represented <2 % of total methane production. See Table 1 for results.
Over the coming months JTI will be completing their research by evaluating the digestate composition and nitrogen balances. Analysis of the carbonized ash will also be made, while sizing and cost estimates will be completed for use at a commercial digester of 1,000m3. These results will be made publically available in the coming months on the Hallbar website.
In 2015, JTI plan to install their in-situ methane enrichment and wood-ash filter technology at a commercial-scale anaerobic digestion facility in Swedish. Additionally, the search is now on to find a suitable commercial digester in North American to install the in-situ methane enrichment and wood-ash filter technology; thereby enabling parallel trials between the two sites. While the North American host will be required to cover some costs associated with this trail, it is expected that at least half will be covered through funding.
If you are interested in being considered as a North American host site, or if you know of anyone that might be interested, please contact Us.