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Biogas in Ireland

On the island of Ireland, there are now around 90 biogas plants, although the development in Northern Ireland has made significant progress with most of the facilities built there. One of the reasons for this may be that over 80% of the Republic is used as grass and pasture land, but liquid manure is only available where livestock is kept indoors. Anyone operating a biogas plant here must therefore look for other types of input materials. Like BioCore Environmental Ltd who have identified the biogas potential of sewage sludge, organic residual materials and waste and have developed an anaerobic digestion (AD) plant to produce renewable electricity and fertilizer, located in County Roscommon. Having previously developed and operated a large-scale AD plant in England, BioCore sold their share in this plant in 2016 to focus on leveraging their expertise in the Irish market.

BioCore: transforming waste into valuable raw materials

Although there is a proud number of 13,800 biogas plants in Europe, they are not evenly distributed across the continent. More than 9,000 of them are located in Germany alone. In France and Slovakia, however, construction work is underway, in Italy the number of plants has more than doubled from 521 to 1,264 within just one year, and the construction of biogas plants is also being promoted in United Kingdom.

While Ireland has lagged far behind its European compatriots in terms of AD plant development, BioCore saw ample potential for this technology to be deployed. But it was not easy. It took ten long years from the development and planning to the commissioning of BioCore’s 1 MW biogas plant, which was ultimately constructed near the town of Ballaghaderreen in County Roscommon in western central Ireland. The main components of the BioCore plant in Roscommon are a 2,500 m3 digester, another 2,500 m3 post digester and two tanks for digestate with a total capacity of 7,000 m3.

Waste as bacterial feed

Agriculture in the grassland region is dominated by sheep and cattle farming, arable farming plays only a minor role. That’s why BioCore’s concept does not even provide for the use of agricultural input materials such as energy crops, dung and slurries. They are primarily interested in transforming a wide range of the organic and bio waste available in the region into valuable energy. They therefore attached great importance to efficient and flexible plant technology already during planning. This technology was selected and installed in cooperation with the German biogas plant constructor BioConstruct. Two combined heat and power units (CHP) are available to convert the biogas into electricity and heat. The plant feeds electric energy into the grid, whereas the heat is used internally. In addition to heating the various tanks and reservoirs, it is also used to treat the digestate.

The PreMix solid matter feeder from Vogelsang proposed by the plant developers is tailor-made for BioCore’s plant. The liquid feeding system PreMix is capable of mashing a wide variety of input materials before feeding the treated material into the digester. It is currently mainly fed with sewage sludge from the surrounding sewage treatment plants – BioCore work closely with Irish Water. Because the sewage treatment plants of the water board, which are mainly rather small, do not usually have anaerobic sludge stabilization, which is why the sewage sludge still contains a great deal of energy. However, the sludge is dewatered on-site at the plants to improve its transportability. Then approximately 20,000 tons of sewage per year are used to generate energy at the BioCore biogas plant.

The feeding process itself is automated. The substrates are fed by means of screw conveyors from the pusher floor container used as a storage container into the PreMix. The combination of a wet cutter and progressive cavity pump mashes them with a liquid to form a homogeneous suspension and the particle size of the contained solids is reduced, which allows the suspension to be pumped quite simply through a pipe into the digester and, if necessary, into the post digester. Thanks to the fact that the PreMix is equipped with an appropriate Performance Control Unit (PCU), it is also irrelevant that the sewage sludge has strongly varying viscosities and properties depending on its origin. The sensors of the monitoring unit record all important data, on the basis of which the PreMix settings are automatically adapted to the substrate so that it is always treated at a consistent level. James Russell, Technical Director of the BioCore plant is happy about his decision to use the PreMix. Particularly because of the first of four process steps during solid matter feeding: the separation of heavy material before further treatment and the pump unit. This is because the sewage sludge contains considerably more stones and metal parts than was expected – even traffic signs! Every week the heavy material separator has to be emptied. The operator is therefore currently considering equipping the solid matter feeder with the Debris Removal System from Vogelsang. With the help of this system, the heavy material could be discharged during operation.

“We chose Vogelsang because it is an established name with a good reputation and we can rely on the technology. The PreMix mashes and treats the substrates reliably and evenly. The RotaCut shreds the material to be hygienized accurately to meet the requirements of class-A quality biosolid matter.”
James Russell, Technical Director of BioCore Roscommon

In addition to the sewage sludge, grease from grease traps ensure an increased gas yield at BioCore. Furthermore, food waste is to be fermented in the digesters. The technology has already been designed for this purpose. The PreMix can also treat and feed in this input material without any problems. At the end of the process, a pasteurization process and a downstream separator ensure that the end product can be prepared
in compliance with the so-called class-A biosolids requirements. The strict separation of what is referred to as the black and white side with their own pipes and pumps prevents contamination of the digestate after this final treatment. A pump with a downstream RotaCut wet cutter has been installed to fill the pasteurization tank. This is because size reduction of all solid matter contained in the suspension to less than 12 mm in two dimensions is mandatory before heating as part of the hygienization process. This is the only way to ensure that it is heated thoroughly and the germs and bacteria in the suspension are mortified. The energy for this comes from the waste heat of the combined heat and power units of the biogas plant. BioCore relies on a RotaCut RCX-48G with a 10 mm honeycomb sieve for the size reduction of the solid matter. The particularly fine  treatment has another advantage in that the suspension can then be dewatered more easily. And while the liquid phase is fed back into the digester, the dewatered portion replaces the artificial fertilizer in the agriculture in line with the principles of recycling management.

Attracting attention to biogas

The BioCore project has another important aspect for James Russell. He would like to show his compatriots, especially those from the region around the biogas plant, the advantages of biogas technology and how they can all benefit from regionally self-contained cycles. He demonstrates this commitment by inviting his community and interested parties to the biogas plant, showing them the installations on-site and explaining how the plant works. He also gives lectures, e.g., to the members of the Irish Cattle & Sheep Farmers’ Association (ICSA), in order to increase the acceptance of biogas technology. Because a higher acceptance and awareness will provide positive attitudes and the progression of biogas plants in Ireland and especially to support James Russell’s new projects. The ambitious Director is already working to develop a number of new AD plants throughout Ireland. And he will also rely on Vogelsang components – like 60% of all Irish biogas plant operators, by the way.

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