A holistic approach to digester care from anaerobic digestion experts FM BioEnergy has helped Vale Green Energy to maximise biogas production and reduce operational downtime at its two gas-to-grid AD plants. Since 2015, FM BioEnergy has supported Vale Green with a range of specialist services including silage additives, bespoke trace elements, iron supplements, consultancy and biogas leakage detection surveys, mitigating against peaks and troughs in performance and ensuring the plants’ output remain stable.
“Working with FM BioEnergy is an educational experience,” says Vale Green Energy’s Nick Reynolds.
A UK first
Located in Worcestershire, Vale Green Energy is a leading biogas plant operator with two gas-to-grid facilities. As well as producing green gas for the grid, both plants capture CO2 which is used in the food industry. Part of the Evesham Vale Growers group, the company also operates a large solar farm and grows salad and arable crops.
The company’s 1.5 MW AD plant, based at Spring Hill, was commissioned in August 2013 and was the first commercial gas-to-grid plant in the UK. It produces 500 kW of electricity and exports up to 7,800m3 of methane to the gas grid each day. A second 4.5 MW plant at nearby Rotherdale was commissioned in May 2015. This produces 1 MW of electricity and exports gas to the grid (up to 22,000m3 per day), while surplus heat is used by a neighbouring chicken business. Both plants also produce digestate which is used as a renewable biofertiliser on the arable farm.
Supercharged silage
Both AD plants are fed by energy crops, largely consisting of grass, wholecrop cereals and maize which is grown on-site and by other local growers. To ensure this feedstock is of a consistently high quality and that its biogas potential is maximised, all silage is treated with specialist AD silage additives from FM BioEnergy before being fed to the digesters.
“Vale Green use our Silasil additive range on all their forage crops – they apply Silasil Energy XD to their maize silage, and Silasil Energy BG on their grass silage,” explains Andy Lee, FM BioEnergy’s National Biogas Silage Specialist.
Nick Reynolds is responsible for producing feedstock for the Vale Green Energy AD plants and has seen first-hand the benefits of using the products: “We compared our own samples with the findings from FM BioEnergy’s labs and the results have given us real confidence in the Silasil additives,” he confirms. “I think the biggest benefit is the lack of heating when the clamps are opened, as we can potentially have several open at one time depending on how much third-party feedstock we’re using. We do everything we can to ensure best practice in the clamp, such as compaction and sheeting, but once we open it, we certainly see a difference from using Silasil Energy. In fact, such is our confidence in the product range that as part of our agreement with our third-party growers, we supply them with the silage additives to use.”
Andy Lee explains further: “Last year’s maize has preserved particularly well, with minimal dry matter losses. We know from analysis that as soon as the clamp is opened, silage begins to heat, losing biogas potential. Our Silasil Energy range prevents that; in fact, XD is the only biogas silage additive approved by the German Agricultural Society for increased methane yield and improved aerobic stability.”
Bespoke trace elements
As well as silage additives, FM BioEnergy also supplies Vale Green Energy with a bespoke mixture of trace elements for their digesters.
“Originally, the AD operator was using an off-the-shelf, bagged, granular trace element product, but the results were sometimes mixed,” outlines Tim Elsome, General Manager at FM BioEnergy. “So, in early 2021, we worked with Vale Green to develop a bespoke feeding plan based on the specific volumes and types of feedstock they were using. In addition, we switched them to a bespoke liquid product that is easier to apply with a lower dosage rate, which has delivered improved, more consistent results.”
Vale Green Energy’s plant manager has witnessed the difference this has made: “Every quarter, we analyse the material from the primary digesters. FM BioEnergy then use these results to blend the trace elements we need to the specific requirements of each of our sites. We certainly see a drop off in gas production if we are waiting for a delivery. The biological balance in the tank definitely benefits from having the right combination of trace elements.”
The company also uses an iron supplement from FM BioEnergy – BC.ATOX Scon – to control hydrogen sulphide (H2S) levels in the tanks, which can inhibit digestion and lead to equipment damage if left untreated. “Regularly using trace elements and iron reduces peaks and troughs in biogas output, meaning operation is more consistent and easier to manage,” explains Tim.
Expert consultancy
Rather than simply offering a supply of additives and trace elements, FM BioEnergy prides itself on its holistic approach to digester care. “We advise on the best holistic solution for an individual plant,” says Tim. “We’re not in the business of selling products our customers don’t need.”
To this end, the two companies maintain an ongoing, proactive dialogue to pre-empt and prevent problems before they start to affect smooth operation. For example, before making any changes to their feeding regime, the Vale Green team will first seek advice from FM BioEnergy, to ensure any alterations will not adversely affect their plants’ performance.
“The team at FM BioEnergy have widespread experience across the entire UK AD sector, so as well as commenting on our individual situation, they can put it into context by comparing it with things they may be seeing elsewhere,” explains Nick. “Working with FM BioEnergy is an educational experience; we’re learning something all the time, which is really useful.”
Preventing methane leakage
FM BioEnergy’s commitment to preventing issues, rather than rectifying them once they’ve occurred, extends to plant equipment as well as biological performance. Earlier this year, the company carried out a gas leakage survey for Vale Green Energy, which the AD operator confirms has been extremely beneficial.
“We commissioned FM BioEnergy to carry out a methane leakage survey on our plants, using their specialist equipment. We found it very useful as we are physically unable to see the leaks without the camera,” says the plant manager. “There were a couple of surprises, particularly in the plant room where the surveyor uncovered a leak directly underneath a sensor that was supposed to detect it. On the infra-red image, we could clearly see the leaking gas flowing away from the sensor. As well as fixing the leak, we are now looking to move the sensor to a better position to ensure it picks up anything like that in the future.”
According to Tim Elsome, Vale Green Energy is far from the only well-operated AD site to discover a leak: “Overall, 80 per cent of the plants we survey show some leakage. And while every plant is different, there are some common areas which are particular leakage hotspots, such as valves and roof seals.”
Feedstock sourcing
From silage protection and biological improvement to operational advice and leakage mitigation, FM BioEnergy is playing a vital role in the ongoing success of Vale Green Energy’s AD operation. And Nick Reynolds also praises the company’s ability to source additional feedstock at short notice: “A clear benefit of working with FM BioEnergy is the broad range of services they offer,” he confirms. “And as they’re part of the wider ForFarmers network, they’re even able to help us out if we are ever short of feedstock by sourcing alternative options. We look forward to continuing our positive working relationship.”
For more information on FM BioEnergy’s holistic approach to digester care, including their feedstock supply service and range of biogas-specific silage additives, contact General Manager Tim Elsome on +44 7802 173130 or [email protected]
