Renewable energy, the farmer and Pentair
22 March 2016
Renewable Energy is a hot topic, with tariffs, AD and biogas featuring in the news of late. Looking back on 50 years as a world-leading manufacturer of valves, actuators and controls for the most challenging applications, Pentair Haffmans tells the story of how the …
Farmers on the Isle of Wight are now energy producers
At a time when the prices for arable crops have collapsed, shipping crops overseas at additional cost for processing becomes unviable, and change is required. Farmers on the Isle of Wight decided to use their crops to provide biomass to generate gas for delivery to the grid. Pentair delivered the biogas upgrading technology and the manpower to meet an important deadline.
The new anaerobic digestor plant was built near the village of Arreton in the middle of the Isle of Wight off the south coast of England. Some of the island’s farm holdings wanted to secure a guaranteed income from their rotation crops, at this time of low prices for conventional crop production. Within six months they turned a liability into an asset, by growing maize and grass silage and turning it into biomethane, for injection into the national grid.
Thomas Smith is one of six farmers who, in partnership with Isle of Wight Grain, founded Wight Farm Energy LLP to become an energy producer. “Shipping our crops all the way to the mainland with associated costs simply does not make sense. We were looking for alternative markets for these bulk products.”
Once the decision for anaerobic digestion (AD) was taken, the Arreton site was selected because of its central location, connections to the agriculture irrigation system, the electricity grids and the gas grids.
The new AD plant will produce biomethane from an annual 55,000 tons of break crops from 53 farms and approximately 1,500 hectares of land. Break crops are used to alternate between the main arable crops (such as wheat, barley and oilseed rape) in order to keep the soil healthy. Maize and grass silage, demand for which has reduced due to the declining livestock sector, are now being digested to produce biomethane, organic fertiliser and liquefied food-grade CO².
Renewable heat incentive
As a financial incentive to increase the uptake of renewable energy the UK government provides a subsidy, payable for 20 years, to renewable heat generators and producers of biomethane for injection. With a 10 per cent cut in tariffs of the Renewable Heat Incentive (RHI) coming up at the start of 2015, Wight Farm Energy had a major deadline to meet when it approached Pentair in August 2014.
In order to inject gas into the grid, it has to meet certain specifications. Biogas consists of roughly 55 per cent methane and 45 per cent carbon dioxide. It turned out that the supplier of the digestor could not deliver a system that included CO² recovery. In fact, some of the methane would also be lost with their Pressure Swing Absorption or PSA process.
With the introduction of sustainability criteria by the government, the carbon footprint had to be reduced. Every aspect of the process of gas production had to be analysed, explained Francois Huberts of Pentair, and Pentair has provided a system providing maximum efficiencies, minimum CO² cost, and zero methane loss.
No methane slip
In September 2014, the first Pentair engineers travelled to the Isle of Wight to start work on a biogas upgrading facility with an integrated CO² liquefaction system, and without any ‘methane slip’.
Tom Smith said: “From the start we had every confidence in the staff and their co-operation. They are excellent engineers, were very thorough and far more involved in the process than I had expected. Roy Barclay from Future Energy Services was the technical integrator and co-ordinator. He studied several options for us to produce renewable energy, and along with Pentair went the extra mile in order to meet the deadline.”
In just 16 weeks they succeeded in building and commissioning the biogas upgrading system, and the first gas was fed into the grid on Christmas Eve.
The AD plant at Arreton is now producing biogas at a rate of 1,050 cubic meters an hour, and the upgrading facility turns it into 580 cubic meters of biomethane and 810kg of liquefied CO². “The original idea was to deliver the CO² to a nearby greenhouse complex by pipeline,” says Smith. “When that deal started to look uncertain, we had to look for alternatives for the CO² off-take.
“Having a steady customer for the food-grade CO² is a vital part of the economics of this project, and we now have a major industrial gases company that is interested in local CO² production because of the transport costs. We feel this AD plant is benefiting the whole island, the environment and the rural economy by providing income with a sustainable process.”
Pentair’s biogas upgrading technology recovers 100 per cent of the CH4, and completely eliminates the methane slip. This results in a higher CH4 yield and no emission of the harmful CH4 greenhouse gas. The biomethane produced with Pentair’s biogas upgrading technology has the same specifications as natural gas, making it fully compatible with the existing natural gas infrastructure and applications. Optionally, the CO² byproduct can be recovered for use in a variety of applications, providing an additional income source.
Pure profitable productivity
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Specialists in valve technology and process management for the pharmaceutical and food and beverage industries, Pentair plc provides highly engineered flow management solutions to the most demanding industries around the globe, enabling safer, more efficient and sustainable operations.
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