Extra support boosts AD uptake in Northern Ireland

A recent increase in the support payments for renewable energy in Northern Ireland is leading to a flurry of planning applications for anaerobic digesters. Blakiston Houston Estates is one of those investing, as one of the company’s directors, John Witchell explains

Since the increased rate for Northern Ireland Renewable Obligation Certificates was introduced in April this year (see panel) there have been 60 planning applications for AD plants in the country.

The management team of Blakiston Houston Estates, near Belfast, have been researching the potential of AD for the last six years, but it was not until April that the opportunity became a reality.

The company owns 2,400ha on several farms across Northern Ireland, including a 365ha dairy farm on the outskirts of Belfast. The farm has been managed by Ivor Lowry for the last 20 years, during which time he has overseen the reconstruction of the two dairy units, now milking a total of 400 cows.

Last year the manager of a 120ha outlying beef and arable farm retired and Mr Lowry took on the management of that as well, with the task of integrating the two farms. He thought the extra land availability was the missing piece in the AD jigsaw and proposed that the time was right to move to procuring a biogas plant at one of the dairy units.

It will digest around 6,000t slurry and 4,000t grass silage, 1,500t wholecrop wheat and 1,000t maize silage per year, producing biogas to run a 250kW combined heat and power plant, with sales of electricity to the grid. Budgeted figures for electricity sold will be around 22p/kWh (comprising approximately 17p from NI ROCs and 5p from power sales).

The capital cost for this is budgeted at £1.2m, less a DARD Biomass Processing Challenge fund grant of £200,000, which gives an expected payback without tax incentives of within seven years.

Making it happen

Blakiston Houston Estates is owned by Dick Blakiston Houston. Both he and I are rural chartered surveyors and also manage other estates in Northern Ireland. I also have an MBA in construction management, and am leading the AD project team. The directors had already decided a business management specialist would be required for this major project, and other projects that will inevitably spin off it; so two years ago they brought in the expertise of Jim Torney from the Department of Agriculture, where he had been involved in farm diversification.

The team spent a lot of time travelling and learning about AD. They visited plants in the UK, Denmark, Germany and Sweden before shortlisting two German manufactures. The final decision was to contract Biogas Hochreiter to install what will be its first plant in Ireland.

Biogas Hochreiter has installed and managed AD plants for the last 20 years using a “ring in ring” digester. In this system the primary digester is a never ending river of heated digestate that is pushed around the outer ring by a paddle wheel. There is no gas bag over the tank, which has a concrete roof with windows for monitoring the process in the tank below. As slurry is pumped into the outer ring from a holding tank and silage is augured in from a static feeder unit, the displaced digestate overflows into the central secondary digester tank.

We have also built a separate sealed storage tank so that the system can be expanded to 500kW in the future by continuing to heat the digestate in the central tank.

The most important consideration when choosing the system was to avoid the crusting of grass silage in the tanks. If we are going to rely on grass as a feedstock in this country, we need a reliable means of keeping it in suspension.

Hochreiter’s “Mississippi paddle” is just that; it is built into the concrete roof of the outer ring and literally paddles the digestate around the tank, constantly breaking up the surface layers. Gas is collected under the concrete roof and only a small bag is needed in the roof space of the power house to balance the supply to the combined heat and power plant.

Excavation started in March and the project is targeted to be on line by the end of the year; but the first spin-off project is already under way. The company owns 600ha of forests in Counties Tyrone and Antrim and now brings pulp wood to the farm to be stockpiled for chipping. As soon as the AD plant is in operation, a chip drying plant will be installed to utilise the surplus heat.

Mr Torney is now looking for markets in and around Belfast for wood chips and he believes that with the Renewable Heat Incentive on the horizon we could soon be very busy in the wood chip market.

The Hochreiter agent for Ireland, Victor Christie, spends much of his time taking farmers to Germany to see their AD units in operation and says “seeing is believing”. He has taken more than 100 farmers to Germany and 35 of the planning applications currently in progress in Northern Ireland are Hochreiter designs.

Northern Ireland exports 80% of its milk and dairy products and imports 99% of its energy. The scope for import substitution of power is immense and farmers are beginning to prepare for big changes in their industry.

Before the invention of the internal combustion engine around 50% of the province’s energy was produced on-farm in the form of hay and oats to feed heavy horses; in the future it may come from grass silage used to feed anaerobic digesters.

Northern Ireland support

The Northern Ireland Renewables Obligation (NIRO) is the main policy measure for supporting development of renewable electricity in the country. Introduced in 2005, it has been amended several times since.

Last year support for all microgeneration (up to 50kW) was increased to two ROCs, regardless of technology and additional ROCs introduced for wind, hydro and photovoltaics. On 1 April 2011, additional ROCs were introduced for AD – units up to 500kW now get four ROCs, while larger plants up to 5MW get three ROCs.

NI ROCs are the same as GB ROCs, and are traded on the UK market.

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