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Efficient AD operation reduces risk and boosts cash flow

Suzie Horne 21 November 2013
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A wide mix of feedstocks and a flexible approach brings Philip Mann cheaper electricity, income from power sales to the grid and the prospect of being self-sufficient in fertiliser next year.


After the first full year of AD operation at Heath Farm, Hopton Heath, Shropshire, Mr Mann is pleasantly surprised by the time required day to day to run the plant, which is just one to one-and-a-half hours a day.


Farm staff at the 263ha broiler and arable unit run the plant, having received Environment Agency-approved training for waste operations. Basic daily maintenance by farm staff is complemented by an annual maintenance contract with supplier and installer Marches Biogas.







Heath Farm AD plant


  • Designed as a 250kW operation, but has a 400kW engine and produces an average of 290kW
  • This is a two-stage semi plug-flow digester – soil from the beet crop is caught in a double grit trap and falls into a settlement tank
  • Gas produced supplies a combined heat and power (CHP) unit to produce electricity. Some 40-50% of the electricity produced is used by the broiler units. The remainder is sold to the grid
  • Digestate in liquid and fibre forms used as fertiliser on the farm’s arable and grassland
  • Net benefit of the AD plant estimated at about £500,000-600,000/year, including c£50,000 value of replacing bought-in fertiliser
  • Efficient feedstock and plant management is key – poor management can lead to costly performance losses
  • Surplus power is traded through broker Inenco
  • Power price was hedged recently on Inenco advice, achieving 1p/kW above market rate, worth £24,000/year

This company also performs a weekly plant optimisation test, sampling the digestate and advising on feedstock mix to keep the plant functioning well. Occasionally the need for trace elements is identified by this process, too.

Mr Mann is convinced this regular service helps the plant operate at significantly higher efficiency than it otherwise would. Having initially expected to run the plant on a mix of 20% chicken muck and 80% maize feed, a couple of poor maize years forced the decision to broaden the feedstock range considerably and this has had multiple benefits.


Feedstocks now include the chicken muck, maize, grass and rye silages, energy beet and fodder beet.


“We’re a mixed farm and the spread of feedstocks has helped with cashflow – for example, there isn’t such a big cash effect on maize drilling and harvesting. Storage is also easier because we take the beet straight off the field and don’t have to clamp or handle it so much,” says Mr Mann.


Biosecurity is a big consideration for the broiler unit, so no muck feedstock is brought in from other farms. All of the other feedstocks are grown on Heath Farm, as Mr Mann is keen to maintain security of supply here, too.


“We are a big potato growing area and I did not want to be at the mercy of the rental market.”


The ratios of different feedstocks within the mix can be altered, but this must be done slowly over a one- to two-week period, says Mr Mann.







Help and advice on AD

The Anaerobic Digestion and Biogas Association (ADBA) offers farmers free initial advice and support relating to the AD process, including assessment of finance options.


DEFRA offers grants of up to £10,000 to farmers interested in sub-250kW plants to create a business plan and a loan of up to £400,000 to help fund the building of the plant through the WRAP on-farm AD fund.


ADBA’s fifth annual national conference takes place in London on Tuesday, 3 December 2013. See the  full programme online or contact Rosaline Hulse – rosaline.hulse@adbiogas.co.uk, 0203 176 5441.


Using the digestate on some arable crops for the 2013 harvest raised yield by 15-20%, says Mr Mann, with nitrogen applied in the liquid digestate to growing crops in spring. “It’s like Yakult for wheat,” says Mr Mann.


The fibrous solid digestate in turn contains phosphate and potash. The farm grows 10ha of blueberries and yields for this high-value crop have seen a 25% increase through the use of digestate, says Mr Mann.


He shows other farmers around the site almost every week and is keen to encourage others into AD in order to share knowledge and gain lobbying strength for the sector.


Inspection


The Environment Agency is responsible for AD inspection and so far has always given notice, but may also do spot checks, so it’s important to demonstrate not only that all the protocols are in place and communicated, but also that they are being observed, says Mr Mann.


Inspections are also carried out by the farm’s insurer, NFU Mutual. Gas escape is one of the key risks and although unlikely because the plant is a fully sealed tank, gas detectors are always worn by staff working on or near the unit. These sound a loud warning if hydrogen sulphide is detected at anything higher than 1ppm.


Philip Mann’s AD tips:



  • Visit as many farm AD plants as possible before making your decisions
  • Don’t be ruled by price when it comes to making a decision – reliability and good local service are vital elements
  • Weigh up the risk if sub-contractors are likely to be involved
  • Feedstock security is crucial – be in complete control, even if you are not growing it all yourself
  • If having feedstock contract-grown, talk to local growers 12-18 months ahead of needing the material and get contracts in place
  • Plan your rotations two years before commissioning likely to start
  • Don’t put all your feedstock eggs in one basket by relying too much on one type. You need to balance the risk of crops not performing as expected
  • Look for chicken muck in your area to produce better-quality digestate
  • Be prepared to be flexible – all may not go according to plan.

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