AD plants turn to capturing carbon
As featured in Arable Farming Magazine
AD plants turn to capturing carbon
by Arable Farming September 2021
New carbon dioxide technology could give anaerobic digestion (AD) plants a fresh lease of life. Cedric Porter reports.
AD plants have been part of the UK farming landscape for more than 15 years. In that time there has sometimes been a love/hate relationship among farmers
and local populations with the domed newcomers.
The main aim of the first generation of AD plants was to produce sustainable energy from crop material, leaving a digestate by-product which could be used
as a soil improver and fertiliser by farmers. That is still the case, but one company believes they will also play an important role in reducing the UKs carbon
dioxide emissions in the battle to become carbon neutral.
Future Biogas already operates 10 AD plants, mainly in the east of England, which use 500,000 tonnes of crop a year. It is due to be floated on the AIM stock exchange this summer, which will provide £35 million in extra funding.
It has ambitious expansion plans, hoping to build 25 new plants in the next seven years.
While those plants will produce energy and digestate, they will also capture and convert carbon dioxide from a gas into a liquid, store it and then transport it to
a new facility in the Humber Estuary, called the Northern Lights Project. The CO2 will then be shipped to an underwater carbon sink in the North Sea, which has been developed in a disused oil field by, among others, Shell International.
Philipp Lukas, chief executive officer of Future Biogas, says: We are capturing carbon dioxide and converting it into a state where it can be removed from the
atmosphere, while also having helped generate green energy and a by-product that is helping the soil store more carbon.
All 25 new plants will have carbon capture systems built alongside them, with plans for another 20, including on the 10 existing plants.
The Northern Lights Project is due to be operational in 2024 when Future Biogas will supply an initial 200,000t of CO2 a year.
The company will receive a carbon credit for each tonne of CO2 delivered, which it will then sell to corporate buyers looking to achieve net carbon zero.
The new plants will require plenty of feedstock around an extra 1.25mt of it. Nationally, up to 85% of feedstock is from specially grown crops, with the remainder from waste material.
Rye, grass and sugar beet are grown for the plants, but three-quarters of the crop stock is maize.
This demand for maize for AD and for forage has led to a 130% increase in the national area of the crop to 228,000 hectares since 2000, according to Defra figures.
The Anaerobic Digestion and Bioresources Association says 57,000ha of maize was grown for AD in 2018. There has been criticism, including from the Soil Association, about the rapid expansion of the maize crop, with many farmers expressing their concern about maizes impact on their soil.
Innes McEwen, head of farming at Future Biogas, says: Ensuring we have the right farmers supplying us with quality feedstock is very important.
We have field managers who scout out new growers and work closely with established ones.
Growers are looking for crops that work in their rotations, while preserving the integrity of their soil. While we want those who can consistently deliver the mix
of crops we need.
The company has developed a six-point checklist to help identify if a farm is suitable to supply or house a plant (see Farm requirements panel).
Each plant needs at least 60,000t of feedstock a year, the composition of which will differ depending on the region and soil type. Plants require planning permission, provision for storage of feedstock and digestate, a biomethane connection to the gas grid and must be within suitable distance of the new Northern
Lights CO2 facility in Hull.
The Maize Growers Association has also published a list of factors that suppliers to AD plants should take into account (see AD suppliers key considerations panel).
Land use concerns
There are 685 AD plants in the UK, of which 380, or about 55%, digest agricultural feedstock, according to the Anaerobic Digestion and Bioresources Association (ADBA).
The combined output of all AD plants produces 16TWh of biogas 5% of the UKs total energy generation.
Bioenergy crops are estimated to generate 5.1TWh of biogas a year.
ADBA estimates current plants can consume up to 48 million tonnes of feedstock a year, with the capacity to produce at least 37mt of digestate. Addressing concerns over the use of land that could grow crops to produce energy, the organisation says: Bioenergy crops can be grown sustainably when using agricultural practices such as sequential cropping, which consists of growing food and bioenergy crops alternately.
ADBA supports sequential cropping and sustainable farming over monocropping as not only does it allow food and fuel to be generated from the same piece of land, it also draws down carbon, thus replenishing soil organic matter, sequestering carbon and improving yields for farmers.
Bioenergy crops are necessary to achieve net zero targets, as recommended by the UKs Climate Change Committee in its sixth Carbon Budget. Sequential cropping ensures they complement, rather than compete, with food crops.
AD suppliers key considerations
- Target drilling date
- Target harvest date
- Field characteristics including soil
- Proximity to watercourses and environmental features
- Accessibility to fields
- Region of the country in England around a third of the country, including the North West, North East and South West, is marginal for maize growing
Source: Maize Growers Association
- Prove carbon neutrality from extended crop rotation, not just AD crops
- Appropriate cultivation to suitably limit carbon release from particular local soil types
- Improve/maintain soil organic matter levels
- Replace artificial inputs with digestate returned from the AD process
- Incorporate perennial, sequential and cover crops appropriately across rotation
- Report annually, as part of accredited supply chain
Source: Future Biogas