RENEWABLE ENERGY INDUSTRY FOCUS Improving the value of food waste

Matt Hale, international sales manager for HRS Heat Exchangers, explains how innovations in heating, pasteurisation and concentration technology can help food waste AD operators to thrive in the face of dwindling renewable energy subsidies


he past five years have seen an unprecedented growth in Britain’s anaerobic digestion (AD)

sector, with the number of operational plants increasing by over 600 per cent outside of the water sector. Alongside facilities treating sewage and agricultural feedstocks, there are now 78 AD plants treating a variety of food wastes, including on-site food and drink processing residues, local authority waste, and commercial and industrial waste. It’s easy to see why food waste AD has proved so popular. Processing organic wastes through anaerobic digestion not only cuts greenhouse gas emissions by diverting waste from landfill, it also generates homegrown renewable energy and produces a biofertiliser (digestate), rich in valuable nutrients such as nitrogen, potassium and phosphorus.

GOVERNMENT’S ASSAULT ON RENEWABLES However, recent government policy has failed to recognise these benefits. No sooner had the industry announced the UK’s 400th AD plant in July 2015, than the new Conservative government slammed on the brakes, removing both pre- accreditation for the Feed-in Tariff (FIT) and AD’s exemption from the Climate Change Levy. Although DECC has recently confirmed its commitment to reintroduce pre-accreditation for the FIT scheme, its ambition remains startlingly low: government will provide support for a maximum of around 20MW of additional AD capacity each year between 2016-19. This compares to an industry deployment of 48MW in 2014 alone. Government’s assault on renewables, which some

feel is paving the way for a zero-subsidy future, has also impacted the finance community and will undoubtedly make it more difficult for AD developers to attract funding. On top of this, some industry experts believe the UK AD industry has reached a ‘tipping point’, with food waste AD plant capacity outstripping available feedstock. And with England looking unlikely to follow Scotland and Wales in banning food waste from landfill any time soon, this situation is not expected to change in the near future. Faced with increasing competition, falling gate fees and diminishing incentives, it is therefore more important than ever that food waste AD plants are

operated efficiently, with every aspect of the process optimised to ensure maximum return on investment. One area that many food waste AD operators are still missing out on is the potential extra income that could be made from the biofertiliser end product of the AD process – digestate. Dismissed as an afterthought by some in the past, today’s successful operators keep it firmly at the heart of their business. They understand that creating a quality end product, which can then be sold to farmers and landowners – and using as little energy as possible to do so – is essential for a thriving AD operation that will continue to appeal to investors.

EFFICIENT DIGESTATE PASTEURISATION In order for digestate to be a saleable commodity, it must be pasteurised to PAS 110 certification standards. This accreditation provides reassurance to growers that it is safe to be applied to land. The 3 Tank Batch Sludge Pasteuriser System from HRS Heat Exchangers achieves this using up to 70 per cent less energy than existing competitor technology. The system works on a three tank principle: while one tank is being filled, the second tank holds the digestate above 70°C, at the same time as the third tank is being emptied. Each process last one hour. Traditionally, systems that heat digestate in a

tank use a heating jacket – a bit like waiting for a giant kettle to boil – and then dump the heat after it has served its original purpose. The HRS system, however, employs energy recovery and is typically two to three times more efficient. By transferring energy from the hotter (pasteurised) sludge to the colder (unpasteurised) sludge, energy consumption can be reduced by up to 70 per cent, maximising heat which would have otherwise been wasted. This also circumvents the need to install an additional heat source such as a biomass boiler, which could add hundreds of thousands of pounds to a project.

REDUCED COSTS With developers looking to reduce costs in every area of their AD operation, today’s efficient pasteurisation systems offer reduced downtime and increased digestate production. The use of intelligent heat exchanger, pasteurisation and concentration technology could help food waste AD operators to recover nearly half the heat produced by their AD plant and assist them in producing a quality biofertiliser, at the same time as making cost and energy savings. Maximising the value of digestate will give AD operators the best chance of not only surviving, but thriving in the face of uncertain government subsidies.

HRS Heat Exchangers /AUTOMATION T: 01923 232335

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