Technology Focus: Biogas upgrading
BIOMETHANE SLIP-UPS
BE FLEXIBLE AND AVOID
Maxine Mayhew, Group Commercial Director of Northumbrian Water Group (NWG), looks at the advances, challenges and opportunities in the development of biogas upgrading technology, with a particular emphasis on the water sector.
“As technology advances, challenges and pitfalls are commonplace, but most importantly, so are opportunities to break new ground. The growth of anaerobic digestion (AD) and advanced anaerobic digestion (AAD) in the water industry is no different. Our work has resulted in NWG being the only water company that uses 100 per cent of its sewage sludge to create renewable energy. This innovation is in use at two industrial scale AAD sites; Howdon in North Tyneside and Bran Sands in Teesside. A third plant, near Leeds, is a joint venture and takes this further by focusing on agricultural AD.
Northumbrian Water Group’s Bran Sands AAD plant
At all of our sites, we ensure that the biogas produced is used effectively. All plants have maximum flexibility, as we have installed sufficient combined heat and power capacity together with gas upgrading equipment (we use water scrubbing or membrane technology). Bran Sands AAD plant has over 4.5 MWe installed CHP capacity. Its location does not allow for a dedicated natural gas supply, so the emphasis here is on maximising the renewable electricity produced. Challenges faced include eliminating the presence of condensate so the siloxane removal system is more effective.
Howdon operates water scrubbing technology to meet the tighter standards expected by the gas distribution network operators. Water scrubbing also requires lower capital expenditure, no pre-treatment and is well suited for larger installations. The emphasis here is to inject all the biomethane directly into the grid and maximise the renewable electricity produced. The plant has 6 MWe installed CHP capacity, together with a local gas connection. However, developers must be aware of the tougher constraints of such a site, such as the need for a larger footprint and additional planning considerations.
The requirement to dispose of wastewater makes AAD particularly suited to wastewater treatment works. However, it is necessary to dry the gas to meet gas quality standards and these sites do produce higher methane emissions. But there is also the opportunity for businesses to diversify. At NWG’s Ridge Road agricultural plant, farm waste is used to produce biogas, with no water requirements, allowing operation away from existing facilities and networks. This represents an opportunity to use a combination of CHP and biomethane gas injection using membrane technology in a way that operates within a smaller
18 AD & BIORESOURCES NEWS | SPRING 2017
www.adbioresources.org adbioresources.org
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