Turning black-bag waste into biogas using gasification technology will open up the opportunity to use a wider range of feedstocks than is possible with anaerobic digestion. This will increase the amount of renewable gas that can contribute towards decarbonising heat. At the recent (13 September) Institution of Gas Engineers and Managers (IGEM) ‘Future of Gas Infrastructure’ conference, Lorna Millington, design manager with Cadent, elaborated on the role of renewable gas, how it can be delivered at scale, the future of full deployment and also what is possible with biohydrogen.

Technologies behind renewable gas

“When we talk about potential for renewable gas in the United Kingdom, we think that 100 terawatt hours is possible through two technologies – anaerobic digestion and bio SNG [synthetic natural gas],” she told delegates at the Grand Hotel Malahide. ‘”That’s around a third of the predicted 2050 domestic demand in the UK. [The UK] has 64 million homes that create waste – and that waste is a significant resource,” she explained. The figure of 100 terawatt hours comes from a 2011 Committee for Climate Change report and at the beginning of this year, the team at Cadent (which supplies around 11 million consumers in the UK) thought it was worth revisiting whether that number was still the right number to use. “Using our innovation allowance, we set about revisiting those numbers with a company called Antithesis and E4tech. We looked at it from high, medium and low perspectives, as did the original report. “The crux of it is that the original 100 terawatt hour figure is still a relevant number to use, but it also does highlight the fact that since 2011, the amount of energy crops that has been planted has been limited. The original report suggested much more growth in this area in the early years, which hasn’t come to pass.” Cadent created a pilot plant in Swindon, in south-west England, after starting with a feasibility study. “There are many different technologies to gasify waste and to create gas of varying qualities out of it,” explained Millington. “We wanted to make sure when we started that we understood which one was the most efficient and would give us the best return of methane for the waste that we were putting in. “We did that and then partnered with several companies to advance to building the pilot plant – Advanced Plasma Power, Progressive Energy and Carbotech, which did the catalytic elements of the work.” The team got European funding along with network innovation competition funding to create this pilot plant. “The pilot plant project concluded in March 2017 and we successfully created methane that can be reformed to the levels of our gas safety management qualities to be put back into the gas grid, meaning that the three years spent doing the work concluded with success.”

Lessons learned from the project

There were four lessons that the team took from the project:
  • “First, technically, there was a lot of thermo-chemical modelling that was carried out that the offline rig and the plant allowed us to verify. That gave us some confidence to move into the commercial plant.
  • “The second was operating the plant and how that would be adapted to a large-scale plant and help us to get ready for this to be deployable.
  • "Thirdly, environmentally, it gave us some figures to understand what it would be like if we could employ carbon capture and storage [CCS].
  • “Lastly, the point at which renewable gas would be at cost parity with fossil gas – that was an important part of making sure that we understood how long the Renewable Heat Incentive or some sort of incentive would need to be in place.
“The pilot plant truly was R&D. It gave a 50KW output for a £5 million price tag. But it does demonstrate how much of a financial gap and risk it is to progress to a full plant at £100 million worth of investment,” added Millington. On that basis, the team began looking for investment to create a commercialisation plant. They secured funding from the Department of Transport as part of an advanced biofuels trial and also through the network innovation competition route to be able to build a commercial demonstrator. To offset the running costs of the plant, there are several income streams. “There are the waste gate fees, there will be enough gas to run 75 HGVs and the rest of the gas will be connected to the gas grid and will supply customers in the local area. Lastly, we are going to sell the CO2 which we will capture as part of the process, and that will go into the food and drinks industry,” said Millington “Construction on the plant is underway. The demonstrator reduced the financial risk to allow funders to take it to the next stage. There is still a need for subsidies but we think that will only be until 2025. “But this will lead us to that 100 terawatt hours figure becoming a reality with around 300 plants deployed by 2050. Each plant would be around a 350 gigawatt size.”

Biohydrogen

“We already reduce emissions just by using the waste and creating biomethane. But if we add CCS, the emissions are reduced even further – and actually, these plants can also produce hydrogen. If that becomes practical in the future, the plants can be converted to produce hydrogen.” The team took an opportunity earlier this earlier to carry out another project using the pilot plant. ”We looked at creating biohydrogen to see how practical that would be, and to create a comparison between bio SNG and biohydrogen. When you have got carbon capture storage, you could achieve negative emissions,” explained Millington. “The efficiency of the biohydrogen plant is marginally better than bio SNG, but it costs us more – it gains less on the waste gate fees but, because it allows for capture of more CO2, the price of the megawatt hour for that is actually greater because there is more CO2 to be sequestered. Even so, you get two very good benefits – more efficient and more CO2 captured.” Millington stated, however, there were greater challenges for biohydrogen: while there is no hydrogen economy yet to begin, there are no incentives to invest in a hydrogen production plant. “We’re beginning to form the standards for both 100% hydrogen and blend hydrogen, but that’s a long way from where we are with methane – we’ve spent 60+ years creating what we have for methane. We’ve a long way to bridge that gap for hydrogen, but we’re on the journey. “We see this as our low-cost route to the decarbonisation of heat and transport by using those waste resources – converted by efficient technologies – to give green gas, which is supplied to our customers via existing infrastructure that’s so wide and dense.” Read more on Cadent’s BioSNG plans.