The six-unit Drax power station in North Yorkshire plans to eliminate its emissions in two phases. First, by replacing old-fashioned coal with sustainably sourced wood pellets – made from trees that naturally sequester carbon as they grow. In the second step, the CO2< generated from burning the pellets will be trapped and stored underground with the help of specialised carbon-capture technology.
This precise sequence of steps makes up a process known as bioenergy with carbon capture and storage (BECCS). In deploying it, Drax will theoretically remove more carbon dioxide from the atmosphere than it creates.
There’s already a successful BECCS pilot scheme in service at the plant – operators claim it captures a tonne of carbon dioxide per day – although scaling it up to its full potential will require serious government support.
“Drax’s ambition is to be carbon negative by 2030,” says a statement from the CEO Will Gardiner. “Having pioneered the use of sustainable biomass, Drax now produces 12% of the UK’s renewable electricity. With the right negative emissions policy, we can do much more, removing millions of tonnes of emissions from the atmosphere each year.”
Scientists and engineers have been experimenting with the CCS portion of BECCS for well over two decades. The very first carbon-capture-and-storage trial was undertaken at the Sleipner West natural gas field in the North Sea back in 1996. The gas produced at the site naturally contained almost 10% CO2 – and this had to be removed to make it fit for distribution and sale.
CCS 'is a necessity'
Under normal procedures, the CO2 would simply have been separated from the gas and released into the atmosphere. Instead, the field’s operators decided to inject it down a 3km-long well, where it could be safely stored inside permeable rock.
There are now 19 CCS facilities in operation around the world. However, climate scientists and policymakers largely agree that the technology must be deployed on a much larger scale if we’re going to meet international CO2 reduction targets. In its landmark roadmap for reducing the UK’s emissions to net zero by 2050, the Committee on Climate Change states that CCS is “a necessity, not an option”. The report forecasts an annual capture and storage of somewhere between 75 and 175 megatonnes of CO2 by mid-century.
Reaching these volumes will mean installing a wide-reaching network of transport and containment infrastructure that services a minimum of five CCS “clusters” across the UK, according to the committee. Existing industrial hotspots are the obvious locations for installing carbon-capture plants around the world. This is partly because certain heavy industries, such as iron and steelmaking, release CO2 as part of their production processes. The continued upward march of coal-fired power in Asia will also create a need for carbon-trapping technologies.
“The current state of the global energy transition, the varying climate commitments and energy future forecasts show that CCS will be necessary to address emissions in a number of industries and sectors, this at least in hard-to-abate sectors,” says Guloren Turan, spokeswoman at the Global CCS Institute, a think-tank. “In some regions, the technology will be necessary to abate emissions from young fleets of coal and gas plants.”
Capturing and storing CO2 will also be a crucial part of scaling up the global production of hydrogen – a solution widely tipped to have a major role in decarbonising heat and transport. The vast majority of hydrogen in use today is made by the carbon-intensive process of steam methane reforming. It can also be produced by splitting water into hydrogen and oxygen inside an electrolyser. If the energy used to power this process is sourced entirely from renewables, the resulting hydrogen is deemed ‘green’.
However, making green hydrogen relies on having ample quantities of clean energy available for this purpose. In places without extensive wind and solar infrastructure, it could make sense to continue producing hydrogen through steam methane reforming, with the addition of CCS to capture the associated CO2. In some cases, Turan notes, it might not ever be logical to divert renewable power to hydrogen production, especially if CCS is an option.
“To meet growing demand, renewable electricity for hydrogen production via electrolysis will also need to be scaled up,” she says. “Where renewable electricity is scarce, using this electricity to displace unabated fossil generation may deliver more emission reductions instead of using it for green hydrogen production.”
Critics have asked whether it’s a good idea to count on the large-scale roll-out of carbon-capture technologies when drawing up carbon targets and emissions forecasts. After all, couldn’t betting on the widespread deployment of CCS in the future keep us from doing the hard work of reducing emissions today?
The picture, as always, is slightly more complex. Where decarbonisation simply isn’t deemed possible or practical, carbon capture could very well prove to be essential.
“To achieve net-zero by 2050, we will need all technologies and climate solutions to deliver the energy transition,” says Turan. “CCS is part of a portfolio of solutions that will support emission mitigation efforts in a number of sectors and industries.”
Want the best engineering stories delivered straight to your inbox? The Professional Engineering newsletter gives you vital updates on the most cutting-edge engineering and exciting new job opportunities. To sign up, click here.
Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.