A study shows that carbon capture and storage technologies may allow continued use of fossil fuels whilst limiting global temperature rises.
The United Nations Framework Convention on Climate Change (the Paris Agreement) was signed by 196 nations on December 12, 2015. It follows the Kyoto agreement whose term finishes in 2020 and commits the signatories to keep temperatures below 2° C, aiming at a temperature rise of only 1.5° C. It’s a necessary but tough ask, that requires the development of green energy technologies such as solar and wind, and new thinking that goes beyond traditional notions of sustainability such as the ideas of the circular economy.
But as we develop cheaper and more productive green energy technology, and change our lifestyles and behaviours, there is also one other technology which may buy some time on the way to a fossil-fuel free future. A new study by researchers at the Sustainable Gas Institute at Imperial College London argues that Carbon Capture and Storage (CCS) technology may enable the use of what is called unburnable carbon.
‘Carbon capture is actually a fairly well established technology,’ says Dr Adam Hawkes, Deputy Director of the Sustainable Gas Institute at Imperial College London. ‘It’s used in the oils and gas industry – they strip out the carbon dioxide from the natural gas stream, they can re-inject the CO2 underground in order to push out more oil and gas. It’s called enhanced oil recovery.’
As Dr Hawkes points out however, the aim of CCS is to fix the CO2 underground and prevent climate change, rather different to the aim of enhanced oil recovery. Says Hawkes, ‘the challenges are, the technology needs to change a bit, and obviously the economics changes a lot – you’re not getting oil and gas out of the ground. But also there is also a different range of technologies that might be considered.’
For many years the oil and gas industry have been using technology such as amine systems, which strip out the CO2 from fuels using an amine concentration which absorbs it. Dr Hawkes explains there are four or five other technologies at the research and development stage, such as oxy-fuel technology. This was first suggested in the early 1980s before climate change even became an issue, but over the last decade there have been industrial-scale tests of this process. In simple terms, this technology involves burning the input fuel to a gas turbine with pure oxygen, which causes gas turbine to output almost pure CO2 – ‘you don’t have to worry so much about stripping the CO2 out of the exhaust stream,’ says Dr Hawkes. It is therefore easier and more efficient to isolate and capture the CO2. But how effective is this, and can it really allow us to burn more fossil fuels whilst preventing temperature rises?
Burning the unburnable
‘Over the past five years or so, it’s not a new concept but there’s a new terminology emerging called unburnable carbon,’ says Dr Hawkes. ‘This is the idea that if you extract all known fossil fuels reserves and combust them, and release CO2 to the atmosphere you are going to cause very, very serious climate change – disaster scenarios, six degrees warming-type levels of climate change.’
The obvious conclusion was that these reserves are unburnable and have to stay in the ground, but this hadn’t considered the impact of CCS. ‘We looked at the previous studies that have been done on that such as the Carbon Tracker Initiative, and the Energy Institute at UCL who have done a few studies and none of them were really asking the question of whether or not technology or engineering options could unlock some of that unburnable carbon. The question we wanted to ask is if there are technical approaches which could allow the world to access more of those reserves without causing serious climate change and still remain within the two degree temperature rise.’
They looked at a range of studies analysing this problem such as the Intergovernmental Panel on Climate Change (IPCC) modelling studies and compared scenarios of those with CCS in them with those that don’t have CCS in them. ‘We found perhaps unsurprisingly that CCS makes a really big difference, that wasn’t really captured in the previous study,’ says Dr Hawkes. ‘The more CCS you have and the earlier you have it the more fossil fuels you can access. There are nuances to that point, firstly most of the studies surveyed only looked to 2050, and CCS really has a big impact beyond 2050. You need to start ramping up now in order to get there but the really big difference in terms of access to fossil fuels reserves is post 2050.’
Capturing more than 90 percent
The second conclusion from the research is that while the expensiveness of CCS is currently an issue for investment now, it won’t be a barrier in the future – other more expensive technologies compared to CCS will be adopted. ‘We are very certain that CCS is very competitive with other low carbon options like renewables,’ says Dr Hawkes. ‘It is a cheap mitigations option.’ Most scenario studies had assumed residual emissions of CO2 from CCS technology – most capture 85-90 percent.
But Dr Hawkes says, ‘we know as chemical engineers we can capture more than 85-90 percent, we can do separations of 99 percent or 99.9 percent. It’s possible technically. It will cost more for sure but that’s not so important because CCS is so cheap. If you doubled its cost it’s still competitive, that capture increases up to 96 percent in the study.’ In terms of CO2 storage, the depleted oil and gas fields can be used. Dr Hawkes estimates that there is room for about a thousand gigatons of CO2 storage which will last maybe three decades of storage. ‘After that you will need to use saline aquifers for the storage,” says Dr Hawkes. These saline aquifiers are deep rock formations saturated with salt water. ‘There is a huge capacity of saline aquifer capacity available, there is no chance we would get anywhere near using it all.’