Feasibility of a wetting layer absorption carbon capture process based on chemical solvents

New ideas for carbon capture are urgently needed to combat climate change. Retro-fitting post-combustion carbon capture to existing power plants has the greatest potential to reduce CO2 emissions considering these sources make the largest contribution to CO2 emissions in the UK. Unfortunately, carbon capture methods based on existing industrial process technology for separation of CO2 from natural gas streams (i.e. amine scrubbing) would be extremely expensive if applied on the scale envisaged, as exemplified by the recent collapse of the Government's CCS project at Longannet power station. Moreover, many of the chemical absorbents used, typically amines, are corrosive and toxic and their use could generate significant amounts of hazardous waste. So, more efficient and 'greener' post-combustion CCS technologies are urgently needed if CCS is to be adopted on a global scale.

Efficient separation of CO2 from flue gases requires at least the following; i) an inexpensive sorbent with high CO2 working capacity and selectivity, ii) high rates of CO2 mass transfer into and out of the sorbent, and iii) a low energy cost for sorbent regeneration. A traditional aqueous amine scrubbing process has high selectivity, but is less effective in terms of capacity, mass transfer rate, and sorbent regeneration energy penalty. Here, we propose to investigate a novel process based on the 'wetting layer absorption' (WLA) concept in which a porous material is used to support liquid-like regions of absorbing solvent, which in turn absorb the gas of interest, in this case carbon dioxide. This process, recently invented by one of the authors (MS) of this proposal at Strathclyde, is being pioneered by researchers in Scotland. Initial work involved investigation of the use of physical solvents. Here the focus is on a process involving chemical solvents, i.e. amines. This process should have a high capacity, high slectivity, and high rates of mass transfer. Another novel aspect of this work is the investigation of microwave regeneration, which could also result in much reduced costs for sorbent regeneration. Finally, the process would involve orders of magnitude reductions in solvent recycling, and could make use of much less toxic and corrosive solvents, leading to a much greener process. Ultimately, the WLA process involving chemical solvents could potentially significantly reduce the cost and environmental impact of carbon capture.

With a rapidly rising global demand for energy, which is mostly provided by burning fossil fuels, the problem of CO2 emissions and global warming is pressing. Since these emissions are not localised this affects everyone on the planet. About 40% of global CO2 emissions are generated by large fossil fuel burning point sources, such as power plants, and so post-combustion CCS, that can be retro-fitted to existing plants, has major potential for reducing CO2 emissions. However, CCS technology based on current commercial acid-gas scrubbing is very expensive and could create substantial amounts of hazardous waste if applied on a global scale. So, more efficient and 'greener' options are needed if CCS is to be applied as hoped. This work aims to improve CCS efficiency and reduce the potential for generating hazardous waste through developing the WLA process in the context of amine impregnated sorbents for carbon capture.

As well as global impact through reducing CO2 emissions, this work would reduce electricity bills for consumers without placing as much financial burden on industry and financial companies (compared to other carbon capture methods), which would eventually be transferred to consumers as well. By reducing hazardous waste this work aims to reduce any other safety or environmental consequences of dealing with that waste.

The application to post-combustion carbon capture investigated here is just one potential application of this novel technology, which, provided the process is viable, would represent the start of a new sub-discipline in gas separation technology. This technique could potentially be applied to many other gas separation processes. For example, pre-combustion carbon capture via IGCC (integrated gasification and combined cycle) power plants requires an efficient method for separating higher pressure H2/CO2 mixtures, while oxy-fuel power plants require an efficient process for separating air.

In terms of human resource, the project will produce researchers with skills, including transferable skills, highly sought by industry.