Last week I was in Canada for the 3rd biennial conference on post-combustion capture organised by the IEA Greenhouse Gas programme, this time co-hosted by regional utility Saskpower to mark their successful commissioning of Boundary Dam 3 – not only the first ever power plant with post-combustion capture, but the first of any kind. Located around a hundred miles south of Regina, the provincial capital where the conference was held, the visit to this facility was clearly a big draw for delegates, though unfortunately one I was unable to stay on for. Fortunately, the event also tied in with a day-long symposium of talks from Saskpower, which I’ve attempted to summarise in a separate blog.
The opening of the Boundary Dam capture facility almost a year ago has cemented the status of CO2 capture with amines as the most established technology and the benchmark to which all alternative approaches will be compared. Besides the solvent from Shell Cansolv used at Boundary Dam, several other companies are offering amine-based solvents with proven performance in large-scale pilots or commercial use in carbon capture outside of the power sector. The capture efficiency of solvents has been steadily improving, with current products generally claiming a heat duty of less than 3 GJ to capture a tonne of CO2, and yet amines are still dogged by concerns relating to their environmental impact and stability. These issues were an ever-present theme at PCCC3, which retains a strong focus on amine-based capture, alongside research into the incremental efficiency gains achievable through more complex processes or new amine blends. For more dramatic reductions in the energy penalty imposed by post-combustion capture, others have looked towards other types of solvent, solid sorbent materials, membranes, or combinations of these, and these sessions were of particular interest to me.
Many of the most innovative capture processes are currently under development in the USA, and a keynote from the US Department of Energy provided an update on the status of some promising technologies. A recent funding announcement by the department has selected several projects to be scaled up to pilots of over 10 MWe, mostly involving process improvements or advanced amines. For example, a pilot at the University of Kentucky detailed later in the conference uses a cooling tower to supply warm, saturated air for use in a secondary CO2 absorption process. A smaller scale pilot is also planned for a more novel process in which a fuel cell fired with natural gas is able to capture carbon from an existing plant as part of its own power generation process. The US Government appears committed to using CCS to retain some of the country’s huge coal fleet in a low carbon future, and it was even suggested that the current tax incentive received by CCS projects may be raised from $20 to $50 per ton of CO2 sequestered, representing a real financial incentive to industry.
A second keynote from the Japan Coal Energy Centre (JCoal) provided a similar overview of Japanese progress in CCS, taking place under the additional pressure of 9% of the country’s generating capacity being shut down in the wake of the Fukushima disaster. Japanese companies such as Toshiba and MHI are leading suppliers of amine solvents, and MHI technology will be used at the world’s largest postcombustion facility currently under construction at WA Parish plant in Texas. More fundamental capture research is meanwhile being conducted by the RITE research institute, which has developed new solvents, sorbents, and a novel membrane based on amine-functionalised dendrimer molecules.
Other prevailing themes in the search to enhance solvent-based capture include the use of enzymes or catalysts to improve CO2 absorption and stripping rates. Addition of carbonic anhydrase, an enzyme used by living things to control cellular CO2 levels, can accelerate CO2 uptake enough to allow the use of usually slow solvents which require less regeneration energy or the use of lower grade heat. CO2 Solutions are a Canadian company currently testing such a process at the scale of 10 tonnes of CO2 per day, using hot water for solvent regeneration in the place of steam. An alternative approach to lowering the regeneration energy in solvent-based capture is to use solvents which precipitate or otherwise phase separate into CO2-rich and lean phases, greatly reducing the volume of solvent to heat during regeneration. Precipitating systems were presented by Waseda University in Japan and Sintef of Norway, with an energy penalty of 2.59 GJ/t of CO2 claimed by the Japanese research. Some of the challenges of precipitating systems and other advanced solvents could be met by a novel process presented by the Lawrence Livermore National Laboratory, which I’ve previously discussed in my blog on the GHGT conference. Essentially, the solvent is encapsulated in a milimetre-scale, CO2 permeable polymer shell, providing a huge surface area of reaction and circumventing problems of slurry-handling or viscous solvents.
The final sessions of the conference assembled results from larger-scale amine pilots around the world, including Shell Cansolv’s tests at the Mongstad facility in Norway, CSIRO’s tests in China, and research conducted by MHI and BASF in their US-based pilots. On this evidence, it is clear that amine-based capture is fast becoming the default option for any new CCS plant, with healthy commercial competition between technology providers acting to drive down costs and energy penalties. It seems likely that more power plant-based demonstrations of the technology will follow those at Boundary Dam and WA Parish, although North America currently seems to be the only region with the right political and economic environment to support such plants. With its much higher natural gas prices, it is perhaps surprising that Europe continues to lag behind other regions in this regard.