4th Post Combustion Capture Conference, 5-8 September
This year’s edition of IEAGHG’s conference on post-combustion capture (PCCC4) was held in Birmingham, Alabama – not far from the US Department of Energy’s National Carbon Capture Centre (NCCC) in Wilsonville. Visits to this research facility and the Kemper County CCS plant across the state border in Mississippi were highlights of the week’s events, bookending its typically high quality technical programme.
Hosted by Southern Company at their Gaston Power Plant, the NCCC forms plays an essential role in the National Energy Technology Laboratory (NETL)’s CCS research by providing a platform for lab-scale capture technologies to be tested at the pilot scale – a crucial stepping stone to full demonstration. With a coal gasifier located close to the conventional coal power plant, the site provides facilities for testing multiple pre-combustion and post-combustion capture technologies on real syngas and flue gas, and at scales of up to around 2 MW. During our visit, the large absorber and stripper columns used for solvent testing were being used by the University of Texas at Austin to test their advanced flash stripper process. Usually used in combination with the group’s piperazine solvent, this process promises to significantly reduce the energy lost in solvent regeneration by harnessing lost heat and generating CO2 at higher pressures. Another of the three post-combustion test sites was occupied by Air Liquide’s cold membrane process, which compresses and cools flue gas to -30°C before separating out the CO2 using one of the company’s commercial polymer membranes. A detailed talk by Air Liquide on the morning of the visit gave us a look at a new, more permeable membrane they have developed to further improve this process. A striking feature of the membrane skid at the NCCC is it’s dramatically smaller size than its solvent-based neighbours with their tall columns – this could be a key advantage for space-restricted applications.
As the conference began in earnest on Wednesday, we heard a keynote from John Litynski of the Department of Energy’s Office of Fossil Energy. Some new research directions for coal power were highlighted, aiming to upgrade the efficiency of the country’s existing coal fleet and develop new coal plant technologies which can compete with natural gas on efficiency. On the other hand, in the wake of the shale gas revolution, coal gasification projects are falling from the programme. In carbon capture, the NETL are dropping their work on relatively advanced ‘second generation’ technologies to focus on ‘transformational’ technologies which can offer more dramatic cost reductions. This research plans to fully exploit the major advances in advanced materials manufacturing, computing, and robotics, to rapidly identify the best prospective technologies. There is also a new programme on CO2 utilisation in useful chemicals and other products – a growing area of interest worldwide which the IEA CCC is currently reviewing. Mr Trump’s well-publicised energy budget cuts have not been approved by the Senate or the House, which apparently wish to allocate greater resources to this fossil energy research.
The talks at PCCC4 had a strong focus on capture processes based on amines and related solvents, although some work on solid sorbents was also in evidence. Following the large-scale CCS demonstration projects at Boundary Dam, Petra Nova, and Quest, amines are undoubtedly the leading contender for post-combustion CCS projects, with a number of major manufacturers offering bespoke commercial solvents. As one of these manufacturers, Mitsubishi gave the second keynote, probably in recognition of the Japanese company’s role in providing the capture technology for the recently opened Petra Nova plant in Texas. Having worked on CO2 capture at various pilot plants since 1991, MHI are now a leader in the field, operating 12 commercial plants around the world. While their KS-1 solvent used at Petra Nova already claims to reach an impressive low heat energy consumption of 2.4 GJ/t CO2, they are developing a new solvent with nearly 10% less steam consumption, half as much as solvent degradation, and less than half the emissions.
Mitsubishi’s achievements in solvent optimisation were echoed by the other amine research on display at the conference, in that efforts to minimise harmful emissions and solvent losses through degradation featured over further energy reductions. Indeed, an interesting talk by Professor Gary Rochelle, a giant of amines research from the University of Texas at Austin, highlighted how much the energy penalty of amine capture has now been optimised, leaving little room for further improvement. In highly optimised processes such as the ‘advanced flash stripper’ being tested at the NCCC, much of the remaining energy losses are intrinsic to the process, and will be difficult to avoid. Many researchers are instead looking at reducing process costs through cheaper equipment (capex) or use of lower grade energy.
Amines can degrade either from exposure to oxygen (mostly in the absorber) or high temperatures (during solvent regeneration), creating a cocktail of volatile organic compounds such as ammonia, aldehydes, and carboxylic acids, and adding to replacement solvent costs. The solvent itself can also be lost from the top of the absorber as an aerosol. Many talks dealt with these issues, which can be mitigated through use of better upstream flue gas cleaning (particularly bag house filters), optimised operating conditions, and washing systems at the top of absorbers. An interesting talk from Japan’s Mizuho Information and Research Institute looked at environmental regulatory issues for amine emissions, and the need for bioassays of ‘whole mixtures’ of degradation products rather than trying to identify each and every compound generated.
Many of the operational issues at the pioneering Boundary Dam CCS plant were discussed at the last PCCC in Regina, Canada, two years ago, and covered in my blog of that event. This time a talk from the International CCS Knowledge Centre – an initiative launched by SaskPower and BHP Billiton at the same event in Regina – provided another fascinating and frank update on the challenges faced by the first ever coal power plant with CCS. Fly ash has been a huge problem for the plant, fouling heat exchangers and accumulating in demisters, and originally requiring regular shutdowns for cleaning. This has now largely been resolved by installing water sprays in several locations upstream of the absorber, as well as improving the main plant’s electrostatic filters. There were also problems with solvent foaming in the stripper, causing damage to the packing and created high pressure drops, but since alleviated with a carbon filtration system. Other issues included a leak in the CO2 compressor and leaks in the amine storage tank, which has since been replaced with a new stainless steel tank. The plant can now operate at its design capture rate when necessary, and SaskPower maintain that a second project could be 30% cheaper, mainly due to savings on the associated upgrades to the power plant.
The conference provided similarly revealing insight into the tribulations of the ill-fated Kemper County project, which we visited on the final day. Having completed the ambitious integrated gasification combined cycle power plant with CCS in late 2016, Southern Company were ordered by a state regulator to simply run the plant on cheap natural gas, rather than spend more money on fixing ongoing technical problems with the coal gasification process. The project has become notorious for its long construction delays and enormous final costs approaching $8 billion, but at PCCC4 Southern Company representatives put up a vigorous defence of their gasification technology and investment in the plant. Although many have criticised their use of their own, relatively untried coal gasifier, they point out that its reliability compares favourably with other gasifier technologies in their early months of operation, and was steadily improving. Most of the technical issues were attributed to standard teething issues or unforeseeable errors by contractors. Having been sitting around for months in the open air, the coal supply had absorbed too much water and weathered into small particles, making it difficult to dry. The refractory lining of the gasifier units had been poorly installed and would flake off and clog other parts of the plant, but was scheduled for replacement. Earlier this year, some of the thin tubes designed to cool the hot gas with steam began to burst in places – apparently due to weak spots where they were welded to supports, but in the end these cooling loops could simply be bypassed.
In short, Southern feel that they would get there in the end with Kemper, but the sharp reduction in natural gas prices in the US have ultimately struck the death knell for the project. Touring the plant brings home the scale of the wasted investment, as most of the enormous site devoted to coal and syngas processing now lies idle, while the two gas turbines quietly generate at one end. It seems unthinkable that all this pioneering equipment and, perhaps more importantly, years of CCS expertise should be lost. A talk from Southern Company’s principal geologist gave some small hope for Kemper’s future, by suggesting that the proposed federal raise in tax credits for sequestered CO2 could make a business case for the plant. This would probably mean using saline aquifer storage which has been characterised close to the plant rather than the original plan to sell CO2 for EOR.