Process Intensification for Post-combustion Carbon Capture using Rotating Packed Bed through Systems Engineering Techniques

The emission of carbon dioxide into the atmosphere has caused huge concerns around the world, in particular because it is widely believed that the increase in its concentration in the atmosphere is a key driver of climate change. If the current trend in the release of carbon dioxide continues, global temperatures are predicted to increase by more than 4 degrees centigrade, which would be disastrous for the world.

With the increase in world population, the energy demand is also increasing. Coal-fired and gas-fired power plants still play a central role in meeting this energy demand for the foreseeable future, even though the share of renewable energy is increasing. These power plants are the largest stationary sources of carbon dioxide. Carbon capture is a technique to capture the carbon dioxide that is emitted in the flue gas from these power plants. This proposal seeks to make a significant improvement in the methods used for carbon capture in order to reduce the total costs.

Post-combustion CO2 capture by chemical absorption using solvents (for example, monoethanolamine - MEA) is one of the most mature technologies. The conventional technology uses large packed columns. The cost to build and run the capture plants for power plants is currently very high because: (1) the packed columns are very large in size; (2) the amount of steam consumed to regenerate solvents for recirculation is significant. If we can manage to reduce the size of packed columns and the steam consumption, then the cost of carbon capture will be reduced correspondingly.

From our previous studies, we found that mass transfer in the conventional packed columns used for carbon capture is very poor. This proposed research is expected to make very significant improvements in mass transfer. The key idea is to rotate the packed column so that it spins at hundreds of times per minute - a so-called rotating packed bed (RPB). A better mass transfer will be generated inside the RPB due to higher contact area. With an intensified capture process, a higher concentration of solvent can be used (for example 70 wt% MEA) and the quantity of recirculating solvent between intensified absorber and stripper will be reduced to around 40%. Our initial analysis has been published in an international leading journal and it indicates that the packing volume in an RPB will be less than 10% of an equivalent conventional packed column.

This proposal will investigate how to design and operate the RPB in order to separate carbon dioxide most efficiently from flue gas. The work will include design of new experimental rigs, experimental study, process modelling and simulation, system integration, scale-up of intensified absorber and stripper, process optimisation, comparison between intensified capture process and conventional capture process from technical, economical and environmental points of view.

The research will include an investigation into the optimum flow directions for the solvent and flue gas stream (parallel flow or counter-current) for intensified absorber and the optimum design of packing inside the RPB.

The proposal will also compare the whole system performance using process intensification vs using conventional packed column for a CCGT power plant. Based on this, an economic analysis will be carried out to quantify the savings provided by this new process intensification technology.

The proposed research project will benefit a broad range of stakeholders:

(1) The Energy sector worldwide and in the UK: Inter-governmental Panel on Climate Change (IPCC) recommended in its 2007 report that global CO2 emissions be cut by 50% by 2050 compared with 1990 levels. Power generation is the single largest contributor of CO2 emissions. There are almost 5,000 power plants worldwide with total emission of 10.5 gigatonnes CO2 per year. In 2008, the UK Government agreed to the binding target of an 80% reduction in CO2 emissions by 2050 from the 1990 baseline. Electricity generation from coal- or gas-fired power plants was 77% in 2009 in the UK. To meet the target in CO2 emissions, it is inevitable to implement carbon capture for the coal- or gas-fired power plants. The UK energy sector will benefit from less capital cost and reduced thermal efficiency penalty when capturing CO2 - the two challenges that this proposed project is to deal with.

(2) Global and the UK CCS research community: In the limited literature, most work deals only with some aspects of intensified absorbers, while intensified strippers are rarely studied (except for one study from Taiwan). New design of intensified absorber proposed in this research is unique. Development of new models from this project (i.e. process models for the intensified capture process and CFD codes) will be published and even commercially exploited. Process analysis of the intensified capture process based on the models newly developed will derive new insights on how and why mass transfer and reaction rate in the new capture process have been improved significantly. Fundamental understanding of the flow regime and flow pattern inside intensified absorber will be obtained. Through publishing in international leading journals, global CCS community will benefit.

(3) UK Policymakers and Regulators: New results (i.e. experimental data, the results on size reduction of intensified absorber and stripper, the results on savings in capital cost and operating cost with the proposed capture process applied to CCGT power plant) potentially obtained from this proposed project will provide reliable evidence base. These are very important for UK policymakers and regulators for strategic decision making.

(4) Power Utilities: Power utilities companies run different power plants. They have to make long term business decisions such as when to implement carbon capture and which technology to choose. They will directly benefit from the proposed project since they can see another choice along the route of post-combustion carbon capture with solvents. E.ON (a typical utility company) owns power plants and sits in the project advisory board of the proposed project.

(5) Original Equipment Manufacturers (OEM) and other technical providers: The OEM companies and other technical providers face different choices in carbon capture. The proposed project will inspire their product development in CCS. ALSTOM (a typical OEM) and software provider PSE Ltd and process technology provider COSTAIN are also in the project advisory board.

(6) Professional training and higher education: The research deliverables and milestones will be fed directly into the teaching programmes in the four universities generally at MSc and MEng levels. The modules relevant with this project are Energy Technologies, and Process Simulation and Design. Companies involved in this project will benefit from staff with improved knowledge and skills and even organisation of short courses for CPD.

(7) The wide public: The wider public will better appreciate the value and role of science and engineering dealing with the challenge of climate change. Technical results will be disseminated with a web site. At Hull City Guild Hall, there will be a Science week each year. University of Hull is a major participator. This proposed project will be disseminated through this event to the wide public.