Why is this research needed?

The UK is implementing two Track 1 carbon capture and storage (CCS) clusters in the NW and NE of the UK. Of the 41 projects in the BEIS ‘Cluster sequencing Phase-2: eligible projects (power CCUS, hydrogen and ICC)’ at least half use amine post-combustion capture (PCC) and further PCC projects (including BECCS) can be expected in subsequent rounds of deployment. PCC uses an amine solvent to ‘wash’ CO2 out of the combustion products, the amine is then gently heated to release the CO2, which can then be compressed and taken away by pipeline for permanent storage a kilometre or more under the seabed offshore. But the amine also washes out most of the impurities in the gas stream; this is a good thing for the environment but may cause problems if the impurities cause the solvent to break down when it is heated or simply cannot be removed from the circulating solvent as fast as they are collected.

As an example of the sorts of problems that can arise, a Best Available Technique Review for the Environment Agency by the applicants describes how the two examples of large-scale PCC – Boundary Dam 3 (Canada) and Petra Nova (USA) – have both had reports of high solvent management costs and associated problems, and Petra Nova is currently not operating. To help avoid similar problems in UK CCS deployment, the Environment Agency ‘Guidance: Post-combustion carbon dioxide capture: best available techniques (BAT)’ recommends that “You must work out the solvent performance, including reclaiming requirements and emissions to atmosphere. Determine this through realistic pilot (or full scale) tests using fully representative (or actual) flue gases and power plant operating patterns over a period of at least 12 months.”

In discussions with both regulators and practitioners it appears, however, that very long tests are generally precluded if large enough pilot plants give realistic absorber performance and energy requirements are used (>0.4 m minimum vessel diameter, ~ 10 tCO2/day, as in a recent study by AECOM for BEIS, also involving the applicants).

What is this research investigating?

The principal purpose of this project is to rapidly demonstrate the novel features required for a long-term (>8000hr) representative, small scale test for amine solvent management at reduced throughput (SMART) capturing 20-80 kg of CO2 per day. This will allow portable units to be designed to commercial standards for on-site use by UK industry, as well as being a key facility for further fundamental research and technology development.

These novel features include:
– integrated thermal reclaimer for representative operation
– externally heated reboiler with low skin temperatures to avoid local thermal degradation hotspots
– acid wash for solvent emission control
– absorber with low-liquid loading packing

The use of a ‘short, fat’ absorber that can still achieve representative solvent CO2 loadings will give easier transport and location on site.

It is proposed to develop a PCC pilot test unit that is focused only on solvent management and emissions control. This can be much smaller, for Solvent Management At Reduced Throughput (SMART), perhaps as low as 20-80 kgCO2/day, roughly 1% of the flue gas of the larger pilot. Conventional vessel designs would be very slender and tall to achieve realistic solvent loadings so, to give a more practicable system, ‘short, fat’ vessels with special low liquid-loading packing will be used. In addition, novel small-scale reclaimers (being developed by the UKCCSRC PCC-CARER project and with additional University of Sheffield funding) and water and acid washes will be included, to allow the full range of solvent management techniques to be tested.

The SMART unit concept is aimed at low cost and size, but very representative thermal and composition conditions for the solvent being tested, including solvent cleaning and exit emissions controls. Thus, while the unit is too small to assess operational energy requirements accurately, it can be expected to give useful indications of ‘showstoppers’ associated with long-term management of the solvent under commercial conditions, principally verifying that a build-up of unwanted degradation products can be avoided and that emissions to atmosphere from the actual long-term solvent inventory can be controlled to acceptable levels.

What does the research hope to achieve?

Once the ‘wet process’ design has been developed and tested, then SMART units can be constructed suitable for operation on industrial sites; it has been confirmed that this is not likely to require significant permitting changes for periods of up to 18 months. These SMART test units will be too late for initial testing on the first UK PCC projects but could still be put into operation in time to give advance warning of any problems that might be encountered after extended operation. For later projects, particularly those with site-specific flue gases (i.e. Energy from Waste, biomass, industrial processes, gas engines) SMART test units could be used from the outset to screen solvents and management methods before larger-scale pilot tests are undertaken, if they are deemed necessary. The lab unit and the on-site units will also facilitate a wide range of fundamental and applicable research.

The SMART project results will be rapidly communicated to key stakeholders who might wish to use such equipment and also to potential suppliers for versions to use on industrial sites.