SMART – Solvent Management At Reduced Throughput & prototype demonstration (Flexible Funding 2022)

Professor Mathieu Lucquiaud, University of Sheffield, was awarded funding in the UKCCSRC’s Flexible Funding 2022 call to look at “SMART – Solvent Management At Reduced Throughput & prototype demonstration”.  Mike Ownsworth, University of Sheffield, provides an insight into the project.

Track-1 of the UK Carbon Capture, Usage and Storage Programme is made up of the initial two CCUS clusters: HyNet and the East Coast Cluster. Both clusters include amine post-combustion capture (PCC). PCC uses an amine solvent to capture CO₂ out of the combustion products, which is heated to release the captured CO₂ and then compressed for permanent storage. Impurities in the flue gas stream are also absorbed and can 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, eventually requiring complete replacement of the solvent inventory.

The first two examples of large-scale PCC – Boundary Dam 3 (Canada) and Petra Nova (USA) – have had reports of high solvent management costs and associated problems, and Petra Nova has only recently restarted operations. To avoid similar problems in UK, the Environment Agency ‘Guidance: Post-combustion carbon dioxide capture: best available techniques (BAT)’ recommends realistic pilot (or full scale) tests using fully representative (or actual) flue gases over a period of at least 12 months.

Very long tests of 8,000 hours or longer, as recommended by the guidance, are prohibitively expensive if pilot plants large enough to give realistic absorber performance and energy requirements are used. The SMART project is developing a pilot test unit focused only on solvent management and emissions control. This can be much smaller, perhaps as low as 10-80 kg CO₂/day, roughly 1% of the flue gas of the larger pilot. In addition, novel small-scale reclaimers and water and acid washes are being included, to allow a range of solvent management techniques to be tested.

The SMART unit concept is aimed at a low cost and size including solvent reclaiming, and environmental emissions controls also having representative thermal and composition conditions for the solvent being tested. The unit is too small to assess operational energy requirements accurately, yet it can be expected to give useful indications of ‘showstoppers’. Principally, verifying that a build-up of unwanted degradation products and heat stable salts can be avoided, and that emissions to atmosphere from the long-term solvent inventory can be controlled to acceptable levels

A model of a first stage reclaimer was produced by Lucas Joel and presented to the GHGT-17 conference in 2024. Graphs of the model output are shown in Figure 1.

Figure 1: Reclaimer temperature as a function of moles of non-volatile impurity in the blowdown. (Joel, 2024)

A standalone reclaimer has been constructed in a laboratory at the University of Sheffield and is being used to validate the models which were presented.

Figure 2: Standalone reclaimer constructed at the University of Sheffield (behind splash guards)

The standalone reclaimer was initially operated on fresh MEA solvent, but has recently moved on to using aged solvent from the Translational Energy Research Centre.  Alongside the standalone reclaimer, a test unit including Absorber, Desorber Reboiler and integral Reclaimer is being constructed.

The size of the SMART test unit fits between bench-top laboratory units, easily made in glassware and tubing, and larger pilot plants, that can be fully fabricated in stainless steel with flanged joints and having fully automated controls. As such, the assembly poses some interesting trade-offs. A choice made early in the design of the SMART unit was to use screwed joints to allow flexibility in the arranging and positioning of the various components. The joints on the components are larger than would usually have threaded connections. That has led to difficulties getting a perfect seal. In the end, many of the joints have been redesigned as flanges or seal welded, losing the intended flexibility in any case.

The SMART prototype is being constructed in a laboratory at the University of Sheffield (figure 3). It will initially address reclaiming of MEA from degraded MEA carbon capture solvent. In the laboratory, a simulated flue gas will be produced from air, added CO₂ and traces of single contaminant gases.

Figure 3: SMART Lab Unit under construction at University of Sheffield

The test rig can be used in a continuous mode of operation to allow investigation of solvent desorption and reclaiming at various temperatures and pressures. The effects of the single trace contaminants, the effects of blowdown from the desorber to the reclaimer and the continuous operation of that reclaimer will also be investigated. Progress on the construction and commissioning of the test unit was made to the PCCC8 conference in 2025 by Mike Ownsworth.

After the SMART unit has been assembled and operated in a lab environment, it will initially be relocated to an industrial location to be attached to a slipstream from a real flue gas. The exact contaminants present in the real flue gas will depend heavily on the upstream industrial process. It is expected that there might be significant NOx, SOx, CO and particulates which could contain metals or other trace organic material. Each industrial flue gas will have a different amount of residual oxygen. All these things will affect the degradation rate and therefore the extent of reclaiming which is desirable and practical.

Because the unit is small, long-term (>8000hr) representative trials will be possible without incurring excessive costs. The small number of previous long-term tests carried out on real flue gases have shown accelerating degradation effects after a period of operation. Following optimisation to confirm operating parameters such as draw off to the reclaimer and reclaiming temperature, the SMART unit can be operated for a long duration to establish whether continuous reclaiming can avoid the onset of the accelerating degradation. The long duration operation can also demonstrate the feasibility at this scale of the of the year-long pilot trial as recommended in the BAT guidance.

Read more on Mathieu’s Flexible Funding 2022 project page (including the GHGT-17 paper and the PCCC8 presentation).