the CCS plant is installed, flue gas heat recovery can be ambitious due to contaminants in the flue gas. In a dusty environment, such as a cement plant, a system is needed to regularly clean the heat exchanger surface to maintain efficiency and prolong its lifespan. This is achieved
100%
DIESTA 7% total plant costs savings 10% p ipe rack savings
40%
80%
37%
60%
40%
47%
Construction
44%
Procurement
20%
13%
12%
Engineering
0%
DIESTA tube
Standard nned tube
Figure 3 Comparison of standard and DIESTA finned tube
Lean solvent cooler When the lean solvent exits the lean/rich heat exchanger, it has not yet reached the temperature required for the absorber column and must be further cooled. This can be achieved through water cooling, with a PHE for example, or via ambient air cooling methods like cooling towers or air-cooled heat exchangers (ACHE). In the case of an ACHE, the air side is normally the weaker heat transfer side, so it is favourable to enhance the heat transfer coefficients on the air side. The Kelvion Groovy fin achieves this by improving the aerodynamic flow around the single fin tube. As solvents normally have a higher viscosity than water, it can make sense to enhance flow turbulence inside the tube using internal structures. In this regard, Kelvion launched the Double Internally and Externally Structured Tube for Air (DIESTA) fin coolers (see Figure 3 ). The use of more efficient ACHE fin tubes allows for smaller complete ACHE installation systems, benefiting the overall plant size, piping, and steel structures. Regeneration reboiler The reboiler is used to break the bond between the solvent and CO2. It is the main thermal energy consumer in the absorption process and mostly uses steam as its energy source. It accounts for around 78% of the annual variable operating costs or 68% of the overall costs of a typical CCS absorption plant ( Barlow, et al., 2025a ). On average, roughly 2.3 GJ/tonne of CO2 is needed as specific regeneration energy for solvent-based CCS systems ( Barlow, et al., 2025b ). An exemplary plant capturing 1 million tonnes of CO2 per year over an operational time of 8,000 hours per year would need a reboiler duty of 80 MW.
using scrubbing, hammering, or soot blower systems. The choice should be made carefully based on conditions, as dust and fibres require different cleaning approaches. For applications where flue gas temperature is decreased below the condensation point, there is an increased risk of forming corrosive compounds, such as sulphuric acid and hydrochloric acid, which require the use of corrosion-resistant materials. Among various specialist steel types, one interesting solution is using polypropylene tubes with a graphite add- on. This results in a material that is fully resistant to acids while demonstrating heat transfer properties similar to those of stainless steel. Additional challenges for CCS heat recovery systems relate to high flue gas temperatures and pressures, which require ongoing technology and design development. The use of pressurised vessels for the gas side or heat recovery units at temperatures of 1,000°C or above are among the decarbonisation project challenges. Lean/rich heat exchanger In the absorption process, it is crucial to set up proper internal heat recovery. The lean/rich heat exchanger is an essential part here, as it transfers massive amounts of heat from the hot lean solvent to the rich solvent side to preheat it before it enters the stripper column. PHEs are exceptionally well-suited for this application, offering a combination of thermal performance and compact design. Fully welded PHEs are used when leak-tightness, compactness, and durability are top priorities. Gasketed plated heat exchangers are used when flexibility, easy maintenance, and cost-efficiency are key. Close attention is needed when choosing the plate and gasket materials.
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