Decarbonisation Technology February 2026 Issue

As the process requires substantial heat input while maintaining a cold end (absorption) and a hot end (desorption), various heat exchangers are integrated into the process. Furthermore, often a central recooling system is needed to dissipate surplus heat from the process in water-based systems or in large air-cooled heat exchanger installations. Flue gas cooling and waste heat recovery The CO 2 absorption process within the absorption column requires a temperature level of around 40°C. Hot flue gas must be cooled before it enters the core process. This can be done in two ways. The first is via a direct contact cooler, which cools the flue gas by spraying water directly into the gas stream. The heated water is collected and recooled in an air-cooled heat exchanger or a PHE. The second option is to cool the flue gases via heat exchangers, enabling heat recovery for use in the CCS process or for other heating purposes. Kelvion provides tubular heat exchangers and welded PHEs for this purpose. They transfer the energy to secondary fluids, such as hot water, thermal oil, or combustion/drying air. There are many tubular heat exchanger designs, with various tube types, flow arrangements, and materials. Welded PHEs, such as Kelvion’s Rekugavo, are the perfect choice for gas-gas heat exchange in a countercurrent flow arrangement. They achieve high heat recovery efficiency, even with low temperature differences. Depending on the specific project, tubular and plate heat exchangers can be combined to integrate multiple heat exchangers for different purposes in a single overall solution (see Figure 2 ). Choosing the right technology for heat exchangers can be challenging, as each option offers unique features. For example, using tubular heat exchangers for gas-to-gas applications provides geometrical flexibility. When dealing with gas streams with significant volume flow differences, multiple passes can be used for one side of the unit. This allows for optimising the range of gas velocities and Reynolds number, leading to a good heat transfer coefficient. Plate technology offers other benefits, such as compactness, a large heat exchange surface, and counterflow efficiency, but it is the best choice for similar gas volume flows. Depending on the process and facility where

Tube heat exchanger

Plate heat exchanger

U-tube heat exchanger

Figure 2 Integrated heat exchanger solution

where CCS systems are installed to separate the CO 2 from the flue gases. Furthermore, point- source CCS systems can be integrated into enhanced gas and oil recovery facilities to store CO 2 in reservoirs, thereby lowering CO 2 emissions from fossil fuel usage. Flue gas absorption CCS system overview In a flue gas absorption CCS system (see Figure 1 ), such as those installed downstream from a waste- to-energy or cement plant, the flue gas must first be cooled. This can be realised by a direct contact cooler or the integration of heat exchangers. The flue gas then enters an absorption column, where it is brought into contact with a solvent, such as an amine solution, to absorb the CO 2 . The CO 2 -rich solvent is then sent to a stripper column, where the CO 2 is released, and the solvent is refreshed. By conducting this reciprocal absorption/desorption process, a continuous CO 2 capture process is realised. After the CO 2 gas leaves the stripper column, it is cooled, compressed, and transported to a storage or utilisation location.