PTQ Q3 2025 Issue

250

STT, 870 psi (60 bar) Structured packing, 870 psi (60 bar)

STT advantaged region

200

150

Conventional tray and packaging

100

150

200

250

Rich amine loading (dimensionless)

Gas ow rate (%)

Hydraulic limits

Structured packing

STT

High-capacity trays

The swirl tube separators also produce gas-free liquid that flows easily to the tray below via the downcomers. Unlike conventional trays, which require larger downcomers to handle gas-rich froth, the new trays’ efficient separation eliminates this need, boosting the hydraulic capacity of the column. This technology provides two key advantages: enhanced gas and liquid handling capacity, from the high turbulence and velocities in the contacting boxes, and improved mass transfer, which is achieved by reaching near-equilibrium conditions within the boxes. This is facilitated by a large liq- uid-to-gas ratio and intense mixing. For the new trays, mass transfer efficiency is best repre - sented by the overall volumetric mass transfer coefficient, which provides a clearer understanding of CO₂ absorption by isolating key factors such as partial pressure and gas velocity. Figure 4 shows that STT trays offer superior mass transfer efficiency compared to a leading structured packing system, with improvements exceeding 100%, depending on CO₂-rich amine loading. Although STT columns may have a higher pressure drop than equivalent columns with packing, they outperform conventional tray technology. Their enhanced mass transfer efficiency means fewer trays are needed to meet the same specifications under similar conditions. Retrofitting STT tray retrofits provide an efficient drop-in solution for increasing capacity in brownfield units. One key challenge in older absorber columns is structural imperfections, such as a lack of roundness or uneven surfaces, which can com- plicate retrofitting. STT technology overcomes these issues with expansion rings, eliminating the need for direct weld- ing to high-pressure column walls and minimising turna- round times. These adjustable expansion rings are installed at various levels and further supported by existing support rings. As tension is applied through bolted wire, the ring conforms to the column’s shape while a flexible gasket ensures a secure seal, accommodating imperfections like bulges or dents. This design ensures fast, reliable installation, making STT trays an ideal upgrade for ageing absorbers. Figure 4 STT performance compared to a leading structured packing system across the full range of amine loading values

through gas inlet channels. The high gas velocity creates intense turbulence within the mixing box, maximising gas-liq- uid mixing and mass transfer, like conventional trays in the spray regime but without the drawback of liquid entrainment. Next, the gas-liquid mixture moves to a swirl tube arrangement in the separation zone, where centrifugal force efficiently separates the liquid from the gas. The liquid is directed to the walls of the tube and collected in a liquid pool on the tray, while the liquid-free gas exits through the top. At the column level, gas flows upwards, while the solvent flows downwards in a countercurrent motion. However, within each tray, gas and liquid flow co-currently, optimising contact and separation on each tray (Figure 2b). Performance comparison with conventional trays In conventional trays, liquid flows downwards and gas flows upwards in a countercurrent manner, often leading to mutual entrainment. As the gas load increases, liquid entrainment rises until it reaches the flooding point, where the liquid flow reverses direction. STT operates on a different principle by allowing inten- tional and controlled entrainment on each tray. This ena- bles the technology to support much higher gas velocities compared to conventional trays or structured packing. The integrated swirl tubes in the tray design ensure efficient sep - aration, preventing entrained liquid from reaching the tray above and enabling higher gas throughput – up to two times more, depending on design choices (see Figure 3 ). Figure 3 Hydraulic performance of STT trays compared with conventional trays and structured packing

Existing absorber column operating vs STT retrofitted design parameters

Parameter

Conventional tray STT tray (operating) (design)

Feed gas flow rate, MMSCFD Solvent flow rate, GPM (m3/h) Column pressure drops, psi (bar)

130

156

966 (227)

1,063 (241)

9 (0.6)

6 (0.4)

H₂S in treated gas specifications, ppmv <4 CO₂ in treated gas specifications, mol% <0.1

<0.1

Table 1

PTQ Q3 2025