PTQ Q1 2026 Issue

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Hybrid conguration

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Hybrid conguration

Only conventional

Figure 3 Comparison of weight – Case 2

Figure 4 Comparison of cost in US dollars – Case 2

HC trays, thereby meeting the new capacity requirements without any change to the main column. For future revamps or debottlenecking projects, replac- ing specific sections of trays with high-capacity designs in a column, rather than a full-scale replacement, provides greater flexibility and reduced downtime. This case study is a classic example of this approach. The weight and cost numbers taken for the previous two studies correspond to the shell and trays only. Components of support, such as beams, girders, skirts, clamps, bolts, and cladding, are not included in the comparison. Case study 3 Another interesting case involved designing a regenerator column for a gas sweetening unit. While the plant capacity was nominal, the over-dimensional consignment (ODC) cri- teria posed a restriction, limiting the equipment dimension to a diameter of approximately 5m, owing to the narrow - ness of the last section of the access road. While the plant was near the highway, the width of the access road alone resulted in this restriction. The regenerator column consisted of 22 trays, with amine as the regenerator solvent. In this configuration, 20 trays (from the bottom) could be designed in an optimal diam- eter of 5.1m. However, two trays in the overhead section could not be accommodated within this diameter due to the high reflux (with a liquid load 23 times that of the bottom section). Increasing the diameter beyond 5.1m imposed two diffi - culties. First, the ODC criteria could not be met, making the transportation of the shell close to impossible. Second, the fabrication of the toricone (the neck-like section between the large and small diameters) at the column top required signifi - cantly more time than fabricating the main shell. The solution was to adopt HC trays for the top two trays in the overhead zone. With this, satisfactory hydraulic performance could be met in the 5.1m diameter, addressing all logistic-based chal - lenges without compromising performance. Inferences and takeaways As one of the most vital components for bulk separation, distillation and fractionation columns continue to play an indispensable role in hydrocarbon processing. In the ever-changing phase of the hydrocarbon industry, due to

their large capacities, columns are expected to be massive in size, which can consume a larger plot space and also pose challenges for mechanical design, supports, and the integrity of internals during operation. It is therefore recom- mended to fully optimise column sizes when possible by the use of various high-capacity/efficiency/specialty internals. Challenges The installation and incorporation of HC trays across an entire distillation column can present several challenges: Overdesign and capital cost: HC trays cost more than conventional trays, mainly due to more intricate fabrica- tion, technical expertise, and proprietary designs. Installing HC trays uniformly, regardless of the actual hydraulic load at each column section, can substantially increase capital expenditure without delivering proportional benefits. Hydraulic mismatch along the column: Vapour and liquid flow rates vary significantly along the column. Installing HC trays in low-load sections may induce instability, such as weeping, and degrade the hydraulic performance, espe- cially at turndown loads. Hybrid tray approach: combining conventional and HC trays The hybrid tray design concept involves the hydraulic and deliberate placement of selective conventional and HC trays based on vapour-liquid load profiles and separation needs, with the following benefits: hydraulic stability, capi - tal and operational cost reduction, structural support/oval- ity issues, crane capacities, erection and alignment issues, and economic implications. Hydraulic stability: By employing conventional trays in lower vapour load zones, the risk of weeping is mini- mised due to better liquid hold-up and vapour distribution. Conversely, HC trays are installed where vapour and liquid rates are highest, such as feed sections, thus maximising hydraulic stability and capacity. Limiting the installation of expensive HC trays to where they are required to meet the hydraulic demand reduces capital investment. Structural support/ovality issues: Limiting the column diameter through the intentional and thoughtful use of a combination of HC trays and conventional trays reduces column diameter, footprint, and probability of ovality, which leads to cascading problems with the fitment of supports

PTQ Q1 2026