Case studies The case studies are based on the takeaways the authors have acquired while executing various projects. The first two cases present a detailed evaluation of the benefits, especially monetary savings, with the utilisation of hybrid tray design and demonstrate how the implementation of HC trays in selective zones of a column can provide stra- tegic solutions to performance and economic issues. The third case narrates a solution to an implementation chal- lenge provided by the hybrid tray configuration. Case study 1 The design of an atmospheric crude distillation column in a refinery with significantly large crude processing capacity is discussed, with tray sections envisaged for the column shown in Table 1 . Typically, the middle pumparound located in the middle section of the atmospheric column is the largest diameter section of the column. These pumparound sections con- trol the column diameter. In the subject case study, these sections also had the dominating flow rates. On the other hand, mass transfer sections are not the controlling section for the column diameter, hence they can have conventional valve trays. The column top typically contains a pumparound section and a light-end fractionation section, requiring many the- oretical stages for achieving finer distillation between the gasoline and naphtha fractions. In view of the stringent product distillation requirements, it is necessary to specify suitable mass transfer internals, which will result in a diameter and height of the top section comparable to that of the rest of the column. The overall diameter of the atmospheric distillation column is governed by various factors, including the crude density (API gravity), flow and duty range of distillates, and the requirement for future capacity expansion. These factors take a toll when it is required to process two or more different types of crudes in the same column. For the loadings across the atmospheric distillation col- umn, the diameter was first estimated with a configuration in conventional trays for all sections. For the significantly higher throughputs, the estimated diameter was 19m. Columns with such large dimensions are very rare, as they call for major mechanical restrictions pertaining to struc- tural support, out-of-roundness, erection, crane capacities, and alignment issues, among others. Hence, exploring other options of internals was indispensable. The hybrid tray configuration, featuring the following types, showed positive results in terms of satisfactory hydraulic performance: • The top 21 trays, subject to the highest vapour load and corresponding to tray sections #36-56, were HC trays. • The heavy diesel section, corresponding to tray sections #13-20, and the light diesel section, corresponding to tray sections #24-35, used conventional valve trays. • The pumparounds for both heavy diesel #10-12 and light diesel #21-23 used HC trays (name and model of trays not disclosed due to confidentiality). With the hybrid tray type, the column diameter could be
• Reliable operation across moderate vapour loads. • High tray efficiency under typical operating conditions. • Relatively simple fabrication and maintenance. However, their capacity can be limiting in high vapour load scenarios, leading to hydraulic constraints such as flooding and, in rare cases, weeping at low vapour loads. HC trays are designed to improve capacity and extend oper- ational range. They employ design enhancements such as: • Increased open area for vapour flow. • Optimised valve geometry and spacing. • Horizontal component in vapour velocity, which ensures reduced fouling and entrainment. These features enable HC trays to handle higher vapour and liquid rates with lower pressure drop and improved hydraulic stability at peak loads. Additionally, they often demonstrate improved overdesign and turndown. Despite these benefits, HC trays typically exhibit lower efficiency at low vapour loads and are more prone to weep - ing when compared to conventional valve trays due to the missing advantage of the floating caps. Additionally, they are more expensive due to complex manufacturing and proprietary designs, which sometimes account for nearly three to four times the price of conventional valve trays. Fixed valve trays or sieve trays are more suitable than HC trays in dirty service. In comparison to floating valve trays, both types of trays operate in a narrow range of flow and thus experience limitations in the turndown. In recent times, a growing trend observed with designs is the implementation of full-column retrofits or new builds with exclusive use of HC trays. This practice is often justi- fied by debottlenecking potential and enhanced capacity. It is, however, noteworthy that the ‘one-item-suits-all’ approach often overlooks the specific hydraulic and sep - aration requirements of the column, leading to subopti- mal performance, higher costs, and reduced operational flexibility. The following case studies show the benefits of employ - ing hybrid tray configurations combining conventional trays and HC trays in distillation and fractionation columns. A strategic approach leverages the advantages of trays from various generations while addressing the operational and economic limitations in a specific tray type. Case studies have been described based on real-time design experience of providing balanced and necessity-driven solutions.
Column tray sections (numbered from bottom to top)
Tray section
Service for the section Heavy diesel pumparound
#10-12 #13-20 #21-23 #24-35 #36-38 #39-53 #54-56
Heavy diesel section
Light diesel pumparound Light diesel section Kerosene pumparound
Kerosene section Top pumparound
Note: Trays above the feed zone are only considered in this study. Stripping trays in sleeve configuration have not been considered.
Table 1
70
PTQ Q1 2026
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