PTQ Q1 2026 Issue

Hybrid trays: strategic configuration for optimal column performance

Various types of trays and their designs are crucial for achieving efficient mass transfer while managing hydraulic limitations such as flooding, weeping, and entrainment

Rasna Rajendran, Anupriya Shahi, and Navneet Agarwal Engineers India Limited

D istillation and fractionation columns represent the backbone of petroleum refining and processing, performing crucial separations that enable the pro - duction of fuels, chemicals, and other valuable products. From conventional distillation in refineries to fractionation operations in petrochemical units, or from extractive distil - lation to absorption and regeneration, distillation columns have always been an integral part of the hydrocarbon industry. Due to their significant energy consumption and capital costs, optimising the design and operation of these ‘columns’ remains a central engineering challenge for designers. Optimal column design not only meets the pro - cess requirements of separation and mass transfer but also provides techno-economic models to refiners worldwide. The mass transfer process within the column, achieved by effective contact between vapour and liquid phases, is strongly influenced by the design of the internals. The commonly used internals include trays and packed beds, available in both conventional and high-capacity models. It has been more than a century since the first distilla - tion column with perforated plates was invented. Since then, the industry has witnessed numerous advancements in internals. Conventional trays, like sieve and valve trays, have long been the default choice in many columns due to their proven performance and simplicity. However, with the increasing demands of enhanced throughput and process flexibility, high-capacity (HC) trays were developed to handle larger vapour and liquid loads, offering advantages in capacity and operational flexibility. To date, designers have a well-defined and still-evolv - ing range of internals to choose from for their respective designs. For hydraulic designers, there are various factors to assess in the selection of internals, including the type of service, degree of foaming, operating pressure, and liq - uid-to-gas (L/G) ratios. While the previously mentioned parameters focus on the process design and performance aspects of the design, there are also economic and feasi - bility considerations that need to be evaluated prior to the finalisation of the configuration. Some of the influencing factors include future capacity margins, cost and space considerations, height limitation, erection, maintenance, and inspection requirements.

The evolution of the hydrocarbon industry is very dynamic, having undergone significant transformation over the years, posing challenges to designers that range from enormous single-train refining capacity and mega-scale naphtha crackers to small-scale refineries. The successful implemen - tation of columns in such installations is largely attributable to the versatile range of internals described earlier. Distillation operates on the basis of the difference in vol - atility between components in a liquid mixture, establishing vapour-liquid equilibrium (VLE) stages where vapour and liquid phases interact. The efficiency of this mass transfer process depends on the quality of the interaction between vapour and liquid. It is facilitated by the contacting surface, which can be either trays or packed beds. For hydraulic designers, there are various factors to assess in the selection of internals, including the type of service, degree of foaming, operating pressure, and liquid-to- gas ratios Types of trays Conventional trays include sieve trays, bubble cap trays, and valve trays, with valve trays being the most widely used tray type. Valve trays feature a perforated plate with ori - fices covered by movable valves with legs that lift to permit vapour passage under operating conditions. The adjustable opening, owing to the leg length, allows for self-regulation of vapour flow and effective liquid hold-up on the tray deck, facilitating mass transfer. Conventional round floating valve trays have been widely used in all clean services, including both low-pres - sure and high-pressure applications. These trays exhibit a broad range of operation without much loss in efficiency. The typical operating range for these trays is 30-110%. They are provided as conventional removable trays in the column. Advantages of conventional valve trays include:

PTQ Q1 2026