PTQ Q3 2026 Issue

Figure 2 Development of liquid phase volume fraction contours at different reactor heights downstream of the in-house developed gas-liquid distributor. Note that the scale of contours is same for both standardised and in-house profiles

suggests better catalyst bed coverage with reduced likeli- hood of channelling.⁴ Observations from the CFD simulations were further vali- dated using pilot-scale cold flow data. The liquid distribution obtained from both distributor configurations was quanti - fied using the maldistribution index (MI), a commonly used parameter to assess distribution uniformity, with a value of 0 representing a perfectly uniform distribution and higher values indicating increasing levels of maldistribution. The experimental results showed MI values of 0.08 for the standardised distributor and 0.06 for the in-house- developed distributor. The lower MI observed for the in-house design indicates a more uniform liquid distribution across the cross-section. These experimental findings are consistent with the CFD predictions, thereby confirming the improved distribution performance of the in-house distribu- tor compared to the standardised configuration. Case study B: Corrective engineering to mitigate flow maldistribution in reactor feed/effluent exchanger trains of DHDT units Flow maldistribution in a heat exchanger train leads to reduced heat recovery, accelerated fouling, and higher pres - sure drop. The issue becomes more severe under multiphase conditions due to phase separation. Addressing maldistri- bution during detailed or corrective engineering is critical to enhance energy efficiency and ensure operational reliability. CFD provides a robust approach to diagnose maldistribu- tion root causes by evaluating design options and providing insight into localised flow and heat transfer. By simulating

the hydrodynamics of headers, distributors, and exchanger passes, it helps identify dead zones, bypassing, vapour-liquid segregation, and uneven velocity profiles that are often diffi - cult to detect through field measurements alone. This allows engineers to virtually evaluate corrective measures prior to physical implementation, enabling rapid screening of poten - tial solutions with minimal operational disruption and reduced engineering risk. Consequently, the use of CFD in both new designs and revamp projects contributes to improved exchanger train reliability and enhanced energy efficiency. Corrective engineering strategies were developed and validated using CFD for the reactor feed/effluent exchanger network of one of the IOCL refinery DHDT units. The mald - istribution problem was observed post-revamp, where the original single train of the heat exchanger network was split into two parallel trains (Train-1 and Train-2) by increasing the number of exchangers and piping configuration. Plant data revealed temperature imbalances, leading to inadequate feed preheat, lower weighted average bed tem - perature (WABT), and unequal pressure drops across par - allel trains. The root cause was identified as hindered flow development in the existing pipeline design for splitting mul - tiphase flows across trains, despite the desired symmetric train arrangement. To resolve the issue, alternative piping configurations pro - viding proper flow development were recommended by the R&D engineering group. Baseline CFD simulations showed significant maldistribution in the existing configuration, with ~78% of the flow through Train-2 and ~22% through Train-1 (see Figure 3 ). With the recommended alternative design, the

Volume fraction (liquid)

Radial plane view along Train-1

Radial plane view along Train-2

1.00e–01 9.00e–02 0.00e+00 1.00e–02 2.00e–02 3.00e–02 4.00e–02 5.00e–02 6.00e–02 7.00e–02 8.00e–02

Train-1

Train-2

Mid plane slice-Front view

Figure 3 Radial profiles of liquid phase volume fraction along the length of original piping configuration leading to heat exchanger Train-1 and Train-2

PTQ Q3 2026