PTQ Q3 2026 Issue

Practical CFD applications in refinery troubleshooting

Case studies show how CFD can enhance design development and benchmarking, delivering performance improvements while reducing risks and costs

Sahithi Ravuluri, SK Shabina, Dr I R Choudhury, and Sarvesh Kumar Research & Development Centre, Indian Oil Corporation Limited

C omputational fluid dynamics (CFD) has evolved into a widely used engineering tool across the refining indus - try for evaluating internal flow behaviour, diagnosing performance limitations, and validating design modifications before implementation. Based on first-principles solutions of the governing conservation equations, CFD provides detailed insight into velocity fields, mixing patterns, phase distribution, and local transport phenomena inside operat - ing equipment and piping systems. This capability comple - ments plant data with reliable insight to uncover root causes that are often inaccessible to direct measurement under high-temperature, high-pressure operating conditions.1 In refinery systems, CFD supports troubleshooting of flow maldistribution, optimisation of equipment internals, bench - marking of alternative designs, and assessment of thermal or hydraulic profiles. Combined with cold-flow experiments for validation, it strengthens confidence in design decisions and enables engineers to efficiently screen multiple options, reducing rework and implementation cost. Case study A: Benchmarking of in-house developed gas-liquid distributors Trickle Bed Reactors (TBRs) are widely used in refining due to their operational simplicity, flexibility, and low liquid hold-up, with gas and liquid flowing co-currently downward over a packed catalyst bed. Some common refinery applica - tions include hydroprocessing units such as diesel hydrodes - ulphurisation (DHDS), diesel hydrotreating (DHDT), and hydrocracking units.

Since reactions occur between gas dissolved in the liquid phase and the catalyst surface, effective liquid wetting is crit - ical for optimal mass transfer and catalyst utilisation, which, in turn, depend on uniform flow distribution. Maldistribution at the inlet can lead to channelling, dry zones, poor heat and mass transfer, hotspots, and faster catalyst deactivation, ulti - mately reducing conversion and throughput. Therefore, the design of reactor internals, especially gas-liquid distributors, is crucial for ensuring uniform radial and axial distribution. In this context, advanced cold-flow experiments combined with CFD are increasingly used to design, screen, and optimise distributor systems by analys - ing phase distribution and sensitivity to operating conditions, enabling improved reactor performance, enhanced catalyst life, and reduced operational risks.² CFD was applied to evaluate and benchmark an in-house developed gas-liquid distributor³ against a standardised design. The assessment was carried out under represent - ative DHDT operating conditions to closely replicate plant performance. Volume fraction contours were generated for both configurations to visualise liquid distribution across the reactor cross-section. The results indicate a significantly more uniform liquid fraction profile for the in-house design, whereas the com - mercial distributor exhibited localised regions of liquid phase. This can be observed from the comparatively more liquid phase gradients (yellow spots in Figure 1 ) for the standardised design compared to the in-house design (see Figure 2 ). This improved uniformity in the in-house design

Figure 1 Development of liquid phase volume fraction contours at different reactor heights downstream of the standard - ised gas-liquid distributor. The yellow spots indicate liquid gradients (sample spots marked)

PTQ Q3 2026