Revamps 2026 Issue

Operational problem solving in heat exchangers and air coolers

Selected case studies of strategies developed for resolving heat exchanger operational problems

Sadhna Singh and Harshita Gupta Engineers India Limited

H eat exchangers and air coolers are the workhorses of any refinery or petrochemical plant. They sit quietly in the background, but when something goes wrong with them, the consequences ripple fast: lost throughput, unplanned shutdowns, and rising cost and emissions. Over the years, the industry has developed solid design standards and engineering practices for equipment such as air-cooled heat exchangers. The standard engineering framework used to design and verify air-cooled heat - ers, mainly from the Tubular Exchange Manufacturer’s Association (TEMA), API 661, and Heat Transfer Research Incorporated (HTRI)-based thermal ratings, is widely used by most design teams. However, despite all of this, operational problems keep showing up, often in ways the original design never antic - ipated. A unit that ran perfectly for five years suddenly starts vibrating. An expansion bellow that looked fine on paper fails within months of a revamp. Air coolers that were never meant to operate in freezing temperatures get pushed through a cold winter with improvised heat tracing and ‘crossed fingers’. What makes troubleshooting these problems genuinely difficult is that there is rarely one single cause. Engineers are usually looking at a combination of things, including process conditions that have drifted from design intent, fluid properties that were not fully characterised during the engineering phase, fouling that built up unevenly, or operating sequences during start-up and shutdown that nobody documented properly. Add mechanical wear and ageing infrastructure into the mix, and it becomes clear why a quick fix rarely holds. Cases 1 and 2 come from real operational challenges encountered in the field. They cover winterisation problems in air coolers, flow-induced vibrations in shell-and-tube heat exchangers, and fouling in preheat trains: three areas that come up repeatedly in plant troubleshooting discus - sions and rarely get the detailed treatment they deserve. The approach taken here goes beyond running a ther - mal check or swapping out a component. It looks at the full picture: operating data, mechanical condition, process configuration, fluid behaviour, and, where needed, more advanced tools like computational fluid dynamics (CFD) analysis or specialised thermal simulation. The goal is

practical, not just to explain what went wrong, but to show how to think through these problems systematically so that the fix actually lasts. Case 1: Safeguards against congealing in air coolers Air coolers do not get much attention until something goes wrong with them. In most refinery settings, they are con - sidered relatively straightforward equipment, comprising bundles, fans, and a plenum. However, when the service involves a high pour-point hydrocarbon stream and win - ter ambient temperatures start dropping, that simplicity becomes deceptive. The margin between ‘operating nor - mally’ and ‘tubes blocked with solidified wax’ can be sur - prisingly thin, and recovering from a congealing event is never as easy as it sounds. The fundamental problem is straightforward enough; if the process fluid temperature drops below its pour point anywhere inside the tube bundle, waxy or heavy hydro - carbon components begin to deposit on the tube walls. What starts as localised fouling quickly compounds, where flow restriction increases, velocity drops, residence time increases, and the solidification front advances further. Left unchecked, it can result in a partially or fully blocked bundle that requires hot oil flushing, steam purging, or, in bad cases, bundle removal and cleaning. None of these is a quick fix, and all of them cost money and production time. For streams with pour points in the 50-60°C range, the design challenge is real from day one. Case background This case comes from a refinery revamp project where the air coolers were specified to handle a hydrocarbon stream with a pour point falling in the 50-60°C range. The engi - neering team incorporated steam coil air preheating as the primary winterisation measure. In this well-established approach, steam coils installed upstream of the tube bun - dles preheat the incoming air before it contacts the pro - cess side. The logic is sound: if the air entering the bundle is warm enough, the tube wall temperatures (TWTs) stay above the pour point even at the cold end of the exchanger. The problem showed up during the detailed design review. When the numbers were worked through properly, the steam consumption required to maintain adequate air

Revamps 2026