Case Study: Reducing Fouling in Polymer Process Fluid Heater

The Challenge

Since 1980, CALGAVIN’s primary technology hiTRAN^® Thermal Systems, a tube side heat transfer enhancement product for industrial heat exchangers, has been used to optimise new designs for mainly utility heat exchangers, e.g. compressor lube oil air coolers, for many years. The hiTRAN product has also been retrofitted to key process heat exchangers giving the benefit of reduced capital costs removing the need to replace underperforming units. A shell & tube heat exchanger located in Ohio and used in polymer processing, was prone to fouling. Polymer flowed through the tube side, heated by hot oil on the shell side. The unit, equipped with non-removable static mixers, experienced performance degradation due to polymer overheating and cross-linking near the tube wall. After five months, the overall heat transfer coefficient dropped by 40%, requiring frequent cleaning shutdowns. Twisted tape inserts were tested in a replacement bundle, but they proved ineffective due to the high laminar flow (Reynolds number ~10). Efforts to counteract this with hotter oil, even operating at an increased supply of hot oil at temperatures greater than 50°C/122°F above the normal set point, did not provide the required increased thermal efficiency, but did increase the fouling rate, especially near the shell fluid inlet.

The Solution

To address this, hiTRAN Thermal Systems were installed, these inserts are optimised for low Reynolds number flows and were predicted to match or outperform the static mixers within the available pressure drop. Unlike the orginal elements, hiTRAN inserts are removeable, enabling the option for tube cleaning and helping to reduce downtime. Upon installation in a new tube bundle and recommissioning a 17% increase in clean U-value was observed, helping to enhance the heat transfer. As well as this, a reduction in the fouling rate was observed, enabling a ~10°C/18°F drop in hot oil supply temperature, lessening the thermal degradation. Also observed was an significant increase in uptime for the unit, showing only a 13% drop in U-value after 5 months when compared to the 40% drop with the original setup, resulting in fewer shutdowns for cleaning.

A Senior Process Engineer at the site commented that "Installing the hiTRAN Thermal Systems permitted further unit optimization which has extended the exchanger's life from barely three months to now over twelve months. This has enabled the exchanger to be swapped out as part of a normal yearly turnaround schedule. The replaceable elements also means that the exchangers are no longer thrown away, but can be cleaned with new elements installed."