Whey protein fouling on polymeric heat exchangers

Abstract

The fouling behavior of whey protein concentrate (WPC) in food-grade polyether ether ketone (PEEK) heat exchangers was compared to benchmark stainless steel (SS) to evaluate if fouling can be better mitigated by using PEEK. No research has been conducted on WPC fouling behavior of PEEK at WPC concentrations of 2–6 g/L and heat flux densities of 45–55 kW/m². It was found that PEEK materials led to a reduction in heat resistance of up to 40%. At WPC concentrations of 6 g/L, a fouling factor of 0.9 m² K/kW was measured for PEEK compared to 1.6 m² K/kW for SS. Despite a constant heat flux, fouling curves for PEEK showed an asymptotic behavior, whereas linear fouling was observed for SS. To achieve a comparable heat resistance between PEEK and SS heat exchangers, the operating time could be extended by 9 h when using PEEK materials. Investigations of the deposit mass showed that even though the heat transfer resistance is limited on PEEK, fouling continued to grow at a decreased rate. It was found that the fluid started to evaporate underneath the fouling layer, which led to a partial detachment of the fouling layer and therefore mitigated the heat resistance effects of fouling. To test whether these results are transferable to larger setups, experiments on a scale-up apparatus were conducted. A very similar behavior was qualitatively observed; however, measured deposition deviated on average by 18%. PEEK surfaces also showed great promise regarding cleanability, with fouling layers detaching completely after drying for 10 min and restarting the process. This restored the heat transfer coefficient to its clean state. A cleaning in place therefore seems feasible. In contrast, fouling layers on SS did not detach through drying and had to be chemically cleaned to restore its heat transfer capacity.