Progress 05/01/05 to 01/31/07
Outputs
Fouling is a common food industry-wide issue during thermal treatment using heat exchangers, which creates the need for cleaning operations every 5-10 hours. Fouling directly contributes towards increased energy costs in operation and maintenance, production losses, and energy and water losses due to the repetitive cleaning. In 1991, estimates for the entire US industrial community was about $4.2-10 billion/year, with the US dairy industry contributing one of the largest fractions. The focus of this project was to evaluate promising alternatives involving four commercially available low energy surfaces to mitigate fouling, i.e., Microlube-PTFE (uniformly distributed Ni-P-PTFE), TM117P (graded Ni-P-PTFE), AMC148 (proprietary hard materials comparable in performance to TeflonTM), and carbon nanotube (CNT) vs. the uncoated stainless steel 316 (control) surface. Based on the literature, Microlube-PTFE, TM117P, and AMC148 coatings have been approved for select applications
in food and/or pharmaceuticals fields; whereas, CNT coating is not approved for food and/or pharmaceutical applications. Fouling of low energy and control surfaces was evaluated using an especially designed bench scale parallel plate heat exchanger system. The bench scale heat exchanger was demonstrated to be a rapid and cost effective way to interrogate the fouling performance of low energy surfaces. The fouling tests were done with vitamin D enriched whole milk at two flow rates, 3 g/s and 10 g/s and two inlet temperatures, 40C and 60C while maintaining the test specimen's - coated and control - temperature at 80C. Experimental results showed that for the four coated and control surfaces, the largest amount of fouling deposits were observed for treatments at 40C milk inlet temperature. Furthermore, among the five surfaces evaluated, stainless steel 316 had the most (0.287 to 0.567 mg/cm2-h), and AMC148 (0.023 to 0.134 mg/cm2-h or 76% to 92% reduction)
and CNT (0.057 mg/cm2-h or 90% reduction) had the least amount of fouling deposits. The least fouled surfaces had deposits that were bubble-like in structure. This was attributed to less contact with the surface (i.e., low energy surface). The fouling deposits on CNT coated surface could not be cleaned without compromising the integrity of nanotube fibers; whereas, fouling deposits on AMC148 could be readily cleaned with lukewarm water and was consistently better at reducing fouling than Microlube-PTFE and TM117P coatings under all conditions. The findings strongly suggest that extended runs are feasible using AMC148 without disrupting the operation in dairy processing plants. This, of course, needs to be demonstrated through full scale testing under real-world conditions. If successful, this could save the dairy industry significant dollar amounts through reductions in the usage of: (1) electrical and thermal energy, (2) water, and (3) environmentally harmful chemical cleaning
agents. Although fluid milk was the only test fluid, the performance of AMC148 is promising and could prove to be equally effective for other food products such as other dairy products, juices, pastes, and wines.
Impacts
Significant reductions, i.e., in excess of 75%, in fouling of plate heat exchangers surfaces are feasible with newly available commercial coatings such as AMC148. This could translate to extended duration runs for processing of dairy products with reductions in the usage of: (1) electrical and thermal energy, (2) water, and (3) environmentally harmful chemical cleaning agents.
Publications
- No significant publications to report at this time (2007).
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