Increased evaporator performance: Stubborn scale removal using hydrogen peroxide.

Abstract

Scale deposition in evaporators impedes heat transfer, slows processing, and can lead to degradation of product. Even after standard cleaning methods have been used (caustic wash, back-boiling, mild acid wash, and physical scrubbing), scale can persist and accumulate to make evaporation the rate limiting step of sugar beet processing and can require the replacement of the fouled heat exchange units.  Plate pack evaporator fouling has limited mechanical cleaning methods and requires aggressive chemical cleaning methods that are effective in low or no flow conditions.  To supplement caustic cleanings, a novel cleaning strategy using hydrogen peroxide in combination with surfactants/solvents was evaluated as a non-capital solution to remove scale buildup inside the evaporators at Amalgamated Sugar’s Mini-Cassia factory in 2021 and 2022. Scale loss on ignition analysis and bench scale testing demonstrated localized reaction of hydrogen peroxide. Multiple methods and cleaning procedures were evaluated using concentrations of 7-20% with bursts of 50%; critical operational and safety considerations were addressed prior to implementation. Of seven falling film plate pack evaporators, four were cleaned in 2021 and five were cleaned in 2022. Observations during cleanings (color, flow pattern, steam rates, pressure drop, and visual inspection) indicated tough scale was being removed or dislodged from historically plugged areas inside the plate pack. Over a comparable period, average evaporation rates in 2020, 2021, and 2022 were 579, 625, and 638 tons/hr, respectively; a 10% increase in a two-year period. In 2021, these improvements were used to realize a 6.5% increase in slice rate and in 2022 these improvements are helping to extract a higher percentage of sugar from existing beet crop with high water evaporation rates. Annual proactive cleanings with hydrogen peroxide have optimized traditional cleaning strategies and have yielded incremental improvement to evaporator performance, resulting in increased production.