Browsing by Author "Khetni, Munir"

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    Design, construction and evaluation of a vacuum evaporation system for the concentration of aqueous whey protein solutions
    (Stellenbosch : Stellenbosch University, 2018-03) Khetni, Munir; Goosen, N. J.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH SUMMARY: Vacuum evaporation is an old and established technology for the industrial concentration of high water content streams. It is a clean, safe and versatile technology with low management costs. The aim of this study was to design, construct and evaluate a vacuum evaporation system, to increase the concentration of aqueous whey protein solution from 5 wt% to the highest possible solution concentration. The system functions to concentrate aqueous whey protein in order to reduce the volume of transportation and storage, thereby minimising costs. The raw material is pre-heated in the feed tank using a heating jacket at temperatures between 65oC and 70oC. It is then pumped by a centrifugal pump to a flash separator at 160 kPa abs through a throttling valve to obtain a pressure drop of up to 149 kPa abs, forming a two-phase mixture of vapour and liquid. The concentrated solution is recirculated until a required concentration is achieved. The vapour is condensed and the condensate, which may itself be a useful product in some applications, leaves the process. The variables affecting the product composition include operating temperatures of between 65oC and 70oC, vacuum level (12 – 15 kPa abs), type of separator internals (half pipe or multi-cyclone), feed flow rate (275 to 350 ml/min), liquid retention time inside the flash separator (2 to 4 minutes) and cooling water flow rate (about 750 ml/min). The design for the two-phase vertical flash separator was done at a ratio (L/D) of 4.8. It was found that the half-pipe internal device was not applicable to the WPC solution since it was foaming. By substituting the half-pipe for the multi-cyclone, the efficiency of the evaporator improved but still foaming persisted due to the laminar flow regime of the solution (inlet momentum of 38 kg/m-sec2). The foaming was finally eliminated by adding antifoam. The initial design of the VES employed direct preheating of the solution in the feed tank with a heating element. This resulted in fouling of the element as the WPC burnt and stuck to the element in the first hour of evaporation, thereby reducing the solids concentration from 10.8 wt% to 8.6 wt%. A modification was done to the preheating system by introducing a heating jacket for indirect heating. This modification managed to eliminate the fouling. The correlation between condensate recovery and solids concentration during evaporation improved with the modification from a coefficient of determination (R2 = 0.6404 to R2 = 0.9942) for direct and indirect preheating respectively. The viscosity measurement was done at temperatures between 59oC to 70oC at a constant shear rate of 23/s. For WPC solutions with concentrations between 4.2 and 14.5 wt%, the viscosity remained constant with increasing temperatures until 62oC, when it started increasing. For 17 wt% solutions of WPC, the viscosity increased with temperature from 59oC. The designed VES managed to concentrate the WPC solution to a maximum concentration of approximately 17 wt% at 65oC and vacuum pressure of 13.3 kPa abs. The viscosity then began to increase and the solution became difficult to recirculate whilst attempting to further evaporate it beyond 17 wt%. Evaporating at 70oC, although giving a higher evaporation ratio than 65oC, caused burning of the solution when the concentration reached 11 wt%. The heat transfer coefficient of the WPC solution with similar initial concentrations (around 5 wt%) was found to be higher at 70oC (433.6 W/m2.K) than at 65oC (431.8 W/m2.K). It was also found to be reduced with increasing solution concentration. When compared to sugar solution with similar initial concentration at 65oC and 13.1kPa abs, the WPC solution was found to have a higher heat transfer coefficient (431.8 W/m2.K and 396.3 W/m2.K for WPC and sugar solution respectively). Due to the differences in heat transfer coefficient, the WPC solution had a higher evaporation ratio than the sugar solution at similar conditions.