Lecture_12___cleaning_in_place - Fouling and Cleaning in...

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1 Fouling and Cleaning in the Dairy Industry Carmen I. Moraru Cornell University Real images from the Dairy Industry
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2 Equipment fouling - During processing, milk residues deposit on the internal surface of processing equipment, leading to fouling. - Fouling can both affect the proper operation of the equipment and its sanitary status - due to the development of microorganisms in the fouling layer. - Examples: - Heating equipment – formation of deposits that are hard to remove on the equipment surface. They reduce the flow rate and efficiency of heat transfer. - Evaporators – formation of deposits can be extremely costly – their costs may represent up to 50% out of the running costs - Membranes – formation of a gel layer on the active surface of the membrane. Effect: significant flux reduction Types of milk deposits At moderate temperatures (up to about 80ºC), the deposit: - Consists of about 35% “ash” and 50% protein in the dry matter - Looks yellowish, voluminous, curd-like - Formation of this deposit is governed by the denaturation of b-lactoglobulin At high temperatures (above 100ºC): - Contains more than 70% “ash” (mostly calcium phosphate) and some protein - Looks yellowish, voluminous, curd-like Note: Streptococcus thermophilus can form biofilms at the surface of heat exchangers at temperatures between 40-50ºC
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3 Deposit formation Involves two subsequent steps: - Adsorption of milk components on the metallic surface - Occurs almost instantaneously, upon contact - It involves mostly serum proteins, which are adsorbed in a monolayer onto the hydrophobic / hydrophilic surface. - Other compounds that get absorbed: calcium phosphate, casein micelles, fat globules, bacteria - Deposition of material on the absorbed layer Time (s) Surface coverage (mg/m 2 ) Factors that affect deposit formation in heat exchangers - Temperature – very little deposit is formed below 60ºC. - Preheating – heating milk quickly to a temperature where b-LG denatures can diminish fouling – this is particularly important for the concentration of milk in an evaporator. - Temperature gradient - The layer of liquid near the wall of a heat exchanger is subjected to a higher temperature as compared to the rest insolubilization occurs faster near the wall - This is particularly problematic in laminar boundary layer, since the turbulence that exists further away from the wall does not allow this to happen, due to intense mixing - The larger DT at the wall, the more pronounced the deposit formation Æ excessive DT should be avoided.
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4 Factors that affect deposit formation in heat exchangers – contd. -
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Lecture_12___cleaning_in_place - Fouling and Cleaning in...

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