Fouling of a heat exchange surface by whey, milk and model fluids. An analytical study

Abstract

Fouling caused by sweet whey, milk, artificial ultrafiltrate, phosphate and calcium solution and prote in solutions was studied in weil defined hydrodynamic (flow rate: 0.096 m.s-1) and thermal conditions (temperatures ranging from 25 to 88 "C with a standard value of 72 "C ; temperature difference with the heat carrier fluid : 0, 5 or 10 "C) using a laboratory fouling deviee. Deposits were assessed quantitatively by weighing and qualitatively by Auger electron spectrocopy, X photoelectron spectroscopy and infrared spectroscopy. These spectra gave evidence for three main groups of compounds: proteins, phosphates and lipids as weil as the corresponding atoms (calcium, phosphorus, nitrogen and carbon). These findings suggest a fouling mechanism based on calcium phosphate building-up, with various structures ranging from simple weil crystallized phases «< phosphate + calcium» solution) to much more complex phases including carboxylate groups ; the latter are present in substances as different as citrate (artificial ultrafiltrate and whey) or proteins (soluble or caseins). In the case of milk and whey, proteins participate in the formation of the first fouling layers. Thus, the best way of preventing fouling seems to be the inhibition of calcium phosphate formation.