Résumé
The structure and composition of the fouling deposits caused by pig slurry heated in a tubular heat exchanger were characterized to understand their formation and thus be able to minimize fouling and define effective routine cleaning methods. Two temperatures (55 degrees C and 80 degrees C) were investigated. Two types of fouling were identified: organic/mineral and biofilm. The first only formed at temperatures above 50 degrees C, often during the heating phase, and was the main problem encountered in treatments at 80 degrees C. Organic/mineral deposits formed a thin compact sub-layer and a thick porous top layer composed of 67-76% minerals, 9-15% proteins, 8-20% carbohydrates and 0-5% fats. Biofilms formed at temperatures between 25 degrees C and 70 degrees C in both the cooling and heating sections of the exchanger. This type of fouling predominated at temperatures below 55 degrees C. The biofilm covered a thin mineral base layer. Strongly acidic or alkaline washing cycle are recommended to clean Type I deposits, while in-line gas-rumbling is recommended for Type II fouling. (C) 2013 Elsevier Ltd. All rights reserved.