29.1 Introduction
29.1.1 Fouling
Fouling can be described as the unwanted build-up of deposits on a surface. This is
a major problem in the food industry, particularly during thermal treatment. The
build-up of deposit increases pressure drop, owing to the increase in surface
roughness and the decrease in cross-sectional area of the flow channels, and
reduces heat transfer efficiency. Increased costs are therefore incurred to operate
the plant. Fouling can also compromise product quality, by cross-contamination or
microbial growth on the deposit. It is necessary to stop production to clean the
process plant, often daily. The overall productivity of the process plant is therefore
reduced, and failure to clean could compromise product quality or sterility.
Often the deposit has a very different chemical composition from the process
fluid. The fouling process and the ways to minimise it have been investigated for
many years (for detailed examples, see the series of conferences including Fryer
et al., 1996 and Wilsonet al., 1999, 2002). There is now focus on understanding
how the deposit is removed in order to improve the efficiency of cleaning
processes. Milk and other dairy fluids have been the subject of much of the
research in this field, but other food materials, such as starches, cause processing
problems.
Fouling occurs in many different situations and can arise from different
mechanisms. The fouling process generally involves a number of steps (Epstein,
1983): initiation, transport, attachment, build-up and ageing. Table 29.1 sum-
marises mechanisms, one or more of which may be involved in a particular
fouling process. Fouling in food processing is common: for example, Bird
29 Improvingthe cleaningof heatexchangers
P. J. Fryer and G. K. Christian, University of Birmingham, UK