30.1 Introduction to cleaning tanks
The hygienic state of food production surfaces has a crucial effect on the quality
of food products. Therefore, the hygienic requirements of the cleaning procedure
must be included in the process design and integration. Hygiene is important in
all processes, because the production cannot be run if it is possible that microbes
will infiltrate the process through surfaces and equipment that are used in
association with the tank. Contamination on tank surfaces can be fatal to the
product quality due to long processing times with nutritious raw materials,
where microbial growth leads to discarding large product batches. It has been
proved that specific hydrodynamic parameters control cleaning in closed process
systems. The fluid flows are important both in production and in cleaning.
Computational fluid dynamics (CFD) is a tool for improving the hygienic design
of equipment components and their integration into the process line.
Tanks are crucial for the operation of food production plants. Major
applications are the storage of raw materials and end-products, buffers for
intermediate products, fermentation, mixing, heating and cooling. Big tanks are
needed in brewery, dairy and fruit juice processes (Birus, 2003). The sizes of the
tanks used in dairies vary from 100 L to 230 000 L. The biggest tanks in dairies
are silo tanks that are used for collection and reception of milk. The holding
capacities of other storage tanks in dairies normally vary from 1000 L to 50 000
L. There are also mixing and processing tanks in different sizes (Bylund, 1995).
For fermentation purposes the equipment, including tanks, must be clean, in
some cases even sterile, at the starting point, because fermentation processes are
prone to contamination. Microbes in nutrient-rich environments grow well in
fermentation (Storga^ rds, 2000). Hence a few unclean niches harbouring harmful
30 Improvingthe cleaningof tanks
S. Salo, VTT Biotechnology, Finland, A. Friis, Technical University
of Denmark and G. Wirtanen, VTT Biotechnology, Finland