Plant and Equipment: Agitators in Milk Processing Plants

Agitation is an essential and common operation in the processing of dairy products, which has the objective of promoting uniformity, dissolution, and heat transfer. There are many different types of agitators depending on the application, the geometry of the mixing vessel, and the product (particularly its rheological properties) being mixed. The mechanical drive system of the agitator consists of an electric motor, power transfer unit (gearbox or belt drive), shaft and impeller, bearings, and seals. A sound understanding of their roles is essential to the correct specification, selection, and maintenance of these components. In a food manufacturing application, such as dairy processing, hygienic design and operation imposes extra stringent requirements on such systems, which are not seen in nonfood areas. Selection of the correct or optimum agitation system for a particular application requires knowledge or calculation of vessel dimension, agitator rotational speed, agitator power consumption, product viscosity, and the effect of liquid vortexing. Heat transfer calculations in agitated vessels can be accomplished using the appropriate Nusselt number correlation. Particular agitator designs are necessary for demanding heat transfer situations. Finally, equipment suppliers and process design companies have the experience and practical knowledge for selecting an appropriate agitator to perform a specified job and should be consulted.