Process integration study of a milk powder plant

Abstract

SummaryA study was undertaken of the heat exchange possible in a milk powder plant consisting of milk treatment, a four-effect evaporator fitted with a thermovapour recompressor and a spray drier fitted with a fluidized bed secondary drier. The study utilized the techniques of process integration analysis and grand composite curve matching. Of particular interest was the optimum utilization of vapours within the evaporator. It was shown that with a minor redesign of the evaporator, and utilization of some vapour in the milk treatment section of the plant, a 6% reduction in total energy consumption of the milk powder plant was possible. If heat exchange between inlet and outlet air of the spray drier was not considered practical, preheating spray drier air with vapour from the evaporator resulted in a 10% reduction in energy consumption. Other minor heat exchange possibilities were also revealed. It was concluded that the use of vapour from the evaporator, and increased steam consumption in the evaporator, may lead in some designs to decreased plant thermal energy consumption overall. As well as the process integration study, formulae are presented for calculating the change in thermal economy of an evaporator when vapour is extracted for use in other sections of the plant. The use of process integration studies needs to be given consideration in overall design of energy-intensive dairy plant.