Heat recovery from spray dryer exhaust air: An example from an infant formula factory installation

Abstract

This article describes a successful installation of a heat recovery system at the exhaust air stream on a commercial spray dryer for infant formulae. The entrained product particles prohibit a straightforward heat exchanger setup. Therefore, special provisions have to be made to avoid fouling: a bag house filter prior to cooling of the exhaust air stream, and an exceptional heat exchanger design with a low on-flow gas velocity, thick fins, and wide gaps, which facilitate wet cleaning. The optimization of the heat integration of the recovered heat into the production line used the pinch point method as a structured approach. It recommended three temperature levels; namely for the supply of the tanks for the cleaning fluids (lye and acid) for the cleaning-in-place (CIP) procedure, the fluid bed inlet air heaters, and the main inlet air pre-heaters. After 1 year of operation, the control software has been adjusted to better consider the buffering characteristics of the CIP tanks, and to operate the preheaters with a seasonally floating setpoint to recover more heat in spring and in autumn.