Energy efficient powder production by closed-loop spray drying

Closed-loop dryers are able to reduce the energy consumption in milk powder production up to 60% compared to current practice. Application of monodisperse droplet atomizers eliminates the presence of fines in the exhaust air of spray dryers. It allows the recirculation of the exhaust air over the dryer and the recovery of latent heat. For recirculation, the air is dehumidified with a membrane contactor using saturated salt solutions, or a zeolite system. During dehumidification heat is released while energy is needed for regeneration of the adsorber. By heat integration of the adsorber-regenerator system with the dryer or a related process, a significant improvement of energy efficiency can be achieved. In this work we present four configurations for closed-loop spray drying. For each system simultaneous optimization of the operational conditions and the heat exchanger network is applied for optimal energy recovery. The results for milk powder production showed that, compared to the current practice, simultaneous optimization for closed-loop dryer system results in a reduction of energy consumption from 38% up to 62%