Closed-loop spray drying solutions for energy efficient powder production

This paper introduces a closed-loop dryer system to reduce the energy consumption for milk powder production. The system is based on a monodisperse droplet atomizer which reduces the amount of fines in the exhaust air, and allows dehumidification and recirculation of the air over the dryer. In this way the latent and sensible heat from the dryer exhaust are recovered. Two adsorbent systems for dehumidification are discussed; a membrane contactor with a liquid desiccant, and a zeolite sorption wheel. Four configurations for closed-loop spray drying are simulated and optimized. By heat integration of the adsorber-regenerator system with the dryer and preceding concentration step, the energy consumption is significantly reduced to 4.9 MJ heat per kg milk powder. The final heat integration solutions were obtained by simultaneous optimization of the operational conditions and the heat exchanger network based on pinch analysis. Industrial relevance: Drying is an energy intensive operation in processing. To comply with the upcoming regulations that arise from the EU goals for sustainable development, the energy consumption of drying processes should be reduced drastically. Emerging technologies are the key for the next step in energy efficiency improvement. A closed-loop spray drying system for milk powder production is simulated and optimized in this work. The proposed technologies are: monodisperse droplet drying, membrane contactor and a zeolite wheel. By applying air dehumidification and heat integration the latent and sensible heat are recovered from the exhaust air. The energy consumption for milk concentration and spray drying has the potential to be lowered from 8.4 to 4.9 MJ heat per kg milk powder. Although milk powder has been considered, the proposed system is also applicable to other food products, as well as in the (bio)chemical, pharmaceutical and paper industry.