Thermohygrometric sensor: A tool for optimizing the spray drying process

Abstract

The introduction of a thermohygrometer into the outlet air of a spray-drying chamber allows measurement and observation of absolute and relative humidities. As an example, there is no powder stuck in a spray-drying chamber of a three-stage pilot plant when the difference between calculated and measured absolute humidity of the outlet air is below 2 g of water kg −1 dry air. To obtain a whole milk, skim milk or whey powder at 0.20±0.02 of water activity (at 25 °C), the relative humidity of the outlet air must be equal to 11%±1 for whole milk powder and 7%±1 for whey and skim milk powders. Industrial Relevance Conventional spray drying processes have been developed mainly through empirical approaches. Consequently this study aims—based on the complexity of milk products—towards the development of a method based on physicochemical and thermodynamic properties. The thermohygrometer used allows to avoid sticking and to optimize water content and water activity in dairy powders. The operator can follow and monitor the relative humidity in the outlet air and thus control powder composition and properties.