The pharmaceutical, nutraceutical, and food industries' main problems in drying are related to powder quality, low solvent removal rates, high production, and investment costs. The market success for a new powder depends on its properties and process economics. Consequently, the current challenges are the development of technologies for enhanced powder quality, low energy use, low cost, and minimum environmental impact. Heat pump fluidized bed multistage drying is a potential alternative to produce protein powder. This drying technology consists of atmospheric lyophilization in order to attain a stable structure and step up the temperature for evaporative drying to increase moisture removal rates. In addition, the multistage drying has to follow a strategic schedule that results in optimized rates and product quality. Seven protein drying runs were made in a laboratory-scale heat pump dryer designed and built for precise operating conditions. The raw materials and powders were characterized and the multistage drying trials were compared based on kinetics, color, density, and deformation. Hence, the specific objectives of this work were to compare performance of multistage drying, to identify ways of improving moisture removal, and to study the effect of drying conditions on powder quality.

Drying of porous media is strictly governed by heat and mass transfer. However, contrary to the definition that drying is simultaneous transport mechanisms of heat and mass, most past and current models either account for temperature or concentration gradient effects on drying. Even though the complexity of computations of these processes varies with area of application, in most cases, the Dufour and Soret effects are neglected. This leads to deviations and uncertainties on the assumptions and interpretations of these and other relevant effects on drying. This paper covers the theoretical methods to derive the coupled transfer effects. In addition, this work proposes and formulates relevant heat and mass transfer equations, as well as the governing equations for drying processes with Dufour and Soret effects. The application of a numerical approach to solve the equations allows for studying of the influence of these effects on the design and operation of dryers. It is shown that the Soret effect can be highly relevant on drying operations with dynamic heating operation. While for drying processes where the steady state drying process predominates, the effect is deemed negligible.

This work covers heat pump drying of protein with high quality and low cost. It consists of atmospheric freeze drying to keep product quality followed by evaporation to reduce time. A sweep numerical method was applied to predict the mass transport from the porous particle to gas. The maximum deviation between predictions and mass transfer data was below 4% indicating that the method well describes mass transport during protein drying.