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Mixer and Blender Options for Vacuum Drying Requirements

Abstract

Throughout the industries, more and more manufacturers are turning to agitated vacuum systems to improve their drying processes. Three common mixing technologies are employed in various vacuum drying requirements: the Vertical Blender/Dryer, Cylindrical Blender/Dryer and Double Planetary Mixer.

This white paper presents the operating theory, advantages and sample applications of each design. The recommendations discussed here are based on Ross's experience as a worldwide mixing and drying equipment supplier for over 170 years.

Introduction

Agitated vacuum drying is an efficient method for removing volatilecomponents from pharmaceutical granulations, chemicals, plastics, ceramics, metals, and other products. Due to the reduced pressure within the dryer, the liquid's boiling point is lower than in atmospheric conditions and drying can proceed at lower temperatures. Vacuum drying is therefore ideal for processing heat-sensitive materials without risk of thermal degradation. It also allows manufacturers to recover costly solvents or safely dispose of any harmful volatiles removed from the closed system.

The combination of deep vacuum, gentle heat and agitation achieves significantly shorter drying times compared to high heat alone. It is not uncommon for atmospheric oven and tray drying operations to run for many hours, sometimes overnight, in order to reach very low moisture levels. The impact on energy costs and production rates is tremendous. Vacuum ovens and tray dryers offer better drying rates than their atmospheric counterparts but agitated vacuum dryers are even more effective. In these systems, materials in direct contact with the dryer's heated surfaces are continuously renewed, ensuring that drying is not only fast but also uniform.

Another advantage of agitated vacuum dryers is the wide range of feed forms that they can accommodate from slurries, wet cakes and pastes, to granules, pellets and powders. A liquid feed material, for example, may undergo a series of relatively swift changes in physical state from slurry to a viscous paste, and from a paste to a dry powder. The characteristics of the feed, intermediate and final dried product are all important considerations when selecting the right equipment for a particular application. Process engineers are faced with many options in today's market but the three most common and superior technologies are the Vertical Blender/Dryer, Cylindrical Blender/Dryer and Double Planetary Mixer.