11 May 2017

Batch drying with vacuum contact dryers

COVER STORY - Chemical Engineering (April 2017)

Drying is a demanding unit operation where solvents need to be removed without altering product chemistry. Vacuum dryers are essential pieces of equipment for accomplishing this task Drying solids is a demanding task that requires both knowledge of process technology and a sound mechanical design of the equipment used. This article provides an overview of batch-drying principles and possible options for vertical vacuum-contact dryers. Most solids in the chemical process industries (CPI) are recovered by precipitation or crystallization. The suspended solids are mechanically separated by filtering or centrifuging in the first instance. In most solid-liquid-separation processes, thermal evaporation does not compare favorably with mechanical separation by filtration or centrifugation with respect to energy efficiency. However, when it comes to the final moisture content, thermal evaporation is often the follow-up step to mechanical dewatering methods in order to achieve the desired dryness. The residual moisture content of the solids after filtration or centrifugation is influenced by the properties of the solid’s crystal structure. A typical filtration cake can show residual moisture content of between 5 and 45%. To dry a wet cake…


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