The Evaporation of Viscose Process Liquors by Low Energy Means

Summary

A research programme leading to the development of a low energy process for the evaporation of water from viscose process liquors is in progress. The process employs mechanical vapour recompression techniques combined with the use of thin walled plastic tubes as a heat transfer surface. Laboratory investigations have been undertaken to determine the physical properties of the liquors involved, and data on viscosities, specific gravities, boiling point elevations, thermal conductivities and specific heat have been gathered. An examination of the properties of plastic tubes has been executed, with particular emphasis on short and long term mechanical stability, resistance to fouling and wettability. A bench scale mechanical vapour recompression evaporator has been constructed; heat transfer coefficients of 800–1000 W M⁻²°K⁻¹across the tube bundle have been obtained with the viscose liquors.

A research plant to evaporate 100–150 kg hr⁻¹water has been designed and construction is in progress. The detailed mechanical design has produced a number of interesting engineering challenges, particularly with regard to the compressor, the concrete vacuum vessel and its corrosion resistant lining and the tube bundle. A strategy to meet these challenges has been formulated.