Energy Saving in Distillation Using Structured Packing and Vapor Recompression

Abstract

"Distillation is a big consumer of energy in process plant operations. A first step to energy cost savings is the use of high efficiency structured packing in place of trays or dumped packings in conventionally operated distillation columns. Larger savings, as much as 80%, may be obtained by using a direct vapor recompression (VRC) heat pump instead of the conventional column operation with a steam heated reboiler.

A main criterion of the suitability of a distillation for VRC is a low temperature difference across the column. VRC uses hot compressed overhead vapors, instead of steam, to heat the reboiler. Cost savings are highest when the pressure ratio for the compressor is low. The pressure ratio depends on the boiling point difference of top and bottom products, the reboiler-condenser driving force temperature and the column pressure drop.

Structured packing has a low pressure drop; thus increasing the savings obtained with VRC - for retrofits or new columns - and increasing the range of applications where VRC is suitable for distillations.

For low pressure distillation application, a column with a small pressure drop is especially important. An example of a vacuum distillation which is made suitable for VRC with use of structured packing is separation of styrene and ethyl benzene. "