Handbook of Industrial Drying

INTRODUCTION

Spurred by continually escalating energy costs, along with the advent of new competitive polymers accom- panied by new and extended applications of polymers and plastics, interest in the energy-intensive operation of drying of polymers has been on the rise in recent years.
Drying is one of the prime polymer recovery op- erations performed before transfer to the compound- ing plant or packaging for direct use. It is the part of the process in which the polymer is handled essen- tially as a solid and liquid and gas streams become relatively minor. In polymer production, other recov- ery operations include salvation of the unreacted monomer and solvent, coagulation and precipitation, concentration and devolatilization, and liquid–solid separation [1].
Although drying is the oldest and most commonly encountered of all unit operations of chemical engin- eering, it is one of the most complex and least under- stood operations. One of the prime reasons for this state of affairs is the enormous diversity of drying equipment; over 100 clearly identifiable different types of dryers are in commercial use around the world. Depending upon the nature of the processing
mode, physical state of the feed, mode of heat and mass transport, operating temperature and pressure, and other factors, one can classify existing dryers into so many different types that it is impossible to de- velop or hope to develop generalized procedures for analysis of all types of dryers [2].
This chapter provides a few guidelines for the selection of polymer dryers and discusses the alterna- tives available. Picking the best dryer for a specific polymer application is beyond the scope of this chap- ter because of many variables involved in such selec- tion. Since most of the work in this area is proprietory in nature with very little information available in the open literature, it is therefore believed that this chap- ter will help to overcome the initial agonies of a polymer engineer in selecting dryers for water- or solvent-wet granular polymer particles.
For better understanding of the subject for a
nonspecialist in polymer technology, a brief survey
is given about the various polymerization techniques employed commercially before discussion of the dry- ing equipment.

2.