Industrial challenges of HDPE fluid bed drying in different grades

Knowing of challenges in drying of HDPE is very essential to improve the process. In this work, thepolymer in terms of production with densities of 940 kg/m3 or higher is produced by slurry polymerizationtechnique using CSTR reactors. Raw materials include ethylene, hydrogen, hexane, butene and Ziegler-Natta catalyst. The slurry product is separated by a decanter (20-30% residual hexane) and a 2-stagefluidized bed dryer where wet powder is dried further down to 0.1% residual hexane content. Acceptabledrying process needs proper fluidization wheras, study of this hydrodynamic behaviour is a complex workas such it’s understanding and mathematical modelling remains a challenge to date and it relies heavilyon collection of meaningful empirical processing plant data. Drying of particles is commonly carried outusing fluidized bed dryers in HDPE plants where their performance evaluation depends mainly onparticles behavior and flow pattern. Understanding factors affecting gas-particle flow regime isimportant for reaching the process with good efficiency. Double-cyclones have commonly been employedto improve separation and prevent powder being transferred to vulnerable plant locations along thedrying path including distributer plate, scrubbing tower trays and blowers impellers. This assists todescribe flow patterns and further reduces particle agglomeration leading to less energy consumption inblowers. Different aspects of factors affecting the drying process in the plant capable of handling a wetfeed of 56000 kg/hr (40000 kg/hr dry polymer of various grades including PE100, BL3 and EX5 and16000 kg/hr hexane) are investigated.

Keywords:

HDPE , fluidized bed dryer , industrial challenges , fluidization