6. Overall distillation column efficiency for most of the refinery columns can be given by (for ? = 0.07 - 1.4 cp and relative volatility < 4) (where ? = overall column efficiency, % ? = molal average viscosity of feed at average column temperature and pressure, cp ?p = pressure drop per tray, psi)
7. Smaller sized packings are generally dumped to the packed columns, and the large ones of size greater than __________ mm are stacked individually, which provides better control over bed porosity and offers lower gas pressure drop.