Polymer Drying - Niro has supplied more than 450 industrial sized
polymer drying plants
Niro has supplied more than 450 industrial sized polymer drying
plants, the first one in 1952, making an average of almost 10 plants a year.
This record probably makes Niro the world's most experienced company in drying
Many polymers need drying and Niro is familiar with all of
As to drying, the polymers can be divided into 2 main groups:
1. wet powders, where the particles are already formed; polymers like
s-PVC, c-PVC, ABS, MBS, HDPE, PP, PAN, c-PE, POM, PVAl
2. emulsions and
solutions, where the particles are formed during the drying process; polymers
like e-PVC, EVA, UF, MF, PF, PMMA, PVAc, PVP, Acrylic Resins, Paraformaldehyde.
Today dry product rates already exceed 35 t/h for some of the wet
powders and 5 t/h for some of the emulsions and solutions. Niro is able to
supply single continuous-running drying units for these capacities.
the wet powders the drying equipment is fluid bed dryers or flash dryers ? in
some cases a combination of those. A special high-energy efficient fluid bed is
the Niro CONTACT FLUIDIZERTM, where 80-85% of the evaporative energy is
supplied from heating panels submerged in the fluidized product layer. The
overall energy saving compared to other types of dryers, for instance for s-PVC
drying, is 10-45% depending on the grade in question.
For emulsions and
solutions the drying equipment is a Spray Dryer, often followed by fluid bed
post drying or cooling.
When the polymers are water wet, which is the
case for most of the polymers, open drying plants are often applied, meaning
that ambient air is taken in, heated up, performing drying, cleaned of
particles and sent back to the atmosphere.
When the polymers are
solvent wet (for example hexane/pentane wet HDPE or PP), the concentration of
oxygen has to be very low in order to avoid explosion/fire in the dryer.
Consequently, Nitrogen is often used as drying gas. In order to save cost, the
Nitrogen is reused in a closed loop: it is heated up, performing drying,
cleaned of particles, the evaporated organic solvent is condensed and pumped
away, after which the Nitrogen gas is recirculated to the inlet heater and used
for drying once more.
For some products a dust explosion can be a
potential risk during drying, for instance for ABS and PVAc. In these cases
open plants in Pressure Shock Resistant execution combined with Explosion
Relief Panels or Explosion Suppression systems can be supplied. Alternatively,
low oxygen plants are applied, using Nitrogen as drying gas in a closed loop. A
speciality is the Self-inertized plant, where the low oxygen content is
achieved by a special direct-fired heater.
Some thermoplastic polymers
can be sticky during the drying, for instance PVAc and UF-resins. In order to
spray dry these, special precautions, such as Jet SweepPT and Air Broom, are
often necessary to avoid product build-up in the dryer.
VOCs (Volatile Organic Compounds) is a special form of heat treatment/drying,
often performed in a specially designed Stripper Fluid Bed.
details, please download the Niro Brochure, Polymer Drying, BNA 777/GB.
Here topics for studying could be: Which Dryer Type for which
Polymer, Dryer Cleaning, Dust Emissions and VOC Emissions.