Niro has supplied more than 450 industrial sized polymer drying plants since 1952, making Niro among the world's more experienced companies in drying of polymers.

TYPES OF POLYMERS
There are two main groups of polymers, which require drying:

1. Wet powders, where the particles have been formed; 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; e-PVC, EVA, UF, MF, PF, PMMA, PVAc, PVP, Acrylic Resins, Paraformaldehyde.

Dry product rates already exceed 35 t/h for certain wet powders and 5 t/h for some emulsions and solutions. Niro is able to supply single continuous-running drying units to meet these capacities.

Drying equipment for wet powders include fluid bed dryers and flash dryers or combinations of these. The Niro CONTACT FLUIDIZER^TM is a special high-energy efficient fluid bed, where 80-85% of the evaporative energy is supplied from heating panels submerged in the fluidized product layer. The overall energy saving compared to that of other types of dryers, such as 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.

HANDLING OF WET POLYMERS
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, dried, 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 must be very low in order to avoid explosion/fire in the dryer. Consequently, Nitrogen is often used as drying gas. To reduce cost, Nitrogen is re-used in a closed loop: it is heated , dried, cleaned of particles, the evaporated organic solvent is condensed and pumped away, after which the Nitrogen gas is re-circulated to the inlet heater and used for drying again.

Dust explosion is a potential risk to some products during drying, for instance for ABS and PVAc. In these situations open plants in Pressure Shock Resistant execution combined with Explosion Relief Panels or Explosion Suppression systems can be used. Alternatively, low oxygen plants are used, using Nitrogen as drying gas in a closed loop. A specialty 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 process, for instance PVAc and UF-resins. Special precautions must be taken when spray drying these. To avoid product build-up in the dryer, use of Jet SweepPT and Air Broom, are often necessary.

Stripping of VOCs (Volatile Organic Compounds) is a special form of heat treatment/drying, often performed in a specially designed Stripper Fluid Bed.