Washing and drying granulate

Why washing sets the price

Contamination decides what you get for a granulate. Sand abrades your customer’s extruder, labels leave marks in the end product, glue residue causes gassing and moisture makes the grain cake in the silo. Each of those four is a reason to reject a load, and together they are why a batch sometimes turns out not to be saleable at all.

A washing and drying line takes that out. How many stages you need depends on how dirty the material arrives and on what your customer accepts. Agricultural film is a different story from clean production waste out of an injection moulding shop.

How a washing and drying line is built up

After reduction the material first goes through a pre-wash, where the coarse dirt and the sand come out. A sink-float separation then removes fractions with a different density, PE from PET for instance. The main wash follows with warm water and a detergent where needed, and finally the drying.

Drying is the step most often underestimated. A mechanical dryer removes most of the water, but the last few per cent cost the most energy. We choose the combination of centrifuge and hot air dryer based on the residual moisture your customer demands, because over-dimensioning is expensive here.

Where it usually goes wrong

Three things come up most often. A water circuit that is not closed, which drives consumption and discharge costs up. A dryer too small for the throughput, which leaves the line waiting behind the shredder. And a line without a buffer, where every stoppage downstream halts the whole chain.

On a new line we take those three into account from the start. On an existing line we first look at where it pinches, because often one change is enough and nothing needs replacing.

What you get out of it

A properly washed and dried granulate earns noticeably more per tonne than a batch that stays just under the standard, and the difference is often a single washing stage. So do not count that stage as a cost, count it as part of the yield.