Drying

Processing a wet or damp product may involve drying.  Occasionally this may be achieved by placing the product in an oven or placed so that it receives heat from a radiant heat source. Most often though the product to be dried is exposed in a heated air flow so that moisture leaves the product and enters the airstream. To aid the process the product may be tumbled in the air either in a rotating drum, a fluidized bed or in a vertical tower or “flash dryer”.  Fine particulates may be created or become dislodged so the exit air may contain dust in addition to the extra moisture loading. Air being delivered into a dryer is usually hot and dry, i.e. having a low relative humidity (R.H.). Air leaving a dryer will be cooler – though still warm - and be heavily laden with moisture i.e. having a high R.H., plus any released dust. The filtration system downstream of the dryer must cope with the high R.H. in addition to removing the particulates. A safe solution is always to use a wet collector – the RotoClone N or RotoClone W. To collect the dust as a dry product requires a pulse jet fabric collector – FabriPulse Fusion – but care must taken in design and when specifying the filter media. The casing will probably need full thermal insulation. Pre-heating the system prior to start up and/or trace heating of the extremities may be required. For example, the hopper outlets may need trace heating to prevent localized condensation of moisture or possibly acids dew point condensation if chlorine or sulphur is present in the gas stream.