Conveyor Dryers

Continuous multi-zone, for minimum physical drying attrition.

Operation:
Conveyor drying uses a perforated belt to transfer feed materials through the dryer. Heated air is either passed under and through, or over and through the belt and product bed before being reheated and re-circulated. Units are normally multi-zoned and may have differing airflow's in successive zones. Additionally each zone may use a different temperature profile and control. Saturated or close to saturated air is exhausted from the dryer via a central exhaust duct.

Conveyor dryers may be multi-pass units, in which the feed is transferred from one belt to another belt below it by gravity. These dryers are usually two or three pass machines. Additionally certain conveyor dryers, such as those used in vegetable dehydration have multiple belts in line, and the feed is transferred from one belt to another.

Feeding / discharge:
Manual, batch, automatic and continuous. Vibrators, oscillating feeders, gravity chutes

Feed Characteristics:
Large granules, agglomerates, pellets, preformed (extruded) products (pressure agglomerates), small solid particles, large solid particles, agricultural products. Low to high feed rates.

Heat Source:
Steam, electrical, coal, liquid fuels, or gas.

Exposure:
Mostly Direct. Flow can be through the bed (under to over, over to under, or both), cross, counter current or co-current. Indirect systems available for certain products.

Residence time:
Highly Controllable. Residence time can be altered by varying the feed and discharge rates affecting the bed depth. Belt can be slowed and modulated.

Extraction:
Normally central induced. Re-circulating fans used in each zone. Exhaust connected to common header

Dust Collection:
Typically little required. For fine product a central baghouse is sometimes used.

Control:
PLC control for each zone, infrequently solid state controllers. System controls on above bed temperature. Can modulate energy.

Benefits:
Very intimate contact with air/gas stream.
Multiple zones offer flexibility for temperature and process control
Excellent transfer of energy
Can vary flows between zones
Gentle handling of product
Self contained with distributed foundation loading
Unit can have integral cooling section.

Limitations:
High temperature units can be troublesome
Heater can clog on carryover
Belt tracking can be problematic

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