Heating Conveyor uses a perforated/wire mesh conveyor belt to transfer product through the Conveyor. 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.
Heating Conveyors may be multi pass units, in which the feed is transferred from one belt to another belt below it by gravity. These heating conveyors are usually two or three pass machines. Additionally certain heating conveyors, such as those used in vegetable dehydration have multiple belts in line, and the feed is transferred from one belt to another.
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.
- Very intimate contact with air/gas stream
- Good for heat sensitive products and products requiring long residence times
- Energy efficient due to recycling of process air 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.
- High temperature units can be troublesome
- Heater can clog on carryover
- Belt tracking can be problematic
- Belt may clog, requires frequent cleaning
- Loss of fimes through perforations on flights or belt
- Single line flow heating/Drying Conveyor
- Single pass (the product travels through the machine once only) Single stage machine (the product travels through the machine on one conveyor)
- Multi Stage heating/drying flow Conveyor:
The advantages of single pass with the added advantage of multi staging, in which at intervals to suit the product, it is transferred from one conveyor to the next, which re-orients the product and allows deeper beds to be used later in the process, making effective use of available space. Especially suitable for very large tonnage machines.
Multipass: In this type of machine, the product travels the length of the machine more than once, traveling back on itself several times. This type of machine has the disadvantage that it cannot be set-up with a true temperature profile, but as it has several conveyors on top of each other, the dwell can be several times longer than the equivalent single stage machine. Suitable for products which need gentle drying for long dwell times. For drying machines operating from high initial moisture contents, multiple plenum chambers must be used, to limit the large temperature drops inherent with this type of machine