Drying Systems

Compact Design, High Efficiency and Quick Response

Principle system variables:

The selection of an appropriate drying system for extruded snacks is based on the following parameters -

  • Product handling - The design of the product handling process of the drying system is dependant on the product being processed. In this aspect there are two main categories of products, each of which needs a different kind of handling - Bulk products (eg. most varieties of snacks, cereals etc.) and oriented products (eg. flat breads, long cut co-extruded products etc.). At Schaaf, the bulk products are mostly handled in drums. These can also be sometimes handled on wire mesh belt systems, where however there is a limitation in terms of the size of the individual product pieces, which should naturally be large enough to prevent getting stuck in the mesh. The oriented products are exclusively handled on wire mesh belts.
  • Product bulk density - For the bulk products the sizing of the handling unit depends on the bulk density of the products and the minimum residence time needed inside the unit for the desired moisture reduction.
  • Heat source - Schaaf uses electric powered, infrared radiators as the most common heat source in its drying systems. This is a neat and efficient system which is also ideal for getting special effects like toasting, drum frying etc. For some standard applications having limited demand in terms of the drying profile, hot air systems are also used, but these must invariably be coupled with a suitable heat recovery system to maintain an acceptable energy efficiency level for the overall system. Other optional heat sources may be offered for specific projects where use of electricity for the generation of infrared radiation may be economically unviable.

Operational basics:

  • Drum systems - The drum is positioned with its axis of rotation  nearly horizontal. There is a slight slope of the drum towards the exit end to assist the movement of the product along the drum. The drum wall has a special angular profile to cause a gentle but positive turning of the product mass during the rotation of the drum in order to cause uniform exposure of all product faces to the heat source above. The level of the product in the drum can be adjusted with the help of the speed of rotation of the drum, which is variable over the whole range, combined with a plate cover at the entry end and a special discharge system at the exit end. The heat source is usually a set of infrared radiators, mounted on a common hood suspended from an arm in the drum in such a manner, that the radiation is directed towards the area of maximum product concentration.
  • Belt systems - They have to be single pass for oriented products. For bulk products they are usually multi-pass systems. When handling bulk products, they contain necessary accessories for feeding, level control, discharge etc.
  • Infrared radiators - For infrared heating, special twin-tube radiators housed in quartz glass tubes with gold reflectors are used. These operate on electric power and have an extremely high energy conversion efficiency. Due to the use of infrared radiations, majority of the heat is applied into the product directly. Changes can be easily made in the target temperatures of the radiators as well as the product mass and a special combination of PID controllers controlling these radiators can achieve them in a short time.
  • Hot air systems - Hot air is generated externally by firing suitable fuel in a heat exchanger. The moisture loaded air, exiting after drying the product, is passed through a suitable heat recovery system for separating the water vapour as condensate, before the same warm air is reheated and recirculated into the drier.

M/c no. Type Heating Capacity Nominal Capacity Remarks
279 Drum/Infrared 42 kW 250 kg/h Standart
280 Drum/Infrared 84 kW 500 kg/h Standart for higher capacity
281 Drum/Infrared 42 kW 225 kg/h 279+PTFE
282 Drum/Infrared 126 kW 750 kg/h Very high capacity
283 Drum/Infrared 84 kW 450 kg/h 280+PTFE
284 Drum/Infrared 126 kW 675 kg/h 282+PTFE
293 Drum/Infrared 28 kW 170 kg/h Combined with coater
294 Belt/Infrared 84 kW 250 kg/h For flat-bread/co-extruded bars
297 Drum/Infrared 35 kW 175 kg/h 293+PTFE
300 Belt/Hot Air 100 kW 360 kg/h For simple shape snacks