Drying of bulk materials and equipment options

For carrying out the drying processes, chambers or ovens are used. In industry, dry bulk materials from moisture, paint and varnish or other coatings on metals. There are various materials and products that undergo drying, therefore, the equipment for this process can be varied. In almost all technologies, drying is carried out by convection: supplying heated air to the product or convective heat exchange from the retort wall, for example, in a drum furnace.

Depending on the volume, drying is carried out in cage or pass-through installations.

A distinctive feature of drying plants is that heating is performed at relatively low temperatures and is localized in a steel heating chamber with external thermal insulation. To organize convection, a fan or pouring is used. Perforated sheets, nets, etc. are used as pallets. Mandatory purging of the heating chamber is performed to remove vapors and moisture reduction. The loading layer for drying should not exceed 80mm, if placed on shelves or a conveyor, as well as 20% of the section of the drum, if dried in a rotary continuous oven.

Drying equipment types

The most widespread are chamber drying cabinets, as the most simple, versatile and inexpensive. They have removable shelves, which allows, if necessary, to load workpieces of different heights..

There are options for dryers for large-sized products, which are rolled on a trolley into the heating chamber. Drying ovens can be hermetically sealed, for example for drying paints and varnishes or compounds. Ribbed heating elements are used as heaters. The drying time in such ovens is, depending on the humidity and cabinet power, 30-40 minutes.

Drying cabinets, vacuum

Used for heating before drying in a vacuum atmosphere. Vacuum drying oven is completed with a special gas-tight chamber and an evacuation system based on a vacuum pump. Vacuuming allows you to significantly lower the evaporation temperature of moisture and more completely to perform drying. No oxidation during heat treatment. Vacuum drying of coatings or materials increases continuity, uniformity and adhesion by removing air bubbles. The disadvantage of vacuum drying ovens in the limitation of the working space, in mind design features of vacuum chambers. The drying time in such installations is, depending on the humidity and cabinet power, 15-20 minutes..

Drying in continuous ovens supported by movable hearth devices.

If it is necessary to dry a large volume of material or workpieces, and at the same time it is undesirable to mix it, then conveyor or roller conveyor furnaces are used for drying. In conveyor ovens it is recommended to dry small-weight workpieces or bulk material. Drying in conveyor ovens is carried out by feeding the material onto a mesh conveyor, subject to uniform filling, which then passes through the heating chamber. In the oven, the material is heated, dried and leaves the heating chamber already dry. The heat treatment cycle is mechanized and automated.

Duration of drying in conveyor ovens is, depending on thickness and humidity, in the range of 40-60 minutes. Drying in roller conveyor furnaces produced with loading into pallets, which must be fed to the receiving roller conveyor. It is recommended to heat large and massive workpieces in roller conveyor furnaces. Products getting into the oven are directed towards the unloading side, while heating up. Pallets with workpieces are brought to the outfeed roller table.

Drying in roller conveyor furnaces strongly depends on the mass and heat capacity of products and is not predicted by general methods.

The most cost-effective method of drying bulk materials is produced in drum kilns. Sauna stoves provide maximum efficiency relative to similar designs, since there is no heat removal from the loading equipment. Loading mechanisms are widely presented, for example, belt or screw feeders. Unloading is done by pouring material out of the drum. Cooling modules after heating are relatively easy to integrate into the design. Sublimates, dust is localized within the sealed drum. A scheme of forced blowing (moisture removal) in a counterflow is organized. Heaters and the material do not contact each other, which in some cases is a decisive criterion in favor of choosing this design. Drying possible in protective or controlled atmospheres.

Of the disadvantages of such furnaces, only a relatively small percentage of drum filling can be noted, on average it is 15-25% of the drum section. The drying time in such ovens is, depending on the humidity, 30-50 minutes..