Drying

dosing belt drying process

Drying is the process of removing moisture from a solid, semi-solid or liquid substance. Dorset dryers remove moisture through an evaporation process.

Contact between dry, warm air and moisture causes the moisture to evaporate. Evaporation leads to a reduction in volume of the drying material. The amount of dry matter in the substance will, for instance, rise from 8% to 90%. Besides a smaller volume, the dry material has other improved properties. You can read more about this under the section ‘Applications’.

Important factors for the drying process

Air temperature

The drying capacity is determined primarily by the available heat source. With poultry, use is made of the air from stables, which has a temperature of approximately 20° C. This is usually sufficient for drying the produced manure. The higher the temperature, the higher the drying capacity. During the drying process of digestate or biomass in biogas installations, use is made of residual heat that is derived from the warm cooling water of the motors.

Air humidity

The lower the air humidity, the better the result of the drying process. Dry air can absorb more moisture.

Air quantity

A larger quantity of air can process a higher amount of moisture. High airspeed, however, leads to dust formation. This is the reason why Dorset dryers use low air speed.

Contact between the material and the dry air

Efficient contact between the material and the dry air ensures an efficient drying process. That is why Dorset Dryers suck the air through the material which is placed on perforated plates. This leads to efficient contact between material and air.

Dryer summary

The Dorset drying machines use plate conveyors. The conveyor consists of perforated steel plates that are linked to one another. These plates have been galvanized and powder-coated, so that they provide sufficient protection against aggressive substances. Ventilators pull the air through the plates, thus drying the material. A precise description of how a dryer works can be found below or in our brochure (PDF).

Dryer operations

The Dorset Dryer is a conveyor belt dryer.

The conveyor belt consists of perforated steel plates, which are covered with a smooth coating. This allows for greater layer thickness (15 – 40 cm), which guarantees a high drying efficiency. This, moreover, makes it possible to build a more compact dryer.

The steel plates are pulled around by a roller chain. Dispensing starts on the top layer, after which the product is transported to the dryer via the conveyor. During this process, warm air is sucked through the dryer.

If a liquid product is being dried, then this product is first transported to a mixer. The mixermixes a new moist product with a previously dried product. This has a number of advantages. The product can be transported into the dryer with a small percentage (a minimum of 8%) of dry material, which means that all of the nutrients in the product will be preserved. Furthermore, it is possible to dry systematically if the supplied product varies in dry material content. This will result in a consistent end product.

In the case of separated products, a pivoting belt places the product loosely on the smooth plates, so that the moist product can be transported to the dryer without having to be dried in advance.

A part of the dried products is saved in the storage bin for mixing. The remaining dried product is transported to the final storage location.

Dorset uses air channels to transport the air from the heat source to the dryer, and then from the dryer to the outside air. These channels are made of sandwich panels. The advantage of these panels is that they offer sufficient space for a calm air stream, thus minimizing dust formation.

At the final storage location, the dried product can be pressed into pellets. Another option is to pack the product.