Mitchell Rotary Dryers, Drum Dryers, Coolers and Calciners

ROTARY DRYERS

CONTINUOUS HANDLING OF POWDERS AND GRANULES

Mitchell Rotary Dryers provide a means of continuously handling powders and granules. Rotary Dryers are divided into two main types dependent on whether direct or indirect heating is employed.

Directly Heated Dryers

Wet material is fed into a revolving drum through which hot gases are blown . The hot gases can either be fed in the same direction as the wet material (parallel operation), or in the opposite direction to the material (counter-current operation). Internal lifting flights cause the material to shower through the air stream. This promotes better heat transfer and efficient drying. Typical applications: organic chemicals,food applications, fertilisers and sand.

Indirectly Heated Dryers

Similar in construction to the directly Heated Rotary Dryers. Heating of the material is by conduction through the rotating shell which is surrounded by an insulated shroud. The shroud can be heated by a line of gas burners, electricity or steam.

Although flighting is not required, disturber bars can be fitted to ensure proper mixing in certain applications. Evaporated moisture is removed by a small purge of air or inert gas.

In applications where the material is easily oxidised, the shell can be enclosed in an inert atmosphere.

Indirectly Heated Rotary Dryers are for applications where the material must not come into direct contact with the products of combustion, or when the particle size of the material is small or of low density.

STEAM TUBE ROTARY DRYERS

These are used for drying a range of materials from fine powders to large particulate solids and sludges. The Steam Tube Rotary Dryer consists of a horizontal rotating shell fitted with a large number of heating tubes.

Saturated steam is admitted to the tubes which maintains the necessary drying temperature. Product is tumbled around the hot tubes and the moisture is driven off as vapour.

Typical applications: spent grains, TA and PTA, soybean, corn fibre, germ, fish meal, bio-solids and industrial sludge.

COOLERS

Air Coolers

The material to be cooled is fed into the shell, lifted and cascaded by the internal flights through the cooling air stream.

Counter-current flow enables the product temperature to approach closely that of the ambient air stream. The exhausted air from the cooler can be fed into preceding dryer stages as an economy measure.

Water Coolers

Water is normally applied externally to the shell by means of spray pipes. The cold cylinder walls in turn cool the material inside. A shroud containing the water pipes encloses the centre portion of the shell.

A cooling section is often incorporated at the end of an indirectly heated rotary calciner, a single shell serving both operations.

CALCINERS

Mitchell Rotary Calciners, or kilns, are very similar in design to rotary dryers, except that much higher temperatures are involved. Again these may be directly heated or indirectly, depending upon the specific application.

Directly Heated Calciners

The refractory lined rotating shell has no lifting flights. Forward flow of the material is effected by the slope and rotation of the shell. Located at the discharge end, a gas or oil burner enables temperatures up to 1650°C to be achieved. For certain applications, the atmosphere within the kiln can be controlled to give oxidising, or slightly reducing conditions.

Indirectly Heated Calciners

Based on the design of the indirectly heated rotary dryer, the calciner is capable of operating at temperatures of 1100°C. Typical applications include: nickel catalysts; carbon regeneration, molecular sieves and china clay.

Mitchell Dryers Ltd
Denton Holme, Carlisle, Cumbria CA2 5DU England
Tel: 44(0)1228 534433
Fax: 44(0)1228 633555
Email: info@mitchell-dryers.co.uk
Contact: Sales Dept.