Rotary Tube Firing – An Increasingly Popular Option

NUTEC Bickley is seeing an uptick in interest in its range of specialist application rotary tube kilns, custom-built for a number of quite diverse processing environments. The company has experience designing and manufacturing these kilns stretching back decades, particularly for gold mining concerns employing the carbon-in-leach (CIL) process. To extract gold from the ore, gold particles are dissolved into a cyanide solution and subsequently adsorped onto activated carbon. The carbon becomes contaminated, so afterwards it undergoes reactivation in a rotary tube kiln and is then suitable for reuse. This can be carried out multiple times.

The particular advantages offered by rotary tube kilns mean that they are highly suitable for a number of important material beneficiation processes. These include rare earths, high-purity alumina, lithium, bauxite and silica sand purification. Many of these materials are becoming increasingly critical in areas such as electromobility, clean energy, construction, and energy storage.

The NUTEC Bickley range offers production capacities from 200kg/h up to 2000kg/h, covering the requirements of the vast majority of specialist heating/calcining treatments. Operating temperatures tend to be up to 1050°C (1920°F). The tubes are generally specified in a 235 MA alloy, a chromium-nickel-silicon grade that provides good strength and heat resistance. Tube sizes range from 300mm to 1.2m in diameter, and 3m to 10m in length. Twin-tube kilns are feasible and, where applicable, are a highly attractive proposition as they offer double the output of a standard single-tube configuration but with only 50% additional energy input cost.

There are a number of instances where a quartz tube is preferred; this could be for processing in a highly acidic environment, dealing with substances such as calcined pitch coke, high-purity processing, laboratory heat treatment, etc. NUTEC Bickley has experience with quartz as well as alloy tube designs.

These kilns use an indirect heating method, with burners situated outside the tube; there is no exposure to flame inside the tube. Burners can be oil, gas, or diesel, while there is also the option of using electric elements instead, for which the company is seeing increasing demand across its offering. The kilns can be installed inside or outside.

The interior design of rotary kilns sees the tube (on its length) at a slight angle, i.e. higher at the entrance than at the exit. A vibrating or screw feeder introduces the material into the kiln, and this is then moved down the length of the tube, and it is extracted at the exit end via a chute and taken into a collector hood. The tube angle and speed of rotation can be adjusted, as can the temperature, which can be zoned if required.

Typical residence time for most of the materials under consideration would be between 20 mins and an hour. The kilns can operate with inert atmospheres, and special injection inlets can be accommodated to introduce superheated steam or nitrogen gas (for instance).

In many cases, the types of firing and calcining operations mentioned could be undertaken in a small tunnel kiln, also a continuous process. However, this involves the use of saggars (which have to be filled/emptied, and which are heat sinks) – so where a rotary tube kiln can do the job, with its increased heat transfer, it’s likely to be more energy and ergonomically efficient.

NUTEC Bickley has many years’ experience across a number of application fields and offers a comprehensive technical service throughout the life of its projects. It can work equally well designing and supplying custom rotary tube kilns direct to clients as it can integrating into wider engineering programs. The latter are quite often dependent on 3D models to facilitate coordination into turnkey plant and processes, and NUTEC Bickley meets all these requirements.

For all further information on NUTEC Bickley rotary kiln options, please contact:

Adam Slater – International Sales Director
NUTEC Bickley
Tel: +44 7717 880888
E-mail: adamslater@nutec.com