Environmental applications for steel belt innovations

Paul Boughton

Håkan Eriksson looks at the development of two steel belt product innovations, a new oil skimming conveyor and an ultra high temperature steel grade.

Two innovative steel belt products, both designed for separating elements as part of environmental processes but making use of different properties of this unique material, have been developed by the developer and producer of advanced alloys and ceramic materials, Sandvik Process Systems.

The first, a new design of oil skimmer conveyor, makes use of the fact that the adhesion of oil-to-steel is greater than that of water-to-steel. This basic principle means that steel, when immersed in contaminated water, can be used to extract or separate oil products and by using a continuously running Sandvik steel belt, this can be a continuous process.

Skimmer conveyor

The skimmer conveyor is mounted vertically so that the lower section is immersed in the liquid to be decontaminated. When running, the upwards strand of the steel belt collects a film of oil while the accompanying water simply drips off, providing a separation rate of almost 100 per cent.

As the belt travels over the top of the unit, it passes between a skimmer device which scraps the oil off both sides of the steel belt, leaving it clean to attract more oil as it returns to the polluted water.

Endless belts

The new development sees the introduction of a much lighter model and, importantly, one that makes use of endless belts - using Sandvik 1200SA grade stainless steel - which can be changed on-site without any need for riveting or welding.

The system is available in belt widths of 100mm, 200mm and 400mm, in lengths of 1, 2 and 3m, or as a non-standard length to match the distance between the inlet of the liquid to be separated and the outlet on the separated liquid.

Applications include the extraction of lubricating oil, motor oil, transformer oil, vegetable oil and fuel oil. The rate of extraction depends on the viscosity of the oil but, typically, a skimmer conveyor with a 400mm wide steel belt could be expected to remove as much as 400 litres of fuel oil per hour.

The second environmental process has been made possible by the development of a new austenitic steel grade, Sandvik 750SA.

The special alloy composition of this product gives the steel excellent resistance to oxidation and carburisation at temperatures up to 1150°C, making it ideal for use in processes requiring particularly high temperatures.

One application to make full use of this property is the reduction-based separation of metals from waste, such as scrap refining, extraction of metals directly after ore mining, melt furnace processes and the removal of nickel from slurry.

In a typical reduction process, the slurry is transported on a 750SA stainless steel belt, first through a gas-fired furnace - in which temperatures will reach as high as 700°C - then a cooling zone and finally to an outlet station.

Based on the use of a 1540mm wide steel belt travelling at 0.15m/min, a reduction process like this would have the capacity to process up to 700kg/h of slurry.

As well as producing the steel belt, Sandvik Process Systems also provide the drive and tension station, cast iron skid bars for belt support, support rollers and tracking devices.

Tracking

Active tracking - the correction of belt movement to keep 'wander' within acceptable limits - is an important aspect of belt-based process systems.

In certain applications, such as those in which the product can be loaded onto the belt differently from time to time, the belt may have a tendency to wander from side to side.

This can be corrected by means of a variety of tracking devices, and it is in this area that Sandvik Process Systems has announced another new product development, its Compact Belt Tracking (CBT) unit.

Designed for quick, easy installation, the device consists of a roller arranged on a cradle, a linear actuator, a pair of belt edge limit sensors and the associated control box.

Frame strength

The device on the belt strand entering the drive drum or tensioning drum and can be positioned either above or below.

The important thing is that the conveyor frame onto which it is fixed is sufficiently strong and stable to allow the belt to be tracked without compensating for the force of the tracking action.

With the two belt edge control sensors in place, any deviation of the belt beyond predetermined limits will trigger the necessary control movement of the tilt roll. These can be adjusted on site by the end user according to the actual conditions.

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Håkan Eriksson is Manager, Application Technology, AB Sandvik Process Systems, Sandviken, Sweden. www.processsystems.sandvik.com

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