Waste tyres are a major problem with well over 400,000 tonnes per year in the UK. Recent legislation on the restriction of disposing at landfill sites could mean a major environmental problem, with illegal dumping and large stockyards brimming with a potential air and water polluting fire hazard. Or it could mean a serious alterative to using fossil fuel. In a vehicle driven society the source of a readily available cheap fuel for forward thinking companies is vast.

The beneficial properties are that tyres include a make up of Rubber Hydrocarbon, Carbon Black and Oil, producing a heat value of 6000 Kcal/kg, which is 20% greater than coal and seven times more efficient compared with natural gas. Heat and energy producers have understood this for many years, but it is only relatively recently that, together with climate change and fossil fuel pricing, waste tyre energy has become more attractive.

A major alterative use for waste tyres is the firing of Cement Kilns. Many cement producers have embraced the tyre as alterative fuel.

The process of tyre chipping has been used to reduce the volume taken up with the whole tyre and on the whole is far easier to handle, but this posed other problems.

• The extra cost considerations involved with the tyre chipping.
• The extra process and equipment needed.
• There is also a tight tolerance of chip size, which is critical for the effective handling and use.
• Also the tyre chips are non flowing so are prone to clogging within storage bins.

Equipment such as the Robson Push Floor conveyor was developed, to effectively slice the chips out of the storage bin and on to a belt conveyor for transport to the kiln. Belt Conveyors and Screw Conveyors were designed specifically to ensure the smooth flow of tyre chips.

An example of a Tyre Chip System has been recently installed by Robson's at a Lime Quarrying and Process Plant which feeds the furnace with five tonne per hour from a Tyre Chip handling plant, with a five hundred tonne capacity.

• Tyre chips are delivered by lorry to storage.
• Chips are then transferred from storage to the push-floor hopper by a loader truck.
• The push floor then is operated automatically by the demands set by the weigh feeder hopper to give a controlled feed of chips into the screw conveyor, which feeds onto the long gantry conveyor.
• The Gantry conveyor discharges into a weigh feeder buffer hopper.
• The weigh feeder controls the flow through the screw feed, and a twin valve system into the furnace

Cost reductions, minimizing double handling, meant a rethink on tyre chipping. Could a whole process be eliminated? Robson headed back to the drawing board. Using such bulky heavy objects in great numbers poses its own problems. Robson had to draw on its experience of other industries, such as Airport Baggage Handling, where there were many similarities such as systems for sizing, orientating and loading could be redesigned for the Waste Tyre use.

Robson developed a Waste Tyre feed system, for transporting tyres directly from the delivery point to the kiln. Starting at the Reception Hopper, the tyres were unloaded via delivery truck directly into the hopper. The base of the hopper has a slat conveyor feeding the tyres towards a singulator, which separates, aligns and evenly spaces the tyres, onto a belt conveyor which transports the tyres to the furnace. Results were that, once the tyres had left the delivery truck, the system did all that was needed, no other manual or mechanical handling had to be untaken.

Robson environmental range of conveyors, are specifically designed to handle alterative and non- standard fuels. With a minimum of moving parts within the conveyor casing, the Airglide conveyors are ideally suited for fuels derived from vegetation. With dust producing products, the Airglide conveyor can be designed to conform to the ATEX (Explosive Atmospheres) regulations.

A recent installation to handle biomass fuel was at a power station in Warrington. Valued in the region of £5 million, the system will initially handle palm kernel chips, which will be burnt alongside coal at the power station. The conveyors innovative design can also handle a wide variety of supplementary fuels derived from vegetation such as olive kernels, wood pellets, citrus pulp, sunflower pellets, maize pellets and olive cake. Currently feeding two of power stations' four boilers, with provision for extension to the others in due course.

The system transfers the biomass from the initial delivery point and after passing through a metal detector and screening for over-size, the biomass is transferred into storage by inclined gantry conveyors and directed through shuttle chutes into either of the silos supplying the boilers. It is withdrawn on demand through variable-speed screw conveyors to be milled down to the appropriate particle size for combustion, and then delivered to the boiler burners independently of the pulverised coal.

Robson's design of a fully enclosed Airglide conveyor for the gantry conveyors eliminates the need to enclose the complete gantry structure. The Robson Airglide conveyor differs from traditional designs by allowing the loaded belt to be supported on a cushion of air along its longitudinal length. This eliminates the need for carrying idlers whilst drastically reducing motor power and energy consumption.

The power station installation is the latest in a long line of alternative fuel projects for Robson, which includes tyre and tyre chip handling systems and 'waste to energy' equipment supplied to sites throughout Europe.

Use of biomass as a fuel is encouraged by the EU Renewables Directive because it is carbon-neutral and therefore gives rise to less 'greenhouse gas'. Boilers can be adapted for firing with up to 20 per cent bio-mass in the fuel mixture, equivalent to a reduction in CO2 emissions of around 40 per cent Some energy industry experts predict that 'clean' coal will be the most suitable fuel for generating energy for at least the next ten years.

Waste Feeders. The incinerator has been a viable alterative to landfill for many years. The constant feeding of the incinerator has been shown to be problematic with early systems, with feed rates and sizing of waste. Robson could see that current and new technology could be combined to create a feed system to give a desire feed rate, whilst shredding the waste materials to allow optimum incineration.

Designed primarily for controlled feed of raw domestic and industrial refuse into fluidised bed incinerators, the Robson waste feeder is a robust twin screw unit providing infinitely variable feed rate to match incinerator demand. A hydraulically movable shaft is fitted to relieve potential blockages detected by torque monitoring devices, plus the automatic control of stripper and hydraulically operated pusher quadrant fitted to the mouth of the feed hopper to again prevent blockages. The machine is capable of passing solid objects up to 300mm3.

The resulting ash deposits have to be constantly removed to ensure smooth running of the incinerator. Robson heavy-duty screws are designed to handle the ash, sand and incombustibles discharged at the bottom of fluidised bed incinerators and can withstand temperatures of up to 900ºC. Often sited in extreme environments, the screw conveyors are specifically designed to perform under the most demanding conditions. The robust design of the Robson Screw Conveyor incorporates sealed bearings, an external gearbox and drive motor, minimises the service cycles and maintenance downtime. The screw conveyor is the ideal design to transport the ash to storage bunker or awaiting vehicle.

Many industries produce waste sludge or, as part of the production process, sludge is a component part. The handling of sludge and sludge cake has been refined over many years and systems are readily available. Robson has extensive experience of handling sludge and other cake from filter presses, belt presses and centrifuges so can offer a system well suited to the individual customers requirements. From the processes of filter pressing, belt pressing and centrifuging the cake produced can be handled on a variety of conveyors including:

• Pushplate Units (twin strand chain and scraper)
• Conventional Troughed Belt
• Screw Conveyors.

Receiving hoppers under filter presses are full width and incorporate breaker bars to pre-break the individual cakes, which are pre-treated with polymer binder. Wide pushplate units convey the pieces of cake to secondary cutters which reduce the bulk still further, allowing transport to storage or trailer in narrower conveyors.

Robson's commitment to provide Engineered, Robust Conveying Systems has been the company's ethos for the last 100 years. In this time of climate change and environmental concern, the company has met the challenges of ever changing materials and processes, offering designs and systems to accommodate the alterative fuel processing, material recycling, waste handling and waste processing worldwide.