11/05/2012 | Author / Editor: Eddie McGee*, Ken Picking** / Marcel Dröttboom
An special technique, developed by Ajax Equipment, uses a multiple stage insert system to overcome bunker flow problems, creating a more favourable approach to existing outlets and spreading the flow to previously “dead” storage areas of the bunker. The insert system has been used at Tata Steel Europe at its plant in Scunthorpe, UK, to overcome coal bunker flow problems.
Many power generation and industrial processes rely on storing coal in large bunkers. Over time changes in the type and quality of coal can lead to poor flow during discharge, causing processing delays and significantly reducing the bunker's storage capacity. Manual intervention is frequently used to promote flow; however, this is a hazardous process for operators, and fails to provide a long-term solution to the problem.
An innovative technique developed by solids handling equipment specialist, Ajax Equipment, uses a multiple stage insert system to overcome bunker flow problems, creating a more favourable approach to existing outlets and spreading the flow to previously 'dead' storage areas of the bunker. The insert system has been used at Tata Steel Europe (formerly Corus Long Products) – a manufacturer of steel products at its plant in Scunthorpe, UK, to overcome coal bunker flow problems.
In the ironmaking process, molten iron is produced in a blast furnace using agglomerated iron ore, limestone and coke. The coke is produced in large coke ovens from coal with special properties. Coal is crushed and blended on the Scunthorpe site and transported to Appleby Coke Ovens via a series of belt conveyors. It is then is stored in a large concrete service bunker which is sited above, and in the centre of, the oven batteries.
The concrete service bunker (Fig. 1) was built in 1937 and is divided into two rectangular sections, one section holding 3000 tonnes of coal and the other holding 1000 tonnes of coal. It is about 17.5 metres tall and the 1000 tonnes section is 8 metres × 13 metres, whilst the 3000-tonne section is 20 metres × 13 metres. Coal is fed into the top of the bunker where it is distributed to one of the two sections and stored ready for discharge under gravity. Coal is discharged via a number of rows of outlets at the base of the bunkers into the charge cars.
In 1968 half of the outlets were blanked off and lightweight concrete was used to build up a steeper approach to the remaining outlets with smooth glass tiles laid on top to encourage flow. The outlets are arranged in five rows of four outlets on the 3000-tonne side and two rows of four outlets on the 1000-tonne section. Each row of four outlets operates together to fill a charge car which feeds the oven. Each outlet has a 640-millimetre diameter steel throat cast into the concrete. Slide gates are fitted to each outlet and the charge cars are filled with 17.5 tonnes of coal in, hopefully, one minute.
The bunker was originally designed to store local Lincolnshire and Yorkshire coal, but today it holds blended imported coal from around the world. A typical blend may consist of 60 percent Australian Coal and 40 percent North American. It is the particularly cohesive properties of the imported coal that has exacerbated the bunker's flow problems, making the material more difficult to handle.
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