In early 2002 a Pulverised Coal Injection (PCI) plant was constructed under a service contract at BHP Steel’s Port Kembla steelworks to reduce blast furnace fuel and energy costs.
In June 2002, Calsun Materials Handling was contracted to install an innovative coal blending solution the company had developed to satisfy the process handling, blending and feed requirements for minimum cost.
Three types of coal can be blended to 2% accuracy in any ratio at rates to 300t/hr. The blending system throughput is 400,000t/year with a 15 year design life.
Feed from the source stockpiles is via a new 988G front end loader (FEL) equipped with a 20m3 bucket to load each of the three 6m wide x 3m deep, 40m3 live capacity hoppers. The hopper size ensures the surge capacity allows a comfortable operating rate by the FEL without building in expensive and unnecessary over-capacity.
The most economical configuration of the blending system, also providing the best use of the very limited real estate, was twin leg hoppers with 150t/hr weigh feeders under each leg. In this way a controlled 300t/hr rate could be achieved from any hopper. When blends require very low outputs from any given hopper, down to the 15t/hr minimum operating rate of a feeder, the system is programmed to oscillate the feeders to ensure even drawdown of the hopper.
The weighfeeders are a 1200mm wide system using picking idlers to form a trough, the latest design from Total Engineering Systems. They eliminate the need for fixed side skirts, preventing the possibility of product wedging affecting weighing accuracy. It also means reduce wear and gouging to the belt surface, long term weighing stability even during wet weather, easier access for belt changeover if required, as well as less wearing components etc. These features were critical to ensure individual weigh feeder accuracy remained better than +/-0.5% so total system blending control within +/-2% could be realistically achieved.
The 750mm wide blending conveyor despatches the coal to a manual by-pass feed hopper that feeds the plant internal holding bins. The blending conveyor is powered by a proven Flender 22kW shaft mounted drive and operated at a relatively slow 2m/sec to keep the duty cycle of equipment low providing very high system reliability.
Various enhancements have been included to maximise the reliability and maintainability of the blending system. Carry idlers are set at 1.2m to minimise their loading and maximise bearing life. Similarly, all pulleys are lagged and conveyor belting is conservatively selected with running capacities at approximately 60% of the rated capacity to ensure excellent belt life. FEL dump hoppers have 5Cr12 stainless steel linings in the bottom 2m high wear zone to provide extended wear life.
The hoppers have all been designed as mass flow to prevent hang-up and bridging leading to chemical erosion of the walls. The concrete barrier at the FEL tipping pad has steel railway sections cast into the sloping face to minimise damage on cleanup operations. And an innovative structural design was developed to allow full walk around access to all weighfeeders with a full size wash-down slab and good access for feeder removal if required.
The system also includes load cells on the hopper legs to trigger a traffic light level system to ensure the FEL operator is aware of the fill level and priority of each hopper.
Calsun Materials Handling 02 4961 0781.