Uncontrolled discharge of large volume granular solids by way of conventional transfer chutes has a...
M&J Engineering is supplying the first Weba Chute Systems in a shiploading application for installation on Portnet’s Shiploaders 1 and 2 at the Port of Saldanha. This follows the successful installation of Weba Chutes at Portnet’s iron ore handling plant some time ago.
"Designed for a transfer of 10,000tph of iron ore, the two boom transfer chutes feature a levelling device that keeps them vertical at all times during the luffing of the boom in a range from 14 degrees to 5 degrees. This will minimise spillage and blockages, and ensure an even load of iron ore onto the boom conveyor," says Alwin Nienaber, technical director of M & J Engineering.
This conveyor has a belt size of 1 650 mm and runs at a speed of 4 metres per second. Bulk density of the iron ore varies from 2.3 to 3 tons per cubic metre and maximum lump size is 40 mm, with a moisture content of about 3%.
Also at the Port of Saldanha, on a contract awarded directly by Portnet, M&J Engineering is currently upgrading the moving head chutes to ensure these conveyor transfer points will be able to cope with the 10 000 tph ship loader capacity.
"The existing conventional chutes had been experiencing ongoing problems relating to spillage and blockages," M&J Engineering’s Ted Cruickshank says. "We’ve been contracted to design and fabricate Weba Chutes for this application and to re-instate all the required instrumentation and piping services.
"To prevent future blockages we’ve carried out Fine Element Analysis (FEA) on the chutes to determine the flow of the iron ore and verify the chutes’ capability to handle 10 000 tph and to load this material central to the ongoing conveyor."
Both projects will be completed by the end of August 2012.
Each Weba Chute System is custom designed for a specific application, taking into account factors such as belt width, belt speed, material sizes and shape and throughput. Cruickshank says there are numerous advantages to be gained from this locally developed transfer point system which, when introduced on a new project, achieves the optimum design configuration for the application with the best belt cleaning arrangement and optimum selection of belt type and size. In addition, spillage can be completely eliminated.
Further benefits that apply equally to retrofitted Weba Chute Systems and new projects alike include up to 80% reduction in material degradation, greatly reduced levels of dust and noise, reduced production losses owing to fewer blockages, significantly reduced spillage and vastly improved safety levels.
Easy access is provided for inspection and maintenance purposes and the system does not require ongoing supervision, again representing a saving in manpower and related costs.
Cruickshank cautions that Weba Chute Systems should not be compared to conventional chute or transfer point systems, but should rather be seen as an improved alternative or "upgrade", because they adopt a completely different and unique approach to control and handling of bulk materials. For instance, the system uses a "supertube" with a cascade scenario, where 95% of the material runs on material at all times.
"When one looks at this process in slow motion, it becomes apparent that the bottom layer of particles in the product stream moves in a tumbling motion and does not slide down the chute," he explains. "This results in significantly reduced wear and in many cases the lip remains completely covered by material and never needs replacement."
This manner of controlling material movement is taken a step further by designing the internal angle of the transfer chute in such a way as to match the product discharge velocity with the belt speed, which either completely eliminates or greatly reduces spillage.
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