Modernisation of Belt Conveyor Systems

The design of the new chute also eliminated corner build-up of the wet sticky coal and reduced the wear due to less impact and not being properly directed that was noticed in the old chute. An upper deflection hood was installed and utilized a hydraulically powered ram that actuated in or out depending if the plant was stacking or reclaiming coal.

This design eliminated the problems of flop-gates which can be a maintenance problem for any plant. The deflector hood was automatically positioned in the head chute to direct the coal during either stack out or reclaim.

The bottom of the chute incorporated a dual spoon design to operate without buildup and the coal is centre loaded onto the 60 inch (1500 millimetre) receiving conveyor belt at the same speed and direction. This has resulted in a nearly "dustless" transfer point, dramatically reduced spillage as well as increased life on the receiving conveyor belt, see Fig. 5. There was less wear on the internal liners and centre loading to minimize any misalignment of the conveyor belt as it was being loaded is now a thing of the past.

Another major concern for plants handling coal is in bunker house or on the tripper/cascade floors where the coal is being loaded into the bunkers or silos prior to being pulverized and being injected into the boiler.

Because these conveyors are located inside the plant, the combustible dust issues are exemplified. Many regulations, like the United State's OSHA NEP combustible dust requirements, has made it mandatory for all coal fired power plants to address any airborne dust issues.

Improvement at a Dual Tripper Car System

The installation shown in Fig 6. was an existing dual tripper car system with two (side-by-side) tripper conveyors, rail mounted, handling a blend of sub-bituminous and bituminous coal with a particle size of 1 inch minus. The conveyors of the system, that feeds the coal bunkers below, are 36 inch (approx. 915 millimetres) wide and run at 400 feet per minute (approx. 2 metres per second), handling 600 tonnes per hour, each.

The major problems were the large amount of airborne dust (see Fig. 6) created from handling the coal and the increased tonnages demanded from the plant. Another concern was the timeline and installation issues of being located ten floors above the ground and having to dismantle the existing tripper cars and transfer chutes was on a tight schedule and had to be accomplished one at a time so at least one of the trippers could run during the day to fill the coal bunkers below.

Two new tripper cars were modelled and designed using ASGCO's 3-DEM material modelling software as well as reviewed with engineers, maintenance and operators from the power plant. Together they came up with the new design that would meet all the goals of the project.

The primary goal was to create a nearly "dustless" transfer of coal and allow the coal to be either loaded down to the bunkers or loaded back onto itself, moving in the same direction, speed and in the centre of the receiving conveyor. The new design improved the flow of the coal and the new combination of internal liners also improved the wear ability of the liners.

The combination of the X-Wear MDX liners, a combination of ceramic cylinders encased in rubber, for the impact area and the chromium carbide overlay plate (double pass and polished) was the answer to the sliding abrasion issues prior to the new design.

As shown in Fig. 7 the amount of airborne dust and spillage is virtually eliminated with the new tripper design. Clamp mount skirting, dust curtains and skalper belt cleaners further aid in the elimination of any fugitive dust and carryback helped the plant meet and exceed its goals for the project.

The newly installed transfer chutes now operate with improved coal flow through the tripper system without buildup and less wear in the internal liners nearly eliminating all spillage and any significant amount of airborne dust. A nearly "dustless" transfer point.

In conclusion, it is necessary for any coal mine or coal handling facility to look at ways to improve productivity, efficiency and safety.