Many times a day at a busy power plant in Ohio, a barge unloads onto a fast moving belt. The familiar noisiness of a speeding conveyor belt being loaded should be reassuring, but when the load zone is losing material, dust is clouding the impact area and components are covered with escaped product; it is clear that adjustments need to be made as soon as possible.
The preceding scenario, productivity coupled with real problems, played out continuously at this large power plant. This led to extreme inefficiency, safety risks, environmental concerns and wear-and-tear on equipment. A growing frustration with standard solutions led the client to contact Richwood to request an evaluation of their application. The details of the application and the resulting recommendations are outlined in the following.
The power plant uses 48 in. belts running at 750 ft/min. and 2000 tph for clean coal.
The immediate concern was the safety hazard created by escaping material. Extreme pressure was blowing out the material and shooting it up the belt line. In spite of best efforts, dust and debris were not sealed or controlled in the load zone.
When evaluating a loading area, it is critical to keep in mind the fundamentals of successful load zone design. It is not enough to chase ‘symptoms’ by focusing on the smaller details, though they are important. For a real solution, it is necessary to examine the big picture – and that means considering a load zone from the ground up.
If a checklist was to be made, a well designed and working load zone would have to include the establishment of:
- Constant belt elevation.
- Proper belt support.
- Impact protection.
- Containment of bulk material.
- Wear protection.
- Sealing of dust and fines.
- This application was no different.
- The first step
The first step in building a reliable load zone is to make sure that constant belt elevation is established with full idler contact in empty running mode. Evaluation of this extremely important first step revealed that the tail pulley of the conveyor was positioned above centre elevation of carrying idlers, preventing the belt from contacting the centre roller of the first several carrying idlers. The tonnage being conveyed – and the incorrect belt support elevation – caused the belt to rise and fall depending on varying load, allowing continual spillage, while the conveyor was in operation. Without correction, the skirting system would never seal as it should. Even though the belt was properly tensioned and had sufficient quantity of carrying idlers, it did not have a stable, consistent plane of support.
According to CEMA standard 575: “the belt must be fully transitioned with properly fitted transition idlers before the entry into the impact bed.” To build a successful load zone, “the belt must be fully troughed”.1 On Richwood’s recommendation, the tail pulley was adjusted to CEMA guidelines for full trough transitions. This means that the top of the pulley was relocated to the same elevation as the top of the idler centre roll (Figure 1). With this arrangement, the belt elevation will not change in normal operations. Achieving this type of transition was step one in the fundamentals for success. In some installations, lack of distance from the tail pulley to the first troughing idler may prevent a full trough transition. This relationship may require both vertical and horizontal adjustments to establish correct full trough transition distance and pulley elevation correction.
Figure 1. CEMA illustration for proper trough transition.
C.J. Ferguson, the Richwood Engineering Group Manager involved in this project, observed: “Because this crucial first step had been previously overlooked, this load zone had become a source of great frustration to the client. They had diligently followed the recommendations of industry texts and even attended well-known training sessions. All of this effort at great cost, with little to show for it. Experience has taught us to master the fundamentals. It sounds simple but it is often overlooked and it was key to building this load zone properly.” In attempts to remedy the situation the operator had made numerous investments. They had rebuilt the transfer chute, put in a combination of skirting clamps and rubber, installed steel kick plates and added ceramic tile to attempt to contain material and control spillage. Unfortunately all of these investments were made without addressing the root cause of the spillage problem: lack of proper belt support and profile through the load zone.
The next step
After finding the discrepancy in the belt elevation, Richwood looked at the next two important components of a working load zone: belt support and impact protection. Once the belt was correctly profiled, Richwood Impact Saddles®, Cushion Arc Idlers® and edge seal supports were installed to protect the belt from material impact damage and provide a continuous support surface for the containment components.
Impact saddles are designed to be a direct replacement for impact idlers and feature a smooth full-belt-width surface without gaps or sharp angles. CEMA Standard 502 can help determine the duty rating needed for idlers based on the impact energy. For help with proper component selection, CEMA uses the idler class rating to determine the corresponding dimensional class of the impact bed/saddle.1 Impact saddles with edge seal bars provide continuous support directly under the seal surface of the skirtboard system to facilitate a positive seal on top of the belt where Canoe Liners® and skirting will be applied.
The next step in creating a safe load zone is to provide wear protection combined with bulk material sealing. Canoe liners provide this wear resistance and contain bulk material flow. Richwood canoe liners are available in rubber or rubber/ceramic matrix. For this application, canoe liners with R2000 rubber were recommended.
The final step
Lastly, successful load zone design needs to seal dust and fines. External skirtboard sealing components manufactured using high-quality bevelled rubber with a user-friendly attachment system for ease of maintenance are ideal to contain smaller particles. The new skirting system replaced one of the operator’s former investments: a skirting system that never sealed the load zone and was attached with a bolt-on rail, discouraging maintenance. The maintenance of the previous system required loosening bolts every 6 – 8 in. to free the skirt sections so they could be adjusted.
To complete the dust control requirement in this load zone, the new skirtboard system was designed and furnished fully covered, incorporating multiple dust stilling chambers and dust curtains to create a fully contained, dust free load zone.
John Bishop of Richwood worked directly with the operator’s maintenance staff. He stated: “The facility has a great crew. They did all that had been recommended and worked hard to make it right. We wanted to provide a lasting solution, not just throw conveyor accessories at the problem.”
According to Bishop, “they were especially pleased with the ease of use of the skirt liner system. No one enjoyed loosening all of the bolts on the old liners.” He added: “Before we started, it was difficult to work in the basement of the building where the tail area is located and needed cleaning regularly. Now the area is free of debris and requires much less maintenance.”
Remembering the fundamentals of load zone design may seem elementary, but as shown, they can be costly to ignore. CEMA offers standardised recommendations for bulk material handling. These standards, along with an experienced engineering team and quality components, can help operations optimise productivity. The client at this power plant now has a reliable, sealed and protected load zone. They are saving time on cleanup and material loss, as well as providing a safer work area.
- Belt Conveyors For Bulk Material, 7th Ed, (CEMA; 2014).
Read the article online at: https://www.worldcoal.com/handling/13042016/steps-to-success-603b/
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