Martin Engineering
For thousands of years, cement production has been heating the components used in the mixture to eliminate impurities to the highest possible temperatures. Today, cement or cement raw material is calcined in a furnace at 1000°C, similar to dropping it into the center of an active volcano. The material is then subjected to a cooling process, but the slightly fragmented aggregate is still hot enough to burn almost everything it encounters, including normal conveyor belts, heat-resistant personal protective equipment.
The presence of hot material has long made safety a priority for cement factory operators. However, reducing buildup and spillage in the hottest parts of the production process to prevent clogging and downtime, is widely considered the least desirable task throughout the factory, independent of individual safety measures protecting the workers.
At a cement plant, a transfer point from the clinker storage to the moving conveyor caught the attention of Martin Engineering technicians. Excessive material spillage at the transfer point creates a potential risk for workers struggling with it.
The transfer point problems at the clinker storage have been an issue that companies have been trying to address for some time. The primary objective here is to reduce the amount of maintenance required for repair and cleaning. Unplanned downtime increases operating costs through increased labor and product loss. By making the system more efficient, safety around the transfer point is also improved.
From the kiln to the stock silo
At the cement factory in question, about 200 tons/hour (181.4 mt/ hr) of raw meal is processed while the melted clinker exits the kiln, loaded onto a conveyor made up of several high-heat metal trays pulled by a chain. The material is rapidly cooled by cold air, reducing the temperature from approximately 760°C to a range of 176 – 426°C.
After the clinker has cooled off, then it is dropped onto a high-heat conveyor belt attached to a moving conveyor that hangs 24 meters above large piles along the length of the clinker silo, which is the size of an airplane hangar, from a 1.5-meter-long inclined channel. The belt, which is 335 meters long and 610 mm wide, carries the material at a speed of 1.32 m/s towards the triggering discharge chute.
The pallet system, which moves slowly back and forth along the entire length of the silo, empties the calcareous clinkers in long piles for storage through a chute mechanism. However, the stored material does not stay at the same location for long, it is constantly moved to different parts of the plant as needed by loaders.
This is a 24-hour operation carried out to meet customer demand. Therefore, when there is a problem with the clinker transfer conveyor, it needs to be addressed immediately. Otherwise, it could halt production.
Feeling The Heat
Various issues experienced in the factory caused an increase in the safety concerns. This can sometimes result in leaks at the original transfer point from the pan conveyor to the initiator, causing some problems related to sealing. Hot materials might spill from the edges and collect on the surrounding walkway. In addition, backups in the transfer channel often stop production until they are cleaned.
This can also make accessing to the transfer point difficult. This can result in increased heat levels due to the clinker when personnel reach the transfer point. Manually cleaning the transfer chute carries the risk of direct contact with hot material. Thus, it is important that a trained worker clean the transfer chute using air jet or CO2 blasting device while wearing high-heat resistant PPE (Personal Protective Equipment).
The authorities at this cement factory, which was experiencing problems, were stating that a 0.9 to 1.5 meter grated shaft was installed under the transfer point platform to capture some of the spillage. The material was dropped down a chute and added to the storage pile below. The aim of this was to reduce worker contact with the material and to decrease some of the production losses associated with spillage. However, excessive leaked material still accumulated around the platform and created a potential hazard that required frequent removal.
However, even if there was a planned maintenance, it still resulted in both safety and cost concerns.
The mentioned area was being serviced approximately twice a month to clean it up. A team of 4 to 5 workers was removing the debris with a vacuum truck. This was costing the plant between 250,000 TL to 350,000 TL a month depending on the scope of the work and how many times the team needed to come.
Handling the Equipment
This harsh environment at the transfer point had a deep impact on the equipment. The rollers would regularly jam or break due to heat, weight of the load, or fine particles stucking into the moving components like bearings. Additionally, the belt was rapidly wearing out, holes were forming and even extra cracks occurred at the splice points.
This causes friction and excessive heat at the return side (bottom) of the belt when a roll is jammed. Friction can cause the belt to quickly degrade and wear on the edges. If left unnoticed for long enough, friction can cause the mechanical splice to wear out and lead to the breakage of the splice. This can result in the potential for fires, as the return side of the belt is likely to be more vulnerable, even though the side of the belt carrying the material has a high heat rating. Additionally, impact rollers were a particular concern as they were most susceptible to bending due to impact damage, freezing and continuous exposure to heat. The gaps between the rollers often allow for grooves and cracks to form on the protected side of the belt. This leads to operators ignoring the holes and increasing spillage until it becomes unmanageable, due to the high cost of belt replacement.
The belt in the loading and settlement zones was a problem that increased the spillage in the sealing concern. The anti-wear linings along the chute wall were not sufficient enough to overcome the high[1]temperature environment and they were bent or torn, creating escape points for the grains. The side rubber sealing would then wear out quickly, leaving large gaps between the rolls where the belt would sag, allowing more spilled material to escape.
One Size Does Not Fit All
The managers did not immediately contact Martin Engineering, instead they chose the option which seemed to be reasonable at the time. The company installed a modular interlocking tubing system that had a closed environment with good access capabilities for maintenance and roll replacement. Alas, the building materials of the system could not handle the harsh environment and demands of the system. And this caused excessive spillage, unplanned halts in production, loss of product and higher cost of production to the company. Due fire hazards, failures related to safety and severe concerns, tubing system had to be replaced early.
The facility has commissioned Martin Engineering, which has many successful projects, for a long-term relationship, various service contracts and overseeing the transfer point and providing solutions. Trained technicians who were already familiar with problems in the clinker bin conducted a Walk the Belt™ procedure that allowed them to complete a full checklist and identify issues throughout the transfer process.
Technicians then proposed a fully modular, heavy-duty Total Transfer Point Solution™ that would be more advisable for the application. This included raising and shortening the casing of the transfer point, significantly improving the sealing, adding supports to the belts, and controlling airflow through the settlement zone.
The authorities of the factory appreciated that the project could be completed in just a few days during the planned outage. Martin equipment in other sectors of the plant was working efficiently. And thus, Marting Engineering was trusted to provide a long-term solution.
High Pressure Installation
Five contractors and one supervisor from Martin Engineering who used a crane to lift the components to the elevated work platform managed to dismantle the old system, install the new components and clear the area in less than 4 days.
This quick completion of the task allowed better testing of the system before the planned outage time had ended. The team installed a new casing which included impact bearing, external wear plate, apron seal anti-wear rubber sealing, sliding rolls, support bars and dust veils. These components work together as a complete solution in order to improve the belt loading, decrease the spillage and dusts and minimize the impact damage in the belt.
The previous casing was 6 meters long. The idea here was to give enough time to the materials and dust that were being conveyed to settle in a closed environment. Roughly speaking, to achieve the same goal at a shorter length, Martin Engineering Technicians increased the height of the casing slightly and decreased its length to 3,6 meters. The impact bearing reduces the severe damage possibility of the belt by preventing the load from crashing into the belt. The unit has chamfered UHMW bars with low friction that supports the edges of the belt and stabilizes the belt line. This eliminates sagging and rebound in the belts associated with impact rolls and minimizes the need to replace defective rotating components that can increase friction on the belt. The “Vat” design allows each bar to be rotated in reverse to provide a second wear life. When loaded at high speeds, the hot material hitting the walls of the casing can quickly erode the metal and create holes through which debris might escape. The external anti-wear plate provides an extra layer of protection and can be replaced from the outside of the chute. Previous designs required a certified worker to enter the enclosed space to remove the plate using an air torch. It can now be done safely from outside the Vat with simple tools.
Apron Seal Rubber Sealing accompanies the anti-wear plate on the outside of the casing. This innovative twin sealing system made from 70 durometer rubber composite material composed of EPDM (Ethylene – Propylene – Diene – Monomer) prevents spillage by providing an effective dust barrier. The first lip is interlocked with a second self-adjustive lip that elongates towards the outside for external coverage to the chute walls.
Following the tail drum to the impact bearing, there are also roller support stations that hold the belt in place between the bearings. The rollers are easy to change since the units can be taken out from the beam for external maintenance. It is very important to prevent belt sagging in order to create a tight seal and control spillage. Properly placed rollers between the bearings help to maintain a smooth belt path along the loading and settlement areas.
The two slidable bearings assist in centering the material by directing the load to the settlement area without problems. These systems, similar in concept to impact belts, have wider flanged bars that prevent impact and thrust movements related to the rollers. When they are arranged in sequence with sliding rollers, they provide a tight seal to prevent spillage with the baseboard.
Dust curtains at both ends of the flange control the turbulent air flow generated by the loading process, reducing the escape of leaking material at both ends of the flange. By controlling air flow, material settles on the belt faster and more product is held.
Sustainable Results
Approximately a year after installation, operators reported increased efficiency and a significant decrease in spillage. Clinker is a dusty material left in open piles, so it is almost impossible to completely prevent dust accumulation anywhere in the clinker warehouse. However, as a result of interventions, the material pile-up on the walkway was greatly reduced and there was less dust in the surrounding area. Therefore, this project has made working around the transfer point much safer.
Damage to the belt such as holes and separation of the splices has not been a problem since the installation and running costs have been significantly reduced as the belt is one of the most expensive and time-consuming components to replace. The casing has remained intact and leak-proof, continuing to control spillage. The removal of most of the rollers from all transfer points reduced the likelihood of jamming and friction damage on the return side of the cylinder.
The customer reduced working hours and significant maintenance and cleaning costs as they no longer required a vacuum crew. The Martin equipment has made the work area safer and more efficient.
