Conveying of Materials, present trends!
Old generation of conveyor belts were used since the 19th century. In 1892, Thomas Robins began a series of inventions which led to the development of a conveyor belt used for carrying coal, ores and other products. In 1901, Sandvik invented and started the production of steel conveyor belts. In 1905, Richard Sutcliffe invented the first conveyor belts for use in coal mines which revolutionised the mining industry. In 1913, Henry Ford introduced the conveyor-belt assembly lines at Ford Motor Company´s Highland Park, Michigan factory.
Cement being a process industry, materials are moved from one end to the other using different systems of transportation, to carry out necessary processes. Here, systems which are economical, easy to maintain and cause less dusting are gaining popularity. However, owing to their versatility and low cost, the easiest and the most commonly used system is the belt conveyor.
A conveyor belt is the carrying medium of a belt conveyor system often referred as belt conveyor. A belt conveyor system is one of many types of conveyor systems. It consists of two or more pulleys (sometimes referred to as drums), with an endless loop of carrying medium-the conveyor belt-that rotates about them. One or both of the pulleys are powered, moving the belt and the material on the belt forward. The powered pulley is called the drive pulley while the unpowered pulley is called the idler pulley. There are two main industrial classes of belt conveyors; those in general material handling such as those moving boxes along inside a factory and bulk material handling such as those used to transport large volumes of powder materials from one end to the other.
Today there are different types of conveyor belts that have been created for different kinds of material available in PVC and rubber. The belt consists of one or more layers of material, with many belts in general material handling, having two layers-an under layer of material, which provides linear strength and shape called a carcass, and an over layer called the cover. The carcass is often a woven fabric having a warp and weft. The most common carcass materials are polyester, nylon and cotton. The cover is often various rubber or plastic compounds specified by use of the belt. Covers can be made from more exotic materials for unusual applications such as silicone for heat or gum rubber when traction is essential.
These conveyors should use only the highest quality premium belting products, which reduces belt stretch and results in less maintenance for tension adjustments. Belt conveyors can be used to transport product in a straight line or through changes in elevation or direction. In certain applications they can also be used for static accumulation or cartons.
Material flowing over the belt may be weighed in transit using a belt weigher. Belts with regularly spaced partitions, known as elevator belts, are used for transporting loose materials up steep inclines. Belt conveyors are used in self-unloading bulk freighters and in live bottom trucks. This technology is also used in conveyor transport such as moving sidewalks or escalators, as well as on many manufacturing assembly lines. Stores often have conveyor belts at the check-out counter to move shopping items.
Some of the major global conveyor belt service providers are Terra Nova Technologies, ThyssenKrupp, HESE Maschinenfabrik GmbH and Tenova Takraf.
The longest belt conveyor system in the world is in Western Sahara. It is 98 km long, from the phosphate mines of Bu Craa to the coast south of El-Aaiun.
The longest single flight-belt international conveyor runs from Meghalaya in India to a cement factory at Chhatak, Bangladesh. It is about 17 km long and conveys limestone and shale at 960 tonne/hour, from the quarry in India to the cement factory (7 km long in India and 10 km long in Bangladesh). The conveyor was engineered by AUMUND France and Larsen & Toubro.
Actuated by three synchronised drive units for a total power of about 1.8 MW supplied by ABB (two drives at the head end in Bangladesh and one drive at the tail end in India), it was manufactured in 300-m length on the Indian side and 500-m length on the Bangladesh side, and was installed on-site by NILOS India. The idlers, or rollers, of the system are unique in that they are designed to accommodate both horizontal and vertical curves along the terrain. Dedicated vehicles were designed for the maintenance of the conveyor, which is always at a minimum height of 5 m above the ground to avoid being flooded during monsoon periods.
Safety system in belt conveyors
The number of accidental incidences are the highest with belt conveyors in industries, thus making it necessary to have a close look at the number of accidents, the man hours lost and ways to prevent those. As such conveyors used in industrial settings include tripping mechanisms such as trip cords along the length of the conveyor. This allows for workers to immediately shut down the conveyor when a problem arises. Warning alarms are included to notify employees that a conveyor is about to turn on. In the US, the Occupational Safety and Health Administration has issued regulations for conveyor safety, as OSHA 1926.555.
Pipe conveyors and their application in the cement industry
Pipe conveyors evolved from conventional modes of transport of bulk solids materials by troughed belt conveyors. CKIT Conveyor Engineers, is presently a well-known company in this field.
The Japan Pipe Conveyor Company (JPC) was responsible for the initial development of the pipe conveyor and patented the original technology that lead to its first successful application in 1979. It had the ability to form a trough belt conveyor into a pipe shape using a special belt construction. Bridgestone Corporation has since obtained all these patents from JPC and operated through a system of international licencees.
The majority of the installations of pipe conveyors are in Japan, built with the original JPC technology followed by USA. Krupp Robins Inc. who were granted the exclusive marketing rights from Bridgestone for the US, have built the longest single flight pipe conveyor of about 5.0 km in length. The majority of pipe conveyors are however lesser than 100 m in length with hourly rates lower than 100 tph.
In India, there are a good number of pipe conveyor installations, the majority have been designed by CKIT of South Africa including the largest pipe conveyor (1,800 tph; 3.2 km) in the world at Dahej for Birla Copper. Besides, pipe conveyor installations are set to grow in numbers for the transport of diverse materials as fluidised rock phosphate, flyash/gypsum and cement, etc.
Advantages of material transport by pipe conveyors
The pipe conveyor resembles a troughed belt conveyor at its tail end where the material is loaded. There upon the belt is made to pass over a series of transition idlers of varying troughing angles to form the pipe shape. Prior to the discharge pulley the belt is made to open to have material discharge over the head pulley drum. Largely due to reasons of engineering geometry as well as with a view to keeping the material with the pipe shape, the return belt is also made to form the pipe shape.
The flexibility of the pipe shape permits the belt to be curved both horizontally as well as vertically. In many instances this is a big advantage as it eliminates transfer points where there is a relatively sharp change in conveyor direction. A single conveyor can thus replace several conventional belt conveyors reducing the need for multiple transfer points, drives, dust collection systems, structures etc. all prone to operation and maintenance.
The basic design feature of the pipe conveyor belt enables using the return side of the belt for conveying materials in the opposite direction. The conveying in and conveying out of materials in a single belt, possible in longer belt conveyor installations, especially for plants in the vicinity of ports offers cost advantages.
Also, when a single pipe conveyor replaces several conveyors in a system, the total power consumed is considerably lower. A series of several conventional belt conveyors also requires additional power to lift material at each transfer point. When the pipe conveyor replaces a pneumatic mode of conveyance, energy savings pay for the pipe conveyor themselves.
Key elements of a pipe conveyor
Like a conventional belt conveyor, a pipe conveyor comprises of the belt, a feed section, the intermediate sections, the head or discharge section and the drive. As with a conventional troughed conveyor which is dependent on the belt tensions, the construction of a pipe conveyor belt could be fabric or steel cord. However, as the belt is required to form the piped shape, several important features are employed in its design.
A special carcass construction is employed as the belt requires adequate stiffness as it is made to form the pipe passing through the idler rolls. Flexibility for transition from the flat to pipe shape at the feed end and pipe to flat at the discharge end is also essential. A layer of special rubber compound is usually placed between each fabric ply to achieve this flexibility.
Belt edge stiffness is reduced for the belt to overlap and prevent material spillage. The plies at belt edge are therefore broken and specially arranged. In addition, top and bottom belt cover grades, as well as curing times, are specially controlled to prevent the belt´s natural tendency to remember its pipe shape.
In steel cord pipe conveyor belts, transverse is used above and below the steel cables with a layer of rubber separating the fabric from the cords. Phoenix Yule India (with the technical backup of its German parent company, a well known international manufacturer of conveyor and pipe conveyor belting, and in close co operation with CKIT is a leading supplier this belt in India.
The feeding section of a pipe conveyor is similar to that of a conventional belt conveyor. To eliminate the problem of material spillage as associated with troughed belt conveyors the pipe conveyor feed zone incorporates a specially designed skirt board for effective sealing with low friction impact slider pads. A quick release mechanism enables impact rollers to be lowered for removal, even with a moving belt and facilitates ease of maintenance. Transitional idlers from the impact zone to the pipe form, comprise of a series of troughing idlers of varying and adjustable troughing angles. A single guide roller is used to press one edge of the belt below the other as the belt comes together. This idler, installed just ahead of the first circular arranged idler set, eliminates belt edge abrasion and allows proper overlap closing of the belt. Uniform feed to the pipe conveyor is important in a pipe conveyor for its stability and tracking. The use of vibrating feeders is recommended to ensure a constant and uniform flow.
The intermediate section of the pipe conveyor is the part where the belt is made to roll into a tubular shape. This is achieved by causing the belt to pass through a set of six idlers arranged in a circle each for the carrying and return run. To prevent squeezing of the belt. With the pipe conveyor belt guided by idlers surrounding the belt on all sides, the conveyor is able to negotiate curves and centerline misalignments. To ensure that the overlap is located as near the top of the belt on the carrying side, a few set of training idlers are provided with adjustable bottom rollers. On the return side, where the overlap is on the bottom of the pipe shape, the extra weight of the overlap maintains the belt´s dynamic stability.
The discharge of the pipe conveyor is similar to that of conventional belt conveyors. The belt in the tubular form is allowed to gradually take the trough shape by a series of idlers of varying troughing angles. Material are discharged over the head pulley. Modern drives are used in all pipe conveyors which include high efficiency, compact space saving bevel helical gear units shaft mounted to respective pulleys using shrink discs. Drive motors are usually squirrel cage and equipped with VVVF AC drives. This modern drive ensures smooth starting, allows for step-less belt speed variation to create the desirable belt load cross section, which is suitable for the application and maintains belt stability.
The facility has been provided with a self propelled traveling maintenance trolley, which is mounted onto the triangular gantry structure and travels along the full length of the conveyor. This man carrying maintenance trolley allows access for inspection and maintenance by plant authorised personnel only. The trolley is independently powered usually by its own onboard diesel engine drive and allows quick access without fatigue.
Operation & Maintenance
Wear due to material attrition in bends, a common phenomena in pneumatic conveyor pipe-work, is eliminated, besides also the down time resulting from material clogging in pneumatic conveying pipes. O&M procedures of pipe conveyors do not exceed those of troughed belt conveyors, as all components of are very similar with no special spare parts inventory which need to be maintained. However, pumps and compressors of pneumatic conveyors require spare part inventory of special parts.
The reliability of pipe conveyors like troughed belt conveyors is very high resulting in extremely low plant downtime. Few of the typical applications in cement industry in India include: ACC Chanda Unit and Madras Cements Ltd. - Alathiyur Line II (under installation).
The ability of pipe conveyors to handle difficult materials, the relative ease in accommodating single conveyors within layouts of existing plants, power savings vis-a-vis pneumatic means of conveyance of fine powders and the ease of O&M, pipe conveyors are finding its application within the cement industry.
Advantages of pipe conveyor
òA big advantage of using pipe conveyors is that the material transported is contained within the rolled tubular shape of the belt for the majority of its conveying distance.
òEnvironmental pollution is minimised as en route spillage is eliminated, ensuring environmental protection and totally enclosed conveying.
- The material conveyed is protected from wind losses, spillage, contamination, rain and theft.
- High angle conveying provides a steeper angle of inclination, due to which the overall length of the conveyor system can be reduced.
- The increased friction between material and the pipe shape of conveyors due to packing makes generally a 50 per cent higher angle of conveyance possible by pipe conveyors, as compared with conventional troughed belt conveyors to angles of inclination as high as 29 degrees.
- This results in smaller space requirements for installation making pipe conveyors viable solutions if there are space restrictions within the plant.