Trends in material handling
- Enclosed, clean and environment friendly transportation eliminating spillage, scattering and return dropping of materials.
- Non-exposure to atmosphere, resulting in retention of material properties while conveying.
- Curvature possible in both horizontal and vertical planes associated with steeper angle of inclination.
- Option of transporting second material through the return side pipe of the system, thereby reducing capital and operating cost.
- Overall savings in space requirement, structural and foundation cost, thereby making the investment decisions easier.
- Elimination of transfer points - which reduces capital costs; pollution and maintenance costs.
- Pipe Conveyors can be used for transportation of almost all bulk materials.
In case of upgradation of plants or even while replacing the old transport system, today pipe conveyors are considered first, and only if it doesn´t work, other options are explored.
High environmental protection, low maintenance
It became apparent that a pipe conveyor was the best solution offering environmental protection and low maintenance. Its closed design protects the environment from transported goods falling down. Another advantage is the lack of dust development on the running line.
Apart from the advantages mentioned above, they are able to navigate long distances and tight curve radii. Due to their ability to negotiate curves, considerably less transfer towers are required compared to belt conveyors. This results in substantial cost savings for the customer and delivery of a system customised for individual routing.
In Europe, drag chains are getting replaced with pipe conveyors. In a running plant it is not easy to replace the existing conveying system with a pipe conveyor. It normally takes around 8-9 months to complete the job.
Another material handling equipment which is essential for the cement plant is a stacker reclaimer. Limestone is extracted from mother earth which is always not uniform in quality. The mineral resource like limestone is depleting very fast, so the plants do not have the luxury of picking the best quality limestone and throwing the inferior quality. It is necessary to use the available material to its fullest (for more details, refer to the article of Promac).
R Murthy and Santhosh Kumar M of Promac in their article say,´Quarry management is an art. Cement producer may also have some material that is not good enough. This might be harder to grind, or be of less suitable chemical composition. If the ´good material´ is all used up first, it may be more difficult to make cement out of what is left. Careful selection on a day-to-day basis is needed to make the optimum use of all the raw materials available.´
Different options have to be considered before selecting the type and size of stacker reclaimer:
- Homogenising effect required
- Future uprating of the store
- Open or roofed store
- Mill feed system
- Chemical characteristics of the materials to be handled
The reclaimer is usually equipped with constant speed motors. The reclaimed material is carried by belt conveyors driven by constant speed motors and is discharged into a feed bin of a relatively large volume. Reclaiming capacity is higher than the mill requirement and the reclaimer therefore operates in an On/Off mode, controlled by maximum/minimum level indicators in the feed bin. On leaving the bin, the material is proportioned and fed into the mill by weigh feeders.
If the materials are difficult to handle, it may be an advantage to avoid the intermediate bin between the reclaimer and the mill. This is possible in cases where material from one (or more) store(s) is to be fed to a single mill. In principle, the reclaimer must be equipped with speed regulated motors and an integrated belt scale. The transport and subsequent proportioning of the reclaimed material and additional raw material is effected by speed regulated conveyors.
Reclaiming capacity will always match the mill requirement and the reclaimer will operate continuously. The reclaimer in combination with the transporting belt conveyors acts as a weigh feeder for the reclaimed material.
The stacker and reclaimer are controlled by a state-of-the-art PLC-based technology, designed for fully automatic operation. The PLC make and type may be chosen in accordance with the individual requirements to facilitate communication with the central control system.