Stacker reclaimer in raw material preparation and pipe conveyor in material transportation are the important handling methods in the cement industry.
Today, cement industry has option of using various modes of material handling. However, pipe conveying is gaining popularity very fast. The other part of material handling is stacker and reclaimer, we catch up with industry experts.Pipe conveyor
Major job in cement plant operations is movement of materials. Attention is always paid to so that the production is not starved for want of materials. The movement of raw materials start from limestone mine and ends at the packing plant. The conveyor belts or pneumatic transportation are the conventional ways of moving powered materials.
However, pipe conveyors are replacing the old thinking.It is even the right solution for transporting alternative fuels such as crushed plastic material, textiles, and paper. This is fully closed conveying system, thus makes transporting bulk material more environmentally friendly and energy-efficient. Maintenance costs are also considerably lower and the system can be optimally adapted to the ambient conditions.PK Madappa of Macmet Engineering provides the advantages of pipe conveyor. Incidentally, Macmet has many firsts to its credit in pipe conveying. He further says that pipe conveyors offer the following advantages over the conventional ones:
- 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.
Transporting material by conventional ways generates dust and considering the restrictions of dust emission, we feel pipe conveyors are more suitable than any other method. In terms of cost, pipe conveyor is quite comparable with that of belt conveyor, taking into account the advantages it gives.
The problem encountered for long distance pipe conveyors is maintaining them along the length. Madappa says it has been addressed by providing maintenance trolleys that are running along tracks mounted on top of the conveyor structure. This also helps to reduce costs (associated with walkways), improve maintenance and reduce accidents. These trolleys are fitted with driving light and flood light for dark/night operations. The trolleys are designed to allow complete access to all parts of the conveyor structure and conveyor components. Each trolley has a terminal station at each end of the conveyor for parking, loading and unloading of personnel and equipment for maintenance. The trolley is controlled by an operator console/dash panel. A diesel generator set is provided on the trolley to meet the requirement for operation of welding set, grinding wheel, and maintenance equipment, for lighting and auxiliary power requirements.
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.
Stacker reclaimer
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
Pre-homogenisation
This is often necessary in cement industry, where the raw material chemical composition varies greatly. It is used primarily for the main components in cement production, i.e. limestone and clay. With the increasing variation in the grades of coal used, there is a growing need for pre-homogenisation and storage of coal. Depending on the properties of the coal used, a pre-homogenising or buffer store is used.
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.