The cement industry can adopt newer material handling concepts with the help of a few innovations. Jai Gupta explores the new material handling ideas available and how these can be implemented.
The Indian cement industry has witnessed rapid growth in the past two decades. The overall production capacity of several sectors has doubled or even quadrupled over this period. Such rapid growth has posed several challenges for the industry, some of which are:
- The conventional?easy to access? locations are no more available. New projects are forced to go for difficult-to-access locations from where material movements are difficult.
- Land is gradually becoming a scarce resource. The industry is facing difficulties in land availability/ acquisition, and is hence being forced to go away from the markets or is being forced to manage in a limited area.
- Unit sizes are becoming larger to harness economies of scale. Such enlargement in size is forcing the industry to market its products in larger areas.
- With specific reference to the cement industry, growing demands and need of fly ash-based PPC production has forced many industry players to set up grinding units close to thermal power plants for fly ash consumption. As these thermal power plants are generally located closer to densely populated areas, space is always a constraint and hence they cannot develop good infrastructure for rail/road movement of material.
All the issues enumerated above are putting more and more pressure on the logistics of material movement. As material transportation is a sizeable portion of the total cost of production, any gains or reduction in cost of material movement could help the industry greatly.
Due to the needs of high capacity material movement at fast pace and inadequacy of road networks in remote areas, the industry?s reliance on rail transportation has substantially increased. Some good ideas have been implemented, relating to material movement through rail routes. These concepts have been successfully employed by Holtec in cement as well as other industries, and could help the industry in optimising expenses on material handling.
New Concepts in Material Handling
i.In-motion loading of material in railway rakes
ii.Movable wagon loader feeding stationary rakes
iii.Use of bottom discharge wagons for transport and its easy and fast unloading iv.Use of wagon shifters to substantially reduce the area required for the installation of a wagon tippler.
In-Motion Loading of Material in Railway Rakes
For majority of the industries requiring bulk material transportation, loading is usually done through either multiple overland hoppers constructed on top of the railway tracks, or manually through pay loaders. The usual time taken for one complete rake varies from three-six hours depending upon the arrangement or equipment employed. More number of hoppers or pay loaders can reduce the time taken; however, they add to certain other issues, such as:
- Heavy to very heavy civil construction
- More number of operators
- Dust nuisance, spillages, material wastage and degradation etc.
- With a rapid loading system, the entire rake can be loaded in about 60-80 minutes, from a single discharge point.
What is Rapid Loading?
In rapid loading of material, material is loaded on a rake, while the railway rake is in motion. One silo (of about one full rake capacity) is constructed on top of the rail track. Below the hopper, another small hopper is provided on load cells, which can accommodate about one wagonload of material. The above two hoppers are connected through hydraulic gates and a large chute, so that within seconds, material gets transferred from the main hopper to the pre-weigh hopper (mounted on the load cell).
Before a rake arrives, the silo is filled, so that fast material loading on the rake does not get disturbed. In the beginning, the load cell hopper is filled with pre-weighed material. As soon as the wagon comes in position, the loading starts and by the time it crosses, the complete wagon is loaded. During the period of wagon change, the pre-weigh hopper again receives the material from the main hopper, so that by the time another wagon comes into position, it is ready with the material. During this entire operation, the railway rake moves at the speed of about 0.6 to 0.7 km/hr. That means a full railway rake of about 650 m length is likely to get loaded in about one hour.
The majority of the collieries in India have been using the rapid loading system for coal rake loading.
Adopting a similar concept, Holtec designed a rapid loading system for lignite. As the system was designed for lignite, it was substantially different from the usual rapid loading system. However, it has been performing very successfully for the last 10-12 years. At this location, a rake of about 40 wagons is being loaded in about 45 minutes. Although the system is located close to a densely populated area, owners do not face any difficulties in operation as the process generates negligible dust. The material filling and closing is done through hydraulic gates, and wagon positioning is sensed through the proximity switches. A little bit of maintenance and care in operation is enough to keep the system spillage free.
At this location, there were several constraints such as poor soil bearing capacity, low water table, limited execution period, etc. Hence, while designing the system, three small silos were constructed to store one rake load of material, rather than a single hopper. A single hydraulic system was considered with three chutes below each of the silos, without affecting the investment cost. Underground construction was reduced to a minimum, and as lignite is light, no pre-weigh hopper was installed. The arrangement as installed for lignite loading has been depicted in Fig.-1.Benefits
The conventional system of rail loading requires three to six hours for loading of one complete rail rake, whereas with rapid loading system, the entire loading operation for one rake could be completed in about one hour. Assuming average savings of three hours per rake, we may save about 2,000 rake-hours annually, for a handling of about 2 million tonnes per annum (MTPA) capacity. Such faster movements help in better utilisation of rakes, especially if the company owns the rakes.
- The total investment required for rapid loading is substantially lower as compared to conventional systems.
- Reduced number of operators and attendants.
- Dust nuisance, material wastage and degradation are substantially reduced.
Prerequisites
For the hauling of railway rake at a constant speed of 0.6 to 0.7 km/hr, creep drives need to be installed on the locomotive. As the normal locomotives from railways do not have this facility, the plant will have to maintain its own locomotive for haulage of the railway rake.Movable Wagon Loader to Load Stationary Rake
The proposal of rapid loading of railway rake is a good option, but it essentially needs full rake space on either side of the loading point. Secondly, it also needs a dedicated loco which can pull the complete rake at a fixed speed.
Recently for a project, the available land was insufficient to go ahead with a rapid loading system. Also, the client was not inclined to go for the purchase of loco. Hence, we looked for alternate options and came out with a solution of movable wagon loader which can load the rake while on the move.
The wagon loader is generally placed in the centre and on its either side, rail tracks are constructed so that two full rakes can be placed on either side. The wagon loader is fed by a stacking conveyor and has a reversible boom conveyor for feeding the wagons on both the tracks as per requirements.
The wagon loader capacity can be in the range of 1,500-2,000 tph without any difficulty. The wagon loader is provided with a diversion chute at the outlet, which is designed in such a way that it diverts the material into the next wagon, at the junction point. After certain travel, it returns back to the earlier discharge point.
As the performance of the equipment largely depends upon consistent feeding of material, we need to either have a dedicated storage with some positive discharge equipment, or connection is made with consistent feed from the existing storage itself.
The speed of the wagon loader is controlled with the material on the conveyor. With capacity variations in feed, loader speed is adjusted automatically. As the material feed to the wagon is gradual, we get a smooth filling to the wagon. The smoother the filling, lesser is the dust nuisance. For the materials conducive to water spray, a foggy water spray ring can be provided around the discharge chute so that the nuisance dust generation can be further reduced. A few typical arrangements of wagon loaders are shown in Pic-1. Benefits
Conventional rail loading/rapid loading requires approximately 1.5 km of rail tracks for the loading of a complete rail rake in one go. With the proposed arrangement for loading of rail rake, only about 800 m of rail track length is required. In many circumstances, rail track length is a constraint and this solution can immensely help.
The loading time of a rake can be within two hours, which is better than the conventional system, and still saves about two hours of loading time per rake. Expected annual savings on rail rake hours will be about 1,400 hours, for a handling of about 2 MTPA capacity. Such faster movements help in better utilisation of rakes, especially if the company owns them.
- The total investment required is low. It does not require any on-track storages.
- Reduced number of operators and attendants.
- Dust nuisance, material wastage and degradation is substantially reduced.
Use of Bottom Discharge Wagons for Material Transport and Its Easy Unloading Traditionally, majority of the industry has been using normal BOX/BOXN type of wagons for transportation of various goods. For the unloading of these wagons, wagon tipplers are installed through which these wagons are unloaded. As the Railways allows seven hours of free time for mechanised unloading, wagon tipplers were typically designed to unload a full rake of 58 wagons in approximately four-five hours (i.e., 12-15 wagons unloading per hour).
As the Railways wishes to go for longer rakes with larger capacity wagons, in recent years RDSO has released certain new guidelines. According to these guidelines, all new installations (installed after November 2010) shall take into consideration larger wagon size and unloading speed shall be increased to about 25 wagons per hour. As per the new designs of wagon tipplers, size of wagon tippler, its civil construction requirements and capacities of the material handling equipment have substantially increased.
As such, installation of a wagon tippler and associated auxiliaries was expensive, and recent enforcement from Railways, has further escalated the cost of installations of the wagon tippler and its associated auxiliaries.
As against BOXC and BOXN type of wagon allocated to the industry, power plants are allocated bottom discharge wagons (BOBRN), which can be emptied through pneumatic gates installed below the wagons. For the discharge of such wagons, thermal power plants install long track hoppers with plough feeders. This is again quite an expensive arrangement. As against normal track hoppers, Holtec designed a simple but effective system for lignite unloading in 2002, which is running successfully since then.
BOBRN is an open hopper car with rapid (pneumatic) bottom discharge doors, air-braked. BOBRN and BOBR are most often used for carrying coal to thermal power plants, and also for ore, stone, track ballast, etc. Each wagon holds some 60 tonnes of coal loaded from top and unloaded from bottom by means of the pneumatically operated doors. The contents can be discharged completely in about 15 seconds. Based on the success of earlier design system for lignite, Holtec has designed two such systems – one for multiple materials such as coal, copper concentrates and rock phosphate, and another for coal. The system designed for coal has been operational since last year.
Handling multiple materials from a single track hopper is usually a challenge. Secondly, some of these materials are fine and difficult to flow. Care has been taken while designing the system.
The proposed wagon unloading system is quite simple, with underground hoppers and apron feeder installed for each wagon unloading track hopper. Typically, about seven to eight minutes is required to unload one set of wagons, which includes wagon placement, connection of compressed air and unloading. If the system is designed with four hoppers, approximately two hours are sufficient to empty out a complete rake of 58 wagons. With more number of unloading hoppers, better speed of emptying can be achieved. The system requires shore compressed air arrangement, which needs to be connected to the wagons, and with one stroke, the complete wagon gets emptied in a matter of seconds.
A general arrangement of track hopper has been shown in Fig.-1 and Fig.-2. If the Railways is approached to provide such wagons to other industries as well, the entire process of material unloading becomes simpler and cost effective. The system proposed is quite simple, effective, fast and economical (not only for installation but also for operation).
Expected benefits
The conventional system of unloading (wagon tippler) requires about four-five hours for unloading of one rake, whereas with the proposed arrangement, the entire unloading operation for one rake could be completed in about two hours. This three-hour saving on one rake could result into substantially large annual savings, considering material movement by bottom discharge wagons.
The total investment required for the proposed system will be lower as compared to the wagon tippler, especially of new design (G-33, Rev-01 May 2010).
Reliability of the system will be much better as compared to the wagon tippler.
Dust nuisance substantially reduces as compared to the conventional systems.
Prerequisites
Initially, it could be difficult for the industry to switch over to bottom discharge wagons, as the Railways has limited quantity of such wagons, but gradually they need to switch over. As many industry players are interested to go for their own wagons, it could be better to go for bottom discharge wagons rather than going for conventional BOXC/BOXN wagons.
Use of Wagon Shifters
As we all know, land for the industry is gradually becoming a scarce resource. It becomes difficult to buy a large piece of land just for the smooth operation of a wagon tippler. For any industrial unit intending to install a wagon tippler, a large strip of land is needed to be bought just to provide sufficient space (equivalent to one railway rake length) on either side of the wagon tippler.
In some cases, we have noticed that the entire production unit needs about 5 hectares of land, whereas about 7.5 hectares of land needs to be acquired only for the necessary rail installation for smooth functioning of the wagon tippler, that too in a very typical plot size of 50 m x 1500 m. In our recent projects, we have faced a lot of problems on this account.
To tackle this issue, the wagon traversers are proposed and are being installed in one of Holtec?s projects.
After the wagon is unloaded on wagon tippler, the sidearm charger places the empty wagon on a traverser table. The wagon is shifted to another rail track (exit track) through a wagon traverser, where the pusher ejects the empty wagon from traverser to exit track. The enclosed arrangement drawing and photograph shows the functioning of a wagon traverser.
The wagon shifter works at the same speed as the wagon tippler and both these equipment work in tandem. This way the space requirement for the rail tracks reduces to almost half. However, one parallel rail track needs to be constructed besides the track for removal of wagons.
Expected benefits
Savings in land cost and veritable size of plot. Benefits of wagon traverser are usually case specific, and in some cases, its inclusion could help the unit greatly.
Conclusion
Development in material handling system is a dynamic process and an emerging area of research. In the view of definition of a project -?completion of a unique activity in a specific time, cost and scope?- the selection of material handling system has become extremely imperative.
We can conclude that adoption of a new material handling concept can:
- Reduce the investment cost and handling time
- Reduce the number of equipment and dust generation
- Make the system more reliable.
About the authorJai P Gupta is Chief General Manager at HOLTEC Consulting Private Limited, and has been associated with the Indian cement industry for almost 35 years. The author has employed fresh concepts for handling of bulk material in cement as well as other industries, with equal ease and success.