There is no doubt that simutaneous feeding on to a conveyor is an effective way to blend any granular material, except that this method will not attenuate any time related variations in the supply stream if any of the components are of irregular composition. This system also demands concurrent access to the supply of the materials.

There are many articles in back copies of the Trans Tech publication 'Bulk Solids' that relate to the widely used method of stacking out in layers and recovery in a systematic manner in order to to affect efficient blending, but some care is needed if the products tend to segregate.

Much is likely to depend on the logistics of supply, stocking plant and ultimate discharge facilities to be employed, so it is difficult to give a simple answer other than blending should be incorporated as an intigrated process rather than considered as an independent operation. ■

Rotary Plow feeders in Tunnel ■

The blending operation is achieved as a part of conveying, stacking and reclaiming operation. The methodology for this is highly dependent on:

1. Incoming material rate mtph

2. Steadiness / variation in mtph of incoming material.

3. Operational hours in a day, a month and a year for incoming material

4. Outgoing material rate mtph

5. Operating hours in a day, a month and a year for outgoing material.

The effectiveness i.e. degree of blending is defined by 2 terms, applied together.

a. Minimum batch size (also called sample size)

b. Blending ratio (also called blending efficiency)

More blending ratio (efficiency) in conjunction with smaller batch size signifies more intimate blending (mixing) and consequently more efforts and expense for blending operation.

In general, the degree of blending required for coal, would be of average category (ie. it will not need class of blending needed for creation of product from precisely mixed raw materials).

Coal blending / homozinisation / mixing function can be easily incorporated in stacking, reclaiming and conveying activity, without unusual price increase. However, it shall demand disciplined and planned operation.

Regards

Ishwar G Mulani - Author book: Engineering Science and Application Design for Belt Conveyor

Advisor (consultant) for bulk material handling systems

EmailID: parimul@pn2.vsnl.net.in ■

All that is required is a tripper in the main line with the secondary ingredient fed from a bin into the main stream. If the capacity of the bin matches the run down time of the conveyor then the blend ratio can be maintained. You should always fill the secondary ingredient bin before starting the mainline. If you want to be a little bit cleverer you can install a belt weigher upstream and do some sums to control the bin feeder output. ■

Coal Blending

Store the diffrent grade of coal in bunkers & draw the coal by weigh feeder in proportion in order to get for desired blending.

Regards.

Atanu Banerjee ■

10,000tpd works out at about 650tph. This throughput does not justify any sort of stockyard. In the UK (and we also did this in Sumatera) we would have to ship this quantity by road. Then you could tip precisely & blend with mobile plant until the business grows. ■

Regarding coal blending issue, there are many suggestions in this forum. Further to my earlier message, I would like to add the following.

Blending implies mixing. So, mixing can be done by many methods; simply by hand shovel to mechanised methods.

Everything hinges on 1) Tonnes / hr 2) Reliability for degree of mixing 3) Guaranteed numerical parameter for blending in terms of blending ratio with respect to batch / sample size.

Thus, quantity and quality requirement of user / buyer of blended material (and consequent monetary losses / penalty for failure in quality of blended material) to be given due consideration.

For example, material blending in cement plant or steel plant needs to be strictly as per technical need or else product will become substandard and of less price. Likewise, even 5% improper burning of fuel in boiler can sum up into huge amount. ■

Blending implies a thorough mixing of the recipe of materials to be mixed. If you are just trying to proportion a group of materials that is much simpler.

For 10000 tpd I recommend that the blending be done in the stockpile. Since you are considering only two materials I would use feeders under the stockpile since the reclaim devices are less expensive than above ground machines.

If you would like to build a pre-blended pile, that can be sampled and then be uniform for the entire pile the best systems would be bridge reclaimers. They can be either bucketwheel or scraper depending on reclaim rate requirements.

Other reclaim equipment can be portal reclaimers or bucketwheels if equipped with a harrow.

Remember, the degree of blending accuracy is determined more by the stacker and stacking method than by the reclaimer.

If your operation is 24 hrs/day I believe your best bet would be a bridge scraper reclaimer with chevron stacking pattern for a two product mix. System could be linear or circular.

If your stockpile needs to be covered the least expensive system would be a circular system unless you need large volumes of stored product to account for shipping limitations or mandated reserves.

Please check our web site for available equipment for stockpile blending and link to the manufacturers ' websites.

You can view our capabilites at www.loefflerengineering.com

Frank Loeffler ■

To facilitate elevating of the coals, in tight spaces, you should consider sandwich-belt high-angle conveyors, particularly DSI Snake-sandwich conveyors by Dos Santos International. These use all conventional conveyor equipment and smooth surfaced rubber belts that can be continuously scraped clean. Check out our web site.

Joseph A. Dos Santos PE ■