When considering the blending by stockpile layering and reclaiming a distinction should be drawn between the blending of different ingredients and the homogenisation of a heterogeneous product. For component blending it is only essential that the cross section of each layer should equate to the proportions required in the final mix. In the case of equal proportions the incremental height of a linear pile should be K(√2 –1)N, where K = depth of initial pile and N = layer from bottom. This compensates for the total cross section increasing as the square of the stockpile height.

Variations in the proportions require that the layer depth be adjusted by a factor which is the root of the ration. For example, to mix in the ration of 3 : 4 : 1 the pile would be deposited with a base pile K deep and increasing layers of K√4 / √3 (√2 – 1) 2 and K. 1/√3 (√2 – 1)3.

For homogenising a variable mono-product feed stream, the optimum layer thickness is (√2 – 1)L, where L is the number of layers. The number of layers determine the ‘coarseness’ or ‘fineness’ of the mix as the collecting mechanism will give a secondary mixing to the collected surface. In practice, consideration should be given to how the feed stream varies with time and the scale of scrutiny that will be applied to a sample before deciding how to disperse the product along the length of the pile, as this may be more important than the layer thickness.

Lyn Bates ■

Dear Sanjay,

During reclaiming operation, the bridge reclaimer simultaneously takes material from all layers. Therefore, the material so reclaimed gets blended / homogenised. For example, if the stock pile is made up of only one layer, there is no blending. As the number of layers increases, the blending (mixing) effect is superior. More number of layers signifies better blending with respect to smaller batch size. For more understanding I recommend you to opt for book on the subject matter.

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyors.

Email : parimul@pn2.vsnl.net.in ■

More layers signify more intimate mixing, which results into smaller batch / sample size. Blending efficiency is not correct word for the particular issue referred by you, as per its definition.

Please refer my reply on this website under the Forum 'Ask Lyn', thread ' Blending of Coal ' which also provides some related information. ■

Dear Mr.Sanjoy,

In the forum giving formula for the same is not possible. I want to refer page nos.from 329 to 335

of Bed Blending theory by Mr. A.G.Gerstel for getting idea. It is best on statistical method.This you will get in the book Stcking,Blending & Reclaiming by Mr.R.H.Wohlbier.

Regards.

A.Banerjee ■