There are numerous charts and tables available. The primary basis for selection of the type of conveyor is the Geldart Powder Classification Chart. This was published in Powder Technology in 1973 on page 285. It has been reproduced extensively. Because of its density and particle size, cement and coal are difficult to convey. In using the Geldart chart, remember that the density is the particle density not the bulk or structural density. This would be especially true for rice husk and wood chips or products that have internal voids.