Hydraulic coarseness

Pneumatic classification can be partitioned conveniently into coarse, ie, fine products above 95% < 100 pm intermediate, ie, fine products ranging between 95% < 100 and 30 pm and fine, ie, fine products below 95% < 30 pm. Pneumatic classification, like hydraulic classification, balances the force of gravity with drag forces (counter flow) in order to bring about a separation. 

Hydraulic (Pressure) Nozzles Manufacturers data such as shown by Fig. 14-88 are available for most nozzles for the air-water system. In Fig. 14-88, note the much coarser solid-cone spray. The coarseness results from the less uniform discharge. 

Feed to be sized is put into hindered-settling condition by hydraulic water in quantity only sufficient to teeter the smallest particle wanted in the coarse product. The finer fractions report to the overflow or pass into the upper column for removal in a three-product unit. 

Coarse solids are discharged by siphons extending to the bottom of the hindered-settling zone. Siphon control is obtained by a novel hydrostatically actuated valve which makes or breaks the siphon to flow only when the teeter zone is in correct condition. Discharge by an intermediate fraction from the upper column is by means of additional siphons. Hydraulic-water consumption is considerably lower than required for multipocket sizers. 

Filter aids should have a narrow fractional composition. Fine particles increase the hydraulic resistance of the filter aid, whereas coarse particles exhibit poor separation. Desired particle-size distributions are normally prepared by air classification, in which the finer size fractions are removed. 

There have been several studies involving the use of media consisting of fine dense particles suspended in water for transporting coarse particles. The fine suspension behaves as a homogeneous fluid of increased density, but its viscosity is not sufficiently altered to have a significant effect on the pressure drop during turbulent flow, the normal condition for hydraulic transport. The cost of the dense particles may, however, be appreciable and their complete separation from the coarse particles may be difficult. 

James, J. G. and Broad, B. A. Transport and Road Research Laboratory, TRRL Supplementary Report 635 (1980) Conveyance of coarse particle solids by hydraulic pipeline Trials with limestone aggregates in 102, 156 and 207 mm diameter pipes. 

Haas, D. B., Gillies, R., Small, M. and Husband, W. H. W. Saskatchewan Research Council publication No. E-835-1-C80 (March 1980). Study of the hydraulic properties of coarse particles of metallurgical coal when transported in slurry form through pipelines of various diameters. 

Chhabra. R. P. and Richardson, J. F. Chem. Eng, Res. Des. 63 (J 9S5J 390. Hydraulic transport ol coarse particles in viscous Newtonian and non-Newtonian media in a horizontal pipe. 

Al.-SAl.lHt, I.. Ph.D. Thesis, University of Wales (1989). Hydraulic transport of coarse particles in vertical pipelines. 

Particles with the lowest specific gravity are carried with the water towards the outside wall of the spiral. The spiral separates at its greatest efficiency when used in the size range of 10 to 200 mesh. Some particles will be recovered both above and below these size ranges, but occasionally, ultrafine and very coarse heavies will be lost in the tailings, as will be middlings or unliberated ore particles. The spiral will benefit, therefore, from the use of hydraulic classification as a feed preparation step. 

Third, coarse fragments should be screened to no more than about 10% gravel-size particles. Soils with a greater percentage of coarse fragments can contain zones of gravel that have high hydraulic conductivities. 

Kellerhals R, Bray DI (1971) Sampling procedures for coarse fluvial sediments. J Hydraulics Division ASCE97(HY8) 1165-1180... 

The technology is best suited for coarse-textured soils that have a moderate to high hydraulic conductivity. The steam extraction system is not applicable for soil contaminated with metals or other inorganic wastes. The system is also not applicable for organics in which the mobility is not increased with elevated temperatures. 

As follows from Figure 4, for coarse coal transport the power consumption of slurry pipelining reaches from 300 % to 100 % higher values than that in case of hydraulic capsule pipeline transport. The energy reduction increases with reduction of the operational velocity. 

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