In Slurry Transport, the solids are first ground to fine grain size and made into slurry with a liquid medium. The slurry is then pumped through the pipes to a desired destination. Even though the concept of slurry pipelining was known at the turn of the century, it was only in 1957 that it became a practical reality. The first long distance pipeline to be established was in Arizona, USA, to transport 0.4 MTPA of gilsonite over a distance of 115 km. Since then the applications are growing. The technical term slurry contains quite a wide concept of solid-liquid mixtures. If a solid-liquid mixture has some fluidity, we call it slurry. Slurry is any mixture of liquid and solids capable of causing significant pump abrasion, clogging, or mechanical failure as a result of high loads or impact shocks However, as suspending solid particles vary in size from very fine colloidal particles to sedimentable rough particles, the flow characteristics of slurry change widely. The solid concentration greatly affects the viscosity of slurry.
[...] In a free-settling slurry with sufficient dilution so that particles do not interfere with one another in settling, the rate of particle settling is expressed as a form of Stokes' law, but for practical purposes the formula cannot be used for sizing equipment. If flocculants are used, these materially affect the sizing and testing of methods used. Based on the flow of slurries and settling tendency, Flows in slurries are divided as the following: Homogeneous slurries - In a truly homogeneous mixture the particles are sufficiently fine so that no settling tendency is apparent in an unstirred sample. [...]
[...] MATERIALS OF CONSTRUCTION: Slurry pumps are available in a variety of materials of construction, to best handle the abrasion, corrosion, and impact requirements of nearly any solids-handling application. In addition to pump design itself, the many available materials of construction present a wide spectrum of choice to meet the challenges found in slurry pumping. Cast iron is the basic pump material, being both low in cost and well suited for mildly abrasive applications. Cast iron with nickel is sometimes used when protection against mild corrosion is needed. [...]
[...] Concentration of the solids It is the ratio of solids to liquid that determines the slurry as a whole. These four static characteristics create unique demands, requiring specific pump design and construction features. Hence various slurry pumps are used depending on the application for which they are put. A slurry pump designed to handle wastes, light slurries and random large solids does not use wear liners. The emphasis here is on very large flow passages through the casing and impeller. [...]
[...] The hindered settling characteristics of a slurry are particularly applicable to the flotation of minerals. Crystal form influences hindered settling. Low bulk density fibrous and leaf like materials have a viscous resistance to flow which is largely due to interparticle friction and particle agglomeration. Fibrous slurries are typical of suspensions which behave as non-Newtonian fluids. Basic Flow Characteristics: The representative flow models for various kinds of slurries are shown in Fig .Figure 12.1 a represents the Newtonian model, τ = μN(du/dr) where μN is a Newonian viscosity. [...]
[...] Effect Of Particle Size Distribution On Slurry Viscosity: Most systems of interest are more complex than the mono disperse suspensions. If particles of a wide size distribution are employed, the maximum possible packing density of particles will change considerably. This change causes a reduction in slurry viscosity. Chong et al. (1971) investigated the effect of bimodal particle size distribution on the slurry viscosity. They showed experimentally that the viscosity of a bimodal suspension is reduced almost in magnitude of unimodal suspension viscosity at: Φ = 0.6 and d/D = where d and D are small and large particle diameters, respectively. [...]
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