The flow behaviour of particulate solids and capsules in wood pulp fibre suspensions

Abstract

This thesis describes an investigation into the flow behaviour of particulate solids and capsules in wood pulp fibre suspensions. Emphasis is placed on measuring pipe friction loss and stability of solids-fibre slurries and fibre-capsule mixtures in straight horizontal pipes. It is shown that low concentrations (1-3 %v) of wood pulp fibre form a structured carrier fluid with ability to support particles while behaving like a liquid of low viscosity. At moderate flow velocities fibres damp turbulence and friction losses become lower than water. If solids are preferentially injected into the fibre suspension as a central core, or in a capsule as dry solids, pipe friction loss is reduced further, as is pipe wear. At very low fibre concentrations (<1%v), fibres reduce the friction loss of conventional solid-water mixtures and act as a drag reducing additive. The network strength properties of five wood fibre suspensions are reported and their application to slurry flow is discussed. Settling data for particulate solids, coherent dense-phase cores and capsules are presented and various mechanisms of support are described. Two flow techniques for transporting coarse and dense-phase particle suspensions are proposed, along with strategies for injecting solid particulates into a pipeline. Pipe friction loss data are presented for solids-fibre mixtures of wood chips (7-15 mm), coarse (+2-10 mm) and fine (+0.5-1.0 mm) coal, sand (+0.32-2.0 mm), iron ore (+0.05-0.28 mm), and cylindrical capsules (loaded with dry solids) flowing in 54, 79 and 101.6 mm diameter PVC pipes. Some pipe friction loss data are presented for solids transported as a central core supported by an annulus of fibre suspension. The key flow parameters are also optimized and a preliminary cost comparison is made. Coarse coal suspensions (up to 4O %v) with fibre concentrations of 0.7 to 1.0 percent have been shown to exhibit friction losses about 40 percent below that of the equivalent coalwater slurry. Adding 0.8 percent fibre to water is shown to reduce capsule friction head loss up to 50 percent.