The flow behaviour of inorganic - wood fibre slurries in pressurised pipes

Abstract

Understanding the flow behaviour of inorganic-wood fibre slurries is important for developing new process equipment for the cement fibreboard industry. Little is reported in the technical literature and generally slurry flow knowledge is limited to a few engineers within the industry. Pipe friction loss characteristics and the settling behaviour of inorganic-wood fibre slurries were studied and data were obtained in pressurised horizontal pipes ranging from 25 to100mm diameter at flow velocities up to 8m/s. The inorganic solids studied were cement and fine silica of size range 10 to 150 m. Solids concentrations ranged from 5-20% and fibre concentrations from 0- 2%.

Wood pulp fibre suspensions at low fibre concentrations form a structured carrier medium with the ability to support fine particulate solids. Unlike fibre-free suspensions, no permanent stationary deposit formed and therefore no minimum settling velocity exists. At low flow rates particles are trapped in the fibre plug and the friction loss is above water. At high flow rates the particles are still supported but the fibres dislodged from the central plug core damp turbulence and friction losses for the cement-silica-fibre system are less than water (drag reduction). The overall flow behaviour is similar to and consistent with previous data reported for coal-fibre slurries. Fibre concentration has a significant affect on the onset of drag reduction and friction loss increases with fibre concentration as with conventional fibre suspensions. Pipe diameter has a minimal effect on the onset of drag reduction but friction loss decreases with diameter as with conventional fluids.