Resumen de Slurry pumping: investigating gravity flow of clay slurry
Using a [Bingham] yield stress of 4.4 Pa and a plastic viscosity of 0.0162 Pa s, the relationship between wall shear stress and pipe flow velocity for a 130mm ID pipe is given in Fig. 2 (Ref. 2). The pipe inner wall is assumed to be smooth and the turbulent flow predictions of wall shear stress were obtained using models developed by Wilson Thomas (Refs. 3 and 4). Thomas Wilson (Ref. 5) then developed a model for when the inner pipe wall is considered rough. The model has been incorporated into later versions of the SRC software (2004, 2007 and 2010) but this improved model has not been used in this study, as the pipe is assumed smooth.
This plot shows that laminar flow will break down in the pipe at a velocity of about 1.5 m/s and at a wall shear stress of about 7 Pa. However, the available wall shear stress when the pipe is running full of clay slurry is 8.7 Pa, and therefore the flow will be turbulent and will reach a velocity of about 1.7 m/s (81 m 3 /h). This velocity exceeds significantly the required velocity of 1.05 m/s, and consequently a pipe ID of 130mm will be able to transport the 22% by weight clay slurry above the specified volume flowrate.
By using approximate values of the two Bingham parameters of yield stress of 13 Pa and plastic viscosity of 0.0140 Pa s, the required wall shear stress to achieve a volume flow rate of 30 m 3 /h (pipe velocity of 0.27 m/s), is about 14.1 Pa. Of this, 11.4 Pa is provided by the static head, so the pump needs to develop an additional wall shear stress of 2.7 Pa, which is equivalent to a pump discharge pressure of 1.64 bar. This compares with the measured values of 2.1 to 5 bar gauge on-site.
