The performance of centrifugal pumps when pumping ultra viscous paste slurries

Abstract

Significant advances have been made in the design of centrifugal slurry pumps that are used for pumping high density viscous and paste slurries. This paper presents the results of a series of centrifugal pump performance tests which were conducted using a FLSmidth 6 x 4 Krebs millMAX centrifugal pump. The pump was fitted with a dry mechanical seal to prevent dilution of the slurry from gland service water, as the rheology of the slurry is sensitive to small changes in slurry density. Tests were done using paste kaolin slurry with Bingham yield stress values between 578–1,120 Pa and plastic viscosities between 728 and 1,491 mPa.s. The viscous properties of the paste during each pump test were measured using a rotational viscometer. Pump head and efficiency derating was measured and compared to the correlations of Walker and Goulas (1984). The test data shows the pump’s best efficiency point (BEP) changes and shifts to the left of the performance curve. The pump efficiency decreases as the slurry yield stress increases. The head derating data shows more head derating at the low flow rates compared to the high flow rates for the high viscosity slurry, which is in line with the findings of Walker and Goulas (1984). This paper demonstrates that it is possible to pump very viscous, high yield stress slurries with limited head and efficiency derating using centrifugal pumps, provided that positive suction conditions are maintained at all times.