Experimental investigation of centripugal pumps when handling solid-liquid mixtures

EXPERIMENTAL INVESTIGATION OF CENTRIFUGAL PUMPS WHEN HANDLING SOLID-LIQUID MIXTURES SUMMARY In order to design a slurry transportation system based on centrifugal pumps, it is necessary to know the influence of solids on the performance of the pumps. If accurate corrections are not made, it is likely that pumps and the system will be mismatched, which will accelerate the rate of wear and increase operating and maintenance costs. Centrifugal pumps, because of their inherent advantages of high and consistent flow rate, low cost, and ease of maintenance and better operational stability are being increasingly employed for pumping slurries in the pipeline transportation systems. In short distance, in plant, slurry pipelines where the head requirements are relatively low, therefore centrifugal pumps are best suited. The selections of pumps for any pipeline transportation system depend mainly on the past experience and/or based on the performance of pump, pumping clear water. On the other hand, the characteristic performance curve of a centrifugal pump differs from its clear water performance curve when solids included and the flow becomes two phase. The performance of the pump will improve or deteriorate depending upon whether the slurry behaves as Newtonian fluid or Bingham fluid. The general conclusions given by most investigators are that the head developed and efficiency of the pump decrease whereas the input power increases when mixture of solids (heavier than water) and water being pumped. The variables affecting the pump performance are the concentration of solids in the mixture, physical properties of solid like its density, shape, size and size distribution of particles and flow inside the pump. Both closed and open impellers have long been used in centrifugal pumps handling slurries. Open impellers have some advantages when compared with closed ones. For instance, low manufacturing cost and low disc friction loss could be said. Furthermore, they are suited for pumping suspensions. In this types of impellers have only one shroud and are open on one side where a tip clearance takes place between open side of the impeller and the stationary casing. One of the most important loss in open impellers is the tip clearance loss. Although tip clearance effects on pump performance have been studied for many years, and the necessity for reliable information is ever increasing, an exact method of prediction of these effects currently does not exist and test data must be relied upon to aid in the development of models to estimate these effects. On the other hand, most publications in the field are either mainly focused on the tip clearance effects on pump performance handling clear water or on the slurry effects on pump performance. Due to complex nature of XVIthe problem, only a limited number of studies on the tip clearance effects on conventional centrifugal pump performance handling slurries have been conducted. In the present study, experiments were conducted to determine the individual effects of solid properties (particle size, solids specific gravity), and solids concentration by weight up to 33.51%, as well as tip clearance effects on an open impeller centrifugal pump characteristics. To do this, 6 different solid minerals were employed and maximum particle size was approximately 2.4 mm. Tip clearance was varied from 1.25 mm to 8 mm over the experiments. Utilizing these test data a comparative evaluation of the existing correlations in the literature was performed. Additionally the influence factors relating to tip clearance losses, for slurry pumping, have been computed and compared with single phase pumping. Test results have shown that slurry characteristics and running tip clearances have a considerable impact on the pump performance. XVII