The effect of sand‐clay slurries on the performance of centrifugal pumps

Abstract

The selection of an operating domain is complicated by the flat system and pump head curves, and additionally by the pump solids effect which lowers the clear water head and efficiency. For example, a reduction of the pump head curve by only a few percent can cause large changes in flow, as shown in Figure 1.It can be seen from Figure 1 that an error in estimating the solids effect could mean that the system might run ineffectively or not at all. Detailed information is needed on the effect of pump head and power consumption in order to achieve reliable and energy-efficient operation.The addition of clay has been found to be effective in reducing friction pipe) of up to 40% and 60% when a phosphate clay was added (sand to clay mass ratio of between 5:l and 6:l) giving a total solids concentration by volume of 25% and 35%, respectively. A further marginal increase of the clay content then resulted in increasing hydraulic gradients. These results illustrated how small variations in the clay content may cause large variations in the pipeline friction losses; thus, the pumping head requirement. Therefore, an important question is how the sand and sand-clay mixtures influence the pump head and efficiency.The objective is to present experimental pump performance results with a 0.15 by 0.1 m branch centrifugal pump for the three narrowly graded sands and mixtures with clay used by Scott (1997). The aim is also to compare the results to simple design criteria and to discuss the mechanism involved. Experimental StudyThe experimental work was carried out at the GIW Hydraulic Testing Laboratory, CIW Industries Inc., Crovetown, CA, U.S.A. A radial type 4-vane all-metal pump with impeller diameter 0.625 m was used in a 0.1 03 m pipeline loop system. Power input to the pump was measured with a torque bar. Solids concentrations were measured in a vertical U-loop and flow rates were obtained from a magnetic flowmeter. Readings of pump suction pressure and discharge pressure, flowrates, input 'Author to whom correspondence may be addressed. E-mail address: anders.sellgren@ sb.hrth.seThe addition of clay to sand slurries has been found to reduce the pipeline friction losses, thus lowering the pumping head and power consumption. Pump water heads and efficiencies are decreased by the presence of solid particles. Experimental results are presented for a centrifugal pump with an impeller diameter of 0.625 m for three narrowly graded sands with average particle sizes of 0.64, 1.27, and 2.2 mm. Reductions in head and efficiency of up to 30% were observed for sand slurries with volume concentrations of up to 35%. Head and efficiency were lowered by about onethird for sand-clay mixtures with sand to clay mass ratios between 4:l and 6:l. Comparisons are made with design criteria and a mechanistic model approach based on a prediction of the relative motion of the solids and water in the volute region of the pump. power, rotary speed, and solids concentration were used to calculate the total pump head developed and pump efficiency. A detaile...

Performance Characteristics of Centrifugal Slurry Pumps

“…The head ratio values of fly ash slurry lie in between the values of head ratios of bed ash slurry and fly ash slurry. This could be attributed to the smaller representative particle size of the fly ash and higher relative viscosity of the slurries compared to the other two slurries which is in agreement with the results available in the literature ͑Fairbank ͓2͔, Wiedenroth ͓3͔, Vocadlo et al ͓4͔,Burgess and Riezes ͓5͔,Sellgren ͓6͔,Walker and Goulas et al ͓7͔,Sellgren and Vappling,͓8͔,Wilson et al ͓10͔,Gahlot et al ͓11͔,Kazim et al ͓12͔,and Ni et al ͓13͔͒. The finer particles of fly ash are homogeneously distributed in the slurry and hence require less energy for transportation leading to higher head ratio values compared to coarser slurry of bed ash.…”

“…Researchers over the years ͑Fairbank ͓2͔, Wiedenroth ͓3͔, Vocadlo et al ͓4͔,Burgess and Riezes ͓5͔,Sellgren ͓6͔,Walker and Goulas ͓7͔,Sellgren and Vappling,͓8͔,Sellgren et al ͓9͔,Wilson et al ͓10͔,Gahlot et al ͓11͔ Kazim et al ͓12͔,and Ni et al ͓13͔͒ have observed that the performance of the pump decreases for increased solid concentration, particle size, and specific gravity. On the other hand, Chand et al ͓14͔ have reported that the head and efficiency of the pump increases due to addition of solid particles.…”

Performance Characteristics of Centrifugal Pump Conveying Soft Slurry

“…The flow of solids through the pump has associated hydraulic losses caused by relative motion of slurry particles (drag effect) wh ich have greater inertia and cannot accelerate as rapidly as the carrier liquid [2]. Sellgren and Vappling [3] have investigated the effect of solid concentration for two tailings materials on the performance of a centrifugal slurry pu mp o f a closed impeller. They observed fall in head and efficiency with increase in solid concentrations.…”

“…The pu mp efficiency in coarse sand slurry service may drop almost 60% compared to that of water service, when C v = 42%. Sellg ren et al [6] showed that the addition of clay to sand slurries has been found to reduce the pipeline friction losses, thus lowering the required energy consumption. Gandhi et al [7] presented a methodology based on a loss analysis procedure to predict the performance of centrifugal slurry pu mps handling solid-liquid mixtures.…”

Effect of Solid Concentration on a Centrifugal Pump Performance

“…Wilson [4j presented practical methods for predicting the performance of centrifugal slurry pumps with extremely fine and coarse particles size, density and concentration of solids The results showed that when pumping slurries, the relative reductions in pump head and efficiency were independent of flow rate and pump speed. Sellgren and Vappling [5] observed higher reduction in the efficiency compared to the head developed by rubber-lined pump for solid concentration higher than 20 percent by volume. Sellgren and Addie [6] investigated the effect of solids on the large centrifugal pumps head and e f f k i e n~ They nsed two tipes of sands and a gravel material with average particle sizes of 0.25, 1.5, and 6 mm, and showed that, for a 70% of the best efficiency point (BEP) flow rate, the clear water head was dropped by 3.5, 7, and 10% respectively, with a solids concentration of 32% by weight in centrifugal slurry pumps having impeller diameters of 1.1 and 1.2 m. Gahlot et al [7] studied the effect of density, size distribution, and concentration of solids on the characteristics of centrifugal pumps.…”