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How To Succeed At Slurry Pumping Full-time Job

Jan 14th, 2022 at 07:00   Marketing & Communication   Basildon   4 views
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How To Succeed At Slurry Pumping

Optimal transfer of two-phase solid-liquid flow (slurry flow) has long been a major industrial challenge. Slurry pumps are among the most common types of centrifugal pumps used to deal with this transfer issue. The approach of improving slurry pumps and consequently increasing the efficiency of a flow transmission system requires overcoming the effects of slurry flow such as the reduction in head, efficiency, and wear. This study attempts to investigate the changes in the pump head by modifying the slip factor distribution in the impeller channel. For this purpose, the effect of splitter blades on slip factor distribution to improve the pump head was investigated using numerical simulation tools and validated based on experimental test data. Next, an optimization process was used to determine the characteristics of the splitter (i.e., length, number, and environmental position of the splitter) based on a combination of experimental design methods, surface response, and genetic algorithm. The optimization results indicate that the splitters were in a relative circumferential position of 67.2% to the suction surface of the main blade. Also, the optimal number and length of splitter blades were 6 and 62.8% of the length of the main blades, respectively. Because of adding splitter blades and the reduction in the flow passage, the best efficiency point (BEP) of the slurry pump moved toward lower flow rates. The result of splitter optimization was the increase in pump head from 29.7 m to 31.7 m and the upkeep of efficiency in the initial values.

 

The effect of solids on a centrifugal horizontal slurry pump performance is a major concern to the design of slurry transportation system. In the present study, the multiphase modeling of centrifugal slurry pump is performed using two models, Mixture and Eulerian-Eulerian multiphase. Sliding mesh approach is employed for unsteady simulation of the pump. The accuracy of the simulations is ascertained by comparing the performance characteristics of the pump obtained numerically and experimentally. Experimental results are obtained by measurements in a pilot plant test rig with three different mean size sand particulate slurries. The Eulerian-Eulerian multiphase model predicted the effect of the solids on pump performance close to the experimental results as compared to Mixture model. The obtained accuracy with Eulerian-Eulerian model for predicting the effect of solids on head and efficiency is around ±2% and ±3%, respectively. The predicted results using Eulerian-Eulerian model confirm that the head and efficiency of the pump decrease with the increase in particle size and concentration. The particles of high specific gravity show less reduction in head and efficiency of the pump. Further, the effect of variation in particle size and concentration on the flow field in the impeller and casing has also been analyzed at best efficiency point operation. Non-homogeneous suspension of particles inside the blade channels and casing passages is examined. The particulate concentration is observed higher near the impeller back shroud, pressure side of the blades, and non-suction side of the casing as compared to other locations.

 

Plants often must handle slurries in applications ranging from processing to wastewater treatment. Dealing with such mixtures of liquid and solids is challenging and difficult. Some key elements in slurry pumping are the size and nature of the solids in the liquid and the kind of the abrasive wear they cause. Another is the corrosiveness of the liquid or the mixture.

 

Sites frequently rely on centrifugal pumps for slurry services. These pumps (and their associated piping systems) need special provisions that call for a detailed knowledge of the solid and slurry properties to prevent wear, corrosion, erosion and other adverse effects such as settling of the solids. Specifying the optimum combination of speed, geometry and materials requires properly balancing often conflicting pump priorities; this demands consideration of stable operation, maximum wear life, operational flexibility and minimal energy consumption.

 

In this article, we’ll cover practical guidelines and rules for centrifugal pumps for slurries. We’ll also discuss key operational features, material selection and other considerations.

 

Tailored Pumps

Horizontal centrifugal pumps usually are used for slurry services, although vertical and other types of pumps are favored for some specific applications. Centrifugal pumps for handling slurries have features tailored to the particular service that reflect the corrosive or abrasive nature of the slurry and the solids concentration. These may include choice of materials, use of liners and even different driver sizing.

 

The first major requirement of a mining slurry pump is to provide adequate service life. Erosion and corrosion effects of slurries, such as the impingement of high velocity flow of liquid/solid mixtures, are really challenging. In many applications, some solids in the mixture are larger than usually specified particles; so, the pump should be able to pass them without any damage or operational problems.

 

As a result of such requirements, a vertical slurry pump often is larger than its clear liquid counterpart. Moreover, it generally sacrifices efficiency, both maximum efficiency and efficiencies over the whole operating range, in exchange for the ability to achieve good operation in these challenging services.

 

Because wear is a function of velocity, a slurry pump’s speed should be as low as possible; units usually operate at 1,200 rpm or slower. Often, direct coupling between the pump and a low-speed electric motor or other driver makes most sense. On the other hand, many other applications favor gearboxes to meet the desired speed and duty point. In services requiring variable flow, variable frequency drives are used to provide the necessary continual speed changes.

 

Although the emphasis on a ceramic slurry pump tends to be on the size and percentage of solids to be pumped, corrosion resistance is also an important factor for material selection in many applications. In such cases, the material chosen must provide an adequate combination of both erosion and corrosion resistance.

 

For slurry services, a pump operating on the left of the pump performance curve or at the best efficiency point (BEP) is usually preferred; as an indication, the rated point should lie somewhere between 85% and 100% of the BEP point.

 

The performance curves of many centrifugal pumps are based on handling water. So, to obtain the performance characteristics for these slurry centrifugal pumps, you must modify the results for the presence of solids. Many correlations and correction methods exist for predicting the performance of centrifugal pumps when handling slurries; these account for factors such as individual effects of particle size, particle size distribution, specific gravity and concentration of solids. They usually provide a head reduction factor and efficiency reduction factor for slurries compared to clear water. However, every pump has unique service-specific factors for a given application. You should verify these by experiments.

 

For slurry services, a pump operating on the left of the pump performance curve or at the best efficiency point (BEP) is usually preferred; as an indication, the rated point should lie somewhere between 85% and 100% of the BEP point.

 

The performance curves of many centrifugal pumps are based on handling water. So, to obtain the performance characteristics for these slurry centrifugal pumps, you must modify the results for the presence of solids. Many correlations and correction methods exist for predicting the performance of centrifugal pumps when handling slurries; these account for factors such as individual effects of particle size, particle size distribution, specific gravity and concentration of solids. They usually provide a head reduction factor and efficiency reduction factor for slurries compared to clear water. However, every pump has unique service-specific factors for a given application. You should verify these by experiments.

 

Wear, Erosion And Corrosion

Major factors that influence wear include the following:

 

• details of erosive particles (material, size, shape, etc.);

• concentration of solids;

• fluid velocity and particle velocity; and

• hydrodynamic properties of the flow (Reynolds number, etc.).

 

Turbulent flow analysis usually isn’t applicable for slurry pumps because the presence of solid materials will directly influence the turbulence parameters. The mechanisms of turbulence become a complex problem particularly for dense slurries. This, combined with the nature of the flow inside a slurry pump, which is characterized by unsteadiness as well as deformed velocity distribution patterns, cause a very chaotic situation. However, some simple rules have been verified both in theory and experiments. For instance, the erosive wear rate is proportional to the flow velocity. It also depends on the solids concentration; as that concentration increases, so, too, does the wear rate. In addition, the sizing and specific gravity of solids in the slurry affect wear.

 

As a very rough indication, in medium and low concentrations, the mechanism of erosion resembles cavitation erosion. Here are some observations about a slurry pump that operated for a short period with low concentration slurry and then with a moderate concentration one. With the slurry at low concentration, the suction side of the blade showed very limited erosion at the leading edge while the rest of the surface was nearly unscathed. Most of the erosion of the back shroud was concentrated in the eye of the impeller and around the leading edge of the back-shroud corner. The maximum erosion appeared on the leading edge and towards the back shroud of the impeller. This pump, operated with a relatively higher concertation slurry, showed a similar erosion pattern — with the only notable difference being that the region close to the back shroud was more heavily eroded. Unfortunately, here and more generally, theoretical studies don’t properly predict the level of erosion.

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How To Succeed At Slurry Pumping