A variety of factors must be considered to ensure satisfactory service. Here are tips for choosing the right pump.
In applications ranging from processing to wastewater treatment, plants often must handle slurries. Handling this mixture of liquids and solids can be challenging and difficult. Some of the key factors in slurry pumping are the size and nature of the solids in the liquid and the type of abrasive wear they cause. Another is the corrosiveness of the liquid or mixture.
Sites often rely on centrifugal pumps for slurry service. These pumps (and their associated piping systems) require special provisions that demand detailed knowledge of the properties of solids and slurries to prevent abrasion, corrosion, erosion and other adverse effects, such as solids settling. Specifying the optimal combination of speed, geometry and material requires a proper balance of often conflicting pump priorities; this requires consideration of stable operation, maximum wear life, operational flexibility and minimum energy consumption.
Ceramic Slurry Pump
In this article, we will present practical guidelines and rules for slurry centrifugal pumps. We will also discuss key operating characteristics, material selection and other considerations.
Horizontal centrifugal pumps are typically used for slurry service, but vertical and other types of pumps are better suited for certain specific applications. Centrifugal pumps used to handle slurries have features tailored to specific services that reflect the corrosive or abrasive nature of the slurry and the concentration of solids. These may include the choice of materials, the use of liners, and even different drive sizes.
The primary requirement for slurry pumps is to provide adequate service life. The erosive and corrosive effects of slurry, such as the impact of high velocity flow of a liquid/solid mixture, can be really challenging. In many applications, some of the solids in the mixture are larger than the particles normally specified; therefore, the pump should be able to pass through them without any damage or operational problems.
Ceramic Slurry Pump
Because of these requirements, a slurry pump is usually larger than its clear liquid counterpart. In addition, it typically sacrifices efficiency, both at maximum efficiency and throughout its operating range, for the ability to achieve good operation in these challenging services.
Because wear is a function of speed, slurry pumps should be operated at the lowest possible speed; units typically operate at 1,200 rpm or slower. Often, direct coupling between the pump and a low-speed motor or other drive makes the most sense. On the other hand, many other applications tend to use gearboxes to meet the desired speed and operating point. In services requiring variable flow rates, variable frequency drives are used to provide the necessary continuous speed variation.
While the focus of slurry pumps tends to be on the size and percentage of solids to be pumped, corrosion resistance is also an important factor in material selection in many applications. In this case, the material selected must provide an adequate combination of corrosion and corrosion resistance.
For slurry service, pumps operating on the left side of the pump performance curve or at the best efficiency point (BEP) are usually preferred; as an indication, the rating point should be between 85% and 100% of the BEP point.