A slurry pump is a type of pump designed for moving liquid containing substantial solid particles. They are often used in mining.[1] Slurry pumps are more robust than liquid pumps and can withstand wear due to abrasion, and often use parts that are designed to be replaced when worn out.
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Slurry pumps are widely used in transport of abrasive solids in industries such as mining, dredging, and steel. They are often designed to be suitable for heavy-wearing and heavy-duty uses. Depending on the mining process, some slurries are corrosive which presents a challenge because corrosion-resistant materials like stainless steel are softer than high-iron steel.
Slurry is usually classified according to the concentration of solids. Engineering classification of slurry is more complex and involves concentration, particle size, shape and weight in order to determine abrasion severity. For engineering selection of slurry pumps, slurry is classified as class 1, class 2, class 3 and class 4.
The most common metal alloy used to build slurry pumps is high chrome, which is white iron with 25% chromium added to make it less brittle. Rubber line casings are used for applications where the solid particles are small.
Slurry pumps vary in design and construction to handle different types of slurry, which has varying concentrations of solids, size and shape of solid particles, and composition of the solution. Centrifugal, positive displacement, and vortex pumps can be used for slurry. Centrifugal slurry pumps can have between bearing-supported shafts with split casing or rubber- or metal-lined casing. Configurations include horizontal, vertical suspended and submersible.
Engineers must consider capacity, head, solids handling capacity, efficiency, power, speed, and NPSH. Many factors and corrections to the duty point affect the calculation of brake horsepower and wear.[3] The peripheral speed of the impeller is one of the main distinguishing features. Speed must match the slurry type classification (abrasion classification) in order to achieve a reasonable service life due to abrasion.
Slurries are specialized compounds found in many processing industries, including sanitary industries such as food, dairy, beverage processing, and biopharmaceutical manufacturing. Slurries combine properties of both liquids and solids, and so specialized consideration must be given when it comes to determining the type and size of slurry pump to use with them.
This article will focus on:
Slurries are mixtures of solids and liquids, with the liquid serving as the transport mechanism used to move the solid. The size of the particles (or solids) in slurries ranges from one micron in diameter up to hundreds of millimeters in diameter. The particle size significantly impacts a pump's ability to move a slurry through a process line.
All slurries share five essential characteristics:
Slurries are further classified by industry into four classes based on how aggressive they are — Class 1 being the least aggressive and Class 4 the most aggressive. The pumping of slurries can have the following wear impacts on both pumps and pipeline components:
As described below, there are several types of pumps that are suitable for pumping slurries. However, we must address a couple of critical considerations before considering which technology to use.
Pumps designed for pumping slurries will be heavier duty than those designed for less viscous liquids since slurries are heavy and difficult to pump.
Slurry pumps are typically larger in size than standard pumps, with more horsepower, and built with more rugged bearings and shafts. The most common type of slurry pump is the centrifugal pump. These pumps use a rotating impeller to move the slurry, similar to how a water-like liquid would move through a standard centrifugal pump.
Centrifugal pumps optimized for slurry pumping will generally feature the following in comparison to standard centrifugal pumps:
For pumping abrasive slurries, these types of pumps may also be made from specialized high wear alloys such as AL-6XN® or Hastelloy® C-22®. Hardening stainless steel is also a common option for abrasive slurries, with Expanite and Armoly being two hardening processes.
For certain types of slurry pumping conditions, positive displacement pumps may be a more appropriate choice than a centrifugal-style pump.
These conditions include:
Common types of positive displacement pumps used in slurry pumping applications include:
These pumps use two meshing lobes rotating within a pump's housing to move fluids from the pump's inlet to its outlet.
These pumps employ rotating screws to move liquids and solids from one end of the pump to another. The screws' turning action creates a spinning motion that pumps material.
These pumps use a flexible membrane that expands the volume of the pumping chamber, bringing in fluid from an inlet valve and then discharging it through an outlet valve.
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Choosing the right pump for your slurry application can be a complex task due to the balance of many factors including flow, pressure, viscosity, abrasiveness, particle size, and particle type. An applications engineer, who knows how to take all of these factors into account, can be a great help in navigating the many pump options available.
~ Matthew Sato, Applied Products Sales Manager, Ampco Pumps
In determining which type of slurry pump is best suited for your particular application, follow these four simple steps.
Consider the following:
If it's a centrifugal pump, is the design of and material used to construct the impeller appropriate for pumping slurries?
It's also important to consider the chemical compatibility of the slurry with any elastomers in the pump. Once one has addressed both the nature of the slurry and the components of different types of pumps, you may select the potential candidate slurry pump for the application.
The most important thing here is figuring out the pump horsepower needed to deliver a specific fluid flow rate at the desired or required differential pressure. Look at the following:
To reduce component wear, most centrifugal slurry pumps run at fairly low speeds — typically less than rpm. Find the sweet spot that allows the pump to run as slowly as possible but fast enough to prevent solids from settling out of the slurry precipitate and clogging the lines.
Then, lower the pump's discharge pressure to the lowest point possible to further reduce wear. And follow proper piping layout and design principles to ensure constant and uniform delivery of the slurry to the pump.
The SolidC Series of centrifugal pumps from Alfa Laval are designed to meet the hygienic requirements of the food, dairy, beverage, personal care, pharmaceutical, light chemical, and water industries.
Suitable for general applications, intermittent product pumping, and clean-in-place (CIP) duties, SolidC pumps combine efficiency with competitive pricing and are compliant with 3-A, CE, FDA, and EHEDG standards.
The LC/LF/LD Series are high-efficiency sanitary duty pumps offering heavy-duty cast construction and a 304 stainless steel adaptor. These pumps handle food-grade products such as mashes and food slurries containing small suspended solids with ease.
The Z Series pump is an industrial-grade centrifugal pump designed for high flow rates in applications where corrosion resistance is of maximum importance. This pump is available in multiple alloys, including 316, 316L, and Duplex stainless steel, nickel aluminum bronze, and Hastelloy C-22.
The OS Series twin-screw pump is a robust product that meets stringent hygienic standards. It is designed with low pulsation characteristics and can handle both solids and abrasives easily, so it's excellent for use in slurry pumping applications.
The company's basic rotary lobe pumps, the OptiLobe Series, are known for their simplicity of installation, operation, and maintenance.
The SRU Series rotary lobe pump is Alfa Laval's premier offering for the gentle handling of sensitive process fluids.
The AL Series positive displacement lobe pumps offer ease of maintenance, CIP performance, uptime reliability, and economical pricing.
The ZP Series rotary piston positive displacement pump features a 304 stainless steel gear case and a front-loading seal for easy maintenance.
For food-grade applications, these ZP pumps can be used for slurries such as fruit fillings and concentrates, curds, relishes, and potato salad.
The front-loading design allows the seal to be easily maintained or changed, and the newly designed rotor case eliminates all dead zones
Bornemann SLH twin screw pumps are self-priming, positive displacement pumps. The SLH Series is the best solution for universal or aseptic processes and applications with high viscosities, high pressures, or sensitive media.
The pump's design provides complete axial balancing of the rotating elements and eliminates all metal-to-metal contact within the pump. SLH can handle virtually any non-homogeneous fluid, regardless of viscosity, lubricity, or abrasiveness.
Matthew Sato is the Applied Products Sales Manager at Ampco Pumps Co. With nearly a decade of pump sales and an engineering background, he is well versed in pumping principles and technology.
Central States Industrial Equipment (CSI) is a leader in distribution of hygienic pipe, valves, fittings, pumps, heat exchangers, and MRO supplies for hygienic industrial processors, with four distribution facilities across the U.S. CSI also provides detail design and execution for hygienic process systems in the food, dairy, beverage, pharmaceutical, biotechnology, and personal care industries. Specializing in process piping, system start-ups, and cleaning systems, CSI leverages technology, intellectual property, and industry expertise to deliver solutions to processing problems. More information can be found at www.csidesigns.com.