Slurry pump
A slurry pump is a type of pump designed for pumping liquid containing solid particles. Slurry pumps changes in design and construction to adjust to multiple type of slurry which varies in concentration of solids, size of solid particles, shape of solid particles, and composition of solution. Slurry pump are more robust than liquid pumps; they have added sacrificial material and replaceable wear parts to withstand wear due to abrasion.
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.
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.
Selection of slurry pumps is more difficult than selection of pumps for water and liquids. Many factors and corrections to the duty point affect brake horsepower and wear. Root-dynamic Centrifugal Slurry Pumps (ANSI/HI 12.1-12.6-2016) provides methods for calculation of slurry pumps. The peripheral speed of the impeller is one of the main features and classification of slurry pumps. Speed must be in accordance with the slurry type classification (abrasion classification) in order to maintain a reasonable life in service due to high abrasion of solids.
Before selecting an appropriate slurry pump the engineers considers capacity, head, solids handling capacity, efficiency and power, speed and NPSH.
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. The most common metal alloy used to build slurry pumps is known as "high chrome", which is basically white iron with 25% chromium added to make it less brittle. Rubber line casings are also used for certain application where the solid particles are small.
Components
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Impeller
The impeller, either elastomer, stainless steel or high-chrome material, is the main rotating component which normally has vanes to impart the centrifugal force to the liquid.
Casing
Split outer casing halves of cast contain the wear liners and provide high operation pressure capabilities. The casing shape is generally of semi-volute or concentric, efficiencies of which are less than that of the volute type.
Shaft and Bearing Assembly
A large diameter shaft with a short overhang minimizes deflection and vibration. Heavy-duty roller bearing are housed in a removable bearing cartridge.
Shaft sleeve
A hardened, heavy-duty corrosion-resistant sleeve with O-ring seals at both ends protects the shaft. A split fit allows the sleeve removed or installed quickly.
Shaft Seal
Expeller drive seal, Packing seal, Mechanical seal.
Types
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Submersible
Submersible slurry pumps are placed at the bottom of a tank, lagoon, pond, or another water-filled environment, and suction solids and liquids right at the pump itself. The materials are taken in at the intake and passed through a hose connected to the discharge valve.
Self-Priming
A self-priming slurry pump is operated from land, and a hose is connected to the pump's intake valve. The self-priming pump draws the slurry to the pump then discharges the material from there.
Flooded Suction
The flooded suction slurry pump is connected to a tank or hopper and uses gravity to move slurry and liquid from the enclosure. Located at the bottom or below the water, the pump uses the force of gravity to continuously fill the pump and then passes the material out through the discharge valve.
Slurry Pump Applications
SLURRY PUMP USAGE
Slurry pumps are used widely throughout the beneficiation section of the mining industry where most plants utilise wet separation systems. These systems usually require the movement of large volumes of slurry throughout the process.
Slurry pumps are also widely used for the disposal of ash from thermal power plants. Other areas where slurry pumps are used include the manufacture of fertilisers, land reclamation, mining by dredges, and the long distance transportation of coal and minerals.
Increased global focus on environmental and energy constraints will certainly generate much wider uses for slurry pumping in years to come.
WHAT IS A SLURRY PUMP
There are a large number of differing pump types used in the pumping of slurries. Positive displacement and special effect types such as Venturi eductors are used but by far the most common type of slurry pump is the centrifugal pump. The centrifugal slurry pump utilises the centrifugal force generated by a rotating impeller to impart energy to the slurry in the same manner as clear liquid type centrifugal pumps.
However, this is where the similarities end.
Centrifugal slurry pumps need to consider impeller size and design, its ease of maintenance, the type of shaft seal to be used and the choice of the optimum materials. This is needed to withstand wear caused by the abrasive, erosive and often corrosive attack on the materials. Many other important considerations are also required.
The centrifugal slurry pump must be designed to allow the passage of abrasive particles which can at time be extremely large. The largest Warman slurry pump, for example, can pump particles up to 530mm in spherical size.
Slurry pumps therefore need much wider and heavier impellers to accommodate the passage of large particles. They must also be constructed in special materials to withstand the internal wear caused by the solids.
SLURRY PUMP DESIGN FEATURES
In terms of design a slurry pump is a unit consisting of a pump and a drive, which is normally an electric or diesel motor. Design solutions for the engineering of slurry pumps are quite special and are determined by a large quantity of solids in the handled media and their abrasive impact on the pump components. Thus, the target is to move large abrasive particles, such as rocks and pebbles entering the pump with soil by increasing the internal cross-section. However a larger cross-section reduces velocity and makes the pump slow-moving, which calls for a larger size and weight. For unimpeded movement of large particles the number of impeller blades should be from two to four and impeller width should be larger. Slurry pump efficiency is much lower than that of the pumps having the same capacity but designed for clean water handling.
The flow path of a slurry pump includes one or two casings (inner and outer), where a centrifugal impeller is located (closed type). Considering that abrasive inclusions in hydraulic fluids may result in early wear of casing cover, the space between the impeller and the cover is equipped with a protection disk preventing from wear. The running gear of a slurry pump is represented by a shaft installed in ball-bearing supports. The impeller is overhung on the shaft. The point of shaft exit from the pump casing is sealed.
The key element is an impeller consisting of two disks (closed type). Blades are arranged between the disks. When rotating the impeller creates negative pressure in its central area which causes suction of handled media. Hydraulic fluid enters the inlet pipe and is fed onto the impeller, where each slurry particle is impacted by centrifugal forces which push the slurry into the pressurized discharge line.
SLURRY PUMP COMPONENT EROSION
However in spite of all these measures the parts of slurry pumps are exposed to excessive wear: hydroabrasive, cavitational and mechanical. Hydroabrasive impact is the main cause of the flow path wear in a slurry pump. Its intensity depends on many characteristics of the slurry or particles in handled materials, as well as on wear resistance of the flow path parts. Hydroabrasive wear may be general and local. General wear is demonstrated by a relatively uniform thinning of parts and is typical for the surfaces of armor disks, side and radial liners, and pipes. Local wear, which is much more intensive than the general one, attacks vortex and cavitation areas.
Cavitational wear usually disrupts the pump operation and builds up vacuum in the suction line. Uneven interfacing of parts, high spots from electric welding and worn-out surfaces contribute to the cavitation, which results in stronger vibration of the pump and wear of absolutely all parts: drive shaft, support bearings and even foundations. To reduce the cavitation effect ejectors are installed into drag heads.
Mechanical wear of a slurry pump is caused by friction and impacts of rocks contained in the fluid on the pump parts. This is typical for handling pebble-rich soils. Any type of wear has a negative impact on the pump characteristics, reduces output by 20 to 30%, after which the pump is subject to immediate repair. Each element of a slurry pump suffers from its own prevailing type of wear.
The slurry pump parts are made of different kinds of alloyed steel with subsequent heat treatment which imparts additional mechanical strength and wear resistance. Steels used for the manufacturing of slurry pump parts are usually alloyed with chromium, silicon, manganese, nickel, tungsten and vanadium. Iron is rarely used for the parts contacting sand, gravel and large solids, since it is practically non-resistant to impact load. Wear resistance of regular gray iron is 10 to 15 times less than that of special steel alloys. One of the upcoming trends in the improvement of slurry pump design is gumming, which is rubber lined slurry pump parts. However rubber is not much resistant to impacts of coarse particles, that is why rubber-lined slurry pumps should only be used for handling fluids containing small solids.
In general the following practices are recommended to reduce the wear of slurry pumps:
1.improvement of hydraulic flow conditions in the lines of slurry pumps;
2.protection of gaps in slurry pumps from penetration of solids;
3.improvement of wear-resistant properties of pump part materials;
4.use of protective liners;
5.improvement of design solutions in slurry pump engineering.
SLURRY PUMP SELECTION
The main parameters to consider when selecting a slurry pump are flow rate, pressure, output and efficiency. Besides, feed rate is of critical importance to slurry pumps, which, if optimal, significantly improves pump service life and energy efficiency. During design stage it is also necessary to consider the hydraulic fluid (slurry) to be moved, its properties and size of solids. Further, the durability of the flow path of a slurry pump is determined by the concentration of solids and their size. Slurry flows demonstrate different behavior depending on their characteristics, thus, the pattern of abrasive wear in the flow systems of slurry pumps will be different. A full process calculation considering all the factors is mostly quite challenging, so in order to select a slurry pump special regulatory documents are used which are universal for the pumping equipment handling the media heavily contaminated with solid inclusions.
SLURRY PUMP APPLICATION FIELDS
wet crushers
SAG mill discharge
ball mill discharge
rod mill discharge
Ni acid slurry
coarse sand
coarse tailings
phosphate matrix
minerals concentrate
heavy media
dredging
bottom/fly ash, lime grinding
oil sands
mineral sands
fine tailings
phosphoric acid
coal
flotation
sugar beets
process chemical
pulp and paper
FGD
waste water
Sand Gravel
Slurry Pump: What is it, and how does it work
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:
Larger impellers made with more material. This is to compensate for wear caused by abrasive slurries.
Fewer, thicker vanes on the impeller. This allows the passage of solids more readily — typically 2-5 vanes, compared to 5-9 vanes on a standard centrifugal pump.
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:
A low slurry flow rate
A high head (i.e., the height to which the pump can move liquid)
A desire for greater efficiency than that afforded by centrifugal pumps
Improved flow control
Common types of positive displacement pumps used in slurry pumping applications include:
Rotary Lobe pumps
These pumps use two meshing lobes rotating within a pump's housing to move fluids from the pump's inlet to its outlet.
Twin-screw pumps
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.
Diaphragm pumps
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.
Selecting and operating a slurry pump
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.
Based on the domestic market and expanding overseas business is the development strategy of vertical slurry pump,horizontal slurry pump
