Slurry pumps are a type of centrifugal or positive displacement pump that is electrically or hydraulically driven, and designed specifically for pumping media that contains solid particles, as well as solvents, acids, alcohol or petroleum. Due to the harsh media these pumps move, they are more robust than other pumps in order to be able to withstand the additional wear they are subject to.
Slurry pump selection is a complex process and requires close cooperation between the pump manufacturer and the end user as the medium to be pumped and the pump operating conditions are extremely important to the correct pump selection.
Some of the important parameters of slurries to consider when selecting a pump include:
- Particle size, shape (angular, round, long and stringy) and hardness
- Chemical compatibility with elastomers
- Solids concentration
- Likelihood of running dry
Other features that slurry pumps may include that could influence final pump selection are:
- Leveling (on/off control devices)
- Thermal overload protection
- Dry running capabilities
Slurry pumps and their components are generally made of aluminum, brass or bronze, cast iron, plastic, or stainless steel. However, ethylene propylene (EPDM) and other specialty or proprietary materials are also available.
Final selection can often be a trade-off between high capital and low maintenance costs, or low capital and high maintenance costs.
Centrifugal slurry pumps
Centrifugal slurry pumps are typically used in mineral extraction process plants, water, sewage, agriculture, petroleum and petrochemical application, and are designed to handle abrasive solids mixed with a carrier fluid.
They often operate 24/7, and in severe conditions the wear life of wetted components can be up to two to three months.
Both horizontal and vertical shaft configurations are available, with transmission of process slurries around a plant usually handled by horizontal pumps, while vertical pumps are used in sumps and generally have a cantilevered shaft so that all bearings are located above fluid level.
These pumps are often chosen for their high flow rate capabilities, abrasive solution compatibility, mixing potential, and relatively simple engineering.
Positive displacement slurry pumps
Positive displacement slurry pumps are often more suitable than centrifugal slurry pumps when one or more of the following conditions or requirements apply:
- Low flow rate
- High head
- Improved efficiency is desired
- Dilution water is either expensive to provide, remove and/or dispose of
- High solids concentration
- High viscosity
- Flow control
Many manufacturers have developed special versions of their positive displacement pumps for slurry services. Some of the most common types of positive displacement pumps that can be used for pumping slurries include: air-operated diaphragm pumps, peristaltic, rotary lobe and progressive cavity pumps.
Air-operated diaphragm pumps
As with centrifugal slurry pumps, abrasion and erosion can be an issue for these pumps in more demanding slurry applications. The balls and seats that form part of the check valve assembly in particular are susceptible if the right materials are not selected.
They are most appropriate for use in light slurry, lime dosing, filter press feed and mine dewatering applications.
These pumps don’t have balls or check valves so they don’t experience the same level of susceptibility to abrasion and erosion as air-operated diaphragm pumps. The only parts that require maintenance are the motor and tube.
The main advantage of this type of pump is that it can handle slurries with high amounts of solids, however its selection is limited to the maximum discharge pressure determined by the tube properties.
These pumps can be used for light slurry, lime dosing, filter press feed, thicknew underflow, slurry transfer and tailings disposal applications.
These pumps use rotating lobes to direct the flow of media around the interior of the casing. They are non-contacting and have large pumping chambers, and are ideal for pushing low-viscosity media, and can handle large solids and slurries.
They are suitable to be used in light slurry, lime dosing, filter press feed and slurry transfer applications.
Progressive cavity pumps
These pumps are well-known for their slurry handling capabilities as they are used extensively in the wastewater and process industries. The rotor can be coated to improve wear resistance.
For more abrasive slurries, the pump can be operated at a slower speed to reduce wear, however this can result in solids falling out of suspension and causing blockages in the pump.
These pumps operate best when handling slurries with solids no larger than 45mm.
They are ideal for light slurry, lime dosing, filter press feed, slurry transfer, tailings disposal and mine dewatering applications.