Selecting And Operating A Slurry Pump
As described below, there are several types of pumps that are suitable for pumping slurries. However, before considering which technology to use, we must address several key issues.
The size and nature of the solids in the liquid: The size and nature will affect the amount of physical wear on the pump and its components, and whether the solids will pass through the pump without being damaged.
One problem with centrifugal pumps is that the velocity and shear forces within the pump may damage the slurry/solids. Typically, twin-screw pumps cause the least damage to solids in the slurry.
Corrosiveness of the liquid or slurry mixture: More corrosive slurries will wear pump components faster and may dictate the choice of pump manufacturing materials.
Pumps designed to pump slurries will be heavier than pumps designed for less viscous liquids because slurries are heavy and difficult to pump.
Slurry pumps are typically larger than standard pumps, with more horsepower and stronger 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 the way aqueous liquids move through a standard centrifugal pump.
Compared to standard centrifugal pumps, centrifugal pumps optimized for slurry pumping typically have the following features.
Larger impellers made of more material. This is to compensate for the wear caused by abrasive slurry.
Fewer and thicker vanes on the impeller. This makes it easier for solids to pass through than the 5-9 vanes on a standard centrifugal pump - typically 2-5 vanes.
Determine the nature of the material to be pumped
Consider the following.
Particle size, shape and hardness (impact on wear and corrosion potential of pump components)
Corrosiveness of the slurry
If the exact in-pump viscosity of the product is unknown, CSI can help
Consider the pump components
If a centrifugal pump, is the design and material used to construct the impeller suitable for pumping slurries?
What are the materials used to construct the pump?
Are the pump discharge components suitable for the slurry being pumped?
What is the best seal arrangement for the application?
Will solids size pass through the pump?
How much solids damage can the customer tolerate?
It is also important to consider the chemical compatibility of the slurry with any elastomers in the pump. Once the nature of the slurry and the components of the different types of pumps have been addressed, you can select potential candidate slurry pumps for the application.
Determine the size of the pump
The most important thing here is to determine the pump power required to deliver a specific fluid flow at the desired or required differential pressure. Consider the following.
The concentration of solids in the slurry - measured as a percentage of the total volume.
The length of the piping. The longer the pipe, the more slurry-induced friction the pump needs to overcome.
Slurry pipe diameter.
Hydrostatic head - i.e. the height to which the slurry must be lifted in the piping system.
Determine the operating parameters of the pump.
To reduce component wear, most centrifugal slurry pumps run at fairly low speeds - typically less than 1200 rpm. Find the optimum position that allows the pump to run as slowly as possible but fast enough to prevent solids from settling out of the slurry deposit and clogging the lines.
Then, reduce the pump discharge pressure to the lowest possible point to further reduce wear. And follow proper piping layout and design principles to ensure consistent and uniform delivery of slurry to the pump.