A Complete Guide To Pumping Slurries

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:

Defining what slurries are

The types of pumps that may be used to pump slurries

Factors to consider when selecting a slurry pump for a particular application

A brief overview of a few of the sanitary processing pumps available from CSI suitable for pumping these unique compounds

What Are Slurries?

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:

More abrasive than pure liquids.

Thicker in consistency than pure liquids.

May contain a high number of solids (measured as a percentage of the total volume).

The solid particles usually settle out of the slurry's precipitate relatively quickly when not in motion (depending on the particle size).

Slurries require more energy to move than do pure liquids.

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:

Abrasions: including gouging, high-stress grinding, and low-stress grinding (applicable only with settling-type slurries).

Erosion: the loss of surface materials caused by the action of the particles in the slurry being pumped. Erosion is primarily found with the pumping of settling-type slurries.

Corrosion: caused by the electrical galvanic action in the fluid being pumped. Certain types of slurries (e.g., highly acidic or alkaline compounds) will have more impact on component corrosion than will more benign slurries.

TYPES OF SLURRY PUMPS

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.

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 if the solids will pass through the pump without being damaged.

A concern for centrifugal pumps is the speed and shear inside the pump may damage the slurry/solids. In general, twin screw pumps allow for the least damage to solids in a slurry.

The corrosiveness of the liquid or slurry mixture: more corrosive slurries will wear pump components more quickly and may dictate the selection of the material from which the pump is constructed.

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.