What is a Slurry Pump? Selection and Types of Slurry Pumps
As the slurry is highly abrasive, thick, corrosive, and contains a high concentration of solids, it is very challenging to move it. For pumps also, it is very tough. But with a proper selection of slurry pumps, the operation can be smooth for long-term performance. In this article, we will discuss the basics of slurry pumps, their working, types, and selection.
What are Slurry Pumps?
Slurry pumps are heavy-duty and robust pumps (majorly centrifugal) that are capable of handling tough and abrasive fluids like slurries.
Some examples of industries that handle slurries are mining, dredging, steel processing, foundries, power generation, drilling mud, pulp and paper, wastewater treatment, mineral processing, etc. Due to the presence of solid particles and their highly thick and viscous nature, slurry movement requires more power than normal fluids. So, specially designed heavy-duty pumps are required to work as slurry pumps.
Selection of Slurry Pumps
There are various types of pumps that can pump slurries. However, the selection of exact slurry pumps depends on some critical considerations as listed below:
Type of Slurry to be handled including the size and nature of the solid particles present.
Corrosive property of the slurry mainly to decide pump material for the service.
Pipe size – the pipe ID must be considerably bigger than the maximum particle size.
Static head requirements; and
Available NPSH
Length of slurry pipe or pipeline
Pump operating parameters specifically discharge pressure and speed, the lower the better.
Slurry Pump Components
There are six basic components in a slurry pump. They are:
Impeller: Two options to choose from, closed impeller or open impeller.
Shell: Two options to select from; Solid single-piece or split shells.
Drive Control: Three types of drive control; Belt drive, gearbox drive, or direct connection of the motor with the shaft.
Suction plate liner
Shaft seals: Three design options; Stuffing box, mechanical seal, or expeller.
Bearing Assembly
Types of Slurry Pumps
Based on the working methodology, there are two types of pumps that are used to handle slurries.
Centrifugal slurry pump and Positive displacement slurry pump
Centrifugal Slurry Pumps
The most common type of slurry pump is the centrifugal pump with a larger impeller, thicker vanes, and more horsepower. The working of the centrifugal slurry pump is quite simple. They use the centrifugal force generated by a rotating impeller which pushes the slurry to move through the discharge.
When choosing a centrifugal slurry pump the following should be decided:
To minimize the wear of the impeller, a recessed type large and thick open impeller can be used. Closed impellers should be avoided.
Metal casing with proper thickness and rubber lining to be considered.
Cavitation issues.
Positive Displacement Slurry Pumps
When a low slurry flow rate with improved flow control and greater efficiency is desired, a positive displacement slurry pump is more suitable. Common positive displacement pumps used for slurry service are:
Rotary lobe pumps
Screw pumps
Diaphragm pump
Peristaltic pumps
Gear pumps, and
Progressive cavity pumps
Again, depending on the installation of the slurry pumps, they are categorized as follows:
Horizontal slurry pumps
Vertical slurry pumps
Submersible slurry pumps.
Horizontal Slurry Pumps
Horizontal slurry pumps have their hydraulic end and the drive unit is located outside the sump. This group of slurry pumps is manufactured for a wide range of head, flow conditions, and material options. Horizontal slurry pumps usually use standardized electrical motors and seals. They are not suitable for plants where there is a risk of flooding.
Vertical Slurry Pumps
There are two types of vertical slurry pumps:
Tank pumps
Cantilever/sump pumps
Tank pumps are dry-installed pumps. The sump is incorporated into the pump. Their open sump and vertical inlet prevent air blocking, which provides a smooth operation. They don’t have submerged bearings or shaft seals, but quite a long shaft overhang from the lower bearing to the impeller.
Cantilever/sump pumps are considered semi-dry installed, as the hydraulic end is lowered into the slurry, but the drive unit and support structure are dry installed. There are no submerged bearings or shaft seals similar to tank pumps, but they have a long shaft overhang.
Submersible Slurry Pumps
Submersible slurry pumps are usually positioned at the bottom of a tank, pond, or lagoon. The slurry materials are taken in at the pump suction and passed through a hose connected to the discharge valve.
Submersible pumps provide a lot of benefits as listed below:
As they directly operate in the slurry, they do not need an additional support structure. Hence, submersible slurry pumps occupy less space.
The motor and volute of submersible slurry pumps are integrated into a single unit. Hence, they are compact and easy to install.
As they operate underwater, they generate low noise and so silent operation.
The surrounding fluid cools the motor which results in smaller and more efficient sumps.
Several installation modes, all of which are either portable or semi-permanent. So, they are enough flexible.
There are other types of classification of slurry pumps as well like Self-priming slurry pumps and flooded suction slurry pumps.
Self-Priming slurry pumps operate from land. A hose is connected to the pump’s intake valve through which the pump draws the slurry to discharge the material.
The flooded suction slurry pump is connected to a tank or hopper. It uses gravity force to move slurry and liquid from the enclosure. They are placed at the bottom or below the water and use the gravity force to continuously fill the pump and then pass the material out through the discharge valve.
Slurry Pump Installations
Depending on the environmental condition, there are three types of slurry pump installations:
Wet Environment– This type of slurry pump installation involves submerging the product fully for underwater operations.
Dry Environment– In a dry environment, the pump drives and bearings are kept away from the abrasive slurry. It calls for a horizontal pump as the shell, impeller, suction liner, and shaft sleeve have to be on the wet side.
Semi-Dry Environment– Since it’s an unusual scenario, a special type of horizontal slurry pump installation is preferred.
What is slurry pump?
Slurry is one of the most challenging fluids to work with. It is highly abrasive, thick, sometimes corrosive, and contains a high concentration of solids. There is no doubt that conveying slurries is difficult for pumps. But choosing the right pump for these material applications can have a significant long-term beneficial impact.
What is “slurry”?
Slurry is any mixture of fluid and fine solid particles. Examples of slurries include: manure, cement, starch or coal suspended in water. Slurries are used as a convenient way to handle solids in mining, steel processing, foundry, power generation, and more recently in frac sand mining.
Slurries typically behave in the same way as thick viscous fluids, flowing by gravity, but can also be pumped as needed. Slurries are divided into two main categories: non-settling or settling.
Non-settling slurries consist of very fine particles that create the illusion of increased apparent viscosity. These slurries usually have low wear characteristics, but require very careful consideration when selecting the right pump, as they behave differently than normal liquids.
Settling slurries are formed by coarse particles, and these particles tend to form unstable mixtures. Special attention should be paid to flow and power calculations when selecting a pump. Most slurry applications consist of coarse particles and therefore have a higher wear performance.
The following characteristics are common to slurries.
Abrasive
Thick consistency
May contain large amounts of solids
Usually settles down quickly
Requires more power to run than a “water” pump
Slurry pump selection
Many types of pumps can be used to pump slurry, but the most common type of slurry pump is the centrifugal pump. Centrifugal slurry pumps use centrifugal force generated by a rotating impeller to impinge kinetic energy into the mud, similar to a watery liquid moving through a standard centrifugal pump.
Slurry applications significantly reduce the expected wear life of pumped components. It is critical to select a pump designed for these heavy-duty applications from the outset. Consider the following when making your selection.
Basic pump components
To ensure that the pump can withstand wear, the impeller size/design, materials of construction and discharge configuration must be properly selected.
Open impellers are most common on slurry pumps because they are the least likely to clog. Closed impellers, on the other hand, are the most likely to clog and, if they do, the most difficult to clean.
Slurry impellers are large and thick. This helps them run longer in harsh slurry mixtures.
Slurry pump structure
Slurry pumps are typically larger in size and often require more horsepower to operate than lower viscosity liquid pumps because they are less efficient. Bearings and shafts must also be more robust and durable.
To protect the pump casing from wear, slurry pumps are often lined with metal or rubber.
The metal casing consists of carbide. These housings can withstand the erosion caused by increased pressure and circulation.
The housing is selected to suit the application. For example, pumps used in cement production handle fine particles at low pressures. Therefore, lightweight construction of the housing is acceptable. If the pump handles rock, the pump casing and impeller will require a thicker and stronger casing.
Slurry pumping considerations
Those who have experience pumping mud know that it is not an easy task. Slurries are heavy and difficult to pump. They can cause excessive wear on the pump and its components, and they can clog suction and discharge lines if they don’t move fast enough.
Making a slurry pump last a reasonable amount of time can be a challenge. But there are steps you can take to extend the life of your slurry pump and make pumping slurry less of a challenge.
Find the best position to make the pump run as slowly as possible (to reduce wear) but fast enough to prevent solids from settling and clogging the line
Reduce the pump discharge pressure to the lowest possible point in order to reduce wear
Follow proper piping principles to ensure consistent and uniform delivery of the slurry to the pump
Pumping slurry can present some challenges and problems, but with the right engineering and equipment selection, you can have long, trouble-free operation. It’s important to work with a qualified pump engineer when selecting a slurry pump, as mud can wreak havoc on a pump if not selected properly.
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