Blog

PUMPS are the backbone of the process industry. In a process plant, it is necessary to move material from one point to another. In keeping with the laws of thermodynamics, fluids move from an area of high pressure to low, and depending on the plant layout often require the assistance of a pump to achieve this. With many different pump types available, selecting the right pump can be tricky, especially when slurries are involved.

This article will discuss some of the variables to consider when characterising a slurry and selecting a suitable pump for transporting those slurries in a plant. This is not definitive and is by no means a complete review of handling slurries by pumping but is meant to provide some useful information and a good starting point of what to consider.

Summary

Pumping of slurries can often lead to blockages or equipment failure. The job of the designer is to assess all the factors of each situation, including client and existing site preferences to design a system and select a pump which is robust enough to minimise blockages and makes maintenance for operators as easy as capital would permit whilst providing a safe system of work.

Slurry type

What is a slurry? Typically, the term slurry is used to refer to a mixture of a liquid and a solid or combination of solids. The liquid is often referred to as the carrier fluid and in most cases is water, although it can be anything from an acid solution (eg nitric acid) to a hydrocarbon (eg diesel).

Producing a slurry or maintaining solid suspension in static conditions is outside the scope of this article.

Slurries can broadly be broken down into two types: settling, and non-settling slurries. This characterisation is based on the nature of the solid(s). Non-settling slurries contain solids made up of fine particles, which largely remain in suspension when the applied mixing energy ceases. Settling slurries, as the name suggests, contain solids whose particles settle out when the applied mixing energy ceases. From a designer’s perspective, it is important to know the type of slurry. For example, non-settling slurries can be transported around under laminar flow conditions, whereas turbulent flow conditions are required for settling slurries, particularly in horizontal sections.

A useful rule of thumb provided in Sinnot and Towler’s Chemical Engineering Design states that solids with particles of less than 200 microns (0.2 mm) will usually be expected to produce non-settling slurries. Larger particle sizes will produce settling slurries.1

Before selecting the right pump, the first step is to determine the pressure drop requirements using the system characteristics. The parameters required are:

The following equations2 are useful in determining the slurry’s density: