Choosing a Slurry Pump - Features

Choosing a Slurry Pump - Features

Nnamdi Nwaokocha offers practical advice on pump selection

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Pumps play a crucial role in the process industry, as they aid in moving materials across a plant. Fluids naturally flow from high to low-pressure areas, but the layout of a plant often necessitates the use of pumps. Choosing the right pump can be challenging, especially when dealing with slurries.

This article delves into the essential variables for characterizing slurries and selecting a pump for their transportation within a plant. While not exhaustive, it aims to provide a starting point for making informed decisions.

Summary

Pumping slurries can lead to blockages or machinery failures. It is essential for designers to consider all relevant factors, including client preferences, to design a system that minimizes blockages and eases maintenance, all while ensuring safety.

Slurry Type

What exactly is a slurry? Generally, it refers to a mixture of liquid, often water, but it could be any carrier fluid, and solids. Slurries are either settling or non-settling, based on the particles involved. Non-settling slurries have fine particles that remain in suspension, while settling slurries consist of particles that settle out when mixing energy stops.

Before selecting a pump, determine the pressure drop requirements using system characteristics. Key parameters include slurry density and the velocity required in the pipework.

Figure 1 from Perry's Chemical Engineers’ Handbook illustrates the relationship between pressure drop and slurry velocity in horizontal pipes. The velocity should exceed the minimum transport velocity to keep solids fully suspended, as per the Durand equation.

Careful consideration is needed to add a safety factor to the calculated transport velocity. High velocity increases pressure drop and work needed by the pump, particularly in vertical flow. Perry's Chemical Engineers’ Handbook advises a 25% correction factor for pressure drop calculations.

For non-settling slurries, non-Newtonian behavior is common, and empirical data is needed to determine pump work. Established formulas are used for calculating pressure drops based on slurry viscosity and density.

When selecting a pump, consider slip conditions, pipe size, piping design, static head requirements, and available NPSH. Additionally, the solid particles' characteristics—such as their hardness, abrasiveness, and corrosiveness—are critical for material selection in wetted parts.

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Pump Types

Various pump types are available, including rotary and positive-displacement pumps. Consult specialists before making a final decision.

Centrifugal Pumps

Centrifugal pumps are commonly used. Key considerations include:

• Impeller type: Recessed, open, or closed impeller designs each have unique benefits and drawbacks.
• Casing type: Metal casings, possibly lined with rubber, can be used, but split casings can be costly.
• Clearances: Larger clearances are needed to allow solids to pass through and reduce pump wear.

While choosing a centrifugal pump, consider impacts on shafts and seals, and avoid cavitation.

Operating curves and efficiency curves by pump vendors are usually provided for water, necessitating translations for slurry applications, as shown in Figure 3 from the Warman Slurry Pumping Handbook.

Positive Displacement Pumps

Positive displacement (PD) pumps include air-driven diaphragm pumps, peristaltic pumps, rotary lobe pumps, progressive cavity pumps, and more. These pumps are suited for fluids displaying pseudo-plastic behavior, making them ideal for slurries.

Air-Driven Diaphragm Pumps

Air-driven diaphragm pumps are effective for slurries but can suffer from abrasion and erosion, primarily affecting check valve assemblies. Consider check valve assembly material, diaphragm material, and clearances.

Peristaltic Pumps

Peristaltic pumps are a viable alternative. Maintenance is limited to the motor and tube. Capable of handling slurries with up to 80% solids, confirm specifics with pump vendors. Key factors include tube material and maximum discharge pressure.

Gear, Lobe, and ECP Pumps

These pumps move fluid in spaces between components. Suitable for slurries with soft particles, but tight clearances make them vulnerable to excessive wear.

Progressive Cavity Pumps

Common in wastewater and process industries, these pumps handle slurries well. A coating can improve rotor wear resistance. Operating the pump at slower speeds can minimize wear but increase the risk of blockages. Consider solid size, abrasiveness, slurry type, and seal arrangement.

Conclusion

Selecting a pump for slurry applications requires careful consideration of various factors. Ensure solids remain suspended and minimize wear and blockages. For specific cases, gather extensive information and consult with pump vendors.

References

1. Sinnot, R., and Towler, G., Chemical Engineering Design, Fifth Edition, Elsevier, 2009.

2. Processing of Solid-Liquid Suspension, ed. Ayazi Shamlou, P., Chapter 11 by Shook, CA, Chapter 12 Etchells, AW, Butterworth-Heinemann, 1993.

3. Green, DW, and Perry, RH, Perry’s Chemical Engineers’ Handbook, Chapter 6, 8th Edition, McGraw-Hill, 2007.

4. Warman Slurry Pumping Handbook, Warman International, Feb 2000.

5. https://bit.ly/2Ud76ls

6. Coulson, JM, Richardson, JF, Backhurst, JR, Harker, JH, Coulson and Richardson’s Chemical Engineering Volume 1 - Fluid Flow, Heat Transfer and Mass Transfer, 6th Edition, Elsevier, 1999.

7. Jones, GM, Pumping Station Design, revised 3rd edition, Elsevier, 2008.

The Best Pump for Moving Heavy Slurry

EDDY Pump’s unique design has been tested in heavy slurry applications since 1984, consistently outperforming traditional pumps. Its large internal flow path handles large solids, and the recessed rotor reduces wear. The EDDY Pump’s ability to generate turbulent flow prevents sedimentation and reduces clogging.

This article includes:

• Difficulties Pumping Heavy Slurry
• Selecting a Pump for Heavier Slurries
• Selecting a Motor for Heavy Slurry
• EDDY Pump – The Best Pump for Heavy Slurries

Difficulties Pumping Heavy Slurry

Heavy slurries, which are abrasive and highly viscous, pose significant challenges. Traditional pumps like water and centrifugal pumps are not suitable for these applications. Ultra-duty pumps designed for heavy slurries are necessary for industries like mining, manufacturing, and construction.

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