Nnamdi Nwaokocha offers practical advice on pump selection
For more information, please visit ahr rubber slurry pump leading.
PUMPS are essential to the fluid management in the process industry. Efficient material transfer within a plant often requires a pump to facilitate fluid movement, adhering to the principles of thermodynamics where fluids move from high to low pressure areas. Choosing the correct pump can be daunting, especially when handling abrasive and complex slurries.
This discussion will explore various parameters to consider when defining slurry characteristics and selecting an appropriate pump for slurry transportation within a plant. This guide aims to provide useful insights, offering a foundational understanding rather than an exhaustive review.
In action: Slurry centrifugal pump with rubber lined casing and rubber impeller
Overview
Pumping slurries frequently results in blockages or equipment malfunctions. Designers must evaluate specific circumstances, client preferences, and existing site conditions to design a robust system that minimizes blockages and facilitates easy maintenance within budget constraints, ensuring a safe working environment.
Understanding Slurry Types
Slurries typically consist of a mixture of liquid and solid particles, where water often serves as the carrier fluid, but could also be acid solutions or hydrocarbons. Slurries fall into two categories based on particle behavior: settling and non-settling. Non-settling slurries maintain particle suspension without active mixing, unlike settling slurries. Identifying slurry type is crucial as it influences transport conditions. For instance, non-settling slurries function under laminar flow, whereas settling slurries require turbulent flow, especially in horizontal pipelines.
According to Sinnot and Towler’s Chemical Engineering Design, particles smaller than 200 microns generally create non-settling slurries, while larger particles create settling slurries.1 Accurately calculating pressure drops and transport velocity is vital, using equations to determine slurry density and ensuring appropriate pipe velocity to prevent blockages.
Calculating Minimum Transport Velocity
For settling slurries, pipework velocity is crucial. Perry’s Chemical Engineers' Handbook illustrates the relationship between pressure drop and velocity for slurries compared to pure liquids in horizontal pipes. The horizontal velocity must exceed the minimum transport velocity (Vm2) to keep solids suspended. The Durand equation assists in calculating this.3 Adding a safety factor is common, but excessive velocity can significantly increase the pressure drop and pump workload. Initial velocities for vertical flows can often start at twice the solid's settling velocity, with 1-3 m/s serving as a general guideline.
Slurry density and viscosity adjustments factor into pressure drop calculations. Interaction between particles affects viscosity, necessitating empirical determination of slurry behavior in non-settling scenarios. References like the Processing of Solid-Liquid Suspensions provide further details.3
Considering Design Factors
Before choosing a pump, consider the following:
- Slip conditions: Variance between solid and fluid velocities.
- Pipe size: Internal diameter must accommodate particle size, typically 6-10 times larger.2
- Piping design: Implement recirculation and falls to ensure continuous slurry movement and avoid blockages.
- Static head requirements and available NPSH.
Abrasiveness, erosion, and corrosivity of solids impact the selection of wetted part materials, influencing the longevity and maintenance requirements of the pump.
Types of Pumps
Pumps suitable for slurries include centrifugal and positive-displacement pumps. Selecting the correct type involves evaluating factors and consulting specialist pump suppliers.
Centrifugal Pumps
Centrifugal pumps are commonly used for slurry applications. Key considerations include:
- Impeller type: Recessed impellers reduce contact with particles, while open impellers ease maintenance. The impeller thickness should allow for suitable wear.
- Casing type: Metal casings, potentially lined with rubber, provide additional wear resistance, though split casings can be costly. Thickness should accommodate wear.
- Clearances: Larger clearances prevent blockage and reduce wear by easing particle passage.
Discussing specifics with pump vendors ensures optimal selections for the system, considering shaft, seals, and cavitation impacts. Centrifugal pump performance relies on fluid properties, necessitating translation of vendor-provided water performance curves to slurry conditions.
Positive Displacement Pumps
Positive displacement pumps, such as air-operated diaphragm, peristaltic, rotary lobe, progressive cavity, and piston diaphragm pumps, suit specific slurry requirements. Their capacity to handle pseudo-plastic fluids and maintain gentleness on solid particles makes them ideal for various slurries despite potential acceleration losses.
Air-Driven Diaphragm Pumps
These pumps effectively manage slurries but face abrasion and erosion challenges, particularly with check valve assemblies. Proper material choices mitigate these issues. For more details, kindly visit ahr rubber slurry pump manufacturer.
Consider choices such as check valve assembly materials, diaphragm materials, and clearances.
Peristaltic Pumps
Peristaltic pumps, free from check valves and balls, simplify maintenance. They handle up to 80% w/w solid slurries, though discharge pressure constraints depend on tube properties. Factors to evaluate include tube material longevity and maximum discharge pressure.
Gear, Lobe, and ECP Pumps
These pumps, effective for soft particle slurries, rely on teeth spaces for fluid transfer. ECP pumps particularly handle readily settling solids through effective re-engagement. Tight clearances necessitate careful application to avoid excessive wear from abrasive slurries.5
Progressive Cavity Pumps
Popular in wastewater and process industries, these pumps provide reliable slurry handling, coated rotors enhance wear resistance, but managing larger solids or slower operations to prevent blockages requires careful consideration.
Conclusion
Choosing the right pump for slurry applications involves diverse and complex factors. Building a robust system to maintain solid suspension and minimize wear and blockages is essential. Collaborate with pump vendors and gather extensive information on fluids and solids for well-informed decisions.
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.
Here are some key considerations to guide your selection process when choosing the best slurry pump for a specific application:
Application Requirements: Understand the specific requirements of your slurry pumping application. Consider factors such as the type and characteristics of the slurry (e.g., particle size, density, viscosity), required flow rate, total head, and the distance over which the slurry needs to be pumped.
Pump Type: Different types of slurry pumps are available, including centrifugal pumps, submersible pumps, and positive displacement pumps. Each type has its advantages and limitations. Centrifugal pumps are commonly used in slurry applications due to their efficiency and ability to handle high flow rates. Submersible pumps are suitable for pumping slurries from submerged locations. Positive displacement pumps can handle high-viscosity slurries or those containing large solids.
Construction Materials: Slurry pumps need to be constructed with materials that can withstand the abrasive and corrosive nature of the slurry being pumped. Consider the compatibility of the pump's wetted parts (impeller, volute, casing) with the slurry composition. Materials such as high-chrome alloys, rubber, or polyurethane may be used for wear resistance.
Solids Handling Capability: Evaluate the pump's ability to handle solids present in the slurry. Look for features such as large passages, agitators, or special designs that prevent clogging or excessive wear.
Efficiency and Operating Costs: Consider the pump's efficiency to ensure optimal energy usage and lower operating costs. Look for pumps with high hydraulic efficiencies and consider the power requirements for your application.
Manufacturer and Reputation: Choose a reputable manufacturer with a track record of producing reliable and high-quality slurry pumps. Consider factors such as after-sales support, warranty, and availability of spare parts.
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Maintenance and Serviceability: Assess the ease of maintenance and serviceability of the pump. Look for features such as easy access to components, replaceable wear parts, and availability of maintenance guidelines.
Budget Considerations: Consider the upfront cost of the pump as well as the long-term operating and maintenance costs. Balance the initial investment with the expected performance and durability of the pump.
Pump Size and Capacity: Consider the physical size and capacity of the pump. Ensure that the pump's size and flow capacity match the requirements of your application. Oversized or undersized pumps may lead to inefficiencies or operational issues.
Pump Head and Pressure: Evaluate the pump's head and pressure capabilities. The pump should be able to provide sufficient pressure to overcome the resistance in the pipeline system and deliver the slurry to the desired location.
Sealing and Leakage Prevention: Slurry pumps operate in demanding conditions, so proper sealing is crucial to prevent leakage. Look for pumps with effective sealing mechanisms such as mechanical seals or gland packing to minimize the risk of leakage.
Pump Reliability and Durability: Choose a pump that is known for its reliability and durability. Consider factors such as the pump's design features, robust construction, and the quality of materials used. A reliable pump will minimize downtime and maintenance costs.
Operational Flexibility: Assess whether the pump offers operational flexibility to adapt to varying slurry conditions, flow rates, or operational requirements. Some pumps may have adjustable impellers or speed controls to optimize performance.
Energy Efficiency: Energy consumption can be a significant operating cost when using slurry pumps. Look for pumps that are designed for energy efficiency, with features such as optimized impeller designs or variable speed drives that can help reduce power consumption.
System Integration: Consider the compatibility and ease of integration with your existing system or equipment. Ensure that the pump can be seamlessly integrated into your slurry handling system without significant modifications or disruptions.
Expert Advice and Support: If you are unsure about the selection process, seek advice from pump manufacturers, distributors, or industry experts. They can provide guidance based on their experience and knowledge to help you choose the best slurry pump for your specific application.
Remember that selecting the best slurry pump involves considering the unique requirements of your application and balancing factors such as performance, durability, cost, and support.
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Contact us to discuss your requirements with the ahr rubber slurry pump factory. Our experienced sales team can help you identify the options that best suit your needs.
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