Pulp pumps are an important component in many industrial processes, particularly for transporting and processing pulp slurries. In this article, we will provide an in-depth look at what pulp pumps are, how they work, their key components, common types, applications, and factors to consider when selecting the right pump for your application.
What is a Pulp Pump?
A pulp pump is a type of centrifugal pump designed specifically for handling pulp fibres suspended in water or other liquids. Pulp is the raw material used in papermaking, consisting of plant fibres, cellulose fibres, lignin, water, and other additives.
Pulp slurries have a thick, abrasive consistency that requires robust pumping equipment. Pulp pumps are built to withstand the abrasion and corrosion caused by fibrous slurries over long operating lifetimes. They consist of a rotating impeller enclosed in a volute casing that accelerates and displaces the pulp mixture for transport.
Pulp pumps generate flow and pressure needed to keep pulp fibres in suspension during processing operations like screening, cleaning, bleaching, and paper sheet forming. They are commonly used in the pulp and paper industry, but also have applications in other process industries like fruit juice production, chemical processing, and wastewater treatment.
How Do Pulp Pumps Work?
Pulp pumps work using centrifugal force. As the impeller spins rapidly inside the casing, it generates radial flow and pressure that pushes the pulp outwards from the eye of the impeller to the perimeter of the casing. The volute casing collects the pulp and forces it to discharge through the outlet port under pressure.
Some key components which enable pulp pumps to generate flow and head include:
Impeller: The rotating component with curved vanes that imparts velocity to the fluid. Pulp pump impellers are typically opened style with large vanes designed to handle bulky media.
Casing: The stationary outer shell that houses the impeller and directs the flow through the volute outlet. Casings have heavy wall castings to resist wear.
Shaft: The motorized shaft that turns the impeller connected to it. Robust shaft seals prevent pulp leakage.
Bearings: Bearings support and stabilize the shaft during rotation under radial and axial loads. Bearings are high capacity to sustain friction from debris.
Mechanical Seal: A specialized seal that prevents process fluid from escaping along the pump shaft. Seals on pulp pumps resist wear from fibres.
Prime Mover: Provides the rotary power to turn the shaft, typically an electric motor or diesel engine. Must be properly sized for the pump operating conditions.
The key to the pumping action is the kinetic energy added to the fluid by the rotating impeller. As velocity increases toward the outer edge of the vanes, the pulp accelerates and gains dynamic pressure. Kinetic energy is converted to pressure energy as the volute casing collects and slows the fluid. This allows pulp to be pumped efficiently even with higher consistencies up to 10% pulp content.
Common Types of Pulp Pumps
There are several common varieties of pulp pump designed for different pressure, capacity, and application requirements:
Centrifugal Pulp Pumps: The most widely used type, single or multistage centrifugal pumps generate high flow rates and moderate heads. The impeller(s) increase velocity and the casing converts velocity to pressure.
Vertical Pulp Pumps: Vertical configurations with a vertical shaft and impeller. Allows mounting closer to liquid source, saves floor space, and needs less priming.
Progressive Cavity Pumps: Useful for shear-sensitive media. Pulp flows through cavities between rotor and stator rather than an impeller. Capacity is lower but can handle higher viscosities.
Positive Displacement Pumps: Reciprocating action allows handling higher pulp consistencies. Rotary designs like screw pumps and gear pumps also work well for thick pulps.
Airlift Pumps: Uses compressed air injection to lift fluid up vertical pipes. No rotating parts and can handle stringy pulps.
Specialty Designs: Custom pumps for specific pulp processes, such as vat pumps, inlet pumps, diffusers, stock dilution pumps.
Pump selection depends on capacity needs, discharge pressure, pulp consistency %, and other liquid properties. Centrifugal types are most common for medium consistency pulps up to 10%, while positive displacement handles higher consistencies.
Pulp Pump Applications
Pulp pumps serve many key transportation and process functions in the pulp and paper mill, including:
Low Consistency Pulp Transfer: Moving diluted pulp between process units like washers, screens, cleaners, and storage towers. Flow rates can reach tens of thousands of gallons per minute.
Medium Consistency Pumping: Higher pulp content applications like feeding pulp to paper machines and chemical reactors. Discharge pressures to 600 psig.
Bleaching Process Pumps: Pumping pulp between bleaching stages at moderate consistencies of 4-8%. High capacity and discharge heads.
Vacuum Pumps: Creating vacuum on suction boxes of paper machines to dewater pulp. Handle wet airstreams with fibres.
Chip Feed Pumps: Delivering low consistency wood chip slurry to digesters up to 15% consistency. Heavy abrasion resistance needed.
Chemical Addition: Metering and injecting process chemicals like bleaches, additives, dyes into pulp lines. Require corrosion resistance and accuracy.
Tailings Transfer: Removing residual tailings after pulp washing stages and transporting it for reprocessing or waste removal.
Deinking Pulp Systems: Specialized pumps for recycled paper stock preparation. Handle difficult ink removal wastewater.
Screen Room: Various duties moving pulp between vibrating, pressure, and centri-cleaning screens to remove contaminants.
Careful pulp pump selection ensures reliable operation and long service life in the demanding production environments of pulp and paper mills, chemical plants, and wastewater facilities.
Factors in Selecting Pulp Pumps
There are several important factors to consider when selecting a pulp pump for your particular process requirements:
Capacity: The flow rate capacity should match your system with some safety factor allowance. Peak flows need accommodation.
Total Head: Includes static lift, friction losses, and required discharge pressure. Adequate NPSH is critical to avoid cavitation.
Pulp Consistency: Dry pulp percentage impacts pump selection and risks like plugging. Measure typical and maximum values.
Abrasion Resistance: Pulp fibres cause abrasive wear on impellers, casings, seals. Materials like high chrome iron and rubber lining help.
Corrosion Resistance: Bleaching and other chemicals can corrode pump parts. Specialty alloy upgrades may be required.
Solids Handling: Pulp contains debris, grit, sand, uncooked chips that necessitate oversized passages and low shear impellers.
Priming: Pumps must self-prime, have good suction ability, and minimum NPSH requirements for reliabile start-up.
Energy Efficiency: Systems like variable speed control offer significant power savings over throttling valves.
Maintenance: Choose rugged pumps with long service intervals, simple designs, and readily available spare parts.
Work closely with experienced pump suppliers ( An Pump Machinery ) during selection. Have operating parameters fully characterized and get solutions engineered specifically for your unique pulp pumping application.
Conclusion
Pulp pumps are an indispensable component enabling the large-scale processing of pulp slurries across many industries. The abrasive and fibrous nature of pulp requires heavy-duty pump designs to provide reliable service life.
With a rotating impeller and fixed casing, these robust pumps impart velocity to pulp mixtures and convert kinetic energy into pressure. Various pump types each have advantages for different capacity, pressure, consistency, and pulp processing requirements.
Careful attention must be given to factors like abrasion resistance, corrosion resistance, solids handling capability and energy efficiency when selecting and installing pulp pumps. With the right pump characteristics matched to your specific process, pulp pumping productivity and efficiency can be optimized.
An Pump Machinery is a professional pulp pump manufacturer. If you require assistance with pulp pumps, please contact us at anpump5@angroupcn.com or +86 15032857866; our technical sales engineers have considerable product knowledge and will be able to assist you.
Here are a few of the pulp pumps made by An Pump Machinery, a reputable manufacturer of centrifugal pumps.
