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The Role of Slurry Pumps in Pulp and Paper Mills

Since the 1980’s economic trends have been developing in the pulp and paper industry that have had major impacts on how mills must operate to survive in the 21st century.  The industry now competes in a global market with foreign competition, must evolve with changing environmental regulations, remain competitive due to constant mergers and acquisitions, and supply products to customer that demand higher quality products, all while cutting its costs per ton.

The pulp and paper industry has been a crucial part of society for generations providing materials essential for communication, packaging, currency, etc.  Throughout its history the industry has evolved, embracing new technologies to improve efficiency and productivity. The manufacturing processes involved in papermaking require the handling of various types of slurries such as Lime slurry, Caustic, black liquor, and white liquor, and making the use of slurry pumps essential.

In the pulp and paper industry the main type of pump used to handle these slurries are ANSI centrifugal.  These are the same type of pumps that are used to handle clear water and pulp fiber slurry in the mill.  The only difference in these units is the materials used in construction of the impeller, casing, stuffing box, and suction wear plates.  The units handling slurries typically use a duplex stainless steel known as CD4MCu on these parts where the units handling water and pup fiber are typically 316ss and ductile iron.  The CD4MCu material has a 240 Brinell Hardness and does offer extended wear versus 316ss and Ductile Iron but is also very expensive.

Slurry pumps have a long history and are commonly used in the mining, power and sand and gravel industries due to the need for handling both very abrasive and corrosive slurries.  Over the years the advancement of materials and design efficiency in slurry pump technology have become crucial for maintaining efficient operations that help lower mining and power companies’ production costs.

For many years slurry pumps were offered in Chrome Iron and Natural Rubber and only used to pump neutral dirt or ore in the wet separation process in the mining industry, but developments in materials have broadened the market for slurry pumps.  There are now various types of Chrome materials used to handle materials with Ph of 2 and a variety type of acids.  They are also available in Elastomer products such as EPDM, Neoprene, and Butyl that can handle elevated temperatures and corrosive liquids.

Schurco recently visited a pulp and paper mill to discuss the use of slurry pumps versus ANSI process pumps the first question asked was “we have a few slurry pumps in the mill but have no idea why they were installed and what is the benefit versus our ANSI pumps”.  The quick answer is they are a more robust pumps that are designed to handle heavy abrasive and corrosive slurries that can dramatically increase the wear life and reliability of the pump installation.  This equated to cost savings by dramatically reducing pump maintenance, spare parts, and downtime.

How and why?  First, a true centrifugal slurry pump is much more robust than an ANSI centrifugal pump based on mass. For instance, a CD4MCu 6×4-13 ANSI unit weighs approximately 450lbs.  A Chrome 6×4-13 Schurco slurry pump weigh 1,000lbs.  To break this down even further the ANSI 13.0” impeller weighs approximately 20lbs.  The Schurco Slurry 13.0” impeller weighs 150lbs.  Which impeller will provide a longer wear life.

Second, technological advancements have allowed for the development of specialized slurry pumps, enabling paper mills to handle a broader range of slurries efficiently. Today, slurry pumps are available with numerous impeller styles such as Hi-Efficiency, Large Particle, Open Style for handling fibrous material and Hi-Head applications.

Today slurry pumps can play a pivotal role in various aspects of the papermaking process. They are extensively used for transporting different types of slurries within the mill, ensuring the continuous flow of materials between the different stages of paper production. Some of the key roles of slurry pumps in pulp and paper mills include:

Slurry Pumps for Pumping Lime Slurry: Lime slurry plays a critical role in the papermaking process. It helps adjust the pH levels of pulp, thereby enhancing the bleaching process. Slurry pumps designed for handling lime slurries are equipped with abrasion-resistant materials, as lime slurries can be highly abrasive. These pumps efficiently transport the lime slurry to the designated points, ensuring proper pH control and contributing to the production of high-quality paper.  Schurco installed a model 6UD100, Chrome lined unit a pulp and paper mill in Georgia.  The competitor’s pump was replaced every 8-10 months.  The Schurco 6UD100 pump operated for three years maintenance free.

Slurry Pumps for Pumping Caustic: Caustic solutions are vital for the pulping process, as they aid in breaking down lignin from wood fibers, making them suitable for papermaking. Slurry pumps used for handling caustic solutions are constructed with materials that are resistant to chemical corrosion. These pumps ensure the safe and efficient transfer of caustic solutions within the paper mill, optimizing the pulping process.  At a mill in South Carolina, Schurco was asked to replace an ANSI stock pump manufactured in CD4MCu that was operating in Causticizer service.  The unit was replaced every 4-5 months.  Schurco installed a model 8SE150 with chrome iron wet end components.  The Schurco unit operated maintenance free for two years.

Slurry Pumps for Pumping White and Black Liquors: White and black liquors are essential byproducts of the pulping process. White liquor is used for cooking wood chips, while black liquor contains valuable chemicals that can be recovered and recycled. Schurco pumps designed for pumping white and black liquor are equipped with specialized materials designed to handle the corrosive nature of these solutions. Efficient pumping of these liquors ensures minimal wastage and optimal resource utilization within the paper mill.

Slurry pumps have played a crucial role in the history of pulp and paper mills, facilitating the transport of various slurries essential for the papermaking process. From handling lime slurry and caustic to pumping white and black liquor, slurry pumps are indispensable in ensuring smooth operations and high productivity.  The result is reduced downtime, increased cost savings, and enhanced productivity for pulp and paper mills.

Looking ahead, the future of slurry pumps in the pulp and paper industry is promising, with advancements in materials, and energy efficiency on the horizon. As technology continues to evolve, slurry pumps will remain a vital component in the ongoing success of the papermaking industry and help mill lower their cost per ton and remain profitable.

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