Progressive Cavity Pumps Streamline Pulp & Paper Applications

Convincing a major player in the pulp and paper industry to break ranks and install a different kind of medium consistency (MC) stock pump was not easy, but after nearly a decade of trying, one progressive cavity pump manufacturer accomplished what they believe has the potential to become a new industry standard.

"Like most industries, over time, processes are refined," said Bob Baron, president and owner of R.W. Baron Process Equipment, an exclusive supplier of this manufacturer's equipment in Wisconsin and Michigan's upper peninsula. "It's a big ship to turn because, in actuality, you're looking at a paradigm shift." In 2000, the manufacturer shipped a progressive cavity pump to one of the largest producers of secondary fiber paper products serving industrial and institutional markets with a multiple machine mill in Green Bay, Wisconsin. Representatives of the pump manufacturer ran an open hopper pump that was not connected to any production line for about 15 employees at the paper company. Because other companies had not been successful with progressive cavity pumps for this application in the pulp and paper industry, this demonstration was an important breakthrough. During the demonstration, the research and development team at the mill kept increasing the consistency of the paper stock. "When we ran the trial, they kept adding more fiber to see how high they could go, and the pump just kept pumping it. The rate moved into the 12 percent range, and they were surprised to see the pump continue to work,' Baron said. Consistency, the ratio of fiber to water, varies depending on the paper being made and the fiber used, and it can reach 20 percent. While the trial was successful and the potential for this new pumping solution seemed promising, nothing happened for almost nine years. In 2008, the pump manufacturer heard from the paper company again and jumped at the chance to provide a solution to what could have been a dire production problem. The facility's existing twin screw pump, a typical choice in the industry, was being used to pump fiber at the plant and needed to be replaced with a larger size to accommodate the rate of flow and reduce wear and maintenance. However, the existing physical space would not accommodate the larger pump. The new twin screw pump would be too tall to fit under the refiner, and installation would require modification of the building. Instead of redesigning the building, the paper company decided to contact the pump manufacturer that had completed the demonstration nine years before. The manufacturer was faced with the challenge of pumping low consistency (7 percent) wood pulp and water. The new solution was a progressive cavity pump with a nominal pumping capacity of 1,120 gallons per minute (GMP) or 9,340 pounds per minute. Running at 147 rpm and 30 pounds per square inch, this type of pump was ideal for this application. The pump has been in place since May 2009 and runs nonstop unless the mill is down, which equates to about 50 weeks per year of consistent operation. The mill has two pumps at the facility so one is readily available at all times. The original pump has never broken down or stopped running but has been replaced with the backup pump for maintenance purposes. Removed earlier this year, the pump was shipped to the manufacturer's headquarters for service. "It had not stopped pumping nor was it compromised, but on a routine inspection, it was discovered that a section of the auger had cracked and the cavity liner had worn through to the metal. At no point in the production process did the pump lose capacity," Baron said. "Folks at the mill are pleased. I spoke with an engineer involved with the project who told me it continues to do a good job for them." From a broad-brush perspective, Baron said that the design of the pumps used at this major paper company is original, durable and easily serviceable. The pumps provide a variety of features that made them ideal for this particular pulp and paper application:

• Unique geometry of the rotors and the rotor coatings
• Durable proprietary coating of the rotors and stators that withstands abrasion
• Ideal fit between the rotor and stator, which is critical to the pump's performance and longevity
• Option for the appropriate use of exotic materials such as duplex stainless, titanium, Hastelloy and Alloy 20, as opposed to typical metals
• The use of more than 25 standard elastomers that are needed for specific applications
• The ideal compression between the rotor and stator to ensure maximum performance

"The rotor is slightly larger so the stator is compressed to create the perfect sealing line for the internal cavities," Baron said. "Maintaining that sealing line is extremely important. It's a fine balance to create proper compression for a specific application." These pumps also feature a device that reliably protects the pump from dry-run damage, which can occur when the stator is not properly lubricated. This phenomenon can cause the rotor to burn the stator's elastomer and potentially result in catastrophic pump failure. If a problem arises upstream and the flow stops, the pump is safeguarded by a run-dry protection device. A thermal sensing element monitors the rotor temperature during every revolution of the rotor, and temperature thresholds are established so that if the rotor's temperature goes above that range, the pump is shut down. The system can be set up to sound an alarm and/or automatically shut the pump off. This device senses the root cause of run-dry failure and eliminates the chance of a false reading. The pump installed at the paper mill is an unusual application at this point in the manufacturer's history, but the tissue and paper towel industry is a growth market for pump experts. "In this specific application, the twin screw pump is the standard, so deviation from that requires a special set of circumstances, like the physical size limitations dictated by the facility in Wisconsin," Baron said. "(This solution) solved serious issues for a major paper mill, and the potential to offer the same solution with other mills certainly exists. Similar pumps could be used in the ethanol industry and in municipal or industrial waste processing because, as we've seen at the facility in Wisconsin, the pump has a strong ability to move high-solids materials that are thick or viscous and fibrous."