Norpac needed to shorten the distance between its dye system and the end product to alleviate technical problems such as clogging
December 2007
A Pulp & Paper Special Report
In real estate, the prevailing adage is "location, location, location." At North Pacific Paper Corporation (Norpac), that adage has proven to hold just as much water.
The location in question in this particular example was that of the dye system Norpac was using in its Longview, WA, facility, where the company produces newsprint and high-bright uncoated mechanical paper for newspapers, commercial printers, book printers, and magazine publishers.
According to Brian Dalgardno, who oversees some of the chemical programs on the Norpac paper machines, the dye control system was simply located too far from the injection point and the measurement point. "We have historically experienced precipitation problems when making down the dye. The types of dye we have always used, which are basic dyes, tend to precipitate out in the water phase and form a gummy deposit that clogs up the lines."
With color quality standards as high as Norpac's, clogged lines in the dye system presented an intolerable problem. "We just felt there was a pressing need to shorten the distance between the dye system and the end product for a number of technical reasons," recalls Dalgardno.
Striving to improve
While any other papermaker may have been satisfied with this kind of dye system and its location, Norpac has established a reputation for not being content with the status quo. In fact, the company's long-standing reticence to rest on its laurels is at least partially responsible for its recent accolades: Dow Jones presented Norpac with its Gold Quality Award for supplier excellence for the second consecutive year, while the Seattle Times ranked Norpac Number 1 in overall performance for 2005 in its Management Survey. Additionally, Gannett Newspapers ranked Norpac "The Best in the West" for "high caliber service and products."
The company's well-deserved reputation has resulted in significant growth. The company was founded in 1976, and its first machine produced 220,000 tons of newsprint in 1979. Today, Norpac boasts three machines capable of manufacturing more than 720,000 tons/yr, making it the largest newsprint facility in North America.
Thus, five years ago, when the opportunity to improve the quality of its operation – and subsequently, its product – presented itself, management decided that the purchase of a completely new dye system was in order. After an exhaustive search, the company purchased a new dye system that was equipped with six 520 Series dye pumps from Watson-Marlow Bredel, a leading manufacturer of peristaltic pumps.
"We are using the 520 Series pumps to meter in dye for tinting control of our white papers," says Dalgardno, who also handles quality development as well as financial, cost and runnability issues for the company. The pumps play an integral role in the system's overall performance. For Dalgardno and Norpac, the most critical factor was flow – both high and low. The original pumps Norpac was using failed to achieve adequate turndown rates from the high flow level required by some dye grades to the very low flow level required by other grades.
"We needed a pump capable of quickly adjusting from a fairly high level of flow to almost zero. We used to dilute our dyes to ratios ranging from 20:1 to 100:1, depending on the dye. Ultimately, we were looking at a much wider range of turndown," explains Dalgardno. "We were convinced that the Watson-Marlow Bredel pumps integral to the dye system would fit those requirements."
Norpac installed the 520 peristaltic metering pumps, which use microprocessor controlled brushless DC drive technology to deliver a flow turndown over a million to one, a maximum flow of 55 gal/hr, +/- 0.1 rpm precise speed controllability, and digital/analog auto control capability.
The right choice
Dalgardno admitts that he was looking at other pumps as well, but all had their shortcomings. "We looked at one brand considered the 'standard' for low dilution, but they were pretty unreasonably priced," he says. "Also, that brand actually offered less turndown than the peristaltic technology from Watson-Marlow Bredel."
The Watson-Marlow Bredel 520 peristaltic pumps originally installed by Norpac were rated to 30 psi, and although Dalgardno was satisfied with the turndown performance, he needed to turn up the pressure in order to further improve his process.
"With the new system, we still needed to dilute the dye and had many problems. In the older dye system, we had larger lines, so the deposits just built up over a longer period of time before we'd have to steam out the lines to remove the deposits," says Dalgardno. "As a result, we decided that we would rather inject the dye directly into our process without going through the current delivery skid system. With this system, we wanted the neat dye to travel all the way from the injection point to an instantaneous dilution stage just before injection to minimize precipitation issues."
For direct injection, some of the dyes required as much as 50 psi of process pressure. Watson-Marlow Bredel's new 520REH high-pressure peristaltic pumphead is capable of 100 psi continuous duty injection and was ideal for Norpac's application. It allowed the mill to achieve the flow rate, high turndown, and direct injection pressure it needed for process optimization.
"Considering the critical shade grades we were moving to, in order to get better shade control we had to go down to very low flows, particularly on red dye – as low as three milliliters per minute," Dalgardno states. "With such a huge turndown, the system of direct injection with the 520 pumps worked much better for this application. Plus, the final dilution pressure and flow was high enough to keep the diluted dye lines pretty well scoured out.
"We pump the dye from the dye tote, through a filter and into the 520 pump, then pass it through 3/8-in. Teflon lines to a final metal injection header that has a 30 psi governed water source," Dalgardno adds. "Twenty-five gallons per minute of water mix with the dyes in a one foot line that is directly injected into the suction of our headbox supply pump. Basically, we're injecting the dye directly into the process – from tote, to filter, to pump, to the process, to the final dilution water site, then to the paper machine headbox."
Norpac is now using six Watson-Marlow Bredel 520 pumps for the neat dyes along with two more for some other additives; four more are currently on order. The pumps are being used for some other low-flow chemical systems, such as optical brightener control and some polymer additions.
Watson-Marlow Bredel pumps are designed to keep fluid contained within the tube at all times, never allowing the often abrasive or caustic process fluid to come into contact with the pump mechanism, ensuring gentle, low shear handling. After the fluid is drawn into a pump, it is trapped between two rollers and finally expelled from the pump. The complete closure of the tube, which is squeezed between the roller and the track, gives the pump an accurate positive displacement action, preventing backflow and eliminating the need for check-valves which can corrode, stick, or clog.
Maintenance of the pumps is an extremely simple procedure. "There haven't been any maintenance issues to-date with the motors," Dalgardno says. "With the tubes, we perform maintenance every 10 weeks by rotating the tube on the lower pressure tubing by half a revolution. With the higher pressure tubing, the different tube design requires that we remove and replace it. But that's a quick, 30-second process: we simply close the plastic valve, remove the tube, and put the new tube on the nipple that ties into the valve."
The high pressure tubing Dalgardno refers to is Watson-Marlow's LoadSure® tube elements which guarantee correct loading every time, as well as easy one-step maintenance – a pump rebuild is achieved by simply switching the tube element.
Overall, the entire dye system project and peristaltic pump technology helped Norpac realize an 80% return on investment. The savings in maintenance time and productivity losses that Norpac was experiencing with diluted dye systems – not to mention the cost of maintaining corroding system versus all plastic – have afforded Norpac the opportunity to uphold its reputation as a company that goes above and beyond.
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