A-C Stephenville reduces steam, turns up productivity.

Producing newsprint in today's market requires lower costs and improved quality. Abitibi-Consolidated's mill in Stephenville, Newfoundland, Canada is no exception. The mill has worked vigorously to increase speed and produce lighter weight grades. However, chronic issues with steam leaks and dryer flooding held back advances and increased operating costs.

In December 2003, the mill commissioned a drying optimization project aimed at producing C$ 800,000 in energy savings based on more efficient steam usage. The project involved installing Johnson PTX joints and stationary syphons in the dryer section. Project payback for this modernization was targeted to be less than a year. Prior to the end of 2004, Abitibi-Consolidated Stephenville had already met their energy savings goal, increased production, improved safety, minimized maintenance, and even improved sheet profiles. In addition, grade changes were less troublesome.

According to Roger Tapp, paper mill superintendent at Abitibi-Consolidated Stephenville, "Once the drying roadblock was removed, we met all of our targets and have been able to sleep through the night. The difference is dramatic."

Added Greg Alexander, assistant paper mill superintendent, "The savings came as soon as we turned the new drying system on. Speed increased 100 feet [per minute], and the wrinkles we had been fighting due to flooded dryers disappeared."

Alexander noted that flooding had become their primary obstacle to meeting productivity and efficiency goals. "We would come in the morning and identify which dryers were flooded," he said. "We would 'shoot' temperatures to see if a particular dryer was cooler. On most days, we would have to blow out up to 4-5 dryers. We repeated this task every day."

Because production speeds had been pushed to 3600 ft/min, Stephenville had to drive up differential pressure to 14 psi to evacuate the dryers. Noted Alexander, "With that kind of high-pressure differential, the piping and elbows couldn't handle it."

THE MAINTENANCE DEBACLE

Roger Tapp confirmed that the habitual dryer problems required four to eight men working for 8-12 hours during scheduled shutdowns to repair leaks resulting from running at such a high differential.

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Said Alexander, "Daily surveys of the dryers would reveal leaks at the joints, flanges, and gaskets. Because there were so many leaks, we could never get to them all. I was in the habit of going to the back of the dryers with my flashlight, opening the doors, and searching for leaks. Since the rebuild, we have not had to put maintenance on anything, except for a minor issue with one dryer, which is no longer a problem. Now, we have improved efficiency in every dryer can. It's great to be able to control to sub-atmospheric pressures in the first two cans, and slightly pressurized in the next two ... and it didn't take long to get there. Now, we simply let the system run, compared to the constant tweaking prior to the project."

WORKPLACE & SAFETY GAINS

Prior to the switch to the Johnson PTX joints and stationary syphons, another issue was safety. Previously, steam was supplied to the back of the dryer and condensate came out from both the front and the back of the dryer section. In the new arrangement, all steam and condensate hardware is on the backside of the machine. This arrangement minimizes potential safety hazards caused by having condensate joints and syphons on the front side of the machine. With the age of the piping system and high velocities due to excessive blow through, pipe leaks had become prevalent prior to the rebuild. Said Alexander, "After starting up the new system, we realized that around dryer number 40 there was a leak we had forgotten about. This leak was repaired, and there has not been a single leak since that incident."

Said Jim Nastrom, senior project leader with Johnson Canada, "The elimination of condensate headers from the front side eliminated a safety hazard for operators. These changes also helped free up the front side of the machine, which helped facilitate easier tail threading." The removal of the cross machine piping in the basement of the machine hood also reduced the piping congestion and the areas where broke can collect."

HIGHER SHEET PERFORMANCE, LIGHTER WEIGHTS

When Stephenville made grade changes in the past, it had to isolate some dryers--especially when the grade went from 48.8 to 40 gsm. Speed limitation was the key issue. The system was operating anywhere from 20-30 psi pressure and 14 psi differential. Today, because of smooth operations, Tapp and Alexander are able to spend more time improving the sheet to meet customer needs.

The mill commented that its 42 gsm bulky sheet compares favorably to the 45 gsm of competitors. This is noteworthy considering that their market is international, with much of their production going to Europe where the aim is to run lower weights and still meet high expectations on printing presses.

In the past, the Stephenville mill experimented with directory grades as low as 36 gsm, including the use of aspen as a further attempt to lower fiber costs. Today, the mill's fiber is primarily softwood, coming from New Brunswick, Quebec, and Labrador. In the past the mill used 50% spruce, but even with a reduction in the spruce content the mill has been able to maintain strength.

TRAINING

Jim Nastrom cited training as an important factor in Stephenville's success. Said Nastrom, "A broad understanding of steam and condensate, as well as the specifics of the system in place, was presented to operators in the machine room. Because steam is a critical tool in papermaking and a major expenditure, knowledge literally turns to money."

Said Tapp, "Now we have a full crew that knows the system and makes educated decisions. Overall steam load to the dryers has come down, and our people continue to find ways to make a better product even more efficiently."

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KEY BENEFITS OF STEAM & CONDENSATE UPGRADE:

* Considerable energy savings

* Productivity increase, running faster--drying is no longer a limitation

* Better profiles, easier grade changes

* Maintenance in the steam and condensate area has been reduced to allow resources to go elsewhere

* Safety gains

* Less stress on water waste treatment system

COMPONENTS OF THE REBUILD

* 32 PTX steam joints and stationary syphons

* 32 Turbulator[R] bars

* 2 Thermocompressors

* 1 Condensate flash system

RELATED ARTICLE: STEAM AND CONDENSATE SYSTEM DESIGN FEATURES

The steam and condensate system at Stephenville is a four-stage system. Steam sections 1 and 2 are designed as a Cascade system with section 1 split into sub-sections 1A and 1B to provide gradual warm up of the sheet. Sections 3 and 4 use thermocompressor recirculation loops, allowing for operational flexibility and improved control.

In steam groups 1A and 1B, the paper web is subjected to sub-atmospheric steam pressures and corresponding low dryer cylinder surface temperatures to minimize picking. As the paper machine in Stephenville was originally designed to produce linerboard, the existing condenser was quite large. This large condenser, in combination with minimal dryers going directly to condenser, results in a very good vacuum. On initial start up, the condenser was producing such a high vacuum that the old water supply valve had to be downsized significantly.

Section 3 is comprised of the middle 12 dryers, and is a suitable size for dry end scanner control. The size of this section, in combination with the thermocompressor loop, results in good responsiveness and operational flexibility.

Abitibi-Consolidated also worked with project vendors to modify the steam and condensate process logic. This logic was in place for start up and the machine has operated at target differentials since that time. Under normal conditions, the steam and condensate system operates as designed with thermocompressors in operating range and all vent valves closed. The end result is an energy efficient operation.

ABOUT THE AUTHOR:

Martin Koepenick of Innova International, Atlanta, Georgia, USA, has written about the paper and allied industries for more than 20 years. He can be reached at [e-mail].