Stora Enso Nymölla in efficiency mission

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Stora Enso Nymölla in efficiency mission

March 17, 2014 - 07:59

When BTG and mill staff at the Stora Enso Nymölla (Sweden) mill put their heads together and launched Project Robin 2012 they focused on enhancing the productivity of PM 2.

Specifically, BTG and mill staff focused on the metering size press (SymSizer), particularly as it relates to rod, bed and sealing blade performance, roll-cover lifetime and the quality of surface-sized fine paper. The project was carried out in about six months’ time, and the full benefits were visible one year after project start-up:

• Improved roll-cover lifetime.


• Improved md and CD moisture profiles.


• Longer rod lifetime.


• Improved worker safety.

These four benefits boil down to money saved. In round figures, that amounts to about 80,000 (US$109,000) per year. But that’s not all. Reduced operation costs weren’t the only benefits of Project Robin. It also stabilized the process enabling not only a more uniform product, but also more efficient use of machine operators.

LOWER COSTS, IMPROVED QUALITY

Roll covers are expensive and the extension of their lifetime on the metering size press is from where the greatest share of the €80,000 cost saving comes.

Typically rolls can be reground five to eight times and then the cover needs replacing. Now with a longer lifetime, the mill does not have to grind or buy new roll covers as often.

A longer lifetime also means time saved during shutdowns as the roll covers don’t require changing as often, a process that usually takes three to four hours and at least two employees to get the job done. Now this staff can be utilized more efficiently elsewhere during a shutdown.

Cost savings as a result of improved moisture profiles are also an important benefit of Project Robin. “This means improved quality and that’s what customers buy,” says Roger Bengtsson, the senior paper technician on PM 2, who led the project from Nymölla’s side.

CONSTANT ADJUSTING

Previous to the project, operators were constantly profiling the metering size press to gain proper moisture profile in CD and uniform application of starch in md. When all was said and done, and these parameters are in proper order, operators can now pay greater attention to other processes on PM 2.

Profiling takes a lot of time, and it wears the rods and roll covers faster. The process involves adjusting some 100 profiling screws on the metering size press. The moisture profile is measured before and after the press and changed accordingly by changing the positions of the screws to either reduce or increase the amount starch necessary to apply to gain uniformity.

But because starch is applied on both sides of the sheet at the same time, it is not possible to know how uniform the application in CD is on each side. And there is no way to measure it online on PM 2. During a shutdown the profiling screws had to be “zeroed” or reset in their original position. This meant that the whole process had to be repeated.

Since Project Robin, profiling is not necessary. The profiling screws have not been touched since the completion of the project and the profiles are fine. In order to gain uniform starch application in md, however, rod loading pressure still needs adjusting every now and then, perhaps once in two weeks.

“Before BTG came into the picture, we were of the opinion that the metering size press itself was the reason it needed constant adjusting. And then there was the problem with the roll covers. They had to be changed too frequently, and they are expensive,” says Bengtsson.

He adds, “We’ve had any number of experts look into these problems, but the very competent BTG technicians understood immediately what the sources of problems were, and they were first to identify why the roll covers wore out so quickly.

“What’s more, they worked closely with our metering size press operators. Theory is one thing, but if you really want to know if the machine functions as it is supposed to,then it has to be tested while in operation with those who operate it and with those who are at the mill for the purpose of correcting the problems. We strongly believe that this kind of collaboration contributed to the success of the project,” says Bengtsson.

GOOD PRODUCTS IMPORTANT, BUT KNOW-HOW IS ESSENTIAL

“Our reception at Nymölla was exceptional in that they let us into the mill and let us actively work on the machine together with the mill staff involved in its operation. The level of collaboration and openness we experienced at the mill was extraordinary,” says Sheryl Hildén, the application manager at BTG durorod.

“Probably more important than the products from BTG were the combined technical know-how BTG and mill staff could apply to the project enabling the beneficial results,” she says.

PROJECT ROBIN 2012: THE PROCEDURE

Initially, BTG evaluated and recommended what they understood would enhance the operation of the metering size press. They then proposed Project Robin 2012 at the mill, a project that would include the use of BTG metering products as well as BTG technical resources working together with mill staff.

“We know that working together with mill staff is the best way to produce satisfactory results in this type of project. We, of course, have the experience of having worked on this kind of problem many times over.

“But, regardless of how many times we’ve worked with this kind of problem, each project is in its own way unique. And that’s why we feel that mill staff knows the local circumstances best and why they are a necessary component for reaching a satisfactory solution,” says Frida Slotte, who was the manager of the project from BTG’s side.

Based on discussions with mill staff working on the metering size press, BTG identified the Critical Success Factors needed to enhance operations. Three factors were determined to be most critical:

Moisture profile variation in CD: The main challenge on PM 2 was the “smiley” moisture profiles, or higher moisture at the edges of the sheet than in the middle. BTG IPI performed a size press audit to determine if the press had any mechanical problems such as beam straightness, profiling or nip loading that could cause uneven application in CD. Base paper properties could also affect moisture profile in CD. Very uneven base paper absorption properties could cause uneven starch transfer from the roll cover to the paper. after checking these various parameters, BTG determined that there was nothing wrong with the size press. The problem with moisture profiles was mostly created before the size press and not by the press itself.

Uniform starch application in MD: Based on a targeted starch application of g/m2, BTG selected rods with four different groove profiles for comparison. a BTG IPI wear analysis revealed the number of days/weeks a rod had been used and how much it was worn. another important factor in md application is the consistency of the groove profiles. in other words, how much does the application from the new rod deviate from that of the previous rod? Of course, application decreases over time due to groove wear and this requires adjusting the rod load.

Roll cover lifetime: BTG determined that process parameters were the main cause of the short lifetime of the roll covers. When a number of these parameters were altered roll cover lifetime improved.

The approach for enhancing the performance of the metering size press that BTG and mill staff developed is summarized in Fig. 1. This procedure was repeated after three months.

Upon completing Project Robin 2012, BTG proposed that the Nymölla mill purchase its products, which during the project proved to enhance the productivity of the metering size press. These products included rods of various dimensions, beds and sealing blades. in addition to these products, BTG agreed to supply ongoing application support.

“The dialog with BTG technicians, whether it was face-to-face or over the telephone contributed greatly to the success of the project. Put it this way. If dialog is compared with a 1,000-page report that nobody reads, dialog wins every time,” says Bengtsson.

“We’re happy with the results of the Robin project. So happy that we’ve begun working together with BTG to enhance the productivity of the SpeedFlow sizer on PM 1,” he concludes.

David Wold has covered the forest products industry for many years. He is a former Swedish editor for PPI and now has his own company, English Language Services AB in Sweden.