Papermakers Hit Big Payoffs by Taking Chances with Clothing Trials

Pulp & Paper, Mar 2005 by Shaw, Monica, Taber, Phil

A willingness to reject the status quo with paper machine clothing selections pays off with production increases and a better bottom line contribution

When capital is scarce, mills often become more risk averse, choosing to stick with the status quo rather than trying a new technology. With paper machine clothing, however, this tendency seems less obvious, according to case studies from clothing suppliers that were recently shared with Pulp & Paper. By running trials, mills in the following sections on forming, pressing, and dryer fabrics gambled on improvement and hit big payoffs in tonnage, contribution, and quality.

In the case studies here, suppliers and mills worked together to find the appropriate clothing for paper machines producing linerboard, copy papers, corrugating medium, and coated groundwood. In addition, the sidebar on p. 39 demonstrates an increasing trend for mills to turn to paper machine clothing suppliers for a variety of diagnostic services, as a case study on headbox instability illustrates.

FORMING

Medium Mill Improves First-Pass Retention, Sheet Tests with High-Support Forming Fabric

Problem: A corrugating medium mill sought a paper machine clothing supplier to partner with in the implementation of forming fabric projects that could improve the economics of its operations in direct and indirect ways. This 270-in. fourdrinier paper machine produces about 650 tpd of semichemical, 112- and 176-gsm corrugating medium.

Project: For its forming fabric projects, the mill chose to work with Weavexx, who suggested an evaluation of newer forming fabric technology that could improve runnability, couch solids, formation, and fabric life.

The forming fabric style used on this former since early in 2000 was a typical "single-layer" design with specifications and properties as listed in Table 1. When operated in the preferred running mode, this style provides only a moderate level of support to the fiber mat, with consequent compromises in formation, first-pass retention, machine cleanliness, and sheet tests. It is well known that when this forming fabric style is designed to provide higher levels of support to the fiber mat, potential running time on the machine is compromised so that it may not be possible to achieve the fabric life required for efficient planning of fabric changes.

With expectations founded on proven results in similar applications, Weavexx suggested the Titan HTX forming fabric to address the goals of this operation. The structure of this fabric has several features that combine to create the potential for delivering the economic benefits targeted by this mill. Most importantly, the arrangement of yarns in the top surface provides the highest possible quality of support to fibers, thereby delivering maximum first-pass retention (Figure 1). The higher retention level facilitates improved formation and contributes to cleaner machine operation. Figure 2 shows a typical drainage "hole" for this forming fabric.

Large, tough yarns on the running side of the Titan HTX presented 50% more sacrificial volume than was available in the current forming fabric on this paper machine. The additional yarn volume enables increased running time of at least 50%. The increased toughness also resists damage.

Results: The first Titan HTX forming fabric trial on this corrugating medium machine is now complete. The following results show significant gains relative to typical results with the previously used single-layer forming fabric:

* Retention on the medium machine's heavier grades was at 86%, up 5% from what the history was at the same weight.

* On heavier grades, couch solids increased to 21.5%, up about one point from the historical average.

* Draws are reduced 12 to 15 ft.

* Sheet tests are better, resulting from the reduced draw, increased retention, and better formation.

* Profiles are improved.

* Steam usage is reduced, enabling shutdown of a standby boiler until the coldest months. Improved drying is the result of more uniform profiles, a smoother sheet, and improved formation.

* Machine cleanliness has improved.

* Speed has slightly increased on every grade.

The fabric was removed after 178 days of operation on a schedule that met this mill's planning needs. Running time of the last ten forming fabrics has ranged from 82 to 132 days, averaging 102 days.

It is estimated that the improvements generated by this project contributed to a 2% increase in tonnage during the 178 days of operation. In the market, this amounted to a pre-tax contribution approaching nearly $500,000.

-Wayne Freeman is technical director, forming fabrics, for Weavexx Corp.

PRESSING

Engineered Felt Overcomes Drying Limitations, Boosts Tonnage on Recycled Linerboard Machine

Problem: Recently, the management of a recycled linerboard machine in the Midwest approached Albany International to evaluate machine operation and paper machine clothing. The paper machine was built in the late 1980s under the mini-mill concept and is severely drying-limited. The evaluations were made to aid in optimizing paper machine performance, while keeping the machine cost competitive. Because this machine is drying-limited and not speed-limited, the first objective was to find ways to produce a dryer sheet exiting the press section.