Machine clothing strategies keep wraps on cost.
"The energy market is in a state of flux, with significant increases in energy costs seen recently," said David Buchanan, business development manager, board and packaging, Voith Fabrics. "Like many manufacturers that rely on natural gas and other sources of energy to generate power for their production, papermakers are struggling to survive during the fuel crisis. Industry data shows that the cost of energy and fiber alone make up about 50% of the overall cost of producing paper, board and tissue products." (See Figure 1).
Since many papermakers are finding fuel costs nearly impossible to control, suppliers have been put on the spot to deliver alternative solutions to reduce fiber and energy requirements. "Papermakers are recognizing significant energy savings by using the right fabric in given applications," said Buchanan. "Voith Fabrics has received data from a number of mills supporting notable results in all machine sections. The proper application of high-performance fabrics has resulted in lower fiber requirements, reduced steam consumption and increased overall machine efficiency."
According to Steve Cole, director-value creation management, Weavexx, "Our business model is precisely about 'value through innovation'. We pride ourselves on continually developing and supplying product technology that directly benefits the paper manufacturer by reducing costs, and improving revenue potential through high sheet quality." Cole cites triple layer forming fabrics as an example of clothing technology that can help mills reduce power consumption on the former, reduce chemical consumption due to higher retention and cleaner operation, reduce fiber consumption, and offer other benefits that can add up to significant cost savings.
"The forming fabric has a significant influence on fines retention, fines distribution and couch solids," noted Wilhelm Grondahl, global vice president of technology, forming, for Albany International Corp. "Therefore, it is important to optimize the forming fabric for the best paper quality and runnability. Degree of retention and dryness, both controllable through fabric construction, are key drivers for energy savings."
Forming fabrics also play an important role in cost management in other areas throughout the mill. Bud Chase, forming product business leader, AstenJohnson, offers a few specifics. "Higher couch solids through optimized sheet formation and/or improved drainage and/or improved vacuum efficiencies are the main ways forming fabric design can contribute to reduced pressing demands and subsequent drying load. Improving mechanical retention characteristics can also lead to reduced chemical retention costs or may allow papermakers to run a lower cost fiber furnish. Increasing forming fabric life is a very small way to impact operating costs compared to the above reasons, but choosing a design with more wear volume on the machine side of the forming fabric design or adding a wear resistant material can extend forming fabric life and potentially reduce operating costs.
"Another often overlooked way forming fabrics can be used to reduce operating costs is to look closely at the wear patterns that develop on fabrics that run to full life," Chase continued. "This wear will be a fingerprint of the fixed elements and roll surfaces and is an excellent preventive maintenance tool papermakers can use to judge the overall condition of their forming sections."
Press fabrics have a direct impact on overall energy consumption, said Daniel Hedou, press product business leader, AstenJohnson. "We know a 1% increase in sheet dryness can reduce drying energy load by 3%-4%. To minimize the energy required to dry the paper, it seems redundant to say that press fabrics must be designed to maximize water removal; however, this is not as common as you may think. Most press fabrics today are over-designed from a water removal point of view to meet an expected life cycle. To truly maximize press water removal, many papermakers would benefit from using lighter fabrics for a shorter life cycle."
Albany International's Scott Carson, vice president of marketing, North America drying, agrees that in mills where steam represents a major cost driver, dryer fabric selection is important. "Since dryer fabrics must assist both in the transfer of heat from the can to the sheet, and then evacuate the moisture laden air, the permeability of the fabric is critical throughout life. To enhance the ability of the fabric to maintain design permeability, contaminant resistant designs can ensure steady state operations and ease of cleaning," he advised.
"In the dryer section, we're finding that certain spiral fabrics run cleaner, offer better sheet contact, and move more air in contact with the sheet," said Voith Fabric's Buchanan. "Spiral fabrics yield improvements in capacity and efficiency and can also be designed with CFM readings in excess of what can be achieved from a woven fabric. Spiral fabrics have 20 to 40% more contact with the surface of the sheet. All these factors lead to improved drying rates and less steam consumption to dry the same ton of paper. Spiral applications have resulted in 3 to 10% documented drying improvements."
NEW OR IMPROVED?
Whether or not costs should come down is an easy decision for any mill. Whether those cost reductions should come from optimizing existing systems and equipment, or from investing in new technologies, is a much tougher call. Mills need to do some homework to determine which operating costs can be reduced by improved machine clothing operations, and which by using new machine clothing designs and/or products.
The first step: set operating cost goals and communicate them to suppliers. "Clothing designs today can be complicated, and their interaction with the complex papermaking process requires a combined effort of clothing and papermaking expert," said AstenJohnson's Bud Chase. "The best way to determine whether forming clothing design changes will help papermakers reach an operating cost goal is to describe the operating cost goal to the forming clothing supplier and challenge them to help hit the goal. Once the goals are clearly defined, the next step is to mathematically document and model existing forming clothing to determine which forming fabric variable(s) would most impact the stated operating cost goal. This 'engineered approach' takes much of the guess work out of forming fabric trials and greatly increases the chance of success."
Grondahl of Albany International agrees. "Sharing mill operating goals and objectives with a good sales/service team will result in a cost/benefit analysis of the process and recommendations for improvement in the context of mill objectives. The analysis may result in recommendations beyond paper machine clothing itself, to include such items as machine clothing handling practices, installation and maintenance, and cleaning and conditioning practices. When the recommendation includes a trial fabric evaluation, the trial plan will analyze the proposed impact of the trial, trial objectives, and measurement methods to calculate financial impact."
Oliver Baumann, product manager for Wangner GmbH, has seen how proper fabric design can significantly improve paper machine production characteristics for clients. "However, such improvements in machine efficiency were only achievable through close coordination between the papermaker and the supplier," he said. "Frank and open discussions with customers are a prerequisite--this is the only way to more effectively analyze problems and potential improvements. Close teamwork leads to new approaches to application-oriented fabric solutions and machine construction modifications that measurably improve paper machine performance."
Once cost goals are set, the best way to identify cost reduction opportunities is by finding the current limits of your machine and designing a strategy to eliminate them, said Hedou of AstenJohnson. This should include evaluation of new clothing technology. "To find the limits of your current clothing, trend your chosen key operating parameters (energy consumption, water removal, draws etc.) and study the trend for events that are clothing-related. Look for evidence either that one style of fabrics is performing better than another, or that performance degrades or improves over the life of a given fabric style. This analysis should guide you in selecting your optimization approach." Performance that degrades over time may signal fabric conditioning issues, he added.
Weavexx's Cole said that the focus needs to be on value generation and documentation. He suggested that machine clothing suppliers should have a plan focused on continuous improvement that includes:
* A focus on quality and cost drivers as defined by customer expectations
* Adding value to products and services with bundled technology solutions
* Reduction of waste and non value-added activities
* The study, focus and prioritization of key performance indicators that impact manufacturing costs and product quality.
"Such a program should deliver incremental savings through value added processes and product technology while driving down the total cost of ownership for both mill and supplier," said Cole.
He also pointed out that, if misapplied, even the best technology can lead to inefficiencies, non value-added activities, and economic loss. That's where goals and guidelines can help. "First, plan the project--define the objectives," said Cole. Next, he suggested the following steps:
* Know the value--for the project to be valid, it must have economic return
* Make an action plan, including product trial, scientific investigation, measurements
* Document the process through data tracking
* Quantify results--calculate and report the value
"It is imperative that the supplier and paper mill team together to match the proper product technology with the precise objectives of the mill," Cole said. For example, Weavexx has developed an online system where paper mills can log into the system from the web browsers, through a secure connection, to provide up-to-date progress reports and value summaries for mills operated by their companies.
Once mill management has made its decision--either to optimize existing paper machine clothing or to purchase new product--the best approach to cost reductions differ. Alain Genereux, dryer product manager, AstenJohnson, outlined the strategy for reducing operating costs with the mill's current dryer fabrics. "Two important ways to reduce operating costs associated with dryer fabrics are fabric cleaning and roll alignment. The inspection of dryer fabrics on down days by mill personnel should help determine if cleaning is required or if roll alignment is needed just by looking at the seam distortion.
"As fabrics get contaminated, permeability is reduced and the fabric loses its drying capability, which increases steam pressures. On steam limited machines, this can result in machine speed loss," he continued. "Dirty fabrics can also show a poor permeability profile, causing moisture profile problems in the sheet, especially on single felted positions. If no cleaning showers are available, changing the fabric more frequently would be advantageous on a cost per ton basis. Steam usage is much more expensive than the dryer fabric cost." Running clean dryer fabrics can reduce steam consumption, Genereaux said. He also warned against pushing the useful life of dryer fabrics past their limit, which can result in costly unscheduled downtime.
"A misaligned position in the dryer section will cause fabric distortion/bowing, which reduces the width and result in early removal as the sheet runs outside the fabric. Proper guiding configurations will help keep the fabric running straight on the paper machine as opposed to the fabric running in the frame of the machine or having the guide roll chasing the fabric," Genereaux advised. "If fabric edge wear is noticed, the position and tension of the guide palm should be examined and adjusted to reduce edge wear. If the fabric is wearing in a specific area, inspect the section and look for stationary objects that could be in direct contact with the fabric."
When selecting new fabrics to help decrease overall operating costs, papermakers should look for low air entrainment. "Certain properties within the newer dryer fabric designs offered today provide higher contact area to aid with heat transfer and increased stability to reduce fabric distortion. Additionally, the use of a contamination resistant material in the making of the dryer fabric will also help the dryer fabric stay open longer and make it easier to clean. If abrasion is the primary cause for fabric replacement, a fabric with high machine side contact area will withstand wear much better as the amount of material available for wear increases its resistance to abrasion.
"Also, fabric components should be geared to specific machine conditions for maximum serviceable life," said Genereaux. "For example, if high heat and moisture are present to promote hydrolysis degradation, consideration should be given to fabrics engineered for these conditions; otherwise, clothing value will be compromised."
If you can't get costs any lower, improved productivity can have the same effect on the bottom line. There are several strategies for mills that want to improve machine productivity through better machine clothing operations.
One strategy, according to Baumann of Wangner, is to raise production speed through clothing optimization. "Sheet support binder (SSB) fabrics feature improved drainage performance and gentle sheet formation. As a result, production speed can be increased, at the same or even higher sheet dryness," he said. "However, it is very important to carefully align machine drainage behavior and the fabric. Fabric drainage performance is impacted by a combination of parameters that establish air permeability, as well as fiber support on the free surfaces of the paper and running sides. These fabric characteristics must be closely aligned with paper machine conditions and paper quality specifications." He added that mills can only achieve optimum operating conditions by considering every relevant data aspect.
"Forming fabrics can have a major effect on sheet formation, sheet tests and general machine runnability," said Chase (AstenJohnson). "Most mills are running either double or triple layer fabrics to achieve more consistent formation, drainage and life vs. single layer designs. Matching the specific forming fabric design to machine goals is the key to optimizing machine productivity. Optimizing formation can lead to improved machine runnability and can also positively impact press and dryer performance."
According to John Hawes, global vice president of technology, pressing, for Albany International, "in today's modern press, intimate sheet contact and water removal of approximately 3kg water per kg. of fiber occur. It is therefore critical that the fabric provide a uniform surface for sheet contact and remain open for maximum dewatering. Measuring press section water flow provides important data on press section efficiency while properly designed and maintained cleaning and conditioning equipment will ensure optimum fabric performance."
AstenJohnson's Hedou pointed to press conditioning as one of the best ways for papermakers to get more from their press section. "It is important to study returned fabrics' analyses to improve conditioning can be improved. In most cases, returned profiles are severely degraded because of uneven water and chemical application. This can be improved through upgrading static showers to oscillating showers, increasing overlap coverage or even nozzle maintenance.
"Also, study returned fabrics' analyses for wear patterns," he advised. "A common practice is increasing high pressure shower psi to maintain fabric openness as indicated by vacuum levels. If the analysis shows consistently high levels of fiber loss, it would probably be advantageous to upgrade to a more open structure and reduce shower pressures."
Process belts are another area of potential improvement. "Belts and fabrics have a strategic impact on the major cost drivers on the paper machine, said Peter Slater, global sales and application director, process belts for Albany International. "As the focus moves from fabric life and snapshot measurement of performance, to consideration of total cost of operation, the impact of paper machine clothing will further improve. The supplier, working with his customer, can create exceptional value for papermaking operations."
As a critical contributor to product quality and process efficiency, machine clothing is clearly "wrapped up" in a host of cost reduction opportunities. "It's crucial for papermakers to embrace paper machine clothing as a valuable asset to help in optimizing machine performance rather than simply a cost center," said Steve Cole of Weavexx. "In most cases, evaluating paper machine clothing only on price and life translates into missed economic opportunities."
CHEMICALS 5% ENERGY 18% LABOR 21% OTHER 15% DELIVERY 10% CLOTHING 2% FIBER 29% Figure 1: Costs per ton of paper. Source: Weavexx Note: Table made from pie chart.
WHAT YOU WILL LEARN:
* Machine clothing strategies that can reduce operating costs.
* How to determine and compare cost savings of new clothing and existing clothing.
* Key ways to improve machine productivity through better clothing use.
* "Machine clothing: How do the best mills operate?", by Janice Bottiglieri, Solutions!, January 2004, Product Code 04JANSO70 (go to www.tappi.org and enter product code in search engine).
* "Make the most of shutdowns with machine clothing checks," by Janice Bottiglieri, Solutions! August 2003, Product Code 03AUGSO35.
* "A combined future: Tracking the trends in machine clothing," by Alan Rooks, Solutions!, January 2003, Product Code 03JANSO53.
EDITED BY JANICE BOTTIGLIERI, SENIOR EDITOR
ABOUT THE AUTHOR
Janice Bottiglieri, senior editor of Solutions! and editor of TAPPI JOURNAL Contact her at firstname.lastname@example.org.
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|Title Annotation:||Machine Clothing|
|Publication:||Solutions - for People, Processes and Paper|
|Date:||Aug 1, 2004|
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