Three featured case histories show excellent results for linerboard and corrugated medium mills
June 2008
By Laura Copeland, program manager, Board & Packaging Grades, Nalco Company
Today’s papermakers continue to be exposed to a number of changes in market dynamics that force them to respond quickly in order to remain competitive. Costs for energy, fiber, maintenance, environmental compliance and additives have continued to rise, which has put increased pressure on margins and the return delivered to stakeholders. There continue to be capacity additions in emerging markets that have introduced new production into global markets. The implications of these market dynamics for the papermaker have been an increasing need to perform efficiently and effectively.
Papermakers may experience any number of issues, including early, rapid drainage, issues with couch vacuum, and low press solids. All of these and many other issues with dewatering lead to lower paper machine efficiencies and can be detrimental to operational effectiveness. Nalco’s Three Dimensions of Dewatering approach delivers mechanical, operational and chemical (MOC) tools to address papermakers’ needs within the different machine zones listed in Table 1.
The Forming Zone
The forming zone indicates the early part of the paper machine before the sheet is consolidated. This is the place where retention, drainage and formation (RDF) occur and are made. Traditional RDF chemistries such as coagulants, flocculants and microparticles play an important role in dewatering for the forming zone. However, chemistry is only one part of the approach, as many operations incorrectly apply the same wet end chemistry as sister machines making like grades when the former type and setup calls for something totally different. Examples of mechanical and operational items to audit include the table layout, free drainage versus vacuum drainage split, and the headbox jet delivery. The key to improving operational effectiveness is to apply the appropriate MOC tools together to maximize fiber yield, speed, formation and desirable sheet characteristics without compromising any of these key drivers.
The following examples are two cases where understanding the forming dimension and utilizing the MOC approach have demonstrated results:
Example 1: Oversized fourdrinier with excessive early table open area: The correct retention tool was matched to deliver optimum formation and was the key to eliminating first dryer section stickies deposition and setting new machine records.
Example 2: Improving BelBond top wire performance. The correct drainage tool increased retentions and slowed dewatering, which resulted in record speeds while maintaining strength.
|
| Dimension |
Description |
| Forming |
The early forming zone on the machine before the sheet is consolidated. |
| Consolidation |
The sheet is already consolidated but can easily be disrupted and destroyed if dewatering is too aggressive. |
| Pressing |
After the sheet leaves the couch where the goal is maximum sustained press solids along with the best sheet profile possible. |
The Consolidation Zone
The consolidation zone is the area where the sheet is already consolidated but can easily be disrupted and destroyed if dewatering is too aggressive. Several chemical tools for this zone of the paper machine exist that complement the gentle vacuum induced dewatering profile that is desired in this area. These include hybrid polymers, amine polymers and cationic micropolymers. A new technology designed to improve the consolidation zone control is Nalco’s ELLIPSIS™ cationic micropolymer technology. In addition to the chemistry, mechanically and operationally it is important to thoroughly understand what vacuum source is available to which vacuum unit and what the vacuum capacity is.
Maximizing dewatering and consolidation while minimizing fines stripping and loss of yield are the goals of the programs for this area.
The Pressing Zone
Simply stated, the pressing zone is the area of the machine after the couch roll, before the dryer section. The goal here is maximum sustained press solids along with the best sheet profile possible. A limited number of press dewatering technologies are available and effectively applied as machine direction (MD) and cross direction (CD) water management programs designed as fabric care technologies.
A new technology in this area has evolved as part of Nalco’s METRIX® productivity and strength technologies. These new press dewatering agents are designed for specific press operations and deliver press solids independently of other common press dewatering improvement tools (Figures 1, 2). Commonly, a papermaker would work to enhance the formation of the sheet to improve couch solids and thus overall press solids. The newest press dewatering tools give better press solids independent of couch solids. When used in combination with other pressing zone tools such as fabric type, press configuration, ingoing and outgoing press solids and press loads, the operational control box of the press has proven to be expanded.
Improved Operational Effectiveness
In this section, three case studies that delivered significant gains to the papermaker through the use of the Three Dimensions of Dewatering approach will be featured. While a few specific technologies are highlighted, these are just a few of the retention, drainage, formation, pressing and cleaning technologies that can be used to improve operational effectiveness. In these case studies, a pattern will be clear. All start with a MOC audit followed by multi-component programs for the papermaker to utilize to meet their goals. This is the heart of the Three Dimensions of Dewatering approach.
Case Study 1: In this example, a 1,200-tonne/day, 100% recycled linerboard producer needed to respond to an increase in customer demand for a heavyweight grade of paper. To meet this demand, a 6% production increase was required. In addition, the mill wanted to eliminate the over weighting required to meet sheet strength specifications. Due to the nature of its recycled furnish, the mill was required to operate refiners at maximum loads and add an additional one pound of basis weight to achieve strength specifications. This refining level caused excessive fines buildup in the white water system, causing drainage issues and ultimately reduced machine speed.
Following the Three Dimensions of Dewatering approach, Nalco completed a machine audit, and a number of MOC options were discussed with the mill. A multi-component program was recommended that consisted of a retention aid, Metrix productivity and strength technology, and adjustments to refining, starch dosage, and chemical feed points. This program was designed to optimize fines retention and stock freeness while increasing strength. The results were increased Mullen by 15%, increased reel speed by 125 ft/min and production by 6% (Figure 3), and reduced basis weight by 1.5 lbs. This increase in production allowed the mill to meet increased customer demand for this finished product.
Case study 2: In the next example, a 500-tonne/day corrugated medium machine using 100% recycled fiber expressed an interest in dry strength and on-machine efficiency (OME). Additional discovery work revealed a Three Dimensions of Dewatering approach was needed. A thorough machine audit was completed and a MOC solution was designed:
• Mechanical: Nalco and the forming blade designer worked with the customer to alter the blade angle and open area in the forming section to control early dewatering.
• Operational: Nalco and the customer worked together to improve standard delivery setups (L/B, rush/drag) by grade.
• Chemical: Two Nalco chemistries were needed to control dewatering in both the forming and consolidation zones. These chemistries were designed to increase drainage and strength.
By implementing the MOC program and focusing on the Three Dimensions of Dewatering, the mill was able to reduce breaks by 25% and reach record production levels. As a result, OME improved by more than 2% and throughput increased by 35 tonnes/day. The value delivered to the mill after the cost of the program was more than $700,000/yr. The success has led to a partnership and an evaluation of additional solutions to improve efficiency, finished sheet performance, and the overall performance of the machine.
Case study 3: In this final example, a 930-tonne/day linerboard machine running 100% recycled fiber wanted to reduce its dependence on natural gas while increasing production, improving strength and lowering basis weight. Of primary importance in lowering natural gas consumption was the elimination of the mill’s size press. Past attempts to shutdown the size press had resulted in an inability to meet strength specifications and an increase in rejected board. Nalco worked with the mill to complete a MOC audit, and from this data, options were presented to improve strength and production while eliminating the need for the size press.
Nalco implemented a new multi-component Three Dimensions of Dewatering program that included a new retention aid chemistry and Metrix productivity and strength technology. At this point, operators made a number of operational changes to reduce basis weight and maximize productivity. For example, water was added to the headbox to convert increased drainage into improved formation, and changes were made to the refiners to improve performance. Also, starch, alum and retention aid feedpoints were optimized. The results of this MOC program were a 2.5-lb decrease in basis weight, a 130-ft/min increase in machine speed, and a 4-tonne/day increase in production (Figure 4). In conclusion, the mill was able to achieve its goals of reduced energy consumption, increased strength and lower basis weight.
Conclusion
Papermakers face various dewatering problems through the forming and press sections of their machines, including rapid early drainage, poor machine profiles, high couch vacuus and low press solids. Nalco’s Three Dimensions of Dewatering approach allows papermakers to achieve improved operational effectiveness and finished product performance through a mechanical, operational, and chemical approach to MD and CD water management.
Laura Copeland is program manager, Board & Packaging Grades, Nalco Company, Paper Services Division. Special thanks to Jim Thomas, industry development manager, James Chavers, Principal Consultant, and Brad Benz, industry technoechenical Consultant, Nalco Company, for their contributions to this article.
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