Business Situation
Growth in graphic grade papers is recognized primarily in emerging markets, including Asia-Pacific and Eastern Europe. This shift in demand has led to a general migration in production for graphic grade producers as they look to move closer to the localities where growth is high and resource costs are typically lower. Capacity in mature market regions, where costs are at historical highs, continues to shrink.
The implications of this trend are clear – only the most efficient operations will survive in mature markets. In this case study, the papermill was experiencing severe buildup of their coating formula on the after-coater dryer fabrics. The contamination was creating sheet defects that often were not detected at the reel.
As a result, customer complaints were high, risking repeat business for the papermill with their customers. Furthermore, the discovery agreement also identified significant opportunity for improving on-machine efficiency by keeping the dryer fabrics cleans. The increased efficiency would come from reduced sheet breaks and reduced down time for cleaning the dryer fabrics in addition to the reduction in quality rejects previously noted.
Papermill Overview
| Grade: | Coated Freesheet |
|---|---|
| Machine: | NA |
| Speed: | 760 mpm (2500 fpm) |
| Production: | 450 TPD |
| Furnish: | 45/35% HW/SW Kraft, 10% recycle fiber |
| Filler: | 10% ash |
Analysis of Business Situation
Key Business Drivers
- On-Machine Efficiency (OME)
- Decreased quality rejects – dryer "dents" and
- Decreased customer complaints of scale on the sheet
- Improved runnability by reducing after-coater sheet breaks
- Improving sheet moisture profile
- Reduce after-coater sheet breaks
- More production from
- Reduced downtime for cleaning dryer fabrics
Challenge
To achieve improvements in on machine efficiency while reducing the time and papermill resources required to keep the dryer fabrics clean.
Program Design:
Mechanical – HelioJET® water conditioning equipment is used to combine steam and water in a highly efficient (98%+) process to deliver 170°F, 250 psi water to the dryer fabrics. Internal brush showers are also provided, which can be rotated to dislodge any buildup within the showers during predefined purge cycles. The entire cleaning process is managed using a Programmable Logic Controller (PLC) that allows for fine tuning the application as needed to match the level of contamination and to do so in an easy and safe manner.
Operational – The wash sequence consists of a HelioJET® rinse (water only), chemical application with HelioJET® off, soak time and then rinse with HelioJET® shower. The entire system is then purged clear to eliminate any residual dripping onto the sheet. The HelioJET® equipment is properly interlocked with the paper machine to prevent premature cleaning while the paper is on the machine and standard operating procedures are clearly defined and followed during each cleaning process.
Chemical – A neutral degreaser is fed at 10% concentration directly onto the felt. The length of time during which the chemical is applied was adjusted depending on the extent of contamination. An anti-scale product is also fed to the suction side of the HelioJET® unit to prevent scale buildup in the unit and showers during water rinsing.
Key Performance Indicators:
- Decreased quality rejects – dryer "dents"
- Eliminate customer complaints of scale on the sheet
- Reduce after-coater sheet breaks
- Improve sheet moisture profile
- Reduce downtime for cleaning dryer fabrics
Program Results
With the after-coater dryer fabric cleaning technology, the papermill reduced the cleaning cycle time by 37%. The cleaning sequence was completed in 22 minutes from beginning to end. A dense foam is created using the neutral degreaser, but is completely removed with only 10 minutes of rinse time with the HelioJET® showers. Upon completion of the rinse cycle, the fabrics are "virtually spotless" and quality rejects and customer complaints have decreased. Furthermore, the chemical usage was reduced by 75% versus the papermill’s previous dryer fabric cleaning method. Though this papermill did not face VOC restrictions, this result has implications at other papermills with strict VOC limitations. Sheet breaks, moisture profiles, and reduction in quality rejects are also trending positively.
Maintaining the Value
Because the water supplied by the HelioJET® is hot (170°F), it was possible to wash the dryer fabrics while the dryers are still relatively hot, without threatening the integrity of the dryer cans. The program enabled the papermill to quickly wash the after-coater dryer fabrics during a sheet break without chemistry. This "quick wash" is capable of removing significant amounts of coating buildup on the fabrics, allowing the papermill to extend the time between shut downs for cleaning the dryer fabrics. This has been an unexpected, but very beneficial additional benefit to the papermill.
As a result of the success of the program in the 5th and 6th dryer sections, the papermill added two showers to the 4th dryer section. The papermill is now able to clean their entire after-coater dryer with one HelioJET® water conditioning unit. In this respect, the solution is somewhat modular. It is possible to add additional showers to the solution and wash them using the same conditioning unit. Care must be taken in matching the required flows (it is a fixed-flow conditioning unit), but this is a relatively inexpensive way to extend the gains throughout the dryer section on a given machine.
Conclusion
The after-coater dryer fabric cleaning technology delivered significant savings to the papermill in terms of reduced downtime and reduced chemical usage. Product quality was improved and customer complaints have decreased. The papermill is very happy with the flexibility of the program, allowing "quick washes" during sheet breaks as well as complete cleaning during longer shuts. Clean dryer fabrics translated to improved runnability and fewer quality problems. The mechanical - operational - chemical (MOC) approach again delivered significant gains in on machine efficiency, one of the key business drivers for the papermill, while doing so in a safe and easily managed application.
Deposits in pulping and papermaking systems result in lost operating efficiency, excess energy use, off-spec product, increased material costs, and potentially hazardous working conditions. By properly implementing a comprehensive cleaning program, we can help improve the safety of the operations, increase on-machine efficiency, improve product quality, and optimize material costs – contributing to sustainability goals and the bottom line.