Supplier Solutions: Wet end rebuild solutions
July 1, 2004 By Pulp & Paper Canada
The frequency of paper machine shutdowns has been quite significant during recent years. The machines that are left running are constantly being evaluated with respect to the running efficiencies as well as the technology associated with the ma…
The frequency of paper machine shutdowns has been quite significant during recent years. The machines that are left running are constantly being evaluated with respect to the running efficiencies as well as the technology associated with the machine. How to win at the survival game?
Ongoing planning is the key to step-by-step improvements in paper machine operation. Once paper mills reach their dimensional capacity and quality at the best possible efficiency rate, their future does not have to be based solely on static operations. The evaluation of further opportunities is based on earnings and is connected to changes in the paper market, competition, and available technology. Lifecycle management refers to a continuous incremental improvement plan that is implemented to stay competitive.
Top managers in the industry have recently called for asset management of the operating tools, which is understood as healthy capacity development in the paper market. This can be carried out by closing down depreciated and uncompetitive machinery while simultaneously adding new capacity and/ or improving the competitiveness of existing machinery.
The following are examples of various tools developed by Metso Technology Teams for improving existing machine operations, as shown in Table 1.
Analysis of machine bottlenecks
It is essential to identify factors that influence operational bottlenecks by analyzing a machine line’s operating efficiency in the light of operating data. When the market absorbs all of the paper produced, opportunities lie in efficiency improvements. However, the available speed increase is limited since the machine speed is mostly dependent on the design adopted, dimensioned capacity, process technology, and controls. Based on the experience of machine builders, the dimensioned design speed can seldom be exceeded by more than 15% without a major rebuild. The existing drainage capacity also depends on basis weight. It is obvious that revenue from cost-efficient small capacity and quality improvements is of interest to every operation. Additional development work has been completed recently to overcome operational bottlenecks with the help of short payback solutions. Various options for improving machine sections are discussed in the following sections.
Basis weight profiles, including filler profile, residual variation, formation and fibre orientation, are common quality measures for evaluating the performance of a headbox. As shown in Table 2, dilution-based profiling has distinctly improved the profiling precision of headboxes. In this headbox dilution retrofit, a dilution chamber beam is fitted between the existing inlet header and manifold piping beam seen in Fig.1. Moreover, emphasis is placed on a simple design and short installation time. Flexibility in the dilution control application range allows the interfacing of the system to the existing mill environment at a reasonable cost. Pilot results show a response in profile control and sheet stability comparable to the latest dilution control headboxes on the market. In the case of slice control design, the dilution retrofit investment can also be justified by improved broke statistics due to better profiles and faster on quality time at startups and grade changes.
Metso Paper has been the owner of Beloit technology since May 2000. Technology update programs for Beloit machines are being actively carried out at Metso Paper’s pilot facilities in Jyvskyl and Inkeroinen in Finland in cooperation with the Beloit, WI, technology team. The BelBaie III design is a well known standard for a blade gap former, that has in many cases reached limitations to high-speed operation compared to a roll blade former. Because the initial dewatering process is two-sided, most of the paper properties, such as filler and fines distribution, fibre orientation, and thus ink absorption, tend to be two-sided. Jet impingement sensitivity at the jet landing area can also create instability, streaking and spotting of the sheet. Finally, the dewatering capacity is not sufficient in newsprint production at speeds of 1,600 m/min and over. Options have therefore been developed for updating these formers.
Cleanliness and drainage problems at high speeds have been solved by applying a high-vacuum flat suction box before the pickup roll and installing more mist removal capacity on the inner and outer fabrics. This type of an extensive improvement package was successfully installed by Metso Paper at StoraEnso Hylte PM4 in May 2002. Cleanliness and mist problems related to the operation of the former were resolved, and the machine operating speed was slightly increased. Metso Paper’s latest upgrade solution for Beloit’s formers is called the BelBaie V. This is a modest investment solution for overcoming identified limitations without touching the existing headbox. Initial dewatering is improved by a stationary porous shoe placed at the jet landing area. The direction of initial dewatering is fine-tuned with the help of vacuum applied to the porous shoe. The shoe allows a larger fabric convergence angle for good jet impingement and minimized jet impingement sensitivity. The design resembles the OptiFormer forming roll/blade arrangement, but the roll is replaced with a non-rotating shoe. An almost identical amount of initial dewatering takes place in two directions in both applications. The dewatering capacity of the drainage process is unlimited with the new solution. Two-sidedness is avoided and even higher filler contents can be used in the furnish. Combined with cleanliness and mist removal improvements, the former’s lifecycle can be extended to match the latest modern newsprint machines. The first BelBaie upgrade application has been running on a commercial newsprint machine since September 2003.
Wet cleaning for former fabrics
Cleaning water volumes are becoming quite large and former cleaning costs should be critically analyzed against the results achieved. In OptiCleaner Wet, a conventional oscillating high-pressure shower pipe is replaced with a traversing multi nozzle cleaning head. A combination of a needle-type nozzle and a fan-type nozzle first ensures the removal of impurities and then flushes the forming fabric simultaneously. The cleaning head operates against the former on the paper side and against the return roll. The traversing speed is adjusted based on machine speed. The operating principle of OptiCleaner Wet is illustrated in Fig.3 Improved cleanliness with reduced water volumes in fabric cleaning and reduced mist volumes contribute to cost efficiency in former operation, with resulting longer fabric lives. Significant cost savings in clear water consumption are reported from the first application at Kaipola Mill PM7.
Press section rebuilds and improvement
A shoe press is an excellent tool for increasing the marginal capacity of a paper machine. Shoe operation in the third nip position also gives flexibility for lower nip pressure during the dewatering impulse for bulk sensitive grades. The extended nip allows longer nip delay times, and the dewatering capacity is thus much greater compared to a roll nip. Higher web dryness also improves runnability between the press and dryer section. Long belt lives are attained through a hybrid shoe, CD adjustment, and the fixing of belt positioning. Dewatering nip straightness is secured by locking the shoe mechanically in the running direction. The SymPress B solution in Fig.4improves both production capacity and machine efficiency.
Metso Paper has earlier introduced its Transbelt technology in the OptiPress design. This was developed with Albany International to find a solution to a no-open-draw paper machine. The application of this technology to the SymBelt combines gentle dewatering in the third nip with a closed draw design. For bulk sensitive grades, like uncoated paper made out of hardwood furnish, this is an excellent application for ensuring higher bulk in the pa
per and the good runnability of the paper machine.
Quality measurement improvement
Reliable wet end CD moisture measurement has been difficult, if not impossible to obtain in the past. Traditional CD moisture scanners are located at or near the dry end of the machine. Slow, mechanical scanning results in a measurement where CD and MD effects cannot be fully separated. Typically the profiles are filtered which allows for acceptable CD control but short-term variations can not be separated or addressed with traditional methods. Metso Automation has developed a product to address these issues.
IQInsight is an instantaneous, full sheet moisture measurement embedded in the wet end of the papermachine. It gives papermakers a new window into the papermaking process at the wet end of the machine. This was not possible with earlier technologies. Because it provides a full sheet measurement papermakers can now diagnose and correct MD and CD variations with total confidence.
The high resolution infrared sensing array is located in a pressurized CD enclosure extending across the full sheet width. The true CD profile is measured and separated from any MD variations. Spectral infrared analysis is used resulting in a measurement that is very sensitive to sheet moisture and is not affected by sheet temperature, air humidity or drying fabric material.
In this review we have discussed some of the tools currently available for upgrading the paper machine The overall evaluation is based on a line specific evaluation of machine data and design. Machine efficiency, availability, productivity and quality gains are the criteria for the payback evaluation when planning the scope of the machine improvements. The shortest payback for machine upgrades is insured by thorough investigation and by implementing the correct improvement at the proper time.P&PC
Frank Swietlik works for Metso Paper USA in Norcross, GA.
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