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Online fiber and shive measurement enhances quality in chemical HW pulping

älkäjä, Tuomo K Metso Automation, Kajaani, Finland

Jarmo Koskinen, Metso Automation, Kajaani, Finland

Maximilian Furley, Metso Automation, Sorocaba, Brazil

RESUMO ções de um analisador kappa on ódulo de medição, Este artigo descreve as aplica -line que inclui um m ém on ísicas das fibras e de shives. tamb -line, das propriedades f ém de apresentar claramente as propriedade físicas da fibra no final do processo, que é a metodologia Al ódulo mede as propriedades da fibra e a quantidade de shives (palitos) nas fases tradicional, este m ções corretivas importantes. Com esta nova iniciais da linha de fibras onde podem ser tomadas a ção, a operação tem um conhecimento melhor d âmica do processo de capacidade de medi a din ção das fibras e do impacto deste nas propriedades das fibras desde o digestor até à celulose deslignifica ém destas características, possibilidades para diferentes aplicações surgiram com a acabada. Al ção on ísicas das fibras e de shives também nos estágios iniciais dos informa -line das propriedades f ímica. processos de celulose qu ências e observações práticas da medição on ísicas Este artigo mostra as experi -line das propriedades f ção do processo para o seu das fibras e de shives na linha de fibras. O potencial dessa nova informa ósticos e controle da qualidade da celulose é melhor gerenciamento de forma mais eficiente, diagn ível, com um melhor gerenciamento do processo discutido. O potencial retorno de investimento dispon á também mostrado nesse artigo. est SUMMARY

This describes the applications of an online Kappa analyzer which includes also an online Fiber- Shive module. Rather than performing fiber property measurements at the end of the fiberline, which is the traditional methodology, this fiber and shive measurement measures fiber properties and shive content in the early stages of the fiberline where effective corrective actions can be taken. With this new measurement capability, one has a better understanding of the fiber delignification process dynamics and the impact on fiber properties from the digester blow line to the finished . Also possibilities for different applications have arisen with the fiber and shive measurement information from early process stages at the chemical pulp mills. 1

This paper discusses practical experiences and observations of online fiber and shive measurements through the fiberline. The potential of the new process information for more efficient process management, diagnostics and pulp quality control is discussed. The potential return on investment available by better pulp quality and process management is also under discussion.

Palavras Chave:

ções das propriedades físicas das fibros, vesos Medi Key Words:

Fiber measurement, vessel cells

1 INTRODUCTION

A major challenge today is to run a fiberline cost effectively and, at the same time, preserve the fiber quality properties as fully as possible. Management of fiberline processes has become more challenging with increasing throughput, sophistication of the process equipment and the wide variety of fiber species with their own specific response to chemical and mechanical degradation and pulp quality. With online fiber property measurements, process management becomes easier and more effective as quality targets can be achieved with lower energy or chemical consumption without damaging the fibers. Finding the optimum level for fiber processing is impossible without information about the process conditions and how they affect the quality of fibers and pulp. This optimum level can only be achieved by controlling the process with accurate and frequently updated information.

The Fiber-Shive module gives statistically more representative and accurate information than the previous online fiber property measurements. Rather than a sample size of thousands of fibers in previous generation analyzers, the new Fiber-Shive module analyzes tens of thousands fibers. Since it can measure fiber and shive properties from the blow line onward, this measurement reveals the magnitude of ’ impact on pulp and fiber quality at various locations. Fiber and shive analysis also indicates the process developing problems with process equipment. The fiber quality information at an early stage of pulping helps pulp makers to find ways to produce more uniform pulp and fibers with higher potential. In addition, the development of different fiber properties for tailor-made paper products can reduce raw material costs at mills using different fiber fractions of pulp for different end products.

This study has been focusing on the applications with chemical pulping processes with eucalyptus. The increasing eucalyptus kraft pulping around the world has been giving new possibilities for paper manufacturers, but it has also brought new problems to some paper mills. The short and narrow fibers of eucalyptus kraft pulps give a unique combination of formation, strength and opacity in papermaking, but larger fines content and the vessel cells have been causing trouble in the paper machines and printing houses. 2

Hardwoods (HW) contain a significant portion of short, large diameter cells called vessel elements through which sap is transported [1]. The size and number of vessels vary strongly from species to species, and with tropical HW species there are more and bigger vessel cells than average HW. Wide vessels are unwanted at printing houses because those large vessels cause more vessel picking [2] and the lesser content of those is desired.

Vessel picking is a phenomenon where the hardwood vessel elements in the paper surface tend to be picked off by the ink-tackiness of the printing press, creating white spots in the printing surface. This problem is nowadays usually tackled by refining at the paper mills. For the paper manufacturer the most important information about the vessel cells are the amount and the dimensions of them. According to recent studies, increased vessel content also correlates with lower strength properties [3], so paper manufacturers have many reasons to deal with this issue.

Other topical issue for paper manufacturers is the fiber deformations. They are not natural on fibers, the pulp and paper manufacturing processes create them. Fiber deformations may reduce individual fiber strengths, but they are important to promote bulk and absorbency properties in paper dry sheet. Many factors affect the tensile and internal strength of pulp, such as the interfiber bonding degree, fiber strength and moisture content [4] and so on. But also fiber morphology plays an important role in determining the final strength of paper, because mechanical treatments such as refining and handling of chemical pulp fibers introduce curl, kinks and microcompressions to the fibers, which affect the tensile strength of the final sheet.

Continuous online fiber and shive measurement creates possibilities to tackle these issues and helps pulp and paper manufacturers to make more uniform and increased quality. This increased quality can easily be transformed to price increases. 2 ONLINE FIBER AND SHIVE MEASUREMENT WITH KAPPA ANALYZER kajaaniKAPPA Q is a modular kappa and brightness analyzer, with measurements selectable according to customer needs. Sampling devices provide samples from the process pipeline and up to 16 sample lines can be connected to one analyzer. The device also contains a sample collector which parallel samples can be collected for subsequent laboratory analysis. Fiber-Shive module measures fiber dimensions (fiber length, width, coarseness, etc.), fines, vessels and their dimensions, fiber deformations (fiber curl and kink index) and shive content. Shives can also be separated to different subgroups, depending on the need of the shive applications.

2.1 Measurement technology

The basic idea of the method is simply to measure only the amount of light received by the camera imaging cell. Because of using scattering optics, almost 100% of the light is scattered from or absorbed by objects in its path and only the light traveling directly into the optics will reach the camera. The amount of light that does not reach the camera equals the shive particle area (figure 1).

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Fig 1 - Fiber and shive measurement principle.

This kind of a method is especially applicable in determining the length and width of an object whose biggest dimension (length) is mapped on at least a couple of pixels. The smaller dimension and thus the whole shape can be accurately determined even if the corresponding dimension covers only a fraction of a pixel in the image.

The combination of the optical devices, measurement principle and highly specialized algorithms has been designed in smallest details to serve optimally the target of accurately and quickly detecting and classifying different types of particles in pulp according to their size, shape and particle types. Subpixel accurate particle size determination enables high measurement resolution resulting in ability to identify also very small differences in particle dimensions. Speed optimized software on the other hand makes it possible to measure a big amount of pulp from each sample which is a definite requirement of high repeatability when the shive content is not high. With a creative and analytical approach the algorithms have been tuned to identify and separate all different types of particles seen on the taken images (figure 2).

– Figure 2 Fiber and vessels analysis image from the analyzer

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3 RESULTS AND DISCUSSION ’s Fiber KAPPA Q -Shive module has been providing results at different mills. The module has been on active use on both bleached and unbleached pulp manufacturing mills. The results from both types of mills have showed that the analyzer can be used for many different applications, which have been tailored for different customer uses. The module has provided possibilities for both direct and indirect savings with increased quality, productivity and energy savings.

The functionality of the Fiber-Shive module in real life industrial environment has been confirmed also by some integrated pulp and paper mills. Mills have tested the accuracy of the measurements by comparing the results of the analyzer to the laboratory results. The accuracy of fiber properties have been tested against the laboratory fiber analyzers and shive content was compared with the Somerville laboratory test ≈ and the correlation coefficients were really good (R2 0,87) (figure 3). These accurate and reliable measurements serve as a ground layer for many different applications and control solutions.

– Fig 3 Excellent correlations with the fiber properties in the chart and very good correlation with shives results displayed at the graph

3.1 Fiber-Shive offers many solutions for vessel picking problem

Fiber-Shive module offers many possible solutions to tackle the vessel picking problem. The basic solution is to offer information about the vessel cell content to the paper manufacturers. As the amount and the dimensions of vessel cells vary, this information can be offered to the customers for every production lot. The information from the fiber analysis is fed to the mill DCS or QCS and results can be easily distributed to the customers who want this information. This way the paper mills know exactly what kind of pulp they get and they can treat it properly and efficiently. Paper manufacturers can now deal with vessel picking problem with accurate information.

Fiber-Shive module also gives another easy possibility to prevent vessel picking as it also measures fiber deformations. Fiber deformations are known to deteriorate the fiber network structure. This information 5

gives possibilities to run the process optimally with minimal fiber damage and therefore increase the fiber bonding. Increased Z-directional strength of the pulp generally decreases the amount of picked vessels because vessel cells are bonded tighter in the fiber network [5]. This makes it possible to reduce the vessel picking problem with continuous fiber measurement information.

The more sophisticated solution is to tackle the vessel picking problem once and for all at the pulp mill. With tropical HW one possibility to remove vessels is centrifugal cleaning before drying machine [6, 7]. Continuous online fiber measurement gives a possibility to adjust the reject levels of the hydrocyclones by vessel cell content and size information from earlier process stages and to remove vessel cells efficiently – and with minimal yield losses - from pulp stream before they get to drying machine.

Eucalyptus (E. globulus, E. grandis) vessel cells do not cause so much picking problem if they are refined properly (with HC refining) [5]. Vessel reject stream from the centrifugal cleaning can be refined separately and then refined pulp can be returned again to the fiber line. This way the yield is not compromised and at the same time pulp mills get leverage to increase the customer price. This reject can also be burnt for energy, but this method decreases yield. In addition, vessel removal also increases the strength of the fiber network and therefore the pulp has increased strength properties [3].

3.2 Shive measurement functions as an insurance for the screens

A worn or partially broken screen basket will cause unsuitable material to pass through screening. In a high capacity pulp mill the loss of production could be substantial. It is possible to set different screen accept lines as sampling points for the Fiber-Shive analysis and continuously compare results to the preset accept levels. Harmful levels can be detected with Fiber-Shive module before an extensive amount poor quality pulp that needs to be compensated later in the process passes through screening.

Reject levels of screening can be optimized when the process is running smoothly and shive content is low. After that screening can be adjusted when the shive content increases. This generates savings by increasing yield and these savings can be achieved with online shive content measurements. 4 CONCLUSIONS

Online fiber and shive measurement enables mill to optimize their processes with increased flow of accurate and continuous information. Many different applications can be tailored depending on the needs of the mill, providing both direct and indirect savings.

At the tropical HW mills these measurements give possibilities to prevent the vessel picking problem. With continuous vessel cell information it is now possible for the first time to take action against vessel picking – problem efficiently at the beginning of the customer chain at the pulp mill. The results give also tools for more uniform quality, possibilities to increase the quality of the product and brand their pulp and to improve the competitiveness of the mill.

Shive measurement can be used to control the screening process very efficiently. Continuous shive measurement gives almost instant information about wrong kind of accept of screening.

This online fiber and shive measurement does not only provide possibilities to increased quality at the pulp mills. It gives a new perspective to look at the whole pulping process and accurate information to improve the pulping process through the whole fiber line.

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REFERENCES

1 Paavilainen, L. Fiber structure, Handbook of physical testing of paper, Marcel Dekker Inc., New York, USA, 2002

2 Gopichand, K. and Maheshwari, S. Vessel picking of printing aproblem in need of greater attention. Ippta. 2(1) – 3 Blomstedt, M. Modification of cellulosic fibers by carboxymethyl cellulose effects on fiber and sheet properties, Helsinki university of technology, doctoral dissertation, 2007 öm, T. Influence of shrinkage and stretch during drying on paper properties. Pap. Technol. 41(6) 4 Wahlstr

5 Panula-Ontto,S. et al. ,Evaluation of vessel picking tendency in printing. 3rd ICEP International Colloquium on Eucalyptus Pulp 2007, Belo Horizonte, Brazil

6 Ohsawa, J. et al., Prevention of vessel picking trouble in tropical hardwood pulps II. Vessel separation and high consistency beating. Jpn. Res. Soc. 30(9)

7 Jopson, N., Coping with hardwood vessels. PPI vol. 47(11)

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