BY JAMES OWINO
The paper sector has as fundamental issues like the high productivity, high operational efficiency (no losses, no problems, no breaks, no stops, no nightmares), the low production costs and the uniform quality in the process and products. It is important to mention that all papermakers have these basic physiological needs, no matter the paper is being made, or the paper-machine being used. For achieving these targets, the raw material must be as uniform as possible, with characteristics in a narrow range of variation in order not to cause strong impacts in the papermaking process and paper qualities.
To tame this variability, the paper mill engineers are used to control a number of pulp quality parameters. However, many times, the selected portfolio of pulp quality specifications does not give a previous idea or a predicted behavior and performance in the pulp utilization, neither in the operation nor in final paper product quality. When the paper maker asks for uniform pulp, he is not making a request only for brightness, brightness reversion, viscosity and cleanliness. He includes here a number of pulp quality parameters that are very important to his conversion process. His objective is to have a papermaking operation with the minimum variability, without undesirable surprises. The final paper quality must be uniform and within the specification limits, and the losses along the process should be as minimum as possible. When standardization in the pulp intake is demanded by the paper mill manager, he is first trying to guarantee a raw material that may perform well in the paper-machine operation (machine runnability and efficiency).
The second important objective is to guarantee in the manufactured paper the quality specifications his customers are demanding. Since fibrous raw material performance behavior is difficult to be measured or predicted, the paper mill manager requests the help from the laboratory chief to perform what is called the “management of peripherical pulp quality specifications”. He needs a number of selected data to help him to justify the problems he may eventually have when the machine run ability is poor, or the paper quality specifications are not being reached. When a uniform pulp intake is guaranteed; refining, chemical additions, sheet drainability, energy and steam consumption, web consolidation, and paper strength/physical properties do not sharply change and the paper process runs smoothly. The process and product qualities are more easily achieved. In an attempt to control some of these pulp quality parameters, the laboratory evaluates pulp brightness reversion, pulp cleanliness, pulp viscosity, pulp conductivity, pitches content, and performs some beating runs. The first and important goal is not to have sharp variations in the general pulp properties.
Brightness, brightness reversion, viscosity, cleanliness, ash and mineral contents, and beating performance are the key issues in these “peripherical quality specifications. The complementary pulp quality parameter is the moisture content. The papermaker does not want to pay more to the pulp he is buying than what he considers to be fair and right.
The second type of management that the mill manager wishes is the variability control. The “management of pulp variability” tries to guarantee a narrow variability in the pulp and its consequences. The variability is also measured indirectly, by watching the paper-machine behavior and performance. When machine works smoothly, without breaks, at pre-settled speeds, and the quality specifications in the final product are met, the process is said to be controlled, and variability has been tamed. When problems start to happen, the usually first accused is the pulp quality.
Management of peripherical quality and management of pulp variability are really basic physiological requirements in any paper mill.
The mill manager needs to have these exigencies fulfilled to go further in the next type of management: the “management for product differentiation”, or “tailor making orientation in the manufacture of products”. This type of management requires substantial changes and offers important challenges to the paper mill personnel. The changes may happen in pulp quality (for example: long fibers and short fibers blends), pulping process conditions (for example: ECF or ECF-Light bleaching sequences reflectingon AOX and/or OX pulp contents), or even others
recently added qualities (certified or non-certified wood in the pulp).
Differentiation of paper products is more easily achieved in mills with more than one paper-machine. This means that the mill may run each machine with a differentiated product, without experiencing the usual troubles with transitions from one product to another using a single paper-machine. Anyhow, the tailor making concept will only be winner when the paper maker has guaranteed the two first mentioned types of management: peripherical pulp quality
specifications and variability plus machine performance.
It is very simple to say, but very difficult to understand and to implement. For this reason, many conflicts and misunderstandings are frequent among the commercial, production and product innovation areas in a paper mill. Each of these areas has its own needs and dreams about product uniformity, product uniqueness, and product differentiation. In most of the cases, each area has difficulties to understand the other side’s position. As a result, few paper mills have products that may be said completely differentiated in their products portfolio.
Most of the paper manufacturers aim to have a single product, as uniform as possible, with the minimum cost and maximum in productivity and in operational efficiency. Having in mind that the behaviors, needs, commitments and purposes are different, what is really important to promote a culture for tailor making in paper manufacturing?
What is important to be managed? How to do this? What properties in the pulpwood may be successfully controlled to offer differentiation in paper products? What are the most important pulp parameters that the mill manager, commercial director and the R&D manager care about?
In integrated paper mills, the paper product differentiation may be built at the forest, at the pulping process and/or at the paper machine. At the forest, it means to segregate the different wood and to cook the different types separately (for example: high and low wood basic density).
At the pulp mill, the differentiation may be achieved taking advantage of the different opportunities the company may have (different bleaching lines, different digesters). Finally, at the paper mill, the different products may be also obtained by different pulp furnishes, involving blends of different pulps (produced onsite or purchased).
In integrated paper mills, it is very common the need to purchase some dried pulp in the market, to facilitate drainage in the wet end. Dried pulps have much better drainage than never dried pulps, because they have substantially lower Water Retention Values. This offers a good opportunity for fiber blends and to improve the product portfolio. In case the company may eventually have difficulties to handle different types of woods coming from forest areas that are not very close, one recommended solution is to work with a single, flexible and uniform wood supply, and to differentiate pulps and/or papers in the mill, not in the forest.
The objective is to select and to develop trees with a broad wood and fiber characteristics and relative concentration on wood components (lignin and hemicelluloses). These trees should be able to provide optimum combination of pulp and paper properties (beyond pulp yield) according to different market segment demands. The wood is improved to provide better pulping attributes. The uniformity and flexibility on wood supply is reached by controlling genetics, species, age, silvicultural practices and forest environments. At the pulp mills, utilizing the different fiber lines the company has, differentiation is defined to supply targeted markets and customers.
It is relatively difficult to say what is the single most important pulp characteristic for a given paper mill.
The reason is that there is no universal pulp property to be managed. Depending on the paper mill bottleneck, the pulp quality is defined to guarantee the maximum performance to this mill. The most common bottlenecks are: refining capacity, drainage and retention in the wire section, paper-machine speed, steam availability, wet web consolidation and strengths, final product uniformity. As a conclusion, it may be said that the type of mill bottlenecks will define the most desirable pulp quality, up to a certain extent.
This is the case for existing mills. For new greenfiend mills, the quality may be previously built and designed, before the construction of the paper-machine and auxiliary equipment’s. However, soon the mill starts up; the bottlenecks will appear to define the new pulp quality standards. This is the reality, no doubt about. This is also the cause for domestic conflicts within the company.
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