Seka's PM at the Kastamonu mill has been producing cigarette papers since1984. But like many older units, market demand shave forced a revamp

by Halil Sönmez, Ludwig Bülow and Rainer Maurer

Adding a modern dimension at double the output

No matter what grade of paper a mill is producing, there usually comes a time when machine efficiency or market quality expectations force management to reinvest or face a gradual process of dwindling profits and leaner market opportunities. In the case of the Turkish producer, Seka (Turkiye Seluloze ve Kagit Fabrikalavi), it was a combination of both of these factors that led the management team to embark on a major modernization program at its Kastamonu mill, situated near the Black Sea.
The Kastamonu mill started up as a greenfield mill back in 1984, using hemp to produce cigarette papers for Turkey's state-owned cigarette suppliers. The equipment became dated over the years and increasing demand for more luxurious cigarettes meant that the company's market share was under threat from higher quality imports.
In response, Seka set about looking for a partner that could provide overall consultancy and design experience, as well as the necessary equipment and technology know-how in cigarette paper manufacturing. PJ Wolff & Söhne based in Germany eventually took up the challenge and was duly appointed to analyze all aspects of the mill's operations, including raw materials and chemical usage.
The mill layout is based on a Jaakko Pöyry design and the basic process begins with the preparation of the hemp before the material batch cooking in the pulp mill. The hemp fibers undergo continuous washing, cleaning, cutting and refining before the furnish is delivered to a 3.7 m wide paper machine and finally cut and packaged in the finishing department. Based on its initial studies, PJ Wolff identified several bottlenecks in the system and made a series of recommendations for technical modifications and upgrades that would provide Seka with the most economically advantageous returns. As a result, a number of proposals were made to improve both the quantity and quality of the end product, and Seka used the report to draw up the contract documents that would form the basis of a major mill upgrade. The main areas identified for modernization were as follows:
• hemp fiber cutting
• pulp cleaning
• stock preparation
• approach flow system
• paper machine
• finishing department
• on-line quality control
• laboratory services.
In addition, Seka also required that operator training would be undertaken by the suppliers involved over the installation and commissioning period as part of a technology transfer arrangement.

Seka accepted PJ Wolff's plans for the modernization and the supplier was appointed to lead the turnkey installation, commissioning and optimization of the rebuild. Among the most challenging targets involved in the rebuild were that the output had to match the technical standards of the world's leading cigarette paper producers and at the same time increase production by 100% to 12,000 tons/yr.

Getting to work

The project was divided into three sub-stages. The first was the modification of the hemp cutting, pulp cleaning, stock preparation and approach flow systems, while the upgrades to the paper machine and the finishing department accounted for a separate part of the overall project. The last element of the work involved the installation of an on-line Measurex MXOpen quality control system.
The first part of the work had to be designed with the specific requirements of hemp processing in mind. Hemp is a very long fiber - approximately 20 mm - and raw hemp cannot be cut sufficiently before cooking. So after washing and bleaching, a beating process is required to cut the fibers. To increase the beating performance and to reduce knife abrasion in the stock preparation lines, the pulp must first be cleaned. This is vital for hemp pulp as the fibers have a tendency to spin and wrap the equipment. The solution was to install a high density cleaner, but process the flows at low density - around 1% consistency in this case. A drum thickener then follows to achieve the required consistency. The beating stage follows after the hemp stock tower, using two chests working in batches in conjunction with a Claflin refiner.

Four to one

Stock preparation at the mill operates in four lines. Two are used for long fiber with a cycling system incorporating a Claflin refiner and a disk refiner. Another line processes the short fibers (mainly eucalyptus) and the fourth is provided for broke. The four fiber lines are connected to the mixing tank along with the filler line, which has regulated consistency and flow control. The mixing system contains four storage chests and a small mixing tank. It also has flow control and a ratio regulator.
The total consumption of stock and filler is controlled by means of the tank level and the bone-dry ratio. The porosity sensor of the quality control system at the paper machine allocates change requirements. To raise the porosity, more short fibers are required, and vice-versa. Any adjustments that are needed are first made by varying the load of the conical refiner after the mixing system. If this is out of range, the composition of the mixing system is changed.
To reduce MD (machine direction) variations in the paper, it was necessary to modify the approach flow system. As a result, there is only one dilution step in the current set-up and the cleaners work at lower consistency with much better results. After the cleaners, a damping tank was installed to ensure a constant flow, free of pulsations. A fan pump runs at high revolutions and flow regulation is carried out by means of a valve setting in the main line. A new pressure screen together with modifications to the silo, the recirculation pipe and the piping, has created a smooth pulp flow to the headbox that is free of air and pulsation effects.

Mostly new

The paper machine was rebuilt in some areas, but many of the major components were completely replaced. Given the rather high ash content (25-30% filler) and the formation quality requirement, a PJ Wolff Z 15 WZ headbox with rectifier rolls was chosen to replace the previous unit.
The discharge width is 4.2 m and because there is little variation in the machine speed, the supplier designed a manifold distributor system without dilution control. Instead, the headbox is equipped with an overflow and automatic slice lip control. The design meant that very few spindle adjustments were necessary during the startup. The total head in the unit is controlled by air pressure, while a level controller in the overflow tank regulates flow. The machine operators can adjust the overflow, but it is normally regulated simply by the machine control system.
A new forming board was added to the wire section, while all the dewatering elements were equipped with ceramic surface and vacuum control was installed in the flatboxes. But the main change in this section was the new design for the dandy roll as well as a slightly altered position of the dandy.
Within the press section, the bottom rolls of the first and second press were covered with polyurethane, blind-drilled and grooved. New swimming rolls on the top position of the second press and the marking press also helped to increase dryness and strength.
Another element of the works involved equipping the size press with two separate applicator rolls to bring burning salt into the paper, which reduced the risk of holes and web breaks in the cigarette paper. When using starch for the tipping paper, the size press works with a swamp. The existing hard nip calenders were replaced by heated steel rolls on the top and polyurethane covered swimming rolls on the bottom position.
The steam and condensate system was also reconfigured into a cascade system, with low heating of the first cylinder section to avoid fiber picking and reduce steam consumption. In fact, after the alteration the overall steam consumption could be kept almost constant at almost double the rate of paper production.

Finishing off

In the finishing department, two new Geobel Optima slitting machines were installed to cope with the increased output. Two new Baasel laser perforators were also installed for the perforation of the tipping paper.
In the other main part of the upgrade, the quality control system was provided with two scanners, one in front of the pope reel and the other one at the size press. This system enabled Seka to measure parameters such as moisture, basis weight, ash content, opacity, porosity and formation. The results are not only used for the control of the basis weight and the cross profile, but also to regulate the fiber composition and refining adjustments.
Now that all the modifications have been completed and the mill has had a chance to optimize the process, it is clear to see that both the quality and the quantity have been increased dramatically. Machine speed went up from 160 m/min to 310 m/min for a basis weight of 25.5 g/m and the MD and CD basis weight profiles on the machine vary by less than 1%. The coefficient of the porosity variation is below 7% and all the other main parameters are within internationally accepted standards.
Added to that, the mill team points out that a more even run has made the machine quieter, as well as delivering a smoother product. The Seka staff at the Kastamonu mill are also more than satisfied with the lower web break rate, which has resulted in less broke and greater all-round efficiency.

Halil Sönmez is Seka's managing director. Ludwig Bülow is project manager at Wolff & Söhne and Rainer Maurer is consulting engineer for the same company

Table 1 - Target Tolerances for the Cigarette Paper