By A PPI Special report
BRUSSELS,
April 29, 2009
(Viewpoint) -
The choice between batch or inline technology for chemical and coating color preparation is usually made according to the type of product to be manufactured. In the case where the product is standard and required in high-volume applications, the continuous technology is adapted, whereas in the case of a large formula range with low-volume applications, batch production is more suitable. Nevertheless, the choice is not so obvious.
To meet paper mill owners’ needs of large-throughput and high-speed production, Cellier Activity of ABB France has developed solutions for the continuous preparation of chemicals and coating color. Continuous solutions can now deal with the production versatility and offer many advantages with respect to today’s concerns of paper manufacturers: lower investment and maintenance costs, process stability and product quality, reduced energy consumption, etc. The following solutions are perfect examples.
Continuous dispersion
Implemented for the dispersion of mineral pigments or fillers (GCC, clay, talc, PCC), the continuous dispersion line has applications in the stock preparation and color preparation. It includes a pre-mixer, an inline mixer and a slurry storage tank working at a constant level. The flow-rate follows the paper machine needs. The product solid content is measured on-line. The maintenance time is included in the 24 hours/day operating cycle time. The inline mixer provides for an intensive mixing at high repeated shear rates. It ensures an improved product quality: the dispersion is finer, stable and free of agglomerates.
This technology, compared with a batch solution, can be profitable. The investment cost is reduced by 30%, mainly due to the reduced equipment size. The operating costs are lower: power consumption is reduced by 70% and the system requires less maintenance.
Starch jet cooking
The solutions offered by Cellier for the preparation of native, modified and cationic starches are based on the technology of inline starch cooking. The main features are:
• Jet cookers with innovative design for efficient direct steam injection and easy tuning of flow-rate and cooking temperature
• Thermal heating of cationic starch for wet end application.
• Enzymatic conversion of native starch followed by inhibition for sizing and coating color preparation.
Jet cooking ensures an improved quality of the starch solution. The cooking is thorough and uniform. The heating efficiency is total due to direct steam injection (no heat loss in the atmosphere) and equal whatever the starch type (potato, tapioca, wheat, maize, etc.). An accurate temperature control and the modulation of steam provide for a stable operation even with variable flows and pressures (low pressure drop, no hammering). This also enables the flexibility and throughput control according to the paper machine consumption.
Because of reduced power consumption and automated cleaning sequences, operation and maintenance costs are very low.
Considering the increasing and fluctuating purchase price of modified starches, paper manufacturers have a growing economical interest in installing their own starch preparation units.
The benefits of inline starch cooking help paper manufacturers overcome the uncertainty concerning the availability of raw materials because the unit is capable of handling all types of starch, even low cost ones without loss of quality. They secure their process by producing tailor-made slurry adapted to the required paper grade.
Re-inventing the coating kitchen
There is no need nowadays to be made aware of the costs of non-quality. A better control of the quality of a continuous coating process can be understood from two points of view:
• Control of the drifts in continuous operating mode
• Control of the production changes.
For several years, there have been reliable techniques for inline analysis of quality criteria for coated paper. These systems offer the possibility to react and to automatically adapt the process to different inline measures.
Combined with inline systems measuring the paper characteristics (whiteness, gloss, shade), a reactive kitchen must offer the possibility to modify the formulation to reach the required quality grade. Hence, production changes are quicker, less risky, without losses and cost effective. To guarantee this reactivity, stocks and wasted volumes must be reduced to a minimum up to the coating head.
Cellier has designed a new type of coating kitchen in order to obtain a great flexibility in the formula percentages as well as a significant reactivity regarding the inline formula change.
The reactivity of this equipment contributes, once again, to the general objective by reducing the manufacturing costs and by securing the margins.
Papcel control
Papcel is a supervisory system that is capable of managing both batch and continuous operations. If the batch is known to bring flexibility, the continuous approach reacts more quickly to the paper machines’ needs. The expertise in this field, to equal batch technique, is to know how to manufacture concentrated product or to deal with formula variations, while generating the lowest volume of intermediate quality. The inline quality measurement of the product always helps to detect any unexpected deviation or disturbance and to correct accordingly. Reports, displays, terminology are affected. We speak of long-term runs instead of batches, formulas (based on percentage) replace recipes (expressed in weight/volume).
To manage continuous operations, one must:
• Control material streams (prevent material shortage)
• Make the equipment available (importance of preventive maintenance)
• Maintain required process conditions by monitoring and adjusting
• Restore process conditions in the event of significant problems on a paper machine
• Measure, adjust and confirm product quality
• Follow start/shut down procedures and ensure safety conditions.
In a certain way, the chemical or coating color continuous preparation processes require a control system that interacts with the paper machine and stock preparation and which can be managed from the paper machine supervisory system. The boundary between chemical preparation and papermaking process becomes thinner.
Benefits of continuous solutions
According to the size of the paper mill and paper grade produced, continuous solutions are an answer for maximizing the uptime of a preparation unit, guaranteeing the quality of the product to be supplied and minimizing operational and maintenance costs. Their profitability is enhanced by the reliability of their components (robustness), the limitation of product loss and effluent generation (low-to-zero rinsing volume, constant cleanliness of equipment), their easy layout (compact and skid-mounted units, ready assembled and pre-tested in workshop). They are automated units guaranteeing the process stability (accuracy and repeatability) and safety, as well as performance with throughput control.
Because continuous solutions are based on high-accuracy measurements, inline filters, self-cleaning systems, high-connectivity nodes, they boost flexibility and reactivity. They adapt to high speed production cycles and quick production changes.
Choosing continuous solutions for chemical or coating color preparation helps make papermaking processes more inline. Continuous technologies create more interactions and help to improve the paper machine performance. They also help to optimize productivity and financial returns by producing only the required product volume with minimum spillage.
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