Integrated paper machine

Details Integrated paper machine Integrated paper machine

2000-12-08

2002-08-06

Chin, Peter (Department: 1731)

Paper making and fiber liberation

Apparatus

Running or indefinite length product forming and/or treating...

C162S301000, C162S308000, C162S343000, C162S358300, C162S359100, C162S361000

Reexamination Certificate

active

06428655

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a paper machine and in particular to an integrated paper machine having, in a machine running direction, a multi-layer head box, a gap former, a press section, a pre-dryer section, a dryer section and a closed web draw.
BACKGROUND OF THE INVENTION
During the last 25 years, the increase in the consumption of paper and board was about 3.2% per year, and it is estimated that the increase will be about 2.8% per year during the following 15 years. Even though the total production of paper and board has increased constantly, the number of machines that produce these products has become lower. This is accounted for by the fact that new machines are always more efficient than their predecessors. A typical newsprint machine of the 1960's produces about 100,000 tons of paper in a year, whereas a typical paper machine of the 1990's produces about 300,000 tons of paper in a year. Such an increase in productivity has been based on constant product development in all of the constituent fields of papermaking.
The maximum width of a paper machine is these days about 10 meters, and it is not estimated that this width will be increased until the problems related to the massive constructions, such as high inertia, limitations related to production methods, and high costs have been solved. This will require considerable development in the fields of material sciences and production processes.
On the contrary, the running speed of the paper machine will still be increased. The speed has become three-fold in the course of the last 30 years, and no signs are seen regarding a slowing down of the increase in speed. The speed of current paper machines is about 1800 meters per minute, and speed records are made almost on a daily basis. The productivity will be increased by increasing the running speed of the machine in spite of the fact that the problems related to papermaking are increased almost exponentially along with an increase in the speed.
In the lecture “Future Paper Production Line Concepts Regarding Energy and Environmental Aspects” by Talja R., et al, Jun. 23 . . . 26, 1997, Baden-Baden, XXVI EUCEPA Conference, future perspectives of the development of paper machines are presented. In said paper, the applicant's vision about a paper machine of a near future is presented, whose running speed is 2000 meters per minute. The paper machine comprises a multi-layer dilution headbox, a SpeedFormer gap former, a SymBelt shoe press, in which there is a closed transfer-belt transfer to the dryer section, a JetSym Run II dryer section, in which there are high-capacity drying units and conventional cylinder dryers, an on-line OptiLoad soft calender, and an OptiReel centre-drive reel-up.
OBJECT AND SUMMARY OF THE INVENTION
The object of the present invention is to construct a paper machine by whose means it is possible to run at a speed higher than 2000 meters per minute and which is shorter than the present-day paper machines, whose overall length is about 130 meters. Further, as a raw-material in the paper machine, it must also be possible to use recycled fibre or some other fibre raw-material whose paper-technical properties are inferior.
By means of a paper machine in accordance with the present invention, it is possible to produce paper of good quality at a speed that is higher than 2000 meters per minute. The length of a paper machine in accordance with the present invention is shorter than the length of present-day paper machines.
The invention involves a number of features by whose means the speed capacity of the paper machine is affected. First, by means of a multi-layer headbox, within the scope of the quality-technical limits of the paper, it is possible to optimize the formation of stock components as layers so that a maximal water draining capacity is obtained in the former. A gap former provides a superb quality and runnability at high running speeds. Its problem is limited water draining capacity in particular with higher basis weights. A pre-press raises the dry solids content before transfer of the web to the press. This makes a pick-up transfer ever more reliable in particular at high speeds. When a major part of the water is already removed in the pre-press, the runnability of the press section proper is also improved. Traditionally, paper machines have an open draw from the press to the dryer section. Since the dry solids content of the web at the time of transfer from the press to the dryer section is about 50% or lower, the web is of low strength and susceptible of web breaks. The biggest problem of traditional cylinder drying is runnability on the first cylinders. The situation is deteriorated further by a closed transfer to the dryer section, because the web has not been tensioned in a draw of open transfer. A pre-drying unit fitted in accordance with the present invention of ours eliminates said problem as the unit dries the web further before the web enters into cylinder drying. A calender integrated in the dryer section permits calendering of the web so that the web is constantly supported. Of course, this also improves the runnability as it eliminates the fluttering and wrinkling of the web, which are typical of open gaps. In particular, a closed calender promotes threading of the web at high speed. The same arguments also apply to a closed draw to the reel-up.
In the solutions known from the prior art, just partial improvements have been suggested for different parts of the machine, but it is only by combining the above factors in one and the same concept that it is possible to put the advantages provided by said factors to use to full extent.
By means of a paper machine in accordance with the invention, it is also possible to have a positive effect on the quality of the paper. A multi-layer headbox provides abundant possibilities for optimizing the paper quality either by means of formation of fibre layers or by means of formation of layers of admixtures/chemicals in particular in combination with a roll-shoe gap former. In this way it is possible to apply a positive effect in particular on the printing quality of paper. As compared with other formers, a gap former provides by far the best paper (formation, uniformity of basis weight, orientation profile, distributions of fibres, fillers and fines in the direction of thickness, etc.), for which reason the gap former has largely replaced other former types in high-speed machines. If necessary, an extended-nip press provides economies in the bulk and porosity of the web. When the web does not have to be drawn between the press and the dryer section, the properties of strength of the paper are improved. Good runnability in the dryer section eliminates possible wrinkles and provides a more uniform tension profile. With a calender integrated in the dryer section, a higher drying capacity is obtained as compared with a dryer section with no pre-calendering. By means of pre-calendering, it is also possible to improve the properties of strength, smoothness and gloss of the paper. Impingement drying makes it possible to utilize drying that prevents shrinkage more efficiently than in the prior art and, thus, to provide, for example, a web whose dimensional stability in the cross direction is uniform. Formation of waves is also reduced.
The length of a paper machine is made shorter by the following features in accordance with the present invention:
pre-pressing removes an abundance of water right in the wire part, in which case, under favourable conditions, just one press nip is needed in the press section,
in the press section, in one embodiment, impulse drying or hot pressing is utilized, each of which increases the dry solids content after the press, which reduces the required need of drying,
in the beginning of the dryer section, there is an efficient pre-drying unit,
in the press section, the relative proportions of cylinders and suction rolls have been optimized,
in the dryer section, there is an impingement drying unit fitted below the floor level, whose dryin

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