This invention relates to a method of drying a pulp web. an apparatus being utilized having a great number of jet boxes, which are arranged in piles positioned parallel with each other, and which are provided with openings through which the heated air. coming into the jet boxes, can stream out. The invention also relates to a drying apparatus for carrying out the method.

When producing pulp bales there is created a long pulp web which is allowed to pass a drying apparatus for drying. After the drying apparatus the pulp web continues to a scissors device where the pulp web is cut off to sheets.

By U.S. patent 3,634,948 is previously known a drying apparatus for paper webs, which comprises jet boxes positioned between upper and lower turning rolls. This known jet box arrangement, however, has so small drying capacity that, in order to achieve a satisfactory drying, it is necessary to arrange the upper and lower turning rolls like drying cylinders. Of course, this becomes a very expensive solution.

This invention intends to eliminate the problems with known technique and to provide a drying apparatus which is not only more effective than known types but also due to its design becomes less space requiring in horisontal direction than the known types. This has been made possible by the fact that the method and the apparatus according to the invention is characterized by the steps and features, respectively, which are apparent from the claims.

The drying apparatus according to the invention is so designed that essentially all that portion of the pulp web which momentarily is between the upper and lower turning rolls is irradiated on both sides by heated air. Due to that fact the drying cylinders mentioned in the cited U.S. patent can be eliminated.

A preferred embodiment of the invention shall be described more closely below with reference to the accompanying drawings, where fig. 1 shows a principal sketch over a pulp web plant of which the drying apparatus according to the invention is an integral part. Fig. 2 shows an outer frame work for the drying apparatus according to the invention, in which frame work the jet boxes and the turning rolls of the drying apparatus are intended to be arranged, fig. 3 shows an embodiment of a jet box arrangement, and fig. 4 shows a jet box couple, seen in the direction of the arrows IV-IV in fig. 3. In fig. 1 is shown how the pulp web 1, after having been produced in the schematically shown production plant P, comes into the drying apparatus 2 according to the invention at the portion 3, whereafter the pulp web goes essentially vertically up towards and rounds a first, upper turning roll 4, turns downwards and goes essentially vertically down

towards a first, lower turning roll 5, which is rounded by the pulp web, whereafter this one turns upwards again. The pulp web passes according to this embodiment six upper turning rolls and five lower turning rolls before going further to a scissors device 6. which is shown schematically in the figure, and where the pulp web is cut off to a uniform length for creating a pulp bale.

The purpose of the passage of the pulp web through the drying apparatus 2 is as appears from the name that the pulp web shall be dried during the passage through the same. For this reason the drying apparatus 2 comprises a plurality of jet boxes which are indicated with the figure 7, and which are arranged in pairs in the areas between the pulp web parts 8, 9, going upwards and downwards. Into these jet boxes heated air is intended to be blown in order to then be directed towards the passing pulp web parts 8, 9 through holes made in me portions of the jet boxes which are directed towards the pulp web parts.

In fig. 2 is shown the outer frame work carrying the drying apparatus according to the invention. The outer frame work comprises partly a lower frame part 10 which carries the lower turning rolls 11, partly an upper frame part 12. In this connection the turning rolls 11 rest on two opposite, horisontal girders 13, 14 which together with two other opposite horisontal girders 15, 16 form a rectangle or a square. These horisontal girders 13 -16 rest on four legs 17 a-d, which in its turn rest on a firm bed.

The upper frame part 12 in similarity with the lower frame part 10 comprises four girders 18 a-d, which form a rectangle/square of essentially the same size as the lower rectangle/square. The upper frame part 12 further comprises four legs 19 a-d. which rest on the lower frame part 10. The upper rectangle/square, the lower rectangle/square and the legs 19 a-d together form a standing parallel -epiped within which the pulp web parts, going upwards and downwards, are intended to move during the drying procedure. The upper turning rolls 20 are arranged on the two opposite girders 18 a, c, whereby the rolls are carried by the girders. The mentioned arrangement means that the upper and the lower turning rolls are fixed to the outer frame work and due to that fact are fixed in relation to the bed.

In fig. 3 the arrangement with the jet boxes is shown more closely. Each jet box 21 has an essentially parallel-epipedic design with a narrowing, farther end portion and has an essentially horisontal extension. In this connection the jet boxes are arranged in pairs parallel with each other within the mentioned parallel-epiped, which is formed by the area within the upper and the lower rectangles/squares and the upper frame legs 19 a-d. Due to that fact the

jet boxes are arranged in pairs both laterally and under each other in the mentioned parallel¬ epiped so that the pairs of jet boxes form parallel piles. In this connection there are created spaces 22, 23 between two piles of jet box pairs, which piles are arranged beside each other, the pulp web being intended to be brought essentially vertically upwards in a first space 22 and essentially vertically downwards in a second, adjacent space 23.

The jet boxes are suspended in the two upper horisontal girders 18 a, c by means, of which only two ones 24 a, b are shown i fig. 3. According to the shown and preferred embodiment the mentioned means is arranged between two adjacent jet boxes 21 a, b, which accordingly are arranged in pairs from top to bottom within the mentioned parallel-epiped. Due to that arrangement the drying apparatus like a steam-boiler can expand from the top to its bottom.

In fig. 4 a jet box couple 21 a, b is shown more closely. Each jet box has a narrowing, farther end portion 29 a, b, which is closed. The heated air is intended to be introduced into respective box at the arrows 30 a, b and be taken out of the same via the holes 26.

For drying the pulp web heated air is intended to be blown into the jet boxes 21 by a not shown fan system through the openings 25 and further out from the boxes through holes

26 arranged in the sidewalls 27 a, b of the jet boxes which are directed towards the pulp web parts. After having passed the jet boxes, the cooled air is sucked by the fan system through a not shown heating device whereafter the air is blown into the jet boxes again.

The parts 8, 9 of the pulp web, going upwards and downwards, are intended as has been mentioned to move between the jet boxes 21 a, b; 28 a, b, arranged in pairs laterally. Due to the fact that the movement of the pulp web parts 8, 9 is made essentially vertically through the drying apparatus, the distance between the jet boxes, arranged in pairs laterally, can be as small as about 30 mm. This fact means that the drying of the pulp web can be made by means of a variable air flow, which means strong savings regarding the expenses for the electric current in comparison with the conditions which are valid in horisontal drying apparatuses, i.e. apparatuses where the paper web moves essentially horisontally through the same. In such appratuses the air flow through the jet boxes has to be at a maximum in order that the pulp web transport between the jet boxes shall be able to be made in a satisfactory way.

Anorther important advantage with the vertical drying apparatus according to the invention compared with a horisontal drying apparatus is that the cleansing of the apparatus

when there is a break in the pulp web is much simplier in the first mentioned apparatus, because the pulp web, teared off. falls very easily out of the vertical drying apparatus.

When the pulp web comes into the drying apparatus it has a high moistness but as it passes the different jet boxes there is a drying of the pulp web so that its moistness is reduced. Due to that fact the pulp web shrinks about 1 % . and therefore there is a difference in velocity between the first and the last turning roll. In order to eliminate the problems that this velocity difference can bring about, each upper turning roll is provided with a so called visco coupling.

In the text the expression "pile" has been used. With pile in this connection is meant a number of jet boxes arranged along an essentially vertical line, which jet boxes not necessarily are in contact with each other.

In the text has further the expression "girder" been used. Of course, this expression comprises also pipes and rods.

The invention is of course not limited to the mentioned embodiment but can be modified within the scope of the following claims.