Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F3/00—Press section of machines for making continuous webs of paper
  • D21F3/02—Wet presses
  • D21F3/04—Arrangements thereof

Definitions

• the present invention concerns a procedure in the press section of a paper machine comprising three or more consecutive press nips, between which the web travels in closed conduction, the first of these nips, preferably one with two felts, being defined between a water-receiving roll and a suction roll and the second nip, between said suction roll and a smooth-surface roll, said smooth-surface roll constituting one of the two rolls in the next nip or nips.
• One object of the present invention is to provide a procedure and a means by which the runability of a paper machine can be improved by enhancing the dewatering in the press section so that the web departs from the press section in a drier and stronger condition than before.
• the object of theinvention is not so much to create an optimum situation of heat economy on paper machines, but the invention rather aims at optimizing the operational economy of the paper machine, taking into account the runability (reliability in operation) of the paper machine as well, and at influencing the properties of the paper that is turned out.
• the first No. 2.907.690 discloses a standard paper machine press where on the felt upon the suction roll before the press nip is directed, through nozzles with small holes, a hot gas jet, the object being to reduce the viscosity of the water residing in the felt and thereby to boost the dewatering action.
• Apparatus serving to boost the dewatering action, based on raising the temperature of the felt, web and/or roll, has not gained any extensive use, particularly not in fast-running paper machines.
• the reason herefor is partly the fact that it has not been possible with apparatus of prior art to introduce any high enough heat flow at the points of supply. This, again, is due to the fact that e.g. with a view to preventing deterioration of the felt the temperature of the treatment gas is limited; owing to the high felt and web velocities the time available for heat transfer is short; and also the heat transfer surface is rather restricted owing to space considerations.
• the object of the present invention is to afford a solution to these problems as well.
• the procedure of the invention is mainly characterized in that both with a view to improving the paper technology properties of the paper web that is being produced and with a view to enhancing the dewatering action and improving the runability of the paper machine, in the above- defined press section is directed on the web from both sides thereof, a heating effect in that by a set of first means a heating effect is directed from a first side of the web in the interval between the first and second nips and that a second heating effect is directed from the other side of the web in the interval between the second and third nips on a sector of substantially large extent, and that the said heating effects have been adjusted to be such of their power that the temperature of the web will before the last nip of the closed press section rise substantially over 50oC, yet with the lastmentioned temperature remaining preferably below about 95oC.
• the favourable effects of the invention may he based, in part at least, on the circumstance that the fibres normally used in paper manufacturing contain, in addition'to cellulose and lignin, also various types of hemicellulose, and these are in wetted condition transformed into a plastic state at remarkably low temperatures, compared with lignin and cellulose.
• the hemicelluloses contribute in the first place to the strength of the paper.
• the lignin content and/or filler content of the pulp stock, or the filler quality may have some significance regarding the mode of action of the new procedure and apparatus of the invention.
• the results of experiment stated in the application already serve to .demonstrate that by the invention new and unexpected effects, and even combination effects, are attained.
• the invention also has a chance, partially at least, to eliminate the paper strength-diminishing effect incurred through the use of fillers.
• the favourable effects of the invention can be attributed to the fact that by heating the web in two separate steps, as taught by the invention, the paper's modulus of elasticity can be substantially lowered, which among other things promotes the dewatering action.
• the web temperature is about 30-40oC, implying that in the heat treatment steps of the invention the temperature of the web is raised in an altogether substantial amount - at least about 20oC and in certain instances up to about
• the web As it leaves the press section, has a dry matter content substantially superior to that of any press sections of prior art, e.g. in excess of 40-50%, depending on the brand of pulp stock.
• the lower limit of 40% refers to those pulps which are well-known to be particularly refractory to dewatering, while the upper limit of 50% applies in the case of those pulps which are are comparatively easy to dewater.
• the invention further affords the advantage that specifically at the supply points as taught by the invention adequate space is available for the thermal energy supplying apparatus.
• the first thermal energy supply point is disposed after the first nip, the web has had time, in the said double-felted nip with efficient bidirectional dewatering action, to attain a dry matter content such (about 20-35%) that there is no need to use the steam supply of the invention towards unnecessary heating of water which is easy to expel from the web.
• Fig. 1 presents, schematically, a press section wherein the procedure and apparatus of the invention are being applied, together with other components associated with the press section.
• Fig. 2 presents, in sectional view, the placement of the apparatus of the invention in conjunction with the press section in question.
• Figs 3,4,5 and 6 present results of experiments carried out with the procedure and apparatus of the invention, concerning the dry matter content of the web that is being made and its paper technology characteristics.
• Fig. 3 displays, in the form of a bar diagram, the dry matter content of the web after various heat treatments, compared with the case of no heat treatment whatsoever.
• Fig. 4 shows the Scott bond of the manufactured web after various heat treatments, and without heat treatment.
• Fig. 5 shows the stretch of the manufactured web, by a bar diagram, compared with a web not subjected to any heat treatment.
• Fig. 6 shows the symmetry of the ink absorbtivity of the manufactured web without heat treatment and after various heat treatments, the latter also including the two-step heat treatment of the invention.
• Fig. 7 illustrates how the drying section of a paper machine can be substantially shortened, or alternatively the production rate increased, thanks to the fact that the web is substantially drier as it arrives in the drying section after the pressing/heat treatment of the invention than it is in any paper machine of prior art.
• the construction and mode of operation of the paper machine depicted in Fig. 1 will be understood through the following.
• the paper web W is detached between the rolls 5 and 53 from the wire 52 with the aid of the pick-up roll 3, which operates within its own felt loop 32.
• the web W remains adherent to the felt 32 by the aid of the vacuum acting within the roll 3.
• This suction zone is indicated by the reference numeral 31.
• the transfer suction roll 4 which operates within the loop of its own felt la.
• the suction zone of the transfer suction roll 4 has been indicated with reference numeral 41.
• the web W transfers from the felt 32 to the felt la.
• Fig. 1 a pair of rolls 3/4 has been shown, it is natural that the invention may equally well be applied in those press sections which have no rolls 3 and 4 and no felt 32 at all, instead of which the felt lb operates in a manner known in itself in the art as a pick-up felt having within its loop a particular pick-up roll corresponding to the roll 3 and which operates in conjunction with the wire 52 between the rolls 5 and 53.
• the latter transports the web W to the first dewatering nip N 1 of the press section, which nip is defined by the rolls 2a and 2b, and the pressing in said nip N 1 taking, place between two felts la and lb.
• the roll 2a is a water-receiving roll, such as a recessed surface roll for instance
• the roll 2b is a suction roll with either a continuous suction zone 21 or a plurality of suction compartments.
• the web W moves, adherent to the surface of the felt lb, to the second dewatering nipN 2 , defined between the rolls 2b and 2c.
• the roll 2c is a smoothsurfaced roll and it has no felt, whereby the dewatering in the second nip N 2 is towards the suction roll 2b.
• the web W transfers from the felt lb to the toll 2c, which conveys it to the third nip N 3 of the press system, the roll 2d of this nip being a recessed surface roll and being provided with a felt Id of its own.
• the web W may be conducted in conventional manner to the drying section. It is possible, however, to provide additional nips against the roll 2c. These may be either felted - if it is desired to obtain enhanced dewatering action - or without felt with a view to a smoothing effect alone, e.g. such as the roll 2e, which has been fitted with a soft covering.
• the press section may comprise, instead of the recessed surface roll 2d, a separate pair of rolls defining a press nip.
• One of these rolls may be a roll with recessed surface and provided with a felt of its own.
• the other roll may be one with a smooth surface.
• the felts of the system shown in the figures have been denoted with the reference numerals la,lb,Id,32; the felt guide rolls, correspondingly, with 23,33.
• the suction zones of the different rolls carry the numerals 21,31,41,51 and the cleaning doctor of roll 2c, the numeral 24.
• Fig. 1 have been shown the first two drying cylinders 81 of the drying section of the paper machine and the so-called lead-in cylinder 80. It is exactly the breaks occurring at the first free draws D 1 ,D 2 ,D 3 etc. of web W which the procedure and apparatus of the invention are meant to help eliminate.
• a first heating means which is a steam supply box 60, of which the supply face opens towards the outer surface, exposed at this point, of the web W running in the suction zone 21 upon the felt lb.
• the structural details of the steam supply box 60 are readable in Fig. 2.
• the supply face ⁇ of the steam supply box 60 is preferably located within the holding sector ⁇ 2 of the suction roll 2b. Adjacent to the first nip N 1 of the press is located a dewatering suction sector ⁇ 1 , and adjacent to the second nip N 2 , the dewatering suction sector ⁇ 3 .
• the shell 25 of the suction roll 2b is perforated (foraminous) in a manner known in itself in the art.
• the steam supply box 60 comprises a steam supply tube 62 disposed therewithin, communicating by the steam supply valve 76 with a steam distribution header, into which the steam is supplied from apparatus inherently belonging to a paper machine.
• control means 75 which govern the actuating motor 77 of the control valve 76. It is possible to provide on the margins of the steam supply box 60, suction means by which any detri mental lateral discharge of steam from the margins of the box 60 is prevented.
• the supply tube 62 of the steam supply box 60 serves as supporting structure thereof.
• To the steam supply tube 62 have been affixed by supporting structures 73, edge beams and a jacket sheet 64.
• the steam supply box 60 comprises the outer jacket
• the supply face of the steam supply box 60 to which corresponds the sector ⁇ , consists of a curved plate 71,72 adjacent to the free outer surface of the web W and made e.g. of sintered material, or so perforated that the steam gains access therethrough to act on the web W.
• the plates 71,72 are not indispensable in every case, and the steam supply box 60 may as well be open at the point of supply.
• the steam supply apertures 67 open in the opposite direction from the supply plates 71,72, whereby the steam jets F have time to slow down and to become equalized in the volume 70 prior to discharging through the plate 71,72 as flows F 1 against the web W.
• second heating means 100 disposed between the second nip N 2 and the third nip N 3 .
• the second heating means 100 have among others the important characteristic feature that they direct a heating effect on the web while this is within the region of the smooth-surfaced roll 2c, on the opposite side of the web with reference to the heating effect of the first heating means 60.
• the second heating means 100 have been disposed to extend over the largest possible sector ⁇ between the nips N 2 and N 3 .
• the second heating means 100 have been disposed to extend over the entire breadth of the web W, and these means comprise a frame component 101, with a front end face and rear end face 102.
• On the curved frame component 101 has been mounted a great number of infra-red radiators 103, which direct against the surface of the web W a radiation of high enough intensity.
• the infra-red radiators 103 are known in themselves in the art, and they are supplied from an electricity supply 104 through a lead 105.
• the web temperature is further elevated with reference to the amount in which the first heating means 60 have heated the web.
• the second means is used to heat the web on the opposite side from that concerned in connection with the first means.
• the intensity of the radiation R brought to bear by means of the second heating means 100 is advantageously in the range of 50 to
• the first heating means 60 of the invention are characterized in that they have been disposed after the first nip N 1 and before the second nip N 2 at the point where the web W passes over the holding sector ⁇ 2 of the suction roll 2b, upon the felt lb.
• the steam supply box 60 or equivalent is placed after a nip where the dry matter content of the web is about 20-35%, preferably at least about 30%.
• the temperature of the web W is raised by subjecting the web from the direction of its outer surface, on a remarkably extensive sector ⁇ , to the effect of hot aqueous steam in such manner that a significant proportion of the treatment steam condenses expressly within the web W, thereby releasing its latent heat and thus increasing the temperature of the web W and reducing the viscosity of the water, and in this way boosting the dewatering action in the subsequent nip N 2 .
• Condensation of steam may also take place into the felt lb, and part of the steam may pass through the felt lb into the suction chamber of the roll 2b.
• the treating steam is substantially under atmospheric pressure in the interior volume 70 of the steam supply box 60, owing to the loss of pressure caused by the nozzle holes 67, and the steam flow into and through the web W, and partly potentially also through the felt lb, is mainly achieved by effect of the vacuum at the suction zone ⁇ 2 adjacent t ⁇ the suction roll 2b.
• the invention produces the favourable ancillary effect that the felt loop lb, which circulates continuously through the sector ⁇ , attains a certain elevated temperature, and as a result hereof in passing through the nip N 1 . it boosts the dewatering action in the nip N 1 .
• the treatment steam used in the first heating means is saturated steam, but it is equally possible to use somewhat superheated steam, however minding the temperature endurance of the web W and, above all, of the felt lb thereinunder.
• the steam box 60 By using the steam box 60, a uniform discharge of the steam over an extensive area on the web W is achieved, and since the steam is substantially under atmospheric pressure in the interior volume 70 of the steam supply box 60, it follows that the steam supply box 60 need not be dimensioned as a pressure vessel, and the construction will be comparatively simple and inexpensive in this part.
• the second heating means is used to the purpose of heating, infra-red radiation of high enough intensity, or another high frequency electromagnetic radiation.
• To use steam in the region of nips N 2 and N 3 is not advantageous in the respect that because the roll 2c is smooth the heating effect of the steam cannot be made to penetrate to the same depth as is feasible in the case of infra-red radiation or microwave radiation or another equivalent heating effect based on radiation.
• Fig. 3 reveals that when using the procedure of the invention, and most specifically a steam box with 2 ATM pressure, together with the infra-red radiation means 100 described in the foregoing, an increase is achieved in the dry matter content of the web W from about 39,5% to about 49%. It is moreover noted that by using the two-step heat treatment of the invention the dry matter content can be increased quite substantially compared with the alternative of using an equivalent steam box alone.
• Fig. 4 reveals the Scott bond of the manufactured paper, and it is seen from this figure that in the procedure of the invention the Scott bond increases altogether drastically compared with the alternative of no heat treatment being applied at all, and that it increases substantially even compared with the use of the equivalent steam box alone, i.e. with single step steam treatment between the first and second nips.
• Fig. 6 presents the symmetry of ink absorptivity, expressed by the ratio of the absorptivity on both sides of the web.
• the inference can immediately be drawn from the figures that when using the two-step heat/pressing treatment of the invention the ink absorptivity can be adjusted, without any difficulty, to TS/WS Regarding the right-hand bar in Fig. 6, representing the present invention, the observation can be made that the value TS/WS will be reached, for instance, by slightly reducing the heating effect of the steam box 60 and/or the infra-red device 100.
• Fig. 7 has been schematically depicted, the paper machine in its entirety, and above it, concerning the standard paper machine known in the art, the increase of the web's dry matter content in the drying section after the press section known in the art (curve A) .
• the paper machine depicted in Fig. 7 comprises a former section 120, a press section 130 and a drying section 140.
• ⁇ D represents the increase of dry matter content according to the invention
• the point P indicates that point on the curve A where, in the case that pressing components known in the art are used, is first attained a dry matter content equally high as that obtained imme diately after the press section already by applying the procedure and apparatus of the invention. If now in the press section 130 the two-step hot pressing of the invention is applied, increase of the dry matter content is achieved from about 40% to 50%, as the curve A reveals. It is then possible, in new paper machines, to.
• the drying section 140 shorten the drying section 140 by the length of the portion 141, which corresponds to approximately 36% of the total length of the drying section 140. In that instance only a drying section with a length consistent with that of the portion 142 is required.
• the advantage afforded by the invention may instead be utilized e.g. by increasing the production rate of the paper machine - it is known that quite often the throughput of the drying section is the actual bottleneck restricting the production rate.
• the second heating step (device 100) of the invention it is not necessary therein to heat any felt, because the web W lies directly against the smooth roll 2c.
• the temperature of the smooth-surface roll 2c for instance a stone roll, fairly soon acquires a certain equilibrium, whereat the roll 2c heats the web in the nip N 2 already, and thereafter.
• the appropriate intensity of the radiation R delivered by the means 100 has been estimated at about 50-500 kW/m 2 . It should be noted, however, that in all likelihood it will be possible in future studies to further augment quite considerably the efficiency of the radiant heating performed with the means 100, e.g. by selecting for the wavelength of the radiation R a value which is optimal in view of the physical and chemical phenomena constituting the basis of the invention. It will then be possible even to go below the above-stated lower limit of 50 kW/m 2 .
• the web temperature can be economically raised e.g. to about 80°C or even higher, unexpectedly high dry matter contents are achieved, yet without impairing the most important service characteristics of the paper.
• certain paper technology characteristics are in fact substantially improved thanks to the invention.
• the increase of the dry matter content after the press section in itself, increases the wet strength of the web and therethrough improves the runability.

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• 1980
  • 1980-09-25 FI FI803021A patent/FI803021A/fi not_active Application Discontinuation
• 1981
  • 1981-09-21 CA CA000386347A patent/CA1170883A/en not_active Expired
  • 1981-09-22 EP EP81902752A patent/EP0060878B1/en not_active Expired
  • 1981-09-22 WO PCT/FI1981/000074 patent/WO1982001203A1/en active IP Right Grant
  • 1981-09-24 ES ES505752A patent/ES505752A0/es active Granted
  • 1981-09-25 IT IT24168/81A patent/IT1138640B/it active

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