EP0763626A2 - Steam shower and process for zonal tempering of a moving paper web - Google Patents

Abstract

The steam blower box, to deliver steam to a paper web passing round a roller (30), of a papermaking machine, has an air mixture outlet channel (96) along the steam spreading zone (76), across the direction (53) of web travel, for temp. control. Also claimed is an operation where air is fed to the entry side (92) of the steam spreading zone (76), to cool the paper web by zones.

Description

The invention relates to a steam blower box for applying steam to a paper web guided over a roller of a paper machine, with a closed steam blowing chamber extending transversely to the web running direction along the roller, the steam being feedable and the front wall of which facing the roller has a plurality of steam outlet openings, whereby a steam spreading space is formed between the front wall of the steam blow box and the roller.

Such a steam blow box is known from DE 41 25 062 A1.

In the known steam blow box, steam is introduced via a steam valve into a steam blow chamber, from which the steam can enter a steam spreading space via steam outlet openings, so as to heat the paper web guided over a roller.

A disadvantage of the known steam blower box is that temperature control on the surface of the paper web is difficult because the steam is evenly distributed within the steam spreading space and is thus largely evenly absorbed by the paper web. As soon as the steam in the layer close to the paper has condensed on the paper web, there is also an insulating air layer in front of the paper web, which prevents further heating of the paper spell. The heating of the paper spell is therefore limited.

A zone-by-zone tempering of the paper web is hardly possible due to the insulating air layer.

The object of the invention is therefore to provide a steam blower box for applying steam to a paper web guided over a roller of a paper machine, which enables a more sensitive temperature control on the surface of the paper spell. Furthermore, the heat transfer to the paper web is to be optimized.

Furthermore, an effective method for zone-wise tempering of a running paper web through a steam spreading space facing the paper spell, into which steam is supplied, essentially uniformly distributed over the width, is to be specified.

This object is achieved in that a steam blower box according to the type mentioned above for temperature control is provided with an outlet channel extending along the steam propagation space transversely to the web running direction for admixing air.

According to the invention, a particularly sensitive, zone-by-zone temperature control is made possible on the surface of the paper web, since the admixture of air creates an insulating air layer in front of the roller surface, so that even with a large excess of steam in the steam spreading space, a quickly responsive and sensitive local influence (reduction) heat transfer to the paper surface is ensured. Furthermore, it is possible to work with a large excess of steam, so that saturated steam can spread in the steam spreading space and thus results in an optimal heating of the paper web, provided that no air is mixed in, or it is ensured that mixed air is removed.

In a preferred development of the invention, the outlet channel is divided into a plurality of separately controllable zones.

In this way, heat transfer to the paper web, which can be delicately influenced in zones, can be made possible over the width of the roller, as a result of which an optimal adaptation of the heat transfer can be set with variations in the operating parameters. If more or less large amounts of air are mixed in zones, this has the consequence, due to the insulating effect of the air layers, which lie on the roller surface in the direction of rotation of the roller, that an immediate effect of steam spreading in the steam expansion space on those areas that are less strong should be heated is avoided. This is a greatly improved overall allows zone-by-zone regulation of heat transfer to the surface of the paper web. A mutual influence of neighboring zones, which are controlled differently, is largely avoided.

According to a further embodiment of the invention, the zones are connected to separate lines for supplying air, to which control valves arranged outside the steam blow box are assigned for regulating the air volume.

In this way, optimal regulation of the heat transfer in the individual zones can be achieved, while at the same time simple maintenance and assembly is ensured by the control valves arranged outside the steam blower box.

In a further advantageous embodiment of the invention, a suction channel extending along the steam expansion space is provided on the outlet side.

In this way, the heat transfer and the controllability of the individual zones is improved, since air admixed in the inlet side of the steam expansion space is sucked out again at the outlet side of the steam expansion space.

In an additional development of this embodiment, the suction channel is divided into a plurality of separately controllable zones.

In particular, when the zones of the suction channel are regulated as a function of the amount of air admixed in the individual zones on the inlet side, this enables optimized controllability and improved heat transfer to the surface of the paper web.

In a preferred development of the invention, the zones can be connected for this purpose with separate lines for air removal, to which control valves arranged outside the steam blow box for air volume regulation are assigned.

This measure enables simplified installation and maintenance of the individual control valves, since improved accessibility is ensured outside the steam blower box.

According to a further embodiment of the invention, a suction channel for suction is provided in front of the outlet channel.

In this way, the effect of the subsequent outlet channel is additionally supported, so that fine control of the heat transfer to the paper web over the individual zones is facilitated.

In a further advantageous embodiment of the invention, sealing means for sealing the steam expansion chamber against the roller are provided on the inlet side, on the outlet side and on the front sides of the steam expansion chamber.

In this way, the heat transfer to the paper web is considerably improved since, due to the vapor spreading space thus largely sealed off to the outside, heat losses through steam escaping at the edges are avoided.

In a preferred embodiment of the invention, a constriction can be provided on the inlet side transversely to the web running direction, in which a wall surface of the steam blow box protrudes toward the roller to form a narrow gap.

In this way, contactless sealing of the steam expansion space is made possible in a simple manner.

In a further preferred embodiment of the invention, a plurality of nozzles for supplying steam are provided behind the constriction, viewed in the direction of web travel.

These nozzles are preferably shaped and arranged in such a way that they produce a steam curtain which peels off air boundary layers from the roller and transports them together with excess steam to the suction channel on the inlet side. This enables particularly good heat transfer to the paper web.

In an additional development of the invention, a scraper or a sealing strip is provided between the steam box and the roller on the outlet side.

In this way, an effective sealing of the steam expansion space on the outlet side can be achieved. The scraper or the sealing strip is preferably arranged so that a seal against the counter-roller is achieved. In this way, heating of the counter roll is made possible at the same time. The farther the scraper or sealing strip is from the gap formed between the roller and the counter roller, the greater the additional heat transfer to the counter roller.

According to a further embodiment of the invention, side surfaces projecting towards the roller or the counter roller are provided for sealing the steam propagation space against the roller or the counter roller.

This measure enables a contactless sealing of the steam expansion space on the side surfaces in a simple manner.

With regard to the method for zone-wise tempering of a running paper web, the object of the invention is achieved in that the paper web can be cooled zone by zone by supplying air on the inlet side of the steam spreading space.

According to the invention, a temperature control of the running paper web that can easily be influenced zone by zone is thus made possible, since admixing of air zone by zone can easily be achieved via corresponding valves. In contrast, regulation of the steam supply, which is difficult to carry out in zones, is not necessary.

A zone-wise temperature control of the running paper web, which is greatly improved compared to the prior art, is thus made possible in a simple manner. Since the temperature is controlled by cooling as a result of the supply of air, the formation of insulating air layers in front of the surface of the paper web is largely avoided, and thus a sensitive, zone-wise regulation of the temperature control is made possible.

In an advantageous further development of the method according to the invention, gas, i. E., Near the pressing point of two rollers, which forms the outlet side of the steam spreading space. Air or an air-vapor mixture, extracted.

In this way, the zone-by-zone temperature control of the running paper web is supported and an even more sensitive, zone-controlled temperature control is made possible.

In this case, either the gas can be sucked off uniformly over the width of the steam expansion space or the gas suction can be controlled zone by zone analogously to the air supply.

In the latter embodiment, a further improved, zone-by-zone, sensitive control of the temperature control is achieved.

It goes without saying that the features of the invention mentioned above and those yet to be explained below can be used not only in the combination specified in each case, but also in another combination or on their own without departing from the scope of the invention.

Fig. 1

eine schematische Darstellung einer Papiermaschinenpresse mit insgesamt drei Preßspalten, bei der ein erfindungsgemäßer Saugkasten vorgesehen ist;

Fig. 2

einen Querschnitt durch den erfindungsgemäßen Saugkasten gemäß Fig. 1 im Bereich der Walze und der Gegenwalze vor dem zweiten Preßspalt und

Fig. 3

eine Vorderansicht des Dampfblaskastens gemäß Fig. 2 von der Walze aus gesehen.

Further features and advantages of the invention result from the following description of a preferred exemplary embodiment with reference to the drawing. In it show:

Fig. 1

a schematic representation of a paper machine press with a total of three press nips, in which a suction box according to the invention is provided;

Fig. 2

a cross section through the suction box according to the invention according to FIG. 1 in the region of the roller and the counter roller in front of the second press nip and

Fig. 3

a front view of the steam box according to FIG. 2 seen from the roller.

In Fig. 1, a press section of a paper machine is shown schematically and generally designated by the number 10. It is a so-called "three-nip press", ie a press with a total of three press nips, a first press nip 12, a second press nip 14 and a third press nip 16, which are traversed by an aqueous paper web 24 in the direction of arrow 26.

The paper web 24 is sucked over by a take-off suction roll 18 from a fabric belt 22 onto a felt web 20, which is passed around a roll 30 through the first press nip 12 between the roll 30 and a counter roll 28 and through the second press nip 14 between the roll 30 and a counter roll 32 is led.

A second felt web 44, which is guided over guide rollers 36, 38, also runs through the first press nip 12.

The third press nip 16 is formed by the roller 32 and a shoe press roller 34, which can also be a shoe press roller with a wide press zone, a felt web 46 again being passed through the press nip 16 and rotating over guide rollers 40, 42. After passing through the third press nip 16, the paper web leaves the counter-roller 32, as indicated by the arrow 48. The circumference of the counter roller 32 is then cleaned by a scraper 52.

In the space between the roller 30 and the counter roller 32, a steam blow box according to the invention is arranged, which is generally designated by the number 50.

The structure and mode of operation of the steam blow box 50 are explained in more detail below with reference to FIGS. 2 and 3.

The steam blow box 50 is shown enlarged in FIG. 2, further sections of the roller 30 and the counter roller 32 being recognizable.

The roller 30 is designed as a so-called suction roller, which has a stationary suction box 55 with a plurality of suction zones 54, 56, 58, over which a perforated roller shell 59 rotates.

The steam blower box 50, which has a substantially rectangular cross section, is arranged in front of the second press nip 14 between the roller 30 and the counter roller 32 and, in a manner explained in more detail below, on the inlet side 92 of the paper web guided in the direction of arrow 53 over the roller 30 against the Sealed roller 30 and sealed against the roller 32 at the outlet side 94 of the paper web.

The steam blower box 50 consists of a box-shaped carrier with four walls 62, 64, 66, 68, which extends over the entire width of the roller 30 and is closed at the end faces by side surfaces 118, which form a narrow gap along the surface of the roller 30 and the counter roller 32 extend (Fig. 3).

Within the steam blow box 50, a steam blow chamber 60 is formed which is closed off from the outside by the four walls 62, 64, 66, 68 and the two side surfaces 118 and into which steam is blown in via a laterally opening steam pipe 70 via outlet openings 72 on its periphery. A condensate drain 78 is provided at the lowest point of the steam pipe 70 for the removal of condensate.

The front wall 62 of the steam blowing chamber facing the roller 30 is perforated in the lower region by a plurality of steam outlet openings 74 (see FIG. 3), through which steam can enter a steam spreading space 76 between the roller 30 and the front wall 62, which downwards is limited by a constriction 90, which is defined by the lower wall surface 68 of the Steam blower box 50 is formed, which protrudes toward the roller 30 to form a narrow gap. The steam spreading space 76 is also sealed against the counter roller 32 by a scraper 52 or a sealing lip which is fastened to the outer, upper end of the steam blowing chamber 60.

The steam-blowing chamber 60 is suitably heat-insulated from the outside by heat insulation 106.

As seen in the web running direction 53, steam nozzles 86 are arranged one after the other across the entire width of the roller 30 and are supplied with steam directly from the steam blowing chamber 60 via pipes 88. Steam is thus blown obliquely against the roller 30 via the steam nozzles 86 immediately behind the constriction 90, so that there is practically a seal of the steam expansion space 76 towards the bottom by a steam curtain.

A good heat transfer to the surface of the paper web can thus take place within the steam spreading space 76 due to the steam emerging from the steam blowing chamber 60 through the steam outlet openings 74.

The tubes 88 for supplying the steam nozzles 86 are raised slightly upward within the steam blowing chamber 60, so that the inlet openings lie above a condensate drain 80 which runs along the lower wall 68 of the steam blowing chamber 60. Entry of condensate into the pipes 88 is thus avoided.

An outlet channel 96 opens below the constriction 90 and also extends over the entire width of the roller 30. The outlet channel 96 is - as can be seen from FIG. 3 - in the longitudinal direction in individual zones 96a, 96b, 96c, 96d, 96e, 96f, into which air can be blown in via a flow distribution grid 98 in the form of a perforated plate made of individual lines, which are schematically shown as square lines 102/1 to 102/30 at the lower end of the steam-blowing chamber 60. The air supply for the total of 30 different lines 102/1 to 102/30 in the example shown is controlled via valves 104, which are each assigned to a line 102/1 to 102/30 and are fastened outside the steam blow box 50, for example in the manner of as is known from DE 44 02 278 A1.

The air supply in the direction of the arrows 100 through the channel 99 can thus be regulated separately for each of the 30 zones of the outlet channel.

Below the channel 99, a suction box 51 is provided, which opens into a suction slot 108 in front of the outlet channel 96, via which air can be sucked off via deflection blades 57.

At the upper end of the steam expansion space 76, a suction channel 112 is provided, which opens into a suction slot just before the second press nip 14. The suction channel 112 extends over the entire width of the steam blow box 50 between the two side surfaces 118 and is divided into a total of 30 zones 112a, 112b, 112c, 112d, 112e, 112f, ... Each of these zones is connected to a separate line 114/1 to 114/30, which are indicated schematically as square lines above the steam blow chamber 60 in FIG. 2 and which are each connected to valves 116 outside the steam blow box 50. The control of the valves 104 and 116 is preferably such that when the amount of air blown in through a zone of the outlet channel 96 is increased, the amount of air extracted from the respective zone at the suction channel 112 is increased accordingly.

The steam blower box 50 is operated in the following way:

Steam is blown into the steam blowing chamber 60 through the steam pipe 70 via the outlet openings 72. Condensate is discharged from the steam pipe 70 via the condensate drain 78 and from the steam blow chamber 60 via the condensate drain 80. The steam passes through the steam outlet openings 74 on the front wall 62 in the direction of the arrows 84 into the steam propagation space 76.

The steam spreading space 76, which is shielded from the outside by the constriction 90 on the inlet side 92, is additionally sealed by a steam curtain which is generated by the steam emerging from the steam nozzles 86.

A temperature control or a regulation of the amount of heat transfer to the surface of the paper web takes place zone by zone over the width of the steam spreading space 76, specifically by blowing air separately against the roller 30 over the individual zones of the outlet channel 96. This blown air creates a boundary layer between the steam spreading space 76 and the roller 30, by means of which heat transfer is hindered. Thus, the amount of heat transferred to the paper web can be regulated in zones separated by the amount of air blown in. The suction of the air / steam mixture takes place at the upper end of the steam spreading space 76 via the suction channel 112 again separately, since the amount of air additionally introduced in a single zone on the inlet side 92 should be discharged in a corresponding manner on the outlet side 94.

The suction slot 108 connected upstream of the outlet channel 96 merely serves to ensure that the individual zones can be controlled separately by a uniform suction, which is unaffected by external influences.

Since the steam spreading space 76 is delimited at the upper end by the scraper 52 against the counter roller 32, there is also a certain heating of the counter roller 32, which is greater the further the scraper 52 is arranged on the counter roller 32 from the second press nip 14 . The arrangement of the scraper 52 can be of variable design, as a result of which the heating of the counter roller 32 can be influenced. The heating of the counter roller 32 ensures that the paper web arrives sufficiently warm in the press nip 14 despite evaporative cooling, so that a considerable improvement in the dry content can be achieved here.

Claims (17)

Steam blower box for applying steam to a paper web (24) guided over a roller (30) of a paper machine, with a closed steam blowing chamber (60) extending along the roller (30) transversely to the web running direction (53), the steam being able to be supplied and the steam thereof the roller (30) facing the front wall (62) has a plurality of steam outlet openings (74), a steam expansion space (76) being formed between the front wall (62) of the steam blow box (50) and the roller (30), characterized in that for Temperature control an outlet channel (96) extending along the steam spreading space (76) transversely to the web running direction is provided for admixing air. Steam blower box according to claim 1, characterized in that the outlet channel (96) is divided into a plurality of separately controllable zones (96a-f, ...). Steam blower box according to claim 2, characterized in that the zones (96a-f, ...) are connected to separate lines (102/1 - 102/30) for air supply, to which control valves (104) arranged outside the steam blower box (50) are connected Air volume regulation are assigned. Steam blower box according to one or more of the preceding claims, characterized in that a suction channel (112) extending along the steam spreading space (76) is provided on the outlet side (94). Steam blower box according to claim 4, characterized in that the suction channel (112) is divided into a plurality of separately controllable zones (112a-f, ...). Steam blower box according to claim 5, characterized in that the zones (112a-f, ...) are connected to separate lines (114/1 - 114/30) for air removal, to which valves (116) arranged outside the steam blower box (50) are connected Air volume regulation are assigned. Steam blower box according to one or more of the preceding claims, characterized in that a suction duct (108) is provided for suction in front of the outlet duct (96). Steam blower box according to one or more of the preceding claims, characterized in that on the inlet side (92), on the outlet side (94) and on the end faces of the steam expansion chamber (76) sealing means (90, 52, 118) for sealing the steam expansion chamber (76) against the roller (30) are provided. Steam blower box according to claim 8, characterized in that the steam blower box (50) is arranged in an intermediate space formed in front of the roller (30) and a counter roller (32), and in that sealing means (90) to the roller (30) are provided on the inlet side (92). to and on the outlet side (94) sealing means (52) to the counter roller (32) are provided. Steam blower box according to claim 8 or 9, characterized in that a constriction (90) is provided on the inlet side (92) transversely to the web running direction (53), at which a wall surface (68) of the steam blower box (50) to form a narrow gap to the roller (30) protrudes. Steam blower box according to one or more of the preceding claims, characterized in that, seen in the web running direction (53), a plurality of nozzles (86) are provided behind the constriction (90) for supplying steam. Steam blower box according to one or more of claims 8 to 12, characterized in that a scraper (52) or a sealing strip is provided on the outlet side (94). Steam blower box according to one or more of Claims 8 to 12, characterized in that side surfaces (118) projecting towards the roller (30) or the counter roller (32) for sealing the steam spreading space (76) against the roller (30) or the counter roller (32) are provided. Method for zone-wise tempering of a running paper web (24) through a steam spreading space (76) facing the paper web (24), into which steam is fed, which is distributed substantially uniformly over the width, characterized in that by supplying air on the inlet side (92) of the steam expansion space (76) the paper web (24) can be cooled zone by zone. A method according to claim 14, characterized in that gas is sucked off close to the pressing point (14) of two rollers (30, 32), which forms the outlet side of the steam expansion chamber (76). A method according to claim 15, characterized in that the gas is sucked off uniformly over the width of the steam spreading space (76). Method according to claim 15, characterized in that the gas extraction can be controlled zone by zone analogously to the air supply.

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