Patent Application
20070209769
The present invention relates to a papermaking machine and papermaking method that make continuous paper by removing moisture while making it travel a layer of paper stock.
Generally, in papermaking machines, by holding a suspension of pulp (suspension of paper stock) jetted from a head box into the shape of a layer by a wire, etc., and removing moisture while making this paper stock layer (also referred to as wet paper web) travel, a paper web is made.
Various methods of dehydration for papermaking machines have been developed. For example, as shown in
In such a papermaking machine, steam from a steam generator 10 is supplied to the steam box 60 through a steam conduit. The steam touches the wet paper web 1 held on a wire 30 and condenses, whereby heat is transferred to the wet paper 1.
It is conceivable that in the final part of the former, the wet paper web 1 will be in a state before completion of dehydration, that is, a state in which minute interstices have been formed by dehydration, or a porous state. By suctioning the under side of the wet paper web 1 through the wire 30 by a suction box 70, steam enters such interstices or pores and permeates into the wet paper web 1. As a result, the latent heat of the steam is converted to the sensible heat of water, whereby the wet paper web 1 is raised in temperature and the dehydration rate rises.
The dehydration rate of the wet paper web 1 traveling through the former is not uniform. In general, the widthwise central portion of the wet paper web 1 is lower in dehydration rate than the widthwise right and left end portions. Hence, as shown in
Similarly, patent document 2 discloses a technique in which by causing steam to touch wet paper, the wet paper is raised in temperature.
Patent document 1: Japanese patent laid-open publication No. Sho 55-137293
Patent document 2: U.S. Pat. No. 5,149,401
The inventors have made various investigations and experiments with respect to a mechanism of raising the dehydration rate of wet paper web by heating the wet paper web with steam and found the following facts. That is, there are cases where even if the supply of steam is increased in order to further raise the dehydration rate, conversely the dehydration rate will be reduced. A possible cause is that an increase in the supply of steam increases the quantity that steam condenses into water.
However, in the conventional papermaking machine described above, such a change in the dehydration rate with respect to the supply of steam is not taken into account and an optimum supply of steam is not always set. Thus, the problem of performing dehydration with good efficiency remains unsolved.
The present invention has been made in view of the problem described above. Accordingly, it is the primary object of the present invention to provide a papermaking machine and papermaking method that are capable of dehydrating a layer of paper stock with better efficiency.
To achieve the aforementioned object, the papermaking machine of the present invention as set forth in claim 1 is a papermaking machine for making paper web by holding a paper stock suspension jetted from a head box into the shape of a layer, and removing moisture while traveling the paper stock layer. The papermaking machine comprises: steam type heating means, provided in a moisture removing part as heating means for heating the paper stock layer (wet paper web) to accelerate the moisture removal, for supplying steam to the paper stock layer and heating the paper stock layer by condensation of the steam; and adjustment means for adjusting the supply of the steam performed by the steam type heating means, on the basis of a stock concentration of the paper stock layer detected when passing through the steam type heating means, so that the paper stock layer reaches a preset target temperature.
The steam used herein is not limited to saturated steam, but may be heated steam, wet air, etc. By detecting the above-mentioned stock concentration of the paper stock layer in real time, the supply of steam may be adjusted based on the information detected. In addition, by obtaining a stock concentration of the paper stock layer beforehand, the supply of steam may be adjusted based on the stock concentration obtained beforehand.
The papermaking machine of the present invention as set forth in claim 2 is characterized in that, in the construction as set forth in claim 1, the moisture removing part is a former (also called a forming part or paper layer forming part) which forms a layer of paper by holding the paper stock suspension jetted from the head box into the shape of a layer, and removing moisture while traveling the paper stock layer, or a press part which further removes moisture by applying pressure to the paper stock layer formed into the paper layer by the former.
The papermaking machine of the present invention as set forth in claim 3 is characterized in that, in the construction as set forth in claim 2, the forming part is constructed as twin wire formers equipped with wires on both sides of the paper stock layer. Note that the present invention is not always limited to twin wires, but may be applied to a long wire former or on-top former which holds only one side of a paper stock layer.
The papermaking machine of the present invention as set forth in claim 4 is characterized in that, in the construction as set forth in claim 3, the steam type heating means is provided with a steam box for guiding the supply of steam to the paper stock layer. In this case, the steam box is arranged so that the fringe of its tip opening abuts the wire or is very near the wire.
The papermaking machine of the present invention as set forth in claim 5 is characterized in that, in the construction as set forth in claim 4, the fringe of the tip opening of the steam box is provided with seal means for sealing the steam box.
The papermaking machine of the present invention as set forth in claim 6 is characterized in that, in the construction as set forth in claim 5, the seal means is a seal member which is attached to the fringe of the tip opening of the steam box and abuts the wire.
The papermaking machine of the present invention as set forth in claim 7 is characterized in that, in the construction as set forth in claim 5, the seal means is a gas jet device which is provided upstream in the traveling direction of the paper stock layer relative to the fringe of the tip opening of the steambox, and suppresses incursion of wake of the paper stock layer into the steam box by jetting gas. In this case, the gas jet device preferably jets gas toward the upstream side at a jet angle which is about 15 to 40° to wet paper web.
The papermaking machine of the present invention as set forth in claim 8 is characterized in that, in the construction as set forth in any one of claims 4 to 7, it further includes a suction box for suctioning steam jetted from the steam box toward a side opposite to the steam box across the paper stock layer.
The papermaking machine of the present invention as set forth in claim 9 is characterized in that, in the construction as set forth in claim 8, a downstream end of the suction box in the traveling direction of the paper stock layer is arranged downstream relative to a downstream end of the steam box in the traveling direction of the paper stock layer.
The papermaking machine of the present invention as set forth in claim 10 is characterized in that, in the construction as set forth in claim 8 or 9, it further includes another suction box arranged on the side opposite to the steam box across the paper stock layer and downstream in the traveling direction of the paper stock layer.
The papermaking machine of the present invention as set forth in claim 11 is characterized in that, in the construction as set forth in claim 10, the suction force of the downstream suction box in the traveling direction of the paper stock layer is set larger than that of the upstream suction box.
The papermaking machine of the present invention as set forth in claim 12 is characterized in that, in the construction as set forth in any one of claims 8 to 11, the steam box is divided into a plurality of parts in the width direction of the paper stock layer and the suction box is divided into a plurality of parts so as to correspond to the divided parts of the steam box. In this case, a jet of steam and suction of steam are adjustable for each of the divided parts.
The papermaking machine of the present invention as set forth in claim 13 is characterized in that, in the construction as set forth in any one of claims 1 to 12, the steam supplied by the steam type heating means heats the paper stock layer by acting on the paper stock layer as a collision jet.
The papermaking machine of the present invention as set forth in claim 14 is characterized in that, in the construction as set forth in any one of claims 1 to 13, it further includes control means for automatically adjusting the adjustment means.
The papermaking machine of the present invention as set forth in claim 15 is characterized in that, in the construction as set forth in claim 14, it further includes stock concentration detecting means, provided in the vicinity of the steam type heating means, for detecting a stock concentration of the paper stock layer when passing through the steam type heating means. In this case, the control means controls the supply of steam performed by the steam type heating means, on the basis of information detected by the stock concentration detecting means, so that the paper stock layer is raised to the target temperature.
In addition, the above-mentioned stock concentration detecting means is, for example, moisture percentage sensor, and the stock concentration can be estimated by moisture percentage of paper stock layer detected by the moisture percentage sensor.
The papermaking machine of the present invention as set forth in claim 16 is characterized in that, in the construction as set forth in any one of claims 1 to 15, it further includes air jet type heating means for blowing high-temperature air against the paper stock layer and heating the paper stock layer by a collision jet of the high-temperature air, provided as heating means for heating the paper stock layer, downstream in the traveling direction of the paper stock layer relative to a position at which the steam type heating means is installed.
The papermaking machine of the present invention as set forth in claim 17 is characterized in that, in the construction as set forth in any one of claims 1 to 16, the heating means comprises first heating means for performing heating on one side of the paper stock layer, and second heating means for performing heating on the other side of the paper stock layer.
The papermaking method of the present invention as set forth in claim 18 is a papermaking method of making paper web by holding a paper stock suspension jetted from a head box into the shape of a layer, and removing moisture while traveling the paper stock layer. The papermaking method comprises a step of supplying steam to the paper stock layer at a heated position and heating the paper stock layer by condensation of the steam, in such a way that the paper stock layer reaches a preset target temperature, and a step of suctioning and removing moisture from the paper stock layer. As described above, the steam used in this method is not limited to saturated steam, but may be heated steam, wet air, etc.
According to the papermaking machine of the present invention as set forth in claims 1 to 3, in the moisture removing part, the adjustment means adjusts the supply of the steam performed by the steam type heating means, on the basis of a stock concentration of the paper stock layer detected when passing through the steam type heating means, so that the paper stock layer reaches a preset target temperature. Therefore, the paper stock layer can be raised in temperature and dehydrated with better efficiency. As a result of this, the dehydration rate can be raised.
According to the papermaking machine of the present invention as set forth in claim 4, the steam type heating means is provided with a steam box for guiding the supply of steam to the paper stock layer. The steam box is arranged so that the fringe of its tip opening abuts the wire or is very near the wire. Therefore, steam can be supplied to the paper stock layer with good efficiency.
According to the papermaking machine of the present invention as set forth in claim 5, the fringe of the tip opening of the steam box is provided with seal means for sealing the steam box. Therefore, steam can be supplied to the paper stock layer with better efficiency.
According to the papermaking machine of the present invention as set forth in claim 6, the seal means is a seal member which is attached to the fringe of the tip opening of the steam box and abuts the wire. Therefore, sealing of the steam box can be enhanced, whereby steam can be supplied to the paper stock layer with good efficiency.
According to the papermaking machine of the present invention as set forth in claim 7, the seal means is a gas jet device which is provided upstream in the traveling direction of the paper stock layer relative to the fringe of the tip opening of the steam box, and suppresses incursion of wake of the paper stock layer into the steam box by jetting gas. Therefore, incursion of wake into the steam box can be reliably suppressed, whereby steam can be supplied to the paper stock layer with good efficiency.
According to the papermaking machine of the present invention as set forth in claim 8, the suction box suctions steam jetted from the steam box toward a side opposite to the steam box across the paper stock layer. Therefore, high-temperature water condensed on the surface of the paper stock layer is able to permeate through the paper stock layer. This makes it possible to reliably raise the temperature of the entire paper stock layer and dehydrate the entire paper stock layer.
According to the papermaking machine of the present invention as set forth in claim 9, a downstream end of the suction box in the traveling direction of the paper stock layer is arranged downstream relative to a downstream end of the steam box in the traveling direction of the paper stock layer. Therefore, moisture in the paper stock layer raised in temperature can be further removed, resulting in a further rise in the dehydration rate.
According to the papermaking machine of the present invention as set forth in claim 10, in addition to the above-mentioned suction box, the papermaking machine further includes another suction box arranged on the side opposite to the steam box across the paper stock layer and downstream in the traveling direction of the paper stock layer. Therefore, the dehydration rate can be further raised.
According to the papermaking machine of the present invention as set forth in claim 11, the suction force of the downstream suction box is set larger than that of the upstream suction box. Therefore, water in the paper stock layer raised in temperature by the upstream steam box can be further removed, resulting in a further rise in the dehydration rate.
According to the papermaking machine of the present invention as set forth in claim 12, the steam box is divided into a plurality of parts in the width direction of the paper stock layer and the suction box is divided into a plurality of parts so as to correspond to the divided parts of the steam box, and a jet of steam and a suction of steam are adjustable for each of the divided parts. Therefore, the dehydration rate can be adjusted for each of the divided parts.
According to the papermaking machine of the present invention as set forth in claim 13, the steam supplied by the steam type heating means heats the paper stock layer by acting on the paper stock layer as a collision jet. Therefore, the paper stock layer can be raised in temperature and dehydrated with better efficiency.
According to the papermaking machine of the present invention as set forth in claim 14, the papermaking machine further includes control means for automatically adjusting the adjustment means. Therefore, the supply of steam can be automatically adjusted.
According to the papermaking machine of the present invention as set forth in claim 15, the control means controls the supply of steam performed by the steam type heating means, on the basis of information detected by the stock concentration detecting means, so that the paper stock layer is raised to the target temperature. Therefore, the supply of steam can be adjusted so that an optimum dehydration rate is obtained.
According to the papermaking machine of the present invention as set forth in claim 16, the papermaking machine further includes air jet type heating means for blowing high-temperature air against the paper stock layer and heating the paper stock layer by a collision jet of the high-temperature air. The air jet type heating means is provided as heating means for heating the paper stock layer, downstream in the traveling direction of the paper stock layer from a position at which the steam type heating means is installed. Therefore, the paper stock layer raised in temperature by the steam type heating means can be further raised in temperature and dehydrated, resulting in a further rise in the dehydration rate.
According to the papermaking machine of the present invention as set forth in claim 17, the heating means comprises first heating means for performing heating on one side of the paper stock layer, and second heating means for performing heating on the other side of the paper stock layer. Therefore, it is possible to evenly dehydrate both sides of the paper stock layer.
According to the papermaking method of the present invention as set forth in claim 18, in such a way that the paper stock layer reaches a preset target temperature, steam is supplied to the paper stock layer at a heated position and the paper stock layer is heated by condensation of the steam. Thereafter, moisture is suctioned and removed from the paper stock layer. Therefore, the paper stock layer can be raised in temperature and dehydrated with better efficiency. This can raise the dehydration rate.
FIGS. 2(a) and 2(b) schematically show a steam box and a suction box according to the first embodiment of the present invention,
FIGS. 8(a) and 8(b) schematically show a steam box and a suction box according to a conventional papermaking machine,
1 Wet paper web(paper stock layer)
1
a Pulp suspension (paper stock suspension)
2 Head box
3
a, 3b Wire
4 Forming roll
5 Blade shoe
6, 6′, 60 Steam box (steam type heating means)
6
a Steam box main body
6
b Heat retaining body
6
c Seal member (seal means)
6
d Partition wall
6
e Steam supply chamber
6
f Steam introducing port
6
g Tip opening
7, 7A, 7′, 70 Suction box
7
d Partition wall
7
e Suction chamber
7
f Suction port
7
g Tip opening
8 Suction roll
9 Suction box
10 Steam generator
11 Valve (adjustment means)
12 Controller (control means)
13 Moisture percentage sensor (stock concentration detecting means)
14 Gas jet device (Seal means)
Embodiments of the present invention will hereinafter be described with reference to the drawings.
FIGS. 1 to 3 are used for explaining a papermaking machine constructed in accordance with a first embodiment of the present invention.
The papermaking machine of the first embodiment adopts twin wire formers, as shown in
Downstream of the blade shoe 5, the wet paper web 1 is raised in temperature by a steam box 6 and is suctioned and dehydrated by a suction box 7 installed across the wet paper web 1 from the steam box 6. Now, the steam box 6 and suction box 7 in the first embodiment will be described in further detail.
As shown in FIGS. 2(a) and 2(b), the steam box (steam type heating means) 6 as heating means is equipped with a steam box main body 6a, a heat retaining body 6b, and a seal member (seal means) 6c.
The steam box main body 6a has, for example, a machine length of about 100 to 1000 mm in the traveling direction of the wet paper web 1, and the internal space is divided into a plurality of steam supply chambers 6e in the width direction of the wet paper web 1 by partition walls 6d. Each of the steam supply chambers 6e divided by the partition walls 6d has a steam introducing port 6f for taking in steam from a steam generator 10, and a tip opening 6g facing the wire 3a. In the first embodiment, the tip opening 6g of the steam box main body 6a has a seal member 6c attached thereto, which abuts the wire 3a.
By supplying steam from the steam generator 10 to each of the steam supply chambers 6e, the wires 3a, 3b and wet paper web 1 can be heated to about 40 to 100° C. Note that it is also possible to cause the supplied steam to act on the wet paper web 1 as a collision jet. This can heat the wet paper web 1 efficiently.
The heat retaining body 6b is, for example, a heat retaining structure with a heat insulating material or heat insulating layer, or a heating device such as an electric heater, a heating steam jacket, a high-temperature air jacket, etc., and is attached to the outside wall of the steam box main body 6a so that it can retain the heat of the steam box main body 6a. This can prevent steam condensation and dew condensation from occurring on the inside wall surface of the steam box main body 6a (i.e., the inside wall surface of the steam supply chamber 6e).
The seal member 6c is attached to the fringe of the tip opening 6g of the each of steam supply chambers 6e so as to abut the wire 3a, and functions to seal the steam box main body 6a and each of the steam supply chambers 6e. This ensures sealing of the interior of the steam box main body 6a and interior of each of the steam supply chambers 6e. As to the seal member 6c, an elastic material such as rubber is suitable from the viewpoint of sealing performance, but since heat-resisting property is required, a heating-resisting material such as bakelite is also suitable. Of course, a material, such as heat-resisting rubber, which has both elasticity and heat-resisting property is more suitable.
In the case where there is no seal member 6c, wake intrudes through the gap between the upstream side of the tip opening 6g and the wire 3a and may disturb the touch of steam with the wet paper web 1, but the installation of the seal member 6c enables steam to touch the whole of the wet paper web 1 located within each of the steam supply chambers 6e. Therefore, a reduction in the efficiency at which steam condenses and adheres to the wet paper web 1 (condensation and adhesion efficiency) can be prevented.
Supply pipes connected to each of the steam supply chambers 6e are provided with valves (adjustment means) 11, through which steam is supplied from the steam generator 10 to the steambox 6. By controlling the opening and closing operation of each valve 11 with a controller 12, the supply of steam into the steam supply chambers 6e can be separately adjusted. Note that the steam used in the first embodiment may be any of saturated steam, heated steam, and wet air.
The suction box 7 has, for example, the same machine length as the steambox 6 or a machine length shorter than the steam box 6, and the interior space is divided into a plurality of suction chambers 7e at intervals of the same width as the steam box main body 6a in the width direction of the wet paper web 1 by partition walls 7d. Each of the suction chambers 7e divided by the partition walls 7d has a suction port 7f connected to a suction device (not shown), and an tip opening 7g facing the wire 3b. The suction box 7 is installed so that the tip opening 7g abuts the surface of the wire 3b.
Generally, the width of the steam box 6 and the width of the wires 3a, 3b are set equal to each other. However, for example, in the case where the width of the steam box 6 is larger than that of the wires 3a and 3b, in order to prevent steam from leaking from the exposed portion of the tip opening 6g, it is preferable to include a member which abuts (or is very near) the exposed portion to prevent the leakage of the steam. In the first embodiment, the width of the suction box 7 is approximately the same as the width of the steam box 6, so this suction box 7 fulfills the function of the aforementioned member.
By the steam box 6 and suction box 7, the wet paper web 1 is heated and dehydrated. Specifically, the steam supplied into the steam box 6 is condensed into high-temperature water in the vicinity of the surface of the wire 3a and surface of the wet paper web 1. Then, the high-temperature water gets into the wet paper web 1 by the suction operation of the suction box 7, the entire wet paper web 1 is raised in temperature by the heat transfer of the high-temperature water, and by suctioning the moisture in the wet paper web 1 by the suction box 7, the wet paper web 1 is dehydrated.
Within the steam box 6 the temperature raising process is being performed and the wet paper web 1 entering the steam box 6 is progressively raised in temperature within the steam box 6, but a time lag occurs until the whole of the wet paper web 1 is raised in temperature. Hence, in the papermaking machine of the first embodiment, as shown in
As previously mentioned, the inventors have found that there are cases where, even if the supply of steam is increased to further raise the dehydration rate, conversely the dehydration rate will be reduced. A possible reason is that an increase in the supply of steam increases the quantity of heat supplied, but the quantity that steam condenses into water is increased and causes an increase in the moisture percentage. Therefore, in order to raise the dehydration rate, how to set the supply of steam becomes important.
Hence, the inventors have investigated how the dehydration rate varies with respect to the paper stock concentration of the wet paper web 1 under a certain suction condition. The results are shown in
For example, the characteristics of the dehydration accelerating effect by steam supply are shown by lines M1 and M2 in
On the other hand, in the case where the suction pressure is fixed, the characteristic of the dehydration accelerating effect by suction is shown by line S in
Therefore, in the case of a large supply of steam, a practical dehydration accelerating effect is obtained by adding the dehydration accelerating effect by steam supply shown by the line M1 and the dehydration accelerating effect by suction shown by the line S together. As shown by line L1 in
Similarly, in the case of a low supply of steam, a practical dehydration accelerating effect is obtained by adding the dehydration accelerating effect by steam supply shown by the line M2 and the dehydration accelerating effect by suction shown by the line S. That is to say, the practical dehydration accelerating effect is represented by line L2.
Generally, the dehydrating speed v equivalent to the dehydration raising rate is expressed according to Darcy's rule by the following equation (1):
[Formula 1]
v=ΔP/(Rmat+2Rw)μ (1)
in which
In the aforementioned equation (1), assuming that the vertical differential pressure ΔP, the dehydration resistance coefficient Rmat of the wet paper web, and the dehydration resistance coefficient Rw of the wire are constant, and directing attention to the relation of the dehydrating speed v and water viscosity μ, the dehydrating speed v has an inversely proportional relation to the water viscosity μ. In addition, between the water viscosity μ and the temperature of the wet paper web, there is a relation in which the water viscosity μ becomes smaller as the temperature of the wet paper web becomes higher. That is, there is a relation in which the dehydrating speed v becomes faster as the temperature of the wet paper web becomes higher.
Normally, according to Darcy' rule, the wet paper web 1 is raised in temperature by heated steam and therefore the dehydrating speed becomes faster and the dehydration rate becomes higher, but at the same time, an increase in the stock concentration increases resistance to dehydration. As a result, the dehydration accelerating effect has a mountainous characteristic shown in
Therefore, to raise the dehydration rate, it is preferable to set an optimum steam supply according to the stock concentration of the wet paper web 1, taking such a characteristic into account. Because of this, the papermaking machine of the first embodiment, as shown in
The controller 12 adjusts the opening and closing operation of each valve 11 and controls the state of steam supplied to each steam supply chamber 6e in real time, based on information detected by each moisture percentage sensor 13, so that the temperature of the wet paper web 1 passing through each steam supply chamber 6e becomes a target wet paper temperature (which is a target temperature set beforehand according to the stock concentration of the wet paper web 1). For example, the steam supply chamber 6e is disposed at a certain spot, and the reference stock concentration of the wet paper web 1 coming to this spot is assumed to be 12%. If the stock concentration of the wet paper web 1 detected by the moisture percentage sensor 13 is 10%, the controller 12 controls the valve 11 so that the supply of steam is increased. If the stock concentration of the wet paper web 1 detected by the moisture percentage sensor 13 is 14%, the controller 12 controls the valve 11 so that the supply of steam is reduced.
In addition, since the steam jetted state and steam suctioned state can be adjusted for each of the divided regions in the steam box 6 and suction box 7, the adjustment of dehydration in the width direction of the wet paper web 1 can be easily performed.
Besides, because steam is supplied to the wet paper web 1 through the wire 3a, there is no possibility that the fringe of the tip opening 6g of the steam box 6 will touch the wet paper web 1 and destroy it. In addition, property and color changes of pulp that occur when high-temperature steam directly touches the wet paper web 1 can be prevented. That is, like prior art, in the case where steam is blown directly against the wet paper web 1, it is necessary to provide a gap between the steam box 6 and the wet paper web 1 to prevent damage to the wet paper web 1, and consequently, a large quantity of steam is discharged. However, in the papermaking machine of the first embodiment, both sides of the wet paper web 1 are supported by twin wires 3a and 3b and the steam box 6 touches the wire 3a, whereby the aforementioned gap can be eliminated without damaging the wet paper web 1 and, compared with the prior art, the quantity of steam discharged can be suppressed. That is, since steam loss can be prevented, steam can be efficiently utilized.
Because sealing of the steam box 6 is ensured by the seal member 6c of the steam box 6, the discharge of steam from inside the steam box 6 to outside the steam box 6 can be further suppressed.
In the conventional papermaking machine, the focus of attention is that steam permeating into the wet paper web 1 raises the temperature of the wet paper web 1 and dehydrates the wet paper web 1. Because of this, it is necessary to install the steam box 60 and suction box 70 (see FIGS. 8(a) and 8(b)) at positions where steam is in a permeable state, that is, a state before completion of dehydration of the wet paper web 1 of the former final part, and where the wet paper web 1 is caused to be in a porous state or a state in which interstices are formed. On the other hand, in the papermaking machine of the first embodiment, attention is further directed to the following points. That is, by the suction operation of the suction box 7, the moisture in the wet paper web 1 is replaced with the high-temperature water condensed near the surface of the wet paper web 1, whereby the wet paper web 1 is raised in temperature and dehydrated. Therefore, steam does not always need to permeate into the wet paper web 1, as is done in prior art.
That is, in prior art, the steam box has to be installed at a position before completion of dehydration (i.e., near the former outlet), but according to the present invention, it is possible to install it more upstream. This makes it possible to accelerate the dehydration of the wet paper web 1 in the former from the upstream side. Moreover, as described above, because the papermaking machine of the first embodiment performs optimum steam supply according to the stock concentration of the wet paper web 1, the heating and dehydration efficiency can be raised. Therefore, it becomes possible to perform the dehydration in the former with great efficiency, and consequently, the former can be made compact, whereby space to install the former can be saved.
The heat transfer efficiency of the papermaking machine of the first embodiment by steam condensation is about 25 times as high as that of the conventional papermaking machine by steam permeation and is extremely high compared with the prior art. Therefore, a rise in the temperature of the wet paper web 1 by the conventional papermaking machine is so insufficient that even if the suction box 9 is provided downstream of the suction box 70, a high effect of dehydration cannot be obtained. On the other hand, in the papermaking machine of the first embodiment, a rise in the temperature of the wet paper web 1 is so sufficient that a high effect of dehydration is obtained by the suction roll 8 and suction box 14 arranged downstream of the suction box 7. Thus, it is possible to accelerate dehydration of the wet paper web 1.
In the first embodiment, the internal spaces of the steam box 6 and suction box 7 are divided into several parts so that the jetted state of steam and the suctioned state of steam can be adjusted for each of the divided regions. However, in the case where a stock concentration difference in the width direction of the wet paper web 1 is practically negligible, it is not necessary to divide these spaces (i.e., the partition walls 6d and 7d are not needed). In this case, a representative stock concentration (e.g., at the laterally central portion of the wet paper web 1) may be obtained from each moisture percentage sensor 13, and based on this representative stock concentration, the supply of steam required for the wet paper web 1 to rise to the target wet paper web temperature may be set. Alternatively, a single moisture percentage sensor 13 may be installed at a single spot in the width direction of the wet paper web 1 (e.g., at the laterally central portion of the wet paper web 1), and based on a stock concentration obtained by this moisture percentage sensor 13, the supply of steam required for the wet paper web 1 to rise to the target wet paper web temperature may be set.
While the first embodiment is constructed such that the opening and closing operations of the valves 11 are automatically adjusted based on information detected from the moisture percentage sensors 13 by the controller 12, the valve opening and closing operations may be manually performed by the operator, based on information detected from the moisture percentage sensors 13.
While the first embodiment is constructed such that the steam box 6 and suction box 7 are provided in the former that forms a layer of paper, they may be provided in a press part (which applies pressure to the paper stock layer formed by the former to further remove moisture) arranged downstream of the former.
Next, a papermaking machine according to a second embodiment of the present invention will be described.
As shown in
As described in the first embodiment, within the steam box 6 the temperature raising process is being performed and the wet paper web 1 traveling through the steam box 6 is gradually raised in temperature within the steam box 6, but a time lag occurs until the whole of the wet paper web 1 is raised in temperature. Hence, in the papermaking machine of the second embodiment, the wet paper web 1 in which the effect of dehydration has become higher by being raised in temperature within the steam box 6 is further dehydrated by the suction box 7A. Since the suction box 7A suctions the wet paper web 1 in which the effect of dehydration has become higher, further dehydration can be performed, even if its suction force is equal to that of the suction box 7. However, it is preferable to set the suction force of the suction box 7A larger than that of the suction box 7. This makes it possible to perform dehydration more efficiently, whereby the dehydration rate can be raised.
Next, a papermaking machine according to a third embodiment of the present invention will be described.
As shown in
As described above, a time lag occurs until the whole of the wet paper web 1 is raised in temperature within the suction box 6. Therefore, by arranging the suction box 7 so as to be shifted downstream, the wet paper web 1 can be dehydrated with better efficiency, resulting in a further rise in the dehydration rate.
In the third embodiment, the suction box 7 according to the first embodiment is arranged so that it is shifted downstream by a predetermined distance. However, with the upstream end of the suction box 7 of the first embodiment fixed at its original position, only the downstream end of the suction box 7 may be positioned downstream relative to the downstream end of the steam box 6.
Next, a papermaking machine according to a fourth embodiment of the present invention will be described.
As shown in
This can suppress incursion of wake into the steam box 6 more reliably. In the case where wake can be sufficiently suppressed by the air jet device 14, the upstream seal member 6c of the steam box 6 may be omitted.
Next, a papermaking machine according to a fifth embodiment of the present invention will be described.
As shown in
While the present invention has been described with reference to the preferred embodiments thereof, the invention is not to be limited to the details given herein, but may be modified within the scope of the invention hereinafter claimed.
The installation position of the steam box 6 can be determined beforehand in making a design, and the stock concentration (the reference stock concentration) of the wet paper web 1 at the installation position can also be predicted in the stage of the design. Therefore, in papermaking machines, steam supply may be performed so that the temperature of the wet paper web 1 becomes a target wet paper temperature which corresponds to the reference stock concentration. In the above-described embodiments, the actual stock concentration of the wet paper web 1 is detected by the moisture percentage sensor 13, and when there is a difference between the stock concentration of the wet paper web 1 passing through the steam box 6 and the aforementioned reference stock concentration, the supply of steam to the steam box 6 is adjusted by feedback control in order to correct for this difference. However, in the case where such a concentration difference is almost negligible, a constant supply of steam may be continuously performed in an open loop without providing the moisture percentage sensor 13.
By providing means for detecting the temperature of the wet paper web 1 and performing feedback control based on the detected information, steam supply may be adjusted so that the wet paper web 1 reaches the target wet paper web temperature. Even in this case, the wet paper web 1 can be raised in temperature and dehydrated with good efficiency, resulting in arise in the dehydration rate.
Downstream of the steam box 6, there may be provided air jet type heating means for blowing high-temperature air against the wet paper web 1 and heating the wet paper web 1 by a collision jet of high-temperature air. With this configuration, the wet paper web 1 raised in temperature within the steam box 6 can be further raised in temperature, whereby it becomes possible to further raise the dehydration rate by the suction roll 8, suction box 9, etc.
Since the steam box 6 has a higher effect if it is employed when the moisture percentage of the wet paper 1 is high, it is preferable to install the steam box 6 in the former in which the moisture percentage of the wet paper 1 is high, but it may be installed in the upstream portion (near the inlet) of the press part. Because the air jet type heating means has a higher effect if it is employed in a state lower than the moisture percentage of the wet paper web 1 in the former, it is preferable to install the air jet type heating means in the press part which is lower in the moisture percentage of the wet paper web 1 than the former, but it maybe installed in the downstream portion (near the outlet) of the former.
The above-described embodiments are constructed such that the seal member 6c abuts the wire 3a in order to ensure sealing of the steam box 6. However, if sealing of the steam box 6 can be ensured, the seal member 6c may be provided in close proximity to the wire 3a. If sealing of the steam box 6 is ensured by causing the tip opening 6g of the steam box 6 to abut the wire 3a or arranging the tip opening 6g in close proximity to the wire 3a, there is no need to provide the seal member 6c.
The present invention is not limited to twin wires, but may be applied to a long wire type former or on-top former which holds only one side of the paper stock layer.
The present invention is applicable to a papermaking machine and papermaking method for making paper web by holding a paper stock suspension into the shape of a layer, and removing moisture while making this paper stock layer travel.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP04/13544 | 9/16/2004 | WO | 2/6/2007 |
