Patent Publication Number: US-6210535-B1

Title: Stock feed system for a multi-layer headbox and method in the operation of a multi-layer headbox

Description:
This application is related to U.S. patent application Ser. No. 08/323,839 filed Oct. 17, 1994, the specification of which is hereby incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a stock feed system for a multi-layer headbox and a method in the operation of a multi-layer headbox. 
     In the prior art, systems for the operation of multi-layer headboxes are known in which there are separate fresh stocks for the surface layers of a pulp flow discharged from the headbox and for the middle layers thereof. Thus, in the prior art systems, there have been at least double fresh-stock systems for the formation of the different pulp layers. In the prior art equipment, the stocks introduced along at least two separate fresh-stock lines have been processed in vortex cleaning and in deaeration tanks, and feeds of fillers or starch complying with the required paper grade have been passed into the at least two fresh-stock lines. 
     With the prior art technology, a paper machine into whose headbox stock is fed at different consistencies requires a complete short circulation which comprises more than one stock systems. This is also the case when the stock in the different layers is in the other respects the same, but the consistencies are different. 
     Increased consistency of layers may be necessary, for example, in order that an improved purity of the layers can be achieved. When the middle layer is thicker than the surface layers, water of the middle layer is drained through the surface layers to a relatively limited extent. In such a case, particles of the middle layer are not carried along with the water into the surface layer, and the purity of the layers remains good. 
     A very thick middle layer is highly flocculated, in which case it has a high bulk. Then, the structure of the paper results in a bulky paper of good bending stiffness, in which the formation of the middle layer is poor but the formation of the surface layers is good, which secures good printing properties. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a new and improved stock feed system for a multi-layer headbox and a method in the operation of a multi-layer headbox in which each layer of a multi-layer pulp web discharged from the headbox can be diluted separately and/or simultaneously, in which case, e.g., the stocks passed into the inlet headers of a multi-layer headbox can be given the desired consistencies. 
     In order to achieve the object stated above, and others, in the present invention, the stock for one or several layers in the feed pipe systems for the inlet headers of the headbox are diluted. The diluting can take place before screens in the feed path through the feed pipe system if each layer has a screen of its own, or after the stock has been divided to be fed into the different layers. 
     In the present invention, in a paper machine that comprises a multi-layer headbox and therein at least two separate inlet headers or equivalent, for the inlet headers, separate stocks are prepared out of the same fresh stock, and they are passed into the inlet headers from the same stock tank. According to the invention, the fresh stock passed out of the stock tank is divided into two or more component flows. Into these component flows to be fed into the multi-layer headbox, chemicals and/or additives purposeful for the quality or the economy of production of different paper grades are passed. 
     Further, according to the invention, the system also includes dilution-water lines passing to the stock system of the headbox. Preferably, the dilution lines are arranged to pass from a dilution-water header through valves and to join the stock line connected with the inlet header for each stock layer. Thus, according to the invention, in the stock feed system, each layer can be diluted separately and/or simultaneously, in which case, e.g., the stocks passed into the inlet headers of a multi-layer headbox can be given the desired consistencies. When certain additives are added to the stock flow, it may be the case that the stock has a low dry solids content before mixing of the additive. Thus, before the additive is passed into the stock, the stock may be diluted to the desired dry solids content to add the additive concerned into the fresh stock in an optimal manner. 
     In the stock system in accordance with the present invention for a multi-layer headbox, into each inlet header of the multi-layer headbox, a stock concept is passed which has been produced out of the same fresh stock by adding the necessary chemicals and fillers to the fresh stock. The stock feed system in accordance with the present invention for a multi-layer headbox thus comprises at least one dilution-water line. 
     In the method in accordance with the invention, the stock for each inlet header is prepared out of a single fresh stock by adding the necessary chemicals and fillers to the fresh stock. Dilution water is passed into at least one stock line that passes into an inlet header of the multi-layer headbox. Thus, in one embodiment, the method is used in the operation of a multi-layer headbox having at least two inlet headers into which a respective stock concept is passed, the stock flowing from the inlet headers through a system of distributor pipes into a turbulence generator and further into a slice cone. A single flow of fresh stock is provided and then divided into a plurality of stock flows. Chemicals and/or fillers are independently added to each of the stock flows. Each of the stock flows is then passed after the chemicals and/or fillers have been added thereto into a respective one of the inlet headers, and a diluting-water flow is passed into at least one of the stock flows. Preferably, the diluting-water flow is passed into individual ones of the stock flows which form outer layers of a web discharged from the headbox. 
     The invention will be described in the following with reference to some preferred embodiments of the invention illustrated in the figures in the accompanying drawings. However, the invention is not confined to the illustrated embodiments alone. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The following drawings are illustrative of embodiments of the invention and are not meant to limit the scope of the invention as encompassed by the claims. 
     FIG. 1 shows an embodiment of the invention in which the stock flow passed out of the fresh-stock tank is divided into three component flows which are passed further, after feeds of chemicals and fillers, into the different inlet headers in the multi-layer headbox, and in which system a dilution-water line is connected with each line passing into an inlet header. 
     FIG. 2 shows a second embodiment related to the stock feed system in accordance with the invention for a multi-layer headbox. 
     FIG. 3 shows the arrangement of introduction of dilution water with the inlet header and the regulation valves. 
     FIG. 4A is a side view of a multi-layer headbox in accordance with the invention. 
     FIG. 4B is a top view of the multi-layer headbox as shown in FIG.  4 A. 
     FIG. 5A shows a first preferred embodiment of the supply of dilution water into the stock. 
     FIG. 5B shows a second preferred embodiment of the supply of dilution water. 
     FIG. 5C shows a third preferred embodiment of the supply of dilution water. 
     FIG. 5D shows a fourth preferred embodiment of the supply of dilution water. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the accompanying drawings wherein like reference numerals refer to the same or similar elements, FIG. 1 is a schematic illustration of a first preferred embodiment of the invention, which is favorably suitable for the production of SC-paper. As shown in the figure, a multi-layer headbox denoted generally by reference numeral  10  comprises three inlet headers, i.e., the inlet headers  11 , 12  and  13 . From the inlet header  11 , a stock M 1  is passed through a distribution manifold having distribution pipes  14   a   1.1 ,  14   a   1.2 , . . . to a turbulence generator  15  into turbulence tubes  15   a   1.1 , 15   a   1.2 , . . . therein and further from the turbulence tubes to a slice cone  16 . From the inlet header  12 , a stock M 2  is passed through respective distribution pipes  14   a   2.1 , 14   a   2.2 , . . . of the distributor manifold  14  to the turbulence generator  15  into respective turbulence tubes  15   a   2.1 , 15   a   2.2 , . . . further into the slice cone  16 . Similarly, from the inlet header  13 , a stock M 3  is passed through distribution pipes  14   a   3.1 , 14   a   3.2 , . . . of the distributor manifold  14  to the turbulence generator  15  into respective turbulence tubes  15   a   3.1 , 15   a   3.2 , . . . and further into the slice cone  16 . Thus, by means of the multi-layer headbox shown in FIG. 1, a paper web is formed out of three stocks or stock concepts M 1 ,M 2  and M 3 . 
     In the present invention, the system comprises a single stock system, the stocks M 1 ,M 2  and M 3  being formed out of the same fresh stock M which is passed out of a single fresh-stock tank  17 . As shown in FIG. 1, the fresh stock M is passed out of the fresh-stock tank  17  along a flow line  18   a  and branched at a branching point P 1  into two branch lines  18   a   2  and  18   a   3 . In the embodiment of FIG. 1, in the branch line  18   a   2 , a chemical solution  3   a  is added to the stock M, and in the branch line  18   a   3 , a chemical solution  3   b  is added. The chemical solutions may be a filler or starch. In the lines  18   a   2 , 18   a   3 , the stocks are made to flow further by means of pumps  19   a   1  and  19   a   2  so that, along the line  18   a   3 , the stock is passed into a machine screen  20   a   1 . A retention agent  5   b  is fed into the stock before the machine screen  20   a   1 , and a retention agent  5   bb  is fed into the stock after the machine screen in a flow line  21   a   1  therefrom. In this manner, a good mixing of the retention agent and the stock is achieved. Along the line  21   a   1 , the stock M 2  that was formed is passed into the middle inlet header  12  of the multi-layer headbox. 
     From the line  18   a   2  after the pump  19   a   1 , from a branch point C, a line  18   a   2.1  passes to a machine screen  20   a   2 , and from the machine screen  20   a   2 , the line  21   a   2  passes to the multi-layer headbox. At the front side of the machine screen  20   a   2 , a retention agent  5   a  is fed into the line  18   a   2.1 , and after the machine screen  20   a   2 , a retention agent  5   aa  is fed into a line  21   a   2  therefrom. Along the line  21   a   2 , the stock flow M 3  is passed into the inlet header  13  of the multi-layer headbox. 
     Also from the branch point C, a line  18   a   2.2  passes to a machine screen  20   a   3  and further into the multi-layer headbox. Into the line  18   a   2.2 , before the machine screen  20   a   3 , a retention agent  5   c  is fed, and after the machine screen  20   a   3 , a retention agent  5   cc  is fed into a flow line  21   a   3  therefrom. Along the line  21   a   3 , the stock flow M 1  is passed into the inlet header  11  of the multi-layer headbox. 
     Thus, in view ofthe above-described construction, the stock will comprise three layers composed of different stock concepts. In FIG. 1, reference arrows  100   a   1 , 100   a   2 , 100   a   3  represent the feed ducts for dilution water and is a preferred embodiment of the invention wherein the dilution water is passed to the front side of the screens  20   a   1 , 20   a   2 , 20   a   3 , seen in the flow direction of the stock flow, after feed points E 1 ,E 2 ,E 3  of the retention agents  5   a,    5   b,    5   c,  respectively. The invention is, however, not restricted to these favorable location of the point of introduction of the dilution-water alone. According to the invention, the desired consistency of the stock flow can be obtained by adding the desired amount of dilution water to each layer. For example, the purity of the layers can be promoted so that the uppermost web layers and the bottommost web layers in relation to the middle layer of the web are kept more dilute, in which case, less water is drained from the middle layer through the surface layers and, thus, the surface layers remain therefore pure. In such a case, out of the middle layer, particles are not removed along with drainage to the same extent as in an embodiment in which a large amount of water is also drained from the middle layer. In the present application, dilution water is understood as a substance in general that is made to flow and by whose means the consistency of the stock can be diluted. For example, clean water may be used a dilution flow or, for example, a water that has a low content of fibers. 
     FIG. 2 shows an embodiment of the invention in which one unified stock flow M is passed out of the stock tank  17  along a line  22   a   1  to a branch point D 1 . After the branch point D 1 , a chemical  3   a ′ is added to the fresh stock M into a line  220   a   1  branching therefrom. 
     By means of the pump  19   a   1 ′, the stock is made to flow further into a machine screen  23   a   1 , and before the machine screen  23   a   1 , a retention agent  5   a ′ is added, and after the machine screen  23   a   1 , a retention agent  5   aa ′ is added to flow line  24   a   1 . The stock M 3 ′ flow is passed along the line  24   a   1  into the inlet header  13  of the multi-layer headbox. 
     From the branch point D 1 , the stock M which does not flow into flow line  220   a   1  is made to flow along a line  22   a′   1  to a branch point D 2 , from which the stock M is branched into the lines  220   a   2  and  220   a   3 . Into the line  220   a   2 , a chemical  3   b ′, such as filler or starch, is added into the stock M before a pump  19   a   2 ′ associated with the flow line. By means of the pump  19   a   2 ′, the stock concept is passed further into a machine screen  23   a   2 . Before the machine screen  23   a   2 , a retention agent  5   b ′, such as some suitable chemical, is added to the stock, and after the machine screen  23   a   2 , the retention agent  5   bb ′ is added to the stock. The stock concept M 2 ′ produced in this manner is passed further along a line  24   a    2  into the multi-layer headbox, and more particularly into its middle inlet header  12 . 
     Similarly, from the branch point D 2  the stock M is passed along the line  220   a   3  into the machine screen  23   a   3  after the feed of chemical  3   c ′ thereto, by means of the circulation produced by a pump  19   a   3 ′. Before the machine screen  23   a   3 , a retention agent  5   c ′ is added, and after the machine screen  23   a   3 , a retention agent  5   cc ′ is added, and the concept M 1 ′ thereby produced is passed further along a line  24   a   3  into the inlet header  11  of the multi-layer headbox  10 . 
     Thus, in the concept in accordance with the invention, just a single circulation of stock is used, in which there is just one starting fresh stock M. The fresh stock M is processed further by to it adding chemicals and fillers, whereby out of one fresh stock M all the necessary different stock concepts M 1 ′,M 2 ′ and M 3 ′ are obtained for the different inlet headers  11 , 12  and  13  of the multi-layer headbox. 
     In FIG. 2, an embodiment is shown in which the dilution-water lines  100   a   1 , 100   a   2 , 100   a   3  are passed to the inlet side of the stock screens  23   a   1 , 23   a   2 , 23   a   3 , respectively, and to the outlet side of the pumps  19   a   1 ′, 19   a   2 ′, 19   a   3 ′. The dilution water is passed to the lines  220   a   1 , 220   a   2 , 220   a   3  preferably to the rear side of the feed points E 1 ,E 2  and E 3  of the retention agents  5   a ′, 5   b ′, 5   c ′, seen in the flow direction. The figure shows an embodiment in which three pump devices  19   a   1 ′, 19   a   2 ′, 19   a   3 ′ are employed. Within the scope of the invention, an embodiment is, of course, possible in which one pump device only is used, for example, in the line  22   a   1 . Thus, it is also possible to make the stock flow out of the tank  17  by means of one pump into the stock lines  220   a   1 , 220   a   2  and  220   a   3 . 
     FIG. 3 illustrates the passing of the dilution water out of an inlet header J 1  into the lines  100   a   1 , 100   a   2  and  100   a   3 . Each of the lines  100   a   1 , 100   a   2  and  100   a   3  comprise a regulation valve V 1 ,V 2  and V 3 , respectively, by whose means the dilution-water flow can be regulated into stock lines  18   a   2.1 , 18   a   3  and  18   a   2.2 . In the embodiment of FIG. 3, the dilution water is introduced after the points E 1 ,E 2 ,E 3  of addition of retention agents  5   a ′, 5   b ′, 5   c ′ to the stock line. The dilution water is introduced before machine screens  23   a   1 , 23   a   2  and  23   a   3 , so that the dilution water is mixed efficiently with the stock M, which has been passed out of the common stock tank  17  of the system. Thus, in the stock circulation system in accordance with the invention exemplified by this embodiment, the fresh stock M is passed from one common tank  17  and branched into one or several branch lines, in which the necessary fillers/additives are added and, moreover, the necessary diluting of the fresh stock is also carried out. 
     FIG. 4A is a side view of a multi-layer headbox used in the system in accordance with the invention, it being understood that the system can be used in any number of headbox having similar or different constructions. In the illustrated embodiment, a fresh stock M is passed out of the same stock tank  17  through the points for addition of additives and further into the inlet header  11 ,  12  and  13  of each of the individual layers in the multi-layer headbox  10 . As shown in FIG. 4A, the construction is in the other respects similar to those shown in the embodiments of FIGS. 1 and 2, except that, after the tube bank or distribution manifold  14  related to each of the inlet headers  11 , 12 , 13 , the headbox comprises intermediate chambers T 1 , T 2  and T 3 . Thus, the fresh stock is introduced from the stock tank  17  and branched into the branch lines and passed, after possible additions of additives and dilution water, into the respective inlet headers  11 , 12 , 13 . From the inlet headers, the stock concepts M 1 ,M 2 ,M 3  are passed into the tube bank  14 , into the intermediate chambers T 1 ,T 2  and T 3 , respectively, and further, through the turbulence tubes in the turbulence generator  15 , into the slice cone  16 . The slice cone  16  comprises aprons f 1 ,f 2 . The aprons f 1 ,f 2  are arranged at least between each of the stock concepts M 1 ,M 2  and M 3  to provide separation for the same in the slice cone  16 . 
     FIG. 4B is a top view of the system shown in FIG.  4 A. In this figure, the dilution-water line  100   a   1  for dilution water connected with the inlet header  11  is shown. 
     FIG. 5A shows an embodiment of the invention in which the dilution water is passed at an acute angle α 1  along the line  100   a   1  into the stock flow, into the stock line  220   a   1 . 
     FIG. 5B shows an embodiment of the invention in which the dilution-water line  100   a   1  is passed centrally into the stock line  220   a   1  through a tube portion extending into the stock flow. The dilution flow is discharged from the dilution-water line  100   a   1  in the direction of the stock flow into the stock line  220   a   1 . 
     FIG. 5C shows an embodiment of the invention in which the dilution water is passed along the line  100   a   1  into the stock line  220   a   1  and at an acute angle α 2  against the stock flow. 
     FIG. 5D shows an embodiment of the invention in which the dilution water is passed along the line  100   a   1  centrally into the stock line  220   a   1  which has a L-shaped portion, i.e., two portions perpendicular to one another. The dilution water is passed into one of the portions of stock line  220   a   1  in the direction of flow of the stock flow. 
     The examples provided above are not meant to be exclusive. Many other variations of the present invention would be obvious to those skilled in the art, and are contemplated to be within the scope of the appended claims. For example, the dilution water may be passed into each of the flow lines  18   a   2.1 , 18   a   2.2 , 18   a   3  in FIG. 1 or  220   a   1 , 220   a   2 , 220   a   3  in FIG. 2 in any of the ways shown in FIGS. 5A,  5 B,  5 C and  5 D.