US3813283A - Controlling drainage by addition of longs and fines to stabilize stock system - Google Patents

Abstract

IN A FOURDRINIER TYPE PAPERMAKING MACHINE HAVING A PLURALITY OF INTERRELATED MATERIAL FLOWS INDICATIVE OF A STATE OF EQUIBRIUM, THAT EQUILIBRIUM CAN BE CONTROLLED BY CONTROLLING ONE OF THE FLOWS, NAMELY THE DRAINAGE FLOW. AN ACTUAL DRAINAGE FLOW IS METERED AND COMPARED TO A DESIRED DRAINAGE FLOW AND LONG OR FINE FIBERS ARE INTRODUCED INTO THE MIXED STOCK IN A RATIO DETERMINED BY THE COMPARISION STEP TO MAKE THE TWO DRAINAGE FLOWS EQUAL.

Description

3,813,283 CONTROLLING DRAINAGE BY ADDITION OF LUNGS AND I y 28, 1974 J. c. URBAS FINES To STABILIZE STOCK"SYSTEM Filed March 10 1972 3 Sheets-Sheet l zozE FLo w PRIOR ART i0 GrzouHDwoob b ocK J. c. URBAS 3,813,283 CONTROLLlHG DRALNAGE BY ADDITION OI LUNGS AND May 28, 1974 FINES TO STABIIJIZE STOCK SYSTEM 7 Filed March 10 3 Sheets-Sheet 21 6rzouNDwooD STOCK J. c. URBAS 3,813,283 CONTROLLING DRAINAGE BY ADDITION OF LUNGS AND May 2s, 1974 FINES TO STABILIZE STOCK SYSTEM 3 Sheets-Sheet 3 Filed March 10 1972 Ill llll l|| United States Patent 3,813,283 CONTROLLING DRAINAGE BY ADDITION OF LONGS AND FINES TO STABILIZE STOCK SYSTEM John Christopher Urbas, 200 Comber Ave., Dorval, Quebec, Canada Filed Mar. 10, 1972, Ser. No. 233,529

Int. Cl. D21f 1/60 US. Cl. 162-190 6 Claims ABSTRACT OF THE DISCLOSURE This invention relates in general to the manufacture of paper and more particularly to a method for stabilizing stock induced drainage variations at the fourdrinier.

The primary objectives of the fourdrinier process are to consistently fulfill certain quality requirements in the finished product and to achieve sufficient dewatering and consolidation of the web to effect ready transfer to subsequent and more efficient dewatering stations. These objectives appear to be very straightforward and perhaps even obvious. However, achievement of these objectives, even in modern mills, is far from straightforward and the techniques used are anything but obvious.

When analysing the fourdrinier portion only of the paper making process, it becomes apparent that a great number of features affect the quality of the web as it is passed to the next section in the process. Some of these influencing features include: changes in fiber or stock characteristics such as structure, dimensions and proportions; changes in chemical and thermal characteristics; changes in the nature of diluent in both quantity and quality; changes in the drainage performance of the fourdrinier due to wear and tear on equipment, plug-ups, readjustments or seasonal capacity losses; lack of reliable and accurate indicators to describe the origin, nature and severity of changes; heavy dependence on subjective analysis (inconsistent due to rotating calibre and attitude of personnel); the fact that the fourdrinier is a composite of several highly interrelated hydraulic circuits which are on manual control and in their ensemble are considered highly complex even to the devout student; and the fact that the fourdrinier is the most accessible area where compensations for deficiencies in other segments of the process can be made, these compensations tending to reduce or hinder the tolerance of the process to other kinds of change.

In an attempt to overcome the above-mentioned problem features, palliative and/or trial and error practices are often relied upon. These practices ultimately prove costly due to losses in output, quality and unnecessary furnish costs. It becomes evident that overcoming the problem features becomes, in itself, a problem in advanced process control, focused on sustaining an optimized equilibrium. The degree of success relates directly to two basic requisites of good process control: (1) the timely availability of information regarding the variables of concern, and (2) the control capability to accommodate them. Paper making, unfortunately, continuously violates in varying degrees these two basic requisites.

The variations which accumulate in the finished product at the reel are commonly referred to as being in machine direction (MD) or in cross direction (CD). It is often 3,813,283 Patented May 28, 1974 difficult to identify the source of the variations and even with correct diagnosis, limited correction facilities at the needed location may frequently impose further restrictions since palliative action must be taken.

Overall process equilibrium might be described as that period when reel caliper is sufliciently uniform and stable that process adjustments are unnecessary. A number of sub-equilibria influence the duration of the overall equilibrium explaining why this duration can range from fifteen minutes to something that lasts for days. The duration and size of change describe the degree of process stability which is a good index of machine performance. Keeping changes to a minimum is papermakings major objective. A change, unattended, can start with quality rejects, multiply into breaks, loss due to torn-off and other rejects as the trouble compounds itself while running its transient and elusive course. In particular, transient MD changes which are of stock origin do not lend themselves to easy solutions, at least not with existing equipment.

Attempts in the past to control the stock have been highly complex, expensive and/ or ineffective. For example in one system for controlling stock, the surface of the paper issuing from the dryers is optically examined for fiber density. The obtained fiber count is compared to a desired fiber count and an error signal proportional to the difference between counts is generated to direct a control device which adjusts the manufacturing process of the fibrous material to provide the desired fiber count per unit length in the manufactured material. This system is especially disadvantageous since it must obtain its count from the essentially finished product and hence the time between detection and correction, when measured in terms of feet of paper manufactured, becomes economically unacceptable. The system is complex, expensive and at the high speeds employed in making paper would not be instantaneous as required.

In another example of a control system a sample of the stock is drawnoif and a measurement of the fiber length, cross-sectional area and volume is made. The sample is diluted, an electrolyte solution is added and signals are produced in the sensing head indicative of particle size. The signal information from the sensing head is then delivered to suitable amplifier and control means for control of the stock input. This system also involves highly complex electronic circuitry and, like the previous example, would not be easily adaptable to existing'equipment. In addition the time lag between detection and correction would not be acceptable. Neither of these systems will readily accommodate the usual condition where the stock includes fibers of highly variable lengths.

Yet another attempt approaches a solution for the problems encountered with stock having coarse (long) and fine (short) constituents. With this process the mixed stock is first sifted to obtain the fine constituents, then to obtain the coarse constituents below a specific size, any left over being ground up and resifted. Then the constituents are mixed in a predetermined and reasonably constant ratio. This should then ensure a paper of a specific desired wet strength. However this system is not a feedback system and it is concerned with the initial preparation of the stock.

There is no provision for continuously determining whether the stock is of the correct proportions and no provision for altering the stock proportions at or near the headbox in response to such a control device.

In order to achieve effective control of stock variations, one must therefore investigate their origin, behaviour and influence.

At equilibrium at the wet end incoming stock is combined in specific proportions with recirculating fibers in the wire pit. Furnish or stock is again a difficult item to characterize but a method called Fines Ratio has proven to be a satisfactory tool for this application. If the fourdrinier wire is considered as a go, no-go gauge, the fibers may be divided into two segments; fines if they can pass through the wire and longs if they cannot. The ratio of fines to longs is called F (Fines Ratio) and is essentially an index of fiber quality. Varying these proportions changes the properties of the paper not only at the dry end but also the behaviour at the wet end, namely drainage rates, flow distribution, fiber fractionation and ultimately fiber consolidation and wet sheet strength.

The mass balance (water and solids) must be maintained at all times and may be expressed as A+B+C=W+X+Y+Z,

wherein A is mixed stock flow, B is dilution water flow.

C is shower water flow, W is the flow to the presses, X is the fiatbox flow, Y is the wirepit flow and Z is the reject flow. In setting up equilibrium, the objective is to have the dryest sheet going to the presses with the best formation. This is achieved by the adjustment of the recirculation (R) and the equilibrium (E). Equilibrium as established may be described by the proportions of W:X:Y:Z. As equilibrium is displaced in either direction, this results in an increasing or decreasing W and produces a new distribution of WzX: YzZ.

vIt is apparent that there is an allowable range of equilibrium positions, each set for a purpose and capable of a numerical description. All ramifications will not be explored here although the three principal methods of displacing equilibrium should be remembered, namely 1. intentional change by flow adjustments of R, A, B

or C

2. gradual deterioration of the drainage capacity of the table 3. uncontrolled changes in stock which alter the mass balance relationships.

Recognizing the importance of sustaining a given equilibrium it is obvious that displacements by the last method, the uncontrolled stock change, can be a major factor in a machine's output, both in quality and runnability.

It can be said that each machine at a given equilibrium can tolerate a fixed variation in stock without atfecting runnability. This variation, termed Tolerance Quotient (TQ), may be either positive or negative and not necessarily by the same amount. It is expressed in appropriate units of stock quality and is plotted vertically against time. The TQ should be expected to diminish with time due to normal wear and tear, but the rate of decay will vary with the service attention given the machine. This varies with the operation and deserves only passing mention since greater importance must be assigned to the specific TQ value at all times.

Peak TQ, at time zero, achieved after a thorough machine clean-up, alignment and adjustment to optimized setting is not necessarily consistent with every start-up. Maximum TQ settings can only be expected occasionally if trial and error techniques are used. This partially explains why papermakers shun on-the-run adjustments and even why two supposedly identical machines perform differently.

Occasionally adjustments are mandatory. Due to lack of controls the stock change may be large enough to exceed-the existing TQ and the sheet will break. An intentional repositioning of the equilibrium is then required to accommodate the new conditions.

Interference with equilibrium is reviewed in the preceding examples with particular emphasis on stock originated MD variations. The following summary merely serves as additional emphasis on the potential which exists in a. truly stable equilibrium.

More paper fewer machine upsets fewer breaks fewer quality rejects less torn-off less loss due to fewer recovery cycles higher machine eflicie'ncy fewer maladjustments like draws, steam pressure,

calendar stack cooling and heating reduced operator workload permits higher attention to otherwise neglected areas Less cost constant conditions identify true CD profile and permit correction and raise to new level.

stability permits use of less chemical furnish because needed margin of safety in'sheet strength is not needed.

Stock variations therefore trigger the majority of all production losses and any method of subduing or eliminating them is equatable to profit gain. This incentive has fostered various developments such as controlled refining, selective screening, special blending, etc.

The present invention provides an automatic stock stabilizing system which reduces the variables to only two, the sum of which is a constant. Thus, a variation in one results in a corresponding variation in the other, specifically in W. The system provides means for making each of the flows constant with two exceptions and provides a means for determining the proper correction required and applying that correction. The measured quantity is the drainage which is sometimes proportional to the tages. The stock stabilizing system can be considered as r the nucleus of a sophisticated fourdrinier controller.

The stock stabilizing system of the present invention will prove eminently useful in automatically controlling a more constant product delivery to the couch, by the reduction of slurry dewatering variation on the fourdrinier. The

Fourdrinier process will be simplified as'constant surveillance at the wet end will not be required and the machine will have greater tolerance to change. In the future, the

paper-maker will be able to identify and describe stock changes in definitive terms and most important, the system will permit optimizing of all machine adjustments and even, in turn, to fiber cost reduction on newsprint machines.

The stock stabilizing system of the present invention will now be described in more detail and with reference to the accompanying drawings wherein:

FIG. 1 illustrates in schematic form the basic Fourdrinier process for making paper.

'FIG. 2 illustrates in schematic form the equipment added to the basic process to achieve constant flows.

FIG. 3 illustrates in schematic form the stock stabilizing system of the present invention.

FIG. 4 illustrates in plan the control device of the present invention and as viewed along the line 4-4 of FIG. 5.

FIG. 5 is a section in elevation looking in the direction of the section line 5-5 of FIG. 4.

FIG. 6, on the same sheet as FIG. 3, is a section in elevation looking in the direction of the section line 6-6' of FIG. 4.

A preferred embodiment of the stock stabilizing system is illustrated in the accompanying drawings. In order to better understand the invention, the basic fourdrinier process with which the present invention is concerned is shown diagrammatically in FIG. 1.

As illustrated in FIG. 1, the stock S flows through a magmeter'20 into the mixed stock chest 22 where it-is combined with the broke flow Br and the groundwood G, the flow of each being controlled by a magmeter 20. The mixed stock is then pumped through pump 24, magmeter 26 and control valve 28 until it reaches fan pump 30. It is then pumped to the cleaners 32 where it is thoroughly cleaned, any rejects exiting as Z. The cleaned mixed stock is pumped to headbox 34 from which it flows as a slice onto the fourdrinier machine 36. This machine consists at the wet and of a fine mesh wire 38 usually known as a fourdrinierwire which rolls about a series of rolls, namely the breast roll 40, the couch roll 42 and a number of a support and tensioning rolls or foils 44L As the web of wet paper proceeds along the wire 38 most of the moisture originally therein is removed through the Wire either through gravity, suction pluses, or natural evaporation. Since the mixed stock is made up primarily of fibers and water, it is useful to categorize the fibers into two groups, the fines and the longs. By utilizing the fourdrinier wire as a go/no-go gauge, fines are those fibers which will pass through the interstices of the wire -mesh. Inasmuch os fibers are not oriented until the web is considerably along the wire, the vast majority of the fines which are to pass through the wire will have done so in the vicinity of the forming boards 46 thereby creating a rich white water. White water is the drainage water containing fibers which have filtered through the wire and is richest near the breast roll, leanest near thecouch roll. The moisture continues to leave the web all along its length, another collection point being the flatboxes 48 situated in front of couch roll 42.

Most of the white water from the web falls into the wirepit 50 from which it can be recirculated as R through to the headbox. The wirepit is formed as a constant headtank such that excess water will flow over wall 52 as overflow Y into overflow tank 54. Overflow from that tank goes into the saveall 56 which is used to reclaim fibers and fillers from the white water. 1

In order to prevent the wire from clogging with fibers it is continuously cleaned with water C flowing through shower 58. The bombardment of the wire by water C dislodges most fibers and hence keeps the wire clean. Make-up water is also fed into the wirepit as dilution water B through nozzles 60. t t 1 As previously mentioned, the desirable state with paper machine is a constant equilibrium. The equilibrium can be observed as a point (B) whereat a specific drainage or dewatering has been achieved, say as a percent dewatering Shifting of this point during a run is indicative of variable dewatering, due in part to a varying fines ratio. Thus, if the drainage can be made constant, the' point of equilibrium, will be constant.

It has already been established that the papermaking machine must obey a conservation law as expressed by the equationi p +C= +Z -(1) e i A is mixed stock flow B is dilution water flow C is shower water flow W is flow to the presses X is flatbox flow Y is wirepit overflow, and Z is reject flow Since equilibrium maybe described by the proportions of W:X:Y:Z, it becomes desirable tomake as many of the flow variables as possible constanLIn fact equation (1) may be reduced to the form; I

To begin with, the flow A can be rendered constant through magmeter .26. This immediately reduces the equation to where K is constant. In order to make X constant, the

water from imput means including flatboxes 48 and conduit 85 is fed into a head tank 62 which has a number of portions, namely 64, 70 and 72 therein. A constant head portion 64 receives the flow X, a constant amount X being drawn off to white water tank. This water may be used elsewhere in the papermaking process, and the tank has associated therewith pump 68. The overflow from portion 64 is fed into constant head tank 70 from which a constant amount X is drawn oil. The remainder of flow X overflows into portion 72 from where it is recycled as X, into the mixed stock. Thus, since fixed portions of X are drawn off for desired functions and the variable remainder has been returned to the system, the flatbox flow X has been made constant with respect to the overall process. In order to make B+C constant, constant flow X is fed into head tank 74. A constant head portion 76 provides a constant flow to the showers 58 and the overflow also constant goes to the dilution nozzles. The equation where K =K +Z=constant.

A variation in the wirepit flow Y is thus an indication of the fiow W since K will have a specific value for each grade of paper on a specific machine. Flow W is diflicult of itself to measure accurately, but not so with Y, hence the simplified equation can be extremely useful to the papermaker. He very quickly has an accurate measurement of W and is then able to utilize many well-known techniques to keep W constant.

' A new method for keeping W constant under most circumstances is the stock stabilizing system of the present invention which has the primary task of maintaining equilibrium through maintaining a constant drainage rate. In most situations a variation in W will be accompanied by avariation in the drainage rate and hence will be accommodated by the ensuing correction therein. Only in special cases will the papermaker have to resort to additional techniques to re-establish W.

' As mentioned above, the goal is a constant equilibrium point, measured as a constant drainage or sometimes by a constant fines ratio. It becomes apparent that in order to maintain a constant drainage rate, it will be necessary to be able to alter the actual quantity of fine or long fibers 'in the mixed stock to thereby return a varying drainage rate to its desired value. It should be pointed out that the, drainage rate is directly related to the quantity or ratio of fibers in the mixed stock as a greater number of fines, for example, in the stock will lower the drainage rate and vice versa.

To that end the stock stabilizing system has been developed. It is illustrated schematically in its simplest or basic form in FIG. 3.

In order to vary the drainage rate of the mixed stock, it is first necessary to have a source of long and fine fibers for addition to the mixed stock. Once the source has been established, means to selectively meter requisite fibers to the mixed stock is required. In the present invention such a means is control device 102 which will be described in detail later. It suflices to say that control device 102 will, when it senses a variation in the drainage introduce the' appropriate' fibers, into the-mixed stock to -re-establish the fines ratio. Irrthis sense, the stock'stabilizing system is a feedback system with a practically zero "time lag. v

However, for the, control device 102 to be effective it mus ang have a' source of long and line fibers. As dis- "cftissedpreviously, fines forsthe' most part drop through the .iourdrinier wire 38 ashort distance beyond breast mull), a forming" boards, 46. n1 seamen [t the lines, fmost jof the'lwa'tpr from the web descends h through the wire' in thisarea and hence the resulting solution is rich in fines, i.e., rich' white water? The rich white water extracted from the formin'glvboards is} taken to head i tank 90, a'fixed amount p n-g drawn .ofi from constant head portion 92tor transmittal tothe control device 102.-. "The overflowfrom portion 92 chllects in portion9 4, from i which it is recycled into theinixed stock as shown byfthe arrowed flow lines. Thus a'supp'ly of fines is made, availa'bleto the control device.-

I W Inorder to provide a supply-of longs, a small portion of the mixed stock is extracted therefrom. and introduced into the constant head portion 98 ofhead' tank'llti The factual amount of mixed stock drawn ofiwill vary depending' on 'machine size and grade'of paper being produced. In some instances an amount of 2% may be" sufiicient to meet the needs of the system. Inasmuch as this stock is rich in fines as well as longs and is of a high fiber consistency, it is necessary to dilute this stock to essentially the same consistency as the rich white water in head tank 90. While any warm, clean Water would sufiice as a dilutent, it is convenient to utilize the lean white water in head tank 62. Thus, an additional constant head portion 88 is provided in head tank 62 to catch the overflow from portion 70 and to supply a constant How of lean white water X,, for diluting the stock from tank 96."

As shown schematically in'FIG. 3 dilution occurs at point 112, the dilute solution being then fed into control device 102.

The control device 102 is shown schematically ascorbprising four compartemnts 104, 106, 108 and 110. Com partment 104 receives the long fibers, compartment 106 receives the fines and compartment 108 dischargefs" the appropriate quantity of either back' into the mixed stock to adjust the fines ratio. Compartment 110 takes the rejects from compartments 104 and 106 and returns them to the" save Compartments 104 and 106 are rotatable together or as a unit through 90 clockwise orlcounterclockwise to present a variable quantity of fines or longs respectively to compartment 108. When in the neutral location, the ratio of fines to longs compartment 108" is identical to thefines ratio of the mixedstock,

It should bereadilyapparent that the stock, stabiliai ng system herein described is an automaticlsystem, with practically instantaneous response, The ,inputof fi lgers to the mixed stock from the control device. maybeponstantly changing, but nevertheless the drainage: rate remains constant." Without the simplifiedfiow equation; this would be impossible since the number of variables would be overwhelming and" problems would only multiplyw With the simplified" flow equation, the 'I'pa' rlerrnaking 'process at the fourdrinier can be readily controlled and inmost instances screen the flow W to the couch.

The basic stock stabilizing system has ""been"'"herein described, but it is readily apparent that it can belmodified I to suit particular needs. As already mentioned, mixed stockmay be diluted with lean white waterfor ev fi'with fresh water. This reduces the fines content in the entral segment. of the long fiber control component. 7

option, a filter device can be added in m gnet-Bar a ns:

.to remove and concentrate fines. These fines conld: be

.:then added to head tank 90-to increase the-concentration of the low freeness circuit while reducing the fines concentration in the long-fiber component. Thus,the dimer-- l ential between fines and" greater, therebyexpanding the range 8 long concentrations would be of-the unit:

1 Additional options include:

I (l)" the installation of an adequate groundwood source ahead or Magmeter 26 to permit readjustment of the stock quality when'needed' by reduction or addition of groundwood or other furnish;

(2) the installation "of a fines recovery system to' accumulate 'the variance in fines and to ire-introduce the stored quantity at the needed'rate to the stock system;

""(3) {the provision of a complete wet end' control centre withcertain instnnnents which when added to the foregoing can reasy" upgrade the value (of the equipment and provide a controlpackage for the complete machine; and

f (4) the" provision of means for rneasuringair flow on the last dry box at constant vacuum to p identify changes in ft'arrnation, as well as basis 'weight.

These modifications are illustrative of the manners in whichthe systemcan: bealtered" to suit theneeds of a ,particular mill, They are only described herein and are .not shown in the drawings, as there are undoubtedly many other options of modifications possible.

A more detailed configuration for the control device is illustrated in-F1GS.4, 5 and 6- the main features ofa .preferred embodiment being shown therein. Only the :basic preferred embodiment of the control device is shown. Ancillary features and components of the entire system are not illustrated as they are merely matters of design expediency and will only draw mention herein.

Control device 102 consists of three basic components, a distributor 113, a collector 117 and a separator 136.

Distributor 113 is essentially a cup-shaped container havingcylindrical wall 114 and an end or bottom wall 115. At the open end of the cylnder, a downwardly and outwardly projecting flange 116 is circumferentially afiixed.

The entire container can be rotated about its longitudinal axis when an appropriate motive source is attached to shaft.160. An effective motive source. might involve a i rack and pinion arrangement, with the pinion 161 mounted coaxially on shaft 160. A suitable bearingmust,

.of course, be provided tor etfective rotation.

The container is divided into chambers 104 and 106 by a plate 138 and separator 136. Plate 138 is sealed, as by welding, along its outer edges to the inside surfaces of wall114 and bottom It has a central cutout formedtoaccept the separator 136 to. which itis fixedly l sealed, as by vwelding, Plate, 138 may extend upwards beyond the open'end of the container so as to ensure that there is no cross-spillage between chambers 104 and 106. 11h addition,: ..pla t'e' 138,, may be equipped with a horizoiital extension 140"which projects outwardly over flange 116. Attached to extension 140 is separator blade 142 whiohitfitted sealingly to move in compartment 110 as separator 136 rotates. The purpose of blade. 142 will become apparent inthe ensuing description of'the operation of the control device.

always directed tothe appropriate compartment, 104 or '106.-To that end, separator 136 is of an essentially cylindrical shapeg'its diameter being large enough so that downwardly directed flow pipes 152., 154 and'156 discharge their flows into the separator without any flow being directed outside its confines. The flow from pipes 150,154 and '156 is always mixed in the remaining portion' of the separatonthe' resulting flow of mixed constituents exiting from discharge hole 144 located in the bottom of separator 136 and being directed into compartment 104. Within separator 136 is a downpipe 146, its internal diameter being greater than the external diameter of pipe 150'. The entrance to downpipe 1 46 is concentric with separator 13-6 and the pipe is directed vertically downwardly towards the bottom. A short distance above the bottom the down pipe is directed to the cylindrical surface of separator 136, exiting into compartment 106 through opening 148. Thus, as separator 136 rotates, the fluid from pipe 150 always enters the separator along its axis, but exits laterally thereof.

The remaining component of control device 102 is collector 117. The collector, as its name implies, collects fluid overflowing over flange 116 from distributor 113. It consists of an annular trough 118 completely surrounding distributor 113 and positioned such that its inside wall is underneath flange 116. Trough 118 is separated into compartments 108 and 110 by diametrically opposed plates 134. Approximately mid-way between plates 134 in compartment 108 and in the bottom of trough 118 is an opening 120 which exits into funnel 122, downpipe 124 and accept pipe 126. Each plate 134 includes a stepped portion 128 lying within compartment 108 and eifectively extending compartment 110 thereunder. In the bottom of trough 118 and under each step 128 is a hole 130, one of which exits into return pipe 131, the other exiting into return pipe 132.

The operation of the control device 102 will now be described. Pipe 150 carries in it a constant flow of rich white water from head tank 90. With the separator 136 and distributor 113 positioned as in FIG. 4, the rich white water will flow through downpipe 14.6, hole 148 and fill compartment 106 until it overflows, 50% going into collector compartment 108 and 50% going into collector compartment 110. The mixed stock enters separator 136 from head tank 96 via pipe 156 and is mixed in the separator with lean white water entering from head tank 62 via pipe 152. If required extra lean white water for dilution may be introduced via pipe 154. The high freeness stock of desired dilution exits from separator 136 through hole 144 into compartment 104. Again with the configuration as in FIG. 4, 50% of the overflow from compartment 104 enters collector compartment 108 and 50% enters collector compartment 110. Blade 142 cffectively separates the rejected long fibers in compartment 110 from the rejected fines therein. Thus, the fines can be returned via pipe 132 to head-tank 90 and the long fibers can be returned via pipe 131 to head tank 96 or to wherever they may be required.

In the FIG. 4 configuration, the control device is in its neutral condition as the consistency of the flows in compartment 108 which ultimately is reintroduced into the mixed stock is the same as the consistency of the mixed stock. The flow collected'in compartment 110 is reject and may be directed to saveall 56 for reclamation of the fibers therein. If, however, meter 86 senses a change in the drainage rate of flatboxes 48, a change in the consistency of the mixed stock has occurred and must be overcome. By known comparison and transducer means such as 87 the change in drainage rate is quantified and translated into a rotation of distributor 113 and separator 136. If, for example, the meter indicates a deficiency of fines in the mixed stock, distributor 113 and separator 136 rotate clockwise (FIG. 4) such that more overflow from compartment 106 than from compartment 104 into compartment 108 will occur. Thus the flow from compartment 108 through accept pipe 126 will be richer in fines than in the neutral state and the deficiency in the mixed stock will be accommodated. Correspondingly the reject flow will be rich in long fibers as compartment 1'10 will receive most of its flow from compartment 104. Thus most of the reject flowwill be exiting via return pipe 131.

It should be borne in mind that the control device herein described need not be restricted to its present application. It could be effectively utilized in most situations where the mixing of liquids in a controlled rate is required. It need not be used solely in a stock stabilizing system as herein disclosed.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a fourdrinier type papermaking machine in which the papermaking process is defined by the equation A+B+Cl=|W+X+Y+Z where A represents a flow of mixed stock, of fine and long fibers of a predetermined consistency, B represents a flow of dilution water, C represents a flow of water to a set of showers, W represents a flow of paper to a couch, X represents a flow of drainage water, Y represents an overflow from said wirepit and Z represents a flow of rejects, said flows being indicative of a state of equilibrium in said machine, a method for controlling said equilibrium comprising the steps of (a) rendering flow A constant;

(b) dividing flows X, Z into constant portions X 2;;

and variable portions X,, Z, respectively and reintroducing said variable portions into said mixed stock;

' (c) dividing said constant portion X into at least two constant portions, one of which is a sole source of water for said flows B+C, thereby rendering said flows B+C constant;

(d) metering said flow X;

(e) comparing said flow X to a desired drainage flow;

and

(f) introducing additional fine and long fibers into said mixed stock in a ratio determined by said comparing step to make said flow X equal to said desired drainage flow.

2. A method according to claim 1 wherein said step of dividing flow X comprises the step of directing said flow X to a first head tank from which said constant portion X is drawn and said variable portion X, is returned to said mixed stock.

3. A method according to claim 2 wherein said additional long fibers are obtained by diverting a portion of said flow A to a second head tank and diluting said portion of flow A with clean water and wherein said additional fine fibers are obtained by diverting drainage water rich in fine fibers from said machine to a third head tank.

4. A method according to claim 3 wherein said clean water is a constant portion X of said constant por- I101! xx- 5. In a fourdrinier type papermaking machine having a plurality of interrelated material flows indicative of a state of equilibrium and wherein said flows include a flow of mixed stock of fine and long fibers of a predetermined desired consistency, a desired drainage flow and an actual drainage flow, apparatus for controlling said equilibrium comprising metering means connected to said machine for metering said actual drainage flow, input means connected between said machine and said metering means to conduct said drainage flow to said metering means, comparison means operatively connected to said metering means for comprising said actual drainage flow to said desired drainage flow, extraction means connected to said machine to remove a small amount of said fine and long fibers therefrom, separate source means each having at least two compartments and connected to said extraction means to store said small amounts of fine and short fibers separate from each other and control means responsive to a signal generated by said comparison means, said control means having mixing means connected to said source means to mix said fine and long fibers in a ratio determined by said comparison means and introduction means connected between said mixing means and 1 said machine to introduce the mixed fine and long fibers into'said'rnachine tomake said actual drainage fiow equal to said desired drainage flow.

6. In a fourdrinier type papermaking machine having a plurality of interrelated material flows indicative of a state of equilibrium and wherein said flows includea flow of mixed stock of fine and long fibers of a predetermined desired consistency, a desired drainage flow and an actual drainage flow, apparatus for controlling said equilibrium comprising metering means connected to said machine for metering said actual drainage flow, input means connected between said machine and said metering means to conduct said drainage flow to said metering means comparison means operatively connected to said metering means-for comparing said actual drainage flow to said desired drainage flow, extraction means connected to said machine to remove a small amount of said fine and long fibers therefrom, separate source means each having at least two compartments and connected to said extraction means to store said small amount of fine and short fibers separate from each other and control means responsive to asignal generated by said comparison means, said control means including a first receptacle having two first compartments, each receiving a dilute flow of said fine or long fibers, a second receptacle adjacent said first receptacle and having at least two second compartments therein, overflow directing means connected to said first compartments for directing an overflow of said dilute flows from said first to said second compartments, said first receptacle being movable with respect to said second receptacle to vary the ratio of mixing said dilute flows 2 in said second compartments, means tor'movi'ng said first receptacle with respect to said secondrece'ptacle and introduction means connected between one of saidsecond compartments and said machine to introduce the mixed fine and long fibers into said machine to 'malte said actual drainage flow equal to said desired drainage flow.

References Cited 7 UNITED STATES PATENTs v01. 47, No. 4 (April 1964), pp. 181Al88A-;"Dig. #6.

J. P, Casey, Pulp and Paper, 2nd edition, vol. 'II'; Interscience Publishers, Inc New York, 1960, p'. 769. i I

s. LEoN BASHORE, Primary Examiner" M. s. ALVO, Assistant Examiner us. 01. x.R.

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