US2272970A - Apparatus for controlling paper manufacture - Google Patents

Description

FehiO, 1942. w. w. FRYMOYER APPARATUS FOR CONTROLLING PAPER MANUFACTURE Filed Sept. 4, 1937 2 Sheets-Sheet 1 INVENTOR Wesler W F;

' F 10, 9 v 2 w. w. FRYMOYER 2,272,970

APPARATUS FOR CONTROLLING PAPER MANUFACTURE Filed Sept. 4, 1937 I 2 Sheets-Sheet 2 4 INVENTOR W6 1? W 1 Z. 683 e] (7171,0961

11:: M 0 ALZ J ATTORNEY Patented Feb. 10, 1942 APPARATUS FOR CONTROLLING PAPER MANUFACTURE Webster W. Frymoyer, Foxboro, Mass., assignor to The Foxboro Company, Foxboro, Mass, a corporation of Massachusetts Application September 4, 1937, Serial No. 162,406

4 Claims.

This invention pertains to an apparatus for controlling consistency of a fibre-liquid mixture such as stuff supplied to a paper-making machine, and for controlling the weight of fibre flowing to such a machine.

One of the objects of the invention is to provide an improved apparatus for controlling the consistency of stuff to be supplied to a papermaking machine.

Another object is to provide an improved apparatus for maintaining a desired flow of pulp fibres measured on a dry basis through a stuff gate Other objects will be in part obvious and in part pointed out hereinafter.

In the accompanying drawings:

Figure l is a diagrammatic layout partly in perspective of a stuff chest and consistency regulator embodying the invention and capable of carrying out the invention;

Figure 2 is a top elevation (somewhat enlarged relative to Figure l) of a mixing chamber and iiowbox embodying the invention;

Figure 3 is a vertical section taken on line 3-3 of Figure 2;

Figure 4 is a verticalsection taken on line #4 of Figure 3;

Figure 5 is a vertical section taken on line 5-5 of Figure 3.

Corresponding reference characters refer, to corresponding parts throughout the several views of the drawings.

In making paper, the fibres from which the paper is made are mixed with a relatively large amount of water and the mixture is delivered to the usual Fourdrinier wire" of the paper-making machine which mats the fibres and draws off a large percentage of the water. Subsequently, the paper mat is passed through a series of d'riers which dry the paper to the degree desired.

In order to obtain a uniform paper sheet, one of the requirements is a uniform flow of the fibres to the paper-making machine. To this end, the volume of the water-fibre mixture (commonly called the "stufi) is regulated and maintained substantially constant. In addition to this, the consistency of the stufi is also regulated. The consistency is generally considered as the per cent of the weight of fibres measured on a dry basis to the-total weight of the waterfibre mixture. is adapted to control the consistency of the The apparatus herein described I stun; and to control the weight of fibre delivered to the paper machine substantially constant even though the volt-nut of flow of the stuff to the paper machine may vary slightly.

Referring to Figure 1, at the lower right-hand corner, stuff is drawn from a stufi chest I through a pipe 2 by a suitable pump 3 whence it is forced upward through a pipe 4 to a supply chamber 5 in a box generally indicated at 6. From this chamber it flows over a spillway or dam l and falls (see Figures 2, 3 and 4) into a mixing chamber in the box generally indicated at 8. From near the bottom of the mixing chamber it flows through an opening 9 in an end wall, into one end of an adjoining elongated flowbox It] in the box 6.

From the flowbox I0 excess stufl flows over an overflow dam II and returns through pipe I2 back to the chest I. Referring to Figure 5, the stuff going to the paper machine or other machine (not shown) flows from the fiowbox l0 through a short tunnel 50 through the lower left-hand corner of the wall or dam II, and out through a discharge port or stuif gate 13.

Theflow through said stuif gate is preferably maintained so that the weight of pulp, measured on a dry basis, is controlled and in the present embodiment is maintained substantially constant-and this regardless of the consistency of the stufi entering supply chamber 5. Such flow of stufi. through the gat is maintained providing the flow through pipe 4 is suflicient to insure an overflow from the flowbox' l0 over dam H and through pipe l2 back to thechest I, and providing, too, that the consistency of the stufi flowing from the chamber 5 is greater than the consistency desired in the stufi flowing from the flowbox l0 through the stufi gate l3.

The consistency is controlled by regulating a supply of diluting water which is mixed with the stuff which has flowed over spillway 'I from chamber 5. Referring to Figures 2 and 4, this diluting water is supplied to an elongated cham-' ber M from a pipe l5 whence it flows over a dam or spillway l6 located opposite and above spillway 1 and parallel to it. The amount of flow of diluting water is controlled by a diaphragm operated valve l1 preferably such as indicated in Figure l havingequal percentage flow characteristics, that is, a valve-so constructed that equal changes in valve position cause equal percentagechanges in flow.

In the present embodiment the weight of pulp fibre flowing is regulated by controlling its consistency which is measured by employing the well-known principle described in U. S. Patent 1,178,193 to Trimbey. who taught that the vispipe 23,

cosity of stufi varies with its consistency; and that the flow of the stuif through a properly designed orifice or nozzle at a constant head is practically independent of the viscosity and consistency of the stufi, whereas the flow through a pipe (herein called a viscosity tube) is dependent on the consistency. Referring to Figures 1,

- 2and 5, the consistency-measuring apparatus for the purposes of the present invention prefe erably comprises a standpipe l8, connected with flowbox I through a sampling orifice 30 in the flowbox wall opposite dam II and more particularly, for reasons hereinafterto be set forth,

opposite the opening of tunnel 50. Said orifice 30 is preferably shaped as the upstream and with rounded edges so as not to catch and collect fibres.

shown, flaring toward ation of the apparatus) is substantially constant regardless of the consistency.

Near the bottom of the standpipe I8 a "viscosity or discharge tube 20 is provided, emptying into a pipe 2| joining pipe l2 and so draining into the stuff chest I. Since the resistance to flow in the tube 20 varies with the consistency, the level of the stufl in the standpipe 18 may be taken as a measure of the consistency. This follows, because, for example, if the consistency increasesits resistanceto flow increases, and the level above the viscosity tube 20 must rise an amount proportional to the increase in resistance' to increase the head on the viscosity tube to maintain the flow out equal to the flow in.

In'the present embodiment mechanism is provided to measure the variation in level of stuff in the standpipe l8 and apparatus connected therewith is also provided to actuate valve H to control the supply of diluting" water to maintain such consistency of stuff in the flowbox as will maintain a desired constant level in the standpipe.

The measuring apparatus in the present embodiment comprises a bubble tube 22, shown in dotted lines in Figure 1, supplied with a substantially constant flow of'air from a supply theair going through a trap 24 and through a reducing valve 25 to the pipe 22. The reducing valve is preferably adjusted to supply suflicient air pressure to the tube 22 to overcome the maximum hydrostatic head that may exist in the standpipe. As the level in the standpipe changes, the pressure in the bubble tube necessary to cause the air to flow out of the tube varies and provides an accurate indication of the level in the standpipe. This air pressure is transmitted to a controller, generally indicated at 26, and in the present embodiment may be of the air-operated type shown and described in Mason U. S. Reissue Patent No. 20,092. This controller controls air supplied from a pipe 21 to the diaphragm motor 28 and is adapted so to control the valve motor as diluting water to maintain the level in the standpipe substantially at a control point. Inasmuch as this controller is well known, it will not here be described in detail other than to say that the pressure in the bubble tube operates mechanism sensitive to this pressure which coacts with opposing air-operated diaphragm motors to operate a relay to change the position of the valve at a rate which is proportional to the to control the flow of.

. chamber.

algebraic sumof the rate of change of the level in the standpipe and the deviation of the level from the control point. The mechanism, as described, is so constructed that there is substantiallyno dead space in it and the valve is adapted to operate without time lags or lost motion.

'In the manufactureof paper the consistency of the stock in the chest I is subject to sudden variations, as by the pumping in of diluted stuff from the couch-pit. Also ineflicient or improper chest agitation and the like cause fluctuations of the consistency. In order that these fluctuations may be counteracted promptly and without producing cycling or hunting in the control, it is desirable to provide both for the rapid and thorough mixing of the stuff with the diluting water and for the prompt testing of the consistency of the resulting mixture by admitting a test portion of it immediately into the standpipe 18. As shown in Figures 2, 3 and "4, mixing chamber 8 is relatively long, narrow and deep so that the stock and diluting water flowing into it may have a considerable distance of free fall before reaching the normal level of liquid in the Further, the stuff falling from one side of the relatively narrow chamber 8 and the water falling from-the other side thereof produce a high degree of turbulence at and slightly below the surface of the liquid in the chamber. The top edge of dam I8 is preferably placed at a higher level than that of dam 'I s that the falling water has a velocity different from that of the stuff falling from the dam I, and this furthers the mixing. In addition, baffles 25 and 26 sloping downwardly toward each other from the ends of the mixing chamber 8 concentrate the stream and increase the velocity of the stuif passing out of said mixing chamber. Further mixing is produced by the right angle turn that the stock takes in passing from baflle 28 and flowing through the opening 9 into the flowbox I0.

This combination of a high, free fall of stuff and diluting water in a narrow chamber followed by an increase in velocity of the flow and then the right angle turn produces a thorough mixing of the stuff and diluting water with a minimum loss of head and in a minimum of time. This enables the control apparatus to make greater counteracting changes that is greater increase or decrease in volume of added water in response to changes in the consistency of the stuff coming from the chest, to maintain the consistency at or near the control point without producing cycling or hunting. Without adequate mixing and immedlatetesting of the mixture, the consistency of the test stufi in the standpipewould not truly represent that of the stuff in the flowbox and of the stufi as delivered through the stuff gate l3 to the paper machine. Likewise, when a considerable time elapses between corrective operation of the control devices and the resultant change in the consistency of the tested stock, similarly unsatisfactory results would follow. Appreciable over or under corrections might be made in the mixing chamber with corresponding undesirable variations in the oppositely disposed stufi gate I 3 and sampling orifice 30. Thus the velocity of the stufi flowing past both openings affects the flow of stock therethrough in relatively the same proportion With this construction there is considerable flow of stock past and between said openings and no dead (stagnant) stuff accumulates in the proximity of the sampling orifice 39. Since flow-through said orifice 39 is not relied upon to keep the stuff moving normally from the mixing chamber and in the vicinity of the opening of the orifice 30, flow of a continuous representative sample into the standpipe of the consistencymeasuring apparatus is assured.

In practice the flow of stuff from the chest to the box G may vary from just enough to supply the consistency sampler and the stufl. gate so that there is practically no overflow over dam II to a flow sufliicient to produce an overflow of two or three times the flow through the stuff gate. This variation in flow causes a small variation in the level above the overflow dam H and so causes a variation in the head over the stuff gate and over the orifice. Inasmuch as correct operation of the consistency-measuring apparatus requires a constant head over the orifice, the above mentioned change in head would naturally tend to throw oif the consistency-measuring apparatusr But in accordance with the present invention this difiiculty has been overcome as will be described.

Tests indicate that with a constant head over the viscosity tube 20 the decrease of flow through it with an increase of consistency is sufficient to produce a slight decrease in the amount of the stock passed, figured on a dry basis. Or, vice versa, 2. decrease in consistency causes an increase in the stock (pulp fibre) flow.

Now an increased volume of 'stufi pumped through the consistency regulator as a whole and returned to the chest causes an increase of depth over the overflow dam ll of the regulator and thereby an increase of head on the stuff gate orifice l3 and on the sampling orifice leading to the standpipe i8. This. of course, increases the volume of flow through both said openings, and unless the consistency of the stuff were reduced a proportionate amount, the flow of stock on a dry basis to the paper machine would be increased.

The increased flow through'the sampling orifice 30 due to said increased head tends to increase the head in the standpipe l8, and the control mechanism correspondingly reduces the consistency to hold the head over the viscosity tube 20 constant even with the increased flow into the standpipe l8. By properly constructing. the apparatus the increase in fiow through the stuff gate l3 may be counteracted by a decrease in consistency so that the amount of stock passed to the paper machine by the stufi gate I3 is independent of the variation in the overflow over dam II.

In the present embodiment this is accomplished by so locating the stuff gate I3 that its transverse center line is at a somewhat greater depth in the chamber I ll than that of the sampling orifice 3G leading to the standpipe l8 so that the per cent increase of head with increased depth of overflow over dam H (and so the percentage increase of volume in flow) is less through the stuff gate l3 than through the sampling orifice 30. By proper choice of the difference between the transverse center line levels of the sampling orifice 30 and stuff gate I3 increase of volume of Let h=Height of overflow dam above center line of sampling orifice 1 d=Height of center line of sampling orifice above center line of stuff gate zc=Height of. stuff over overflow dam k0: Constant of sampling orifice kg Constant of stuif gate 161:: Constant of viscosity tube ht: Height of stufi in the sampling tube above the center line of the viscosity tube (ht in the present analysis is assumed to be controlled constant) Q0: Stufi flow through sampling orifice (wetstock) Qg: Stuff flow through stuiT gate (wet stock) Qt: Stuff flow through viscosity tube (wet stock) 0: Consistency of the stuii. V U: Time for unit quantity of stock on dry weight basis to pass through gate Z=A constant by which the flow-consistency relationship departs from strict proportionality. As described above, the present invention utilizes the principle that flow through a, tube is inversely proportional to viscosity and that within a certain range of values viscosity bears a definite relation to consistency. If e the entire range of consistency values between 0 and is consid- I ered, the relationship between viscosity and consistency is not a linear one because of P the fact that the values of viscosity increase very rapidly when the consistency increases beyond about 4% to 6%. However, within the operative range of the present apparatus the relation between viscosity and consistency closely approximates a linear one. It has been experimentally determined that the relationship between flow through the viscosity tube and consistency may be expressed by the following equation:

The constants in the above equation may be determined experimentally.

- mined by substituting empirical values of flow and consistency in the above expression. Then Since the head ht in the sampling tube is assumed to be constant, flow through the sampling l the diaphragm motor because if it fluctuates too orifice equals flow through the viscosity tube at a given consistency! The rate of stock on a dry weight basis through the stuff gate equals the volume of flow times its consistency.

Substituting the value of Qg from Equation 2 and the value of C from Equation 5 in Equation 6 gives It is apparent that a value of d can be chosen which will make the value of the expression J; c zero for a diven value of as. a I

Since a: is small with respect to h, a value of d can be chosen which will make the value of the 40 expression approximately zero for any value of a: normally encountered in practice.

With this value of d, within the working range of the consistency controller change in flow of stock on a dry weight basis through the stufi gate to the paper machine will be very nearly zero regardless of variation in head over the overflow dam. It is further apparent that the range of operation of this compensation depends on the constancy of the constants k0, ks, kt and Z. Tests show that k0 and kg are independent of fibre characteristics and kt is fairly steady within the working range, providing the temperature of the sample stuff is nearly constant. Z varies with the character of the stufi but this usually remains substantially constant for a given run.

White water is generally used for diluting the stuff. It is pumped from a settling tank which sometimes runs dry. Hence it is desirable to record the pressure of the water on the high side of the valve H. In the present embodiment this is accomplished by providing a pressure diaphragm 3| of known construction communicating with the pressure in the pipe l5 and operat: ing (through suitable known mechanism) a pen 32 of a recorder 33. If the pressure in this line falls, the operators are thus immediately informed of this fact.

It is also desirable to record the pressure on widely in response to demands from the instrument 26, the operators, being warned, can takesteps to remedy the wide variation probably occurring in the consistency of the stock" in the chest I. 76

of pulp which :Inasmuch as the valve l! to operate satisfacequal percentages of lift produce equal percentage changes'in flow, it is desirable to provide means for flushing this valve out to clear it might otherwise accumulate on its edgeportions. To this end fresh water from a supply pipe controlled by a hand valve 343 may be flushed through the valve I! with valves 35 and 31 in the line closed andvalve 36 (communicating with a drain) open. Also with valves 35 and 36 closed and valve 31 open, the box 5 may be'flushed out with fresh water.

I claim:

1. A device for measuring the dry weight of material in a suspension flowing from a delivery opening of a flow box, comprising, in combination, a flow box having a weir dividing said box into an overflow chamber and a delivery chamber, said delivery chamber having a delivery orifice and a sampling orifice located at right angles to the direction of flow in said deliverychamber, a measuring chamber receiving flow from said sampling orifice and having a discharge tube near its base capable of influencingflow through said tube to vary the head in said measuring chamber in accordance with the viscosity of the suspension flowing therethrough, and a measuring device responsive to the head in said measuring chamber.

2. A device for controlling the dry-weight of pulp in a stuff flowing from a flow box comprising, in combination, a flow box having a weir dividing said boxointo an overflow chamber and a delivery chamber, said delivery chamber havin a delivery orifice and asampling orifice located at right angles to the direction oi. flow through said delivery chamber, means closely associated with said flow box for supplying stufl thereto, means for adding diluting water to said stufi while passing through said last-named means, a

measuring chamber receiving flow -from said sampling orifice and having a discharge tube near its base capable of influencing flow through said tube to vary the head in said measuring chamber in accordance with the viscosity of the stuflf flowing therethrough, andmeans responsive to the head in said measuring chamber for regulating said diluting water means.

3. A device for controlling the dry weight of pulp in a stufl of varying consistency flowing from a flow box,'comprising, in combination, a flow box having a weir dividing said box into an overflow chamber and a delivery chamber, means for supplying'stuii to said flcw box, means for adding diluting water to said stuff, a sampling orifice in said delivery chamber, a measuring chamber receiving flow from said sampling orifice and having a discharge tube near its base capable of influencing flow through said tube to vary the head in said measuring chamber in accordance with the viscosity of stuff flowing there- .through, means responsive to the head in said measuring chamber for regulating'said diluting water means, and a delivery orifice located in said delivery chamber and at such a distance below said sampling orifice as to compensate for variations in the dry weight of pulp flowing through said delivery orifice due to the departure of the efiective viscosity-consistency relationship of said stuff from strict proportionality.

. 4. A device for controlling the dry weight of pulp in a stufi of varying consistency flowing from a flow box, comprising, in combination, a

aaraoro flow box having a weir dividing said box into overflow chamber and a delivery chamber, means for supplying stui! to said flow box, means for adding diluting water to said stuii, a sampling oriflce in said delivery chamber, a measuring chamber communicating with said sampling oriflce and having a discharge tube near its base capable of influencing flow through said tube to vary the head in said measuring chamber in accordance with the viscosity of the stud flowing therethrough, means responsive to the head in said measuring chamber for regulating said diluting water means, and a delivery orifice located in said delivery chamber and at such a-- distance below the top of said weir as to satisfy 15 approximately the following equation:

[15: aft- 1 wherein:

ko=the flow constant 01' the sampling orifice; ht=the height or stufl in the measuring chamber; 5 ki=the flow constant of the discharge tube;

d=the height oi the center line of the sampling orifice above the center line 01 the delivery orifice; v h=the height of the weir above the center line or the sampling orifice; z=the height oi the stud over the top of the weir; and Z=a constant by which-the efl'ectiveviscosityconsistency relationship of the'stuiideparts from strict proportionality over the operating range used.

i w. mmovna.

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