US2122394A - Thin stock process and apparatus for making paper - Google Patents

Description

July 5, 1938. c; ALLEN 4 2,122,394

THIN STOCK PROCESS AND APPARATUS FOR MAK-ING PAPER Filed oct. ve, 193s IIR Wu f HHII' Patented July 5, 1938 UNITED STATES THIN STOCK PROCESS AND APPARATUS FOR MAKING PAPER carlton n. Auen, Glens Falls, 'N. Y. Application october c, 19s6,`seria`1No. 104,220

3 Claims.

This invention relates to the continuous process for making paper and the apparatus essential to this process. i.

'I'he objects attained in the practice of the invention are a greater eillciency of the process, better quality paper and reduced cost of manufacture. v

' The improvements are particularly useful in the making of news and similar grades, but may lo be applied to advantage in the making'of other grades where conditions are suitable. As will hereinafter become apparent, greater advantages are attained where the paper making pulpor pulps are produced at or near the paper mill. This is the usual situation wherever news print is manufactured, and this description is made with special reference to this paper.

According to the present most advanced practice as employed by the majority of manufac- 20 turers, solutions are made of each of the paper making ingredients which thereafter are flowed v continuously through an apparatus for metering and proportioning each ingredient to form a composite paper stock, or a common stream of paper stock, and the consistency of the ground Wood solution and the sulphite solution is held at a point somewhere between 2% and 4% by aid of thick stock consistency regulators, socalled." Some of the wood from which the paper is made, is ground mechanically, screened at a consistency of about 0.45% to remove the larger particles and dirt, and then thickened to a consistency of about 3.0% to form the ground wood solution. A smaller proportion of the wood is digested by the action of acid and heat, screenedA at a consistency of about 0.3% and then thickened to a consistency of about 2.5% to form the sulphite solution. The ground wood is thickened after screening by machines known as deckers or the operation may be ancomplished by vacuum' filters. Deckers permit the escape of nearly onethird of the ground wood pulp which thereafter must be recovered and returned for re-screening and re-thickening. The recovery operation loads the screens making necessary additional screens, and loads the thickening machines making necesbsary additional deckers. The recovery operation is expensive in many ways, and in some mills the deckers have been replaced with vacuum filters in an effort to reduce the loss of pulp due to the thickening operation. About 14% of the pulp supplied to the lters escapes in the white water and as much as possible is recovered and returned to the system. Vacuum lters are expensive in first cost, expensive also in power required for their operation and in maintenance.

`When ground Wood pulp is deckered or filtered a separation of the ne from the coarser pulp takes place. The portion of the pulp retained on the filter surface is formed to a lumpy mass which must again be broken down to a solution before it is suitable to meter and run on the paper machine. The ner material which escapes to the white water system'has a faculty for coating the inside of the pipe lines, forming slime which after a time becomes discolored, and upon loosening and travelling on through the system eventually causes black specks and slime spots in the finished paper with the result that the paper is poorer in quality and trouble is experienced in keeping the sheet from breaking on the paper machine.

Use of the herein described improvements in process eliminates most of the thickening operation and in some cases, all of the thickening operation which heretofore has been applied to a pulp. Either or both, the ground wood solution and the sulphite solution before metering are held at consistencies very like those required for screening. At these consistencies the mixing after metering is more thorough and eihcient resulting in better formation of the paper making web. My process is more direct acting, giving less time and opportunity for troublesome lumps and slime to form in the pulp and in the pipe lines. The present necessities for separating the fine ilbre and lignin of the ground wood pulp from, the coarser and-longer fibre of the same pulp and again reassembling the two'classes of this pulp before metering are voided. Moreover, the cost of operating and maintaining deckers, filters and vacuum pumps is saved. Greater production of better quality paper at lowered cost is accomplished.

This invention is herein illustrated and described both as an improved process for making paper and as suitable apparatus in a preferred combination for practicing the invention, the accompanying drawing serving to illustrate the vcoordinated apparatus and improved process, the invention being defined inthe appended claims within the limitations of the illustrations and description and also in the broader aspects contemplated in its general practice in the maling of different kinds and grades of paper or the like.

In the drawing:

Fig. 1 is a view in elevation, partly in section and partly diagrammatic, illustrating an apparatus in preferred form suitable for practicing the invention; A

Fig. 2 is a View in elevation, partly in section and partly diagrammatic, illustrating an apparatus for controlling the consistency of a pulp solution at ava1ue slightly lower than that required for screening a pulp-ingredient of the paper.

In the drawing, details of apparatus which would only serve to confuse the reader are omitted. The arrow-head lines indicate pipe lines and the arrow-heads show the directionof ow.

Referring now to Fig. 1: after grinding the ground wood pulp is pumped through line I to the screens 2, from where after screening, it drops through line 3 to. vat located on the main iloor At screening consistency, about 0.5%, the greater quantityof the screened pulp drops from vat i3 through iine 6 to vat llocated on the lower oor t, the liquid level in which is controlled'by the float valve 9. Any quantity of the screened pulp net accepted in the vat 'I overows the darn i0 of the vat d to the thickening machines II', fro which point thickened pulp of aconsistency of about 3.0% drops through line I2 to the slush pulp storage i3. From the slush storage I3, the

thickened pulp flows to the vat-1 under control of the regulating valve lli.' The mixtureof the two streams ci pulp in vat 'I is withdrawn continuously by a pump I5 and delivered to the Ametering apparatus I5 on the main floor 5. A

thin watery solution passes through pump i5 having a consistency somewhat higherthan' screening consistency, as for example a consistency of 0.65%. A small portion of the pulp passing through line i1 is diverted through line I8 to the thin stock indicator I9 from which point-it is Jreturnedto vat 'I throughline 20.

' Instrument I9 .is sensitive to changes in the consistency of vthe thin pulp passing through pump` I5 and it controls the operation of the power 'driven regulatingvalve I4, direeting either a slow openingor closing .movement cf the valve I4 to maintain the consistency of the solution passing through pump I5 and the line l1 to the metering apparatus E5 at a constant value of the magnitude desired.

Instrument f 9 is f ully illustrated and described in my applicationfor patent, Serial No. 741,908, filed in the United States Patent .Oi'iice August p23, 1934. In practice the instrument .I9 .has proven extremely sensitivete the consistency of a thin pulp solution and for the purpose here used it is especially well adapted.

The sulphite solutionmay be processed as described for the .ground wood solution and ilowed lt0 the metering apparatus I6 through the line 2|. Other ingredients required in the paper such as color and alum are also supplied to meter I6 through suitable lines (not shown).

A meteringv apparatus of the class required of meter II is fully shown and described in United States Patent No. 15,311reissued tov me andl Edward J. 'lrimbey March 21, 1922, and again in March 15A, 1927. Such metering apparatus is now well known and widely used by paper makers in the United States and in many foreign countries. Y

l'Iihemeter I6' is understood to include one meter for each ingredient of the paper stock. 'I'he meters are individually adjustable as torrate of metering'to fix the proportion of ingredient to ,otheringredienta Further, all of the meters are interlocked mechanically in a way such that-a single adjustment of one `master control may -the paper stock and white water and discharges the mixture through line 26 and hand regulating valve 2l to the head box 20 'and on to the paper machine wire 2d. The rate at which white water is drawn from pit 2li depends uponthe setting of handfregulating valveQl, i. e. when this valve is given a greater opening more white water is drawn from pit 2li and when given a lesser opening iess white water is drawn from the pit. Pit 2d is supplied only by water and stock which drains by gravity through wire 29 near the breast roll 30, thus forming a white water solution having a consistency of about 0.12% to 0.20%. Joining and mixing the stream of paper stock from meter It with White water from pit 2d reduces the consistency of the paper stock flowing to' wire 29 to a degree depending upon the 'rate of flow from pit' 24 to pump 23,`as for example to a consistency of 0.5%.

Paper stock as delivered to the wire of a paper machine is a thin solution, the consistency of which is different fer different paper machines as determined by the length of wire, the speed of the paper production, and the emciency of the points of ci'insistency control being the regulating valve I4 under automaticl direction of the thin stock indicator I9, and the hand regulating valve 21, the weight and composition of the paper being controlled by and at the meter I6. y While the paper web is forming on wire 29 most lvof the water of the paper stock drains through it by gravity to the wire pit 2f. Some of the pulp of the paper stock also drains through wire 29, but most of the pulp drainage occurs near breast roii 20 before there has been time for the paper we le to form and close the apertures of wire 23. Aneconomy in the process is effected by re- .turning to the stream ofV paper stock that portion of the drainage which takes place near breast roll 20. To insure the immediate recovery of practically all of thestoek lostthroughwire 29,`

suitable 'names 3! may be installed in pit 2d, thus directing the white water of the higher pulp content to pump 23 and the later drainage over the dam 32 to pit 3,3, and thence through line 34 to white water storage 35 to which, pulp white water-also flows from the thickeners I I throughthe line 30," Y

White water from the wire' suction boxes (not shown) and or from a suction couch roll `3l may also be owed to storage 35 through suitable lines (not shown).

From storage 35 white water is impelled by a pump .3B through lines 39 to points in advance ofthe pulp screens 2 for use in thinning the ground wood pulp as received from the grinders l toav consistency suitable for scrning.

` At times when there may be a deciency in the amount of screened pulp ilowing to vat 4 from screens 2, white water is automatically supplied through line 40 and oat valve 4I to vat 4 to compensate for such deciency. Float valve 4I is located below the crest of dam i0 and under normal operation of the process and yapparatus remains closed. It is evident that in case of a complete or a temporary stoppage of the production of ground wood, there is no overiow at dam I0 and no thickened pulp flowing to slush storage i3. 1n either case the apparatus continues to operate automatically to supply the paper machine until the pulp in slush storage i3 is exhausted, or provided dry pulp is reduced to slush and supplied to storage i3 by the usual breaker means (not shown) the system continues to operate indefinitely.

customarily, the white water flowing to storage 85 through line 34 is more than sufficient to supply float valve 4d, for ,this water may include clear water used in showers (not shown) to clean ,the wire 20, but clear water vmay be supplied to storage 35 through line .42 and iloat valve 43 to start the process initially, as for instance on a Monday morning after the plant has been shut down .overSunday However, in the ordinary' operation, more white water flows to storage 35 than is required for re-use and the excess is permitted to overow to recovery lters (not shown) from which point vthe recovered stock is flowed to the broke storage 44 and the filtered water may be discharged to the mill drains.

Broken paper or broke is reduced to slush pulp by means of a beater 45 supplied with white water for thinning through line 46 from the couch pit 41, the excess from the couch pit overflowing to line 3,4 and thence to storage 35. Beater 45 discharges to broke storage 44. Pump 48 gradually returns the broke from this storage 44 through line 40 to the ground wood slush storage i3 forl re-entrance to the stock circulating system. Stop valves 50 and 5i are for use only when the system is shut down.

Float valves and regulating valves have a' tendency to leak in the closed position. As a matter of convenience a small line 52 is provided to care I 55 machine and the sulphite solution may also be processed in the same manner. Ordinarily from two thirds to three quarters oi' the number oi.' thickening machines il as required in the thick stock process are eliminated as will hereinafter become clearer from an example in which'the paper production, the percentage of broke. and 'all consistenciesare ilxed at representative values.

In Fig. 2 a method and apparatus is illustrated maintains the level in vat 1 at substantially constant elevation. Power driven regulating valve I4 controlled and directed by the thin stock indicator i9 supplied by a continuous sample through line I8 from pump i5, regulates the admission of white water through line 39 to maintain the consistency of the pulp solution at a slightly lower value than that at which the pulp is screened.

Where the method of Fig. 2 is used to regulate the consistency of the ground wood solution, it may be necessary, depending upon the conditions, to use slush sulphite for combining with the ground wood at meter i8 to prevent the consistency or the paper stock from falling too low for delivery to the paper machine and too low to permit the direct return of sumcient white water from pit 24 for economy. The method of Fig. 2 is suitablefor new mill construction where the length of wire 29 may be given a suilicient lengthl and the storage 53 made large to compensate for loss of capacity at low consistency.

As a concrete example of the operation of the process as related to Fig. 1, we may assume, a daily paper production of 100 tons per day, (bone dry weight) with 8% broke over and above this production, a required consistency of the paper stock of 0.5%, as it goes to the wire, the use oi 18% sulphite in the nished paper, the ground wood to be screened at 0.5% consistency, a portion of the ground wood thickened to 3.09% consistency, a portion ci the sulphite thickened to 2.50% consistency, the ground wood white water (using vacuum lters) having a consistency of 0.07%,l a supply of 600 gallons per minute of clear water to clean the paper machine wire, and a Y setting of the thin stock indicator to hold the nated. However, the consistency oi' the pulp Y solution is necessarily maintained at lower value than that maintained by the apparatus of Fig. `1. This method has a more limited application than that oi' Fig. 1 because most existing paper machines are unable to accommodate the necessarily ,itiiowstovatlthroughtheiloatvalve.whichv consistency of the ground wood solution at 0.65%.

Now provided 16 tons per day are returned through line 25 to pump 23, as may be the case, the tons per day going to wire 29 is equal to the daily production of tons, plus 16 tons, plus the 8% broke or 8 tons, and plus an amount flowing through line 34 to storage 35 which is here assumed as 11 tons daily, or to a total oi.'

tons per day owing through head box 28 Y to wire 29. At 0.5% consistency the rate of ilow of paper stock at this point is 4500 gallons per minute. Since 16 tons per day are returned to the wire pit 24. and through une 25 tu pump za, f

then by subtraction H8 tons per day must come from meter I5, and further, since we have assumed a'consistency of 0.65% at meter I8, the 119 tons which flows through this meter daily is a thin solution ilowing at the rate of 3050 gallons per minute and a ilow of 1450 gallons per minute at a consistency of 0.184% is required in line 25. For simplicity o! this explanation or example, we may assume that no stock which is rejected at the paper machine either in the broke or inthe white water, is returned to the system in the sulphite, and since the ilnished paper has a sulphite content of 18%, this pulp is supplied to meter Il at the rate of 18 tons per day or at` the rate of 460 gallons per minute and 0.65% consistency. subtracting the rate of ow of the sulphite from the rate of flow of the paper stock through line 22, it is found that. the rate of iiow of the ground wood solution through line i1 is at the rate of 101 tons daily, or 2590 gallons per minute at 0.65% consistency. By the assumptions the ground wood flows through line 5 at 0.5% consistency and through regulating valve i4 at 3.09% consistency and by computation from these values, the `ilow through line 4 is, revealed as 73.4 tous per day or 2444 gallons per minute and the ilorthrough regulating valve I Il is 27.6 tons per day or 146 gallons per minute. 8 tons of broke per day at 3.09% are returned to the system through line 49 to slush storage I3, thus leaving 19.6 tons per day at 3.09% to be supplied to storage I3 through thickeners Il. From these values, by computation the now from vat 4 to thlckeners II is at the rate of 22.28 tons daily or '143 gallons per minute of 0.5% consistency. 19.6 tons daily of this amount are delivered to slush storage I3 through line I2 at the rate of 106 gallons per minute of 3.09% con sistency, and the balance or 2.68 tons daily flows through line 36 to storage 35 at the rate oi' 63'7 gallons per minute of 0.07% consistency. Thus there is available at pump 38, a total of 4136 gallons per minute for supply to pointsin advance l of screens 2. The tonnage rate through line 3 is equal to the sum of the rates through lin'es I2 and 6 or 95.68 tons daily which at a consistency of 0.5% amounts to 3197 gallons per minute, leaving an excess vor 939 4gallons per minute for the recovery lters (not shown) as hereinbefore mentioned. y Now comparing the now through screensA 2 with the flowi'rom vat I to thickeners II, vit is learned that 23% .of the ow through the screens is byfpassed to the thickeners, butv that 77% of pulp after screening ows directly as a thin solution to meterfl.

Having illustrated and described my invention both in the abstract and with a concrete example of its practical workability, what I claim asnewandusetulisz. y

1. The process o'making paper comprising,

screeningv a pulp, flowing the main body of the pulp directly to a paper stock meter, thickening.y rsome of the pulp to increase the consistency ,thereof, regulating the rate at which the thickened pulp re-joins the main body of the pulp, .supplying other paper making ingredients to said meter, metering each ingredient'to form a common stream of paper stock, mixing with said stream a stream of water containing all of the pulp which drains through the papermachine wire near the breast roll and delivering the mixture to the paper machine.

2. The herein described process for making paper consisting in screening a pulp, dividing the screened pulp, flowing one portion directly to a common point for union with other paper making ingredients, extracting white Water from the other portion of the pulp, impounding the portion v from which white water is extracted, regulating the ilow of the impoundedpulp to a location of union with the portion owing to said common point, and metering all ingredients to form a composition forl delivery tothe paper machine.

3. In a.A paper making apparatus, the combination of screens for screening a pulp, a meter for l metering said pulp., means for moving-thescreened 'fpulp to said meter, means for diverting some of the screened pulp and extracting someY of the water therefrom and means for returning to the screenedpulp the portion from which the water was extracted to regulate the consistency of said screened pulp in advance of said meter.

CARLTON I-I. ALLEN.

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