US2614656A

US2614656A - Deaerating a suspension of papermaking stock

Info

Publication number: US2614656A
Application number: US110450A
Authority: US
Inventors: Carleton L Clark; Vicario Carlo
Original assignee: ROTAREAED CORP
Current assignee: ROTAREAED Corp
Priority date: 1949-08-15
Filing date: 1949-08-15
Publication date: 1952-10-21
Anticipated expiration: 1969-10-21

Description

Oct, 21, 1952 c. L. CLARK ET AL 2,614,656

DEAERATING A SUSPENSION OF PAPERMAKING s'rocx Filed Aug. 15. 1949 4 Sheets-Sheet 1 Fig. l.

INVENTORS carletlonvp. CQork BY Car 0 lcono ATTO RN EY Oct. 21, 1952 c. 1.. CLARK ETAL 2,614,656

DEAERATING A SUSPENSION OF PAPERMAKING STOCK Filed Aug. 15, 1949 4 Sheets-Sheet 2 Willi/ E I, lllllllll llllllllld/p x g INVENTORS Carleton Cl urk Carlo V|c0r|o ATTORNEY 4 Sheets-Sheet 5 c. 1.. CLARK ETAL INVENTORS Carleton C lurk BY Carlo V|cor|o ATTORNEY DEAERATING A SUSPENSION OF PAPERMAKING STOCK Oct. 21, 1952 Filed Aug. 15, 1949 Ml r Patented Oct. 21, 1952 T UNIT D mm J B I Q iimsnzirisiii s grsfision or PAPERMAKING s'rocn Carleton L. Clark; North. Tarrytown anil' Car-16 I Vicario', New York, N. Y.-,;=assignors;120= The I a e dzcorp ra n, BrcnxvifleiN- rsac 0 poration of New York v 7 Application August-1'5, 1949'; s rial neimiist 3 Claims. (01. 183-1145) I .imsimv'enfion relates to the conditioning of cellu1ose. fibersin wateresuspension', for use in paper-making namely either as pulp issuingfi'om a digester that must be washed .and

v screenedlor asstock supplied tovapaperimaking machine. Both such pulp and t such stockare" insolvedtair causes objectionable foaming in the headi-boxorcylindeitmold of the paper machine; The elimination of such is desirable inasmuch as even: small quantities: of it reaching therpaperx machine: are diable to, 1 interfere with the: proper fiberr 'dispersion during sheet formation and toproduce breaks, flaws, orwthin spots inlthezpapieri H I I J So it-isL one of theobject'sof this invention devise; a method and" apparatus for continuouslyg' rapidly; effectively and uniformlyveffecting deer-aeration of the stock' to an extent. that the foam nuisance is practically eliminatedr- Another object is; to deviseways and: means for treating: the stockto improve significantly its drainage rate-, that being the chara'cte'ristic of the stock that readily yields upits diluting waterwhile on': the traveling foraminous-web or" Wire screen-of the paper I m'achinei Thus bys inc'reas ing -the' drainagerata:thetravelingscreen may be increase in the rate-of (ice-aeration is" realized if the; d'e aerating vacuum has" its degree 01' value controlled to lie within: a narrow' critical range: In order todescribe that range; it i5 firstiieees sary: sto' point out: that: paper-making stock is,

maintained at an elevated temperature that is established; as being:. appropriate to operations in eacl particular paper" mill. This temperature, thus varies with different mills so it must' be, taken into consideration-- in" defining that critical range of the 'degree o'rmeasure of vacuum to be used, because. that degree of vacuum under Which thestock. suspension will boil at its mill temperatureisour beginning point in-measuring our critical range-"of vacuum to be used- This point represents? the vaporpressure of; thestockto be' den-aerated at its established-temperature:

more-dilute than normal thus producinga' p'aper of higherquality due to more homogeneous-i and uniform-fiber "distribution. Indeed, it 'is'. an objectfof. this invention-to make paper faster and of:-better quality;

This'inventi'on'is base'dupon the fact thatwhen stock in. dilut'e suspension" is to" be vde-aerated by the use of: reduced pressure or vacuum; the cellua loselfibersin theirwater suspension must be injected into the reduced pressure atmosphere: of a vacuum tank: as an atomized spray. or mist; which. descends or settles throughthe atmosphere of-the tank and 'finallyv collects in a -pool in the bottom of the tank. Due: to this fine state -of subdivision during; such descent, a-ma-ximum quantity of surfaceiarea of the-particles is ex+ posed to the vacuum priorsto their collectionin thepool in the tank. This action is" herein referred-"togenerally; as disruption ofv the stock suspension, 7 I t I n nt of at lea tlsome of these-objects ba ed EJ149911: 0 in;v discovery; that an' unexpected Ifthe teachingz'ofthis-invention is followed, there can be removed substantially allrof the air from the stock" above' the-0.1 by volume that ac-: cepted as being unextraotable; V

. 'More" particularly; our discovery is-that onthe disrupted stock to be.de-aerated, VI there must maintained as closely as practic&ble-,-= a; vacuum in degree such that thepressure of the vacuum does not'e'x'ceeds 05-3 inch-(1 mercury pressure above the absolute vapor pressure (boiling point)- of.thesupplied-stock. As far as practical operation-'- is concerned] deviation fromthis 7 limit seems to be more critical in an upwardd' ction from; the 0.3 value than in adownward direction. This I means that' it is more criticalto I deviate away from the=vaporpressure than-toward-that pressures :Wliat has'just-been statedwith-re gard "to this critical range can be visually shown on a graph marked on the ordinate withpercentages of air remaining in the stoclsbeingideaerated; and-Ron the abscissa the'absolute pres-'- sure: of the vacuum above; the boiling point- 91 the stock at its supplie'd temperature The -curve onisuch a graph drawn as-a result of -tests, presefitsr-a sow and very shallower I almost horizontal initial "portion thatmerges with asteep ly rising portion. The shallow: portion comprises a measure of the critica'l range extending from -a bef ginning point on the ordinate which represents,

rality of the stock-injecting atomizing nozzles feeding directly into the vacuum tank in which the level of de-aerated stock is kept constant. The vacuum in the tank is adjustably maintained within the critical range of this invention by the joint effectof a steam jet and a vacuum pump. A discharge leg together with a discharge pump removes the de-aerated stock from the pool thereof in the vacuum tank to the head box of the. paper machine. An automatic control. device maintains constant a desired level of thepool of de-aerated stock in the tank for insuring a constant supply head for the discharge pump so the pump will feed the paper machine at a. uniform rate. This control device proposed for the purpose operates in a manner to correct the stock level by throttling automatically, first one and then sequentially others of the spray nozzles or vice versa opening first one and then others.

This invention finds embodiment in a vacuum tank which is in the form of a horizontal drum provided with a double row of stock-injecting atomizing nozzles fed froma header extending longitudinally of the :tank. The nozzles discharge into the tank in a downwardly inclined direction and preferably against impingementiaces spaced 1 a suitable distance both from the nozzles and from the level of the de-aerated stock in the tank. i

The best embodiment of our invention now known to us has-been chosen as an example for illustration, but it is to be understood as being illustrative and not limiting because obviously changes can be madetherein so long as they do not depart from the requirements of the appended claims or of their equivalents. This embodiment is shown in the accompanying drawings, in which i Fig. 1 shows semi-diagrammatically an apparatus arrangement embodying the invention including the improved vacuum tank for the de-aeration of the stock. Y Fig. 2 is an enlarged side view of the vacuum tank showing structural details of the improved vacuum tank including the arrangement of spray nozzles. Fig. 3 is a cross-sectional viewon the line 3-3 of Fig. 2. v

" Fig. 4 is an enlarged perspective detail view of oneof the spray nozzles with wall portions thereof broken away.

Fig. 5 is a diagrammatic view of the apparatus arrangement of Fig. 1 with automatic control means added for maintaining stock levels constant by means of automatically controlled valves.

Fig. 6 is an enlarged although semi-diagramm'atic detail view of one of the automatically con:- trolled valves.

" Fig. 7 is'a graph showing the critical range of high vacuum to be maintained in the vacuum tank-in accordance with this invention.

The apparatus arrangement embodying this invention is shown semi-diagrammatically in Fig. l and comprises an open supply tank or chest I0 containing suspended stock S currently supplied thereto as is indicated by a connection I I having a control valve 12. The stock levelLi in this tank is to be maintained constant at a suitable heightby controlling the feed. thereto.

From the tank II], the stock is supplied to a vacuum tank or de-aerator I 3 to which stock from chest Ill is supplied gravitationally by conduit l4 through a control valve l5,'leading to and into'one end of a horizontal header llfrom which in turn lead lateral branch conduits l8 to respective spray nozzles indicated at 19 which are mounted upon the vacuum tank [3 and through which the-stock is injected into the tank. This tank is in the form of a horizontally extending drum while header [1 extends substantially horizontally to the horizontal axis of that drum. The. stock being injected into this tank I3' is projected onto an impingement plate. 20, hereinafter more fully described for further disrupting the sprayed particles of fiber and water, if they need it.

is withdrawn from the tank bottom through a sump 2| by means of a pump 22. A conduit 23 leads from the sump 2i to the inlet end of the pump, while a conduit 24 provided with a control valve 25 leads to the head'box' 28 of a papermaking machine 21 indicated by its endless screen bandit.

The level L1 of the stock in the supply chest I0 is defined by the height H1 relative to the header H, while the levelLz in the vacuum tank an exhaust conduit'3l. .A .vacuum gauge..32is

shown for indicating the degree, of reduced pres:

sure thus maintained in tank; I 3 in terms of inches of mercury. I The de-aerating vacuum tank andits immediate appurtenances, especially theatomizing sprayv nozzles with their supply conduits, and the impingement structure within the tankareshown in. greater detail in Figs. 2. 3,]and 4. In, these figures the horizontally extending drum-like tank designated as [3' has a horizontally extending cylindrical body portion 33 and outwardly

convex end portions

33 and 33 The horizontally extending. feed header for the tank is. indicated as H andaits branch conduits as 18.. Especially Fig. 3 shows that there are provided two rows of branch conduits extending from the header in opposite directions to supply accordingly two rows of spray nozzles I91 and I92. Each of the branch conduits l8 has a control valve 34 for controlling or throttling the supply of stock to the respective spray nozzles. I v The impingement plates extending horizontally within the tank [3' is designated aslll whichis. in the nature of a hollow ridge having a cross-'- section resembling an inverted V This structure presents a pair of outer inclinedplates or faces 35 and 36 extending under about 45 against the vertical or at about with respect to each other,

upon which faces impinge sprays S1 and S2 of the stock injected into the tank by the correspondingly disposed rows of nozzles I91 and [92". The distance of the nozzles from these impingement faces is designated as Di, while the distance of the lower horizontal edges of these faces from the stock level L2 is designatedas-Dz. '3

The structure of the atomiz'ing spray nozzle is exemplified in the nozzle unit 31 shown perspec tively in Fig. 4 with'wall portions thereof broken away to show particularl the internally 'unob structed nature thereof. This nozzle unit has an inlet neck 38 having a flange connection 39 actuate with:a -respectivebranch conduit-1 8x and-amputlet-neck '4n having ":a flange connection-'4! with the :tank. "The inlet neck 38' leads tangentially int'm'a body portion-which represents an internally unobstru'cteel -sw-irl-chamber 4Z', whereas the outlet neck leads ofi from the centerIor-the swirl-chamber an'd' in a direction a t-right angles tothe'directioncf theinlet neck. v

Fig. 5'represents in principle the same apparatus arrangement that is shown in although more diagrammati -andwith emphasis being placed upon the addition of devices for controlling the-stock levels L1- and-L2.-- "That is to say','there is indicated-astock supply 'I l a stock chest'or tank it", aheade-r- H, supplied from tank 'I0" throug-h-a conduit I4",'and acontrol valve l 5--.- The header supplies a vacuum tank 1-3" through branch conduits i8 and nozzles 19. From this vacuum-tank the de-aerated stock is withdrawn byway of a sump 2 l through a conduit 23" leading to'a pump "22" whence a air 44' at a constant pressure and has operative connection with afloat 45 having a vertical guide 45 The movements of thisfloat through mechanism'Mi 'con'trol'air pressure admitted through pipe 45 to the diaphragm chamber of the valve unit 43 and thereby actuate the'val've in a manner to compensate for fluctuation of the level L1. Such level" control devices need not be described :in'anygreater' detail, inasmuch as they are wellknown per se and commercially obtainable.

In order t'o eifectthe automatic control of level L2 of thepoolof tie-aerated fibers and de-aerated 6 i As applied-Ito the; apparatus .lembodymg-this inventionpeach oi the va'lve units Ur, U zan d U3 has its diaphragm spring adjusted so thatith'ese valve units. will respond, sequentially .to respectively stepped-up auxiliary .air pressures to meet the demand as dictated by the up. or downm'o'vements of a float 52 :withthe fluctuations for the pulp leVelLz'.- Thatis, the movements of the float il having a vertical guide 51, influence afrelay mechanism indicated. at Ma which receives: aux iliary air 53 at a constant pressure. The mechanism athen acts to admit consecutivelyv higher actuating Jair pressures through a header 53 and branch conduits 46 to the diaphragm'chambers water in the vacuum tank. l3 one or more of the v controlled air pressure 46 isadmitted to a diaphragm chamber 48 and will. actuate the-valve stem to open or close the valve through the deflection, of this diaphragm. The air pressure above the diaphragm is opposed by the pressure of a compression coil spring 49 herein termed the diaphragm spring which surrounds the valve stem and is confined between the diaphragm and a bushing 50 which in turn is threaded into the frame or yoke 51 of the valve unit. By screwing this bushing up or down the pressure of the spring upon the underside of the diaphragm can be adjusted, so that the response of the valve unit is thereby adjusted to meet the level control requirements.

of-the respective valve unitsUi, U2, and -U3 so that they will function sequentially.

For instance, if the demand requires-throttling down the supply of stock passing to thevacuum tank within narrow limits when all three nozzles P1, P2, and P3 are running at full capacity", then as a result of movements of the float only-the first valve unit U1- will respond within-the range of its own capacity. If the demand tor maintain ing a constant level La requires a further reduc tion of stock supply after the first valve unit U1 has fully closed, then the second valve unit Us will begin to close in response to the movements orposition of the float, and so on. Vice versa., all three valve unitS'U L U2, and U3 should b'e assumed to have been closed, and the demand is for-increased stock supply, then the valves will sequentially open in accordance with that demand. In this way, a maximum number of spray nozzles is always kept running at theirfull capac- 'ityand therefore at maximum 'efiiciency, thatis withz maximum force of impingement upon'th'e impingement faces 35 and '36. I

The desired vacuum is maintained in the tank l3' by a vacuum pump 29" operating jointly with or boosted by a steam jet 30" having a control valve 301 in an exhaust conduit 3| and is indicated by a vacuum pressure gauge 32". By means of the vacuumpump and the steam jet there is jointly maintained in the tank l3 or I3 a vacuum which according to the requirements of this invention should be maintained (as closely as practicable)" at 0.3 inch of mercury pressure above the vapor pressure corresponding to the temperature of the supplied stock, the reasons for this limitation being presented by the graph in Fig. 7. That graph shows a concave curve C taken under stock de-aeratin'g conditions with the stock being injected and projected into the vacuum tank against the impingement faces therein. This curve has a shallow initial portion '0'; extending substantially from point Q1 topoint Q'zof that curvefand a steep portion C2 extendlug-from point Q2, points Q1 and Q2 being points upon a parallel-to the abscissa.

By maintaining the vacuum substantially withina range of pressures corresponding to 'therange C1 or shallow portion of the curve a surprisingly high degree of de-ae'rationof the stock is attainablerat a rapid rate and with a minimum of volumetric spacerequired for the vacuum tank.

A dot-and-dash line curve C also shown in the Fig. 7 graph shows similar or only slightly deviating conditions as a result of plotting these conditions when no impingement plate was used.

Naturally, the higher the established temperature of the stock to be de-aerated, the less vacuum in terms of total absolute pressure is needed to reach the critical range thereof and vice versa. Actual boiling of the stock will produce some refrigerating effect which is to be minimized.

. Referring to Fig. 5, the operation'isas follows: Stock from tank flows to theheader l1" under a head H1, maintained by the level-control device M1. The header distributes the stock to the various spray nozzles l9" as well as to spray nozzles P1, P2, P3. The supply of stock to nozzles 19" is set for their maximum capacity. and maximum stock disrupting efficiency, while nozzles P P2, P3 are automatically controlled in sequential order by the level control device M2 so as to maintain the level L2 of de-aerated stock constant. The automatic control of nozzles P1, P2, P: by the device. M2 and valves U1, U2, U3 is such that as many of these nozzles as possible operate at their full capacity, while only one of them is being correctively regulated. .For example, if a condition exists where all nozzles P1, P2, P3 run at their full capacity, and a rise of level L: requires throttling down the stock supply to the tank, then the control device will automatically effect such throttling, say, upon nozzle P1. If the degree of throttling required exceeds the corrective capacity of nozzle P1, then the control device will automati cally start throttling down the stock supply to nozzle P2, and then similarly the supply to nozzle Pa.

Vice versa, if a condition exists where the supply to all nozzles P1, P2, P3 is closed, then if a dropping of level L2 requires correction, the control device M1 through valves U1, U2, U3 will sequentially open up the supply to these nozzles depending upon the amount of correction required.

Thus the de-aerated stock which continuously collects in a pool in the tank, is delivered under a head Hz to pump 22 which in turn delivers it to head box 2 6 of paper machine 21".

All the while the vacuum in tank I3" is being maintained as by the joint suction effect of pump 29" and ejector 30" at a value corresponding to a pressure of about 0.3 inches of mercury (indicated by gauge 32") above the absolute vapor pressure of the stock at the established temperature, in order to attain a maximum of de-aeration at a maximum speed.

Such treatment gives the de-aerated stock a frozen appearance in which a, thin layer of water covers the entire surface of the stock in the head box without any bubbles appearing. This results in a distinct grouping of the fibers, which when dispersed give a uniform de-flocked dispersion and thus an extremely good formation on the paper. machine.

Whereas in the foregoingreference has been made to ways and means for treating papermaking fibers in dilute suspension, called stock in the foregoing description, this invention is also applicable to such fibers that are used earlier in the paper-making process, namely when they are called pulp after issuance from a digester. Such pulp requires washing and screening. Such pulp can be de-aerated to advantage by the use of this invention since effective de-aeration improves the drainage rate of the pulp which in turn increases the capacity of the screen or washer.

Whereas in the foregoing, dilute paper-making stock has been described as the material to be treated for de-aeration thereof, it is to be understood that by the word dilute" is meant liquidsuspended solids in, any proportion that is fluid enough to be pumpable, and the paper-making stock can comprise any liquid-suspended solids that are used in the making of paper, the deaeration of which solids by this invention, is advantageous.

What we claim is:

1. The process of treating paper-making solids in suspension to effect de-aeration thereof, which comprises subjecting such suspension while at an established temperature to a degreevof vacuum that lies within a range indicated on a curve on a graph representing on the ordinate the proportions of air left in the suspension after deaeration and on the abscissa the pressure above the absolute pressure of the boiling point of the suspension at said temperature, which curve exhibits an initial shallow portion merging into a steeply ascending portion whereon the range is indicated by the shallow portion that extends from a beginning oint corresponding to the boiling point of the suspension at said temperature, whereupon maximum de-aeration will be accomplished.

2. The process of treating paper-making solids in suspension to effect de-aeration thereof, which comprises subjecting such suspension Whileat an established temperature to a degree of vacuum that lies in a critical range extending from the absolute pressure corresponding to the boiling point to an absolute pressure of about 0.3 inch of mercury above that point.

3. The process of treating paperemaking solids in suspension to, effect de-aeration thereof, which comprises subjecting such suspension while at an established temperature to a degree of vacuum maintained to correspond substantially to an absolute pressure of 0.3 inch of mercury above the boiling point of the suspension at that temperature.

CARLETON L. CLARK. CARLO VICARIO.v

REFERENCES CITED The following references are of record in the file of this patent:

' UNITED STATES PATENTS Germany Oct. 25, 1939