US2685937A - Deaerating a susp ension of cellulosic fibers - Google Patents

Description

1954 c. L. CLARK ET AL DEAERATING A SUSPENSION 0F CELLULOSIC FIBERS Original Filed Aug. 15, 1949 4 Sheets-Sheet l INVENTORS Carleton I Clark Carlo V|cur|o i s/5w .8 dWAJEEZZ:

ATTORNEY 1954 c. CLARK ET AL 2,635,937

DEAERATING A SUSPENSION OF CELLULOSIC FIBERS Original Filed Aug. 15, 1949 4 Sheets-Sheet 2 INVENTORS Carleton L. Clark BY Carlo Vicorio ATTORNEY Aug. 10, 1954 c, L. CLARK ET AL 2,685,937

DEAERATING A SUSPENSION OF CELLULOSIC FIBERS Original Filed Aug. 15, 1949 4 Sheets-Sheet 4 '5 2 0) s "2 E U! B U LL 3 N a; o a.

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I Q? l o 9 d d o d o INVENTORS 76 101013030 bug/mm spogg u 9 1w abmuaaaa comm" chm BY Carlo Vicario WWW ATTORNE Y Patented Aug. 10, 1954 UNITED STATES PATENT OFFICE DEAERATING A SUSPENSION OF CELLULOSIC FIBERS Carleton L. Clark, North Tarrytown, and Carlo Vicario, New York, N. 1 assignors to The Rotareald Corporation, Bronxville, N. Y., a corporation of New York 6 Claims.

This invention relates to the conditioning of cellulose fibers in water-suspension, for use in paper-making, .namely either as pulp issuing from a digester that must be washed and screened, or as stock supplied to a paper-making machine. Both such pulp and such stock are intended to be covered herein, but for illustrative purposes, the invention is being described mainly as applied to dilute stock supplied'to a papermaking machine wherein entrained and dissolved air causes objectionable foaming in the head box or cylinder mold of the paper machine. The elimination of such air is desirable inasmuch as even small quantities of it reaching the paper machine are liable to interfere with the proper fiber dispersion during sheet formation and to produce breaks, flaws, or thin spots in the paper.

So it is one of the objects of this invention to devise a method and apparatus for continuously, rapidly, effectively and uniformly effectingcleaeration of the stock to an extent that the foam nuisance is practically eliminated. Of course, the term de-aeration is meant to include removal of gases, such as air, which are entrained in the stock. Another object is to devise ways and means for treating the stock to improve significantly its drainage rate, that being the characteristic of the stock that readily yields up its diluting water while on the traveling foraminous web or wire screen of the paper machine. Thus by increasing the drainage rate, the traveling screen may be run faster, giving a greater rate of production of paper of given quality; or in view of the increased drainage rate the starting stock may be more dilute than normal thus producing a paper of higher quality due to more homogeneous and uniform fiber distribution. Indeed, it is an object of this invention to make paper faster and of better quality.

This invention is based upon the fact that when stock in dilute suspension is to be deaerated by the use of reduced pressure or vacuum, the cellulose fibers in their water suspension must be injected into the reduced pressure atmosphere of a vacuum tank as an atomized spray or mist, which descends or settles through the atmosphere of the tank and finally collects in a pool in the bottom of the tank. Due to this line state of subdivision during such descent, a maximum quantity of surface area of the particles is exposed to the vacuum prior to their collection in the pool in the tank. This action is herein referred to generally as disruption of the stock suspension.

Attainment of at least some of these objects is based upon our discovery that an unexpected increase in the rate of tie-aeration is realized if the-de-aerating vacuum has its degree of value controlled to lie within a narrow crtical range. In order to describe that range, it is first necessary to point out that paper-making stock is maintained at an elevated temperature that is established as bein appropriate to operations in each 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 or measure of vacuum to be used, because that degree of vacuum under which the stool; suspensionwill boil at its mill temperature is our beginning point in measuring our critical range of vacuum to be used. This point represents the vapor pressure of the stock to be de-aerated at its'establis'hed temperature. if the teaching of this invention is followed, there can be removed substantially all of the air from the stock above the 0.1% by volume that is accepted as being unextractable.

.More particularly, our discovery is that on the disrupted stock to be (la-aerated, there must be maintained as closely as practicable, a vacuum in degree such that the pressure of the vacuum does not exceed 0.3 inch of mercury pressure above the absolute vapor pressure (boiling point) of the supplied stock. As far as practical operation is concerned, deviation from this limit seems to be more critical in an upward direction from the 0.3 value than in a downward direction. This means that it is more critical to deviate away from the vapor pressure than toward that pressure. What has just been stated with regard to this critical range can be visually shown on a graph marked on the ordinate with percentages of air remaining in the stock being tie-aerated, and on the abscissa the absolute pressure of the vacuum above the boiling point of the stock at its supplied temperature. The curve on such a graph drawn as a result of tests, presents a low and very shallow or almost horizontal initial portion that. merges with a steeply rising portion.

The shallow portion comprises a measure of the critical range extending from a beginning point on the ordinate which represents that boiling point. So it is a teaching of this invention that the degree of vacuum to be used on the disrupted stock is indicated by this shallow portion of the curve on such'a graph,'since that is the range in which can be accomplished maximim deaeration at the greatest speed.

In the practice of this invention, the stock to be desaeratedis supplied to a constant level chest from whence it flows to a header supplying a plurality 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 effect of 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 the pool 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 pur pose 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 the 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 from a header extending longitudinally of the tank. The nozzles discharge into the tank in a downwardly inclined direction and preferably against impingement faces spaced a suitable distance both from the nozzles and from the level of the de-aerated stock in the tank.

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 made therein 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 Fig. 1 shows semi-diagrammatically an appara tus arrangement embodying the invention including the improved vacuum tank for the de-aeration of the stock.

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 view on the line 3-3 of Fig. 2.

Fig. 4 is an enlarged perspective detail view of one of 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-diagrammatic 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.

Ihe apparatus arrangement embodying this invention is shown semi-diagrammatically in Fig. l and comprises an open supply tank or chest I!) containing suspended stock S currently supplied llll ' an exhaust conduit 3i.

4 tive spray nozzles indicated at I9 which are mounted upon the vacuum tank l3 and through which the stock is injected into the tank. This tank is in the form of a horizontally extending drum while header l'i extends substantially horizontally to the horizontal axis of that drum. The stock being injected into this tank is is projected onto an impingement plate 29, hereinafter more fully described for further disrupting the sprayed particles of fiber and water, if they need it.

De-aerated stock collects in a pool thereof below the impingement plate to a certain level L2 and is withdrawn from the tank bottom through a sump 2| by means of a pump 22. A conduit 23 leads from the sump 2! to the inlet end of the pump, while a conduit 2 provided with a control valve 25 leads to the head box 2t of a paper-making machine 2? indicated by its endless screen band 2%.

The level L1 of the stock in the supply chest Hi is defined by the height H1 relative to the header H, while the level L2 in the vacuum tank is defined by the height H2 above the inlet end of pump The levels L1 and L2 both are to be maintained substantially constant through automatic level control devices hereinafter more fully described in conjunction with Figs. 5 and 6. Such level control devices, however, are wellknown and are commercially available.

The degree of vacuum required according to this invention is maintained in the tank as by means of a vacuum oump 29 shown to operate jointly with and to be boosted by a steam jet 38, both the pump and the jet operating in series in A vacuum gauge 32 is shown for indicating the degree of reduced pressure thus maintained in tank it in terms of inches of mercury.

The tie-aerating vacuum tank and its immediate appurtenances, especially the atomizing spray nozzles with their supply conduits, and the impingement structure Within the tank are shown in greaterdetail in Figs. 2, 3, and 4. In these figures the horizontally extending drum-like tank designated as i3 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 and its branch conduits as it. 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 lei and its. Each of the branch conduits It has a control valve 34 for controlling 01' throttling the supply of stock to the respective spray nozzles.

The impingement plates extending horizontally within the tank i3 is designated as 2% which is in the nature of a hollow ridge having a cross section resembling an inverted V. This structure presents a pair of outer inclined plates or faces 35 and 33 extending under about against the vertical or at about with respect to each other, upon which faces impings sprays S1 and S2 of the stock injected into the tank by the correspondingly disposed rows of nozzles E91 and 82. The distance of the nozzles from these impingement faces is designated as D1, while the distance of. the lower horizontal edges of these faces from the stock level L2 is designated as D2.

The structure of the atomizing spray nozzle is exemplified in the nozzle unit Bl shown perspectively in Fig. 4 with wall portions thereof broken away to show particularly the internally unobstructcd nature thereof. This nozzle unit has an assess-7 inlet'nec'k'38 having a flange connection 39 with a respective branch conduit I 8, and an outlet neck it having a flange connection '4'! with the tank. The inlet neck 38 leads tangentially into a body portion which represents an internally unobstructed swirl-chamberfl, Whereas the outlet neck 4% leads off from thecenter of the swirlchamber and ma direction at right angles to the direction of the inlet neck.

Fig. 5 represents in principle the same apparatusarrangement that is shown in Fig. 1, although more diagrammatic, and with emphasis being placed upon the addition of devices for controlling the stock levels L1 and L2. That is to say, there is indicated a stock supply ii", a stock chest or tank H)", a header l'i, suppliedfrom tank iii through a conduit M, and a'control valve i5". The header supplies a vacuum tank 13" through branch conduits. i8" and nozzles 19''. From this vacuum tank the de-aerated stock is withdrawn by way'of a sump 2 l through 'a conduit 23" leading to a pump 22 whence a conduit 2%" through a valve 25" delivers the "stock to a head box 26" of a paper-making machine 21" indicated by itsendless screen band 28"". The horizontally extending impingement structure although indicated in Fig. l and shown in Figs. 2 and 3, has not been shown in Fig. '5.

In Fig. '5 there is included the showing of a diaphragm-actuated valve unit 43 controlled by fluctuations of the level L1 and through auxiliary air pressure, to regulate the supply of stock to the tank ill" for automatically maintaining the level L1 therein constant. There is indicated relay mechanism M1 which is supplied with auxiliary air 4-4 at 'a constant pressure and has operative connection with a float 45 having a vertical guide 45 The movements of this float through mechanism M1 control .air pressure admitted through pipe :15 to the diaphragm chamber of the valve unit '43 and thereby actuate'the valve in a manner to compensate for fluctuation oi the level L1. Such level control devices need not be described in any greater detail, inasmuch as they are wellknown per se and commercially obtainable.

In order to effect the automatic control of level L2 of the pool of de-aerated fibers and de-aeratecl waterin the vacuum tank 13" one or more of .the

spray nozzles are each provided with an auto- .matically controlled valve unit similar to that provided for the tank H!" and shown more fully inFigfi. In this instance three such valve units U1, U2 and Us are provided for respective spray nozzles P1, P2, and. P3 to throttle them.individual- .ly while all other nozzles may be allowed to operate unchanged at their full capacity. Such diaphragm-controlled valve units are well-known and commercially obtainable and the valve unit exemplified in Fig. 6 is therefore substantially self-explanatory. In such .a valve unit a diaphragm i is connected to a valve stem i1, and controlled air pressure 46 is admitted to a dia- :phragm chamber 18 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 58 which in turn is threaded into the frame or yoke '5! 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 6 unit is thereby adjusted to meet the level control requirements.

As applied to the apparatus embodying this invention, each of the valve units U1, U2, and U3 has its diaphragm spring adjusted so that these valve units will respond sequentially to respectively stepped-upaux iliary air pressures to meet *the'demand as-dictated by the up or down movements of a float 52 with the fluctuations of the pulplevel L2. That is, the movements of the float 52 having a vertical guide 52 influence a relay "mechanism indicated at M2 which receives auxiliary air 53 at a constant pressure. The mechanism then acts to admit consecutively higher actuating air pressures through a header 53 and branch conduits it to the diaphragm chambers of the respective valve units U1, U2, and U3 so that 'they'will function sequentially.

For instance, if the demand requires throttling "down "the supply of stock passing to the vacuum 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 for maintaining a constant level L; requires a further reducticn 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 or position of the float, and so on. Vice versa, if all three valve units U1, U2, and U3 should "be 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 their full capacity and therefore at maximum efficiency, that is with "a maximum force of impingement upon the impingement faces 35 and 3E.

The desired vacuum is maintained in the tank 43 by a vacuum pump 29" operating jointly with or boosted by a steam jet 33 having a control valve ea" in an exhaust conduit 3i" and is indicated by a vacuum pressure gauge 32'. By means of the vacuum pump and the steam jet there is jointly maintained in the tank 53 or ii 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 correspondin 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 tie-aerating conditions with the stock being i-niccted and projected into the vacuum tank against the impingement faces therein. This curve has a shailcw initial porticn C1 extending substantially from point Q1 to point Q2 i that curve, and steep p01 in C extending from point points Q1 and Q; being upon a parallel to the abscissa.

By maintaining the vacuum substantially within a range of ")ldSSlll'fiS corresponding to the range (31 or shallow portion of the curve a surprisingly high degree of de-aeraticn of the stack is attainable at a rapid rate and with a minimum of volumetric space required for the vacuum tank.

A dot-and-dash line vs C" also shown in the Fig. 7 graph shows si. lar or only slightly deviating conditions as a result 01 plotting these conditions When no impingement plate was used.

Naturally, the higher the established temper ature of the stock to be de-aerated, the less vacuin terms of total absolute pressure is needed 7 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 is as follows:

Stock from tank it" flows to the header I?" 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 l 9" is set for their maximum capacity and maximum stock disrupting emciency, while nozzles P1, P2, P3 are automatically controlled in sequential order by the level control device M2 so as to maintain the level L2 of ole-aerated stock constant. The automatic control of nozzles P1, P2, P3 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 or so 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 L2 requires throttling down the stock supply to the tank, then the control device will automatically efiect such throttling, say, upon nozzle P1. If the degree of throttling required exceeds the corrective capacity of nozzle P1, then the control device will automatically 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 droppin 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 or 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 25", of paper machine 2i.

All the while the vacuum in tank l3" is being maintained as by the joint suction effect of pump iii" and ejector 3%" 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 ole-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 ale-flocked dispersion and thus an extremely good formation on the paper machine.

Whereas in the foregoing, reference has been made to ways and means for treating papermaking fibers in dilute suspension, called stock in the foregoin 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 ole-aeration improves the drainage rate of the pulp which in tur increases the capacity of the screen or washer.

The present application is a divisional application of our parent application Serial No. 110,450, filed August 15, 1949, now issued as patent 2,614,656.

What we claim is:

1. Apparatus for treating paper making solids in dilute suspension to efiect de-aeration thereof, comprising a vacuum tank, a plurality of suspension-introducing nozzle means communicating with said tank, means operable responsive to a drop in suspension level in the vacuum tank to control now through at least one of said suspension-introducing means, outlet means communieating with said tank for discharging from the tank de-aerated suspension, vacuum producing means communicating with said vacuum tank and including means operable to maintain the degree of vacuum in the tank at a value approximately equal to an absolute pressure corresponding to the boiling point of the suspension at the temperature of the stock.

2. Apparatus according to claim 1 wherein each nozzle includes a body portion providing a swirl chamber, an inlet neck tangential thereto for tangentially introducing suspension into the swirl chamber of the body portion, and an outlet neck leading ofi from the center of the swirl chamber in a direction substantially perpendicularly to the direction of the inlet neck.

3. Apparatus for treating paper making solids in dilute suspension to eiiect ole-aeration thereof, comprising a vacuum tank, a plurality of suspension-introducing means connected with a suspension supply chest, several of said means normally continuously communicating with said tank to deliver suspension thereto from said chest, the remaining several means having valved control means therefor individually and sequentially operable responsive to predetermined drops below a preselected suspension level in the vacuum tank, an initial drop in the suspension level operating a first or said valved control means to open the same to introduce suspension into the tank at a faster rate than possible with the several means normally continuously communicating with the tank, and a continued drop in the suspension level sequentially operating the others of said valved control. means to open the same to introduce suspension at a still faster rate, outlet means communicating with said vacuum tank for discharging therefrom de-aerated suspension, and vacuum producing means communicating with said vacuum tank and including means operable to maintain the degree of vacuum in the tank at about 0.3" l-lg. above the vapor pressure corresponding to the temperature of the stock. l. Apparatus for continuous treating paper making solids in dilute suspension to effect deaeration thereof, comprising an enclosed treatment tank, a plurality of suspension-introducing means associated with the tank for disruptively atomizing such suspension into the tank, means for subjecting the tank and its contents to a deaerating reduced pressure for maintaining the absolute pressure in the tank at a value approximately corresponding to the boiling point of the suspension at the temper ture of the suspension therein, means for the withdrawal of ole-aerated suspension from the tank at a rate to leave in the tank a pool thereof having a liquid-level, and means for maintaining substantially constant the liquiddevel of the pool regardless of the rate of withdrawal of tie-aerated suspension therefrom including devices for regulating the inflow of suspension through the suspension-introducing means at a rate based upon the tendency of the pool to change its liquid-level.

5. The continuous process of treating paper making solids in dilute suspension to effect deaeration thereof, which comprises disruptively atomizing such suspension into an enclosed zone,

subjecting the zone to a ole-aerating reduced pressure and maintaining the absolute pressure in the zone at a value approximately corresponding with the boiling point of the suspension at the temperature of the suspension, collecting a pool of thus de-aerated suspension in that zone, withdrawing de-aerated suspension from the pool, and maintaining substantially constant the liquidlevel of the pool regardless of the rate of withdrawal by regulating correspondingly the rate of supplying suspension to the zone based upon tendency of the pool to change its level.

6. The continuous process of treating paper making solids in dilute suspension to effect deaeration thereof which comprises introducing suspension at a substantially constant rate and disruptively atomizing such suspension into an enclosed zone, subjecting the zone to de-aerating reduced pressure and maintaining the absolute pressure in the zone at a value approximately corresponding with the boiling point of the suspension at the temperature of the suspension, collecting a pool of thus de-aerated suspension in that zone, withdrawing de-aerated suspension from the pool, and maintaining substantially constant the liquid-level of the pool regardless of the rate of withdrawal by separately introducing suspension and disruptively atomizing such suspension into the zone at a rate regulated correspondingly to the tendency of the pool to change its level.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,569,105 West Jan. 12, 1926 1,853,849 Decrew Apr. 12, 1932 2,201,870 Piercy et a1 May 21, 1940 2,463,671 Bach Mar. 8, 1949

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