US3421622A - Cleaning and deaerating paper pulp suspensions - Google Patents

Description

Jan. 14,1969

G. G. WURTMANN -CLEANING AND DEAERATING PAPER PULP SUSPENSIONS Filed Aug. 19, 1965 Sheet of 2 VQCUUM PUM P r0 HERD Box or PAPER MRcHINi: OR

vacuum PUMP Jan. 14, 1969 G. G. WURTMANN 3,421,622

CLEANING AND DEAERATING PAPER PULP SUSPENSIONS Filed Aug. 19, 1965 Sheet 2 United States Patent 3 Claims ABSTRACT OF THE DISCLOSURE Hydrocyclone system and method for cleaning and deaerating paper pulp. Hydrocyclone overflow tube discharges to an accepts vacuum receiver. The apex outlet discharges rejects through a restricted tangential outlet to a rejects vacuum receiver. The restricted outlet isolates the lower end of the air core with respect to the rejects vacuum receiver. Pressure is varied within the rejects vacuum receiver to control percentage of rejects.

This invention relates to equipment and methods for cleaning and deaerating paper pulp suspensions and the like.

One well known form of apparatus for cleaning such suspensions to remove dirt or other undesired particles comprises a chamber which is generally conical, at its lower portions at least, and into the upper portion of which the pulp is forced under pressure tangentially so as to establish an outer downwardly swirling helical vortex which becomes constricted at its lower portions, and the inner portions of which become reversed as an inner and upwardly'fiowing helical vortex which is discharged as accepted cleaned stock at the mid portion of the upper end of the chamber, whereas a small quantity of the stock embodying dirt and heavier undesired particles, is discharged as rejected material from the conical lower apex of the chamber. Such rejected stock may pass directly down into a tank which may be evacuated. In order to deaerate the cleaned accepted stock, in some installations the central accepted stock discharge outlet at the upper end of this chamber is connected directly into a relatively large evacuated tank, into which the stock is projected as a spray and so as to become substantially atomized. The lower part of such tank contains a body of the cleaned and deaerated pulp from which same is pumped to the paper mill screens or paper mill headbox, whereas the upper portion within this tank and into which the stock is sprayed, is connected to a vacuum pump for constantly withdrawing the air and any other gases which emanate from the stock as it is sprayed into this space.

With the arrangement above described, a more or less liquid-free central core will extend throughout the height of the vortices and up through the central portion of the accepted stock outlet into the evacuated space in the deaerating tank above, and the same core will extend down through the rejected stock outlet into whatever chamber or space is provided below for receiving the rejected material. Because of the presence of this liquidfree core, the space within the deaerating chamber above is brought into direct communication with the rejected stock-receiving space below the cleaning chamber and thus of necessity these two spaces will be maintained with the same degree of vacuum. And since for efficient deaeration purposes, the vacuum in the deaerating space above must generally be kept as high as possible, this will mean also that the space for receiving the rejected stock will be subjected to the same high vacuum. But this is a condition which is often not favorable for the removal of appropriate but not excessive amounts of rejected stock. Furthermore, with this arrangement, it is not possible to adjust or vary the percentage or amount of the rejected stock as compared with the amount of accepted stock. In fact, to vary such percentage, it would ordinarily be necessary to remove and replace some portion of the apex connections of the cleaner in order effectively to enlarge or restrict the cavity therethrough and this is normally not possible in any practical or convenient way without interrupting operation of the equipment.

According to the present invention, the arrangement and manner in which equipment of the general class above described is combined, is so altered and modified as to make possible at all times an accurate adjustment or readjustment of the percentage of the stock which is rejected and to do so while the equipment remains in opera tion and without removing or replacing any of the parts. In summary, this is accomplished by so isolating the lower end of the liquid-free core with respect to the connections for carrying away the rejected stock to a rejected stock tank, that the liquid-free core is trapped or stopped near the bottom of the vortices in the cleaning device, and so that the rejected stock passes to one side therefrom and through connections which remain filled with rejected liquid material, but are so restricted that the space within the rejected stock tank is in effect isolated from and can be kep at a subatmospheric or other pressure which is quite independent of the pressure conditions in and near the vortices and independent of the degree of vacuum in the deaerating tank at the top of the equipment. As a consequence, according to the present invention, the pressure or degree of vacuum within the rejected stock tan k may be thus independently varied, with the result that the percentage of the stock which is withdrawn through said restricted connections and rejected, may be accurately varied Without disturbing the vortices or any of the pressure conditions in the cleaner or the deaerating tank above. This affords a very important practical advantage for the following reasons.

In most paper mills, the consistency of the pulp to be cleaned and deaerated must rather frequently be changed to manufacture paper of different thicknesses or it frequently becomes necessary to utilize pulp stock of different qualities or containing various different materials or different amounts or kinds of undesired particles, depending on the type and quality of the paper being made. These factors render it highly desirable that the amount of stock which is rejected in cleaning as compared with the accepted amount, be frequently adjusted, sometimes at intervals as often as hourly. With the present invention, this may be quickly accomplished merely by turning a valve to vary the pressure or subatmospheric pressure in the rejected stock receiving tank without necessarily varying the rate of feed of stock into the apparatus and without interfering with the desired relatively high vacuum conditions in the deaerating tank.

In apparatus of the general nature above described, there is a complexity of velocity and pressure conditions, particularly at the region of the reversal of the vortices and at the regions of the lower end of the liquid-free core, and it is an unforeseen and surprising fact that these conditions may be kept constant and stable for highest efficiency cleaning operations, despite the varying of the subatmospheric or other pressure in the rejects tank when it is desired to adjust the rejected stock percentage. During such adjustments it has been found that the pressure just ahead of the restricted rejects outlet surprisingly remains constant and the adjustment of the rejects tank vacuum or pressure merely changes the rate of flow of the rejects to the tank.

It should be noted that while hereinabove, as well as in the remaining parts of the specification and claims, certain portions of the apparatus are referred to by the terms upper and lower, these terms are used for convenience and in their relative sense, inasmuch as the equipment may be installed and used in various oriented positions and even upside down, if desired, as compared with the position thereof in the appended drawings.

Various further and more specific objects, features and advantages of the invention will appear from the description given below, taken in connection with the accompanying drawings, illustrating by way of example preferred forms of the invention.

In the drawings:

FIG. 1 is a diagram, portions of which are somewhat schematic, and which illustrates the general arrangement of a preferred form of apparatus for carrying out the present invention;

FIG. 2 is a vertical cross-sectional view of one of the stock cleaner chambers of a preferred form and which comprises a part of the combination of the invention;

FIGS. 3, 4 and 5 illustrate respectively three alternative outlet arrangements through which the rejected stock is discharged to the rejected stock receiving tank.

Referring to FIG. 1 in further detail, there is here shown an installation embodying a plurality of vortextype cleaning devices for removing dirt and other undesired particles, particularly heavier particles, from the paper pulp suspension, three of such devices, as at 10, 11 and 12, being here shown by way of example, each having at the top tangentially-directed inlets, as at 13, into which the stock to be treated is fed through a supply pipe 14 from a pump 15. A pressure gauge 16 is preferably provided for indicating the inlet pressure to these cleaning devices.

The construction and operation of each of such cleaning devices will be apparent in further detail from the vertical sectional view of FIG. 2. As indicated, the suspension is fed in through a tangentially-positioned inlet 13 at the top, thereby causing a downwardly-directed helical outer vortex 19 to be established in the cylindrical chamber portion 10' of the device. This vortex extends down into another and lower portion 10", which preferably is of a generally conical shape with elements of the walls being curved somewhat inwardly, as shown, so that the downward vortex 19 becomes more and more restricted down to the lower end portion thereof which may be contained within a short cylindrical extension piece 20 opening into a more or less annular chamber portion 21, which is closed by a bottom plate 22. Such bottom plate preferably is formed with an upstanding conical mid portion 23, the apex of which has an inverted, preferably conical or otherwise generally depressed central portion 24.

As the downwardly-flowing vortex 19 becomes more and more restricted, inner portions thereof become reversed and gradually form an upwardly-flowing helical inner vortex surrounded by the downward vortex 19. This inner vortex extends up through, and fills the peripheral portions of an accepted stock outlet 26 which discharges into an evacuated tank 27, as hereinafter further explained.

Meanwhile, throughout the length of these vortices, an inner, axial, substantially liquid-free core 28 is maintained, which core is terminated and positively closed, however, at its lower end by the depressed portion 24, but the upper end of this liquid-free core 28 extends up into communication with the evacuated space in the tank 27 above. It will be understood that as the suspension proceeds downwardly in the outer vortex 19, the heavier or undesired particles will be forcefully thrown to the peripheral portions of such vortex and at the same time further undesired particles will be centrifugally thrown radially outward from the peripheral portions of the upward vortex 25 into the downward vortex, so that at the bottom ends of the vortices where the outer vortex has largely become reversed to form an upward vortex, most of the undesired r 4 or heavier particles will have been thrown to the perip ery within the bottom piece 20. It will be noted that there is an annular passage 30 formed between the conical closure portion 23 and the lower end of the short cylindrical portion 20, and through this annular passage the desired quantity of rejected stock is allowed to flow into the chamber portion 31, from which same is allowed to flow out through a tangentially located outlet connection 32.

The cleaning device per se, as above described in reference to FIG. 2, is similar to that shown and described in US. patent to Freeman et al. No. 2,927,693, granted May 8, 1960, more specifically the form shown in FIGS. 1 and 7 of that patent, but preferably with some changes in proportions and shapes of the parts, as will be evident from FIG. 2 as hereinabove described.

Referring again to FIG. 1, it will be noted that the accepted stock comprised in the upwardly-flowing vortices 25 of each cleaning device, is carried in each ease up through a conduit 35 which extends up into the tank 27 to a level well above the normal liquid level 36 therein and into the upper space 37 thereof which is kept evacuated as by a vacuum pump 38. Normally the upper portions of this tank are maintained by the vacuum pump at a maximum vacuum commensurate with the liquid saturation temperature within the tank and usually within a range of 27" to 29" of mercury vacuum. Generally the incoming supply of pulp suspension within the conduit 14 is kept at a pressure such that the differential between this pressure and the vacuum within the upper portion of the tank 27, will be in the neighborhood of 40 to 50 pounds per square inch. This differential may vary, depending on the relative cost of providing larger equipment for a desired capacity, as compared with the cost of power for operating larger pumps to attain the desired capacity, but ordinarily if the differential is changed, the change will arise from a different input pressure, as it is preferable to keep the degree of vacuum in the tank 27 as high as possible to insure good deaeration of the suspension, and thus ordinarily the degree of vacuum in the tank should remain substantially constant.

The liquid-free core 28 within the accepted stock outlet pipe 35 will extend in a more or less liquid-free condition clear to the top of the pipe 35 where the accepted stock of the upper vortex 25 is discharged in the form of a spray 40, which preferably impinges against the inner top surface of the tank as a forceful and widely-distribk uted spray, from which, due to the evacuated condition of the space 37, the suspension becomes quite effectively deaerated as it falls to the liquid level.

The tank 27 may be constructed and arranged, if desired, in accordance with the construction of the type known under the trademark Deculator, although not necessarily conforming thereto. In the construction shown, a partition is located in this tank to provide a weir, as at 41, so that the liquid level will remain constant, as indicated at 36, in the main part of the tank, while any excess flows over the weir into another body 36' of the suspension for example. The cleaned, deaerated suspension may be pumped from the main body thereof in the tank 27 by means of a pump 42 discharging through a conduit running to the headbox of the paper machine or to the paper mill screens, or to storage, if desired. Excess suspension from the body 36 thereof may be discharged through a conduit 43 having an adjusting valve 44, and carried back to an inlet 45 of the pump 15 for recirculation through the system.

At the lower end of each of the cleaners 10, 11 and 12, the rejected stock which flows out tangentially from the apex end of the liquid-free core 28, through the connection 32, may pass through suitable adjustable valves as at 46 (FIG. 1) thence through any of various types of restricting means, as shown in FIGS. 3, 4 and 5 hereinafter described. From these means the rejected stock is discharged freely as through conduits 47 into a rejected stock tank 48 within the lower portions of which a body 49 of the stock accumulates and which may be supple mented by incoming supplies of white-water through a valve, as indicated at 50. The upper portion within the tank 48 is generally kept under subatmospheric pressure as by a vacuum pump 51. The degree of such pressure may be varied as by adjusting the valve 52, or, if preferred, varying amounts of air from the atmosphere may be bled into the tank through adjustable valve 53.

Rejected stock from the body 49 thereof may be constantly pumped, as by pump 54, through a conduit 55 adjustable by a valve 56 to a so-called secondary stock cleaner, such as indicated at 57. The main body portions of this cleaner may be like those indicated at 10, 11 and 12, as above described, or like the secondary cleaner indicated at D in FIG. of the above-mentioned Freeman et a1. patent. Accepted stock from the secondary cleaner may be discharged through a pipe 58 as a spray 59 within the tank 27, this spray as it falls becoming deaerated and forming a part of the body of suspension (indicated at 36) which is recirculated through the equipment.

Reference will now be made to FIG. 3 showing one example of means through which the rejected stock flowing out as through conduit 32 becomes discharged into the rejected stock tank. Here the flow may enter tangentially into a chamber 60 in which a flow of spiral formation is maintained with a restricted discharge therefrom through a central bottom outlet, as at 61, into a conduit 62, which may form a part of the conduit 47 above referred to in FIG. 1, and through which the rejects freely fall or flow down into the tank 48. The flow through the device of FIG. 3, and the restriction of the fiow caused thereby, is such that the conduit 32 entering same will be maintained liquid-filled and at a pressure above whatever pressure is normally maintained in the rejected stock tank 48. If desired, sometimes this tank may be operated at atmospheric pressure (or even above), although usually (and particularly when making the adjustments hereinafter further explained of the percentage of rejected stock to be withdrawn) this tank is maintained under a substantial vacuum, but in any event the pressure therein is always less than the pressure maintained in the constantly liquid-filled conduit 32 from which the rejects are allowed to flow to one side of the lower end of the liquid-free core within each cleaning device 10, 11 or 12. Under these conditions the stock will flow tangentially from the lower end of the cleaning devices smoothly and without causing disturbance or wobbling of the lower end of the liquid-free core 28 within the cleaning device. Thus conditions at this region remain stable and the rejects discharge conduit 32 remains liquid-filled and under some pressure, usually constant, even though immediately adjacent thereto there is located the lower end of the liquid-free core, the space within which is under a vacuum (as high as possible) since it communicates up through the central vortices directly with the evacuated space in the tank 27 above.

With the form of outlet device shown in FIG. 4, conduit 32 from the lower end of the cleaning device may be shaped as an elbow, a lower end portion 64 of which may be connected, as by detachable clamping means 65 for example, to the upper end of a conduit portion 47' discharging into the tank 48. As indicated, a disc as at 66 may be mounted within the upper end of conduit 47' having a central restricted outlet aperture 67 through which the rejects are discharged, thereafter freely to flow down into the tank 48. With the form shown in FIG. 5, the outlet conduit 32" from the lower end of the cleaner, may simply be restricted as shown, so that the rejected stock may pass through an elbow connection 70 and be discharged therefrom freelythrough conduit 47" into the rejects tank.

Now, as explained in the introductory portions hereof, it is often important to be able readily and quickly to adjust such apparatus to vary the percentage or amount of the stock which is to be rejected, as compared with the amount of accepted stock, and to do so without interruption of any of the other efl'lcient operation aspects of the equipment. But as hereinabove indicated, some installations of stock cleaning and deaerating apparatus of this general character have heretofore been made, but in which the cleaning devices each discharge the rejects axially down through the apex or lower ends thereof, so that the liquid-free cores within the cleaning device extend axially thereof all the way from the rejects-receiving tank at the bottom (or the equivalent) up through the apparatus to the evacuated space in the accepted stock tank above, thus bringing the two tanks into direct communication with each other, so that if the pressure in the rejects tank is attempted to be varied, this will necessarily alter the desired deaeration pressure conditions in the accepted stock tank and otherwise disturb the operating conditions throughout the system. Hence it is not feasible in such cases to vary the percentage of rejected stock except possibly by altering the dimensions of the discharge portions in the region of the lower ends of the vortices, as by uncoupling and replacing some of the parts by others of different dimensions.

However, with the combination of equipment as above described and embodying the present invention, the percentage of rejected stock may be immediately varied or adjusted simply by adjusting either the valve 52 or the valve 53, or both, thereby to vary the subatmospheric pressure within the rejected stock tank. That is, the degree of vacuum is lowered or raised, thereby to reduce or increase respectively the rate of flow through the restricted rejected stock passage portions, such as shown in FIGS. 3, 4 or 5. This can ordinarily be done so as not to cause any variation in the pressure within the conduits 32 through which the rejects flow from the lower end of the vortices. (Such pressure may be indicated as by gauges, as at 72 in FIG. 1.) Stated otherwise, the arrangements at the bottom portions of the cleaners are such as effectively to isolate the evacuated space within the accepted stock tank and the liquid-free vortex cores from the space within the rejected stock tank, and this is accomplished in a manner such that variations in the subatmospheric pressure of the rejects tank cause no disturbance of the desired stable conditions within the lower portions of the vortices. Thus the deaeration operation may be kept free of disturbance or interruption and highly efiicient and the percentage of rejects may be quickly varied at any time to meet varying operating requirements as to the character of the pulp suspension being used in the paper mill. Sometimes also, if the equipment is running with a small percentage of rejects being withdrawn from a pulp suspension of relatively high consistency, there may be a tendency for the rejects outlet portions to become clogged. This condition can, however, generally be quickly overcome by increasing the degree of vacuum in the rejects tank.

The fact that this adjustment of the rejects tank subatmospheric pressure and consequent adjustment of the rejects percentage may be carried out without disturbing other operating conditions of the equipment, is quite surprising, but tests have confirmed that such results may be readily accomplished. For example, in one case a cleaner was used having an internal cylinder diameter of eight inches and with a constant inlet pressure of 38 psi. and with a pressure differential of slightly more than 51 pounds per square inch as between the inlet pressure and the vacuum within the accepted stock tank. Then, in one trial, the vacuum in the rejects tank was adjusted to about fourteen inches of mercury, causing a little over 5% (by volume) of the stock to be rejected. (The stock was fed in at the average rate of about gallons per minute.) Then, while other conditions remained approximately the same, the rejects vacuum was reduced to seven inches of mercury, whereupon about 3.9% of the stock was rejected without disturbing the previous condition of the vortices or materially varying the pressure differential between the intake and the accepted stock tank and without reducing the desired high degree of vacuum in the latter. And in another trial, the rejects tank was operated at about atmospheric pressure, whereupon the rejects percentage amounted to some 3.7% by volume, with other conditions remaining undisturbed. In these three trials, the vacuum in the deaerating tank at the top remained close to 27" of mercury.

Other trials were made with a cleaner being used having an internal cylinder diameter of and with a constant inlet pressure of 28 psi. and a pressure differential of about 41.7 psi. as between the inlet pressure of the vacuum within the accepted stock tank. Then in one instance the vacuum in the rejects tank was adjusted to about 27.8" of mercury, causing about 5.6% by volume of the stock to be rejected, the stock being fed in at the average rate of about 329 gallons per minute. On a second trial with the same equipment and with other conditions remaining substantially the same, the rejects tank vacuum was maintained at about 21" of mercury, causing about 4.58% of the stock to be rejected. In each of these two trials, the pressure of the rejects suspension flowing out from the lower end of the cleaner, as indicated by gauges as at 72, remained at about 8" vacuum and the vacuum in the deaerating tank above remained at 27.8".

What is claimed is:

1. Apparatus for cleaning and deaerating paper pulp suspensions and the like comprising in combination: a cleaning chamber having a tangential stock inlet at its upper end, and in which chamber a downwardly-flowing helical vortex of the suspension is adapted to be maintained with a restricted lower end where inner portions thereof are reversed to form an inner upwardly-flowing helical vortex surrounding a substantially liquid-free axial core; a deaerating tank; a conduit extending from the mid portion of the top of said chamber up into the upper portion of said tank for receiving said upward vortex and discharging same as accepted stock in the form of a spray in said tank; means for maintaining said tank evacuated, whereby such spray becomes deaerated, and said liquid-free core extending down through the vortices is likewise maintained evacuated, the lower end of said chamber being of restricted cross-section and having a bottom closure which closes said liquid-free core at a predetermined point, a small generally annular chamber being provided to surround the lower end of said core and having a tangential outlet through which rejected stock may flow to one side of said core; a passage for receiving such flow of rejected stock, such passage having outlet portions which are sufiiciently restricted whereby the passage is normally maintained liquid-filled; a rejected stock enclosure in the lower portion of which a body of stock accumulates and into which the rejected stock is discharged from such restricted passage through a conduit, means for establishing and maintaining the level of rejected stock in said enclosure; and means for subjecting said enclosure to subatmospheric pressure and for raising or lowering such pressure to reduce or increase respectively the rate of flow or rejected stock through such passage, thereby correspondingly to vary the percentage of treated stock which is rejected, independently of the degree of vacuum maintained in the tank for deaerating the accepted stock.

2. In the operation of apparatus for cleaning and deaerating paper pulp suspensions and the like wherein a downwardly-flowing helical vortex of the suspension is maintained within a restricted lower end where inner portions thereof are reversed to form an inner upwardlyfiowing helical vortex, the upper end of the upward vortex being discharged into an evacuated space as accepted stock in the form of a spray which becomes there deaerated, the vortices having a generally liquid-free central core communicating with said space, rejected stock embodying undesired particles being withdrawn from the lower ends of the vortices: the method of controlling and adjusting the percentage of the stock which is thus rejected as compared with the amount of accepted stock, which comprises maintaining the lower end of such liquid-free core closed at the apex end while allowing the rejected stock to flow tangentially to one side thereof through a passage, restricting the outlet portions to such passage sufiiciently to keep said passage liquid-filled at a positive pressure, communicating said passage through a conduit for discharge into the air evacuated space of a rejected stock enclosure containing a quantity of the rejected stock therein, maintaining a subatmospheric pressure in a portion of said enclosure and lowering or raising the subatmospheric pressure of such enclosure to reduce or increase respectively the rate of flow through said passage thereby correspondingly varying the percentage of the treated stock which is rejected.

3. In the operation of apparatus for cleaning and deaerating paper pulp suspensions and the like wherein a downwardly-flowing helical vortex of the suspension is maintained with a restricted lower end where inner portions thereof are reversed to form an inner upwardlyflowing helical vortex, the upper end of the upward vortex being discharged into an evacuated space as accepted stock in the form of a spray which becomes there deaerated, the vortices having a generally liquid-free central core communicating with said space, rejected stock embodying undesired particles being withdrawn from the lower ends of the vortices: the method of controlling and adjusting the percentage of the stock which is thus rejected compared with the amount of accepted stock, which comprises maintaining the lower end of such liquid-free core closed at the apex end while allowing the rejected stock to flow tangentially to one side thereof through a passage at substantially constant pressure, restricting said passage sufiiciently at its outlet portions to keep same liquid-filled, communicating such passage through a conduit for discharge into the air evacuated space of a rejected stock enclosure containing a quantity of rejected stock therein, maintaining a portion of such rejected stock enclosure under a substantially lower pressure than in said passage and, while maintaining substantial constant low subatunospheric pressure in said accepted stock space, lowering or raising the pressure of said rejected stock enclosure to reduce or increase respectively the rate of flow through said passage thereby correspondingly varying the percentage of the treated stock which is rejected, independently of the degree of vacuum which deaerates the accepted stock.

References Cited UNITED STATES PATENTS 2,717,536 9/1955 Clark 2092ll 2,927,693 3 1960 Freeman 209211 3,206,917 9/1965 Kaiser 41 FRANK W. LUTTER, Primary examiner.

U.S. Cl. X.R. 554l, 194

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