US3534912A - Low speed refining of a papermaking pulp solution - Google Patents

Description

2 Sheets-Sheet l m 0 T 0 m mmuaqwm 5 V L kw 7 d .lisfl e qowfizou azmkwGzou M N\ T mwhwmr mm e #9 m} ww Oct. 20, 1970 y K. J. BROWN LOW SPEED RBFINING OF A PAPERMAKING PULP SOLUTION Filed Jan. 11. 1967 N [yNN (I 4 ATTORNEYS Oct. 20, 1970 RO 3,534,912 I LOW SPEED REFINING OF A PAPERMAKING PULP SOLUTION Filed Jan. 11, 1967 2 Sheets-Sheet 2 l 1 14 1e l8 PEB/PHEEAL v51. oc/ry (FE-E7- Pc'eM/M A00 I l l I I I w n r m N (MW 83;? saw a9) 3.16 8 QN/N/JJJ JNVENTOR.

n/o/r Brow/7 m \CZZML/MWTTORNEYS United States Patent 3,534,912 LOW SPEED REFENING OF A PAPERMAKHNG PULP SOLUTION Kenton J. Brown, Rockford, ill, assignor to Beloit Corporation, Beloit, Wis., a corporation of Wisconsin Filed Jan. 11, 1967, Ser. No. 608,582 Int. Cl. D2111 1/02 US. Cl. 241-28 2 Claims ABSTRACT OF THE DISCLOSURE A method of and apparatus for greatly increasing, among other factors, the rate of refining of a pulp refiner by controlling the surface velocity of the rotor with respect to the stator to speeds less than 2,000 feet per minute. In addition to controlling the speed, the method of and apparatus for controlling the pulp consistency, the clearance between the rotor and the stator, and the temperature of the pulp solution to within certain ranges also increases, among other factors, the rate of refining. The control system and method of control is advantageously employed with a rotor and a stator having a greater number of bar edges than heretofore contemplated by the prior art.

This invention relates generally to a method and apparatus for the preparation of pulp or the like, which method andapparatus are for use primarily in the paper making industry. More particularly, the present invention relates to several novel improvements in the methods and apparatus for the preparation of pulp which provide many desirable results.

There are three major types of pulp refiners known in the prior art for processing a coarse pulp solution. The disk refiner employs a pair of circular disks facing one another and having bars and-corresponding grooves in the opposing faces. One disk is rotated with respect to the other disk while the pulp solution passes therethrough for refinement. The Jordan refiner employs a conical rotor having bars and corresponding grooves in the surface thereof and a conically shaped stator into which the rotor is received also having bars and corresponding grooves in the inner surface thereof. The Hollander refiner employs a cylindrical, drum rotor having bars and corresponding grooves in a surface thereof and a bedplate spaced a predetermined distance from the surface of the drum and also having bars and corresponding grooves therein through which the pulp solution passes.

Each of these known commercial pulp refiners normal- 1y operates at rotor surface speeds of between 2,000 and 5,000 feet per minute with the cylindrical heaters and conical refiners falling in the lower range and the disk refiners in the upper range. These relatively high speeds produce a pressure differential between the stator and the rotor which forces the stator and rotor apart from one another. As a result, delicate control is required to maintain the stator and the rotor at a fixed distance with respect to one another. As will be more fully explained hereinbelow, the dstance between the stator and the rotor is of primary importance in determining many of the resulting characteristics of the refined pulp stock.

In the disk refiners, the high speeds produce a pressure differential between the center and the peripheral edges of the disks causing inconsistencies in the refining process. Although this pressure differential will exist for all speeds, it can be readily appreciated that the differential will be greater at the higher speeds. Furthermore, air bubbles or cavitation results at the higher speeds mentioned above which is highly undesirable for the refining process. This pressure differential in the Jordan refiner produces axial forces on the rotor plug which displaces the plug from the stator causing similar results as those found in the disk and Hollander refiners.

3,534,912 Patented Oct. 20, 1970 ICC Usually from 50% to of the total energy used in present commercial machines in refining pulp is consumed merely by the rotor acting like a centrifugal pump impeller without contributing to the development of the fibers. The power required to circulate stock in a refiner usually varies directly with the cube of the speed of the rotor.

Lowering the speed of a refiner improves its efficiency (by decreasing the amount of power wasted in circulating the stock, but refining has not been heretofore accomplished at rotor surface speeds of less than 1,800 feet per minute. There are three reasons why such a range of rotor surface speeds is not obvious and, therefore, has not been employed in present-day commercial pulp refiners. First, the circulating energy at rotor surface speeds less than 1,800 feet per minute is relatively low. Second, many of the present-day commercial pulp refiners are driven directly from electric motors which operate in the higher speed ranges and, therefore, the extra cost of speed reduction equipment has made any attempts to refine at lower surface speeds unattractive. Third, the capacity of the refining machine is expected to decrease with decreases in speed, since the rate of refining is thought to vary directly with the rate at which the bars on the rotor and stator cross one another. It is primarily this latter reasoning which has kept researchers from investigating the low-speed area.

Another problem, although related to the pressure differential, is that of the dynamic film which occurs on the operating edges of the stator and rotor bars of all types of refiners which defeats shear of the pulp stock. It has been found that this dynamic film disappears at relatively low speeds and the effect begins at approximately the range of 2,000 to 1,800 feet per minute. As a result, the pulp fibers dewater and shear at the slower speeds. Furthermore, the quality of the pulp is more uniform for the lower speeds. Many other factors and resulting characteristics are improved at speeds below 2,000 feet per minute of the rotor as will be more fully understood hereinbelow.

Other considerations in addition to speed have been found to influence the resultant refined pulp. For instance, in addition to the output or rate of refining of the refiner being greatly increased by decreasing the surface velocity of the rotor, the output is also increased by increasing the pulp consistency, decreasing the clearance between the rotor and the stator, providing a greater number of bar edges on the bedplate of the rotor and/ or stator than heretofore contemplated, and increasing the temperature of the pulp solution. Although some of these conditions may have been practiced independently of one another by the prior art, the effects of several of these conditions occurring simultaneously in a particular refiner produce results not realized by present day commercial refiners.

Therefore, it is an object of the present invention to provide a pulp refiner having a greater output or increased rate of refining as compared to present commercial machines.

Still another object of the present invention is to provide a pulp refiner having lower power losses and greater efiiciency as compared to present commercial machines.

Still another object of the present invention is to provide a pulp refiner wherein the displacement between the rotor and the stator is substantially reduced and delicate control problems are not evidenced.

A further object of the present invention is to provide a pulp refiner wherein the static pressure between the stator and the rotor is substantially reduced.

Yet a further object of the present invention is to provide a pulp refiner wherein the turbulence of the pulp solution therein is greatly reduced.

And still another object of the present invention is to provide a pulp refiner wherein the hydrodynamic film is completely eliminated between the stator and the rotor thereof.

Still a further object of the present invention is to provide a pulp refiner wherein the cavitation is reduced or eliminated.

An important feature of the present invention resides in the control of the speed of the rotor within a relatively low range to provide a greater rate'of beating and increased rate of refining.

Another feature of the present invention resides in the provision of a temperature control for the pulp solution passing through a pulp refiner. It has been generally found that the rate of beating and rate of refining is greatly increased by increasing the temperature of the pulp solution above an ambient temperature.

Still another feature of the present invention resides in maintaining a relatively small clearance between the rotor and stator of a refiner to greatly increase the rate of beating and rate of refining of a pulp solution.

A further feature of the present invention resides in the control of the consistency of the pulp solution supplied to a refiner within a predetermined range for increasing the rate of beating and rate of refining.

And still another feature of the present invention resides in the provision of a greater number of bar edges on either the stator or the rotor for increasing the rate of refining.

These and other objects, features and advantages of the present invention will be more fully realized and understood from the following detailed description when taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a somewhat diagrammatic view in perspective of a pulp refiner which employs the teachings of the present invention; and

FIG. 2 is a graph illustrating the relationship between speed of the rotor of a refining machine with respect to the rate of refining.

With reference to FIG. 1, there is shown a pulp refining apparatus generally designated with the reference numeral 10 and having the several elements thereof connected to various control structures. The refining apparatus 10 generally includes a rotor 12 having a plurality of grooves in an outer surface thereof which define defibrating bars. The rotor 12 is mounted for rotation in close proximity to a bedplate 14 within a tank 16. The bedplate 14 also includes a plurality of grooves in an exposed surface thereof which define a plurality of defibrating bars which co operate with the difibrating bars on the rotor 12 to defibrate a pulp solution passing therebetween. The exposed surface of the bedplate 14 is generally semi-cylindrically shaped and conformable to the cylindrical rotor 12. The bedplate 14 is mounted in a bottom wall 18 of the tank 16.

The tank 16 is partially filled with a pulp solution, generally designated with the reference numeral 20. The pulp solution 20 passes between the rotor 12 and the bedplate 14 for defibration thereof, and subsequently passes over a backfall 22 into a conduit 24. The conduit 24 conveys the defibrated pulp solution to a subsequent station of a paper making machine (not shown).

The pulp solution is supplied to the tank 16 by means of a conduit 26 connected thereto. A heater 28 is provided in the conduit 26 for controlling the temperature of the pulp solution passing into the tank 16. Preceding the heater 28 is a consistency control device 30' to which is supplied the pulp solution through a conduit 32 and is further supplied with water through a conduit 34. The consistency control device 31} maintains the consistency of the pulp solution within predetermined, preset limits by the addition of water from the conduit 34- to the pulp P solution supplied through the conduit 32.

The rotor 12 of the refining apparatus 10 is mounted for rotation on a shaft 36 passing therethrough, which shaft is movable in opposite radial directions as indicated by the arrows 38 to control the clearance between the outer surface of the rotor 12 at the defibrating surface of the bedplate 14. Any suitable means well known in the art for controlling the linear displacement of the rotor 12 with respect to the bedplate 14 may be employed. The shaft 36 of the rotor 12 is connected, as indicated by the line designated with the reference numeral 40, through a speed reducer 42 to a motor 44. Although the speed reducer 42 is illustrated as being connected between the motor 44 and the shaft 36 and would suggest a gear reduction train, it is to be understood that the speed reducer 42 may also represent an electrical and/or electronic speed control device for the motor 44. By such an arrangement, the speed of the rotor 12 is accurately maintained.

By the use of the control systems for the pulp refining apparatus 10, the methods of the present invention can be achieved. The most important step of these processes is that of controlling the surface speed of the rotor 12 to less than 2,000 feet per minute with respect to the stator or bedplate 14. Further advantages are realized by maintaining the clearance between the rotor 12 and the bedplate 14 within predetermined limits. In addition, a control of the temperature and the consistency of the pulp solution contribute to increasing the output or rate of refining of the refining apparatus 10. By increasing the number of bar edges on the bedplate 14 and/or rotor 12 than heretofore contemplated by the prior art, the rate of refining of the refining apparatus 10 is also increased.

FIG. 2 is a graph illustrating the relationship between speed of the rotor 12 of the refining machine 10 with respect to the rate of refining thereof. The particular values given in the graph of FIG. 2 are those obtained from an experimental refiner substantially identical to that illustrated in FIG. 1. In particular, the rotor 12 had the defibrating surface thereof formed of bars having a width of 0.25 inch and a height of 7 inch and spaced 0.25 inch apart. The bedplate 14 had the defibrating surface thereof formed of bars having a width of inch and a height of 0.04 inch and spaced 0.25 inch apart. In addition, the characteristics illustrated in FIG. 2 were obtained with a pulp solution of 1.1% consistency reduced to a bulk of 2.0 cc./g., with a clearance between the rotor 12 and stator 14 of 0.0051 inch, and the pulp solution maintained at a temperature of 18 C.

It is readily apparent from the graph illustrated in FIG. 2 that by decreasing the peripheral velocity of the rotor 12 from 1,820 to 860 feet per minute the amount of pulp beaten to 2.0 bulk increased from 0.6 to 6.3 grams/minute, an increase of over ten times. It is particularly noteworthy that the dowward trend in the refining rate as the speed is decreased from 2,300 feet per minute reaches a minimum at approximately 1,800 feet per minute. It is also noteworthy that there is very little change in the refining rate between 1,300 and 2,300 feet per minute of the rotor with respect to the stator. This relatively stable portion of the curve possibly provides an insight into the reasons why previous researchers did not investigate the lower speed ranges. That .is, if one were investigating the relationship of speed with respect to rate of refining and plotted such characteristics in the normal speed ranges of 2,000 to 5,000 feet per minute, and then proceeded to plot such characteristics at speeds lower than 2,000 feet per minute, it would appear almost immediately that the refining rate would continue to decrease, rather than make an abrupt increase at approximately 1,200 feet per minute.

Experimental results show that decreasing the speed of the rotor to produce peripheral velocities of less than 1,200 feet per minute decreased cavitation and turbulence in the refining zone which led to a substantial increase in the rate of refining. Furthermore, the compression of fiber flocs formed on the moving bar edges at low speeds was believed to be chiefly responsible for this accelerated beating. When the pulp passing between the rotor and stator was closely examined, it was found that the great increase in the rate of refining at low speeds in the beater was associated with the collection of fiber fiocs on the bar edges. In particular, flocs were observed being pinched between the bar-s at low values of peripheral velocity of the rotor 12.

At high speeds, the hydrodynamic film present on the defibrating surfaces and on the fibers themselves aided in maintaining the fibers from coming into contact with each other and with the bar edges. As the peripheral velocity of the rotor was decreased below a critical point of approximately 1,800 feet per minute, it is possible that the lubricating film of water disappeared from the surfaces so that the fibers could come into intimate contact with the moving edges of the defibrating surfaces and, instead of being sloughed off, were allowed to dewater and accumulate. In this manner, the flocs formed on the moving bar edges were not only compressed severely against the stationary bars but also were probably rubbed by the bar surfaces where a high coefficient of friction existed because of the loss of a hydrodynamic film. Thus, a fast rate, high consistency-type refining action resulted.

Within the speed range of less than 2,000 feet per minute, the static pressure on the bedplate 14 increases with increasing rotor speed and also with increasing clearance between the rotor and the stator. Furthermore, within this speed range, cavitation and turbulence within the refining zone decreases with reduction in speed while flocculation increases. The latter characteristic is believed to be the main reason for faster beating at low speeds.

In addition to decreasing the speed of the rotor with respect to the stator below 2,000 feet per minute, the efiiciency of the beater 10 was increased considerably by increasing the consistency of the pulp solution. In particular, the number of revolutions per gram (r.p.g.) required to produce handsheets with a bulk of 2.0 cc./ g. was reduced from 4,000 to 120 by raising the fiber concentration from 0.8% to 1.7%. The term efficiency is used herein in the sense that it is inversely proportional to the r.p.g. and energy required to develop the pulp to a given sheet bulk.

In one particular measured run of the beater illustrated in FIG. 1, the influence of pulp consistency was measured while maintaining other conditions constant. Table I contains the results of beating southern pine kraft pulp at constant bulk and Table II contains the results of the same runs compared at constant freeness. The particular results set forth in Tables I and II were achieved with a peripheral velocity of the rotor 12 held constant at 1,500 feet per minute, the temperature of the pulp constant at 18 C., the radial clearance between the rotor 12 and the bedplate 14 surfaces held constant at 0.0069 inch, and with the defibrating bars of the rotor and bedplate being the same as that described above with reference to the curve illustrated in FIG. 2.

TABLE I.INFLUENCE OF 'BEATING CONSISTENCY COMPARED AT CONSTANT BULK Pulp OS. Beating consistency, Bulk, ireeness, extent, percent ce./g. m r.p.g.

TABLE II.INFLUENCE OF BEATING CONSISTENCY COMPARED AT CONSTANT FREENESS Pulp C.S. Beating consistency, Bulk, freeness, extent,

Run N0 percent cc./g. 1n r.p.g

In addition to speed control and consistency control, it was found that the temperature of the pulp stock, which is subjected to a defibrating action, also controls the rate of refining. Results of beating a southern pine kraft pulp at temperatures of 12, 32, 46, and 69 are given in Tables III and IV. Table III contains the results of measurements taken of different beating temperatures compared at constant bulk and Table IV contains the results of measurements taken of different beating temperatures compared at constant freeness. The reults given in Tables III and IV were achieved while maintaining the peripheral velocity of the beater rotor 12 at a constant speed of 1,360 feet per minute, the radial clearance between the rotor 12 and the bedplate 14 surfaces at a constant dimension of 0.0049 inch, the consistency of the pulp solution constant at 1.1%, and with the design of the rotor and stator being the same as that employed in obaining the results discussed with respect to the curve illustrated in FIG. 2.

TABLE IIL-INFLUENCE OF BEATING TEMPERATURE COMPARED AT CONSTANT BULK Average 0.8. Beating temperature, Bulk, freeness, extent,

Run No C. ce./g. m1. r.p.g.

TABLE IV.INFLUENCE OF BEATING TFMPERATURE COMPARED AT CONSTANT FREENESS Average 0 .S. B eating temperature, Bulk, freeness, extent,

The rate of beating of the refining machine 10 was found to increase rapidly if the number of bar edges on the bedplate is increased from the usual number heretofore employed. In particular, during a particular run of the refining machine 10, it was found that increasing the bar edges on the bedplate 14 from four to ten resulted in a decrease of the revolutions per gram of pulp from 2,000 to 330 while the radial clearance between the rotor 12 and bedplate 14 surfaces was held at 0.0045 inch. During another run of the refining machine 10, and while the radial clearance between the rotor 12 and bedplate 14 surfaces was held constant at 0.0032 inch, an increase of the bar edges on the bedplate 14 from four to ten resulted in a decrease in the revolutions per gram of pulp from 510 to 41. Each of the above two mentioned runs of the refining machine 10 was operated at a speed of the rotor 12 maintained constant at 1,800 feet per minute, a consistency of the pulp maintained constant at 1.1%, and a temperature of the pulp maintained constant at 18 C. to produce a pulp having a specific volume of 2.0 cc./ g.

The radial clearance between the rotor 12 and the bedplate 14 surfaces also contributes to influencing the output of the refining machine 10. Table V below gives the results of changing the radial clearance between the rotor and the stator when a bedplate was employed having a bar width of 7 inch, a bar height of 0.04 inch, and with the bars spaced 0.25 inch apart.

TABLE V.INFLUENCE OF BEAT- ER CLEARANCE COMPARED AT CONSTANT BULK OF 2.0 cc./g.

Clearance, Beating inch extent, r.p.g.

the bars spaced from one another at a distance of 0.25 inch.

TABLE VI.INFLUENCE OF BEATER CLEARANCE COM- PARED AT CONSTANT BULK OF 2.0 cc./g.

Clearance, Beating Run No inch extent, r.p.g.

BEATER CLEARANCE COM- PARED AT CONSTANT BULK OF 2.0 cc./g.

Clearance, Beating Run No. inch extent, r.p.g.

The results given in Tables V, VI, and VII were obtained under constant conditions of speed, pulp temperature, and pulp consistency, and employed a southern pine kraft pulp. In particular, the speed was held constant at 1,800 feet per minute, the temperature at 18 C., and the consistency at 1.1%. The bedplates described with respect to Tables V and VI had the bars thereof at an angle of zero degrees with respect to the bars on the rotor. The rotor contained bars in the defibrating surface thereof having a width of 0.25 inch, a height of inch, and spaced from one another 0.25 inch.

From the above results, it is obvious that the eificiency of the beating apparatus is greatly improved by decreasing either the radial clearance between the rotor 12 and the bedplate 14 surfaces or the peripheral velocity of the rotor 12 or by increasing the consistency of the pulp solution, the temperature of the pulp solution, or the number of bar edges on the bedplate 14.

The principles of the invention explained in connection with the specific exemplifications thereof will suggest many other applications and modifications of the same. It is accordingly desiredthat, in construing the breadth of the appended claims they shall'not be 1imit- 8 ed to the specific details shown and described in connection with the exemplifications thereof The invention claimed is:

1. In a method of refining a pulp solution having a substantially low consistency, of at most about 1.7%, in a pulp refiner having a stationary, semi-cylindrical bedplate and a rotatable, cylindrical surface closely confronting the bedplate for defining a refining zone therebetween through which the pulp solution passes, the stationary and rotatable surfaces having feeder bars thereon extending into the refining zone, with the height of the bars formed on the cylindrical surface being about inches and the height of the bars on the bedplate being about inch, the improvement comprising rotating the rotatable cylindrical surface relative to the stationary surface at a uniform operating speed below a maximum speed of about 1800 feet per minute wherein a dynamic fluid film forms on the surfaces and wherein turbulence within the refining zone is sufficiently eliminated to permit concentration of fiber flocs on the bar edges, thereby to increase interfiber friction for dewatering and compressing the pulp fibers 'and radially spacing the bars formed on the cylindrical surface from the stationary bars at a distance of less than 0.0069 inch.

2. In a method of refining pulp solutions as defined in claim 1 and further characterized by rotating the cylindrical surface at a speed not exceeding about 1200 feet per minute.

References Cited UNITED STATES PATENTS 5/1968 Henderson 162-26 X OTHER REFERENCES S. LEON BASHORE, Primary Examiner R. H. TUSHIN, Assistant Examiner US. Cl. X.R.

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