Pulper tank
United States Patent [191 Honeyman et al.  
 [ PULPER TANK [75] Inventors: Robert Blakeley Honeyman, Carmel,  
 Calif.; Robert Lee Crawford, Portland, Oreg.  
 [73] Assignee: Morden Machines Company,  
 Portland, Oreg.  
 [22] Filed: June 20, 1973 [21] Appl. N0.: 371,745  
 [52] US. Cl. 24l/46.l7 [51] Int. Cl. B04c 5/081 [58] Field of Search 241/46 R, 46.02, 46.04,  
 [56] References Cited UNITED STATES PATENTS 2,345,474 3/1944 Haverland 24l/46.06 X  
 [111 3,874,600 Apr. 1, 1975 3,009,656 11/1961 Martindale 24l/46.17 3,085,756 4/1963 Danforth et al. 241/46.l7 X 3,310,243 3/1967 Duncan et al. 241/46.17 X  
 Primary Examiner-Roy Lake Assistant Examiner-Craig R. Feinberg Attorney, Agent, or Firm-Dawson, Tilton, Fallon &amp; Lungmus [57] ABSTRACT A pulper tank structure wherein a horizontal bottom wall associated with a rotor is connected to a verti cally extending cylindrical sidewall thereabove and interconnected by at least two upwardly divergent intermediate frusto-conical walls and where the fillet angles are specified for advantageously increasing stock surface rate or reducing power consumption.  
 1 Claim, 2 Drawing Figures PATENTEBAPR 1197s FIG. I  
 FIG.2  
  I) D Wm PULPER TANK BACKGROUND AND SUMMARY for defiberizing paper making material and extracting refined pulp therefrom.  
  The major considerations in the design of a pulper tank are installed cost, space requirement (diameter and height), maximum circulation for applied power and service ability. The important factors influencing the circulation pattern are the bottom configuration and the diameter-to-height ratio. We are concerned here only with the former.  
  The stock (at 4-77c consistency) discharges from the rotor blades or vanes at a given velocity and resultant angle caused by the combined centrifugal reaction, the blade angle, and the peripheral speed of the rotor. The resultant flow is normally angular, not radial, causing a circular motion of the body of stock or water in the tank. Excessive rotational circulation will cause the stock and/or water to rise up the wall of the tank to an uncontrollable level and can create an excessive prerotation effect causing an open vortex above the rotor, allowing extensive air entrainment and general deterioration of the pulping cycle. Excessive rotation is prevented or controlled by the well-known practice of placing stationary baffles or deflectory on the bottom or sidewalls of the tank. Because the pulper, even when being operated continuously, is essentially a closed system, the effect of the discharge flow from the impeller creates a suction in the eye of the rotor. In turn, this results in a rapid flow of material back into the working zone of the rotor for repeated difibering action. The return flow can best be measured on the surface of the tank by simple means and related to the efficiency of defibering on the basis of horsepower/day/ton of stock. Ideally, the surface flow or circulation rate will be rapid but not excessive and will rotate sufficiently to cause a vigorous but closed vortex to aid in the submergency of any material additions.  
  The velocity of flow of material decreases rapidly after leaving the blade area due to friction and dispersion. Any abrupt change in direction, particularly in the high velocity areas, causes turbulence and internal friction in the mass of material even though the tank walls are smooth and provide little surface friction. We have determined that to avoid abrupt angular changes in flow, an ideal tank bottom configuration would be elliptical in cross section with the rotor centered on the short axis. Cost prevents practical consideration of this approach, particularly for fabricated construction. We have determined therefore that optimum results are obtained when the generally horizontal bottom wall is joined to the much larger diameter cylindrical sidewall by at least two upwardly divergent, generally frustoconical walls, one above the other, and with the fillet angles being defined as follows. The lower of the frustoconical walls forms a first exterior angle of at least about but not more than about 30 with the horizontal. A second exterior angle is that between the upper and lower frusto-conical walls and is equal to or greater than the first angle. A third exterior angle is that between the upper frusto-conical sidewall and is equal to or greater than the second mentioned angle and with all of the angles being not more than about 40.  
 DETAILED DESCRIPTION The invention is described in conjunction with the accompanying drawing, in which FIG. 1 is a fragmentary side elevational view of a tank constructed according to teachings of this invention; and  
  FIG. 2 is a reduced scale version of the tank seen in FIG. 1 and with certain lettering applied thereto relating to fillet angles.  
  Referring now to FIG. 1 the numeral 10 designates generally a pulper tank which is seen to include in the central bottom a rotor generally designated 11 equipped with a plurality of laterally extending vanes or blades. As will be brought out in the test description given hereinafter, we have worked with types of rotors,  
 one of which is described in U.S. Pat. No. 2,858,990  
 and the other in my copending application Ser. No. 330,081 filed Feb. 6, 1973. The invention provides advantages with both types of rotors.  
  Still referring to FIG. 1, the numeral 13 designates a generally cylindrical, upwardly extending sidewall which is connected to the bottom wall 14 by at least two intermediate, upwardly divergent, generally frustoconical walls as at 15 and 16. The level of stock is designated 17 providing an axial vortex at 18 while the dotted line designated 19 shows the stationary or static level of the stock in the tank 10.  
  In FIG. 2, we have shown a schematic representation of a pulper tank and have applied certain symbols to refer to various fillet angles. The symbols, A, B and C are exterior fillet angles and are those referred to hereinbefore. For example, the fillet angle A is defined between the lower frusto-conical wall and the horizontal. The second fillet angle B is included between the exterior of the upper frusto-conical wall and the extension of the lower frusto-conical wall. The third exterior angle C is defined between the exterior of the generally cylindrical sidewall and the extension of the upper generally frusto-conical wall. For convenience we have also designated an interior fillet angle D which is included between the horizontal and the interior of the upper generally frusto-conical wall.  
  It will be apparent from a consideration of FIG. 2 that the sum of the angles A and B is equal to the angle D, being alternate interior angles. Still further, it will be apparent that the sum of the angles C and D is The tanks generally employed in production today have an interior fillet angle D of 45 and with a lower fillet angle A of about 10 to 15. In testing the invention,-we first considered the bottom wall 14 and the lower frusto-conical sidewall 15. For good drainage to a circumferential extraction plate surrounding the rotor we have determined that the angle A should not be less than about 15. We further have found that increasing the angle A is beneficial so to approximate optimum results selected an angle of 20 as not creating excesssive deflection to flow from the rotor 11 but at the same time providing good drainage. We thereupon constructed three laboratory scale pulping tanks, each with a bottom angle A of 20. The first test unit approximated the prior art (as optimized) by having an interior fillet angle D of 45. The other two laboratory tanks had fillet angles D of 55. The second of the tanks had the fillets so arra ged that the heights of the two frusto-conical sidewalls l and 16 (as designated h, and 11 in FIG. 2) approximately equal. In the third case the height I1 was approximately twice the value of 11,;  
  The tests were run using printed news material repulped to standardized condition with a consistency of 4% and 5% on the air-dried basis.  
 In general, advantageous results were obtained in utilizing the larger interior fillet angles (tanks 2 and 3.)-  
 over the tank with the smaller interior fillet angle (tank 1). The difference in results were even greater than comparing the small interior fillet angle tank (tank 1) with tank 3. Although the measurement of surface stock rates varied considerably due to uncontrollable physical variables of the fiber as well as temperature and stability, the general trend of results indicate that the tank 3 averaged 1 1% higher surface ratesthan tank 1. This circulation increase appeared about the same with either the rotor of U.S. Pat. No. 2,858,990 or the rotor of my above-identified application, Ser. No. 330,081 when operated in the range of 45% A.D consistency. It was also found that to produce the same given level of surface circulation, thethird tank required approximately 6% less power as compared with the first tank.  
  At the normal rated stock level for each tank (2.132 cubic feet), there was no significant change in direction of stock flow, either at the surface or along the outer elevation, when a comparison was made at equal rotor speed, input power or surface rate. However, if rotor speed or input power was held constant and the stock level was lowered, surface circulation increased and the vortex was proportionally deepened resulting in a tighter involute surface pattern, but not to the extent of exposing the rotor at a 25% reduction in capacity. Tank 3 showed better circulation at 25% increase in level than tanks 1 and 2, or conversely lower power at equal circulation rates.  
  The table below indicates the range of fillet angles which can be employed advantageously in the practice of the invention.  
 A B C D 15 35 40 5O 15 37.5 37.5 52.5 20 30 4O 50 20 32.5 37.5 52.5 20 35 35 55 25 3O 35 55 25 32.5 32.5 57.5 30 -30 30 60 From the foregoing, it is seen that no angle of deflection (A, B or C) should exceed 40 and, that in the direction of flow, the relationship of the deflection angles, from lower to higher, should be equal or increasing, but never decreasing. At the same time, in order to achieve the advantageous results of the invention, the height, 11 of the upper frusto-conical wall 16 should be at least 50% larger than the height, h of the lower frusto-conical wall 15, but not greater than In other words, the range of the ratio 11 /11 is 1.5 to 2.5.  
  Although only a single-rotor embodiment has been illustrated, persons skilled in the art will readily appreciate that the invention could be incorporated into a double-rotor pulper of the type disclosed in co-owned U.S. Pat. No. 3,602,440, issued Aug. 31, 1971.  
 We claim:  
  1. A pulper tank having an upright, generally cylindrical sidewall spaced above a generally horizontal bottom wall of similar diameter than said cylindrical sidewall, a rotor mounted above said bottom wall and below said cylindrical sidewall, and at least two up.- wardly divergent generally frusto-conical walls, one above the other, coupling said bottom wall with said cylindrical sidewall, the lower of said frusto-conical walls forming a first exterior angle in the range 20 25 with the horizontal, a second exterior angle being that between the upper and lower frusto-conical walls and being at least equal to said first angle, and in the range 30 35, a third exterior angle being that between the upper frusto-conical wall and said upright cylindrical wall and being at least equal to said second angle, and in the range 30 35, the ratio of the height of said upper frusto-conical wall to the height of said lower frusto-conical wall being in the range of 2.5 to 1.5.