Abstract:
A mixing method and system for the thorough intermixing of liquids of widely different viscosities in which there is interposed at least one perforated plate in the line of flow ahead of a conventional static mixer.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The subject matter of this Application relates to the invention of Application Ser. No. 306,921, filed Nov. 15, 1972, now U.S. Pat. No. 3,861,652, of common assignment. 
     BRIEF SUMMARY OF THE INVENTION 
     Generally, this invention comprises a mixing method and system for liquids of widely different viscosities incorporating one or more perforated plates interposed in the line of flow of the liquids during their supply under pressure to conventional mixing apparatus of static design. 
    
    
     DRAWINGS 
     The following drawings detail a preferred embodiment of the invention and the physical principles of operation, wherein: 
     FIG. 1 is a partially schematic longitudinal sectional view of a preferred embodiment of apparatus constructed according to this invention for the mixing of two liquids of widely different viscosities in which three perforated plates in series were utilized in conjunction with a plurality of static mixer elements, 
     FIG. 2 is a plan view of a preferred design of perforated plate for the apparatus of FIG. 1, 
     FIGS. 3 and 4 are plan views of second and third alternative designs of perforated plates utilized as elements for the apparatus of FIGS. 1 and 2 to obtain an operational comparison with the FIG. 2 plate design, and 
     FIGS. 5-10, inclusive, are plan views of additional designs of perforated plates which were all tested and found to be of varying effectiveness as hereinafter reported. 
     DETAILED DESCRIPTION 
     Continuous mixing of widely different viscosity liquids, and gases with liquids, is difficult to achieve. A wide variety of dynamic (power-driven) mixers have been employed in this service, including multiple-blade turbines, multistage helical ribbon designs, torpedo designs, and two-shaft, wiped surface mixers. Such mixers are relatively expensive and, for very intimate mix uniformities, require lengthy periods of operation and high power consumption. 
     Recently, various designs of static mixers have become available commercially, these including warped deflection plate types such as those disclosed in Armeniades et al. U.S. Pat. No. 3,286,992 and Potter U.S. Pat. No. 3,635,444, which operate by successive stream division followed by a folding recombination of ingredients. The static mixers are less expensive in first and operational costs but they, too, have been less than completely effective, especially unless used in large numbers in series flow circuit. 
     I have now discovered that very substantial mixing advantages can be obtained by interposing one or more perforated plates in series flow disposition with respect to the fluids to be mixed while they are fed under pressure to static mixing apparatus. 
     Referring to FIG. 1, a preferred embodiment of system according to my invention, utilizing static mixer elements of the general design taught in U.S. Pat. Nos. 3,286,992 and 3,635,444 supra, comprises a tubular flow conduit 10 which is supplied at entrance and 10a with the high viscosity liquid to be mixed from a pump or other pressure source not shown. The low viscosity liquid component is supplied under pressure through a line 11 terminating in a discharge outlet 11a oriented generally axially of conduit 10 with its vent opening downstream of the flow of high viscosity liquid. 
     In the system of FIG. 1 three perforated plate elements 12a, 12b and 12c are utilized in series arrangement spaced approximately one conduit 10 diameter apart, with the first perforated plate, 12a, disposed approximately 0.5 to 2.0 conduit 10 diameters downstream from the vent 11a of conduit 11. For convenience in mounting the perforated plates 12a, 12b and 12c, flanged sections of conduit were assembled in prolongation one with another as shown in FIG. 1 to provide the continuous flow conduit 10 in the plate region. 
     Deferring description of the plate perforation details until later, the static mixer elements disposed in seriatim one with another and with perforated plates 12a, 12b and 12c consist of 20 to 30 warped plate pairs 15a, 15b to 15n, 15n&#39;, alternate members of each pair having opposite directions of twist, mounted fixedly in place within conduit 10 with the entrance end of the first static mixer pair preferably spaced not more than about 10 conduit 10 diameters downstream from the last perforated plate element 12c. After traversing the last plate pair, 15n, 15n&#39;, the intimately combined liquid mixture discharges from the system via outlet 10b. 
     Turning now to FIG. 2, an actual design of perforated plate element 12, which in this instance was a 1inch diameter perforated area size (surrounded by an annular flange section of 2 inch outside diameter), consisted of a 1/8inch thick steel plate provided with 85 holes 13 each 0.07 inch in diameter spaced uniformly at center-to-center distances of 0.100 inch ±0.017 inch taken parallel with respect to lines inclined 60° counter-clockwise from the horizontal and 0.0867 inch ±0.015 inch taken normally with respect to lines drawn 60° counter-clockwise with respect to the horizontal. The twelve holes denoted 14 were each approximately tangent to the inside wall of conduit 10 which, for the design portrayed, had a 1 inch inside diameter. 
     A less preferred alternate design of perforated plate 12&#39; is detailed in FIG. 3, wherein the construction is generally the same as for FIG. 2, consisting again of a 1/8inch thick steel plate provided, in this instance, with 43 holes 13&#39;, 0.07 inch diameter, distributed in alternate rows along the ordinate at 0.134 inch hole-to-hole vertical spacing and at 60° inclination 0.116 inch ±0.020 inch spacing. Six holes 14&#39; were disposed tangent to the inside wall of the conduit 10 which, for this design, also was 1 inch inside diameter. 
     An oversize perforated plate 12 inches is detailed in FIG. 4, this being a 2 inch diameter perforated area (4 inches outside diameter flange size) 1/8 inch thick steel plate provided with 241 drilled holes, each 0.07 inch diameter, spaced 0.120 inch between hole centers and 0.104 inch ±0.01 inch between adjacent parallel rows of hole centers the six holes denoted 14 inches being tangent to the supply conduit 10 which, in this instance, was 2 inches inside diameter. This perforated plate was provided immediately downstream with a 4 inch transition length conventional pipe reducer, not shown, constricting the flow to 1 inch prior to introduction into static mixers 15a, 15b - 15n, 15n&#39; for the comparative performance tests hereinafter reported. 
     Additional designs of perforated plates (of thicknesses reported in TABLE I) had hole dispositions and sizes as indicated in FIGS. 5-10, respectively, as to which all perforated area diameters were 1 inch diameter, some plates being of 2 inches outside diameter flange design, whereas others were secured, in place in the flow conduit by cementing around the peripheries, none of this detail being further provided because it has no bearing on the operation of the perforated plates. 
     The mixing action of apparatus constructed according to this invention, using glass conduits 10 permitting visual observation of the mixing obtained, appears to be as follows: Perforated plates 12, 12&#39; and 12&#34; divide the single stream of low viscosity liquid into many smaller streams and thus greatly increase the interfacial area between the low and high viscosity liquids. Downstream of each perforated plate 12 there is created a multiplicity of wakes in which the pressure is lower than that in the liquid more remote from these wakes. The low viscosity liquid preferentially accumulates in the flow wakes and, moreover, the lower viscosity liquid appears to be able to move laterally across the higher viscosity liquid streamlines within the wakes. The lower viscosity liquid leaves the wakes in sheets or threads where streamlines of high viscosity liquid meet again downstream of the wakes. 
     From the foregoing, it will be understood that perforated plates 12 provide preliminary break-up, subdivision and distribution of low viscosity liquids in high viscosity liquids. Completion of the mixing of the liquids to obtain a uniform effluent, when they are miscible or soluble, is dependent on molecular diffusion plus the action of subsequent mixing devices such as the static laminar mixers hereinafter described. 
     My tests have revealed the following: 
     1. The plan view shapes of holes 13, 13&#39;, 13&#34; can be widely varied: circular, square, triangular, hexagonal and other configurations being all operable; however, circular holes are preferred because of ease of fabrication. 
     2. Hole diameters can be anywhere in the range of about 1/4 to 1/100 of the conduit 10 diameter; however, 1/8 to 1/32 is preferred. 
     3. The ratio of total cross-sectional area of all holes 13, 13&#39;, 13&#34; divided by the cross-sectional area of conduit 10 can be from about 1/20 to about 3/4, but 1/3 to 1/2 is preferred. 
     4. The number of plates 12 utilized can range from one to about ten, with two to four being preferred. 
     5. Plates 12 can be disposed all upstream of the mixers, or they can be interspersed between successive mixer elements, such as the ones denoted 15a, 15b - 15n, 15n&#39;, FIG. 1. If the plates 12 are located upstream from the mixers, the spacing between adjacent plates should be in the range of about 1/4 to about 10 conduit 10 diameters, with 1-3 diameters being preferred. 
     6. The supply of lower viscosity liquid to be mixed can be via one or more holes in a conventional distributor ring, but a single injection tube such as that detailed at 11, 11a, FIG. 1, is preferred. 
     7. The distance between the lower viscosity liquid injection point and the first downstream perforated plate 12 should be in the range of about 1/8 to 10 or more conduit 10 diameters, with 1/2 to 2 diameters preferred. 
     8. Mixing according to this invention is effective where the proportion of low viscosity liquid to be mixed with high viscosity liquid is in the volumetric flow ratio range of about 0.01 to 0.2, and where the ratio of viscosities of high viscosity liquid to low viscosity liquid is in the range of about 4 × 10 3  to 10 6 . 
     A vertically oriented test apparatus was constructed generally resembling that shown in FIG. 1. Corn syrup (Corn Products Co. Code 1132) was utilized as the high viscosity liquid to be blended, this material having a viscosity of 1050 poises at 20° C. and 450 poises at 30° C. Water dyed with 0.5 gm of methylene blue for each 5 gallons volume was utilized as the low viscosity liquid. 
     The corn syrup was stored in a 30 gal. Binks tank under air pressure, which could be adjusted to vary the corn syrup flow rate. The syrup was supplied to the apparatus via an 18 inch long horizontal 1 inch dia. pipe, thence through a pipe tee and vertically upwards for 12 inches of 1 inch dia. pipe to the first perforated plate 12. 
     The dyed water was stored in a 5 ga. Binks tank under air pressure. A rotameter and needle valve were used to adjust and measure the water flow rate. Water was injected into the syrup through a 1/8 inch outside diameter, 1/16 inch inside diameter tube pointed upwards (i.e., downstream) near the center of the syrup flow pipe 10. The point of water injection was 1 inch to 2 inches upstream of the first perforated plate 12. After the sixteenth test tabulated in the following TABLE III, i.e., after Test 2-7-14, the feed tanks were wrapped with 1/4 inch tubing for circulation of constant temperature water, and then encased in insulation. 
     Perforated plates 12, disposed transverse conduit 10, were followed downstream by static spiral mixers of the Kenics Static® design, which generally resembled those disclosed in U.S. Pat. No. 3,286,992 supra, arranged in series sequence up conduit 10. Four, four-element edgesealed Kenics® modules were employed in most of the mixing tests herein reported. The mixer elements were fabricated from stainless steel, whereas conduit 10 was 1 inch i.d. glass. 
     The effluent flow rate discharged from outlet 10b was determined by weighing the effluent for a measured period of time. 
     The characteristics of the perforated plates 12 utilized are given in TABLE I, with typical hole arrangements shown in FIGS. 2-10, inclusive. The characteristics of any screens employed in supplementation are given in TABLE II. 
     
                                           TABLE I__________________________________________________________________________PERFORATED PLATE DIMENSIONS__________________________________________________________________________Hole diameter, in.     1/4 3/16             1/8 3/32                     1/16                         0.070                             0.070 0.070                                       0.070Drawing FIGURE     5   7   8   9   10  3   not shown                                   2   4Number of holes     3   7   19  19  19  43  61    85  241Plate diam.*, in.     1   1   1   1   1   1   1     1   2Fraction open area     0.19         0.25             0.30                 0.17                     0.07                         0.21                             0.30  0.44                                       0.30Thickness, in.     1/8 1/8 1/8 1/8 1/8 0.04                             0.04  0.04                                       1/8__________________________________________________________________________ *Diameter of circle tangent to outer holes. 
    
     
                       TABLE II______________________________________WIRE SCREENS______________________________________Mesh          35       60       150    270Wire diameter, in.       0.012    0.009    0.0026 0.0016Weave       Plain    Plain    Plain  TwillOpening, in.       0.017    0.008    0.004  0.002Fraction open area       0.34     0.21     0.37   0.32______________________________________ 
    
     
                                           TABLE III__________________________________________________________________________            Syrup         Effluent                                  Total            Temp (° C.)                    Per Cent                          Rate (lbs/hr)                                  ApparatusTest             Viscosity,                    Water in                          Viscosity,                                  Pressure Drop, ΔP,No.  Equipment   poises  Effluent                          poises  p.s.i.     Observations__________________________________________________________________________1-6-3020 Kenics.sup.®            (31)    0.6   (42)    --         A few 1/16&#34;Mixer elements            385           --                 water globulesin a 1&#34; glass                                were observedpipe.                                        in the effluent.No perforatedplates.2-6-30 &#34;                  2.1   (47)                          --      21         1/8&#34;-1/4&#34; water                                             globules in the                                             effluent.1-7-3In series, in 1&#34;            (31)    9.8   (42.7)  10         A few 1/8&#34; waterglass pipe: 385           12                 globules wereA perforated plate                           observed afterthick provided                               10 Kenics.sup.®with 3-1/4&#34; holes                            elements, but(FIG. 5) + 4                                 mostly striations.Kenics.sup.®  elements +                 No water globulesa perforated plate                           and only a fewwith 7 1/8&#34; holes                            trace striations(FIG. 6) + 4                                 observed afterKenics.sup.®  elements +                 20 Kenics.sup.®a perforated plate                           elements.with 19 1/8&#34; holes(FIG. 8) + 12Kenics.sup.®  elements.2-7-3In series, in 1&#34;            (31)    2.5   (41.4)  14.5       No water globulesglass pipe: 385           94                 and very attenuatedA perforated plate                           striations observed1/8&#34; thick provided                          after 14                                             Kenics.sup.®with 3-1/4&#34; holes                            elements. No stria-(FIG. 5) + 4                                 tions seen after 20Kenics.sup.®  elements +                 Kenics.sup.®                                             elements.a perforated platewith 7 1/8&#34; holes(FIG. 6) + 4Kenics.sup.®  elements +a perforated platewith 19 1/8&#34; holes(FIG. 8) + 12Kenics.sup.®  elements.1-7-5In series in a 1&#34;   15.3  (27.5)  48         Water spread acrossglass pipe:                                  all of down streamOne perforated plate                         side of plate.thick, provided with                         Channeling was ob-19 1/16&#34; (FIG. 10)                           served thru first 8holes + 16 Kenics®                       Kenics.sup.®                                             elements.elements.                                    Water globules re-                                             formed. Extreme                                             striations and water                                             globules after 16                                             elements.2-7-5In series in        15    (27)    48         Same as Testa 1&#34; glass pipe:                             #1-7-5, except thatOne perforated                               water globules didplate 1/8&#34; thick pro-                        not reform.vided with 19 1/16&#34;(FIG. 10) holes + 4Kenics.sup.®  elements +one perforatedplate with 19 1/8&#34;holes (FIG. 8) +12 Kenics.sup.®elements.1-7-7In series in a      10    (42)    19         Same observations1&#34; glass pipe:                               as Test 1-7-5.Three perforatedplates having (1)3 1/4&#34; holes (FIG.5), (2) 7 3/16&#34; holes(FIG. 7), (3) 191/8&#34; holes (FIG. 8)+ 16 Kenics®elements.1-7-114 Perforated            400 (ap-                    8.1   (51.6)  13         Water layer seenplates each hav-                prox.)                       downstream ofing 19 1/8&#34;                                  each plate.holes (FIG. 8),                              Channeling occurredplates spaced 1&#34;                             after first 4apart + 16                                   Kenics.sup.®                                             elements.Kenics.sup.®                             No channeling inelements.                                    9th-12th elements.                                             Weak striations ob-                                             served after 12th                                             element.2-7-11 &#34;          400 (ap-                    2.2   (48.5)  16         No segregated water                prox.)    150                seen after 4th                                             plate. No channeling                                             in Kenics.sup.®                                             ele-                                             ments. No stria-                                             tions observed after                                             8th element.3-7-11Same apparatus            (26)    2.4   (43.3)  17         Same observationsas Test 1-7-11,            400 (ap-      177                as Test 2-7-11.except that 3/32&#34;                prox.)holes (FIG. 9) weresubstituted.4-7-11Same apparatus            400 (ap-                    8.4   (50.2)  12         No channeling inas Test 1-7-11, prox.)    22                 Kenics.sup.®                                             elements.except that 3/32&#34;                            Very weak stria-holes (FIG. 9)                               tions observed - were                                             substituted.      after                                             12th element.1-7-12 &#34;          (26)    8.8   (47.5)  16         Same observations            400 (ap-      24                 as Test 4-7-11.                prox.)2-7-12 &#34;          (27)    9.6   (23.4)  9          Same observations            400 (ap-      20                 as Test 4-7-11,                prox.)                       except that syrup                                             fragments were de-                                             tected in 12th ele-                                             ment effluent.1-7-13Same apparatus            (26)    9.2   (45.8)  13         1/8&#34; water layer ob-as Test 3-7-11,            400 (ap-      25                 served on back-except that 61  prox.)                       sides of 3rd and 4th0.07&#34; holes were                             plates. There wassubstituted.                                 some channeling in                                             first 4                                             Kenics.sup.®                                             elements. 1/32&#34;-1/16&#34;                                             syrup fragments ob-                                             served after 12                                             elements.1-7-14Same apparatus            (25)    2.3   (45.7)  19         1/16&#34; wateras Test 3-7-11,            400 (ap-      138                layer on thirdexcept that 61  prox.)                       plate but none0.07&#34; holes were                             on fourth.substituted.                                 No channeling                                             in Kenics.sup.®                                             elements. No                                             syrup frag-                                             ments after                                             12 elements.2-7-14Same apparatus            400 (ap-                    2.3   (46.5)  15         No water onas Test 1-7-14, prox.)                       first plate,except that per-                             &lt;1/8&#34; onforated plates                               third and nonewere spaced                                  on fourth. No6&#34; apart.                                    channeling in                                             Kenics.sup.®  ele-                                             ments. No                                             striations or                                             syrup fragments                                             after 8th                                             element.1a-8-3Four plates (20)    7.8   (25.4)  9          Water layers onwith 19 1/8&#34;            1046          27                 4 plates.holes in each                                Channeling after(FIG. 8)                                     4th plate and forfollowed by 16                               4 Kenics.sup.®                                             ele-Kenics.sup.®                             ments. No syrupelements.                                    fragments after                                             16 Kenics.sup.®                                             elements. Occa-                                             sional water glob-                                             ules after 16                                             Kenics.sup.®                                             elements.2-8-3Four plates (20)    9.1   (46.0)  17         Less channeling,with 61 0.07&#34;            1046          22                 less pulsing,dia. holes in                                smaller scale non-each +  16                                   uniformities thanKenics.sup.®                             those in Testelements.                                    1a-8-3. 1/32&#34;                                             syrup fragments                                             after 16                                             Kenics.sup.®                                             elements.                                             No globules.1c-8-3Same as     (20)    4.5   (26.6)  9          No pulsing above1a-8-3      1046          60                 4th plate. Stria-                                             tions but no syrup                                             fragments after 16th                                             Kenics.sup.®                                             element.                                             No water globules                                             after 16th element.1-8-25Three per-  (20)    11.5  (48.8)  17         Good water distri-forated     1046          --                 bution across whole ofplates, 4&#34;                                   of first 2&#34; plate.separation,                                  1/4&#34; water layer on241 0.07&#34;                                    1st plate, 1/8&#34; onholes in each                                2d, none on 3d. No(FIG. 4), 2&#34; dia.                            water pulsing abovetubing + 16                                  2d plate. 1/32&#34;Kenics.sup.®  elements                   syrup fragments andin 1&#34; pipe.                                             Kenics.sup.®                                             elements.1-9-27Four 43 hole            (20)    7.1   (26.2)  36         Relatively uniform(0.07&#34; dia)               --                 water distributionplates, spaced                               past plates, without2&#34; apart,                                    pulsing above anyfollowed by                                  plate. No channel-16 Kenics®                               ing in                                             Kenics.sup.®elements.                                    elements. A few                                             1/16&#34;-1/8&#34; syrup                                             fragments after 16                                             elements.2-9-27Same as Test            (20)    6.8   (27.3)  24         Some maldistribu-1-9-27 except            1046          --                 tion on 1st plate,85 0.07&#34; holes                               cleared up after 3dused in all                                  plate. Manyplates.                                      1/32-1/16&#34; syrup                                             fragments after 16th                                             Kenics.sup.®                                             element.                                             Syrup jets above 1st                                             plate didn&#39;t                                             &#34;snake&#34; as much as                                             those in Test                                             1-9-27.4-9-27Four 85 hole            (20)    33.2  (25.1)  15         Pulsing through 3d(0.07&#34; dia) 1046          --                 plate. Plug flowplates followed                              between 1st 4 plates.by 4 43 hole                                 Channeling between(0.07&#34; dia)                                  5th-8th plates andplates, followed                             first 6                                             Kenics.sup.®by 4 Kenics.sup.®                        elements. Screenselements then A                              refined syrup frag-70 mesh screen                               ments to smallerwith elements +                              size. Many stria-screen repeated                              tions and some syruptwice more and                               fragments after 16terminated with                              elements.4 Kenics.sup.®elements.5-9-27Same as Test            (20)    42    (19.6)  --         No syrup fragments4-9-27      1046)         --                 after 16                                             Kenics.sup.®                                             elements, but many                                             striations. Flow                                             in elements was                                             erratic, with some                                             backflow due to                                             settling syrup                                             agglomerates.__________________________________________________________________________ 
    
     Study of the recorded observations for Tests 3-6-30 and 1-7-3 in TABLE III shows that the addition of perforated plates interspersed between Kenics® mixing elements provided more complete mixing than Kenics® elements alone. 
     A similar improvement in performance was noted in Tests 2-7-3 and 2-7-11 relative to Test 2-6-30 at a lower water rate. 
     The mixing superiority of multiple perforated plates over a single perforated plate is shown by comparision of the results of Tests 2-7-5 and 1-7-5. 
     Smaller 0.070 inch dia. holes provided better mixing than 1/8 inch dia. holes. Occasionally, the last Kenics® element effluent would show a water globule(Test 1a-8-3) when the larger holes were used, but never when the smaller 0.070 inch holes were used (Test 2-8-3). 
     When screens were disposed after the 4th, 8th and 12th Kenics® elements, the syrup fragments were reduced to a smaller size (Test 4-9-27). Also, a higher ratio of water to corn syrup could be tolerated. as shown by Tests 1-10-10, 3-10-10 and 2-10-18.