CA1158234A - Low power off centered agitator with partial baffles for buoyant solids mixing drum - Google Patents
Low power off centered agitator with partial baffles for buoyant solids mixing drumInfo
- Publication number
- CA1158234A CA1158234A CA000368905A CA368905A CA1158234A CA 1158234 A CA1158234 A CA 1158234A CA 000368905 A CA000368905 A CA 000368905A CA 368905 A CA368905 A CA 368905A CA 1158234 A CA1158234 A CA 1158234A
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- Prior art keywords
- tank
- baffles
- mixing apparatus
- agitator
- baffle
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
- B01F27/00—Mixers with rotary stirring devices in fixed receptacles; Kneaders
- B01F27/80—Mixers with rotary stirring devices in fixed receptacles; Kneaders with stirrers rotating about a substantially vertical axis
- B01F27/86—Mixers with rotary stirring devices in fixed receptacles; Kneaders with stirrers rotating about a substantially vertical axis co-operating with deflectors or baffles fixed to the receptacle
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- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Mixers Of The Rotary Stirring Type (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A mixing apparatus is provided comprising a cy-lindrical tank having a downpumping turbine bladed agita-tor displaced radially from the axis of the tank a distance of from about 1/10 to 1/4 of the tank diameter. The ap-paratus preferably includes at least one baffle and more preferably a plurality of equally-spaced baffles mounted on the inside wall of the tank, each of which comprises a rectangular member extending substantially from the bot-tom of the tank to the maximum slurry level of the tank and having a radial width of between about 1/36 and 1/100 of the tank diameter. Four equally-spaced baffles are par-ticularly preferred, each having a radial width of about 1/50 of the tank diameter.
A mixing apparatus is provided comprising a cy-lindrical tank having a downpumping turbine bladed agita-tor displaced radially from the axis of the tank a distance of from about 1/10 to 1/4 of the tank diameter. The ap-paratus preferably includes at least one baffle and more preferably a plurality of equally-spaced baffles mounted on the inside wall of the tank, each of which comprises a rectangular member extending substantially from the bot-tom of the tank to the maximum slurry level of the tank and having a radial width of between about 1/36 and 1/100 of the tank diameter. Four equally-spaced baffles are par-ticularly preferred, each having a radial width of about 1/50 of the tank diameter.
Description
1~582~
1 The present invention relates to a mixing
1 The present invention relates to a mixing
2 apparatus comprising a mixing tank having an off-centered
3 agitator and also preferably employing at least two par-
4 tial baffles which tank is particularly useful for but not limited to the mixing of buoyant particle slurries.
6 Generally the efficient mixing of buoyant par-7 ticle slurries is very important to many process opera-8 tions, as for example in the manufacture of elastomers.
9 In this process buoyant polymer particles in the form of a water slurry are fed to a slurry drum in the finishing 11 sections and then to product extruders. The primary func-12 tion of the sluxry drum is to form a uniform slurry and 13 supply it as feed to the extruders. The slurry drum also 14 provides reliable surge capacity between the polymeriza-tion and solids finishing sections. The mixing of these 16 buoyant particles is also an important operation during 17 other aspects of chemical manufacture, such as during the 18 dissolving of polymer particles in processing lubricating 19 oil additives.
The systems used at present for mixing such 21 buoyant particles slurries generally comprise a baffled 22 tank for receiving the slurries containing means for agi-23 tating the slurry such as a single or multiple-bladed 24 turbine agitator or stirrer. Ideally, such systems should produce homogeneous, concentrated particle slurries, the 26 prevention of agglomeration of solids in regions of the 27 tank which could lead to plugging of the tank outlets, and 28 a relatively constant change in the outlet slurry concen~
29 tration to the extruders with changes in the slurry level in the tank. With the present emphasis on energy conser-31 vation it is also desired that these systems operate on 32 low powerO
33 Previous attempts to provide efficient mixing 34 systems have included employing unbaffled slurry tanks hav-ing a centrally disposed agitator to provide a central vor-36 tex in the tank. However, it has been found that various 37 deficiencies exist in such tanks including the need for ~15~2~
~ 2 --higher mi~ing speeds and hence more power than normally anticipated and the concentration of particles between the bottom of the vortex and top of the vortex-creating agitator.
Present mixing designs which include baffling typically have employed full baffles, i.e. baffles which extend vertically for the full length of the tank walls at spaced locations and radially a distance of 1/10 or more of the tank's diameter. This type of full baffling eliminates tank swirl and vortex formation except when the liquid sur-face is very close to the top of the agitator. The art has also disclosed further mixing arrangements wherein baffles are located at or near the bottom of the tank, at the center of the tank and annular baffles about the agitator at the liquid surface.
The combination of partial baffles and a centered agitator in a mixing system has also been described. In U.S.
Patent No. 4,150,900, issued April 241 1979 to D,L. Smith Jr, et al, for example, an improved mixing system is des-cribed which employs partial baffling and a central agi-tator assembly in a mixing tank. The partial baffles des-cribed therein comprise small rectangular or triangular finger baffles which are locatedl at various positions in the mixing tank. These baffles are secured about the tank 2 5 inner surface and are preferably located just below the liquid surface level, In the case of variable level mixing -tanks, fixed partial baffles are employed in the form of narrow, elongated rectangles located adjacent to the tank wall and extending from the ma~imum operating liquid level to the bottom of the tank. If triangular baffles are employed the size of each can be determined by providing a horizontal leg which equal~ 10% to 15% of tank diameter and a vertical leg which equals 15% to 200/o of tank diameter, If rectangular baffles are used the size of each baffle is selected so that the sum of the surface areas of the baffles is the same as the total surface area for four baffles in a triangular configuration. If four rectangular partial baffles are used , 2~
1 the width of the rectangles in the radial direction should 2 be approxima~ely 2% or 1/50 of the tank diam~ter.
3 In the article, "The Suspension of Floating 4 Solids In Stirred Vessels", G o E ~ H ~ Joosten et. al., Trans.
I. Chem. E. 55, (July, 220, 1977) a number o experiments 6 using baffled and unbaffled vessels equipped with a cen-7 trally disposed agitator were conducted to determine their 8 effect in forming suspensions of floating particles in a 9 liquid. The optimal flow pattern for suspension of the floating particles was found to be a fast rotating liquid 11 whose rotation was disturbed by a single baffle having a 12 width equa~ to 0.2 of the diameter of the vessel immersed 13 at the top of the liquid to a wetted depth equal to 0.3 14 of the diameter of the vessel.
The present invention provides a mixing appara-16 tus comprising a cylindrical tank having a bladed down-17 pumping turbine agitator assembly associated therewith 18 wherein the shaft of the agitator assembly is displaced 19 radially from the central axis of the tank a distance equal to from about 1/10 to 1/4 of the tank diameter. By 21 using such an off-centered agitator it has been found that 22 efficient mixing of buoyant particle slurries is achieved 23 with power savings of up to about 38% compared to central-24 ly or axially disposed agitators.
The apparatus is also equipped with at least two 26 partial baffles and preferably with four partial bafflesl 27 equally-spaced about the inside circumference of the tank.
28 Such par~ial baffles comprise vertical rectangular or tri-29 angular members attached to the inside wall of the tank which extend substantially from the bottom of the tank to 31 the maximum slurry height of the tank, each baffle having 3~ a radial width ranging from about 1/36 to 1/100 of the dia-33 meter of the tank. Particularly preferred are four e-34 qually-spaced rectangular partial baffles having a radial width of about 1/50 of the tank diameter. Such a system 36 of partial baffles in conjunction with an off-centered 37 downpumping agitator provide concentrated, homogeneous 38 particle slurries whose characteristics are not appreci-141 5~2~ -1 ably changed with changes in the slurry level in the tank.
2 Also, such an apparatus provides excellent dispersion and 3 contacting of systems such as, for example, immiscible 4 liquids, gas and liquids, and gas and slurries.
In the drawings: Figs. 1 and 2 show a side view 6 and a top view of the preferred mixing apparatus of the 7 invention having an off-centered agitator and four equal-8 ly-spaced partial baffles.
9 Fig. 3 is a top view of an unbaffled mixing ap-paratus having an off-centered agitator showing, by ref-11 erence numerals, a set of baffle positions about the cir~
12 cumference of the tank.
13 Referring to Figs. 1 and 2 there is shown a pxe-14 ferred mixing apparatus 11 according to the invention com-prising a cylindrical tank 12. An agitator shaft 13 ex-16 tends axially into the tank and i5 displaced away from the 17 axis of the tank, as shown by the dotted lines, a distance 18 d varying from about 1/10 to 1/4 of the diameter of the 19 tank. The top portion of the agitator 13 is connected with a means for rotating the shaft (not shown) such as 21 an electric motor. Centrally mounted on the shaft is an 22 agitator assembly 14 shown generally by consisting of 4 23 equally-spaced downpumping turbiIle blades pitched to an 24 angle of 45 as shown and positioned adjacent the bottom lg of the tank. The bottom section 13a of the agitator 26 shaft may be totally supported in the bottom 19 of the ~7 tank by a steady bearing. Liquid 16 in the tank may be 28 kept at a constant lev~l or may be varied. Spaced 90 29 from one another around the inside wall of the tank are preferably four (4) rectangular partial baffles 17, each 31 of which comprises a thin, elongated rectangular member 32 comprised of metal, for example extending from the maximum 33 height of the tank to a point just adjacent the bottom of 34 the tank. Each baffle 17 is secured to the lnside wall of the tank by means of a pair of brackets 18 or other 36 conventional securing means fastened at the top and bottom 37 of each baffle. The radial width of each baffle 17 is lL 15~2~
l between about l/36 and l/100 of the width of the tank and ~ preferably about l/50 cf the width of the tank. The baf-3 fles are spaGed from the wall about 1/50 of the width of 4 the tankO The diameter of the agitator assembly 14 should be from about l/3 to about l/2 the diameter of the tank.
6 FigO 3 shows a top view of a slurry tank 12 hav-7 ing off-centered agitator 13 and also indicates 16 possible g positions, spaced 22.5 apart, for locating one or more g baffles according to the invention. These positions will be discussed in more detail in connection with the exam-ll ples.
12 Experimentally, it has been found that the use 13 of an off-centered agitator in a tank design such as des-14 cribed above for forming buoyant particle slurries provides consistently higher outlet slurry concentrations than tanks 16 equipped with a centered agitator. Use of this invention, 17 however, is not restricted to mixing of buoyant particle 18 slurry and has broad utility as mentioned above for immis-l9 cible liquids, gas and liquid, and gas and slurries and the like. Moreover, lower tip speeds and hence lower power 21 is required by the of~-centered agitator according to the 22 invention than a centered agitator to achieve the same de-23 gree of mixing. This savings in power is from about 50%
24 to 80% compared to multiple-turbined central agitators and fully baffled tanks and up to about 38% in the case of sin-26 gle turbined agitators.
27 By employing at least two equally spaced partial 28 baffles with an off-centered agitator mixing efficiency 29 is further enhanced. By using four equally-spaced partial baffles, optimum mixing efficiency is obtained with change~
31 in outlet slurry concentration being relatively small with 32 increases in slurry level.
33 It has also been found that the baffle radial 34 width is important to the mixing efficiency of the inven-tion. At widths of fxom between l/36 and l/100 of tank 36 diameter, and preferably l/50 of tank diameter, concentra-37 ted and homogeneous slurries are obtained. At widths sub-~582~
1 stantially above and helow these ranges the slurry char-2 acteristics become unsatisfactoryO
3 Triangular bafles may be similarly employed in 4 this invention provided they have surface areas equivalent to the rectangular partial baffles described above.
6 ~n order to more fully define the present inven-7 tion, the following examples are given.
8 Example 1 9 In this and the following examples, a 0.9 m dia-meter tank with a flat bottom was employed comprised of 11 Plexiglas and having a height of 1.8 m. A 0.3 m diameter 12 45 downpumping pitched blade turbine ~ith four (4) 54 mm 13 wide blades was mounted on a vertical agitator shaft dis 14 placed from the axis of the tank by 90 mm (1~10 of tank diameter). The agitator drive equipment consisted of a 16 3 HP electric motor which, through a variable speed drive r 17 was capable of rotating the agitator at speeds of up to 18 260 RPM. The agitator shaft was supported at the tank 19 bottom by a steady bearing. Four baffles, each 1/50 of the tank diameter, were mounted at equal intervals inside 21 the internal periphery of the tank spaced from the ~ank 22 wall a distance equal to 1/50 of the tank diameter. This 23 arrangement is shown in Figs. 1 and 2.
24 A Vibrac ~Q-5120 (range 0-5120 in-oz) torque transducer was included in the shaft for measurement of 26 torque. The TQ-5120 unit was also equipped with a magnet-27 ic speed transducer which put out 60 pulses per shaft re 28 volution. This was translated to RPM hy m~ans of a fre-29 quency meter. A slurry outlet, 127 mm above the tank bot-tom, was connected to the inlet of a positive displacement 31 pump by a 25 mm diameter pipe. The outlet from the pump 32 was directed back into the tank to provide recycle loop.
33 In all the examples the slurry consisted of 4% by weight 34 o 3.2 mm polypropylene pellets in water. The outlet slurry concentration was measured by collecting samples 3~ at the recycle loop into the tank. The pellets from each 37 sample were filtered and weighed while the volume of water 1 ~58~3~
1 was measured to determine outlet concentration.
2 In this example a comparison of mixing charac-3 teristics was made between the off-centexed agitator and 4 a centered agitator used in the same tank having the same blade pitch and width as the off-centered agitator. The 6 speeds used for both agitator types were 200 and 225 RPM.
7 Outlet slurry concentrations were determined for both agi-8 tators as the percent of bulk concentration at different 9 slurry levels in the tank measured as the percent (%) of full height of the tank.
11 The results are given in Table 1 below.
12 Table 1 14 ~ _ _ OUTLET SLURRY CONC.(1 of Bulk Concentr_tion 15 ;lurry LevelCentered Off-Centered (% ofAt Speed - RPM At Speed - RPM
l7 Eull helght) _ 200 225 _200 225 18 48 56.1 65.6 71.3 74.2 37.9 50.3 58.0 61.8 21 As Table 1 shows the o~f-centered agitator pro-22 vided consistently higher outlet slurry concentrations at 23 each slurry level than those with the centered agitator.
24 In addi~ion, the change in outlet slurry concentration with change in slurry level was smaller for the off-cen-26 tered agitator than for the centered agitator.
27 Next, agitator speeds required to achieve an out-28 let slurry concentration equal to 60% of the bulk concen-29 tration were then determined for both the centered and off-centered agitator. It was found that lower speeds were 31 required by an off-centered agitator than a centered agi-32 tator to achieve the same degree of mixing. The differ-33 ence in these speeds decreased as the slurry level was in-34 creased. For the tank design described above the maximum slurry level was 93~ which c~rresponds to a 14% lower agi-36 tator speed requirement than the centered agitator system.
37 This can amount to a savings of about 38% in power con-38 sumption.
~ ~5~234 -- S --1 Example 2 . _ 2 In this Example, outlet slurry concentration 3 measured as the percent of bulk concentration was deter-4 mined at an 83% slurry level using the tank and baffling arrangement described in Example 1 except that the agita-6 tor assembly comprised a 15" diameter pitched blade tur-7 bine, the agitator shaft of which was displaced a distance 8 equal to 0.225 of the tank diameter. The agitator speeds 9 used were 125 and 150 RPM. Table 2 below summarizes the 10 results.
11 Table 2 13 _ (RPM) (% of Bulk Concentratio_) _ 16 7~
87 As Table 2 shows high outlet slurry concentra-tions were obtained at each speed using an agitator cen-trally offset a distance nearly 1/4 of the tank diameter.
21 Example 3 .
22 Xn this Example, a series of four (4) equally 23 spaced partial baffles as shown :in Fig. 1 were inserted 24 around the inside wall of khe tank at the following posi-tions, shown in Fig. 3:
26 Series A - Positions 1, 5, 9 and 13 27 Series B - Positions 2, 6, 10 and 14 28 Series C - Positions 3, 7, 11 and 15 29 Series D - Positions 4, 8, 12 and 16 In each series, the baffle width was varied from 31 1/36 to 1/50 to 1/100 of the tank diameter, viz 25mm, 18 mm 32 and 9 mm respectively. Stirring of the off-centered agi-33 tator was carried out at speeds of 200 and 225 RPM. Out 34 let slurry concentrations measured as the percent of bulk concentration were determined for each baffle width in each 36 series. The slurry level was 100% of fu~l tank height.
37 Table 3 below summarizes the results.
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115823~
~o i`l~
V V ~ . .
; ~L
~3 u~ o ,_ ,~ ~
23~
1 As Table 3 shows, baffle widths from 1/36 to 2 1/100 of tank diameter in conjunction with an off-centered 3 agitator provide efficient mixing. However a baffle width 4 of 1/50 of tank diameter is particularly preferred since it provided consistently higher slurry outlet concentra-6 tions at the speeds employed. The position of the baffles 7 did not significantly vary the outlet concentrations.
8 Example 4 9 In this Example the effect of slurry level on the concentration of outlet slurry was measured using two 11 and four partial baffles with an off-centered agitator as 12 shown in Fig. 1 having radial widths of 1/50 of tank dia-13 meter. For each baffle arrangement, the slurry level was 14 raised to 28%, 46% and 100~ of full height while outlet lS slurry concentrations were measured at agitator speeds of 16 200 and 225 RPM. Table 4 summarizes the results.
.
11 15~34 ~ ~1 ~ w ~ ~r ~ ~
.
~.
. . .
1 ~58~
1 With two baffles the outlet slurry concentration 2 increases ~rom about 20% to 90% of the bulk concentra~ion 3 as the slurry level is increased from about 30~ to 100%.
4 With four baffles the outlet slurry concentration decreases from about 75% to 60~ over the same slurry level rangeO
6 This indicates that a four baffle arrangement is prefer-7 able to a two baffle arrangement for buoyant particle 8 slurries because of the relatively small change in outlet 9 slurry concentration with varying slurry levels.
6 Generally the efficient mixing of buoyant par-7 ticle slurries is very important to many process opera-8 tions, as for example in the manufacture of elastomers.
9 In this process buoyant polymer particles in the form of a water slurry are fed to a slurry drum in the finishing 11 sections and then to product extruders. The primary func-12 tion of the sluxry drum is to form a uniform slurry and 13 supply it as feed to the extruders. The slurry drum also 14 provides reliable surge capacity between the polymeriza-tion and solids finishing sections. The mixing of these 16 buoyant particles is also an important operation during 17 other aspects of chemical manufacture, such as during the 18 dissolving of polymer particles in processing lubricating 19 oil additives.
The systems used at present for mixing such 21 buoyant particles slurries generally comprise a baffled 22 tank for receiving the slurries containing means for agi-23 tating the slurry such as a single or multiple-bladed 24 turbine agitator or stirrer. Ideally, such systems should produce homogeneous, concentrated particle slurries, the 26 prevention of agglomeration of solids in regions of the 27 tank which could lead to plugging of the tank outlets, and 28 a relatively constant change in the outlet slurry concen~
29 tration to the extruders with changes in the slurry level in the tank. With the present emphasis on energy conser-31 vation it is also desired that these systems operate on 32 low powerO
33 Previous attempts to provide efficient mixing 34 systems have included employing unbaffled slurry tanks hav-ing a centrally disposed agitator to provide a central vor-36 tex in the tank. However, it has been found that various 37 deficiencies exist in such tanks including the need for ~15~2~
~ 2 --higher mi~ing speeds and hence more power than normally anticipated and the concentration of particles between the bottom of the vortex and top of the vortex-creating agitator.
Present mixing designs which include baffling typically have employed full baffles, i.e. baffles which extend vertically for the full length of the tank walls at spaced locations and radially a distance of 1/10 or more of the tank's diameter. This type of full baffling eliminates tank swirl and vortex formation except when the liquid sur-face is very close to the top of the agitator. The art has also disclosed further mixing arrangements wherein baffles are located at or near the bottom of the tank, at the center of the tank and annular baffles about the agitator at the liquid surface.
The combination of partial baffles and a centered agitator in a mixing system has also been described. In U.S.
Patent No. 4,150,900, issued April 241 1979 to D,L. Smith Jr, et al, for example, an improved mixing system is des-cribed which employs partial baffling and a central agi-tator assembly in a mixing tank. The partial baffles des-cribed therein comprise small rectangular or triangular finger baffles which are locatedl at various positions in the mixing tank. These baffles are secured about the tank 2 5 inner surface and are preferably located just below the liquid surface level, In the case of variable level mixing -tanks, fixed partial baffles are employed in the form of narrow, elongated rectangles located adjacent to the tank wall and extending from the ma~imum operating liquid level to the bottom of the tank. If triangular baffles are employed the size of each can be determined by providing a horizontal leg which equal~ 10% to 15% of tank diameter and a vertical leg which equals 15% to 200/o of tank diameter, If rectangular baffles are used the size of each baffle is selected so that the sum of the surface areas of the baffles is the same as the total surface area for four baffles in a triangular configuration. If four rectangular partial baffles are used , 2~
1 the width of the rectangles in the radial direction should 2 be approxima~ely 2% or 1/50 of the tank diam~ter.
3 In the article, "The Suspension of Floating 4 Solids In Stirred Vessels", G o E ~ H ~ Joosten et. al., Trans.
I. Chem. E. 55, (July, 220, 1977) a number o experiments 6 using baffled and unbaffled vessels equipped with a cen-7 trally disposed agitator were conducted to determine their 8 effect in forming suspensions of floating particles in a 9 liquid. The optimal flow pattern for suspension of the floating particles was found to be a fast rotating liquid 11 whose rotation was disturbed by a single baffle having a 12 width equa~ to 0.2 of the diameter of the vessel immersed 13 at the top of the liquid to a wetted depth equal to 0.3 14 of the diameter of the vessel.
The present invention provides a mixing appara-16 tus comprising a cylindrical tank having a bladed down-17 pumping turbine agitator assembly associated therewith 18 wherein the shaft of the agitator assembly is displaced 19 radially from the central axis of the tank a distance equal to from about 1/10 to 1/4 of the tank diameter. By 21 using such an off-centered agitator it has been found that 22 efficient mixing of buoyant particle slurries is achieved 23 with power savings of up to about 38% compared to central-24 ly or axially disposed agitators.
The apparatus is also equipped with at least two 26 partial baffles and preferably with four partial bafflesl 27 equally-spaced about the inside circumference of the tank.
28 Such par~ial baffles comprise vertical rectangular or tri-29 angular members attached to the inside wall of the tank which extend substantially from the bottom of the tank to 31 the maximum slurry height of the tank, each baffle having 3~ a radial width ranging from about 1/36 to 1/100 of the dia-33 meter of the tank. Particularly preferred are four e-34 qually-spaced rectangular partial baffles having a radial width of about 1/50 of the tank diameter. Such a system 36 of partial baffles in conjunction with an off-centered 37 downpumping agitator provide concentrated, homogeneous 38 particle slurries whose characteristics are not appreci-141 5~2~ -1 ably changed with changes in the slurry level in the tank.
2 Also, such an apparatus provides excellent dispersion and 3 contacting of systems such as, for example, immiscible 4 liquids, gas and liquids, and gas and slurries.
In the drawings: Figs. 1 and 2 show a side view 6 and a top view of the preferred mixing apparatus of the 7 invention having an off-centered agitator and four equal-8 ly-spaced partial baffles.
9 Fig. 3 is a top view of an unbaffled mixing ap-paratus having an off-centered agitator showing, by ref-11 erence numerals, a set of baffle positions about the cir~
12 cumference of the tank.
13 Referring to Figs. 1 and 2 there is shown a pxe-14 ferred mixing apparatus 11 according to the invention com-prising a cylindrical tank 12. An agitator shaft 13 ex-16 tends axially into the tank and i5 displaced away from the 17 axis of the tank, as shown by the dotted lines, a distance 18 d varying from about 1/10 to 1/4 of the diameter of the 19 tank. The top portion of the agitator 13 is connected with a means for rotating the shaft (not shown) such as 21 an electric motor. Centrally mounted on the shaft is an 22 agitator assembly 14 shown generally by consisting of 4 23 equally-spaced downpumping turbiIle blades pitched to an 24 angle of 45 as shown and positioned adjacent the bottom lg of the tank. The bottom section 13a of the agitator 26 shaft may be totally supported in the bottom 19 of the ~7 tank by a steady bearing. Liquid 16 in the tank may be 28 kept at a constant lev~l or may be varied. Spaced 90 29 from one another around the inside wall of the tank are preferably four (4) rectangular partial baffles 17, each 31 of which comprises a thin, elongated rectangular member 32 comprised of metal, for example extending from the maximum 33 height of the tank to a point just adjacent the bottom of 34 the tank. Each baffle 17 is secured to the lnside wall of the tank by means of a pair of brackets 18 or other 36 conventional securing means fastened at the top and bottom 37 of each baffle. The radial width of each baffle 17 is lL 15~2~
l between about l/36 and l/100 of the width of the tank and ~ preferably about l/50 cf the width of the tank. The baf-3 fles are spaGed from the wall about 1/50 of the width of 4 the tankO The diameter of the agitator assembly 14 should be from about l/3 to about l/2 the diameter of the tank.
6 FigO 3 shows a top view of a slurry tank 12 hav-7 ing off-centered agitator 13 and also indicates 16 possible g positions, spaced 22.5 apart, for locating one or more g baffles according to the invention. These positions will be discussed in more detail in connection with the exam-ll ples.
12 Experimentally, it has been found that the use 13 of an off-centered agitator in a tank design such as des-14 cribed above for forming buoyant particle slurries provides consistently higher outlet slurry concentrations than tanks 16 equipped with a centered agitator. Use of this invention, 17 however, is not restricted to mixing of buoyant particle 18 slurry and has broad utility as mentioned above for immis-l9 cible liquids, gas and liquid, and gas and slurries and the like. Moreover, lower tip speeds and hence lower power 21 is required by the of~-centered agitator according to the 22 invention than a centered agitator to achieve the same de-23 gree of mixing. This savings in power is from about 50%
24 to 80% compared to multiple-turbined central agitators and fully baffled tanks and up to about 38% in the case of sin-26 gle turbined agitators.
27 By employing at least two equally spaced partial 28 baffles with an off-centered agitator mixing efficiency 29 is further enhanced. By using four equally-spaced partial baffles, optimum mixing efficiency is obtained with change~
31 in outlet slurry concentration being relatively small with 32 increases in slurry level.
33 It has also been found that the baffle radial 34 width is important to the mixing efficiency of the inven-tion. At widths of fxom between l/36 and l/100 of tank 36 diameter, and preferably l/50 of tank diameter, concentra-37 ted and homogeneous slurries are obtained. At widths sub-~582~
1 stantially above and helow these ranges the slurry char-2 acteristics become unsatisfactoryO
3 Triangular bafles may be similarly employed in 4 this invention provided they have surface areas equivalent to the rectangular partial baffles described above.
6 ~n order to more fully define the present inven-7 tion, the following examples are given.
8 Example 1 9 In this and the following examples, a 0.9 m dia-meter tank with a flat bottom was employed comprised of 11 Plexiglas and having a height of 1.8 m. A 0.3 m diameter 12 45 downpumping pitched blade turbine ~ith four (4) 54 mm 13 wide blades was mounted on a vertical agitator shaft dis 14 placed from the axis of the tank by 90 mm (1~10 of tank diameter). The agitator drive equipment consisted of a 16 3 HP electric motor which, through a variable speed drive r 17 was capable of rotating the agitator at speeds of up to 18 260 RPM. The agitator shaft was supported at the tank 19 bottom by a steady bearing. Four baffles, each 1/50 of the tank diameter, were mounted at equal intervals inside 21 the internal periphery of the tank spaced from the ~ank 22 wall a distance equal to 1/50 of the tank diameter. This 23 arrangement is shown in Figs. 1 and 2.
24 A Vibrac ~Q-5120 (range 0-5120 in-oz) torque transducer was included in the shaft for measurement of 26 torque. The TQ-5120 unit was also equipped with a magnet-27 ic speed transducer which put out 60 pulses per shaft re 28 volution. This was translated to RPM hy m~ans of a fre-29 quency meter. A slurry outlet, 127 mm above the tank bot-tom, was connected to the inlet of a positive displacement 31 pump by a 25 mm diameter pipe. The outlet from the pump 32 was directed back into the tank to provide recycle loop.
33 In all the examples the slurry consisted of 4% by weight 34 o 3.2 mm polypropylene pellets in water. The outlet slurry concentration was measured by collecting samples 3~ at the recycle loop into the tank. The pellets from each 37 sample were filtered and weighed while the volume of water 1 ~58~3~
1 was measured to determine outlet concentration.
2 In this example a comparison of mixing charac-3 teristics was made between the off-centexed agitator and 4 a centered agitator used in the same tank having the same blade pitch and width as the off-centered agitator. The 6 speeds used for both agitator types were 200 and 225 RPM.
7 Outlet slurry concentrations were determined for both agi-8 tators as the percent of bulk concentration at different 9 slurry levels in the tank measured as the percent (%) of full height of the tank.
11 The results are given in Table 1 below.
12 Table 1 14 ~ _ _ OUTLET SLURRY CONC.(1 of Bulk Concentr_tion 15 ;lurry LevelCentered Off-Centered (% ofAt Speed - RPM At Speed - RPM
l7 Eull helght) _ 200 225 _200 225 18 48 56.1 65.6 71.3 74.2 37.9 50.3 58.0 61.8 21 As Table 1 shows the o~f-centered agitator pro-22 vided consistently higher outlet slurry concentrations at 23 each slurry level than those with the centered agitator.
24 In addi~ion, the change in outlet slurry concentration with change in slurry level was smaller for the off-cen-26 tered agitator than for the centered agitator.
27 Next, agitator speeds required to achieve an out-28 let slurry concentration equal to 60% of the bulk concen-29 tration were then determined for both the centered and off-centered agitator. It was found that lower speeds were 31 required by an off-centered agitator than a centered agi-32 tator to achieve the same degree of mixing. The differ-33 ence in these speeds decreased as the slurry level was in-34 creased. For the tank design described above the maximum slurry level was 93~ which c~rresponds to a 14% lower agi-36 tator speed requirement than the centered agitator system.
37 This can amount to a savings of about 38% in power con-38 sumption.
~ ~5~234 -- S --1 Example 2 . _ 2 In this Example, outlet slurry concentration 3 measured as the percent of bulk concentration was deter-4 mined at an 83% slurry level using the tank and baffling arrangement described in Example 1 except that the agita-6 tor assembly comprised a 15" diameter pitched blade tur-7 bine, the agitator shaft of which was displaced a distance 8 equal to 0.225 of the tank diameter. The agitator speeds 9 used were 125 and 150 RPM. Table 2 below summarizes the 10 results.
11 Table 2 13 _ (RPM) (% of Bulk Concentratio_) _ 16 7~
87 As Table 2 shows high outlet slurry concentra-tions were obtained at each speed using an agitator cen-trally offset a distance nearly 1/4 of the tank diameter.
21 Example 3 .
22 Xn this Example, a series of four (4) equally 23 spaced partial baffles as shown :in Fig. 1 were inserted 24 around the inside wall of khe tank at the following posi-tions, shown in Fig. 3:
26 Series A - Positions 1, 5, 9 and 13 27 Series B - Positions 2, 6, 10 and 14 28 Series C - Positions 3, 7, 11 and 15 29 Series D - Positions 4, 8, 12 and 16 In each series, the baffle width was varied from 31 1/36 to 1/50 to 1/100 of the tank diameter, viz 25mm, 18 mm 32 and 9 mm respectively. Stirring of the off-centered agi-33 tator was carried out at speeds of 200 and 225 RPM. Out 34 let slurry concentrations measured as the percent of bulk concentration were determined for each baffle width in each 36 series. The slurry level was 100% of fu~l tank height.
37 Table 3 below summarizes the results.
~ ..
115823~
~o i`l~
V V ~ . .
; ~L
~3 u~ o ,_ ,~ ~
23~
1 As Table 3 shows, baffle widths from 1/36 to 2 1/100 of tank diameter in conjunction with an off-centered 3 agitator provide efficient mixing. However a baffle width 4 of 1/50 of tank diameter is particularly preferred since it provided consistently higher slurry outlet concentra-6 tions at the speeds employed. The position of the baffles 7 did not significantly vary the outlet concentrations.
8 Example 4 9 In this Example the effect of slurry level on the concentration of outlet slurry was measured using two 11 and four partial baffles with an off-centered agitator as 12 shown in Fig. 1 having radial widths of 1/50 of tank dia-13 meter. For each baffle arrangement, the slurry level was 14 raised to 28%, 46% and 100~ of full height while outlet lS slurry concentrations were measured at agitator speeds of 16 200 and 225 RPM. Table 4 summarizes the results.
.
11 15~34 ~ ~1 ~ w ~ ~r ~ ~
.
~.
. . .
1 ~58~
1 With two baffles the outlet slurry concentration 2 increases ~rom about 20% to 90% of the bulk concentra~ion 3 as the slurry level is increased from about 30~ to 100%.
4 With four baffles the outlet slurry concentration decreases from about 75% to 60~ over the same slurry level rangeO
6 This indicates that a four baffle arrangement is prefer-7 able to a two baffle arrangement for buoyant particle 8 slurries because of the relatively small change in outlet 9 slurry concentration with varying slurry levels.
Claims (15)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A mixing apparatus comprising:
(a) a cylindrical tank;
(b) an agitator shaft rotatably mounted in said tank, said shaft being radially displaced from the axis of said tank a distance of from about 1/10 to 1/4 of the tank dia-meter;
(c) a bladed turbine assembly centrally mounted on said shaft; and (d) at least two baffles mounted on the inside wall of said tank.
(a) a cylindrical tank;
(b) an agitator shaft rotatably mounted in said tank, said shaft being radially displaced from the axis of said tank a distance of from about 1/10 to 1/4 of the tank dia-meter;
(c) a bladed turbine assembly centrally mounted on said shaft; and (d) at least two baffles mounted on the inside wall of said tank.
2. The mixing apparatus of claim 1 wherein said baffle comprises a rectangular member having a radial width of between about 1/36 and 1/100 of said tank diameter.
3. The mixing apparatus of claim 2 wherein said baffle has a radial width of about 1/50 of said tank diameter.
4. The mixing apparatus of claim 1 wherein each baffle is spaced from the inside wall of said tank a distance equal to 1/50 of the tank diameter.
5. The mixing apparatus of claim 1 which comprises four equally spaced baffles, each baffle comprising a member having a radial width of about 1/50 of said tank diameter.
6. The mixing apparatus of claim 1 wherein each baffle is a triangular baffle.
7. A mixing apparatus comprising:
(a) a cylindrical tank for receiving a slurry up to a predetermined level in said tank;
(b) an agitator shaft rotatably mounted in said tank, said shaft being radially displaced from the axis of said tank a distance of from about 1/10 to 1/4 of the tank dia-meter;
(c) a bladed turbine assembly centrally mounted on said shaft; and (d) at least two baffles mounted on the inside wall of said tank, said baffle comprising a member having a radial width of between about 1/36 and 1/100 of said tank diameter and extending substantially from said tank bottom to said predetermined level.
(a) a cylindrical tank for receiving a slurry up to a predetermined level in said tank;
(b) an agitator shaft rotatably mounted in said tank, said shaft being radially displaced from the axis of said tank a distance of from about 1/10 to 1/4 of the tank dia-meter;
(c) a bladed turbine assembly centrally mounted on said shaft; and (d) at least two baffles mounted on the inside wall of said tank, said baffle comprising a member having a radial width of between about 1/36 and 1/100 of said tank diameter and extending substantially from said tank bottom to said predetermined level.
8. The mixing apparatus of claim 7 wherein the radial width of said baffle is about 1/50 of said tank diameter.
9. The mixing apparatus of claim 8 wherein each of said baffles is spaced from the inside wall of said tank a dis-tance equal to 1/50 of the tank diameter.
10. The mixing apparatus of claim 7 which comprises four equally-spaced rectangular baffles.
11. The mixing apparatus of claim 10 wherein each of said baffles has a radial width of about 1/50 of said tank dia-meter.
12. The mixing apparatus of claim 7 wherein said bladed turbine assembly comprises four equally-spaced downpumping turbine blades, each of said blades pitched at an angle of 45°.
13. The mixing apparatus of claim 7 wherein each of said baffles is a triangular baffle.
14. A mixing apparatus for liquids comprising:
(a) a cylindrical tank for receiving a liquid up to a predetermined level in said tank;
(b) an agitator shaft rotatably mounted in said tank, said shaft being radially displaced from the axis of said tank a distance of from about 1/10 to 1/4 of the tank dia-meter;
(c) a bladed turbine assembly centrally mounted on said shaft; and (d) four equally-spaced baffles mounted along the in-side wall of said tank, each of said baffles comprising a rectangular member having a radial width of about 1/50 of said tank diameter and extending substantially from said tank bottom to said predetermined level; and being spaced from the inside wall of said tank a distance equal to l/50 of the tank diameter.
(a) a cylindrical tank for receiving a liquid up to a predetermined level in said tank;
(b) an agitator shaft rotatably mounted in said tank, said shaft being radially displaced from the axis of said tank a distance of from about 1/10 to 1/4 of the tank dia-meter;
(c) a bladed turbine assembly centrally mounted on said shaft; and (d) four equally-spaced baffles mounted along the in-side wall of said tank, each of said baffles comprising a rectangular member having a radial width of about 1/50 of said tank diameter and extending substantially from said tank bottom to said predetermined level; and being spaced from the inside wall of said tank a distance equal to l/50 of the tank diameter.
15. The apparatus of claim 14 wherein said bladed turbine assembly comprises four equally spaced downpumping turbine blades, each of said blades being pitched at an angle of 45°.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US11350980A | 1980-01-21 | 1980-01-21 | |
| US113,509 | 1980-01-21 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1158234A true CA1158234A (en) | 1983-12-06 |
Family
ID=22349858
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000368905A Expired CA1158234A (en) | 1980-01-21 | 1981-01-20 | Low power off centered agitator with partial baffles for buoyant solids mixing drum |
Country Status (9)
| Country | Link |
|---|---|
| JP (1) | JPS56124434A (en) |
| AU (1) | AU533490B2 (en) |
| BE (1) | BE887159A (en) |
| CA (1) | CA1158234A (en) |
| DE (1) | DE3101666A1 (en) |
| FR (1) | FR2473901A1 (en) |
| GB (1) | GB2068247B (en) |
| IT (1) | IT1194733B (en) |
| NL (1) | NL8100294A (en) |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS6331482U (en) * | 1986-08-14 | 1988-03-01 | ||
| US4934828A (en) * | 1989-06-07 | 1990-06-19 | Ciba-Geigy Corporation | Apparatus for mixing viscous materials |
| JPH0537336U (en) * | 1991-10-28 | 1993-05-21 | 佐竹化学機械工業株式会社 | Stirrer |
| JPH0929084A (en) * | 1995-07-21 | 1997-02-04 | Fuji Photo Film Co Ltd | Stirring apparatus |
| FR2850039B1 (en) * | 2003-01-21 | 2006-06-02 | Dietrich Process Systems De | SOLIDARIZED BLADE BREAKER OF THE INTERNAL WALL OF AN ENAMELLED CONTAINER BY LOCAL CONNECTION |
| CN107960399B (en) * | 2017-12-25 | 2023-07-07 | 南京信息工程大学 | Pesticide concentration control system of greenhouse and application |
-
1981
- 1981-01-13 GB GB8100928A patent/GB2068247B/en not_active Expired
- 1981-01-20 FR FR8100962A patent/FR2473901A1/en active Granted
- 1981-01-20 AU AU66349/81A patent/AU533490B2/en not_active Expired - Fee Related
- 1981-01-20 DE DE3101666A patent/DE3101666A1/en not_active Withdrawn
- 1981-01-20 CA CA000368905A patent/CA1158234A/en not_active Expired
- 1981-01-21 JP JP653581A patent/JPS56124434A/en active Pending
- 1981-01-21 BE BE2/58967A patent/BE887159A/en not_active IP Right Cessation
- 1981-01-21 NL NL8100294A patent/NL8100294A/en not_active Application Discontinuation
- 1981-01-21 IT IT19249/81A patent/IT1194733B/en active
Also Published As
| Publication number | Publication date |
|---|---|
| AU533490B2 (en) | 1983-11-24 |
| JPS56124434A (en) | 1981-09-30 |
| IT1194733B (en) | 1988-09-28 |
| GB2068247B (en) | 1983-02-23 |
| FR2473901B3 (en) | 1982-11-19 |
| DE3101666A1 (en) | 1981-11-26 |
| GB2068247A (en) | 1981-08-12 |
| IT8119249A0 (en) | 1981-01-21 |
| BE887159A (en) | 1981-07-22 |
| NL8100294A (en) | 1981-08-17 |
| IT8119249A1 (en) | 1982-07-21 |
| AU6634981A (en) | 1981-07-30 |
| FR2473901A1 (en) | 1981-07-24 |
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