FR2473901A1 - FLUID AND SLUDGE MIXER APPARATUS - Google Patents

Abstract

THE INVENTION RELATES TO A MIXING APPARATUS. THE APPARATUS IS CHARACTERIZED IN THAT IT INCLUDES A CYLINDRICAL TANK 12, AN AGITATOR 14 MOUNTED ON A SHAFT 13 ARRANGED AXIALLY IN THE TANK AND WHOSE AXIS IS RADIALLY OFFSET WITH THE TANK AXIS BY A DISTANCE INCLUDED BETWEEN APPROXIMATELY 110 AND 14 OF THE TANK DIAMETER, THE AGITATOR INCLUDING FOUR BLADES 15 WHICH ARE DISTRIBUTED AT EQUAL ANGULAR INTERVALS AND WHICH ARE PROVIDED WITH AN ANGLE OF 45 STEPS, AT LEAST TWO DEFLECTORS 17 BE FIXED ON THE INSIDE WALL OF TANK 12 WITH A SPACING EQUAL TO 150, TANK DIAMETER. APPLICATION TO THE MANUFACTURING OF ELASTOMERS.

Description

The present invention relates to a mixing apparatus comprising a tank

  mixing machine containing an eccentric stirrer and also preferably using at least two partial deflectors, said vessel being usable in particular, but not to a limited extent, in the particulate sludge mixture

in flotation.

  In general, it is very important to mix efficiently

  Flotation particle sludge is used in many processes, such as in the manufacture of elastomers. In such a process, flotation polymer particles in the form of an aqueous slurry are introduced into a sludge drum operating in the final processing stages and then in the product extruders. The main function of the drum is to train

  a uniform mud and introduce it into the extruders.

  The sludge drum also constitutes an absorption and clogging buffer between the polymerization / final treatment / liquid stages. The mixing of these floating particles is also an important operation during other chemical processes, for example during the dissolution of polymer particles during the treatment of additives for

lubricating oils.

  Systems currently used for mixing such sludge with flotation particles generally include a sludge tank for receiving the sludge and containing means for agitating the sludge, for example, a sludge tank.

  turbine stirring device with one or more blades.

  Theoretically, all systems must produce homogeneous sludge and concentrate in particles, they must prevent an agglomeration of solids in areas of the tank, which could cause an obstruction of the outlets

  of the latter, and there must also be a

  relatively constant concentration of the sludge transferred to the extruders during this variation of the level of sludge in the tank. Depending on the current trend towards energy savings, it is also desirable

  that these systems consume little energy.

  Attempts made in the past to create efficient mixing systems have involved the use of non-sludge tanks. provided with baffles and having a central agitator for producing a central vortex in the vessel. However, these tanks have been found to have various disadvantages, including the requirement to use relatively high mixing speeds, which results in higher than normal energy consumption and particle concentration. between the base of the vortex and the top of the agitator creating this vortex. In known designs of mixers using deflectors, deflectIPrggui have been used to extend vertically along the entire length of the walls of the vessel.

  at spaced locations that also extend radially

  over a distance equal to 1/10 /, us of the diameter of the

  tank. This type of deflector extends over the entire length of

  the vat eliminates vortex formation and when

  turbulence, except / the surface of the liquid is very

  from the upper part of the agitator. Other mixing devices are also known in which baffles are placed on or near the bottom of the tank,

  in the center of the tank, or bierannularly around the agita-

  in the area corresponding to the surface of the liquid.

  A combination of baffles has also been described

  and a central stirrer in a mixing system.

  For example, US Pat. No. 4,150,900 discloses an improved mixing system which uses deflectors.

  and a central stirrer in a mixing tank.

  The partial deflectors described in this patent are

  formed by small triangular or rectangular plates

  which are placed in different positions in the mixing tank. These baffles are fixed on the periphery of the inner vessel surface and they are preferably

  places just below the superficial level of liquid.

  24739a1 In the case of variable-level mixing vessels, fixed partial deflectors in the form of narrow elongated rectangular plates placed in positions adjacent to the cell wall and extending from the maximum liquid level are used. -

  from the bottom of the tank. When deflections are used

  With triangular heads, the dimensions of each of them can be determined by providing a horizontal branch which is between 10 and 15% of the tank diameter and a vertical branch which is between 15 and 20% of the tank diameter. When rectangular deflectors are used, the dimensions of each deflector are chosen so that the sum of the surfaces of the deflectors is equal to

  total area of four deflectors of

  gular. If four rectangular partial deflectors are used, the width of the rectangles in the radial direction should be approximately 2% or 1/50

the diameter of the tank.

  In the article The Suspension of Floating Solids in Stirred Vessels, G. E. H. Joosten et al., Trans. Chem.E.55,

  (July 22, 1977), a number of experiments have been described

  those that were made using deflection vessels

  and without deflectors equipped with a central stirrer

  to determine their influence on the formation of suspen-

  particles in flotation in a liquid. It has been found that the optimum flow regime for suspending floating particles is to rapidly rotate the liquid while disrupting its rotation with a single baffle having a width equal to 0.2 times the diameter. of the container, this deflector being immersed, from the upper surface / lquide, to a depth times equal to 0, 3 / the diameter of the containers

  The present invention relates to a mixing apparatus

  comprising a cylindrical vessel provided with a blade-fan and down-pump agitator device, the agitator shaft being radially offset from the central axis of the vessel a distance

24739'01

  between about 1/10 and 1/4 of the vessel diameter.

  Using such an eccentric stirrer, it has been found that efficient mixing of floating particle sludge can be achieved while achieving energy savings of about 38% compared to agitators arranged

in the center or axially.

  The apparatus is also equipped with at least two partial deflectors, preferably four partial deflectors, distributed at equal intervals on the inner periphery of the vessel. Such partial deflectors

  consist of vertical elements of rectangular shape

  or triangular which are fixed on the inner wall of the tank and which extend essentially from the bottom of this tank toThe maximum height of sludge in the latter, each deflector having a radial width which

  is between 1/36 and 1/100 of the tank diameter.

  It is particularly advantageous to provide four deflections

  Rectangular shaped partial members, which are distributed at equal intervals and have a radial width corresponding to about 1/50 of the vessel diameter. Such a set of partial deflectors makes it possible to obtain, in cooperation with an off-center down-pump, homogenous particles which are homogeneous and whose characteristics are not appreciably modified during variations in the level of sludge in the tank. Also such an apparatus makes it possible to establish an excellent dispersion and good contact between systems such as for example immiscible liquids, gases and liquids as well as gases and sludges. Other advantages and characteristics of the invention

  will be highlighted in the following description,

  given by way of nonlimiting example, with reference to the accompanying drawings in which: Fig.1 and 2 are respectively a side view and a plan view of a preferred embodiment of a mixing apparatus according to the invention, comprising an eccentric stirrer and four partial deflectors distributed at equal intervals;

24? 79'01

  Fig. 3 is a plan view of a mixing apparatus not equipped with baffles and having an eccentric stirrer, a series of deflector positions being indicated by

  numerical references on the circumference of the tank.

  In FIGS. 1 and 2, there is shown a preferred embodiment of a mixer device 11 that complies with

  to the invention, which comprises a cylindrical vessel 12.

  An agitator shaft 13 is axially disposed in the vessel and is offset from the axis of the latter, as indicated by the dashed lines, with a distance d of between about 1/10 and 1/4 the diameter of the tank. The upper part of the feeder 13 is connected to a rotational drive means

  (not shown), such as an electric motor.

  An agitator assembly 14, mounted at the center of the shaft, generally represented as having four downwardly pumped turbine blades, distributed at equal intervals, inclined at an angle of 45c as indicated and placed in positions adjacent to the bottom 19 of the tank. The lower part 13a of the agitator shaft can be fully supported in the bottom 19 of the tank with a permanent action bearing. The liquid 16 in the tank

  can be maintained at a constant or variable level.

  Four partial deflectors 17 of rectangular shape are provided.

  gular, distributed at intervals of 900 around the inner wall of the tank and each comprising a thin and elongated element of rectangular shape which is made of a metal, this element extending for example from the maximum height of the tank up to at a point just adjacent to the bottom of the latter. Each deflector 17 is fixed on the inner wall of the tank using two brackets 18 or other conventional means of assembly which are placed respectively at the top and bottom of each baffle. The radial width of each deflector 17 is between about 1/36 and 1/100 of the width of the tank and is

  preferably about 1/50 of the width of the tank.

  The baffles are spaced from the wall a distance

  corresponding to approximately 1/50 of the width of the tank.

  The diameter of the agitator assembly 14 is between

  about 1/3 and half the diameter of the tank.

  Figure 3 is a plan view of a sludge tank

  12 containing an eccentric stirrer 13 and it also indicates

  sixteen possible locations, spaced

  others of 22.5, positioning one or more

  in accordance with the present invention. These positions will be described in more detail with reference to

examples that will follow.

  It has been found experimentally that the use of an eccentric stirrer in a tank such as that described above to form sludge particles in flotation made it possible to obtain outgoing sludge concentrations that are much greater than those of tanks equipped with a tank. central agitator. However, the use of the invention is not limited to flotation particle sludge mixing processes and is generally applicable, as mentioned above, to immiscible liquids or mixtures of gases and liquids or mixtures of gases and sludges. Furthermore, by using the off-center stirrer according to the invention, in place of a centered stirrer, the same degree of mixing can be obtained by adopting lower extreme peripheral speeds and consequently consuming less energy. This energy saving can be 50 to 80%, compared to multi-turbine central stirrers / and tanks with full-length baffles, and can also be as high as 38% in the case

single-turbine agitators.

  By using at least two partial deflectors which are spaced at equal intervals and which cooperate with an off-center stirrer, the mixing efficiency is further improved. By using four partial deflectors distributed at equal intervals, an optimal mixing efficiency is obtained and the variations in the outgoing mud concentration are relatively low when the level

mud increases.

  It has also been found that the radial width of

  deflector is a parameter with a significant influence

  on the efficiency of the mixer of the invention.

  For widths between about 1/36 and 1/100 of the tank diameter, and preferably 1/50 of the diameter

  of the tank, concentrated and homogeneous sludge was obtained.

  For widths much greater and well below the aforementioned ranges, the mud has been obtained for

unsatisfactory characteristics.

  In the mixing apparatus according to the invention,

  triangular deflectors can be used in the same way

  res, provided that they have surfaces of equivalent extent to those of the partial deflectors

rectangular described above.

  To further define the present invention, examples have been given below which, however, have not been

  no limiting influence on the invention.

EXAMPLE 1

  In this example, and in the following examples, a 0.9 m diameter vessel with a flat bottom consisting of Plexiglas and a height of 1.8 m was used. A turbine with a diameter of 0.3 m was fitted with four blades with a width of 54 mm, inclined by 450 and downwardly pumping, on a shaft of agitator oriented vertically and offset with respect to the axis of the

  tank with a distance of 90 mm (1/10 of the tank diameter).

  An electric motor with a power of 3 hp was used to drive the agitator, which could drive the agitator in rotation by means of a variable speed drive at speeds of up to 260 tons / hour. min. The agitator shaft was supported on the bottom of the vessel via a fixed bearing. Four deflectors, each having a width equal to 1/50 of the tank diameter, were distributed at equal intervals over the inner periphery of the tank, spacing them from the tank wall by a distance equal to 1/50 of the diameter. of

  tank. This arrangement is shown in FIGS. 1 and 2.

  A torque transducer has been incorporated in the shaft

  Vibrac TQ-5120 (range 0-3.6 m.kg) for torque measurement.

  The TQ-5120 has also been equipped with a magnetic speed transducer producing 60 pulses per shaft revolution. This value has been translated in revolutions per minute using a frequency counter. A sludge outlet, placed 127 mm above the bottom of the tank, was connected to the inlet of a pump using a 25mm diameter pipe. The outlet of the pump was connected to the vessel so as to establish a recycling loop. In all the examples, we used

  a sludge containing 4% by weight of polyproton granules

  3.2 mm pylene in water. The concentration was measured

  outgoing sludge by taking samples from the recycling loop leading to the

  tank. Granules of each sample were filtered and -

  we weighed them and in addition we measured the volume of water for

  determine the concentration of the outflow.

  In this example, a comparison of the mixing characteristics between the off-center stirrer and a centered stirrer used in the same vessel and having the same pitch and the same blade width as the off-center stirrer was performed. Both speeds of 200 and 225 rpm were adopted for both types of agitators. Outlet sludge concentrations for both agitators were determined by the apparent percent concentration for different sludge levels in the tank, measured

  by the percentage (%) of the total height of the tank.

  The results are given in Table 1 below.

TABLE 1

  Sludge Level EXTRUDING SLUDGE CONCENTRATION (% of% of Apparent Concentration Height) (% Aggregate Stirrer Total Offset Height) Centered Speed (RPM2 Speed (RPM)

225 - 200 225

48 56.1 65.6 71.3 74.2

98 37.9 50.3 58.0 61.8

Z473901

  As shown in Table 1, the off-center agitator yielded higher outflow sludge concentrations for each sludge level than those obtained.

  with the agitator centered. In addition, the variation in

  outflow sludge concentration for sludge level variation was lower for the off-axis agitator than for

the agitator centered.

  The stirrer rates necessary to establish an outflow sludge concentration of 60% of the apparent concentration were then determined for both the centrally and eccentric agitators. It was found that in order to achieve the same degree of mixing, the off-center agitator had to be rotated at lower speeds than the centric agitator. The difference between these

  speeds decreased as the level of sludge increased.

  For the tank design described above, the maximum sludge level was 93%, which corresponds to a 14% reduction in speed between the off-center agitator and the centered agitator. This saves money

about 38% energy.

EXAMPLE 2

  In this example, the outflow sludge concentration, as measured by the percent of apparent concentration, was determined for a mud level of 83%, using the vessel and all baffles described in Example 1 except that an agitator assembly having a blade impeller of 38 cm in diameter was used, the agitator shaft being offset by a distance equal to 0.225 times the vessel diameter. The agitator was fitted with speeds of 125 and 150 rpm. Table 2 gives a

summary of results.

TABLE 2

  AGITATOR SPEED CONCENTRATION OF OUTGOING MUD

  (rpm) (% apparent concentration)

66

76

  As shown in Table 2, high concentrations were obtained for the outgoing sludge for each of the speeds using an off-center stirrer a distance

  corresponding approximately to 1/4 of the tank diameter.

EXAMPLE 3

  In this example, a series of four

  partial deflectors spaced at equal intervals, as indicated

  1, around the inner wall of the tank in the following positions shown in Figure 3: Series A - Positions 1, 5, 9 and 13 Series B - Positions 2, 6, 10 and 14 Series C - Positions 3.7, 11 and 15 Series D - positions 4.8, 12 and 16 In each series, the deflector width was varied giving it values of 1/36, 1/50 and 1/100 of the diameter respectively vat, that is to say 9 mm, 18 mm and 25 mm. The eccentric stirrer was rotated at speeds of 200 and 225 rpm. For each deflector width of each series, the concentrations of the outgoing sludge as measured by the apparent concentration percentage were determined. The level of mud has been

  100% of the total tank height. Table 3 below

  after gives the condensed results.

  As shown in Table 3, deflection widths

  from 1/36 to 1/100 of the tank diameter have made it possible, in cooperation with an eccentric stirrer, to obtain

  effective mixing. However, it is particularly

  In order to provide the deflector with a width corresponding to 1/50 of the tank diameter, this value gives higher concentrations of the outgoing sludge at the speeds used. The positions of the deflectors did not vary the concentrations of the outgoing sludge

in important proportions.

EXAMPLE 4

  In this example, the influence of the level of the

  mud on the concentration at the outlet using respectively

  two, four partial deflectors with an eccentric stirrer, as shown in Figure 1,

247390 1

  1 1 these deflectors having a radial width equal to 1/50 of the vessel diameter. For each baffle arrangement, the sludge level was respectively raised to 28%, 46% and 100% of the total vessel height and the concentrations of the outgoing sludge were measured for stirrer speeds. 200 and 225 rpm. Table 4 gives

a summary of the results.

  With two baffles, the concentration of the outgoing sludge has increased from about 20% up to 90% of the apparent concentration when the sludge level has risen from about 30% to 100%. With four baffles, the concentration of outgoing sludge decreased by approximately 60% for the same range of mud levels. This shows that a four-baffle assembly is preferable to a two-baffle assembly for floating-particle sludges because of the relatively small variation in the concentration of the outgoing sludge at a time.

  variation of its level in the tank.

TABLE 3

  apparent concentration using four Series A Series B Series D series D Series B Speed deflector deflector width deflector width deflec deflec rpm (mm) (mm) tor (mm) tor (mm)

9 18 25 9 18 25 9 18 25 9 18 25

  225 37.0 54.8 22.3 46.8 65.3 32.5 46.0 58.8 24.0 45.8 61.8 37.0

  260 49.5 71.3 45.8 49.8 56.0 52.8 p1.8 64.5 41.0 51.8 61.0 46.3

TABLE 4

  Concentration of the outgoing sludge (% of apparent concentration) velocity of a- 2 deflectors 4 deflectors sludge level sludge (% of height sludge level (% of total tank height) total rpm of tank)

28 46 100 28 46 100

19.5 41.8 72.3 74.5 71.3 58.0

225 35.5 89.0. 74.3 61.8

  Concentration of outgoing sludge, expressed as the percentage of NI ru o at

Claims (9)

  Mixing apparatus, characterized in that it comprises: (a) a cylindrical vessel (12); (b) an agitator shaft (13) rotatably mounted in said vessel and radially offset from the vessel axis by a distance of about 1/10 to 1/4 of the vessel diameter; (c) a blade turbine assembly (14) mounted centrally of said shaft (13); (d) at least two deflectors (17) mounted on the   inner wall of said vessel (12).   2. Mixing device according to claim 1, characterized in that said deflectors (17) have a radial width of between approximately 1/36 and 1/100 of the bowl diameter.   Mixing device according to claim 2, characterized in that said deflectors comprise   rectangular elements having a radial width correspon-   at about 1/50 of the tank diameter.   4. Mixing apparatus according to any one   Claims 1 to 3, characterized in that each   deflector (17) is spaced from the inner wall of the vessel   (12) a distance equal to 1/50 of the vessel diameter.   ang rr 5. Apparatus / eon any of the   Claims 1 to 4, characterized in that it comprises   four deflectors 17 spaced at equal intervals.   6. Mixing apparatus according to any one of   Claims 1 to 5, characterized in that the tank   (12) is arranged to receive sludge (16) to a predetermined level in said tank and in that said baffles (17) extend substantially from the bottom   (19) of the tank to said predetermined level.   7.Mixing apparatus according to any one   Claims 1 to 6, characterized in that it is   provided four spaced rectangular deflectors (17) of equal intervals.   8. Apparatus according to any one of   Claims 1 to 7, characterized in that said set   The blade turbine comprises four blades (15) with downward pumping, distributed at equal intervals / each having a pitch angle of 450. 9. Mixing device according to one   any of claims 1, 2 and 4 to 7, characterized in that   each of said deflectors (17) has a triangular shape.