JP4761216B2 - Two-stage coagulation mixing tank - Google Patents

Description

  This invention is a two-stage type in which two sets of stirring blades having different shapes are arranged in two stages in the agglomeration mixing tank, and the floc is granulated by rapidly stirring and slowly stirring the slurry to which the flocculant has been added. The present invention relates to an improvement of the coagulation mixing tank.

Conventionally, when a slurry is concentrated or dehydrated or pressurized and dehydrated using a screw press or a belt press, a polymer flocculant or an inorganic flocculant is supplied to the slurry as a pretreatment operation, and the mixture is stirred and mixed in a flocculent mixing tank. It is well known to granulate. Then, a flat plate-shaped radial blade and a flat plate-shaped swept blade fixed to the disc base are arranged in two stages on the rotating shaft hanging down in the cylindrical processing tank, and agglomerated slurry is supplied from the tank bottom to granulate. The agglomeration reaction apparatus is known, for example, as described in Patent Document 1. In addition, a stirring shaft is suspended in a cylindrical solid-liquid separation tank, a turbine blade is fixed to the tip of a disk fixed to the stirring shaft, and a cross-shaped or grid-shaped paddle is attached to the stirring shaft suspended in the solid-liquid separation tank. A solid-liquid separation device that fixes a stirring blade and granulates and separates a suspension is also known, for example, as described in Patent Document 2.
Japanese Patent No. 3146371 (paragraph number 0006 and paragraph number 0007, FIG. 3) Japanese Patent No. 3368978 (paragraph number 0010 and paragraph number 0020, FIGS. 1 and 2)

  Conventionally, screw presses and belt presses for the purpose of press dewatering need to granulate the slurry into flocs suitable for dewatering. The conventional two-stage agglomeration and mixing tank for granulating floc requires a long residence time, increases the tank capacity, and increases the equipment cost. Moreover, in order to raise the stirring effect, the stirring blade matched with the tank internal diameter is required, and a stirring blade becomes large, so that a two-stage type coagulation mixing tank becomes large. The stirring power varies greatly depending on the size of the blades and the number of rotations. In particular, the size of the blades greatly affects the stirring power. Since the flowing slurry constantly changes in flow rate and viscosity, it is necessary to change the number of rotations in order to obtain an optimal aggregation state. The conventional agglomeration reaction apparatus described in Patent Document 1 is capable of granulating a good agglomeration floc with flat receding blades and flat radial blades suspended from a disk, and does not cause a short circuit in the swirling circulation flow. Although it is possible to increase the size of the tank, it is difficult to select the optimal coagulation state speed for the pair of stirring blades fixed to the same rotating shaft, depending on the constantly changing slurry flow velocity and viscosity. It will also be difficult. In the case of sewage slurry containing a large amount of fiber, the tip protruding in the circumferential direction from the disk base may be entangled with a curved flat-plate receding blade.

  In the agglomeration reaction apparatus described in Patent Document 2, the paddle stirring blade and the turbine blade can be stirred at different rotational speeds, and the liquid to be treated can be dispersed by the turbine blade, and a large volume treatment can be performed by the paddle stirring blade. However, the volume of the cylindrical solid-liquid separation tank becomes larger than necessary. When the cylindrical agglomeration mixing tank is enlarged, the swirl circulation flow is short-circuited at the stirring portion of the turbine blade, and floc granulation may be uneven. In a sewage slurry containing a large amount of fiber, the fiber may get tangled with the turbine blade fixed to the disk. The present invention divides the agglomeration mixing tank into a rapid stirring part and a slow stirring part, combines a rapid stirring blade and a slow stirring blade, devise a stirring means to granulate a good floc, and simultaneously a two-stage agglomeration It is intended to reduce the coagulation volume of the mixing tank.

The agglomeration reaction apparatus according to the present invention is a flocculation apparatus in which stirring blades are arranged in two stages in the agglomeration mixing tank, and the slurry to which the aggregating agent is added is fed in an upward flow to be stirred and mixed. divided into slow agitation of rapid stirring portion and the upper half of the halves, rapid stirring unit cylinder inner diameter and a slow stirring section smaller than the trunk inside diameter of the one side to the upright rapidly stirring unit drive shaft Protruding rapid stirrer blades are installed, and a flat slow stirrer blade is placed on the drive shaft suspended from the slow stirrer. The quick stirrer blades are arranged radially on the surface of the rotating plate. It is composed of a turbine blade with a tip corner cut out on a circular arc, and a slow stirring blade is composed of a flat paddle blade. If the diameter is smaller than the inner diameter of the stirrer, the agglomeration volume of the rapid agitation part of the agglomeration mixing tank can be reduced, and the size of the agitation blade can be reduced. Also of change it becomes easy. And since the rapid stirring part and the slow stirring part are united, there is no need for connecting piping, and the coagulation mixing tank can be made compact. And the blade height of the blade plate forming the rapid stirring blade is narrowed in the direction in which the centrifugal force is generated, or it is notched, so even if the slurry contains many fibers, the blade is not entangled and the stirring blade rotates rapidly. Can be made. Since there is no entanglement of the fibers, an uneven load is not applied to the drive shaft, and stable operation is possible.

  The agglomeration mixing tank divided into a small-diameter rapid stirring part and a large-diameter slow stirring part has a volume ratio of the rapid stirring part to the slow stirring part of 1: 3 to 1:20. A small volume of slurry that has flowed into the tank is stirred and mixed by rapid stirring, the internal rotation of the rapid stirring section is decelerated by the slow stirring section with a large volume, and a turbulent flow is caused by the differential speed effect to generate an appropriate floc. Can be granulated. The volume ratio between the rapid stirring unit and the slow stirring unit can be set according to the amount of slurry processed.

The supply port and discharge port of the agglomeration mixing tank have a supply port for the stock solution provided on the peripheral wall of the rapid stirring unit opened in the vicinity of the tip of the turbine blade and a discharge port opened on the upper peripheral wall of the slow stirring unit in, since the flow in the vicinity of the distal end portion of the strong stirring blade most stirring force the slurry was added a coagulant, Ru enhances mixing efficiency by flowing smoothly giving centrifugal force to the slurry.

The peripheral speed of the stirring blade disposed in the mixing flocculation tank, the outer periphery speed of turbines piece wings rapid stirring unit as 100 to 300 m / min, the outer peripheral speed of the paddle blades of slow stirring unit and 10 to 100 m / min in which the, for turbines piece blade and paddle blade is driven separately, depending on the flow rate and viscosity which changes constantly slurry, it is possible to obtain an optimal aggregation state and set the appropriate speed.

The slurry and flocculant are supplied to the agglomeration and mixing tank, and the residence time of the slurry to be agitated, mixed and granulated is 0.5 to 4 minutes. By combining slow stirring in the fast stirring section, the residence time of the slurry can be shortened and the agglomeration effect can be enhanced . Each external dimensions of turbines piece blade and paddle blades, if 60% to 90% of the tank inner diameter of rapid stirring portion and slow stirring unit, the strongest to a slurry of rapid stirring of small capacity with the addition of flocculant It is arranged to give stirring power, and the large-capacity slow stirring section where slurry is likely to stay is moved near the inner peripheral wall, and uniform stirring and mixing is performed throughout the tank. Can be greatly shortened.

The two-stage agglomeration mixing tank according to the present invention is configured as described above, and if the appropriate number of rotations of the stirring blade of the small volume rapid stirring unit and the stirring blade of the large capacity slow stirring unit is set, The residence time of the slurry can be shortened to increase the mixing efficiency due to the differential speed effect, and the optimum floc can be granulated. Since the rapid stirring unit and slow stirring unit are integrated, it becomes a compact agglomeration and mixing tank, and even in the slurry containing fibers, there is no entanglement of fibers in the rapid stirring blade, and there is no uneven load on the drive shaft even during rapid rotation. stable operation in is performed. Larger agglomeration and mixing tanks and large capacity treatment are also possible.

  The two-stage agglomeration mixing tank according to the present invention will be described in detail with reference to the drawings. First, FIG. 1 is a flowchart of the two-stage agglomeration mixing tank according to the present invention. The lower half of the rapid stirring section 3 provided with the blades 2 and the upper half of the slow stirring section 5 provided with the flat plate-like slow stirring blades 4 are divided so that the inner diameter of the quick stirring section 3 is reduced. The diameter is smaller than the inner diameter of the fast stirring portion 5. If the cylinder inner diameter of the rapid stirring unit 3 is smaller than the cylinder inner diameter of the slow stirring unit 5, the aggregate volume of the rapid stirring unit 3 can be reduced, and the size of the rapid stirring blade 2 can be easily changed. Since the rapid stirring unit 3 and the slow stirring unit 5 are integrated, there is no need for a connecting pipe, and the compact coagulation mixing tank 1 is obtained. The chemical solution supply pipe 6 is connected to the stock solution supply pipe 7 connected to the rapid stirring section 3, and the slurry and the flocculant are supplied to the rapid stirring section 3, and the agglomerated slurry stirred and mixed in the flocculation mixing tank 1 is the slow stirring section. Supplied to a screw press 9 from a discharge pipe 8 connected to 5.

  FIG. 2 is a longitudinal sectional view of the flocculation mixing tank. A rapid stirring motor 12 is suspended from a drive base 11 connected to a tail plate 10 at the lower end of the flocculation mixing tank 1, so The rapid stirring blade 2 is fixed to a drive shaft 13 suspended from the stirring unit 3. A slow agitation motor 16 is mounted on a driving machine base 15 connected to a cover plate 14 at the upper end of the agglomeration mixing tank 1, and a slow speed is applied to a drive shaft 17 suspended from the slow agitation unit 5 of the agglomeration mixing tank 1. A paddle blade 4 a is fixed as the stirring blade 4. A supply port 7 a on the peripheral wall of the rapid stirring unit 3 connected to the stock solution supply pipe 7 is opened in the vicinity of the protruding tip of the rapid stirring blade 2, and a discharge port 8 a connected to the discharge pipe 8 is connected to the slow stirring unit 5. Opened in the upper peripheral wall. While applying centrifugal force to the slurry flowing into the projecting tip of the rapid stirring blade 2, the flow rate of the slurry is increased, and the rotation of the slurry in the tank in the rapid stirring portion 3 is decelerated by the paddle blade 4 a of the slow stirring portion 5. In addition, the slurry and the flocculant can be uniformly stirred and mixed to be agglomerated in a short residence time. The stock solution supply pipe 7 and the discharge pipe 8 may be connected to the agglomeration mixing tank 1 in a tangential manner or in a cross shape.

FIG. 3 is an external view of the rapid stirring blade. The single-sided rapid stirring blade 2 interlocked with the rapid stirring motor 12 has a plurality of blade plates 23 on the surface of a disk-shaped rotating plate 22. A turbine wing 24 is formed by suspending radially and having a tip corner 23a cut out in an arc shape. A connecting pipe 19 connected to the drive shaft 13 is fitted in the center of the rotating plate 22 . Since centrifugal force blade height of vane 2 3 forming the turbines piece blade 24 is notched in a circular arc shape on the outer circumferential direction generated, it is with entanglement of the fibers in the turbines piece wing 24 in a slurry containing much fiber It can be rapidly rotated. Since there is no with entangled fibers, without even by rapidly rotating the turbines piece wings 24 offset load exerted on the drive shaft, thereby enabling stable operation.

  The agglomeration mixing tank 1 shown in FIG. 2 has a volume ratio of the rapid stirring section 3 and the slow stirring section 5 to be divided approximately 1 to 3 to 20, and the volume ratio is set according to the amount of slurry processed or the properties of the slurry. To do. The small volume rapid stirring section 3 The slurry flowing into the coagulation mixing tank 1 is rapidly stirred by the rapid stirring blade 2, decelerated by the large volume slow stirring section 5, and granulated to an appropriate floc. By combining the rapid stirring in the small volume rapid stirring unit 3 and the slow stirring in the large volume slow stirring unit 5, the retention time of the slurry is shortened to increase the agglomeration effect. Since the residence time can be shortened, the residence time of the slurry in the coagulation mixing tank 1 is set to 0.5 to 4 minutes.

Stirring speed of the stirring blade to be arranged rapidly stirring portion 3 and the slow stirring part 5 of the mixing flocculation tank 1 shown in FIG. 2, the outer peripheral speed of the turbines piece blade 24 rapidly stirring blade 2 as 100 to 300 m / min The outer peripheral speed of the paddle blade 4a of the slow stirring unit 5 is 10 to 100 m / min. The in-tank rotation in the rapid stirring unit 3 can be decelerated by the slow stirring unit 5, and turbulent flow can be caused by the differential speed effect to granulate appropriate flocs . For turbines piece wings 24 and paddle blade 4a is driven separately, with respect to variations in seasonal variations and sludge properties, depending on the flow rate and viscosity of the constantly changing slurry, by setting each of the appropriate number of revolutions, An optimal aggregation state can be obtained . Each external dimensions of turbines piece wings 24 and paddle blade 4a, is obtained by 60 to 90% of the vessel internal diameter of rapid stirring portion 3 and the slow stirring part 5, rapid stirring of small capacity with the addition of flocculant It becomes the arrangement that gives the strongest stirring force to the slurry of the part 3, the movement near the inner peripheral wall of the large-capacity slow stirring part 5 in which the slurry tends to stay is also performed, and uniform stirring and mixing throughout the tank is performed. The residence time in the flocculation mixing tank 1 can be greatly shortened.

  The conventional single-stage flocculation mixing tank was compared with a line insertion type high-speed stirrer (hereinafter referred to as a line mixer), and the advantages and disadvantages of each were compared and examined. In the conventional single-stage flocculation / mixing tank, a residence time of 4 minutes or more is required to stir and mix the slurry and the polymer flocculant, and a long residence time is required, so the capacity of the flocculation / mixing tank increases. The stirring blades of the single stage agglomeration mixing tank are low-speed stirring, and if the blades are small, the mixing efficiency of the slurry and the polymer flocculant is poor and cannot be sufficiently mixed. In order to increase the stirring effect, a stirring blade that matches the inner diameter of the coagulation mixing tank is required, and the stirring blade is enlarged. Normally, the appropriate outer diameter of the blade is based on about 80 to 85% of the inner diameter of the tank, and the larger the tank, the larger the outer diameter of the blade. The stirring power varies greatly depending on the blade size and the rotational speed, and the influence of the blade size is particularly large. The stirring power is also influenced by the viscosity of the fluid, and in order to obtain an optimal aggregation state, it is necessary to change the rotational speed in accordance with the viscosity of the changing liquid. Since the power calculation is performed in the state of the maximum viscosity and the maximum rotation speed in the use range, the safety factor is increased and the power setting is useless. The proper rotation speed of the agglomeration mixing tank is based on the outer peripheral speed of the stirring blade of about 110 m / min. When the capacity of the agglomeration mixing tank is 500 liters, the blade outer diameter is 600 mm, and the rotation speed is about 60 rpm. .

  On the other hand, the conventional line mixer provided with baffle blades has a stirring effect due to the flow velocity of the fluid flowing into the pipe. The flow rate flowing into the pipe constantly changes, and the stirring of the slurry and the flocculant has a defect that sufficient stirring force cannot be obtained only by the flow rate. The line mixer may have a residence time of 10% or less of that of a single-stage coagulation mixing tank for a dehydrator, and has a merit that the baffle blades are small. If the blades are rotated, the line mixer has a small tank capacity. In the case of 50 liters, the blade outer diameter is 290 mm, and the rotational speed may be 120 rpm. Accordingly, the rotation speed of the blades of the line mixer is about twice that of the coagulation mixing tank. The size of the stirring blade is twice as large as the diameter of the line mixer and 6 times as large as the width of the line mixer, and the required power is 3.5 to 4 times that of the line mixer. In the pressure dehydrator, the flocculent state of the slurry requires a strong flock, and therefore, it is necessary to supply the slurry that is sufficiently granulated by stirring and mixing the slurry and the polymer flocculant. In a single-stage agglomeration and mixing tank, since mixing and granulation are performed in the same tank, a long stirring time and a large stirring blade suitable for the tank size are required. On the other hand, since the line mixer is intended for mixing, a smaller volume is easier to mix. For this reason, there is an advantage that the blade diameter can be reduced and the power can be reduced.

Considering the characteristics of the conventional single-stage flocculation mixing tank and line mixer, combining the rapid stirring section and slow-speed stirring section in the flocculation mixing tank, mixing and feeding position of the slurry in the two-stage flocculation mixing tank, and the blade structure The stirring power was examined. First, the mixing input position of the slurry added with the polymer flocculant is
a. If the slurry charging position is close to the rotation trajectory of the tip of the stirring blade, the position where the stirring force is strongest is obtained, and the mixing efficiency can be increased. Next, the blade structure and stirring force for stirring and mixing are as follows:
b. The prevention of fiber entanglement is an important factor. In a slurry with many fibers, entanglement is quick and stable continuous operation is not possible even in a short time. The stirring force is determined based on a blade peripheral speed of about 110 m / min in order to improve the mixing rate and floc strength in the dehydrator. For example, considering a 500 liter single-stage agglomeration mixing tank, if the outer diameter of the blade is 80% of the inner diameter of the tank, the rotational speed is about 60 rpm, and in order to have this function in a 50 liter mixing device, 120 rpm is required. I need it.
c. Since the stirring blade for rapid stirring can be made small, the agglomeration volume of the stirring chamber can also be reduced. If the slurry in the coagulation mixing tank is stirred and mixed by rapid stirring, it can be applied to a wide range of slurry throughput by changing the stirring force of the stirring blade.
Therefore, it was decided that the peripheral speed of the agitating blade was set to 100 to 300 m / min so that the drive could be changed by an inverter.

  Based on the results of the considerations of the mixing and feeding position of the slurry, the blade structure, and the stirring force in the single-stage coagulation mixing tank, the rapid stirring section applying the line mixer and the slow stirring applying the single-stage coagulation mixing tank We decided to join the department. After rapidly stirring the polymer flocculant and slurry in the rapid stirring part, if slowly flowing in the slow stirring part, supply the slurry in which a strong floc is generated by the differential speed effect to the pressure dehydrator, Realization of high pressure dehydration can be predicted. In order to obtain actual measurement data, the two-stage agglomeration mixing tank divided into an 8 liter rapid stirring section and a 92 liter slow stirring section as the flow chart flocculation mixing tank shown in FIG. A liter single stage agglomeration mixing tank was used. First, sewage mixed raw sludge is used as a target stock solution, and a slurry with a stock solution concentration of 2.0% and a polymer flocculant with an injection rate of 1.1% are respectively supplied to a single-stage agglomeration and mixing tank. The mixture was agitated and granulated with a residence time of 0.8 to 1.6 min. Agglomerated slurries under the same operating conditions as the stock solution concentration and the polymer flocculant injection rate were pumped to a screw press, and the difference in filtration rate was investigated when the water content of the dewatered cake was varied from approximately 76% to 81%. Table 1 shows a comparison of the screw press capacity for the sewage mixed raw sludge flocculated slurry in the two-stage flocculation mixing tank and the single-stage flocculation mixing tank.

  Table 2 is a sewage mixture with the horizontal axis representing cake moisture (%) and the vertical axis representing filtration rate (kg / h), based on the measured data of the single-stage agglomeration and mixing tanks in Table 1. It is a relationship figure of the cake water-treatment amount of the screw press with respect to sludge.

  In addition, a verification test was conducted using sewage digested sludge as the target stock solution. A slurry having a stock solution concentration of 1.7% and a polymer flocculant having an injection rate of 1.7% are respectively supplied to a single-stage agglomeration and mixing tank and a residence time of 1.7 to 5.4 min. The mixture was stirred and granulated. The agglomerated slurry was supplied to a screw press, and the difference in filtration rate when the water content of the dewatered cake was varied from approximately 82% to 86% was investigated. The resulting screw press capacity comparison is shown in Table 3.

  Table 4 shows sewage digestion sludge with the horizontal axis representing cake moisture (%) and the vertical axis representing filtration rate (kg / h) based on the measured data of the single-stage coagulation and mixing tanks in Table 3. It is a relationship figure of the cake water-treatment amount of the screw press with respect to.

  Table 5 shows the same cake moisture in the single-stage flocculation mixing tank and the single-stage flocculation mixing tank, by extracting the filtration rate of the mixed raw sludge with the equivalent cake moisture of the screw press from the graph of the capacity comparison in Table 1 and Table 2. It is the table | surface which compared the processing amount with respect to intelligibly.

  From the experimental results, in the mixed raw sludge based on the verification data in Table 1, as shown in Table 5, when the cake moisture is 78%, the filtration rate is 83.0 kg / h in the single-stage coagulation mixing tank, and the two-stage coagulation mixing tank. Has a filtration rate of 98.6 kg / h, and the throughput of the screw press for the agglomerated slurry in the two-stage agglomeration mixing tank is 15.6 kg / h higher. When the cake moisture is 79.5%, the filtration rate of the single-stage flocculation mixing tank is 117.7 kg / h, and the filtration speed of the two-stage flocculation mixing tank is 148.5 kg / h. The amount of the coagulated slurry in the mixing tank is 30.8 kg / h higher. That is, it can be seen that the higher the cake moisture, the greater the difference in the amount of processing of the screw press with respect to the agglomerated slurry in the single-stage agglomeration and mixing tank.

  Table 6 extracts the digestion sludge filtration rate for the equivalent cake moisture of the screw press from the graph of the performance comparison of Table 3 and Table 4, and for the same cake moisture in the single stage coagulation and mixing tank. It is the table | surface which compared the processing amount easily.

  In the digested sludge based on the verification data in Table 3, as shown in Table 6, when the cake moisture is 83%, the filtration rate of the single-stage coagulation mixing tank is 16.0 kg / h, and the filtration speed of the two-stage coagulation mixing tank is 25. The throughput is 9.1 kg / h more in the two-stage agglomeration mixing tank. When the cake moisture is 84.5%, the filtration rate of the single-stage agglomeration tank is 28.7 kg / h, and the filtration speed of the two-stage agglomeration tank is 37.2 kg / h. The processing amount is 8.5 kg / h higher. That is, in digested sludge, it can be judged from the measured data that the amount of processing of the screw press with respect to the agglomerated slurry in the two-stage agglomeration mixing tank is large regardless of the cake moisture.

  The two-stage flocculation / mixing tank according to the present invention is a compact flocculation / mixing tank because the rapid stirring section and the slow stirring section are integrated. There is no entanglement of fibers in the stirring blade, stable operation is performed even with rapid stirring, and the agglomeration mixing tank can be increased in size and processed in a large volume. And by setting the appropriate number of rotations of the stirring blades of the small volume rapid stirring section and the large capacity slow stirring section, the mixing efficiency is increased due to the differential speed effect, and the slurry residence time in the two-stage coagulation mixing tank Is shortened, and an optimal floc can be granulated. Therefore, it becomes suitable for the coagulation mixing tank installed in the front | former stage of the screw press and belt press which require a high pressure pressing and a large capacity process.

It is a flowchart of the two-stage type coagulation mixing tank which concerns on this invention. Similarly, it is a principal part enlarged view of the longitudinal cross-sectional view of a two-stage-type agglomeration mixing tank. Similarly, it is an external view of a rapid stirring blade .

DESCRIPTION OF SYMBOLS 1 Agglomeration mixing tank 2 Rapid stirring blade 3 Rapid stirring part 4 Slow stirring blade 4a Paddle blade 5 Slow stirring part 7a Supply port 8a Discharge port 13, 17 Drive shaft
22 Rotating plate
23 slats
23a Tip corner 24 Turbine single blade

Claims (6)

In the agglomeration apparatus in which the stirring blades are arranged in two stages in the agglomeration and mixing tank and the slurry added with the aggregating agent is supplied in an upward flow and stirred and mixed, the agglomeration and mixing tank (1) is a rapid stirring part in the lower half. (3) and divided slow agitation portion of the upper half (5), and a smaller diameter than the cylinder inside diameter of the slow agitation portion cylinder inner diameter of the stirred rapidly section (3) (5), rapid stirring portion (3 ) Is provided with a rapid stirring blade (2) having a single-sided projection on a drive shaft (13) erected on the drive shaft (17), and a flat slow stirring blade ( 4) and a rapid stirring blade (2) with a plurality of blade plates (23...) Radially radiating on the surface of the rotating plate (22) and the tip corner (23a) on an arc. A two-stage agglomeration mixing tank characterized by comprising a turbine single blade (24) notched in the shape and a slow stirring blade (4) comprising a flat paddle blade (4a) .
  The two-stage agglomeration mixing according to claim 1, wherein the volume ratio of the rapid agitation part (3) and the slow agitation part (5) of the agglomeration mixing tank (1) is 1 to 3 to 1:20. Tank. Upper Symbol rapid stirring portion (3) supply port of the stock solution formed in the peripheral wall of (7a) with an opening near the tip of the turbines piece wings (24) of waste in the upper wall of the slow agitation portion (5) The two-stage agglomeration mixing tank according to claim 1 or 2, wherein the outlet (8a) is opened. The rapid stirring portion outer peripheral speed of the turbines piece wings (24) of (3) as a 100 to 300 m / min, the outer peripheral speed of the paddle blades (4a) of the slow stirring unit (5) was 10 to 100 m / min The two-stage agglomeration mixing tank according to any one of claims 1 to 3, wherein   The two-stage agglomeration mixing tank according to any one of claims 1 to 4, wherein a residence time of the slurry granulated in the agglomeration mixing tank (1) is 0.5 to 4 minutes. On Northern turbine piece blades (24) each of external dimensions of the paddle blades (4a) has a feature that it has 60 to 90% of the vessel internal diameter of rapid stirring portion (3) and slow stirring unit (5) The two-stage agglomeration mixing tank according to any one of claims 1 to 5.