JP2003062405A - Solid-liquid separating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid-liquid separating method, using a screen type centrifugal separator in which a screw conveyor is arranged, which is improved such that an operation of the centrifugal separator is efficiently carried out. SOLUTION: When a solid-liquid separation is carried out by continuously feeding a slurry containing undefined particles as a solid substance into the screen type centrifugal separator in which the screw conveyor is arranged, a staying time of the solid-liquid separation on a screen is set to 2 to 20 seconds. Provided that in the case where a washing liquid-feeding port is provided, the staying time is the one after it passed through a feeding area of the washing liquid. A centrifugal force of 300 to 5,000 G acts on the screen.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-liquid separation method, and more particularly to a solid-liquid separation method using a screen type centrifuge having a screw conveyor inside.

[0002]

2. Description of the Related Art For example, in a process for producing terephthalic acid by liquid-phase oxidation of para-silene, terephthalic acid is precipitated as crystals to form a slurry. The solid matter (terephthalic acid crystals) obtained by such crystallization is amorphous particles having a particle size distribution.

As one of the methods for solid-liquid separation of a slurry containing irregular particles as described above, the slurry is continuously supplied to a screen type centrifuge in which a screw conveyor is arranged, and centrifugal force is applied. There is a method of solid-liquid separation on the screen by the action of.

In the above continuous solid-liquid separation method, how to set the residence time of the solid-liquid separation on the screen is important from the viewpoint of efficient operation of the centrifuge. However, there is no sufficient proposal on this point yet.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to provide a solid-liquid separation method using a screen type centrifugal separator having a screw conveyor arranged therein. Another object of the present invention is to provide an improved solid-liquid separation method so that the centrifugal separator can be operated efficiently.

[0006]

Means for Solving the Problems That is, the gist of the present invention is to continuously supply a slurry containing amorphous particles as a solid substance to a screen type centrifuge in which a screw conveyor is arranged to solidify. In the liquid separation, the residence time of the solid-liquid separation on the screen is set to 2 to 20 seconds,
However, when the cleaning liquid supply port is provided, it is required that the residence time is after passing through the cleaning liquid supply area, and 300 to 5000 G is displayed on the screen.
The present invention resides in a solid-liquid separation method characterized in that the centrifugal force is applied.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.

First, the slurry will be described. The slurry used in the present invention is a slurry containing amorphous particles as a solid. Specific examples of such a slurry include a crude terephthalic acid crystal-containing slurry recovered from a terephthalic acid production process by liquid-phase oxidation of para-silene as described above. Such a slurry is usually composed of acetic acid as a reaction solvent, terephthalic acid crystals, a catalyst dissolved in the reaction solvent, unreacted raw materials, by-products and unprecipitated terephthalic acid. The average particle size of terephthalic acid crystals is usually 120 μm ± 40 μm.

Next, a screen type centrifuge in which a screw conveyor is arranged will be described. In the present invention, as long as it is a separator capable of solid-liquid separation by the action of centrifugal force while transferring the object to be treated by a screw conveyor on the screen, screen-type centrifuges of various structures regardless of designation Can be used. For example, the so-called "decanter type centrifugal separator" (Japanese Patent Laid-Open No. 7-155643).
No.), "Screen ball decounter centrifuge" (JP-A-2000-350946, WO98 / 1).
No. 8750) are known.

FIG. 1 is a sectional explanatory view of a suitable screen type centrifuge which can be used in the present invention. The screen-type centrifuge shown in this figure is a screw conveyor including an outer rotary cylinder (1) and a cylindrical rotary shaft (21) and a screw (22) provided in the outer rotary cylinder so as to be rotatable relative to each other. (2) and a slurry supply pipe (3) arranged inside the rotary shaft of the screw conveyor and supplying slurry into the rotary shaft. The rotating cylinder (1) is provided with a slurry supply port (23) for supplying a slurry, and the outer rotating cylinder (1) has a large diameter portion (11) on the base end side and an inclined portion (12) with a gradually reduced diameter. And a small diameter portion (13) provided with a screen (13a) are sequentially arranged, and a large diameter portion (1
An overflow port (4) is provided at the base end of (1), and a small diameter part (1
The tip of 3) has a structure in which a solid matter discharge port (5) is provided.

Furthermore, in a preferred embodiment, the inside of the rotary shaft (21) of the screw conveyor is partitioned into a slurry supply section (21a) on the base end side and a cleaning liquid supply section (21b) on the tip side, and the slurry supply section. (21a) is configured so that slurry can be supplied by the slurry supply pipe (3), and the cleaning liquid supply unit (21b) is formed by the slurry supply pipe (3).
A cleaning liquid is configured to be able to be supplied by a cleaning liquid supply pipe (6) inserted into the inside of the screw conveyor, and the cleaning liquid is supplied to the small diameter portion (13) of the outer rotary cylinder (1) at the tip side of the screw conveyor (2). A supply port (24) is provided.

The flange (7) of the drive shaft (7) for the outer rotary cylinder
A plurality of openings (71c) are provided in the outer peripheral portion of 1), and thereby a solid matter discharge port (5) is formed. In addition, the flange (8) of the drive shaft (8) for the screw conveyor
A plurality of openings (81c) are provided in the outer peripheral part of 1), and the overflow port (4) is constituted by this.

The above-mentioned elements are housed in a casing (9). The interior of the casing (9) is divided by the partition wall into the overflow liquid storage chamber (91) and the filtrate storage chamber (9).
2), it is divided into a solid material storage chamber (93), and the filtrate storage chamber (92) is further divided into three chambers (92) along the longitudinal direction of the small diameter portion (13) for convenience of sampling the filtrate.
It is divided by a partition wall into a), (92b), and (92c). Then, the overflow liquid storage chamber (91) and the filtrate storage chamber (92) in the respective chambers (92a), (92b),
(92c) and the solid matter storage chamber (93) are respectively provided with extraction pipes.

In the case of a screen type centrifugal separator in which a screw conveyor is arranged, clogging is promoted by a solidified layer (cake layer) formed inside the screen in a compacted state by the screw. Therefore, in the present invention,
In order to prevent clogging of the screen type centrifuge and enable efficient solid-liquid separation, a screen with an opening that allows 1 to 10% by weight of the solid matter in the supplied slurry to leak. Use of is recommended.

The opening of the screen is, for example, A
Solid matter in the slurry continuously supplied at a rate of (Kg / hr): 1 to 10% by weight (preferably 1.5 to 8% by weight) of a (Kg / hr), which is a continuous amount. It means that the size can be leaked. Since it is considered that the leakage of the irregular particles having a smaller particle diameter is given priority, the irregular particles having a relatively small particle diameter in the slurry will be leaked from the screen.

As a result of the above, the solidified layer (cake layer) formed in a compacted state inside the screen, specifically, in the space between the outer rotary cylinder (1) and the screw (22), is relatively It is composed of large-sized irregular particles. The reason why large clogging is not caused in the case of such a solidified layer (cake layer) is not necessarily clear, but is presumed as follows.

That is, generally, a solidified layer (cake layer)
In the case of containing irregularly-shaped particles having a relatively small particle diameter, the element becomes strong due to the strong bridging action. On the other hand, the solidified layer (cake layer) composed of irregularly-shaped particles having a relatively large particle size is likely to collapse because there is no strong bridging action. Therefore, it is presumed that the above solidified layer (cake layer) is constantly collapsed and renewed,
Therefore, it does not seem to cause a big clogging.

When the above-described screen screed having a ratio of the leakage amount of less than 1% by weight is used, the effect of preventing clogging is not achieved, and the screed of the screen opening exceeding 10% by weight is used. When it is used, the clogging prevention effect is saturated, but the amount of leakage is too large and it is not efficient.

The most important feature of the present invention is that the residence time for solid-liquid separation on the screen is set to 2 to 20 seconds, except that when a cleaning liquid supply port is provided, it passes through the cleaning liquid supply area. The condition is that the residence time is set, and further, a centrifugal force of 300 to 5000 G is applied on the screen.

When the centrifugal force is less than 300 G, the residence time of solid-liquid separation on the screen becomes too long, and 500
If it exceeds 0 G, stable operation of the centrifuge becomes difficult. A preferable centrifugal force is 500 to 3000G. Such adjustment of the centrifugal force is performed by controlling the rotation speed of the drive motor of the outer rotary cylinder (1).

In the present invention, it is important to set the residence time of the solid-liquid separation (deliquoring) on the screen to 2 to 20 seconds under the above centrifugal force. If the residence time is less than 2 seconds, sufficient solid-liquid separation is not performed, and if it exceeds 20 seconds, the solid-liquid separation effect is saturated and the operation efficiency of the centrifuge is reduced. The preferred residence time is 3 to 5 seconds.
The adjustment of such residence time depends on the size (length) of the screen.
In addition to the design method described above, it can be performed by controlling operating conditions such as a rotational speed difference between the outer rotary cylinder (1) and the screw conveyor (2) (that is, a transfer speed of the object to be processed on the screen).

In the present invention, the above residence time is calculated as shown in FIG.
When the cleaning liquid supply pipe (5) is provided as in the centrifugal separator shown in (1), the condition is that the cleaning liquid has been passed through the cleaning liquid supply area injected from the cleaning liquid supply port (24). That is, the above-mentioned residence time in the present invention means the time on the screen after only the deliquoring is performed without the increase of the liquid content due to the influence of the cleaning liquid.

In the present invention, solid-liquid separation is performed as follows. The slurry is supplied from the slurry supply pipe (3) via the slurry supply section (21a) to the large diameter section (1) of the outer rotary cylinder (1).
1). Then, here, solid-liquid separation is performed by the centrifugal separation action of the outer rotating cylinder (1) rotating at high speed.

The separated liquid is taken out from the overflow port (4) through the overflow liquid storage chamber (91). On the other hand, the solid matter is transferred from the inclined portion (12) to the small diameter portion (13) by the screw (22). At this time, the mother liquor in the solid matter is separated by the centrifugal force on the screen (13a). At the same time, the cleaning liquid is supplied from the cleaning liquid supply pipe (6). The cleaning liquid is
The cleaning liquid is supplied from the cleaning liquid supply (24) through the cleaning liquid supply unit (21b) to the solid matter being transferred. The solid matter that has been washed and dehydrated is discharged from the solid matter discharge port (5) into the solid matter storage chamber (93).
Be taken out through.

[0025]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

Examples 1 to 4 and Comparative Examples 1 to 2 A terephthalic acid crystal-containing slurry (average particle size) obtained in the process of producing terephthalic acid was added to a screen type centrifuge (screen opening: 100 μm) shown in FIG. : 100μ
m) was continuously supplied and solid-liquid separation was performed under the conditions shown in Table 1 (however, the centrifugal force on the screen was 750 G). The liquid content of the recovered cake is shown in Table 1.

[0027]

[Table 1]

The residence time in Table 1 is the cleaning liquid supply port (2
4) The time after passing through the supply area of the cleaning liquid injected from 4) (specifically, the time after 2 seconds has passed from immediately below the cleaning liquid supply port (24)), including each residence time and the collected cake. The liquid ratio was determined as follows for convenience. That is, the filtrate sample was collected from the position corresponding to each of the above retention times, the solid concentration in the filtrate sample at each retention time was measured, and the liquid content of the recovered cake was calculated by mass balance calculation.

As is clear from the results shown in Table 1, in each of the examples, since the residence time was appropriate, the centrifuge was operated efficiently and the sufficiently dewatered cake was recovered. To be done. On the other hand, in the case of each comparative example, since the retention time is short, the liquid content of the recovered cake is high.

Reference Example A terephthalic acid crystal-containing slurry obtained in the process of producing terephthalic acid was used in a screen type centrifuge shown in FIG. 1 equipped with an opening screen shown in Table 2 below (average particle size: 1
(00 μm) was continuously supplied to perform solid-liquid separation. The results are shown in Table 2.

[0031]

[Table 2]

As is clear from the results shown in Table 2, in the case of Reference Example 1, the liquid content of the recovered solid is lower than that of Reference Example 2. This is because clogging was prevented and liquid was satisfactorily drained.

[0033]

According to the present invention described above, a solid-liquid separation method using a screen type centrifuge in which a screw conveyor is arranged is provided, and the centrifuge is operated efficiently. The present invention is provided with an improved solid-liquid separation method, and the industrial value of the present invention is great.

[Brief description of drawings]

FIG. 1 is a cross-sectional explanatory view of a suitable screen type centrifuge that can be used in the present invention.

[Explanation of symbols]

1: Outer rotary cylinder 11: Large diameter part 12: Inclined part 13: Small diameter part 13a: screen 2: Screw conveyor 21: rotating shaft 21a: Slurry supply unit 21b: Cleaning liquid supply unit 22: Screw 23: Slurry supply port 24: Cleaning liquid supply port 3: Slurry supply pipe 4: Overflow port 5: Solid matter discharge port 6: Cleaning liquid supply pipe 7: Drive shaft for outer rotary cylinder 71: Flange 71c: opening 8: Drive shaft for screw conveyor 81: Flange 81c: opening 9: Casing 91: Overflow liquid storage chamber 92: Filtrate storage room 93: Solid object storage chamber

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Claims (4)

[Claims] 1. When solid-liquid separation is performed by continuously supplying a slurry containing amorphous particles as a solid to a screen-type centrifuge in which a screw conveyor is arranged, solid-liquid separation on a screen is performed. The dwell time is set to 2 to 20 seconds, provided that the dwell time after passing through the wash liquid supply area is set when the wash liquid supply port is provided, and 300 to 5 is set on the screen.
A solid-liquid separation method comprising applying a centrifugal force of 000 G. 2. A screen type centrifuge, wherein an outer rotary cylinder (1), a cylindrical rotary shaft (21) and a screw (2) which are provided in the outer rotary cylinder so as to be rotatable relative to each other.
A screw conveyor (2) provided with 2) and a slurry supply pipe (3) arranged inside the rotary shaft of the screw conveyor and supplying slurry into the rotary shaft. A slurry supply port (23) for supplying slurry to the outer rotary cylinder (1) on the base end side of the
The outer rotary cylinder (1) is provided with a large diameter portion (1
1), a sloping portion (12) having a gradually reduced diameter, and a small diameter portion (13) provided with a screen (13a) are sequentially arranged, and the base end of the large diameter portion (11) overflows. An outlet (4) is provided, and a solid matter outlet (5) is provided at the tip of the small diameter portion (13).
The solid-liquid separation method according to claim 1, wherein a screen type centrifugal separator provided with is used. 3. The inside of the rotary shaft (21) of the screw conveyor is partitioned into a slurry supply part (21a) on the base end side and a cleaning liquid supply part (21b) on the tip end side, and the slurry supply part (21a) is The slurry supply pipe (3) is configured to be capable of supplying the slurry, and the cleaning liquid supply unit (21b).
Is configured such that the cleaning liquid can be supplied by the cleaning liquid supply pipe (6) inserted inside the slurry supply pipe (3), and the outer rotary cylinder (1) is provided at the tip side of the screw conveyor (2).
Cleaning liquid supply port (2) for supplying the cleaning liquid to the small diameter part (13) of
The solid-liquid separation method according to claim 2, wherein 4) is provided. 4. A screen of a screen type centrifuge, which comprises 1 to 10% by weight of solids in a slurry supplied.
The solid-liquid separation method according to any one of claims 1 to 3, wherein a screen having an opening that allows a considerable amount to leak is used.