JP2000350946A - Screen bowl type decanter type centrifugal separator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a screen bowl type decanter type centrifugal separator by which filtration of crystals can be continuously and stably performed better than the conventional screen bowl type decanter type centrifugal separator wherein a parallel part with a small diameter of an outside rotating cylinder is constituted as a filter medium part and recovery efficiency of the crystals is improved. SOLUTION: Two conveyors consisting of a main conveyor 8a wherein a gap in the radial direction between the conveyor blade 8 and the inner wall of a filter medium part 10 is enlarged as a screw conveyor in the filter medium 3b and at least one sub-conveyor 8b wherein it is arranged between pitches of the main conveyor and a gap in the radial direction between the conveyor blade and the inner wall of the filter medium part 10 is made small than that in the main conveyor 8a, are provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an outer rotary cylinder and a screw conveyor provided in the outer rotary cylinder so as to be relatively rotatable. The outer rotary cylinder has a large-diameter parallel portion and a parallel portion. The parallel portion having a small diameter is provided on the solid matter discharge side, and an inclined portion connecting both parallel portions is formed. The parallel portion having the small diameter has a filtrate discharge hole formed therein, and a cylindrical filter medium is formed on an inner wall thereof. And a screen bowl type decanter-type centrifuge comprising a filter medium portion provided with a washing nozzle for washing a processed material at a portion of the filter medium portion.

[0002]

2. Description of the Related Art An example of a conventional decanter centrifuge is shown in FIG. The centrifugal separator shown in FIG. 1 is generally called a solid bowl type, and has a large-diameter parallel portion 1 provided with a clarified liquid overflow port 5 called a dam at the left end and a right-end connected to the large-diameter parallel portion. A high-speed rotating outer rotary cylinder 4 including a so-called beach-containing inclined portion 2 provided with a solid material discharge port 6, and a spiral in the outer rotary cylinder 4 while maintaining a slight radial gap. A screw conveyor 7 having a conveyer blade 8 is provided to be relatively rotatable.

When a processed slurry composed of a crystalline solid and a solvent is introduced into the solid bowl type centrifugal separator, the crystalline solid as the processed material is moved outward by centrifugal force as shown in FIG. The crystalline solid that has settled on the inner wall surface of the rotating cylinder 4 and has adhered to the surface thereof impurities in the process of forming the processed product or the solvent of the processed product slurry has the same axis as the outer rotary cylinder 4. The screw conveyor 7 which is at the top and rotates at a different speed from the outer rotary cylinder 4 is sent to the inclined portion 2 and rises up the beach.
At the same time. The solvent that forms the processed slurry and a part of the crystalline solid that cannot be settled out overflow from the overflow port 5 provided at the left end of the large-diameter parallel portion 1 and are discharged to the outside.

The crystalline solid discharged from a solid bowl type centrifuge generally has impurities formed in the process of producing the product crystal or a solvent itself attached to the crystal surface. In order to reduce the degree of adhesion of these impurities or solvents, reslurry with a fresh solvent or replacement with another solvent is repeated several times for solid-liquid separation to increase product purity. It is normal that there is. Impurities thus adhering to the surface of the crystalline solid,
Alternatively, when using a centrifugal separator for the purpose of lowering the degree of adhesion of the solvent and performing dewatering, the washing solvent may be mixed with the separation solution which is the processing solvent for washing the crystalline solid. If not, as shown in FIG. 9, a cleaning chamber 13 is provided inside the conveyor at the slope 2 where the beach is raised, and one of the fixed feed tubes 11 that guides the processing slurry into the outer rotary cylinder 4. A cleaning liquid passage 12 is provided in the section, the cleaning liquid is introduced from the outside into the cleaning chamber 13, and the cleaning liquid nozzle 14 or the like attached to the conveyor body 9 is used to remove impurities such as water introduced into the inclined section 2. It is common practice to wash crystalline solids that are processed using a washing liquid.

[0005] However, if the cleaning liquid is continuously applied to the processed material from the upper part of the inclined portion 2 rising to the beach to the vicinity of the solid matter discharge port 6 in order to enhance the cleaning effect, the degree of drainage of the product crystal deteriorates. For this reason, it is conceivable to limit the washing to just after or near the product crystal out of the liquid layer.In this case, the washing liquid comes into contact with the crystal for a short time, so that the product purity is improved to some extent, but the number of separator stages In fact, no effective cleaning effect can be obtained to the extent that it can be reduced.

In order to improve the degree of drainage of product crystals and the effect of washing in a solid bowl type centrifugal separator, as shown in FIG. 10, a parallel portion 3 having a small diameter is connected to an inclined portion 2 having a beach. A large number of filtrate discharge holes 3a are formed in the small-diameter parallel portion 3, and a cylindrical filter medium 3b such as a bar screen is disposed on the inner wall thereof to constitute a filter medium section 10. The filter medium section 10 performs centrifugal filtration. A centrifuge designed to do this has already been developed and is commonly called a screen bowl centrifuge. In the screen bowl type centrifugal separator, a filter material such as a mesh screen or a porous ceramic can be used as the cylindrical filter material 3b in the filter material portion 10.

In the screen bowl type centrifuge, the processed slurry introduced from one end of the outer rotary cylinder 4 via the feed tube 11 is fed into the large-diameter parallel portion 1 of the outer rotary cylinder 4 rotating at high speed. The crystalline solid and the separated liquid are separated by centrifugal force, sent to the inclined section 2 by the screw conveyor 7, and the crystalline solid that has gone up the beach is subjected to a liquid removing action at the site of the inclined section 2 to be solid-liquid. The mechanism of separation is the same as that of the solid bowl type described above, except that the bowl has two stages, a large-diameter parallel portion 1 and a small-diameter parallel portion 3, and a small-diameter parallel portion. 3 in that a cylindrical filter medium 3b is held on the inner wall of the feed tube 11 at the beginning of the small-diameter parallel section 3 based on the configuration. part The cleaning liquid is introduced from outside and used as the cleaning liquid passage 12, and in the cleaning chamber 13 inside the conveyor, the cleaning liquid is applied to the crystalline solid by the cleaning liquid nozzle 14 or the like attached to the conveyor body 9 to clean the crystalline solid. Further, it is possible to remove liquid adhering to the surface of the crystalline solid in the latter half of the filter medium portion 10 in the small diameter parallel portion 3. The washing liquid containing the liquid attached to the crystal surface by this washing action passes through the filtration opening of the filter medium 3b in the filter medium part 10 and passes through the filtrate discharge hole 3a or the slot provided in the small diameter parallel part 3 to the outside of the centrifuge. Is discharged.

[0008] As described above, in the screen bowl type centrifugal separator, in addition to the primary dewatering at the inclined portion 2 rising up the beach,
In the small diameter parallel portion 3, since the filter material is subjected to the filtration and dewatering action by the secondary dewatering in the filter material portion 3b, the crystal shape is relatively round, and the treated material is easy to move on the filter material surface in a simple surface state, When the crystal is matched with the filter medium, such as a processed substance in which the crystals are easily dissolved by the cleaning liquid, the liquid exhibits superior performance in terms of dewatering performance and cleaning performance as compared with the solid bowl type.

[0009]

However, in the screen bowl type centrifugal separator, in order to perform the filtration and dewatering at the filter medium portion 10 in the small-diameter parallel portion 3, the physical properties such as the crystal grain size, shape, and abrasion property are required. In addition to the necessity of selecting the filter medium 3b, it is unavoidable that the crystal escapes from the filter medium section 10 because the filter medium is filtered, and the escape of the crystal is reduced as much as possible. Therefore, when a bar screen or a mesh screen having a small opening is used, the filtration is performed only for a short time because crystals are clogged in the filtration opening of the filter medium 3b, so that the filtration unit 10 cannot be used effectively. The problem arose. The escape of the crystals resulted in deterioration of the crystal recovery efficiency as compared with the solid bowl type centrifuge.

Further, since a radial gap is provided between the conveyor blades 8 of the screw conveyor 7 and the inner wall surface of the filter medium portion 10, it is unavoidable mechanically that a residual layer having a certain thickness is formed. By the way, even if the thickness of the remaining layer is slightly increased, the filter layer 3b having a small surface friction coefficient is appropriately selected depending on the internal friction of the crystalline solid to make the remaining layer easier to move. Have been.

On the other hand, as shown in FIG. 11, a part of the conveyor blade 8 for transporting the crystalline solid in the small-diameter parallel part 3 which faces the filter medium part 10 is notched, so that the space between the conveyor blade 8 and the inner wall of the filter medium part 3b is formed. In the case where a large radial gap is provided, the crystalline solid sent by the screw conveyor 7 remains on the plane formed by the gap to form a residual layer D, which is no longer sent by the conveyor blades 8. The portion of the residual layer D varies depending on the physical properties such as the transportability of the crystalline solid by the conveyor blade 8, but if the stagnation time is long, the residual layer D exhibits a compacted state, and the cleaning liquid cannot pass therethrough. It is not necessarily said that increasing the thickness of the polymer is effective for all crystalline solids. When the thickness of the remaining layer D is increased,
The stagnant crystalline solid is in a state of crystal filtration that prevents most of the crystals conveyed by the conveyor blade 8 from escaping from the filter medium portion 3b. Continue to stagnate at the same position, the remaining crystal is compacted by centrifugal force due to rotation and by the contact of the end face of the tip of the conveyor blade 8, and as a result, the filtering effect by the remaining crystalline solid is impaired. The problem had arisen. That is, in the case of the screen bowl type centrifugal separator, the problem of escape of the crystalline solid from the filter opening of the filter medium 3b in the filter medium section 10 and the problem of a decrease in the dewatering effect due to the consolidation of the remaining layer occur.

[0012] As is true of not only the screen bowl type but also the decanter type centrifugal separator in general, the radial gap between the conveyor blade 8 of the screw conveyor 7 and the inner wall of the small-diameter parallel portion 3 is the screw conveyor 7. And the outer rotary cylinder 4 are required to rotate at different speeds. However, the remaining layer D has a higher filtering effect by washing with the thin gap b than with the thick gap a. It was common to think that it is better to make this gap as small as possible because it is advantageous for drainage. However, if the thickness of the residual layer D is too small, the height H of the transport cross-sectional area of the crystalline solid transported by the conveyor blade 8 increases as shown in FIG. Since the water flows down the surface and is discharged out of the machine through the remaining layer formed by the thin gap b, there is a problem that the cleaning effect is reduced.

The present invention has been made in view of the above-mentioned problems, and has as its object to form a filtrate discharge hole in a small-diameter parallel portion of an outer rotating cylinder and to dispose a cylindrical filter medium on the inner wall thereof. In a screen bowl type decanter-type centrifuge provided with a washing nozzle for washing a processed material at a portion of the filter medium portion, a screw conveyor at the portion of the filter material portion is improved. The washing solvent for the crystalline solid that moves on the surface of the filter medium can be separated from the treated solvent and taken out of the machine. At this time, by performing the crystal filtration continuously and stably, Eliminating the amount of crystalline solids as small as possible increases the crystalline solids recovery rate, and furthermore, without causing internal blockage of the crystalline solids by selecting the filtration opening of the filter medium to be relatively large. impurities Can increase the effect of purification, simplified function is to provide a screen bowl type decanter centrifuge which attained the peripheral facilities reduced.

[0014]

In order to achieve the above object, a screen bowl type decanter centrifuge according to the present invention is characterized by what is described in the claims. In particular, a screen bowl type decanter centrifuge according to the invention according to claim 1 as an independent claim has an outer rotating cylinder and a screw conveyor rotatably provided in the outer rotating cylinder, and the outer rotating cylinder. Is composed of a large-diameter parallel portion, a small-diameter parallel portion provided on the solid matter discharge side of the parallel portion, and an inclined portion connecting the parallel portions, and the small-diameter parallel portion is provided with a filtrate discharging portion. A screen bowl type decanter centrifuge in which a hole is formed, a cylindrical filter medium is disposed on the inner wall thereof to form a filter medium part, and a washing nozzle for washing the processed material in the filter medium part is provided. A screw conveyor in the filter medium portion, a main conveyor having a large radial gap between the conveyor blade and the inner wall of the filter material portion, and a screw conveyor disposed between the pitches of the main conveyor. It is characterized by comprising at least one sub-conveyor having a radial gap between itself and the inner wall of the filter medium portion smaller than that of the main conveyor.

[0015]

According to the present invention, both the primary and secondary conveyors in the filter medium portion, which is configured as a small diameter parallel portion, are always rotated relative to the outer rotating cylinder so that they are continuous from the conveyor feed port. In contrast to the main conveyor blade with a large radial gap, the sub-conveyor blade has a smaller radial gap between it and the inner wall of the filter medium part, so both the positive and sub conveyors have the respective gaps. Since the crystalline solid is left as a residual layer, each of the conveyor blades applies the conveying force in the axial direction to the crystalline solid by the difference of the gap. Both the primary and secondary conveyor blades have the same axial conveying force as sent by a single conveyor blade, are not continuously exposed to the centrifugal force field, and are held down by the end of the conveyor blade. Without being condensed due to being carried out, it is subjected to washing with the washing liquid in the transported form of the smoothed crystalline solid.

As shown in FIG. 12, in the conventional conveying form of one conveyor blade, since the portion pushed by the conveyor blade is high and is sent in a state close to a triangle having a height H, the cleaning liquid flows on a triangular slope. Down, it will flow to the thinner remaining layer portion of the crystal. On the other hand, when both the positive and secondary conveyor blades according to the present invention as shown in FIG. 5 are used, the crystal cleaning is performed by providing the cake cleaning nozzle 14 between the respective conveyor blades 8a and 8b. Then, the surface on which the cleaning liquid is applied is smoothed as compared with the case of FIG. 12, so that the cleaning liquid penetrates into the conveyed crystalline solid, and cleaning can be performed more effectively. When the flat crystal layer has a filtering effect, it is possible to further reduce the escape of crystals from the filter medium.

Further, in this crystal filtration state, the opening can be selected to be larger than the crystal grain size, and washing and dewatering can be performed without closing the crystal in the opening.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. In the following embodiment, a description will be given of a case where the number of conveyor blades at the portion of the filter medium portion 10 formed in the small-diameter parallel portion 3 is two, that is, a main conveyor blade 8a and a sub-conveyor blade 8b.

The screen bowl type centrifugal separator according to the present embodiment has an outer rotating cylinder 4 and a screw conveyor 7 provided to be relatively rotatable in the outer rotating cylinder 4, and the outer rotating cylinder 4 has a large diameter. Parallel portion 1 and a small-diameter parallel portion 3 provided on the solid matter discharge port 6 side of the parallel portion 1.
And an inclined portion 2 connecting both parallel portions 1 and 3,
The small-diameter parallel portion 3 has a filtrate discharge hole 3a formed therein, and a cylindrical filter medium 3b is disposed on the inner wall of the small-diameter parallel section 3.
In the screen bowl type centrifugal separator provided with a washing nozzle 14 for washing the processed material in the filter medium section 10, the screw conveyor 7 in the filter medium section 10 is constituted by a conveyor blade 8a and the filter medium section 10 A main conveyor having a large radial gap a between itself and an inner wall thereof, and a conveyor blade 8b disposed between the pitches of the main conveyor.
A radial gap b between the main conveyor and the inner wall of the filter medium portion 10 is smaller than that of the main conveyor.

As shown in FIG. 3, the screw conveyor 7
In order to have an appropriate remaining layer thickness, the radial direction of the conveyor blades facing the filter medium portion 10 is shortened or cut out by an appropriate height so as to have an appropriate remaining layer thickness.
The main conveyor blade 8a having a large gap in the radial direction with the filter medium portion 10 is provided.

Further, as a sub-conveyor, a sub-conveyor blade 8b having a small radial gap is wound between the pitches of the main conveyor blades 8a having a large radial gap as shown in FIG.
The crystal that has climbed the inclined portion 2 is not conveyed until only the radial gap a of the main conveyor blade 8a having the large radial gap is rotated until the other sub-conveyor blade 8b having the small radial gap rotates. Becomes The remaining layer formed by the main conveyor blade 8a having the notch with the large radial gap is sent by the other sub-conveyor blade 8b having the small radial gap, and the crystal transport form is shown in FIG. As a result, the conveyor blades are further smoothed as compared with the single crystal transport mode shown in FIG.

The main conveyor blade 8 having a large clearance in the radial direction.
a and the sub-conveyor blade 8b having a small radial gap and the cleaning liquid nozzle 14 are arranged as shown in FIG.

The main conveyor blade 8a having a large gap in the radial direction.
Notch height and radial gap a determine the feed crystal amount of the sub-conveyor blade 8b having the small radial gap without the other notch, and the two main and sub-conveyor blades 8a and 8b respectively. Is determined so that the feed height of the crystal is substantially the same. In addition, each conveyor blade 8
As shown in FIG. 6, when the crystal forms a bridge E between the conveyor blades 8a and 8b, it is impossible to transfer the conveyor blades 8a and 8b. Therefore, it is necessary to determine an appropriate conveyor blade pitch interval based on the crystal transport amount. This is determined by design as appropriate in consideration of the physical properties of the crystalline solid.

In this situation, as shown in FIG. 12, as compared with the crystal transport mode of the screw conveyor comprising only one conveyor blade 8 of the same pitch, the crystal transport mode is smoothed, and the crystal filtration section is formed. As the area of the substrate is increased, the cleaning liquid uniformly penetrates the crystal layer, and an effective crystal cleaning effect can be obtained. In addition, as shown in FIG. 5, as compared with FIG. 12, the thin portion b of the remaining layer is narrow, so that the crystal filtration portion can be widened, and the escape of crystals from the filter medium portion 10 can be reduced. .

When the pitch of the conveyor blades is sufficiently large, solid material as shown by b, c and a in FIG. 7 is used in addition to the two main and sub conveyor blades 8a and 8b. Second to set large in stepwise in the transport direction
If the sub-conveyor blades 8c are provided, it is expected that the crystal transport form will be further smoothed and the cleaning effect will be enhanced.

On the other hand, it is possible to form the remaining layer of the crystal only by the conveyor blade 8 having a slightly larger gap in the radial direction shown in FIG. 12, and it is possible to filter the crystal over the entire surface of the filter medium 3a. However, since the force for pushing the remaining layer portion of the crystal in the axial direction is only the shearing force between the conveyor blade 8 and the crystalline solid, the remaining layer portion becomes larger when the radial gap is increased. This results in stagnation at the same position on the inner wall surface, resulting in compaction as described above, which significantly reduces the filtering effect.

Further, as shown in FIG.
In the case where it is set at the part where the conveyance starts at the part of the filter medium part 10,
By providing a portion where cleaning is not performed in the latter half and removing the crystal surface liquid replaced with the cleaning liquid in this portion, it is possible to further reduce the remaining impurities.

[0028]

The product crystals produced in the chemical and food industries have unpolymerized substances and a solvent constituting the slurry adhere to the crystal surface during the production process. This deposit can be washed and replaced with a certain other solvent. According to the present invention, in which a plurality of conveyor blades having different radial gaps are used at a portion of a filter medium portion in a screen bowl type centrifugal separator, crystals moving on the surface of the filter medium are applied by a washing liquid nozzle provided on a conveyor body or the like. The washing solvent can be separated from the treated solvent and taken out of the centrifuge, and the improved screw conveyor enables more continuous and stable crystal filtration compared to this type of conventional machine. The crystal recovery rate can be increased by minimizing the amount of crystals that escape in the filtrate, and the filtration opening of the filter medium can be made relatively large. The effect of simplification of functions and reduction of peripheral equipment can be obtained.

[Brief description of the drawings]

FIG. 1 is a side sectional view of a screen bowl type centrifuge according to an embodiment of the present invention.

FIG. 2 is a partial cross-sectional view in which a cleaning liquid nozzle is disposed between main and sub-conveyor blades at a portion where the conveyance starts at a filter medium portion according to an embodiment of the present invention.

FIG. 3 is a side view of a screw conveyor disposed in an outer rotating cylinder including a large-diameter parallel portion, an inclined portion, and a small-diameter parallel portion according to an embodiment of the present invention.

FIG. 4 is an explanatory view of two main and sub-conveyor blades in the screw conveyor according to the embodiment of the present invention.

FIG. 5 is an explanatory view of a crystal transport mode by two main and sub-conveyor blades in the embodiment of the present invention.

FIG. 6 is an explanatory view of a crystal transport mode in a case where a pitch is narrow by two main and sub-conveyor blades.

FIG. 7 is an explanatory view of a crystal transfer mode using one main sheet and two sub sheets of three-conveyor blades in another embodiment of the present invention.

FIG. 8 is a side sectional view of a conventional solid bowl type centrifuge.

FIG. 9 is a partial cross-sectional view showing the washing of solids on the inclined beach in the solid bowl type centrifuge.

FIG. 10 is a side cross-sectional view of a single-conveyor blade screen bowl centrifuge according to the prior art.

FIG. 11 is a partial cross-sectional view showing a residual layer formed on a filter medium portion in a single-conveyor blade screen bowl type centrifugal separator.

FIG. 12 is an explanatory view of a crystal transport mode by a single-conveyor blade in a filter medium portion.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Large diameter parallel part 2 ... Inclined part 3 ... Small diameter parallel part 3a ... Filtrate discharge hole or slot 3b ... Filter medium 4 ... Outer rotating cylinder 5 ... Clarified liquid overflow port 6 ... Solid matter outlet 7 ... Screw conveyor 8 ... Conveyor blade 8a ... Main conveyor blade 8b ... Sub-conveyor blade 8c ... Second sub-conveyor blade 9 ... Conveyor body 10 ... Filter medium part 11 ... Feed tube 12 ... Cleaning liquid passage 13 ... Cleaning chamber 14 ... Cleaning liquid nozzle

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Toshiyuki Sakata 1-2-1, Waki, Waki-cho, Kuga-gun, Yamaguchi Prefecture F-term in Mitsui Chemicals, Inc. (reference) 4D057 AA01 AA07 AB01 AC02 AD01 AE03 AF01 AF05 BA17 BA36 BC16

Claims (2)

[Claims] An outer rotating cylinder and a screw conveyor provided in the outer rotating cylinder so as to be rotatable relative to each other. The outer rotating cylinder has a large-diameter parallel portion and a solid material discharge side from the parallel portion. The small-diameter parallel portion includes a parallel portion having a small diameter, and an inclined portion connecting the two parallel portions. The parallel portion having the small diameter has a filtrate discharge hole formed therein, and a cylindrical filter medium is disposed on an inner wall thereof to form a filter medium. A screen bowl type decanter-type centrifuge provided with a washing nozzle for washing a processed material at a portion of the filter medium section, wherein a screw conveyor in the filter medium section has a conveyor blade and the filter medium section. A main conveyor having a large radial gap between the main conveyor and the main conveyor, and a radial gap between the conveyor blades and the inner wall of the filter medium portion is disposed between the pitches of the main conveyor. It At least one screen ball decanter centrifuge, characterized in that is composed of a sub-conveyor was small in comparison. 2. A plurality of sub-conveyors in which the radial gap is gradually increased stepwise in the solids conveying direction between the pitches of the main conveyor having the large radial gap as a screw conveyor at the filter medium portion. The screen bowl type decanter centrifuge according to claim 1, wherein a centrifuge is provided.