JP4001490B2 - Filtration device, seawater treatment method using the same, and coagulant regeneration method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is a filtration device for efficiently filtering suspended particles in seawater at high speed and removing them to obtain clear seawater, and reducing the amount of suspended particles flowing into the ion exchange membrane electrodialysis tank in salt production, The present invention relates to a seawater treatment method using the filtration device and a method for regenerating the flocculant in the seawater filtration treatment.
[0002]
[Prior art]
When making salt using seawater, the ion-exchange membrane salt production method usually concentrates seawater in an ion-exchange membrane electrodialysis tank to obtain brine. The structure of this electrodialysis tank consists of an anion membrane and a cation membrane. In general, a type called a clamping type in which spacers with rubber frames are sandwiched and stacked alternately is used, and the ion exchange membranes are arranged at a narrow interval of 0.3 to 0.5 mm. For this reason, if clogging or adhesion due to suspended particles in seawater occurs between the flow path (tide channel) or the membrane surface or the membrane surface that supplies seawater to the desalination chamber, it becomes a flow resistance, and ions are supplied to the membrane surface. The shortage of water near the surface increases the electrical resistance to generate heat, causing troubles such as hydrolysis that deteriorates the film and an increase in electrical resistance due to the accumulation of deposits.
[0003]
Therefore, salt production plants generally remove seawater suspended particles from seawater through a primary filter and a secondary filter, and supply seawater to an ion exchange membrane electrodialysis tank. This seawater treatment facility uses sand filtration that is often used in water and sewage systems, and many use sand with an effective diameter of 0.3 to 0.5 mm in a single layer configuration for primary and secondary filters. . In some cases, in order to improve the clarification of filtered seawater, direct agglomeration filtration is performed in which a flocculant is added directly to seawater and filtration is performed. A two-layer structure of sand is used.
[0004]
However, although 70 to 90% of suspended particles in seawater can be removed normally with current filters, the effects of suspended particles described above have not been prevented or reduced, and most salt mills can avoid trouble. For this reason, the electrodialysis tank must be periodically disassembled and washed. In order to reduce the influence of suspended particles in seawater, it is necessary to supply seawater water quality of 3.0 or less in FI value (Fouling Index) and 0.05 mg / L or less in turbidity value to the electrodialysis tank. It is said that.
[0005]
Moreover, although about 4000 m < ³ > / H seawater treatment is performed in the salt production factory, the filtration flow rate of the above-mentioned filter is about 8 to 15 m / H for the primary filter and about 10 to 30 m / H for the secondary filter. Therefore, the installation area is enormous.
On the other hand, in recent high-speed filtration technology, as described in Japanese Patent Publication No. 4-36723 and Japanese Patent Publication No. 5-11482, a fiber having a larger porosity than a mineral filter medium is used as a long fiber. The technique of the filtration method and apparatus which are used for the filter medium in the shape of a bundle or a fiber lump has been reported. However, fiber bundles and long fiber bundles are packed with fiber bundles so that the trapping effect at the beginning of filtration is good, but the loss head is likely to rise and there is a problem with the sustainability of filtration. Has been. In the case of fiber mass filter media, the porosity is high due to the high porosity, but the trapping (adsorption) effect is low compared to the filter media of long fiber bundles, and the inside of the filter media voids. It has been pointed out that turbidity tends to remain.
[0006]
Further, there is disclosed a filtration method and an apparatus structure in which the compression rate of the filter medium is changed by the flow pressure by increasing the downstream filtration flow rate from the upstream side, and suspended particles are captured by layer for each particle size. Although it describes in 10-263315 gazette and Unexamined-Japanese-Patent No. 11-123304, the specific example which applied such a filtration method and apparatus structure to seawater treatment is not known until now.
[0007]
[Problems to be solved by the invention]
The present invention enables efficient removal of suspended particles in seawater by high-speed filtration, clarifying the quality of seawater, reducing the size of filtration equipment in salt production, and further, agents such as flocculants used during filtration The purpose is to reduce the amount of waste through recycling.
[0008]
[Means for solving problems]
The above-described problems of the present invention have been achieved by the following filtration device and a seawater treatment method using the same. Listed below together with preferred embodiments.
(1) In a filtration apparatus in which a cylindrical column and a conical column with a reduced aperture ratio are provided below the cylindrical column and a perforated plate is provided at the upper end of the cylindrical column and the lower end of the conical column. A filtration apparatus for removing suspended particles of seawater, comprising a filter medium layer made of a fibrous filter medium in a cylindrical column and a baffle plate on the upper part of the cylindrical column.
[0009]
(2) The filtration device according to (1), wherein the fibrous filter material is a nonwoven fabric having an 8 to 15 mm square and a thickness of 5 to 10 mm.
(3) The filtration device according to (1) or (2), wherein the aperture ratio between the upper end and the lower end of the conical column is 2: 1 to 5: 4.
(4) From the upper end of the cylindrical column of the filtration device according to (1), seawater to which a flocculant is added is allowed to flow at 30 to 100 m / H to filter the seawater, and suspended particles and aggregated floc particles in seawater. To the filter medium, to supply water and air to which acid is added from the lower end of the conical column and backwash, to separate and remove suspended particles adsorbed on the filter medium, and to the filter medium And a step of ionizing and recovering the adsorbed aggregated floc particles.
[0010]
(5) The seawater treatment method according to (4), wherein 0.25 to 1.0 mg of the flocculant is added to 1 L of seawater.
(6) The seawater treatment method according to (4) or (5), wherein the flocculant is selected from a sulfate band and ferric chloride.
(7) A method for regenerating a flocculant in a seawater filtration process, comprising the step of using the recovered floc particles as a flocculant for filtration again in the method according to (4).
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described in detail below, but the present invention is not limited to those described below.
In the filtration device of the present invention, a fibrous filter material such as a nonwoven fabric can be used as the filter medium used for the filter medium layer. For example, polyester, polyester / rayon mixture, or the like is used. The shape is, for example, a sheet-like nonwoven fabric having a size of 8 to 15 mm square, preferably 9 to 12 mm square, a thickness of 5 to 10 mm, and a porosity of 90% or more.
The packing amount of the filter medium is not particularly limited because it varies depending on the size of the filtration device to be used, the size of the cylindrical column, and the size of the conical column, but practically from the lower end of the conical column to the height of the cylindrical column 300 to 600 mm. Filling is preferred.
[0012]
According to the filter structure of the present invention, a compact filter medium layer is formed in a conical column at the lower part of the filter apparatus, and a filter medium layer having a relatively high porosity is formed in an upper cylindrical column in a short time. Is possible.
[0013]
The size of the filtration device of the present invention is not particularly limited, but practically a height of 2000 to 3000 mm, a cylindrical column inner diameter of 200 to 4000 mm, and a conical column bottom inner diameter of 100 to 3200 mm. Those having an aperture ratio of 2: 1 to 5: 4 are preferably applicable.
[0014]
Next, a seawater treatment method using the filtration device of the present invention will be described.
When performing seawater filtration using the filtration device of the present invention, it is preferable to add a flocculant to the seawater to be filtered before passing water in order to facilitate aggregation and removal of suspended particles contained in the seawater. Examples of the flocculant include sulfate band, ferric chloride, polyiron (polyferric sulfate) and the like.
[0015]
When seawater filtration is performed using the filtration device of the present invention, even if a flocculant is added to the seawater to be filtered, the pressure loss due to accumulation in the filtration device is very small, and highly clear filtered seawater is used for a long time. Can be obtained.
In addition, by providing a baffle plate at the top of the cylindrical column, the filter media is suspended and flowed by the swirling flow and upward flow of backwash water during backwashing of the filtration device, and suspended particles that are trapped and adsorbed by the filter media Can be efficiently separated and discharged to the outside of the system. As a result, it is possible to reduce the amount of backwash water, and further, by adding an acid such as hydrochloric acid to the backwash water so as to be 0.01 to 0.05 N, the aggregated flocs captured by filtration are ionized. Thus, the flocculant can be recycled such that the collected floc floc is used again as a flocculant for filtration.
[0016]
As the shape of the baffle plate installed in the filtration device of the present invention, one having a width of 1/5 to 1/4 of the inner diameter of the cylindrical portion of the filtration device and a length of 1/5 to 1/4 of the inner circumference is preferable. A baffle plate is installed diagonally on the inner wall surface of the filtration device at a position 20 to 50 cm below the upper portion of the filtration device so as to block the flow of backwash water, and at a lower portion 20 to 50 cm at a position intersecting with the above position. Is preferred. The baffle plate is attached at an angle of 30 to 45 ° so that the filter medium is not laminated.
[0017]
It does not specifically limit as a material of the column which comprises the filtration apparatus of this invention, SUS (stainless steel), FRP, a vinyl chloride resin, an acrylic resin, etc. are mentioned. Examples of the perforated plate and baffle plate include SUS and vinyl chloride resin.
[0018]
FIG. 1 shows an example of the filtration device of the present invention. The filtration device 1 is provided with a cylindrical column 2 and a conical column 3 having a shape in which the inner diameter of the cylindrical column is reduced, and a swirling flow is generated in the upper part of the cylindrical column 2 in the case of backwashing. A perforated plate 5 was installed on the baffle plate 4 and the upper end to prevent the filter material from flowing out during backwashing, and a perforated plate 5 was also installed on the lower end of the conical column 3. The filter medium layer 6 is formed by filling a sheet-like piece nonwoven fabric in a wet state from the lower end of the conical column to the middle level of the cylindrical column.
[0019]
When filtering the seawater to be filtered with the filtration device 1 of the present invention, the following is performed.
After opening the valves 16, 18, 19 and backwashing with air and seawater together and stirring the filter medium layer uniformly, the valves 16, 18, 19 are closed and the valves 14, 15, 17 are opened The seawater to be filtered is introduced from the seawater supply pipe 8 to be filtered, and the air is vented by the air vent pipe inside the filtration device. When the valve 14 is closed after the air inside the filtration device is completely removed, the filter medium suspended by the flow is laminated on the perforated plate 5 of the conical column 3 to form the filter medium layer 6 and the filtration operation is performed. . For example, ferric chloride is added to the seawater to be filtered as a flocculant so that the iron concentration in the seawater is 0.5 mg / L.
[0020]
If the filtration is continued, suspended particles and aggregated floc particles in seawater accumulate on the filter medium layer 6 so that the pressure loss gradually increases and the filter medium layer 6 is compressed in the filtration direction. When the pressure loss reaches a certain level, the supply of the filtered seawater from the filtered seawater supply pipe 8 and the discharge of the filtered seawater from the filtered seawater discharge pipe 10 are stopped, the valves 15 and 17 are closed, and the valve 16 is opened. Next, the valves 18 and 19 are opened, backwashing water is supplied from the backwashing water supply pipe 11 and backwashing is performed by supplying air from the air supply pipe 12, and the compacted filter material layer 6 is broken and fluidized. Then, turbid particles and aggregated floc particles captured from the backwash water discharge pipe 9 are discharged. At this time, by adding hydrochloric acid to the backwash water so as to be 0.01 to 0.05 N, the flocs accumulated in the filter medium layer 6 can be ionized again by the continuation of filtration and recovered. The recovered material can be reused as a flocculant.
[0021]
【Example】
In the following Examples, findings obtained experimentally will be described in detail, but the present invention is not limited thereto.
[0022]
As a filtration device used in the experiment, a device having the shape shown in FIG. 1 was used. Specifically, a cylindrical column 2 made of vinyl chloride resin having an inner diameter of 300 mm and a height of 1500 mm in a filtration device 1 having a height of 2000 mm, and a vinyl chloride resin made by narrowing the inner diameter of the cylindrical column to 3: 2. A conical column 3 (height 500 mm) is provided continuously, and a vinyl chloride resin baffle plate 4 for generating a swirling flow in the upper part of the cylindrical column 2 and a filter medium at the upper end during backwashing. A perforated plate 5 made of vinyl chloride resin for preventing the outflow of water was installed, and a perforated plate 5 made of vinyl chloride resin for laminating the filter medium was also installed at the lower end of the conical column 3. The filter material layer 6 was formed by filling a thin and small polyester nonwoven fabric of 10 mm × 10 mm × 5 mm as a filter medium and filling it in a wet state from the lower end of the conical column to 50 cm above the lower end of the cylindrical column.
[0023]
Next, the valves 16, 18, and 19 are opened and backwashing is performed using air and seawater in combination to uniformly stir the filter medium layer. Then, the valves 16, 18, and 19 are closed, and the valves 14, 15, and 17 are closed. The seawater to be filtered was flown in at 60 m / H from the seawater supply pipe 8 to be filtered, and the air was vented through the air vent pipe inside the filtration apparatus. After the air inside the filtration device is completely removed, when the valve 14 is closed, the filter medium that has floated by the flow is laminated on the perforated plate 5 of the conical column 3 to form the filter medium layer 6 and the filtration operation is performed. It was. In addition, ferric chloride as a flocculant was added to the seawater to be filtered so that the iron concentration in the seawater was 0.5 mg / L.
[0024]
In the examples, FI value measurement and turbidity measurement using a laser turbidimeter were performed as the water quality evaluation of filtered seawater and filtered seawater, and the filtration loss head elevation rate (ΔP) was measured as an evaluation of the sustainability of filtration. The measurement method is shown below.
The FI value is measured by filtering the sample seawater with a 0.45 μm pore size filter (MILLIPORE) under a constant pressure of 0.2 MPa, and the time required to filter 500 ml of the sample solution after the initial filtration and 15 minutes of filtration. (t ₁ , t ₂ ) was measured and calculated by the following formula.
[0025]
FI value _{= (1 - t 1 / t} 2) / 15 × 100 (1)
t ₁ : Time for the first sample seawater 500ml to pass
t ₂ : Time required for 500 ml of sample seawater to pass after 15 minutes
The maximum FI value is 6.7, and the lower the value, the clearer the water quality. The water quality of the seawater supplied to the electrodialysis tank in salt production is an FI value of 3.0 or less.
[0026]
The filtration loss head rise rate (ΔP) is determined by continuously measuring the inlet pressure of the filtration device with a pressure gauge, the head loss (P _S ) immediately after backwash (t _S ), and immediately before the start of backwash (t _E ). From the loss head (P _E ), the following formula was used.
ΔP = (P _E −P _S ) / (t _E −t _S ) (2)
In the examples, seawater of Sagami Bay was used as filtered seawater. This filtered seawater had a temperature of 20 to 23 degrees and an FI value of 5.5 to 6.0.
[0027]
FIG. 2 shows the change over time in the FI value of filtered seawater that was passed using the filtration device of the present invention. At the beginning of filtration, the FI value of filtered seawater was 3.48, but 30 minutes passed. After that, it is 3.0 or less, and it can be seen that good filtration is performed. In the turbidity measurement results shown in FIG. 3, the turbidity was 0.06 mg / L at the beginning of filtration, but after that, the turbidity decreased rapidly and after 5 minutes, 0.01 mg / L. After that, the turbidity was maintained and good filtration was observed. This is considered to be because the apparent sieving effect was improved because the accumulation of suspended particles and aggregated floc particles in seawater progressed in the gaps between the filter media layers 6 as filtration progressed.
[0028]
FIG. 4 shows the change over time in the inlet pressure of the filtration device. The inlet pressure of the filtration device was 0.046 MPa at the beginning of filtration, and 0.091 MPa after 4 hours. The speed was 0.01 MPa / H. Thereby, since the upper limit of the filtration loss head of the pressure type filter used for normal sand filtration is about 0.2 to 0.3 MPa, it is 10 hours or more at a filtration flow rate of 60 m / H without using excessive pressure-resistant equipment. It was found that it was possible to drive.
[0029]
After the filtration operation, the supply of filtered seawater and the discharge of filtered seawater were stopped, and backwashing water was supplied from the backwash water supply pipe 10 of the filtration device 1 and air was supplied from the air supply pipe 11 to perform backwashing. The filter medium layer 6 before backwashing was considerably dense due to the filtration operation, but the filter medium was thin and small by flowing backwash water and air, so it collapsed immediately and formed with a device structure such as a baffle plate 4 The adsorbed and trapped turbid particles and the aggregated floc particles were efficiently separated by the swirling flow and the upward flow, and discharged out of the filtration device 1 system by the backwash drainage pipe 9.
[0030]
Also, FIG. 5 shows the FI value of the filtered seawater when hydrochloric acid is added to the backwashing water so that it becomes 0.05 N during the backwashing, and the flocculant is recovered from the drainage and used again for filtration. It was. From FIG. 5, it was found that when the flocculant was reused, the filtration ability was somewhat lower than when the unused flocculant was used, but recycling (reuse) was possible. . As a result, it was found that not only the amount of chemicals used can be reduced by recycling the flocculant, but also the amount of waste by filtration can be reduced.
[0031]
【The invention's effect】
As described above, the high-speed filtration device of the present invention can effectively remove turbid particles in seawater by high-speed treatment, and can reduce the size of the filtration device in salt production. . Furthermore, the amount of chemicals used can be reduced by recycling the flocculant, thereby reducing the amount of waste by filtration.
[0032]
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a basic configuration of a filtration device according to the present invention.
FIG. 2 is a graph showing the change over time of the FI value measurement result of filtered seawater in order to show the filtration performance when the filtration device of the present invention is used.
FIG. 3 is a graph showing the change over time in the turbidity measurement results of filtered seawater in order to show the filtration performance when using the filtration device of the present invention.
FIG. 4 is a graph showing a change with time of the inlet pressure of the filtration device during the filtration operation in order to express the filtration performance when the filtration device of the present invention is used.
FIG. 5 is a diagram showing a change with time of the FI value measurement result of filtered seawater in order to represent the reusability of the flocculant in the embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Filtration apparatus main body 2 Cylindrical column 3 Cone column 4 Baffle plate 5 Porous plate 6 Filter material layer 7 Air vent pipe 8 Filtered seawater supply pipe 9 Backwash drainage pipe 10 Filtered seawater extraction pipe 11 Backwash water supply pipe 12 Backwash air Supply piping 13 Drainage piping 14-20 Valve

Claims (4)

In the filtration apparatus in which a cylindrical column and a conical column with a reduced aperture ratio are provided below the cylindrical column and a perforated plate is provided at the upper end of the cylindrical column and the lower end of the conical column, From the upper end of the cylindrical column of the filtration device for removing suspended particles of seawater, which has a filter medium layer made of a fibrous filter medium and a baffle plate at the upper part of the cylindrical column, the seawater to which the flocculant is added is added. A process of inflowing at 30 to 100 m / H to filter seawater to adsorb suspended particles and agglomerated floc particles in the seawater to the filter medium, and supply water and air to which acid is added from the lower end of the conical column to counter flow A seawater treatment method comprising a step of washing, a step of separating and removing suspended particles adsorbed on a filter medium, and a step of ionizing and recovering aggregated floc particles adsorbed on the filter medium. The seawater treatment method according to claim 1 , wherein 0.25 to 1.0 mg of the flocculant is added to 1 L of seawater. The seawater treatment method according to claim 1 or 2 , wherein the flocculant is selected from a sulfate band and ferric chloride. 2. The method for regenerating a flocculant in a seawater filtration process according to claim 1 , further comprising the step of using the recovered floc floc particles as a flocculant for filtration again.

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