JP2000325705A - Flocculating settling apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate the maintenance of and reduce the running cost of a flocculating settling apparatus by minimizing the wear of a discharge line in such a manner that an intermediate receiver is equipped in the discharge line, and that a low flow rate passage is set from a settling vessel to the intermediate receiver and a high flow rate passage from the intermediate receiver to a cyclone. SOLUTION: Suspended substances in raw water are flocculated as flocculated substances containing an inorganic fluocculant 6, a high molecular flocculant 8 and sand 9 in a flocculating vessel 2 equipped with an agitator 11 driven by a motor 10. The water to treat is introduced into a settling vessel 3 through a weir 12, and precipitates 13 are separated from the upper water to treat. A discharge line 18 which discharge the precipitates 13 and which separates into sludge 17 and the sand 9 by a cyclone 16, and which feeds back the sand 9, is connected with the bottom of the settling vessel 3. Then discharge line 18 is provided with an intermediate receiver 19 storing the precipitates 13. A low flow rate passage 20 is provided from the settling vessel 3 to the intermediate receiver 19, and a high flow rate passage 21 from the receiver 19 to the cyclone 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coagulation sedimentation apparatus for separating suspended substances in raw water into sludge and treated water by coagulation sedimentation, and more particularly, to an improvement in the structure of a sediment transport line after a sedimentation step. .

[0002]

2. Description of the Related Art Substances suspended in raw water (hereinafter referred to as SS
Sometimes called [Suspended Solid]. Is known. S in conventional raw water
As a coagulation sedimentation apparatus for removing S, an apparatus is known which simply adds a coagulant to raw water to precipitate coagulation, pulls out the coagulation as sludge, and discharges treated water from the upper part. .

In such a general coagulation / sedimentation apparatus, it takes a long time to settle the coagulates, and an extremely large sedimentation tank is required. A coagulating sedimentation apparatus has been proposed.

[0004] For example, French Patent No. 1411172 discloses that in a coagulation tank, a granular material (typically, sand) is added to raw water together with a coagulant, and the inside of the coagulation tank is stirred to reduce SS in the raw water to a specific gravity. There is disclosed a coagulation / sedimentation apparatus which coagulates as relatively large flocs containing large particulate matter, sediments the flocs in the water to be treated introduced from the coagulation tank in the sedimentation tank, and separates them from the treated water. The sediment floc pulled out of the sedimentation tank is separated into sludge and particulate matter by a cyclone as a separator, and the separated particulate matter is returned to the flocculation tank and used for circulation.

[0005] This coagulation-sedimentation apparatus is constructed, for example, as shown in FIG. In FIG. 2, for example, an inorganic coagulant 102 is added to raw water 101 and a line mixer 10 is added.
3 and the polymer flocculant 105 in the flocculation tank 104.
And sand 106 as granular material is added to the coagulation tank 1
The SS in the raw water is agglomerated while being stirred by the stirrer 107 in the inside 04, and grows into flocs containing the sand 106 and having a large specific gravity and easy to precipitate. Since the water to be treated containing the grown sand-containing flocs is introduced into the sedimentation tank 108, the flocs precipitate more efficiently and quickly, and the precipitates 109 can be separated from the treated water 110 in a shorter time. The sediment 109 that has settled at the bottom of the sedimentation tank 108 is drawn by a sludge drawing pump 111, sent to a cyclone 113 through a drawing line 112 (transportation pipe), and separated into sludge 114 and sand 106 by centrifugation in the cyclone 113. ,
The separated sand 106 is returned to the coagulation tank 104 and used for circulation.

[0006]

However, in the coagulating sedimentation apparatus as described above, the sediment containing the sand 106 extracted from the sedimentation tank 108 is centrifuged into the sludge 114 and the sand 106 using the cyclone 113. Since they are separated, they need to be sent to the cyclone 113 at a high flow rate. Also,
It is necessary to use a pump capable of discharging at a high discharge pressure and a high flow rate as the sludge extraction pump 111 for transportation.

[0007] Therefore, the sediment containing the sand 106 flows through the drawing line 112 at high pressure and high flow rate in the cyclone 11.
3 will be transported. When the sediment containing the sand 106 is transported at high pressure and high flow rate in the pipes of the pump 111 and the drawing line 112, a polishing action by the sand 106 occurs,
At the seal portion of the pump 111, the impeller, the bent tube portion of the drawing line 112, etc., the abrasion proceeds, and undesirable damage may occur in a relatively short period of time. As a result, the frequency of replacement of parts especially at these parts increases, which causes problems in maintenance work and running costs.

[0010] Countermeasures such as using a material having high hardness can be considered for the wear of the pipe. However, the cost of equipment is soared, and the time required until the damage is slightly prolonged. It is not a solution.

Accordingly, an object of the present invention is to focus on the problems described above, and to fundamentally improve the structure of a separation line for extracting a precipitate from a sedimentation tank to suppress the occurrence of abrasion and damage to reduce the life of the line. The present invention is to provide a coagulation sedimentation apparatus that can greatly reduce the frequency and amount of replacement of parts, thereby facilitating maintenance and reducing running costs.

[0010]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, a coagulation / sedimentation apparatus according to the present invention comprises a coagulation tank for coagulating a suspended substance in raw water by adding a coagulant and particulate matter, and a coagulation tank. A sedimentation tank for sedimenting aggregates in the treated water to be separated into treated water and sediment, a cyclone for extracting the sediment from the sedimentation tank, and separating the extracted sediment into sludge and particulate matter, A coagulating sedimentation device having a drawing separation line for returning the separated particulate matter to the coagulation tank, an intermediate receiving tank is provided in the drawing separation line, and a low flow rate is set between the sedimentation tank and the intermediate receiving tank of the drawing separation line. The path is configured such that a path from the intermediate receiving tank to the cyclone is formed as a high flow velocity flow path.

The ratio of the flow velocity in the low flow velocity flow path to the flow velocity in the high flow velocity flow path is preferably 1: 2 or more, more preferably 1: 3 or more, and further preferably 1: 5 or more. . Further, the flow velocity in the pipe in the low flow velocity channel is preferably 1.5 m / s or less,
More preferably 1 m / s or less, further preferably 0.5 m / s
m / s or less, particularly preferably 0.1 m / s or less.

Although the form of the intermediate receiving tank is not particularly limited, it is preferable that the intermediate receiving tank be an open-to-air tank. By using an open-to-atmosphere intermediate receiving tank, the edges of the low-flow channel and the high-flow channel located on the upstream and downstream sides can be cut completely once, so that each channel affects each other. Instead, each channel can be independently configured as a channel having a desired flow rate.

In order to obtain a preferable flow rate in each flow path, a low-speed flow path is provided with a low-speed transport pump, and a high-speed flow rate pump is provided in the high-flow rate flow path. As the low-speed transport pump, a pump capable of achieving the desired flow rate in the pipe in the low-velocity flow path as described above is selected, and the high-speed transport pump basically achieves a flow rate capable of performing centrifugal separation in a cyclone. Pumps that can be selected are selected.

As the granular material used for the generation of the flocculated floc, sand can be typically used, and those having a uniform particle size are particularly preferable. Also, as a coagulant, usually,
Inorganic and polymeric flocculants can be used. The inorganic flocculant can efficiently flocculate the suspended substance in the raw water, and the polymer flocculant grows fine flocculated flocs generated by the inorganic flocculant into larger flocs by further entanglement of the polymer. Granules made of sand or the like having a large specific gravity are mixed in the grown flocks, and flocs having a large specific gravity (density) and easy to precipitate are formed as a whole.

In the coagulating sedimentation apparatus according to the present invention as described above, an intermediate receiving tank is provided in a separation line for drawing out from the sedimentation tank. From the intermediate receiving tank to the cyclone is configured as a high flow rate channel. In the low flow velocity flow path, the precipitate containing the particulate matter is transported at a low speed, so that the conventional problems of wear of the pump and abrasion of the transport pipe are greatly reduced. In addition, the high flow velocity flow path basically requires a flow velocity necessary for centrifugal separation in a cyclone. However, since the entire length of the drawing separation line is once divided at the intermediate receiving tank, this high flow velocity flow path is required. The flow path is easily formed into a short pipe, and may be formed substantially only with a straight pipe. Therefore, although a high flow velocity in the pipe is required, a high pressure is not required, and the pressure can be reduced to a value significantly lower than the conventional pressure. As a result, even in the high flow velocity flow path, the wear of the pump and the wear in the transport pipe can be significantly reduced. That is, it is possible to reduce abrasion caused by transport of particulate matter over the entire drawing separation line.

Therefore, the life of each part of the pull-out separation line is greatly extended, the frequency of replacement of parts and the amount of replacement of piping and the like are greatly reduced, maintenance is greatly facilitated, and the running cost of the apparatus is also greatly increased. To be reduced.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a coagulation / sedimentation apparatus 1 according to one embodiment of the present invention. The coagulation / sedimentation apparatus 1 includes a coagulation tank 2 and a sedimentation tank 3 disposed adjacent thereto. The coagulation tank 2 has a raw water supply line 4
The raw water 5 is supplied via a line, and in the present embodiment, the inorganic coagulant 6 is injected into the line. A line mixer 7 composed of a static mixer or the like is interposed downstream of the injection position of the inorganic coagulant 6, so that the injected coagulant is mixed well with the raw water. However, the inorganic coagulant 6 can be directly charged into the coagulation tank 2.

The coagulation tank 2 is added with a polymer coagulant 8 and sand 9 as a granular material. The polymer flocculant 8 can be injected in a line, for example, in a line downstream of the mixer 7. The flocculation tank 2 is provided with a stirrer 11 driven by a motor 10, and the suspended substance in the raw water is stirred by the stirrer 11 to form a floc containing the inorganic coagulant 6, the polymer coagulant 8, and the sand 9. Agglomerated.

As the inorganic coagulant 6, for example, polyaluminum chloride (PAC), ferric chloride, and ferric sulfate can be used. As the polymer coagulant 8, for example, a nonionic, anionic or amphoteric polymer can be used. Flocculants can be used. Examples of the anionic polymer coagulant include a polymer of acrylic acid or a salt thereof, a copolymer of acrylic acid or a salt thereof and acrylamide, and a copolymer of acrylamide and 2-acrylamido-2-methylpropanesulfonic acid salt And a tertiary copolymer of acrylic acid or a salt thereof, acrylamide and 2-acrylamido-2-methylpropanesulfonate, and a partial hydrolyzate of polyacrylamide, but are not particularly limited thereto. A typical nonionic polymer flocculant includes polyacrylamide, but is not particularly limited thereto. Examples of the amphoteric polymer flocculant include at least one cationic monomer such as a tertiary salt and a quaternary salt of dimethylaminoethyl (meth) acrylate (eg, a methyl chloride salt), acrylic acid and a salt thereof. (Salts such as sodium and calcium), 2-
A copolymer of at least one anionic monomer such as acrylamide-2-methylpropanesulfonate (salts such as sodium and calcium), or at least one of the above cationic monomers and at least one of the above 1
Ternary or quaternary or higher copolymers of at least one kind of anionic monomer and at least one kind of nonionic monomer such as acrylamide are exemplified, but not particularly limited thereto. The range of the molecular weight of the polymer flocculant is not particularly limited, but is preferably in the range of 5,000,000 to 20,000,000. These polymer flocculants can be used alone or as a mixture. The addition amount of the polymer flocculant is generally about 0.3 to 2 mg / l from an economic viewpoint.

In the coagulation in the coagulation tank 2, the inorganic coagulant 6 coagulates the suspended substance to form fine flocs, and the polymer coagulant 8 becomes entangled to grow into larger flocs. The resulting floc contains sand 9 as a particulate matter having a large specific gravity, and as a whole, grows into a relatively large floc having a large specific gravity and easy to precipitate.

The water to be treated containing the grown flocculants is
In the present embodiment, the water is introduced into the precipitation tank 3 through a submerged weir 12. An overflow weir may be used in place of the underwater weir 12. In the settling tank 3, flocculated flocs in the introduced water are settled downward, and the precipitate 13 is separated from the treated water 14 above. A plurality of inclined plates 15 are juxtaposed at the upper part in the sedimentation tank 3 to prevent the floc (sediment) from flowing out together with the treated water 14.

At the bottom of the sedimentation tank 3, a slurry-like precipitate 13 is withdrawn from the sedimentation tank 3, and the withdrawn sediment 13
Is separated from the sludge 17 by centrifugation using a cyclone 16.
And a drawing / separation line 18 for returning the separated sand 9 to the coagulation tank 2. The separated sand 9 is returned to the flocculation tank 2 again and used for circulation.

In the drawing separation line 18, there is provided an intermediate receiving tank 19 for storing the precipitate 13 once transported. And, from the settling tank 3 to the intermediate receiving tank 19
Up to, a low flow velocity channel 20 having a lower flow velocity in the pipe is formed, and from the intermediate receiving tank 19 to the cyclone 16, a high flow velocity flow path 21 having a higher flow velocity in the pipe is formed. This flow velocity difference is caused by the low speed transport pump 22 provided in the low flow velocity flow path 20.
Is provided by the high-speed transport pump 23 provided in the high flow velocity channel 21.

As described above, the ratio of the flow velocity in the low flow velocity flow path 20 to the flow velocity in the high flow velocity flow path 21 is 1: 2.
It is preferably at least 1: 3, more preferably at least 1: 3, even more preferably at least 1: 5. Further, the flow velocity in the pipe in the low flow velocity channel 20 is preferably 1.5 m / s or less, more preferably 1 m / s or less,
It is more preferably at most 0.5 m / s, particularly preferably at most 0.1 m / s. For example, as shown in an example described later, the flow velocity in the pipe in the low flow velocity flow path 20 is 0.05
Preferably, the flow velocity in the pipe in the high flow velocity channel 21 is set to about 3 m / s, which is the same as the conventional flow velocity.

In the present embodiment, the intermediate receiving tank 19 is configured as a tank that is open to the atmosphere, but it may be configured as a closed tank. The position of the intermediate receiving tank 19 is preferably a position as close to the cyclone 16 as possible. Cyclone 1
By arranging the intermediate receiving tank 19 at a position close to 6,
The flow path length of the high flow velocity flow path 21 can be kept short, and in some cases, the high flow velocity flow path 21 can be composed of only a substantially short straight pipe.

In the coagulating sedimentation apparatus 1 constructed as described above, the sediment 13 withdrawn from the sedimentation tank 3 is first passed through the low-speed transport pump 22 through the low-velocity flow path 20 at a low pipe flow rate. It is transported to the receiving tank 19. Since a low flow rate is sufficient, wear in the pipe in the low flow rate flow path 20 is significantly reduced, and wear of the seal portion and the main body of the low-speed transport pump 22 is also reduced.

In addition, the flow velocity in the pipe in the high flow velocity flow path 21 is basically required to be a flow velocity required for centrifugal separation in the cyclone 16. However, the drawing separation line 18 is once cut off in the intermediate receiving tank 19, and the high flow velocity channel 21 from the intermediate receiving tank 19 to the cyclone 16 may be a short flow path. The required load is kept relatively low, and thus the pressure generated is kept relatively low. That is, in the high flow velocity channel 21, it is possible to maintain a relatively low pressure while achieving a high flow velocity required for centrifugation in the cyclone 16. As a result, abrasion in the pipe in the high flow velocity channel 21 is also greatly reduced, and wear of the seal portion and the main body portion in the high-speed transport pump 23 is also reduced.

In order to confirm the effect of the present invention, FIG.
An experiment was performed under the following conditions using the apparatus according to the present invention shown in FIG. 1 and the conventional apparatus shown in FIG.

[0029] [common condition in apparatus according to the conventional apparatus and the present invention] Experimental Conditions raw water flow ^{rate: 300m 3 /day(12.5m 3 / h)} · settling tank Load: treated water rising rate 50 m / h, for agglomeration Sand: silica sand, specific gravity 2.5, effective diameter 0.1mm,
Addition amount in coagulation tank 20g / l Raw water turbidity: 12 degrees Raw water pH: 7.1 Inorganic coagulant: PAC 10mg / l Polymer coagulant: anionic organic polymer 1mg / l
(Polyacrylamide-based anionic polymer) Sludge withdrawal amount: 5% (10.4 liter / min) with respect to raw water flow rate

[Sludge transport conditions in conventional apparatus]-Sand separator: cyclone-Sludge transporter: High-speed sand transport pump, sand transport rate 5.2 l / min, flow velocity in pipe 3 m / s-High-speed sand transport pipe length: 6 m

[Sludge transport conditions in the apparatus according to the present invention] Sand separator: cyclone Intermediate receiving tank: Sludge residence time 1 min Low flow velocity flow path: Low-speed sand transport pump, transport volume 5.2 l / min, inside pipe Flow velocity: 0.05 m / s-High flow velocity flow path: High-speed sand transport pump, transport volume: 5.2 l / min, flow velocity in pipe: 3 / s, transport pipe length: 1 m

Experiments were carried out under the above conditions, and the apparatus of the present invention and the conventional apparatus were compared mainly with respect to the exchange amount of tubes (cumulative length). Table 1 shows the results. As can be seen from Table 1, in the device of the present invention, the exchange amount of the tube was greatly reduced. Further, the replacement frequency of the pump seal portion and the replacement frequency of the pump main body (impeller and the like) were significantly reduced by the apparatus of the present invention.

[0033]

[Table 1]

[0034]

As described above, according to the coagulation / sedimentation apparatus of the present invention, the drawing / separation line is provided with an intermediate receiving tank, and the line is divided. Since the high-speed flow path from the intermediate receiving tank to the cyclone is configured, the wear of pipes and pumps can be significantly reduced in low-flow rate flow paths, and the pressure is also reduced in high-flow rate flow paths to greatly reduce pipe and pump wear. The occurrence of abrasion is reduced as a whole of the pull-out separation line, and the replacement frequency and replacement amount of each part can be greatly reduced. As a result, not only can maintenance be facilitated, but also running costs can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a coagulation / sedimentation apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a conventional coagulation / sedimentation apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Coagulation sedimentation apparatus 2 Coagulation tank 3 Sedimentation tank 4 Raw water supply line 5 Raw water 6 Inorganic coagulant 7 Line mixer 8 Polymer coagulant 9 Granular sand 10 Motor 11 Stirrer 12 Cough 13 Precipitate 14 Treated water 15 Inclined plate 16 Cyclone 17 Sludge 18 Extraction separation line 19 Intermediate receiving tank 20 Low flow velocity channel 21 High flow velocity flow path 22 Low speed pump 23 High speed pump

Claims (7)

[Claims] 1. A flocculation tank for flocculating a suspended substance in raw water by adding a flocculant and a particulate matter, and an aggregate in water to be treated introduced from the flocculation tank is precipitated to be separated into treated water and a precipitate. A coagulating sedimentation apparatus comprising a sedimentation tank, a cyclone for extracting the sediment from the sedimentation tank, separating the extracted sediment into sludge and particulate matter, and a drawing separation line for returning the separated particulate matter to the coagulation tank In the drawing, an intermediate receiving tank is provided in the drawing separation line, and a low flow path is formed from the settling tank to the intermediate receiving tank of the drawing separation line, and a high flow path is formed from the intermediate receiving tank to the cyclone. Coagulation sedimentation equipment. 2. The coagulation sedimentation apparatus according to claim 1, wherein the ratio of the flow velocity in the low flow velocity flow path to the flow velocity in the high flow velocity flow path is 1: 2 or more. 3. The flow velocity in the pipe in the low flow velocity flow path is 1.5 m.
3. The coagulation sedimentation device according to claim 1, wherein the concentration is not more than / s. 4. The intermediate receiving tank comprises an open-to-atmosphere tank.
The coagulation sedimentation apparatus according to claim 1. 5. The coagulating sedimentation apparatus according to claim 1, wherein a low-speed transport pump is provided in the low-flow-rate channel, and a high-speed transport pump is provided in the high-flow-rate channel. 6. The coagulating sedimentation apparatus according to claim 1, wherein the granular material is sand. 7. The coagulation / sedimentation apparatus according to claim 1, wherein the coagulant includes an inorganic coagulant and a polymer coagulant.