JPH09299713A - Sludge rake-up device in precipitator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance corrosion resistance and to reduce driving power cost. SOLUTION: A driving shaft 11 installed in the central part of a precipitator 2 in the height direction, a feed well 13 concentric with the driving shaft 11, a feed pipe 15 for making the inside and the outside of the precipitator 11 to communicated with each other, rake arms 16 fixed in the lower part of the driving shat 11, rake supporting members 17A for supporting the rake arms 16, rakes 18 fixed on the rake arms 16 and the like are made of fiber reinforced plastic.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sludge scraper for scraping sludge settling at the bottom of a settling tank in wastewater treatment to a sludge collecting pit at the center bottom.

[0002]

2. Description of the Related Art For example, in a wastewater treatment facility for treating various kinds of wastewater (hereinafter simply referred to as "sewage") such as public sewerage, hot spring wastewater, factory wastewater, etc., generally, sedimentation that separates wastewater into supernatant liquid and sludge The settling tank is equipped with a so-called sludge scraper that scrapes sludge settling at the bottom into the sludge collecting pit.

The sludge scraper is conventionally made of a metal material because it needs a sufficiently high strength to scrape the sludge. On the other hand, this sludge scraper is in contact with sewage for a long time, and sewage contains various types of substances such as oxygen, acidic substances, and oxidizers that are involved in corrosion. Has become.

Therefore, conventionally, a steel material has been mainly used in which the SS material is coated with tar epoxy to improve the corrosion prevention effect. Further, in the case of a sludge scraper that is more likely to be corroded, for example, in a sludge scraper in a hot water drainage treatment facility with high acidity, for example, SUS304 steel may be used.

[0005]

The material obtained by coating the SS material with the tar epoxy does not always show sufficient corrosion resistance, and therefore, it is necessary to recoat the material once in about two years, whereas SUS304. When steel is used, it generally has high corrosion resistance.

However, when SUS304 steel is used, not only the material cost increases, but also highly corrosive sewage that cannot be coped with, especially public sewer mixed with seawater, hot spring drainage, and factory drainage with low PH are used. There are many examples of processing.

Further, since all of the conventional examples use a metal material, they are heavy in weight, and the rotational driving power cost and the installation cost increase.

[0008] Therefore, the main object of the present invention is to reduce the operating power cost by excellent corrosion resistance and weight saving.

[0009]

The present invention, which has solved the above-mentioned problems, provides a settling tank for separating sewage into sludge and supernatant.
A drive shaft that is rotationally driven about the vertical axis by a drive unit and that is vertically arranged in the center, a rake arm that is connected to the bottom of the drive shaft in a state that extends substantially horizontally, and a rake that is fixed to the rake arm. A rake support member that enhances the support strength of the rake arm by connecting the drive shaft and the rake arm, and sludge precipitated by the rotation of the rake arm and the rake about the longitudinal axis of the rake arm along with the rotation of the drive shaft at the central bottom. A sludge scraper for scraping into a mud collecting pit, characterized in that at least the drive shaft, the rake arm and the rake support member are made of fiber reinforced plastic resin.

In the sludge scraper according to the present invention, the drive shaft, the rake arm and the rake support member, which come into contact with wastewater and have a large strength load, are made of fiber reinforced plastic resin. The fiber reinforced plastic has better corrosion resistance than any of the conventional examples and has a semi-permanent service life. Furthermore, along with this improvement in corrosion resistance, SS41 has a specific gravity of 7.8, while fiber-reinforced plastic (polyester) has a specific gravity of 1.9, which is about 1
Since it is about / 4, the rotary drive power cost of the scraper can be reduced and the installation cost can be reduced.

On the other hand, initially, it was feared that the strength of the fiber-reinforced plastic was not sufficient, but it was confirmed that the scraper according to the present invention could actually secure sufficient strength.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 1 is a longitudinal sectional view of a central drive type sewage treatment facility provided with a sludge attractor 1 according to the present invention in a settling tank 2, and FIG. 2 is a plan view thereof.

In the settling tank 2, sludge is settled and separated from the supernatant. Above the inner surface of the settling tank 2,
An overflow weir 3 is provided, and the overflow weir 3 discharges the supernatant to the outside of the settling tank 2. A weir plate 3A made of resin, for example, PVC resin, is attached to the inner peripheral edge of the overflow weir 3.

The bottom of the settling tank 2 has an inverted conical shape with a depressed central portion, and sludge collected at the bottom is collected in the central portion. A corn scraper 19 for accumulating sludge collected by the sludge scraper 1 is provided in the sludge collecting pit 4 in this central portion, and a sludge drawing pipe 5 for discharging sludge to the outside is provided in the sludge collecting pit 4. It is connected. Further, a steel bridge 6 is installed on the upper surface of the settling tank 2, and the sludge attractor 1 is suspended.

The sludge attractor 1 according to the present invention provided inside the settling tank 2 is provided with a drive shaft 11 extending in the height direction at the center of the settling tank 2, and the drive shaft 11 of the bridge 6. It is rotated about a vertical axis by a drive motor 12 installed on the upper side. An upper portion of the drive shaft 11 inside the precipitation tank 2 is covered with a feed well 13, and the feed well 13 is fixed to the bridge 6 via a mounting bracket 14. Further, the inside of the feed well 13 is communicated with a feed pipe 15 into which waste water flows from the outside of the settling tank 2.

The settling tank 2 is fed through the feed pipe 15.
Sewage is introduced into the feed well 13, introduced into the feed well 13, and then introduced into the precipitation tank 2.

Below the drive shaft 11, a settling tank 2 is provided.
Two rake arms 16 extending along the radial direction of the rake arm 16 to the inner peripheral surface thereof are fixed. Since the rake arm 16 is long, rake support members 17A and 17A are provided between the rake arm 16 and the central portion of the drive shaft 11 in the height direction to support the rake arm 16. Further, in order to increase rigidity, the four stays 17 are formed in a square shape in a plan view.
B, 17B ... Are provided, and auxiliary rake support members 17C, 17C are connected between the two points and the drive shaft 11.

Four rakes 18, 18 ... Are fixed to the rake arm 16 so as to be spaced apart from each other in the longitudinal direction, and as the drive shaft 11 and the rake arm 16 rotate, the rakes 18, 18 ,. The sludge that has settled on the lower surface of the settling tank 2 is moved to the sludge collecting pit 4 at the center of the lower surface of the settling tank 2 as it moves along.

Characteristically, in the present invention, a member of the sludge attractor 1 located inside the wastewater, specifically, in this embodiment, the drive shaft 11, the feed well 13, the mounting bracket 14, and the feed. Pipe 15, rake arm 1
6, the rake support member 17A, the stay 17B, the auxiliary rake support member 17C, the rake 18, and the cone scraper 19 are all made of fiber reinforced plastic, for example, fiber reinforced polyesdel resin.

Although not shown in detail with reference numerals in particular, for example, small members such as bolts and nuts for connecting them are not limited to the driving means (driving motor 12) and all the members located in the precipitation tank are included. It is more desirable to use a resin member.

In the sludge scraper 1 having the above structure, a large torque is applied to the drive shaft 11 and the rake arm 1 is used.
6 is bent. Therefore, at least these and each rake support member 17A must be made of fiber reinforced plastic. Preferably, all structural members are made of fiber reinforced plastic, including stays 17B and auxiliary rake support members 17C. The structural member has a large weight ratio in the sludge attractor 1, and it is necessary to make the structural member in order to reduce the weight. Other members not constituting the structural member may be general-purpose plastic such as polyethylene instead of fiber reinforced plastic.

(Strength Trial Calculation) In the following, model calculation was carried out in order to know the strength required for the sludge attractor when actually operating the sludge attractor. This model calculation was performed by assuming the first settling basin for treating urban sewage and calculating the energy required for the sludge attractor 1 in the sludge treatment facility shown in FIG. 1 to scrape the sludge. As shown in FIG. 3, the initial settling tank was assumed to have a diameter D = 20 m, which is relatively large in this type of wastewater treatment facility. Sewage is introduced here to a water depth of 2.5 m. In addition, the various conditions shown in Table 1 were assumed for the calculation.

[0023]

[Table 1]

First, the transport amount V [m ³ ] of sludge in the settling basin is obtained from the equation (1).

[0025] V = The ^{(πD 2/4) × H} = (π × 20 2 /4)×2.5 = 785.4 ...... (1), since the precipitation time is 1.5 hours, the first precipitation The amount of sewage Q [m ³ / hour] flowing into the pond can be obtained from the equation (2). Q = V / 1.5 = 785.4 / 1.5 = 523.6 [m ³ ] ... (2) The quality of the inflowing sewage is 250 ppm, and the removal rate is 40%, so the amount of dry sludge Q _D [t / hour] is (3)
Calculated from the formula. Q _D = 523.6 × 250 × 0.4 × 10 ^-6 = 0.0524 [t / hr] (3) If the sludge water content of the first settling tank is 98%, the amount of sludge Q ₉₈
[M ³ / hour] is obtained from the equation (4). _{Q 98 = 0.0524 × 100 / (} 100-98) = 2.62 [m ³ / h] ... (4) energy scrape the sludge, transport the sludge sludge raking device is deposited during one rotation It was calculated as the driving electric horsepower required to perform.

The time t [hours] required for one rotation when the peripheral speed is 3 [m / min] is calculated by the equation (5). t = π × 20 / (3 × 60) = 0.35 [hours] (5) The sludge amount Q _t [t / rotation] deposited during t hours can be obtained from the equation (6). _{Q t = Q 98 × 1.03 ×} 0.35 = 0.945 [t / rotation] ... (6) Therefore, the power spent to transport sludge [N · kw]
Is calculated from the equation (7). N = Q _t × μ × 3 / (6120 × η) = 0.00022 [kw] (7) where η; cyclodeceleration mechanical efficiency (= 0.9 × 0.9)
× 0.9 = 0.729) μ; Sludge friction coefficient (= 0.035) From the above model calculation, even if the sludge scraper installed in a sedimentation tank with a diameter of 20 m is relatively large, sludge Since the power required to scrape the object is as small as 0.00022kw, the torque applied to the shaft is very small. From this, it is understood that the strength can be sufficiently endured even if the resin member is used.

Next, a sludge scraper using a FRP member shown in FIG. 1 (hereinafter referred to as "FRP product") and a sludge using a member made of SS41 steel coated with tar epoxy instead of the FRP member. The tensile strength, specific gravity, and corrosion resistance of the scraper (hereinafter referred to as "SS41 product") were compared. The results are shown in Table 2.

[0028]

[Table 2]

As can be seen from Table 2, the FRP products are S
Although it is slightly inferior to the S41 product in tensile strength,
As shown in the above model experiment, there is no problem as the strength of the sludge scraper. On the other hand, the specific gravity is about 1 for SS41 products.
Since it is / 4, the energy consumed during operation can be greatly reduced. Regarding corrosion resistance,
In the case of SS41 products, in order to maintain corrosion resistance, repainting is inevitable at intervals of about 2 years, but FRP products do not corrode and can be said to have excellent corrosion resistance.

[0030]

As described above, according to the present invention, the drive power cost and the installation cost can be reduced because it does not corrode even when it comes into contact with sludge and is lightweight.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a sewage treatment facility equipped with a sludge scraper according to the present invention.

FIG. 2 is a plan view thereof.

FIG. 3 is a schematic diagram showing the dimensions of the first settling tank used in the model calculation.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Sludge attractor, 2 ... Sedimentation tank, 3 ... Overflow weir, 4 ... Mud collecting pit, 5 ... Sludge extraction pipe, 6 ... Bridge, 11 ... Drive shaft,
12 ... Drive motor, 13 ... Feed well, 14 ... Mounting bracket, 15 ... Feed pipe, 16 ... Rake arm, 17A ... Rake support member, 17B ... Stay, 17C
... auxiliary rake support member, 18 ... rake, 19 ... corn scraper.

Claims (2)

[Claims] 1. A settling tank for separating sewage into sludge and supernatant liquid, a drive shaft rotationally driven by a drive means about a vertical axis center and arranged vertically in the center, and a horizontal shaft at the bottom of the drive shaft. And a rake arm fixed to the rake arm, and a rake support member for connecting the drive shaft and the rake arm to enhance the support strength of the rake arm. Is a sludge scraper that scrapes sludge deposited by rotation of the rake arm and the rake about the longitudinal axis of the rake into a central bottom mud collecting pit, and at least the drive shaft, the rake arm and the rake support member are made of fiber reinforced plastic resin. A sludge trapping machine in a settling tank characterized by the above. 2. A sludge scraper in a settling tank according to claim 1, wherein all members except the driving means are made of fiber reinforced plastic resin.