JPS6330052B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for backwashing a liquid filter filled with granular material and having a material outflow prevention mechanism.

[Prior art and problems to be solved by the invention]

It is a well-known fact that when backwashing a liquid filter using granular material, by simultaneously supplying water and air, a much higher cleaning effect can be obtained than when water is supplied alone.

However, the suitable conditions in this case have not been studied much in the past. The reason for this is that in the conventional structure of the overflow machine, when water and air are used at the same time, granular material flows out and is lost, and consideration must first be given to avoid this. This is because the cleaning time could not be set freely.

The structure of a conventional liquid filter filled with granular material is as shown in FIG. 1, for example. That is, in the vertical cylindrical filter machine 12, a cleaning drainage gutter 10 is provided on the upper side inside the filter main body 12a, a fluid inflow/outflow mechanism 13 is provided on the lower side, and a material layer 7 made of granular material is provided on the upper side as a filling material. The lower side is filled with a material support layer 8. On the other hand, on the outside upper side thereof, a raw water supply pipe 14 equipped with a raw water valve 1 connected to a cleaning drainage gutter 10 and a cleaning water discharge pipe 15 equipped with a cleaning drainage valve 6 are arranged. Further, a fluid inflow/outflow pipe 16 is connected to the fluid inflow/outflow mechanism 13, which includes an overwater valve 2, a water waste valve 3, a water backwash valve 4, and an air backwash valve 5.
are branched into the fluid inflow and outflow mechanism 13.

To explain the method for backwashing the filter machine 12, in order to prevent granular material from flowing out when backwashing is performed using water and air at the same time, the drain valve 3 is opened in advance to drain water. The water level in the machine 12 is lowered to near the top of the material layer 7, and then backwashing is performed at the same time. Air supply is stopped before the water level reaches the top of the washing and draining gutter 10, and thereafter backwashing is performed by supplying water alone. This is what we do.

In such backwashing of the filter machine 12, it is necessary to prevent the granular material from flowing out during simultaneous backwashing, so there is a drawback that the water supply rate is limited and a sufficient backwashing effect cannot be obtained. To compensate for this drawback, the water supply time is increased and the same process is repeated twice.
The current situation is that this is happening frequently. In this way, conventional backwashing methods are complicated and require a long time to operate.
Furthermore, it was difficult to obtain a sufficient backwashing effect.

[Purpose of the invention]

An object of the present invention is to provide an effective method for backwashing a liquid filtration machine that solves the above-mentioned conventional problems. That is, an object of the present invention is to disclose conditions for supplying backwash fluid when backwashing a liquid filter using granular material and having a material outflow prevention mechanism.

[Means for solving problems]

The present invention is characterized in that a packed layer of granular material is formed inside the filter body, a gas-liquid separation plate is provided with a gap between the periphery of the cleaning drainage gutter installed in the filter body and the inner wall of the filter body, and The upper end opening of the liquid separation plate is located lower than the upper end of the cleaning drainage gutter, forming a free water surface above, and forming a gas-liquid multiphase flow path and a sedimentation flow path for the separated material on the inside and outside of the gas-liquid separation plate. At the same time, a method for cleaning a liquid filtration machine is provided in which a backflow prevention plate is provided at an angle with a gap in the lower opening formed by the gas-liquid separation plate so as to face below the sedimentation channel of the separation material. , after backwashing the liquid filtration machine through a simultaneous water and air backwashing step, when backwashing is performed through a water-only backwashing step by stopping the supply of air and supplying only water, the simultaneous backwashing is While maintaining the liquid level in the filter at the same height as or higher than the surface of the packed bed, the linear velocity of the water is set to 1/15 to 1/10 of the terminal velocity of the granular material in water in the field of gravity. This is a method for cleaning a liquid permeator, characterized in that the cleaning method is carried out by setting the linear velocity of the air within the range of 20 to 40 m/h.

Generally, the suitable linear velocity of water supply in water-only backwashing is about 1/10 of the terminal velocity of a single material particle in water under the force of gravity. At this backwashing speed, the number of collisions between the material particles is theoretically the highest, and according to experiments, a good fluidity state of the material particles is observed.

On the other hand, in simultaneous backwashing with water and air, it was generally thought that the water supply rate could be reduced due to the effect of the combined use of air, but according to experiments conducted by the present inventors, fluidization of material particles was It was confirmed that the backwashing effect was almost entirely controlled by the water supply rate, and that the presence or absence of air supply or the level of the supply rate had little effect, and that the backwashing effect was significantly reduced when the water supply rate was lowered. This is a phenomenon that can be easily understood if we consider the density difference between water and air.

The effect of air backwashing is that bubbles burst and coalesce unsteadily in the material layer that is being fluidized by water flow, resulting in a violent stirring action similar to a boiling phenomenon. This phenomenon is observed only when the material layer is fluidized by water backwashing, and when the water supply rate is low and the fluidization of the material layer is weak or stopped, air may flow into the material layer. The material simply passes through a certain path, and no effect of shaking the material is observed. The commonly held belief that the water supply rate can be reduced when simultaneous backflow of water and air is performed as described above is incorrect.

In the present invention, the linear velocity of the supplied air during simultaneous backflow is set to 20 to 40 m/h, but this is based on the experimental results of the present inventors. That is, the linear velocity
If it is less than 20m/h, the backwashing effect is insufficient because the airflow distribution to the material layer becomes uneven, and although the backwashing effect improves as the linear velocity increases,
This is because in the range exceeding 40 m/h, the speed remains almost the same, and when the backwashing effect and the economical efficiency of backwashing are comprehensively judged, it is concluded that the above range is preferable.

As mentioned above, since the fluidization of the material layer is controlled only by the linear velocity of water supply, the linear velocity of air supply can be set within the above certain range regardless of the density and particle size of the material particles. .

On the other hand, regarding the simultaneous backwashing time, that is, the supply time of cleaning fluid, the total amount of backwash water supplied is 2 to 3 times the volume of the filling space of the material bed (the space inside the filter machine from the top surface to the bottom surface of the material bed). It is set as follows. Expressing this in an equation, the simultaneous backwashing time T ₁ (min) is T ₁ =60k ₁ Z/LVl (1). However, _k1 is the coefficient (2 to 3), Z is the layer thickness of the material layer (m), and LVl is the linear velocity of the cleaning water (m/h).
(The linear velocity LVl is the flow rate of the wash water divided by the cross-sectional area of the filter, and the same is true for the wash air).

On the other hand, regarding the conditions for water-only backwashing, the linear velocity of the washing water is set to 1/15 to 1/10 of the terminal velocity of the granular material in water in the field of gravity, as described above, and the supply time is set to The supply amount is set to be 2 to 3 times the total volume of the filling space of the material layer and the volume of the water layer above the material layer. Expressing this in an equation, the water-only backwashing time T ₂ (min) is T ₂ =60k ₂ ·(Z+H)/LVl (2). However, k ₂ is a coefficient (2 to 3), H is the difference in height (m) between the upper end surface of the granular material layer and the washing water discharge surface (usually the upper end of the washing drainage gutter), and Z and LVl are the above (1). The meaning is the same as in the expression.

The conditions of the present invention explained using equations (1) and (2) above are all conclusions obtained by summarizing various experimental results by the present inventors.

When backwashing is performed simultaneously with water and air, the agitation of the material layers is extremely intense, so when multi-layered material layers are used, mixing of the material layers occurs. In order to stratify the material, simultaneous backwashing may be followed by water-only backwashing for 2 minutes or more under conditions that sufficiently fluidize the material layer. Usually, the backwashing time T ₂ is 2 minutes or more, so water backwashing and stratification can be performed simultaneously.

〔Example〕

Next, an example of a conventional method and an embodiment of the present invention will be compared and explained with reference to the drawings.

(Conventional Example) A conventional liquid filter is shown in FIG. 1, and the outline of its structure is as described above. In Figure 1, Z is 1.7m and H is 0.7m, and the material layer is a single layer filled with sand with an effective diameter of 1.2mm as granular material.

For example, backwashing in such a filter is quoted from the Japan Sewage Works Association Magazine vo1.13, No.140, P.37-50,
As shown in the simplified figure 2, draining water,
The backwashing operation, which consists of the four steps of air (single) backwashing, water/air simultaneous backwashing, and water (single) backwashing, was performed twice, and after finally discarding the water, the regular overflow process resumed. be done. The opening/closing status of each valve in each step in this case is as shown in Figure 2, where horizontal lines indicate "open" and areas without horizontal lines indicate "closed".

In this case, the optimal value of the water supply speed determined from the terminal velocity of the granular material sand in water under the force of gravity is approximately 72 m/h, but in simultaneous water and air backwashing, the above linear velocity is only 10 m/h. h, and it is clear that under these conditions, the material particles do not fluidize, so the effect is insufficient. Furthermore, in the subsequent water (single) backwashing, it is said that a water supply speed of 40 m/h is sufficient since it is a simultaneous backwash, but complete fluidization cannot be achieved and water backwashing is The effect will also be unsatisfactory.

The linear velocity of cleaning air is 60 m/min for both air (single) backwashing and simultaneous backwashing.
h, and in Fig. 2, the horizontal lines indicating the opening of the water backwash valve are in two levels, upper and lower. The upper line indicates a linear velocity of 10 m/h, and the lower line indicates a linear velocity of 40 m/h. .

In order to compensate for the above problems, as is clear from FIG. 2, each backwashing time is set longer and washing is performed twice. However, as long as the material particles are not fluidized, even if the backwashing time is extended, the suspended matter trapped between the material particles will not be released, so the backwashing will inevitably be incomplete.

(Embodiment of the present invention) On the other hand, the filter machine shown in FIG. 3 to which the present invention is applied has a gas-liquid separation plate 9 as a material outflow prevention mechanism, so that the linear velocity of the cleaning fluid can be freely supplied. It is configurable.

That is, this filter 12 is a liquid filter that has a material layer 7 made of granular material and performs backwashing using a combination of air and water. A gas-liquid separation plate 9 is provided on the inner wall of the main body 12a with a gap maintained, and the upper end opening of the gas-liquid separation plate 9 is connected to the cleaning drainage gutter 1.
A free water area is formed above the upper end of the gas-liquid separation plate 9, and a gas-liquid multiphase flow path and a sedimentation flow path for the separated material are formed on the inside and outside of the gas-liquid separation plate 9. This is a liquid filtration machine in which a backflow prevention plate 11 is provided in an inclined manner with a gap maintained in the lower opening of the separation material so that the sedimentation channel for the separation material faces downward.

Therefore, in the above figure, H is 1.0m,
Material layer 7 is a two-layer type, with the upper layer having a layer of sand with an effective diameter of 1.2 mm.
0.3 m, the lower layer is filled with anthracite with an effective diameter of 2.4 mm to a layer thickness of 0.7 m, and the total thickness Z of the material layer 7 is 1.0 m.

The difference in device structure between the above-mentioned permeator shown in FIG. 3 and the example shown in FIG. 1 is that the former has a gas-liquid separation plate 9,
The only difference is that the backflow prevention plate 11 is disposed and the drain valve 3 is omitted, but the rest is the same.

Next, to explain the backwashing operation of the filter shown in Figure 3, first, the linear velocity of water is set to the optimum value of 72 m/h obtained from the terminal velocity of the two types of granular materials in water in the field of gravity, and the The linear velocity of was set at 40 m/h. On the other hand, the backwash time was determined by substituting the above conditions into equations (1) and (2) above. That is, T ₁ will be 1.7 to 2.5 minutes, but to be safe, it will be set to 2.5 minutes, and T ₂ will be 3.3 to 5.0 minutes, but it will be set to 3.5 minutes, and the total will be 2.5 minutes.
It was set as 6.0 minutes.

Thus, as shown in Figure 4, water and air backwashing was carried out simultaneously for 2.5 minutes with the water level inside the filter machine raised higher than the surface of the material layer by omitting water removal and air backwashing for the filter machine after the completion of the overprocessing process. and then water backwash 3.5
When the backwashing was carried out for several minutes, the effect of backwashing was complete.

On the other hand, when comparing the above conventional example and the embodiment of the present invention in terms of washing water consumption per unit area,
Calculating from the linear velocity, backwashing time, and number of operations, the amount was 8.3 m ³ /m ² and 7.2 m ³ /m ² , respectively, and it can be said that the amount in the example of the present invention is smaller. The same applies to cleaning air consumption.

Furthermore, as is clear from comparing the cleaning schedules of the two in Figures 2 and 4, the conventional method requires extremely complicated valve opening and closing operations, and the time required for backwashing is 38 minutes. In comparison, the embodiment of the present invention requires extremely simple valve searching and only 6 minutes of backwash time. This fact not only simplifies the equipment for backwashing the filter, but also
This means that the capacity of storage tanks before and after the filtration machine required for backwashing operations is considerably reduced, and if these indirect effects are also taken into account, there are direct and indirect economic effects of the present invention. is extremely large.

〔Effect of the invention〕

As described above, the present invention provides optimal operating conditions for backwashing in a liquid filter machine equipped with a material outflow prevention mechanism, of which the liquid filter machine shown in FIG. 3 is a typical example. According to the company, this method has many advantages over conventional methods, such as simple operations that allow complete cleaning to be achieved in a short time, simplified backwashing equipment, and reduced consumption of cleaning water and cleaning air. It is something that you have.

[Brief explanation of the drawing]

Figures 1 and 2 show a conventional example, Figure 1 is a longitudinal cross-sectional view of the filter, Figure 2 is an explanatory diagram of the backwashing process, and Figures 3 and 4 are examples of the present invention. FIG. 3 is a longitudinal sectional view of the filter, and FIG. 4 is an explanatory diagram of the backwashing process. 1... Raw water valve, 2... Overwater valve, 3... Discharge valve, 4...
Water backwash valve, 5...Air backwash valve, 6...Washing drain valve, 7
... material layer, 8 ... material support layer, 9 ... gas-liquid separation plate, 1
0... Washing drain gutter, 11... Backflow prevention plate, 12... Filter machine, 12a... Filter machine main body, 13... Fluid inflow/outflow mechanism.

Claims (1)

[Scope of Claims] 1. A packed layer of granular material is formed inside the filter body, and a gas-liquid separation plate is provided with a gap between the periphery of the cleaning drainage gutter built into the filter body and the inner wall of the filter body. , and the upper end opening of the gas-liquid separation plate is located lower than the upper end of the cleaning drainage gutter, so that a free water surface is formed above, and a gas-liquid multiphase flow path and a sedimentary flow of the separated material are formed on the inside and outside of the gas-liquid separation plate. A method for cleaning a liquid filtration machine in which a backflow prevention plate is provided at an angle with a gap formed in the lower opening formed by the gas-liquid separation plate facing downwardly from the sedimentation channel of the separation material. After backwashing a liquid filtration machine through a simultaneous water and air backwash process, when backwashing is performed through a water-only backwash process by stopping the air supply and supplying only water, the simultaneous backwash process While maintaining the liquid level in the filter at the same height as or higher than the surface of the packed bed, the linear velocity of the water is set to 1/15 to 1/15 of the terminal velocity of the granular material in water in the field of gravity. to a range of 1/10,
A method for cleaning a liquid filtration machine, characterized in that the cleaning method is carried out by setting the linear velocity of air in a range of 20 to 40 m/h. 2 The backwashing time T ₁ (min) of the simultaneous backwashing step is
The following formula T ₁ = 60k ₁ Z/LVl (where, k ₁ is the coefficient (2 to 3), Z is the layer thickness of the granular material layer (m), and LVl is the linear velocity of the cleaning water (m/h))
The cleaning method according to claim 1, wherein the cleaning method is set by calculating. 3 The backwash time T ₂ (min) of the water-only backwash process is
The following formula T ₂ = 60k ₂・(Z+H)/LVl (where, k ₂ is the coefficient (2 to 3), Z is the layer thickness of the granular material layer (m), and H is the upper end surface of the granular material layer and the washing water discharge surface. 2. The cleaning method according to claim 2, wherein the cleaning method is calculated and set using the difference in height (m) of the cleaning water (LVl is the linear velocity of the cleaning water (m/h)).