JP6732308B2 - How to remove sand from a sand basin - Google Patents

Description

The present invention relates to a sand removal method in which sediment deposited in a sedimentation basin of a sewage treatment facility is collected together with water in a sand collecting pit and the collected sediment and water are pumped up and removed.

A low pressure water of less than 3 kg/cm ² is jetted from the nozzle to the inclined bottom of the sand basin where water has been discharged (drainage state) to flush the sediment deposited on the bottom of the sand basin Patent Document 1 discloses a low-pressure sand collecting system that collects the collected sand in a sand collecting pit provided at the bottom of the tank and pumps the collected sand along with water to a wastewater settling basin. It is disclosed.

In the sand remover, low pressure water from the water supply pump is installed at the end of the trough of the sand basin and the nozzle of the nozzle header installed at the end of the area where the bottom of the sand basin is divided into multiple parts (hereinafter, these The nozzles are collectively referred to as sand collecting nozzles) and the stirring nozzles installed in the sand collecting pit are supplied in a predetermined order. The water jetted from the sand collecting nozzle causes sediment to flow from the bottom of the sand basin and is collected in the sand collecting pit. The water mixed with earth and sand collected in the sand collecting pit is agitated by the jet water from the agitation nozzle, and is pumped up by a sand pump to remove sand.

Japanese Patent No. 3315489

By the way, the discharge amount of the water supply pump is set in consideration of the discharge amount of each nozzle and the number of nozzles that are in the water-passing state at the same time. When the discharge rate of the sand pump is set larger than that of the water supply pump and the sand pump is operated, the position of the water surface in the sand collecting pit is detected to start the operation of the sand pump. By controlling the stop, the discharge amount of the water supply pump and the discharge amount of the sand pump are balanced so that the water surface in the sand collecting pit can always maintain the drainage state.

However, the discharge amount of each of the water supply pump, each nozzle, and the sand lifting pump is constant in design, but the actual discharge amount varies depending on the characteristics of the sediment, the accumulated amount, the sand collection efficiency, and the like. The balance between the discharge rate of the pump and the discharge rate of the sand pump may be lost. This imbalance (in which the water surface in the sand collecting pit cannot always maintain the drainage state) may occur due to a reduction in the capacity of the sand pump or a failure of the nozzle switching valve.

If the discharge amount is unbalanced and left as it is, the water surface in the sand collecting pit becomes an abnormally high water level considerably higher than the upper surface of the sand collecting pit, and there is a possibility that low pressure sand collecting cannot be performed. That is, there was a possibility that the sand collection efficiency would be low.

The present invention has been made in view of the above circumstances, the low pressure water supplied from the water supply pump is sprayed from the nozzle to the inclined bottom surface of the sand basin in the drainage state to deposit the sediment deposited on the bottom surface of the sand basin. Increase the sand collection efficiency in a sand removal method in which the sediment is washed away and collected in a sand collecting pit provided at the bottom of the settling basin, and the collected sediment is pumped up with water by a sand pump installed in the sand collecting pit. The purpose is to

In order to achieve the above object, the present invention, in one aspect, injects low pressure water of less than 3 kg/cm ² from a water supply pump from a nozzle onto the inclined bottom surface of a sand basin in a drained state to settle in the sand basin. In the sand removal method of collecting the sediment in the sand collecting pit and removing the collected sediment by pumping it with the sand pump, the discharge amount of the sand pump is set to be larger than the discharge amount of the water supply pump, and the discharge of the water supply pump is set. It was detected that the balance between the amount of sand and the amount of discharge of the sand lifting pump was lost, and the water level in the sand collecting pit could not maintain the drainage state below the highest position of the inclined bottom of the sand basin. When it does, the operation of the water supply pump is stopped.

In order to achieve the above object, the present invention, in another aspect, injects low pressure water of less than 3 kg/cm ² from a water supply pump from a nozzle onto the inclined bottom surface of a sand basin in a drained state to settle in the sand basin. In the sand removal method, which collects sediment in the sand collecting pit and removes the collected sediment by pumping it up with a sand pump,
The bottom surface of the sand basin is divided into a plurality of areas in the water flow direction in the sand basin, and the order of injecting the low pressure water to the plurality of areas is set, and the sand pump is configured to drain the sand basin. In order to maintain in, the water level in the sand collecting pit starts operation at a high water level or higher, and the one that stops operation at a low water level is used, and after the operation of the sand lifting pump starts, the water level in the sand collecting pit is Every time the water level drops to an intermediate water level between a predetermined high water level and a predetermined low water level, the low pressure water injection to the preceding region is stopped, and the low pressure water injection to the subsequent region is performed, and the intermediate water level is increased. Is set to a height at which the water surface in the sand collecting pit does not drop to a low water level during the switching operation of low pressure water injection to the area, and the water level of the sand basin is equal to or lower than the highest position of the bottom surface of the sand basin. When low pressure sand collection is performed, the discharge amount of the sand pump is set to be larger than the discharge amount of the water supply pump, and the balance between the discharge amount of the water supply pump and the discharge amount of the sand pump is destroyed. When it is detected that the water level in the sand collecting pit cannot maintain the drainage state below the highest position of the inclined bottom surface of the sand basin, the operation of the water supply pump is stopped. And

Further, the low pressure sand collecting is performed when the water level in the sand collecting pit is equal to or lower than an abnormally high water level higher than the high water level, and is stopped when the water level is equal to or lower than the low water level.
Further, a preferred embodiment is characterized in that the operation of the sand pump is stopped when the detection of the abnormally high water level continues for a predetermined time or longer.

According to the present invention, it is possible to enhance the efficiency of sand collection from the bottom surface of the sand basin by the low pressure sand collecting method.

It is a longitudinal cross-sectional view of rainwater treatment equipment including a sand basin. FIG. 2 is a partially omitted plan view of a range of line XX in FIG. 1. FIG. 3 is a sectional view taken along line Y1-Y1 of FIG. 2. It is the Y2-Y2 sectional view taken on the line of FIG. FIG. 3 is a sectional view taken along line Y3-Y3 of FIG. 2. It is a water supply system diagram. It is a control system diagram explaining the control device of a sand remover. It is a figure explaining the function of a water level sensor. It is a top view which shows an example at the time of abnormally high water level of a sand basin. It is the ZZ sectional view taken on the line of FIG. It is a control flowchart figure of a water supply pump control means. It is a control flowchart figure of a sand pump control means. It is a control flowchart figure of a switching valve control means.

Next, embodiments of the present invention will be described with reference to the drawings.
In FIG. 1, reference numeral 1 is a rainwater treatment facility, which has a sand basin 2 and a pump well 3 formed between the side walls Wa and Wb (see FIG. 2). The sand basin 2 is connected to an inflow channel 4 where sewage such as rainwater and sewage is collected from a sewer pipe (not shown). A dam device 5 for allowing or blocking the inflow of sewage from the inflow 4 to the sand basin 2 is installed at the downstream end of the inflow 4. On the downstream side of the dam device 5, immediately before the upstream end of the sand basin 2, a contaminant capturing screen 6 is installed.

In order to perform low-pressure sand collection, the bottom surface 2a of the sand basin 2 is inclined so that the center becomes the deepest and a sand collection pit 7 is formed in the center thereof, as described above. A main trough 8a extending parallel to the water flow direction in the sand basin is formed in the center of the bottom of the sand basin so that the sand collecting pit side becomes deeper, and at the center of the bottom of the sand basin in the longitudinal direction from the side walls Wa and Wb. A slope 8b (hereinafter referred to as a sand collecting pit slope) that slopes down to the bottom of No. 7 is formed. Further, the bottom of the sand basin is parallel to the water flow direction from the vicinity of the side walls Wa and Wb to the main trough 8a. A large number of small troughs 8c extending in the direction of the vertical axis are formed. When the width of the sand basin is small, the main trough 8a is formed not at the center of the bottom of the sand basin in the width direction but at a position closer to one of the side walls Wa and Wb.

The pump well 3 is provided with a drainage pump P1 and a water supply pump P2 that also functions as a accumulated water pump, and a sand pump P3 that is a spiral pump in the sand collecting pit 7 has a rotation axis vertical. It is installed in. A filter F is installed at the downstream end of the sand basin 2 in FIG.

In addition, nozzles 9a and 9a' are installed at the upper ends of the main trough 8a and the sand collecting pit slope 8b, and the bottom of the sand basin is divided into a plurality of areas on both sides of the main trough 8a in the water flow direction in the sand basin (Fig. 2 and Fig. 2). In No. 6, the nozzle 9b is installed at the upper end of the divided area. A plurality of nozzles 9b installed in the area are installed at equal intervals in a nozzle header NH installed in the vicinity of the side walls Wa and Wb in each area. FIG. 5 shows an example in which nozzle headers NH1, NH2... In which a plurality of nozzles 9b are attached to the mother pipe 10 at predetermined intervals are used. In the sand collecting pit 7, a nozzle 9c for stirring earth and sand is installed. A plurality (four in FIG. 2) of the nozzles 9c are installed substantially horizontally toward the suction port of the sand pump P3, and the jetting direction thereof is directed toward the vortex flow outside the rotation center of the sand pump P3. Has been done. For simplification of the drawing, the nozzle 9c for stirring the earth and sand is omitted in FIG. 4, and the lift pump P3 is omitted in FIG.

Then, as illustrated in FIG. 5 and FIG. 6, water from the water supply pump P2 of the pump well 3 is supplied to the nozzles 9a, 9b, 9c (water flow), or the supply is stopped (water stop). There are provided switching valve groups VG1 and VG2 constituted by automatic valves for performing the above, that is, nozzle switching valve Va, nozzle header switching valve Vb, and stirring nozzle switching valve Vc. As illustrated in FIG. 6, when the bottom surface of the sand basin is divided into eight regions, eight nozzle header switching valves Vb (Vb1 to Vb8) are used. A relief circuit 11 is provided via a switching valve Vd in a pipeline connecting the water supply pump P2 and the switching valve groups VG1 and VG2, and water from the water supply pump P2 when all the switching valves are closed is provided. It is configured to escape to the sand basin 2.

As illustrated in FIG. 7, an operation panel 101 having a sand removal start button (not shown) is added to the control device 100 provided in the sand removal device for carrying out the method of the present invention, and the drainage pump control means PCON1, The water supply pump control means PCON2 and the sand lift pump control means PCON3 are incorporated, and further, the switching valve control means VCON is incorporated. As will be described later, the switching valve control means VCON sends control signals for driving the switching valve groups Va, Vb, Vc, and Vd to open (pass water) or close (stop water) in a predetermined order. To give. In particular, for the nozzle header switching valve Vb, the order of injecting low-pressure water to a plurality of regions is set, as will be described later.

A water level sensor 14 (see FIGS. 7 and 8) installed in the sand collecting pit 7 is electrically connected to the control device 100. As shown in FIG. 8, the water level sensor 14 has a high water level when the water level of the sand collecting pit 7 is equal to or higher than a predetermined high water level HWL, a predetermined intermediate water level MWL, or a predetermined low water level LWL. In addition to outputting the above detection signal, intermediate water level detection signal, and low water level detection signal, when the water surface of the sand collecting pit 7 rises to an abnormal high water level HHWL that is higher than the predetermined high water level HWL, this is detected and an error It is configured to output a high water level detection signal.

The water supply pump control means PCON2 is shown in FIG. 11 and, as will be described in detail later, after the switching valve control means VCON switches the switching valve Vd of the relief circuit 11 to the water-passing state by operating the sand removal start button ( 11 is Y. When S1 is Y. S1 is a step number. The same applies hereinafter), and the water supply pump P2 is started (S2). Then, normally, when the sand collecting operation/sand removing operation is completed and the low water level detection signal is input from the water level sensor 14 (Y in S3), the switching valve control means VCON operates the switching valve Vd of the relief circuit 11. After switching to the water stop state (when Y in S4), the water supply pump P2 is stopped (S5). Further, when the abnormal high water level detection signal is input from the water level sensor 14 without lowering the water level (Y in S6) or when the input continues for a predetermined time (Y in S7), S5 Then, the water supply pump P2 is stopped.

Further, the sand lifting pump control means PCON3, as will be described in detail later, after starting the automatic operation mode of the sand lifting pump P3 by operating the sand removal start button, until it stops the automatic operation mode. When the switching valve control means VCON switches the trough nozzle switching valve Va to the water-passing state, the sand pump P3 is started to operate, and thereafter, the operation of the sand pump P3 is stopped when the low water level detection signal is input. Let Further, when the detection signal of a high water level or higher is input, the sand pump P3 is started to operate. Then, even when the abnormal high water level detection signal is input, the operation of the sand pump P3 is stopped.

Next, the operation of the above configuration will be described. When the dam device 5 is opened, the sewage flows into the sand basin 2 and further into the pump well 3, and when the water level reaches a predetermined level, the drainage pump control means of the control device 100 of the sand removing device. The operation of the drainage pump P1 provided in the pump well 3 is started by the PCON 1, and the water in the pump well 3 is pumped up and transferred to an end treatment plant or the like (not shown).

During the transfer, sediment is precipitated from the sewage mixed with sediment that has flowed into the sand basin 2, and is deposited on the bottom surface 2a of the sand basin. When the accumulated amount reaches a predetermined value, the dam device 5 is closed to prevent the inflow of sewage into the sand basin 2. Then, the water level of the sand basin 2 and the pump 3 is lowered by the drainage of the drainage pump P1, and when the predetermined water level (WL in FIG. 1) equal to the upper surface of the weir provided between the sand basin 2 and the pump well 3 is reached, the drainage is performed. The operation of the drainage pump P1 is stopped by the pump control means PCON1.

When detecting that the water level of the pump well 3 has reached the predetermined water level (WL in FIG. 1), the control device 100 activates the water supply pump control means PCON2, the sand pump control means PCON3, and the switching valve control means VCON.

As shown in FIG. 12, the sand lift pump control means PCON3 starts the automatic operation mode of the sand lift pump P3 (S11), and the detection signal from the water level sensor 14 causes the water surface in the sand collecting pit 7 to have a predetermined low water level. It is checked whether or not it is LWL (S12), and when it is not the low water level LWL, that is, when it is higher than the high water level HWL, whether or not the nozzle switching valve Va is switched to the water-passing state by the signal from the switching valve control means VCON. Is checked (S13), and when switched, the operation of the sand pump P3 is started (S14).

Further, as shown in FIG. 13, the switching valve control means VCON first opens the switching valve Vd of the relief circuit 11 (in a water-passing state) and prepares to drive the water supply pump P2 (S21). Then, after opening the switching valve Va for nozzles and the switching valve Vc for stirring nozzles (S22), the switching valve Vd of the relief circuit 11 is closed (S23), so that less than 3 kg/cm ² of water from the water supply pump P2 is discharged. It is discharged from the nozzles 9a and 9a' to the main trough 8a and the slope 8b of the sand collecting pit.

In a preferred embodiment of the present invention, the switching valve control means VCON switches the nozzle switching valve Va to the water-passing state and simultaneously switches the stirring nozzle switching valve Vc to the water-passing state. Further, as described above, at the same time, the sand lift pump control means PCON3 is configured to start the operation of the sand lift pump P3.

The water from the water supply pump P2 was discharged from the nozzles 9a and 9a' of the main trough 8a and the sand collecting pit slope 8b by the passage of water through the nozzle switching valve Va, and accumulated on the trough 8a and the sand collecting pit slope 8b. The earth and sand are made to flow along with the water, and made to flow toward the sand collecting pit 7. Further, since water is discharged from the stirring nozzle 9c of the sand collecting pit by the water flow of the switching valve Vc for the stirring nozzle, a small amount of earth and sand already existing in the sand collecting pit is stirred and fluidized. Therefore, the earth and sand flowing into the sand collecting pit from the trough thereafter merges with the agitating earth and sand and is similarly fluidized. On the other hand, since the pumping sand pump P3 starts operating almost at the same time as the water discharge from the stirring nozzle 9c, the sewage mixed with the sand and sand that is stirred in the sand collecting pit is pumped up, and the sediment is separated by the sand separator 12 on the way. After that, it is transferred to the sewage settling basin 13.

Since the discharge amount of the sand pump P3 is set to be larger than the discharge amount of the water supply pump P2, the water level in the sand collecting pit 7 will eventually decrease. When the water level sensor 14 detects that the water level has reached the predetermined intermediate water level MWL (when Y in S24), the switching valve control means VCON determines the first region based on the intermediate water level detection signal from the water level sensor 14. In order to open the nozzle header switching valve Vb1 of B1 (S25), water is jetted from each nozzle of the nozzle header, the sediment accumulated in the first region B1 is flowed toward the main trough 8a, and the sand is further collected. It flows into pit 7. In this way, the sewage mixed with the sand that is collected and stirred in the sand collecting pit 7 temporarily rises in water level, but since it is pumped up by the sand pump P3 and transferred to the wastewater settling basin 13, it will eventually decline. To do.

When the water level sensor 14 detects that the water surface has reached the predetermined intermediate water level again (when Y in S26), the switching valve control unit VCON closes the nozzle header switching valve Vb1 in the first region B1. In order to open the nozzle header switching valve Vb2 in the second area B2 (S27), water is jetted from each nozzle of the nozzle header, and the earth and sand accumulated in the second area B2 flow toward the main trough 8a. And flows into the sand collecting pit 7.

Therefore, as in the case of the first region B1, the water surface in the sand collecting pit 7 temporarily rises but then decreases, so that when the water surface reaches a predetermined intermediate water level (when Y in S28). Since the switching valve control means VCON closes the nozzle header switching valve Vb2 in the second area B2 and opens the nozzle header switching valve Vb3 in the next third area B3 (S29), each nozzle of the nozzle header is closed. Water is sprayed from.

Therefore, as in the previous case, the water surface in the sand collecting pit 7 temporarily rises but then decreases, so when the water surface reaches a predetermined intermediate water level (Y in S210), the switching valve Since the control means VCON closes the nozzle header switching valve Vb3 in the third region B3 and opens the nozzle header switching valve Vb4 in the fourth region B4 (S211), water is jetted from each nozzle of the nozzle header. ..

Therefore, as in the previous case, the water surface in the sand collecting pit 7 temporarily rises but then decreases, so that when the water surface reaches a predetermined intermediate water level (Y in S212), the switching valve The control means VCON determines that the water discharge to the fourth region B4, that is, the last region has been completed, and opens the switching valve Vd of the relief circuit 11, while switching the nozzle switching valve Va, the stirring nozzle switching valve Vc, and the switching valve Vc. Control for closing the nozzle header switching valve Vb4 in the fourth region B4 is performed (S213), and a series of switching valve control is completed.

Further, the water supply pump control means PCON2 that has started the water supply pump P2 by operating the sand removal start button also stops the operation of the water supply pump P2 because the water level becomes low as a result of ending the water discharge to the last region. (S3, S4, S5 in FIG. 11).

On the other hand, the sand pump control means PCON3 constantly monitors the detection state of the water level sensor 14 from the start of the operation of the sand pump P3 (S14 in FIG. 12) (S15), and the water level in the sand collecting pit 7 is low. If the water level does not drop to LWL, the sand pump P3 continues to operate until the water level drops to LWL (S16). However, by closing the nozzle header switching valve Vb4 in the fourth region B4, the water level in the sand collecting pit 7 drops to the low water level LWL (when Y in S15), so the operation of the sand pump P3 is stopped. Yes (S17). After that, the sand lifting pump control means PCON3 checks whether or not the control of the switching valve is completed (S18), and if not completed, the water level in the sand collecting pit is high due to the operation stop of the sand lifting pump P3. It is checked whether or not the water level is above the HWL (S19), and when the water level is above the high water level HWL, the operation of the sand pump is restarted (S110). After that, it returns to S15. After recognizing the completion of the switching valve control in S18, the automatic operation mode of the sand pump P3 is canceled (S111), and the sand pump control means PCON3 ends the control of the sand pump P3.

As described above, when the sand pump P3 starts the automatic operation mode, the sand pump P3 is automatically operated when the water level in the sand collecting pit is equal to or higher than the predetermined high water level HWL in order to maintain the inside of the sand collecting pit 7 in the drainage state. Operation is automatically started, and when the water surface falls to a predetermined low water level LWL, the operation is automatically stopped. Further, when the water level in the sand collecting pit drops to the intermediate water level MWL between the predetermined high water level HWL and the predetermined low water level LWL, the nozzle header switching valve Vbi in the previous order area is closed and the subsequent order area is closed. Nozzle header switching valve Vbi+1 is opened. During the switching operation of those switching valves, the water surface in the sand collecting pit is stopped in the previous area by the closing operation of the nozzle header switching valve Vbi, the water injection is stopped, the sand pump is pumped up, and the downstream area is removed. It changes with the start of water injection by the opening operation of the nozzle header switching valve Vbi+1.

However, since the intermediate water level MWL, which is the time reference for the switching operation of the switching valve, is set to a height position where the water level in the sand collecting pit does not drop to the predetermined low water level LWL during the switching operation of the switching valve. The operation of the lift pump P3 can be stopped from the start of sand collection to the end of sand collection/sand removal from the entire area of the sand basin. The intermediate water level MWL, which is a time reference for the switching operation of the switching valve, can be calculated from the discharge amount of the water supply pump P2, the cross-sectional area of the sand collecting basin, the discharge amount of the sand pump P3, and the like.

If an automatic solenoid valve with a fast switching operation is used for the nozzle header switching valve Vb, the water surface in the sand collecting pit from the end of water injection to the previous area to the start of water injection to the next area. Since it is possible to reduce the amount of decrease in the water level, the accuracy of setting the position of the intermediate water level is relaxed. In addition, the load on the sand pump is stable and the life is extended.

From the start to the end of the sand removal operation, it is possible to maintain a normal drainage state in which the water surface of the sand collecting pit exists in the sand collecting pit without stopping the operation of the sand lifting pump P3. The reason is that the discharge amount of the water supply pump P2 and the discharge amount of the sand lift pump P3 normally maintain a predetermined balance. On the other hand, when the predetermined balance between the discharge amount of the water supply pump P2 and the discharge amount of the sand pump P3 collapses in the direction in which the latter is smaller than the former, as shown in FIGS. 9 and 10, The surface (water surface) of the water W in the sand collecting pit 7 will rise above the high water level HWL. Then, when the raised water surface reaches the abnormal high water level HHWL (Y in S112), the water level sensor 14 inputs an abnormal high water level detection signal to the water supply pump control means PCON2 and the sand pump control means PCON3.

The water supply pump control means PCON2 supplies water when the abnormal high water level detection signal is input (Y in S6 of FIG. 11), preferably when the input continues for a predetermined time or more (Y in S7). The operation of the pump P2 is stopped (S8). This prevents the water level from becoming higher than the abnormally high water level when the balance between the discharge rate of the water supply pump P2 and the discharge rate of the sand pump P3 is disrupted.

When the abnormal high water level detection signal is input (when Y in S112), preferably, when the input continues for a predetermined time or longer (when Y in S113), the sand pump control means PCON3. The operation of P3 is stopped (S114). It is desirable to give an alarm when the operation is stopped. If the condition of the operation stop is that the abnormal high water level detection signal continues for a predetermined time or longer, the water surface can be expected to drop from the abnormal high water level, and the effect of waves from water or strong winds flowing from the bottom of the sand basin. Thus, it is possible to prevent the operation of the sand pump from being unnecessarily stopped when an abnormally high water level detection signal is input for less than the predetermined time.

When the abnormal high water level HHWL is detected, it is possible to stop only the operation of the water supply pump P2 and not stop the operation of the sand pump P3. As a result, it can be expected that the abnormally high water level state will be resolved early.

The above-mentioned abnormal high water level HHWL is the height at which the height of the water surface of the sand basin is such that low-pressure sand collection from the bottom of the sand basin cannot be performed even if the water supply from the water supply pump P2 is continued. The upper limit of the abnormal high water level HHWL is the highest position of the inclined bottom surface of the sand basin, that is, the water level at which the entire bottom surface of the sand basin is submerged, and the lower limit thereof is the upper surface of the sand collecting pit, that is, the same water level as HWL. That is, the abnormally high water level HHWL can be set to any water level between the upper limit and the lower limit. In addition, it is natural that the water level above the high water level HWL, which is the water level at which the sand pump P3 is restarted, must be lower than the abnormal high water level HHWL. To summarize the above description, when the water level of the sand basin is between the upper surface (HWL) of the sand pit and the highest position (HHWL) of the inclined bottom of the sand basin, the low pressure sand collection from the bottom of the sand basin Therefore, in the embodiment of the present invention, when the water level of the sand basin is between the upper surface (HWL) of the sand collecting pit and the highest position (HHWL) of the inclined bottom surface of the sand basin, the low pressure collecting is performed. You can do sand. Then, when an abnormally high water level is detected, and when a low water level or less is detected, the water supply pump and the sand pump are stopped. The sand is stopped when it is below the low water level.

1 Rainwater treatment facility 2 Sand basin 2a Bottom of sand basin 3 Pump well 7 Sand collecting pit 8a Main trough 8b Second trough 8c Small trough 9a, 9b, 9c Nozzle NH1 to NH4 Nozzle header P1 Drainage pump P2 Water pump P3 Sand pump 14 Water level sensor PCON1 Drain pump control means PCON2 Water supply pump control means PCON3 Sand pump control means VCON Switching valve control means HHWL Abnormal high water level HWL High water level MWL Intermediate water level LWL Low water level

Claims (1)

Low pressure water of less than 3 kg/cm ² from a water supply pump is jetted from the nozzle to the inclined bottom of the drainage sand basin, and the sediment deposited in the sand basin is collected in a sand collecting pit, and the collected sand is lifted. In the sand removal method to remove by pumping up,
The discharge rate of the sand pump is set larger than the discharge rate of the water supply pump,
The balance between the discharge rate of the water supply pump and the discharge rate of the lift pump is upset, and the water level in the sand collecting pit cannot maintain the drainage state below the highest position of the inclined bottom surface of the sand basin. When it is detected that the water supply pump is stopped,
A sand removal method characterized by that.

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