A weir gate water flow measurement method

Abstract

The present application relates to sewage treatment technical field, specifically to a kind of weir gate water flow measurement method.The method measures the liquid level before weir gate, flow rate, the opening height of weir gate and the flow rate after water flow through weir gate, by measuring these more accurate data, avoid the flow rate of directly measuring weir gate water flow in traditional measurement, due to the existence of liquid level collapse and flow rate fluctuation, inaccurate condition, and these accurate data are calculated, more accurate measurement results can be obtained.The method of the present application overcomes the limitation that the traditional flow measurement must be straight inlet channel, can be applied to the application scene that water flow inlet channel has no straight pipe section and water flow changes greatly, has wide application range, compared with traditional measurement method, measurement error is reduced from about 20% to about 5%, greatly improves the precision of measurement, has important guiding significance for subsequent process control and reagent dosage in sewage treatment process.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a method for measuring the flow rate through a weir gate. Background Technology

[0002] In wastewater treatment plants, the water entering the biological tanks is first introduced into the inlet channel, and then distributed to multiple biological tanks. At this time, the flow rate of the water entering the biological tanks is regulated by the weir gate, which provides a basis for the amount of chemicals to be added. Therefore, the flow rate of the weir gate is quite important.

[0003] Existing weir gate flow rate measurement devices mostly use flow velocity meters to measure flow velocity and level gauges to measure the change in liquid level before and after the weir gate. The flow rate is then calculated using the following formula:

[0004] Flow rate = Flow velocity × Cross-sectional area of ​​water passage = Flow velocity × Liquid level × Channel width

[0005] This measurement method uses an ultrasonic level gauge to measure the liquid level and a radar velocimeter to measure the flow velocity. However, it is only suitable for situations where the water flow fluctuation is small and a long, regular, straight inlet channel is required for accurate measurement. Otherwise, it may result in situations where the measurement is impossible or inaccurate.

[0006] Due to factors such as land occupation and cost, existing methods often do not design straight inlet channels or pipes before and after weirs. The water flow velocity at the weir fluctuates greatly, resulting in a large error in the measurement results obtained using the above methods. In actual measurements, the error is around 20%. Therefore, an accurate method for measuring the flow rate through a weir is of great guiding significance for subsequent process control and the determination of reagent dosage in wastewater treatment. Summary of the Invention

[0007] The purpose of this invention is to provide a method for measuring the flow rate of a weir gate, in order to solve the problem that existing measurement methods have significant limitations, and that when there are no straight sections of inlet channels or pipelines before and after the weir gate, the measurement results are often inaccurate, causing inconvenience to subsequent sewage treatment.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: a method for measuring the flow rate through a weir gate, comprising the following steps:

[0009] 1) Install a level gauge in the inlet channel, install a flow meter B in front of the inlet of the biological tank, install a flow meter A behind the inlet of the biological tank, and install a rangefinder above the actuator screw of the weir gate.

[0010] 2) Measure the actual height of the reference surface at the bottom of the inlet from the bottom of the inlet channel. Based on the liquid level measured by the level gauge, obtain the height H between the liquid level in the inlet channel and the reference surface at the bottom of the inlet.

[0011] 3) The actual width D of the weir gate was measured;

[0012] 4) Measure the height of the weir gate rise using a rangefinder, that is, the height h0 between the reference surface at the top of the weir gate and the reference surface at the bottom of the inlet.

[0013] 5) Measure the water flow velocity v1 before the inlet using flow meter B, and measure the water flow velocity v2 after the inlet using flow meter A;

[0014] 6) The flow rate Q of the weir gate is obtained by calculation.

[0015] Furthermore, in step 1), the level gauge is a radar level gauge, the flow meter A and flow meter B are radar flow meters, and the rangefinder is a laser rangefinder.

[0016] Furthermore, in step 1), the installation angle between flowmeter A and flowmeter B and the horizontal plane is 30° to 60°.

[0017] Furthermore, in step 6), the water flow rate Q is adopted. Perform the calculation.

[0018] Furthermore, in step 4), the change in weir gate height Δh is used to determine the flow rate Q. Perform the calculation.

[0019] Furthermore, in step 5), when v1 = 0, the water flow rate Q is adopted. Perform the calculation.

[0020] The beneficial effects of this invention are: it overcomes the limitation that traditional flow measurement requires a straight inlet channel, and is applicable to application scenarios where the water inlet channel has no straight pipe section and the water flow changes greatly, thus having a wide range of applications. At the same time, compared with traditional measurement methods, the measurement error is reduced from about 20% to about 5%, which greatly improves the measurement accuracy and has important guiding significance for the dosage of agents in subsequent sewage treatment processes. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the installation of the various measuring instruments in this invention;

[0022] Figure 2 This is a schematic diagram of the liquid level height parameters of this invention.

[0023] The names corresponding to each mark in the diagram:

[0024] 1. Biological tank; 11. Tank wall; 111. Liquid surface of biological tank; 112. Reference surface at the bottom of the inlet; 12. Inlet; 121. Rangefinder; 13. Flow meter A; 2. Weir gate; 21. Reference surface at the top of the weir gate; 3. Inlet channel; 31. Inlet pipe; 311. Water flow; 312. Liquid surface of the inlet channel; 32. Level gauge; 33. Flow meter B. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0026] like Figure 1-2 As shown, this invention includes an inlet channel 3, with an inlet pipe 31 at the bottom. Water flows 311 into the inlet channel 3 along the inlet pipe 31. A level gauge 32 is installed in the inlet channel 3. A biological tank 1 is arranged on one side of the inlet channel 3. A tank wall 11 is provided between the biological tank 1 and the inlet channel 3. An inlet 12 is provided on the tank wall 11. A weir 2 is installed at the inlet 12. A rangefinder 121 is installed above the screw of the actuator of the weir 2. A rear-mounted... A flow meter B33 is installed behind the inlet 12. The height between the bottom reference surface 112 of the inlet and the inlet channel 3 is H. The height between the bottom reference surface 112 of the inlet and the top reference surface 21 of the weir is h0. The height between the top reference surface 21 of the weir and the liquid surface 312 of the inlet channel is h1. The height between the top reference surface 21 of the weir and the liquid surface 111 of the biological tank is h2. The flow velocity of the water flow 311 in front of the weir 2 is v1, and the flow velocity of the water flow behind the weir 2 is v2.

[0027] The principle of this invention is as follows: The measuring device and instrument used in this invention are arranged in a split manner, which is flexible in installation. It is used to measure the flow rate when passing through the weir gate 2. The method of this invention is applied to the scenario where there is no straight inlet channel 3 that meets the general conditions before and after the weir gate 2. Therefore, the flow velocity before the weir gate 2 is unstable and the flow velocity fluctuates, so an accurate measurement data cannot be obtained.

[0028] There are two types of intake channels 3 in front of this type of weir gate 2:

[0029] The first method involves water flowing into the inlet channel 3, passing through the weir gate 2, and then into the biological pool 1. The water flow velocity v1 before the weir gate 2 (measured by flow meter B33), the liquid level before the weir gate 2 (measured by liquid level gauge 32), and the water flow velocity v2 after passing through the weir gate (measured by flow meter A13) can be measured.

[0030] The second method involves water flowing in from the bottom of the inlet channel 3 in front of the weir gate 2, rising and overflowing the weir gate 2 before flowing into the biological pool 1. The liquid level in front of the weir gate 2 can be measured (by level gauge 32), and the water flow velocity v2 after passing through the weir gate can be measured (by flow meter A13).

[0031] The second case mentioned above is essentially a special case of the first case, where the horizontal flow velocity v1 = 0.

[0032] Generally, the flow rate through weir 2 can be calculated by multiplying the cross-sectional area of ​​the water flowing through weir 2 by the flow velocity through that cross-sectional area. However, due to the collapse phenomenon when the water flows through weir 2, it is impossible to accurately measure the liquid level and flow velocity when flowing through weir 2. In actual measurement, if the water flow is too large, the cross-sectional area of ​​the water flowing through weir 2 will increase, and the flow velocity will also increase significantly, resulting in an overestimation of the final measurement result, making the measurement meaningless.

[0033] Since the liquid level before weir 2 is relatively stable, and the water flow after weir 2 is the volume of water flowing through the weir, it is possible to measure the cross-sectional area before weir 2 and the flow velocity after weir 2. After the water flows through weir 2 into biological tank 1, the liquid level drops compared to before weir 2. This drop in liquid level converts its gravitational potential energy into kinetic energy, and the flow velocity after weir 2 increases. Therefore, the following identity is obtained (see appendix). Figure 2 ):

[0034]

[0035] Where: h1 = H - h0

[0036] The calculation shows that:

[0037]

[0038] Therefore, the water flow rate is:

[0039]

[0040] Where: H is the distance from the liquid surface in front of the weir gate to the weir lift;

[0041] h0 is the height at which the weir gate is raised;

[0042] h1 is the water clearance height in front of the weir gate;

[0043] v1 is the flow velocity before the liquid level;

[0044] h2 is the water passage height at a point behind the weir gate;

[0045] v2 is the flow velocity at a point downstream of the weir gate;

[0046] D is the width of the weir gate;

[0047] v1 and v2 are measured by a flow meter;

[0048] H is measured using a level gauge;

[0049] h0 is measured using a rangefinder.

[0050] Meanwhile, since weir gate 2 is adjustable, adjusting it is equivalent to a change in the reference plane of the water passage height, that is, a change in the reference plane 21 at the top of the weir gate, and the water passage area will also change accordingly. Therefore, a rangefinder 121 is used to measure the adjustment distance of weir gate 2 and automatically correct the measured water level. If the change in the height of weir gate 2 is Δh, then:

[0051] h1 = H - (h0 + Δh)

[0052] So:

[0053]

[0054] The corresponding flow rate Q will then change:

[0055]

[0056] Finally, by calculating the accurate water flow rate and correcting the water level, the radar flow meter 13, radar level gauge 32, and laser rangefinder 121 transmit the multi-measured data to the gearbox for data processing and display. The entire data processing process is based on existing mature technology and will not be described in detail here.

[0057] Example 1

[0058] This embodiment takes the second case in the above practical application, that is, the water flow in the inlet channel 3 before the weir gate 2 flows out from bottom to top and there is no horizontal flow velocity, that is, v1=0. In this case, there is no need to install a flow meter in front of the weir gate 2. In this case, a radar level gauge is installed on one side of the inlet channel 3, a laser rangefinder is installed above the actuator screw of the weir gate 2, and a radar flow meter is installed behind the inlet 12. The angle between the radar flow meter and the horizontal plane is 30-60°, which is 45° in this embodiment. An electromagnetic flow meter is installed on the inlet pipe 31, and other weir gates are closed during measurement, leaving only one weir gate for water to pass through. Thus, the flow rate measured by the electromagnetic flow meter is the actual water flow rate through the weir gate 2.

[0059] The measured flow rate Q is then calculated using the following formula:

[0060]

[0061] The parameters in the formula are as described above.

[0062] In response to this situation, the actual flow rate and the measured flow rate are shown in the table below:

[0063]

[0064] Table 1. Error values ​​between actual flow rate and measured flow rate

[0065] As can be seen from the table above, there is a certain error between the actual flow rate and the measured flow rate, which is about ±5%. This error is caused by slight fluctuations in the installation accuracy, installation location, liquid level, and flow rate of the equipment, and is unavoidable. An error of about ±5% is acceptable in practical applications. Compared with the error of about 20% in traditional measurement methods, the measurement accuracy is greatly improved, which has important guiding significance for the control of wastewater treatment processes and the addition of chemicals in biological tanks.

[0066] This invention is not limited to the preferred embodiments described above. Anyone can derive other forms of products under the guidance of this invention. However, regardless of any changes made in their shape or structure, any technical solution that is the same as or similar to this application falls within the protection scope of this invention.

Claims

1. A method for measuring the flow rate through a weir gate, characterized in that, Includes the following steps: 1) Install a level gauge (32) in the inlet channel (3), install a flow meter B (33) in front of the inlet (12) of the biological pool (1), install a flow meter A (13) behind the inlet (12) of the biological pool (1), and install a rangefinder (121) above the actuator screw of the weir gate (2). 2) The actual height of the reference surface (112) at the bottom of the inlet is measured from the bottom of the inlet channel (3). Based on the liquid level measured by the level gauge (32), the height between the liquid level (312) in the inlet channel and the reference surface (112) at the bottom of the inlet is obtained. H ; 3) The actual width of the weir gate (2) was measured. D ; 4) Measure the height of the rise of the weir gate (2) using the rangefinder (121), that is, the height between the reference surface (21) at the top of the weir gate and the reference surface (112) at the bottom of the inlet. h 0; 5) Measure the water flow velocity before the inlet (12) using flow meter B (33). v 1. Measure the flow velocity of the water after the inlet (12) using flow meter A (13). v 2; 6) The flow rate Q of the weir gate (2) is obtained by calculation; In step 6), the water flow rate Q is adopted. Perform the calculation.

2. The method for measuring the flow rate of a weir gate according to claim 1, characterized in that: In step 1), the level gauge (32) is a radar level gauge, the flow meter A (13) and the flow meter B (33) are radar flow meters, and the rangefinder (121) is a laser rangefinder.

3. The method for measuring the flow rate of a weir gate according to claim 2, characterized in that: In step 1), the installation angle between the flow meter A (13) and the flow meter B (33) and the horizontal plane is 30~60°.

4. The method for measuring the flow rate of a weir gate according to claim 1, characterized in that: The height change of the weir gate (2) in step 4) △h， The flow rate Q is adopted Perform the calculation.

5. The method for measuring the flow rate of a weir gate according to claim 1, characterized in that: In step 5) v When 1=0, the water flow rate Q is adopted. Perform the calculation.

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