Method for acquiring critical position of circulating air flow in vertical shaft with air circulation system

Abstract

The invention provides a method for acquiring a critical position of circulating airflow in a vertical shaft with an air circulation system, which comprises the following steps of: on the basis of establishing a theoretical calculation model, analyzing that gas in the vertical shaft in a circulation loop is pressurized downstream in a wet well due to a pump effect of water flow and then flows from the wet well to a gas well due to an air pressure difference between the two wells; and the pressure in the gas well is reduced due to on-way loss, the gas finally flows to the wet well through the horizontal pipe to complete one-time air circulation process, and when the pressure difference of the gas flowing through the whole loop is 0, the system can just form the air circulation process, so that a loop theoretical equation is established, and the critical position of the circulating gas flow is obtained. The method provided by the invention can be suitable for different airflow circulation systems of the vertical shaft, so that the limitation of single model is eliminated, and the influence factors of the critical position of the airflow circulation loop interface in the vertical shaft air circulation system can be obtained through the method; scientific basis and effective engineering application value are provided for design and implementation of an airflow circulation system arranged in the vertical shaft.

Description

Technical Field

[0001] The invention relates to the technical field of municipal engineering sewage pipes, and in particular to a method for obtaining a critical position of a circulating airflow in a shaft with an air circulation system. Background Art

[0002] As the most widely used hydraulic structure in municipal drainage systems and various water conservancy and hydropower engineering fields, the vertical shaft is mainly used to transport the water collected by the shallow drainage network at a high place to the deep drainage network at a low place. The water flow falls freely during the entire process of the vertical shaft transportation, and after falling to a certain height, the continuous sheet water flow gradually collides, breaks and decomposes. When it is closer to the bottom of the vertical shaft, the water flow almost appears in the shape of water drops, which increases the contact area between the water and gas phases in the vertical shaft, thereby dragging more gas to gather downstream. This is likely to cause a large amount of air to be sucked into the vertical shaft, causing its air pressure gradient to be too large, affecting the safe and stable operation of the drainage system.

[0003] The shaft air circulation system is one of the effective physical ways to solve the problem of large-scale air intake in the shaft. The Chinese patent with publication number CN108104242A discloses a direct current water drop structure that reduces the amount of gas intake. The structure is a baffle with holes at the bottom and top of the shaft in the central area directly opposite the shaft inlet pipe. The baffle divides the shaft into a water-passing side and a water-free side. During the free fall of the shaft, the water flow squeezes the gas on the water-passing side into the downstream pipeline, causing the gas in the downstream pipeline to gather; because the baffle has holes at the bottom of the shaft, the gathered gas will flow to the water-free side under the action of the pressure difference, and then flow to the water-passing side through the baffle and the holes at the top of the shaft, so that part of the gas in the shaft circulates, reducing the degree of the shaft sucking in external gas. However, the specific position of the top hole of the above-mentioned shaft structure only gives a single qualitative analysis, and there is no clear algorithm guidance, which increases the engineering workload when arranging the structure. If the arrangement is improper, the airflow in the shaft may not circulate.

[0004] Chinese patent publication number CN113901635A discloses a method for calculating the circulation path of circulating airflow in a direct flow shaft structure. The method is to calculate the air pressure of each section of the wet well and the gas well respectively under certain specific flow rates, and when the air pressure on both sides is equal, the critical position is obtained. However, this method is only suitable for the airflow internal circulation mode formed by setting a partition in the shaft. Chinese patent publication number CN113962106A discloses a shaft and a method for obtaining the position of a horizontal pipe in the shaft. The method is to calculate and analyze the critical position in the circulating airflow system outside the shaft. This method is only suitable for the circulation mode outside the shaft.

[0005] Although both of the above two calculation methods can determine the critical position of the shaft air circulation system, the mode is single and the corresponding circulation mode needs to be calculated for each model. In addition, no systematic loop theoretical calculation model and estimation method are proposed in the calculation process. It is impossible to point out the influencing factors of the critical position of the air circulation loop interface in the shaft air circulation system, and it does not provide more intuitive guidance for actual engineering. The theoretical guidance for the overall system structure design is too limited. Summary of the invention

[0006] The purpose of the present invention is to address the deficiencies in the prior art and provide a method for obtaining the critical position of circulating airflow in a shaft with an air circulation system. The method is based on the loop theory method and can be applied to different airflow circulation systems in the shaft, thereby getting rid of the limitation of a single model. In addition, the method can be used to obtain the influencing factors of the critical position of the airflow circulation loop interface in the shaft air circulation system, thereby providing a scientific basis and effective engineering application value for the design and implementation of the airflow circulation system in the shaft.

[0007] According to the purpose of the present invention, a method for obtaining a critical position of a circulating airflow in a shaft having an air circulation system is provided, comprising:

[0008] A calculation model was established, which is as follows:

[0009] A partition is arranged at the central axis of the vertical shaft with the top sealed, the bottom end of the vertical shaft is connected to the outflow pipe through a bend pipe, so that the vertical shaft is connected to the atmosphere, the top end of the partition is connected to the top end of the vertical shaft, the bottom end of the partition is flush with the bottom end of the vertical shaft, and the partition divides the vertical shaft into a wet well and an air well; an air inlet pipe and a water inlet pipe are connected to the wet well, and the air inlet pipe is located above the water inlet pipe;

[0010] The baffle is provided with an opening as an air circulation loop interface. It is assumed that the position of the air circulation loop interface is a critical position for the gas between the wet well and the gas well to form a circulation. The section from the air circulation loop interface to the bottom of the baffle where a circulating airflow can be formed is defined as the wet well bottom.

[0011] According to the established calculation model, the position of the airflow circulation loop interface, that is, the critical position of the circulating airflow, is obtained according to the first method and / or the second method;

[0012] The first method comprises:

[0013] The water tongue inlet is defined as the base point, and the wet well below the base point is divided into the first section, the second section and the outlet pipe from top to bottom; and the part extending downward from the bottom end of the partition to the bend section is defined as the end point;

[0014] The air pressure equations at the air inlet pipe, the first section, the second section, and the outlet pipe are obtained, and the circulation loop equation is established at the same time, and the gas flow equation in the shaft is established, and the position of the airflow circulation loop interface is obtained by the simultaneous equations; wherein, the distance between the connection point of the first section and the second section and the base point is 2.64m, and the first section is the water tongue barrier section and the constant air pressure section distributed in sequence from the base point downward;

[0015] The second method comprises:

[0016] Define the water tongue inlet as the base point, divide the wet well below the base point into the third section, the fourth section and the outlet pipe from top to bottom; and define the part extending downward from the bottom end of the partition to the bend section as the end point;

[0017] The air pressure equations at the air inlet pipe, the third section, the fourth section, and the outlet pipe are obtained, and the circulation loop equation is established at the same time, and the gas flow equation in the shaft is established. The position of the airflow circulation loop interface is obtained by the simultaneous equations; wherein, the distance between the connection between the third section and the fourth section and the base point is 5m, and the third section is a nonlinear growth section.

[0018] As an optional implementation, the specific calculation steps of the first method include:

[0019] S11. Establish equation

[0020] The air pressure equation at the intake pipe is as follows:

[0021]

[0022] Where P a is the air pressure outside the intake pipe, which is atmospheric pressure, taken as 0Pa; P0 is the air pressure inside the intake pipe, Pa; k I is the loss coefficient of external gas when it flows through the intake pipe; ρ a is the air density of standard atmosphere at room temperature, kg / m 3 ; V a I is the average flow velocity of the gas in the intake pipe, m / s;

[0023] The first section is divided into a water tongue barrier section and a constant air pressure section. The air pressure equations are respectively as shown in equation (2) and equation (3):

[0024]

[0025] In the formula, the dimensionless inflow flow is Q w is the water flow, L / s, g is the acceleration of gravity, m / s 2 ;D s is the diameter of the vertical shaft wet well, m; P1 is the air pressure at 0.64 m below the base point in the wet well, pa; Va is the average gas velocity in the wet well, m / s; a and b are coefficients related to the vertical well structure;

[0026] P1=P3(3)

[0027] Where, P1 is the air pressure at 0.64m below the base point in the wet well, pa; P3 is the air pressure at 2.64m below the base point in the wet well, pa;

[0028] The air pressure equation of the second section is as follows:

[0029]

[0030] Where p is the air pressure in the second section, Pa; z is a certain height in the wet well where the drop height is greater than 2.64m, m; Q w is the incoming flow, L / s; D s is the diameter of the wet well, m; d is the diameter of the water droplet; C d is the coefficient of water droplet dragging gas; V is the average velocity of water droplet falling; V a is the average gas velocity in the wet well, m / s; ρ a is the air density of the standard atmosphere at room temperature;

[0031] The air pressure equation at the outlet pipe is as follows:

[0032] P8=0(5)

[0033] Where, P8 represents the air pressure at the outlet of the flow tube, pa;

[0034] The circulation loop equation is as follows:

[0035]

[0036] Where P L is the air pressure at the interface of the air circulation loop on the wet well side, Pa; L is the height from the critical position to the end point of the circulating airflow, m; H c is the drop height from the bottom of the partition to the end point, m;

[0037] P lloss1 =k b ρ a (V a t ) 2 / 2, is the local pressure loss of gas from the bottom of the wet well to the gas well; where k b V is the local loss coefficient of gas passing through the bottom of the partition, which can be taken as 20 according to experimental determination; a t is the average velocity of gas at the bottom of the wet well, m / s;

[0038] P floss =λ(LH c )ρ a (V a c ) 2 / 2D c , is the pressure loss along the gas well; where λ is the gas loss coefficient along the gas well; V a c is the average flow rate of circulating gas in the gas well, m / s; D c is the diameter of the gas well, m; ρ a is the air density of standard atmosphere at room temperature, kg / m 3 ;H c is the drop height from the bottom of the partition to the end point, m; L is the height from the critical position of the circulating airflow to the end point, m;

[0039] P lloss2 =k o ρ a (V a c ) 2 / 2, is the local pressure loss when the gas circulates from the gas well to the wet well through the gas circulation loop interface; where k o =1.5, which is the local loss coefficient of gas flowing from the gas well to the wet well through the gas circulation loop interface; ρ a is the air density of standard atmosphere at room temperature, kg / m 3 ; V a c is the average flow rate of circulating gas in the gas well, m / s;

[0040] The gas flow equation at the bottom of the wet well is as follows:

[0041] V a A s +V a c A c =V a t A s (7)

[0042] Where As and Ac are the cross-sectional areas of the wet well and gas well, respectively, m 2 ; V a , V a c , V a t are the gas velocity at the bottom of the first section, gas well, and wet well, m / s;

[0043] The relationship between the circulating air volume in the shaft and the amount of gas sucked from the outside by the shaft is as follows:

[0044]

[0045] In the formula, Q a c =V a c A c , is the circulating air flow rate in the gas well, L; Q a I =V a I A I , is the entrained air flow rate at the air circulation loop interface, L; V a c and V a I Respectively represent the gas flow rate at the gas well and the gas circulation loop interface, m / s; A c and A I Represent the cross-sectional area of ​​the gas well and the gas circulation loop interface, m 2 ;

[0046] S12, combining equations (1) to (8) in step S11 to obtain the value of the position L of the airflow circulation loop interface, that is, the critical position of the circulating airflow.

[0047] As an optional implementation, the specific calculation steps of the second method include:

[0048] S21. Establish equation

[0049] The air pressure equation at the intake pipe is as follows:

[0050]

[0051] Where P a is the air pressure outside the intake pipe, which is atmospheric pressure, taken as 0Pa; P0 is the air pressure inside the intake pipe, Pa; k I is the loss coefficient of external gas when it flows through the intake pipe; ρ a is the air density of standard atmosphere at room temperature, kg / m 3 ; V a I is the average flow velocity of the gas in the intake pipe, m / s;

[0052] The third section is a nonlinear growth section, and the pressure equations are as follows:

[0053] (P5-P1) / (z5-z1)=0.5dp / dz (9)

[0054] Wherein, P5 is the air pressure at z5 = 5m below the base point in the wet well, Pa; P1 is the air pressure at z1 = 0.64m below the base point in the wet well, Pa; dp / dz is the pressure gradient value of the fourth linear growth;

[0055] The air pressure equation for the fourth section is as follows:

[0056]

[0057] Where p is the air pressure in the fourth section, Pa; z is a certain height in the wet well where the drop height is greater than 2.64m, m; Q w is the incoming flow, L / s; D s is the diameter of the wet well, m; d is the diameter of the water droplet; C d is the coefficient of water droplet dragging gas; V is the average velocity of water droplet falling; V a is the average gas velocity in the third section, m / s; ρ a is the air density of standard atmosphere at room temperature, kg / m 3 ;

[0058] The air pressure equation at the outlet pipe is as follows:

[0059] P8=0(5)

[0060] Where, P8 represents the air pressure at the outlet of the flow tube, pa;

[0061] The circulation loop equation is as follows:

[0062]

[0063] Where P L is the air pressure at the opening of the wet well, Pa; L is the height from the critical position to the end point of the circulating airflow, m; H c is the drop height from the bottom of the partition to the end point, m;

[0064] P lloss1 =k b ρ a (V a t ) 2 / 2, is the local pressure loss of gas from the bottom of the wet well to the gas well; where k b V is the local loss coefficient of gas passing through the bottom of the partition, which can be taken as 20 according to experimental determination; a t is the average velocity of gas at the bottom of the wet well, m / s;

[0065] P floss =λ(LH c )ρ a (V ac ) 2 / 2D c , is the pressure loss along the gas well; where λ is the gas loss coefficient along the gas well; V a c is the average flow rate of circulating gas in the gas well, m / s; D c is the diameter of the gas well, m; ρ a is the air density of the standard atmosphere at room temperature; H c is the drop height from the bottom of the partition to the end point, m; L is the height from the critical position of the circulating airflow to the end point, m;

[0066] P lloss2 =k o ρ a (V a c ) 2 / 2, is the local pressure loss when the gas circulates from the gas well to the wet well through the gas circulation loop interface; where k o =1.5 is the local loss coefficient of gas flowing from the gas well to the wet well through the gas circulation loop interface; ρ a is the air density of the standard atmosphere at room temperature; ρ a V is the air density of the standard atmosphere at room temperature; a c is the average flow rate of circulating gas in the gas well, m / s;

[0067] The gas flow equation at the bottom of the wet well is as follows:

[0068] V a A s +V a c A c =V a t A s (7)

[0069] Where As and Ac are the cross-sectional areas of the wet well and gas well, respectively, m 2 ; V a , V a c , V a t are the gas velocity at the bottom of the third section, gas well, and wet well, m / s;

[0070] The relationship between the circulating air volume in the shaft and the amount of gas sucked from the outside by the shaft is as follows:

[0071]

[0072] In the formula, Q ac =V a c A c , is the circulating air flow rate in the gas well, L; Q a I =V a I A I , is the entrained air flow rate at the air circulation loop interface, L; V a c and V a I Respectively represent the gas flow rate at the gas well and the gas circulation loop interface, m / s; A c and A I Represent the cross-sectional area of ​​the gas well and the gas circulation loop interface, m 2 ;

[0073] S22, combining equations (1), (4) to (9) in step S21 to obtain the value of the position L of the airflow circulation loop interface, that is, the critical position of the circulating airflow.

[0074] As an optional implementation, when the inflow rate is constant, the influencing factors of the critical position of the circulating airflow are the shaft diameter, the gas well diameter, the wet well diameter, and the ratio of the cross-sectional diameters of the wet well and the gas well.

[0075] As an optional implementation, when the inflow rate is constant, the critical position of the circulating airflow increases with the increase of the shaft diameter.

[0076] As an optional implementation, when the inflow rate and the wet well diameter are constant, the critical position of the circulating airflow first decreases and then remains unchanged as the diameter of the air well increases.

[0077] As an optional implementation, when the inflow rate and the gas well diameter are constant, the critical position of the circulating gas flow first decreases and then remains unchanged as the wet well diameter increases.

[0078] As an optional implementation, when the inflow rate and the wet well diameter are constant, the critical position of the circulating airflow first decreases and then increases as the ratio of the cross-sectional diameters of the wet well to the gas well increases.

[0079] As an optional implementation, the relationship between the critical position of the circulating airflow and the influencing factor is as shown in formula (10):

[0080] L * =0.54-0.21D s * -0.057α, R 2 =0.80 (10)

[0081] Where, L *=L / H, which is the dimensionless quantity of the critical position L of the horizontal pipe; L is the height from the critical position of the circulating airflow to the end point, m; H is the drop height of the shaft, m; D s * is the dimensionless quantity of the vertical shaft wet shaft diameter Ds, take D s * =D s / D m ;D m is the shaft diameter of the theoretical calculation model, which is 0.38m; α=D s / D c , which is the ratio of the cross-sectional diameters of the wet well to the gas well.

[0082] As an optional embodiment, air circulation can occur when the air circulation loop interface is located at any position from the critical position to the top of the shaft.

[0083] It can be seen from the above technical solutions of the present invention that the method for obtaining the critical position of the circulating airflow in the vertical shaft with the air circulation system proposed by the present invention, on the basis of establishing a theoretical calculation model, analyzes that the gas in the vertical shaft in the circulation loop is first pressurized in the wet well due to the pump effect of the water flow in the downstream, and then flows from the wet well to the gas well due to the pressure difference between the two wells, and is depressurized in the gas well due to the loss along the way, and finally flows to the wet well through the horizontal pipe to complete an air circulation process. When the pressure difference of the gas flowing through the entire loop is 0, the system can just form an air circulation process, thereby establishing the loop theoretical equation ∫ L dp = 0, the critical position of the circulating airflow is obtained;

[0084] The method of the present invention is based on the loop theory method and can be applied to different air circulation systems in shafts, thereby getting rid of the limitation of a single model. The principal component analysis and multivariate linear fitting analysis of the calculation results of the method can be used to obtain the relationship between the critical position of the air circulation loop interface in the shaft air circulation system and the two main influencing factors of the incoming flow and the shaft diameter. At the same time, the method of the present invention can verify each other through two calculation modes to improve accuracy, thereby providing clear algorithm guidance for the structural design of the shaft air circulation system, thereby improving construction efficiency and accuracy and reducing use costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0085] Figure 1 It is a structural schematic diagram of an air circulation system that can be arranged inside a shaft in the prior art.

[0086] Figure 2 It is a structural schematic diagram of an air circulation system in the prior art that can be arranged outside the shaft.

[0087] Figure 3 It is a schematic diagram of the calculation model structure of the method for obtaining the critical position of the circulating airflow in the shaft with the air circulation system according to the present invention.

[0088] Figure 4 It is a statistical diagram of the critical position and circulating air flow rate at different flow rates in Example 1 of the present invention.

[0089] Figure 5 It is a statistical diagram of critical positions and circulating air flow rates under different shaft diameters in Example 2 of the present invention.

[0090] Figure 6 It is a statistical diagram of critical position and circulating gas flow rate under different gas well diameters in Example 2 of the present invention.

[0091] Figure 7 It is a statistical diagram of critical position and circulating air flow rate under different wet well diameters in Example 2 of the present invention.

[0092] Figure 8 It is a statistical diagram of the critical position and circulating gas flow rate under different ratios of the diameters of the wet well and the gas well in Example 2 of the present invention.

[0093] Fig. 9 It is a comparison diagram of circulating air flow at different air circulation loop interface positions in Example 4 of the embodiment of the present invention. DETAILED DESCRIPTION

[0094] In order to better understand the technical content of the present invention, specific embodiments are given and described as follows in conjunction with the accompanying drawings.

[0095] Various aspects of the present invention are described in this disclosure with reference to the accompanying drawings, in which many illustrative embodiments are shown. The embodiments of the present disclosure are not necessarily intended to include all aspects of the present invention. It should be understood that the various concepts and embodiments introduced above, as well as those described in more detail below, can be implemented in any of many ways.

[0096] In a shaft with an air circulation system, the air circulation system can be arranged inside the shaft (such as Figure 1 As shown), it can also be set outside the shaft (as shown Figure 2 As shown in the figure, in the process of forming the circulation loop, the local pressure loss of different modes is different. Therefore, in the prior art, it is necessary to establish models respectively to calculate and determine the critical position of the airflow circulation loop interface in the corresponding mode. The model is single and the process is cumbersome. It is also impossible to point out the influencing factors of the critical position of the airflow circulation loop interface in the shaft air circulation system. It does not provide more intuitive guidance for actual projects and is too limited in the theoretical guidance of the overall system structure design.

[0097] Therefore, the present invention is based on the theoretical calculation model and the loop theory method, establishes the theoretical air pressure equation of the gas in the vertical shaft along the circulation loop, finds out the factors affecting the critical position of the horizontal pipe through calculation, and proposes an estimation formula for the critical position calculation when the circulating airflow system is set in the vertical shaft, which provides correct theoretical guidance for practical engineering applications, greatly increases the gas circulation efficiency, and thus greatly reduces the degree of external gas suction in the vertical shaft, providing a scientific basis and effective engineering application value for the design and implementation of the airflow circulation system set in the vertical shaft.

[0098] All heights in the present invention are calculated based on the base point as the starting point unless otherwise specified, and the base point is the water tongue inlet.

[0099] In an exemplary embodiment of the present invention, a method for obtaining a critical position of circulating airflow in a shaft having an air circulation system is provided, comprising:

[0100] (1) Establish a calculation model, the model is as follows:

[0101] like Figure 3 As shown, a partition 2 is arranged at the central axis of the vertical shaft 1 which is sealed at the top, the bottom end of the vertical shaft 1 is connected to the atmosphere through an outlet pipe 3, one end of the partition 2 is connected to the top of the vertical shaft, and the other end of the partition 2 is flush with the bottom end of the vertical shaft, and the partition 2 divides the vertical shaft into a wet well 11 and an air well 12; the air inlet pipe 4 and the water inlet pipe 5 are both connected to the wet well 11, and the air inlet pipe 4 is located above the water inlet pipe 5.

[0102] An opening 21 is provided on the partition 2 as an airflow circulation loop interface. It is assumed that the position of the airflow circulation loop interface is the critical position for the gas to flow between the wet well 11 and the gas well 12. The section from the airflow circulation loop interface to the bottom of the partition where a circulating airflow can be formed is defined as the wet well bottom 11-1.

[0103] (2) Based on the established calculation model, the position of the airflow circulation loop interface, that is, the critical position of the circulating airflow, is obtained according to the first method and / or the second method.

[0104] [First method]

[0105] The first method includes:

[0106] The water tongue inlet is defined as the base point O (Z0=0), and the wet well below the base point O is divided into the first section, the second section and the outlet pipe from top to bottom; and the portion extending downward from the bottom end of the partition to the curved pipe section is defined as the end point E.

[0107] The air pressure equations at the air inlet pipe, the first section, the second section, and the outlet pipe are obtained, and the circulation loop equation is established at the same time, and the gas flow equation in the shaft is established, and the position of the airflow circulation loop interface is obtained by the simultaneous equations; wherein, the distance between the connection between the first section and the second section and the base point is 2.64m, and the first section is the water tongue barrier section and the constant air pressure section distributed in sequence from the base point downward.

[0108] In an optional example, the specific calculation steps of the first method include:

[0109] S11. Establish equation

[0110] Air pressure equation at the intake manifold

[0111] Since the top of the shaft is sealed, external gas can only enter the wet well through the air inlet pipe. Therefore, the pressure difference at both ends of the air inlet pipe can be expressed by the Bernoulli equation, as shown in formula (1):

[0112]

[0113] Where P a is the air pressure outside the intake pipe, which is atmospheric pressure, taken as 0Pa; P0 is the air pressure inside the intake pipe, Pa; k I is the loss coefficient of external gas flowing through the intake pipe, including an inlet and an expanded outlet, and is taken as 1.5; ρ a is the air density of standard atmosphere at room temperature, which is 1.2 kg / m 3 ; V a I is the average flow rate of gas in the intake pipe, m / s.

[0114] The air pressure equation for the first paragraph

[0115] The first section is divided into a water tongue barrier section and a constant air pressure section. In the water tongue barrier section, when the inflow with a certain speed hits the opposite shaft wall, a water tongue will be formed, thereby blocking the gas flow and causing the negative pressure at that place to increase sharply. The air pressure change at that place is as shown in formula (2):

[0116]

[0117] In the formula, the dimensionless inflow flow is Q w is the water flow, L / s, g is the acceleration of gravity, m / s 2 ;D s is the diameter of the vertical shaft wet well, m; P1 is the air pressure below the water tongue, Pa; V a is the average gas velocity in the first section, m / s; a and b are coefficients related to the shaft structure, and in this calculation model, a=485.2 and b=20.

[0118] The constant pressure section is considered to be a section in the vertical shaft wet well where the pressure change is extremely small, so it is specifically called the constant pressure section. According to experimental data, it is generally believed that the height of the constant pressure section is z = 0.64 ~ 2.64m (P1-P3) below the base point. Therefore, the pressure distribution of this section is as shown in formula (3):

[0119] P1=P3(3)

[0120] Where, P1 is the air pressure at 0.64 m below the base point in the wet well, pa; P3 is the air pressure at 2.64 m below the base point in the wet well, pa.

[0121] The air pressure equation for the second paragraph

[0122] The air pressure in the second section increases linearly, mainly because the water flow in this area is broken into small water droplets, and the water droplets drag the air flow downward. Therefore, the air pressure gradient in the second section is as follows:

[0123]

[0124] Where p is the air pressure in the second section, Pa; z is a certain height in the wet well where the drop height is greater than 2.64m, m; Q w is the incoming flow, L / s; D s is the diameter of the wet well, m; d is the diameter of the water drop, which is 2 mm; C d is the coefficient of water droplet dragging gas, which is 0.4; V is the average velocity of water droplet falling, which is 6m / s; V a is the average gas velocity in the first section, m / s; ρ a is the air density of the standard atmosphere at room temperature, which is 1.2 kg / m 3 .

[0125] The pressure equation at the outlet pipe

[0126] Since the shaft outlet pipe is directly connected to the outside atmosphere, the air pressure in the outlet pipe is about ±10Pa according to experimental measurements. Compared with the negative pressure of several hundred Pa in the shaft, the air pressure P8 at the outlet pipe can be regarded as 0 to simplify the calculation. Therefore, the air pressure equation at the outlet pipe is as follows:

[0127] P8=0(5)

[0128] Where P8 represents the air pressure at the outlet of the flow tube, pa.

[0129] Circulation loop equation

[0130] The gas in the vertical shaft is first pressurized in the wet well due to the drag of the water flow, and then flows from the wet well to the gas well due to the pressure difference between the two wells, and is depressurized in the gas well due to the loss along the way, and finally completes the airflow circulation process to the wet well through the circulation loop interface. When the system can just form an airflow circulation, the position of the corresponding horizontal pipe is the critical position. In fact, after subsequent calculations, it is found that the critical position is always below 5m. Therefore, the air pressure equation along the circulation loop is as follows:

[0131]

[0132] Where P L is the air pressure at the interface of the air circulation loop on the wet well side, Pa; L is the height from the critical position to the end point of the circulating airflow, m; H c is the drop height from the bottom of the partition to the end point, m;

[0133] P lloss1 =k b ρ a (V a t ) 2 / 2, is the local pressure loss of gas from the bottom of the wet well to the gas well; where k b V is the local loss coefficient of gas passing through the bottom of the partition, which can be taken as 20 according to experimental determination; a t is the average velocity of gas at the bottom of the wet well, m / s;

[0134] P floss =λL-H c )ρ a (V a c ) 2 / 2D c , is the pressure loss along the gas well; where λ is the gas loss coefficient along the gas well; V a c is the average flow rate of circulating gas in the gas well, m / s; D c is the diameter of the gas well, m; ρ a is the air density of the standard atmosphere at room temperature, and is taken as 1.2 kg / m 3 ;H c is the drop height from the bottom of the partition to the end point, m; L is the height from the critical position of the circulating airflow to the end point, m;

[0135] P lloss2 =k o ρ a (V a c ) 2 / 2, is the local pressure loss when the gas circulates from the gas well to the wet well through the gas circulation loop interface; where k o =1.5, which is the local loss coefficient of gas flowing from the gas well to the wet well through the gas circulation loop interface; ρ a is the air density of the standard atmosphere at room temperature; ρ a V is the air density of the standard atmosphere at room temperature; a c is the average velocity of the circulating gas in the gas well, m / s. In fact, for the case of external circulation in the vertical well, P lloss2 It is the pressure loss of the horizontal connecting pipe and its inlet and outlet.

[0136] Supplementary conditions

[0137] Since the top of the vertical shaft is sealed, external gas can only flow into the vertical shaft through the air inlet pipe. Therefore, the gas at the bottom of the wet well can be composed of two parts: one part is the gas flowing into the wet well from the air inlet pipe, and the other part is the gas flowing from the gas well to the wet well through the horizontal pipe. Therefore, the gas flow equation at the bottom of the wet well is as follows:

[0138] V a A s +V a c A c =V a t A s (7)

[0139] Where As and Ac are the cross-sectional areas of the wet well and gas well, respectively, m 2 ; V a , V a c , V a t are the gas velocity at the bottom of the first section, gas well, and wet well, m / s;

[0140] The relationship between the circulating air volume in the shaft and the amount of gas sucked from the outside by the shaft is as follows:

[0141]

[0142] The value of 0.5 is selected in the model of the present invention.

[0143] In the formula, Q a c =V a c A c , is the circulating air flow rate in the gas well, L; Q a I =V a IA I , is the entrained air flow rate at the air circulation loop interface, L; V a c and V a I Respectively represent the gas flow rate at the gas well and the gas circulation loop interface, m / s; A c and A I Represent the cross-sectional area of ​​the gas well and the gas circulation loop interface, m 2 .

[0144] S12, combining equations (1) to (8) in step S11, solving the equations in Matlab, and obtaining the value of the position L of the airflow circulation loop interface, i.e., the critical position of the circulating airflow, given the incoming water flow.

[0145] [Second method]

[0146] The second method includes:

[0147] The water tongue inlet is defined as the base point O, and the wet well below the base point is divided into the third section, the fourth section and the outlet pipe from top to bottom; and the part extending downward from the bottom end of the partition to the bend section is defined as the end point E;

[0148] The air pressure equations at the air inlet pipe, the third section, the fourth section, and the outlet pipe are obtained, and the circulation loop equation is established at the same time, and the gas flow equation in the shaft is established. The position of the airflow circulation loop interface is obtained by the simultaneous equations; wherein, the distance between the connection between the third section and the fourth section and the base point is 5m, and the third section is a nonlinear growth section.

[0149] In an optional example, the specific calculation steps of the second method include:

[0150] S21. Establish equation

[0151] Air pressure equation at the intake manifold

[0152] Since the top of the shaft is sealed, external gas can only enter the wet well through the air inlet pipe. Therefore, the pressure difference at both ends of the air inlet pipe can be expressed by the Bernoulli equation, as shown in formula (1):

[0153]

[0154] Where P a is the air pressure outside the intake pipe, which is atmospheric pressure, taken as 0Pa; P0 is the air pressure inside the intake pipe, Pa; k I is the loss coefficient of external gas flowing through the intake pipe, including an inlet and an expanded outlet, and is taken as 1.5; ρ a is the air density of standard atmosphere at room temperature, which is 1.2 kg / m 3 ; Va I is the average flow rate of gas in the intake pipe, m / s.

[0155] The air pressure equation for the third paragraph

[0156] Compared with the linear growth of air pressure in the fourth section of the shaft, the air pressure gradient in the third section of the shaft is about 1 / 2 to 1 / 3 of that in the fourth section, that is, (1 / 2 to 1 / 3)dp / dz. In the subsequent calculation, 1 / 2 is taken, where dp / dz is the air pressure gradient value of the linear growth of the fourth section of the shaft. Therefore, the third section is considered to be a nonlinear growth section, and the air pressure equations are as follows:

[0157] (P5-P1) / (z5-z1)=0.5dp / dz (9)

[0158] Wherein, P5 is the air pressure at z5=5m below the base point in the wet well, Pa; P1 is the air pressure at z1=0.64m below the base point in the wet well, Pa; dp / dz is the pressure gradient value of the fourth linear growth segment.

[0159] The air pressure equation in the fourth paragraph

[0160] The air pressure in the fourth section increases linearly, mainly because the water flow in this area is broken into small water droplets, and the water droplets drag the air flow downward. Therefore, the air pressure gradient in the fourth section is as follows:

[0161]

[0162] Where p is the air pressure in the fourth section, Pa; z is a certain height in the wet well where the drop height is greater than 2.64m, m; Q w is the incoming flow, L / s; D s is the diameter of the wet well, m; d is the diameter of the water drop, which is 2 mm; C d is the coefficient of water droplet dragging gas, which is 0.4; V is the average velocity of water droplet falling, which is 6m / s; V a is the average gas velocity in the third section, m / s; ρ a is the air density of the standard atmosphere at room temperature, which is 1.2 kg / m 3 .

[0163] The pressure equation at the outlet pipe

[0164] Since the shaft outlet pipe is directly connected to the outside atmosphere, the air pressure in the outlet pipe is about ±10Pa according to experimental measurements. Compared with the negative pressure of several hundred Pa in the shaft, the air pressure P8 at the outlet pipe can be regarded as 0 to simplify the calculation. Therefore, the air pressure equation at the outlet pipe is as follows:

[0165] P8=0(5)

[0166] Where P8 represents the air pressure at the outlet of the flow tube, pa.

[0167] Circulation loop equation

[0168] The gas in the vertical shaft is first pressurized in the wet well due to the drag of the water flow, and then flows from the wet well to the gas well due to the pressure difference between the two wells, and is depressurized in the gas well due to the loss along the way, and finally completes the airflow circulation process to the wet well through the circulation loop interface. When the system can just form an airflow circulation, the position of the corresponding horizontal pipe is the critical position. In fact, after subsequent calculations, it is found that the critical position is always below 5m. Therefore, the air pressure equation along the circulation loop is as follows:

[0169]

[0170] Where P L is the air pressure at the interface of the air circulation loop on the wet well side, Pa; L is the height from the critical position to the end point of the circulating airflow, m; H c is the drop height from the bottom of the partition to the end point, m;

[0171] P lloss1 =k b ρ a (V a t ) 2 / 2, is the local pressure loss of gas from the bottom of the wet well to the gas well; where k b V is the local loss coefficient of gas passing through the bottom of the partition, which can be taken as 20 according to experimental determination; a t is the average velocity of gas at the bottom of the wet well, m / s;

[0172] P floss =λ(LH c )ρ a (V a c ) 2 / 2D c , is the pressure loss along the gas well; where λ is the gas loss coefficient along the gas well; V a c is the average flow rate of circulating gas in the gas well, m / s; D c is the diameter of the gas well, m; ρ a is the air density of standard atmosphere at room temperature, kg / m 3 ;H c is the drop height from the bottom of the partition to the end point, m; L is the height from the critical position of the circulating airflow to the end point, m;

[0173] P lloss2 =k oρ a (V a c ) 2 / 2, is the local pressure loss when the gas circulates from the gas well to the wet well through the gas circulation loop interface; where k o =1.5, which is the local loss coefficient of gas flowing from the gas well to the wet well through the gas circulation loop interface; ρ a is the air density of the standard atmosphere at room temperature; ρ a V is the air density of the standard atmosphere at room temperature; a c is the average velocity of the circulating gas in the gas well, m / s. In fact, for the case of external circulation in the vertical well, P lloss2 It is the pressure loss of the horizontal connecting pipe and its inlet and outlet.

[0174] Supplementary conditions

[0175] Since the top of the vertical shaft is sealed, external gas can only flow into the vertical shaft through the air inlet pipe. Therefore, the gas at the bottom of the wet well can be composed of two parts: one part is the gas flowing into the wet well from the air inlet pipe, and the other part is the gas flowing from the gas well to the wet well through the horizontal pipe. Therefore, the gas flow equation at the bottom of the wet well is as follows:

[0176] V a A s +V a c A c =V a t A s (7)

[0177] Where As and Ac are the cross-sectional areas of the wet well and gas well, respectively, m 2 ; V a , V a c , V a t are the gas velocity at the bottom of the first section, gas well, and wet well, m / s;

[0178] The relationship between the circulating air volume in the shaft and the amount of gas sucked from the outside by the shaft is as follows:

[0179]

[0180] In the formula, Q a c =V a c A c , is the circulating air flow rate in the gas well, L; Q a I =V aI A I , is the entrained air flow rate at the air circulation loop interface, L; V a c and V a I Respectively represent the gas flow rate at the gas well and the gas circulation loop interface, m / s; A c and A I Represent the cross-sectional area of ​​the gas well and the gas circulation loop interface, m 2 ;

[0181] S22. Equations (1), (4) to (9) in step S21 are combined and solved in Matlab. Given the incoming water flow, the value of the position L of the airflow circulation loop interface, i.e., the critical position of the circulating airflow, is obtained.

[0182] It can be understood that the first method and the second method have different definitions of the height of the first section of the shaft; the first method considers the first section of the shaft to be the constant pressure section, so it ends at z=2.64m; the second method refers to the linear growth of air pressure in the second section of the shaft, and the study believes that the linear growth section starts from a drop height greater than 5m, so the third section of the shaft in the second method ends at z=5m.

[0183] Both the first method and the second method can accurately calculate the critical position of the air circulation loop interface when the shaft air circulation system can circulate. The calculated values ​​of the two methods are very close. Therefore, in the actual calculation process, you can choose which method to use according to the actual situation, or you can verify the two methods with each other to improve the accuracy of the values.

[0184] As an optional example, the first method and / or the second method may be used to adjust certain parameters and perform random forest and multivariate linear regression analysis on the results to obtain influencing factors of the critical position of the circulating airflow.

[0185] Among them, when the inflow rate is constant, the influencing factors of the critical position of the circulating airflow are the gas well diameter, the wet well diameter, and the ratio of the cross-sectional diameters of the wet well and the gas well.

[0186] When the inflow rate and the wet well diameter are constant, the critical position of the circulating airflow first decreases and then remains unchanged as the well diameter increases.

[0187] When the inflow rate and the gas well diameter are constant, the critical position of the circulating airflow first decreases and then remains unchanged as the wet well diameter increases.

[0188] When the inflow rate and the diameter of the wet well are constant, the critical position of the circulating airflow first decreases and then increases with the increase of the ratio of the cross-sectional diameter of the wet well to the gas well.

[0189] Among them, the importance of each influencing factor on the critical position of the circulating airflow is: wet well diameter > vertical shaft diameter > ratio of the cross-sectional diameter of the wet well to the gas well > gas well diameter > flow rate, and the importance of the gas well diameter and flow rate is less than 1, that is, the impact on the critical position of the horizontal pipe is very small.

[0190] In a further example, through random forest and multivariate linear regression analysis, when the two factors of wet well diameter and the ratio of the cross-sectional diameter of the wet well to the gas well jointly affect the critical position, the regression equation meets the two conditions of significance P<0.05 and multicollinearity VIF<5 between variables, thus obtaining the relationship between the critical position of the circulating airflow and the influencing factors, as shown in formula (10):

[0191] L * =0.54-0.21D s * -0.057α, R 2 =0.80 (10)

[0192] Where, L * =L / H, which is the dimensionless quantity of the critical position L of the horizontal pipe; L is the height from the critical position of the circulating airflow to the end point, m; H is the drop height of the shaft, m; D s * is the dimensionless quantity of the vertical shaft wet shaft diameter Ds, take D s * =D s / D m ;D m is the shaft diameter of the theoretical calculation model, which is 0.38m; α=D s / D c , which is the ratio of the cross-sectional diameters of the wet well to the gas well.

[0193] The critical position of the circulating airflow can be directly estimated by formula (10). In actual engineering applications, the critical position of the circulating airflow can be directly obtained by formula (10) according to the actual situation, which further simplifies the preliminary engineering calculations.

[0194] In an optional example, air circulation may occur when the air circulation loop interface is located at any position from a critical position to the top of the shaft.

[0195] In an optional example, when the air circulation loop interface is located below the wet well water tongue inlet, approximately 0.64m below the base point, the gas circulation effect in the vertical shaft is optimal.

[0196] It can be understood that the above calculations can be performed directly using the software Matlab, or can be calculated manually or using other software.

[0197] For better understanding, the present invention is further described below in conjunction with several specific examples, but the preparation process is not limited thereto, and the content of the present invention is not limited thereto.

[0198] Unless otherwise specified, the materials in the examples were prepared according to existing methods or directly purchased from the market.

[0199] The parameters used in the following examples are:

[0200] The shaft diameter D, D* = D / Dm; Dm is the shaft diameter of the theoretical calculation model, which is 0.38m;

[0201] Wet well diameter Ds, Ds* = Ds / Dm; Dm is the shaft diameter of the theoretical calculation model, which is 0.38m;

[0202] Gas well diameter Dc, Dc* = Dc / Dm; Dm is the shaft diameter of the theoretical calculation model, which is 0.38m;

[0203] The height L from the critical position of the circulating airflow to the end point, L* = L / H is the dimensionless value of L; H is the drop height of the shaft

[0204] Circulating air flow rate Q in the shaft a c , Q a c * is the circulating air flow Q a c The dimensionless quantity,

[0205] Inflow flow Qw, Qw* is the dimensionless quantity of Qw,

[0206] Example 1

[0207] use Figure 3 The schematic diagram of the model structure is shown, in which the drop height H of the vertical shaft 1 is 7.72m, the diameter of the air inlet pipe 4 is 0.1m, the diameter of the water inlet pipe 5 is 0.19m, and the central partition 2 0.77m away from the end point E divides the vertical shaft 1 with a diameter of 0.38m into a wet well 11 and a gas well 12 with equivalent diameters of 0.269m. After the water flows into the water inlet pipe 5, it enters the wet well 11 and is finally discharged from the outlet pipe 3 with a diameter of 0.38m.

[0208] Define the base point O of the water tongue inlet, point P0 is located at z = -0.72m, point P1 is located at z = 0.64m, and point P3 is located at z = 2.64m.

[0209] Method 1: Thus, equations (1) to (8) are combined and solved in Matlab. Given a water flow rate of 1-100 L / s, we obtain L = 1.64-2.46 m, L* = 0.21-0.32, that is, the distance from the bottom of the shaft is 1.64-2.46 m.

[0210] Method 2: Combine equations (1), (4) to (9) and solve them in Matlab. Given a water flow rate of 1-100 L / s, we get L = 2.01-3.34 m, L* = 0.26-0.43, which means the distance from the bottom of the shaft is 2.01-3.34 m.

[0211] Two calculation methods in Q w =1-100L / s (31 flow changes in total), the results of the critical position L or L* are shown in Table 1:

[0212] Table 1

[0213]

[0214]

[0215] Combining Table 1 and Figure 4 As shown, in the case of Qw = 1-100 L / s, the average value of the critical position of the circulating airflow calculated by method 1 is L* = 0.29, and the average value of the critical position of the circulating airflow calculated by method 2 is L* = 0.33. It can be seen that the results calculated by the two methods are not much different, and both methods can obtain the critical position of the circulating airflow.

[0216] Example 2

[0217] The vertical shaft size structure is the same as that in Example 1, and the changes in the critical position and circulating air flow rate of the circulating airflow system are considered when changing the vertical shaft diameter, the gas well diameter, the wet well diameter, and the ratio of the wet well to the gas well diameter.

[0218] When the flow rate Qw = 10L / s, the shaft diameter is changed (D* = 0.79-1.18, a total of 16 diameter changes), the specific change results are shown in Table 2 and Figure 5 shown.

[0219] It can be seen that, when other conditions remain unchanged, the circulating airflow increases with the increase of the shaft diameter, and the critical position of the circulating airflow is closer to the bottom of the shaft as the shaft diameter increases, so appropriately increasing the shaft diameter can increase the amount of circulating gas.

[0220] Table 2

[0221]

[0222]

[0223] When the wet well diameter remains unchanged and the gas well diameter changes (gas well diameter Dc* = 0.22-2.63, 47 diameter changes), at the same water flow rate Qw = 10L / s, the results of the critical position L or L* and the circulating gas flow rate are shown in Table 3 and Figure 6 shown.

[0224] It can be seen that when other conditions remain unchanged, the dimensionless gas well diameter Dc*<0.39, the circulating gas flow increases with the increase of the gas well diameter; but when the gas well diameter Dc*>0.39, the critical position height and circulating gas flow remain constant. Therefore, considering the economic and cost-effectiveness of the structure, the gas well diameter is best when it is close to 0.4.

[0225] Table 3

[0226]

[0227]

[0228] When Qw = 10 L / s, the gas well diameter remains unchanged, and the wet well diameter gradually increases (wet well diameter Ds* = 0.22-2.63, a total of 49 diameter changes), the results of the critical position L or L* and the circulating gas flow rate are shown in Table 4 and Figure 7 shown.

[0229] It can be seen that when other conditions remain unchanged, the critical position first decreases and then remains basically constant, while the circulating gas flow first increases and then decreases. The inflection point appears at the wet well diameter D s * =1.05, at this time the maximum circulating gas flow is Q a c* =0.51.

[0230] Table 4

[0231]

[0232]

[0233] When the inflow Qw = 10 L / s and the shaft diameter is constant, and only the ratio of the wet well to the gas well diameter is changed (α = 0.33-3, 17 changes), the results of the critical position L or L* and the circulating gas flow are shown in Table 5 and Figure 8 shown.

[0234] It can be seen that, under the condition that other conditions remain unchanged, the critical position of the circulating gas flow first decreases and then increases slightly with the increase of the diameter ratio of the two wells. When α = 2, the lowest critical position is L * =0.22, the maximum circulating gas flow is Qa c* = 0.5. At this time, α = 2 is recommended in system design, that is, the wet well diameter is twice the gas well diameter.

[0235] Table 5

[0236]

[0237] Example 3

[0238] For a series of calculated data in Example 2, about 320 groups, random forest analysis was first performed using Matlab to analyze the importance of the five factors in Examples 1 and 2, namely, flow rate, shaft diameter, gas well diameter, wet well diameter, and the ratio of the cross-sectional diameters of the wet well and the gas well, in affecting the critical position of the horizontal pipe of the system.

[0239] The analysis results show that the importance is: wet well diameter > vertical well diameter > ratio of cross-sectional diameters of wet well and gas well > gas well diameter > inflow rate, and the importance of the last two influencing factors is less than 1, which means that the impact on the critical position of the horizontal pipe is very small.

[0240] Subsequently, SPSS was used to perform multiple linear regression analysis in different combinations of the first three influencing factors (wet well diameter, vertical shaft diameter, and the ratio of the cross-sectional diameters of the wet well to the gas well). It was found that only when the two factors of wet well diameter and the ratio of the cross-sectional diameters of the wet well to the gas well jointly affected the critical position, the regression equation met the two conditions of significance P<0.05 and multicollinearity VIF<5 between variables.

[0241] Finally, the horizontal critical position of the data airflow cycle can be expressed as: L* = 0.54-0.21Ds*-0.057α(R 2 =0.80); where L*=L / H is the dimensionless quantity of the critical position L of the horizontal pipe; H is the drop height of the shaft, m; Ds* is the dimensionless quantity of the wet well diameter Ds of the shaft, and Ds*=Ds / Dm is taken; Dm is the shaft diameter of the theoretical calculation model, and is taken as 0.38m; α=Ds / Dc is the ratio of the cross-sectional diameters of the wet well and the gas well.

[0242] Substituting the data in the embodiment, that is, Ds*=0.71, α=1, the above formula is used to calculate L*=0.33, that is, L=2.55m. The results calculated by the above two methods are not much different, but the above formula can more quickly and roughly calculate the critical position of the horizontal pipe.

[0243] Example 4

[0244] The shaft size structure is the same as that in Example 1, except that the positions of the air circulation loop interface are different (z = 5, 4, 3, 2.64, 1.5, 1, 0.64, 0, -1m). At this time, the circulating air flow at several interface positions is calculated, such as Fig. 9 shown.

[0245] As can be seen from the figure, air circulation can occur at any position from the critical position to the top of the shaft when the air circulation loop interface is located. However, as the position of the air circulation loop interface gradually rises, the circulating airflow also gradually increases. When the position of the air circulation loop interface is higher than the inlet water tongue, the circulating airflow will decrease.

[0246] In addition, when the air circulation loop interface is just below the inflow water tongue of the vertical shaft, near z=0.64, the circulating air volume is the largest. This is because the air pressure value at this position is the lowest, which makes it easier to generate a larger pressure difference and thus form a larger air circulation.

[0247] Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. A person with ordinary knowledge in the technical field to which the present invention belongs may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be determined by the definition of the claims.

Claims

1. A method for obtaining a critical position of circulating airflow in a shaft having an air circulation system, characterized in that: include: A calculation model was established, which is as follows: A partition is arranged at the central axis of the vertical shaft with the top sealed, the bottom end of the vertical shaft is connected to the outflow pipe through a bend pipe, so that the vertical shaft is connected to the atmosphere, the top end of the partition is connected to the top end of the vertical shaft, the bottom end of the partition is flush with the bottom end of the vertical shaft, and the partition divides the vertical shaft into a wet well and an air well; an air inlet pipe and a water inlet pipe are connected to the wet well, and the air inlet pipe is located above the water inlet pipe; The baffle is provided with an opening as an air circulation loop interface. It is assumed that the position of the air circulation loop interface is a critical position for the gas between the wet well and the gas well to form a circulation. The section from the air circulation loop interface to the bottom of the baffle where a circulating airflow can be formed is defined as the wet well bottom. According to the established calculation model, the position of the airflow circulation loop interface, that is, the critical position of the circulating airflow, is obtained according to the first method and / or the second method; The first method comprises: The water tongue inlet is defined as the base point, and the wet well below the base point is divided into the first section, the second section and the outlet pipe from top to bottom; and the part extending downward from the bottom end of the partition to the bend section is defined as the end point; The air pressure equations at the air inlet pipe, the first section, the second section, and the outlet pipe are obtained, and the circulation loop equation is established at the same time, and the gas flow equation in the shaft is established, and the position of the airflow circulation loop interface is obtained by the simultaneous equations; wherein, the distance between the connection point of the first section and the second section and the base point is 2.64m, and the first section is the water tongue barrier section and the constant air pressure section distributed in sequence from the base point downward; The second method comprises: Define the water tongue inlet as the base point, divide the wet well below the base point into the third section, the fourth section and the outlet pipe from top to bottom; and define the part extending downward from the bottom end of the partition to the bend section as the end point; The air pressure equations at the air inlet pipe, the third section, the fourth section, and the outlet pipe are obtained, and the circulation loop equation is established at the same time, and the gas flow equation in the shaft is established. The position of the airflow circulation loop interface is obtained by the simultaneous equations; wherein, the distance between the connection between the third section and the fourth section and the base point is 5m, and the third section is a nonlinear growth section.

2. The method according to claim 1, characterized in that: The specific calculation steps of the first method include: S11. Establish equation The air pressure equation at the intake pipe is as follows: Where P a is the air pressure outside the intake pipe, which is atmospheric pressure, taken as 0Pa; P0 is the air pressure inside the intake pipe, Pa; k I is the loss coefficient of external gas when it flows through the intake pipe; ρ a is the air density of standard atmosphere at room temperature, kg / m 3 ; V a I is the average flow velocity of the gas in the intake pipe, m / s; The first section is divided into a water tongue barrier section and a constant air pressure section. The air pressure equations are respectively as shown in equation (2) and equation (3): In the formula, the dimensionless inflow flow is Q w is the water flow, L / s, g is the acceleration of gravity, m / s 2 ;D s is the diameter of the vertical shaft wet well, m; P1 is the air pressure at 0.64 m below the base point in the wet well, pa; V a is the average gas velocity in the wet well, m / s; a and b are coefficients related to the vertical well structure; P1=P3(3) Where, P1 is the air pressure at 0.64m below the base point in the wet well, pa; P3 is the air pressure at 2.64m below the base point in the wet well, pa; The air pressure equation of the second section is as follows: Where p is the air pressure in the second section, Pa; z is a certain height in the wet well where the drop height is greater than 2.64m, m; Q w is the incoming flow, L / s; D s is the diameter of the wet well, m; d is the diameter of the water droplet; C d is the coefficient of water droplet dragging gas; V is the average velocity of water droplet falling; V a is the average gas velocity in the wet well, m / s; ρ a is the air density of the standard atmosphere at room temperature; The air pressure equation at the outlet pipe is as follows: P8＝0(5) Where, P8 represents the air pressure at the outlet of the flow tube, pa; The circulation loop equation is as follows: Where P L is the air pressure at the interface of the air circulation loop on the wet well side, Pa; L is the height from the critical position to the end point of the circulating airflow, m; H c is the drop height from the bottom of the partition to the end point, m; P lloss1 =k b ∑ a (V a t ) 2 / 2, is the local pressure loss of gas from the bottom of the wet well to the gas well; where k b V is the local loss coefficient of gas passing through the bottom of the partition, which can be taken as 20 according to experimental determination; a t is the average velocity of gas at the bottom of the wet well, m / s; P floss =λ(LH c )∑ a (V a c ) 2 / 2D c , is the pressure loss along the gas well; where λ is the gas loss coefficient along the gas well; V a c is the average flow rate of circulating gas in the gas well, m / s; D c is the diameter of the gas well, m; ρ a is the air density of standard atmosphere at room temperature, kg / m 3 ;H c is the drop height from the bottom of the partition to the end point, m; L is the height from the critical position of the circulating airflow to the end point, m; P lloss2 =k o ρ a (V a c ) 2 / 2, is the local pressure loss when the gas circulates from the gas well to the wet well through the gas circulation loop interface; where k o =1.5, which is the local loss coefficient of gas flowing from the gas well to the wet well through the gas circulation loop interface; ρ a is the air density of standard atmosphere at room temperature, kg / m 3 ; V a c is the average flow rate of circulating gas in the gas well, m / s; The gas flow equation at the bottom of the wet well is as follows: In a And s +V a c And c =V a t And s (7) Where As and Ac are the cross-sectional areas of the wet well and gas well, respectively, m 2 ; V a , V a c , V a t are the gas velocity at the bottom of the first section, gas well, and wet well, respectively, m / s; The relationship between the circulating air volume in the shaft and the amount of gas sucked from the outside by the shaft is as follows: In the formula, Q a c =V a c A c , is the circulating air flow rate in the gas well, L; Q a I =V a I A I , is the entrained air flow rate at the air circulation loop interface, L; V a c and V a I Respectively represent the gas flow rate at the gas well and the gas circulation loop interface, m / s; A c and A I Represent the cross-sectional area of ​​the gas well and the gas circulation loop interface, m 2 ; S12, combining equations (1) to (8) in step S11 to obtain the value of the position L of the airflow circulation loop interface, that is, the critical position of the circulating airflow.

3. The method according to claim 1, characterized in that: The specific calculation steps of the second method include: S21. Establish equation The air pressure equation at the intake pipe is as follows: Where P a is the air pressure outside the intake pipe, which is atmospheric pressure, taken as 0Pa; P0 is the air pressure inside the intake pipe, Pa; k I is the loss coefficient of external gas when it flows through the intake pipe; ρ a is the air density of standard atmosphere at room temperature, kg / m 3 ; V a I is the average flow velocity of the gas in the intake pipe, m / s; The third section is a nonlinear growth section, and the pressure equations are as follows: (P5-P1) / (z5-z1)=0.5dp / dz (9) Wherein, P5 is the air pressure at z5 = 5m below the base point in the wet well, Pa; P1 is the air pressure at z1 = 0.64m below the base point in the wet well, Pa; dp / dz is the pressure gradient value of the fourth linear growth; The air pressure equation for the fourth section is as follows: Where p is the air pressure in the fourth section, Pa; z is a certain height in the wet well where the drop height is greater than 2.64m, m; Q w is the incoming flow, L / s; D s is the diameter of the wet well, m; d is the diameter of the water droplet; C d is the coefficient of water droplet dragging gas; V is the average velocity of water droplet falling; V a is the average gas velocity in the third section, m / s; ρ a is the air density of standard atmosphere at room temperature, kg / m 3 ; The air pressure equation at the outlet pipe is as follows: P8＝0(5) Where, P8 represents the air pressure at the outlet of the flow tube, pa; The circulation loop equation is as follows: Where P L is the air pressure at the opening of the wet well, Pa; L is the height from the critical position to the end point of the circulating airflow, m; H c is the drop height from the bottom of the partition to the end point, m; P lloss1 =k b ρ a (V a t ) 2 / 2, is the local pressure loss of gas from the bottom of the wet well to the gas well; where k b V is the local loss coefficient of gas passing through the bottom of the partition, which can be taken as 20 according to experimental determination; a t is the average velocity of gas at the bottom of the wet well, m / s; P floss =λ(LH c )ρ a (V a c ) 2 / 2D c , is the pressure loss along the gas well; where λ is the gas loss coefficient along the gas well; V a c is the average flow rate of circulating gas in the gas well, m / s; D c is the diameter of the gas well, m; ρ a is the air density of the standard atmosphere at room temperature; H c is the drop height from the bottom of the partition to the end point, m; L is the height from the critical position of the circulating airflow to the end point, m; P lloss2 =k o ρ a (V a c ) 2 / 2, is the local pressure loss when the gas circulates from the gas well to the wet well through the gas circulation loop interface; where k o =1.5 is the local loss coefficient of gas flowing from the gas well to the wet well through the gas circulation loop interface; ρ a is the air density of the standard atmosphere at room temperature; ρ a V is the air density of the standard atmosphere at room temperature; a c is the average flow rate of circulating gas in the gas well, m / s; The gas flow equation at the bottom of the wet well is as follows: In a And s +V a c And c =V a t And s (7) Where As and Ac are the cross-sectional areas of the wet well and gas well, respectively, m 2 ; V a , V a c , V a t are the gas velocity at the bottom of the third section, gas well, and wet well, m / s; The relationship between the circulating air volume in the shaft and the amount of gas sucked from the outside by the shaft is as follows: In the formula, Q a c =V a c A c , is the circulating air flow rate in the gas well, L; Q a I =V a I A I , is the entrained air flow rate at the air circulation loop interface, L; V a c and V a I Respectively represent the gas flow rate at the gas well and the gas circulation loop interface, m / s; A c and A I Represent the cross-sectional area of ​​the gas well and the gas circulation loop interface, m 2 ; S22, combining equations (1), (4) to (9) in step S21 to obtain the value of the position L of the airflow circulation loop interface, that is, the critical position of the circulating airflow.

4. The method according to claim 1, characterized in that When the inflow rate is constant, the influencing factors of the critical position of the circulating airflow are the shaft diameter, the gas well diameter, the wet well diameter, and the ratio of the cross-sectional diameters of the wet well and the gas well.

5. The method according to claim 4, characterized in that When the inflow rate is constant, the critical position of the circulating airflow increases with the increase of the shaft diameter.

6. The method according to claim 4, characterized in that When the inflow rate and the wet well diameter are constant, the critical position of the circulating airflow first decreases and then remains unchanged as the well diameter increases.

7. The method according to claim 4, characterized in that When the inflow rate and the gas well diameter are constant, the critical position of the circulating airflow first decreases and then remains unchanged as the wet well diameter increases.

8. The method according to claim 4, characterized in that When the inflow rate and the diameter of the wet well are constant, the critical position of the circulating airflow first decreases and then increases with the increase of the ratio of the cross-sectional diameter of the wet well to the gas well.

9. The method according to claim 4, characterized in that The relationship between the critical position of the circulating airflow and the influencing factor is as shown in formula (10): L * =0.54-0.21D s * -0.057α,R 2 =0.80 (10) Where, L * =L / H, which is the dimensionless quantity of the critical position L of the horizontal pipe; L is the height from the critical position of the circulating airflow to the end point, m; H is the drop height of the shaft, m; D s * is the dimensionless quantity of the vertical shaft wet shaft diameter Ds, take D s * =D s / D m ;D m is the shaft diameter of the theoretical calculation model, which is 0.38m; α=D s / D c , which is the ratio of the cross-sectional diameters of the wet well to the gas well.

10. The method according to claim 1, characterized in that Air circulation can occur when the air circulation loop interface is located at any position from the critical position to the top of the shaft.

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