A ground multi-stage orifice throttle valve for preventing ice blockage and its design method

Abstract

The present invention discloses a ground multi-stage orifice throttle valve for preventing and controlling ice blockage and a design method thereof, which comprises the following steps: a parameter setting and a design calculation part, wherein the parameter setting includes: natural gas physical property parameters and gas well production and operation parameters; the design calculation part specifically comprises the following steps: starting from the first-stage orifice throttle valve, performing design calculation step by step until the downstream pressure of a certain stage throttle valve is less than the maximum pressure of the natural gas after throttling, stopping the design; performing temperature calibration on the entire multi-stage orifice throttle valve, ensuring that the temperature of the contraction zone of each stage throttle valve is higher than the critical temperature for forming hydrates, and improving the natural gas hydrate prevention and control effect of the ground multi-stage orifice throttle valve through reasonable temperature calibration.

Description

Technical Field

[0001] The present invention belongs to the field of natural gas collection, and in particular relates to a ground multi-stage orifice throttle valve for preventing and controlling ice blockage and a design method thereof. Background Art

[0002] In natural gas production projects, throttle valves are required to reduce the natural gas temperature to a safe range to protect downstream pipelines and equipment. Due to the high velocity and low temperature in the contraction zone downstream of the throttle valve throat, natural gas reacts with water at high pressure and low temperature to form hydrates. Solid natural gas hydrates can clog the throttle valve throat, so proper design is essential to prevent hydrate formation.

[0003] To prevent hydrate formation and achieve a throttling effect, the downhole throttling process is currently widely used in production. The throttle valve is installed deep in the gas well and the natural gas is heated by geothermal energy. However, the monitoring and maintenance costs of this design are too high.

[0004] Currently, there is no reasonable and universal design method for ground multi-stage orifice throttle valves. It is necessary to fully consider the flow state of natural gas inside the multi-stage throttle valve and examine whether the temperature of natural gas inside the throttle valve is higher than the critical temperature for natural gas hydrate formation. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a ground multi-stage orifice throttle valve and its design method for preventing and controlling ice blockage, so as to solve the problem that the prior art lacks a reasonable and universal design method and the throttle valve installed underground has too high a cost in monitoring and maintenance.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A design method for a ground multi-stage orifice throttle valve for preventing ice blockage includes the following steps:

[0008] Step 1: Set natural gas physical properties and gas well production and operation parameters;

[0009] Step 2: Calculate the back pressure of the first-stage orifice plate and the diameter of the holes in the orifice plate using the natural gas physical properties and gas well production and operation parameters in combination with the Bernoulli equation. Calculate the back pressure of the second-stage orifice plate and the diameter of the holes in the orifice plate using the first-stage orifice plate back pressure, natural gas physical properties, and gas well production and operation parameters in combination with the Bernoulli equation. This process continues in this order until the calculated post-throttling pressure of the nth-stage orifice plate is less than the maximum pressure of the natural gas.

[0010] Step 3: Calculate the average mass flow temperature of the cross section of each orifice plate and the critical temperature of the natural gas hydrate in the cross section of each orifice plate. If the average mass flow temperature of the same cross section is lower than the critical temperature of the natural gas hydrate, repeat step 2 to redesign the diameters of the holes in all orifice plates. If the average mass flow temperature of all cross sections is lower than the critical temperature of the corresponding natural gas hydrate, the design of the multi-stage orifice throttling valve is completed.

[0011] A further improvement of the present invention is:

[0012] Preferably, in step 1, the natural gas physical property parameters include the natural gas state equation, natural gas viscosity coefficient and natural gas specific heat ratio; the gas well production operation parameters include the gas well wellhead pressure, gas well production, natural gas temperature before throttling and natural gas maximum pressure after throttling.

[0013] Preferably, in step 2, the back pressure formula for each level of orifice plate is calculated as:

[0014]

[0015] Among them, p 1,i The first subscript "1" in the p 2,i The first subscript "2" in the formula represents "after throttling", is the back pressure of the orifice plate, i represents the number of orifice plates, k is the specific heat ratio of the gas, p is the back pressure of the orifice plate, and 1,i It is the back pressure after throttling by the previous stage orifice plate.

[0016] Preferably, in step 2, the Bernoulli equation is:

[0017]

[0018] Among them, q m is the mass flow rate of the single-stage throttle valve, C is the outflow coefficient; β is the ratio of the diameter of the circular hole to the diameter of the pipe; ε is the expansion coefficient of natural gas, ρ 1,i is the density of natural gas before throttling by the i-th stage orifice plate.

[0019] Preferably, after step 2, the calculated diameter of the holes in each stage of the orifice plate is multiplied by the design coefficient to obtain the final diameter of the holes in the orifice plate.

[0020] Preferably, in step 3, for any cross section at x=x0, the mass flow average temperature is defined as:

[0021]

[0022] Where ρ, u and T are the fluid density, axial velocity and temperature at x = x0 through the microelement area dA, respectively. m is the mass flow rate of the single-stage throttle valve.

[0023] Preferably, the calculation formula of the critical temperature of the natural gas hydrate is:

[0024]

[0025] in, It is the average pressure of mass flow on the section at x=x0.

[0026] Preferably, the The calculation formula is:

[0027]

[0028] Wherein, p is the pressure of the fluid passing through the micro-area dA at x=x0, ρ, u and T are the density, axial velocity and temperature of the fluid passing through the micro-area dA at x=x0 respectively.

[0029] A ground multi-stage orifice throttle valve for preventing and controlling ice blockage is designed using the above-mentioned design method. Several orifice plates are arranged in the throttle valve along the length direction, the distances between adjacent orifice plates are equal, and a hole is opened in the center part of the orifice plate.

[0030] Preferably, the diameter of the holes in the orifice plate gradually increases along the direction of fluid flow.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The present invention discloses a method for designing the aperture of a ground multi-stage orifice throttle valve for preventing ice blockage. The method comprises the following steps: parameter setting and design calculation, wherein the parameter setting includes natural gas physical properties and gas well production and operation parameters; the design calculation comprises the following specific steps: starting with the first-stage orifice throttle valve, performing design calculations step by step until the downstream pressure of a particular throttle valve is less than the maximum pressure of the natural gas after throttling; and performing temperature calibration on the entire multi-stage orifice throttle valve to ensure that the temperature of the contraction zone of each throttle valve is above the critical temperature for hydrate formation. This reasonable temperature calibration improves the natural gas hydrate prevention and control effect of the ground multi-stage orifice throttle valve. The method can determine the orifice plate size of the ground multi-stage orifice throttle valve for preventing ice blockage. The method is efficient, objective, universal, and reliable, and can be designed according to different working conditions and environments. The method is efficient and objective, reduces the manual calculation cost of multi-stage orifice throttle valve design and calculation, and avoids subjective errors in manually selecting the orifice throttle valve aperture during design. This design method is applicable to the design of ground multi-stage orifice throttle valves for preventing ice blockage under various natural gas production conditions, and can provide data support for the automatic control of the orifice throttle valve opening.

[0033] The present invention also discloses a ground multi-stage orifice throttle valve for preventing and controlling ice blockage. The interior of the throttle valve is composed of multiple orifice plates, each of which has a separate hole, so that the pressure of the fluid is reduced after the fluid passes through each orifice plate. The throttle valve is universal and suitable for a variety of working conditions. Installing the throttle valve on the ground can facilitate monitoring and maintenance, and facilitates the automation of throttle valve monitoring, which is consistent with the current concept of "smart gas fields".

[0034] Furthermore, the diameter of the holes in the orifice plate of the multi-stage orifice throttle valve continuously increases along the direction of fluid flow, so that the pressure reduction ratio gradually decreases, which conforms to the flow law of the airflow. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Shown is a schematic diagram of the structure of a ground multi-stage orifice throttle valve for preventing and controlling ice blockage.

[0036] Figure 2 Shown is a general design flow chart of a design method for a ground multi-stage orifice throttle valve for preventing and controlling ice blockage.

[0037] Figure 3 Shown is Figure 2 Input parameters in the theoretical design flow chart.

[0038] Figure 4 The cross-sectional mass flow average temperature T in one embodiment is shown. m,x The critical temperature T for the formation of natural gas hydrate c,x The curve of the change along the axial coordinate x. DETAILED DESCRIPTION

[0039] The present invention is described in further detail below with reference to the accompanying drawings:

[0040] In the description of the present invention, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention; the terms "first", "second", and "third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance; in addition, unless otherwise expressly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection or a detachable connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be a communication between the internal parts of two components. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0041] This design method requires the use of thermodynamic principles to Figure 1 The sizes of the orifice plates of each stage of the multi-stage orifice throttle valve shown are reasonably specified, so that the natural gas temperature inside the throttle valve can be higher than the critical temperature of the local natural gas hydrate formation, thereby preventing natural gas ice blockage.

[0042] The technical solution of the present invention is to provide a method for designing the aperture of a ground multi-stage orifice throttle valve for preventing ice blockage, such as Figure 2 As shown, it includes the following design steps:

[0043] Step 1, parameter setting: This includes setting natural gas physical properties and gas well production parameters. The natural gas physical properties include the natural gas equation of state, natural gas viscosity coefficient, and natural gas specific heat ratio; the gas well production parameters include wellhead pressure, gas well production, pre-throttling natural gas temperature, and post-throttling maximum natural gas pressure.

[0044] Step 2: Start designing and calculating the first-stage orifice throttle valve step by step until the downstream pressure of a certain throttle valve is less than the maximum pressure of the natural gas after throttling. When designing and calculating a certain throttle valve, calculate the minimum aperture constraint of that stage through the pressure reduction characteristics of the single-stage orifice throttle valve and give the aperture. Calculate the downstream parameters including the downstream pressure of that throttle valve and use them as the upstream parameters of the next-stage orifice throttle valve to continue the design calculation. It is necessary to ensure that the natural gas before each stage of the orifice throttle valve is in a fully developed state. Specifically, the following steps are included:

[0045] (1) Determine the ratio of the orifice plate back pressure to the pressure before throttling;

[0046]

[0047] Among them, p 1,i The first subscript "1" in the p 2,i The first subscript "2" in stands for "after throttling," i represents the number of stages of the orifice plate, and k represents the specific heat ratio of the gas, which is k = 1.30 for natural gas. The minimum orifice plate back pressure can be obtained using formula (1).

[0048] Since the smaller the aperture of the orifice throttle valve, the more obvious the pressure reduction effect, that is, when the pressure before throttling remains unchanged, the pressure after throttling is lower, in order to satisfy formula (1), each stage of the orifice throttle valve has a minimum aperture.

[0049] (2) The mass flow rate q of a single-stage throttle valve can be derived from the Bernoulli equation and the continuity equation m , the relationship between the hole diameter d and Δp is:

[0050]

[0051] Where C is the outflow coefficient, determined by the Reader-Harris / Gallagher formula; β is the ratio of the diameter of the hole to the diameter of the pipe; ε is the expansion coefficient of natural gas, ρ 1,i is the density of natural gas before throttling at the i-th stage orifice plate, Δp is the p calculated by formula (1) 1,i and p 2,i The difference.

[0052] The minimum aperture of the orifice plate of this level is obtained by formula (2).

[0053] (3) Repeat steps (1) and (2) until the throttled pressure of a certain throttle valve is lower than the maximum pressure of the natural gas after throttling, and then stop the design;

[0054] Specifically, when the inlet pressure before the first-stage orifice plate is known, the aperture of the first-stage orifice plate can be calculated by formula (1) and formula (2), and the stage number i = i + 1, and the post-throttling pressure of the first-stage orifice plate throttle valve is set as the pre-throttling pressure of the second-stage orifice plate throttle valve, that is, p 1,2 =p 2,1 Repeat the above calculation until the throttle pressure of a certain throttle valve is lower than the maximum pressure of natural gas after throttling, and then stop the design.

[0055] The distance between adjacent orifice plates is determined based on the need to ensure that the natural gas is in a fully developed state before the throttle valve of each orifice plate.

[0056] Step 3: Temperature-calibrate the entire multi-stage orifice throttle valve to ensure that the temperature of the contraction zone of each stage is higher than the critical temperature for hydrate formation. If the temperature of the contraction zone of a stage throttle valve is lower than the critical temperature for hydrate formation, adjust the aperture of the throttle valve at that stage and its downstream according to Step 1. The specific process includes the following steps:

[0057] For any cross-section at x = x0, the average mass flow temperature is defined as:

[0058]

[0059] Where ρ, u and T represent the density, axial velocity and temperature of the fluid passing through the infinitesimal area dA at x = x0, respectively. m Represents the mass flow rate of a single-stage throttle valve. The calculation formula for u is:

[0060]

[0061] The same method is used to obtain the average mass flow pressure on the cross section at x = x0:

[0062]

[0063] Where p represents the pressure of the fluid passing through the infinitesimal area dA at x = x0. The critical temperature for the formation of natural gas hydrate at this pressure is calculated by the Ponomarev method:

[0064]

[0065] The above formula (3) can be used to calculate the average temperature definition of mass flow on any section. Furthermore, the critical temperature of natural gas hydrate on the section can be calculated by formula (5). It is then checked whether the temperature of the current multi-stage orifice throttle valve design can meet the conditions for preventing the formation of natural gas hydrates, that is, by comparing the average temperature T of the section mass flow on each axial coordinate x. m,x The critical temperature T for the formation of natural gas hydrate c,x If there is T in the contraction area of ​​a certain level of orifice throttle valve m,x ≤T c,x In this case, we need to return to Figure 2 The theoretical design link shown in the figure is redesigned, and the aperture of the throttle valve of the stage and the subsequent stage is adjusted accordingly. Until any axial position of a certain design satisfies T m,x >T c,x .

[0066] The throttle valve designed using the above method features an array of orifice plates within the pipe. Each orifice plate is tightly connected to the inner wall of the pipe, with adjacent orifice plates spaced equidistant from each other. The orifice plates are perpendicular to the throttle valve's axis, and each plate has a central hole for fluid passage. As the fluid flows, the diameter of the central hole increases, slowing the rate of pressure reduction.

[0067] Example

[0068] In one embodiment of the present invention, a method is designed for a gas volume of 15000m3 under standard conditions (20°C, 1 atm). 3 / d, with a wellhead pressure of 18MPa and a wellhead temperature of 15℃, the ground multi-stage orifice throttle valve for preventing ice blockage in a natural gas well is designed to reduce the natural gas pressure to below 3.5MPa. It is easy to understand that the design in this specific embodiment is for a gas volume of 15000m 3 / d, the throttle valve with a wellhead pressure of 18MPa is only exemplary. The design method of the present invention is applicable to any gas volume and any wellhead pressure. For example, the gas volume is 20000m 3 / d, 30000m 3 / d or any other gas volume, and the wellhead pressure is 15MPa, 20MPa or any other wellhead pressure.

[0069] The pipe diameter in this embodiment is... Through simulation, it is found that when the natural gas is in a fully developed state in front of the adjacent stage orifice plate throttle valve, specifically through the simulation results, the various physical field parameters are evenly distributed in the mainstream area of ​​the cross section, and the distance between adjacent orifice plates is about 15 cm. The distance between adjacent stage orifice plate throttle valves is further designed to be between 20 and 50 cm, and the preferred distance between adjacent stage orifice plate throttle valves is 25 cm.

[0070] In one embodiment, it is necessary to ensure that the orifice throttle valve at each stage does not have blocked flow, that is, to ensure that the back pressure p at each stage is 2,i and the pre-throttle pressure p 1,i The ratio satisfies the following formula:

[0071]

[0072] Wherein, k is the specific heat ratio of the gas. The specific heat ratio of natural gas is k=1.30, so the value on the right side of the above formula is 0.5457.

[0073] In addition, since the state of the natural gas at the wellhead in this embodiment has reached the conditions for forming hydrates, the wellhead temperature needs to be increased to 30°C.

[0074] The mass flow rate q of a single-stage throttle valve can be derived from the Bernoulli equation and the continuity equation: m The relationship between the circular hole diameter d and the design pressure drop Δp is:

[0075]

[0076] Where C is the outflow coefficient, determined by the Reader-Harris / Gallagher formula; β is the ratio of the diameter of the hole to the diameter of the pipe; ε is the expansion coefficient of natural gas, ρ 1,i is the density of natural gas before throttling by the i-th stage orifice plate.

[0077] The theoretical design of the aperture of each stage of orifice throttle valve is realized by writing an iterative calculation program using MATLAB software, such as Figure 3 First, input the corresponding natural gas physical parameters, the inlet pressure is p in =18MPa, inlet temperature T in =303K and the mass flow rate of natural gas q m =0.1130kg / s. Let stage number i = 1, and the pressure before throttling of this stage is p 1,1 =p in (The expression "p 1,1 The first subscript "1" in "" means "before throttling", the second subscript "1" means "first stage"), the lowest pressure after throttling is p 2,1,min =0.5457p 1,1, the first-stage minimum aperture d is obtained by formula (2) 1,min =2.5325mm. Under the constraint of the minimum aperture, take the first-level aperture design coefficient K1=1.3>1, and each subsequent aperture must be multiplied to obtain the aperture value d1=K1d 1,min =3.30mm, and then the pressure after throttling is obtained by formula (2) as p 2,1 =15.9354MPa. In the subsequent calculation process, it is assumed that the mass flow rate of each stage is equal. Record the design aperture d1 of the throttle valve of this stage and the pressure p before and after the throttle valve. 1,1 and p 2,1 At this point, the aperture design of the first-stage orifice plate throttle valve is completed, and the next-stage orifice plate needs to be designed. Let the stage number i = i + 1, and set the throttle pressure of the first-stage orifice plate throttle valve to the throttle pressure before the second-stage orifice plate throttle valve, that is, p 1,2 =p 2,1 Repeat the above calculations until the post-throttling pressure of a particular throttle valve stage falls below 3.5 MPa. This stage becomes the final stage of the multi-stage orifice throttle valve design. Output the apertures and pre- and post-throttling pressures for each stage to enable temperature verification of the currently designed multi-stage orifice throttle valve using numerical simulation methods.

[0078] ANSYS Fluent software was used to numerically simulate the natural gas flow field within the throttle valve. The calculations required ensuring flow compressibility. The governing equations were the flow equation, the gas state equation, and the energy equation. Boundary conditions included the pressure inlet, pressure outlet, and adiabatic walls. Furthermore, a reasonable turbulence model was required. Numerical simulations of the currently designed multi-stage orifice throttle valve revealed the flow state of natural gas within the throttle valve. The pressure field and gas flow rate were verified, ensuring that the flow in front of the throat of each throttle valve was fully developed.

[0079] The average temperature weighted by mass flow is calculated on each cross section perpendicular to the axis. This average temperature fully considers the size of the effective flow tube and has important guiding significance for the actual temperature distribution. The mass flow average temperature on the cross section at x = x0 is defined as:

[0080]

[0081] Where ρ, u and T represent the density, axial velocity and temperature of the fluid passing through the infinitesimal area dA at x = x0, respectively. m Represents mass flow. The same method is used to obtain the average mass flow pressure on the cross section at x = x0.

[0082]

[0083] Where p represents the pressure of the fluid passing through the infinitesimal area dA at x = x0. The critical temperature for the formation of natural gas hydrate at this pressure is calculated by the Ponomarev method:

[0084]

[0085] The relative density is γ g = 0.60 for natural gas, parameter B = 17.67.

[0086] Check whether the temperature of the current multi-stage orifice throttle valve design can meet the conditions for preventing the formation of natural gas hydrates, that is, compare the average temperature T of the cross-section mass flow on each axial coordinate x. m,x The critical temperature T for the formation of natural gas hydrate c,x If there is T in the contraction area of ​​a certain level of orifice throttle valve m,x ≤T c,x In this case, we need to return to Figure 2 The theoretical design link shown in the figure is redesigned, and the aperture of the throttle valve of the stage and the subsequent stage is adjusted accordingly. Until any axial position of a certain design satisfies T m,x >T c,x ,like Figure 4 As shown, the temperature check passed, indicating that the design meets the requirements. The apertures of each stage, the pressures before and after throttling, and the temperature of the contraction zone after throttling are shown in Table 1. At the same time, it is necessary to ensure that the natural gas flow is fully developed before reaching the throat of each throttle valve. The spacing between the two stages is 250mm.

[0087] Table 1 Design of apertures at various levels

[0088]

[0089] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A design method for a ground multi-stage orifice throttle valve for preventing ice blockage, characterized in that: The following steps are involved: Step 1: Set natural gas physical properties and gas well production and operation parameters; Step 2: Calculate the back pressure of the first-stage orifice plate and the diameter of the holes in the orifice plate using the natural gas physical properties and gas well production and operation parameters in combination with the Bernoulli equation. Calculate the back pressure of the second-stage orifice plate and the diameter of the holes in the orifice plate using the first-stage orifice plate back pressure, natural gas physical properties, and gas well production and operation parameters in combination with the Bernoulli equation. This process continues in this order until the calculated post-throttling pressure of the nth-stage orifice plate is less than the maximum pressure of the natural gas. Step 3: Calculate the average mass flow temperature of the cross section of each orifice plate and the critical temperature of the natural gas hydrate in the cross section of each orifice plate. If the average mass flow temperature of the same cross section is lower than the critical temperature of the natural gas hydrate, repeat step 2 to redesign the diameters of the holes in all orifice plates. If the average mass flow temperature of all cross sections is lower than the critical temperature of the corresponding natural gas hydrate, the design of the multi-stage orifice throttling valve is completed.

2. The design method of a ground multi-stage orifice throttle valve for preventing ice blockage according to claim 1 is characterized in that: In step 1, the natural gas physical property parameters include the natural gas state equation, natural gas viscosity coefficient and natural gas specific heat ratio; the gas well production operation parameters include gas well wellhead pressure, gas well production, natural gas temperature before throttling and natural gas maximum pressure after throttling.

3. The design method of a ground multi-stage orifice throttle valve for preventing ice blockage according to claim 1 is characterized in that: In step 2, the formula for calculating the back pressure of each orifice plate is: Among them, p 1,i The first subscript "1" in the p 2,i The first subscript "2" in the formula represents "after throttling", is the back pressure of the orifice plate, i represents the number of orifice plates, k is the specific heat ratio of the gas, and p is the back pressure of the orifice plate. 1,i It is the back pressure before the previous stage orifice plate throttling.

4. The design method of a ground multi-stage orifice throttle valve for preventing ice blockage according to claim 1 is characterized in that: In step 2, the Bernoulli equation is: Among them, q m is the mass flow rate of the single-stage throttle valve, C is the outflow coefficient; β is the ratio of the diameter of the circular hole to the diameter of the pipe; ε is the expansion coefficient of natural gas, ρ 1,i is the density of natural gas before throttling by the i-th stage orifice plate.

5. The design method of a ground multi-stage orifice throttle valve for preventing ice blockage according to claim 1 is characterized in that: After step 2, the calculated diameter of the holes in each stage of the orifice plate is multiplied by the design coefficient to obtain the final diameter of the holes in the orifice plate.

6. The design method of a ground multi-stage orifice throttle valve for preventing ice blockage according to claim 1 is characterized in that: In step 3, for any cross section at x = x0, the mass flow average temperature is defined as: Where ρ, u and T are the fluid density, axial velocity and temperature at x = x0 through the microelement area dA, respectively. m is the mass flow rate of the single-stage throttle valve.

7. The design method of a ground multi-stage orifice throttle valve for preventing ice blockage according to claim 1 is characterized in that: The calculation formula of the critical temperature of the natural gas hydrate is: in, It is the average pressure of mass flow on the section at x=x0.

8. The design method of a ground multi-stage orifice throttle valve for preventing ice blockage according to claim 7 is characterized in that: described The calculation formula is: Wherein, p is the pressure of the fluid passing through the infinitesimal area dA at x=x0, ρ and u are the density and axial velocity of the fluid passing through the infinitesimal area dA at x=x0, respectively.

9. A ground multi-stage orifice throttle valve for preventing ice blockage designed by the design method of any one of claims 1 to 8, characterized in that: A plurality of orifice plates are arranged in the throttle valve along the length direction, the distances between adjacent orifice plates are equal, and a hole is opened in the center part of the orifice plate.

10. The ground multi-stage orifice throttle valve for preventing ice blockage according to claim 9, characterized in that: Along the direction of fluid flow, the diameter of the holes in the orifice plate gradually increases.

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