Full-rotational-flow supersonic natural gas purification device

Abstract

The invention belongs to the technical field of supersonic separation, and particularly relates to a full-rotational-flow supersonic natural gas purification device which comprises a Laval nozzle, a front rotational flow assembly, a rear rotational flow separation assembly, a diffuser and the like, natural gas forms a strong rotational flow field on the Laval nozzle under the action of the front rotational flow assembly and the rear rotational flow separation assembly, and the natural gas is purified through the diffuser. Expanding to supersonic velocity to form low temperature and low pressure, so that the natural gas is condensed to form a gas-liquid mixture; meanwhile, liquid drops of natural gas are thrown to the pipe wall through strong centrifugal force on the side, close to the diffuser, of the Laval spray pipe and finally flow out of a liquid outlet, and separation of the gas and condensate liquid is achieved. According to the device, under the condition that the Laval nozzle enables the conversion from the axial speed to the tangential speed of the natural gas to occur under the subsonic speed condition, shock waves cannot be generated after the cyclone assembly is arranged in the front, the natural gas expands to the supersonic speed in the cyclone state, the influence of re-evaporation of liquid drops is effectively reduced in the mode that cyclone and condensation are conducted simultaneously, and the separation efficiency is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of supersonic separation, and in particular relates to a full-cyclonic supersonic natural gas purification device. Background Art

[0002] Ultrasonic separation technology is a new technology currently used in natural gas processing. The device has the advantages of simple structure, high working efficiency, no need to add chemical agents, energy saving and environmental protection. According to the position of the swirl blades in the separator, the supersonic separator is mainly divided into two types: expansion first and then swirl type separator and swirl first and then expansion type separator.

[0003] The main representative of the expansion-then-cyclone separator is the Twister I cyclone separator developed by Twister BV. Fig. 9 As shown. The natural gas expands adiabatically through the Laval nozzle 1 and reaches the speed of sound at the throat. Under low temperature and low pressure, the water vapor in the natural gas condenses. Under the action of the supersonic wing 2, the gas droplets obtain a large centrifugal force and are thrown to the wall to form a liquid film and flow into the liquid separation tank, realizing gas-liquid separation. In the diffuser section 3, due to the existence of shock waves, the nozzle temperature rises, the flow rate decreases, and the pressure rises. The first expansion and then cyclone type separator represented by "TwisterⅠ" has cyclone blades installed after the nozzle. Under supersonic conditions, the axial velocity is converted to tangential velocity, which can produce a large cyclone intensity, but it is easy to have uncontrollable shock waves, causing the airflow temperature and pressure to rise, causing the condensed droplets to evaporate again.

[0004] The main representative of the cyclone-follow-expansion separator is the "3S" cyclone separator developed by ENGO Petroleum Company. Fig.10 As shown in the figure, and the Twister II cyclone separator developed by Twister BV, such as Fig.11 As shown. This structure adopts the method of pre-positioning swirl blades, among which "3S" adopts the traditional Laval nozzle 1 plus blades 2, and TwisterII adopts the structure of swirl blades 3 plus center body 4. The swirl device 5 is located before the Laval nozzle 1, and the natural gas completes the transformation from axial velocity to tangential velocity under subsonic conditions. Although the generation of shock waves can be avoided, its tangential flow velocity is smaller than that of the post-swirl separator, which is not conducive to the separation of condensed droplets and the separation efficiency is relatively low. Summary of the invention

[0005] In order to solve the problems existing in the prior art, the purpose of the present invention is to provide a full-swirl supersonic natural gas purification device, so that the natural gas is transmitted in a swirl state throughout the Laval nozzle, and the front swirl component is used to make the conversion of the axial velocity of the natural gas to the tangential velocity occur under subsonic conditions, and no shock wave will be generated after the front swirl component. The rear swirl separation component is used to make the natural gas achieve a gas-liquid separation effect of swirl and condensation after expanding to a supersonic speed, which can effectively reduce the influence of droplet re-evaporation on separation and improve the separation efficiency.

[0006] The technical solution of the present invention is: A full cyclonic supersonic natural gas purification device, comprising: The invention comprises a Laval nozzle, which is divided into a straightening section, a tapered section, a throat section and a gradually expanding section from the inlet to the outlet, and is characterized in that it also comprises a swirl unit arranged in the Laval nozzle, a flow channel for natural gas to pass through is reserved between the swirl unit and the tube wall of the Laval nozzle, and the swirl unit comprises: A front swirl assembly comprises a central body and a plurality of static swirl blades, wherein the central body is inserted in the straightening section and the tapered section, and the plurality of static swirl blades are located in the straightening section and are sleeved on the central body at equal intervals; A post-cyclone separation component, comprising a shaft body and a spiral blade, wherein one end of the shaft body passes through the throat and is connected to the center body, and the other end passes through the entire gradually expanding section, the spiral blade is wound around the shaft body, and the spiral radius of the spiral blade gradually increases with the diameter of the gradually expanding section of the Laval nozzle, and the axes of the shaft body and the center body coincide with the axis of the Laval nozzle; The natural gas begins to accelerate in the swirl in the rectifying section through the action of the static swirl blades, and is accelerated to the speed of sound at the throat through the gradually contracting section. In the gradually expanding section, the spiral blades further guide the natural gas to accelerate and expand to the supersonic speed, forming a low temperature and low pressure, so that the natural gas condenses into a gas-liquid mixture while swirling. Under the action of the centrifugal force of the swirl, the natural gas is separated into gas and liquid in the gradually expanding section. The separated liquid flows out from the liquid outlet, and the separated gas continues to be transmitted.

[0007] Preferably, the central body is composed of a semi-ellipsoid and a curved body, both of which are rotating bodies with the axis of the Laval nozzle as the rotation center, the semi-ellipsoid is placed in the rectifying section, the curved body is placed in the tapered section, and the contour surface of the semi-ellipsoid is determined by the following formula: , in, is the length of the straightening section of the Laval nozzle, is the diameter of the Laval nozzle's converging section inlet, x , y , zis the three-dimensional coordinate value of the semi-ellipsoid surface, h is the static swirl blade y The height of the axis.

[0008] Preferably, the number of the static swirl blades is at least 3.

[0009] Preferably, the rotation angle of the static swirl blades ranges from 73° to 82°.

[0010] Preferably, the diameter of each part of the Laval nozzle after the center body is placed is determined according to the following formula: , in, is the diameter of the Laval nozzle after it is inserted into the center body. It is a reduction in proportion. D is the design diameter for the Laval nozzle.

[0011] Preferably, the length of the straightening section of the Laval nozzle is determined according to the following formula: , in, L 0 Length of the straightening section of the Laval nozzle; d is the inlet diameter of the tapered section of the Laval nozzle.

[0012] Preferably, the length of the diverging section of the Laval nozzle is determined according to the following formula: , in, L 2 is the length of the diverging section of the Laval nozzle; r 2 is the radius of the Laval nozzle exit section; φ is the divergence angle of the diverging section of the Laval nozzle; r 1 is the radius of the Laval nozzle throat.

[0013] Preferably, the throat of the Laval nozzle is determined according to the following formula: p=RT / (vb)-a / (v(v+b)-c) , in, T is the initial temperature at the throat of the Laval nozzle, p is the throat pressure of the Laval nozzle, R is the universal gas constant, v is the molar volume, a and b is a constant specific to the substance, a =0.45724× R 2 Tc 2 / Pc , b=0.0778× Rtc2 / Pc ; c = ab / 27 R 2 Tc 2 , Tc is the critical temperature of the throat of the Laval nozzle, Pc is the critical pressure at the throat of the Laval nozzle.

[0014] Compared with the prior art, the full cyclone supersonic natural gas purification device of the present invention has the following beneficial effects: 1. In the natural gas purification process, when the natural gas is separated into gas and liquid, the front swirl assembly arranged inside the straightening section and the tapered section of the Laval nozzle is used to make the natural gas realize the conversion of axial velocity into tangential velocity after entering the Laval nozzle, forming a strong swirl field, and the natural gas is accelerated by the straightening section and the tapered section of the Laval nozzle under the action of the front swirl assembly, reaching the sonic velocity at the throat, and then the rear swirl separation assembly arranged in the expanding section is used to cause the natural gas to continue to accelerate and expand to supersonic speed, and after the natural gas increases from the sonic speed to the supersonic speed, a low-temperature and low-pressure zone is formed, so that the water vapor and heavy hydrocarbons, acidic gases and other components contained in the natural gas condense during the swirl process, that is, condense while swirling to form a gas-liquid mixture, and then under the strong swirl action, the gas-liquid mixture generates a strong centrifugal force to throw the droplets to the tube wall and discharge from the liquid outlet, and the separated gas is continuously transmitted, and the process of the natural gas swirling and condensing can effectively reduce the influence of the droplet re-evaporation, and effectively improve the separation efficiency; 2. The front swirl assembly is used to make the conversion of natural gas from axial velocity to tangential velocity occur under subsonic conditions, so that no shock wave will be generated after the front swirl assembly, so the pressure drop is reduced, so that it can operate at a lower inlet pressure or improve the processing effect under the same pressure drop; at the same time, the rear swirl separation assembly composed of a shaft body and spiral blades can be used to realize the swirl and condensation of natural gas in the gradually expanding section, suppress the generation of shock waves, effectively reduce the impact of droplet re-evaporation, and improve the separation efficiency. Then, the diffuser is used to make the conversion of the separated gas from the tangential velocity to the axial velocity also occur under subsonic conditions, so that the separated natural gas will not generate shock waves and achieve stable transmission.

[0015] 3. The front swirl assembly composed of a center body and multiple static swirl blades is used to make the natural gas flow around the center body after entering the Laval nozzle to form a coaxial swirl, so that the natural gas can form a stable swirl to achieve acceleration and separation; 4. Through the action of the pre-swirl component, the natural gas forms a swirl state from the initial stage when entering the Laval nozzle, so that the natural gas begins to realize swirl separation when condensation occurs instead of separation after passing through the rectification section, thereby reducing the impact of evaporation and improving separation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the overall structure in an embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of a front swirl assembly in an embodiment of the present invention; Figure 3 Schematic diagram of the structure of the Laval nozzle in an embodiment of the present invention; Figure 4 It is a curve diagram of the Laval nozzle tapered section change in an embodiment of the present invention; Figure 5 It is a schematic diagram of the structure of the post-cyclone separation component in an embodiment of the present invention; Figure 6 : is a distribution diagram of swirl acceleration at different cross sections of the Laval nozzle expansion section in an embodiment of the present invention; Figure 7 1. The axial pressure distribution diagram of the spiral blades with different blade thicknesses in the gradually expanding section in the embodiment of the present invention; Figure 8 The thickness of the blades of different spiral blades in the embodiment of the present invention is the axial distance x= Tangential velocity distribution diagram of each point on the horizontal center line of the 325mm cross section; Fig. 9 It is a schematic diagram of the structure of a Twister I type cyclone separator in the background technology of the present invention; Fig.10 It is a structural schematic diagram of a "3S" cyclone separator in an embodiment of the present invention; Fig.11 Schematic diagram of the structure of a Twister II cyclone separator in an embodiment of the present invention.

[0017] Reference numerals: 1. Laval nozzle; 2. Flow straightening section; 3. Converging section; 4. Throat; 5. Expanding section; 6. Front swirl assembly; 61. Center body; 62. Static swirl blades; 7. Rear swirl separation assembly; 71. Shaft; 72. Spiral blades; 8. Diffuser. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0019] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without making any creative work shall fall within the scope of protection of the present invention.

[0020] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0021] See also Figures 1 to 5 As shown, in order to effectively reduce the influence of droplet re-evaporation when natural gas is in a gas-liquid mixed state for separation during supersonic separation of natural gas, the separation efficiency is improved. This embodiment provides a full cyclone supersonic natural gas purification device, including a Laval nozzle 1, a cyclone unit and a diffuser 8. The cyclone unit is arranged in the Laval nozzle 1, and a flow channel for natural gas to pass through is reserved between the cyclone unit and the inner wall of the Laval nozzle 1. The specific cyclone unit is composed of a front cyclone assembly 6 and a rear cyclone separation assembly 7. The Laval nozzle 1 is divided into a rectifying section 2, a tapered section 3, a throat 4 and a gradually expanding section 5 from the inlet to the outlet, and a liquid outlet is opened on the side wall of the gradually expanding section 5 away from the throat 4; the diffuser 8 is connected to the outlet end of the Laval nozzle 1 (the end of the gradually expanding section 5, which is used to increase the pressure and temperature of the separated gas, realize the recovery of pressure energy and further enter the subsequent gas transmission pipeline for transmission). The front swirl assembly 6 is installed in the rectifying section 2 and the tapering section 3, and is used to apply a tangential velocity to the natural gas entering the Laval nozzle 1 to form a strong swirl field to accelerate the flow toward the expanding section 5; the rear swirl separation assembly 7 is installed in the expanding section 5, and the input end of the rear swirl separation assembly 7 is connected to the output end of the front swirl assembly 6 at the throat 4 of the Laval nozzle 1. The rear swirl separation assembly 7 is used to maintain the swirl state of the natural gas, so that the gas-liquid mixture generated by condensation can be separated from the gas and liquid under the centrifugal force of the swirl, and the separated liquid flows out from the liquid outlet of the Laval nozzle 1, and the separated gas enters the gas delivery pipeline through the diffuser 8 for continued transmission.

[0022] Specifically, during the natural gas purification process, when the natural gas is subjected to gas-liquid separation, after the natural gas enters the Laval nozzle 1, the front swirl assembly 6 provided inside the straightening section 2 and the tapered section 3 of the Laval nozzle 1 can be used to convert the axial velocity of the natural gas into a tangential velocity, so that the natural gas forms a strong swirl field for accelerated transmission. The natural gas is accelerated through the straightening section 2 and the tapered section 3 of the Laval nozzle 1, reaches the speed of sound at the throat 4, and then is accelerated and expanded to a supersonic speed in the diverging section 5 by the action of the rear swirl separation assembly 7. At this time, after the natural gas increases from the speed of sound to the supersonic speed, a low-temperature and low-pressure zone is formed, and components such as water vapor, heavy hydrocarbons, and acid gases in the natural gas condense into liquid, that is, the natural gas forms a gas-liquid mixture. Among them, since the conversion of the axial velocity of natural gas to the tangential velocity in the rectifying section 2 and the tapering section 3 occurs under subsonic conditions, the natural gas will not generate shock waves after the front swirl component 6 in the Laval nozzle 1, that is, the natural gas will not generate shock waves in the throat 4 and the gradually expanding section 5, and the natural gas is transmitted in a swirl-to-condensation manner under the action of the rear swirl separation component 7, which will suppress the generation of shock waves and effectively reduce the influence of the re-evaporation of droplets in the formed gas-liquid mixture. Then, the formed gas-liquid mixture generates a strong centrifugal force under the action of the strong swirl field to throw the droplets to the pipe wall and discharge from the liquid outlet. After the gas passes through the diffuser 8, the flow velocity is reduced from supersonic to subsonic under the action of the diffuser 8, and shock waves are also not generated. Then, the gas is further transmitted into the gas transmission pipeline after the pressure and temperature are increased to achieve the recovery of pressure energy. Therefore, through the cooperation of the front swirl component 6 and the rear swirl separation component 7, the separation efficiency of gas and liquid in natural gas can be effectively improved to obtain purer natural gas.

[0023] The device integrates the expansion cooling, cyclone gas-liquid separation, recompression and other processing processes in a closed and compact device, overcoming the defects of traditional separation devices such as difficult to control shock waves and low separation efficiency. It has the advantages of being closed and leak-free, no need for chemicals, compact and lightweight structure, no rotating parts, unmanned support, energy saving and environmental protection.

[0024] See also Figure 1 and Figure 2As shown, in order to improve the cyclone separation efficiency, the front cyclone assembly 6 includes a center body 61 and a plurality of static cyclone blades 62. The center body 61 has a center line that coincides with the axis of the Laval nozzle 1. The center body 61 is composed of a semi-ellipsoid and a curved body. Both the semi-ellipsoid and the curved body are rotating bodies with the center line as the rotation center. The semi-ellipsoid is placed in the straightening section 2 of the Laval nozzle 1, and the curved body is placed in the tapered section 3 of the Laval nozzle 1. A flow channel for natural gas to pass through is reserved between the semi-ellipsoid and the curved body and the tube wall of the Laval nozzle 1. The flow channel forms a subsonic contraction section, a neck and a supersonic expansion section in an annular manner from the straightening section 2 to the tapered section 3 of the Laval nozzle 1. The semi-ellipsoid is located in the subsonic contraction section. In the design stage, the Laval nozzle 1 needs to be scaled proportionally according to the size structure of the center body 61 to ensure that the gas flow area remains unchanged after the center body 61 is built in. The multiple static swirl blades 62 are all spiral structures, and the multiple static swirl blades 62 are equidistantly arranged on the side wall of the semi-ellipsoid. In order to make the natural gas reach the expected swirl intensity, the static swirl blades 62 are set to at least 3 pieces, and the rotation angle of the static swirl blades 62 in the semi-ellipsoid of the central body 61 is set between 73° and 82°. After experimental testing, and in order to facilitate processing, the preferred number of static swirl blades 62 is 3, and the rotation angle of the static swirl blades 62 is preferably set to 81.79°. The specific verification analysis is as follows:

[0025] The swirl angle parameters of the static swirl blades 62 corresponding to different pitches are shown in the following table: In the experimental verification, it was found that: as the swirl angle increases, the tangential velocity that can be achieved in the nozzle increases continuously, and the swirl intensity increases. When the swirl angle increases from 73.9° to 81.79°, the maximum tangential velocity in the nozzle can increase from 119.6m / s to 212.5m / s. Therefore, the overall swirl intensity of the potential swirl assembly set by the static swirl blade 62 with a rotation angle of 81.79° is higher than that of the swirl angles of 73.9° and 77.78°. Therefore, the device finally selected 3 blades, a center body 61, and a front swirl device with a rotation angle of 81.79°.

[0026] After entering the Laval nozzle 1, the natural gas flows in a swirl state in the annular flow channel between the center body 61 and the Laval nozzle 1 through the drainage effect of the spiral blades 72, realizing the conversion of the axial velocity of the natural gas to the tangential velocity to form a strong swirl field. At this time, since the conversion of the axial velocity of the natural gas to the tangential velocity occurs in the subsonic contraction section, the natural gas in the swirl state will not generate shock waves in the subsequent flow, and the natural gas in the swirl state reaches the speed of sound at the throat 4 of the Laval nozzle 1, and then expands to supersonic speed in the gradually expanding section 5, forming low temperature and low pressure, and water vapor, heavy hydrocarbon components and acidic gases condense to form a gas-liquid mixture. In addition, by utilizing the above-mentioned structural design, the presence of the center body 61 can eliminate the turbulent flow of gas at the center of the Laval nozzle 1, help solve the vortex dissipation problem of the rotating gas, and thus reduce energy loss. And the annular cross section shortens the sedimentation distance of the condensed droplets, which is conducive to the separation of the droplets and the gas phase, and improves the swirl separation efficiency.

[0027] See also Figure 1 and Figure 5 As shown, in order to improve the cyclone separation efficiency, the post-cyclone separation assembly 7 includes a shaft body 71 and a spiral blade 72, the shaft body 71 coincides with the axis of the Laval nozzle 1, one end of the shaft body 71 passes through the throat 4 and is connected to the end of the curved body away from the semi-ellipsoid, and the connection between the two is located at the throat 4 of the Laval nozzle 1, and the other end of the shaft body 71 passes through the entire gradually expanding section 5 and extends to the outlet of the Laval nozzle 1 and is connected to the diffuser 8; the spiral blade 72 surrounds the shaft body 71, and the spiral radius of the spiral blade 72 gradually increases from the throat 4 to the diffuser 8 side. After the natural gas enters the gradually expanding section 5, it expands to a supersonic speed due to the action of the spiral blades 72. At this time, the gas-liquid mixture still maintains a strong swirl field due to the drainage effect of the spiral blades 72, that is, it flows in a supersonic swirl state. At this time, due to the strong swirl field, the gas-liquid mixture generates a strong centrifugal force to throw the droplets to the pipe wall and discharge from the liquid outlet. After the gas passes through the diffuser 8, a shock wave is generated, and the flow velocity is reduced from supersonic to subsonic, and the pressure and temperature are increased, thereby realizing the recovery of pressure energy and further entering the gas transmission pipeline for transmission.

[0028] Furthermore, the contour surface of the ellipsoid is determined by the following formula: , in, is the length of the straightening section 2 of the Laval nozzle 1, is the diameter of the inlet of the tapered section 3 of the Laval nozzle 1, x , y , z is the three-dimensional coordinate value of the semi-ellipsoidal surface, h is the static swirl blade 62 y The height of the axis.

[0029] Preferably, the number of the static swirl blades 62 is at least three.

[0030] Furthermore, after the central body 61 is placed, the diameters of the Laval nozzle 1 at various locations and the diameters of the curved surface at various locations of the rear end of the central body 61 are determined according to the following formula: , in, is the diameter of the Laval nozzle 1 at the corresponding position of the tapered section 3, is a reduction ratio, here you can take =1.5, D is the design diameter of the Laval nozzle 1.

[0031] The design of each section of the Laval nozzle 1 is as follows: The design of the straightening section 2 of the Laval nozzle 1, see Figure 1 and Figure 3 shown.

[0032] Before the gas enters the tapered section 3 of the Laval nozzle 1, a straight pipe section needs to be designed, called the straightening section 2. It is located after the valve or pipeline diversion. Since the gas has a high degree of turbulence after flowing through the valve or pipeline diversion, it is not conducive to the acceleration of gas contraction in the tapered section 3. Therefore, the straightening section 2 needs to be set before the tapered section 3 of the Laval nozzle 1, so that the gas has enough time to stabilize and ensure that the inlet flow velocity distribution of the tapered section 3 is uniform. The length of the straightening section 2 of the Laval nozzle 1 is determined according to the following formula:

[0033] , in, L 0 is the length of the straightening section 2 of the Laval nozzle 1, in mm; d is the inlet diameter of the convergent section 3 of the Laval nozzle 1, in mm. In practical applications, such as offshore natural gas extraction, due to the large gas processing volume of the offshore platform, it is necessary to design multiple Laval nozzles 1 to process natural gas in parallel. After the gas is divided, it enters the convergent section 3 through the rectifying section 2. Therefore, the length of the rectifying section 2 is 85 mm to ensure that the airflow velocity at the inlet of the Laval nozzle 1 is evenly distributed.

[0034] Laval nozzle 1 tapered section 3 design The tapered section 3 of the Laval nozzle 1 is used to accelerate the airflow uniformly to the speed of sound, provide a good flow field for the subsequent condensation and expansion of water vapor in the nozzle, improve the airflow stability, and reduce the turbulence. Therefore, the following requirements should be met when designing the tapered section 3 of the nozzle: when the airflow reaches the throat 4, the airflow turbulence is small and does not separate from the wall; considering that the airflow pressure, temperature, and flow rate of the offshore platform are high, the diameter of the nozzle throat 4 is large, and for the convenience of processing, a properly longer tapered section 3 is selected, and the length of the straightening section 2 is L1 indicates the design reference of the contraction section of Laval nozzle 1 Figure 4 As shown, the analysis is as follows: the Vickers curve shrinks faster at the inlet section of the Laval nozzle 1, and the curve is relatively gentle when approaching the outlet of the tapered section 3, which is conducive to rectification before the throat 4 of the Laval nozzle 1, ensuring uniform airflow distribution at the throat 4 of the Laval nozzle 1; the bicubic curve and the quintic curve have basically the same line shape, and both curves shrink faster at the outlet of the tapered section 3, which will lead to poor airflow uniformity at the throat 4; the Vickers displacement curve reduces the contraction ratio of the contraction section by increasing the axis shift, and the entire curve is relatively gentle at the inlet and outlet. Comprehensive analysis shows that the use of the Vickers curve to design the tapered section 3 of the Laval nozzle 1 can achieve a better cooling effect.

[0035] Laval nozzle 1 expansion section 5 design In order to ensure that the water vapor can obtain a lower temperature and a larger tangential velocity, the design of the expansion section 5 has a decisive influence on the velocity of the airflow in the nozzle. In the design of the work, the nozzle throat 4 is designed with a Mach number of 1, and the Mach number at the exit of the nozzle expansion section 5 is generally designed to be 1.5-2. For the Laval nozzle 1 expansion section 5, in order to simplify the design process and achieve the purpose of expansion and rectification at the same time, a conical tube structure is used for design, and the length of the expansion section 5 meets the following requirements:

[0036] , in, L 2 is the length of the diverging section 5 of the Laval nozzle 1, in mm; r 2 is the radius of the exit section of the Laval nozzle 1, in mm; φ is the expansion angle of the expansion section 5; r 1 is the radius of the throat 4 of the Laval nozzle 1, in mm.

[0037] In order to ensure that the airflow is uniformly accelerated to the speed of sound and to prevent the airflow from being unstable due to a sudden change in the flow area, a continuous smooth curve is used to connect the converging section 3 and the expanding section 5 of the Laval nozzle 1 to achieve a smooth transition.

[0038] Design of throat 4 of Laval nozzle 1 The gas reaches the local sound speed at the critical section in the Laval nozzle 1, and accelerates to the supersonic speed through the expansion section 5 after the critical section. This critical section is the throat 4 of the Laval nozzle 1. Since high pressure and low pressure have a great influence on the physical properties of the gas, especially the gas density, according to actual engineering experience, when designing the throat 4 of the Laval nozzle 1, the gas in the tube no longer satisfies the ideal gas state equation. If the low-pressure ideal gas is used to calculate the diameter of the throat 4 of the Laval nozzle 1, the error is large. Therefore, the PR equation is used to calculate the nozzle throat diameter.

[0039] The PR equation, the full name of which is the Peng-Robinson state equation, is a state equation widely used to describe the behavior of multi-component fluid systems, especially when dealing with non-ideal gases under high pressure and low temperature conditions. The expression is:

[0040] p=RT / (vb)-a / (v(v+b)-c) , in, T is the initial temperature of the throat 4, p is the air flow pressure at the throat 4 of the Laval nozzle 1, R is the universal gas constant, v is the molar volume, a and b is a constant specific to the substance, a =0.45724× R 2 Tc 2 / Pc , b=0.0778× Rtc 2 / Pc . c = ab / 27 R 2 Tc 2 , Tc is the critical temperature of the throat 4 of the Laval nozzle 1, Pc is the critical pressure at the throat 4 of the Laval nozzle 1.

[0041] Gas has a flow characteristic. When the gas reaches the speed of sound, as the pressure and temperature decrease and the speed increases, it loses energy and the internal energy is converted into kinetic energy. Therefore, the flow rate when the gas speed is the speed of sound is the critical flow rate. According to the equal flow principle, the inlet flow rate and cross-sectional area are determined, and the radius of the throat 4 of the Laval nozzle 1 can be calculated.

[0042] Specific calculation: The throat 4 of the Laval nozzle 1 needs to meet the critical state, that is, the gas flow rate at the Laval nozzle 1 = the local sound velocity, assuming an initial temperature T 1 The enthalpy equation establishes the equation for the change in gas velocity in the Laval nozzle 1 and the change in temperature, so based on the assumed temperature T 1 The flow rate of the gas in the Laval nozzle 1 can be obtained by combining the inlet gas temperature and velocity V 1 Based on the assumed initial temperature T 1, substituting into the PR equation, we can find the compression factor of the throat 4 and the density of the gas at the throat 4, and then we can substitute into the local sound speed equation (density, compression factor, local sound speed can be calculated) to find the local sound speed V 2 .if V 1 = V 2 , which means that the assumed T 1 Very accurate. If they are not equal, you need to iterate again. V 3 =( V 1 + V 2 ) / 2, and substitute it into the enthalpy equation to recalculate the temperature T 2 , and then find the local speed of sound V 4 ,look V 3 and V 4 The relationship between is equal, and the iterative calculation is repeated until it is equal. The local sound speed is calculated. According to the principle of equal (mass) flow, the inlet flow rate and cross-sectional area are determined, and the radius of the throat 4 of the Laval nozzle 1 can be calculated. R .

[0043] In order to achieve effective natural gas purification effect, the design parameters of Laval nozzle 1 can refer to the following table: Structural design of spiral blade 72 in post-cyclone separation assembly 7 In the diverging section 5 of the Laval nozzle 1, the condensation of the condensable gas under the action of supersonic speed is different from the condensation phenomenon caused by the external cold source. The condensed droplets in the diverging section 5 of the Laval nozzle 1 are evenly distributed in the mainstream gas. To achieve efficient separation, the condensed droplets must be aggregated and then removed from the mainstream gas. The function of the spiral blade 72 required in this link is to keep the high-speed airflow in a swirl state, that is, to achieve a high rotation of the natural gas, generate a strong centrifugal force, so that the condensed droplets are thrown to the wall of the Laval nozzle 1 under the action of the centrifugal force, and further achieve effective gas-liquid separation.

[0044] This paper compares and analyzes the structures of two different post-cyclone separation components 7. Figure 5 The designed post-cyclone separation component 7 should be able to generate high-speed cyclone while ensuring that it does not affect the full expansion of the upstream gas, so that the temperature of the gas is reduced to the maximum extent. The key to achieving this goal is that the pressure loss when the airflow passes through the designed post-cyclone separation component 7 should be as small as possible and the cyclone intensity should be as large as possible.

[0045] contrast Figure 5 From the two structures, it can be seen that the (a) structure makes the gas flow more stable and has a better guiding effect. At the same time, due to the special spiral structure of the spiral blade 72, the airflow can produce a strong swirl effect. Therefore, it can be confirmed that the (a) structure can better achieve the purpose of swirl separation. Figure 6 The distribution of swirl acceleration obtained by using structure (a) on the downstream section of the spiral blade 72 is given. It can be seen from the figure that the magnitude of the swirl acceleration behind the post-swirl separation component 7 is about 105 or more, which is about 10,000 times the acceleration of gravity, indicating that the device can produce a strong swirl effect.

[0046] Further comparative analysis of the blade thickness of the spiral blade 72 is as follows: Figure 7 and Figure 8 is the blade thickness d The axial static pressure of the expanding section 5 under the conditions of 0.5mm, 1.0mm, 1.5mm, 2.0mm, and 2.5mm respectively P Axial distance x= The tangential velocity distribution of each point on the horizontal centerline of the cross section 325 mm (the distance from the corresponding position of the divergent section 5 to the inlet of the Laval nozzle 1). When other conditions are the same, such as Figure 7 Blade thickness shown d When the axial static pressure increases from 0.5mm to 2.5mm, P The maximum fluctuation value increases from 0.64MPa to 4.03MPa, indicating that the thicker the spiral blade 72 is, the greater the axial static pressure is. P The more obvious the influence is, the reason is that the existence of the spiral blade 72 makes the gas flow area smaller and the flow field distorted, that is, the thicker the blade is, the greater the influence on the flow field is; Figure 8 As shown, the average tangential velocity v It dropped from 84.07m / s to 38.41m / s, indicating that the thicker the blade, the higher the tangential velocity. v Therefore, under the premise of ensuring that the blade thickness meets the gas impact strength requirements, the blade thickness should be minimized to reduce the impact on the gas flow field. In summary, the best effect is achieved by using a 0.5 mm thickness for the spiral blade 72 structure design.

[0047] Laboratory Validation: In order to further verify the performance of the designed full-swirl supersonic natural gas purification device, in cooperation with Dongying Keli Petroleum Machinery Co., Ltd., a set of experimental systems was designed and constructed, and the corresponding Laval nozzle 1 was made according to the design parameters for indoor experiments. The effect of changes in inlet pressure and inlet temperature on the working performance of Laval nozzle 1 was tested experimentally. According to the purpose of the experiment, an experimental system was built. The system mainly tests the gas composition and droplet generation rate at the outlet to study the removal effect of water vapor and CO2 gas in this device. The process is: the air compressor pressurizes the gas to 1~3MPa, enters the gas storage tank for buffering, and then pressurizes it to 6~8MPa through the supercharger, and then enters the buffer tank for pressure stabilization and enters the gas humidifier for humidification. By controlling the CO2 inlet valve, CO2 is mixed with moisture. After stabilization, the moisture enters the supersonic stage for expansion and cooling. The CO2 content is controlled at about 12%. The experimental working flow is 2000m 3 / d.

[0048] Experimental results and analysis The experiment shows that the dew point of gas water treated by the device can reach -3° at room temperature, the separation efficiency is 71%, and the CO2 content at the outlet can be reduced to 2%-4%, which is in line with GB / T 17283-2014, GB 17820-2012 and other natural gas transportation industry standards, has good dehydration and deacidification performance, and the experimental and simulation results are similar.

[0049] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A full cyclonic supersonic natural gas purification device, comprising a Laval nozzle (1), wherein the nozzle is divided into a rectifying section (2), a gradually contracting section (3), a throat section (4) and a gradually expanding section (5) from the inlet to the outlet, characterized in that: It also includes a swirl unit arranged in the Laval nozzle (1), a flow channel for natural gas to pass through is reserved between the swirl unit and the tube wall of the Laval nozzle (1), and the swirl unit includes: A front swirl assembly (6) comprising a central body (61) and a plurality of static swirl blades (62), wherein the central body (61) is inserted into the straightening section (2) and the tapered section (3), and the plurality of static swirl blades (62) are located in the straightening section (2) and are sleeved on the central body (61) at equal intervals; A post-cyclone separation component (7) comprises a shaft (71) and a spiral blade (72), wherein one end of the shaft (71) passes through the throat (4) to be connected to the center body (61), and the other end passes through the entire gradually expanding section (5), and the spiral blade (72) is wound around the shaft (71), and the spiral radius of the spiral blade (72) gradually increases with the diameter of the gradually expanding section (5) of the Laval nozzle (1), and the axes of the shaft (71) and the center body (61) both coincide with the axis of the Laval nozzle (1); The natural gas begins to accelerate in a swirling manner in the rectifying section (2) through the action of the static swirling blades (62), and is accelerated through the converging section (3) to reach the speed of sound at the throat (4). The natural gas is further guided and expanded to a supersonic speed through the spiral blades (72) in the expanding section (5), thereby forming a low temperature and low pressure, so that the natural gas condenses into a gas-liquid mixture while swirling. Under the action of the centrifugal force of the swirling flow, the natural gas is separated from the gas and liquid in the expanding section (5), and the separated liquid flows out from the liquid outlet, while the separated gas continues to be transmitted.

2. A full cyclone supersonic natural gas purification device according to claim 1, characterized in that: The central body (61) is composed of a semi-ellipsoid and a curved body, and the semi-ellipsoid and the curved body are both rotating bodies with the axis of the Laval nozzle (1) as the rotation center. The semi-ellipsoid is placed in the rectifying section (2), and the curved body is placed in the tapered section (3). The contour surface of the semi-ellipsoid is determined by the following formula: ， in, is the length of the fairing section (2) of the Laval nozzle (1), is the diameter of the inlet of the tapered section (3) of the Laval nozzle (1), x , y , z is the three-dimensional coordinate value of the semi-ellipsoid surface, h is the static swirl blade (62) y The height of the axis.

3. The full cyclone supersonic natural gas purification device according to claim 1, characterized in that: The number of the static swirl blades (62) is at least three.

4. A full cyclone supersonic natural gas purification device according to claim 1, characterized in that: The rotation angle of the static swirl blade (62) has a value range of 73°-82°.

5. The full cyclone supersonic natural gas purification device according to claim 1, characterized in that: After the center body (61) is placed, the diameters of the Laval nozzle (1) at various locations are determined according to the following formula: ， in, is the diameter of the Laval nozzle (1) after it is inserted into the center body (61), It is a reduction in proportion. D is the design diameter of the Laval nozzle (1).

6. The full cyclone supersonic natural gas purification device according to claim 1, characterized in that: The length of the straightening section (2) of the Laval nozzle (1) is determined according to the following formula: ， Among them, the Laval nozzle (1) L 0 rectifier section (2) length; d is the inlet diameter of the tapered section (3) of the Laval nozzle (1).

7. The full cyclone supersonic natural gas purification device according to claim 1, characterized in that: The length of the diverging section (5) of the Laval nozzle (1) is determined according to the following formula: ， in, L 2 is the length of the diverging section (5) of the Laval nozzle (1); r 2 is the radius of the exit cross section of the Laval nozzle (1); φ is the divergence angle of the diverging section (5) of the Laval nozzle (1); r 1 is the radius of the throat (4) of the Laval nozzle (1).

8. The full cyclone supersonic natural gas purification device according to claim 1, characterized in that: The radius of the throat (4) of the Laval nozzle (1) is determined according to the following formula: p=RT / (vb)-a / (v(v+b)-c) ， in, T is the initial temperature at the throat (4) of the Laval nozzle (1), p is the air flow pressure at the throat (4) of the Laval nozzle (1), R is the universal gas constant, v is the molar volume, a and b is a constant specific to the substance, a =0.45724× R 2 Tc 2 / Pc , b=0.0778× Rtc 2 / Pc ; c = ab / 27 R 2 Tc 2 , Tc is the critical temperature at the throat (4) of the Laval nozzle (1), Pc is the critical pressure at the throat (4) of the Laval nozzle (1).

Images