LNG Unloading Arm Gas Replacement System, Establishment of System Model and Simulation Method

Abstract

The present invention relates to an LNG unloading arm gas replacement system, a system model establishment and a simulation method. The system includes: a replacement system upper pipe section, a replacement system middle pipe section and a replacement system lower pipe section which are connected in series from top to bottom in sequence. The replacement system upper pipe section and the replacement system middle pipe section are separated by a partition pipe plate. A plurality of microporous separators are suspended at the lower end of the partition pipe plate. An energy aggregation device is correspondingly arranged at the top of the microporous separator. A replacement gas inlet is arranged near the lower end of the replacement system middle pipe section. A replacement gas outlet is arranged on the replacement system upper pipe section. The calculation model adapted to the gas replacement system established by the present invention is used to guide the optimization design of the scheme, providing a reference for the overall structural design optimization and safe and stable operation of the LNG cryogenic unloading and conveying system.

Description

Technical Field

[0001] The present invention relates to a gas replacement system for an LNG unloading arm, a system model establishment method and a simulation method, and particularly relates to a gas flow system, a system model establishment method and a simulation method suitable for gas replacement inside an LNG rigid unloading arm, belonging to the technical field of oil and gas development. Background Art

[0002] A floating liquefied natural gas production storage and offloading unit (FLNG) is a floating production device used for the development of offshore gas fields. It is positioned at sea through a mooring system and has the functions of exploiting, processing, liquefying, storing and loading / unloading natural gas. By cooperating with a liquefied natural gas (LNG) ship, it realizes the exploitation of offshore gas fields and the transportation of natural gas. The use of FLNG for offshore gas field development has ended the single mode of only using pipeline transportation to bring the gas ashore, saving transportation costs and not occupying land space. In addition, FLNG can be reused after the gas field exploitation is completed and placed in other gas fields, with relatively high economic performance.

[0003] An LNG unloading arm is a rigid articulated pipeline system installed on a wharf or an FLNG for LNG unloading. Its main structures include a swivel joint, an outer arm, an inner arm, a top swivel joint, a base riser, and a swivel joint connecting the inner arm and the base riser, as well as process pipelines, their support structures and accessories. The large LNG unloading arm stands at the very front of the LNG receiving terminal wharf area. This huge object, about 50 m high and weighing 80 tons, as a key core equipment connecting the LNG ship with the onshore pipeline and storage facilities in the receiving terminal, is the "throat" of the entire receiving terminal. When the LNG carrier arrives at the dedicated wharf of the receiving terminal, through the liquid-phase unloading arm and the unloading pipeline, the LNG is sent into the storage tank of the receiving terminal by using the cryogenic pump on the ship. At the same time, the BOG gas in the storage tank returns to the LNG carrier through the return gas pipeline and the gaseous return gas arm. During the operation of the LNG unloading arm, a towing line is used to guide the connection between the end of the unloading arm and the receiving end of the LNG ship to ensure accurate docking under relative movement conditions, and the hydraulic system of the unloading arm is controlled to enable it to withstand the influence of the speed and acceleration caused by the hull movement.

[0004] In summary, the key technologies of the LNG rigid unloading arm system involve many aspects such as the selection of cryogenic materials, forming manufacturing, sealing, and test verification. The material selection and structural design are difficult, the processing manufacturing and performance testing are difficult, the cryogenic sealing, connection, and leakage monitoring are highly difficult, and the entire cryogenic conveying system has a complex structure and high safety requirements. Among them, the gas displacement system is a key component unit of the LNG cryogenic conveying system, and its performance directly affects the safe and stable operation of the LNG cryogenic unloading system. The existing technologies mainly have the following technical defects:

[0005] The gas displacement system is a key structure of the LNG unloading arm. Usually, the gas displacement system unit is interconnected with the quick connection device of the LNG unloading arm. As an independent unit, it is used to displace the inside of the LNG unloading arm with nitrogen before commissioning or during maintenance and repair, ensuring that the inside is in a dry and inert gas state.

[0006] Through the analysis of the existing technologies and the experience in the actual operation process of the LNG unloading arm, the technical defect of the gas displacement system unit adopted in the existing technologies is that the operating parameters of the gas displacement system are mainly set based on experience, resulting in a large gas consumption, high energy consumption, and long operation duration, leading to low gas displacement efficiency. There is an urgent need to establish a calculation model adapted to the gas displacement system to guide the optimization design of the scheme. Summary of the Invention

[0007] In view of the above technical problems, the present invention provides an LNG unloading arm gas displacement system, a system model establishment method, and a simulation method. The present invention establishes a calculation model adapted to the gas displacement system to guide the optimization design of the scheme, providing a reference for the overall structural design optimization and safe and stable operation of the LNG cryogenic unloading and conveying system.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] An LNG unloading arm gas displacement system, comprising:

[0010] A replacement system upper pipe section, a replacement system middle pipe section, and a replacement system lower pipe section connected in series from top to bottom. The replacement system upper pipe section and the replacement system middle pipe section are separated by a partition pipe plate. A plurality of microporous separators are suspended at the lower end of the partition pipe plate. An energy aggregation device is correspondingly arranged at the top of the microporous separator. A replacement gas inlet is arranged near the lower end of the replacement system middle pipe section, and a replacement gas outlet is arranged on the replacement system upper pipe section.

[0011] For the LNG unloading arm gas displacement system described above, preferably, the microporous separator is a hollow tubular structure, and ventilation holes are provided on its tube wall.

[0012] In the LNG unloading arm gas replacement system, preferably, the vent holes are evenly or discretely distributed on the tube wall of the microporous separator.

[0013] In the LNG unloading arm gas replacement system, preferably, the vent hole has a diameter of 30 μm-50 μm.

[0014] In the LNG unloading arm gas replacement system, preferably, the average permeability of the microporous separator is 1×10 -12 m 2 .

[0015] A second aspect of the present invention provides a method for establishing a gas displacement system model for an LNG unloading arm, comprising the following steps:

[0016] Use the software to set the initialization conditions and activate the user-defined initialization function;

[0017] Start the loop based on the initialization function, and then use the user-defined adjustment function to adjust the variable value;

[0018] Solve the U, V, W momentum equations, mass conservation equations and update velocity values, solve the energy equation, component equations, and turbulent kinetic energy and turbulent kinetic energy dissipation equations;

[0019] Update the properties and determine whether the solution converges. If it converges, exit the loop. If it does not converge, go to the user-defined adjustment function to adjust the variable value and start the next loop.

[0020] A third aspect of the present invention provides a device for establishing a model of an LNG unloading arm gas replacement system, comprising:

[0021] The first processing unit is used to set initialization conditions using software and activate the user-defined initialization function;

[0022] A second processing unit is configured to start a loop based on the initialization function and then adjust the variable value using a user-defined adjustment function;

[0023] The third processing unit is used to solve the U, V, W momentum equations, the mass conservation equation and update the velocity value, and solve the energy equation, the component equation, and the turbulent kinetic energy and turbulent kinetic energy dissipation equation;

[0024] The fourth processing unit is used to update the properties and determine whether the solution converges. If it converges, the loop is exited. If not, the user-defined adjustment function is used to adjust the variable value and the next loop is started.

[0025] A fourth aspect of the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method for establishing the LNG unloading arm gas replacement system model.

[0026] The fifth aspect of the present invention provides a computer device, including a memory, a processor, and a computer program stored on the memory and executable on the processor, wherein when the processor executes the computer program, the steps of the method for establishing the LNG unloading arm gas replacement system model described above are implemented.

[0027] The sixth aspect of the present invention provides a numerical simulation method for an LNG unloading arm gas replacement system. The numerical simulation method is based on the model established in the second aspect of the present invention and includes the following steps:

[0028] Based on the physical conservation law, establish a control equation set;

[0029] Based on the turbulence intensity and hydraulic diameter, determine the gas inlet boundary condition and outlet boundary condition of the gas replacement system;

[0030] Based on the wall function method and Reynolds stress model, determine the wall boundary condition of the gas replacement system;

[0031] Based on the porous medium model method, determine the porous medium boundary condition of the gas replacement system;

[0032] Based on the control equation set, gas inlet boundary condition and outlet boundary condition, wall boundary condition, and porous medium boundary condition, analyze the gas-phase flow field of the gas replacement system.

[0033] The seventh aspect of the present invention provides a numerical simulation device for an LNG unloading arm gas replacement system, including:

[0034] The first processing unit is used to establish a control equation set based on the physical conservation law;

[0035] The second processing unit is used to determine the gas inlet boundary condition and outlet boundary condition of the gas replacement system based on the turbulence intensity and hydraulic diameter;

[0036] The third processing unit is used to determine the wall boundary condition of the gas replacement system based on the wall function method and Reynolds stress model;

[0037] The fourth processing unit is used to determine the porous medium boundary condition of the gas replacement system based on the porous medium model method;

[0038] The fifth processing unit is used to analyze the gas-phase flow field of the gas replacement system based on the control equation set, gas inlet boundary condition and outlet boundary condition, wall boundary condition, and porous medium boundary condition.

[0039] The eighth aspect of the present invention provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the steps of the numerical simulation method of the above-mentioned LNG unloading arm gas replacement system are realized.

[0040] The ninth aspect of the present invention provides a computer device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the computer program, the numerical simulation method of the above-mentioned LNG unloading arm gas replacement system is realized.

[0041] Due to the above technical solutions adopted by the present invention, it has the following advantages:

[0042] Aiming at a series of problems in the prior art, such as mainly relying on experience to set the operating parameters of the gas replacement system, large gas consumption, high energy consumption, long operation duration, and low gas replacement efficiency, the present invention establishes a calculation model adapted to the gas replacement system to guide the optimization design of the scheme, providing a reference for the overall structural design optimization and safe and stable operation of the LNG cryogenic unloading and transportation system. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a schematic diagram of the overall structure of the LNG unloading arm and its gas replacement system provided by an embodiment of the present invention;

[0044] Figure 2 It is a schematic diagram of the structure of the LNG unloading arm gas replacement system provided by an embodiment of the present invention;

[0045] Figure 3 It is a top view of the microporous separator and the partition tube sheet provided by this embodiment of the present invention;

[0046] Figure 4 It is a flowchart of the method for establishing the LNG unloading arm gas replacement system model provided by this embodiment of the present invention;

[0047] Figure 5 It is a schematic diagram of each value-taking point of the gas replacement system provided by this embodiment of the present invention;

[0048] Figure 6 It is a schematic diagram of each value-taking section of the gas replacement system provided by this embodiment of the present invention;

[0049] Figure 7 It is a static pressure distribution contour map of the gas phase flow field in the gas replacement system provided by this embodiment of the present invention, y = -8.87 mm;

[0050] Figure 8 It is a sectional static pressure distribution contour map of the gas phase flow field in the gas replacement system provided by this embodiment of the present invention, z = 1000 mm;

[0051] Figure 9 This is the cross-sectional gas-phase flow field velocity distribution diagram of the gas displacement system provided by this embodiment of the present invention, where y = -28.87 mm. Among them, a is the combined velocity distribution nephogram, and b is the axial velocity distribution nephogram;

[0052] Figure 10 This is the distribution nephogram of the cross-sectional turbulent kinetic energy (Figure a), turbulent viscosity (Figure b), and turbulent intensity (Figure c) of the gas displacement system provided by this embodiment of the present invention, where y = -28.87 mm;

[0053] Figure 11 This is the velocity vector diagram of the cross-section in the gas displacement system provided by this embodiment of the present invention. In Figure a, z = 100 mm, in Figure b, z = 1400 mm, and in Figure c, z = 1000 mm.

[0054] The reference numerals are as follows:

[0055] 1 - Lower pipe section of the displacement system; 2 - Middle pipe section of the displacement system; 3 - Upper pipe section of the displacement system; 4 - Displacement gas inlet; 5 - Displacement gas outlet; 6 - Microporous separator; 7 - Partition pipe plate; 8 - Energy aggregation device; 9 - Unloading arm; 10 - Column; 11 - Rotary wheel mechanism; 12 - Quick connection joint; 13 - Emergency disconnection device; 14 - Main pipeline; 15 - Outer wall support; 16 - Balanced transmission mechanism. Detailed implementation manners

[0056] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0057] The present invention establishes a calculation model adapted to the gas displacement system to guide the optimization design of the scheme, providing a reference for the overall structural design optimization and safe and stable operation of the LNG cryogenic unloading and transportation system.

[0058] Next, the technical solutions of the present invention will be described in detail with reference to the drawings.

[0059] As Figure 1As shown in the figure, it is a schematic diagram of the overall structure of an LNG unloading arm and its gas replacement system. It can be seen from the schematic diagram that the main body of the unloading arm 9 mainly includes a column 10, a swivel mechanism 11, a balance drive mechanism 16, an outer arm support 15, a main pipeline 14, an emergency disconnection device 13, and a quick connection joint 12, etc. The gas replacement system, as an independent unit, is connected to the quick connection joint 12 of the unloading arm 9 and is a key component outside the main body of the LNG unloading arm. It is used to replace the gas inside the LNG unloading arm before commissioning or during maintenance and repair. Nitrogen is used as the replacement gas to ensure that the inside is in a dry and inert gas state.

[0060] As Figure 2 shown, the gas replacement system of the LNG unloading arm provided by the present invention includes the following steps:

[0061] A replacement system upper pipe section 3, a replacement system middle pipe section 2, and a replacement system lower pipe section 1 are connected in series from top to bottom. The replacement system upper pipe section 3 and the replacement system middle pipe section 2 are separated by a partition pipe plate 7. Several microporous separators 6 are suspended at the lower end of the partition pipe plate 7. An energy aggregation device 8 is correspondingly arranged at the top of the microporous separator 6. A replacement gas inlet 4 is arranged near the lower end of the replacement system middle pipe section 2, and a replacement gas outlet 4 is arranged on the replacement system upper pipe section 3.

[0062] Furthermore, the microporous separator 6 is a hollow tubular structure, and ventilation holes are arranged on its tube wall. The ventilation holes are evenly or discretely distributed on the tube wall of the microporous separator 6, and the aperture of the ventilation holes is 30μm - 50μm.

[0063] Furthermore, the average permeability of the microporous separator 6 is 1×10 -12 m 2 .

[0064] As Figure 4 shown, the present invention also provides a method for establishing a model of the gas replacement system of the LNG unloading arm, including the following steps:

[0065] First, the commercial fluid calculation and simulation software FLUENT is adopted, and the segregated solution method is selected. The user-defined program function provided by the FLUENT software itself offers some interfaces for users to exercise more advanced control and modification over the calculation to a certain extent. For example, users can set boundary conditions, initial conditions, physical properties of the fluid, interphase interactions, source terms, user-defined equations, etc. The work that can be achieved using user-defined functions (UDFs) includes: (1) customizing boundary conditions, material properties, surface and volume reaction rates, source terms of transport equations, user-defined scalars, etc.; (2) adjusting calculated values based on each iteration step; (3) initializing the solution; (4) asynchronously executing UDFs; (5) enhancing preprocessing; (6) improving existing models (such as multiphase flow models). When it comes to specific models, the software has a set of related program interfaces. The UDF program interfaces used in this technology are the inlet boundary condition and the momentum source term.

[0066] Specifically, first set the initialization conditions, activate the user-defined initialization function (such as setting boundary conditions, initial conditions, physical properties of the fluid, interphase interactions, source terms, user-defined equations, etc.), start the loop, then use the user-defined adjustment function to adjust the variable values, then successively solve the U, V, and W momentum equations, solve the mass conservation equation and update the velocity values, solve the energy equation, solve the component equation, solve the turbulent kinetic energy and turbulent kinetic energy dissipation equations, then update the properties, and finally determine whether the solution converges. If it converges, exit the loop; if not, transfer to the user-defined adjustment function to adjust the variable values and start the next loop.

[0067] According to the geometric model established above, the gas displacement system unit consists of three metal microporous separators. The metal microporous separators are 1500 mm long, and their inner and outer diameters are 40 and 60 mm respectively. The metal microporous separators have an average permeability of 1×10 -12 m 2 . Figure 5 and 6 For the schematic diagrams of various value-taking cross-sections and value-taking points of the gas displacement system for simulation, where s represents the distance from the measurement point to the outer surface of the metal microporous separator, α represents the measurement point angle, and z represents the measurement position height.

[0068] The third aspect of the present invention provides a numerical simulation method for an LNG unloading arm gas displacement system, including the following steps:

[0069] (1) Establishment of the control equation set:

[0070] Fluid flow is governed by physical conservation laws. The basic conservation laws include: the law of conservation of mass, the law of conservation of momentum, and the law of conservation of energy. If the flow involves the mixing or interaction of different components (constituents), the system also needs to abide by the law of conservation of constituents. If the flow is in a turbulent state, the system also needs to abide by additional turbulent transport equations. Governing Equations are the mathematical descriptions of these conservation laws. To simulate the gas-phase flow field within a gas displacement system unit using numerical methods, the governing equations need to be established first. The gas-phase flow field within the gas displacement system unit is three-dimensional turbulent, and its hydrodynamic characteristics can be described by the mass conservation equation, the momentum conservation equation, and the energy conservation equation. The basic equations are as follows:

[0071] The parameter definitions in Equation 1-19 are specifically as follows:

[0072] Latin letter symbols:

[0073] C Particle-phase concentration kg / m 3

[0074] C2 Inertial drag coefficient

[0075] C ij Convection term

[0076] D H Hydraulic diameter m

[0077] D L,ij Molecular diffusion term

[0078] D p Average diameter of the material constituting the porous medium m

[0079] D T,ij Turbulent diffusion term

[0080] e Particle collision restitution coefficient

[0081] I Turbulence intensity

[0082] k Turbulent pulsation kinetic energy m 2 / s 2

[0083] k c Resistance of the particle layer m -2

[0084] K Permeability of the porous medium

[0085] l Turbulence characteristic dimension m

[0086] L Thickness of the porous medium m

[0087] m Particle layer content kg / m 3

[0088] P ij Shear force generation phase

[0089] P Pressure Pa

[0090] Re p Reynolds number

[0091] s Distance from the measurement point to the outer surface of the microporous separator mm

[0092] S Generalized source term

[0093] S Area m 2

[0094] t Time s

[0095] T Temperature K

[0096] u, v, w Velocity components m / s

[0097] v Gas displacement velocity m / s

[0098] x, y, z Three coordinates of the rectangular coordinate system

[0099] z Measurement position height mm

[0100] Greek letter symbols:

[0101] α Angle °

[0102] α Permeability m 2

[0103] β Correction coefficient

[0104] γΘ p Energy diffusion coefficient

[0105] ε Porosity

[0106] ε ij Stress dissipation term

[0107] η Gas viscosity Pa.s

[0108] μ Viscosity Pa.s

[0109] ρ Density kg / m 3

[0110] τ Time s

[0111] Γ Generalized diffusion coefficient

[0112] φ gp Energy exchange coefficient between gas phase and solid phase

[0113] φij Pressure strain term

[0114] Superscript:

[0115] ’ Fluctuation

[0116] — Mean value

[0117] → Vector

[0118] Subscript:

[0119] b Backflush

[0120] g Gas phase

[0121] l Fluid

[0122] p Particle phase

[0123] s Solid

[0124] 2D two-dimensional model

[0125] 3D three-dimensional model

[0126] i, j, k Coordinate directions.

[0127] Continuity equation:

[0128]

[0129] Momentum equation:

[0130]

[0131] Where is the stress tensor, and the expression is:

[0132]

[0133] In the formula, μ, I and are viscosity, unit tensor and gravity respectively; is the source term caused by the porous medium, which consists of two parts: viscous loss and inertial loss. C2 is the inertial resistance coefficient, and α is the permeability of the metal microporous separator. Its relationship with the pressure drop of the metal microporous separator is expressed by the Darcy formula:

[0134]

[0135] Energy equation:

[0136]

[0137] Where, E f and E sis the energy of the fluid and the solid (the porous medium of the metal microporous separator here); γ is the porosity of the porous medium, k eff = γk f +(1 - γ)k s is the effective thermal conductivity, k f and k s are the thermal conductivities of the fluid and the solid. h i and J i are the enthalpy and the component diffusion flux.

[0138] Using the Reynolds time-averaging method to perform time-averaging processing on each transient control equation above, the resulting time-averaged equations contain time-averaged unknowns of the product of fluctuating quantities. Thus, the number of equations is less than the number of unknowns. The task of the turbulence model is to relate these additional terms of turbulent pulsation values to the time-averaged values through some specific relationships or transport equations starting from physical concepts or certain assumptions, so as to close the system of equations. Considering the characteristics of the rotating flow existing in the gas displacement system unit, the transport equations of each component of the Reynolds stress in the turbulence model of the present invention are:

[0139]

[0140] The first term on the left end is the time rate of change of the stress, C ij is the convection term, and D T,ij on the right end is the turbulent diffusion term, D L,ij is the molecular diffusion term, P ij is the stress generation term, φ ij is the pressure strain term, ε ij is the dissipation term, where C ij 、D L,ij and P ij only contain second-order correlation terms and do not need to be processed. D T,ij ,φ ij and ε ij contain unknown correlation terms and must be approximated by turbulence simulation, that is, using low-order correlation terms to simulate high-order correlation terms. The calculation methods of D T,ij 、φ ij and ε ij are as follows:

[0141] (1) Calculation of the turbulent diffusion term D T,ij :

[0142] D T,ij is calculated using the gradient diffusion model of Daly-Harlow:

[0143]

[0144] Many cross-diffusion terms will be generated during the calculation of this equation, causing computational instability. Therefore, it is simplified in the FLUENT software to:

[0145]

[0146] Among them, μ t is the turbulent viscosity, calculated according to and is the turbulent pulsation kinetic energy, C μ = 0.09, σ k = 0.082.

[0147] (2) Calculation of the pressure-strain term φ ij :

[0148] The simulation of the pressure-strain term in the FLUENT software gives a typical form:

[0149] φ ij = φ ij,1 + φ ij,2 + φ ij,w (9)

[0150] Among them, φ ij,1 is the slow term, also known as the regression to isotropy term; φ ij,2 is the fast term, φ ij,w is the wall reflection term. The slow term φ ij,1 is:

[0151]

[0152] Among them, C1 = 1.8. The fast term φ ij,2 is:

[0153]

[0154] Among them, C2 = 0.6. The wall reflection term φ ij,w is:

[0155]

[0156] In the formula, C1' = 0.5, C'2 = 0.3, n k is the x k component of the unit normal vector of the wall; d is the perpendicular distance to the wall; k is the Karman constant, k = 0.4187.

[0157] (3) Calculation of the turbulent dissipation rate ε ij :

[0158] ε ijIt represents the dissipation caused by molecular viscosity to the Reynolds stress. When establishing the calculation formula for the dissipation term, it is generally considered that large-scale vortices are responsible for kinetic energy transport, and small-scale vortices are responsible for viscous dissipation. Therefore, small-scale vortex clusters are approximately considered to be isotropic, that is, locally isotropic. Therefore, the turbulent dissipation rate can be expressed by the following formula:

[0159]

[0160] where a is the speed of sound, which is used to correct the compressibility of the fluid.

[0161] In the Reynolds stress transport equation obtained above, the turbulent kinetic energy k and the dissipation rate ε are included. Therefore, the equations for k and ε are supplemented as follows:

[0162] k equation:

[0163]

[0164] ε equation:

[0165]

[0166] In the formula, C ε1 = 1.44, C ε2 = 1.92, σ ε = 1.0.

[0167] In this way, the basic equations for the closed three-dimensional turbulent flow problem are composed of the continuity equation, momentum equation, energy equation, Reynolds stress transport equation, k equation and ε equation.

[0168] (2) Boundary conditions:

[0169] (2.1) The inlet boundary conditions are as follows:

[0170] The gas inlet of the gas displacement system unit is a velocity inlet, and the operating pressure is 0.3 MPa. The inlet pressure is a function of time. The shear stress and the porosity ε of the microporous separator can be indirectly given through the turbulent intensity I and the hydraulic diameter D H The specific process is as follows:

[0171]

[0172]

[0173]

[0174]

[0175] where, C μ = 0.09, h = 1.42, u avgis the average flow velocity at the inlet, I is the turbulence intensity, taking I = 0.04, D H is the inlet hydraulic diameter, l is the turbulence characteristic size, l = 0.07D H .

[0176] (2.2) Outlet boundary conditions:

[0177] The outlet boundary conditions are treated according to the fully developed pipe flow conditions, and the axial gradients of all variables at the outlet section are zero, that is Therefore, in the calculation, the outlet pipeline of the gas displacement system unit is lengthened to ensure the establishment of fully developed conditions. The setting method of the turbulence parameters at the outlet is similar to that at the inlet.

[0178] (2.3) Wall boundary conditions:

[0179] Since the Reynolds stress transport model is only applicable to the turbulent region at a certain distance from the wall, that is, the fully developed turbulent region, and the flow in the viscous sublayer near the wall is a low Reynolds number flow, this model is not applicable. In order to connect the transition from the wall to the fully developed turbulent region, the wall function method is used near the wall. Its basic idea is to use the Reynolds stress model at high Reynolds numbers for calculation in the turbulent core region, and no nodes are arranged in the viscous sublayer. The first node connected to the wall is arranged in the vigorous turbulent region, and is connected to the corresponding variables on the solid wall through some semi-empirical formulas and functions, so as to avoid using the Reynolds stress model at high Reynolds numbers in the viscous influence region.

[0180] (2.4) Porous medium boundary conditions:

[0181] The metal microporous separator in the gas displacement system unit is a porous medium. To simulate the flow in it in detail requires a large number of grids. To simulate this flow, the distributed resistance method, also known as the porous medium model method, is used. The main idea of this method is to consider the action of the solid structure in the flow region as the distributed resistance added to the fluid, so as to simulate the flow with a coarser grid. The porous medium model is established by specifying the resistance coefficients in each direction.

[0182] (3) Gas-phase flow field analysis of the gas displacement system unit

[0183] (3.1) Gas-phase flow field distribution in the steady-state gas displacement process

[0184] Simulation calculation results of the incompressible flow in the steady-state gas displacement process. The gas passes through the metal microporous separator at an apparent velocity of 0.025 m / s. The operating pressure and operating temperature are 0.3 MPa and 873 K respectively. Figure 7 、 8It is the contour map of the static pressure distribution of the gas-phase flow field in the cross-section of the gas displacement system unit at y = -28.87 mm and x = 0 mm. It can be seen from the figure that during the gas displacement process, the static pressure distribution in the outer region of the metal microporous separator 6 in the gas displacement system unit is uniform, and the pressure at each point is almost equal. A relatively large pressure drop occurs when the gas passes through the metal microporous separator 6. The pressure inside the metal microporous separator 6 gradually decreases along the metal microporous separator towards its open end, and the static pressure in the top space of the displacement gas is the lowest. And during the entire gas displacement process, the pressure drop is mainly concentrated in the process of the gas passing through the metal microporous separator 6.

[0185] Figure 9 It is the contour map of the resultant velocity (a) and axial velocity (b) of the gas-phase flow field in the cross-section of the gas displacement system at y = -28.87 mm. After the gas enters the gas displacement system from one side, it passes through the metal microporous separator 6, flows through the energy aggregation device 8, enters the top space of the displacement gas, and then is discharged from the displacement gas outlet 5. As the gas continuously passes through the porous medium wall of the metal microporous separator 6 and enters the inside of the metal microporous separator 6, the gas velocity inside it gradually increases from the closed end to the open end.

[0186] Figure 10 It is the contour map of the turbulent kinetic energy (a), turbulent viscosity (b), and turbulent intensity (c) distribution in the cross-section of the gas displacement system unit at y = -28.87 mm. It can be seen from the figure that near the open end of the metal microporous separator 6, the turbulent kinetic energy, turbulent viscosity, and turbulent intensity are relatively high. Outside the metal microporous separator 6, in the region approximately 500 mm below the partition tube sheet 7, the turbulent viscosity and turbulent intensity are relatively high.

[0187] Figure 11 The velocity vector diagrams on the cross-sections of the gas displacement system unit at z = 100, z = 1000, and z = 1400 mm are shown. It can be seen from the figure that the gas enters the metal microporous separator 6 radially and then flows towards the top of the metal microporous separator 6. The cross-section position of z = 100 mm is close to the gas inlet, and the fluid disturbance is obvious near the metal microporous separator 6 on the gas displacement system inlet side. It can be seen from these figures that the gas velocity varies greatly along the height distribution of the metal microporous separator 6.

[0188] The fourth aspect of the present invention provides a device for establishing a model of an LNG unloading arm gas displacement system, including:

[0189] The first processing unit is used to set the initialization conditions using software and activate the user-defined initialization function;

[0190] The second processing unit is used to start a loop based on the initialization function and then adjust the variable values using the user-defined adjustment function;

[0191] A third processing unit for solving the U, V, and W momentum equations, the mass conservation equation, and updating the velocity values, and solving the energy equation, the component equation, and the turbulent kinetic energy and turbulent kinetic energy dissipation equations;

[0192] A fourth processing unit for updating properties, determining whether the solution converges. If it converges, the loop is exited; if it does not converge, it then transfers to a user-defined adjustment function to adjust the variable values and start the next loop.

[0193] The fifth aspect of the present invention provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the steps of the method for establishing the LNG unloading arm gas replacement system model are implemented.

[0194] The sixth aspect of the present invention provides a computer device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. The processor, when executing the computer program, implements the steps of the method for establishing the LNG unloading arm gas replacement system model.

[0195] The seventh aspect of the present invention provides a numerical simulation device for an LNG unloading arm gas replacement system, including:

[0196] A first processing unit for establishing a control equation set based on the physical conservation law;

[0197] A second processing unit for determining the gas inlet boundary condition and the outlet boundary condition of the gas replacement system based on the turbulence intensity and the hydraulic diameter;

[0198] A third processing unit for determining the wall boundary condition of the gas replacement system based on the wall function method and the Reynolds stress model;

[0199] A fourth processing unit for determining the porous medium boundary condition of the gas replacement system based on the porous medium model method;

[0200] A fifth processing unit for analyzing the gas phase flow field of the gas replacement system based on the control equation set, the gas inlet boundary condition and the outlet boundary condition, the wall boundary condition, and the porous medium boundary condition.

[0201] The eighth aspect of the present invention provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the steps of the numerical simulation method for the LNG unloading arm gas replacement system are implemented.

[0202] The ninth aspect of the present invention provides a computer device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. The processor, when executing the computer program, implements the numerical simulation method for the LNG unloading arm gas replacement system.

[0203] The present invention is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to specific embodiments. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, and combinations of flows and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to the processors of general-purpose computers, special-purpose computers, embedded processors, or other programmable data processing devices to produce a machine, such that the instructions executed by the processors of the computer or other programmable data processing devices generate means for implementing the functions specified in one or more flows and / or blocks Figure 1 one or more flows and / or blocks Figure 1 or in one or more blocks.

[0204] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, such that the instructions stored in the computer-readable memory produce a manufactured article including instruction means for implementing the functions specified in one or more flows and / or blocks Figure 1 one or more flows and / or blocks Figure 1 or in one or more blocks.

[0205] These computer program instructions can also be loaded onto a computer or other programmable data processing device, such that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, and thus the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in one or more flows and / or blocks Figure 1 one or more flows and / or blocks Figure 1 or in one or more blocks.

[0206] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An LNG unloading arm gas replacement system, characterized in that, Comprising: A replacement system upper pipe section (3), a replacement system middle pipe section (2), and a replacement system lower pipe section (1) connected in series from top to bottom. The replacement system upper pipe section (3) and the replacement system middle pipe section (2) are separated by a partition pipe plate (7). A number of microporous separators (6) are suspended at the lower end of the partition pipe plate (7). An energy aggregation device (8) is correspondingly arranged at the top of the microporous separator (6). A replacement gas inlet (4) is arranged near the lower end of the replacement system middle pipe section (2), and a replacement gas outlet (5) is arranged on the replacement system upper pipe section (3); The microporous separator (6) is a hollow tubular structure, and ventilation holes are arranged on its tube wall; The average permeability of the microporous separator (6) is 1×10 -12 m 2 .

2. The LNG unloading arm gas replacement system according to claim 1, wherein, The ventilation holes are evenly or discretely distributed on the tube wall of the microporous separator (6).

3. The LNG unloading arm gas replacement system according to claim 1, characterized in that, The aperture of the ventilation hole is 30μm - 50μm.

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