A BOG recovery system and method based on LNG-ANG coupling conditions

Abstract

The present application belongs to the technical field of clean energy storage and efficient utilization, and particularly relates to a BOG recovery system and method based on LNG-ANG coupling conditions. Through LNG-ANG deep coupling technology, a heat and mass transfer coupling model containing LNG variable property characteristics and adsorption bed dynamic boundary characteristics is constructed. Based on the dynamic regulation and control of the model, the precise control of LNG refrigerant from extensive cooling to "cold supply on demand" is realized, the waste of cold energy or insufficient heat removal is avoided, and the system energy consumption is significantly reduced. A complete "monitoring-inversion-regulation" closed-loop control strategy is established, which significantly prolongs the service life of the adsorbent. The present application introduces exergy efficiency, takes energy grade matching as the optimization target, realizes the theoretical leap from "energy conservation" to "exergy balance", makes the system run in the optimal working condition of thermodynamics, and realizes the efficient cascade utilization of energy.

Description

Technical Field

[0001] This invention belongs to the field of clean energy storage and efficient utilization technology, specifically relating to a BOG recovery system and method based on LNG-ANG coupling conditions. Background Technology

[0002] Liquefied natural gas (LNG), as a clean and efficient fossil fuel, occupies an increasingly important position in the global energy structure. In LNG receiving terminals, storage and distribution facilities, and related transshipment processes, unavoidable factors such as environmental heat leakage, atmospheric pressure fluctuations, and pumping operations continuously generate bottled gas (BOG) within LNG storage tanks. If BOG is not treated promptly and effectively, it will lead to increased tank pressure, triggering safety valves to release bottled gas. This not only causes serious greenhouse gas pollution and energy waste but also results in significant economic losses and safety hazards. Therefore, developing efficient, economical, and low-carbon BOG treatment technologies has become a critical issue that the LNG industry chain urgently needs to address.

[0003] Currently, mainstream BOG (Boiled Air Glow) processing technologies mainly include recondensation and direct compression export. Patent CN104033727A discloses a typical process and apparatus for recovering cold energy in an LNG receiving terminal to process BOG. ​​Its core lies in utilizing the cold energy of LNG to condense and recover compressed BOG in a recondenser. This process reduces the equipment load and size of the recondenser by introducing cold energy recovery and saves energy to some extent. However, this type of process still highly depends on continuous LNG export. When the receiving terminal is under low export load (such as minimum export conditions), the LNG cold energy available for BOG condensation is insufficient, resulting in incomplete BOG processing and posing a serious challenge to the stability and adaptability of the process. Patent CN117537262A discloses an apparatus for cryogenic adsorption storage of BOG using LNG cold energy. This involves setting up multiple adsorption tanks to achieve cryogenic adsorption storage of BOG using LNG cold energy. Patent CN119665136A proposes a system that directly liquefies BOG using a refrigeration unit and maintains the subcooling of the storage tanks. These technologies attempt to provide new ideas for flexible handling of BOG, but the following core issues still need to be addressed:

[0004] First, there is insufficient understanding of the mechanisms of heat and mass transfer and energy matching. Low-temperature adsorption is a strongly exothermic process, especially during the high-density adsorption stage of BOG (Bottle-Oxide-Gas). If the large amount of adsorption heat released instantaneously cannot be effectively removed, it can cause a sharp rise in the adsorption bed temperature, potentially leading to ignition risks or damage to the adsorbent structure. Existing technologies often employ simple natural convection or heat exchange structures not optimized for low-temperature conditions, making it difficult to meet the requirements of efficient thermal management. More critically, the LNG flowing within the heat exchange tubes is near its critical point, and its physical properties such as density, specific heat capacity, and viscosity undergo drastic nonlinear changes with temperature and pressure (i.e., "variable property" characteristics). Simultaneously, the adsorption waves and heat waves within the adsorption bed continuously shift over time, resulting in highly dynamic "moving boundary" characteristics in the boundary conditions of the heat exchange tubes. Traditional heat exchange design methods based on constant physical properties and fixed boundary assumptions cannot accurately describe this complex process, leading to large deviations in heat exchange area calculations, imbalances in the supply and demand of hot and cold energy, and poor system operational stability.

[0005] Second, there are shortcomings in the engineering application of high-performance adsorption materials. Conventional activated carbon has extremely low thermal conductivity at low temperatures (<0.5 W / m·K) and increased intracrystalline diffusion resistance, which severely restricts the adsorption / desorption rate and makes it difficult to meet the requirements for rapid BOG response in industrial scenarios. Although some metal-organic frameworks (MOFs) exhibit extremely high theoretical adsorption capacities in the laboratory, their poor mechanical strength, difficulty in molding, and high cost make it difficult to implement in large-scale industrial applications.

[0006] In summary, existing BOG processing technologies lack a systematic solution that can deeply understand and utilize the fluid dynamics and dynamic boundary characteristics of the adsorption bed, and deeply couple the efficient heat exchange structure with the LNG cold energy when facing complex operating conditions.

[0007] To overcome the dependence of traditional condensation processes on LNG exports, research on BOG (Boiled Gas) treatment using Adsorbed Natural Gas (ANG) technology has gradually emerged in recent years. ANG technology is considered a potential solution for small- to medium-sized gas storage for peak shaving and BOG recovery due to its advantages such as mild storage conditions (room temperature, medium to low pressure), simple equipment, and low cost. In particular, combining the cold energy released from LNG vaporization with cryogenic ANG technology (LNG-ANG coupling), using the cold energy of LNG to cool the adsorption bed to a low temperature (160K-200K), can significantly increase the adsorption capacity of the adsorbent for methane, theoretically 3-5 times that at room temperature.

[0008] Therefore, developing a novel LNG-ANG synergistic BOG recovery system that fully considers the aforementioned complex heat and mass transfer mechanisms and possesses efficient thermal management capabilities and high-performance adsorbents is of great scientific significance and engineering application value for achieving efficient, low-carbon, and low-cost BOG recovery and improving the overall operational flexibility and economy of LNG receiving terminals. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a BOG recovery system and method based on LNG-ANG coupling conditions. By deeply coupling the cold energy of LNG with ANG technology and using high-performance modified activated carbon adsorbent, and under the guidance of the complex heat and mass transfer mechanism that fully considers the fluid property characteristics and dynamic boundary conditions, the BOG can be stored and recovered at low temperature, low pressure and high density.

[0010] The technical solution adopted is as follows:

[0011] A BOG recovery system based on LNG-ANG coupling conditions includes:

[0012] A modified activated carbon adsorption storage tank, wherein the adsorption storage tank is a pressure vessel with a vacuum insulation layer, the interior is filled with highly thermally conductive modified activated carbon adsorbent, and is equipped with a built-in tube bundle heat exchange structure.

[0013] The LNG cold energy supply unit is used to transport liquefied natural gas from the LNG receiving terminal to the heat exchange structure inside the adsorption storage tank as a dynamic cold source.

[0014] The BOG intake unit is used to introduce the BOG generated by the receiving station into the adsorption tank for low-temperature adsorption.

[0015] The desorption and regeneration unit is used to provide a heat source to regenerate the adsorbent after it has become saturated.

[0016] The system includes a control unit, and several temperature and pressure sensors are installed inside and around the adsorption tank as needed. Each temperature and pressure sensor is connected to the control unit.

[0017] The control unit has a built-in heat and mass transfer coupling model based on variable properties and dynamic boundary conditions, which is used to adjust the flow rate of the LNG cold energy supply unit and the intake rate of the BOG intake unit according to the real-time monitored temperature and pressure field data.

[0018] The heat and mass transfer coupling model includes a thermal fluid energy sub-model and a cold fluid energy sub-model within the adsorption tank. The thermal fluid energy sub-model within the adsorption tank is used to calculate the total generated heat energy Q based on adsorption kinetics and porous media heat transfer. 热The energy sub-model of the cold fluid inside the adsorption tank is used to calculate the cold energy Q provided by LNG in the heat exchange tubes. 冷 The nonlinear changes in LNG density, specific heat capacity, and thermal conductivity with temperature and pressure during the flow process are corrected in real time through the database; the spatial positions of the adsorption front and temperature front in the adsorption bed and the position of the LNG liquid surface in the heat exchange tube with temperature changes are tracked through dynamic boundary conditions.

[0019] The control unit operates according to the energy matching principle Q. 热 ≈Q 冷 With the goal of adjusting the LNG flow rate in the heat exchange tube in real time, and based on the reverse heat conduction algorithm, the magnitude and location of the adsorption heat source term inside the adsorption bed are inverted in real time according to the temperature of the outer wall of the heat exchange tube, so as to realize the dynamic control of the temperature field of the adsorption bed.

[0020] Preferably, the modified activated carbon adsorbent uses coconut shell activated carbon with a specific surface area of ​​not less than 2000 m² / g as the matrix, and is compounded with 2-5 wt% thermally conductive filler, wherein the thermally conductive filler is selected from one or more of graphite nanosheets, expanded graphite, carbon fiber or metal powder; the adsorbent is formed and extruded into spherical activated carbon by binder, and undergoes secondary activation treatment to open up the pores, and the volume adsorption capacity for methane in the temperature range of 160K-298K is not less than 140 V / V.

[0021] Preferably, the built-in tube bundle heat exchange structure adopts a staggered arrangement, and the outer surface of the heat exchange tubes is welded with heat transfer reinforcing fins; the reverse heat conduction algorithm is based on the real-time inversion of the outer wall temperature of the heat exchange tubes to determine the magnitude and location of the adsorption heat inside the adsorption bed, and combined with the LNG variable property model, calculates the LNG mass flow rate required to offset the adsorption heat generated inside the adsorption bed. And output to the regulating valve; The formula is:

[0022] ;

[0023] in, The instantaneous mass flow rate of LNG that the system needs to regulate at time t;

[0024] The heat generation rate of the adsorption bed at time t, obtained through the dynamic boundary and thermal conductivity inversion model (or inlet flow rate calculation);

[0025] Based on the LNG inlet temperature and pressure measured by sensors inside the storage tank, the inlet specific enthalpy is read in real time by calling the built-in physical property database (such as the NIST database);

[0026] The outlet specific enthalpy is read in real time based on the LNG outlet temperature and pressure measured by the heat exchanger tube outlet sensor.

[0027] Preferably, the thermal fluid energy sub-model inside the adsorption storage tank, i.e., the total generated heat model, is as follows:

[0028] (1);

[0029] Among them, Q 热 U1 is the total heat of formation during the natural gas storage process, and E is the total internal energy within the adsorption tank. k1 Q1 is the total kinetic energy inside the adsorption tank; Q2 is the sum of convective heat transfer between natural gas and adsorbent, heat conduction between adsorbents, and heat conduction between adsorbent and tank wall; ε is the porosity of the adsorbent. The density of natural gas, c is the density of the adsorbent. pg For the specific heat of natural gas, c Ps The specific heat of the adsorbent. Let λ be the Darcy velocity of the natural gas, T be the temperature inside the adsorption tank, P be the pressure inside the adsorption tank, and λ be the pressure inside the adsorption tank. e h is the effective thermal conductivity of the adsorbent. i The specific enthalpy of each component of natural gas. For the diffusion flux of each component of natural gas, Let h be the stress tensor. w Let T be the heat transfer coefficient between LNG and the heat exchange tube wall, A be the area of ​​the LNG heat exchange tube, and T be the heat transfer coefficient between LNG and the heat exchange tube wall. w T is the temperature of the heat exchanger tube wall. LNG The temperature of the natural gas;

[0030] The energy sub-model of the cold fluid inside the adsorption storage tank, i.e., the variable property model, is as follows:

[0031] (2);

[0032] Among them, Q 冷 U2 is the cold energy generated by convective heat transfer during the LNG flow process, and E is the internal energy of the LNG in the heat exchange tube. k2 Q1 represents the kinetic energy of the LNG in the heat exchange tube, and Q2 represents the energy generated by the LNG during its flow due to heat conduction. c is the density of LNG. pl For the specific heat of LNG, Let λ be the LNG flow velocity within the heat exchanger tube. eff,f Thermal conductivity including turbulent motion;

[0033] The dynamic boundary model is:

[0034] The dynamic boundary model includes the transient heat conduction problem of the heat exchanger tube wall and the inverse heat flow problem of the inner wall based on the temperature measurement data of the outer wall.

[0035] First, a one-dimensional transient heat conduction equation along the radial direction of the heat exchanger tube wall is established as the physical basis for solving the reverse heat conduction problem. The transient heat conduction formula for the heat exchanger tube wall is:

[0036] (3);

[0037] in, : Volumetric specific heat capacity of the heat exchanger tube wall material;

[0038] Transient temperature of the heat exchanger tube wall at radial position r and time t;

[0039] Thermal conductivity of the heat exchanger tube wall material;

[0040] The initial conditions for formula (3) are:

[0041] ;

[0042] in, This refers to the initial temperature distribution of the heat exchange tube wall at the end of precooling or the end of the previous control cycle.

[0043] The inner wall boundary conditions of formula (3) are:

[0044] ;

[0045] in, Let be the instantaneous heat flux density of the inner wall of the heat exchange tube at time t, and be the unknown boundary quantity to be determined.

[0046] The inverse objective functional is calculated using the least squares method or regularization method:

[0047] (4);

[0048] in, The objective function that needs to be minimized;

[0049] T mea (t) i Temperature sensors arranged on the outer wall of the heat exchange tubes at t i The actual temperature collected at all times;

[0050] T calc (t) i，q ): The theoretical temperature of the outer wall is calculated by formula (3) under the premise that the heat flux density of the inner wall is q;

[0051] : Tikhonov regularization term;

[0052] Set the initial iterative value of the heat flux density on the inner wall. The control unit iteratively modifies the unknown through the conjugate gradient method or the sequence function reduction method. until Reaching less than or equal to 10 -4 The value of (the minimum value), that is, when the calculated theoretical temperature of the outer wall is extremely close to the actual collected temperature of the outer wall, is obtained at this point. This is the actual instantaneous heat flux density inside the tube;

[0053] The heat flux density of the inner wall will be calculated in reverse. Using the inner wall boundary condition of formula (3) and combining the outer wall temperature measurement boundary and the initial temperature condition, the transient heat conduction equation of the heat exchanger tube wall is solved to obtain the transient temperature field of the heat exchanger tube wall. And then in Extraction of inner wall temperature :

[0054] ;

[0055] in, Let be the transient temperature of the inner wall of the heat exchanger tube at time t;

[0056] Furthermore, considering the LNG-side fluid temperature The real-time convective heat transfer coefficient inside the pipe was calculated. ;

[0057] According to Newton's law of cooling:

[0058] ;

[0059] The real-time convective heat transfer coefficient inside the heat exchange tube can be obtained. :

[0060] ;

[0061] in, Instantaneous heat flux density of the inner wall obtained by inversion;

[0062] : Transient temperature of the inner wall of the tube obtained by inversion;

[0063] The real-time bulk temperature of the LNG fluid inside the pipe is obtained by coupling calculations using the inlet and outlet temperatures, pressures, mass flow rates, and physical property databases of the heat exchanger pipe.

[0064] The convective heat transfer coefficient inside the pipe dynamically changes with flow velocity, fluid properties, and temperature difference;

[0065] Calculate the third type boundary that changes dynamically over time:

[0066] The side boundary coupling equation of the adsorption bed is:

[0067] ;

[0068] : Effective thermal conductivity of the adsorption bed;

[0069] Temperature gradient of the adsorption bed along the normal direction of the tube wall;

[0070] : Local temperature at the interface between the adsorption bed and the outer wall of the heat exchange tube;

[0071] : Equivalent convective heat transfer coefficient; based on inversion, the internal heat transfer coefficient of the pipe. The overall heat transfer coefficient, calculated by taking into account the thermal resistance of the pipe wall itself and applying it to the outer wall of the pipe, is also included.

[0072] : The dynamic temperature of the LNG cold fluid inside the pipe;

[0073] The calculation results are used as dynamic boundary conditions for the adsorption bed energy equation to achieve precise coupling between the adsorption side and the heat exchange side models.

[0074] Preferably, the control unit has a built-in thermodynamic matching optimization module aimed at maximizing efficiency, wherein efficiency is defined as:

[0075] ;

[0076] in:

[0077] ;

[0078] in, For the actual utilization of the adsorption bed, The total cooling capacity provided to the LNG fluid; h and s are the specific enthalpy and specific entropy of the fluid under real-time temperature and pressure conditions, respectively; h0 and s0 are the specific enthalpy and specific entropy of the fluid under ambient reference temperature conditions, respectively; T0 is the ambient reference temperature;

[0079] The control unit adjusts the LNG flow rate to make the system operate at the peak point of the efficiency curve, thereby achieving uniformity of the temperature difference field between the hot and cold fluids.

[0080] Preferably, the built-in tube bundle heat exchange structure includes at least three heat exchange straight tubes, with reinforced heat transfer fins welded to the outside of the tubes. The tube diameter, tube spacing, and fin size of the heat exchange tubes are optimized by CFD design. The heat exchange tubes are made of low-temperature resistant stainless steel, and LNG to be vaporized is introduced into the tubes as a refrigerant.

[0081] This invention also provides a BOG recovery method based on LNG-ANG coupling conditions, employing a BOG recovery system based on LNG-ANG coupling conditions according to this invention, comprising the following steps:

[0082] S1 Pre-cooling stage: Control the LNG cold energy supply unit to introduce LNG into the heat exchange structure of the adsorption tank, and use the sensible heat and latent heat of LNG to reduce the temperature of the adsorption bed to the preset working temperature range.

[0083] S2 Co-adsorption Stage: The BOG inlet unit is activated, and the BOG, pressurized by the compressor, is introduced into the ANG adsorption tank, where it is captured by the activated carbon bed. Simultaneously, the LNG refrigerant supply pipeline is activated, allowing low-pressure LNG from the storage tank to flow into the enhanced heat exchange tube bundle in the adsorption tank after being pressurized by the submerged pump. This LNG absorbs the latent heat and adsorption heat of the BOG, and the heat-absorbed LNG is then sent to the downstream vaporizer to be converted into gaseous natural gas before being fed into the external pipeline network. During this process, data recorded in real time from flow meters, temperature sensors, and pressure sensors located at each node is collected, and the instantaneous total heat of generation Q is calculated using the built-in heat and mass transfer coupling model. 热 Instantaneous heat transfer capacity Q with LNG cold fluid 冷 ;

[0084] S3 Dynamic Regulation: Based on the Energy Matching Principle Q 热 ≈Q 冷 The control unit adjusts the LNG mass flow rate in the heat exchange tube according to the calculation results of the S2 stage. When the temperature gradient inside the adsorption bed exceeds the set threshold or the LNG properties in the heat exchange tube fluctuate drastically, the flow rate set value is adjusted through the correction algorithm to maintain the low temperature environment at the adsorption front.

[0085] S4 Saturation Judgment and Switching: When the methane concentration at the outlet of the adsorption tank reaches the set threshold or the pressure inside the tank reaches the design upper limit, it is determined that the adsorption is saturated, the gas intake and cooling supply are stopped, and the system is switched to the desorption and regeneration unit.

[0086] S5 Desorption and Regeneration: First, open the inlet and outlet valves of the heating medium and the external heater to introduce the heating medium into the heat exchange tube bundle in the ANG adsorption tank, so that the temperature of the adsorbent rises from the low temperature state to the desorption temperature, i.e., ≥298 K. Methane desorption causes the pressure inside the tank to rise. When the pressure reaches the external transmission threshold, open the top exhaust valve to send the high-pressure methane gas generated by desorption into the external transmission pipeline or downstream via the BOG compressor. When the pressure drops to near atmospheric pressure, close the top exhaust valve and turn on the vacuum pump. Under the dual action of high temperature and negative pressure, the residual methane is removed, and the extracted gas is sent to the collection pipeline. Finally, close the vacuum pump, heater and related valves, and introduce a small amount of room temperature natural gas or inert gas for micro-positive pressure replacement purging to remove residual impurities in the bed, complete the deep regeneration and reset to the standby state.

[0087] Preferably, the preset working temperature range in step S1 is 160K-200K; the temperature gradient setting threshold in step S3 is 10K; and the desorption setting temperature in step S5 is 353K±5K.

[0088] Preferably, the LNG flow rate adjustment in step S3 takes into account the property distortion of supercritical LNG near the quasi-critical point, and uses a modified turbulence model to calculate the local convective heat transfer coefficient in the pipe. The modified turbulence model is selected from the RNG k-ε model or the SST k-ω model.

[0089] Preferably, the energy matching principle Q described in step S3 热 ≈Q 冷 The PID algorithm built into the control unit is used to correct the flow rate set value when the temperature gradient inside the adsorption bed exceeds the set threshold or the LNG properties in the heat exchange tube fluctuate drastically, so as to maintain the low temperature environment at the adsorption front.

[0090] Compared with the prior art, the significant advantages of the present invention are as follows:

[0091] (1) This invention utilizes LNG-ANG deep coupling technology to pre-cool the adsorption bed using LNG cold energy instead of directly condensing BOG, thus achieving "decoupling" between cold energy and BOG processing capacity. Even under conditions of extremely low or zero external output, the system can still utilize the limited LNG cold energy in the storage tank to maintain the low temperature of the adsorption bed, achieving high-density BOG storage (≥140 V / V), significantly improving the flexibility and stability of the receiving station in handling complex operating conditions. The adsorption storage tank, through precise low-temperature control (160K-200K), significantly improves the adsorption capacity and achieves high heat and mass transfer efficiency.

[0092] (2) This invention introduces a "variable property + dynamic boundary" model for the first time, realizing precise on-demand supply of cooling capacity. This invention constructs a coupled mathematical model of heat and mass transfer that includes the variable property characteristics of LNG and the dynamic boundary characteristics of the adsorption bed: calling the NIST property database to correct LNG property parameters in real time, accurately describing the heat transfer enhancement phenomenon of supercritical LNG near the quasi-critical point; through the reverse heat conduction algorithm, the position and intensity of the adsorption heat source term are inverted in real time based on the temperature of the outer wall of the heat exchange tube, and the calculation results are used as the third type of boundary condition of the adsorption side energy equation. Based on the dynamic control of this model, a leap from "large flow flood" type extensive cooling to precise control of "on-demand supply of cooling capacity" is realized, avoiding waste of cooling capacity or insufficient heat transfer, and significantly reducing system energy consumption.

[0093] (3) The present invention introduces the efficiency η ex= Ex absorbed / Ex supplied By using energy grade matching as the optimization objective, a theoretical leap from "energy conservation" to "thermal balance" is achieved, upgrading system design from "meeting basic functions" to "pursuing thermodynamic perfection." Adsorption heat accumulation is suppressed through "temperature difference field homogenization." Maximizing thermal efficiency means minimizing irreversible losses during heat exchange, i.e., minimizing the local temperature difference between hot and cold fluids. Minimize. The heat exchange process at different LNG flow rates was simulated using Fluent, and a "flow rate-efficiency" curve was plotted. When the flow rate is too low, heat accumulates in the bed, reducing adsorption performance and efficiency; when the flow rate is too high, LNG is discharged before sufficient heat exchange (extremely low outlet temperature), wasting cooling capacity and further reducing efficiency. The peak point of the curve at the highest point represents the optimal matching flow rate, where Q0 is minimized. 热 =Q 冷 Furthermore, the temperature field is the most uniform. The introduction of efficiency achieves dynamic energy balance, significantly reduces the system's gas storage energy ratio (SEC), enables the system to operate under thermodynamically optimal conditions, and realizes efficient cascade utilization of energy.

[0094] (4) This invention constructs a fully automated closed-loop control system, improving the thermal stability and safety of the system. This invention establishes a complete "monitoring-inversion-regulation" closed-loop control strategy: real-time acquisition of temperature and pressure data at multiple points within the adsorption tank; calculation of instantaneous Q using a heat and mass transfer coupling model. 热 With Q 冷 When the temperature gradient inside the adsorption bed exceeds 10K or LNG properties fluctuate drastically, the flow rate setpoint is corrected using a PID algorithm to maintain Q. 热 ≈Q 冷 The radial and longitudinal temperature gradients of the bed are both controlled within 10K. This closed-loop control strategy effectively suppresses the temperature rise caused by the accumulation of adsorption heat, ensures the structural stability of the adsorbent and the safety of system operation, and significantly extends the cycle life of the adsorbent. Attached Figure Description

[0095] Figure 1 This is a flow chart of the adsorption process of the LNG-ANG synergistic BOG low-temperature high-efficiency recovery system of the present invention.

[0096] Figure 2 This is a flow chart of the desorption process of the LNG-ANG synergistic BOG cryogenic high-efficiency recovery system of the present invention.

[0097] In the diagram, 1-pressure reducing valve, 2-gas flow meter, 3-1. first liquid flow meter, 3-2. second liquid flow meter, 4-adsorption storage tank, 5-adsorbent, 6-thermal insulation layer, 7-low temperature submersible pump, 8-gas distributor, 9-explosion-proof electric heater.

[0098] T1-T11 are temperature sensors installed in the system; P1-P6 are pressure sensors installed in the system; V1-V9 are system valves installed. Detailed Implementation

[0099] The accompanying drawings are for illustrative purposes only. To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0100] It should be understood that the prior art used in this invention may be omitted; unless otherwise specified, the materials and testing methods used are commercially available and can be measured by conventional methods.

[0101] Example 1.

[0102] like Figure 1 As shown, a BOG recovery system based on LNG-ANG coupling conditions includes:

[0103] Modified activated carbon adsorption storage tank 4 is designed as a vertical cylindrical pressure vessel with a volume of 1.5 m³.

[0104] Thermal insulation design: The tank wall is equipped with a vacuum powder insulation layer to minimize heat leakage from the environment and maintain the working temperature range of 160K-298K inside the tank.

[0105] Internal heat exchange structure: It is a tube bundle heat exchange structure with three straight heat exchange tubes evenly distributed inside the tank. The tubes are welded with fins to enhance heat exchange. The tube diameter, tube spacing, fin shape and size are all designed after CFD optimization. The heat exchange tubes are made of low-temperature resistant stainless steel (such as S30408), and LNG to be vaporized is introduced into the tubes as the refrigerant.

[0106] The LNG cooling supply unit includes an LNG storage tank, a cryogenic submersible pump 7, a mass flow meter, and a regulating valve. It is used to transport liquefied natural gas from the LNG receiving terminal to the heat exchange structure within the adsorption storage tank, serving as a dynamic cooling source; and to regulate the flow rate according to control commands.

[0107] The gas distributor 8 is located at the top of the adsorption tank 4 and is connected to the adsorption tank 4, the natural gas tank, and the LNG tank. It is used to distribute BOG evenly and achieve precise control in conjunction with the dynamic boundary model.

[0108] The BOG intake unit includes a BOG buffer tank, an oil and water removal filter, a pressure regulating valve, and a flow meter. Its function is to introduce the BOG generated by the receiving station into the adsorption storage tank after stabilizing the pressure.

[0109] The desorption and regeneration unit includes a blower, an explosion-proof electric heater 9, and a hot air delivery pipeline, which are used to provide a heat source to regenerate the adsorbent after it has become saturated.

[0110] The system includes a control unit, and as needed, several temperature and pressure sensors are installed inside and around the adsorption tank, with each temperature and pressure sensor connected to the control unit.

[0111] The control unit has a built-in heat and mass transfer coupling model based on variable properties and dynamic boundary conditions, which is used to adjust the flow rate of the LNG cold energy supply unit and the intake rate of the BOG intake unit according to the real-time monitored temperature and pressure field data.

[0112] The heat and mass transfer coupling model includes a thermal fluid energy sub-model and a cold fluid energy sub-model within the adsorption tank. The thermal fluid energy sub-model within the adsorption tank is used to calculate the total generated heat energy Q based on adsorption kinetics and porous media heat transfer. 热 The energy sub-model of the cold fluid inside the adsorption tank is used to calculate the cold energy Q provided by LNG in the heat exchange tubes. 冷 The model uses the NIST database to correct the nonlinear changes in the density, specific heat capacity, and thermal conductivity of LNG with temperature and pressure during the flow process in real time; it tracks the spatial positions of the adsorption front and temperature front in the adsorption bed and the position of the LNG liquid surface in the heat exchange tube with temperature changes through dynamic boundary conditions.

[0113] The control unit operates according to the energy matching principle Q. 热 ≈Q冷 With the goal of adjusting the LNG flow rate in the heat exchange tube in real time, and based on the reverse heat conduction algorithm, the magnitude and location of the adsorption heat source term inside the adsorption bed are inverted in real time according to the temperature of the outer wall of the heat exchange tube, so as to realize the dynamic control of the temperature field of the adsorption bed.

[0114] The energy matching control strategy is as follows: the control unit calculates Q in real time. 热 With Q 冷 When Q 热 >Q 冷 At this time, there is a risk of heat accumulation in the bed layer. The system automatically increases the LNG pump speed or opens the regulating valve to increase the cooling supply; when Q 热 <Q 冷 When this occurs, it indicates that there is excess cooling inside the adsorption tank. The system automatically reduces the LNG flow rate to prevent the adsorbent from becoming too cold, which could slow down adsorption kinetics or waste cooling energy. The goal is to maintain Q... 热 =Q 冷 To control significant fluctuations in bed temperature, the radial and longitudinal temperature gradients inside the storage tank should both be controlled within 10K. In practice, achieving absolute equality is difficult; therefore, Q is used as the basis for this control. 热 ≈Q 冷 For the goal.

[0115] The modified activated carbon adsorbent uses coconut shell activated carbon with a specific surface area of ​​about 2100 m² / g as the matrix, and is compounded with 3wt% thermally conductive filler, which is selected from graphite nanosheets and carbon fibers. The adsorbent is formed and extruded into spherical activated carbon by binder, and then undergoes secondary activation treatment to open up the pores. The volume adsorption capacity for methane is 160 V / V in the temperature range of 160K-298K.

[0116] The built-in tube bundle heat exchange structure adopts a staggered arrangement, and the outer surface of the heat exchange tubes is welded with reinforced heat transfer fins. The reverse heat conduction algorithm is based on the real-time inversion of the outer wall temperature of the heat exchange tubes to determine the magnitude and location of the adsorption heat inside the adsorption bed, and combined with the LNG variable property model, calculates the LNG mass flow rate required to offset the adsorption heat generated inside the adsorption bed. And output to the regulating valve; The formula is:

[0117] ;

[0118] in, The instantaneous mass flow rate of LNG that the system needs to regulate at time t;

[0119] The heat generation rate of the adsorption bed at time t, obtained through the dynamic boundary and thermal conductivity inversion model (or inlet flow rate calculation);

[0120] Based on the LNG inlet temperature and pressure measured by sensors inside the storage tank, the inlet specific enthalpy is read in real time by calling the built-in physical property database (such as the NIST database);

[0121] The outlet specific enthalpy is read in real time based on the LNG outlet temperature and pressure measured by the heat exchanger tube outlet sensor.

[0122] The thermal fluid energy sub-model inside the adsorption storage tank, i.e., the total generated heat model, is as follows:

[0123] (1);

[0124] Among them, Q 热 U1 is the total heat of formation during the natural gas storage process, and E is the total internal energy within the adsorption tank. k1 Q1 is the total kinetic energy inside the adsorption tank; Q2 is the sum of convective heat transfer between natural gas and adsorbent, heat conduction between adsorbents, and heat conduction between adsorbent and tank wall; ε is the porosity of the adsorbent. The density of natural gas, c is the density of the adsorbent. pg For the specific heat of natural gas, c Ps The specific heat of the adsorbent. Let λ be the Darcy velocity of the natural gas, T be the temperature inside the adsorption tank, P be the pressure inside the adsorption tank, and λ be the pressure inside the adsorption tank. e h is the effective thermal conductivity of the adsorbent. i The specific enthalpy of each component of natural gas. For the diffusion flux of each component of natural gas, Let h be the stress tensor. w Let T be the heat transfer coefficient between LNG and the heat exchange tube wall, A be the area of ​​the LNG heat exchange tube, and T be the heat transfer coefficient between LNG and the heat exchange tube wall. w T is the temperature of the heat exchanger tube wall. LNG The temperature of the natural gas.

[0125] The energy sub-model of the cold fluid inside the adsorption storage tank, i.e., the variable property model, is as follows:

[0126] (2);

[0127] Among them, Q 冷 U2 is the cold energy generated by convective heat transfer during the LNG flow process, and E is the internal energy of the LNG in the heat exchange tube. k2 Q1 represents the kinetic energy of the LNG in the heat exchange tube, and Q2 represents the energy generated by the LNG during its flow due to heat conduction. c is the density of LNG. pl For the specific heat of LNG, Let λ be the LNG flow velocity within the heat exchanger tube.eff,f The thermal conductivity includes turbulent motion.

[0128] The dynamic boundary model is:

[0129] The dynamic boundary model includes a forward problem of transient heat conduction in the heat exchanger tube wall and a reverse problem of heat flow in the inner wall based on external wall temperature measurement data. First, a one-dimensional transient heat conduction equation along the radial direction of the heat exchanger tube wall is established as the physical basis for solving the reverse heat conduction problem. The transient heat conduction formula for the heat exchanger tube wall is:

[0130] (3).

[0131] in, : Volumetric specific heat capacity of the heat exchanger tube wall material;

[0132] Transient temperature of the heat exchanger tube wall at radial position r and time t;

[0133] Thermal conductivity of the heat exchanger tube wall material.

[0134] The initial conditions for formula (3) are:

[0135] ;

[0136] in, This refers to the initial temperature distribution of the heat exchanger tube wall at the end of precooling or the end of the previous control cycle.

[0137] The inner wall boundary conditions of formula (3) are:

[0138] ;

[0139] in, Let be the instantaneous heat flux density of the inner wall of the heat exchange tube at time t, and be the unknown boundary quantity to be determined.

[0140] The inverse objective functional is calculated using the least squares method or regularization method:

[0141] (4);

[0142] in, The objective function that needs to be minimized;

[0143] T mea (t) i Temperature sensors arranged on the outer wall of the heat exchange tubes at t i The actual temperature collected at all times;

[0144] T calc (t) i，q): The theoretical temperature of the outer wall is calculated by formula (3) under the premise that the heat flux density of the inner wall is q;

[0145] :Tikhonov regularization term.

[0146] Set the initial iterative value of the heat flux density on the inner wall. The control unit iteratively modifies the unknown through the conjugate gradient method or the sequence function reduction method. until Reaching less than or equal to 10 -4 The value obtained is when the calculated theoretical temperature of the outer wall is extremely close to the actual collected temperature of the outer wall. This is the actual instantaneous heat flux density inside the tube.

[0147] The heat flux density of the inner wall will be calculated in reverse. Using the inner wall boundary condition of formula (3) and combining the outer wall temperature measurement boundary and the initial temperature condition, the transient heat conduction equation of the heat exchanger tube wall is solved to obtain the transient temperature field of the heat exchanger tube wall. And then in Extraction of inner wall temperature :

[0148] ;

[0149] in, Let be the transient temperature of the inner wall of the heat exchanger tube at time t;

[0150] Furthermore, considering the LNG-side fluid temperature The real-time convective heat transfer coefficient inside the pipe was calculated. .

[0151] According to Newton's law of cooling:

[0152] ;

[0153] The real-time convective heat transfer coefficient inside the heat exchange tube can be obtained. :

[0154] ;

[0155] in, Instantaneous heat flux density of the inner wall obtained by inversion;

[0156] : Transient temperature of the inner wall of the tube obtained by inversion;

[0157] The real-time bulk temperature of the LNG fluid inside the pipe is obtained by coupling calculations using the inlet and outlet temperatures, pressures, mass flow rates, and physical property databases of the heat exchanger pipe.

[0158] The convective heat transfer coefficient inside the pipe varies dynamically with changes in flow velocity, fluid properties, and temperature difference.

[0159] Calculate the third type boundary that changes dynamically over time:

[0160] The side boundary coupling equation of the adsorption bed is:

[0161] ;

[0162] : Effective thermal conductivity of the adsorption bed;

[0163] Temperature gradient of the adsorption bed along the normal direction of the tube wall;

[0164] : Local temperature at the interface between the adsorption bed and the outer wall of the heat exchange tube;

[0165] : Equivalent convective heat transfer coefficient; based on inversion, the internal heat transfer coefficient of the pipe. The overall heat transfer coefficient, calculated by taking into account the thermal resistance of the pipe wall itself and applying it to the outer wall of the pipe, is also included.

[0166] : The dynamic temperature of the LNG cold fluid inside the pipe;

[0167] The calculation results are used as dynamic boundary conditions for the adsorption bed energy equation to achieve precise coupling between the adsorption side and the heat exchange side models.

[0168] The control unit has a built-in thermodynamic matching optimization module aimed at maximizing efficiency, whereby efficiency is defined as:

[0169] ;

[0170] in:

[0171] ;

[0172] in, For the actual utilization of the adsorption bed, The total cooling capacity provided to the LNG fluid; h and s are the specific enthalpy and specific entropy of the fluid under real-time temperature and pressure conditions, respectively; h0 and s0 are the specific enthalpy and specific entropy of the fluid under ambient reference temperature conditions, respectively; T0 is the ambient reference temperature.

[0173] The control unit adjusts the LNG flow rate to make the system operate at the peak point of the efficiency curve, thereby achieving uniformity of the temperature difference field between the hot and cold fluids.

[0174] The built-in tube bundle heat exchange structure includes three heat exchange straight tubes with reinforced heat transfer fins welded to the outside of the tubes. The tube diameter, tube spacing and fin size of the heat exchange tubes are optimized by CFD. The heat exchange tubes are made of low-temperature resistant stainless steel and LNG to be vaporized is introduced into the tubes as a refrigerant.

[0175] This invention also provides a BOG recovery method based on LNG-ANG coupling conditions, employing a BOG recovery system based on LNG-ANG coupling conditions according to this invention, comprising the following steps:

[0176] S1 Pre-cooling stage: Control the LNG cold energy supply unit to introduce LNG into the heat exchange structure of the adsorption tank, and use the sensible heat and latent heat of LNG to reduce the temperature of the adsorption bed to the preset working temperature range.

[0177] S2 Co-adsorption Stage: The BOG inlet unit is activated, and the BOG, after being moderately pressurized by the compressor, is introduced into the ANG adsorption tank through valve V6, where it is captured by the activated carbon bed. Simultaneously, the LNG refrigerant supply pipeline is activated, allowing low-pressure LNG from the storage tank to be pressurized by the submersible pump and flow into the enhanced heat exchange tube bundle in the adsorption tank through inlet valve V3. This LNG absorbs the latent heat and adsorption heat of the BOG, and the heat-absorbing LNG is then sent to the downstream vaporizer through outlet valve V4, where it is converted into gaseous natural gas and then fed into the external pipeline network. During this process, data recorded in real time from flow meters, temperature sensors, and pressure sensors located at each node is acquired, and the instantaneous total heat of formation Q is calculated using the built-in heat and mass transfer coupling model. 热 Instantaneous heat transfer capacity Q with LNG cold fluid 冷 ;

[0178] S3 Dynamic Regulation: Based on the Energy Matching Principle Q 热 ≈Q 冷 The control unit adjusts the LNG mass flow rate in the heat exchange tube according to the calculation results of the S2 stage. When the temperature gradient inside the adsorption bed exceeds the set threshold or the LNG properties in the heat exchange tube fluctuate drastically, the flow rate set value is adjusted through the correction algorithm to maintain the low temperature environment at the adsorption front.

[0179] S4 Saturation Judgment and Switching: When the methane concentration at the outlet of the adsorption tank reaches the set threshold or the pressure inside the tank reaches the design upper limit, it is determined that the adsorption is saturated, the gas intake and cooling supply are stopped, and the system is switched to the desorption and regeneration unit.

[0180] S5 desorption and regeneration: such as Figure 2As shown, firstly, open the inlet and outlet valves V7 and V8 of the heating medium and the external heater to introduce the heating medium into the heat exchange tube bundle in the ANG adsorption tank, causing the adsorbent temperature to rise from a low temperature state to the desorption temperature (≥298 K). Methane desorption causes the pressure inside the tank to rise. When the pressure reaches the external transmission threshold, open the top exhaust valve V5 to send the high-pressure methane gas generated by desorption into the external transmission pipeline or downstream via the BOG compressor. When the pressure drops to near atmospheric pressure, close V5 and open the vacuum valves V9 and V10 and the vacuum pump. Under the dual action of high temperature and negative pressure, the residual methane is removed. The extracted gas is sent to the collection pipeline via valve V11 or V2. Finally, close the vacuum pump, heater and related valves, and introduce a small amount of room temperature natural gas or inert gas for micro-positive pressure replacement purging to remove residual impurities in the bed, complete deep regeneration and reset to standby state.

[0181] In step S1, the preset working temperature range is 160K-200K; in step S3, the temperature gradient setting threshold is 10K; and in step S5, the desorption setting temperature is 353K±5K.

[0182] The adjustment of LNG flow rate in step S3 takes into account the property distortion of supercritical LNG near the quasi-critical point. A modified turbulence model is used to calculate the local convective heat transfer coefficient in the pipe. The modified turbulence model is selected from the RNG k-ε model or the SST k-ω model.

[0183] The energy matching principle Q mentioned in step S3 热 ≈Q 冷 The PID algorithm built into the control unit is used to correct the flow rate set value when the temperature gradient inside the adsorption bed exceeds the set threshold or the LNG properties in the heat exchange tube fluctuate drastically, so as to maintain the low temperature environment at the adsorption front.

[0184] Example 2.

[0185] A BOG recovery method based on LNG-ANG coupling conditions includes the following steps:

[0186] Step 1: System precooling and preparation.

[0187] The control program is initiated. The control unit commands the LNG cold energy supply valve to open, and the cryogenic submersible pump injects -162℃ LNG into the heat exchange straight pipe of the adsorption tank at a low flow rate. The LNG absorbs heat and vaporizes inside the pipe, and the outlet gas is sent to the receiving station's external pipeline network. As the heat exchange process proceeds, the temperature of the adsorption bed gradually decreases. The control unit monitors the average bed temperature, and when the temperature inside the storage tank drops to 180K and the radial temperature gradient does not exceed 10K, precooling is considered complete.

[0188] Step 2: Synergistic adsorption and energy matching control.

[0189] When the BOG inlet valve is opened, the BOG generated by the receiving station's storage tank enters the adsorption tank through the pipeline. The adsorbent begins to adsorb methane molecules, generating a large amount of adsorption heat. At this time, the control unit enters the dynamic control mode.

[0190] Hot-end calculation: Based on the real-time collected bed temperature and pressure change rates, the current heat production power is calculated using the total generation heat model. In the model, the increment of adsorption and the corresponding equivalent heat of adsorption are calculated based on the Dubinin-Astakhov equation according to the internal energy change term.

[0191] Cold end calculation: Read the LNG inlet temperature, pressure, and flow rate. The system calls the NIST database to obtain parameters such as LNG density and specific heat under this condition. If the pressure exceeds the critical pressure (approximately 4.6 MPa), the current heat exchange capacity is calculated using supercritical fluid heat transfer correlation.

[0192] Closed-loop regulation: If the total generated heat shows an upward trend (initial adsorption), the control unit will issue a command to increase the opening of the LNG flow regulating valve to increase the cooling capacity of the input system. The temperature control target can be set by using an algorithm to ensure that the highest temperature point of the bed does not exceed 200K and the radial and longitudinal temperature gradients within the bed do not exceed 10K.

[0193] Dynamic boundary correction: The system uses the reverse heat conduction algorithm, combined with the pipe wall temperature monitoring value, to correct the heat transfer coefficient in real time by modifying the correlation of the semi-empirical heat transfer criterion and the turbulence model, ensuring that the lag time predicted by the model is less than the system response time.

[0194] During this process, the pressure in the adsorption tank is maintained at 1.2-1.6 MPa, and the bed temperature is stabilized between 180K-200K.

[0195] Step 3: Adsorption saturation and switching.

[0196] When the rate of increase in outlet pressure of the adsorption tank accelerates during the adsorption process, and the outlet methane concentration approaches the inlet concentration, the adsorption in the tank is determined to be saturated. Close the BOG inlet valve and the LNG supply valve (or switch the LNG to the bypass vaporizer).

[0197] Step 4: Desorption and regeneration.

[0198] Start the desorption unit. Heat the nitrogen to 350K using an explosion-proof electric heater, and then introduce the heated nitrogen gas into the heat exchange straight tube of the adsorption tank.

[0199] Other areas not mentioned are the same as in Example 1.

[0200] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A BOG recovery system based on LNG-ANG coupling conditions, characterized in that, include: A modified activated carbon adsorption storage tank, wherein the adsorption storage tank is a pressure vessel with a vacuum insulation layer, the interior is filled with highly thermally conductive modified activated carbon adsorbent, and is equipped with a built-in tube bundle heat exchange structure. The LNG cold energy supply unit is used to transport liquefied natural gas from the LNG receiving terminal to the heat exchange structure inside the adsorption storage tank as a dynamic cold source. The BOG intake unit is used to introduce the BOG generated by the receiving station into the adsorption tank for low-temperature adsorption. The desorption and regeneration unit is used to provide a heat source to regenerate the adsorbent after it has become saturated. The system includes a control unit, and several temperature and pressure sensors are installed inside and around the adsorption tank as needed. Each temperature and pressure sensor is connected to the control unit. The control unit has a built-in heat and mass transfer coupling model based on variable properties and dynamic boundary conditions, which is used to adjust the flow rate of the LNG cold energy supply unit and the intake rate of the BOG intake unit according to the real-time monitored temperature and pressure field data. The heat and mass transfer coupling model includes a thermal fluid energy sub-model and a cold fluid energy sub-model within the adsorption tank. The thermal fluid energy sub-model within the adsorption tank is used to calculate the total generated heat energy based on adsorption kinetics and heat transfer through porous media. Q 热 The cold fluid energy sub-model inside the adsorption tank is used to calculate the cold energy provided by LNG in the heat exchange tubes. Q 冷 The nonlinear changes in LNG density, specific heat capacity, and thermal conductivity with temperature and pressure during the flow process are corrected in real time through the database; the spatial positions of the adsorption front and temperature front in the adsorption bed and the position of the LNG liquid level in the heat exchange tube with temperature changes are tracked through dynamic boundary conditions. The control unit operates based on the principle of energy matching. Q 热 ≈ Q 冷 With the goal of adjusting the LNG flow rate in the heat exchange tube in real time, and based on the reverse heat conduction algorithm, the magnitude and location of the adsorption heat source term inside the adsorption bed are inverted in real time according to the temperature of the outer wall of the heat exchange tube, so as to realize the dynamic control of the temperature field of the adsorption bed.

2. The BOG recovery system based on LNG-ANG coupling conditions according to claim 1, characterized in that, The modified activated carbon adsorbent uses coconut shell activated carbon with a specific surface area of ​​not less than 2000 m² / g as the matrix, and is compounded with 2-5 wt% thermally conductive filler. The thermally conductive filler is selected from one or more of graphite nanosheets, expanded graphite, carbon fiber or metal powder. The adsorbent is formed and extruded into spherical activated carbon by binder, and then undergoes secondary activation treatment to open up the pores. The volume adsorption capacity for methane in the temperature range of 160K-298K is not less than 140 V / V.

3. The BOG recovery system based on LNG-ANG coupling conditions according to claim 1, characterized in that, The built-in tube bundle heat exchange structure adopts a staggered arrangement, and the outer surface of the heat exchange tubes is welded with reinforced heat transfer fins. The reverse heat conduction algorithm is based on the real-time inversion of the outer wall temperature of the heat exchange tubes to determine the size of the adsorption heat source inside the adsorption bed and its position in the bed. Combined with the LNG variable property model, it calculates the LNG mass flow rate required to offset this heat. And output to the regulating valve; The formula is: ； in, The instantaneous mass flow rate of LNG that the system needs to regulate at time t; The heat generation rate of the adsorption bed at time t, obtained through the dynamic boundary and thermal conductivity inversion model; Based on the LNG inlet temperature and pressure measured by sensors inside the storage tank, the inlet specific enthalpy is read in real time by calling the built-in physical property database; The outlet specific enthalpy is read in real time based on the LNG outlet temperature and pressure measured by the heat exchanger tube outlet sensor.

4. A BOG recovery system based on LNG-ANG coupling conditions according to claim 3, characterized in that, The thermal fluid energy sub-model inside the adsorption storage tank, i.e., the total generated heat model, is as follows: （1）； in, Q 热 It is the total heat generated during the natural gas storage process. U 1 It is the total internal energy inside the adsorption tank. E k1 It is the total kinetic energy inside the adsorption tank. Q 1 represents the sum of convective heat transfer between natural gas and adsorbent within the adsorption tank, heat conduction between adsorbents, and heat conduction between the adsorbent and the tank wall. Q 2 represents the heat absorbed from the LNG heat exchanger tubes; ε represents the porosity of the adsorbent. For the density of natural gas, c is the density of the adsorbent. pg For the specific heat of natural gas, c Ps The specific heat of the adsorbent. Let λ be the Darcy velocity of the natural gas, T be the temperature inside the adsorption tank, P be the pressure inside the adsorption tank, and λ be the pressure inside the adsorption tank. e h is the effective thermal conductivity of the adsorbent. i The specific enthalpy of each component of natural gas. For the diffusion flux of each component of natural gas, For stress tensor, h w The heat transfer coefficient between LNG and the heat exchange tube wall is given. A Let be the area of ​​the LNG heat exchanger tube. T w The temperature of the heat exchange tube wall. T LNG The temperature of the natural gas; The energy sub-model of the cold fluid inside the adsorption storage tank, i.e., the variable property model, is as follows: （2）； in, Q 冷 It is the cold energy generated by convective heat transfer during the flow of LNG. U 2 It is the internal energy of the LNG in the heat exchanger tube. E k2 The kinetic energy of the LNG in the heat exchange tubes. Q 3 represents the energy generated by LNG during its flow due to heat conduction; For the density of LNG, c pl For the specific heat of LNG, Let λ be the LNG flow velocity within the heat exchanger tube. eff,f Thermal conductivity including turbulent motion; The dynamic boundary model is: First, a one-dimensional transient heat conduction equation along the radial direction of the heat exchanger tube wall is established as the physical basis for solving the reverse heat conduction problem. The transient heat conduction formula for the heat exchanger tube wall is: （3）； in, : Volumetric specific heat capacity of the heat exchanger tube wall material; Transient temperature of the heat exchanger tube wall at radial position r and time t; Thermal conductivity of the heat exchanger tube wall material; The initial conditions for formula (3) are: ； in, This refers to the initial temperature distribution of the heat exchange tube wall at the end of precooling or the end of the previous control cycle. The inner wall boundary conditions of formula (3) are: ； in, Let be the instantaneous heat flux density of the inner wall of the heat exchange tube at time t, and be the unknown boundary quantity to be determined. The inverse objective functional is calculated using the least squares method or regularization method: （4）； in, The objective function that needs to be minimized; T mea ( t i Temperature sensors arranged on the outer wall of the heat exchange tubes t i The actual temperature collected at all times; T calc ( t i，q ): Assuming the heat flux density of the inner wall is q Under the premise of, the theoretical temperature of the outer wall is calculated by formula (3); : Tikhonov regularization term; Set the initial iterative value of the heat flux density on the inner wall. The control unit iteratively modifies the unknown through the conjugate gradient method or the sequence function reduction method. until Reaching less than or equal to 10 -4 The value obtained is when the calculated theoretical temperature of the outer wall is very close to the actual collected temperature of the outer wall. This is the actual instantaneous heat flux density inside the tube; The heat flux density of the inner wall will be deduced. Using the inner wall boundary condition of formula (3) and combining the outer wall temperature measurement boundary and the initial temperature condition, the transient heat conduction equation of the heat exchanger tube wall is solved to obtain the transient temperature field of the heat exchanger tube wall. And then in Extraction of inner wall temperature : ； in, Let be the transient temperature of the inner wall of the heat exchanger tube at time t; Furthermore, considering the LNG-side fluid temperature The real-time convective heat transfer coefficient inside the pipe was calculated. ; According to Newton's law of cooling: ； The real-time convective heat transfer coefficient inside the heat exchange tube can be obtained. : ； in, Instantaneous heat flux density of the inner wall obtained by inversion; : Transient temperature of the inner wall of the tube obtained by inversion; The real-time bulk temperature of the LNG fluid inside the pipe is obtained by coupling calculations using the inlet and outlet temperatures, pressures, mass flow rates, and physical property databases of the heat exchanger pipe. The convective heat transfer coefficient inside the pipe dynamically changes with flow velocity, fluid properties, and temperature difference; Calculate the third type boundary that changes dynamically over time: The side boundary coupling equation of the adsorption bed is: ； : Effective thermal conductivity of the adsorption bed; Temperature gradient of the adsorption bed along the normal direction of the tube wall; : Local temperature at the interface between the adsorption bed and the outer wall of the heat exchange tube; : Equivalent convective heat transfer coefficient; based on inversion, the internal heat transfer coefficient of the pipe. The overall heat transfer coefficient, calculated by taking into account the thermal resistance of the pipe wall itself and applying it to the outer wall of the pipe, is also included. : The dynamic temperature of the LNG cold fluid inside the pipe; The calculation results are used as dynamic boundary conditions for the adsorption bed energy equation to achieve precise coupling between the adsorption side and the heat exchange side models.

5. A BOG recovery system based on LNG-ANG coupling conditions according to claim 1, characterized in that, The control unit has a built-in thermodynamic matching optimization module aimed at maximizing efficiency, whereby efficiency is defined as: ； in: ； in, For the actual utilization of the adsorption bed, The total cooling capacity provided to the LNG fluid; h and s are the specific enthalpy and specific entropy of the fluid under real-time temperature and pressure conditions, respectively; h0 and s0 are the specific enthalpy and specific entropy of the fluid under ambient reference temperature conditions, respectively. T 0 For ambient reference temperature; The control unit adjusts the LNG flow rate to make the system operate at the peak point of the efficiency curve, thereby achieving uniformity of the temperature difference field between the hot and cold fluids.

6. A BOG recovery system based on LNG-ANG coupling conditions according to claim 1, characterized in that, The built-in tube bundle heat exchange structure includes at least three heat exchange straight tubes, with reinforced heat transfer fins welded to the outside of the tubes. The tube diameter, tube spacing, and fin size of the heat exchange tubes are optimized by CFD. The heat exchange tubes are made of low-temperature resistant stainless steel, and LNG to be vaporized is introduced into the tubes as a refrigerant.

7. A BOG recovery method based on LNG-ANG coupling conditions, characterized in that, The BOG recovery system based on LNG-ANG coupling conditions according to any one of claims 1-6 includes the following steps: S1 Pre-cooling stage: Control the LNG cold energy supply unit to introduce LNG into the heat exchange structure of the adsorption tank, and use the sensible heat and latent heat of LNG to reduce the temperature of the adsorption bed to the preset working temperature range. S2 Co-adsorption Stage: The BOG inlet unit is activated, and the BOG, pressurized by the compressor, is introduced into the ANG adsorption tank, where it is captured by the activated carbon bed. Simultaneously, the LNG refrigerant supply pipeline is activated, allowing low-pressure LNG from the storage tank to flow into the enhanced heat exchange tube bundle in the adsorption tank after being pressurized by the submerged pump. This LNG absorbs the latent heat and adsorption heat of the BOG, and the heat-absorbed LNG is then sent to the downstream vaporizer to be converted into gaseous natural gas before being fed into the external pipeline network. During this process, data recorded in real time from flow meters, temperature sensors, and pressure sensors located at each node is collected, and the instantaneous total heat of generation is calculated using the built-in heat and mass transfer coupling model. Q 热 Instantaneous heat transfer capability with LNG cold fluid Q 冷 ; S3 Dynamic Regulation: Based on the Principle of Energy Matching Q 热 ≈ Q 冷 The control unit adjusts the LNG mass flow rate in the heat exchange tube according to the calculation results of the S2 stage. When the temperature gradient inside the adsorption bed exceeds the set threshold or the LNG properties in the heat exchange tube fluctuate drastically, the flow rate set value is adjusted through the correction algorithm to maintain the low temperature environment at the adsorption front. S4 Saturation Judgment and Switching: When the methane concentration at the outlet of the adsorption tank reaches the set threshold or the pressure inside the tank reaches the design upper limit, it is determined that the adsorption is saturated, the gas intake and cooling supply are stopped, and the system is switched to the desorption and regeneration unit. S5 Desorption and Regeneration: First, open the inlet and outlet valves of the heating medium and the external heater to introduce the heating medium into the heat exchange tube bundle in the ANG adsorption tank, so that the temperature of the adsorbent rises from the low temperature state to the desorption temperature, i.e., ≥298 K. Methane desorption causes the pressure inside the tank to rise. When the pressure reaches the external transmission threshold, open the top exhaust valve to send the high-pressure methane gas generated by desorption into the external transmission pipeline or downstream via the BOG compressor. When the pressure drops to near atmospheric pressure, close the top exhaust valve and turn on the vacuum pump. Under the dual action of high temperature and negative pressure, the residual methane is removed, and the extracted gas is sent to the collection pipeline. Finally, close the vacuum pump, heater and related valves, and introduce a small amount of room temperature natural gas or inert gas for micro-positive pressure replacement purging to remove residual impurities in the bed, complete the deep regeneration and reset to the standby state.

8. A BOG recovery method based on LNG-ANG coupling conditions according to claim 7, characterized in that, The preset operating temperature range in step S1 is 160K-200K; the temperature gradient setting threshold in step S3 is 10K; and the desorption setting temperature in step S5 is 353K±5K.

9. A BOG recovery method based on LNG-ANG coupling conditions according to claim 7, characterized in that, The adjustment of LNG flow rate in step S3 takes into account the property distortion of supercritical LNG near the quasi-critical point. A modified turbulence model is used to calculate the local convective heat transfer coefficient in the pipe. The modified turbulence model is selected from the RNG k-ε model or the SST k-ω model.

10. A BOG recovery method based on LNG-ANG coupling conditions according to claim 7, characterized in that, The energy matching principle described in step S3 Q 热 ≈ Q 冷 The PID algorithm built into the control unit is used to correct the flow rate set value when the temperature gradient inside the adsorption bed exceeds the set threshold or the LNG properties in the heat exchange tube fluctuate drastically, so as to maintain the low temperature environment at the adsorption front.

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