LNG ship CH4 unorganized escape flux monitoring method and system

Abstract

The invention relates to the technical field of ship methane monitoring, and discloses a method and a system for monitoring CH4 unorganized escape flux of an LNG (Liquefied Natural Gas) ship. A monitoring system adaptive to the motion state and environmental conditions of the ship is constructed by obtaining the navigational speed, course and wind speed data of the ship in real time, it is ensured that monitoring equipment is located at the optimal sampling position all the time, and the space capturing capacity for dispersive methane leakage is remarkably improved; secondly, the CO2 concentration is innovatively introduced to serve as a marker of tail gas interference, accurate removal of combustion source methane emission is achieved through the concentration ratio relation of CH4 and CO2 in tail gas, and pure leakage concentration data of unorganized escape is effectively separated out; and finally, in combination with the dynamically corrected diffusion coefficient and diffusion equation, discrete concentration distribution data is converted into an accurate escape flux value, the applicability limitation of a traditional static diffusion model in a ship motion scene is overcome, and reliable technical support is provided for quantitative supervision of ship methane leakage.

Description

Technical Field

[0001] The present invention relates to the technical field of ship methane monitoring, and particularly to a method and system for monitoring the unorganized escape flux of CH4 on LNG ships. Background Art

[0002] The use of liquefied natural gas (LNG) as a marine fuel is growing rapidly, and its promotion plays an important role in the decarbonization process of the shipping industry. However, the problem of unorganized methane escape accompanying this transformation process is becoming a new environmental challenge. During the operation of ships, there are risks of trace methane leakage in links such as the fuel supply system, engine combustion chamber, and natural gas storage and transportation equipment. Such emissions are characterized by dispersion and intermittence and are difficult to be completely captured by traditional tail gas treatment systems. Especially during the loading and unloading operations of LNG carriers, working conditions such as changes in storage tank pressure and seal failure at pipeline joints will exacerbate the escape of gaseous methane, forming an unorganized emission source that is difficult to accurately measure.

[0003] The characteristics of methane as a potent greenhouse gas result in significant differences from carbon dioxide in terms of environmental effects. Although its persistence time in the atmosphere is short, its ability to absorb solar radiation in the initial stage after release is extremely prominent. This short-term high-intensity warming effect directly exacerbates the risk of imbalance in the global climate system. The superposition of the continuous expansion of the international shipping industry and the process of ship fuel cleaning has made the methane escape problem no longer limited to the impact on local environmental quality, but has evolved into a key factor related to global carbon budget control.

[0004] The existing regulatory system has obvious limitations in the monitoring means of ship methane emissions. The traditional on-board inspection method is not only subject to the cooperation willingness of ship operators, but also difficult to achieve real-time dynamic monitoring. The dispersion characteristics of unorganized emission sources make it impossible for fixed monitoring points to effectively capture instantaneous concentration fluctuations, and manual sampling has inherent deficiencies in terms of spatial coverage and timeliness.

[0005] Therefore, how to accurately and quickly monitor the unorganized escape flux of CH4 on LNG ships has become an urgent problem to be solved. Summary of the Invention

[0006] In order to accurately and quickly monitor the unorganized escape flux of CH4 on LNG ships, on the one hand, the present invention provides a method for monitoring the unorganized escape flux of CH4 on LNG ships, including the following steps: S1: Obtain the navigation information of the LNG ship and the wind speed; the navigation information includes the ship speed and heading of the ship; S2: Adjust the real-time distance between the monitoring device and the LNG ship according to the navigation information and the wind speed, and determine the sampling path of the monitoring device; S3: The monitoring device collects data along the sampling path, and the obtained sampling information includes the CH4 concentration and the CO2 concentration; S4: According to the CO2 concentration, by using the concentration ratio relationship between CH4 and CO2 in the tail gas, eliminate the CH4 concentration in the tail gas in the sampling information to obtain the concentration distribution of unorganized escaped CH4 of the LNG ship; S5: According to the concentration distribution of unorganized escaped CH4 of the LNG ship, combined with the corrected diffusion coefficient, use the diffusion equation to obtain the unorganized escape flux of CH4 of the LNG ship.

[0007] Furthermore, according to the navigation information and the wind speed, adjust the real-time distance between the monitoring device and the LNG ship to determine the sampling path of the monitoring device, including the following steps: S21: Based on the ship's speed and wind speed at a future moment, calculate the effective length of the prospective plume; S22: According to the effective length of the prospective plume and the preset coverage range, determine the coverage range of the sampling path; S23: Based on the actual speed and the real-time distance between the monitoring device and the LNG ship, calculate the plume compensation factor; S24: According to the plume compensation factor, adjust the coverage range of the sampling path to determine the sampling path of the monitoring device.

[0008] Furthermore, the adjustment of the coverage range of the sampling path according to the plume compensation factor includes: S241: Adjust the coverage range of the sampling path according to the plume compensation factor to obtain the optimized coverage range of the sampling path; S242: Based on the vector synthesis of the course and the wind speed direction, determine the main axis direction of plume diffusion; S243: With the main axis direction as the reference, position the monitoring device within the optimized coverage range of the sampling path on the leeward side of the ship.

[0009] Furthermore, the determination of the sampling path of the monitoring device is specifically: S244: According to the optimized coverage range of the sampling path, determine the horizontal boundary and vertical boundary of the sampling path; S245: According to the preset spacing and the plume compensation factor, calculate the horizontal boundary and vertical boundary of the sampling path respectively to obtain the number of horizontal path points and the number of vertical path points; S246: According to the number of horizontal path points and the number of vertical path points, in the ship coordinate system, determine the coordinates of the horizontal path points of each layer and the coordinates of the vertical path points of each column to obtain the sampling path of the monitoring device.

[0010] Further, in S21, based on the ship's speed and wind speed at a future moment, calculate the prospective plume effective length, and the calculation formula is: ; In the formula, represents the prospective plume effective length, represents the ship's speed at a future moment, represents the wind speed, and L0 represents the static plume length.

[0011] Further, in S23, based on the actual speed and the real-time distance between the monitoring device and the LNG ship, calculate the plume compensation factor, and the calculation formula is: ; In the formula, r represents the plume compensation factor, m represents the diffusion coupling coefficient, represents the monitoring time interval, represents the real-time distance between the monitoring device and the LNG ship, represents the actual speed.

[0012] Further, in S5, according to the concentration distribution of the unorganized escape CH4 of the LNG ship, combined with the corrected diffusion coefficient, through the diffusion equation, obtain the unorganized escape flux of CH4 of the LNG ship, including: S51: Simulate the ship's wake flow field through fluid dynamics, and establish a mapping relationship between the speed and the turbulent flow field distribution; S52: Correct the diffusion coefficient according to the mapping relationship between the speed and the turbulent flow field distribution and the real-time speed; S53: According to the concentration distribution of the unorganized escape CH4 of the LNG ship and the corrected diffusion coefficient, through the diffusion equation, obtain the unorganized escape flux of CH4 of the LNG ship.

[0013] Further, in S51, simulating the ship's wake flow field through fluid dynamics and establishing a mapping relationship between the speed and the turbulent flow field distribution includes: Determine the reference speed of the LNG ship according to the ship design requirements; At the reference speed, simulate the ship's wake flow field through fluid dynamics, determine the basic diffusion coefficient at the reference speed, and obtain the mapping relationship between the speed and the turbulent flow field distribution; The calculation formula for the basic diffusion coefficient is: ; In the formula, represents the basic diffusion coefficient, represents the turbulent model constant, represents the turbulent kinetic energy, represents the dissipation rate.

[0014] Furthermore, the correction formula for the correction diffusion coefficient is as follows: ; In the formula, represents the corrected diffusion coefficient, represents the basic diffusion coefficient, represents the reference ship speed, represents the real-time ship speed.

[0015] On the other hand, the present invention also provides a monitoring system for the unorganized escape flux of CH4 on an LNG ship, which is used to implement the monitoring method for the unorganized escape flux of CH4 on an LNG ship described in any one of the above, including: an information acquisition module, a sampling path determination module, monitoring equipment, a sampling information processing module, and a flux calculation module; The information acquisition module is used to acquire the navigation information and wind speed of the LNG ship; the navigation information includes the ship speed and heading of the ship; The sampling path determination module is used to adjust the real-time distance between the monitoring equipment and the LNG ship according to the navigation information and wind speed, and determine the sampling path of the monitoring equipment; The monitoring equipment is used to collect data along the sampling path, and the sampling information obtained includes the CH4 concentration and the CO2 concentration; The sampling information processing module is used to eliminate the CH4 concentration in the exhaust gas in the sampling information according to the CO2 concentration through the concentration ratio relationship between CH4 and CO2 in the exhaust gas, and obtain the concentration distribution of the unorganized escape CH4 of the LNG ship; The flux calculation module is used to obtain the unorganized escape flux of CH4 on the LNG ship through the diffusion equation in combination with the corrected diffusion coefficient according to the concentration distribution of the unorganized escape CH4 of the LNG ship.

[0016] The embodiments of the present invention have the following technical effects: The monitoring method for the unorganized escape flux of CH4 on the LNG ship provided by the present invention constructs a monitoring system that adapts to the ship's motion state and environmental conditions by real-time acquiring ship speed, heading and wind speed data, ensuring that the monitoring equipment is always in the best sampling position, and significantly improving the spatial capture ability for diffusive methane leakage; secondly, innovatively introducing the CO2 concentration as an indicator of exhaust gas interference, and using the concentration ratio relationship between CH4 and CO2 in the exhaust gas to accurately eliminate the methane emissions from combustion sources, effectively separating the pure leakage concentration data of unorganized escape; finally, combining the dynamically corrected diffusion coefficient and the diffusion equation to convert the discrete concentration distribution data into accurate escape flux values, overcoming the applicability limitations of traditional static diffusion models in ship motion scenarios, and providing reliable technical support for the quantitative supervision of ship methane leakage. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0018] Figure 1 is a flowchart of the steps of a method for monitoring the unorganized escape flux of CH4 on an LNG ship provided by an embodiment of the present invention; Figure 2 is a schematic diagram of a drone carrying a sensor provided by an embodiment of the present invention; Figure 3 is a schematic diagram of the sampling path of the monitoring device provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] To make the objectives, technical solutions, and advantages of the present invention clearer, the following will clearly and completely describe the technical solutions of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope protected by the present invention.

[0020] The existing regulatory system has limitations in the monitoring means of ship methane emissions: the traditional on-board detection method is not only restricted by the cooperation willingness of the ship operator, but also difficult to achieve real-time dynamic monitoring; the dispersion characteristics of unorganized emission sources lead to the inability of fixed monitoring points to effectively capture instantaneous concentration fluctuations, and manual sampling has inherent deficiencies in terms of spatial coverage and timeliness.

[0021] Based on this problem, the present invention provides a method for monitoring the unorganized escape flux of CH4 on an LNG ship, as Figure 1 shown, including the following steps: S1: Obtain the navigation information and wind speed of the LNG ship; the navigation information includes the ship's speed and heading; among them, the speed and heading include both the current actual speed and actual navigation, and may also include the predicted speed and predicted heading at future times; During the operation of a liquefied natural gas carrier, the monitoring of unorganized methane leakage needs to comprehensively consider the interaction between ship dynamics and environmental factors. Therefore, the actual speed and actual navigation data can be collected in real time through navigation units installed at multiple points on the hull, combined with the real-time wind speed information obtained from a weather station. Ships usually have an automatic identification system and predicted track data. Therefore, the predicted speed and predicted heading at future times can be directly obtained from the automatic identification system of the ship.

[0022] S2: Adjust the real-time distance between the monitoring device and the LNG ship according to the navigation information and wind speed, and determine the sampling path of the monitoring device. Exemplarily, the monitoring device can be a drone carrying a sensor to extract air samples for analyzing the mixing ratio rich in target species, such as Figure 2 shown. Its compact size and light weight make it possible to be used as a payload on a drone. Figure 2 In [the figure], 1 is a wind speed monitoring device for wind speed monitoring, 2 is a gas collection device for gas collection. The position of the sampling inlet makes it not affected by the drone itself. The black long rod part at the front end of this part draws the gas to be monitored into the box at the rear end, and a laser CO2 sensor and a laser CH4 sensor are arranged in the box.

[0023] The laser CO2 sensor and the laser CH4 sensor adopt the advanced tunable diode laser absorption spectroscopy (TDLAS) detection technology. The detection range of the CH4 sensor is 3% - 100% LEL; the detection range of the CO2 sensor is 0 - 1000 PPM.

[0024] CO2 and CH4 share a detection gas chamber and are detected in the same gas chamber with the same sampling frequency to ensure that the concentration curves of CO2 and CH4 maintain good synchronization for subsequent evaluation of methane escape in ship exhaust by calculating the CH4 / CO2 ratio.

[0025] The real-time monitoring of the CO2 concentration in the air by the monitoring device. Once it is found that the CO2 concentration is higher than the preset air background value, it indicates that ship exhaust has been detected at this time, and then sampling starts according to the sampling path in the following steps. The methane monitored at this time includes the methane generated by the exhaust + the methane escaping without organization. Until the CO2 concentration returns to not higher than the preset air background value, the drone carrying the monitoring device continues to fly downwind following the ship's chimney. Exemplarily, the preset value can be 50 ppm, and this value can be set according to the monitoring accuracy. If the monitoring accuracy requirement is high, this value is appropriately reduced.

[0026] In some embodiments, adjusting the real-time distance between the monitoring device and the LNG ship according to the navigation information and wind speed, and determining the sampling path of the monitoring device includes the following steps: S21: Calculate the effective length of the prospective plume based on the ship's speed and wind speed at a future time. In some embodiments, in S21, calculating the effective length of the prospective plume based on the ship's speed and wind speed at a future time, the calculation formula is: ; In the formula, It represents the effective length of the forward-looking smoke plume and is used to quantify the physical deformation of the smoke plume stretched by the ship speed. Indicates the speed of the ship at a future time. represents wind speed and L0 represents static plume length.

[0027] The construction of the forward-looking plume length formula is based on the simplified solution of the convection-diffusion equation, which equates the ship speed to the additional wind speed component. The static plume length L0 in the formula is calibrated through wind tunnel experiments to reflect the typical diffusion characteristics of a specific ship type at rest. The ratio of the ship's speed to the wind speed at a future moment characterizes the degree of influence of the ship's own motion on the plume stretching effect.

[0028] When a ship sails against the wind, the speed component and the natural wind speed produce a superposition effect, significantly increasing the effective extension length of the smoke plume. This formula quantifies this motion enhancement effect through a linear combination relationship, allowing the monitoring system to predict the development trend of the smoke plume in advance.

[0029] The forward-looking calculation of the length of the smoke plume fully considers the impact of the ship's future navigation state on the spread of the leak. Based on the predicted track data of the ship's automatic identification system, the speed and wind speed at future moments are superimposed and analyzed to calculate the effective length of the smoke plume that may extend. This length value is input as a basic parameter into the monitoring path planning algorithm to ensure that the sampling range always covers the frontier of the leak spread in advance, preventing sudden situations such as sudden acceleration or deceleration of the ship, and the risk of lag or inaccuracy caused by the drone leaving the core area of ​​the smoke plume due to the acceleration of the ship.

[0030] S22: Determine the sampling path coverage based on the forward-looking effective length of the smoke plume and the preset coverage; For example, based on historical navigation and wind direction data, the coverage range is preset. For example, the horizontal coverage range is set to [0.8L eff-future , 1.2L eff-future ], and the vertical coverage is [-0.2L eff-future , 0.2L eff-future ].

[0031] S23: Calculate the plume compensation factor based on the actual speed, the real-time distance between the monitoring equipment and the LNG ship; In some implementations, in S23, the plume compensation factor is calculated based on the actual speed and the real-time distance between the monitoring equipment and the LNG ship, and the calculation formula is: ; In the formula, r represents the plume compensation factor, m represents the diffusion coupling coefficient, Indicates the monitoring time interval, Indicates the real-time distance between the monitoring equipment and the LNG ship. Indicates the actual ship speed.

[0032] The calculation formula of the plume compensation factor reveals the dynamic balance relationship between monitoring delay and spatial coverage. Diffusion coupling coefficient k Reflects the coupling characteristics between the ship wake flow field and plume diffusion. It is a dimensionless coefficient calibrated through experiments, comprehensively reflecting complex factors such as atmospheric turbulence intensity and gas molecule diffusion rate, and is used to quantify the non-linear impact of ship speed on the plume stretching effect. Its value is determined through multi-condition experiments, and regression analysis is performed on multiple sets of experimental data (different ship speeds, wind speeds, distances) to determine k The optimal value, which can make the formula adapt to different ship types (such as the wake differences between container ships and tankers) and environmental conditions (such as open waters and narrow channels). The time interval parameter is directly related to the sampling frequency of the monitoring equipment, ensuring that the data update rate matches the ship's motion state. The real-time distance between the monitoring equipment and the LNG ship in the formula is in reciprocal form, reflecting the adjustment effect of the monitoring equipment proximity on the compensation intensity. When Shortens, the increment of the compensation factor decreases, avoiding resource waste caused by over-compensation. Successfully solves the problem of spatio-temporal synchronization in mobile monitoring and can still maintain continuous coverage of the sampling grid under sudden changes in ship speed conditions.

[0033] The plume compensation factor r is used to correct the effective length of the plume, directly affecting the coverage range of the UAV sampling path. Use r to scale the prospective plume effective length and adjust the coverage range. According to the real-time distance between the monitoring equipment and the LNG ship and the monitoring time interval

[0034] S24: Adjust the coverage range of the sampling path according to the plume compensation factor to determine the sampling path of the monitoring equipment.

[0035] In some embodiments, adjusting the coverage range of the sampling path according to the plume compensation factor includes: S241: Adjust the coverage range of the sampling path according to the plume compensation factor to obtain the optimized coverage range of the sampling path; Exemplarily, multiply the plume compensation factor by the coverage range of the sampling path to optimize the coverage range.

[0036] S242: Determine the main axis direction of plume diffusion based on the vector synthesis of the heading and the wind speed direction; Exemplarily, the main axis of plume diffusion is determined using a vector synthesis method by spatially vectorially superposing the ship's heading and the real-time wind direction. By establishing a three-dimensional coordinate system, the heading vector is projected onto the horizontal plane and synthesized with the wind speed vector to obtain the dominant direction of plume diffusion. This direction serves as the reference axis for monitoring path layout to ensure that the sampling points are distributed along the direction of the maximum concentration gradient.

[0037] S243: Based on the main axis direction as a reference, position the monitoring equipment within the optimized sampling path coverage area downwind of the ship.

[0038] By tracking the changes in the main axis of diffusion in real time, the system can quickly capture the spatial migration trajectory of sudden leakage events, significantly enhancing the response ability to transient leakage events.

[0039] By first setting the path coverage area (step S22): Based on the predicted ship speed at a future time Plan the monitoring area of the monitoring equipment in advance to avoid path lag caused by ship movement; then correct the plume parameters (steps S23 and S24): Based on the real-time distance between the monitoring equipment and the LNG ship and the actual ship speed , determine the plume compensation factor and adjust the sampling path coverage area to ensure that the path matches the current plume shape.

[0040] In some embodiments, determining the sampling path of the monitoring equipment specifically includes: S244: Determine the horizontal and vertical boundaries of the sampling path according to the optimized sampling path coverage area; S245: Calculate the horizontal and vertical boundaries of the sampling path respectively according to the preset spacing and the plume compensation factor to obtain the number of horizontal path points and the number of vertical path points; S246: According to the number of horizontal path points and the number of vertical path points, in the ship coordinate system, determine the coordinates of the horizontal path points of each layer and the coordinates of the vertical path points of each column to obtain the sampling path of the monitoring equipment. As Figure 3 shown, if the CO2 concentration is detected to be 50 ppm higher than the air background at point a, then sampling is carried out in the way of traversing the coordinates of the horizontal path points of each layer and the coordinates of the vertical path points of each column.

[0041] Exemplarily: (1) Establish the ship's real-time coordinate system Origin setting: Use the ship's real-time position (obtained by differential GPS) as the coordinate origin O(0, 0, 0); Axial definition: X-axis: Along the ship's real-time heading θ ship ; Y-axis: perpendicular to the X-axis and pointing towards the starboard side; Z-axis: perpendicular to the sea level and pointing upwards.

[0042] (2) Determine the horizontal cross-section boundary Coverage correction: Adjust the path coverage range R based on the compensation factor r cover-new = [0.8×L eff-future ×r, 1.2×L eff-future ×r]; Definition of the horizontal cross-section: The length range therein: along the plume diffusion direction of the X-axis, covering X ∈ [0.8×L eff-future ×r, 1.2×L eff-future ×r]; The width range: along the transverse diffusion range of the Y-axis, according to the effective plume width W eff = 0.2×L eff-future ×r, set Y ∈ [−Weff, Weff].

[0043] (3) Generate equally spaced path points Calculation of path point density: ; Among them, is the number of path points in the X-axis direction, is the number of path points in the Y-axis direction, d base is the reference spacing (such as 10 meters).

[0044] Generation of path point coordinates: Along the X-axis, generate a point sequence x at a spacing of d x = d base ×r, where i = 0.8×L eff-future ×r + i×d x (i = 0, 1,..., N x ); Along the Y-axis, generate a point sequence y at a spacing of d y = d base ×r, where j = −W eff + j×d y (j = 0, 1,..., N y ); The horizontal cross-section path point set is P horizontal = {(x i , y j , z0)}, where z0 is the current sampling height.

[0045] (4) Dynamic path optimization Course adaptation adjustment: According to the real-time course θship , perform a rotation transformation on the path point coordinates ( x, y ), and obtain the transformed path point coordinates ( , ): ; ; Through the rotation transformation, obstacle avoidance correction is realized. If the path point conflicts with an obstacle (such as other ships), delete the conflict point and re-interpolate.

[0046] S3: The monitoring device collects data along the sampling path, and the obtained sampling information includes the CH4 concentration and the CO2 concentration; it also includes the position information of the sampling points at the same time.

[0047] S4: According to the CO2 concentration, through the concentration ratio relationship between CH4 and CO2 in the tail gas, eliminate the CH4 concentration in the tail gas from the sampling information, and obtain the concentration distribution of unorganized escaped CH4 of the LNG ship; In some embodiments, in S4, according to the CO2 concentration, through the concentration ratio relationship between CH4 and CO2 in the tail gas, eliminate the CH4 concentration in the tail gas from the sampling information, and obtain the concentration distribution of unorganized escaped CH4 of the LNG ship, including: S41: Obtain the concentration of CH4 and the concentration of CO2 in the historical tail gas, and fit to obtain the concentration ratio relationship between CH4 and CO2 in the tail gas; S42: According to the CO2 concentration, through the concentration ratio relationship between CH4 and CO2 in the tail gas, determine the concentration of CH4 in the tail gas; S43: Eliminate the concentration of CH4 in the tail gas from the sampling information to obtain the concentration of unorganized escaped CH4 of the LNG ship; S44: Based on the concentration of unorganized escaped CH4 of the LNG ship and the position information in the sampling information, obtain the concentration distribution of unorganized escaped CH4 of the LNG ship.

[0048] Although due to the dilution of the exhaust plume, the absolute concentration of the target gas decreases with the increase of the distance from the chimney, in the mixed and turbulent plume emitted from the chimney, the concentrations of these two gases maintain a certain proportional relationship. Therefore, the method in step S4 effectively solves the problem of component aliasing between the combustion source and the leakage source, and can still maintain a stable separation accuracy even under the condition of frequent fluctuations in the main engine load.

[0049] S5: According to the concentration distribution of unorganized escaped CH4 of the LNG ship, combined with the corrected diffusion coefficient, through the diffusion equation, obtain the unorganized escape flux of CH4 of the LNG ship.

[0050] In some embodiments, in S5, according to the concentration distribution of unorganized escaped CH4 from the LNG ship and in combination with the corrected diffusion coefficient, the unorganized escape flux of CH4 from the LNG ship is obtained through the diffusion equation, including: S51: Simulate the wake flow field of the ship through hydrodynamics and establish the mapping relationship between the ship speed and the turbulent flow field distribution; In some embodiments, in S51, simulating the wake flow field of the ship through hydrodynamics and establishing the mapping relationship between the ship speed and the turbulent flow field distribution includes: S511: Determine the reference ship speed according to the ship design requirements; for example, use the designed ship speed required during ship design as the reference ship speed, and the designed ship speed is the speed with the highest efficiency or the most stable emissions determined during ship design. Or use the ship speed corresponding to a specific emission standard as the reference ship speed, and the most energy-efficient ship speed can also be used as the reference ship speed.

[0051] S512: At the reference ship speed, simulate the wake flow field of the ship through hydrodynamics, determine the basic diffusion coefficient at the reference ship speed, and obtain the mapping relationship between the ship speed and the turbulent flow field distribution; The construction of the mapping relationship of the turbulent flow field distribution adopts computational fluid dynamics simulation technology, and the existing simulation technology can be directly used, and the specific process of the simulation will not be elaborated here.

[0052] Taking the reference ship speed as the reference working condition and as the only input ship speed, the turbulent parameters (k, ϵ) of the wake flow field of the ship at this ship speed can be obtained by solving the Navier-Stokes equation, and the basic diffusion coefficient can be obtained therefrom, forming the mapping relationship between the ship speed and the turbulent flow field distribution. The calculation formula is: ; In the formula, represents the basic diffusion coefficient, represents the turbulent model constant, represents the turbulent kinetic energy, represents the dissipation rate.

[0053] The calculation of the basic diffusion coefficient is based on the standard turbulent model, that is, the hydrodynamic simulation model established with the reference ship speed. The turbulent kinetic energy characterizes the irregular motion intensity of fluid particles, and the dissipation rate reflects the conversion rate of kinetic energy into thermal energy. By introducing the turbulent model constant , the complex turbulent transport process is simplified into a computable algebraic relationship.

[0054] S52: Correct the diffusion coefficient according to the mapping relationship between the ship speed and the turbulent flow field distribution and the real-time ship speed; In some embodiments, the correction formula for correcting the diffusion coefficient is: ; In the formula, represents the corrected diffusion coefficient, represents the basic diffusion coefficient, which is fixed at the reference ship speed and is the diffusion coefficient under this condition, represents the reference ship speed, which is the calibrated benchmark ship speed, represents the real-time ship speed.

[0055] The real-time correction of the diffusion coefficient adopts the form of a logarithmic function. This mathematical expression can effectively capture the non-linear influence of ship speed changes on the turbulence intensity. Because the introduction of the logarithmic function effectively smooths the parameter jumps caused by sudden changes in ship speed and avoids numerical instability during the calculation process. When the ship accelerates, the growth rate of the correction term gradually slows down, which conforms to the physical law of kinetic energy conversion in fluid mechanics. The corrected diffusion coefficient can more accurately reflect the flow field disturbance effect caused by the hull movement.

[0056] Although , which is fixed itself and is a static parameter, it needs to be dynamically corrected according to the real-time ship speed of the ship in practical applications: When , directly use the reference value; When , adjust through the correction formula to obtain matched with the current ship speed.

[0057] S53: According to the concentration distribution of the unorganized escape CH4 of the LNG ship and the corrected diffusion coefficient, the unorganized escape flux of CH4 of the LNG ship is obtained through the diffusion equation.

[0058] Exemplarily, based on Fick's second law, the diffusion equation can be set to obtain the unorganized escape flux of CH4 of the LNG ship at each point.

[0059] When monitoring the unorganized escape flux of CH4 from LNG ships, the present invention acquires the ship's speed, heading and wind speed data in real time, builds a monitoring system that is adaptive to the ship's motion state and environmental conditions, ensures that the monitoring equipment is always in the best sampling position, and significantly improves the spatial capture capability of diffuse methane leakage; secondly, innovatively introduces CO2 concentration as a marker of exhaust interference, and uses the concentration ratio of CH4 to CO2 in exhaust gas to achieve accurate elimination of methane emissions from combustion sources, effectively separating the pure leakage concentration data of unorganized escape; finally, combined with the dynamically corrected diffusion coefficient and diffusion equation, the discrete concentration distribution data is converted into an accurate escape flux value, overcoming the applicability limitations of the traditional static diffusion model in the ship motion scenario, and providing reliable technical support for the quantitative supervision of ship methane leakage. Each step works synergistically to achieve accurate and rapid monitoring of unorganized escape flux of CH4 from LNG ships.

[0060] On the other hand, the present invention also provides a monitoring system for the unorganized CH4 escape flux of an LNG ship, which is used to implement the above-mentioned monitoring method for the unorganized CH4 escape flux of an LNG ship, including: an information acquisition module, a path determination module, a monitoring device, a sampling information processing module, and a flux calculation module; An information acquisition module is used to acquire the navigation information and wind speed of the LNG ship; the navigation information includes the speed and heading of the ship; A path determination module is used to adjust the real-time distance between the monitoring equipment and the LNG ship according to the navigation information and the wind speed, and determine the sampling path of the monitoring equipment; A monitoring device, used for the monitoring device to collect data along the sampling path, and the obtained sampling information includes CH4 concentration and CO2 concentration; A sampling information processing module is used to remove the CH4 concentration of the tail gas in the sampling information according to the CO2 concentration and the concentration ratio of CH4 and CO2 in the tail gas, so as to obtain the concentration distribution of the unorganized escaped CH4 of the LNG ship; The flux calculation module is used to obtain the unorganized escape flux of CH4 from the LNG ship through the diffusion equation according to the concentration distribution of the unorganized escape CH4 from the LNG ship and the modified diffusion coefficient.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the technical solutions of the embodiments of the present invention.

Claims

1. A monitoring method for the unorganized escape flux of CH4 in an LNG ship, characterized in that, It includes the following steps: S1: Obtain the navigation information of the LNG ship and the wind speed; the navigation information includes the ship's speed and heading; S2: Adjust the real-time distance between the monitoring device and the LNG ship according to the navigation information and the wind speed, and determine the sampling path of the monitoring device; S3: The monitoring device collects data along the sampling path, and the obtained sampling information includes the CH4 concentration and the CO2 concentration; S4: According to the CO2 concentration, through the concentration ratio relationship between CH4 and CO2 in the tail gas, eliminate the CH4 concentration in the tail gas in the sampling information, and obtain the concentration distribution of unorganized escaped CH4 of the LNG ship; S5: According to the concentration distribution of unorganized escaped CH4 of the LNG ship, combined with the corrected diffusion coefficient, through the diffusion equation, obtain the unorganized escape flux of CH4 of the LNG ship.

2. The monitoring method for the unorganized escape flux of CH4 in an LNG ship according to claim 1, characterized in that, In S2, adjusting the real-time distance between the monitoring device and the LNG ship according to the navigation information and the wind speed, and determining the sampling path of the monitoring device includes the following steps: S21: Calculate the prospective plume effective length based on the ship's speed and wind speed at a future time; S22: Determine the sampling path coverage according to the prospective plume effective length and the preset coverage; S23: Calculate the plume compensation factor based on the actual speed and the real-time distance between the monitoring device and the LNG ship; S24: Adjust the sampling path coverage according to the plume compensation factor to determine the sampling path of the monitoring device.

3. The monitoring method for the unorganized escape flux of CH4 in an LNG ship according to claim 2, characterized in that, Adjusting the sampling path coverage according to the plume compensation factor includes: S241: Adjust the sampling path coverage according to the plume compensation factor to obtain the optimized sampling path coverage; S242: Determine the main axis direction of plume diffusion based on the vector synthesis of the heading and the wind speed direction; S243: Taking the main axis direction as the reference, position the monitoring device within the optimized sampling path coverage in the downwind direction of the ship.

4. The monitoring method for the unorganized escape flux of CH4 in an LNG ship according to claim 3, characterized in that, Determining the sampling path of the monitoring device specifically is: S244: Determine the horizontal boundary and vertical boundary of the sampling path according to the optimized sampling path coverage; S245: Calculate the horizontal path point number and vertical path point number of the sampling path respectively according to the preset spacing and the plume compensation factor; S246: According to the horizontal path point number and vertical path point number, in the ship coordinate system, determine the coordinates of the horizontal path points of each layer and the coordinates of the vertical path points of each column to obtain the sampling path of the monitoring device.

5. The monitoring method for the unorganized escape flux of CH4 in an LNG ship according to claim 2, characterized in that, In S21, calculating the prospective plume effective length based on the ship's speed and wind speed at a future time, the calculation formula is: ； In the formula, represents the effective length of the prospective plume, represents the ship's speed at a future time, represents the wind speed, and L0 represents the static plume length.

6. The monitoring method for the unorganized escape flux of CH4 in an LNG ship according to claim 2, characterized in that, In S23, calculating the plume compensation factor based on the actual speed and the real-time distance between the monitoring device and the LNG ship, the calculation formula is: ； In the formula, r represents the plume compensation factor, m represents the diffusion coupling coefficient, represents the monitoring time interval, represents the real-time distance between the monitoring device and the LNG ship, represents the actual speed.

7. The monitoring method for the unorganized escape flux of CH4 in an LNG ship according to claim 1, characterized in that, In S5, according to the concentration distribution of unorganized escaped CH4 of the LNG ship, combined with the corrected diffusion coefficient, through the diffusion equation, obtaining the unorganized escape flux of CH4 of the LNG ship includes: S51: Simulate the ship wake flow field through fluid dynamics, and establish the mapping relationship between the speed and the turbulent flow field distribution; S52: correcting the diffusion coefficient according to the mapping relationship between the ship speed and the turbulence field distribution and the real-time ship speed; S53: According to the concentration distribution of the unorganized escaped CH4 from the LNG ship and the corrected diffusion coefficient, the unorganized escape flux of CH4 from the LNG ship is obtained through the diffusion equation.

8. The monitoring method for the unorganized escape flux of CH4 in an LNG ship according to claim 7, wherein, In S51, the ship wake flow field is simulated by fluid dynamics to establish a mapping relationship between the ship speed and the turbulence field distribution, including: Determine the reference speed of LNG carriers based on ship design requirements; At a reference speed, the wake flow field of the ship is simulated by fluid dynamics, the basic diffusion coefficient at the reference speed is determined, and the mapping relationship between the speed and the turbulence field distribution is obtained; The calculation formula of the basic diffusion coefficient is: ； In the formula, represents the base diffusion coefficient, represents the turbulence model constant, represents the turbulent kinetic energy, represents the dissipation rate.

9. The monitoring method for the unorganized escape flux of CH4 in an LNG ship according to claim 7, wherein, The correction formula of the corrected diffusion coefficient is: ； In the formula, represents the corrected diffusion coefficient, represents the basic diffusion coefficient, represents the reference speed, represents the real-time speed.

10. A monitoring system for the unorganized escape flux of CH4 in an LNG ship, wherein, A method for monitoring the unorganized escape flux of CH4 from an LNG ship according to any one of claims 1 to 9, comprising: an information acquisition module, a path determination module, a monitoring device, a sampling information processing module, and a flux calculation module; An information acquisition module is used to acquire the navigation information and wind speed of the LNG ship; the navigation information includes the speed and heading of the ship; A path determination module is used to adjust the real-time distance between the monitoring equipment and the LNG ship according to the navigation information and the wind speed, and determine the sampling path of the monitoring equipment; A monitoring device, used for the monitoring device to collect data along the sampling path, and the obtained sampling information includes CH4 concentration and CO2 concentration; A sampling information processing module is used to remove the CH4 concentration of the tail gas in the sampling information according to the CO2 concentration and the concentration ratio of CH4 and CO2 in the tail gas, so as to obtain the concentration distribution of the unorganized escaped CH4 of the LNG ship; The flux calculation module is used to obtain the unorganized escape flux of CH4 from the LNG ship through the diffusion equation according to the concentration distribution of the unorganized escape CH4 from the LNG ship and the modified diffusion coefficient.

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