A method and system for calculating cooling loss during the pipeline transportation of cryogenic liquefied hydrocarbons.

Abstract

This invention discloses a method for calculating the cold loss during the pipeline transportation of cryogenic liquefied hydrocarbons. The method includes: dividing the pipeline into several sections and measuring the wall temperature and air temperature of each section; obtaining fluid property data for each section, consisting of air kinematic viscosity and thermal conductivity, based on the wall temperature and air temperature; classifying the air on the outer wall of each section into three flow states: laminar, transitional, and turbulent, based on the fluid property data; and obtaining the cold loss of each section based on the flow state of the air on the outer wall, thereby obtaining the cold loss of the cryogenic liquefied hydrocarbons during pipeline transportation. This invention provides a more scientific and reasonable calculation method, improves the accuracy of cold loss calculation, and enables a scientific and precise assessment of the cold energy utilization value of cryogenic pipelines.

Description

Technical Field

[0001] This invention relates to a method and system for calculating cold loss during the pipeline transportation of cryogenic liquefied hydrocarbons, belonging to the field of cryogenic pipeline technology. Background Technology

[0002] With the ongoing efforts in energy conservation and emission reduction, the demand for cryogenic liquefied hydrocarbons (CHL), a highly efficient and clean energy source, is constantly increasing. CHL requires extremely low temperatures during transportation to maintain its liquid state. Specifically, cryogenic natural gas has a liquefaction temperature of -162℃, ethane -89℃, and propylene -47.7℃. Compared to other energy transportation methods, such as gas pipelines or tank trucks, using pipelines for CHL transportation can more effectively reduce losses and costs during transport, and this method is currently the mainstream approach for CHL transportation.

[0003] In the pipeline transportation of cryogenic liquefied hydrocarbons, the insulation effect of the cold insulation layer installed outside the pipeline is not absolute and cannot completely isolate the influence of the ambient temperature outside the pipe. Natural convection heat transfer from the atmosphere outside the pipe will inevitably carry away some of the cold energy, resulting in cold loss. Accurately obtaining the cold loss during cryogenic liquefied hydrocarbon pipeline transportation can provide a basis for pipeline design, pipeline operation cost assessment, energy efficiency improvement, and environmental impact assessment. However, calculating the cold loss of cryogenic liquefied hydrocarbon pipelines is a complex process involving convection heat transfer of the cryogenic fluid inside the pipe, heat conduction through the pipe wall, and natural convection heat transfer outside the pipe wall. Currently, technicians generally use the following two methods to calculate cold loss. The first method uses the heat dissipation loss formula for cylindrical insulation or cold insulation layers in the national standard as the basis for calculating cold loss. The formula for the heat dissipation loss of cylindrical insulation or cold insulation layers is:

[0004]

[0005] In the formula, q represents the heat loss per meter of the outer surface of the insulation layer, in W / m; t represents the outer surface temperature of the equipment and pipes, in °C; t a R represents ambient temperature, in °C. i Thermal resistance of the insulation layer, m·℃ / W; R s λ is the surface thermal resistance of the insulation layer, m·℃ / W; λ is the thermal conductivity of the insulation material, W·m℃; α is the heat transfer coefficient of the outer surface of the insulation layer to the atmosphere, W·m℃; D0 is the outer diameter of the insulation layer, m; D i The outer diameter of the equipment or pipe, in meters (m).

[0006] The heat transfer coefficient α of the outer surface of the insulation layer facing the atmosphere in this formula is a key parameter for calculation based on the principle of heat transfer. This parameter is not easy to obtain accurately due to the influence of many complex factors such as atmospheric temperature, humidity, flow velocity, and wind direction. In actual calculations, empirical values ​​are generally used. Therefore, the cold loss result obtained by the first type of method often does not have high accuracy and is only suitable as a preliminary estimate.

[0007] The second type of method utilizes methods from other fields to calculate cold loss during pipeline transportation of cryogenic liquefied hydrocarbons. However, due to differences in the fields, the factors considered in the calculation process and the causes of cold loss vary. For example, prior art (CN102706484A) provides a method for measuring cold loss during seawater transportation along a pipeline. This method takes into account the elevation difference during seawater transportation and emphasizes the energy conversion process of seawater potential energy into thermal energy. However, elevation differences are rare in cryogenic liquefied hydrocarbon pipeline transportation, and the calculation of cold loss mainly considers convective heat transfer on the outer wall of the pipeline. Therefore, this second type of method is often unsuitable for direct application in obtaining cold loss during cryogenic liquefied hydrocarbon pipeline transportation.

[0008] Furthermore, since pipelines transporting cryogenic liquefied hydrocarbons are generally quite long, the external environment at different locations within the pipeline can vary significantly. Changes in the external environment alter the convective heat transfer rate between the pipeline and the surrounding environment. Therefore, under natural convection conditions, variations in the heat transfer characteristics of the pipeline's outer wall mean that the rate of cold loss of cryogenic liquefied hydrocarbons during pipeline transportation is not entirely consistent. Neither of the two methods mentioned above considers the impact of changes in the heat transfer characteristics of the pipe's outer wall on cold loss. Therefore, the cold loss data obtained by these two methods is more inclined towards theoretical research under ideal conditions and is not suitable for obtaining cold loss data under natural convection conditions.

[0009] Therefore, how to combine the characteristics of cryogenic liquefied hydrocarbon pipeline transportation to obtain accurate cold loss during pipeline transportation is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0010] To address the problems existing in the prior art, the present invention provides a method and system for calculating the cooling loss during the pipeline transportation of cryogenic liquefied hydrocarbons.

[0011] The technical solution of the present invention is as follows:

[0012] A method for calculating cooling loss during the pipeline transportation of cryogenic liquefied hydrocarbons includes:

[0013] The pipeline for transporting cryogenic liquefied hydrocarbons is divided into several sections, and the wall temperature and air temperature of each section are measured.

[0014] Based on the air temperature of each pipe section, obtain the fluid property data of each pipe section, which consists of air kinematic viscosity and thermal conductivity.

[0015] Based on the fluid properties data of each pipe section, as well as the wall temperature and air temperature, the air on the outer wall of each pipe section is classified into three flow states: laminar, transitional, and turbulent.

[0016] Based on the air flow pattern on the outer wall of each pipe section, the cooling loss of each pipe section is obtained, and thus the cooling loss of cryogenic liquefied hydrocarbons during pipeline transportation is obtained.

[0017] Furthermore, the specific steps of dividing the cryogenic liquefied hydrocarbon transport pipeline into several sections include:

[0018] The conveying pipeline is divided into several pipe segments according to a preset distance. For conveying pipelines with an inner diameter d of d≤50mm, the preset distance is 3m; for conveying pipelines with an inner diameter d of 50mm<d≤100mm, the preset distance is 5m; for conveying pipelines with an inner diameter d of 100mm<d≤200mm, the preset distance is 8m; and for conveying pipelines with an inner diameter d of 200mm<d≤300mm, the preset distance is 10m.

[0019] Furthermore, the specific steps of dividing the cryogenic liquefied hydrocarbon transport pipeline into several sections include:

[0020] The conveying pipeline is divided into several pipe sections according to the location of its pipe support.

[0021] Furthermore, the specific steps for measuring the wall temperature and air temperature of each pipe section include:

[0022] Temperature measurement points are selected at the beginning and end of each pipe section. The average wall temperature of the pipe section is taken as the average wall temperature of the pipe section, and the average air temperature of the pipe section is taken as the average air temperature of the pipe section.

[0023] Furthermore, after measuring the wall temperature and air temperature of each pipe segment, the process further includes: merging the pipe segments based on their wall temperature and air temperature, and further dividing the pipe segments; wherein,

[0024] The method for merging pipe sections based on the wall temperature and air temperature of each section includes: when the air temperature difference between two adjacent pipe sections is less than or equal to J1℃ and the wall temperature difference between the two pipe sections is less than or equal to J2℃, then the two pipe sections are merged into one pipe section; J1 is 1 to 2, and J2 is 1 to 2.

[0025] The method for further dividing the pipe section includes: if there are environmental change points in the pipe section, the pipe section is further divided based on the environmental change points; wherein, the environmental change points are the locations where the convective heat exchange rate between the pipeline and the outside world is likely to change, including the locations where there is water accumulation below the pipe section, the locations where there is shade from trees or buildings due to obstructions above the pipe section, and the locations where the pipe section is located at a wind vent.

[0026] Furthermore, the specific steps for obtaining fluid property data for each pipe section, consisting of air kinematic viscosity and thermal conductivity, based on the air temperature of each section include:

[0027] The kinematic viscosity and thermal conductivity of air corresponding to the air temperature in each pipe section are obtained from the air physical property parameter table.

[0028] Furthermore, the specific steps for classifying the air on the outer wall of each pipe section into three flow regimes—laminar, transitional, and turbulent—based on the fluid property data, wall temperature, and air temperature of each pipe section include:

[0029] Based on the fluid property data of each pipe section, calculate the Grashof number G for each pipe section. r Grashof number G r The calculation formula is as follows:

[0030]

[0031] In the formula, g is the acceleration due to gravity, m / s². 2 α is the volume expansion coefficient, the value of which is determined by the absolute temperature of the air; for an ideal gas, it is equal to the reciprocal of absolute zero; d is the inner diameter of the pipe, in meters; ΔT is the difference between the air temperature and the wall temperature, in degrees Celsius; v is the kinematic viscosity of air, in cubic meters per second. 2 / s;

[0032] Then, based on the Grashof number G of each pipe section r The size of the pipe section is used to classify the airflow pattern on the outer wall.

[0033] If 10 4 <G r <5.76×10 8 Then the air on the outer wall of the pipe section is in a laminar flow state;

[0034] If 5.76×10 8 <G r <4.65×10 9 Then the air on the outer wall of the pipe section is in a transition state;

[0035] If G r >4.65×10 9 If so, the air on the outer wall of the pipe section is in a turbulent state.

[0036] Furthermore, the specific steps for obtaining the cooling loss of each pipe section based on the air flow pattern on the outer wall of each pipe section, and thus obtaining the cooling loss of cryogenic liquefied hydrocarbons during pipeline transportation, include:

[0037] Determine the Nusselt number N in each pipe section based on the airflow pattern on the outer wall. u The coefficient C and exponent n in the calculation formula are as follows: if the air on the outer wall of the pipe section is in a laminar flow state, then the coefficient C = 0.48 and the exponent n = 1 / 4; if the air on the outer wall of the pipe section is in a transition state, then the coefficient C = 0.0445 and the exponent n = 0.37; if the air on the outer wall of the pipe section is in a turbulent flow state, then the coefficient C = 0.1 and the exponent n = 1 / 3.

[0038] Then, based on the experimental relationship of natural convection heat transfer in large spaces, combined with the determined coefficient value C and exponent value n, the Nusselt number N for each pipe section is calculated. u Nusselt number N u The calculation formula is as follows:

[0039] N u =C(G r P r ) n

[0040] In the formula, P r It is a Prandtl number;

[0041] Then, the heat dissipation φ of each pipe section is calculated. The formula for calculating the heat dissipation φ is as follows:

[0042] φ=N u πlλΔT

[0043] In the formula, l is the length of the pipe section, m; λ is the thermal conductivity coefficient, W / (mK);

[0044] The heat loss of each pipe section is then weighted and summed to obtain the cooling loss of cryogenic liquefied hydrocarbons during pipeline transportation.

[0045] Furthermore, the cryogenic liquefied hydrocarbon is liquefied natural gas, LNG, ethane, ethylene, or propylene.

[0046] A system for measuring cold loss during the pipeline transportation of cryogenic liquefied hydrocarbons includes: a measurement module, a fluid property data acquisition module, a flow regime classification module, and a cold loss calculation module;

[0047] The measurement module is used to divide the pipeline for transporting cryogenic liquefied hydrocarbons into several sections and measure the wall temperature and air temperature of each section.

[0048] The fluid property data acquisition module is used to acquire fluid property data for each pipe section, consisting of air kinematic viscosity and thermal conductivity, based on the air temperature of each pipe section.

[0049] The flow regime classification module is used to classify the air on the outer wall of each pipe section into three flow regimes: laminar, transitional, and turbulent, based on the fluid properties data, wall temperature, and air temperature of each pipe section.

[0050] The cold loss calculation module is used to obtain the cold loss of each pipe section based on the air flow pattern on the outer wall of each pipe section, and then obtain the cold loss of cryogenic liquefied hydrocarbons during pipeline transportation.

[0051] Compared with the prior art, the present invention has the following advantages:

[0052] This invention provides a method for calculating the cooling loss during the pipeline transportation of cryogenic liquefied hydrocarbons. This method fully considers the pipeline transportation characteristics of cryogenic liquefied hydrocarbons under natural convection conditions. Specifically, the cooling loss rate of cryogenic liquefied hydrocarbons changes with the heat transfer characteristics of the pipeline's outer wall. The method classifies the airflow on the outer wall of different pipe sections into three flow states: laminar, transitional, and turbulent. The cooling loss of each pipe section is obtained under the corresponding flow state, thus allowing the determination of the total cooling loss of cryogenic liquefied hydrocarbons throughout the entire pipeline transportation process. Therefore, this invention's calculation method is more scientific and reasonable, improves the accuracy of cooling loss calculation, and improves upon traditional, coarse calculation methods, enabling a scientific and accurate assessment of the cold energy utilization value of cryogenic pipelines.

[0053] The calculation method of the present invention uses the wall temperature and air temperature of each pipe section as the reference data. The reference data is easy to obtain and the accuracy of the obtained reference data is high.

[0054] The calculation method of the present invention also specifically designs the pipe segment division method, providing two division methods: division by a fixed preset distance and division by the location of the pipe support. The division by a fixed preset distance is to determine the preset distance based on the inner diameter of the pipe and divide the pipe segment by the preset distance. This division method takes into account the different convective heat transfer characteristics exhibited by pipe segments of different diameters. Therefore, the division method is scientific and reasonable, making the calculation results of the present invention more accurate. The division by the location of the pipe support is simple and easy to implement, avoiding the inconvenience caused by manual division operation.

[0055] The calculation method of this invention further divides and merges pipe sections based on their wall temperature and air temperature. Specifically, two pipe sections whose external environment remains largely unchanged are merged and treated as a single section for subsequent calculations. This design reduces subsequent computational workload, allowing the calculation method to obtain results more quickly. Simultaneously, the pipe sections are further divided based on points of environmental change within them. This design considers the impact of locations where the convective heat transfer rate between the pipeline and the outside environment easily changes on the rate of cold loss of low-temperature liquefied hydrocarbons within the pipe section. This makes the calculation results of this invention more accurate and more suitable for calculating cold loss under natural convection environments.

[0056] The calculation method of this invention combines the characteristics of cryogenic liquefied hydrocarbon pipeline transportation to obtain accurate cold loss during pipeline transportation. Accurate cold loss can provide a basis for the design of cryogenic liquefied hydrocarbon transportation pipelines and accurately assess the operation and maintenance costs of the pipelines, contributing to the formulation of reasonable economic decisions and resource allocation schemes. Based on the magnitude of cold loss in each pipe section and the distribution of cold loss during pipeline transportation obtained according to this invention, the insulation layer thickness, insulation material, and pipe size for different pipe sections can be determined to meet the required temperature requirements and transportation efficiency. It can also be used to assess the potential environmental impact of the pipeline transportation process, including temperature changes and ecosystem impacts, contributing to the formulation of corresponding environmental management and protection measures. Attached Figure Description

[0057] Figure 1 A flowchart illustrating the method for calculating cold loss during the pipeline transportation of cryogenic liquefied hydrocarbons;

[0058] Figure 2 A block diagram of a system for calculating cold loss during the pipeline transportation of cryogenic liquefied hydrocarbons;

[0059] Figure 3 This is a line graph showing the wall temperature changes in different pipe sections. Detailed Implementation

[0060] The present invention will be further described below with reference to specific embodiments and corresponding drawings.

[0061] Example 1:

[0062] This invention provides a method for calculating the cooling loss during the pipeline transportation of cryogenic liquefied hydrocarbons, specifically for obtaining the cooling loss of cryogenic liquefied hydrocarbons such as liquefied natural gas, LNG, ethane, ethylene, or propylene during pipeline transportation under natural convection conditions. This calculation method simplifies the pipeline for transporting cryogenic liquefied hydrocarbons as a horizontally swept-by-circular pipe, such as... Figure 1 As shown, the specific steps include the following:

[0063] 1) Divide the pipeline for transporting cryogenic liquefied hydrocarbons into several sections and measure the wall temperature and air temperature of each section.

[0064] 2) Based on the air temperature of each pipe section, obtain the fluid property data of each pipe section, consisting of air kinematic viscosity and thermal conductivity.

[0065] 3) Based on the fluid properties data of each pipe section, as well as the wall temperature and air temperature, the air on the outer wall of each pipe section is classified into three flow states: laminar, transitional, and turbulent.

[0066] 4) Based on the air flow pattern on the outer wall of each pipe section, obtain the cooling loss of each pipe section, and then obtain the cooling loss of low-temperature liquefied hydrocarbons during pipeline transportation.

[0067] Example 2:

[0068] This embodiment further designs the specific steps for dividing the pipeline into sections based on Embodiment 1. The following two methods can be used for pipe section division:

[0069] Method 1: Divide the conveying pipeline into several sections according to a preset distance. For conveying pipelines with an inner diameter d of d≤50mm, the preset distance is 3m; for conveying pipelines with an inner diameter d of 50mm<d≤100mm, the preset distance is 5m; for conveying pipelines with an inner diameter d of 100mm<d≤200mm, the preset distance is 8m; and for conveying pipelines with an inner diameter d of 200mm<d≤300mm, the preset distance is 10m.

[0070] Method 2: Divide the pipeline into several sections according to the location of its pipe support.

[0071] Example 3:

[0072] This embodiment further designs the specific steps for measuring the wall temperature and air temperature of each pipe section based on Embodiment 1 or Embodiment 2 as follows:

[0073] Temperature measurement points are selected at the beginning and end of each pipe section. The average wall temperature of the pipe section is taken as the average wall temperature of the pipe section at the beginning and end of the pipe section, and the average air temperature of the pipe section is taken as the average air temperature of the pipe section at the beginning and end of the pipe section. The wall temperature is the temperature of the outer wall of the pipe section, which can be obtained by an infrared thermometer, and the air temperature is the temperature of the air at the location of the temperature measurement point of the pipe section, which can be obtained by an air temperature measuring instrument.

[0074] Example 4:

[0075] This embodiment, based on Embodiment 1, Embodiment 2, or Embodiment 3, is further designed in that: after measuring the wall temperature and air temperature of each pipe segment, it also includes: merging the pipe segments according to their wall temperature and air temperature, and further dividing the pipe segments; wherein,

[0076] Methods for merging pipe sections based on their wall temperature and air temperature include:

[0077] If the temperature difference between two adjacent pipe sections is less than or equal to J1 degrees and the wall temperature difference between the two pipe sections is less than or equal to J2 degrees, then the external environment of the two pipe sections is considered to have not changed significantly, and therefore the two pipe sections are merged into one pipe section. J1 is generally taken as 1℃, and J2 is generally taken as 1℃.

[0078] Specific methods for further dividing the pipe sections include:

[0079] If there are environmental change points in the pipe section, the pipe section is divided according to these environmental change points. These environmental change points generally refer to locations where there is water accumulation below the pipe section, locations where there is shade from trees or buildings due to obstructions above the pipe section, and locations where the pipe section is located in a ventilated area, which are places where the convective heat exchange rate between the pipeline and the outside world is easily changed.

[0080] Example 5:

[0081] This embodiment, based on Embodiment 1, is further designed in the following way: The specific steps for obtaining the fluid property data (composed of air kinematic viscosity and thermal conductivity) of each pipe section based on the air temperature of each pipe section include:

[0082] The kinematic viscosity and thermal conductivity of air corresponding to the air temperature in each pipe section are obtained from the air property parameter table. This property parameter table can be obtained from "Engineering Thermodynamics".

[0083] Example 6:

[0084] This embodiment, based on Embodiment 1, further incorporates the following design: The specific steps for classifying the air on the outer wall of each pipe section into three flow regimes—laminar, transitional, and turbulent—according to the fluid property data of each pipe section include:

[0085] Based on the fluid property data of each pipe section, calculate the Grashof number G for each pipe section. r Grashof number G r The calculation formula is as follows:

[0086]

[0087] In the formula, g is the acceleration due to gravity, m / s². 2 α is the volume expansion coefficient, the value of which is determined by the absolute temperature of the air; for an ideal gas, it is equal to the reciprocal of absolute zero; d is the inner diameter of the pipe, in meters; ΔT is the difference between the air temperature and the wall temperature, in degrees Celsius; v is the kinematic viscosity of air, in cubic meters per second. 2 / s;

[0088] Then, based on the Grashof number G of each pipe section r The size of the pipe section is used to classify the airflow pattern on the outer wall.

[0089] If 10 4 <G r <5.76×10 8 Then the air on the outer wall of the pipe section is in a laminar flow state;

[0090] If 5.76×10 8 <G r <4.65×10 9 Then the air on the outer wall of the pipe section is in a transition state;

[0091] If G r >4.65×10 9 If so, the air on the outer wall of the pipe section is in a turbulent state.

[0092] Example 7:

[0093] This embodiment, based on Embodiment 1, is further designed in the following way: The specific steps for obtaining the cooling loss of each pipe section based on the air flow pattern on the outer wall of each pipe section, and thus obtaining the cooling loss of cryogenic liquefied hydrocarbons during pipeline transportation, include:

[0094] Determine the Nusselt number N for each pipe section based on the airflow pattern on the outer wall of each pipe section. u The coefficient C and exponent n in the calculation formula are as follows: if the air on the outer wall of the pipe section is in a laminar flow state, then the coefficient C = 0.48 and the exponent n = 1 / 4; if the air on the outer wall of the pipe section is in a transition state, then the coefficient C = 0.0445 and the exponent n = 0.37; if the air on the outer wall of the pipe section is in a turbulent flow state, then the coefficient C = 0.1 and the exponent n = 1 / 3.

[0095] Then, based on the experimental relationship of natural convection heat transfer in large spaces, combined with the determined coefficient value C and exponent value n, the Nusselt number N for each pipe section is calculated. u Nusselt number N u The calculation formula is as follows:

[0096] N u =C(G r P r ) n

[0097] In the formula, P r Let P be a Prandtl number. r The air temperature can be obtained from the air property parameter table based on the air temperature of the pipe section.

[0098] Then, the heat dissipation φ of each pipe section is calculated. The formula for calculating the heat dissipation φ is as follows:

[0099] φ=N u πlλΔT

[0100] In the formula, l is the length of the pipe section, m; λ is the thermal conductivity coefficient, W / (mK);

[0101] The heat loss of each pipe section is then weighted and summed to obtain the cooling loss of cryogenic liquefied hydrocarbons during pipeline transportation.

[0102] Example 8:

[0103] This invention provides a system for calculating cold loss during the pipeline transportation of cryogenic liquefied hydrocarbons, such as... Figure 2 As shown, it includes: a measurement module, a fluid property data acquisition module, a flow regime classification module, and a cold loss calculation module;

[0104] The measurement module is used to divide the pipeline for transporting cryogenic liquefied hydrocarbons into several sections and measure the wall temperature and air temperature of each section.

[0105] The fluid property data acquisition module is used to acquire fluid property data for each pipe section, consisting of air kinematic viscosity and thermal conductivity, based on the air temperature of each pipe section.

[0106] The flow regime classification module is used to classify the air on the outer wall of each pipe section into three flow regimes: laminar, transitional, and turbulent, based on the fluid properties data, wall temperature, and air temperature of each pipe section.

[0107] The cold loss calculation module is used to obtain the cold loss of each pipe section based on the air flow pattern on the outer wall of each pipe section, and then obtain the cold loss of cryogenic liquefied hydrocarbons during pipeline transportation.

[0108] Application Examples:

[0109] This example uses the calculation method of the present invention to calculate the cooling loss in the cryogenic liquefied hydrocarbon pipeline transportation process between an LNG receiving terminal and a cold storage facility. The pipeline used in the transportation process is 12 km long, with an inner diameter of 216 mm, and the pipeline material is 0Cr18Ni9. The insulation material installed on the outside of the pipeline is polystyrene foam. The specific calculation process is as follows:

[0110] Since the inner diameter of the pipeline is within the range of (200mm, 300mm), this example initially divides the pipeline into 1200 segments at a preset distance of 10m. The wall temperature and air temperature at both ends of each segment are measured to calculate the wall temperature and air temperature of each segment. Then, combining the air temperature difference and wall temperature difference between adjacent segments along the pipeline, some segments are merged and subdivided. It is worth noting that segment 2 is affected by direct sunlight, resulting in a higher wall temperature than surrounding segments; therefore, it is a subdivided segment. All other segments are merged, resulting in a total of 24 segments. The wall temperature and air temperature data for some segments are shown in Table 1 below. The wall temperature of each segment is as follows: Figure 3 As shown.

[0111] Table 1

[0112] Pipeline section number Temperature Wall temperature K 1 306.5 113 2 305.8 170 3 306.2 113.7 … … … … … … 23 307.6 116.7 24 307.1 117.2

[0113] Based on the air temperature of each pipe section, fluid property data consisting of air kinematic viscosity and thermal conductivity were obtained for each pipe section; fluid property data for some pipe sections are shown in Table 2 below.

[0114] Table 2

[0115]

[0116]

[0117] Based on the fluid properties data of each pipe section, as well as the wall temperature and air temperature, the air on the outer wall of each pipe section is classified into three flow states: laminar, transitional, and turbulent.

[0118] The airflow patterns on the outer wall of some pipe sections are shown in Table 3 below.

[0119] Table 3

[0120] Pipeline section number Flow 1 transition state 2 Laminar flow 3 transition state … … … … 23 transition state 24 transition state

[0121] Based on the air flow pattern on the outer wall of each pipe section, the cooling loss of each pipe section is obtained, and then the cooling loss of cryogenic liquefied hydrocarbons during pipeline transportation is obtained. The cooling loss in some pipe sections is shown in Table 4 below.

[0122] Table 4

[0123] Pipeline section number Cooling loss (KW) 1 556.5 2 436.1 3 555.7 … … … … 23 554.6 24 552.4

Claims

1. A method for calculating cold loss during the pipeline transportation of cryogenic liquefied hydrocarbons, characterized in that, include: The pipeline for transporting cryogenic liquefied hydrocarbons is divided into several sections, and the wall temperature and air temperature of each section are measured. Based on the air temperature of each pipe section, obtain the fluid property data of each pipe section, which consists of air kinematic viscosity and thermal conductivity. Based on the fluid properties data of each pipe section, as well as the wall temperature and air temperature, the air on the outer wall of each pipe section is classified into three flow states: laminar, transitional, and turbulent. Based on the air flow pattern on the outer wall of each pipe section, the cooling loss of each pipe section is obtained, and then the cooling loss of low-temperature liquefied hydrocarbons during pipeline transportation is obtained. The specific steps for obtaining fluid property data, consisting of air kinematic viscosity and thermal conductivity, for each pipe section based on its air temperature include: Obtain the air kinematic viscosity and thermal conductivity coefficient corresponding to the air temperature of each pipe section based on the air physical property parameter table; The specific steps for classifying the air on the outer wall of each pipe section into three flow regimes—laminar, transitional, and turbulent—based on the fluid property data, wall temperature, and air temperature of each pipe section include: Based on the fluid property data of each pipe section, calculate the Grashof number for each pipe section. , Glaschov number The calculation formula is as follows: ; In the formula, It is the acceleration due to gravity. ; This is the volume expansion coefficient, the value of which is determined by the absolute temperature of the air, and for an ideal gas it is equal to the reciprocal of absolute zero. The inner diameter of the pipe. ; The difference between air temperature and wall temperature. ; The viscosity of air motion. ; Then, based on the Grashof number of each pipe section The size of the pipe section is used to classify the airflow pattern on the outer wall. like Then the air on the outer wall of the pipe section is in a laminar flow state; like Then the air on the outer wall of the pipe section is in a transition state; like Then the air on the outer wall of the pipe section is in a turbulent state; The specific steps for obtaining the cooling loss of each pipe section based on the air flow pattern on the outer wall of each pipe section, and thus obtaining the cooling loss of cryogenic liquefied hydrocarbons during pipeline transportation, include: determining the Nusselt number in each pipe section based on the air flow pattern on the outer wall. Coefficient values ​​in the calculation formula and exponent value Specifically, if the air on the outer wall of the pipe section is in a laminar flow state, then the coefficient value is... index value If the air on the outer wall of the pipe section is in a transition state, then the coefficient value is... index value If the air on the outer wall of the pipe section is in a turbulent state, then the coefficient value is... index value ; Then, based on the experimental relationship of natural convection heat transfer in large spaces and the determined coefficient values... and exponent value Calculate the Nusselt number for each pipe section. Nusel number The calculation formula is as follows: ; In the formula, It is a Prandtl number; Then the heat dissipation of each pipe section was calculated. Heat dissipation The calculation formula is as follows: ; In the formula, For the length of the pipe section, ; The thermal conductivity coefficient, ; The heat loss of each pipe section is then weighted and summed to obtain the cooling loss of cryogenic liquefied hydrocarbons during pipeline transportation.

2. The method for calculating cold loss during the pipeline transportation of cryogenic liquefied hydrocarbons according to claim 1, characterized in that: The specific steps for dividing the cryogenic liquefied hydrocarbon transport pipeline into several sections include: The conveying pipeline is divided into several pipe segments according to a preset distance, wherein the inner diameter d of the pipeline satisfies the following conditions: The conveying pipeline has a preset distance of 3m; the pipeline inner diameter d satisfies The conveying pipeline has a preset distance of 5m; the pipeline inner diameter d satisfies The conveying pipeline has a preset distance of 8m; the pipeline inner diameter d satisfies The delivery pipeline has a preset distance of 10m.

3. The method for calculating cold loss during the pipeline transportation of cryogenic liquefied hydrocarbons according to claim 1, characterized in that: The specific steps for dividing the cryogenic liquefied hydrocarbon transport pipeline into several sections include: The conveying pipeline is divided into several pipe sections according to the location of its pipe support.

4. The method for calculating cold loss during the pipeline transportation of cryogenic liquefied hydrocarbons according to any one of claims 1 to 3, characterized in that: The specific steps for measuring the wall temperature and air temperature of each pipe section include: Temperature measurement points are selected at the beginning and end of each pipe section. The average wall temperature of the pipe section is taken as the average wall temperature of the pipe section, and the average air temperature of the pipe section is taken as the average air temperature of the pipe section.

5. The method for calculating cold loss during the pipeline transportation of cryogenic liquefied hydrocarbons according to claim 1, characterized in that: The process of measuring the wall temperature and air temperature of each pipe segment also includes: merging the pipe segments based on their wall temperature and air temperature, and further dividing the pipe segments; wherein, The method for merging pipe sections based on their wall temperature and air temperature includes: when the temperature difference between two adjacent pipe sections is less than or equal to... And the temperature difference between the two pipe sections is less than or equal to Then the two pipe sections will be merged into one pipe section; Take 1~2, Take 1~2; The method for further dividing the pipe section includes: if there are environmental change points in the pipe section, the pipe section is further divided based on the environmental change points; wherein, the environmental change points are the locations where the convective heat exchange rate between the pipeline and the outside world is likely to change, including the locations where there is water accumulation below the pipe section, the locations where there is shade from trees or buildings due to obstructions above the pipe section, and the locations where the pipe section is located at a wind vent.

6. The method for calculating cold loss during the pipeline transportation of cryogenic liquefied hydrocarbons according to claim 1, characterized in that: The cryogenic liquefied hydrocarbon is liquefied natural gas, LNG, ethane, ethylene, or propylene.

7. A system for calculating cold loss during the pipeline transportation of cryogenic liquefied hydrocarbons, characterized in that, include: Measurement module, fluid property data acquisition module, flow regime classification module, and cold loss calculation module; The measurement module is used to divide the pipeline for transporting cryogenic liquefied hydrocarbons into several sections and measure the wall temperature and air temperature of each section. The fluid property data acquisition module is used to acquire fluid property data for each pipe section, consisting of air kinematic viscosity and thermal conductivity, based on the air temperature of each pipe section. The flow regime classification module is used to classify the air on the outer wall of each pipe section into three flow regimes: laminar, transitional, and turbulent, based on the fluid properties data, wall temperature, and air temperature of each pipe section. The cold loss calculation module is used to obtain the cold loss of each pipe section based on the air flow pattern on the outer wall of each pipe section, and then obtain the cold loss of cryogenic liquefied hydrocarbons during pipeline transportation.

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