Method and system for calculating thermophysical property of ammonia nitrogen mixture

Abstract

The invention discloses a thermophysical property calculation method and system for an ammonia nitrogen mixture, and the method comprises the steps: obtaining basic parameters of an ammonia elementary substance and a nitrogen elementary substance; obtaining the fluid temperature and the fluid pressure of the ammonia nitrogen mixture and the content of a first phase component in the ammonia nitrogen mixture; the first phase component is a liquid phase or a gas phase; determining a dew point temperature and a bubble point temperature of the nitrogen-ammonia mixture based on the fluid pressure of the ammonia-nitrogen mixture; determining the fluid phase state of the nitrogen-ammonia mixture based on the dew point temperature and the bubble point temperature of the nitrogen-ammonia mixture and the fluid temperature of the ammonia-nitrogen mixture; based on the fluid phase state, constructing a thermophysical parameter calculation model of the ammonia nitrogen mixture; and obtaining various thermophysical parameters of the ammonia nitrogen mixture based on the thermophysical parameter calculation model of the ammonia nitrogen mixture. The ammonia thermophysical property parameter calculation result of the physical property / phase characteristic calculation model established by the invention is well matched with experimental data.

Description

Technical Field

[0001] The present invention relates to the technical field of ammonia storage and transportation, and particularly relates to a method and system for calculating the thermal physical properties of an ammonia-nitrogen mixture. Background Art

[0002] Due to the influence of different synthetic ammonia processes, purge gas often enters the pipeline along with liquid ammonia, resulting in gas blockage during ammonia transportation. This part of gas impurities is mainly non-condensable nitrogen, which inevitably changes the phase equilibrium characteristics and physical properties of the medium in the pipeline, and further affects the hydraulic and thermal characteristics and other transient process characteristics of the ammonia transportation pipeline. Therefore, it is necessary to study the thermal physical property calculation model of ammonia considering the coupling effect of nitrogen.

[0003] Since the thermal physical property parameters of ammonia are greatly affected by impurities and temperature sensitivity, the hydraulic and thermal calculations of ammonia transportation pipelines require fluid thermal physical property data in a large-scale temperature range. Limited by the high cost of conventional experimental methods and the calculation accuracy of general empirical formulas, it is often difficult to measure the thermal physical properties of ammonia-nitrogen mixtures under relatively wide temperature and pressure conditions. Therefore, the thermal physical property prediction method of ammonia under the coupling effect of nitrogen described in this patent is of great significance in the technical field of ammonia storage and transportation. Summary of the Invention

[0004] The purpose of the present invention is to provide a method and system for calculating the thermal physical properties of an ammonia-nitrogen mixture, so as to provide scientific guidance for the design and safe and stable operation of ammonia transportation pipelines. To achieve the above purpose, the present invention provides the following technical solutions:

[0005] A method for calculating the thermal physical properties of an ammonia-nitrogen mixture, the method includes,

[0006] Obtain the basic parameters of ammonia and nitrogen;

[0007] Obtain the fluid temperature, fluid pressure, and the content of the first phase component in the ammonia-nitrogen mixture; the first phase component is a liquid phase or a gas phase;

[0008] Based on the fluid pressure of the ammonia-nitrogen mixture, determine the dew point temperature and bubble point temperature of the nitrogen-ammonia mixture;

[0009] Based on the dew point temperature and bubble point temperature of the nitrogen-ammonia mixture and the fluid temperature of the ammonia-nitrogen mixture, determine the fluid phase state of the nitrogen-ammonia mixture;

[0010] Based on the fluid phase state, construct a calculation model for the thermal physical property parameters of the ammonia-nitrogen mixture;

[0011] Based on the calculation model for the thermal physical property parameters of the ammonia-nitrogen mixture, obtain the thermal physical property parameters of the ammonia-nitrogen mixture.

[0012] Further, the basic parameters of the elemental ammonia and elemental nitrogen include critical temperature, critical pressure, molecular mass, and acentric factor.

[0013] Further, determining the dew point temperature and bubble point temperature of the nitrogen-ammonia mixture based on the fluid pressure of the ammonia-nitrogen mixture includes:

[0014] Based on the Antoine equation, obtain the estimated dew point temperature and estimated bubble point temperature of the nitrogen-ammonia mixture according to the fluid pressure of the ammonia-nitrogen mixture;

[0015] According to the estimated dew point temperature, estimated bubble point temperature, and the content of the first-phase component in the ammonia-nitrogen mixture, calculate the content of the second-phase component in the ammonia-nitrogen mixture under the phase equilibrium state;

[0016] When the content of the second-phase component in the ammonia-nitrogen mixture under the phase equilibrium state meets the threshold, the estimated dew point temperature and estimated bubble point temperature of the nitrogen-ammonia mixture are the dew point temperature value and bubble point temperature value of the nitrogen-ammonia mixture;

[0017] When the content of the second-phase component in the ammonia-nitrogen mixture under the phase equilibrium state does not meet the threshold, re-obtain the estimated dew point temperature and estimated bubble point temperature, and repeat the above steps once or multiple times until the content of the second-phase component in the ammonia-nitrogen mixture calculated meets the threshold.

[0018] Further, calculating the content of the second-phase component in the ammonia-nitrogen mixture under the phase equilibrium state according to the estimated dew point temperature, estimated bubble point temperature, and the content of the first-phase component in the ammonia-nitrogen mixture includes:

[0019] According to the estimated dew point temperature, estimated bubble point temperature, and the content of the first-phase component in the ammonia-nitrogen mixture, calculate the gravitational term coefficient of the nitrogen component, the gravitational term coefficient of the ammonia component, the co-volume term coefficient of the nitrogen component, and the co-volume term coefficient of the ammonia component;

[0020] Combine the gravitational term coefficient of the nitrogen component, the gravitational term coefficient of the ammonia component, the co-volume term coefficient of the nitrogen component, and the co-volume term coefficient of the ammonia component, and calculate according to the content of the first-phase component in the nitrogen mixture to obtain the gas and liquid fugacity coefficients of the nitrogen component in the ammonia-nitrogen mixture and the gas and liquid fugacity coefficients of the ammonia component and nitrogen component in the ammonia-nitrogen mixture;

[0021] Based on the gas and liquid fugacity coefficients of the nitrogen component and the gas and liquid fugacity coefficients of the ammonia component and nitrogen component in the ammonia-nitrogen mixture, obtain the content of the second-phase component in the ammonia-nitrogen mixture under the phase equilibrium state.

[0022] Further, the second-phase component in the ammonia-nitrogen mixture is a liquid phase or a gas phase, where

[0023] When the first-phase component is in the liquid phase, the second-phase component is in the gas phase;

[0024] When the first-phase component is in the gas phase, the second-phase component is in the liquid phase.

[0025] Furthermore, the calculation formulas for the gravitational term coefficient of the nitrogen component, the gravitational term coefficient of the ammonia component, the co-volume term coefficient of the nitrogen component, and the co-volume term coefficient of the ammonia component are as follows:

[0026]

[0027]

[0028]

[0029]

[0030]

[0031]

[0032] Among them, a i is the gravitational term coefficient of the nitrogen component, a j is the gravitational term coefficient of the ammonia component, b i is the co-volume term coefficient of the nitrogen component, b j is the co-volume term coefficient of the ammonia component, ω i and ω j are the fluid eccentricity factors of the nitrogen component and the ammonia component respectively, R is the gas constant, p ci and p cj are the critical pressures of the nitrogen component and the ammonia component respectively, T ri and T rj are the reduced temperatures of the nitrogen component and the ammonia component respectively, T ci and T cj are the critical temperatures of the nitrogen component and the ammonia component respectively, T0 d is the dew point temperature estimate and T0 b is the bubble point temperature estimate.

[0033] Furthermore, the calculation formulas for the gas-phase and liquid-phase fugacity coefficients of the nitrogen component and the gas-phase and liquid-phase fugacity coefficients of the ammonia component and the nitrogen component are as follows:

[0034]

[0035]

[0036]

[0037]

[0038] Among them,

[0039]

[0040]

[0041] Among them, R is the gas constant; p is the pressure of the ammonia-nitrogen mixture; Z is the compressibility factor; φ i v is the fugacity coefficient of the nitrogen component in the gas phase, φ i l is the fugacity coefficient of the nitrogen component in the liquid phase, φ j v is the fugacity coefficient of the ammonia component in the gas phase, φ j l is the fugacity coefficient of the ammonia component in the liquid phase, x i and y i respectively represent the gas-phase mole fraction and liquid-phase mole fraction of the nitrogen component, x j and y j respectively represent the gas-phase mole fraction and liquid-phase mole fraction of the nitrogen component, a and b are respectively the attractive term coefficient and co-volume term coefficient of the ammonia-nitrogen mixture, a i 、a j are respectively the attractive term coefficients of the nitrogen and ammonia components, b i 、b i are respectively the co-volume term coefficients of the nitrogen and ammonia components, a ij is the interaction term between component nitrogen and component ammonia; k ij is the ammonia-nitrogen binary interaction coefficient; Q2, Q1, Q0, D1, D0, C1, C0 are empirical constants; T rj 、T cj are respectively the reduced temperature and critical temperature of the ammonia component; ω i is the acentric factor of the nitrogen component.

[0042] Furthermore, based on the gas-phase and liquid-phase fugacity coefficients of the nitrogen component and the gas-phase and liquid-phase fugacity coefficients of the ammonia component and the nitrogen component, the content of the second-phase component in the ammonia-nitrogen mixture under the phase equilibrium state is obtained, and the calculation formula is as follows:

[0043]

[0044]

[0045] Furthermore, the condition for the content of the second-phase component in the ammonia-nitrogen mixture under the phase equilibrium state to satisfy the threshold is:

[0046] or

[0047] Further, the fluid phase state of the nitrogen-ammonia mixture is determined by calculating based on the dew point temperature and bubble point temperature of the nitrogen-ammonia mixture in combination with the fluid temperature of the nitrogen-ammonia mixture, including:

[0048] When the mixture temperature is higher than the bubble point temperature value, it is in the gas phase region; when the mixture temperature is lower than the bubble point temperature and higher than the dew point temperature value, it is in the gas-liquid two-phase region; when the mixture temperature is lower than the dew point temperature value, it is in the liquid phase region.

[0049] Further, the calculation model of the thermophysical property parameters of the ammonia-nitrogen mixture includes:

[0050] Calculation formulas for various thermophysical property parameters of the ammonia-nitrogen mixture based on the fluid phase state and the van der Waals mixing rule, where

[0051] The various thermophysical property parameters of the ammonia-nitrogen mixture include density, specific enthalpy, specific entropy, and dynamic viscosity.

[0052] Further, the van der Waals mixing rule has the following expression:

[0053]

[0054]

[0055] where a and b are the gravitational term coefficient and the co-volume term coefficient of the ammonia-nitrogen mixture respectively, a i is the gravitational term coefficient of the nitrogen component, a j is the gravitational term coefficient of the ammonia component, b i is the co-volume term coefficient of the nitrogen component, b j is the co-volume term coefficient of the ammonia component, x i represents the gas-phase mole fraction of the nitrogen component, x j represents the gas-phase mole fraction of the nitrogen component, k ij is the ammonia-nitrogen binary interaction coefficient.

[0056] Further, the calculation expression for the mixture density ρ is as follows:

[0057]

[0058] where V (k+1) is the (k + 1)-th iteration result of the mixture molar volume; M is the average relative molecular mass of the ammonia-nitrogen mixture;

[0059] When |V (k+1) -V (k) | ≤ 10 -3 , V = V (k+1) The iteration ends, otherwise, continue to take the V (k+1) value for iteration until |V(k+1) -V (k) |≤10 -3 。

[0060] Furthermore, the calculation expression of the specific enthalpy H is as follows:

[0061]

[0062] Wherein, H* is the ideal gas enthalpy of the ammonia-nitrogen mixture under standard conditions, p is the pressure of the ammonia-nitrogen mixture; V is the molar volume of the ammonia-nitrogen mixture; R is the gas constant; T is the fluid temperature of the ammonia-nitrogen mixture; a and b are the gravitational term coefficient and the co-volume term coefficient of the mixture respectively.

[0063] Furthermore, the calculation expression of the specific entropy S is as follows:

[0064]

[0065] Wherein, S* is the ideal gas entropy of the fluid under standard conditions; p is the fluid pressure of the ammonia-nitrogen mixture; V is the molar volume of the ammonia-nitrogen mixture; R is the gas constant; T is the fluid temperature of the ammonia-nitrogen mixture.

[0066] Furthermore, the calculation expression of the dynamic viscosity μ is as follows:

[0067]

[0068]

[0069]

[0070] Wherein, μ is the dynamic viscosity of the ammonia-nitrogen mixture; Z c is the critical compression factor of the ammonia-nitrogen mixture; p r is the reduced pressure, p r = p / p c ; Tr is the reduced temperature, Tr = T / Tc; T is the fluid temperature of the ammonia-nitrogen mixture; p c is the critical pressure of the mixture; T c is the critical temperature of the mixture; ω is the acentric factor of the ammonia-nitrogen mixture, R’ represents the modified value of the gas constant, and b’ represents the modified value of the co-volume term of the ammonia-nitrogen mixture.

[0071] The present invention provides a thermal property calculation system for an ammonia-nitrogen mixture, characterized in that the system includes,

[0072] A first acquisition unit for acquiring the basic parameters of ammonia and nitrogen.

[0073] A second acquisition unit, configured to acquire the fluid temperature, fluid pressure, and the content of the first phase component in the ammonia-nitrogen mixture; the first phase component is a liquid phase or a gas phase;

[0074] A first determination unit, configured to determine the dew point temperature and the bubble point temperature of the nitrogen-ammonia mixture based on the fluid pressure of the ammonia-nitrogen mixture;

[0075] A second determination unit, configured to determine the fluid phase state of the nitrogen-ammonia mixture based on the dew point temperature and the bubble point temperature of the nitrogen-ammonia mixture in combination with the fluid temperature of the ammonia-nitrogen mixture;

[0076] A construction unit, configured to construct a calculation model for the thermophysical property parameters of the ammonia-nitrogen mixture based on the fluid phase state;

[0077] A third acquisition unit, configured to acquire various thermophysical property parameters of the ammonia-nitrogen mixture based on the calculation model for the thermophysical property parameters of the ammonia-nitrogen mixture.

[0078] Technical effects and advantages of the present invention:

[0079] The physical property / phase characteristic calculation model established by the present invention has a good agreement between the calculation results of the ammonia thermophysical property parameters and the experimental data. Based on the PR equation and the gas-liquid phase equilibrium principle, the present invention uses the vdW mixing rule to calculate various thermophysical property parameters of ammonia, and establishes an ammonia-nitrogen thermophysical property calculation model. Compared with relying on a limited set of empirical parameters, the model takes into account molecular interactions and thermodynamic properties on a theoretical basis, is applicable to a wider range of ammonia-nitrogen mixture composition conditions, and has a high calculation efficiency for the phase equilibrium properties and thermodynamic property parameters of the ammonia-nitrogen mixture, and can provide the required fluid thermophysical property information for the design of ammonia pipelines and process simulations.

[0080] Other features and advantages of the present invention will be described in the following specification, and some of them will be obvious from the specification or understood by implementing the present invention. The objectives and other advantages of the present invention can be realized and obtained by the structures pointed out in the specification and the drawings. Description of the Drawings

[0081] Figure 1 It is a flowchart of a method for calculating the thermophysical properties of an ammonia-nitrogen mixture according to the present invention;

[0082] Figure 2 It is a flowchart for calculating the thermophysical property parameters of an ammonia-nitrogen mixture in a specific embodiment of the present invention;

[0083] Figure 3 It is a phase diagram of an ammonia-nitrogen mixture calculated by the model in a specific embodiment of the present invention;

[0084] Figure 4It is the curve graph showing the relationship between the density of ammonia-nitrogen mixture calculated by the model and temperature and pressure in the specific embodiment of the present invention;

[0085] Figure 5 It is the curve graph showing the relationship between the dynamic viscosity of ammonia-nitrogen mixture calculated by the model and temperature and pressure in the specific embodiment of the present invention;

[0086] Figure 6 It is the curve graph showing the relationship between the specific enthalpy of ammonia-nitrogen mixture calculated by the model and temperature and pressure in the specific embodiment of the present invention;

[0087] Figure 7 It is the curve graph showing the relationship between the specific entropy of ammonia-nitrogen mixture calculated by the model and temperature and pressure in the specific embodiment of the present invention. Specific Embodiment

[0088] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0089] To solve the deficiencies of the prior art, the present invention discloses a method for calculating the thermal physical properties of ammonia-nitrogen mixture, as Figure 1 shown, the method includes: Step 1: Obtain the basic parameters of ammonia and nitrogen; obtain the fluid temperature, fluid pressure of the ammonia-nitrogen mixture, and the content of the first-phase component in the ammonia-nitrogen mixture; the first-phase component is a liquid phase or a gas phase; Step 2: Based on the fluid pressure of the ammonia-nitrogen mixture, determine the dew point temperature and bubble point temperature of the nitrogen-ammonia mixture; Step 3: Based on the dew point temperature and bubble point temperature of the nitrogen-ammonia mixture and the fluid temperature of the ammonia-nitrogen mixture, determine the fluid phase state of the nitrogen-ammonia mixture; Step 4: Based on the fluid phase state, construct a calculation model for the thermal physical property parameters of the ammonia-nitrogen mixture; Step 5: Based on the calculation model for the thermal physical property parameters of the ammonia-nitrogen mixture, obtain various thermal physical property parameters of the ammonia-nitrogen mixture.

[0090] Combined with Figure 2 , for Step 1: Based on the Thermo Data Engine (TDE) database platform, determine the basic parameters of ammonia and nitrogen, including critical temperature, critical pressure, molecular mass, and acentric factor. And input the fluid temperature T, fluid pressure P, and the content of the first-phase component of the ammonia-nitrogen mixture.

[0091] For Step 2: Based on the fluid pressure of the ammonia-nitrogen mixture, determine the dew point temperature and bubble point temperature of the nitrogen-ammonia mixture, specifically as follows:

[0092] Based on the Antoine equation, obtain the dew point temperature estimate and the bubble point temperature estimate of the nitrogen-ammonia mixture according to the fluid pressure of the nitrogen-ammonia mixture;

[0093] Calculate the content of the second-phase component in the nitrogen-ammonia mixture at the phase equilibrium state according to the dew point temperature estimate, the bubble point temperature estimate, and the content of the first-phase component in the nitrogen-ammonia mixture;

[0094] When the content of the second-phase component in the nitrogen-ammonia mixture at the phase equilibrium state meets the threshold, the dew point temperature estimate and the bubble point temperature estimate of the nitrogen-ammonia mixture are the dew point temperature value and the bubble point temperature value of the nitrogen-ammonia mixture;

[0095] When the content of the second-phase component in the nitrogen-ammonia mixture at the phase equilibrium state does not meet the threshold, re-obtain the dew point temperature estimate and the bubble point temperature estimate, and repeat the above steps one or more times until the content of the second-phase component in the nitrogen-ammonia mixture calculated meets the threshold.

[0096] In a specific embodiment of the present invention, given the fluid pressure p of the nitrogen-ammonia mixture, estimate the dew point temperature estimate T0 d and the bubble point temperature estimate T0 b Specifically:

[0097]

[0098]

[0099] where F, E, and K are empirical coefficients of the saturated vapor pressure of the nitrogen-ammonia mixture; p is the fluid pressure of the mixture, in Pa.

[0100] In a specific embodiment of the present invention, according to the dew point temperature estimate T0 d and the bubble point temperature estimate T0 b obtained above, calculate the gravitational term coefficients a i , a j and the co-volume term coefficients b i , b j of the nitrogen and ammonia components respectively. Specifically:

[0101]

[0102]

[0103]

[0104]

[0105]

[0106]

[0107] Among them, i is the nitrogen component, and j is the ammonia component; a i is the gravitational term coefficient of the nitrogen component, a j is the gravitational term coefficient of the ammonia component, b i is the co-volume term coefficient of the nitrogen component, b j is the co-volume term coefficient of the ammonia component, ω i and ω j are the fluid eccentricity factors of the nitrogen component and the ammonia component respectively. R is the gas constant, taken as 8.314 J / (mol·K); pci and p cj are the critical pressures of the nitrogen component and the ammonia component respectively, in Pa; T ri and T rj are the reduced temperatures of the nitrogen component and the ammonia component respectively, T ci and T cj are the critical temperatures of the nitrogen component and the ammonia component respectively, in K; T0 d is the estimated dew point temperature and T0 b is the estimated bubble point temperature.

[0108] In a specific embodiment of the present invention, according to the obtained gravitational term coefficients a i and a j and co-volume term coefficients b i and b j , and the known gas-phase (liquid-phase) mole fraction x (y), calculate the gas-phase and liquid-phase fugacity coefficients φ v and φ l and the liquid-phase (gas-phase) mole component y (x) at the phase equilibrium state. Specifically:

[0109]

[0110]

[0111]

[0112]

[0113]

[0114]

[0115]

[0116]

[0117]

[0118] Among them, R is the gas constant, taking 8.314 J / (mol·K); p is the pressure of the ammonia-nitrogen mixture; Z is the compressibility factor; φ i v is the fugacity coefficient of the nitrogen component in the gas phase, φ i l is the fugacity coefficient of the nitrogen component in the liquid phase, φ j v is the fugacity coefficient of the ammonia component in the gas phase, φ j l is the fugacity coefficient of the ammonia component in the liquid phase, x i and y i respectively represent the gas-phase mole fraction and liquid-phase mole fraction of the nitrogen component, x j and y j respectively represent the gas-phase mole fraction and liquid-phase mole fraction of the nitrogen component, a and b are respectively the attractive term coefficient and co-volume term coefficient of the ammonia-nitrogen mixture, a i 、a j are respectively the attractive term coefficients of the nitrogen and ammonia components, b i 、b i are respectively the co-volume term coefficients of the nitrogen and ammonia components, a ij is the interaction term between component nitrogen and component ammonia; k ij is the ammonia-nitrogen binary interaction coefficient; Q2, Q1, Q0, D1, D0, C1, C0 are empirical constants; T rj 、T cj are respectively the reduced temperature and critical temperature of the ammonia component; ω i is the acentric factor of the nitrogen component.

[0119] In a specific embodiment of the present invention, it is determined whether the content of the second-phase component in the ammonia-nitrogen mixture in the phase equilibrium state of the iterative calculation result meets the threshold, specifically:

[0120] or

[0121] wherein, x j and y j respectively represent the gas-phase mole fraction and liquid-phase mole fraction of the nitrogen component.

[0122] For step 3: Based on the dew point temperature and bubble point temperature of the nitrogen-ammonia mixture and combined with the fluid temperature of the ammonia-nitrogen mixture, determine the fluid phase state of the nitrogen-ammonia mixture, including: when the mixture temperature is higher than the bubble point temperature value, it is in the gas phase region; when the mixture temperature is lower than the bubble point temperature and higher than the dew point temperature value, it is in the gas-liquid two-phase region; when the mixture temperature is lower than the dew point temperature value, it is in the liquid phase region.

[0123] For Step 4: Based on the fluid phase state, a calculation model for the thermophysical properties of the ammonia-nitrogen mixture is constructed. Among them, the calculation model for the thermophysical properties of the ammonia-nitrogen mixture is constructed based on the fluid phase state and the van der Waals mixing rule;

[0124] The calculation model for the thermophysical properties of the ammonia-nitrogen mixture includes calculation formulas for various thermophysical properties of the ammonia-nitrogen mixture, including calculation formulas for the density, specific enthalpy, specific entropy, and dynamic viscosity of the ammonia-nitrogen mixture.

[0125] In a specific embodiment of the present invention, the van der Waals mixing rule has the following expression:

[0126]

[0127]

[0128] Among them, a and b are the gravitational term coefficient and the co-volume term coefficient of the ammonia-nitrogen mixture, respectively. a i is the gravitational term coefficient of the nitrogen component, a j is the gravitational term coefficient of the ammonia component, b i is the co-volume term coefficient of the nitrogen component, b j is the co-volume term coefficient of the ammonia component, x i represents the gas-phase mole fraction of the nitrogen component, x j represents the gas-phase mole fraction of the nitrogen component, k ij is the ammonia-nitrogen binary interaction coefficient.

[0129] In a specific embodiment of the present invention, the calculation expression for the mixture density ρ is as follows:

[0130]

[0131]

[0132] Among them, V (k+1) is the (k + 1)th iteration result of the mixture molar volume, m 3 / mol; M is the average relative molecular mass of the ammonia-nitrogen mixture;

[0133] If Equation (23) holds, the iteration result converges; otherwise, continue the iterative calculation.

[0134] |V (k+1) -V (k) |≤10 -3 (23)

[0135] When |V (k+1) -V (k) |≤10 -3 , V = V (k+1) The iteration ends. Otherwise, continue to take the V (k+1) value for iteration until |V (k+1) - V (k) | ≤ 10 -3 .

[0136] In a specific embodiment of the present invention, the calculation expression of the specific enthalpy H is as follows:

[0137]

[0138] where H* is the ideal gas enthalpy of the ammonia-nitrogen mixture under standard conditions, kJ / kg; p is the pressure of the ammonia-nitrogen mixture, Pa; V is the molar volume of the ammonia-nitrogen mixture, m 3 / mol; R is the gas constant, taking 8.314 J / (mol·K); T is the fluid temperature of the ammonia-nitrogen mixture, K; a and b are the gravitational term coefficient and the co-volume term coefficient of the mixture, respectively.

[0139] In a specific embodiment of the present invention, the calculation expression of the specific entropy S is as follows:

[0140]

[0141] where S* is the ideal gas entropy of the fluid under standard conditions, kJ / (kg·K); p is the fluid pressure of the ammonia-nitrogen mixture, Pa; V is the molar volume of the ammonia-nitrogen mixture, m 3 / mol; R is the gas constant, taking 8.314 J / (mol·K); T is the fluid temperature of the ammonia-nitrogen mixture, K.

[0142] In a specific embodiment of the present invention, the calculation expression of the dynamic viscosity μ is as follows:

[0143]

[0144]

[0145]

[0146] where μ is the dynamic viscosity of the mixture, μPa·s; Z c is the critical compression factor of the mixture; p r is the reduced pressure, p r = p / p c ; T r is the reduced temperature, T r = T / T c ; T is the temperature of the mixture, K; p c is the critical pressure of the mixture, Pa; T cis the critical temperature of the mixture, K; a and b are the attractive term coefficient and the co-volume term coefficient of the mixture respectively; ω is the acentric factor of the mixture, R’ represents the modified value of the gas constant, and b’ represents the modified value of the co-volume term of the ammonia-nitrogen mixture.

[0147] Step 5: Based on the calculation model of the thermophysical property parameters of the ammonia-nitrogen mixture, obtain various thermophysical property parameters of the ammonia-nitrogen mixture, and the various thermophysical property parameters of the ammonia-nitrogen mixture include density, specific enthalpy, specific entropy, and dynamic viscosity.

[0148] Compared with the prior art, the present invention has the following beneficial effects: The calculation results of the physical property / phase property calculation model established by the present invention for the ammonia thermophysical property parameters are in good agreement with the experimental data. Based on the PR equation and the gas-liquid phase equilibrium principle, the present invention uses the vdW mixing rule to calculate various thermophysical property parameters of ammonia, and establishes an ammonia-nitrogen thermophysical property calculation model. Compared with relying on a limited set of empirical parameters, the model considers molecular interactions and thermodynamic properties on a theoretical basis, is applicable to a wider range of ammonia-nitrogen mixture composition conditions, and at the same time has a high calculation efficiency for the phase equilibrium properties and thermodynamic property parameters of the ammonia-nitrogen mixture, and can provide the required fluid thermophysical property information for the design of ammonia pipelines and the process simulation process.

[0149] The present invention also provides a thermophysical property calculation system for an ammonia-nitrogen mixture, and the system includes,

[0150] The first acquisition unit is used to acquire the basic parameters of ammonia and nitrogen;

[0151] The second acquisition unit is used to acquire the fluid temperature, fluid pressure, and the content of the first phase component in the ammonia-nitrogen mixture of the ammonia-nitrogen mixture; the first phase component is a liquid phase or a gas phase;

[0152] The first determination unit is used to determine the dew point temperature and bubble point temperature of the nitrogen-ammonia mixture based on the fluid pressure of the ammonia-nitrogen mixture;

[0153] The second determination unit is used to determine the fluid phase state of the nitrogen-ammonia mixture based on the dew point temperature and bubble point temperature of the nitrogen-ammonia mixture in combination with the fluid temperature of the ammonia-nitrogen mixture;

[0154] The construction unit is used to construct a calculation model of the thermophysical property parameters of the ammonia-nitrogen mixture based on the fluid phase state;

[0155] The third acquisition unit obtains various thermophysical property parameters of the ammonia-nitrogen mixture based on the calculation model of the thermophysical property parameters of the ammonia-nitrogen mixture.

[0156] Regarding the system in the above embodiments, the specific manner in which each unit performs operations has been described in detail in the embodiments related to the method, and will not be elaborated here.

[0157] In order to better illustrate the accuracy of the model for calculating the phase equilibrium of ammonia-nitrogen mixtures, the model is used to calculate the phase diagram of an ammonia-nitrogen mixture containing 10% mole fraction of nitrogen. The calculation results are as Figure 3 shown. The calculation results include the bubble point line, dew point line of the mixture, and the two-phase region enclosed by the two lines. The critical temperature and critical pressure are 404.9 K and 14.53 MPa respectively. The model calculation results are in good agreement with the experimental results.

[0158] In order to better illustrate the calculation stability and accuracy of the thermal property model for ammonia-nitrogen mixture thermal property parameters, different working conditions are selected for calculation. Due to the limited existing experimental data, the density, dynamic viscosity, specific enthalpy, and specific entropy of an ammonia-nitrogen mixture containing 10% mole fraction of nitrogen are calculated under the temperature conditions of 303.15 K, 313.15 K, 323.15 K, 333.15 K, 343.15 K and the pressure range of 0.1 - 12 MPa. The relative error, that is, the ratio of the absolute difference between the model calculation value and the experimental value to the experimental value, is used to characterize the calculation accuracy of the model. From Figures 4 - 7 it can be seen that the average relative deviations of the model for calculating density, dynamic viscosity, specific enthalpy, and specific entropy are 1.26%, 2.24%, 4.58%, and 4.76% respectively, and their maximum relative errors do not exceed 10%. At the same time, the deviation fluctuations of the model calculation results under each group of working conditions are small. This shows that the model has good accuracy and stability.

[0159] In summary, based on the PR equation and the gas-liquid phase equilibrium principle, the present invention establishes a calculation model for ammonia-nitrogen thermal properties. Compared with relying on a limited set of empirical parameters, the calculation model takes into account molecular interactions and thermodynamic properties on a theoretical basis, is applicable to a wider range of ammonia-nitrogen mixture composition conditions, and at the same time has a high calculation efficiency for the phase equilibrium properties and thermodynamic property parameters of ammonia-nitrogen mixtures. In a preferred embodiment, preset mixing rules are used to calculate various thermal property parameters of ammonia in the temperature range of 303.15 - 343.15 K and the pressure range of 0.1 - 12 MPa, and the results have high accuracy and good stability. It can provide the required fluid thermal property information for the design of ammonia pipelines and process simulations.

[0160] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for calculating the thermal properties of an ammonia-nitrogen mixture, characterized in that, The method includes: Obtaining the basic parameters of ammonia and nitrogen; Obtaining the fluid temperature, fluid pressure of the ammonia-nitrogen mixture, and the content of the first-phase component in the ammonia-nitrogen mixture; the first-phase component is a liquid phase or a gas phase; Based on the fluid pressure of the ammonia-nitrogen mixture, determining the dew point temperature and bubble point temperature of the nitrogen-ammonia mixture; Based on the dew point temperature and bubble point temperature of the nitrogen-ammonia mixture and the fluid temperature of the ammonia-nitrogen mixture, determining the fluid phase state of the nitrogen-ammonia mixture; Based on the fluid phase state, constructing a calculation model for the thermophysical properties of the ammonia-nitrogen mixture; Based on the calculation model for the thermophysical properties of the ammonia-nitrogen mixture, obtaining various thermophysical properties of the ammonia-nitrogen mixture.

2. The method for calculating the thermophysical properties of an ammonia-nitrogen mixture according to claim 1, wherein: The basic parameters of the ammonia and nitrogen include critical temperature, critical pressure, molecular mass, and acentric factor.

3. The thermal property calculation method of an ammonia-nitrogen mixture according to claim 1, characterized in that The determining the dew point temperature and bubble point temperature of the nitrogen-ammonia mixture based on the fluid pressure of the ammonia-nitrogen mixture includes: Based on the Antoine equation, obtaining the estimated dew point temperature and estimated bubble point temperature of the nitrogen-ammonia mixture according to the fluid pressure of the ammonia-nitrogen mixture; According to the estimated dew point temperature, estimated bubble point temperature, and the content of the first-phase component in the ammonia-nitrogen mixture, calculating the content of the second-phase component in the ammonia-nitrogen mixture under the phase equilibrium state; When the content of the second-phase component in the ammonia-nitrogen mixture under the phase equilibrium state meets the threshold, the estimated dew point temperature and estimated bubble point temperature of the nitrogen-ammonia mixture are the dew point temperature value and bubble point temperature value of the nitrogen-ammonia mixture; When the content of the second-phase component in the ammonia-nitrogen mixture under the phase equilibrium state does not meet the threshold, re-obtaining the estimated dew point temperature and estimated bubble point temperature, and repeating the above steps once or multiple times until the content of the second-phase component in the ammonia-nitrogen mixture calculated under the phase equilibrium state meets the threshold.

4. The thermal property calculation method of an ammonia-nitrogen mixture according to claim 3, characterized in that, The calculating the content of the second-phase component in the ammonia-nitrogen mixture under the phase equilibrium state according to the estimated dew point temperature, estimated bubble point temperature, and the content of the first-phase component in the ammonia-nitrogen mixture includes: According to the estimated dew point temperature, estimated bubble point temperature, and the content of the first-phase component in the ammonia-nitrogen mixture, calculating the gravitational term coefficient of the nitrogen component, the gravitational term coefficient of the ammonia component, the co-volume term coefficient of the nitrogen component, and the co-volume term coefficient of the ammonia component; Combining the gravitational term coefficient of the nitrogen component, the gravitational term coefficient of the ammonia component, the co-volume term coefficient of the nitrogen component, and the co-volume term coefficient of the ammonia component, and calculating based on the content of the first-phase component in the nitrogen mixture to obtain the gas and liquid fugacity coefficients of the nitrogen component and the gas and liquid fugacity coefficients of the ammonia component and nitrogen component in the ammonia-nitrogen mixture; Based on the gas and liquid fugacity coefficients of the nitrogen component and the gas and liquid fugacity coefficients of the ammonia component and nitrogen component, obtaining the content of the second-phase component in the ammonia-nitrogen mixture under the phase equilibrium state.

5. The method for calculating the thermophysical properties of an ammonia-nitrogen mixture according to claim 3 or 4, wherein: The second-phase component in the ammonia-nitrogen mixture is a liquid phase or a gas phase, wherein, When the first-phase component is in the liquid phase, the second-phase component is in the gas phase; When the first-phase component is in the gas phase, the second-phase component is in the liquid phase.

6. The thermal property calculation method of an ammonia-nitrogen mixture according to claim 5, characterized in that, The gravitational term coefficient of the nitrogen component, the gravitational term coefficient of the ammonia component, the co-volume term coefficient of the nitrogen component, and the co-volume term coefficient of the ammonia component, and the calculation formula is as follows: Among them, a i is the coefficient of the gravitational term of the nitrogen component, a j is the coefficient of the gravitational term of the ammonia component, b i is the coefficient of the co-volume term of the nitrogen component, b j is the coefficient of the co-volume term of the ammonia component, ω i and ω j are the fluid eccentricity factors of the nitrogen component and the ammonia component respectively. R is the gas constant, p ci and p cj are the critical pressures of the nitrogen component and the ammonia component respectively, T ri and T rj are the reduced temperatures of the nitrogen component and the ammonia component respectively, T ci and T cj are the critical temperatures of the nitrogen component and the ammonia component respectively, is the estimated dew point temperature and is the estimated bubble point temperature.

7. The thermophysical property calculation method of an ammonia-nitrogen mixture according to claim 6, characterized in that The calculation formulas for the gas-phase and liquid-phase fugacity coefficients of the nitrogen component and the gas-phase and liquid-phase fugacity coefficients of the ammonia and nitrogen components of the ammonia component are as follows: Among them, wherein, R is the gas constant; p is the pressure of the ammonia-nitrogen mixture; Z is the compressibility factor; φ i v is the fugacity coefficient of the nitrogen component in the gas phase, φ i l is the fugacity coefficient of the nitrogen component in the liquid phase, φ j v is the fugacity coefficient of the ammonia component in the gas phase, φ j l is the fugacity coefficient of the ammonia component in the liquid phase, x i and y i respectively represent the mole fraction of the nitrogen component in the gas phase and the mole fraction in the liquid phase, x j and y j respectively represent the mole fraction of the nitrogen component in the gas phase and the mole fraction in the liquid phase, a and b are respectively the attraction term coefficient and the co-volume term coefficient of the ammonia-nitrogen mixture, a i、 a j are respectively the attraction term coefficients of the nitrogen and ammonia components, b i 、b i are respectively the co-volume term coefficients of the nitrogen and ammonia components, a ij is the interaction term between component nitrogen and component ammonia; k ij is the ammonia-nitrogen binary interaction coefficient; Q2, Q1, Q0, D1, D0, C1, C0 are empirical constants; T rj 、T cj are respectively the reduced temperature and the critical temperature of the ammonia component; ω i is the acentric factor of the nitrogen component.

8. A method for calculating the thermal properties of an ammonia-nitrogen mixture according to claim 7, characterized in that, Based on the gas-phase and liquid-phase fugacity coefficients of the nitrogen component and the gas-phase and liquid-phase fugacity coefficients of the ammonia and nitrogen components of the ammonia component, the content of the second-phase component in the ammonia-nitrogen mixture under the phase equilibrium state is obtained, and the calculation formula is as follows:

9. A method for calculating the thermal properties of an ammonia-nitrogen mixture according to claim 8, characterized in that, The condition for the content of the second-phase component in the ammonia-nitrogen mixture under the phase equilibrium state to satisfy the threshold is: or 10. A method for calculating the thermal properties of an ammonia-nitrogen mixture according to claim 1, characterized in that, Based on the dew point temperature and bubble point temperature of the ammonia-nitrogen mixture and combined with the fluid temperature of the ammonia-nitrogen mixture for calculation, to determine the fluid phase state of the ammonia-nitrogen mixture, including: When the mixture temperature is higher than the bubble point temperature value, it is in the gas phase region; when the mixture temperature is lower than the bubble point temperature and higher than the dew point temperature value, it is in the gas-liquid two-phase region; when the mixture temperature is lower than the dew point temperature value, it is in the liquid phase region.

11. The thermal property calculation method of an ammonia-nitrogen mixture according to claim 1, characterized in that The calculation model of the thermophysical property parameters of the ammonia-nitrogen mixture includes: The calculation formulas for the various thermophysical property parameters of the ammonia-nitrogen mixture based on the fluid phase state and the van der Waals mixing rule, where The various thermophysical property parameters of the ammonia-nitrogen mixture include density, specific enthalpy, specific entropy, and dynamic viscosity.

12. A method for calculating the thermal properties of an ammonia-nitrogen mixture according to claim 11, characterized in that, The van der Waals mixing rule, the expression is as follows: Among them, a and b are the gravitational term coefficient and the co-volume term coefficient of the ammonia-nitrogen mixture, respectively. a i is the gravitational term coefficient of the nitrogen component, a j is the gravitational term coefficient of the ammonia component, b i is the co-volume term coefficient of the nitrogen component, b j is the co-volume term coefficient of the ammonia component, x i represents the gas-phase mole fraction of the nitrogen component, x j represents the gas-phase mole fraction of the nitrogen component, k ij is the ammonia-nitrogen binary interaction coefficient.

13. According to the thermophysical property calculation method of an ammonia-nitrogen mixture described in claim 12, characterized in that The calculation expression of the mixture density ρ is as follows: Among them, V (k+1) is the (k + 1)-th iteration result of the molar volume of the mixture; M is the average relative molecular mass of the ammonia-nitrogen mixture; When |V (k+1) - V (k) | ≤ 10 -3 , V = V (k+1) The iteration ends, otherwise continue to obtain the V (k+1) value for iteration until |V (k+1) - V (k) | ≤ 10 -3 .

14. According to the thermophysical property calculation method of an ammonia-nitrogen mixture described in claim 12, characterized in that The calculation expression of the specific enthalpy H is as follows: Where, H* is the ideal gas enthalpy of the ammonia-nitrogen mixture under standard conditions, p is the pressure of the ammonia-nitrogen mixture; V is the molar volume of the ammonia-nitrogen mixture; R is the gas constant; T is the fluid temperature of the ammonia-nitrogen mixture; a and b are respectively the gravitational term coefficient and co-volume term coefficient of the mixture.

15. A method for calculating the thermal properties of an ammonia-nitrogen mixture according to claim 12, characterized in that, The calculation expression of the specific entropy S is as follows: Where, S* is the ideal gas entropy of the fluid under standard conditions; p is the fluid pressure of the ammonia-nitrogen mixture; V is the molar volume of the ammonia-nitrogen mixture; R is the gas constant; T is the fluid temperature of the ammonia-nitrogen mixture.

16. A method for calculating the thermal properties of an ammonia-nitrogen mixture according to claim 12, characterized in that, The calculation expression of the dynamic viscosity μ is as follows: Among them, μ is the dynamic viscosity of the ammonia-nitrogen mixture; Z c is the critical compression factor of the ammonia-nitrogen mixture; p r is the reduced pressure, p r = p / p c ; Tr is the reduced temperature, Tr = T / Tc; T is the fluid temperature of the ammonia-nitrogen mixture; p c is the critical pressure of the mixture; T c is the critical temperature of the mixture; ω is the acentric factor of the ammonia-nitrogen mixture, R’ represents the modified value of the gas constant, and b’ represents the modified value of the co-volume term of the ammonia-nitrogen mixture.

17. A thermal property calculation system for an ammonia-nitrogen mixture, characterized in that, The system includes A first acquisition unit for acquiring the basic parameters of ammonia and nitrogen; A second acquisition unit for acquiring the fluid temperature, fluid pressure, and the content of the first-phase component in the ammonia-nitrogen mixture; the first-phase component is a liquid phase or a gas phase; A first determination unit for determining the dew point temperature and bubble point temperature of the ammonia-nitrogen mixture based on the fluid pressure of the ammonia-nitrogen mixture; A second determination unit for determining the fluid phase state of the ammonia-nitrogen mixture based on the dew point temperature and bubble point temperature of the ammonia-nitrogen mixture and combined with the fluid temperature of the ammonia-nitrogen mixture; A construction unit for constructing a calculation model of the thermophysical property parameters of the ammonia-nitrogen mixture based on the fluid phase state; A third acquisition unit for acquiring the various thermophysical property parameters of the ammonia-nitrogen mixture based on the calculation model of the thermophysical property parameters of the ammonia-nitrogen mixture.

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