Calculation method and system of hydrate phase diagram

Abstract

The embodiment of the invention provides a hydrate phase diagram calculation method and system, and the method comprises the steps: carrying out the interpolation calculation between a temperature of one atmospheric pressure and a temperature Q1, calculating the pressure according to the temperature through a three-phase line determination method, and drawing a three-phase line L-H-V; calculating a four-phase point Q2L corresponding to the bubble point of the to-be-processed component through a PR equation and a flash evaporation algorithm; if Q2L exists, determining a four-phase point Q2U corresponding to the dew point; if Q2U exists, based on the Q2U and the Q2L, pressure is calculated according to the temperature, a four-phase line Lw-H-V-LHC is drawn, the temperature is calculated according to the pressure, a three-phase line Lw-H-LHC is drawn, and a hydrate phase diagram corresponding to the to-be-treated component is completed.

Description

Technical Field

[0001] The embodiments of the present application belong to the technical field of hydrate phase diagram calculation, and in particular, relate to a method and system for calculating a hydrate phase diagram. Background Art

[0002] Natural gas hydrate is a new type of clean energy commonly known as "combustible ice". It has attracted widespread attention due to its abundant reserves and environmental friendliness. Compared with traditional petrochemical energy, natural gas hydrate has obvious advantages, especially in terms of cleanliness and resource reserves. The material morphology of natural gas hydrate presents a crystal structure similar to ice. It is composed of natural gas and water molecules. Its general molecular formula can be expressed by M·nH2O, where H2O is called the host molecule and M is called the guest molecule. Due to the different molecular sizes of guest molecules, the hydrates formed are of two types, I and II. The empty hydrate lattice without guest filling is in a metastable state, and the empty hydrate gradually stabilizes with the filling of guest molecules. The earliest research on hydrates originated from its blockage phenomenon in natural gas transportation and Arctic oil transportation pipelines, so researchers are committed to predicting and inhibiting the conditions for the formation of hydrates. However, with the in-depth understanding of the characteristics of hydrates, people gradually realize its great potential in energy utilization and environmental protection. At present, China has successfully mined natural gas hydrates as a supplement to natural gas resources.

[0003] In order to explore the conditions for hydrate formation, there have been many studies on the phase equilibrium of hydrates. As early as 1941, Wilcox and Katz et al. proposed a semi-empirical K-factor and Gas gravity correlation model to predict the formation of hydrates. However, since this method is based on empirical formulas to a certain extent, it may produce errors or inaccurate results under conditions beyond its scope of use. Van der Waals and Plattteeuw quantitatively characterized the thermodynamic properties of hydrates using statistical thermodynamic methods based on the structural rules of natural gas hydrates. On this basis, Parrish and Prausnitz calculated the IHV (ice-hydrate-gas) and Lw-HV (water-hydrate-gas) phase diagrams using the Kihara molecular potential energy model. Ng and Robinson proposed a method for calculating the second quadruple point and a method for calculating the Lw-H-LHC (water-hydrate-liquid hydrocarbon) phase diagram. However, there is currently no systematic method for calculating phase diagrams containing one, two or three quadruple points.

[0004] Based on this, a calculation method for the hydrate phase diagram is needed. Summary of the invention

[0005] The embodiments of this specification provide a method and system for calculating a hydrate phase diagram to solve some or all of the problems: Although there has been some research on hydrate phase diagrams in the prior art, there is currently no systematic method for calculating phase diagrams containing one, two or three quadruple points.

[0006] To solve the above technical problems, the embodiments of this specification are implemented as follows:

[0007] The present specification provides a method for calculating a hydrate phase diagram, the method comprising:

[0008] Perform interpolation calculation between the temperature of 1 atmosphere and the temperature Q1, calculate the pressure according to the temperature using the three-phase line determination method, and draw the three-phase line LHV;

[0009] The four-phase point Q corresponding to the bubble point of the component to be treated is calculated by the PR equation and flash evaporation algorithm. 2L ;

[0010] If there is Q 2L , then determine the four-phase point Q corresponding to the dew point 2U ;

[0011] If there is Q 2U , then based on the Q 2U And the Q 2L , calculate the pressure according to the temperature, and draw the four-phase line L w -HVL HC , calculate the temperature according to the pressure, and draw the three-phase line L w -HL HC , complete the hydrate phase diagram corresponding to the component to be treated.

[0012] The present specification also provides a calculation system for a hydrate phase diagram, the calculation system comprising:

[0013] The first determination module performs interpolation calculation between the temperature of 1 atmosphere and the temperature Q1, calculates the pressure according to the temperature using the three-phase line determination method, and draws the three-phase line LHV;

[0014] The bubble point determination module calculates the four-phase point Q corresponding to the bubble point of the component to be treated through the PR equation and flash evaporation algorithm. 2L ;

[0015] Dew point determination module, if there is Q 2L , then determine the four-phase point Q corresponding to the dew point 2U ;

[0016] Four-phase line determination module, if there is Q 2U , then based on the Q 2U And the Q 2L, calculate the pressure according to the temperature and draw the four-phase line L w -HVL HC , calculate the temperature according to the pressure, and draw the three-phase line L w -HL HC , complete the hydrate phase diagram corresponding to the component to be treated.

[0017] At least one of the above technical solutions adopted in the embodiments of this specification can achieve the following beneficial effects: interpolation calculation is performed between the temperature of 1 atmosphere and the temperature Q1, and the pressure is calculated according to the temperature using the three-phase line determination method, and the three-phase line LHV is drawn; the four-phase point Q corresponding to the bubble point of the component to be treated is calculated by the PR equation and the flash evaporation algorithm. 2L ;If there is Q 2L , then determine the four-phase point Q corresponding to the dew point 2U ;If there is Q 2U , then based on the Q 2U And the Q 2L , calculate the pressure according to the temperature and draw the four-phase line L w -HVL HC , calculate the temperature according to the pressure, and draw the three-phase line L w -HL HC , completing the hydrate phase diagram corresponding to the component to be treated, and being able to simultaneously calculate the phase diagram containing one, two or three quadruple points, and the accuracy of the calculation results is relatively high. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. Some specific embodiments of the present application will be described in detail in an illustrative and non-restrictive manner with reference to the drawings. The same reference numerals in the drawings indicate the same or similar components or parts. It should be understood by those skilled in the art that these drawings are not necessarily drawn to scale. In the drawings:

[0019] Figure 1 A schematic diagram of a method for calculating a hydrate phase diagram provided in an embodiment of this specification;

[0020] Figure 2 A schematic diagram of a flow chart of a three-phase line determination method provided in an embodiment of this specification;

[0021] Figure 3 A temperature and pressure diagram provided for the embodiments of this specification;

[0022] Figure 4 A block diagram of a method for calculating a hydrate phase diagram provided in an embodiment of this specification;

[0023] Figure 5 A schematic diagram of experimental verification results of a hydrate calculation method provided in an embodiment of this specification;

[0024] Figure 6 A schematic diagram of a system for calculating a hydrate phase diagram provided for this illustrative embodiment. DETAILED DESCRIPTION

[0025] In order to enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only embodiments of a part of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work should fall within the scope of protection of the present application.

[0026] Figure 1 The following is a flow chart of a method for calculating a hydrate phase diagram provided in an embodiment of the present specification. From a program perspective, the execution subject of the method for calculating a hydrate phase diagram is a program installed on an application server or an application terminal. It can be understood that the method can be executed by any device, equipment, platform, or device cluster with computing and processing capabilities. Figure 1 As shown, the calculation method includes:

[0027] Step S101: perform interpolation calculation between the temperature of 1 atmosphere and the temperature Q1, calculate the pressure according to the temperature using the three-phase line determination method, and draw the three-phase line LHV.

[0028] In the embodiment of this specification, the temperature Q1 is 273.15K.

[0029] The basis of this embodiment is the three-phase equilibrium principle of gas-water (or ice)-hydrate. When the three phases are in equilibrium, the chemical potential of water in the hydrate lattice phase (H phase) should be equal to its chemical potential in the water-rich (or ice) phase (α phase):

[0030]

[0031] in

[0032] represents the chemical potential of water in the hydrate lattice phase;

[0033] Represents the chemical potential of water in the water (or ice) phase α.

[0034] Since it is difficult to directly calculate the chemical potential of water in the hydrate lattice and in the water-rich (or ice) phase, the chemical potential of water in the empty hydrate lattice is usually selected as the reference state to compare the chemical potential difference between the two. At this time, the thermodynamic equilibrium condition for hydrate formation can be converted into:

[0035]

[0036] in

[0037] represents the chemical potential of water in the empty hydrate lattice,

[0038] represents the chemical potential difference between water in the filled hydrate lattice phase and the empty hydrate lattice phase,

[0039] Represents the chemical potential difference between water in the water-rich (or ice) phase and the empty hydrate lattice phase.

[0040] In the embodiment of this specification, the three-phase line determination method specifically includes:

[0041] Based on the hydrate type corresponding to the component to be treated, the Langmuir constant C is calculated. ji ;

[0042] Based on the Langmuir constant C ji , determine the chemical potential difference between water in the filled hydrate lattice phase and the empty hydrate lattice phase and the chemical potential difference between the water-rich (or ice) phase and the empty hydrate lattice phase

[0043] like The point corresponding to the temperature and pressure at this time is the three-phase parallel point, thereby generating a three-phase line.

[0044] In the embodiments of this specification, the hydrate types include type I hydrate and type II hydrate;

[0045] The Langmuir constant C ji The calculation formula is:

[0046]

[0047] in,

[0048] C ji represents the Langmuir constant of the j component for type i vacancies;

[0049] A ji is a pressure coefficient, and the pressure coefficient is determined by the component to be treated and the hydrate type;

[0050] B ji is a temperature coefficient, and the temperature coefficient is determined by the component to be treated and the hydrate type;

[0051] T represents temperature.

[0052] Table 1 Cavity constants of hydrate structures

[0053]

[0054] Table 2 Coefficients for calculating Langmuir constants

[0055]

[0056] In the embodiment of this specification, the chemical potential difference between the filled hydrate lattice phase and the empty hydrate lattice phase of water is The calculation formula is:

[0057]

[0058] in,

[0059] represents the chemical potential of water in the hydrate lattice phase;

[0060] represents the chemical potential of water in the empty hydrate lattice;

[0061] v i is the constant of type i holes;

[0062] f j is the fugacity of component j in the natural gas mixture;

[0063] C ji is the Langmuir constant of component j for type i vacancy;

[0064] R represents the gas constant;

[0065] T represents temperature;

[0066] The chemical potential difference between the water-rich (or ice) phase and the empty hydrate lattice phase The calculation formula is:

[0067]

[0068] in,

[0069] It represents pure liquid water at temperature T and hydrate dissociation pressure P R The chemical potential under

[0070] It represents pure liquid water at temperature T and hydrate dissociation pressure P R The chemical potential difference under

[0071] P R represents the hydrate dissociation pressure;

[0072] represents the hydrate reference state;

[0073] T0 represents the freezing temperature;

[0074] P0 represents the dissociation pressure of hydrate at freezing temperature;

[0075] represents the molar difference in volume between the empty hydrate lattice and ice;

[0076] represents the molar difference in enthalpy between the empty hydrate lattice and ice;

[0077] represents the molar difference in volume between ice and liquid water;

[0078] represents the molar difference in enthalpy between ice and liquid water;

[0079] R represents the gas constant;

[0080] T represents temperature.

[0081] The chemical potential difference between the water-rich (or ice) phase and the empty hydrate lattice phase is described in detail below. The acquisition process.

[0082] In the water-rich (or ice-rich) phase, It can be calculated according to the thermodynamic equilibrium theory:

[0083]

[0084] in:

[0085] represents the chemical potential of pure liquid water at temperature T and pressure P,

[0086] x ω represents the molar fraction of water in the liquid phase;

[0087] represents the chemical potential of ice at temperature T and pressure P. And further we can get:

[0088]

[0089]

[0090] and The calculated chemical potential difference is called the calculated chemical potential difference, and the two-step method for calculating the experimental chemical potential difference is used: (1) First, a hydrate reference state is introduced Where T0 and P0 represent the freezing point temperature and the dissociation pressure of the hydrate at this temperature, respectively. Then, according to the classical thermodynamic principles, the dissociation pressure P of the hydrate at the specified temperature T and its corresponding R (2) Then, based on the properties of the state function, the chemical potential difference at any temperature and pressure can be calculated using thermodynamic principles:

[0091]

[0092] The chemical potential difference between the water-rich (or ice) phase and the empty hydrate lattice phase is obtained.

[0093] In order to further understand the three-phase line determination method provided by the embodiments of this specification, this specification further provides a flow chart of the three-phase line determination method. Figure 2 A flow chart of a method for determining a three-phase line provided in an embodiment of this specification is shown in FIG. Figure 2 As shown in the figure, input the basic data and the hydrate formation phase equilibrium temperature under the assumed pressure conditions; according to the gas phase components, the Peng-Robinson (PR) state equation is used to calculate the fugacity f of the j component in the natural gas mixture. j ; Determine the hydrate type and calculate the Langmuir constant C ji ; Calculate the chemical potential difference between water in the empty hydrate lattice and in the hydrate phase Calculate the chemical potential difference between water in the empty hydrate lattice and in the water-rich (or ice) phase judge and Whether the difference meets the second preset tolerance, if so, the temperature and pressure are the three-phase equilibrium point, and the continuous temperature and pressure values ​​constitute the three-phase line.

[0094] The second preset tolerance can be determined according to the specific business scenario. In the embodiment of this specification, the second preset tolerance is 10 -4 .

[0095] Step S103: Calculate the quadruple point Q corresponding to the bubble point of the component to be treated by using the PR equation and flash evaporation algorithm 2L .

[0096] In the embodiments of this specification, the calculation formula of the PR equation is:

[0097]

[0098] in,

[0099] represents the chemical potential difference between water in the empty hydrate lattice and in the water-rich and ice phases

[0100] R represents the gas constant;

[0101] T represents temperature;

[0102] α j Represents an adjustable constant;

[0103] Y j 2 represents the quadratic mole fraction of component j in the hydrate phase

[0104] Y j 3 represents the cubic mole fraction of component j in the hydrate phase

[0105] m indicates cavity type m;

[0106] v m represents the number of m-type cavities per water molecule in the hydrate;

[0107] C mj is the Langmuir constant of component j in cavity type m;

[0108] f j is the fugacity of component j in the natural gas mixture;

[0109] x w It represents the molar fraction of water in the liquid phase.

[0110] In the examples of this specification, the PR equation and the flash evaporation algorithm are used to calculate the four-phase point Q corresponding to the bubble point of the component to be treated. 2L , specifically including:

[0111] The temperature Q1 is used as the initial temperature, and based on the PR equation, Newton's method is used to iterate until the PR equation satisfies the first preset tolerance, which is used as the quadruple point Q corresponding to the bubble point of the component to be treated. 2L .

[0112] The determination of the first preset tolerance needs to be determined according to the specific business scenario. In this embodiment, the first preset tolerance is 10 -5 .

[0113] In the examples of this specification, the quadruple point Q corresponding to the bubble point is calculated by the PR equation and the flash evaporation algorithm. 2L , further comprising:

[0114] If there is no Q2L , then the three-phase line determination method is used to extend outward from Q1, and the pressure is calculated according to the temperature to generate the three-phase line L w -HV.

[0115] In the embodiment of this specification, if Q does not exist 2L , then it belongs to the situation with a quadruple point, that is, small molecule gas is difficult to liquefy under high pressure. Such small molecule gas and water can usually only form a quadruple point, such as methane and nitrogen. Its phase diagram is as follows Figure 3 (a). It consists of two lines, IHV and L w -HV, all points on the line represent the three-phase coexistence state. A four-phase point Q1 is formed at the intersection of the two three-phase lines, that is, the four-phase coexistence state of IHV-Lw (ice-hydrate-gas phase-liquid water) formed at a temperature of 273.15K

[0116] Step S105: If Q exists 2L , then determine the four-phase point Q corresponding to the dew point 2U When drawing the equilibrium curve, first draw the IHV curve, set the starting point to 1atm and the end point to 273.15K. Since this curve is relatively flat, when the temperature changes greatly, the pressure changes very little. Use temperature as the independent variable to calculate the pressure. w In the case of -HV curve, since the curve is very steep, the pressure changes greatly when the temperature changes very little, so the pressure is used as the independent variable to calculate the temperature.

[0117] In the embodiments of this specification, if Q 2L , then determine the four-phase point Q corresponding to the dew point 2U , including:

[0118] At the temperature Q 2L As the initial temperature, based on the PR equation, Newton's method is used for iteration until the PR equation satisfies a first preset tolerance, and as the quadruple point Q corresponding to the dew point of the component to be treated 2U .

[0119] In the embodiments of this specification, if Q 2L , then determine the four-phase point Q corresponding to the dew point 2U , further comprising:

[0120] If there is no Q 2U , then from the Q 2L Extending outward, using the Clapeyron equation, the temperature is calculated based on the pressure to generate the three-phase line L w -VL HC .

[0121] In the present embodiment, there is Q 2L , but not Q 2U , it is considered to belong to the phase diagram containing two quadruple points. At this time, Q 2L It can be considered as Q2. For some pure components (such as heavier hydrocarbons), their bubble point and dew point are the same under high pressure, and this system will form an additional three-phase line Lw-HL HC , it and the three-phase line L w -HV intersection usually generates a second quadruple point Q2, that is, the HV-Lw-L HC (hydrate-gas phase-liquid water-liquid hydrocarbon) four-phase equilibrium state, such as Figure 3 (b) as shown.

[0122] To obtain such a hydrate phase diagram containing two quadruple points, it is first necessary to calculate the temperature and pressure of the quadruple point Q2. However, in condensate systems, conventional methods usually cannot give good prediction results. Ng and Robinson improved the method proposed by Parrish and Prausnitz by introducing an adjustable constant α j The chemical potential difference between water in the empty hydrate lattice and in the water-rich and ice phases is for:

[0123]

[0124] According to the theory of Ng and Robinson, the calculation of hydrate formation in condensed liquids first requires determining the minimum pressure and temperature at which hydrates form in the system. The first step is to assume the temperature at which hydrates form and use the appropriate state equation to calculate the bubble point pressure and bubble point vapor composition at that temperature. Therefore, temperature can be used as an iterative variable, and the pressure of the hydrate calculated from the gas phase composition and the bubble point pressure of the gas phase are used as equations. Newton's method can be used for iterative calculations until the equation meets the first preset tolerance, that is, the temperature and pressure of Q2 are determined.

[0125] Like IHV and L in the figure w -HV is calculated in the same way as methane. When the calculation point reaches Q2, then L w -HL HC Phase equilibrium curve. Since the propane has been completely liquefied at this time, the state of hydrate formation in the condensate system satisfies the following phase change process:

[0126]

[0127] Since there is no gas phase, all phases are condensed, and the volume change caused by phase change is very small, L w -HL HCis a line close to a vertical line. Therefore, in this embodiment, according to the Clapeyron equation Calculate the slope from point Q2 The calculation is done by gradually extending outward. w -HL HC The curve is very steep and requires the use of pressure as an independent variable.

[0128] in,

[0129] ΔH and ΔV are the enthalpy change and volume change when the liquid transforms into a hydrate.

[0130] ΔH can be measured based on experimental data. In the embodiment of this specification, ΔH=65400 J / mole.

[0131] ΔV is calculated according to the following formula:

[0132] ΔV=V H -V Lw -V HC

[0133] Where V H is the volume of the hydrate structure based on the unit cell,

[0134] V LW and V HC is the volume of liquid water and liquid hydrocarbon in each unit cell of hydrate, which can be calculated using IF97 and PR equations of state, respectively. IF97 is an internationally recognized standard for the thermophysical properties of water and water vapor and is a prior art, which will not be described in detail here.

[0135] Step S107: If Q exists 2U , then based on the Q 2U And the Q 2L , calculate the pressure according to the temperature and draw the four-phase line L w -HVL HC , calculate the temperature according to the pressure, and draw the three-phase line L w -HL HC , complete the hydrate phase diagram corresponding to the component to be treated.

[0136] In the present embodiment, there is Q 2U and Q 2L , then the composition of natural gas is a natural gas mixture. Figure 3 (b) Lw-VL HC The three-phase line will become wider and become an area, such as Figure 3(c) The CFK region marked in Figure 2 is because the natural gas mixture will have different bubble points and dew points at high pressure. Therefore, the four-phase point of the natural gas mixture will become a four-phase line, with the low point called Q 2L , the high point is called Q 2U .

[0137] In order to further understand the calculation method of the hydrate phase diagram provided in the embodiments of this specification, a block diagram of the calculation method of the hydrate phase diagram is further provided, such as Figure 4 shown. Figure 4 A block diagram of a method for calculating a hydrate phase diagram provided in an embodiment of this specification specifically includes the following steps:

[0138] Step S401: Calculate the temperature T of 1 atmosphere 1atm ;

[0139] Step S403: In T 1atm Interpolate between Q1 and Q1 (273.15K) and calculate the pressure based on the temperature;

[0140] Step S405: Calculate the quadruple point Q corresponding to the bubble point 2L (L w -HVL HC );

[0141] Step S407: From Q1 to Q 2L Interpolate between and calculate pressure based on temperature;

[0142] Step S409: Calculate the quadruple point Q corresponding to the dew point 2U (L w -HVL HC );

[0143] Step S411: In Q 2L To Q 2U Interpolate between and calculate pressure based on temperature;

[0144] Step S413: From Q 2U Extending outward, because the volume difference between the liquid and solid phases is very small, the curve becomes very steep, and the temperature is calculated based on the pressure.

[0145] In step S405, when there is no Q 2L When , it extends outward from Q1 and the calculation stops.

[0146] In step S409, when there is no Q 2U When, from Q 2L The calculation stops when the number of cells extends outward.

[0147] In order to further verify the calculation method of the hydrate phase diagram provided in the embodiments of this specification, this application further verifies the results of the phase diagram simulation calculation of multi-component natural gas hydrates using the SimTech Simulator of this application and experimental data, taking natural gas from two anonymous gas fields as an example, Figure 5 (a) is a comparison of simulation results for a gas field 1, for example, Figure 5 (b) The comparison of the simulation results of a gas field 2 shows that the phase diagram calculated by the method provided in this application is consistent with the actual experimental data and has high accuracy.

[0148] The calculation method of the hydrate phase diagram provided in the embodiment of this specification performs interpolation calculation between the temperature of 1 atmosphere and the temperature Q1, uses the three-phase line determination method to calculate the pressure according to the temperature, and draws the three-phase line LHV; calculates the four-phase point Q corresponding to the bubble point of the component to be treated by the PR equation and the flash evaporation algorithm. 2L ;If there is Q 2L , then determine the four-phase point Q corresponding to the dew point 2U ;If there is Q 2U , then based on the Q 2U And the Q 2L , calculate the pressure according to the temperature, and draw the four-phase line L w -HVL HC , calculate the temperature according to the pressure, and draw the three-phase line L w -HL HC , completing the hydrate phase diagram corresponding to the component to be treated, and being able to simultaneously calculate the phase diagram containing one, two or three quadruple points, and the accuracy of the calculation results is relatively high.

[0149] The foregoing embodiments of the present specification provide a method for calculating a hydrate phase diagram. Based on the same idea, the embodiments of the present specification also provide a system for calculating a hydrate phase diagram. Figure 6 A schematic diagram of a calculation system for a hydrate phase diagram provided in this embodiment. Figure 6 As shown, the computing system includes:

[0150] The first determination module 601 performs interpolation calculation between the temperature of 1 atmosphere and the temperature Q1, calculates the pressure according to the temperature using the three-phase line determination method, and draws the three-phase line LHV;

[0151] The bubble point determination module 603 calculates the four-phase point Q corresponding to the bubble point of the component to be treated by using the PR equation and the flash evaporation algorithm. 2L ;

[0152] Dew point determination module 605, if there is Q 2L , then determine the four-phase point Q corresponding to the dew point 2U ;

[0153] The four-phase line determination module 607, if there is a Q 2U , then based on the Q 2U And the Q 2L , calculate the pressure according to the temperature, and draw the four-phase line L w -HVL HC , calculate the temperature according to the pressure, and draw the three-phase line L w -HL HC , complete the hydrate phase diagram corresponding to the component to be treated.

[0154] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for calculating a hydrate phase diagram, characterized in that: The calculation method includes: Perform interpolation calculation between the temperature of 1 atmosphere and the temperature Q1, calculate the pressure according to the temperature using the three-phase line determination method, and draw the three-phase line LHV; The four-phase point Q corresponding to the bubble point of the component to be treated is calculated by the PR equation and flash evaporation algorithm. 2L ; If there is Q 2L , then determine the four-phase point Q corresponding to the dew point 2U ; If there is Q 2U , then based on the Q 2U And the Q 2L , calculate the pressure according to the temperature, and draw the four-phase line L w -HVL HC , calculate the temperature according to the pressure, and draw the three-phase line L w -HL HC , complete the hydrate phase diagram corresponding to the component to be treated.

2. The calculation method according to claim 1, characterized in that: The four-phase point Q corresponding to the bubble point is calculated by the PR equation and the flash algorithm. 2L , further comprising: If there is no Q 2L , then the three-phase line determination method is used to extend outward from Q1, and the pressure is calculated according to the temperature to generate the three-phase line L w -HV.

3. The calculation method according to claim 1, characterized in that: If there is Q 2L , then determine the four-phase point Q corresponding to the dew point 2U , further comprising: If there is no Q 2U , then from the Q 2L Extending outward, using the Clapeyron equation, the temperature is calculated based on the pressure to generate the three-phase line L w -VL HC .

4. The calculation method according to claim 1, characterized in that: The three-phase line determination method specifically includes: Based on the hydrate type corresponding to the component to be treated, the Langmuir constant C is calculated. ji ; Based on the Langmuir constant C ji , determine the chemical potential difference between water in the filled hydrate lattice phase and the empty hydrate lattice phase and the chemical potential difference between the water-rich (or ice) phase and the empty hydrate lattice phase like The point corresponding to the temperature and pressure at this time is the three-phase parallel point, thereby generating a three-phase line.

5. The calculation method according to claim 4, characterized in that: The hydrate types include type I hydrate and type II hydrate; The Langmuir constant C ji The calculation formula is: in, C ji represents the Langmuir constant of the j component for type i vacancies; A ji is a pressure coefficient, and the pressure coefficient is determined by the component to be treated and the hydrate type; B ji is a temperature coefficient, and the temperature coefficient is determined by the component to be treated and the hydrate type; T represents temperature.

6. The calculation method according to claim 4, characterized in that: The chemical potential difference between the filled hydrate lattice phase and the empty hydrate lattice phase The calculation formula is: in, represents the chemical potential of water in the hydrate lattice phase; represents the chemical potential of water in the empty hydrate lattice; v i is the constant of type i holes; f j is the fugacity of component j in the natural gas mixture; C ji is the Langmuir constant of component j for type i vacancy; R represents the gas constant; T represents temperature; The chemical potential difference between the water-rich (or ice) phase and the empty hydrate lattice phase The calculation formula is: in, It represents pure liquid water at temperature T and hydrate dissociation pressure P R The chemical potential under It represents pure liquid water at temperature T and hydrate dissociation pressure P R The chemical potential difference under P R represents the hydrate dissociation pressure; represents the hydrate reference state; T0 represents the freezing temperature; P0 represents the dissociation pressure of hydrate at freezing temperature; represents the molar difference in volume between the empty hydrate lattice and ice; represents the molar difference in enthalpy between the empty hydrate lattice and ice; represents the molar difference in volume between ice and liquid water; represents the molar difference in enthalpy between ice and liquid water; R represents the gas constant; T represents temperature.

7. The calculation method according to claim 1, characterized in that: The calculation formula of the PR equation is: in, represents the chemical potential difference between water in the empty hydrate lattice and in the water-rich and ice phases R represents the gas constant; T represents temperature; α j Represents an adjustable constant; represents the quadratic mole fraction of component j in the hydrate phase represents the cubic mole fraction of component j in the hydrate phase m indicates cavity type m; v m represents the number of m-type cavities per water molecule in the hydrate; C mj is the Langmuir constant of component j in cavity type m; f j is the fugacity of component j in the natural gas mixture; x w It represents the molar fraction of water in the liquid phase.

8. The calculation method according to claim 1, characterized in that: The PR equation and flash evaporation algorithm are used to calculate the four-phase point Q corresponding to the bubble point of the component to be treated. 2L , specifically including: The temperature Q1 is used as the initial temperature, and based on the PR equation, Newton's method is used to iterate until the PR equation satisfies the first preset tolerance, which is used as the quadruple point Q corresponding to the bubble point of the component to be treated. 2L .

9. The calculation method according to claim 1, characterized in that: If there is Q 2L , then determine the four-phase point Q corresponding to the dew point 2U , specifically including: At the temperature Q 2L As the initial temperature, based on the PR equation, Newton's method is used for iteration until the PR equation satisfies a first preset tolerance, and as the quadruple point Q corresponding to the dew point of the component to be treated 2U .

10. A hydrate phase diagram calculation system, characterized in that: The water quality calculation system comprises: The first determination module performs interpolation calculation between the temperature of 1 atmosphere and the temperature Q1, calculates the pressure according to the temperature using the three-phase line determination method, and draws the three-phase line LHV; The bubble point determination module calculates the four-phase point Q corresponding to the bubble point of the component to be treated through the PR equation and flash evaporation algorithm. 2L ; Dew point determination module, if there is Q 2L , then determine the four-phase point Q corresponding to the dew point 2U ; Four-phase line determination module, if there is Q 2U , then based on the Q 2U And the Q 2L , calculate the pressure according to the temperature, and draw the four-phase line L w -HVL HC , calculate the temperature according to the pressure, and draw the three-phase line L w -HL HC , complete the hydrate phase diagram corresponding to the component to be treated.

Images