Natural gas double-water dew point calculation method and system based on modified Newton method

Abstract

The embodiment of the invention provides a natural gas double-water dew point calculation method and system based on a modified Newton method, and the calculation method comprises the steps: determining the fugacity coefficient of each component in to-be-processed natural gas based on a PR state equation; determining a target function based on the fugacity coefficient of each component in the natural gas and the material composition of the natural gas to be processed; determining a derivative f '(T0) of the objective function at an initial temperature T0; taking the temperature when f '(T0) is less than 0 as the updated initial temperature T0'; based on the initial temperature T0'and the minimum temperature boundary, a Newton method is adopted to conduct iterative calculation on the target function, and the water dew point of the natural gas to be processed is obtained.

Description

Technical Field

[0001] The embodiments of the present application belong to the field of natural gas processing technology, and in particular, relate to a method and system for calculating the double water dew point of natural gas based on the modified Newton method. Background Art

[0002] As an important energy source, natural gas is widely used in power generation, heating, industrial production and other fields around the world. In order to ensure the safe transportation of natural gas, the gas quality parameters must be controlled, among which the water dew point is a key indicator. Under supercritical conditions, the reverse gasification phenomenon occurs in the calculation process of the water dew point of natural gas due to the large proportion of methane or hydrogen in the gas phase of the system, that is, there are two water dew points at the same pressure (one with a higher temperature T H and a lower temperature Τ L ), usually only the water dew point with a higher temperature is considered, because once it is lower than this temperature, water will precipitate, which will easily cause the formation of hydrates during transportation and lead to pipeline blockage. The calculation of water dew point often faces the situation of improper selection of initial value of iteration, resulting in jump oscillation or invalid solution. The existing numerical iteration method is difficult to effectively deal with this multi-solution phenomenon, and a correction method is needed to ensure the convergence of the iteration process.

[0003] In the prior art, the water dew point is calculated using a traditional numerical iteration method (such as Newton's method). The numerical iteration method is prone to jump oscillation problems in the calculation of the water dew point of natural gas, and it is difficult to accurately calculate a water dew point with a large value.

[0004] Based on this, a calculation method for the double water dew point of natural gas based on the modified Newton method is needed. Summary of the invention

[0005] The embodiments of this specification provide a method and system for calculating the double water dew point of natural gas based on the modified Newton method to solve some or all of the problems: In the prior art, the water dew point is calculated using a traditional numerical iteration method (such as Newton's method). The numerical iteration method is prone to jump oscillation problems in the calculation of the water dew point of natural gas, and it is difficult to accurately calculate the water dew point with a larger value. In addition, since the pressure of natural gas is greater than the critical pressure, the iterative process of solving the water dew point may result in invalid solutions or fail to converge to the correct solution. The existing state equation method does not discuss the dew point solution under the reverse gasification phenomenon (such as the SRK state equation), and lacks an effective numerical solution method to deal with the continuity problem of the supercritical gas phase.

[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 the double water dew point of natural gas based on the modified Newton method, the method comprising:

[0008] Based on the PR state equation, the fugacity coefficient of each component in the natural gas to be processed is determined;

[0009] Determining an objective function based on the fugacity coefficient of each component in the natural gas and the material composition of the natural gas to be processed;

[0010] Determine the objective function at the initial temperature T 0 The derivative f′(T 0 );

[0011] f′(T 0 )<0 as the updated initial temperature T 0 ′;

[0012] Based on the initial temperature T 0 ′ and the minimum temperature boundary, and the objective function is iteratively calculated using the Newton method to obtain the water dew point of the natural gas to be processed.

[0013] The embodiment of this specification also provides a calculation system for the double water dew point of natural gas based on the modified Newton method, the calculation system comprising:

[0014] The fugacity coefficient determination module determines the fugacity coefficient of each component in the natural gas to be processed based on the PR state equation;

[0015] An objective function determination module determines an objective function based on the fugacity coefficient of each component in the natural gas and the material composition of the natural gas to be processed;

[0016] The derivative module determines the objective function at the initial temperature T 0 The derivative f′(T 0 );

[0017] Update module, f′(T 0 )<0 as the updated initial temperature T 0 ′;

[0018] The water dew point calculation module is based on the initial temperature T 0 ′ and the minimum temperature boundary, and the objective function is iteratively calculated using the Newton method to obtain the water dew point of the natural gas to be processed.

[0019] At least one of the above technical solutions adopted in the embodiments of this specification can achieve the following beneficial effects: based on the PR state equation, determine the fugacity coefficient of each component in the natural gas to be processed; based on the fugacity coefficient of each component in the natural gas and the material composition of the natural gas to be processed, determine the objective function; determine the objective function at the initial temperature T 0 The derivative f′(T 0 ); f′(T0 )<0 as the updated initial temperature T 0 '; Based on the initial temperature T 0 ′ and the minimum temperature boundary, and adopting Newton's method to iteratively calculate the objective function to obtain the water dew point of the natural gas to be processed, which can improve the accuracy of the calculated water dew point of the natural gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] 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:

[0021] Figure 1 A flow chart of a method for calculating the double water dew point of natural gas based on the modified Newton method provided in an embodiment of this specification;

[0022] Figure 2 A graph showing the objective function of the embodiment of this specification changing with temperature;

[0023] Figure 3 A schematic diagram of the solution result of the water dew point of the objective function provided in the embodiment of this specification.

[0024] Figure 4 A schematic diagram of solving the water dew point for the objective function provided in the embodiments of this specification;

[0025] Figure 5 An iterative schematic diagram of a method for calculating the double water dew point of natural gas based on a modified Newton method provided in an embodiment of this specification;

[0026] Figure 6 A schematic diagram of calculation results of an example of a method for calculating the double water dew point of natural gas based on the modified Newton method provided in an embodiment of this specification;

[0027] Figure 7 A schematic diagram of a calculation system for the double water dew point of natural gas based on the modified Newton method is provided for this illustrative embodiment. DETAILED DESCRIPTION

[0028] 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.

[0029] According to GB 50251-2003, the water dew point of natural gas at the highest operating pressure of the pipeline must be 5°C lower than the lowest ambient temperature, and the hydrocarbon dew point must not be higher than the lowest ambient temperature. When the operating temperature is higher than the water dew point, the natural gas is in an unsaturated state and no liquid water will precipitate; when it is lower than the water dew point, the gas is oversaturated and liquid water will precipitate. The presence of liquid water in the pipeline may cause problems, such as reducing the transmission efficiency, increasing the risk of pipeline corrosion, and even forming hydrates under high pressure and low temperature conditions, causing equipment or pipeline blockage.

[0030] Since the method of calculating water dew point using the SRK state equation does not take into account the reverse gasification phenomenon of natural gas that occurs when the pressure is higher than the critical pressure, the method of calculating water dew point based on the SRK state equation cannot calculate the water dew point required for actual production and transportation.

[0031] In addition, when the temperature falls in the gas phase region, the liquid phase composition solved by the traditional Newton iteration method is consistent with the gas phase composition. This is actually because the liquid phase does not exist in the supercritical gas phase region. Poling, Gundersen and Veeranna described this situation and gave different methods. Poling described this phenomenon and proposed to use the isothermal compression factor as a criterion, but his criterion has some fuzzy areas between the gas and liquid phases. Gundersen proposed to solve the compression factor by numerical method without using the analytical solution algorithm of the compression factor, and make some corrections to it by modifying the compression factor curve when necessary. Since the compression factor is calculated every time the phase equilibrium constant is calculated, this will greatly increase the calculation load of flash evaporation.

[0032] Based on this, this specification proposes a method for calculating the double water dew point of natural gas based on the modified Newton method. The water dew point in the reverse gasification phenomenon is calculated by the PR state equation. This state equation performs well under high pressure and high temperature and is applicable to a variety of gas and liquid mixtures. For the phase equilibrium calculation of non-ideal gases and liquids, the PR equation usually provides a more accurate K value (phase equilibrium constant) prediction, especially when approaching the critical point. When solving the water dew point of natural gas in the high critical region, firstly, based on the characteristics since the initial value of the Newton iteration, an effective initial value calculation strategy is formulated to ensure that the algorithm converges to a water dew point with a larger value. At the same time, when using the Newton method to iteratively solve the PR state equation, the present invention adopts a virtual density method to solve the problem of consistency between the liquid phase composition and the gas phase composition solved using the traditional Newton iteration method, ensure the continuity of the objective function, and ensure that it finally converges to a valid solution.

[0033] Figure 1 The following is a flow chart of a method for calculating the double water dew point of natural gas based on the modified Newton method provided in the embodiment of this specification. From the program perspective, the execution subject of the method for calculating the double water dew point of natural gas based on the modified Newton method is a program installed on an application server or 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 optimization method includes:

[0034] Step S101: Based on the PR state equation, the fugacity coefficient of each component in the natural gas to be processed is determined.

[0035] The PR state equation is applicable to a wide range of temperature and pressure, and can accurately calculate the gas-liquid phase equilibrium, so it is widely used in upstream natural gas processing. Its definition is as follows:

[0036]

[0037] For pure components, the parameters a and b in the above formula are:

[0038] a i =a ci α i (T)

[0039]

[0040] T ri =T / T ci

[0041] Mixing rules:

[0042]

[0043] in,

[0044] P: pressure;

[0045] V: molar volume;

[0046] T: temperature; R: gas constant;

[0047] ω: Pitzer eccentricity factor;

[0048] Subscript C: critical point;

[0049] i: component i,

[0050] K ij : binary interaction parameter;

[0051] a: correction term for intermolecular attraction;

[0052] b: correction term for intermolecular repulsion;

[0053] x: mole fraction;

[0054] m: mixture;

[0055] Since flash evaporation is needed to calculate the water dew point, the PR state method is needed to calculate the fugacity coefficient of the gas and liquid phases. Specifically, the PR equation is converted into the cubic form of the compression factor Z, assuming:

[0056]

[0057] Combining the above formula with the PR equation, we get the following formula:

[0058] Z 3 (1-B)Z 2 +(A-3B 2 -2B)Z-(AB-B 2 -B 3 )=0

[0059] According to the basic thermodynamic relationship The compression factor Z at a specified temperature and pressure can be calculated from the above formula. When the compression factor Z is obtained, the fugacity coefficient of component i can be calculated by the following formula:

[0060]

[0061] Thus, the fugacity coefficients of the liquid and gas phases can be calculated.

[0062] In the embodiments of this specification, the gas phase components include: CO2, N2, C1, C3, IC4, NC4, IC5, NC5, NC6, NC7, NC8, NC9, NC10 and H2O.

[0063] Step S103: determining an objective function based on the fugacity coefficient of each component in the natural gas and the material composition of the natural gas to be processed.

[0064] In the embodiments of the present specification, the objective function is determined based on the fugacity coefficient of each component in the natural gas and the material composition of the natural gas to be processed at the water dew point, specifically including: determining the objective function based on the fugacity coefficient of each component in the natural gas and the material composition of the natural gas to be processed according to the phase equilibrium constant and the mass conservation equation.

[0065] The process of determining the objective function will be described in detail below.

[0066] Under constant pressure, when a substance exists in the gas phase, as the temperature decreases, the temperature at which the first drop of liquid precipitates is called the dew point temperature. Since the gas phase fraction at the dew point is 1, the gas phase composition is the composition of the current substance, and its mass conservation equation is:

[0067]

[0068] In the formula

[0069] z i is the proportion of component i. When calculating the dew point, the component is pure gas phase, so z i =y i

[0070] K i is the phase equilibrium constant of component i, K i The fugacity coefficient obtained by the above calculation Calculate, specifically, the formula for the phase equilibrium constant is:

[0071]

[0072] in, represents the liquid phase fugacity coefficient of component i, represents the gas phase fugacity coefficient of component i.

[0073] Based on the above phase equilibrium constant and the above mass conservation equation, the objective function is further determined. In the embodiment of this specification, the objective function is the objective function of water dew point, and the formula of the objective function is:

[0074]

[0075] in,

[0076] f(x) represents the objective function;

[0077] x i represents the mole fraction of component i,

[0078] and is a function of temperature T.

[0079] In the embodiment of this specification, the objective function changes with the temperature. Figure 2 A graph showing the objective function of an embodiment of this specification changing with temperature.

[0080] like Figure 2 As shown, as the temperature decreases, the objective function f(x) gradually decreases, and when f(x) = 0, it is the solution to the equation.

[0081] Step S105: Determine the derivative f′ (T 0 ).

[0082] The objective function for water dew point calculation at a given pressure is a single variable equation and can therefore be solved using Newton's method. Figure 3 This is a schematic diagram of the solution result of the water dew point of the objective function provided in the embodiment of this specification. Figure 3 As shown in the figure, when the pressure of natural gas dew point is higher than the critical point, there are two solutions, T H The curve on the right is consistent with the general situation at low pressure. It is the water dew point caused by reverse condensation and belongs to the solution with higher temperature of weather hot water dew point. The curve on the left is caused by reverse condensation and belongs to the solution with lower temperature of natural gas water dew point. The method provided in the embodiment of this specification is used to calculate the water dew point caused by reverse condensation, that is, to calculate Figure 3 T H .

[0083] Due to the characteristics of Newton's method, the choice of initial value is very important when solving the objective function. From the objective function curve, it can be seen that in order to obtain T H The initial temperature should be as high as possible. The saturation temperature under the current water vapor partial pressure is usually the same as T H Therefore, in the embodiment of this specification, the initial temperature is the saturation temperature under the current water vapor partial pressure. Specifically, the saturation temperature can be calculated by the saturation vapor pressure curve of IF97.

[0084] Step S107: f′(T 0 )<0 as the updated initial temperature T 0 ′.

[0085] Continue to combine Figure 3 To explain, in order to ensure that the initial value point (ie, the initial temperature) is located on the right side of the center line, there is no need to verify the initial temperature point, and the efficiency of the initial temperature point is ensured to be less than 0.

[0086] In the embodiment of this specification, if f′(T 0 )>0, then based on the initial temperature T 0 , increase the temperature according to the preset step size to update the initial temperature T 0 , until f′(T 0 )<0.

[0087] The obtained f′(T 0 )<0 as x 0 , which is used as the updated initial temperature T 0 ′.

[0088] In the embodiments of this specification, the preset step size needs to be determined according to the actual situation. Generally, it can start with a smaller step size, such as 1 or 10, and gradually adjust it according to the initial slope and the feedback of the objective function.

[0089] Step S109: Based on the initial temperature T 0 ′ and the minimum temperature boundary, and the objective function is iteratively calculated using the Newton method to obtain the water dew point of the natural gas to be processed.

[0090] Although the selection of the initial value of the iteration has been strictly processed, the water dew point calculated using the Newton method may still fall below T L Instead of the T we care about H .like Figure 4 As shown, this is because in the first iteration, the derivative is too small, resulting in a large step size retracement, and the first solution (x 1 ,f(x 1 )) is already on the left side of point a. Continuing to solve will keep approaching T l , the final solution temperature will be T L , instead of T H .

[0091] Based on this, in the embodiment of this specification, a minimum temperature boundary is added to the Newton method. In the iterative process, the minimum temperature boundary T is added. min , T min The initial value of can be obtained by linear search, that is, all objective functions in the effective interval of x are traversed and calculated to obtain the maximum value of the objective function. At this time, the corresponding temperature is set to T min .

[0092] In the embodiment of this specification, the minimum temperature boundary is based on the updated initial temperature T 0 ', traverse the objective function and take the temperature at the maximum value of the objective function as the minimum temperature boundary.

[0093] In the embodiment of this specification, the initial temperature T based on the update 0′ and the minimum temperature boundary, and using Newton's method to iteratively calculate the objective function to obtain the water dew point of the natural gas to be processed, specifically including:

[0094] Based on the updated initial temperature T 0 ' and the minimum temperature boundary, the objective function is iterated using Newton's method;

[0095] If the temperature estimate x obtained iteratively at step (k+1) k+1 Less than T min , then for x k+1 Reassign value to x k+1 =(x k+1 +x k ) / 2;

[0096] Based on the reassigned value of x k+1 =(x k+1 +x k ) / 2, recalculate f′(x k+1 ), until f′(x k+1 )≤0, obtain the temperature estimate x of the (k+1)th step that meets the conditions k+1 ;

[0097] The temperature estimate x of the (k+1)th step based on the conditions met k+1 , determined as the dew point of the natural gas to be processed.

[0098] In the embodiments of this specification, the Newton iteration formula of the Newton method is:

[0099]

[0100] in,

[0101] x k+1 represents the temperature estimate of the (k+1)th step;

[0102] x k Indicates the temperature estimate of the kth step at the current point;

[0103] f(x k ) indicates that the objective function is at the current point x k The value of

[0104] f′(x k ) indicates that the objective function is at the current point x k The derivative value of .

[0105] In the embodiment of this specification, the temperature estimation x of the (k+1)th step based on the condition satisfied is k+1 , determining the dew point of the natural gas to be processed, specifically including:

[0106] The temperature estimate x of the (k+1)th step based on the conditions met k+1 , use the iterative formula of Newton's method to calculate and determine f(x n );

[0107] If |f(x k+1 )-f(x n )|<preset tolerance or f(x n ) satisfies the preset number of iterations, the current optimal value is used as the dew point of the natural gas to be processed.

[0108] In the embodiment of this specification, the preset tolerance is 0.001, and the preset number of iterations is 10. Of course, the preset tolerance and the preset number of tolerances can be determined according to specific business requirements.

[0109] In order to further understand the process of calculating the double water dew point of natural gas based on the modified Newton method provided in the embodiments of this specification, Figure 5 The following is an iterative schematic diagram of a method for calculating the double water dew point of natural gas based on the modified Newton method provided in the embodiments of this specification. Figure 5 As shown, first construct the objective function f(x), then determine the initial temperature T 0 , solve the objective function at T 0 The derivative f′(T 0 ), if f′(T 0 )<0, then determine the minimum temperature boundary through linear search, if so, then update the initial temperature until f′(T 0 )<0, and determine the minimum temperature boundary T through linear search min . Then Newton's method is used to solve the function x k+1 , if x k+1 <T min , then x k+1 Reassign x k+1 =(x k+1 +x k ) / 2, recalculate f′(x k+1 ), if the recalculated f′(x k+1 ) is greater than 0, then reassign x k+1 =(x k+1 +x k ) / 2, until f′(x k+1 )≤0, then proceed to the next iteration. k+1 ≥T min , then based on |f(x k+1 )-f(x n )|<preset tolerance, then the water dew point temperature x r =x k+1 .

[0110] In order to further verify the calculation effect of the method for calculating the double water dew point of natural gas based on the modified Newton method provided in the embodiments of this specification, this specification further verifies it with specific embodiments.

[0111] The product gas composition of a natural gas processing unit is as follows (the second column represents y i ):

[0112]

[0113] According to the traditional method, two water dew points can be calculated. However, using the method provided in the embodiment of this specification, the water dew point calculated is 289.12K. The calculation process is as follows: Figure 6 shown.

[0114] The method for calculating the double water dew point of natural gas based on the modified Newton method provided in the embodiment of this specification determines the fugacity coefficient of each component in the natural gas to be processed based on the PR state equation; determines the objective function based on the fugacity coefficient of each component in the natural gas and the material composition of the natural gas to be processed; determines the objective function at the initial temperature T 0 The derivative f′(T 0 ); f′(T 0 )<0 as the updated initial temperature T 0 '; Based on the initial temperature T 0 ′ and the minimum temperature boundary, and the Newton method is used to iteratively calculate the objective function to obtain the water dew point of the natural gas to be processed, which can improve the accuracy of the calculated water dew point of the natural gas. At the same time, since the initial value and the boundary temperature are set, the problem of invalid solution can be avoided, and the stability and convergence of the calculation result can be achieved.

[0115] The aforementioned embodiment of this specification provides a method for calculating the double water dew point of natural gas based on the modified Newton method. Based on the same idea, the embodiment of this specification also provides a system for calculating the double water dew point of natural gas based on the modified Newton method. Figure 7 A schematic diagram of a calculation system for the double water dew point of natural gas based on the modified Newton method is provided for this embodiment. Figure 7 As shown, the computing system includes:

[0116] The fugacity coefficient determination module 701 determines the fugacity coefficient of each component in the natural gas to be processed based on the PR state equation;

[0117] The objective function determination module 703 determines the objective function based on the fugacity coefficient of each component in the natural gas and the material composition of the natural gas to be processed;

[0118] The derivative module 705 determines the target function at the initial temperature T 0The derivative f′(T 0 );

[0119] Update module 707, f′(T 0 )<0 as the updated initial temperature T 0 ′;

[0120] The water dew point calculation module 709 is based on the initial temperature T 0 ′ and the minimum temperature boundary, and the objective function is iteratively calculated using the Newton method to obtain the water dew point of the natural gas to be processed.

[0121] 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 the double water dew point of natural gas based on the modified Newton method, characterized in that: The calculation method includes: Based on the PR state equation, the fugacity coefficient of each component in the natural gas to be processed is determined; Determining an objective function based on the fugacity coefficient of each component in the natural gas and the material composition of the natural gas to be processed; Determining the derivative f′(T0) of the objective function at the initial temperature T0; The temperature when f′(T0)<0 is taken as the updated initial temperature T0′; Based on the initial temperature T0′ and the minimum temperature boundary, the objective function is iteratively calculated using the Newton method to obtain the water dew point of the natural gas to be processed.

2. The calculation method according to claim 1, characterized in that: The objective function is the objective function of water dew point, and the formula of the objective function is: f(x)=∑x i -1 in, f(x) represents the objective function; x i represents the mole fraction of component i.

3. The calculation method according to claim 1, characterized in that: If f′(T0)>0, based on the initial temperature T0, the temperature is increased according to a preset step size to update the initial temperature T0 until f′(T0)<0.

4. The calculation method according to claim 1, characterized in that: The initial temperature is the saturation temperature under the current water vapor partial pressure.

5. The calculation method according to claim 1, characterized in that: The minimum temperature boundary is based on the updated initial temperature T0′, traverses the objective function, and takes the temperature at the maximum value of the objective function as the minimum temperature boundary.

6. The calculation method according to claim 1, characterized in that: The method of iteratively calculating the objective function based on the updated initial temperature T0′ and the minimum temperature boundary by using the Newton method to obtain the water dew point of the natural gas to be processed specifically includes: Based on the updated initial temperature T0′ and the minimum temperature boundary, iterating the objective function using Newton's method; If the temperature estimate x obtained iteratively at step (k+1) k+1 Less than T min , then for x k+1 Reassign value to x k+1 =(x k+1 +x k ) / 2; Based on the reassigned value of x k+1 =(x k+1 +x k ) / 2, recalculate f′(x k+1 ), until f′(x k+1 )<0, obtain the temperature estimate x of the (k+1)th step that meets the conditions k+1 ; The temperature estimate x of the (k+1)th step based on the conditions met k+1 , determined as the dew point of the natural gas to be processed.

7. The calculation method according to claim 1, characterized in that: The Newton iteration formula of the Newton method is: in, x k+1 represents the temperature estimate of the (k+1)th step; x k Indicates the temperature estimate of the kth step at the current point; f(x k ) indicates that the objective function is at the current point x k The value of f′(x k ) indicates that the objective function is at the current point x k The derivative value of .

8. The calculation method according to claim 6, characterized in that: The temperature estimation x of the (k+1)th step based on the condition satisfied k+1 , determining the dew point of the natural gas to be processed, specifically including: The temperature estimate x of the (k+1)th step based on the conditions met k+1 , use the iterative formula of Newton's method to calculate and determine f(x n ); If |f(x k+1 )-f(x n )|<preset tolerance or f(x n ) satisfies the preset number of iterations, the current optimal value is used as the dew point of the natural gas to be processed.

9. A calculation system for double water dew point of natural gas based on modified Newton method, characterized in that: The computing system comprises: The fugacity coefficient determination module determines the fugacity coefficient of each component in the natural gas to be processed based on the PR state equation; An objective function determination module determines an objective function based on the fugacity coefficient of each component in the natural gas and the material composition of the natural gas to be processed; A derivative module, determining a derivative f′(T0) of the objective function at an initial temperature T0; Update module, taking the temperature when f′(T0)<0 as the updated initial temperature T0′; The water dew point calculation module uses Newton's method to iteratively calculate the objective function based on the initial temperature T0' and the minimum temperature boundary to obtain the water dew point of the natural gas to be processed.

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