Method and system for predicting generation of hydrate in impurity-containing supercritical carbon dioxide conveying pipeline

Abstract

The impurity-containing supercritical carbon dioxide conveying pipeline hydrate generation prediction method comprises the steps that heat exchange between a pipeline and the surrounding environment and distribution of water drops in the pipeline are considered, hydrate generation thermodynamic factors are considered, and a Chenn-Guo hydrate generation model is used for determining phase equilibrium parameters of hydrate generation in impurity-containing carbon dioxide; and determining the hydrate generation position by combining the temperature-pressure distribution of the pipeline. The volume of the carbon dioxide hydrate particles is calculated according to the sum of the volume of the water drops and the volume of the hydrate film covering the water drops, hydrate growth kinetic factors are considered, the volume of the hydrate film is related to the transverse growth rate and thickness of the hydrate film, and the transverse growth rate is determined through a comprehensive growth model; and the thickness growth of the hydrate film is similar to condensation heat transfer. And predicting the generation amount of the hydrate particles in the pipeline by combining the distribution characteristics of the water drops in the pipeline. According to the method, the generation position and the generation amount of the hydrate in the pipeline are predicted.

Description

Technical Field

[0001] The invention belongs to the technical field of carbon dioxide transportation, and in particular relates to a method and system for predicting hydrate formation in a supercritical carbon dioxide transportation pipeline containing impurities. Background Art

[0002] Carbon dioxide (CO2) transportation is a key link connecting the upstream and downstream in the CCUS industry chain. Pipeline transportation has good economic benefits. According to the transportation phase, CO2 pipeline transportation is generally divided into three modes of transportation: gas phase transportation, liquid phase transportation and supercritical dense phase transportation. During the transportation of supercritical CO2, as the pressure and temperature of CO2 decrease, the phase of CO2 will change from supercritical state to dense phase (when the pressure is above the critical pressure). The temperature and pressure of supercritical CO2 are higher than the critical point (critical pressure 7.38MPa, critical temperature 31.4℃). The pressure of dense phase CO2 is higher than the critical pressure and the temperature is lower than the critical temperature. Figure 2 As shown. Supercritical CO2 has both the low viscosity and high fluidity of gas and the high density of liquid, which makes the transmission capacity of supercritical CO2 pipelines greater than that of gas and liquid CO2 pipelines. In addition, the pressure change of CO2 can easily lead to two-phase flow in the gas or liquid CO2 transmission pipeline, resulting in discontinuous flow. When the phase state of CO2 changes from supercritical to dense phase, no two-phase flow will be generated, which can avoid the safety problems caused by two-phase flow. Therefore, supercritical-dense phase CO2 pipeline transportation is the most suitable transportation method for large-scale long-distance CO2 transportation in engineering.

[0003] The transported carbon dioxide generally contains impurities (usually less than 5%) such as H2O, CH4, N2, H2 and CH3OH, which have a great influence on the physical properties of carbon dioxide. The presence of water can also lead to the formation of carbon dioxide hydrates in the dense phase pipeline area. CO2 hydrate refers to a non-stoichiometric crystalline solid formed by the guest molecule CO2 filling the cage-type pores formed by the hydrogen bonds of water molecules. Hydrate particles deposit and block the flow cross section, promoting the production of more hydrates, causing a serious risk of pipeline blockage, leading to unstable transportation conditions, and increasing the risk of pipeline explosion or even shutdown. In addition, hydrates in pipelines can easily cause local corrosion and general corrosion of carbonic acid, which may cause pore leakage. The leakage of high-concentration, high-pressure CO2 can damage the ecological environment around the pipeline and pose a suffocation hazard to people and animals near the leakage point. The formation of hydrates in transmission pipelines causes billions of dollars in economic losses every year. Therefore, it is of great significance to accurately predict the formation of hydrates in supercritical CO2 transmission pipelines.

[0004] At present, some scholars use the hydrate formation thermodynamic model to determine whether hydrates are formed at specific temperatures and pressures. This method is easy to predict, but it can only roughly predict the hydrate formation area and cannot predict the hydrate formation amount. Other scholars use big data methods such as population equilibrium theory and probability models to predict the hydrate deposition amount. This method requires a large amount of operating data to train the prediction model and is inconvenient to use. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a method and system for predicting hydrate formation in a supercritical carbon dioxide transmission pipeline containing impurities. The present invention takes a supercritical carbon dioxide transmission pipeline containing impurities as the object, adopts a theoretical analysis method, combines the thermodynamic and kinetic factors of hydrate formation, considers the heat exchange between the pipeline and the surrounding environment and the distribution of water droplets in the pipe, and realizes the prediction of the hydrate formation position and generation amount in the pipeline. First, considering the thermodynamic factors of hydrate formation, the Chen-Guo hydrate formation model is used to determine the phase equilibrium parameters of hydrate formation in impure carbon dioxide, and the hydrate formation position is determined in combination with the pipeline temperature-pressure distribution. Secondly, the volume of carbon dioxide hydrate particles is calculated according to the volume of the water droplet and the volume of the hydrate film covering the water droplet. Considering the hydrate growth kinetics factor, the volume of the hydrate film is related to the lateral growth rate and thickness of the hydrate film. The lateral growth rate is determined by a comprehensive growth model, and the thickness growth of the hydrate film is compared with condensation heat transfer. Finally, combined with the distribution characteristics of water droplets in the pipeline, the generation amount of hydrate particles in the pipeline is predicted.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] The method for predicting hydrate formation in a supercritical carbon dioxide transmission pipeline containing impurities includes:

[0008] Step 1: Determine the phase equilibrium parameters of hydrate formation in impurity-containing carbon dioxide according to the Chen-Guo hydrate formation model;

[0009] Step 2: Preliminarily determine the temperature-pressure distribution of the pipeline at the initial moment based on pipeline specification parameters, flow parameters and fluid composition;

[0010] Step 3: Determine the location of hydrate formation in the pipeline by combining the hydrate formation phase equilibrium parameters and the pipeline temperature-pressure distribution; when the temperature of the fluid in the pipeline is higher than the hydrate formation phase equilibrium temperature corresponding to the fluid pressure, no hydrate is generated; when the temperature of the fluid in the pipeline is lower than or equal to the hydrate formation phase equilibrium temperature corresponding to the fluid pressure, the pipeline is divided into M sections, and the research time is divided into N intervals, with j representing the jth pipe section and i representing the ith time period;

[0011] Step 4: Assign i=1;

[0012] Step 5: Assign j=1;

[0013] Step 6: Assign an initial value T' to the temperature at the outlet of pipe section j;

[0014] Step 7: Assuming that the distribution of hydrate particles in the pipeline is Poisson distribution, the volume of carbon dioxide hydrate particles is calculated based on the sum of the volume of the water droplet and the volume of the hydrate film covering the water droplet. The lateral growth rate of the hydrate film is calculated using the Chen-Guo comprehensive growth model, and the thickness of the hydrate film is calculated using the condensation analogy method. The hydrate volume V generated in the jth pipeline section is calculated. p ′;

[0015] Step 8: According to the pressure difference equation Calculate the pressure p″ at the outlet of pipe section j, where ΔP is the pressure drop in the pipe and ρ is the density of carbon dioxide, kg / m 3 ; r is the pipeline radius, m, β is the pipeline angle, °, v p is the velocity of hydrate particle flow, m / s, τ f is the pipe shear stress, N / m 2 , L pipe section length, m;

[0016] Step 9: According to the temperature difference equation Calculate the temperature T″ at the outlet of pipe section j; where Δq is the heat transfer rate per unit length of the carbon dioxide pipeline, W / m, M is the CO2 pipeline mass flow rate, kg / s, v c is the flow rate of carbon dioxide in the pipeline, m / s, h is the enthalpy, kJ / kg;

[0017] Step 10: If |T'-T"|≤ε1 holds, assign T' to T", if not, re-assume T';

[0018] Step 11: Recalculate the hydrate volume V generated in the jth pipeline segment p ″;

[0019] Step 12: If |V P '-V P ”|≤ε2 holds true, then V p ′ is assigned to V p ″; If not, return to step 6 and re-assume T′; if it is true, proceed to step 13;

[0020] Step 13: If j≥M is not, then j=j+1, and repeat steps 6-12 until j=M; if i≥N is not, then i=i+1, and return to step 5 until i=N.

[0021] A further improvement of the present invention is that in step 1, the phase equilibrium parameters of hydrate formation in impurity-containing carbon dioxide are determined according to the Chen-Guo hydrate formation model, including:

[0022] (1) Determine the critical parameters of each component in the fluid and give the initial values ​​of p and T;

[0023] (2) Press Calculate the fugacity f of each component i ,in T c is the critical temperature, K; p c is the critical pressure, Pa;

[0024] (3) Press Calculate the Langmuir constant C of each component j , MPa, where X j ,Y j and Z j is a constant, fitted by the Lenard-Jones potential energy model;

[0025] (4) Press Determine the proportion of connected cavities occupied by each j component gas θ j , and calculate

[0026] (5) Press formula f i,0 =f iT,0 (T)·f(P)·f(a w ) Calculate the minimum fugacity f required for pure gas component i to stabilize the hydrate structure i,0 ;in Among them, for carbon dioxide hydrate, β, λ1 and λ2 are 0.4242K / bar, 1 / 23 and 3 / 23 respectively; is the activity of water, a i ,b i and c i is the Antoine constant;

[0027] (6) Press Calculate the mole fraction of component i in the polynary gas hydrate and calculate ∑x i ;

[0028] (7) If |∑x i If -1|<ε holds, the phase equilibrium parameters p and T are output; if not, p and T are modified and (2) to (7) are recalculated.

[0029] A further improvement of the present invention is that in step 2, preliminarily determining the temperature-pressure distribution of the pipeline at the initial moment according to pipeline specification parameters, flow parameters and fluid components includes:

[0030] Considering the heat exchange between the buried pipeline and the soil, the temperature of carbon dioxide at a certain point on the pipeline is T x Calculate as follows:

[0031] T x =T0+(T1-T0)e -αx

[0032] T0 is the average soil temperature, K; T1 is the temperature of carbon dioxide at the entrance of the micro-element pipe segment, K; x is the length of the micro-element pipe segment, m; Where K is the total heat transfer coefficient between carbon dioxide and soil, W / (m 2 ·K), D is the outer diameter of the pipeline, m; M is the mass flow rate of carbon dioxide in the pipeline, kg / s; C is the specific heat capacity of carbon dioxide at constant pressure, J / (kg·K);

[0033] The pressure drop ΔP of the fluid in the pipeline is calculated as follows:

[0034]

[0035] Where λ is the resistance loss coefficient along the way; L is the length of the pipeline, m; d is the inner diameter of the pipeline, m; v c is the flow rate of carbon dioxide, m / s; g is the acceleration due to gravity, m / s 2 ; H is the pipeline elevation difference, m.

[0036] A further improvement of the present invention is that, in step 7, it is assumed that the distribution of hydrate particles in the pipeline is Poisson distribution, and the volume of carbon dioxide hydrate particles is calculated according to the sum of the volume of water droplets and the volume of the hydrate film covering the water droplets. The lateral growth rate of the hydrate film is calculated using the Chen-Guo comprehensive growth model, and the thickness of the hydrate film is calculated using the condensation analogy method. The hydrate volume V generated in the jth pipeline section is calculated. p ',include:

[0037] The hydrate volume V generated in the jth pipeline section is calculated as follows: p ′:

[0038]

[0039] Where, v is the lateral growth rate of hydrate, which is calculated according to the Chen-Guo comprehensive growth model. ρ h is the molar density, g·mol / mm 3 ; Δh h is the latent heat of hydrate, J / (g·mol); k1 is the heat transfer coefficient, J / (s·mm 2 ·K); k2 is the reaction rate constant, (m / (s·K n ));Ts is the hydrate film temperature, K; T sys is the system temperature, K; h is the thickness of the hydrate film, which is compared with the condensation process; R d is the radius of the water drop, m; is the number of water drops per unit length of the pipeline, M is the pipeline mass flow rate, kg / s; y w is the mass fraction of water; t MN It is the time it takes for the fluid in the pipe to flow from point M to point N.

[0040] A further improvement of the present invention is that the calculation formula of the thickness h of the hydrate film is as follows:

[0041]

[0042] Among them, μ w and ρ f are the densities of water and fluid, kg / m 3 ;μ w is the viscosity of water, Pa·s; λ w is the thermal conductivity of water, W / (m·K); k is the condensation heat transfer coefficient.

[0043] The hydrate formation prediction system for supercritical carbon dioxide transmission pipeline containing impurities includes:

[0044] A first parameter determination module determines the phase equilibrium parameters of hydrate formation in impurity-containing carbon dioxide according to the Chen-Guo hydrate formation model;

[0045] The second parameter determination module preliminarily determines the temperature-pressure distribution of the pipeline at the initial moment according to the pipeline specification parameters, flow parameters and fluid components;

[0046] The position determination module combines the hydrate formation phase equilibrium parameters with the pipeline temperature-pressure distribution to determine the position of hydrate formation in the pipeline; when the temperature of the fluid in the pipeline is higher than the hydrate formation phase equilibrium temperature corresponding to the fluid pressure, no hydrate is generated; when the temperature of the fluid in the pipeline is lower than or equal to the hydrate formation phase equilibrium temperature corresponding to the fluid pressure, the pipeline is divided into M sections, and the research time is divided into N intervals, with j representing the jth pipe section and i representing the ith time period;

[0047] The first assignment module assigns i=1;

[0048] The second assignment module assigns j=1;

[0049] The third assignment module assigns an initial value T′ to the temperature at the outlet of the j-pipe segment;

[0050] In the first calculation module, the distribution of hydrate particles in the pipeline is assumed to be Poisson distribution. The volume of carbon dioxide hydrate particles is calculated based on the sum of the volume of the water droplet and the volume of the hydrate film covering the water droplet. The lateral growth rate of the hydrate film is calculated using the Chen-Guo comprehensive growth model. The thickness of the hydrate film is calculated using the condensation analogy method. The hydrate volume V generated in the jth pipeline section is calculated. p ′;

[0051] The second calculation module, based on the pressure difference equation Calculate the pressure p″ at the outlet of pipe section j, where ΔP is the pressure drop in the pipe and ρ is the density of carbon dioxide, kg / m 3 ; r is the pipeline radius, m, β is the pipeline angle, °, v p is the velocity of hydrate particle flow, m / s, τ f is the pipe shear stress, N / m 2 , L pipe section length, m;

[0052] The third calculation module uses the temperature difference equation Calculate the temperature T″ at the outlet of pipe section j; where Δq is the heat transfer rate per unit length of the carbon dioxide pipeline, W / m, M is the CO2 pipeline mass flow rate, kg / s, v c is the flow rate of carbon dioxide in the pipeline, m / s, h is the enthalpy, kJ / kg;

[0053] The first judgment module, if |T'-T"|≤ε1 holds, assign T' to T", if not, re-assume T';

[0054] The fourth calculation module recalculates the hydrate volume V generated by the jth pipeline segment p ″;

[0055] The second judgment module, if |V P '-V P ”|≤ε2 holds true, then V p ′ is assigned to V p ″; If not, return to the third assignment module to re-assume T′; if established, proceed to the third judgment module;

[0056] The third judgment module, if j≥M is not, then j=j+1, repeat step 6-step 12 until j=M; if i≥N is not, then i=i+1, return to step 5 until i=N.

[0057] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of the method for predicting hydrate formation in a supercritical carbon dioxide transmission pipeline containing impurities.

[0058] Compared with the prior art, the present invention has at least the following beneficial technical effects:

[0059] The present invention provides a method and system for predicting hydrate formation in a supercritical carbon dioxide transmission pipeline containing impurities. The Chen-Guo hydrate formation model is used to determine the phase equilibrium parameters of hydrate formation in carbon dioxide containing impurities, and the thermodynamic factors of hydrate formation are taken into consideration. The hydrate formation position in the pipeline is determined by combining the hydrate formation phase equilibrium parameters with the pipeline temperature-pressure distribution. The present invention uses the Chen-Guo comprehensive growth model to calculate the lateral growth rate of the hydrate film, compares the hydrate thickness growth with condensation, calculates the thickness of the hydrate film, and calculates the volume of the hydrate film according to the lateral growth rate of the hydrate film and the thickness of the hydrate film, taking into consideration the kinetic factors of hydrate growth, and calculates the volume of carbon dioxide hydrate particles according to the sum of the volume of a water droplet and the volume of the hydrate film covering the water droplet. The present invention also takes into consideration the distribution of hydrate particles in the pipeline, so that the generation amount of hydrate particles in the pipeline can be quickly and accurately predicted. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 The present invention is a logic block diagram of the method for predicting hydrate formation in a supercritical carbon dioxide transmission pipeline containing impurities.

[0061] Figure 2 This is the phase diagram of CO2 under supercritical-dense phase CO2 pipeline conditions.

[0062] Figure 3 Schematic diagram of the amount of hydrate generated along the pipeline at different transportation times.

[0063] Figure 4 The present invention is a structural block diagram of the hydrate formation prediction system for the impurity-containing supercritical carbon dioxide transmission pipeline. DETAILED DESCRIPTION

[0064] In the following, only some exemplary embodiments are briefly described. As those skilled in the art will appreciate, the described embodiments may be modified in various ways without departing from the spirit or scope of the present invention. Therefore, the drawings and descriptions are considered to be exemplary and non-restrictive in nature.

[0065] It should be understood that when used in this specification and the appended claims, the terms "include" and "comprises" indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0066] It should also be understood that the terms used in the present specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, the singular forms "a", "an" and "the" are intended to include plural forms unless the context clearly indicates otherwise.

[0067] It should be further understood that the term "and / or" used in the present description and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.

[0068] Various structural schematic diagrams of the embodiments disclosed in the present invention are shown in the accompanying drawings. These figures are not drawn to scale, and some details are magnified and some details may be omitted for the purpose of clear expression. The shapes of various regions and layers shown in the figures and the relative sizes and positional relationships therebetween are only exemplary, and may deviate in practice due to manufacturing tolerances or technical limitations, and those skilled in the art may additionally design regions / layers with different shapes, sizes, and relative positions according to actual needs.

[0069] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0070] Example 1

[0071] like Figure 1 As shown, the method for predicting hydrate formation in a supercritical carbon dioxide transmission pipeline containing impurities provided by the present invention comprises:

[0072] Step 1: Determine the phase equilibrium parameters of hydrate formation in impurity-containing carbon dioxide according to the Chen-Guo hydrate formation model;

[0073] Step 2: Preliminarily determine the temperature-pressure distribution of the pipeline at the initial moment based on pipeline specification parameters, flow parameters and fluid composition;

[0074] Step 3: Determine the location of hydrate formation in the pipeline by combining the hydrate formation phase equilibrium parameters and the pipeline temperature-pressure distribution; when the temperature of the fluid in the pipeline is higher than the hydrate formation phase equilibrium temperature corresponding to the fluid pressure, no hydrate is generated; when the temperature of the fluid in the pipeline is lower than or equal to the hydrate formation phase equilibrium temperature corresponding to the fluid pressure, the pipeline is divided into M sections, and the research time is divided into N intervals, with j representing the jth pipe section and i representing the ith time period;

[0075] Step 4: Assign i=1;

[0076] Step 5: Assign j=1;

[0077] Step 6: Assign an initial value T' to the temperature at the outlet of pipe section j;

[0078] Step 7: Assuming that the distribution of hydrate particles in the pipeline is Poisson distribution, the volume of carbon dioxide hydrate particles is calculated based on the sum of the volume of the water droplet and the volume of the hydrate film covering the water droplet. The lateral growth rate of the hydrate film is calculated using the Chen-Guo comprehensive growth model, and the thickness of the hydrate film is calculated using the condensation analogy method. The hydrate volume V generated in the jth pipeline section is calculated. p ′;

[0079] Step 8: According to the pressure difference equation Calculate the pressure p″ at the outlet of pipe section j, where ΔP is the pressure drop in the pipe and ρ is the density of carbon dioxide, kg / m 3 ; r is the pipeline radius, m, β is the pipeline angle, °, v p is the velocity of hydrate particle flow, m / s, τ f is the pipe shear stress, N / m 2 , L pipe section length, m;

[0080] Step 9: According to the temperature difference equation Calculate the temperature T″ at the outlet of pipe section j; where Δq is the heat transfer rate per unit length of the carbon dioxide pipeline, W / m, M is the CO2 pipeline mass flow rate, kg / s, v c is the flow rate of carbon dioxide in the pipeline, m / s, h is the enthalpy, kJ / kg;

[0081] Step 10: If |T'-T"|≤ε1 holds, assign T' to T", if not, re-assume T';

[0082] Step 11: Recalculate the hydrate volume V generated in the jth pipeline segment p ″;

[0083] Step 12: If |V P '-V P ”|≤ε2 holds true, then V p ′ is assigned to V p ″; If not, return to step 6 and re-assume T′; if it is true, proceed to step 13;

[0084] Step 13: If j≥M is not, then j=j+1, and repeat steps 6-12 until j=M; if i≥N is not, then i=i+1, and return to step 5 until i=N.

[0085] Example 2

[0086] The method for predicting hydrate formation in a supercritical carbon dioxide transmission pipeline containing impurities provided by the present invention comprises:

[0087] Step 1: Determine the phase equilibrium parameters for hydrate formation in impure carbon dioxide according to the Chen-Guo hydrate formation model. The determined phase equilibrium parameters for hydrates in impure carbon dioxide are used to subsequently determine whether hydrates are formed at a specific temperature and pressure. The specific steps are as follows:

[0088] (1) Determine the critical parameters of each component in the fluid and give the initial values ​​of p and T.

[0089] (2) Press Calculate the fugacity f of each component i ,in T c is the critical temperature, K; p c is the critical pressure, Pa.

[0090] (3) Press Calculate the Langmuir constant C of each component j , MPa, where X j ,Y j and Z j is a constant, fitted by the Lenard-Jones potential energy model.

[0091] (4) Press Determine the proportion of connected cavities occupied by each j component gas θ j . And calculate

[0092] (5) Press formula f i,0 =f iT,0 (T)·f(P)·f(a w ) Calculate the minimum fugacity f required for pure gas component i to stabilize the hydrate structure i,0 .in Among them, for carbon dioxide hydrate, β, λ1 and λ2 are 0.4242 K / bar, 1 / 23 and 3 / 23 respectively. is the activity of water, a i ,b i and c i is the Antoine constant.

[0093] (6) Press Calculate the mole fraction of component i in the polynary gas hydrate. And calculate Σx i .

[0094] (7) If |Σx i If -1|<ε holds, the phase equilibrium parameters p and T are output; if not, p and T are modified and (2) to (7) are recalculated.

[0095] Step 2: Based on the pipeline specification parameters, flow parameters and fluid composition, preliminarily determine the temperature-pressure (TP) distribution of the pipeline at the initial moment. Considering the heat exchange between the buried pipeline and the soil, the temperature of carbon dioxide at a certain point on the pipeline is T x (K) is calculated as follows:

[0096] T x =T0+(T1-T0)e -αx T0 is the average soil temperature, K; T1 is the temperature of carbon dioxide at the entrance of the micro-element pipe segment, K; x is the length of the micro-element pipe segment, m; Where K is the total heat transfer coefficient between carbon dioxide and soil, W / (m 2 ·K), D is the outer diameter of the pipeline, m; M is the mass flow rate of carbon dioxide in the pipeline, kg / s; C is the specific heat capacity of carbon dioxide at constant pressure, J / (kg·K).

[0097] The pressure drop ΔP of the fluid in the pipeline is calculated as follows:

[0098]

[0099] Where ρ is the density of carbon dioxide, kg / m 3 ; λ is the resistance loss coefficient along the way; L is the length of the pipeline, m; d is the inner diameter of the pipeline, m; v c is the flow rate of carbon dioxide, m / s; g is the acceleration due to gravity, m / s 2 ; H is the pipeline elevation difference, m.

[0100] Step 3: Combine the hydrate formation phase equilibrium parameters with the pipeline temperature-pressure distribution to determine the location of hydrate formation in the pipeline. When the temperature of the fluid in the pipeline is higher than the phase equilibrium temperature of the hydrate at the pressure, no hydrate is formed. When the temperature of the fluid in the pipeline is lower than or equal to the phase equilibrium temperature of the hydrate at the pressure, the pipeline is divided into M sections (j represents the jth section), the study time is divided into N intervals (i represents the i-th time period), and j=1, i=1 are assigned.

[0101] Step 4: Assign an initial value T' to the outlet temperature of pipe segment j.

[0102] Step 5: The present invention calculates the volume of the carbon dioxide hydrate particles based on the sum of the volume of the water droplet and the volume of the hydrate film covering the water droplet. The lateral growth rate of the hydrate film adopts the Chen-Guo comprehensive growth model, and the thickness of the hydrate film is calculated using the condensation analogy method. It is assumed that the distribution of hydrate particles in the pipeline is Poisson distribution. The hydrate volume V generated in the jth pipeline section during the i-th time period is calculated as follows: p ′:

[0103]

[0104] Where, v is the lateral growth rate of hydrate, which is calculated according to the Chen-Guo comprehensive growth model. ρ h is the molar density, g·mol / mm 3 ; Δh h is the latent heat of hydrate, J / (g·mol); k1 is the heat transfer coefficient, J / (s·mm 2 ·K); k2 is the reaction rate constant, (m / (s·K n ));T s is the hydrate film temperature, K; T sys is the system temperature, K. h is the thickness of the hydrate film, which is compared with the condensation process, according to Calculate, ρ w and ρ f are the densities of water and fluid, kg / m 3 ;μ w is the viscosity of water, Pa·s; λ w R is the thermal conductivity of water, W / (m·K). d is the radius of the water drop, m; is the number of water drops per unit length of the pipeline, M is the pipeline mass flow rate, kg / s; y w is the mass fraction of water. MN It is the time it takes for the fluid in the pipe to flow from point M to point N.

[0105] Step 6: According to the pressure difference equation Calculate the pressure p″ at the outlet of pipe segment j.

[0106] Step 7: According to the temperature difference equation Calculate the temperature T″ at the outlet of pipe section j. Where Δq is the heat transfer rate per unit length of the carbon dioxide pipeline, W / m. c is the flow rate of carbon dioxide in the pipeline, m / s. p is the pipeline angle, °.

[0107] Step 8: If |T'-T"|≤ε1 holds, assign T' to T", if not, re-assume T'.

[0108] Step 9: Recalculate the hydrate volume V generated in the jth pipeline section at the i-th time period p ″.

[0109] Step 10: If |V P '-V P ”|≤ε2 holds true, then V p ′ is assigned to V p ″. If not, re-assume T′.

[0110] Step 11: Calculate the hydrate volume V of each pipe section at time i in sequence p ′.

[0111] Step 12: Calculate the hydrate volume V of each pipe section at each time p ′.

[0112] Example 3

[0113] The present invention is used to predict the amount of hydrate generated in a supercritical CO2 transmission pipeline containing impurities. The components of the fluid in the pipeline include CO2, CO, H2, N2 and H2O, and the molar fractions are 99.08%, 0.5%, 0.2%, 0.2% and 0.02%, respectively. The pipeline design parameters are shown in Table 1. The mass flow rate of CO2 in the pipeline is 310,000 tons / year, the fluid pressure at the pipeline inlet is 15MPa, and the temperature is 14.58°C. By calculating pT along the pipeline, the fluid pressure at the pipeline outlet is 13.98MPa and the temperature is 7.02°C. Using the hydrate generation prediction method proposed in the present invention, the hydrate generation along the pipeline at different times is obtained, such as Figure 3 shown.

[0114] Table 1. Pipeline design parameters

[0115]

[0116] Example 4

[0117] like Figure 4 As shown, the hydrate formation prediction system for the impurity-containing supercritical carbon dioxide transmission pipeline provided by the present invention comprises:

[0118] A first parameter determination module determines the phase equilibrium parameters of hydrate formation in impurity-containing carbon dioxide according to the Chen-Guo hydrate formation model;

[0119] The second parameter determination module preliminarily determines the temperature-pressure distribution of the pipeline at the initial moment according to the pipeline specification parameters, flow parameters and fluid components;

[0120] The position determination module combines the hydrate formation phase equilibrium parameters with the pipeline temperature-pressure distribution to determine the position of hydrate formation in the pipeline; when the temperature of the fluid in the pipeline is higher than the hydrate formation phase equilibrium temperature corresponding to the fluid pressure, no hydrate is generated; when the temperature of the fluid in the pipeline is lower than or equal to the hydrate formation phase equilibrium temperature corresponding to the fluid pressure, the pipeline is divided into M sections, and the research time is divided into N intervals, with j representing the jth pipe section and i representing the ith time period;

[0121] The first assignment module assigns i=1;

[0122] The second assignment module assigns j=1;

[0123] The third assignment module assigns an initial value T′ to the temperature at the outlet of the j-pipe segment;

[0124] In the first calculation module, the distribution of hydrate particles in the pipeline is assumed to be Poisson distribution. The volume of carbon dioxide hydrate particles is calculated based on the sum of the volume of the water droplet and the volume of the hydrate film covering the water droplet. The lateral growth rate of the hydrate film is calculated using the Chen-Guo comprehensive growth model. The thickness of the hydrate film is calculated using the condensation analogy method. The hydrate volume V generated in the jth pipeline section is calculated. p ′;

[0125] The second calculation module, based on the pressure difference equation Calculate the pressure p″ at the outlet of pipe section j, where ΔP is the pressure drop in the pipe and ρ is the density of carbon dioxide, kg / m 3 ; r is the pipeline radius, m, β is the pipeline angle, °, v p is the velocity of hydrate particle flow, m / s, τ f is the pipe shear stress, N / m 2 , L pipe section length, m;

[0126] The third calculation module uses the temperature difference equation Calculate the temperature T″ at the outlet of pipe section j; where Δq is the heat transfer rate per unit length of the carbon dioxide pipeline, W / m, M is the CO2 pipeline mass flow rate, kg / s, v c is the flow rate of carbon dioxide in the pipeline, m / s, h is the enthalpy, kJ / kg;

[0127] The first judgment module, if |T'-T"|≤ε1 holds, assign T' to T", if not, re-assume T';

[0128] The fourth calculation module recalculates the hydrate volume V generated by the jth pipeline segment p ″;

[0129] The second judgment module, if |V P '-V P ”|≤ε2 holds true, then V p ′ is assigned to V p ″; If not, return to the third assignment module to re-assume T′; if established, proceed to the third judgment module;

[0130] The third judgment module, if j≥M is not, then j=j+1, repeat step 6-step 12 until j=M; if i≥N is not, then i=i+1, return to step 5 until i=N.

[0131] The present invention provides a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the steps of the method for predicting hydrate formation in a supercritical carbon dioxide transmission pipeline containing impurities are implemented.

[0132] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that include computer-usable program code.

[0133] The present application is described with reference to the flowcharts and / or block diagrams of the methods, systems and computer program products according to the embodiments of the present application. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of the processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A system that specifies the functions of a box or multiple boxes.

[0134] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0135] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0136] The invention points of the present invention are:

[0137] 1. The present invention combines the thermodynamic and kinetic factors of hydrate formation, the temperature-pressure distribution of the pipeline and the distribution of water droplets in the pipeline, and establishes a prediction method for the amount of hydrate generated in the pipeline. The generation location and amount of hydrate in the pipeline are predicted, and the calculation is simple and accurate.

[0138] 2. The present invention compares the growth of hydrate film thickness with condensation to calculate the thickness of the hydrate film.

[0139] 3. The present invention calculates the volume of the carbon dioxide hydrate particles based on the sum of the volume of the water droplet and the volume of the hydrate film covering the water droplet.

[0140] 4. The present invention takes into account the distribution of water droplets in the pipeline.

[0141] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the attached claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention. Any figure mark in the claims should not be regarded as limiting the claims involved.

[0142] In addition, it should be understood that although this specification is described in accordance with the implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation modes that can be understood by those skilled in the art. The above content is only to illustrate the technical idea of ​​the present invention, and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution according to the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for predicting hydrate formation in a supercritical carbon dioxide transmission pipeline containing impurities, characterized in that: include: Step 1: Determine the phase equilibrium parameters of hydrate formation in impurity-containing carbon dioxide according to the Chen-Guo hydrate formation model; Step 2: Preliminarily determine the temperature-pressure distribution of the pipeline at the initial moment based on pipeline specification parameters, flow parameters and fluid composition; Step 3: Determine the location of hydrate formation in the pipeline by combining the hydrate formation phase equilibrium parameters and the pipeline temperature-pressure distribution; when the temperature of the fluid in the pipeline is higher than the hydrate formation phase equilibrium temperature corresponding to the fluid pressure, no hydrate is generated; when the temperature of the fluid in the pipeline is lower than or equal to the hydrate formation phase equilibrium temperature corresponding to the fluid pressure, the pipeline is divided into M sections, and the research time is divided into N intervals, with j representing the jth pipe section and i representing the ith time period; Step 4: Assign i=1; Step 5: Assign j=1; Step 6: Assign an initial value T' to the temperature at the outlet of pipe section j; Step 7: Assuming that the distribution of hydrate particles in the pipeline is Poisson distribution, the volume of carbon dioxide hydrate particles is calculated based on the sum of the volume of the water droplet and the volume of the hydrate film covering the water droplet. The lateral growth rate of the hydrate film is calculated using the Chen-Guo comprehensive growth model, and the thickness of the hydrate film is calculated using the condensation analogy method. The hydrate volume V generated in the jth pipeline section is calculated. p ′; Step 8: According to the pressure difference equation Calculate the pressure p″ at the outlet of pipe section j, where ΔP is the pressure drop in the pipe and ρ is the density of carbon dioxide, kg / m 3 ; r is the pipeline radius, m, β is the pipeline angle, °, v p is the velocity of hydrate particle flow, m / s, τ f is the pipe shear stress, N / m 2 , L pipe section length, m; Step 9: According to the temperature difference equation Calculate the temperature T″ at the outlet of pipe section j; where Δq is the heat transfer rate per unit length of the carbon dioxide pipeline, W / m, M is the CO2 pipeline mass flow rate, kg / s, v c is the flow rate of carbon dioxide in the pipeline, m / s, h is the enthalpy, kJ / kg; Step 10: If |T'-T"|≤ε1 holds, assign T' to T", if not, re-assume T'; Step 11: Recalculate the hydrate volume V generated in the jth pipeline segment p ″; Step 12: If |V P '-V P ”|≤ε2 holds true, then V p ′ is assigned to V p ″; If not, return to step 6 and re-assume T′; if it is true, proceed to step 13; Step 13: If j≥M is not true, then j=j+1, and repeat steps 6-12 until j=M; If i≥N is not, then i=i+1 and return to step 5 until i=N.

2. The method for predicting hydrate formation in a supercritical carbon dioxide transportation pipeline containing impurities according to claim 1, characterized in that: In step 1, the phase equilibrium parameters for hydrate formation in impurity-containing carbon dioxide are determined according to the Chen-Guo hydrate formation model, including: (1) Determine the critical parameters of each component in the fluid and give the initial values ​​of p and T; (2) Press Calculate the fugacity f of each component i ,in T c is the critical temperature, K; p c is the critical pressure, Pa; (3) Press Calculate the Langmuir constant C of each component j , MPa, where X j ,Y j and Z j is a constant, fitted by the Lenard-Jones potential energy model; (4) Press Determine the proportion of connected cavities occupied by each j component gas θ j , and calculate (5) Press formula f i,0 =f iT,0 (T)·f(P)·f(a w ) Calculate the minimum fugacity f required for pure gas component i to stabilize the hydrate structure i,0 ;in Among them, for carbon dioxide hydrate, β, λ1 and λ2 are 0.4242K / bar, 1 / 23 and 3 / 23 respectively; is the activity of water, a i ,b i and c i is the Antoine constant; (6) Press Calculate the mole fraction of component i in the polynary gas hydrate and calculate ∑x i ; (7) If |∑x i If -1|<ε holds, the phase equilibrium parameters p and T are output; if not, p and T are modified and (2) to (7) are recalculated.

3. The method for predicting hydrate formation in a supercritical carbon dioxide transportation pipeline containing impurities according to claim 2, characterized in that: In step 2, based on pipeline specification parameters, flow parameters and fluid composition, the temperature-pressure distribution of the pipeline at the initial moment is preliminarily determined, including: Considering the heat exchange between the buried pipeline and the soil, the temperature of carbon dioxide at a certain point on the pipeline is T x Calculate as follows: T x =T0+(T1-T0)e -αx T0 is the average soil temperature, K; T1 is the temperature of carbon dioxide at the entrance of the micro-element pipe segment, K; x is the length of the micro-element pipe segment, m; Where K is the total heat transfer coefficient between carbon dioxide and soil, W / (m 2 ·K), D is the outer diameter of the pipeline, m; M is the mass flow rate of carbon dioxide in the pipeline, kg / s; C is the specific heat capacity of carbon dioxide at constant pressure, J / (kg·K); The pressure drop ΔP of the fluid in the pipeline is calculated as follows: Where λ is the resistance loss coefficient along the way; L is the length of the pipeline, m; d is the inner diameter of the pipeline, m; v c is the flow rate of carbon dioxide, m / s; g is the acceleration due to gravity, m / s 2 ; H is the pipeline elevation difference, m.

4. The method for predicting hydrate formation in a supercritical carbon dioxide transportation pipeline containing impurities according to claim 3, characterized in that: In step 7, it is assumed that the distribution of hydrate particles in the pipeline is Poisson distribution. The volume of carbon dioxide hydrate particles is calculated based on the sum of the volume of the water droplet and the volume of the hydrate film covering the water droplet. The lateral growth rate of the hydrate film is calculated using the Chen-Guo comprehensive growth model. The thickness of the hydrate film is calculated using the condensation analogy method. The hydrate volume V generated in the jth pipeline section is calculated. p ',include: The hydrate volume V generated in the jth pipeline section is calculated as follows: p ′: Where, v is the lateral growth rate of hydrate, which is calculated according to the Chen-Guo comprehensive growth model. ρ h is the molar density, g·mol / mm 3 ; Δh h is the latent heat of hydrate, J / (g·mol); k1 is the heat transfer coefficient, J / (s·mm 2 ·K); k2 is the reaction rate constant, (m / (s·K n ));T s is the hydrate film temperature, K; T sys is the system temperature, K; h is the thickness of the hydrate film, which is compared with the condensation process; R d is the radius of the water drop, m; is the number of water drops per unit length of the pipeline, M is the pipeline mass flow rate, kg / s; y w is the mass fraction of water; t MN It is the time it takes for the fluid in the pipe to flow from point M to point N.

5. The method for predicting hydrate formation in a supercritical carbon dioxide transportation pipeline containing impurities according to claim 4, characterized in that: The calculation formula of the thickness h of the hydrate film is as follows: Among them, ρ w and ρ f are the densities of water and fluid, kg / m 3 ;μ w is the viscosity of water, Pa·s; λ w is the thermal conductivity of water, W / (m·K); k is the condensation heat transfer coefficient.

6. A hydrate formation prediction system for supercritical carbon dioxide transportation pipeline containing impurities, characterized in that: include: A first parameter determination module determines the phase equilibrium parameters of hydrate formation in impurity-containing carbon dioxide according to the Chen-Guo hydrate formation model; The second parameter determination module preliminarily determines the temperature-pressure distribution of the pipeline at the initial moment according to the pipeline specification parameters, flow parameters and fluid components; The position determination module combines the hydrate formation phase equilibrium parameters with the pipeline temperature-pressure distribution to determine the position of hydrate formation in the pipeline; when the temperature of the fluid in the pipeline is higher than the hydrate formation phase equilibrium temperature corresponding to the fluid pressure, no hydrate is generated; when the temperature of the fluid in the pipeline is lower than or equal to the hydrate formation phase equilibrium temperature corresponding to the fluid pressure, the pipeline is divided into M sections, and the research time is divided into N intervals, with j representing the jth pipe section and i representing the ith time period; The first assignment module assigns i=1; The second assignment module assigns j=1; The third assignment module assigns an initial value T′ to the temperature at the outlet of the j-pipe segment; In the first calculation module, the distribution of hydrate particles in the pipeline is assumed to be Poisson distribution. The volume of carbon dioxide hydrate particles is calculated based on the sum of the volume of the water droplet and the volume of the hydrate film covering the water droplet. The lateral growth rate of the hydrate film is calculated using the Chen-Guo comprehensive growth model. The thickness of the hydrate film is calculated using the condensation analogy method. The hydrate volume V generated in the jth pipeline section is calculated. p ′; The second calculation module, based on the pressure difference equation Calculate the pressure p″ at the outlet of pipe section j, where ΔP is the pressure drop in the pipe and ρ is the density of carbon dioxide, kg / m 3 ; r is the pipeline radius, m, β is the pipeline angle, °, v p is the velocity of hydrate particle flow, m / s, τ f is the pipe shear stress, N / m 2 , L pipe section length, m; The third calculation module uses the temperature difference equation Calculate the temperature T″ at the outlet of pipe section j; where Δq is the heat transfer rate per unit length of the carbon dioxide pipeline, W / m, M is the CO2 pipeline mass flow rate, kg / s, v c is the flow rate of carbon dioxide in the pipeline, m / s, h is the enthalpy, kJ / kg; The first judgment module, if |T'-T"|≤ε1 holds, assign T' to T", if not, re-assume T'; The fourth calculation module recalculates the hydrate volume V generated by the jth pipeline segment p ″; The second judgment module, if |V P '-V P ”|≤ε2 holds true, then V p ′ is assigned to V p ″; If not, return to the third assignment module to re-assume T′; if established, proceed to the third judgment module; The third judgment module, if j≥M is not, then j=j+1, and repeat steps 6 to 12 until j=M; If i≥N is not, then i=i+1 and return to step 5 until i=N.

7. The hydrate formation prediction system for supercritical carbon dioxide transportation pipeline containing impurities according to claim 6 is characterized in that: In the first parameter determination module, the phase equilibrium parameters of hydrate formation in impurity-containing carbon dioxide are determined according to the Chen-Guo hydrate formation model, including: (1) Determine the critical parameters of each component in the fluid and give the initial values ​​of p and T; (2) Press Calculate the fugacity f of each component i ,in T c is the critical temperature, K; p c is the critical pressure, Pa; (3) Press Calculate the Langmuir constant C of each component j , MPa, where X j ,Y j and Z j is a constant, fitted by the Lenard-Jones potential energy model; (4) Press Determine the proportion of connected cavities occupied by each j component gas θ j , and calculate (5) Press formula f i,0 =f iT,0 (T)·f(P)·f(a w ) Calculate the minimum fugacity f required for pure gas component i to stabilize the hydrate structure i,0 ;in Among them, for carbon dioxide hydrate, β, λ1 and λ2 are 0.4242K / bar, 1 / 23 and 3 / 23 respectively; is the activity of water, a i ,b i and c i is the Antoine constant; (6) Press Calculate the mole fraction of component i in the polynary gas hydrate and calculate Σx i ; (7) If |Σx i If -1|<ε holds, the phase equilibrium parameters p and T are output; if not, p and T are modified and (2) to (7) are recalculated.

8. The hydrate formation prediction system for supercritical carbon dioxide transportation pipeline containing impurities according to claim 7 is characterized in that: In the second parameter determination module, based on the pipeline specification parameters, flow parameters and fluid components, the temperature-pressure distribution of the pipeline at the initial moment is preliminarily determined, including: Considering the heat exchange between the buried pipeline and the soil, the temperature of carbon dioxide at a certain point on the pipeline is T x Calculate as follows: T x =T0+(T1-T0)e -αx T0 is the average soil temperature, K; T1 is the temperature of carbon dioxide at the entrance of the micro-element pipe segment, K; x is the length of the micro-element pipe segment, m; Where K is the total heat transfer coefficient between carbon dioxide and soil, W / (m 2 ·K), D is the outer diameter of the pipeline, m; M is the mass flow rate of carbon dioxide in the pipeline, kg / s; C is the specific heat capacity of carbon dioxide at constant pressure, J / (kg·K); The pressure drop ΔP of the fluid in the pipeline is calculated as follows: Where λ is the resistance loss coefficient along the way; L is the length of the pipeline, m; d is the inner diameter of the pipeline, m; v c is the flow rate of carbon dioxide, m / s; g is the acceleration due to gravity, m / s 2 ; H is the pipeline elevation difference, m.

9. The hydrate formation prediction system for supercritical carbon dioxide transportation pipeline containing impurities according to claim 8 is characterized in that: In the first calculation module, the distribution of hydrate particles in the pipeline is assumed to be Poisson distribution. The volume of carbon dioxide hydrate particles is calculated based on the sum of the volume of the water droplet and the volume of the hydrate film covering the water droplet. The lateral growth rate of the hydrate film is calculated using the Chen-Guo comprehensive growth model. The thickness of the hydrate film is calculated using the condensation analogy method. The hydrate volume V generated in the jth pipeline section is calculated. p ',include: The hydrate volume V generated in the jth pipeline section is calculated as follows: p ′: Where, v is the lateral growth rate of hydrate, which is calculated according to the Chen-Guo comprehensive growth model. ρ h is the molar density, g·mol / mm 3 ; Δh h is the latent heat of hydrate, J / (g·mol); k1 is the heat transfer coefficient, J / (s·mm 2 ·K); k2 is the reaction rate constant, (m / (s·K n ));T s is the hydrate film temperature, K; T sys is the system temperature, K; h is the thickness of the hydrate film, which is compared with the condensation process; R d is the radius of the water drop, m; is the number of water drops per unit length of the pipeline, M is the pipeline mass flow rate, kg / s; y w is the mass fraction of water; t MN It is the time it takes for the fluid in the pipe to flow from point M to point N.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of the method for predicting hydrate formation in a supercritical carbon dioxide transportation pipeline containing impurities according to any one of claims 1 to 5.

Images