A method and device for calculating temperature and pressure of high-pressure CO2 after multi-stage throttling

Abstract

The application discloses a high-pressure CO2 multi-stage throttling post-temperature and pressure calculation method, which comprises the following steps: determining the throttling stage number of CO2, and measuring the throttling aperture and the throttling pipeline volume; obtaining the pre-throttling pressure and pre-throttling temperature of CO2, and determining the preset regulating pressure of a throttling outlet; calculating the minimum post-throttling pressure of CO2, and judging whether the preset regulating pressure of the throttling outlet needs to be corrected; calculating the post-throttling flow rate of CO2; calculating the CO2 enthalpy value at different temperatures based on the real gas enthalpy value; iteratively calculating the post-throttling temperature of single-stage CO2 based on the CO2 enthalpy value at different temperatures; judging whether the post-iteration CO2 enthalpy value meets the set accuracy requirement; calculating the pressure of each throttling inlet; calculating the temperature in each throttling pipeline; and based on the pressure of each throttling inlet and the throttling pipeline temperature, iteratively calculating in the time-increasing mode until the CO2 emission in the throttling pipeline is completed, so as to obtain the change curve of the high-pressure CO2 multi-stage throttling post-temperature and pressure with time.

Description

Technical Field

[0001] The present invention relates to the technical field of petrochemical industry, and in particular to a method and device for calculating the temperature and pressure of high-pressure CO2 after multi-stage throttling. Background Art

[0002] Water-gas alternating flooding (WAG) is an effective method for enhancing oil recovery. The displacement media in WAG are water and gas, with high-purity CO2 often used as the gas to achieve the highest displacement efficiency. In actual projects, CO2 sources are very limited, so N2, hydrocarbon gas, and high-CO2 hydrocarbon gas may be used as a substitute. WAG involves the alternating injection of water and CO2 slugs, effectively addressing the viscous fingering and gas channeling that can occur when using CO2 as a displacement medium. It also enhances oil-gas mass transfer, effectively expands the swept volume, increases gas utilization, and improves the CO2 flooding effect.

[0003] The water-gas alternation process of WAG flooding technology requires reducing downhole high-pressure gas, typically exceeding 35 MPa, to atmospheric pressure for release or subsequent treatment, allowing water to be injected into the wellbore. This decompression process typically involves multiple stages, so calculating how the pressure at each throttle outlet changes with throttling time is crucial for controlling the throttling system and the release process. Furthermore, the throttling process of high-pressure CO2 produces a significant scorching effect, causing significant temperature fluctuations. Therefore, calculating how the main pipeline temperature changes with throttling time is also crucial for throttling pipeline design and preventing freezing and blockage. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides a method for calculating the temperature and pressure of high-pressure CO2 after multi-stage throttling, which is intended to accurately and quickly calculate the temperature and pressure of high-pressure CO2 after multi-stage throttling.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] In the first aspect, the present invention provides a method for calculating the temperature and pressure after multi-stage throttling of high-pressure CO2, comprising the following steps: determining the throttling level of CO2, and measuring the throttling aperture and the volume of the throttling pipe; obtaining the pre-throttling pressure and pre-throttling temperature of CO2, and determining the preset regulating pressure of the throttling outlet; calculating the minimum pressure of CO2 after throttling, and judging whether it is necessary to correct the preset regulating pressure of the throttling outlet; constructing the Bernoulli equation based on the pressure before and after throttling of CO2 and the adiabatic index of CO2 to calculate the flow rate of CO2 after throttling; calculating the CO2 flow rate at different temperatures based on the real gas enthalpy. CO2 enthalpy value; iteratively calculate the temperature after single-stage CO2 throttling based on the CO2 enthalpy values ​​at different temperatures; determine whether the CO2 enthalpy value after iteration meets the set accuracy requirements. If so, end the iteration and proceed to the next step. Otherwise, repeat the previous step until the set accuracy requirements are met; calculate the pressure at the throttling inlet of each level: calculate the temperature in the throttling pipe at each level; based on the calculated pressure at the throttling inlet of each level and the temperature in the throttling pipe at each level, iterate according to the time-increasing rule until the CO2 in the throttling pipe is completely discharged, and obtain the time-varying curve of the temperature and pressure after high-pressure CO2 multi-stage throttling.

[0007] As a preferred embodiment, the “calculating the minimum pressure of CO2 after throttling and determining whether it is necessary to correct the preset regulating pressure of the throttling outlet” is specifically as follows:

[0008] 1) Calculate the minimum pressure p of CO2 after throttling by the following formula (1): c :

[0009]

[0010] Where, p1 is the pressure before throttling; p c is the minimum pressure after throttling; k is the CO2 adiabatic index, with an average value of about 1.3;

[0011] 2) Compare the minimum pressure p after throttling c The size of the preset adjustment pressure p2 of the throttle outlet: If the minimum pressure p after throttling c If the minimum pressure after throttling is less than or equal to the preset regulating pressure p2, the preset regulating pressure p2 is appropriate; c If the preset regulating pressure value p2 is greater than the preset regulating pressure value, the preset regulating pressure p2 is corrected to the minimum pressure p after throttling. c .

[0012] Preferably, the Bernoulli equation is expressed as follows:

[0013]

[0014] Where w1 is the flow rate of CO2 before throttling; w2 is the flow rate of CO2 after throttling; v1 = 1 / ρ is the specific volume of CO2.

[0015] As preferred: the "calculating the CO2 enthalpy value at different temperatures based on the real gas enthalpy value" is specifically:

[0016] The real gas enthalpy value is equal to the ideal gas enthalpy value and the isothermal enthalpy difference, i.e.:

[0017]

[0018] H 0 = 11.11374 + 0.47911T + 7.62195x10 -4 T 2

[0019] -3.59392x10 -7 T 3 + 8.47438x10 -11 T 4 - 0.57752x10 -14 T 5 (4)

[0020]

[0021] In the formula, H is the real gas enthalpy value; H 0 is the ideal gas enthalpy value; ΔH T is the isothermal enthalpy difference; p is the CO2 pressure; v is the CO2 volume; ρ is the CO2 density; R is the universal gas constant; T is the CO2 temperature; P c , T c are the critical temperature and critical pressure of CO2 respectively; T r = T / T c ; f ω = 0.37464 + 1.54226ω - 0.26992ω 2 , ω is the eccentric factor.

[0022] As preferred: the iterative calculation formula of the single-stage CO2 throttling temperature is as follows:

[0023]

[0024] In the formula, T 2i is the CO2 throttling temperature obtained by the i-th step iterative calculation; T 2(i-1) is the CO2 throttling temperature obtained by the i-1-th step iterative calculation; α is the step length of each iteration; H1 is the CO2 enthalpy value before throttling; H 2(i-1) is the CO2 enthalpy value after throttling obtained by the i-1-th step iterative calculation.

[0025] As a preferred embodiment, the step of “determining whether the CO2 enthalpy value after iteration meets the set accuracy requirement, and if so, ending the iteration and proceeding to the next step, and otherwise repeating the previous step until the set accuracy requirement is met” is specifically as follows:

[0026] The following formula (7) is used to determine whether the CO2 enthalpy value after iteration meets the set accuracy requirement: if it does, the iteration is terminated and the single-stage CO2 throttling temperature is output; if it does not meet the set accuracy requirement, the calculated single-stage CO2 throttling temperature is used as the initial value to repeat the previous step until the set accuracy requirement is met, the iteration is terminated, and the single-stage CO2 throttling temperature is output;

[0027]

[0028] Where H 2i is the CO2 enthalpy value after throttling obtained by iterative calculation in the i-th step; θ is the setting accuracy; i represents the number of iteration steps.

[0029] As a preferred method, the calculation formula for the pressure at each level of throttling inlet is as follows:

[0030]

[0031] P i =P i-1 +dp (9)

[0032] Where, dp is the pressure change at the throttle inlet; p is the current actual pressure, p amb is the atmospheric pressure; t is the throttling time; C w is the velocity coefficient, the recommended value is 0.85, F is the adjustment coefficient, take 1, V is the main pipe volume, p out is the pressure at the final stage throttling outlet, T out is the temperature of the last stage throttling outlet; P i is the pressure at the throttling inlet calculated in the i-th iterative step.

[0033] As a preferred method, the temperature calculation formula of each level of throttling pipe is as follows:

[0034]

[0035] Z 3 -(1-B)Z 2 +(A-2B-3B 2 )Z-(AB-B 2 -B 3 )=0 (12)

[0036] Where T0 is the initial temperature of CO2 at each level of throttling inlet; m is the mass flow rate; Z is the compressibility factor; d is the throttling aperture; D is the throttling pipe diameter; A = ap / (RT)2 B = bp / (RT).

[0037] As preferred: the judgment standard of complete CO2 emission is that the remaining CO2 mass in the throttle pipe is reduced to 0 value, and the calculation formula is:

[0038]

[0039] In the formula, G is the remaining CO2 mass in the throttle pipe; G0 is the total amount of CO2 in the pipe at the initial moment.

[0040] In the second aspect, the application provides a high-pressure CO2 multi-stage throttling temperature and pressure calculation device, which comprises:

[0041] A first processing unit is configured to determine the throttling stage number of CO2, measure the throttling aperture and the volume of the throttle pipe;

[0042] A second processing unit is configured to obtain the pre-throttling pressure and pre-throttling temperature of CO2 and determine the preset adjustment pressure of the throttling outlet;

[0043] A third processing unit is configured to calculate the minimum pressure of CO2 after throttling and judge whether the preset adjustment pressure of the throttling outlet needs to be corrected;

[0044] A fourth processing unit is configured to construct a Bernoulli equation based on the pre-throttling pressure of CO2, the preset adjustment pressure and the adiabatic index of CO2 to calculate the flow rate of CO2 after throttling;

[0045] A fifth processing unit is configured to calculate the enthalpy value of CO2 at different temperatures based on the real gas enthalpy value;

[0046] A sixth processing unit is configured to iteratively calculate the temperature of CO2 after single-stage throttling based on the enthalpy value of CO2 at different temperatures;

[0047] A seventh processing unit is configured to judge whether the enthalpy value of CO2 after iteration meets the set accuracy requirement, and if yes, end the iteration and proceed to the next step, otherwise, repeat the previous step until the set accuracy requirement is met;

[0048] An eighth processing unit is configured to calculate the pressure of the throttle inlet of each stage;

[0049] A ninth processing unit is configured to calculate the temperature in the throttle pipe of each stage;

[0050] A tenth processing unit is configured to iteratively calculate based on the calculated pressure of the throttle inlet of each stage and the temperature in the throttle pipe of each stage in the order of time increment until the CO2 in the throttle pipe is completely emitted, so as to obtain the change curve of the temperature and pressure of high-pressure CO2 after multi-stage throttling with time.

[0051] The application has the following advantages due to the above technical solutions:

[0052] The high-pressure CO2 multi-stage throttling temperature and pressure calculation method provided by the application adopts specific steps, can quickly calculate the change of the pressure and temperature of each stage in the CO2 multi-stage throttling process with the throttling time, improves the accuracy and convenience of the CO2 throttling pressure and temperature calculation, and has important significance for the throttling pipeline design and throttling effect prediction. BRIEF DESCRIPTION OF DRAWINGS

[0053] Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The accompanying drawings are included to provide a description of the preferred embodiments and are not intended to limit the scope of the application. Throughout the drawings, like reference numerals are used to designate like parts. In the drawings:

[0054] Figure 1 The flow chart of the high-pressure CO2 multi-stage throttling temperature and pressure calculation method provided by the application;

[0055] Figure 2 The pressure change curve of the high-pressure CO2 multi-stage throttling with time;

[0056] Figure 3 The temperature change curve of the high-pressure CO2 multi-stage throttling with time. DETAILED DESCRIPTION

[0057] In order to make the objectives, technical solutions and advantages of the application clearer, the specific embodiments of the application are further described below with reference to the drawings. Although the exemplary embodiments of the application are shown in the drawings, it should be understood that the application can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the application and to fully convey the scope of the application to those skilled in the art.

[0058] The high-pressure CO2 multi-stage throttling post-temperature and pressure calculation method provided by the application comprises the following steps: determining the throttling stage number of CO2, measuring the throttling aperture and the throttling pipeline volume, obtaining the pre-throttling pressure and pre-throttling temperature of CO2, and determining the preset regulating pressure of the throttling outlet; calculating the post-throttling minimum pressure of CO2, and judging whether the preset regulating pressure of the throttling outlet needs to be corrected; calculating the post-throttling flow rate of CO2; calculating the CO2 enthalpy value at different temperatures based on the real gas enthalpy value; iteratively calculating the post-throttling temperature of single-stage CO2 based on the CO2 enthalpy value at different temperatures; judging whether the post-iteration CO2 enthalpy value meets the set accuracy requirement; calculating the pressure of each throttling inlet; calculating the temperature in each throttling pipeline; and iteratively calculating based on the pressure of each throttling inlet and the throttling pipeline temperature in a time-increasing manner until the CO2 emission in the throttling pipeline is complete, so as to obtain the variation curve of the high-pressure CO2 multi-stage throttling post-temperature and pressure with time. The application can quickly calculate the variation of the pressure and temperature of each stage in the CO2 multi-stage throttling process with the throttling time, improves the accuracy and convenience of the CO2 throttling pressure and temperature calculation, and has important significance for throttling pipeline design and throttling effect prediction.

[0059] The high-pressure CO2 multi-stage throttling post-temperature and pressure calculation method and device provided by the embodiments of the application will be described in detail below with reference to the drawings.

[0060] Embodiment 1

[0061] Please refer to Figure 1 The high-pressure CO2 multi-stage throttling post-temperature and pressure calculation method provided by the embodiment comprises the following steps:

[0062] Step one, determining the throttling stage number n of CO2, and measuring the throttling aperture d and the throttling pipeline volume V.

[0063] High-pressure CO2 throttling generally adopts multi-stage throttling, and the application is applicable to the throttling process of at most three-stage throttling, that is, n≤3;

[0064] The throttling aperture d represents the aperture of each throttling valve or orifice plate that has throttling effect;

[0065] The throttling pipeline volume V represents the total volume of CO2 participating in the throttling process.

[0066] Step two, obtaining the pre-throttling pressure p1 and pre-throttling temperature T1 of CO2, and determining the preset regulating pressure p2 of the throttling outlet.

[0067] Step three, calculating the post-throttling minimum pressure p c of CO2, and judging whether the preset regulating pressure p2 of the throttling outlet needs to be corrected, specifically:

[0068] 1) Calculate the minimum pressure p of CO2 after throttling by the following formula (1): c :

[0069]

[0070] Where, p1 is the pressure before throttling; p c is the minimum pressure after throttling; k is the CO2 adiabatic index, with an average value of about 1.3;

[0071] 2) Compare the minimum pressure p after throttling c The size of the preset adjustment pressure p2 of the throttle outlet: If the minimum pressure p after throttling c If the minimum pressure after throttling is less than or equal to the preset regulating pressure p2, the preset regulating pressure p2 is appropriate; c If the preset regulating pressure value p2 is greater than the preset regulating pressure value, the preset regulating pressure p2 is corrected to the minimum pressure p after throttling. c .

[0072] Step 4: Based on the CO2 pre-throttling pressure p1, the preset adjustment pressure p2 and the CO2 adiabatic index, the Bernoulli equation is constructed to calculate the CO2 post-throttling flow rate:

[0073]

[0074] Where w1 is the flow rate of CO2 before throttling; w2 is the flow rate of CO2 after throttling; v1 = 1 / ρ is the specific volume of CO2.

[0075] Step 5: Calculate the CO2 enthalpy at different temperatures based on the real gas enthalpy, specifically:

[0076] The real gas enthalpy is equal to the sum of the ideal gas enthalpy and the isothermal enthalpy difference, that is:

[0077]

[0078] H 0 =11.11374+0.47911T+7.62195×10 -4 T 2

[0079] -3.59392×10 -7 T 3 +8.47438×10 -11 T 4 -0.57752×10 -14 T 5 (4)

[0080]

[0081] Where H is the real gas enthalpy; H 0is the ideal gas enthalpy; ΔH T is the isothermal enthalpy difference; p is the CO2 pressure; v is the CO2 volume; ρ is the CO2 density; R is the universal gas constant; T is the CO2 temperature; P c 、T c are the critical temperature and critical pressure of CO2, which are 7.38MPa and 31.1℃ respectively; T r =T / T c ;f ω =0.37464+1.54226ω-0.26992ω 2 , ω is the eccentricity factor, and the recommended value is 0.21.

[0082] Step 6: Based on the CO2 flow rate before and after throttling and the CO2 enthalpy at different temperatures, the single-stage CO2 post-throttling temperature is iteratively calculated using the following formula (6):

[0083]

[0084] Where, T 2i is the CO2 throttling temperature obtained by iterative calculation in step i; T 2(i-1) is the CO2 temperature after throttling obtained by the iterative calculation in step i-1; α is the step size of each iteration, which can be flexibly determined according to the required accuracy of the calculation and the actual experimental situation; H1 is the CO2 enthalpy value before throttling; H 2(i-1) The CO2 enthalpy after throttling calculated in the i-1th iterative calculation step.

[0085] Step 7. Use the following formula (7) to determine whether the CO2 enthalpy value after iteration meets the set accuracy requirements: if it does, end the iteration and output the single-stage CO2 throttling temperature; if it does not meet the set accuracy requirements, use the calculated single-stage CO2 throttling temperature as the initial value and repeat step 6 until it meets the set accuracy requirements, end the iteration, and output the single-stage CO2 throttling temperature.

[0086]

[0087] Where H 2i is the throttled CO2 enthalpy value obtained by the iterative calculation in the i-th step; θ is the set accuracy, which can be flexibly determined according to the required accuracy of the calculation and the actual experimental situation; i represents the number of iterations, starting from 1 and increasing with the number of iterations, that is, i = i + 1 for each iteration.

[0088] Step 8. Calculate the pressure at each level of throttling inlet using the formula (8) of the law of change of throttling inlet pressure with throttling time and the following formula (9):

[0089]

[0090] Pi =P i-1 +dp (9)

[0091] Where, dp is the pressure change at the throttle inlet; p is the current actual pressure, p amb is the atmospheric pressure; t is the throttling time; C w is the velocity coefficient, the recommended value is 0.85, F is the adjustment coefficient, take 1, V is the throttling pipe volume, p out is the pressure at the final stage throttling outlet, T out is the temperature of the last stage throttling outlet; P i is the pressure at the throttling inlet calculated in the i-th iterative step.

[0092] Step 9: Calculate the temperature in each level of throttling pipes using the temperature variation law of the throttling pipes with the throttling time formula (10);

[0093]

[0094] Z 3 -(1-B)Z 2 +(A-2B-3B 2 )Z-(AB-B 2 -B 3 )=0 (12)

[0095] Where T0 is the initial temperature of CO2 at each level of throttling inlet; m is the mass flow rate; Z is the compressibility factor, which can be calculated from the PR state equation; d is the throttling aperture; D is the throttling pipe diameter; A = ap / (RT) 2 ,B=bp / (RT).

[0096] Step 10: Based on the calculated pressure at each level of throttling inlet and the temperature at each level of throttling pipe, iterate according to the law of increasing time until the CO2 in the throttling pipe is completely discharged, and obtain the temperature and pressure change curve of high-pressure CO2 after multi-stage throttling with time (taking the inlet pressure of 41MPa and the inlet temperature of 313K as an example, the change curve is as follows Figure 2 、 Figure 3 shown).

[0097] The criterion for determining the complete emission of CO2 is that the mass of the remaining CO2 in the throttling pipe drops to 0. The calculation formula is:

[0098]

[0099] Where G is the mass of CO2 remaining in the throttling pipe; G0 is the total amount of CO2 in the pipe at the initial moment.

[0100] Example 2:

[0101] The above-mentioned embodiment 1 provides a method for calculating the temperature and pressure of high-pressure CO2 after multi-stage throttling. Correspondingly, this embodiment provides a device for calculating the temperature and pressure of high-pressure CO2 after multi-stage throttling. The device for calculating the temperature and pressure of high-pressure CO2 after multi-stage throttling provided in this embodiment can implement the method for calculating the temperature and pressure of high-pressure CO2 after multi-stage throttling in embodiment 1. The device for calculating the temperature and pressure of high-pressure CO2 after multi-stage throttling can be implemented through software, hardware, or a combination of software and hardware. For example, the device for calculating the temperature and pressure of high-pressure CO2 after multi-stage throttling can include integrated or separate functional modules or functional units to perform the corresponding steps of each method in embodiment 1. Since the device for calculating the temperature and pressure of high-pressure CO2 after multi-stage throttling in this embodiment is basically similar to the method embodiment, the description of this embodiment is relatively simple. For relevant details, please refer to the partial description of embodiment 1. The device for calculating the temperature and pressure of high-pressure CO2 after multi-stage throttling in this embodiment is merely illustrative.

[0102] The device for calculating the temperature and pressure of high-pressure CO2 after multi-stage throttling provided in this embodiment includes:

[0103] The first processing unit is used to determine the throttling level of CO2 and measure the throttling aperture and throttling pipe volume;

[0104] The second processing unit is used to obtain the pre-throttling pressure and pre-throttling temperature of CO2 and determine the preset regulating pressure of the throttling outlet;

[0105] The third processing unit is used to calculate the minimum pressure of CO2 after throttling and determine whether the preset adjustment pressure of the throttling outlet needs to be corrected;

[0106] A fourth processing unit is configured to calculate a CO2 post-throttling flow rate by constructing a Bernoulli equation based on the CO2 pre-throttling pressure, a preset regulating pressure, and a CO2 adiabatic index;

[0107] a fifth processing unit, configured to calculate the enthalpy of CO2 at different temperatures based on the real gas enthalpy;

[0108] a sixth processing unit, configured to iteratively calculate the single-stage CO2 post-throttling temperature based on the CO2 enthalpy values ​​at different temperatures;

[0109] The seventh processing unit is used to determine whether the CO2 enthalpy value after iteration meets the set accuracy requirement. If it does, the iteration is terminated and the next step is entered. Otherwise, the previous step is repeated until the set accuracy requirement is met.

[0110] The eighth processing unit is used to calculate the pressure at each level of throttling inlet:

[0111] The ninth processing unit is used to calculate the temperature in each level of throttling pipe;

[0112] The tenth processing unit is used to iterate according to the time-increasing rule based on the calculated pressures at the throttling inlets of each level and the temperatures at each level of the throttling pipes until the CO2 in the throttling pipes is completely discharged, thereby obtaining a curve of temperature and pressure changes with time after high-pressure CO2 multi-stage throttling.

[0113] Example 3:

[0114] This embodiment provides a processing device for implementing the method for calculating the temperature and pressure of high-pressure CO2 after multi-stage throttling provided in this embodiment 1. The processing device can be a processing device for a client, such as a mobile phone, laptop computer, tablet computer, desktop computer, etc., to execute the method of embodiment 1.

[0115] The processing device includes a processor, a memory, a communication interface, and a bus. The processor, memory, and communication interface are connected via the bus to facilitate communication between them. The memory stores a computer program executable by the processor. When the processor executes the computer program, it executes the method for calculating the temperature and pressure after multi-stage throttling of high-pressure CO2 provided in Example 1.

[0116] Preferably, the memory may be a high-speed random access memory (RAM), and may also include a non-volatile memory, such as at least one disk memory.

[0117] Preferably, the processor may be a central processing unit (CPU), a digital signal processor (DSP), or other general-purpose processors of various types, which are not limited here.

[0118] Example 4:

[0119] The method for calculating the temperature and pressure of high-pressure CO2 after multi-stage throttling in this embodiment 1 can be specifically implemented as a computer program product. The computer program product may include a computer-readable storage medium carrying computer-readable program instructions for executing the method described in this embodiment 1.

[0120] Computer readable storage media can be tangible devices that hold and store instructions used by instruction execution devices. Computer readable storage media can be, for example, but not limited to, electronic storage devices, magnetic storage devices, optical storage devices, electromagnetic storage devices, semiconductor storage devices, or any combination thereof.

[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 them. 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 make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A method for calculating temperature and pressure after high-pressure CO2 multi-stage throttling, characterized in that: The following steps are involved: Determine the throttling level of CO2 and measure the throttling aperture and throttling pipe volume; Obtain the pre-throttling pressure and pre-throttling temperature of CO2, and determine the preset regulating pressure of the throttling outlet; Calculate the minimum pressure of CO2 after throttling and determine whether the preset adjustment pressure of the throttling outlet needs to be corrected; The Bernoulli equation is constructed based on the CO2 pre-throttling pressure, the preset regulating pressure and the CO2 adiabatic index to calculate the CO2 post-throttling flow rate; Calculate the CO2 enthalpy at different temperatures based on the real gas enthalpy; Iteratively calculate the temperature after single-stage CO2 throttling based on the CO2 enthalpy at different temperatures; Determine whether the CO2 enthalpy value after iteration meets the set accuracy requirements. If so, end the iteration and proceed to the next step. Otherwise, repeat the previous step until the set accuracy requirements are met. Calculate the pressure at each level of throttling inlet: Calculate the temperature inside the throttling pipes at all levels; Based on the calculated pressures at the throttling inlets of each level and the temperatures of the throttling pipes at each level, iterations are performed according to the time-increasing rule until the CO2 in the throttling pipe is completely discharged, and the curves of temperature and pressure changes with time after high-pressure CO2 multi-stage throttling are obtained.

2. The method for calculating temperature and pressure after high-pressure CO2 multi-stage throttling according to claim 1, characterized in that: The aforementioned "calculating the minimum pressure of CO2 after throttling and determining whether it is necessary to correct the preset regulating pressure of the throttling outlet" is specifically as follows: 1) Calculate the minimum pressure p of CO2 after throttling by the following formula (1): c : Where, p1 is the pressure before throttling; p c is the minimum pressure after throttling; k is the CO2 adiabatic index, with an average value of about 1.3; 2) Compare the minimum pressure p after throttling c The size of the preset adjustment pressure p2 of the throttle outlet: If the minimum pressure p after throttling c If the minimum pressure after throttling is less than or equal to the preset regulating pressure p2, the preset regulating pressure p2 is appropriate; c If the preset regulating pressure value p2 is greater than the preset regulating pressure value, the preset regulating pressure p2 is corrected to the minimum pressure p after throttling. c .

3. The method for calculating temperature and pressure after high-pressure CO2 multi-stage throttling according to claim 2, characterized in that: The expression of the Bernoulli equation is as follows: Where w1 is the flow rate of CO2 before throttling; w2 is the flow rate of CO2 after throttling; v1 = 1 / ρ is the specific volume of CO2.

4. The method for calculating temperature and pressure after high-pressure CO2 multi-stage throttling according to claim 3 is characterized in that: The "calculation of CO2 enthalpy at different temperatures based on real gas enthalpy" is specifically: The real gas enthalpy is equal to the sum of the ideal gas enthalpy and the isothermal enthalpy difference, that is: H 0 =11.11374+0.47911T+7.62195×10 -4 T 2 -3.59392×10 -7 T 3 +8.47438×10 -11 T 4 -0.57752×10 -14 T 5 (4) Where H is the real gas enthalpy; H 0 is the ideal gas enthalpy; ΔH T is the isothermal enthalpy difference; p is the CO2 pressure; v is the CO2 volume; ρ is the CO2 density; R is the universal gas constant; T is the CO2 temperature; P c 、T c are the critical temperature and critical pressure of CO2 respectively; T r =T / T c ;f ω =0.37464+1.54226ω-0.26992ω 2 , ω is the eccentricity factor.

5. The method for calculating temperature and pressure after high-pressure CO2 multi-stage throttling according to claim 4 is characterized in that: The iterative calculation formula of the single-stage CO2 throttling temperature is as follows: Where, T 2i is the CO2 throttling temperature obtained by iterative calculation in step i; T 2(i-1) is the CO2 temperature after throttling calculated by the iterative calculation in the i-1th step; α is the step length of each iteration; H1 is the CO2 enthalpy before throttling; H 2(i-1) The CO2 enthalpy after throttling calculated in the i-1th iterative calculation step.

6. The method for calculating temperature and pressure after high-pressure CO2 multi-stage throttling according to claim 5, characterized in that: The specific steps of "determining whether the CO2 enthalpy value after iteration meets the set accuracy requirement, if so, ending the iteration and proceeding to the next step, otherwise repeating the previous step until the set accuracy requirement is met" are: The following formula (7) is used to determine whether the CO2 enthalpy value after iteration meets the set accuracy requirement: If it does, the iteration is terminated and the single-stage CO2 throttling temperature is output; If the set accuracy requirement is not met, the calculated single-stage CO2 throttling temperature is used as the initial value and the previous step is repeated until the set accuracy requirement is met. The iteration is ended and the single-stage CO2 throttling temperature is output; Where H 2i is the CO2 enthalpy value after throttling obtained by iterative calculation in the i-th step; θ is the setting accuracy; i represents the number of iteration steps.

7. The method for calculating temperature and pressure after high-pressure CO2 multi-stage throttling according to claim 6, characterized in that: The calculation formula for the pressure at each level of throttle inlet is as follows: P i =P i-1 +dp (9) Where, dp is the pressure change at the throttle inlet; p is the current actual pressure, p amb is the atmospheric pressure; t is the throttling time; C w is the velocity coefficient, the recommended value is 0.85, F is the adjustment coefficient, take 1, V is the main pipe volume, p out is the pressure at the final stage throttling outlet, T out is the temperature of the last stage throttling outlet; P i is the pressure at the throttling inlet calculated in the i-th iterative step.

8. The method for calculating temperature and pressure after high-pressure CO2 multi-stage throttling according to claim 7, characterized in that: The calculation formula for the temperature in each level of throttling pipe is as follows: Z 3 -(1-B)Z 2 +(A-2B-3B 2 )Z-(AB-B 2 -B 3 )=0 (12) Where T0 is the initial temperature of CO2 at each level of throttling inlet; m is the mass flow rate; Z is the compressibility factor; d is the throttling aperture; D is the throttling pipe diameter; A = ap / (RT) 2 ,B=bp / (RT).

9. The method for calculating temperature and pressure after high-pressure CO2 multi-stage throttling according to claim 8, characterized in that: The criterion for determining whether CO2 is completely discharged is that the mass of the remaining CO2 in the throttling pipe drops to 0. The calculation formula is: Where G is the mass of CO2 remaining in the throttling pipe; G0 is the total amount of CO2 in the pipe at the initial moment.

10. A device for calculating temperature and pressure after high-pressure CO2 multi-stage throttling, characterized in that: include: The first processing unit is used to determine the throttling level of CO2 and measure the throttling aperture and throttling pipe volume; The second processing unit is used to obtain the pre-throttling pressure and pre-throttling temperature of CO2 and determine the preset regulating pressure of the throttling outlet; The third processing unit is used to calculate the minimum pressure of CO2 after throttling and determine whether the preset adjustment pressure of the throttling outlet needs to be corrected; A fourth processing unit is configured to calculate a CO2 flow rate after throttling by constructing a Bernoulli equation based on the CO2 pre-throttling pressure, a preset regulating pressure, and a CO2 adiabatic index; a fifth processing unit, configured to calculate the enthalpy of CO2 at different temperatures based on the real gas enthalpy; a sixth processing unit, configured to iteratively calculate the single-stage CO2 post-throttling temperature based on the CO2 enthalpy values ​​at different temperatures; The seventh processing unit is used to determine whether the CO2 enthalpy value after iteration meets the set accuracy requirement. If it does, the iteration is terminated and the next step is entered. Otherwise, the previous step is repeated until the set accuracy requirement is met. The eighth processing unit is used to calculate the pressure at each level of throttling inlet: The ninth processing unit is used to calculate the temperature in each level of throttling pipe; The tenth processing unit is used to iterate according to the time-increasing rule based on the calculated pressures at the throttling inlets of each level and the temperatures at each level of the throttling pipes until the CO2 in the throttling pipes is completely discharged, thereby obtaining a curve of temperature and pressure changes with time after high-pressure CO2 multi-stage throttling.

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