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

Abstract

The invention discloses a method for calculating temperature and pressure after multi-stage throttling of high-pressure CO2, which comprises the following steps of: determining the throttling stage number of CO2, and measuring the throttling aperture and the throttling pipeline volume; the pressure and the temperature of CO2 before throttling are obtained, and the preset adjusting pressure of a throttling outlet is determined; the minimum pressure of CO2 after throttling is calculated, and whether the preset adjusting pressure of a throttling outlet needs to be corrected or not is judged; calculating the flow velocity after CO2 throttling; cO2 enthalpy values at different temperatures are calculated based on the real gas enthalpy value; iteratively calculating the temperature after single-stage CO2 throttling based on CO2 enthalpy values at different temperatures; judging whether the CO2 enthalpy value after iteration meets the setting precision requirement or not; calculating the pressure of each stage of throttling inlet; calculating the temperature in each stage of throttling pipeline; and based on the pressure of each stage of throttling inlet and the temperature of the throttling pipeline, iteration is carried out according to a time increasing rule until CO2 in the throttling pipeline is completely discharged, and a change curve of the temperature and the pressure along with time after high-pressure CO2 multi-stage throttling is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of petrochemical industry, and more particularly to a high pressure CO 2 Method and device for calculating temperature and pressure after multi-stage throttling. Background Art

[0002] Water-gas alternating flooding (WAG) is an effective way to improve oil recovery. The displacement media of WAG flooding are water and gas, and the gas is often high-purity CO. 2 In order to obtain the highest displacement efficiency, in actual engineering, CO 2 The gas source is very limited, and N 2 , hydrocarbon gas and high CO 2 Hydrocarbon gas is used as a substitute. 2 Water-gas alternation is water slug and CO 2 Slug injection can effectively solve the problem of using CO 2 As a displacement medium, it is prone to viscous fingering and gas channeling. At the same time, the oil and gas mass transfer effect is enhanced, effectively expanding the swept volume, improving gas utilization, and improving CO 2 The oil displacement effect.

[0003] The water-gas alternation process of WAG flooding technology requires that the high-pressure gas, which is generally above 35MPa, be reduced to normal pressure and released or subsequently processed so that water can be injected into the wellbore in the subsequent process. The pressure reduction process generally adopts multi-stage pressure reduction, so calculating the change of the pressure value of each throttling outlet with the throttling time is very important for controlling the throttling system and the release process. In addition, high-pressure CO 2 The throttling process will produce a significant coke effect, resulting in CO 2 The temperature of the main pipeline changes significantly, so calculating the change of temperature in the main pipeline with throttling time is also of great significance for throttling pipeline design and prevention of 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 high pressure CO 2 The multi-stage throttling temperature and pressure calculation method is designed to accurately and quickly calculate the high-pressure CO 2 Temperature and pressure after multi-stage throttling.

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

[0006] In a first aspect, the present invention provides a high pressure CO 2 The method for calculating the temperature and pressure after multi-stage throttling comprises the following steps: determining the CO 2 The throttling level is measured, and the throttling aperture and throttling pipe volume are measured; CO2 The pre-throttling pressure and pre-throttling temperature are calculated, and the preset regulating pressure of the throttling outlet is determined; the CO 2 The minimum pressure after throttling is determined and it is judged whether the preset regulating pressure of the throttling outlet needs to be corrected; based on CO 2 Pressure and CO before and after throttling 2 Adiabatic exponential construction of Bernoulli equation to calculate CO 2 Flow rate after throttling; Calculation of CO at different temperatures based on real gas enthalpy 2 Enthalpy value; based on CO at different temperatures 2 Enthalpy iteration calculation single-stage CO 2 Temperature after throttling; determine CO after iteration 2 Check whether the enthalpy value meets the set accuracy requirements. If it does, 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 pipeline at each level. Based on the calculated pressure at the throttling inlet of each level and the temperature of the throttling pipeline at each level, iterate according to the law of increasing time until the CO in the throttling pipeline is 2 Complete exhaust, high pressure CO 2 The temperature and pressure change curves with time after multi-stage throttling.

[0007] As a preferred embodiment: the "calculation of CO 2 The minimum pressure after throttling, and judge whether it is necessary to correct the preset adjustment pressure of the throttling outlet. Specifically:

[0008] 1) Calculate CO by the following formula (1): 2 The minimum pressure after throttling p c :

[0009]

[0010] In the formula, p 1 is the pressure before throttling; p c is the minimum pressure after throttling; k is CO 2 Adiabatic index, the average value is about 1.3;

[0011] 2) Compare the minimum pressure p after throttling c With the preset regulating pressure p at the throttle outlet 2 Size: If the minimum pressure after throttling p c Less than or equal to the preset adjustment pressure p 2 , then the preset adjustment pressure p 2 Appropriate; if the minimum pressure after throttling p c Greater than the preset adjustment pressure value p 2 , then the preset adjustment pressure p 2 Corrected to the minimum pressure after throttling p c .

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

[0013]

[0014] In the formula, w 1 For CO 2 Flow rate before throttling; w 2 For CO 2 Flow rate after throttling; v 1 =1 / ρ is CO 2 Specific volume.

[0015] As a preferred embodiment: the "calculation of CO at different temperatures based on real gas enthalpy value" 2 The specific enthalpy value is:

[0016] The real gas enthalpy is equal to the sum of the ideal gas enthalpy and the isothermal enthalpy difference, that is:

[0017]

[0018] H 0 =11.11374+0.47911T+7.62195×10 -4 T 2

[0019] -3.59392×10 -7 T 3 +8.47438×10 -11 T 4 -0.57752×10 -14 T 5 (4)

[0020]

[0021] Where H is the real gas enthalpy; H 0 is the ideal gas enthalpy; ΔH T is the isothermal enthalpy difference; p is CO 2 pressure; v is CO 2 volume; ρ is CO 2 density; R is the universal gas constant; T is CO 2 temperature; P c 、T c CO 2 The critical temperature and critical pressure of r =T / T c ;f ω =0.37464+1.54226ω-0.26992ω 2 , ω is the eccentricity factor.

[0022] As a preference: the single-stage CO 2 The iterative calculation formula for the post-throttling temperature is as follows:

[0023]

[0024] Where, T 2i CO is the CO calculated in the iterative step i 2 After throttling temperature; T 2(i-1) CO is the CO calculated in the i-1th step. 2 The temperature after throttling; α is the step length of each iteration; H 1 CO before throttling 2 Enthalpy; H 2(i-1) is the CO after throttling calculated in the i-1th step. 2 Enthalpy value.

[0025] As a preferred embodiment: the “judgment of the CO after iteration” 2 Whether the enthalpy value meets the set accuracy requirements, if it does, the iteration ends and goes to the next step, otherwise repeat the previous step until it meets the set accuracy requirements.

[0026] The following formula (7) is used to determine the CO after iteration: 2 Does the enthalpy value meet the set accuracy requirements? If it does, the iteration ends and the single-stage CO is output. 2 After throttling, the temperature will be calculated. If the setting accuracy requirement is not met, the single-stage CO 2 The throttling temperature is used as the initial value to repeat the previous step until the set accuracy requirement is met, the iteration is ended, and the single-stage CO is output. 2 Post-throttling temperature;

[0027]

[0028] In the formula, H 2i is the CO after throttling calculated in the i-th step. 2 Enthalpy value; 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 change in pressure at the throttle inlet; p is the current actual pressure, p amb is the atmospheric pressure; t is the throttling time; C wis the velocity coefficient, the recommended value is 0.85, F is the adjustment coefficient, take 1, V is the main pipeline volume, p out is the pressure at the final throttling outlet, T out is the temperature of the final stage throttling outlet; P i is the pressure at the throttling inlet calculated in the i-th iteration.

[0033] As a preferred method, the calculation formula for the temperature in 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, T 0 The CO inlet of each level of throttling 2 Initial temperature; m is mass flow; Z is compression factor; d is throttling aperture; D is throttling pipe diameter; A = ap / (RT) 2 ,B=bp / (RT).

[0037] As a preference: CO 2 The criterion for judging whether the exhaust is complete is the residual CO in the throttling pipe. 2 The quality drops to 0 value, and the calculation formula is:

[0038]

[0039] Where G is the remaining CO in the throttling pipe. 2 Quality; G 0 is the CO in the tube at the initial moment 2 Total amount.

[0040] In a second aspect, the present invention provides a high pressure CO 2 The temperature and pressure calculation device after multi-stage throttling includes:

[0041] The first processing unit is used to determine the CO 2 The throttling level, and measure the throttling aperture and throttling pipe volume;

[0042] The second processing unit is used to obtain CO 2 The pre-throttling pressure and pre-throttling temperature of the throttling outlet are determined, and the preset regulating pressure of the throttling outlet is determined;

[0043] The third processing unit is used to calculate CO 2 The minimum pressure after throttling is determined, and it is determined whether the preset regulating pressure of the throttling outlet needs to be corrected;

[0044] The fourth processing unit is used for 2 Pre-throttling pressure, preset regulating pressure and CO 2 Adiabatic exponential construction of Bernoulli equation to calculate CO 2 Flow rate after throttling;

[0045] The fifth processing unit is used to calculate CO at different temperatures based on the real gas enthalpy 2 Enthalpy;

[0046] The sixth processing unit is used for 2 Enthalpy iteration calculation single-stage CO 2 Post-throttling temperature;

[0047] The seventh processing unit is used to determine the CO after iteration 2 Whether the enthalpy value meets the set accuracy requirement. If so, end the iteration and proceed to the next step. Otherwise, repeat the previous step until the set accuracy requirement is met.

[0048] The eighth processing unit is used to calculate the pressure at each level of throttling inlet:

[0049] The ninth processing unit is used to calculate the temperature in each level of throttling pipe;

[0050] The tenth processing unit is used to iterate according to the time increasing law based on the calculated pressure of each level of throttling inlet and the temperature of each level of throttling pipeline until the CO in the throttling pipeline is 2 Complete exhaust, high pressure CO 2 The temperature and pressure change curves with time after multi-stage throttling.

[0051] The present invention adopts the above technical solution, which has the following advantages:

[0052] The high pressure CO provided by the present invention 2 The temperature and pressure calculation method after multi-stage throttling adopts specific steps to quickly calculate CO 2 The changes of pressure and temperature of each stage with throttling time in the multi-stage throttling process improve the CO 2 The accuracy and convenience of throttling pressure and temperature calculation are of great significance for throttling pipeline design and throttling effect prediction. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Throughout the accompanying drawings, the same reference numerals are used to represent the same components. In the accompanying drawings:

[0054] Figure 1 The high pressure CO provided by the present invention 2 Flow chart of the method for calculating temperature and pressure after multi-stage throttling;

[0055] Figure 2 For high pressure CO 2 The curve of pressure changing with time after multi-stage throttling;

[0056] Figure 3 For high pressure CO 2 Temperature variation with time after multi-stage throttling. DETAILED DESCRIPTION

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

[0058] The high pressure CO provided by the present invention 2 The calculation method of temperature and pressure after multi-stage throttling includes: determining CO 2 The throttling level is measured, and the throttling aperture and throttling pipe volume are measured; CO 2 The pre-throttling pressure and pre-throttling temperature are calculated, and the preset regulating pressure of the throttling outlet is determined; the CO 2 The minimum pressure after throttling is calculated and it is judged whether the preset regulating pressure of the throttling outlet needs to be corrected; calculate CO 2 Flow rate after throttling; Calculation of CO at different temperatures based on real gas enthalpy 2 Enthalpy value; based on CO at different temperatures 2 Enthalpy iteration calculation single-stage CO 2 Temperature after throttling; determine CO after iteration 2 Whether the enthalpy value meets the set accuracy requirements; calculate the pressure at the throttling inlet of each level: calculate the temperature in the throttling pipeline at each level; based on the pressure at the throttling inlet of each level and the throttling pipeline temperature, iterate according to the law of increasing time until the CO in the throttling pipeline is 2 Complete exhaust, high pressure CO 2 The temperature and pressure change curves over time after multi-stage throttling. The present invention can quickly calculate CO 2 The changes of pressure and temperature of each stage with throttling time in the multi-stage throttling process improve the CO 2 The accuracy and convenience of throttling pressure and temperature calculation are of great significance for throttling pipeline design and throttling effect prediction.

[0059] Next, the high pressure CO provided by the embodiment of the present invention is described in conjunction with the accompanying drawings. 2 The temperature and pressure calculation method and device after multi-stage throttling are described in detail.

[0060] Embodiment 1:

[0061] See also Figure 1 This embodiment provides a high pressure CO 2 The method for calculating temperature and pressure after multi-stage throttling comprises the following steps:

[0062] Step 1: Determine CO 2 The throttling level n is measured, and the throttling aperture d and the throttling pipe volume V are measured.

[0063] High pressure CO 2 Throttling generally adopts multi-stage throttling, and the present invention is applicable to the throttling process of at most three stages of throttling, that is, n≤3;

[0064] The throttling aperture d indicates the aperture of the throttling valves or orifice plates at each level where throttling occurs;

[0065] The volume V of the throttling pipe represents the CO involved in the throttling process. 2 Total volume.

[0066] Step 2: Obtain CO 2 The pre-throttle pressure p 1 and pre-throttling temperature T 1 , and determine the preset regulating pressure p of the throttle outlet 2 .

[0067] Step 3: Calculate CO 2 The minimum pressure after throttling p c , and determine whether it is necessary to adjust the preset pressure p of the throttle outlet 2 Make corrections, specifically:

[0068] 1) Calculate CO by the following formula (1): 2 The minimum pressure after throttling p c :

[0069]

[0070] In the formula, p 1 is the pressure before throttling; p c is the minimum pressure after throttling; k is CO 2 Adiabatic index, the average value is about 1.3;

[0071] 2) Compare the minimum pressure p after throttling c With the preset regulating pressure p at the throttle outlet 2 Size: If the minimum pressure after throttling p cLess than or equal to the preset adjustment pressure p 2 , then the preset adjustment pressure p 2 Appropriate; if the minimum pressure after throttling p c Greater than the preset adjustment pressure value p 2 , then the preset adjustment pressure p 2 Corrected to the minimum pressure after throttling p c .

[0072] Step 4: Based on CO 2 Pressure before throttling p 1 , preset adjustment pressure p 2 and CO 2 Adiabatic exponential construction of Bernoulli equation to calculate CO 2 Flow rate after throttling:

[0073]

[0074] In the formula, w 1 For CO 2 Flow rate before throttling; w 2 For CO 2 Flow rate after throttling; v 1 =1 / ρ is CO 2 Specific volume.

[0075] Step 5: Calculate CO at different temperatures based on real gas enthalpy 2 Enthalpy value, 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 0 is the ideal gas enthalpy; ΔH T is the isothermal enthalpy difference; p is CO 2 pressure; v is CO2 volume; ρ is CO 2 density; R is the universal gas constant; T is CO 2 temperature; P c 、T c CO 2 The critical temperature and critical pressure 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 CO 2 Flow rate before and after throttling and CO at different temperatures 2 The enthalpy value is calculated by iterative calculation of single-stage CO through the following formula (6): 2 After throttling temperature:

[0083]

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

[0085] Step 7: Determine the CO after iteration by the following formula (7): 2 Does the enthalpy value meet the set accuracy requirements? If it does, the iteration ends and the single-stage CO is output. 2 After throttling, the temperature will be calculated. If the setting accuracy requirement is not met, the single-stage CO 2 The throttling temperature is used as the initial value to repeat step 6 until the set accuracy requirement is met, the iteration ends, and the single-stage CO is output. 2 After throttling temperature.

[0086]

[0087] In the formula, H 2i is the CO after throttling calculated in the i-th step. 2Enthalpy value; θ is the setting 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, for each iteration, i=i+1.

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

[0089]

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

[0091] Where dp is the change in pressure 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, which is 1, V is the volume of the throttling pipe, p out is the pressure at the final throttling outlet, T out is the temperature of the final stage throttling outlet; P i is the pressure at the throttling inlet calculated in the i-th iteration.

[0092] Step 9, calculating the temperature in each level of throttling pipes by 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, T 0 The CO inlet of each level of throttling 2 Initial temperature; m is mass flow rate; Z is compression factor, which can be calculated by PR state equation; d is throttling aperture; D is 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 CO in the throttling pipe is 2 Complete exhaust, high pressure CO 2The temperature and pressure change curves with time after multi-stage throttling (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] Among them, CO 2 The criterion for judging whether the exhaust is complete is the residual CO in the throttling pipe. 2 The quality drops to 0 value, and the calculation formula is:

[0098]

[0099] Where G is the remaining CO in the throttling pipe. 2 Quality; G 0 is the CO in the tube at the initial moment 2 Total amount.

[0100] Embodiment 2:

[0101] The above embodiment 1 provides a high pressure CO 2 The temperature and pressure calculation method after multi-stage throttling, correspondingly, this embodiment provides a high pressure CO 2 The temperature and pressure calculation device after multi-stage throttling. The high-pressure CO 2 The temperature and pressure calculation device after multi-stage throttling can implement the high pressure CO 2 The temperature and pressure calculation method after multi-stage throttling is 2 The temperature and pressure calculation device after multi-stage throttling can be implemented by software, hardware or a combination of software and hardware. 2 The multi-stage throttling temperature and pressure calculation device may include integrated or separate functional modules or functional units to execute the corresponding steps in each method of Example 1. 2 The temperature and pressure calculation device after multi-stage throttling is basically similar to the method embodiment, so the process described in this embodiment is relatively simple. For relevant parts, please refer to the partial description of embodiment 1. The high-pressure CO 2 The temperature and pressure calculation device after multi-stage throttling is only schematic.

[0102] The high pressure CO provided in this embodiment 2 The temperature and pressure calculation device after multi-stage throttling includes:

[0103] The first processing unit is used to determine the CO 2 The throttling level, and measure the throttling aperture and throttling pipe volume;

[0104] The second processing unit is used to obtain CO 2 The pre-throttling pressure and pre-throttling temperature of the throttling outlet are determined, and the preset regulating pressure of the throttling outlet is determined;

[0105] The third processing unit is used to calculate CO 2 The minimum pressure after throttling is determined, and it is determined whether the preset regulating pressure of the throttling outlet needs to be corrected;

[0106] The fourth processing unit is used for 2 Pre-throttling pressure, preset regulating pressure and CO 2 Adiabatic exponential construction of Bernoulli equation to calculate CO 2 Flow rate after throttling;

[0107] The fifth processing unit is used to calculate CO at different temperatures based on the real gas enthalpy 2 Enthalpy;

[0108] The sixth processing unit is used for 2 Enthalpy iteration calculation single-stage CO 2 Post-throttling temperature;

[0109] The seventh processing unit is used to determine the CO after iteration 2 Whether the enthalpy value meets the set accuracy requirement. If so, end the iteration and proceed to the next step. Otherwise, repeat the previous step 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 law based on the calculated pressure of each level of throttling inlet and the temperature of each level of throttling pipeline until the CO in the throttling pipeline is 2 Complete exhaust, high pressure CO 2 The temperature and pressure change curves with time after multi-stage throttling.

[0113] Embodiment 3:

[0114] This embodiment provides a method for realizing the high pressure CO 2 The processing device of the temperature and pressure calculation method after multi-stage throttling can be a processing device used for a client, such as a mobile phone, a laptop computer, a tablet computer, a desktop computer, etc., to execute the method of Example 1.

[0115] The processing device includes a processor, a memory, a communication interface and a bus. The processor, the memory and the communication interface are connected through the bus to complete mutual communication. The memory stores a computer program that can be run on the processor. When the processor runs the computer program, the high-pressure CO 2Calculation method of temperature and pressure after multi-stage throttling.

[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] Embodiment 4:

[0119] The high pressure CO in Example 1 2 The method for calculating the temperature and pressure after multi-stage throttling can be specifically implemented as a computer program product. The computer program product may include a computer-readable storage medium on which computer-readable program instructions for executing the method described in this embodiment 1 are loaded.

[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 replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate 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 the temperature and pressure of high-pressure CO2 after 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 regulating pressure of the throttling outlet needs to be corrected; Based on the CO2 pre-throttling pressure, the preset regulating pressure and the CO2 adiabatic index, the Bernoulli equation is constructed to calculate the CO2 post-throttling flow rate; Calculate the enthalpy of CO2 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 requirement. If so, end the iteration and proceed to the next step. Otherwise, repeat the previous step until the set accuracy requirement is met. Calculate the pressure at each level of throttling inlet: Calculate the temperature in each level of throttling pipe; Based on the calculated pressures at the throttling inlets of each level and the temperatures of the throttling pipes of each level, iterations are performed according to the time-increasing rule until the CO2 in the throttling pipe is completely discharged, and the temperature and pressure variation curves of the high-pressure CO2 after multi-stage throttling with time are obtained.

2. The method for calculating the temperature and pressure of high-pressure CO2 after multi-stage throttling according to claim 1 is characterized in that: The "calculating the minimum pressure of CO2 after throttling and judging whether it is necessary to correct the preset regulating pressure of the throttling outlet" is specifically: 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, then the preset regulating pressure p2 is appropriate; c If the preset pressure value p2 is greater than the preset pressure value p2, the preset pressure value p2 is corrected to the minimum pressure after throttling p c .

3. The method for calculating the temperature and pressure of high-pressure CO2 after multi-stage throttling according to claim 2 is characterized in that: The expression of the Bernoulli equation is as follows: Wherein, 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 the temperature and pressure of high-pressure CO2 after 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 the 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 calculated in the iterative calculation of the i-th step; T 2(i-1) is the CO2 temperature after throttling calculated 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 enthalpy value of CO2 after throttling calculated in the i-1th iterative calculation step.

6. The method for calculating the temperature and pressure of high-pressure CO2 after multi-stage throttling according to claim 5, characterized in that: The "determine whether the CO2 enthalpy value after iteration meets the set accuracy requirement, if it meets the requirement, end the iteration and proceed to the next step, otherwise repeat the previous step until the set accuracy requirement is met" is specifically: 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 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; In the formula, H 2i is the CO2 enthalpy value after throttling calculated in the i-th step; θ is the setting accuracy; i represents the number of iteration steps.

7. The method for calculating the temperature and pressure of high-pressure CO2 after multi-stage throttling according to claim 6, characterized in that: The calculation formula for the pressure at each level of throttling inlet is as follows: P i =P i-1 +dp (9) Where dp is the change in pressure 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 pipeline volume, p out is the pressure at the final throttling outlet, T out is the temperature of the final stage throttling outlet; P i is the pressure at the throttling inlet calculated in the i-th iteration.

8. The method for calculating the temperature and pressure of high-pressure CO2 after 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 compression factor; d is the throttling aperture; D is the throttling pipe diameter; A = ap / (RT) 2 ,B=bp / (RT).

9. The method for calculating the temperature and pressure of high-pressure CO2 after multi-stage throttling according to claim 8, characterized in that: The criterion for judging whether CO2 emission is complete is that the remaining CO2 mass in the throttling pipe drops to 0. The calculation formula is: Where G is the remaining CO2 mass 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 the 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 it is necessary to correct the preset adjustment pressure of the throttling outlet; A fourth processing unit, for calculating the flow rate of CO2 after throttling by constructing a Bernoulli equation based on the pre-throttling pressure of CO2, the preset regulating pressure and the adiabatic index of CO2; A fifth processing unit, for calculating the enthalpy of CO2 at different temperatures based on the real gas enthalpy; A sixth processing unit, for iteratively calculating a single-stage CO2 throttling temperature based on 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 meets the requirement, 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 law based on the calculated pressure of each level of throttling inlet and the temperature of each level of throttling pipeline until the CO2 in the throttling pipeline is completely discharged, and obtain the temperature and pressure change curve of high-pressure CO2 after multi-stage throttling with time.

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