Supercritical CO2 stable pressurization method based on compression factor change
By using a multi-stage pressurization and precise temperature control system, the problem of equipment damage and instability caused by phase changes during CO2 pressurization is solved, and stable compression of CO2 from the conventional gaseous state to the high-pressure supercritical state is achieved, ensuring the safe and stable operation of the equipment.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHINA PETROLEUM & CHEMICAL CORP
- Filing Date
- 2025-12-30
- Publication Date
- 2026-05-08
AI Technical Summary
In existing technologies, phase changes during CO2 pressurization can prevent pressurization from taking place, leading to equipment damage, instability in the pressurization process, abnormal noise and vibration in the equipment, and shortened lifespan.
A multi-stage pressurization method is adopted, and the stability of the pressurization process is expressed by the rate of change of the compressibility factor z. The temperature is precisely controlled by the interstage cooler to ensure that the compressibility factor z value is within the set rate of change range. A precise temperature control system is used, including components such as air coolers, variable frequency fans and louvers, to achieve precise temperature control.
It achieves stable compression of CO2 from the conventional gaseous state to the high-pressure supercritical state, avoiding the formation of liquid phase caused by temperature changes, ensuring the stability of the pressurization process, avoiding equipment damage and noise vibration, and extending equipment life.
Smart Images
Figure CN121993740A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of CCUS engineering technology. More specifically, this invention relates to a method for stable supercritical CO2 pressurization based on changes in compressibility factor. Background Technology
[0002] Carbon capture, utilization, and storage (CCUS) technology is a key technology for addressing the climate crisis, and its urgency has reached a global consensus, as it is crucial for achieving green and low-carbon development. Modern CCUS technology typically injects captured carbon resources (CO2 and CO2 mixtures) into depleted oil fields to achieve enhanced oil recovery (EOR), forming a closed-loop circular economy of "black gold" and "greenhouse gases." To achieve CO2 injection for enhanced production, the captured carbon resources (CO2 and CO2 mixtures) need to be pressurized to a high-pressure supercritical state before being injected into the oil well.
[0003] Supercritical CO2 booster equipment is a core component of CCUS (Carbon-to-Gas System). However, the domestic application of CO2 booster equipment in various oil fields is currently limited, and the self-sufficiency capability of domestically produced supercritical CO2 mixed-medium injection booster equipment is insufficient. In order to respond to the green and low-carbon development strategy and help my country achieve the goal of "carbon peaking and carbon neutrality", it is urgent to develop high-pressure supercritical CO2 booster technology and find a stable supercritical CO2 booster method to meet the high-pressure supercritical CO2 injection needs of CCUS projects in major oil and gas fields in China.
[0004] CO2 has high critical parameters (critical temperature Tc = 31.1℃, critical pressure Pc = 7.38MPa), and its supercritical state combines the advantages of high density of liquids and low viscosity of gases. During pressurization, CO2 transitions from its conventional gaseous state to the supercritical state, accompanied by temperature changes. Therefore, controlling the temperature of the CO2 medium and preventing pressure and flow rate fluctuations, or even CO2 liquefaction, during pressurization is of paramount importance.
[0005] The main technical problems currently are as follows: 1. Changes in the gaseous phase of CO2 or CO2 mixtures during the pressurization process (changes in parameters such as temperature and pressure causing the supercritical state to change into a liquid state) can prevent pressurization from proceeding or even damage the equipment. 2. Significant changes in pressure and flow rate of the medium during the pressurization process due to temperature changes lead to instability in the pressurization process, causing abnormal noise and vibration in the equipment, and even shortening the equipment's lifespan. Summary of the Invention
[0006] One objective of this invention is to provide a method for multi-stage stable pressurization of high-pressure supercritical CO2 based on compressibility factor variation. This method comprehensively considers both phase stability and state parameter stability during the multi-stage pressurization process. While ensuring the phase stability of the pressurization process, it proposes a method that uses the rate of change of the compressibility factor z during pressurization to express the degree of stability, and uses precise temperature control of the interstage cooler to stabilize the z value. This method can pressurize CO2 and CO2 mixtures from a conventional gaseous state to a supercritical state, achieving a maximum pressure of 50 MPa, meeting the high-pressure injection requirements of CCUS projects.
[0007] To address the aforementioned technical problems, this invention provides a method for stable pressurization of supercritical CO2 based on changes in compressibility factor. This method employs a multi-stage pressurization approach to stably pressurize atmospheric or low-pressure gaseous CO2 and CO2 mixtures to a high-pressure supercritical state, comprising the following steps: Step 1: First, determine the temperature threshold of each stage of boosting based on the boosting parameters. Then, combine the intake pressure and exhaust pressure to set the number of boosting stages, the exhaust pressure and temperature of each stage, and the intake temperature of the next stage. Step 2: Obtain the trend graph of the rate of change of the compressibility factor z with temperature and pressure; Step 3: Based on the pressure changes during the boosting process and the trend chart of the rate of change, determine the variation law of the compression factor z with temperature under each intake and exhaust pressure, and limit the variation range of the compression factor z to the set rate of change range, thereby obtaining the corresponding temperature control limit range. Step 4: Set up an interstage temperature precision control system during the process from each stage of exhaust to the next stage of intake. Based on the rate of change range of the compression factor z set in Step 3, and according to the temperature control limit range, precisely control the temperature within the next stage intake temperature fluctuation range set in Step 1.
[0008] Preferably, step two specifically includes: First, set and calculate the compressibility factor z value for each set temperature unit span within a set temperature range under a specific pressure; Secondly, through calculation and analysis, the set pressure range is obtained. Within the corresponding pressure range, the temperature range corresponding to the set pressure unit span is calculated. At the same time, the compression factor z value under each set temperature unit span is calculated and recorded. Next, organize and save all the calculated z values above, with temperature on the horizontal axis and pressure on the vertical axis. Then, calculate and record the rate of change of z-values under all pressure and temperature changes. The formula for calculating the rate of change of z-values is: the difference between the z-values of the highest and lowest temperatures within a temperature unit span, divided by the z-value of the lowest temperature. Finally, the above calculation results are displayed graphically, with temperature on the horizontal axis and pressure on the vertical axis, and the range of the drastic change rate of the z-value is divided by different colors.
[0009] Preferably, in step four, before precisely controlling the temperature, the compressibility factor of each booster stage under intake conditions is ranked according to the degree of temperature change, and the priority of temperature control is determined for priority control during the control process.
[0010] Preferably, in step four, the precise temperature control system includes an air cooler, which includes a hollow sealed housing, a variable frequency fan located at the bottom of the housing, and various louvers and multi-stage cooling tube bundles located on the housing. A pair of louvers C are symmetrically arranged at the bottom of the housing. The housing contains multi-stage cooling tube bundles corresponding to each stage of the temperature control system, each corresponding to a louver X1~X4 located inside the housing and operated independently. Louvers X1~X4 independently control the cooling of each stage of the temperature control system. The top of the housing also has louvers D covering the multi-stage cooling tube bundles. The housing also contains hot air circulation louvers R covering the multi-stage cooling tube bundles. Each louver is controlled by a stepper motor to adjust the opening angle and thus control the cooling.
[0011] Preferably, the precision temperature control system also includes an intelligent central controller, which includes a temperature measuring component and a central controller. The temperature measuring component is located downstream of each stage of the cooling tube bundle, i.e., at the inlet position of the next stage of booster equipment. The temperature measuring component transmits data to the central controller, which controls the air cooler to regulate the temperature.
[0012] Preferably, during system debugging, the hysteresis of the temperature sensing component to temperature changes is evaluated, and the central controller is adjusted accordingly. Specifically, after the air cooler louvers switch 5% actuation, the difference between the actuation time and the time when the downstream temperature sensing component begins to show significant changes and stabilizes is recorded. Then, the fluid transmission delay time of the system is measured, and this time parameter is input into the delay function module of the central controller to apply a delay time waiting judgment cycle to the output of all temperature control commands, so as to avoid issuing repeated or contradictory commands during the feedback signal lag period.
[0013] Preferably, in step four, the precise temperature control method is as follows: First, the booster stage with the most dramatic change in compression factor z value with temperature is given the highest priority. Its intake temperature is required to ensure that the z value does not fall within the range of the rate of change set in step three. The booster intake temperature is determined as tx. The control logic is designed to determine the condition judgment based on the accuracy setting value, so that the accuracy value is the steady state and no action is required in the interval between tx ± accuracy value. Secondly, temperature values below the tx- accuracy value are identified as low-temperature ranges, and temperature compensation logic is performed based on temperature measurement feedback; temperature values above the tx+ accuracy value are identified as high-temperature ranges, and cooling logic is performed based on temperature measurement feedback.
[0014] Preferably, the temperature compensation logic operation and the cooling logic operation are as follows: The temperature monitored by the temperature measuring component is obtained, and it is determined whether the temperature is within the steady state and no action is required range. If it is, the current state is maintained; otherwise, the next step is determined. If the temperature is below the low temperature range, determine whether the variable frequency fan has stopped. If it has not stopped, reduce the opening angle of the corresponding louver X until it is closed. If the temperature is still below the low temperature range, open the louver R or reduce the speed of the variable frequency fan. If it has stopped, determine whether the corresponding louver X is closed. If it is not closed, close the louver X. If it is closed, close the louvers D and C. If the temperature is higher than the high temperature range, determine whether the corresponding louver X is fully open. If it is not fully open, increase the opening angle of the corresponding louver X. If it is fully open, determine whether the variable frequency fan is at its maximum speed. If it is, open louvers D and C and close louver R. If not, increase the speed of the variable frequency fan.
[0015] Preferably, in step one, the pressurization process is as follows: the process medium enters the primary intake scrubbing tank, the filtered gas enters the buffer tank for buffering, and then undergoes primary pressurization. The pressurized gas, after being buffered in the buffer tank, enters the secondary temperature control system for cooling and temperature control, and then enters the secondary intake scrubbing tank. The filtered gas, after being buffered in the buffer tank, undergoes secondary pressurization, and then enters the tertiary temperature control system for cooling and temperature control, and then enters the tertiary intake scrubbing tank. The filtered gas, after being buffered in the buffer tank, undergoes tertiary pressurization, and then enters the quaternary temperature control system for cooling and temperature control, and then enters the quaternary intake scrubbing tank. The filtered gas, after being buffered in the buffer tank, undergoes quaternary pressurization, and then enters the outlet temperature control system for cooling and temperature control. At this point, the medium reaches the required pressure and is discharged.
[0016] The present invention has at least the following beneficial effects: 1. The method of the present invention ensures the phase state during the compression process, and realizes stable compression of CO2 and CO2 mixture from the conventional gaseous state to the 50MPa high-pressure supercritical state, avoiding the occurrence of liquid phase due to temperature changes during the compression process, which would endanger equipment safety.
[0017] 2. The method of the present invention stabilizes the compression process by controlling the interstage temperature to stabilize the change of the compression factor z value, ensuring that the change of medium properties during the compression process is stable, and avoiding instability in the pressurization process caused by changes in medium properties (changes in the compression factor z value reflect changes in medium pressure, density, etc.), abnormal noise and vibration of equipment, or even shortened equipment life and damage.
[0018] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description
[0019] Figure 1 This is a schematic diagram illustrating the rate of change of the compressibility factor Z as a function of temperature and pressure according to the present invention. Figure 2 This is a process flow diagram for the present invention; Figure 3 This is a front view schematic diagram of the air cooler of the present invention; Figure 4 This is a side view of the air cooler of the present invention. Figure 5 This is a schematic diagram of the control logic design of the present invention; Figure 6 This is a schematic diagram illustrating the process of generating the trend graph of the rate of change of the compressibility factor z as a function of temperature and pressure according to the present invention. Figure 7 This is a schematic diagram of the process for generating the trend graph of the rate of change of the compressibility factor z as a function of temperature and pressure in this invention (Figure 2). Figure 8 This is a schematic diagram of the process of generating the trend graph of the rate of change of the compressibility factor z as a function of temperature and pressure in this invention. Detailed Implementation
[0020] To better understand the purpose, structure, and function of this invention, the invention will be further described in detail below with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.
[0021] It should be noted that, unless otherwise specified, the experimental methods described in the following embodiments are all conventional methods, and the reagents and materials described are all commercially available unless otherwise specified. In the description of this invention, the terms "lateral", "longitudinal", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.
[0022] This invention proposes a method for stable pressurization of supercritical CO2 based on changes in compressibility factor, as detailed below: 1. Working medium: CO2 and CO2 mixture.
[0023] 2. Application: To stably pressurize atmospheric or low-pressure gaseous CO2 and CO2 mixtures to a high-pressure supercritical state.
[0024] 3. Features: (1) The multi-stage boosting method is used to calculate and analyze the boosting process to ensure that the exhaust temperature of each stage is ≤150℃. Based on the boosting parameters (generally based on the intake and exhaust pressure, the compressibility factor of the medium and the pressure ratio distribution), the temperature threshold of the exhaust temperature of each boosting stage is automatically calculated and determined by the compression thermodynamics calculation software. Then, combined with the actual required intake and exhaust pressure, the required number of boosting stages and the exhaust pressure, exhaust temperature of each stage and the intake temperature of the next stage are set and determined according to the actual situation.
[0025] (2) A method for describing the rate of change of the compressibility factor z is proposed: Based on the composition of the medium, the law of change of the compressibility factor z with temperature and pressure is analyzed, and a trend graph of the rate of change of the compressibility factor z with temperature and pressure is designed, as shown in the appendix. Figure 1 As shown in the figure, this graph visually illustrates the percentage change in compressibility factor z as pressure and temperature change.
[0026] The specific process for generating the trend chart of the rate of change of the compressibility factor z as a function of temperature and pressure is as follows: Taking a working medium of 97% carbon dioxide and 3% natural gas (methane) as an example, this paper explains the process of generating the Z-value change rate distribution table under this medium.
[0027] 1. Considering industry-standard practices and compressor standard specifications (API 618), the exhaust temperature for each stage should not exceed 150℃. Industry-recognized property calculation software (such as NIST, ASPEN, etc.) is used to calculate parameters such as the Z-value at specific pressures (based on the thermodynamic properties of carbon dioxide mixtures, the properties of carbon dioxide change drastically in subcritical and just-below-supercritical states; therefore, calculations are typically performed from the initial inlet pressure to the exhaust pressure of the unit) ranging from 30℃ to 150℃, with each 5℃ increment representing a Z-value. See attached... Figure 6 As shown.
[0028] 2. Based on calculations and analysis, the Z-value changes are relatively small and within acceptable ranges when the pressure is below 6 MPa and above 20 MPa. Therefore, considering a range of 6.5 MPa to 20 MPa, with each 0.5 MPa increment, calculate the Z-value for the corresponding temperature range of 30℃ to 150℃ at each pressure, with each 5℃ increment. Record and save the Z-value in Excel, as shown in the attached figure. Figure 7 and Figure 8 As shown.
[0029] 3. Compile all the calculated Z values above into an Excel spreadsheet, with temperature on the x-axis and pressure on the y-axis.
[0030] 4. Considering the compressor is designed based on pressure ratio and that the interstage intake and exhaust pressures are relatively stable, calculate the rate of change of the Z-value using a formula. For example, to calculate the rate of change of the Z-value when the pressure is 10 MPa and the temperature changes from 30℃ to 35℃, the formula is: (Z...) 35℃ -Z 30℃ ) / Z 30℃ Based on this, the rate of change of Z value under all pressure and temperature changes is calculated and recorded.
[0031] 5. Based on the company's experience and the industry standard for compressor wear parts, a Z-value within 10% indicates a relatively stable compression process, meeting the normal operating requirements of the compressor. Using this as a benchmark, the range of Z-value variation rates is defined as follows: (See attached table). Figure 1 As shown, the color changes from brown to dark blue, and the Z value becomes increasingly stable.
[0032] (3) Combining the pressure changes during the pressurization process, according to the attached... Figure 1 The variation of the compressibility factor z with temperature under different intake and exhaust pressures was determined. To ensure stability during the boosting process, precise temperature control is required throughout the entire boosting process to limit the range of z variation. Considering the characteristics of the boosting equipment, the variation range of z is limited to within 10%, essentially ensuring that it does not exceed the limits. Figure 1 The range of the brown area is sufficient, which can ensure a relatively stable boosting process while keeping equipment configuration and cost acceptable.
[0033] (4) A precise temperature control method for the supercritical CO2 boosting process was invented: Based on the degree of drastic change in z-value with temperature at each pressure stage during the boosting process, a progressive temperature feedback adjustment method was adopted. An interstage temperature precision control system was set up during the process from each stage of exhaust to the next stage of intake to precisely control the intake temperature of the next stage and stabilize the phase state and compressibility factor z. The scheme of the interstage temperature precision control system is as follows: A. Rank the compressibility factor of each booster stage under intake conditions according to the degree of temperature change, and determine the priority of temperature control; the degree of temperature change of the compressibility factor is attached... Figure 1 In the process, depending on the pressure of the boost, for example, when boosted to 12 MPa, the transverse compressibility factor corresponding to 12 MPa has a relatively wide brown range, and the temperature control requirements are higher. Therefore, it is the priority control level and needs to be focused on. For example, when boosted to 20 MPa, the transverse compressibility factor corresponding to 20 MPa has no brown range, and the temperature control requirements are relatively low.
[0034] B. Considering the operating environment of the booster equipment, and to meet the requirements for interstage cooling and temperature control, a precise temperature control system is designed based on the air cooler and combined with an intelligent central controller. The intelligent central controller includes a temperature measuring component and a central controller. The temperature measuring component is located downstream of each stage of the cooling tube bundle, i.e., at the inlet position of the next stage of booster equipment. The temperature measuring component transmits data to the central controller, which then controls the air cooler to regulate the temperature.
[0035] C. The cooling tube bundles required at each stage are integrated into one air cooler. Temperature measuring components are installed downstream of each tube bundle, i.e. at the inlet of the next stage of booster equipment, which can transmit the data back to the central controller. D. Evaluate the hysteresis of the temperature sensing components to temperature changes, and adjust the central controller accordingly to avoid abnormal temperature fluctuations caused by excessive operation and control in a short period of time. During system debugging, evaluate the hysteresis of the temperature sensing components to temperature changes, and adjust the central controller accordingly. Specifically, after the air cooler louvers operate at 5%, record the difference between the time point of action and the time point after the downstream temperature sensing components begin to show significant changes (generally considered as the temperature increasing or decreasing by more than 1°C per minute in one direction) and then stabilize. Then, measure the fluid transmission delay time of the system and input this time parameter into the delay function module of the central controller to apply a delay time waiting judgment cycle to the output of all temperature control commands, avoiding issuing repeated or contradictory commands during the feedback signal lag period.
[0036] E. Configuration Instructions (see attached diagrams) Figure 3 and Figure 4 ): 1) Each tube bundle of the air cooler is equipped with independently operated small louvers X1~X4, i.e., reference 3~6 in the attached drawings.
[0037] 2) Design the hot air circulation system of the air cooler. The top air box of the hot air circulation hood is equipped with a large louver D covering the four-stage tube bundle, i.e., attached drawing 7.
[0038] 3) Install hot air circulation louvers R, i.e., reference numeral 9 in the attached diagram, opposite the pipe (pipe box) to cover the four-stage pipe bundle. Opening R can circulate the hot gas from the upper part back to the inlet of the fan.
[0039] 4) The bottom frame is closed on all four sides, with louvers C1~C2 on two sides, i.e., reference numerals 1~2 in the attached drawings.
[0040] 5) The opening angle of all louvers can be adjusted using a stepper motor.
[0041] 6) The air cooler fan uses a variable frequency motor, and the frequency is adjusted from 5 to 50 Hz.
[0042] The precision temperature control system includes an air cooler, comprising a hollow, sealed housing, a variable frequency fan located at the bottom of the housing, and various louvers and multi-stage cooling tube bundles mounted on the housing. A pair of louvers C are symmetrically arranged at the bottom of the housing. The housing contains multi-stage cooling tube bundles corresponding to each stage of the temperature control system, each corresponding to an independently operated louver X1 to X4 located within the housing. Louvers X1 to X4 independently control the cooling of each stage of the temperature control system. The top of the housing also has louvers D covering the multi-stage cooling tube bundles. The opening angle of each louver is controlled by a stepper motor to regulate cooling. During the entire pressurization process, each stage of pressurization shares a single air cooler. The secondary temperature control system corresponds to the tube bundle under louver X1, the tertiary temperature control system corresponds to the tube bundle under louver X2, the quaternary temperature control system corresponds to the tube bundle under louver X3, and the outlet temperature control system corresponds to the tube bundle under louver X4. Air is drawn in through louvers C1 and C2 by a variable frequency fan, which blows air through each stage of the tube bundle to cool it. The air is then blown out through louver D. Louvers X1, X2, X3, and X4 respectively control their respective temperature control systems at each stage; louvers C1 and C2, as well as louvers D and R, are used to control the overall temperature.
[0043] F. The control logic design is as follows: 1) The boost stage with the most drastic change in z-value with temperature is given the highest priority. To ensure stability during the boosting process, its intake air temperature must meet the requirement that the z-value does not fall below the upper limit. Figure 1 Within the brown zone, the inlet temperature range is limited to tx±5℃ as required for control. The boosted inlet temperature tx is determined, and the control logic is designed to determine the condition as tx±3℃ as the steady state and no action is required. 2) Temperature values below tx-3℃ are classified as low-temperature ranges, and temperature compensation logic operations need to be performed based on temperature measurement feedback.
[0044] 3) Temperature values above tx+3℃ are classified as high-temperature ranges, and cooling logic operations need to be performed based on temperature measurement feedback.
[0045] 4) The above temperature accuracy of 3℃ needs to be modified by the user according to actual needs, such as adjusting flexibly based on the actual temperature probe accuracy, minimum or maximum temperature tolerance limits, etc.; the temperature range is generally recommended not to exceed 5℃, according to the attached... Figure 1 As shown, the compressibility factor z changes more significantly when the temperature exceeds 5°C.
[0046] 5) The specific operation of temperature compensation logic and cooling logic is shown in the attached figure. Figure 5 As shown, the temperature monitored by the temperature measuring component is obtained, and it is determined whether the temperature is within the steady state and no action is required range. If it is, the current state is maintained; otherwise, the next step is determined. If the temperature is below the low temperature range, determine whether the variable frequency fan has stopped. If it has not stopped, reduce the opening angle of the corresponding louver X until it is closed. If the temperature is still below the low temperature range, open the louver R or reduce the speed of the variable frequency fan. If it has stopped, determine whether the corresponding louver X is closed. If it is not closed, close the louver X. If it is closed, close the louvers D and C. If the temperature is higher than the high temperature range, determine whether the corresponding louver X is fully open. If it is not fully open, increase the opening angle of the corresponding louver X. If it is fully open, determine whether the variable frequency fan is at its maximum speed. If it is, open louvers D and C and close louver R. If not, increase the speed of the variable frequency fan.
[0047] (5) A supercritical CO2 pressurization process flow has been formed, as shown in the attached diagram. Figure 2 As shown, the process medium enters the primary intake scrubbing tank. After filtration, the gas enters a buffer tank for buffering and then undergoes primary pressurization. The pressurized gas then enters the secondary temperature control system for cooling and temperature control. Subsequently, it enters the secondary intake scrubbing tank, where the filtered gas enters a buffer tank for buffering and then undergoes secondary pressurization. The pressurized gas then enters the tertiary temperature control system for cooling and temperature control. This process is repeated three times in the diagram. The filtered gas enters a buffer tank for buffering and then undergoes tertiary pressurization. The pressurized gas then enters the quaternary temperature control system for cooling and temperature control. Finally, the medium reaches the required pressure and is discharged.
[0048] Example: The pressurization method of the present invention is applied in the supercritical CO2 pressurization unit of a carbon capture and storage (CCUS) project.
[0049] : Goal setting The CO2 mixture (92% CO2 content) was pressurized from 2.6 MPa to 50 MPa and then injected into the oil well for gas injection and oil displacement.
[0050] Implementation of the booster process 1. Thermodynamic analysis and calculations were performed on the pressurization process, and multi-stage pressurization was adopted to ensure that the exhaust temperature of each stage is <150℃. Calculations showed that a 4-stage pressurization was used, with the first stage pressurization pressure at 4.83MPa, the second stage at 9.53MPa, the third stage at 22.01MPa, and the fourth stage at 50MPa.
[0051] 2. Obtain the trend graph of the rate of change of compressibility factor z with temperature and pressure, as shown in the attached figure. Figure 1As shown, to ensure the stability of the z-value and that the z-value change rate is <10% when the temperature fluctuates by ±5℃, the secondary intake temperature is confirmed to be 54℃, the tertiary intake temperature to be 60℃, and the quaternary intake temperature to be 60℃.
[0052] 3. The design process flow diagram is attached. Figure 2 .
[0053] The realization of a precise temperature control system: ① The compressibility factor of each booster stage under intake conditions was ranked according to the degree of drastic change with temperature, and the priority of temperature control was determined to be level 2; ② Configure one air cooler, as shown in the attached document. Figure 3 and Figure 4 As shown; ③Temperature measuring components are installed downstream of each stage of the tube bundle, i.e. at the inlet of the next stage of booster equipment, which can transmit the data back to the central controller. ④ Evaluate the hysteresis of the temperature sensing component to temperature changes: During the system commissioning phase, an evaluation was conducted using a step test method—after the air cooler louvers opened and closed by 5%, the difference between the time of the action and the time when the downstream temperature sensing component began to show significant changes and stabilized was recorded. The fluid transport delay time τ of the system was determined to be approximately 30 seconds. This parameter was written into the delay function block of the central controller to apply a 30-second waiting and judgment cycle to the output of all temperature control commands, avoiding the issuance of duplicate or contradictory commands during the feedback signal lag period.
[0054] ⑤ The control logic design is as follows; see the attached diagram for details. Figure 5 : 1) The boost stage with the most drastic change in z-value with temperature is given the highest priority. To ensure stability during the boosting process, its intake air temperature must meet the requirement that the z-value does not fall below the threshold. Figure 1 Within the brown zone, the inlet temperature range is limited to tx±5℃ as required for control. The boosted inlet temperature tx is determined, and the control logic is designed to determine the condition as tx±3℃ as the steady state and no action is required. 2) Temperature values below tx-3℃ are classified as low-temperature ranges, and temperature compensation logic operations need to be performed based on temperature measurement feedback.
[0055] 3) Temperature values above tx+3℃ are classified as high-temperature ranges, and cooling logic operations need to be performed based on temperature measurement feedback.
[0056] 4) The above temperature accuracy of 3℃ needs to be modified by the user according to actual needs, such as temperature probe accuracy, minimum or maximum temperature acceptance limit.
[0057] Through the above specific implementation methods, the present invention successfully transforms an unstable compression problem of supercritical CO2 pressurization into a specific, reliable, programmable, and automated control pressurization method, ensuring that the supercritical CO2 pressurization process is always efficient and stable.
[0058] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. It can be applied to various fields suitable for the present invention, and other modifications can be easily implemented by those skilled in the art. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and examples shown and described herein.
Claims
1. A method for stable pressurization of supercritical CO2 based on changes in compressibility factor, characterized in that, A multi-stage pressurization method is used to stably pressurize atmospheric or low-pressure gaseous CO2 and CO2 mixtures to a high-pressure supercritical state, including the following steps: Step 1: First, determine the temperature threshold of each stage of boosting based on the boosting parameters. Then, combine the intake pressure and exhaust pressure to set the number of boosting stages, the exhaust pressure and temperature of each stage, and the intake temperature of the next stage. Step 2: Obtain the trend graph of the rate of change of the compressibility factor z with temperature and pressure; Step 3: Based on the pressure changes during the boosting process and the trend chart of the rate of change, determine the variation law of the compression factor z with temperature under each intake and exhaust pressure, and limit the variation range of the compression factor z to the set rate of change range, thereby obtaining the corresponding temperature control limit range. Step 4: Set up an interstage temperature precision control system during the process from each stage of exhaust to the next stage of intake. Based on the rate of change range of the compression factor z set in Step 3, and according to the temperature control limit range, precisely control the temperature within the next stage intake temperature fluctuation range set in Step 1.
2. The supercritical CO2 stable pressurization method based on compressibility factor variation as described in claim 1, characterized in that, Step two specifically includes: First, set and calculate the compressibility factor z value for each set temperature unit span within a set temperature range under a specific pressure; Secondly, through calculation and analysis, the set pressure range is obtained. Within the corresponding pressure range, the temperature range corresponding to the set pressure unit span is calculated. At the same time, the compression factor z value under each set temperature unit span is calculated and recorded. Next, organize and save all the calculated z values above, with temperature on the horizontal axis and pressure on the vertical axis. Then, calculate and record the rate of change of z-values under all pressure and temperature changes. The formula for calculating the rate of change of z-values is: the difference between the z-values of the highest and lowest temperatures within a temperature unit span, divided by the z-value of the lowest temperature. Finally, the above calculation results are displayed graphically, with temperature on the horizontal axis and pressure on the vertical axis, and the range of the drastic change rate of the z-value is divided by different colors.
3. The supercritical CO2 stable pressurization method based on compressibility factor variation as described in claim 1, characterized in that, In step four, before precisely controlling the temperature, the compressibility factor of each booster stage under intake conditions is ranked according to the degree of temperature change, and the priority of temperature control is determined for priority control during the control process.
4. The supercritical CO2 stable pressurization method based on compressibility factor variation as described in claim 1, characterized in that, In step four, the precise temperature control system includes an air cooler, which comprises a hollow sealed housing, a variable frequency fan located at the bottom of the housing, and various louvers and multi-stage cooling tube bundles located on the housing. A pair of louvers C are symmetrically arranged at the bottom of the housing. The housing contains multi-stage cooling tube bundles corresponding to each stage of the temperature control system, each corresponding to a louver X1~X4 located inside the housing and operated independently. Louvers X1~X4 independently control the cooling of each stage of the temperature control system. The top of the housing also has louvers D covering the multi-stage cooling tube bundles. The housing also contains hot air circulation louvers R covering the multi-stage cooling tube bundles. Each louver is controlled by a stepper motor to adjust its opening angle and thus control the cooling.
5. The supercritical CO2 stable pressurization method based on compressibility factor variation as described in claim 4, characterized in that, The precision temperature control system also includes an intelligent central controller, which includes a temperature measuring component and a central controller. The temperature measuring component is located downstream of each stage of the cooling tube bundle, i.e., at the inlet of the next stage of the booster equipment. The temperature measuring component transmits data to the central controller, which then controls the air cooler to regulate the temperature.
6. The supercritical CO2 stable pressurization method based on compressibility factor variation as described in claim 5, characterized in that, During system debugging, the hysteresis of the temperature sensing components to temperature changes is evaluated, and the central controller is adjusted accordingly. Specifically, after the air cooler louvers switch 5% actuation, the difference between the actuation time and the time when the downstream temperature sensing components begin to show significant changes and stabilize is recorded. Then, the fluid transmission delay time of the system is measured, and this time parameter is input into the delay function module of the central controller. This is used to apply a delay time waiting judgment cycle to the output of all temperature control commands to avoid issuing repeated or contradictory commands during the feedback signal lag period.
7. The supercritical CO2 stable pressurization method based on compressibility factor variation as described in claim 5, characterized in that, In step four, the precise temperature control method is as follows: First, the booster stage with the most dramatic change in compression factor z value with temperature is given the highest priority. Its intake temperature is required to ensure that the z value does not fall within the range of the rate of change set in step three. The booster intake temperature is determined as tx. The control logic is designed to determine the condition judgment based on the accuracy setting value, so that the accuracy value is the steady state and no action is required in the interval between tx ± accuracy value. Secondly, temperature values below the tx- accuracy value are identified as low-temperature ranges, and temperature compensation logic is performed based on temperature measurement feedback; temperature values above the tx+ accuracy value are identified as high-temperature ranges, and cooling logic is performed based on temperature measurement feedback.
8. The supercritical CO2 stable pressurization method based on compressibility factor variation as described in claim 7, characterized in that, The specific operations for temperature compensation and cooling are as follows: The temperature monitored by the temperature measuring component is obtained, and it is determined whether the temperature is within the steady state and no action is required range. If it is, the current state is maintained; otherwise, the next step is determined. If the temperature is below the low temperature range, determine whether the variable frequency fan has stopped. If it has not stopped, reduce the opening angle of the corresponding louver X until it is closed. If the temperature is still below the low temperature range, open the louver R or reduce the speed of the variable frequency fan. If it has stopped, determine whether the corresponding louver X is closed. If it is not closed, close the louver X. If it is closed, close the louvers D and C. If the temperature is higher than the high temperature range, determine whether the corresponding louver X is fully open. If it is not fully open, increase the opening angle of the corresponding louver X. If it is fully open, determine whether the variable frequency fan is at its maximum speed. If it is, open louvers D and C and close louver R. If not, increase the speed of the variable frequency fan.
9. The supercritical CO2 stable pressurization method based on compressibility factor variation as described in claim 1, characterized in that, In step one, the pressurization process is as follows: the process medium enters the primary intake scrubbing tank, the filtered gas enters the buffer tank for buffering, and then undergoes primary pressurization. After being buffered in the buffer tank, the pressurized gas enters the secondary temperature control system for cooling and temperature control, and then enters the secondary intake scrubbing tank. After being buffered in the buffer tank, the filtered gas undergoes secondary pressurization, and then enters the tertiary temperature control system for cooling and temperature control, and then enters the tertiary intake scrubbing tank. After being buffered in the buffer tank, the filtered gas undergoes tertiary pressurization, and then enters the quaternary temperature control system for cooling and temperature control, and then enters the quaternary intake scrubbing tank. After being buffered in the buffer tank, the filtered gas undergoes quaternary pressurization, and then enters the outlet temperature control system for cooling and temperature control. At this point, the medium reaches the required pressure and is discharged.