An automatic control method for a supercritical CO2 compressor

Abstract

This invention discloses an automatic control method for a supercritical CO2 compressor, comprising the following steps: S1, correcting the pressure-temperature phase diagram curve; S2, obtaining X sets of temperature and pressure data from -40 to 200°C, forming a two-dimensional data table and storing it; S3, during compressor startup, fully opening the compressor bypass loading regulating valve to ensure that the exhaust pressure of each stage cylinder is less than the query pressure corresponding to the current temperature in the two-dimensional data; S4, after the compressor reaches the set speed, entering an unloaded state, keeping the bypass loading regulating valve fully open to ensure that the exhaust pressure of each stage cylinder is less than the query pressure corresponding to the current temperature in the two-dimensional data; S5, when it is necessary to enter the loading state, querying and reading the pressure corresponding to the current exhaust temperature of the last stage cylinder in the two-dimensional data table, and automatically controlling the opening of the intake valve and the bypass loading regulating valve. This invention maintains CO2 in a gaseous or supercritical fluid state, which can prevent liquid slugging in the compressor cylinders and pipe blockage, improving the safety of compressor operation.

Description

Technical Field

[0001] This invention relates to the field of automatic control methods for supercritical CO2 compressors. More specifically, this invention relates to an automatic control method for a supercritical CO2 compressor. Background Technology

[0002] CO2 is a gas with supercritical fluid properties, and its phase diagram is as follows: Figure 1 As shown, CO2 changes through four states—solid, liquid, gas, and supercritical fluid—as pressure and temperature change. The region above the AOB curve is the solid region, the region enclosed by the BOC curve is the liquid region, the region below the AOC curve is the gas region, and the region indicated by the rectangle is the supercritical fluid region. Point O is called the triple point where gas, liquid, and solid coexist, point C is called the critical point, the corresponding temperature is called the critical temperature, and the corresponding pressure is called the critical pressure.

[0003] Reciprocating compressors require CO2 to be kept in a gaseous or supercritical fluid state during compression. If CO2 is in the liquid state, it will cause liquid slugging in the cylinder, leading to malfunction; if CO2 enters the solid state, it will cause blockage of valves and pipelines. Both situations will damage the compressor, leading to shutdown or safety accidents. Summary of the Invention

[0004] To achieve these objectives and other advantages according to the present invention, a preferred embodiment of the present invention provides an automatic control method for a supercritical CO2 compressor, comprising the following steps:

[0005] S1. Based on the CO2 content in the actual gas to be compressed, correct the pressure-temperature phase diagram curve of CO2 in the CO2 mixture;

[0006] S2. Starting from -40℃ and ending at 200℃, take one of the temperature values ​​between 0.02℃ and 0.1℃ as the interval value, obtain the corresponding pressure of CO2 at different temperatures on the pressure-temperature phase diagram curve, obtain X sets of temperature data and pressure data between -40℃ and 200℃, form a two-dimensional data table and store it.

[0007] S3. During compressor startup, fully open the compressor bypass loading regulating valve to ensure that the exhaust pressure of each stage cylinder is less than the query pressure corresponding to the current temperature in the two-dimensional data. When the exhaust pressure of any stage cylinder is greater than or equal to the query pressure corresponding to the two-dimensional data table, stop the machine immediately. The stop response time is less than 500ms.

[0008] S4. After the compressor starts and reaches the set speed, the compressor enters the no-load state. Keep the compressor bypass loading regulating valve fully open to ensure that the exhaust pressure of each stage cylinder is less than the query pressure corresponding to the current temperature in the two-dimensional data. If the exhaust pressure of any stage cylinder is greater than or equal to the query pressure corresponding to the two-dimensional data table, stop the machine immediately for inspection. The stop response time is less than 500ms.

[0009] S5. When it is necessary to enter the loading state, query and read the pressure corresponding to the current exhaust temperature of the last stage cylinder in the two-dimensional data table, gradually close the bypass loading regulating valve to achieve loading, and automatically control the opening of the intake valve and the bypass loading regulating valve to stabilize the exhaust pressure of the last stage cylinder at the level of the query pressure in the two-dimensional data table minus the preset value.

[0010] S6. Every 10-60 seconds, query the pressure corresponding to the current exhaust temperature of the last stage cylinder in the two-dimensional data table, and automatically control the opening of the intake valve and the bypass loading regulating valve to stabilize the exhaust pressure of the last stage cylinder at a value close to the corresponding query pressure in the two-dimensional data table minus the preset value.

[0011] S7. When the exhaust temperature of the last stage cylinder exceeds the critical temperature and the difference between the two is greater than the preset value, maintain the current opening of the bypass loading regulating valve and wait for the exhaust temperature of other cylinders to exceed the critical temperature.

[0012] When the exhaust temperature of all cylinders exceeds the critical temperature and the difference between the two is greater than the preset value, the bypass loading regulating valve will be completely closed to complete the loading.

[0013] Preferably, during the compressor startup, no-load, loading, and shutdown processes, the exhaust pressure and exhaust temperature of each stage cylinder are monitored in real time, and the corresponding pressure at the current temperature is queried from the two-dimensional data table.

[0014] Preferably, the measured temperature needs to be preprocessed before querying to ensure that the temperature data conforms to the temperature format in the two-dimensional data table.

[0015] Preferably, in S5 and S6, when the actual discharge pressure is about to exceed the query pressure, the opening of the bypass loading regulating valve can be increased, while the opening of the intake valve can be decreased, or the vent valve can be opened to control the discharge pressure of each stage to be below the query pressure corresponding to the current temperature in the two-dimensional data table.

[0016] Preferably, in S5 and S6, when the actual discharge pressure is about to exceed the query pressure, the temperature rise can be adjusted by controlling the opening of the compressor interstage cooling system, so that the actual pressure is below the query pressure corresponding to the current temperature in the two-dimensional data table.

[0017] Preferably, in S5 and S6 above, the exhaust pressure of each cylinder is ensured to be less than the query pressure corresponding to the current cylinder exhaust temperature in the two-dimensional data. If the pressure is greater than or equal to the query pressure corresponding to the current temperature in the two-dimensional data table, the machine is stopped immediately, and the shutdown response time is less than 500ms.

[0018] Preferably, in S5 and S6, during the loading operation, when a shutdown is required or a shutdown failure occurs, the main drive is shut down, the bypass loading regulating valve is gradually opened to unload the load, and after the loading regulating valve is fully opened, the intake valve and exhaust valve are closed, the vent valve is opened, and when the internal pressure of the unit is less than the set value, the vent valve is closed to complete the shutdown process.

[0019] This invention offers at least the following beneficial effects: During startup, no-load, and loading processes, the invention monitors the exhaust temperature and pressure of each cylinder in real time. Based on the CO2 pressure-temperature phase diagram curve, the monitoring system infinitely regulates the flow rate and the valve opening of the bypass loading return pipeline system, thereby ensuring that CO2 is in a gaseous or supercritical fluid state. When CO2 is not in a gaseous or supercritical fluid state, the compressor immediately shuts down. Maintaining CO2 in a gaseous or supercritical fluid state prevents liquid slugging in the compressor cylinders and pipe blockage, thus improving the safety of compressor operation.

[0020] 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

[0021] Figure 1 The background diagram is a phase diagram of CO2.

[0022] Figure 2 This is the overall control logic diagram of the automatic control method for supercritical CO2 compressors in this invention.

[0023] Figure 3 This is the control logic diagram for starting up the supercritical CO2 compressor in the automatic control method of the present invention.

[0024] Figure 4 This is the no-load control logic diagram of the automatic control method for supercritical CO2 compressors in this invention.

[0025] Figure 5 This is the control logic diagram loaded in the automatic control method for supercritical CO2 compressors in this invention.

[0026] Figure 6 This is the control logic diagram for shutdown in the automatic control method of the supercritical CO2 compressor of the present invention. Detailed Implementation

[0027] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0028] The following description is intended to disclose the present invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious modifications will occur to those skilled in the art. The basic principles of the invention defined in the following description can be applied to other embodiments, modifications, improvements, equivalents, and other technical solutions that do not depart from the spirit and scope of the invention.

[0029] Those skilled in the art should understand that, in the disclosure of this invention, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., 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, the above terms should not be construed as limiting this invention.

[0030] It is understood that the term "a" should be understood as "at least one" or "one or more", that is, in one embodiment, the number of an element can be one, while in another embodiment, the number of the element can be multiple, and the term "a" should not be understood as a limitation on the number.

[0031] like Figure 2-6 As shown, a preferred embodiment of the present invention provides an automatic control method for a supercritical CO2 compressor, comprising the following steps:

[0032] S1. Based on the CO2 content in the actual gas to be compressed, correct the pressure-temperature phase diagram curve of CO2 in the CO2 mixture;

[0033] S2. Starting from -40℃ and ending at 200℃, take one of the temperature values ​​between 0.1℃ as the interval value, obtain the corresponding pressure of CO2 at different temperatures on the pressure-temperature phase diagram curve, obtain X sets of temperature data and pressure data from -40 to 200℃, form a two-dimensional data table and store it.

[0034] S3. During compressor startup, fully open the compressor bypass loading regulating valve to ensure that the exhaust pressure of each stage cylinder is less than the query pressure corresponding to the current temperature in the two-dimensional data. When the exhaust pressure of any stage cylinder is greater than or equal to the query pressure corresponding to the two-dimensional data table, stop the machine immediately. The stop response time is less than 500ms.

[0035] S4. After the compressor starts and reaches the set speed, the compressor enters the no-load state and keeps the compressor bypass loading regulating valve fully open to ensure that the exhaust pressure of each stage cylinder is less than the query pressure corresponding to the current temperature in the two-dimensional data. If the exhaust pressure of any stage cylinder is greater than or equal to the query pressure corresponding to the two-dimensional data table, the machine will stop immediately with a stop response time of less than 500ms.

[0036] S5. When it is necessary to enter the loading state, query and read the pressure corresponding to the current exhaust temperature of the last stage cylinder in the two-dimensional data table, gradually close the bypass loading regulating valve to achieve loading, and automatically control the opening of the intake valve and the bypass loading regulating valve to stabilize the exhaust pressure of the last stage cylinder at the value of the query pressure in the two-dimensional data table minus 1MPa.

[0037] S6. Every 60 seconds, query the pressure corresponding to the current exhaust temperature of the last stage cylinder in the two-dimensional data table, and automatically control the opening of the bypass loading regulating valve to stabilize the exhaust pressure of the last stage cylinder at a value close to the corresponding query pressure in the two-dimensional data table minus 1 MPa.

[0038] S7. When the exhaust temperature of the last stage cylinder exceeds the critical temperature and the difference between the two is greater than 1℃, maintain the current opening of the bypass loading regulating valve and wait for the exhaust temperature of other cylinders to exceed the critical temperature.

[0039] When the exhaust temperature of all cylinders exceeds the critical temperature and the difference is greater than 2°C, the bypass loading regulating valve will be completely closed to complete the loading process.

[0040] This invention monitors the exhaust temperature and pressure of each cylinder in real time during startup, no-load, and loading processes. Based on the CO2 pressure-temperature phase diagram curve, the monitoring system infinitely adjusts the flow rate and the valve opening of the bypass loading return pipeline system to keep CO2 in a gaseous or supercritical fluid state. If CO2 is not in a gaseous or supercritical fluid state, the compressor immediately stops. Maintaining CO2 in a gaseous or supercritical fluid state prevents liquid slugging in the compressor cylinders and pipe blockage, thus improving the safety of compressor operation.

[0041] Specifically, during the compressor's start-up, no-load, loading, and shutdown processes, the exhaust pressure and exhaust temperature of each stage cylinder are monitored in real time, and the corresponding pressure for the current temperature is queried from the two-dimensional data table.

[0042] In another technical solution, the measured temperature needs to be preprocessed before querying to ensure that the temperature data conforms to the temperature format in the two-dimensional data table.

[0043] In another technical solution, in S5 and S6, when the actual discharge pressure is about to exceed the query pressure, the opening of the bypass loading regulating valve can be increased, while the opening of the intake valve can be decreased, or the vent valve can be opened to control the discharge pressure of each stage to be below the query pressure corresponding to the current temperature in the two-dimensional data table.

[0044] In S5 and S6, when the actual discharge pressure is about to exceed the query pressure, the temperature rise can be adjusted by controlling the opening of the compressor interstage cooling system, so that the actual pressure is below the query pressure corresponding to the current temperature in the two-dimensional data table.

[0045] In S5 and S6 above, ensure that the exhaust pressure of each cylinder is less than the query pressure corresponding to the current cylinder exhaust temperature in the two-dimensional data. If the pressure is greater than or equal to the query pressure corresponding to the current temperature in the two-dimensional data table, stop the machine immediately, and the stop response time is less than 500ms.

[0046] In another technical solution, during the loading operation, when a shutdown is required or a shutdown failure occurs, the main motor is shut down, and the loading regulating valve is opened by 2% per second for unloading (the opening speed can be adjusted according to temperature changes). After the loading regulating valve is fully opened, the inlet valve and exhaust valve are closed, and the vent valve is opened. When the internal pressure of the unit is less than the set value, the vent valve is closed, and the shutdown process is completed.

[0047] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. 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 illustrations shown and described herein.

Claims

1. An automatic control method for a supercritical CO2 compressor, characterized in that, Includes the following steps: S1. Based on the CO2 content in the actual gas to be compressed, correct the pressure-temperature phase diagram curve of CO2 in the CO2 mixture; S2. Starting from -40℃ and ending at 200℃, take one of the temperature values ​​between 0.02℃ and 0.1℃ as the interval value, obtain the corresponding pressure of CO2 at different temperatures on the pressure-temperature phase diagram curve, obtain X sets of temperature data and pressure data between -40℃ and 200℃, form a two-dimensional data table and store it. S3. During compressor startup, fully open the compressor bypass loading regulating valve to ensure that the exhaust pressure of each stage cylinder is less than the query pressure corresponding to the current temperature in the two-dimensional data. If the exhaust pressure of any stage cylinder is greater than or equal to the query pressure corresponding to the two-dimensional data table, immediately stop the machine for inspection. The shutdown response time is less than 500ms. S4. After the compressor starts and reaches the set speed, the compressor enters the no-load state. Keep the compressor bypass loading regulating valve fully open to ensure that the exhaust pressure of each cylinder is less than the query pressure corresponding to the current temperature in the two-dimensional data. If the exhaust pressure of any stage cylinder is greater than or equal to the corresponding query pressure in the two-dimensional data table, the machine should be stopped immediately for inspection, and the shutdown response time should be less than 500ms. S5. When it is necessary to enter the loading state, query and read the pressure corresponding to the current exhaust temperature of the last stage cylinder in the two-dimensional data table, gradually close the bypass loading regulating valve to achieve loading, and automatically control the opening of the intake valve and the bypass loading regulating valve to stabilize the exhaust pressure of the last stage cylinder at the level of the query pressure in the two-dimensional data table minus the preset value. S6. Every 10-60 seconds, query the pressure corresponding to the current exhaust temperature of the last stage cylinder in the two-dimensional data table, and automatically control the opening of the intake valve and the bypass loading regulating valve to stabilize the exhaust pressure of the last stage cylinder at a value close to the corresponding query pressure in the two-dimensional data table minus the preset value. S7. When the exhaust temperature of the last stage cylinder exceeds the critical temperature and the difference between the two is greater than the preset value, maintain the current opening of the bypass loading regulating valve and wait for the exhaust temperature of other cylinders to exceed the critical temperature. When the exhaust temperature of all cylinders exceeds the critical temperature and the difference between the two is greater than the preset value, the bypass loading regulating valve will be completely closed to complete the loading.

2. The automatic control method for a supercritical CO2 compressor according to claim 1, characterized in that, In S3-S7, during the compressor start-up, no-load, loading, and shutdown processes, the exhaust pressure and exhaust temperature of each stage cylinder are monitored in real time, and the corresponding pressure at the current temperature is queried from the two-dimensional data table.

3. The automatic control method for a supercritical CO2 compressor according to claim 2, characterized in that, Before querying, the measured temperature needs to be preprocessed to ensure that the temperature data conforms to the temperature format in the two-dimensional data table.

4. The automatic control method for a supercritical CO2 compressor according to claim 1, characterized in that, In S5 and S6, when the actual discharge pressure is about to exceed the query pressure, the opening of the bypass loading regulating valve can be increased, while the opening of the intake valve can be decreased, or the vent valve can be opened to control the discharge pressure of each stage to be below the query pressure corresponding to the current temperature in the two-dimensional data table.

5. The automatic control method for a supercritical CO2 compressor according to claim 1, characterized in that, In S5 and S6, when the actual discharge pressure is about to exceed the query pressure, the temperature rise can be adjusted by controlling the opening of the compressor interstage cooling system, so that the actual pressure is below the query pressure corresponding to the current temperature in the two-dimensional data table.

6. The automatic control method for a supercritical CO2 compressor according to claim 1, characterized in that, In S5 and S6 above, ensure that the exhaust pressure of each cylinder is less than the query pressure corresponding to the current cylinder exhaust temperature in the two-dimensional data. If the pressure is greater than or equal to the query pressure corresponding to the current temperature in the two-dimensional data table, stop the machine immediately, and the stop response time is less than 500ms.

7. The automatic control method for a supercritical CO2 compressor according to claim 1, characterized in that, In S5 and S6, during the loading operation, when a shutdown is required or a shutdown failure occurs, the main drive is shut down, and the bypass loading regulating valve is gradually opened to unload the load. After the loading regulating valve is fully opened, the intake valve and exhaust valve are closed, and the vent valve is opened. When the internal pressure of the unit is less than the set value, the vent valve is closed to complete the shutdown process.

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