Automatic control method for supercritical CO2 compressor

Abstract

The invention discloses an automatic control method for a supercritical CO2 compressor. The automatic control method comprises the following steps that S1, a pressure-temperature physical property phase diagram curve is corrected; s2, X groups of temperature data and pressure data at-40 to 200 DEG C are obtained, and a two-dimensional data table is formed and stored; s3, in the starting process of the compressor, a bypass loading adjusting valve of the compressor is fully opened, and it is ensured that the exhaust pressure of each stage of air cylinder is smaller than the query pressure corresponding to the current temperature in the two-dimensional data; s4, after the compressor reaches the set rotating speed, the compressor enters a no-load state, the bypass loading regulating valve is kept to be fully opened, and it is ensured that the exhaust pressure of each stage of air cylinder is smaller than the query pressure corresponding to the current temperature in the two-dimensional data; and S5, when a loading state needs to be entered, querying and reading the pressure corresponding to the exhaust temperature of the current final-stage cylinder in the two-dimensional data table, and automatically controlling the opening degrees of an air inlet valve and a bypass loading regulating valve. CO2 is kept in a gas or supercritical fluid state, liquid impact of an air cylinder of the compressor and pipeline blockage can be prevented, and the running safety of the compressor is improved.

Description

Technical Field

[0001] The present invention relates to the field of automatic control methods for supercritical CO2 compressors. More specifically, the present invention relates to an automatic control method for supercritical CO2 compressors. Background Art

[0002] CO2 is a gas with supercritical fluid properties. Its phase diagram is as follows Figure 1 As shown, with the changes in pressure and temperature, CO2 will change in four states: solid, liquid, gas, and supercritical fluid. The area above the AOB curve belongs to the solid area, the area surrounded by the BOC curve is the liquid area, the area below the AOC curve is the gas area, and the area indicated by the rectangle is the supercritical fluid area. Point O is called the triple point of gas-liquid-solid coexistence, 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] When compressing CO2, the reciprocating compressor needs to keep CO2 in the gas or supercritical fluid area. If CO2 is in the liquid area, it will cause cylinder liquid hammer and malfunction; if CO2 enters the solid area, it will cause valve and pipeline blockage. Both situations will damage the compressor, leading to shutdown failure or safety accidents. Summary of the invention

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

[0005] S1. According to the CO2 content in the actual gas to be compressed, the pressure-temperature physical property phase diagram curve of CO2 in the CO2 mixed gas is corrected;

[0006] S2, taking -40°C as the starting point and 200°C as the end point, taking one of the temperature values ​​between 0.02 and 0.1°C as the interval value, obtaining the corresponding pressure of CO2 at different temperatures on the pressure-temperature physical property phase diagram curve, obtaining X groups of temperature data and pressure data at -40 to 200°C, forming a two-dimensional data table and storing it;

[0007] S3. During the compressor startup process, the compressor bypass loading regulating valve is fully opened 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. When the exhaust pressure of any cylinder is greater than or equal to the query pressure corresponding to the two-dimensional data table, the compressor is shut down immediately, and the shutdown response time is less than 500ms.

[0008] S4. When the compressor is started and reaches the set speed, the compressor enters the no-load state, and the compressor bypass loading regulating valve is kept 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; when the exhaust pressure of any cylinder is greater than or equal to the query pressure corresponding to the two-dimensional data table, the compressor is immediately shut down for inspection, and the shutdown response time is less than 500ms;

[0009] S5. When it is necessary to enter the loading state, the pressure corresponding to the current exhaust temperature of the final cylinder in the two-dimensional data table is queried and read, and the bypass loading regulating valve is gradually closed to realize loading. At the same time, the opening of the intake valve and the bypass loading regulating valve is automatically controlled to stabilize the exhaust pressure of the final cylinder at the corresponding 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 final cylinder in the two-dimensional data table, automatically control the opening of the intake valve and the bypass loading regulating valve, and stabilize the exhaust pressure of the final cylinder at the corresponding query pressure in the two-dimensional data table minus the preset value;

[0011] S7, when the exhaust temperature of the last cylinder exceeds the critical temperature and the difference between the two is greater than the preset value, the current bypass loading regulating valve opening is maintained, and the exhaust temperature of other cylinders is waited to exceed the critical temperature;

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

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

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

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

[0017] Preferably, in the above S5 and S6, ensure that the exhaust pressure of each cylinder level is less than the query pressure corresponding to the current cylinder exhaust temperature in the two-dimensional data. If the pressure is ≥ the query pressure corresponding to the current temperature in the two-dimensional data table, shut down immediately, and the shutdown response time is less than 500ms.

[0018] Preferably, in S5 and S6, during the loading operation, when shutdown is required or a shutdown failure occurs, the main driver is turned off, and the bypass loading regulating valve is gradually opened for unloading. When the loading regulating valve is fully opened, the intake valve and the 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.

[0019] The present invention at least includes the following beneficial effects: the present invention detects the exhaust temperature of each level of cylinder and the pressure of each level of cylinder in real time during the startup, no-load and loading processes, and according to the CO2 pressure-temperature physical property phase diagram curve, the flow rate and the valve opening of the bypass loading return pipeline system are infinitely regulated by the monitoring system, so that CO2 is in a gas or supercritical fluid state. When CO2 is not in a gas or supercritical fluid state, the machine is shut down immediately. Keeping CO2 in a gas or supercritical fluid state can prevent liquid hammer in the compressor cylinder and pipeline blockage, thereby improving the safety of compressor operation.

[0020] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The phase diagram of CO2 in the background technology.

[0022] Figure 2 It is the overall control logic diagram of the supercritical CO2 compressor automatic control method in the present invention.

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

[0024] Figure 4 This is a no-load control logic diagram of the supercritical CO2 compressor automatic control method of the present invention.

[0025] Figure 5 This is the control logic diagram loaded in the supercritical CO2 compressor automatic control method of the present invention.

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

[0027] The present invention is further described in detail below in conjunction with the accompanying drawings so that those skilled in the art can implement the invention with reference to the description.

[0028] The following description is used to disclose the present invention so that those skilled in the art can implement the present invention. The preferred embodiments described below are only examples, and those skilled in the art can think of other obvious variations. The basic principles of the present invention defined in the following description can be applied to other embodiments, variations, improvements, equivalents, and other technical solutions that do not deviate from the spirit and scope of the present invention.

[0029] Those skilled in the art should understand that, in the disclosure of the present invention, the orientation or position relationship indicated by the terms "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc. are based on the orientation or position relationship shown in the drawings, which are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the above terms should not be understood as limiting the present invention.

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

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

[0032] S1. According to the CO2 content in the actual gas to be compressed, the pressure-temperature physical property phase diagram curve of CO2 in the CO2 mixed gas is corrected;

[0033] S2, taking -40°C as the starting point and 200°C as the end point, taking one of the temperature values ​​between 0.1°C as the interval value, obtaining the corresponding pressure of CO2 at different temperatures on the pressure-temperature physical property phase diagram curve, obtaining X groups of temperature data and pressure data at -40 to 200°C, forming a two-dimensional data table and storing it;

[0034] S3. During the compressor startup process, the compressor bypass loading regulating valve is fully opened 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. When the exhaust pressure of any cylinder is greater than or equal to the query pressure corresponding to the two-dimensional data table, the compressor is shut down immediately, and the shutdown response time is less than 500ms.

[0035] S4. When the compressor is started and reaches the set speed, the compressor enters the no-load state, and the compressor bypass loading regulating valve is kept 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 cylinder is greater than or equal to the query pressure corresponding to the two-dimensional data table, the compressor will be shut down immediately, and the shutdown response time is 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 final 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 at the same time, so as to stabilize the exhaust pressure of the final cylinder at the corresponding 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 final cylinder in the two-dimensional data table, automatically control the opening of the bypass loading regulating valve, and stabilize the exhaust pressure of the final cylinder at a value near the corresponding query pressure in the two-dimensional data table minus 1MPa;

[0038] S7, when the exhaust temperature of the last cylinder exceeds the critical temperature and the difference between the two is greater than 1°C, the current bypass loading regulating valve opening is maintained, waiting 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 is completely closed to complete the loading.

[0040] The present invention detects the exhaust temperature of each cylinder and the pressure of each cylinder in real time during the startup, no-load and loading processes. According to the CO2 pressure-temperature physical property phase diagram curve, the flow rate and the valve opening of the bypass loading return pipeline system are infinitely regulated by the monitoring system, so that CO2 is in a gas or supercritical fluid state. When CO2 is not in a gas or supercritical fluid state, the machine is shut down immediately. Keeping CO2 in a gas or supercritical fluid state can prevent liquid hammer in the compressor cylinder and pipeline blockage, thereby improving the safety of compressor operation.

[0041] Among them, during the compressor startup, no-load, loading and shutdown processes, the exhaust pressure and exhaust temperature of each stage of the cylinder are monitored in real time, and the query pressure corresponding to the current temperature in the two-dimensional data table is queried.

[0042] In another technical solution, the measured temperature needs to be preprocessed before querying so 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 exhaust pressure is about to exceed the query pressure, the opening of the bypass loading regulating valve can be adjusted to be large, while the opening of the intake valve can be adjusted to be small, or the vent valve can be opened to control the exhaust pressure at each level to be below the query pressure corresponding to the current temperature in the two-dimensional data table.

[0044] Among them, 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 to control the actual pressure to be below the query pressure corresponding to the current temperature in the two-dimensional data table.

[0045] Among them, in the above S5 and S6, it is ensured that the exhaust pressure of each cylinder level is less than the query pressure corresponding to the current cylinder exhaust temperature in the two-dimensional data. If the pressure is ≥ the query pressure corresponding to the current temperature in the two-dimensional data table, the machine is shut down immediately, and the shutdown response time is less than 500ms.

[0046] In another technical solution, in S5 and S6, during the loading operation, when shutdown is required or a shutdown failure occurs, the main motor is turned off, and the loading regulating valve is opened 2% per second for unloading (the opening speed can be adjusted according to temperature changes). When the loading regulating valve is fully opened, the air inlet valve and the exhaust valve are closed, and the vent valve is opened. When the internal pressure of the unit is lower than the set value, the vent valve is closed to complete the shutdown process.

[0047] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the implementation modes, and they can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and the illustrations shown and described herein.

Claims

1. A supercritical CO2 compressor automatic control method, characterized in that: The following steps are involved: S1. According to the CO2 content in the actual gas to be compressed, the pressure-temperature physical property phase diagram curve of CO2 in the CO2 mixed gas is corrected; S2, taking -40°C as the starting point and 200°C as the end point, taking one of the temperature values ​​between 0.02 and 0.1°C as the interval value, obtaining the corresponding pressure of CO2 at different temperatures on the pressure-temperature physical property phase diagram curve, obtaining X groups of temperature data and pressure data at -40 to 200°C, forming a two-dimensional data table and storing it; S3. During the compressor startup process, fully open the compressor bypass loading regulating valve 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. When the exhaust pressure of any cylinder is greater than or equal to the query pressure corresponding to the two-dimensional data table, immediately stop the machine for inspection, and the shutdown response time is less than 500ms. S4. When the compressor is started and reaches the set speed, the compressor enters the no-load state, and the compressor bypass loading regulating valve is kept 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; When the exhaust pressure of any cylinder is ≥ the corresponding query pressure in the two-dimensional data table, the machine will be stopped for inspection immediately, and the shutdown response time is less than 500ms; S5. When it is necessary to enter the loading state, the pressure corresponding to the current exhaust temperature of the final cylinder in the two-dimensional data table is queried and read, and the bypass loading regulating valve is gradually closed to realize loading. At the same time, the opening of the intake valve and the bypass loading regulating valve is automatically controlled to stabilize the exhaust pressure of the final cylinder at the corresponding 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 final cylinder in the two-dimensional data table, automatically control the opening of the intake valve and the bypass loading regulating valve, and stabilize the exhaust pressure of the final cylinder at the corresponding query pressure in the two-dimensional data table minus the preset value; S7, when the exhaust temperature of the last cylinder exceeds the critical temperature and the difference between the two is greater than the preset value, the current bypass loading regulating valve opening is maintained, waiting for the exhaust temperature of other cylinders to exceed the critical temperature; When the exhaust temperatures of all cylinders exceed the critical temperature and the difference between the two is greater than the preset value, the bypass loading regulating valve is completely closed to complete the loading.

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

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

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

5. The supercritical CO2 compressor automatic control method 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 to control the actual pressure to be below the query pressure corresponding to the current temperature in the two-dimensional data table.

6. The supercritical CO2 compressor automatic control method according to claim 1, characterized in that: In the above S5 and S6, 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, shut down immediately, and the shutdown response time is less than 500ms.

7. The supercritical CO2 compressor automatic control method according to claim 1, characterized in that: In S5 and S6, during the loading operation, when shutdown is required or a shutdown failure occurs, the main driver is turned off, and the bypass loading regulating valve is gradually opened for unloading. When the loading regulating valve is fully opened, the intake valve and the 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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