CN115454180A - Supercritical CO 2 Extraction system pressure and temperature control method - Google Patents
Supercritical CO 2 Extraction system pressure and temperature control method Download PDFInfo
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- 238000000605 extraction Methods 0.000 title claims abstract description 85
- 238000000034 method Methods 0.000 title claims abstract description 37
- 230000008569 process Effects 0.000 claims abstract description 19
- 230000001105 regulatory effect Effects 0.000 claims abstract description 18
- 230000001276 controlling effect Effects 0.000 claims description 12
- 230000008859 change Effects 0.000 claims description 7
- 230000000630 rising effect Effects 0.000 claims description 2
- 230000000903 blocking effect Effects 0.000 claims 1
- 238000012937 correction Methods 0.000 abstract description 8
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 6
- 230000006870 function Effects 0.000 description 5
- 238000010586 diagram Methods 0.000 description 4
- 229910002092 carbon dioxide Inorganic materials 0.000 description 3
- 239000001569 carbon dioxide Substances 0.000 description 3
- 230000001965 increasing effect Effects 0.000 description 3
- 238000000194 supercritical-fluid extraction Methods 0.000 description 3
- 230000000694 effects Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000004891 communication Methods 0.000 description 1
- 230000008878 coupling Effects 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
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- 230000002708 enhancing effect Effects 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 238000004880 explosion Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 230000004044 response Effects 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 230000001360 synchronised effect Effects 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 238000009834 vaporization Methods 0.000 description 1
- 230000008016 vaporization Effects 0.000 description 1
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- G05D27/00—Simultaneous control of variables covered by two or more of main groups G05D1/00 - G05D25/00
- G05D27/02—Simultaneous control of variables covered by two or more of main groups G05D1/00 - G05D25/00 characterised by the use of electric means
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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/50—Improvements relating to the production of bulk chemicals
- Y02P20/54—Improvements relating to the production of bulk chemicals using solvents, e.g. supercritical solvents or ionic liquids
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Abstract
The invention provides supercritical CO 2 The pressure and temperature control method of the extraction system integrates the advantages of fuzzy control and PID control, introduces series correction and feedback correction, eliminates mutual interference of temperature and pressure in the system, solves the problem of overshoot of temperature in the boosting process to a certain degree, and reduces the interference of external uncontrolled factors. By judging supercritical CO 2 Whether the difference value of the temperature and the pressure of an extraction kettle in the extraction system meets an expected value or not is judged, fuzzy control is carried out on a temperature regulating valve in a feedback correction mode, so that the influence of pressure rise on the temperature in the system is eliminated, the problem of overshoot of the temperature in the pressure rise process is solved to a certain extent, the interference of flow fluctuation on the system operation is eliminated, and the system can operate stably and efficiently.
Description
Technical Field
The invention belongs to the technical field of supercritical extraction, and particularly relates to supercritical CO 2 A control method of an extraction system.
Background
Supercritical CO 2 The extraction is carried out by using supercritical CO 2 I.e. CO in a thermodynamic state at a temperature above the critical temperature and a pressure above the critical pressure 2 A technique for extracting a specific component from a liquid or a solid as an extractant. CO in supercritical state 2 Has high solubility and fluidity, and the solubility can change along with the change of temperature and pressure, thereby realizing the purpose of separating and purifying the substances. In production and use, the extraction kettle is in a high-pressure low-temperature state, wherein CO is contained in the extraction kettle 2 The fluctuation of pressure and temperature can cause the unstable extraction process, thus causing long extraction time and poor extraction effect; the excessive overshoot of the pressure can even cause the explosion of the kettle body to cause personal and property damage; and excessive temperature overshoot may cause deterioration of the extract in the kettle.
At present, the control of temperature and pressure in the supercritical extraction process mostly adopts a simple PID control method, and in some cases, a PID controller designed for a specific system can be well controlled, but the problems still exist in the prior art. When the control system is in a closed-loop working state, a test signal needs to be inserted into the control process, but the method can cause disturbance, and the PID controller can generate overshoot under the influence of the disturbance. In the supercritical extraction process of the carbon dioxide, various measurable and undetectable interferences exist, and certain coupling and mutual interference problems exist between the temperature and the pressure; the effect of the heat absorbed or released by the vaporization or liquefaction of the carbon dioxide on temperature; part of the carbon dioxide is not in a supercritical state, so that the solvent amount is reduced, and the extraction rate is reduced.
Disclosure of Invention
In order to solve the above problems, the present invention provides a method for greatly enhancing supercritical CO 2 The anti-interference performance of the operation of the extraction system, and the stability and the high efficiency of the system are improved.
In order to realize the technical content, the invention adopts the following technical scheme.
Supercritical CO 2 The pressure and temperature control method of the extraction system integrates the advantages of fuzzy control and PID control, introduces series correction and feedback correction, eliminates mutual interference of temperature and pressure in the system, solves the problem of overshoot of temperature in the boosting process to a certain extent, and reduces the interference of external uncontrolled factors. The system operation is divided into a boosting process, a heating process and a constant-pressure and constant-temperature process. When the system is in a pressure boosting process, the temperature can be greatly increased along with the increase of the pressure according to a thermodynamic equation, and the system is required to be stopped or slowly subjected to heat exchange operation at the moment so as to prevent the temperature overshoot from being too large.
Through pressure transmitter, temperature transmitter read the pressure value, the temperature value of extraction cauldron and transmit for the PLC system, the PLC system calculates according to received signal, transmits pressure regulating valve, temperature regulating valve and controls after turning into current signal with the operation result to adjust pressure value, temperature value to the target parameter setting, PLC system operation control process includes following step:
s1: taking a pressure value P read by a pressure transmitter in the extraction system as an input value, and establishing a PID controller to control the opening of a pressure regulating valve;
s2: determination of supercritical CO 2 Reading whether the pressure value P in the extraction system reaches Ps, if not, indicating that the system is in a boosting process, controlling the rising rate of the temperature to prevent the temperature from being overshot, and executing a step S3;
s3: determination of supercritical CO 2 Reading whether a temperature value T in the extraction system is smaller than Ts, if so, indicating that the temperature of the system is not overshot and further controlling the change degree of the temperature and the pressure, and executing a step S4;
s4: judging whether the value of [ (P-P0)/(Ps-P0) - (T-T0)/(Ts-T0) ] is less than or equal to the expected value, if not, executing the step S5; if yes, go to step S6. Wherein P0 is the initial pressure, ps is the expected pressure, T0 is the initial temperature, ts is the expected temperature, and an evaluation range is a constant of [0,1 ];
s5: controlling the opening degree of the heat exchange valve by taking [ (P-P0)/(Ps-P0) - (T-T0)/(Ts-T0) ] as an input variable of fuzzy control, and returning to execute the step S3;
s6: supercritical CO 2 Adjusting the pressure value P of the extraction kettle in the extraction system to a target pressure value Ps;
further, step S6 includes the following substeps:
s61: determination of supercritical CO 2 CO entering the extraction kettle in the extraction system 2 Whether the flow rate Q meets the first flow rate condition or not, if yes, executing step S65, and if not, executing step S62;
s62: determination of supercritical CO 2 CO entering the extraction kettle in the extraction system 2 Whether the flow rate Q meets the second flow rate condition or not, if yes, executing step S65, and if not, executing step S63;
s63: determination of supercritical CO 2 CO entering the extraction kettle in the extraction system 2 Whether the flow rate Q meets the third flow rate condition or not, if yes, executing step S65, and if not, executing step S64;
s64: determination of supercritical CO 2 CO entering the extraction kettle in the extraction system 2 Whether the flow rate Q meets the fourth flow rate condition, if yes, go to step S65;
the first flow conditions are: supercritical CO 2 CO entering the extraction kettle in the extraction system 2 Flow rate Q<QMAX, and Q>3/4QMAX；
The second flow conditions were: supercritical CO 2 CO entering the extraction kettle in the extraction system 2 Flow rate Q<3/4QMAX, and Q>1/2QMAX；
The third flow conditions were: supercritical CO 2 CO entering the extraction kettle in the extraction system 2 Flow rate Q<3/4QMAX, and Q>1/2QMAX；
The fourth flow condition is: supercritical CO 2 CO entering the extraction kettle in the extraction system 2 Flow rate Q<1/2QMAX；
Wherein QMAX is the maximum output flow of the booster pump;
s65: establishing a fuzzy controller by taking the flow Q as an input variable to carry out PID parameter regulation on a PID controller of the pressure regulating valve;
further, in step S2,if supercritical CO 2 When the pressure value P in the extraction system reaches a set value Ps, the system is indicated to have reached a constant pressure process, and the temperature needs to be adjusted to the set value as soon as possible and kept balanced, and then the step S7 is executed;
s7: controlling the opening degree of the heat exchange valve by taking Ts-T as an input variable of fuzzy control, and executing a step S6;
further, in step S3, if the supercritical CO is existed 2 If the temperature value T in the extraction system is not less than the set value Ts, the system temperature is over-adjusted, the heat exchange function of the heat exchanger needs to be blocked, and the opening of the heat exchange valve is controlled to be 0, then the step S8 is executed;
s8: controlling the opening of the heat exchange valve to be 0, and executing the step S6;
compared with the prior art, the method has the advantages that the supercritical CO is judged 2 Whether the difference value of the change rates of the temperature and the pressure of the extraction kettle in the extraction system meets the expected value or not is judged, fuzzy control can be performed on the temperature regulating valve in a feedback correction mode, so that the influence of the temperature in the system caused by the pressure rise is eliminated, and the problem of overshoot of the temperature in the pressure rise process is solved to a certain extent. Judging the supercritical CO according to the first flow condition, the second flow condition, the third flow condition and the fourth flow condition 2 The pressure change trend of an extraction kettle in the extraction system can adopt feedforward correction, and the PID control parameters are corrected by applying fuzzy control, so that the interference of flow fluctuation on the system operation is eliminated, and the system can stably and efficiently operate.
Drawings
FIG. 1 is a flow chart of the steps of the present control method;
FIG. 2 is supercritical CO 2 A simple structure diagram of an extraction system;
fig. 3 is a schematic structural diagram of a control system in an embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to specific examples.
It should be understood that the structures, proportions, and dimensions shown in the drawings and described herein are for illustrative purposes only and are not intended to limit the scope of the present invention, which is defined by the claims, but rather the claims, and the drawings and the appended claims are for illustrative purposes only and are not intended to limit the scope of the present invention. In addition, the terms such as "upper", "lower", "left", "right" and "middle" used in the present specification are for convenience of description only, and are not intended to limit the scope of the present invention, and changes or modifications of the relative relationship thereof may be regarded as the scope of the present invention without substantial changes in the technical contents.
Example one
The simple structure of the control system is shown in fig. 2, an S7-1500 series PLC of Germany Siemens company is selected as a main control element, and the structural block diagram is shown in fig. 3. The PLC system comprises a power supply module, a CPU module, an analog input module and an analog output module, wherein the analog input module is an AI module, and the analog output module is an AO module. The flowmeter is communicated with the CPU module through a CAN bus, the pressure transmitter and the temperature transmitter transmit the pressure value and the temperature value to the AI module through a 4-20mA current loop communication mode, and the AI module transmits the input current signal to the CPU after digital processing. The CPU module is used as a controller, compares the detection value with a set value, and sends out a control instruction by using the control method. The control instruction sent by the CPU is converted into a current signal through the AO module and is transmitted to the pressure regulating valve and the temperature regulating valve, so that the pressure value and the temperature value are regulated to target set parameters. The PLC controller is connected with an industrial personal computer provided with TIA Portal configuration software through a Profinet industrial Ethernet, and a program written by the control method in a ladder diagram language is downloaded to a CPU module of the S7-1500 PLC.
Supercritical CO 2 The pressure and temperature control method of the extraction system comprises the following steps after the system is started, as shown in figure 1.
Step S1: establishing a PID controller to control the opening degree of a pressure regulating valve by taking a pressure value P read by a pressure transmitter in the extraction system as an input value, executing the step S2, pre-setting PID parameters of the PID controller by using a PID module debugging function carried by TIA Portal configuration software, and further setting and adjusting the PID parameters by establishing a fuzzy controller;
step S2: determination of supercritical CO 2 Reading whether the pressure value P in the extraction system reaches a set value Ps, if not, indicating that the system is in a pressure increasing process, wherein the temperature can greatly increase along with the increase of the pressure in the process, and the temperature increasing rate needs to be controlled to be equal to or lower than the pressure changing rate as much as possible to prevent the temperature from being overshot, so that the step S3 can be executed; otherwise, the system is indicated to reach the constant pressure process, the temperature needs to be adjusted to the set value as soon as possible and kept balanced, and the step S7 can be executed;
and step S3: determination of supercritical CO 2 Whether the temperature value T read in the extraction system is smaller than a preset value Ts or not, if yes, executing a step S4; otherwise, the system temperature is over-regulated, the heat exchange function of the heat exchanger needs to be blocked, and the step S8 can be executed;
and step S4: judging whether the value of [ (P-P0)/(Ps-P0) - (T-T0)/(Ts-T0) ] is less than or equal to the expected value, if not, executing the step S5; wherein, the smaller the value of the constant with the value range of [0,1], the more synchronous the change of the temperature and the pressure is, but the larger the fluctuation of the system is, the more difficult the stable operation is, generally the value is 0.1; if yes, executing step S6;
step S5: controlling the opening degree of the heat exchange valve by using [ (P-P0)/(Ps-P0) - (T-T0)/(Ts-T0) ] = e as an input variable of fuzzy control, and returning to execute the step S3;
the fuzzy controller comprises the following creation rules:
rule 1: when e <0, the valve is closed;
rule 2: when e >0, divide e into 5 fuzzy sets: VS, S, M, L, VL, whose value range is [0,1], fuzzifying the VS, S, M, L, VL by adopting a triangular membership function;
rule 3: the valve opening K is divided into 5 fuzzy sets: NB, NS, O, PS, PB, a value range [0,100], and fuzzifying the values by adopting a triangular membership function;
rule 4: the larger the difference e is, the larger the opening K is;
s6: will exceed criticalBoundary CO 2 And adjusting the pressure value P of the extraction kettle in the extraction system to be a target pressure value Ps, and performing online correction on PID parameters by using a fuzzy control rule in order to meet the stable control requirement of pressure at different flow rates. It comprises the following substeps:
s61: determination of supercritical CO 2 CO entering the extraction kettle in the extraction system 2 Whether the flow rate Q meets the first flow rate condition, if yes, executing step S65, and if no, executing step S62;
s62: determination of supercritical CO 2 CO entering the extraction kettle in the extraction system 2 Whether the flow rate Q meets the second flow rate condition or not, if yes, executing step S65, and if not, executing step S63;
s63: determination of supercritical CO 2 CO entering the extraction kettle in the extraction system 2 Whether the flow rate Q meets the third flow rate condition or not, if yes, executing step S65, and if not, executing step S64;
s64: determination of supercritical CO 2 CO entering the extraction kettle in the extraction system 2 Whether the flow rate Q satisfies the fourth flow rate condition, if yes, execute step S65;
the first flow conditions are: supercritical CO 2 CO entering the extraction kettle in the extraction system 2 Flow rate Q<QMAX, and Q>3/4 QMAX；
The second flow conditions were: supercritical CO 2 CO entering the extraction kettle in the extraction system 2 Flow rate Q<3/4QMAX, and Q>1/2 QMAX；
The third flow conditions were: supercritical CO 2 CO entering the extraction kettle in the extraction system 2 Flow rate Q<3/4QMAX, and Q>1/2 QMAX；
The fourth flow condition is: supercritical CO 2 CO entering the extraction kettle in the extraction system 2 Flow rate Q<1/2QMAX；
Wherein QMAX is the maximum output flow of the booster pump;
s65: establishing a fuzzy controller by taking the flow as an input variable to carry out PID parameter regulation on a PID controller of the pressure regulating valve; it satisfies the following rules:
rule 1: when the flow is large, a larger Kp and a smaller Kd are required to accelerate the response of the valve, so that the valve can quickly respond, and Ki =0 is used for avoiding the excessive pressure overshoot;
rule 2: when the flow is moderate, a small Kp is required, and a valve can be slightly overshot due to proper Ki and Kd;
rule 3: when the flow is small, large Kp and Ki should be taken, and the Kd value is appropriate to reduce the steady state error.
S7: if supercritical CO 2 Controlling the opening degree of the heat exchange valve by taking Ts-T as an input variable of fuzzy control when the pressure value P in the extraction system reaches a set value Ps, and executing the step S6;
s8: if supercritical CO 2 Controlling the opening of the heat exchange valve to be 0 when the temperature value T in the extraction system is not less than the set value Ts, and executing the step S6;
the above description is only for the purpose of illustrating the preferred embodiments of the present invention and should not be taken as limiting the scope of the present invention, which is intended to cover any modifications, equivalents, improvements, etc. within the spirit and scope of the present invention.
Claims (4)
1. Supercritical CO 2 The pressure and temperature control method of the extraction system comprises the steps of reading a pressure value and a temperature value of an extraction kettle through a pressure transmitter and a temperature transmitter and transmitting the pressure value and the temperature value to a PLC system, calculating by the PLC system according to a received signal, converting an operation result into a current signal and then transmitting the current signal to a pressure regulating valve and a temperature regulating valve for control, and regulating the pressure value and the temperature value to a target set parameter, wherein the operation process of the PLC system comprises the following steps:
s1: taking a pressure value P read by a pressure transmitter in the extraction system as an input value, and establishing a PID controller to control the opening of a pressure regulating valve;
s2: determination of supercritical CO 2 Reading whether the pressure value P in the extraction system reaches Ps, if not, indicating that the system is in a boosting process, controlling the rising rate of the temperature to prevent the temperature from being overshot, and executing a step S3;
s3: determination of supercritical CO 2 Whether the temperature value T read in the extraction system is less than Ts, if yes, the system temperature is not overshot, and the temperature needs to be further controlledIf the degree and the pressure change degree, executing the step S4;
s4: judging whether the value of [ (P-P0)/(Ps-P0) - (T-T0)/(Ts-T0) ] is less than or equal to the expected value, if not, executing the step S5; if yes, executing step S6;
s5: controlling the opening degree of the heat exchange valve by taking [ (P-P0)/(Ps-P0) - (T-T0)/(Ts-T0) ] as an input variable of fuzzy control, and returning to execute the step S3;
s6: supercritical CO 2 Adjusting the pressure value P of the extraction kettle in the extraction system to a target pressure value Ps;
wherein P0 is the initial pressure, ps is the desired pressure, T0 is the initial temperature, ts is the desired temperature, and Δ is a constant with a value range of [0,1 ].
2. The control method according to claim 1, wherein step S6 includes the steps of:
s61: determination of supercritical CO 2 CO entering the extraction kettle in the extraction system 2 Whether the flow Q satisfies Q<QMAX, and Q>3/4QMAX, if yes, go to step S65, if no, go to step S62;
s62: determination of supercritical CO 2 CO entering the extraction kettle in the extraction system 2 Whether the flow Q satisfies Q<3/4QMAX, and Q>1/2QMAX, if yes, executing step S65, if no, executing step S63;
s63: determination of supercritical CO 2 CO entering the extraction kettle in the extraction system 2 Whether the flow Q satisfies Q<3/4QMAX, and Q>1/2QMAX, if yes, executing step S65, if no, executing step S64;
s64: determination of supercritical CO 2 CO entering the extraction kettle in the extraction system 2 Whether the flow Q satisfies Q<1/2QMAX, if yes, executing step S65;
s65: establishing a fuzzy controller by taking the flow Q as an input variable to carry out PID parameter regulation on a PID controller of the pressure regulating valve;
where QMAX is the maximum output flow of the booster pump.
3. The control method according to claim 2, characterized by further comprising step S7:
s7: if the supercritical CO is present in the step S2 2 And (4) when the pressure value P in the extraction system reaches a set value Ps, the system is indicated to have reached a constant pressure process, the temperature needs to be adjusted to the set value as soon as possible and kept balanced, the opening degree of the heat exchange valve is controlled by taking Ts-T as an input variable of fuzzy control, and step S6 is executed.
4. The control method according to claim 3, characterized by further comprising step S8:
s8: if the supercritical CO is present in step S3 2 And (4) controlling the temperature value T in the extraction system to be not less than Ts, indicating that the temperature of the system is over-regulated, blocking the heat exchange function of the heat exchanger, controlling the opening of the heat exchange valve to be 0, and executing the step S6.
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