Tower liquid level control system and tower liquid level control method

Abstract

The invention discloses a tower liquid level control system and a tower liquid level control method. The tower liquid level control system comprises an upper tower liquid level controller and a lower tower liquid level controller, the upper tower liquid level controller is respectively connected with the upper tower liquid level controller and the lower tower liquid level controller, and the upper tower liquid level controller measures an upper tower liquid level measurement value of an upper tower. An upper tower liquid level set value of an upper tower liquid level controller is determined according to a lower tower liquid level measurement value measured by a lower tower liquid level controller, and an upper tower flow set value of an upper tower is controlled according to a first deviation absolute value of the upper tower liquid level measurement value and the upper tower liquid level set value; and the lower tower liquid level controller is connected with the lower tower, and the lower tower flow set value of the lower tower is corrected by the lower tower liquid level controller according to the second deviation absolute value of the lower tower liquid level measurement value of the lower tower and the lower tower liquid level set value through the nonlinear gain value proportional integral. Non-linear gain value correction is carried out on the lower tower, so that self-adaptive control of the liquid level is realized, the operation frequency is reduced, the control precision is improved, and the anti-interference capability is enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical industry, in particular to a tower liquid level control system and a tower liquid level control method. Background Art

[0002] Liquid level is a crucial control parameter in chemical processes. From a process operation perspective, this parameter can be used to characterize the stability of plant operations and ensure the smooth production of qualified products. From a process safety perspective, controlling this parameter is a crucial means of ensuring safe plant operation, thereby improving the safety and reliability of the production process.

[0003] With the development of petrochemical production, the production processes of many products have become extremely complex. Production processes are constantly being intensified, with each component closely interconnected. Often, the discharge from one device becomes the feed to the next. While liquid level control is crucial, other parameters may require even greater attention, such as stable reactor feed flow and precise tower temperature distribution. Equipment with buffering capacity can be utilized to some extent to safeguard these more critical parameters, ensuring that the liquid level can be adjusted, does not exceed alarm thresholds, and does not trigger interlocks, prioritizing the requirements of other parameters. A distillation tower is preferred.

[0004] like Figure 1 The figure shows a tower level control scheme of a conventional line tower. The upper tower 1' is connected to the lower tower 2' via a first valve 3', and the lower tower 2' is connected to the final device 5' via a second valve 4'. The device 5' can be a variety of devices, Figure 1 Take the reactor as an example. The first liquid level controller 6' (direct action, DIR) outputs the set value of the first flow controller to the first flow controller 7' (reverse action, REV) according to the liquid level measurement value of the upper tower 1', and the first flow controller 7' controls the first valve 3' according to the flow measurement value. At the same time, the second liquid level controller 8' (direct action, DIR) outputs the set value of the first flow controller to the second flow controller 9' (reverse action, REV) according to the liquid level measurement value of the lower tower 2', and the second flow controller 9' controls the second valve 4' according to the flow measurement value. Among them, the first liquid level controller 6' and the second liquid level controller 8' both adopt proportional integral control (PI Control).

[0005] However, for continuous equipment, when the liquid level controller controls multiple devices in series, due to the proportional and integral effects of the controller continuously giving the outlet flow control signal to return the liquid level to its set point, this control signal is likely to have overshoot / tailing, and the measured value will have normal fluctuations, and will increase with the addition of each consecutive liquid level controller, passing like waves, causing the fluctuation of the last device 5' connected to the lower tower 2' to become abnormally significant. Summary of the Invention

[0006] Based on this, it is necessary to provide a tower liquid level control system and a tower liquid level control method to address the technical problem that the existing technology causes abnormal fluctuations in the equipment connected to the last tower during continuous tower liquid level control.

[0007] The present invention provides a tower liquid level control system for a continuous tower system, wherein the continuous tower system comprises at least an upper tower located upstream and a lower tower located downstream, wherein the upper tower is connected to the lower tower, and the tower liquid level control system comprises: an upper tower liquid level controller and a lower tower liquid level controller, wherein:

[0008] The upper tower liquid level controller is connected to the upper tower and the lower tower liquid level controller respectively, the upper tower liquid level controller measures the upper tower liquid level measurement value of the upper tower, determines the upper tower liquid level setting value of the upper tower liquid level controller according to the lower tower liquid level measurement value of the lower tower measured by the lower tower liquid level controller, and controls the upper tower flow rate setting value of the upper tower through proportional integral according to the absolute value of the first deviation between the upper tower liquid level measurement value and the upper tower liquid level setting value;

[0009] The lower tower liquid level controller is connected to the lower tower, and adopts a nonlinear gain value to proportionally integrally correct the lower tower flow rate setting value of the lower tower according to the second absolute value of the deviation between the lower tower liquid level measurement value of the lower tower and the lower tower liquid level setting value. When the second absolute value of the deviation is within the control dead zone, the lower tower liquid level controller controls the lower tower flow rate setting value to remain stable. When the second absolute value of the deviation exceeds the control dead zone, the lower tower liquid level controller controls the lower tower flow rate setting value to increase.

[0010] Furthermore, it also includes an upper tower flow controller, an upper tower valve, a lower tower flow controller and a lower tower valve;

[0011] The upper tower liquid level controller is connected to the upper tower flow controller, and the upper tower liquid level controller outputs the upper tower flow set value of the upper tower flow controller to the upper tower flow controller, and the upper tower flow controller controls the valve opening of the upper tower valve according to the upper tower flow set value and the upper tower actual flow;

[0012] The lower tower liquid level controller is connected to the lower tower flow controller, and the lower tower liquid level controller outputs the lower tower flow setting value of the lower tower flow controller to the lower tower flow controller. The lower tower flow controller controls the valve opening of the lower tower valve according to the lower tower flow setting value and the actual flow of the lower tower.

[0013] Furthermore, it also includes a deviation gain calculation block, the upper tower liquid level controller is connected to the lower tower through the deviation gain calculation block, the deviation gain calculation block performs deviation gain calculation on the lower tower liquid level measurement value obtained from the lower tower and outputs it to the upper tower liquid level controller as the upper tower liquid level set value.

[0014] Furthermore, a nonlinear filter is included, and the deviation gain calculation block is connected to the lower tower through the nonlinear filter.

[0015] The present invention provides a tower liquid level control method for a continuous tower system, wherein the continuous tower system comprises at least an upper tower located upstream and a lower tower located downstream, wherein the upper tower is connected to the lower tower, and the liquid level control method comprises:

[0016] Obtaining a measured value of an upper tower liquid level of the upper tower and a measured value of a lower tower liquid level of the lower tower;

[0017] Determine the upper tower liquid level setting value according to the lower tower liquid level measurement value;

[0018] Calculating an upper tower flow rate setting value of the upper tower by proportional integration according to an absolute value of a first deviation between the upper tower liquid level measurement value and the upper tower liquid level setting value;

[0019] A nonlinear gain value is used for proportional integral correction according to a second absolute value of a deviation between the lower tower liquid level measurement value and the lower tower liquid level setting value to calculate a lower tower flow setting value of the lower tower.

[0020] Furthermore, it also includes:

[0021] The nonlinear gain value is determined according to a relationship between the second deviation absolute value and the control dead zone.

[0022] Furthermore, determining the nonlinear gain value according to the relationship between the absolute value of the second deviation and the control dead zone includes:

[0023] In the process of gradually increasing the absolute value of the second deviation, if the absolute value of the second deviation is less than or equal to the control dead zone plus the hysteresis value, the nonlinear gain value is fixed; if the absolute value of the second deviation is greater than the control dead zone plus the hysteresis value, the nonlinear gain value is increased as the absolute value of the second deviation increases;

[0024] During the process of gradually decreasing the absolute value of the second deviation, if the absolute value of the second deviation is greater than the control dead zone, the nonlinear gain value is reduced as the absolute value of the second deviation decreases; if the absolute value of the second deviation is less than or equal to the control dead zone, the nonlinear gain value is a fixed value.

[0025] Furthermore, the method of calculating the lower tower flow rate setting value of the lower tower by using a nonlinear gain value for proportional integral correction based on the second absolute value of the deviation between the lower tower liquid level measurement value and the lower tower liquid level setting value comprises:

[0026] Calculate the flow setting value of the lower tower as follows:

[0027] Wherein: is the second deviation absolute value, OUT(s) is the lower tower flow rate setting value corresponding to the second deviation absolute value s, and KNL is the nonlinear gain value.

[0028] Furthermore, determining the upper tower liquid level setting value according to the lower tower liquid level measurement value includes:

[0029] A deviation gain calculation is performed on the lower tower liquid level measurement value to obtain an upper tower liquid level setting value.

[0030] Furthermore, the performing of deviation gain calculation on the lower tower liquid level measurement value to obtain the upper tower liquid level setting value includes:

[0031] Obtaining a filtered liquid level measurement value obtained by performing nonlinear filtering on the lower tower liquid level measurement value;

[0032] Calculate the upper tower liquid level setting value to be OUT 偏差 =(SP+IN_1)×Gain, where IN_1 is the liquid level measurement value after filtering, SP is the deviation setting value, Gain is the deviation gain setting value, OUT 偏差 Set the value for the upper tower liquid level.

[0033] The present invention uses proportional-integral control for the upper tower, while correcting the proportional-integral for the lower tower using a nonlinear gain value. When the absolute value of the second deviation between the measured liquid level of the lower tower and the set liquid level of the lower tower is within the control dead band, the flow rate set value of the lower tower is controlled to remain stable. When the absolute value of the second deviation exceeds the control dead band, the flow rate set value of the lower tower is controlled to increase. By using the nonlinear gain value correction for the lower tower, adaptive control of the liquid level is achieved, the operating frequency is reduced, the control accuracy is improved, and the anti-interference capability is enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a system principle diagram of the tower liquid level control system of the prior art;

[0035] Figure 2 This is a system principle diagram of a tower liquid level control system according to one embodiment of the present invention;

[0036] Figure 3 This is the principle diagram of nonlinear gain correction;

[0037] Figure 4 Schematic diagram for calculating deviation gain;

[0038] Figure 5 This is a working flow chart of a tower liquid level control method according to one embodiment of the present invention;

[0039] Figure 6 This is a workflow diagram of a tower liquid level control method according to another embodiment of the present invention.

[0040] Marking Description

[0041] 1. Upper tower; 2. Lower tower; 3. Upper tower liquid level controller; 4. Lower tower liquid level controller; 5. Upper tower flow controller; 6. Upper tower valve; 7. Lower tower flow controller; 8. Lower tower valve; 9. Deviation gain calculation block; 10. Nonlinear filter; 11. Reactor. DETAILED DESCRIPTION

[0042] The following further describes specific embodiments of the present invention with reference to the accompanying drawings. Like components are denoted by like reference numerals. It should be noted that the terms "front," "rear," "left," "right," "up," and "down" used in the following description refer to directions in the accompanying drawings, and the terms "inward" and "outward" refer to directions toward or away from the geometric center of a particular component, respectively.

[0043] like Figure 2 The figure shows a tower liquid level control system according to an embodiment of the present invention, which is used in a continuous tower system. The continuous tower system includes at least an upper tower 1 located upstream and a lower tower 2 located downstream. The upper tower 1 is connected to the lower tower 2. The tower liquid level control system includes: an upper tower liquid level controller 3 and a lower tower liquid level controller 4, wherein:

[0044] The upper tower liquid level controller 3 is connected to the upper tower 1 and the lower tower liquid level controller 4 respectively, and the upper tower liquid level controller 3 measures the upper tower liquid level measurement value of the upper tower 1, determines the upper tower liquid level setting value of the upper tower liquid level controller 3 according to the lower tower liquid level measurement value of the lower tower 2 measured by the lower tower liquid level controller 4, and controls the upper tower flow setting value of the upper tower 1 through proportional integral according to the first absolute value of the deviation between the upper tower liquid level measurement value and the upper tower liquid level setting value;

[0045] The lower tower liquid level controller 4 is connected to the lower tower 2. The lower tower liquid level controller 4 uses a nonlinear gain value to proportionally integrally correct the lower tower flow set value of the lower tower 2 according to the second absolute value of the deviation between the lower tower liquid level measurement value of the lower tower 2 and the lower tower liquid level set value. When the second absolute value of the deviation is within the control dead zone, the lower tower liquid level controller 4 controls the lower tower flow set value to remain stable. When the second absolute value of the deviation exceeds the control dead zone, the lower tower liquid level controller 4 controls the lower tower flow set value to increase.

[0046] Specifically, an upper tower 1 and a lower tower 2 are connected by a pipeline. The upper tower 1 is the upstream tower, while the lower tower 2 is the downstream tower. The towers are preferably distillation towers. An upper tower liquid level controller 3 measures the liquid level of the upper tower 1 to obtain an upper tower liquid level measurement value. A lower tower liquid level controller 4 measures the liquid level of the lower tower 2 to obtain a lower tower liquid level measurement value.

[0047] The downstream of the lower tower 2 may be other equipment. In some embodiments, the downstream of the lower tower 2 is a reactor 11.

[0048] The upper tower liquid level controller 3 is a proportional-integral (PI) controller. Using a proportional-integral algorithm, the upper tower liquid level controller 3 determines its setpoint based on the lower tower liquid level measurement. It then calculates the absolute value of the first deviation between the upper tower liquid level measurement and the upper tower liquid level setpoint. Based on this absolute value, the proportional-integral algorithm is used to control the upper tower flow rate setpoint of upper tower 1. This upper tower flow rate setpoint is used to control the valve opening of upper tower valve 6 between upper tower 1 and lower tower 2, thereby controlling the flow rate of material flowing from upper tower 1 to lower tower 2.

[0049] The lower tower liquid level controller 4 also uses a proportional integral (PI) algorithm to control the lower tower flow rate set value of the lower tower 2 according to the second absolute value of the deviation between the lower tower liquid level measurement value and the lower tower liquid level set value. However, unlike the upper tower liquid level controller 3, the lower tower liquid level controller 4 uses a nonlinear gain value to correct the proportional integral so that when the second absolute value of the deviation is within the control dead zone, the lower tower liquid level controller 4 controls the lower tower flow rate set value to remain stable. When the second absolute value of the deviation exceeds the control dead zone, the lower tower liquid level controller 4 controls the lower tower flow rate set value to increase. Wherein, the lower tower liquid level set value is the liquid level of the process requirement and can be considered as a fixed value. The lower tower flow rate set value is used to control the valve opening of the lower tower valve 8 connected to the lower tower 2. Wherein the lower tower valve 8 is used to connect the lower tower 2 with downstream equipment, for example, connecting the lower tower 2 with the reactor 11.

[0050] The present invention is a continuous multi-tower adaptive liquid level control system, which is applied to a continuous tower system with a certain buffering capacity, especially a continuous distillation tower system. It plays a role in controlling the stable extraction flow of the last tower, greatly reducing the impact of upstream disturbances on downstream production, improving control accuracy, reducing operating frequency, and providing a stable feed load for downstream equipment for the continuous tower. Among them, for two or more continuous towers, preferably the two adjacent towers in the last stage can be determined as the upper tower 1 and the lower tower 2 according to the upstream and downstream, and the upper tower 1 and the lower tower 2 are controlled by the tower liquid level control system of the present invention. Among them, the lower tower 2 is the last tower before the reactor 11. The other towers upstream of the upper tower 1 can adopt the liquid level control system of the prior art. For example, for the tower upstream of the upper tower 1, a proportional integral algorithm is used to control the extraction flow of the tower according to the absolute value of the deviation between the liquid level measurement value of the tower and the set value. Alternatively, the towers of other stages are also determined as the upper tower and the lower tower according to the upstream and downstream, and the upper tower and the lower tower of other stages are controlled by the tower liquid level control system of the present invention.

[0051] The present invention uses proportional-integral control for the upper tower, while correcting the proportional-integral for the lower tower using a nonlinear gain value. When the absolute value of the second deviation between the measured liquid level of the lower tower and the set liquid level of the lower tower is within the control dead band, the flow rate set value of the lower tower is controlled to remain stable. When the absolute value of the second deviation exceeds the control dead band, the flow rate set value of the lower tower is controlled to increase. By using the nonlinear gain value correction for the lower tower, adaptive control of the liquid level is achieved, the operating frequency is reduced, the control accuracy is improved, and the anti-interference capability is enhanced.

[0052] like Figure 2 FIG. 1 shows a tower liquid level control system according to another embodiment of the present invention, which is used in a continuous tower system. The continuous tower system includes at least an upper tower 1 located upstream and a lower tower 2 located downstream, wherein the upper tower 1 is connected to the lower tower 2. The tower liquid level control system includes: an upper tower liquid level controller 3, a lower tower liquid level controller 4, an upper tower flow controller 5, an upper tower valve 6, a lower tower flow controller 7, a lower tower valve 8, and a deviation gain calculation block 9, wherein:

[0053] The upper tower liquid level controller 3 is connected to the upper tower 1 and the lower tower liquid level controller 4 respectively, and the upper tower liquid level controller 3 measures the upper tower liquid level measurement value of the upper tower 1, determines the upper tower liquid level setting value of the upper tower liquid level controller 3 according to the lower tower liquid level measurement value of the lower tower 2 measured by the lower tower liquid level controller 4, and controls the upper tower flow setting value of the upper tower 1 through proportional integral according to the first absolute value of the deviation between the upper tower liquid level measurement value and the upper tower liquid level setting value;

[0054] The lower tower liquid level controller 4 is connected to the lower tower 2, and the lower tower liquid level controller 4 uses a nonlinear gain value to proportionally integrally correct the lower tower flow set value of the lower tower 2 according to the second absolute value of the deviation between the lower tower liquid level measurement value of the lower tower 2 and the lower tower liquid level set value. When the second absolute value of the deviation is within the control dead band, the lower tower liquid level controller 4 controls the lower tower flow set value to remain stable. When the second absolute value of the deviation exceeds the control dead band, the lower tower liquid level controller 4 controls the lower tower flow set value to increase.

[0055] The upper tower liquid level controller 3 is connected to the upper tower flow controller 5, and the upper tower liquid level controller 3 outputs the upper tower flow set value of the upper tower flow controller 5 to the upper tower flow controller 5. The upper tower flow controller 5 controls the valve opening of the upper tower valve 6 according to the upper tower flow set value and the upper tower actual flow;

[0056] The lower tower liquid level controller 4 is connected to the lower tower flow controller 7, and the lower tower liquid level controller 4 outputs the lower tower flow set value of the lower tower flow controller 7 to the lower tower flow controller 7. The lower tower flow controller 7 controls the valve opening of the lower tower valve 8 according to the lower tower flow set value and the actual flow of the lower tower;

[0057] The upper tower liquid level controller 3 is connected to the lower tower 2 through the deviation gain calculation block 9. The deviation gain calculation block 9 calculates the deviation gain of the lower tower liquid level measurement value obtained from the lower tower 2 and outputs it to the upper tower liquid level controller 3 as the upper tower liquid level set value. The deviation gain calculation block 9 is connected to the lower tower 2 through the nonlinear filter 10.

[0058] Specifically, the tower liquid level control system of this embodiment is a liquid level control system for a continuous multi-tower system. Figure 2As shown, taking the upper and lower towers as an example, the tower liquid level control system of this embodiment includes an upper tower liquid level controller 3, a cascade upper tower flow controller 5 control loop, a lower tower liquid level controller 4, a cascade lower tower flow controller 7 control loop, an upper tower valve 6, a lower tower valve 8, a deviation gain calculation block 9 (Scaling), and a nonlinear filter 10 (Filter). Among them, the upper tower liquid level controller 3 adopts the proportional integral control (proportional integral) in the standard proportional integral method, and the output value is used as the set value of the upper tower flow controller 5 in the secondary loop, that is, the upper tower flow set value. The upper tower flow controller 5 uses the existing flow control method based on the comparison result of the upper tower flow set value and the detected actual flow of the upper tower to calculate and control the valve opening of the upper tower valve 6 so that the actual flow of the upper tower is close to or consistent with the upper tower flow set value. The lower tower liquid level controller 4 adopts nonlinear gain value correction, and the output value is used as the set value of the lower tower flow controller 7 in the secondary loop, that is, the lower tower flow set value. The lower tower flow controller 7 uses existing flow control methods to calculate and control the valve opening of the lower tower valve 8 based on the comparison result of the lower tower flow set value and the lower tower actual flow rate, so that the lower tower actual flow rate is close to or consistent with the lower tower flow set value. At the same time, the measured value (PV) of the lower tower liquid level controller 4 is calculated by the deviation gain calculation block 9, and the scaled signal is sent to the upper tower liquid level controller 3 as its set value (SV), i.e., the upper tower liquid level set value.

[0059] In one embodiment, a nonlinear filter 10 is further included, and the deviation gain calculation block 9 is connected to the lower tower 2 via the nonlinear filter 10 .

[0060] The measured value (PV) of the lower tower liquid level controller 4 is used as the lower tower liquid level measurement value. After filtering by the nonlinear filter 10 and eliminating the spike, it is sent to the deviation gain calculation block 9 for deviation gain calculation. The scaled signal is sent to the upper tower liquid level controller 3 as its set value (SV), that is, the upper tower liquid level set value

[0061] In this embodiment, a nonlinear filter is used to eliminate the peak of the lower tower liquid level measurement value.

[0062] The principle analysis of this control scheme is as follows:

[0063] The upper tower liquid level controller 3 is direct acting (DIR), the upper tower flow controller 5 is reverse acting (REV), the lower tower liquid level controller 4 is direct acting (DIR), the lower tower flow controller 7 is reverse acting (REV), and all valves are air-open valves.

[0064] (1) Nonlinear gain correction principle

[0065] like Figure 3 The figure shows the principle diagram of nonlinear gain correction, where the relevant parameters of nonlinear gain correction are:

[0066] KNL is the output gain correction value, preferably 0≤KNL≤1;

[0067] NL_MINMOD is the gain applied when the absolute value of the deviation is lower than NL_GAP. When NL_MINMOD is set to 0, there is no output.

[0068] NL_GAP is the control dead zone. When the absolute value of the deviation is lower than NL_GAP, KNL = NL_MINMOD.

[0069] NL_TBAND is the conversion area where the nonlinear gain value is linearly corrected by the deviation function. It is a linear change area. In this interval, the nonlinear gain value changes linearly.

[0070] NL_HYST is a hysteresis value. When the absolute value of the deviation is less than NL_GAP + NL_HYST, KNL = NL_MINMOD. Once the absolute value of the deviation exceeds NL_GAP + NL_HYST, the absolute value of the deviation must return to a value less than NL_GAP before KNL returns to the value of NL_MINMOD.

[0071] In some embodiments:

[0072] In the process of gradually increasing the absolute value of the second deviation, if the absolute value of the second deviation is less than or equal to the control dead zone plus the hysteresis value, the nonlinear gain value is fixed; if the absolute value of the second deviation is greater than the control dead zone plus the hysteresis value, the nonlinear gain value is increased as the absolute value of the second deviation increases;

[0073] During the process of gradually decreasing the absolute value of the second deviation, if the absolute value of the second deviation is greater than the control dead zone, the nonlinear gain value is reduced as the absolute value of the second deviation decreases; if the absolute value of the second deviation is less than or equal to the control dead zone, the nonlinear gain value is a fixed value.

[0074] During actual use, the parameters depend on the liquid level fluctuation range that tower 2 can withstand. The selection of NL_GAP value and N_HYST value determines the initial control dead zone range of liquid level fluctuation. The larger the sum of the two, the larger the control dead zone, and the larger the liquid level fluctuation range that the tower needs to be able to withstand; the selection of NL_TBAND value and NL_MINMOD value determines the strength of the proportional-integral controller after exceeding the control dead zone. The larger the NL_TBAND value, the slower the change in the strength of the proportional-integral controller after the liquid level exceeds the control dead zone, that is, the slower the output changes. The larger the NL_MINMOD value, the stronger the initial effect of the proportional-integral controller after the liquid level exceeds the control dead zone.

[0075] By adjusting the above four parameters to select the desired liquid level range and the proportional-integral control intensity after exceeding the range, the controller output with nonlinear gain correction is calculated as follows, where KNL is the nonlinear gain correction value used during the change:

[0076]

[0077] Wherein, s is the second deviation absolute value, OUT(s) is the lower tower flow rate setting value corresponding to the second deviation absolute value s, and KNL is the nonlinear gain value.

[0078] In some embodiments, the lower tower liquid level controller 4 uses a nonlinear gain value to proportionally integrate and correct the lower tower flow rate set value of the lower tower 2 according to the second absolute value of the deviation between the lower tower liquid level measurement value of the lower tower 2 and the lower tower liquid level set value, including:

[0079] Calculate the flow setting value of the lower tower as follows:

[0080] Wherein: is the second deviation absolute value, OUT(s) is the lower tower flow rate setting value corresponding to the second deviation absolute value s, and KNL is the nonlinear gain value.

[0081] (2) Deviation gain calculation principle

[0082] like Figure 4 The following is the principle diagram of deviation gain calculation. Among them, IN_1 is the input value, SP is the deviation setting value, Gain is the deviation gain setting value, OUT 偏差 The output is used as the upper tower liquid level setting value. Its calculation formula is as follows, which is the calculation formula of the deviation gain calculation block 9:

[0083] OUT 偏差 =(SP+IN_1)×Gain (2)

[0084] For the deviation gain calculation block 9, ax+b can also be used as the output, where:

[0085] x is IN_1;

[0086] a is Gain;

[0087] b is SP×Gain.

[0088] The output value of the deviation gain calculation block 9 serves as the upper tower liquid level setpoint for the upper tower liquid level controller 3. The input value of the deviation gain calculation block 9 is the lower tower liquid level measurement value. Furthermore, the input value of the deviation gain calculation block 9 is the filtered liquid level measurement value after the lower tower liquid level measurement value is filtered by the nonlinear filter 10.

[0089] In actual application, the Gain value must be determined based on the liquid level relationship between lower tower 2 and upper tower 1 and the buffering capacity of each liquid level. If the liquid level controlled by upper tower 1 is lower than that of lower tower 2, the SP value is negative; if the liquid level controlled by upper tower 1 is higher than that of lower tower 2, the SP value is positive. If the buffering capacity of upper tower 1 is greater than that of lower tower 1, the Gain value is less than 1; if the buffering capacity of upper tower 1 is less than that of lower tower 2, the Gain value is greater than 1. By adjusting the above parameters, the liquid level and change signal of lower tower 2 are sent to upper tower 1.

[0090] In some embodiments, the deviation gain calculation block 9 calculates the deviation gain of the lower tower liquid level measurement value obtained from the lower tower 2 and outputs it to the upper tower liquid level controller 3 as the upper tower liquid level set value, including:

[0091] Calculate the upper tower liquid level setting value to be OUT 偏差 =(SP+IN_1)×Gain, where IN_1 is the liquid level measurement value after filtration or the liquid level measurement value of the lower tower, SP is the deviation setting value, Gain is the deviation gain setting value, OUT 偏差 Set the value for the upper tower liquid level.

[0092] (3) Analysis of the working mode of the control scheme

[0093] Before the interference, the upper and lower towers were in a stable operating state, the feeding of the upper tower 1 was unperturbed, the upper tower liquid level measurement value measured by the upper tower liquid level controller 3 was stable, the set value of the upper tower flow controller 5 for controlling the production flow of the upper tower 1 was stable, the feeding of the lower tower 2 was unperturbed, the lower tower liquid level measurement value measured by the lower tower liquid level controller 4 was stable, the set value of the lower tower flow controller 7 for controlling the production flow of the lower tower 2 was stable, and there was no disturbance in the feeding to the downstream reactor 11.

[0094] When the feed flow of the upper tower 1 increases, the upper tower liquid level measurement value increases. Since the upper tower liquid level controller 3 adopts standard proportional integral control and is positive, its output increases, the set value of the upper tower flow controller 5 increases, the production flow increases, and the lower tower liquid level measurement value increases. Since the lower tower liquid level controller 4 adopts nonlinear gain value correction control, the lower tower liquid level measurement value is in the control dead zone. Although the liquid level will rise, it will not control the set value of the lower tower flow controller 7 to increase, and the set value of the lower tower flow controller 7 remains stable. At the same time, the lower tower liquid level measurement value of the lower tower is filtered by the nonlinear filter 10 (if the liquid level changes smoothly and there is no measurement burr, the nonlinear filter can be selected without using it). After eliminating the spike, the deviation gain calculation block 9 performs deviation gain calculation, and the scaled signal is sent to the upper tower liquid level controller 3 as its set value. The set value of the upper tower liquid level controller 3 increases, and the absolute value of the first deviation from the upper tower liquid level measurement value decreases. The output value of the upper tower liquid level controller 3 becomes gentle, and then the increase in the set value of the upper tower flow controller 5 slows down. The set value of the upper tower flow controller 5 changes smoothly, and the increase in the lower tower liquid level measurement value further slows down, and it is in the control dead zone for a longer time. The set value of the lower tower flow controller 7 remains stable.

[0095] After the upper tower feed flow is restored, the upper tower liquid level measurement value no longer increases, the lower tower liquid level measurement value no longer increases, and is in the control dead zone, and the set value of the lower tower flow controller 7 is stable.

[0096] If the lower tower liquid level measurement continues to rise and exceeds the control dead zone, the output of lower tower liquid level controller 4 will slowly increase under the nonlinear gain correction, and the set point of lower tower flow controller 7 will slowly increase, with minimal impact on the downstream. Until the lower tower liquid level measurement re-enters the control dead zone, the set point of lower tower flow controller 7 will return to its original value and no longer change.

[0097] Similarly, when the feed flow rate of the upper tower decreases, the upper tower liquid level measurement value decreases. Since the upper tower liquid level controller 3 adopts standard proportional integral control and is positive, its output decreases, the set value of the upper tower flow controller 5 decreases, the production flow decreases, and the lower tower liquid level measurement value decreases. Since the lower tower liquid level controller 4 adopts nonlinear gain value correction control, the lower tower liquid level measurement value is in the control dead zone. Although the liquid level will decrease, it will not control the lower tower flow controller 7 set value to decrease, and the lower tower flow controller 7 set value remains stable. At the same time, the lower tower liquid level measurement value of the lower tower is filtered by the nonlinear filter 10 (if the liquid level changes steadily and there is no measurement burr, the nonlinear filter can be selected without using it). After eliminating the spike, the deviation gain calculation block 9 is used to calculate the deviation gain. The scaled signal is sent to the upper tower liquid level controller 3 as its set value. The set value of the upper tower liquid level controller 3 decreases, and the absolute value of the first deviation from the upper tower liquid level measurement value decreases. The output value of the upper tower liquid level controller 3 becomes gentle, and then the decrease amplitude of the set value of the upper tower flow controller 5 slows down. The set value of the upper tower flow controller 5 changes steadily, and the decrease amplitude of the lower tower liquid level measurement value further slows down, and it is in the control dead zone for a longer time. The set value of the lower tower flow controller 7 remains stable.

[0098] After the feed flow of the upper tower 1 is restored, the upper tower liquid level measurement value no longer decreases, the lower tower liquid level measurement value no longer decreases, and is in the control dead zone, and the set value of the lower tower flow controller 7 is stable.

[0099] If the lower tower liquid level measurement continues to drop, exceeding the control dead zone, the lower tower liquid level controller 4, under nonlinear gain correction, slowly reduces its output, and the setpoint of the lower tower flow controller 7 slowly decreases, with minimal impact on the downstream. Until the lower tower liquid level measurement re-enters the control dead zone, the setpoint of the lower tower flow controller 7 returns to its original value and does not change.

[0100] This embodiment can achieve adaptive control of the liquid level in the continuous tower system by introducing the nonlinear gain value correction of the proportional-integral controller, a nonlinear filter (used as needed), and a deviation gain calculation module. When a disturbance occurs at the source, there is almost no impact on the downstream. The buffering capacity of the liquid level is fully utilized, the operating frequency is reduced, the control accuracy is improved, the anti-interference ability is enhanced, and a stable feed load is ensured for the downstream equipment.

[0101] This embodiment is described by taking two continuous distillation towers in a certain process of citral as an example.

[0102] Upper tower level controller 3 uses proportional integral control (PI) in the standard proportional integral method, which is a positive action. The output value is used as the set value of upper tower flow controller 5 in the auxiliary loop. Upper tower flow controller 5 is a negative action. Lower tower level controller 4 uses nonlinear gain correction control (SSVC) for positive action. The output value is used as the set value of lower tower flow controller 7 in the auxiliary loop. Lower tower flow controller 7 is a negative action. All valves are air-open valves. The lower tower liquid level changes smoothly without measurement glitches. No nonlinear filter is used.

[0103] (1) Nonlinear gain correction

[0104] The lower tower liquid level high alarm value is 80%, the liquid level high-high interlock value is 90%, the liquid level low alarm value is 20%, the liquid level low-low interlock value is 10%, and the normal liquid level is controlled at 50%. The GAP value is 10, the HYST value is 5, the TBAND value is 10, the MINMOD value is 0, and the liquid level control deadband range is 35%-65%.

[0105] (2) Deviation gain calculation

[0106] The upper tower liquid level high alarm value is 80%, the high-high liquid level interlock value is 90%, the low liquid level alarm value is 20%, the low-low liquid level interlock value is 10%, and the normal liquid level is controlled at 50%. The upper and lower tower liquid level buffering capacities are equivalent. SP is set to 0, and GAIN is set to 1.

[0107] (3) Control scheme example

[0108] During normal operation, the feed rate of upper tower 1 is 6.8 t / h, and the discharge rate of lower tower 2 to reactor 11 is 5.8 t / h. The liquid levels of the two towers and their respective extraction rates are stable, and the downstream reactor is fed smoothly.

[0109] At a certain moment, the feed flow rate of the upper tower gradually increases to 7.5 t / h, and the upper tower liquid level measurement value rises. Since the upper tower liquid level controller 3 uses standard proportional-integral control and is positive-acting, its output increases, the set value of the upper tower flow controller 5 increases, the extraction flow rate increases, and the lower tower liquid level measurement value rises. Since the lower tower liquid level controller 2 uses nonlinear gain correction control, the lower tower liquid level measurement value is within the control dead zone. Although the liquid level will rise, it will not cause the set value of the lower tower flow controller 7 to increase. The set value of the lower tower flow controller 7 remains stable at 5.8 t / h. At the same time, the rising lower tower liquid level measurement value is calculated through the deviation gain, scaled, and sent to the upper tower liquid level controller 3 as its set value. The set value of the upper tower liquid level controller 3 increases, and the deviation from the upper tower liquid level measurement value decreases, and its output value becomes smoother. As a result, the increase in the set value of the upper tower flow controller 5 slows down, and the set value of the upper tower flow controller 5 changes steadily. The increase in the lower tower liquid level measurement value further slows down, and the set value of the lower tower flow controller 7 remains stable at 5.8 t / h.

[0110] After the feed flow rate of the upper tower gradually recovered to 6.8t / h, the liquid level measurement value of the upper tower no longer increased, the liquid level measurement value of the lower tower no longer increased, and was in the control dead zone. The setting value of the lower tower flow controller 7 was 5.8t / h from beginning to end.

[0111] At another moment, the feed flow rate of the upper tower gradually decreases to 5.8 t / h, and the upper tower liquid level measurement value decreases. Since the upper tower liquid level controller 3 adopts standard proportional-integral control and is positive, its output decreases, the set value of the upper tower flow controller 5 decreases, the extraction flow rate decreases, and the lower tower liquid level measurement value decreases. Since the lower tower liquid level controller 4 adopts nonlinear gain correction control, the lower tower liquid level measurement value is within the control dead zone. Although the liquid level will decrease, it will not cause the set value of the lower tower flow controller 7 to decrease. The set value of the lower tower flow controller 7 remains stable at 5.8 t / h. At the same time, the lower tower liquid level measurement value is calculated by the deviation gain, scaled, and sent to the upper tower liquid level controller 3 as its set value. The set value of the upper tower liquid level controller 3 decreases, and the deviation from the upper tower liquid level measurement value decreases. Its output value becomes smoother, and the decrease in the set value of the upper tower flow controller 5 slows down. The set value of the upper tower flow controller 5 changes steadily, and the decrease in the lower tower liquid level measurement value further slows down. The set value of the lower tower flow controller 7 remains stable at 5.8 t / h.

[0112] After the feed flow rate of the upper tower gradually recovered to 6.8t / h, the liquid level measurement value of the upper tower no longer decreased, and the liquid level measurement value of the lower tower no longer decreased, and was in the control dead zone. The setting value of the lower tower flow controller 7 was 5.8t / h from beginning to end.

[0113] After citral device implements the continuous distillation tower adaptive control scheme described in the present embodiment, the liquid level buffering capacity of distillation tower is fully utilized, the problem of frequent changes in the reactor feed load caused by the deviation transmission of upstream disturbance and controller is perfectly solved, and the scheme is to carry out configuration adjustment based on existing hardware equipment, without normal impact on production. The liquid level buffering capacity of upper and lower two towers is strong, can withstand long-term disturbance, gives enough self-regulation time to the system, significantly reduces operating frequency, improves control accuracy. If abnormal operating condition duration is long, disturbance is large, the scheme can also provide longer process safety time for operating personnel to carry out abnormal disposal.

[0114] like Figure 5 The figure shows a workflow diagram of a tower liquid level control method according to an embodiment of the present invention, which is used in a continuous tower system. The continuous tower system includes at least an upper tower 1 located upstream and a lower tower 2 located downstream. The upper tower 1 is connected to the lower tower 2. The liquid level control method includes:

[0115] Step S501, obtaining the upper tower liquid level measurement value of the upper tower 1 and the lower tower liquid level measurement value of the lower tower 2;

[0116] Step S502, determining the upper tower liquid level setting value according to the lower tower liquid level measurement value;

[0117] Step S503, calculating the upper tower flow rate setting value of the upper tower 1 by proportional integration according to the first absolute value of the deviation between the upper tower liquid level measurement value and the upper tower liquid level setting value;

[0118] Step S504 , calculating the lower tower flow rate setting value of the lower tower 2 by performing proportional integral correction using a nonlinear gain value according to the second absolute value of the deviation between the lower tower liquid level measurement value and the lower tower liquid level setting value.

[0119] Specifically, the tower liquid level control method of this embodiment can be applied to the tower liquid level control system described above.

[0120] First, step S501 is performed to obtain the upper tower liquid level measurement value of the upper tower 1 and the lower tower liquid level measurement value of the lower tower 2.

[0121] Specifically, an upper tower 1 and a lower tower 2 are connected by a pipeline. The upper tower 1 is the upstream tower, and the lower tower 2 is the downstream tower. The towers are preferably distillation towers. The liquid level of the upper tower 1 can be measured by an upper tower liquid level controller 3 to obtain an upper tower liquid level measurement value. The liquid level of the lower tower 2 can be measured by a lower tower liquid level controller 4 to obtain a lower tower liquid level measurement value.

[0122] In some embodiments, downstream of the lower column 2 is a reactor 11 .

[0123] Then, step S502 is executed to determine the upper tower liquid level setting value according to the lower tower liquid level measurement value.

[0124] Then, step S503 is executed to calculate the upper tower flow rate setting value of the upper tower 1 by proportional integration according to the first absolute value of the deviation between the upper tower liquid level measurement value and the upper tower liquid level setting value.

[0125] Specifically, a proportional-integral algorithm is used to calculate the absolute value of a first deviation between the upper tower liquid level measurement value and the upper tower liquid level set value. Based on this absolute value, the proportional-integral algorithm is used to control the upper tower flow set value of upper tower 1. The upper tower flow set value is used to control the valve opening of upper tower valve 6 between upper tower 1 and lower tower 2, thereby controlling the flow rate of material flowing from upper tower 1 to lower tower 2.

[0126] Specifically, the upper tower flow rate set value is a set value of the upper tower flow rate controller 5. The upper tower flow rate controller 5 controls the valve opening of the upper tower valve 6 according to the upper tower flow rate set value and the upper tower actual flow rate.

[0127] At the same time, step S504 is executed to calculate the lower tower flow rate setting value of the lower tower 2 by using a nonlinear gain value for proportional integral correction according to the second absolute value of the deviation between the lower tower liquid level measurement value and the lower tower liquid level setting value.

[0128] Specifically, a proportional-integral algorithm is used to control the lower tower flow set value of the lower tower 2 according to the second absolute value of the deviation between the lower tower liquid level measurement value and the lower tower liquid level set value. However, unlike the control of the upper tower 1, the control of the lower tower 2 uses a nonlinear gain value to correct the proportional integral and output the lower tower flow set value, so that when the second absolute value of the deviation is within the control dead zone, the lower tower flow set value is controlled to remain stable; when the second absolute value of the deviation exceeds the control dead zone, the lower tower flow set value is controlled to increase.

[0129] The lower tower flow rate setting value is used to control the valve opening of the lower tower valve 8 connected to the lower tower 2. The lower tower valve 8 is used to connect the lower tower 2 with downstream equipment, such as connecting the lower tower 2 with the reactor 11.

[0130] Specifically, the lower tower flow rate setting value is the setting value of the lower tower flow rate controller 7. The lower tower flow rate controller 7 controls the valve opening of the lower tower flow controller 8 according to the lower tower flow rate setting value and the actual flow rate of the lower tower.

[0131] The present invention uses proportional-integral control for the upper tower, while correcting the proportional-integral for the lower tower using a nonlinear gain value. When the absolute value of the second deviation between the measured liquid level of the lower tower and the set liquid level of the lower tower is within the control dead band, the flow rate set value of the lower tower is controlled to remain stable. When the absolute value of the second deviation exceeds the control dead band, the flow rate set value of the lower tower is controlled to increase. By using the nonlinear gain value correction for the lower tower, adaptive control of the liquid level is achieved, the operating frequency is reduced, the control accuracy is improved, and the anti-interference capability is enhanced.

[0132] like Figure 6 FIG2 is a flowchart of a tower liquid level control method according to another embodiment of the present invention, which is used in a continuous tower system. The continuous tower system includes at least an upper tower 1 located upstream and a lower tower 2 located downstream, wherein the upper tower 1 is connected to the lower tower 2. The liquid level control method includes:

[0133] Step S601 , obtaining the upper tower liquid level measurement value of the upper tower 1 and the lower tower liquid level measurement value of the lower tower 2 .

[0134] Step S602: determining the upper tower liquid level setting value according to the lower tower liquid level measurement value.

[0135] In one embodiment, determining the upper tower liquid level setting value according to the lower tower liquid level measurement value includes:

[0136] A deviation gain calculation is performed on the lower tower liquid level measurement value to obtain an upper tower liquid level setting value.

[0137] In one embodiment, performing deviation gain calculation on the lower tower liquid level measurement value to obtain the upper tower liquid level setting value includes:

[0138] Obtaining a filtered liquid level measurement value obtained by performing nonlinear filtering on the lower tower liquid level measurement value;

[0139] Calculate the upper tower liquid level setting value to be OUT 偏差 =(SP+IN_1)×Gain, where IN_1 is the liquid level measurement value after filtering, SP is the deviation setting value, Gain is the deviation gain setting value, OUT 偏差 Set the value for the upper tower liquid level.

[0140] Step S603 , calculating the upper tower flow rate setting value of the upper tower 1 by proportional integration according to the first absolute value of the deviation between the upper tower liquid level measurement value and the upper tower liquid level setting value.

[0141] Step S604: determining the nonlinear gain value according to the relationship between the absolute value of the second deviation and the control dead zone.

[0142] In one embodiment, determining the nonlinear gain value according to the relationship between the absolute value of the second deviation and the control dead zone includes:

[0143] In the process of gradually increasing the absolute value of the second deviation, if the absolute value of the second deviation is less than or equal to the control dead zone plus the hysteresis value, the nonlinear gain value is fixed; if the absolute value of the second deviation is greater than the control dead zone plus the hysteresis value, the nonlinear gain value is increased as the absolute value of the second deviation increases;

[0144] During the process of gradually decreasing the absolute value of the second deviation, if the absolute value of the second deviation is greater than the control dead zone, the nonlinear gain value is reduced as the absolute value of the second deviation decreases; if the absolute value of the second deviation is less than or equal to the control dead zone, the nonlinear gain value is a fixed value.

[0145] Step S605 , calculating the lower tower flow rate setting value of the lower tower 2 by performing proportional integral correction using a nonlinear gain value according to the second absolute value of the deviation between the lower tower liquid level measurement value and the lower tower liquid level setting value.

[0146] In one embodiment, the calculating of the lower tower flow rate setting value for controlling the lower tower 2 by using a nonlinear gain value for proportional-integral correction based on the second absolute value of the deviation between the lower tower liquid level measurement value and the lower tower liquid level setting value comprises:

[0147] Calculate the flow setting value of the lower tower as follows:

[0148] Wherein: is the second deviation absolute value, OUT(s) is the lower tower flow rate setting value corresponding to the second deviation absolute value s, and KNL is the nonlinear gain value.

[0149] Specifically, first, step S601 is performed to obtain the upper tower liquid level measurement value of the upper tower 1 and the lower tower liquid level measurement value of the lower tower 2.

[0150] Then, step S602 is executed to determine the upper tower liquid level setting value according to the lower tower liquid level measurement value.

[0151] In one embodiment, determining the upper tower liquid level setting value according to the lower tower liquid level measurement value includes:

[0152] A deviation gain calculation is performed on the lower tower liquid level measurement value to obtain an upper tower liquid level setting value.

[0153] Specifically, the deviation gain calculation block 9 can be used to perform the deviation gain calculation. After the deviation gain calculation is performed based on the lower tower liquid level measurement value, the output is used as the upper tower liquid level setting value.

[0154] In one embodiment, performing deviation gain calculation on the lower tower liquid level measurement value to obtain the upper tower liquid level setting value includes:

[0155] Obtaining a filtered liquid level measurement value obtained by performing nonlinear filtering on the lower tower liquid level measurement value;

[0156] Calculate the upper tower liquid level setting value to be OUT 偏差 =(SP+IN_1)×Gain, where IN_1 is the liquid level measurement value after filtering, SP is the deviation setting value, Gain is the deviation gain setting value, OUT 偏差 Set the value for the upper tower liquid level.

[0157] Specifically, a nonlinear filter 10 can be used to filter the lower tower liquid level measurement value, eliminate the peak, and obtain the filtered liquid level measurement value, and then use formula (2) to calculate the upper tower liquid level setting value.

[0158] In actual application, the Gain value must be determined based on the liquid level relationship between lower tower 2 and upper tower 1 and the buffering capacity of each liquid level. If the liquid level controlled by upper tower 1 is lower than that of lower tower 2, the SP value is negative; if the liquid level controlled by upper tower 1 is higher than that of lower tower 2, the SP value is positive. If the buffering capacity of upper tower 1 is greater than that of lower tower 1, the Gain value is less than 1; if the buffering capacity of upper tower 1 is less than that of lower tower 2, the Gain value is greater than 1. By adjusting the above parameters, the liquid level and change signal of lower tower 2 are sent to upper tower 1.

[0159] Then, step S603 is executed to control the upper tower flow rate setting value of the upper tower 1 through proportional integral calculation according to the first absolute value of the deviation between the upper tower liquid level measurement value and the upper tower liquid level setting value.

[0160] Specifically, the output value of the upper tower liquid level controller 3 is calculated by a proportional integral algorithm according to the first absolute value of the deviation between the upper tower liquid level measurement value and the upper tower liquid level setting value, and is used as the upper tower flow setting value. The upper tower flow setting value is used as the setting value of the upper tower flow controller 5, and the upper tower flow controller 5 is used to control the valve opening of the upper tower valve 6.

[0161] At the same time, step S604 is executed to determine the nonlinear gain value according to the relationship between the second deviation absolute value and the control dead zone.

[0162] In one embodiment, determining the nonlinear gain value according to the relationship between the absolute value of the second deviation and the control dead zone includes:

[0163] In the process of gradually increasing the absolute value of the second deviation, if the absolute value of the second deviation is less than or equal to the control dead zone plus the hysteresis value, the nonlinear gain value is fixed; if the absolute value of the second deviation is greater than the control dead zone plus the hysteresis value, the nonlinear gain value is increased as the absolute value of the second deviation increases;

[0164] During the process of gradually decreasing the absolute value of the second deviation, if the absolute value of the second deviation is greater than the control dead zone, the nonlinear gain value is reduced as the absolute value of the second deviation decreases; if the absolute value of the second deviation is less than or equal to the control dead zone, the nonlinear gain value is a fixed value.

[0165] Specifically, when the absolute value of the second deviation increases, the nonlinear gain value is changed only when it exceeds the control dead zone plus the hysteresis value. After exceeding the control dead zone plus the hysteresis value, the nonlinear gain value increases with the increase of the absolute value of the second deviation.

[0166] When the absolute value of the second deviation decreases, the nonlinear gain value is set to a fixed value as long as it is less than the control dead zone. When the absolute value of the second deviation exceeds the control dead zone, the nonlinear gain value is reduced as the absolute value of the second deviation decreases.

[0167] In some embodiments, when the absolute value of the second deviation increases, after the absolute value of the second deviation exceeds the control dead zone plus the hysteresis value, the nonlinear gain value is proportional to the absolute value of the second deviation; when the absolute value of the second deviation decreases, when the absolute value of the second deviation is greater than the control dead zone, the nonlinear gain value is proportional to the absolute value of the second deviation.

[0168] Specifically, when the absolute value of the second deviation increases, after the absolute value of the second deviation exceeds the control dead band plus the hysteresis value, the absolute value of the second deviation is input into the linear deviation function, and the corresponding nonlinear gain value is output. When the absolute value of the second deviation decreases, after the absolute value of the second deviation exceeds the control dead band, the absolute value of the second deviation is input into the linear deviation function, and the corresponding nonlinear gain value is output.

[0169] In this embodiment, as the absolute value of the second deviation increases, the change in the nonlinear gain value is delayed. However, as the absolute value of the second deviation decreases, the nonlinear gain value is set to a fixed value until it falls below the control dead band. This embodiment can expand the control dead band range, making greater use of the buffering capacity of the liquid level, and can more quickly adaptively adjust back to the dead band range when the measured value exceeds the dead band range.

[0170] Finally, step S605 is executed to calculate the lower tower flow rate setting value for controlling the lower tower 2 by using a nonlinear gain value for proportional integral correction according to the second absolute value of the deviation between the lower tower liquid level measurement value and the lower tower liquid level setting value.

[0171] In one embodiment, the calculating of the lower tower flow rate setting value for controlling the lower tower 2 by using a nonlinear gain value for proportional-integral correction based on the second absolute value of the deviation between the lower tower liquid level measurement value and the lower tower liquid level setting value comprises:

[0172] Calculate the flow setting value of the lower tower as follows:

[0173] Wherein: is the second deviation absolute value, OUT(s) is the lower tower flow rate setting value corresponding to the second deviation absolute value s, and KNL is the nonlinear gain value.

[0174] The proportional-integral correction of this embodiment, by introducing a nonlinear gain coefficient, better utilizes the buffering capacity of the system itself, expands the adaptive adjustment range, reduces the operating frequency, and improves the control accuracy.

[0175] This embodiment can achieve adaptive control of the liquid level by introducing nonlinear gain correction, nonlinear filtering, and deviation gain calculation of the proportional-integral controller. When disturbances occur at the source, there is almost no impact on the downstream. The buffering capacity of the liquid level is fully utilized, the operating frequency is reduced, the control accuracy is improved, the anti-interference ability is enhanced, and a stable feed load is ensured for the downstream equipment.

[0176] It should be understood that the size of the serial numbers of the steps in the above embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0177] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A tower liquid level control system for a continuous tower system, the continuous tower system comprising at least an upper tower (1) located upstream and a lower tower (2) located downstream, the upper tower (1) being connected to the lower tower (2), characterized in that: The tower liquid level control system comprises: an upper tower liquid level controller (3) and a lower tower liquid level controller (4), wherein: The upper tower liquid level controller (3) is connected to the upper tower (1) and the lower tower liquid level controller (4) respectively, and the upper tower liquid level controller (3) measures the upper tower liquid level measurement value of the upper tower (1), determines the upper tower liquid level setting value of the upper tower liquid level controller (3) according to the lower tower liquid level measurement value of the lower tower (2) measured by the lower tower liquid level controller (4), and controls the upper tower flow setting value of the upper tower (1) through proportional integral according to the first absolute value of the deviation between the upper tower liquid level measurement value and the upper tower liquid level setting value; The lower tower liquid level controller (4) is connected to the lower tower (2). The lower tower liquid level controller (4) uses a nonlinear gain value to proportionally integrally correct the lower tower flow rate setting value of the lower tower (2) according to a second absolute value of a deviation between a lower tower liquid level measurement value of the lower tower (2) and a lower tower liquid level setting value. When the second absolute value of the deviation is within a control dead zone, the lower tower liquid level controller (4) controls the lower tower flow rate setting value to remain stable. When the second absolute value of the deviation exceeds the control dead zone, the lower tower liquid level controller (4) controls the lower tower flow rate setting value to increase.

2. The tower liquid level control system according to claim 1, characterized in that: It also includes an upper tower flow controller (5), an upper tower valve (6) located between the upper tower (1) and the lower tower (2), a lower tower flow controller (7), and a lower tower valve (8) connected to the lower tower (2); The upper tower liquid level controller (3) is connected to the upper tower flow controller (5), the upper tower liquid level controller (3) outputs the upper tower flow setting value of the upper tower flow controller (5) to the upper tower flow controller (5), and the upper tower flow controller (5) controls the valve opening of the upper tower valve (6) according to the upper tower flow setting value and the upper tower actual flow; The lower tower liquid level controller (4) is connected to the lower tower flow controller (7), and the lower tower liquid level controller (4) outputs the lower tower flow setting value of the lower tower flow controller (7) to the lower tower flow controller (7). The lower tower flow controller (7) controls the valve opening of the lower tower valve (8) according to the lower tower flow setting value and the lower tower actual flow.

3. The tower liquid level control system according to claim 1, characterized in that: The invention also comprises a deviation gain calculation block (9), wherein the upper tower liquid level controller (3) is connected to the lower tower (2) via the deviation gain calculation block (9), and the deviation gain calculation block (9) performs deviation gain calculation on the lower tower liquid level measurement value obtained from the lower tower (2) and outputs the obtained value to the upper tower liquid level controller (3) as the upper tower liquid level set value.

4. The tower liquid level control system according to claim 3, characterized in that: It also includes a nonlinear filter (10), and the deviation gain calculation block (9) is connected to the lower tower (2) through the nonlinear filter (10).

5. A tower liquid level control method for a continuous tower system, the continuous tower system comprising at least an upper tower (1) located upstream and a lower tower (2) located downstream, the upper tower (1) being connected to the lower tower (2), characterized in that: The liquid level control method comprises: Obtaining a measured value of the upper tower liquid level of the upper tower (1) and a measured value of the lower tower liquid level of the lower tower (2); Determine the upper tower liquid level setting value according to the lower tower liquid level measurement value; Calculating an upper tower flow rate setting value of the upper tower (1) by proportional integration according to a first absolute value of a deviation between the upper tower liquid level measurement value and the upper tower liquid level setting value; According to the absolute value of the second deviation between the lower tower liquid level measurement value and the lower tower liquid level setting value, a nonlinear gain value is used for proportional integral correction to calculate the lower tower flow setting value of the lower tower (2).

6. The tower liquid level control method according to claim 5, characterized in that: Also includes: The nonlinear gain value is determined according to the relationship between the second deviation absolute value and the control dead zone.

7. The tower liquid level control method according to claim 6, characterized in that: The determining the nonlinear gain value according to the relationship between the second deviation absolute value and the control dead zone includes: In the process that the absolute value of the second deviation gradually increases, if the absolute value of the second deviation is less than or equal to the control dead zone plus the hysteresis value, the nonlinear gain value is a fixed value; if the absolute value of the second deviation is greater than the control dead zone plus the hysteresis value, the nonlinear gain value is increased as the absolute value of the second deviation increases; In the process of gradually decreasing the absolute value of the second deviation, if the absolute value of the second deviation is greater than the control dead zone, the nonlinear gain value is reduced as the absolute value of the second deviation decreases; if the absolute value of the second deviation is less than or equal to the control dead zone, the nonlinear gain value is a fixed value.

8. The tower liquid level control method according to claim 5, characterized in that: The method of using a nonlinear gain value to perform proportional integral correction according to a second absolute value of a deviation between the lower tower liquid level measurement value and the lower tower liquid level setting value to calculate the lower tower flow setting value of the lower tower (2) comprises: Calculate the flow setting value of the lower tower: Wherein s is the second deviation absolute value, OUT(s) is the lower tower flow setting value corresponding to the second deviation absolute value s, and KNL is the nonlinear gain value.

9. The tower liquid level control method according to claim 5, characterized in that: Determining the upper tower liquid level setting value according to the lower tower liquid level measurement value comprises: The deviation gain calculation is performed on the lower tower liquid level measurement value to obtain the upper tower liquid level setting value.

10. The tower liquid level control method according to claim 9, characterized in that: The step of performing deviation gain calculation on the lower tower liquid level measurement value to obtain the upper tower liquid level setting value comprises: Obtaining a filtered liquid level measurement value obtained by performing nonlinear filtering on the lower tower liquid level measurement value; Calculate the upper tower liquid level setting value to be OUT 偏差 =(SP+IN_1)×Gain, where IN_1 is the liquid level measurement value after filtering, SP is the deviation setting value, Gain is the deviation gain setting value, OUT 偏差 Set the value for the upper tower liquid level.

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