Multivariable interface control method of electric desalting tank

Abstract

The invention discloses a multivariable interface control method of an electric desalting tank. The multivariable interface control method comprises the following steps: determining an interface control interval of an emulsification area and a water area; a plurality of viscosity sensors are arranged in the electric desalting tank; the arrangement positions of the viscosity sensors at least comprise a first detection position located between the electrode plate and the oil distribution pipe, a second detection position where the upper limit of the control interval is located, a third detection position where the lower limit of the control interval is located, and a fourth detection position between the third detection position and the sewage cut-out pipe; reading the viscosity measurement value of the viscosity sensor at each detection position, comparing the viscosity measurement value at each detection position with the viscosity value of the emulsification area and the viscosity value of the water area, and adjusting the sewage cut-out valve according to the comparison result. According to the method, the relative interval of the viscosity detection result is combined with multivariable control, so that the oil-water interface can be effectively controlled to fluctuate in a control interval, and the requirements of industrial production are met.

Description

Technical Field

[0001] The invention relates to a control method design for an industrial process, and in particular to a multivariable boundary position control method in an electric desalination tank, which controls the boundary position of an emulsification zone and a water zone. Background Art

[0002] The electric desalter is an indispensable device for oil refining enterprises. Accurate control of the oil-water interface of the electric desalter is an important guarantee for the stable operation of the atmospheric and vacuum desalter. If the oil-water interface is too high, the crude oil will carry water after desalting, resulting in tower flushing accidents in the primary distillation tower, increased power consumption and waste of water resources. If the oil-water interface is too low, the oil content of the discharged wastewater will increase, making it more difficult to treat the subsequent oily and salty wastewater, and significantly increasing the cost of wastewater treatment, and even causing oil leakage accidents and environmental accidents such as substandard wastewater discharge.

[0003] The primary problem facing the interface control of the electric desalter is that it is difficult to accurately and stably detect the interface between the emulsified area and the water area. At present, most of the oil-water interface detection instruments for domestic electric desalters are instruments based on electromagnetic principles such as radio frequency admittance and microwaves. Changes in crude oil types, salt content in oil and water, and changes in the emulsification form of sewage will cause the interface instruments to be inaccurate. Taking microwave radar-type interface instruments as an example, they are usually installed near the pipeline of the electric desalter. It is impossible to avoid multiple reflections caused by microwaves hitting the pipeline wall, resulting in enhanced reflected waves and amplified received microwaves, causing inaccurate measurements. As a result, it is impossible to automatically control the interface between the emulsified area and the water area. In addition, the control requirement for the interface of the electric desalter is to control the oil-water interface within a range, and the fluctuations within the range can be regarded as normal production conditions. Therefore, from the perspective of industrial needs, the detection requirements for the interface between the emulsified area and the water area are also relative to the range, rather than requiring absolute physical positions.

[0004] The second problem faced by the interface control of the electric desalination tank is that when the interface between the emulsification zone and the water zone is at different positions, the control requirements are different. Simple single-loop interface control is difficult to meet the control requirements of multiple areas. Summary of the invention

[0005] The purpose of the present invention is to overcome the problems existing in the above-mentioned prior art and provide a multivariable interface control method for an electric desalting tank, which uses the viscosity value to indirectly react to the interface position between the emulsification zone and the water zone in the tank and control the interface within a desired range.

[0006] To achieve the above object, the present invention adopts the following scheme:

[0007] A multivariable boundary position control method for an electric desalting tank, comprising:

[0008] Determine the control interval of the boundary between the emulsification zone and the water zone;

[0009] Multiple viscosity sensors are arranged in the electric desalination tank, and the arrangement positions of the viscosity sensors include at least:

[0010] a first detection position between the electrode plate and the oil distribution pipe, a second detection position where the upper limit of the control interval is located, a third detection position where the lower limit of the control interval is located, and a fourth detection position between the third detection position and the sewage cut-out pipe;

[0011] Read the viscosity measurement value of the viscosity sensor at each detection position, compare the viscosity measurement value at each detection position with the viscosity value of the emulsification area and the water area, and adjust the sewage cut-out valve according to the comparison result.

[0012] The present invention arranges viscosity sensors at multiple positions in the electric desalting tank to detect viscosity, and uses the viscosity value to indirectly react to the boundary position between the emulsification zone and the water zone in the tank, thereby controlling the boundary position within a required range.

[0013] As a preferred embodiment, the control interval of the boundary between the emulsification zone and the water zone is set to be between 1-2 cm above the water flushing pipe in the electric desalination tank and 1-5 cm below the water flushing pipe.

[0014] As a preferred embodiment, the viscosity sensor is a vibration viscosity sensor. The principle of the vibration online viscometer is that the sensor probe performs an amplitude motion of a certain frequency in the fluid. Due to the effect of the fluid viscous damping, the amplitude of the probe will decay, and the energy lost due to the fluid viscous damping will be supplemented to maintain the amplitude of the probe at the state before the effect with the fluid. This part of the supplemented energy is related to the viscosity of the fluid. By measuring this part of the supplemented energy, the viscosity of the fluid can be calculated according to a certain relationship. Therefore, when measuring the oil-water interface of electrical desalination, the viscosity values ​​of the water layer, the emulsion layer and the oil layer are very different. Using a vibration viscometer, the position of the water layer can be directly reflected according to the size of the supplemented amplitude energy.

[0015] As a preferred embodiment, the first detection position is located below the electrode plate in the electric desalting tank and 2-4 cm above the oil distribution pipe;

[0016] The second detection position is located 1-2 cm above the water flushing pipe in the electric desalination tank;

[0017] The third detection position is located 1-5 cm below the water flushing pipe in the electric desalination tank;

[0018] The fourth detection position is located below the third detection position in the electric desalination tank and 1-5 cm above the sewage cut-out pipe.

[0019] As a preferred implementation, the adjustment of the sewage cut-out valve according to the comparison result includes:

[0020] Respectively read the first viscosity measurement value μ1, the second viscosity measurement value μ2, the third viscosity measurement value μ3, and the fourth viscosity measurement value μ4 collected by the viscosity sensor at the first, second, third, and fourth detection positions;

[0021] Determine the typical viscosity values ​​of the emulsified zone and the water zone as μ 乳化区 , μ 水区 ;

[0022] When μ2>μ 水区 And μ3<μ 乳化区 , maintain the current boundary position;

[0023] When μ2≤μ 水区 , adjust the sewage cut-out valve to increase the flow rate;

[0024] When μ3 ≥ μ 乳化区 , adjust the sewage cut-out valve to reduce the flow rate;

[0025] Or μ1≤μ 水区 or μ4 ≥ μ 乳化区 , manually adjust the sewage cut-out valve to open / close. When the interface is between the second and third detection positions, the electric desalination tank operates stably. At this time, the control requirement is a smooth response, with the system operating stably as the main goal; when the interface is above the second detection position or below the third detection position, the electric desalination tank already has safety or environmental risks, and the controller needs to respond quickly to intervene to eliminate possible future risks; when the interface is above the first detection position or below the fourth detection position, the electric desalination tank is already under safety risks, and the controller has failed. The controller needs to stop automatic operation and open or close the sewage cut-out valve in manual mode for emergency and rapid intervention to avoid safety and environmental accidents.

[0026] As a preferred embodiment, the PID controller is a gain-scheduled PID controller with a decision system. The decision system selects a combination of different control parameters to control the sewage cut-out valve of the electric desalting tank according to the comparison results of the viscosity measurement value of the viscosity sensor at each detection position with the typical viscosity values ​​of the emulsification zone and the water zone. The control parameters include the operation mode, proportional gain, integral time and valve opening of the PID controller. Combined with the gain-scheduled PID controller, a multivariable decision system is used to adaptively adjust the control parameters to control the external drainage volume of the electric desalting tank, meet the control requirements of the boundary between the emulsification zone and the water zone in different areas, and then achieve accurate water cutting, so that the boundary between the emulsification zone and the water zone in the electric desalting tank can be controlled within a given range, meet the production needs, and ensure the stable operation of the constant pressure reduction device.

[0027] As a preferred implementation, the PID controller uses the viscosity measurement value of the viscosity sensor at each detection position as a detection variable to control the sewage cut-out valve of the electric desalination tank, and determines the valve opening according to the detection variable values ​​at different positions.

[0028] As a preferred embodiment, the method further comprises:

[0029] According to the comparison between the viscosity measurement value and the typical viscosity values ​​of the emulsified zone and the water zone, the corresponding control parameters are assigned to the PID controller based on the comparison result;

[0030] For the comparison result of μ2>μ 水区 And μ3<μ 乳化区 In the case of, the first control parameter combination is assigned to the PID controller, including the operation mode, proportional gain and integral time of the PID controller, the operation mode is automatic, and the PID controller adopts the PI control form;

[0031] For the comparison result μ2≤μ 水区 Or μ3 ≥ μ 乳化区 In the case of, the second control parameter combination is assigned to the PID controller, including the operation mode and proportional gain of the PID controller, the operation mode is automatic, and the PID controller adopts the P control form;

[0032] For the comparison result μ1≤μ 水区 In the case of, the third control parameter combination is assigned to the PID controller, including the operation mode and valve opening of the PID controller, and the operation mode is manual;

[0033] For the comparison result μ4≥μ 乳化区 In this case, the fourth control parameter combination is assigned to the PID controller, including the operation mode and valve opening of the PID controller, and the operation mode is manual.

[0034] Furthermore, the set value of the PID controller is configured as the average of the typical viscosity of the emulsification zone and the typical viscosity of the water zone; and the measured value of the PID controller is configured as the average of the second viscosity measurement value and the third viscosity measurement value.

[0035] As a preferred implementation, the viscosity sensor is installed by inserting into the tank bottom and arranged at a corresponding detection position in the electric desalination tank.

[0036] The water, oil and emulsion entering the electric desalter from the distribution pipe tend to move in plug flow in the tank. There is a density difference between water and oil. Water will automatically settle to the bottom of the tank due to its own gravity. In addition, the material distribution ports of the oil distribution pipe and the water flushing pipe in the electric desalter are evenly distributed along the axis of the shell. During the continuous feeding process, the feed amount is basically stable, and the flow rate of the distribution port of the oil distribution pipe and the water flushing pipe will not fluctuate greatly. Therefore, a viscosity sensor is installed in the middle of the electric desalter. The feedback measurement value is representative and can reflect the properties of the liquid layer at this point.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1) The present invention arranges a plurality of vibration viscosity sensors in the electric desalting tank to indirectly reflect the relative interval position of the interface between the emulsification zone and the water zone. The viscosity sensor is convenient and sensitive to detect, thus solving the problem of difficulty in directly and accurately detecting the interface.

[0039] 2) The present invention uses at least four vibrating viscosity sensors arranged at specific positions to obtain viscosity values ​​(multivariable) at different positions. Based on the comparison between the viscosity values ​​at different positions and the viscosity values ​​of the emulsified area / water area, different processing methods are adopted for different positions to ensure operation efficiency and safety.

[0040] 3) The present invention is based on the relative interval of viscosity test results combined with multivariable control, which can effectively control the oil-water interface to fluctuate within the control range to meet the needs of industrial production.

[0041] 4) The present invention can be based on the gain-scheduled PID controller and the detection data of multiple vibration viscosity sensors. The decision system assigns different control parameters (operation mode (manual / automatic), proportional gain, integral time, and valve opening of the PID controller) to meet the control requirements of the electric desalination tank position control in different areas. The position of the electric desalination tank can be automatically controlled within a given range, reducing labor intensity and improving the automation level of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a schematic diagram of the layout of the viscosity sensor in the electric desalination tank.

[0043] Figure 2 It is a schematic diagram of the decision process for valve control based on the viscosity measurement values ​​collected by each viscosity sensor. DETAILED DESCRIPTION

[0044] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and specific implementation methods.

[0045] Figure 1The present invention is a schematic diagram of the structure of a horizontal electric desalter, wherein the internal device of the electric desalter includes: electrode plate, oil distribution pipe, water flushing pipe, sewage cut-out pipe, sewage cut-out valve, etc. The electric desalter is divided from top to bottom into: oil zone, strong electric zone, emulsification zone and water zone, wherein the boundary between the emulsification zone and the water zone is the control object of the present invention, and its most ideal position should be between the second detection position (position ② in the figure, located 1-2 cm above the water flushing pipe in the electric desalter, hereinafter referred to as position ②) and the third detection position (position ③ in the figure, located 1-5 cm below the water flushing pipe in the electric desalter, hereinafter referred to as position ③). The purpose of the present invention is to control the boundary between the emulsification zone and the water zone between the second detection position and the third detection position by adjusting the sewage cut-out valve based on the viscosity detection data of multiple positions in the electric desalter.

[0046] In this embodiment, a viscosity sensor is arranged at the second detection position and the third detection position respectively, and at the first detection position above the second detection position (position ① in the figure, located below the electrode plate in the electric desalting tank and 2-4 cm above the oil distribution pipe, hereinafter referred to as position ①) and the fourth detection position below the third detection position (position ④ in the figure, located below the third detection position in the electric desalting tank and 1-5 cm above the sewage cut-out pipe, hereinafter referred to as position ④).

[0047] The measured values ​​of the viscosity sensors at positions ①, ②, ③, and ④ are , , and .

[0048] The present invention adopts Figure 2 The control method shown completes the control of the interface between the emulsification zone and the water zone.

[0049] The control method of the present invention is constructed based on a gain-scheduled PID controller. The gain-scheduled PID controller adds a decision system based on the general PID algorithm. The decision system can switch the parameters of the PID controller or the controller itself according to various data measured on site, thereby enhancing the ability of the PID controller to cope with nonlinear controlled objects. The PID controller itself is a single variable controller, but in the present invention, viscosity detection values ​​at multiple positions are used to participate in the decision system of the PID parameters, so it is essentially a multivariable control method.

[0050] The control method of the present invention aims to control the interface between the emulsification zone and the water zone between the control positions, that is, between positions ② and ③ in this embodiment. The set value (SP) of the gain-scheduled PID controller in the present invention is set to the viscosity of the typical emulsification zone. (This parameter is obtained by collecting and analyzing samples from the emulsified area multiple times on site and taking the average value) and typical water area viscosity The average value of the gain-scheduled PID controller is the viscosity measurement value at position ② and ③. and The output (OP) of the gain-scheduled PID controller will be given to the sewage cut-out valve, and the control of the interface between the emulsification zone and the water zone will be completed by continuously adjusting the opening of the sewage cut-out valve. Figure 2 The control parameters shown in the figure usually refer to the operating mode (manual / automatic), proportional gain, integral time, and valve opening of the PID controller.

[0051] The key to the control method of the present invention lies in the control decision system of the gain-scheduled PID controller, which determines the control performance of the control method of the present invention.

[0052] exist ,and At this time, the interface between the emulsification zone and the water zone is between positions ② and ③, which is in the optimal position. The electric desalination tank operates normally and stably. The decision system will provide control parameter combination 1 to the gain-scheduled PID controller. Control parameter combination 1 includes: the operation mode (automatic), proportional gain, and integral time of the PID controller. The controller adopts PI control. The setting principle of control parameter 1 is that the proportional gain is small and the integral time is large to ensure that the controller responds smoothly and has high stability. At this time, if the PV value of the controller is close to the typical value of the emulsification zone , indicating that the interface between the emulsified zone and the water zone is close to position ③, and the PV value is higher than SP ( and The controller will increase the interface between the emulsified zone and the water zone by closing the sewage cut-out valve. On the contrary, if the PV value of the controller is close to the typical value of the water zone, , indicating that the interface between the emulsified area and the water area is close to position ②, and the PV value is lower than the SP value. The controller will lower the interface between the emulsified area and the water area by opening the sewage cut-out valve.

[0053] exist or When the interface between the emulsified area and the water area in the electric desalting tank is above position ②, or the interface is below position ③. At this time, the electric desalting tank is operating in a non-optimal state and there are safety hazards. When the interface is above ②, it may cause the electrode plate to short-circuit, and when the interface is below ③, it may cause the oil content in the sewage to increase. In this case, the decision-making system assigns control parameter combination 2 to the gain-scheduled PID controller to quickly adjust the sewage cut-out valve to reduce safety hazards. Control parameter combination 2 includes: the operation mode (automatic) of the PID controller, the proportional gain, and the controller adopts the P control form. The setting principle of control parameter combination 2 is that the proportional gain is large to ensure that the controller responds quickly. At this time, if the PV value of the controller is already much smaller than or greater than the SP value, a quick response is required. By quickly opening or closing the sewage cut-out valve, the interface between the emulsified area and the water area can quickly range between positions ② and ③.

[0054] exist , the interface between the emulsified area and the water area in the electric desalter is above position ①. The oil-water interface is too high and has begun to affect the operation of the electrode plate. There is a great risk of short circuit of the electrode plate. The interface position needs to be quickly lowered, and it indicates that the normal control method has failed. The decision system will use control parameter combination 3, including: PID controller operation mode (manual), valve opening. The gain-scheduled PID controller will be set to manual and give a valve opening, which is usually greater than the upper limit of the opening in the automatic mode, so as to urgently lower the interface position to avoid damage to the electrode plate and cause production accidents.

[0055] exist When the interface between the emulsified area and the water area in the electric desalting tank is below position ④, the oil-water interface is too low, and the oil content in the discharged sewage may exceed the standard. The interface position needs to be quickly raised, and it indicates that the normal control method has failed. The decision system will use control parameter combination 4, including: PID controller operation mode (manual), valve opening. The gain-scheduled PID controller will be set to manual and give a valve opening, which is usually less than the lower limit of the opening in the automatic mode, so as to urgently raise the interface position and avoid oil in the discharged water, which may cause environmental accidents.

Claims

1. A multivariable position control method for an electric desalination tank, characterized in that: include: Determine the control interval of the boundary between the emulsification zone and the water zone; Multiple viscosity sensors are arranged in the electric desalination tank, and the arrangement positions of the viscosity sensors include at least: a first detection position between the electrode plate and the oil distribution pipe, a second detection position where the upper limit of the control interval is located, a third detection position where the lower limit of the control interval is located, and a fourth detection position between the third detection position and the sewage cut-out pipe; Read the viscosity measurement value of the viscosity sensor at each detection position, compare the viscosity measurement value at each detection position with the viscosity value of the emulsification area and the water area, and adjust the sewage cut-out valve according to the comparison result.

2. The method according to claim 1, characterized in that The control interval of the boundary between the emulsification zone and the water zone is set to be between 1-2 cm above the water flushing pipe in the electric desalination tank and 1-5 cm below the water flushing pipe.

3. The method according to claim 1, characterized in that The viscosity sensor is a vibration type viscosity sensor.

4. The method according to claim 1, characterized in that: The first detection position is located below the electrode plate in the electric desalting tank and 2-4 cm above the oil distribution pipe; The second detection position is located 1-2 cm above the water flushing pipe in the electric desalination tank; The third detection position is located 1-5 cm below the water flushing pipe in the electric desalination tank; The fourth detection position is located below the third detection position in the electric desalination tank and 1-5 cm above the sewage cut-out pipe.

5. The method according to claim 1, characterized in that The adjustment of the sewage cut-out valve according to the comparison result includes: Read the first viscosity measurement value collected by the viscosity sensor at the first, second, third and fourth detection positions respectively μ 1. Second viscosity measurement value μ 2. Third viscosity measurement value μ 3. Fourth viscosity measurement value μ 4; Determine the typical viscosity values ​​of the emulsion zone and water zone respectively μ 乳化区 , μ 水区 ; when μ 2> μ 水区 and μ 3< μ 乳化区 , maintain the current boundary position; when μ 2≤ μ 水区 , adjust the sewage cut-out valve to increase the flow rate; when μ 3≥ μ 乳化区 , adjust the sewage cut-out valve to reduce the flow rate; or μ 1≤ μ 水区 or μ 4≥ μ 乳化区 , manually adjust the sewage cut-out valve to open / close.

6. The method according to claim 1 or 5, characterized in that: According to the viscosity measurement value of the viscosity sensor at each detection position, the PID controller is used to adjust the sewage cut-out valve.

7. The method according to claim 6, characterized in that The PID controller is a gain-scheduled PID controller with a decision-making system. The decision-making system selects a combination of different control parameters to control the sewage cut-out valve of the electric desalination tank based on the comparison results of the viscosity measurement values ​​of the viscosity sensors at each detection position with the typical viscosity values ​​of the emulsification zone and the water zone. The control parameters include the operation mode, proportional gain, integral time and valve opening of the PID controller.

8. The method according to claim 6, characterized in that Also includes: According to the comparison between the viscosity measurement value and the typical viscosity values ​​of the emulsified zone and the water zone, the corresponding control parameters are assigned to the PID controller based on the comparison result; The comparison results are μ 2> μ 水区 and μ 3< μ 乳化区 In the case of, the first control parameter combination is assigned to the PID controller, including the operation mode, proportional gain and integral time of the PID controller, the operation mode is automatic, and the PID controller adopts the PI control form; The comparison results are μ 2≤ μ 水区 or μ 3≥ μ 乳化区 In the case of, the second control parameter combination is assigned to the PID controller, including the operation mode and proportional gain of the PID controller, the operation mode is automatic, and the PID controller adopts the P control form; The comparison results are μ 1≤ μ 水区 In the case of, the third control parameter combination is assigned to the PID controller, including the operation mode and valve opening of the PID controller, and the operation mode is manual; The comparison results are μ 4≥ μ 乳化区 In this case, the fourth control parameter combination is assigned to the PID controller, including the operation mode and valve opening of the PID controller, and the operation mode is manual.

9. The method according to claim 5 or 8, characterized in that: The set value of the PID controller is configured as the average of the typical viscosity of the emulsification zone and the typical viscosity of the water zone; the measurement value of the PID controller is configured as the average of the second viscosity measurement value and the third viscosity measurement value.

10. The method according to claim 1, characterized in that The viscosity sensor is installed by inserting into the tank bottom and arranged at a corresponding detection position in the electric desalination tank.

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