Control method and system for a pre-cooling system of an air separation plant

Abstract

The application provides a control method and system of a precooling system of an air separation device, and is applied to the technical field of the precooling system. The technical scheme of the application optimizes the mass flow of normal-temperature circulating water and refrigerated water through an MCU, and the total power supply electric power of the circulating pressurizing pump and the refrigerated water pump is minimum under the condition that the outlet gas temperature is 12 DEG C. The MCU iteratively calculates and gives the mass flow set value of the corresponding frequency converter of the circulating pressurizing pump and the refrigerated water pump based on the hot air flow F, the total power supply current I and the outlet gas temperature T2, so as to control the water flow of the circulating pressurizing pump and the refrigerated water pump. The negative feedback value of the set value of the frequency converter of the refrigerated water is constructed based on the deviation value of T2 and 12 DEG C, so that the outlet gas temperature T2 is stabilized at about 12 DEG C. Based on the control system and the control method, the original manual adjustment is replaced, and the energy-saving optimization response speed, efficiency, reliability and automation level of the precooling system of the air separation device are improved.

Description

Technical Field

[0001] This invention relates to the field of precooling system technology, and specifically to a control method and system for a precooling system of an air separation unit. Background Technology

[0002] The precooling system of the air separation unit is the cooling system for the hot air exiting the air compressor, hereinafter referred to as the precooling system. The cooling media in the precooling system include ambient temperature circulating water and chilled water. The main equipment includes an air-cooled tower, a water-cooled tower, a circulating water booster pump, and a chilled water pump. The circulating water booster pump pressurizes and delivers ambient temperature circulating water from the circulating water station into the middle of the air-cooled tower. The chilled water pump pressurizes and delivers chilled water cooled by 5°C polluted nitrogen in the water-cooled tower into the upper part of the air-cooled tower. Based on direct contact cooling, the hot air in the air-cooled tower is gradually cooled to approximately 12°C. Then, the cooled air is delivered to the air separation unit's purification system.

[0003] In existing technologies, frequency converters are often chosen to meet the energy-saving requirements of the precooling system. That is, while meeting their respective cooling water process parameters, the ambient temperature circulating water pump and chilled water pump reduce their power consumption through frequency converters, thereby achieving the energy-saving requirements of the precooling system.

[0004] In practice, for different operating conditions, existing technologies rely solely on manual adjustment of the frequency converter based on experience to minimize the total electrical power of the precooling system. This total electrical power includes the power of the circulating water booster pump, the chilled water pump, and the frequency converter. Because manual adjustment is inherently arbitrary, it is time-consuming.

[0005] Therefore, there is an urgent need for a control method and system for the precooling system of an air separation unit to solve the above problems. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] To address the shortcomings of existing technologies, this invention provides a control method and system for a precooling system in an air separation unit. By using an MCU (Microcontroller Unit) to automatically adjust the frequency converter in the precooling system, the mass flow rates of ambient temperature circulating water and chilled water are managed. Under the condition that the outlet gas temperature is 12°C, the total electrical power in the precooling system is minimized, thus solving the technical problem that manual adjustment is time-consuming when facing different operating conditions.

[0008] (II) Technical Solution

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] In a first aspect of the present invention, a control method for a precooling system of an air separation unit is provided, the method being applied to a microcontroller unit (MCU) of the control system, the method comprising:

[0011] S1. Initialize n=1. Based on the inherent parameters of the precooling system of the air separation unit, obtain the initial set value of the mass flow rate of the ambient temperature circulating water. Initial setpoint for chilled water mass flow rate

[0012] S2, obtain the flow rate value F of hot air, the total current signal I, the outlet gas temperature T2 of the air-cooled tower, and the mass flow rate W2 of chilled water;

[0013] S3. Based on the outlet gas temperature T2, flow rate F, and chilled water mass flow rate W2, determine the negative feedback coefficient K and the negative feedback quantity A;

[0014] S4. Based on the negative feedback quantity A, determine the set value of the chilled water mass flow rate. And The input is given to the setting terminal of the frequency converter VF2, so that the frequency converter VF2 adjusts the output power of the chilled water pump motor, and sets the mass flow rate W2 of the chilled water to be...

[0015] S5. Based on the total current signal I, determine the total power P of the air separation unit precooling system;

[0016] S6. A set value based on the total power P and the mass flow rate of chilled water. Determine the set value of the mass flow rate of the circulating water at ambient temperature. And The input is sent to the frequency converter VF1, so that the frequency converter VF1 adjusts the output power of the circulating booster pump motor, so that the mass flow rate W1 of the ambient temperature circulating water is...

[0017] S7. Determine whether |T2-12|≤ε1 is true. If yes, go to S8; if no, then n=n+1 and go to S2. Where ε1 represents the first preset value.

[0018] S8, Judgment | P n -P n-1 | / |P n If |≤ε2 is true, the adjustment process of the control method ends; if not, n=n+1, go to S2;

[0019] Among them, P n P represents the total power in the nth cycle. n-1 ε1 represents the total power during the (n-1)th cycle, and ε2 represents the second preset value.

[0020] Optionally, in step S3, determining the negative feedback coefficient K and the negative feedback quantity A based on the outlet gas temperature T2, flow rate F, and chilled water flow rate W2 includes:

[0021] Determine whether |T²-1²|≥2 is true; if so, then K=C pa F / [C pw (T wh -T c2 If not, then K = 1;

[0022] Among them, C pa F represents the average heat capacity of air, and C represents the hot air flow rate. pw Indicates the heat capacity of water, T wh The temperature of the hot water in the air-cooled tower, T, is displayed. c2 Indicates the temperature of the chilled water;

[0023] The negative feedback quantity A represents the digital negative feedback e and the analog negative feedback e. ′ The sum, that is, A = e + e ′ ;

[0024] Wherein, digital negative feedback e = (K-1)(T2-12); analog negative feedback e ′ =T2-12.

[0025] Optionally, in step S1, an initial set value for the mass flow rate of ambient temperature circulating water is obtained based on the inherent parameters of the air separation unit's precooling system. Initial setpoint for chilled water mass flow rate include:

[0026]

[0027] Where T1 represents the inlet gas temperature of the air-cooled tower; T c1 Indicates the temperature of circulating water at room temperature; T c2 Indicates the temperature of chilled water; T c1 This indicates the temperature of the circulating water at room temperature;

[0028]

[0029]

[0030] Where η1 represents the power efficiency of the ambient temperature circulating water pump P1, including the frequency converter; Δp1 represents the operating pressure difference between the air-cooled tower and the ambient temperature circulating water; ρ w η represents the density of water; g represents the gravitational constant; H1 represents the rise height of the circulating water at normal temperature; η2 represents the power efficiency of the chilled water pump P2 including the frequency converter; Δp2 represents the operating pressure difference between the air-cooled tower and the chilled water.

[0031] Optionally, the set value in S6 is based on the total power P and the mass flow rate of the chilled water. Determine the set value of the mass flow rate of the circulating water at ambient temperature. include:

[0032] make judge Is it greater than 0? If so, then If not, then

[0033] in, P represents the first judgment value in the nth iteration. n P represents the total power in the nth cycle. n-1 This represents the total power in the (n-1)th cycle; This represents the setpoint for the mass flow rate of the circulating water at room temperature in the (n+1)th cycle. s represents the set value of the mass flow rate of the ambient temperature circulating water in the nth cycle, and s represents the third preset value.

[0034] Optionally, the input signals of the MCU may also include: the pressure difference Δp3 across the circulating water booster pump valve V1 and the pressure difference Δp4 across the chilled water pump valve V2;

[0035] The MCU's output signals include: the set value of the mass flow rate of ambient temperature circulating water and the set value of the mass flow rate of chilled water.

[0036] Optionally, in step S4, determining the total power P of the air separation unit precooling system based on the total current signal I includes:

[0037]

[0038] Where f represents the current transformation coefficient of the current transformer, U represents the motor power supply voltage of the circulating water booster pump and chilled water pump in the precooling system, and I represents the transformer measurement value of the power frequency current.

[0039] In a second aspect of the invention, a control system for a precooling system of an air separation unit is provided. The control system includes a circulating water booster pump, a chilled water pump, a frequency converter VF1 corresponding to the circulating water booster pump, a frequency converter VF2 corresponding to the chilled water pump, a current transformer (CT), a negative feedback element, an MCU, and thyristors JZ1 and JZ2. The connection relationships within the control system are as follows:

[0040] The flow rate F of hot air is input to the start ports of VF1 and VF2, the anodes of thyristors JZ1 and JZ2, and the input port of the MCU, respectively.

[0041] The current signal I output by the current transformer CT, the gas outlet temperature T2, and the measured value of the chilled water mass flow rate are all input to the input port of the MCU;

[0042] The pressure difference Δp3 across the circulating water booster pump valve V1 and the pressure difference Δp4 across the chilled water pump valve V2 are both input to the MCU input port;

[0043] The MCU outputs the set value W1 for the mass flow rate of the circulating water at room temperature. ′ The set value W2 for the mass flow rate of chilled water ′ ;

[0044] The set value W1 for the mass flow rate of circulating water at ambient temperature ′ Input to the input port of inverter VF1, chilled water mass flow rate setpoint W2 ′ It is input to the input port of inverter VF2 along with the negative feedback quantity;

[0045] The measurement port of inverter VF1 is used to receive the measurement value of the mass flow rate of circulating water at normal temperature; the measurement port of inverter VF2 is used to receive the measurement value of the mass flow rate of chilled water.

[0046] Optionally, the connection relationships within the control system also include:

[0047] The gate of thyristor JZ1 receives the pressure difference Δp3 across the valve of the circulating water booster pump;

[0048] The gate of thyristor JZ2 receives the pressure difference Δp4 across the chilled water pump valve;

[0049] The cathode of thyristor JZ1 is connected to the signal input port of valve V1 of the circulating water booster pump;

[0050] The cathode of thyristor JZ2 is connected to the signal input port of chilled water pump valve V2.

[0051] Optionally, in the control system:

[0052] The circulating water booster pump is used to transport circulating water at room temperature.

[0053] The chilled water pump is used to transport chilled water;

[0054] The frequency converter VF1 is used to control the mass flow rate of the circulating water at room temperature output by the circulating water booster pump;

[0055] The frequency converter VF2 is used to control the mass flow rate of chilled water output by the chilled water pump;

[0056] Current transformers (CTs) are used to convert the total current in the precooling system of an air separation unit into a power frequency current signal.

[0057] Negative feedback elements are used to provide analog negative feedback to the MCU;

[0058] The MCU is used to execute S1, initialize n=1, and obtain the initial set value of the mass flow rate of the ambient temperature circulating water based on the inherent parameters of the air separation unit's precooling system. Initial setpoint for chilled water mass flow rate

[0059] S2, obtain the flow rate value F of hot air, the total current signal I, the outlet gas temperature T2 of the air-cooled tower, and the mass flow rate W2 of chilled water;

[0060] S3. Based on the outlet gas temperature T2, flow rate F, and chilled water mass flow rate W2, determine the negative feedback coefficient K and the negative feedback quantity A;

[0061] S4. Based on the negative feedback quantity A, determine the set value of the chilled water mass flow rate. And The input is given to the setting terminal of the frequency converter VF2, so that the frequency converter VF2 adjusts the output power of the chilled water pump motor, and sets the mass flow rate W2 of the chilled water to be...

[0062] S5. Based on the total current signal I, determine the total power P of the air separation unit precooling system;

[0063] S6. A set value based on the total power P and the mass flow rate of chilled water. Determine the set value of the mass flow rate of the circulating water at ambient temperature. And The input is sent to the frequency converter VF1, so that the frequency converter VF1 adjusts the output power of the circulating booster pump motor, so that the mass flow rate W1 of the ambient temperature circulating water is...

[0064] S7. Determine whether |T2-12|≤ε1 is true. If yes, go to S8; if no, then n=n+1 and go to S2. Where ε1 represents the first preset value.

[0065] S8, Judgment | P n -P n-1 | / |P n If |≤ε2 is true, the adjustment process of the control method ends; if not, n=n+1, go to S2.

[0066] Optionally, the control system further includes:

[0067] The thyristor JZ1 is used for the switching control of the valve V1 switching signal;

[0068] The thyristor JZ2 is used for the switching control of the valve V2 switching signal.

[0069] (III) Beneficial Effects

[0070] This invention provides a control method and system for a precooling system of an air separation unit, which has the following advantages compared with the prior art:

[0071] A control method for a precooling system of an air separation unit, the method being applied to a microcontroller unit (MCU) of the control system, the method comprising: S1, initializing n=1, obtaining an initial setpoint value for the mass flow rate of ambient temperature circulating water based on the inherent parameters of the precooling system of the air separation unit. Initial setpoint for chilled water mass flow rate S2. Obtain the hot air flow rate F, the total current signal I, the outlet gas temperature T2 of the air-cooled tower, and the mass flow rate W2 of the chilled water; S3. Based on the outlet gas temperature T2, the flow rate F, and the mass flow rate W2 of the chilled water, determine the negative feedback coefficient K and the negative feedback quantity A; S4. Based on the negative feedback quantity A, determine the setpoint value of the chilled water mass flow rate. And The input is given to the setting terminal of the frequency converter VF2, so that the frequency converter VF2 adjusts the output power of the chilled water pump motor, and sets the mass flow rate W2 of the chilled water to be... S5. Based on the total current signal I, determine the total power P of the air separation unit precooling system; S6. Based on the total power P and the set value of the chilled water mass flow rate... Determine the set value of the mass flow rate of the circulating water at ambient temperature. And The input is sent to the frequency converter VF1, so that the frequency converter VF1 adjusts the output power of the circulating booster pump motor, so that the mass flow rate W1 of the ambient temperature circulating water is... S7. Determine if |T2-12|≤ε1 is true. If yes, go to S8; if no, then n=n+1, go to S2. S8. Determine if |P n -P n-1 | / |P n If |≤ε2 is true, the adjustment process of the control method ends; if not, n=n+1, go to S2.

[0072] Based on the above processing, the MCU performs iterative calculations based on the hot air flow rate F and the outlet temperature, and assigns mass flow rate setpoints to the inverters of the circulating booster pump and chilled water pump, thereby controlling the input flow rates of ambient temperature circulating water and chilled water. Simultaneously, based on the deviation between the outlet gas temperature T2 and 12℃, a negative feedback variable is constructed for the chilled water setpoint, stabilizing the outlet gas temperature T2 at approximately 12℃. This control system and method replaces the manual adjustment in the original technology, thereby improving the energy-saving optimization response speed, efficiency, reliability, and automation level of the air separation unit's precooling system. Furthermore, in this control system, the MCU has 6 input variables and 2 output variables, thus reducing the computational load and specification requirements for the MCU in the precooling system. Attached Figure Description

[0073] To more clearly illustrate the technical solutions in this invention or the prior art, the accompanying drawings used in the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0074] Figure 1 A schematic diagram of a control system provided by the present invention;

[0075] Figure 2 A schematic diagram of the control system for the outlet valve provided by the present invention;

[0076] Figure 3 This invention provides a flowchart of a program for MCU control operations. Detailed Implementation

[0077] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0078] This invention provides a control method and system for a precooling system of an air separation unit. The MCU performs iterative calculations based on the hot air flow rate F, total current signal I, outlet gas temperature T2, and chilled water flow rate W2, and assigns mass flow rate setpoints to the frequency converters of the circulating booster pump and chilled water pump, thereby controlling the input flow rates of ambient temperature circulating water and chilled water. Simultaneously, based on the deviation of the outlet gas temperature T2 from 12°C, a negative feedback variable is constructed for the chilled water setpoint, stabilizing the outlet gas temperature T2 at approximately 12°C. This control system and method replace manual adjustment in previous technologies, thereby improving the energy-saving optimization response speed, efficiency, reliability, and automation level of the air separation unit precooling system. Furthermore, in this control system, the MCU has 6 input variables and 2 output variables, reducing the computational load and specification requirements for the MCU in the precooling system.

[0079] The technical solution of this invention aims to achieve the aforementioned beneficial effects, and the overall concept is as follows:

[0080] In existing technologies, frequency converters are often used to reduce the power consumption of ambient temperature circulating water pumps and chilled water pumps in precooling systems, thereby meeting the energy-saving requirements of precooling systems.

[0081] However, during the adjustment process of the aforementioned frequency converter, the ambient temperature circulating water pump and the chilled water pump were considered as two isolated subsystems. However, after performing a degree-of-freedom analysis on the pre-air separation unit's cooling system, it was found that the mass flow rates of the ambient temperature circulating water and the chilled water are mutually constrained. That is, during the adjustment process, there exists a theoretically optimal operating point, where the total power consumption of the ambient temperature circulating water pump and the chilled water pump is minimized when the parameters in the pre-cooling system are adjusted to this optimal point.

[0082] Regarding the aforementioned optimization points, if the design values ​​of the precooling system in the air separation unit are accurate, the precooling system can maintain consistency between design and operation under a specific operating condition. However, in actual operation, the operating conditions of the precooling system frequently change according to production needs, and the changed operating conditions will deviate from the operating conditions corresponding to the original design values ​​in the precooling system.

[0083] When operating conditions change, the precooling system is currently adjusted manually based on experience. Because manual adjustment is highly arbitrary and cannot quickly pinpoint the optimal point, the adjustment time is long, leading to significant energy waste.

[0084] To address the aforementioned issues, a control system can be constructed. This control system automatically finds the optimal operating point for the precooling system, thus easily meeting its energy-saving requirements, improving the ease of operation, and reducing energy waste during adjustment.

[0085] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0086] The precooling system of the air separation unit can be understood as a heat exchange device. The working principle of this heat exchange device is: based on the combined action of ambient temperature circulating water and chilled water in the air-cooled tower, the hot air input to the air-cooled tower is cooled to below 12°C.

[0087] In the precooling system, the total power consumption equation and heat balance equation for the circulating water booster pump and the chilled water pump are as follows:

[0088]

[0089] In the above formula, P represents the total electrical power consumption of the circulating water booster pump and the chilled water pump; Δp1 represents the operating pressure difference between the air-cooled tower and the ambient temperature circulating water; Δp2 represents the operating pressure difference between the air-cooled tower and the chilled water; ρ w H1 represents the density of water; g represents the gravitational constant; H1 represents the lift height of the ambient temperature circulating water; W1 represents the mass flow rate of the ambient temperature circulating water; η1 represents the electrical efficiency of the ambient temperature circulating water pump P1 (including the frequency converter); H2 represents the lift height of the chilled water; W2 represents the mass flow rate of the chilled water; η2 represents the electrical efficiency of the chilled water pump P2 (including the frequency converter); C pa T1 represents the average heat capacity of air; F represents the hot air flow rate; T2 represents the outlet gas temperature of the air-cooled tower; T1 represents the inlet gas temperature of the air-cooled tower; C pw T represents the heat capacity of water. wh The temperature of the hot water in the air-cooled tower is indicated by T. c1 Indicates the temperature of circulating water at room temperature; T c2 Indicates the temperature of the chilled water; m1 represents m2 represents

[0090] Formulas 1-2 and 1-3 are the constraints of Formula 1-1.

[0091] Based on the Lagrange multiplier method, the extremum condition of P is obtained as follows:

[0092]

[0093] Based on formulas 2-1 and 2-2, the theoretical values ​​of the mass flow rates W1 and W2 of the ambient temperature circulating water and chilled water can be calculated. Simultaneously, the theoretical values ​​of W1 and W2 can be used as the initial setpoints for the mass flow rates of the ambient temperature circulating water and chilled water during the control system's regulation process. Furthermore, based on formula 1-1, the theoretical minimum total power of the circulating water booster pump and the chilled water pump can be calculated.

[0094] Therefore, once the airflow rate F of the hot air is obtained, setting the efficiency of the circulating water booster pump and the chilled water pump to between 0.8 and 0.9 (determined based on actual measurements during operation), and using preset values ​​for other parameters, the conditions for the control system to automatically adjust the precooling system can be met. This approach reduces the computational requirements of the control system, thereby lowering the requirements for its software and hardware.

[0095] Furthermore, due to the approximations of the above formulas and their parameters, and the variations in motor efficiency within the precooling system of the air separation unit, if the control system only automatically adjusts the precooling system based on Formulas 1-1 and 1-2, it will be unable to adjust the mass flow rates of ambient temperature circulating water and chilled water to the optimal operating point. Therefore, the automatic adjustment process of the control system needs to be optimized without a model based on the actual measured values ​​of some parameters.

[0096] The control system includes a current transformer (CT). Based on the current transformer, the control system converts the total current in the precooling system into a power frequency current signal of ≤20mA. Then, the power frequency current signal is input to the MCU in the control system, which is used by the MCU to calculate the actual total electrical power P of the circulating water booster pump and chilled water pump (including the frequency converter) in the precooling system.

[0097] Specifically, the formula for calculating P is:

[0098] Where f represents the current transformation coefficient of the current transformer, U represents the motor power supply voltage of the circulating water booster pump and chilled water pump in the precooling system, and I represents the transformer measurement value of the power frequency current.

[0099] When the mass flow rates of ambient temperature circulating water and chilled water change, the MCU in the control system can obtain the corresponding actual total electrical power P based on the calculation formula of P.

[0100] When the mass flow rates of ambient temperature circulating water and chilled water change, the outlet gas temperature of the air-cooled tower will change. To prevent the outlet gas temperature T2 of the air-cooled tower from deviating too much from 12℃, a negative feedback quantity A is set for T2 based on the mass flow rate W2 of the chilled water.

[0101] Feedback quantity A represents the difference between digital negative feedback e and direct analog negative feedback e. ′ The sum, that is, A = e + e ′ .

[0102] Where e = (K-1)(T2-12), K represents the feedback coefficient; ′ =T2-12.

[0103] Furthermore, formula 1-2 is transformed to obtain formula 3-1, which is as follows:

[0104]

[0105] When the outlet gas temperature T2 of the air-cooled tower deviates significantly from 12℃, such as when T2 > 15℃, the feedback coefficient K is obtained based on formula 3-1, K = C. pa F / [C pw (T wh -T c2 As can be seen, the value of K can be directly calculated based on the preset value of the control system.

[0106] When the outlet gas temperature deviates slightly from 12℃, K = 1.

[0107] Once the MCU receives the specific value of feedback quantity A, it uses this value as digital negative feedback for the setpoint of the chilled water mass flow rate and outputs it to the input port of the inverter VF2 corresponding to the chilled water pump. Furthermore, since feedback quantity A includes direct analog negative feedback e... ′ Therefore, when the deviation between the outlet gas temperature T2 and 12℃ of the air-cooled tower is small, the control system can directly simulate negative feedback e. ′ The setpoint for the chilled water flow rate is used as digital negative feedback and output to the input port of VF2, so that T2 is stabilized at 12℃. This avoids the drawbacks of long adjustment time and large fluctuation of T2 during automatic adjustment caused by a relatively large feedback coefficient K.

[0108] Based on the above, it can be seen that the negative feedback quantity A serves as the setpoint W2 for the mass flow rate of the chilled water. ′ The digital negative feedback enables the control system to respond to W2 ′ Continuous adjustments are made. This includes each adjustment to W2. ′ After adjustments, all adjusted W2 will be... ′ The input is fed to the input port of the frequency converter VF2 to adjust the output power of the chilled water pump motor, thereby adjusting the mass flow rate of the chilled water, ultimately making T2 = 12℃.

[0109] Analysis of the degrees of freedom of W1 and W2 shows that W1 and W2 are interrelated in controlling T2 to around 12℃; that is, changing W1 will lead to a corresponding change in W2. Therefore, adjusting W1 is sufficient to optimize the total electrical power P.

[0110] However, the change of W1 cannot be completed by iterative operation based on the existing model. Therefore, the MCU adopts a trial-and-error iterative operation and uses a posterior method to determine the direction of change of W1.

[0111] When the MCU performs the nth iteration operation and adjusts W1, P is obtained. n It can be calculated that:

[0112]

[0113]

[0114] in, k1 represents the value after the nth iteration, where k1 represents the first judgment value. k2 represents the value after the nth iteration, k2 represents the second judgment value, and P represents the second judgment value. n P represents the total electrical power after the nth iteration. n-1 This represents the total electrical power after the (n-1)th iteration. This represents the setpoint value for the mass flow rate of the circulating water at room temperature after the (n-1)th iteration. This represents the setpoint value for the mass flow rate of the circulating water at room temperature after the nth iteration. This represents the setpoint for the mass flow rate of chilled water after the (n-1)th iteration. This represents the set value of the mass flow rate of chilled water after the nth iteration.

[0115] Because each iteration operation results in W1 = W1 ′ Therefore, after the first iteration operation Therefore It cannot be applied to control systems, which can only adjust based on k2.

[0116] Based on the above, it is clear that W2 and W1 are interconnected; a change in W1 inevitably leads to a change in W2. After each iteration of control is completed, there is...

[0117] The control system determines W1 through k2. ′ Based on the analysis of the relationship between k2 and P and W1, the following conclusions can be drawn regarding the adjustment direction:

[0118] when When P increases, W2 decreases. At this time, W1 should be decreased to reduce the total power P.

[0119] when When P increases, W2 increases. At this time, W1 should be increased to reduce the total power P.

[0120] Based on the above conclusions, the following optimization iteration relationship can be established:

[0121] when hour,

[0122] when hour,

[0123] s can be any value in the range 0 to 1, and is generally taken as 0.1.

[0124] When |P n+1 -P n | / |P n+1 If |≤ε2, then the MCU calculation iteration operation is terminated.

[0125] See Figure 1 and Figure 2 , Figure 1 This is a schematic diagram of a control system provided in an embodiment of the present invention. Figure 2 This is a schematic diagram of a control system for an outlet valve provided in an embodiment of the present invention. Figure 1 , Figure 2 As shown, the connection method of each device in the control system is as follows:

[0126] The air flow signal F is connected to the start port qd of VF1 and VF2.

[0127] The air flow signal F and the inlet and outlet pressure difference signal Δp3 of valve V1 are connected to the controller signal input port of the outlet switch valve V1 of P1 after passing through thyristor JZ1; the air flow signal F and the inlet and outlet pressure difference signal Δp4 of valve V2 are connected to the controller signal input port of the outlet switch valve V2 of P2 after passing through thyristor JZ2.

[0128] Among them, the air flow signal F is connected to the anode of thyristors JZ1 and JZ2, Δp3 is connected to the gate of thyristor JZ1, and Δp4 is connected to the gate of thyristor JZ2.

[0129] The air flow signal F, the current signal I of the current transformer CT, the gas outlet temperature signal T2, and the mass flow signal W2 of the chilled water are all connected to the input port of the MCU.

[0130] The signals Δp3 and Δp4 are connected to the input interface of the MCU.

[0131] The MCU output signals include the set value W1 for the mass flow rate of the ambient temperature circulating water. ′ The set value W2 for the mass flow rate of chilled water ′ .

[0132] The VF1's measurement port acquires the measured value W1 of the mass flow rate of the circulating water at room temperature. The VF1's setting port receives the setting value W1 output by the MCU. ′ So that VF1 is based on the set value W1 ′ Adjust the power of P1 to adjust the mass flow rate of the circulating water at room temperature.

[0133] Similarly, the measurement port of VF2 acquires the signal of the chilled water mass flow rate W2. The setting port of VF2 receives the set value W2 output by the MCU. ′ So that VF1 is based on the set value W2 ′ Adjust the electrical power of P2 to adjust the mass flow rate of the chilled water.

[0134] Among them, the setting port of VF2 receives W2 ′ It includes digital negative feedback e = (K-1)(T2-12) and analog negative feedback e ′ =T2-12.

[0135] It should be noted that all analog signals input to the MCU must be converted into digital signals via an A / D converter; all digital signals output from the MCU must be converted into analog signals via a D / A converter. For example, after the analog negative feedback e′ is input to the MCU, the MCU outputs W2. ′ digital signals, W2 ′ The digital signal is converted into an analog signal by a D / A converter, and then connected to the setting terminal of the frequency converter VF2, so that the frequency converter VF2 is set based on W2. ′ Adjust the electrical power of P2 to adjust the mass flow rate of the chilled water.

[0136] The control methods of a control system include:

[0137] When the circulating water booster pump P1 and the chilled water pump P2 start, the inlet and outlet pressure difference signals Δp3 and Δp4 of valve V1 and valve V2 are both greater than zero. Based on thyristors JZ1 and JZ2, the air flow signal F of hot air is activated by the control circuits of valves V1 and V2 respectively, so valves V1 and V2 open and gradually open to the fully open state.

[0138] The start-up process of the precooling system of the air separation unit is a routine operation, which takes about 30 seconds.

[0139] When the hot air flow signal F is generated, the MCU, based on the acquired F, T2, and the process parameters and physical property parameters (including Δp1, Δp2, H1, H2, ρ) stored in the MCU, performs the following operations: w The theoretical optimal operating point is calculated using preset values ​​of η1 and η2. This theoretical optimal operating point includes the setpoint W1 for the mass flow rate of the ambient temperature circulating water. ′ , setpoint W2 for chilled water mass flow rate ′ And digital negative feedback e.

[0140] During the startup process of the precooling system of the aforementioned air separation unit, W1 is the theoretically optimal operating point. ′ W2 ′The values ​​of the digital negative feedback e remain unchanged. As the valve opens and the inverter increases its frequency, the mass flow rates of the ambient temperature circulating water and chilled water gradually increase. Correspondingly, the MCU acquires the actual mass flow rate signals W1 and W2, as well as the actual power frequency current signal I.

[0141] After the above startup process is completed, valves V1 and V2 are fully open, Δp3 and Δp4 are both equal to 0, and the MCU's optimization calculation program restarts. Specifically, the MCU, based on F and T2, combines the process parameters and physical property parameters (including Δp1, Δp2, H1, H2, ρ) stored within the MCU. w Calculate the corresponding theoretical optimal operating point using the preset values ​​of η1 and η2. Similarly, this theoretical optimal operating point includes the set value W1 of the mass flow rate of the ambient temperature circulating water. ′ The set value W2 for the mass flow rate of chilled water ′ And digital negative feedback e.

[0142] During the operation of the precooling system, when the hot air flow rate F changes significantly, the MCU will recalculate W1. ′ and W2 ′ And based on the MCU's W1 ′ W2 ′ Output is made through the port. If W1 ≠ W1 ′ The control system will then adjust the mass flow rate of the ambient temperature circulating water to W1′ via a frequency converter. If W2≠W2 ′ The control system will then adjust according to the digital negative feedback e and the analog negative feedback e. ′ The mass flow rate of chilled water was adjusted to the mass flow rate corresponding to an outlet gas temperature of 12°C, ultimately achieving the same level as W1. ′ The state of adaptation, where W2 = W2 ′ .

[0143] Then, based on the inputs F, I, and T2, the MCU gradually changes W1 using the aforementioned optimization iterative relationship. ′ This allows the system to be gradually optimized to the optimal operating point between the air flow rate F and the inlet temperature of the air-cooled tower.

[0144] After measuring and calculating the mass flow rates of ambient temperature circulating water and chilled water, the MCU will continuously acquire the measured value of T2 to calculate the temperature negative feedback coefficient K and the negative feedback quantity A.

[0145] Furthermore, based on the value of T2, the control system determines W1 after each adjustment. ′ Has it reached a stable state?

[0146] When the precooling system of the air separation unit is shut down, the air flow rate F = 0, which leads to the de-energization of the anodes JZ1 and JZ2, disconnecting the control signals of valves V1 and V2, and V1 and V2 will gradually close.

[0147] When the air flow rate F = 0, the negative feedback coefficient K for the outlet gas temperature of the chilled water pump P2 = 0, resulting in zero negative feedback for the outlet gas temperature. As valves V1 and V2 gradually close, the actual flow rates of the ambient temperature circulating water and chilled water will gradually decrease, while W1... ′ and W2 ′ As the pumps gradually decrease in size, pumps P1 and P2 will also gradually stop under the power supply connection, with the MCU and frequency converter working together to stop the pumps.

[0148] Although there is a lag time between the valve starting to close and the MCU starting the pump stop program, it has almost no impact on the air separation unit's precooling system relative to the valve closing time, and will not damage the circulating water booster pump and chilled water pump.

[0149] See Figure 3 , Figure 3 This invention provides a flowchart of a MCU control operation, the control operation method in the MCU including:

[0150] Based on Δp1, Δp2, H1, H2, ρ w Given the preset values ​​of η1 and η2, calculate K1 and K2. When other parameters, except for the hot air flow rate, do not change significantly, K1 and K2 can be set as fixed parameters and stored in the memory of the MCU.

[0151] Within approximately 30 seconds of the air separation unit's precooling system starting up, the MCU calculates the negative feedback quantities A and W1 based on the air flow rate F and T2. ′ and W2 ′ And it outputs continuously without changing.

[0152] When valves V1 and V2 are fully open, Δp3 and Δp4 are both equal to 0. The MCU calculates W1 based on the newly received air flow signal F. ′ and W2 ′ The initial value is then output to the input terminals of the frequency converters VF1 and VF2, i.e., W1. 0 =W1′, W2 0 =W2′. Then, according to Formula 1-1, calculate the theoretical minimum total power consumption P. 0 .

[0153] Simultaneously, the MCU calculates the negative feedback coefficient K and the negative feedback quantity A based on the measured outlet gas temperature T2, i.e., it calculates K. l A l And apply it to the setting signal of the frequency converter VF2.

[0154] Where, when |T2-12|≥2, K=C pa F / [C pw (T wh -T c2 When |T2-12|<2, K=1.

[0155] The MCU continuously measures T2. When T2 satisfies |T2-12|≤ε1, it calculates the current signal I at that time. 1 Calculate the actual total power consumption P 1 .

[0156] Among them, ε1 is the first preset value, which is set according to the control accuracy requirements, and the value range is generally 0.05 to 0.1.

[0157] When |P 1 -P 0 | / |P 0 When |≤ε2, the corresponding and As an optimization result. Otherwise, based on Formula 4-1 and Formula 4-2, calculate...

[0158] when

[0159] when

[0160] Wherein, ε2 is the second preset value, and the value of ε2 is set according to the control accuracy requirements of the control system, and the value range is generally 0.05 to 0.1. S is the third preset value, which can be any value from 0 to 1, and is generally taken as 0.1.

[0161] The process repeats in the above manner until |P n+1 -P n | / |P n+1 Stop if |≤ε2, accept W1 n+1 and W2 n+1 As the final result of the adjustment.

[0162] During the adjustment process, the MCU continuously assigns the set value W2 of the chilled water mass flow rate output by the MCU to the set value W2 of the chilled water mass flow rate. ′ .

[0163] After the control system completes its iteration Therefore, when the precooling system of the air separation unit is shut down, the control system can operate autonomously according to the above-mentioned optimized procedure.

[0164] When the air separation unit's precooling system is shut down, F = 0, causing valves V1 and V2 to gradually close. At this time, regardless of the MCU output W1... ′ and W2′ The values ​​of W1 and W2 will decrease as the valves gradually close. The circulating water pump P1 can then optimize its program according to the above adjustment process, gradually reducing the flow rate setting, and VF1 will gradually reduce its power output until it eventually stops. During this adjustment process, the MCU continuously assigns W2 to W2. ′ VF1 will also eventually stop pumping independently, as V2 gradually shuts down.

[0165] After the pump is finally stopped, V1 and V2 will be completely closed, effectively isolating the air-cooled tower and the circulating water system. A pressure difference will appear before and after the valves of V1 and V2, and Δp3 and Δp4 will both be greater than zero, and the control system will stop.

[0166] This invention provides a control method for a precooling system of an air separation unit. The method is applied to a microcontroller unit of the control system and includes:

[0167] S1. Initialize n=1. Based on the inherent parameters of the precooling system of the air separation unit, obtain the initial set value of the mass flow rate of the ambient temperature circulating water. Initial setpoint for chilled water mass flow rate

[0168] S2, obtain the flow rate value F of hot air, the total current signal I, the outlet gas temperature T2 of the air-cooled tower, and the mass flow rate W2 of chilled water;

[0169] S3. Based on the outlet gas temperature T2, flow rate F, and chilled water mass flow rate W2, determine the negative feedback coefficient K and the negative feedback quantity A;

[0170] S4. Based on the negative feedback quantity A, determine the set value of the chilled water mass flow rate. And The input is given to the setting terminal of the frequency converter VF2, so that the frequency converter VF2 adjusts the output power of the chilled water pump motor, and sets the mass flow rate W2 of the chilled water to be...

[0171] S5. Based on the total current signal I, determine the total power P of the air separation unit precooling system;

[0172] S6. A set value based on the total power P and the mass flow rate of chilled water. Determine the set value of the mass flow rate of the circulating water at ambient temperature. And The input is sent to the frequency converter VF1, so that the frequency converter VF1 adjusts the output power of the circulating booster pump motor, so that the mass flow rate W1 of the ambient temperature circulating water is...

[0173] S7. Determine whether |T2-12|≤ε1 is true. If yes, go to S8; if no, then n=n+1 and go to S2. Where ε1 represents the first preset value.

[0174] S8, Judgment | P n -P n-1 | / |P n If |≤ε2 is true, the adjustment process of the control method ends; if not, n=n+1, go to S2;

[0175] Among them, P n P represents the total power in the nth cycle. n-1 ε1 represents the total power during the (n-1)th cycle, and ε2 represents the second preset value.

[0176] Specifically, in step S3, based on the outlet gas temperature T2, flow rate F, and chilled water flow rate W2, the negative feedback coefficient K and negative feedback quantity A are determined, including:

[0177] Determine whether |T²-1²|≥2 is true; if so, then K=C pa F / [C pw (T wh -T c2 If not, then K = 1;

[0178] Among them, C pa F represents the average heat capacity of air, and C represents the hot air flow rate. pw Indicates the heat capacity of water, T wh The temperature of the hot water in the air-cooled tower, T, is displayed. c2 Indicates the temperature of the chilled water;

[0179] The negative feedback quantity A represents the digital negative feedback e and the analog negative feedback e. ′ The sum, that is, A = e + e ′ ;

[0180] Wherein, digital negative feedback e = (K-1)(T2-12); analog negative feedback e ′ =T2-12.

[0181] Specifically, in step S1, the initial set value of the mass flow rate of the ambient temperature circulating water is obtained based on the inherent parameters of the air separation unit's precooling system. Initial setpoint for chilled water mass flow rate include:

[0182]

[0183] Where T1 represents the inlet gas temperature of the air-cooled tower; T c1 Indicates the temperature of circulating water at room temperature; Tc2 Indicates the temperature of chilled water; T c1 This indicates the temperature of the circulating water at room temperature;

[0184]

[0185]

[0186] Where η1 represents the power efficiency of the ambient temperature circulating water pump P1, including the frequency converter; Δp1 represents the operating pressure difference between the air-cooled tower and the ambient temperature circulating water; ρ w η represents the density of water; g represents the gravitational constant; H1 represents the rise height of the circulating water at normal temperature; η2 represents the power efficiency of the chilled water pump P2 including the frequency converter; Δp2 represents the operating pressure difference between the air-cooled tower and the chilled water.

[0187] Specifically, in step S6, the set value is based on the total power P and the mass flow rate of the chilled water. Determine the set value of the mass flow rate of the circulating water at ambient temperature. include:

[0188] make judge Is it greater than 0? If so, then If not, then

[0189] in, P represents the first judgment value in the nth iteration. n P represents the total power in the nth cycle. n-1 This represents the total power in the (n-1)th cycle; This represents the setpoint for the mass flow rate of the circulating water at room temperature in the (n+1)th cycle. s represents the set value of the mass flow rate of the ambient temperature circulating water in the nth cycle, and s represents the third preset value.

[0190] Specifically, the input signals of the MCU also include: the pressure difference Δp3 across the circulating water booster pump valve V1 and the pressure difference Δp4 across the chilled water pump valve V2;

[0191] The MCU's output signals include: the set value of the mass flow rate of ambient temperature circulating water and the set value of the mass flow rate of chilled water.

[0192] Specifically, in step S4, determining the total power P of the air separation unit precooling system based on the total current signal I includes:

[0193]

[0194] Where f represents the current transformation coefficient of the current transformer, U represents the motor power supply voltage of the circulating water booster pump and chilled water pump in the precooling system, and I represents the transformer measurement value of the power frequency current.

[0195] An embodiment of the present invention also provides a control system for a precooling system of an air separation unit. The control system includes a circulating water booster pump, a chilled water pump, a frequency converter VF1 corresponding to the circulating water booster pump, a frequency converter VF2 corresponding to the chilled water pump, a current transformer (CT), a negative feedback element, an MCU, and thyristors JZ1 and JZ2. The connection relationships within the control system are as follows:

[0196] The flow rate F of hot air is input to the start ports of VF1 and VF2, the anodes of thyristors JZ1 and JZ2, and the input port of the MCU, respectively.

[0197] The current signal I output by the current transformer CT, the gas outlet temperature T2, and the measured value of the chilled water mass flow rate are all input to the input port of the MCU;

[0198] The pressure difference Δp3 across the circulating water booster pump valve V1 and the pressure difference Δp4 across the chilled water pump valve V2 are both input to the MCU input port;

[0199] The MCU outputs the set value W1 for the mass flow rate of the circulating water at room temperature. ′ The set value W2 for the mass flow rate of chilled water ′ ;

[0200] The set value W1 for the mass flow rate of circulating water at ambient temperature ′ Input to the input port of inverter VF1, chilled water mass flow rate setpoint W2 ′ It is input to the input port of inverter VF2 along with the negative feedback quantity;

[0201] The measurement port of inverter VF1 is used to receive the measurement value of the mass flow rate of circulating water at normal temperature; the measurement port of inverter VF2 is used to receive the measurement value of the mass flow rate of chilled water.

[0202] Specifically, the connection relationships within the control system also include:

[0203] The gate of thyristor JZ1 receives the pressure difference Δp3 across the valve of the circulating water booster pump;

[0204] The gate of thyristor JZ2 receives the pressure difference Δp4 across the chilled water pump valve;

[0205] The cathode of thyristor JZ1 is connected to the signal input port of valve V1 of the circulating water booster pump;

[0206] The cathode of thyristor JZ2 is connected to the signal input port of chilled water pump valve V2.

[0207] Specifically, in the control system:

[0208] The circulating water booster pump is used to transport circulating water at room temperature.

[0209] The chilled water pump is used to transport chilled water;

[0210] The frequency converter VF1 is used to control the mass flow rate of the circulating water at room temperature output by the circulating water booster pump;

[0211] The frequency converter VF2 is used to control the mass flow rate of chilled water output by the chilled water pump;

[0212] Current transformers (CTs) are used to convert the total current in the precooling system of an air separation unit into a power frequency current signal.

[0213] Negative feedback elements are used to provide analog negative feedback to the MCU;

[0214] The MCU is used to execute steps S1 to S8, including S1, initializing n=1, and obtaining the initial set value of the mass flow rate of the ambient temperature circulating water based on the inherent parameters of the air separation unit's precooling system. Initial setpoint for chilled water mass flow rate

[0215] S2, obtain the flow rate value F of hot air, the total current signal I, the outlet gas temperature T2 of the air-cooled tower, and the mass flow rate W2 of chilled water;

[0216] S3. Based on the outlet gas temperature T2, flow rate F, and chilled water mass flow rate W2, determine the negative feedback coefficient K and the negative feedback quantity A;

[0217] S4. Based on the negative feedback quantity A, determine the set value of the chilled water mass flow rate. And The input is given to the setting terminal of the frequency converter VF2, so that the frequency converter VF2 adjusts the output power of the chilled water pump motor, and sets the mass flow rate W2 of the chilled water to be...

[0218] S5. Based on the total current signal I, determine the total power P of the air separation unit precooling system;

[0219] S6. A set value based on the total power P and the mass flow rate of chilled water. Determine the set value of the mass flow rate of the circulating water at ambient temperature. And The input is sent to the frequency converter VF1, so that the frequency converter VF1 adjusts the output power of the circulating booster pump motor, so that the mass flow rate W1 of the ambient temperature circulating water is...

[0220] S7. Determine whether |T2-12|≤ε1 is true. If yes, go to S8; if no, then n=n+1 and go to S2. Where ε1 represents the first preset value.

[0221] S8, Judgment | P n -P n-1 | / |P n If |≤ε2 is true, the adjustment process of the control method ends; if not, n=n+1, go to S2.

[0222] Specifically, the control system also includes:

[0223] The thyristor JZ1 is used for the switching control of the valve V1 switching signal;

[0224] The thyristor JZ2 is used for the switching control of the valve V2 switching signal.

[0225] In summary, compared with existing technologies, it has the following beneficial effects:

[0226] The MCU iteratively calculates and assigns mass flow rate setpoints to the corresponding frequency converters of the circulating booster pump and chilled water pump based on the hot air flow rate F, the total supply current I, and the outlet gas temperature T2, thereby controlling the water delivery flow rate of the circulating booster pump and chilled water pump. Based on the deviation between T2 and 12℃, a negative feedback variable is constructed for the frequency converter setpoint of the chilled water, stabilizing the outlet gas temperature T2 at around 12℃. This control system and method replaces the manual adjustment in the original technology, improving the energy-saving optimization response speed, efficiency, reliability, and automation level of the air separation unit's precooling system. Furthermore, in this control system, the MCU has 6 input variables and 2 output variables, thus reducing the computational load and specification requirements of the MCU in the precooling system.

[0227] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0228] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A control method for a precooling system of an air separation unit, wherein, The precooling system includes an air-cooled tower, a water-cooled tower, a circulating water booster pump, and a chilled water pump. The cooling medium of the precooling system includes ambient temperature circulating water and chilled water. The circulating water booster pump pressurizes and delivers ambient temperature circulating water from the circulating water station into the middle of the air-cooled tower. The chilled water pump pressurizes and delivers chilled water from the water-cooled tower into the upper part of the air-cooled tower. Based on direct contact cooling, the hot air in the air-cooled tower is gradually cooled, and the cooled air is delivered to the air separation unit purification system. The method is characterized by being applied to a microcontroller unit (MCU) of the control system, and the method includes: S1. Initialize n=1. Based on the inherent parameters of the precooling system of the air separation unit, obtain the initial set value of the mass flow rate of the ambient temperature circulating water. Initial setpoint for chilled water mass flow rate ; S2, Obtain the hot air flow rate F, total current signal I, and outlet gas temperature of the air-cooled tower. and the mass flow rate of chilled water ; S3, based on the outlet gas temperature Flow rate value F and mass flow rate of chilled water Determine the negative feedback coefficient K and the negative feedback quantity A; S4. Based on the negative feedback quantity A, determine the set value of the chilled water mass flow rate. and will The input is given to the setting terminal of the frequency converter VF2, so that the frequency converter VF2 adjusts the output power of the chilled water pump motor, and sets the mass flow rate W2 of the chilled water to be... ; S5. Based on the total current signal I, determine the total power P of the air separation unit precooling system; S6. A set value based on the total power P and the mass flow rate of chilled water. Determine the set value of the mass flow rate of the circulating water at ambient temperature. and will The input is sent to the frequency converter VF1, so that the frequency converter VF1 adjusts the output power of the circulating booster pump motor, making the mass flow rate W1 of the ambient temperature circulating water... ; S7, Judgment If the condition is true, proceed to S8; otherwise, set n = n + 1 and proceed to S2. Indicates the first preset value; S8, Judgment If the condition is met, the adjustment process of the control method ends; otherwise, n = n + 1, and proceed to S2. in, Represents the total power in the nth cycle. Represents the total power in the (n-1)th cycle. This indicates the second preset value.

2. The control method according to claim 1, characterized in that, In step S3, based on the outlet gas temperature Given the flow rate F and the chilled water flow rate W2, determine the negative feedback coefficient K and the negative feedback quantity A, including: Judgment | Does |≥2 hold true? If so, then If not, then K=1; in, F represents the average heat capacity of air, and F represents the hot air flow rate. Indicates the heat capacity of water, The temperature of the hot water in the air-cooled tower is indicated. Indicates the temperature of the chilled water; The negative feedback quantity A represents digital negative feedback. and analog negative feedback The sum, that is, ; Among them, digital negative feedback Analog negative feedback .

3. The control method according to claim 1, characterized in that, In step S1, the initial set value of the mass flow rate of the ambient temperature circulating water is obtained based on the inherent parameters of the air separation unit's precooling system. Initial setpoint for chilled water mass flow rate ,include: in, This indicates the inlet gas temperature of the air-cooled tower; This indicates the temperature of the circulating water at room temperature; Indicates the temperature of the chilled water; This indicates the temperature of the circulating water at room temperature; ； ； in, This represents the power efficiency of the ambient temperature circulating water pump P1, including the frequency converter. This indicates the operating pressure difference between the air-cooled tower and the ambient temperature circulating water; The density of water is represented by g; g represents the gravitational constant. This indicates the height to which the circulating water at room temperature is lifted. This indicates the power efficiency of chilled water pump P2, including the frequency converter. This indicates the operating pressure difference between the air-cooled tower and the chilled water; This indicates the height to which the chilled water rises.

4. The control method according to claim 1, characterized in that, The set value in S6 is based on the total power P and the mass flow rate of the chilled water. Determine the set value of the mass flow rate of the circulating water at ambient temperature. ,include: make ,judge Is it greater than 0? If so, then If not, then ; in, This represents the first judgment value in the nth iteration. Represents the total power in the nth cycle. This represents the total power in the (n-1)th cycle; This represents the setpoint for the mass flow rate of the circulating water at room temperature in the (n+1)th cycle. This represents the setpoint for the mass flow rate of the ambient temperature circulating water in the nth cycle. This indicates the third preset value.

5. The control method according to claim 1, characterized in that, The input signals of the MCU also include: the pressure difference before and after the circulating water booster pump valve V1. Pressure difference across valve V2 of chilled water pump ; The MCU's output signals include: the set value of the mass flow rate of ambient temperature circulating water and the set value of the mass flow rate of chilled water.

6. The control method according to claim 1, characterized in that, In step S4, determining the total power P of the air separation unit precooling system based on the total current signal I includes: Where f represents the current transformation coefficient of the current transformer, U represents the motor power supply voltage of the circulating water booster pump and chilled water pump in the precooling system, and I represents the transformer measurement value of the power frequency current.

7. A control system for a precooling system of an air separation unit, characterized in that, The control system executes the control method for the precooling system of the air separation unit according to any one of claims 1-6, for controlling the precooling system. The control system includes a circulating water booster pump, a chilled water pump, a frequency converter VF1 corresponding to the circulating water booster pump, a frequency converter VF2 corresponding to the chilled water pump, a current transformer (CT), a negative feedback element, an MCU, thyristors JZ1 and JZ2; the connection relationships within the control system are as follows: The flow rate F of hot air is input to the start port of the inverter VF1 corresponding to the circulating water booster pump, the inverter VF2 corresponding to the chilled water pump, the anode of thyristor JZ1 and thyristor JZ2, and the input port of the MCU, respectively. Current signal I output by current transformer CT, outlet gas temperature The measured values ​​of both the chilled water mass flow rate and the chilled water mass flow rate are input to the input port of the MCU; Pressure difference across valve V1 of circulating water booster pump Pressure difference across valve V2 of chilled water pump All inputs are sent to the MCU's input ports; The MCU outputs the set value of the mass flow rate of the circulating water at room temperature. and the set value of the mass flow rate of chilled water ; Set value of mass flow rate of circulating water at ambient temperature The setpoint for the mass flow rate of chilled water is input to the input port of the inverter VF1. It is input to the input port of inverter VF2 along with the negative feedback quantity; The measurement port of the inverter VF1 corresponding to the circulating water booster pump is used to receive the measurement value of the mass flow rate of the circulating water at normal temperature; the measurement port of the inverter VF2 corresponding to the chilled water pump is used to receive the measurement value of the mass flow rate of the chilled water.

8. The control system according to claim 7, characterized in that, The connection relationships within the control system also include: The gate of thyristor JZ1 receives the pressure difference across valve V1 of the circulating water booster pump. ; The gate of thyristor JZ2 receives the pressure difference across valve V2 of the chilled water pump. ; The cathode of thyristor JZ1 is connected to the signal input port of valve V1 of the circulating water booster pump; The cathode of thyristor JZ2 is connected to the signal input port of chilled water pump valve V2.

9. The control system according to claim 7, characterized in that, In the control system: The circulating water booster pump is used to transport circulating water at room temperature. The chilled water pump is used to transport chilled water; The frequency converter VF1 corresponding to the circulating water booster pump is used to control the mass flow rate of the ambient temperature circulating water output by the circulating water booster pump; The frequency converter VF2 corresponding to the chilled water pump is used to control the mass flow rate of the chilled water output by the chilled water pump; Current transformers (CTs) are used to convert the total current in the precooling system of an air separation unit into a power frequency current signal. Negative feedback elements are used to provide analog negative feedback to the MCU; The MCU is used to execute the control method of the precooling system of the air separation unit.

10. The control system according to claim 9, characterized in that, The control system also includes: The thyristor JZ1 is used for the switching control of the valve V1 switch signal of the circulating water booster pump; The thyristor JZ2 is used for the switching control of the V2 valve switch signal of the chilled water pump.

Images