Automatic start-stop and variable load control method for air separation and argon purification system

Abstract

This invention discloses an automatic start-up and load-variable control method for an air separation argon purification system. Automatic start-up, load-variable operation, and steady-state adjustment of the argon purification system no longer require operator intervention; operators only need to change the system's load flow rate setpoint. During automatic start-up, load-variable operation, and steady-state adjustment, the system operates stably, and the nitrogen content of the liquid argon in the product meets requirements. This completely solves the problems of easy overpressure in the argon purification tower and the necessity of discharging substandard liquid argon during the initial automatic operation of the argon purification system, eliminating safety hazards and saving energy consumption. When the argon purification system is operated at reduced load, the minimum load can reach 20% of the normal load, and the operating conditions remain stable, while the product quality still meets requirements. This solves the problem of frequent start-up and shutdown of the argon purification system when user usage fluctuates significantly.

Description

Technical Field

[0001] This invention relates to a method for automatic start-up, shutdown, and variable load control of an air separation argon system. Background Technology

[0002] Oxygen Plant No. 1, 40000Nm³, Energy Center of a steel company 3 The / h air separation argon refining system uses liquid-phase feed, making its commissioning and shutdown operations complex and prone to overpressure. It requires continuous manual adjustments to maintain stable operation under steady-state conditions, resulting in high operational intensity. Since its commissioning in 2008, the nitrogen content in the pure argon produced during each commissioning process has consistently failed to meet standards, necessitating liquid drainage and energy waste. This project, based on the multivariate predictive control technology of the EAOC-ASU system, developed a complete and reliable strategy tailored to the actual operation process. This overcomes the bottleneck of similar systems like EAOC-ASU, which can only be used for steady-state adjustments. It achieves automatic start-up and shutdown, variable load operation, and automatic steady-state adjustment of the argon refining system, ensuring that the nitrogen content in the liquid argon produced in each process meets requirements. The refined argon system consists of a crude argon liquefaction unit, a refined argon tower evaporator, a refined argon tower condenser, and the tower body. It utilizes heat integration and material recirculation technology, exhibiting a high degree of energy and material coupling. The operation of each valve affects upstream and downstream processes. To ensure operational stability, operators need to continuously adjust their procedures during both variable and normal load operations, resulting in high operational intensity and unstable conditions. After shutdown, the refined argon tower lacks a cooling source, undergoing a slow reheating process. During restart, the feed is liquid, and significant vaporization occurs each time, easily leading to overpressure in the tower, potentially damaging internal accessories, the tower body, and piping. To prevent pressure increases during restart, a cooling source must be provided to reduce the tower pressure. However, this pressure reduction also condenses a large amount of nitrogen, resulting in substandard nitrogen content in the liquid argon product. After restarting, the substandard liquid must be discharged, accumulated again, and the operating conditions re-established. Each discharge is approximately ≥2m³. 3 This results in energy waste. When the argon refiner is operated under reduced load, the manual operation range is small, making it impossible to achieve the ideal minimum load state. When the user's consumption is small, the argon refiner must be shut down, and when the user's consumption increases, the argon refiner must be put back into operation. This causes frequent start-ups and shutdowns of the argon refiner, resulting in stress alternation and affecting its service life. Summary of the Invention

[0003] The purpose of this invention is to provide an automatic start-up and variable load control method for an air separation and argon system. By utilizing the multivariable predictive control technology of the EAOC-ASU system under steady state and combining it with practical operating experience to formulate corresponding strategies, the normal adjustment of the steady-state operating condition of the argon system can be achieved, replacing manual operation.

[0004] The technical solution adopted in this invention is an automatic start-up and variable load control method for an air separation and argon purification system, implemented according to the following steps:

[0005] A. Automatic Adjustment Operation under Steady-State: The nitrogen-side pressure PICA702 of the crude argon liquefaction unit is automatically controlled at 105 kPa by the V716 valve using PID control; the argon-side pressure PICA706 of the crude argon liquefaction unit is controlled at 21.5 ± 0.5 kPa by the V705 valve operated through the EAOC-ASU system. Kpa; The argon column load FICA701 is controlled via EAOC-ASU software using valve V711 to maintain flow within the operator-defined target range. Since flow and pressure are interdependent, the EAOC-ASU system sets the pressure rating of PICA706 higher than the flow rating of FICA701. Valve V711 manages both flow and pressure control simultaneously, while valve V705 manages both pressure and flow control. Valve V766 is manually operated, opened to its full position in one go and maintained at 50%. For product liquid argon nitrogen analysis (AIAA717), valve V707 in the argon column evaporator is adjusted via EAOC-ASU system to maintain nitrogen content within the operator-defined target range of 0.5-1.2 ppm. The argon column internal pressure (PICAS704) is adjusted via EAOC-ASU system using valve V706 in the argon column condenser to maintain pressure within the operator-defined range of 16-22 ppm. Within the target kPa range, the nitrogen-side pressure of the argon tower condenser is automatically controlled at around 47 kPa by the V715 valve via PID control. The V766 valve is manually operated by the operator to open to the full position in one go and maintain a constant 100% opening. The V708 valve is automatically controlled by PID control according to the liquid level setting to ensure the stability of the LICA704 liquid level.

[0006] B. Automatic load change operation:

[0007] Load reduction operation: The operator reduces the load on the argon purification tower by the FICA701 flow rate setpoint; valve V711 closes gradually according to the FICA701 flow rate setpoint to reduce the flow rate; valve V705 closes gradually according to the set step while maintaining the argon side pressure PICA706 at 21.5±0.5 kPa, taking into account the FICA701 flow rate; the argon purification tower pressure PICAS704 and the product liquid argon nitrogen content analysis AIAA717 are controlled by the EAOC-ASU system using valves V706 and V707, always maintaining the pressure between 16-22 kPa. Within the range of 0.5-1.2 ppm; Valves V766 and V751 are manually operated by the operator, opened to the full position in one go, and maintained at 50% and 100% opening respectively; The nitrogen side pressure of the crude argon liquefaction unit PICA702 is automatically controlled at 105 kPa by valve V716 using PID control; The nitrogen side pressure of the fine argon tower condenser is automatically controlled at around 47 kPa by valve V715 using PID control, and valve V708 is automatically controlled by PID control according to the liquid level setting to ensure stable liquid level;

[0008] Loading operation: The operator only needs to increase the setpoint of the FICA701 flow rate in the argon column load. All valves involved in the process will operate automatically until the FICA701 flow rate in the argon column reaches the set target value. Given the instability of the multivariate predictive control technology of the EAOC-ASU system under unsteady conditions, to ensure stable operation during the load change process, the rate of change of the FICA701 flow rate in the argon column load during the load change process must not exceed 10 m³ / s. 3 / h;

[0009] C. Automatic start-up and shutdown operation of the argon system:

[0010] Valve V705 is pre-opened by 5%, valve V706 by 4%, and valve V707 by 6%. The nitrogen-side pressure PICA702 of the crude argon liquefaction unit is automatically controlled at 105 kPa by valve V716 using PID control. The nitrogen-side pressure of the condenser in the refined argon tower is automatically controlled at 47 kPa by valve V715 using PID control. Valves V766 and V751 are manually operated by the operator, opened to their full positions in one go, and maintained at 50% and 100% opening respectively. The operator sets the target flow rate of the refined argon tower load FICA701. The EAOC-ASU system controls the actions of valves V705, V706, V711, and V707, and the refined argon system is slowly increased in load. During this period, the rate of change of the refined argon tower load FICA701 flow rate must not exceed 5 m / s. 3 / h; the step size of valve V707 is no greater than 0.001; the step size of valves V705 and V711 is no greater than 0.05. When valve V711 is opened to 25%, the EAOC-ASU system will use this as a trigger point to automatically restore the step size of the above valves to the normal step size of 0.15, so as to accelerate the argon column to reach the set target load. Valve V708 is automatically controlled according to the liquid level setting to ensure the stability of the LICA704 liquid level.

[0011] The system advantages of this invention are as follows: 1. Automatic start-up and shutdown, load variation, and steady-state adjustment of the argon refining system no longer require operator intervention; operators only need to change the load flow setting of the argon refining system. 2. During automatic start-up and shutdown, load variation, and steady-state adjustment, the operating conditions of the argon refining system are stable, and the nitrogen content of the liquid argon in the product meets the requirements. 3. It completely solves the problem of easy overpressure in the argon refining tower and the need to discharge substandard liquid argon during the initial automatic operation of the argon refining system, eliminating safety hazards and saving energy consumption (6000 yuan / time). 4. When the argon refining system is operated under reduced load, the minimum load can reach 20% of the normal load, and the operating conditions are stable, while the product quality still meets the requirements. This solves the problem of frequent start-up and shutdown of the argon refining system when the user's usage fluctuates greatly, reduces the alternating stress changes during equipment start-up and shutdown, and extends the service life. 5. When the argon refining system is operated under increased load, under the same product quality conditions, the output increases by 7.6% compared to before, increasing revenue by approximately 1.02 million yuan / year. Based on the principles of safety, stability, and energy saving, this control system breaks through the bottleneck that EAOC-ASU and other similar multivariable predictive control technologies in the industry can only be used for steady-state adjustment. Currently, there is no literature or data showing a similar control system. It is unique in the industry at home and abroad, with outstanding economic benefits and broad application prospects. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the control system of the present invention. Detailed Implementation

[0013] An automatic start / stop and variable load control method for an air separation and argon purification system, such as Figure 1 As shown, follow these steps:

[0014] A. Automatic Adjustment Operation under Steady-State: The nitrogen-side pressure PICA702 of the crude argon liquefaction unit is automatically controlled at 105 kPa by the V716 valve using PID control; the argon-side pressure PICA706 of the crude argon liquefaction unit is controlled at 21.5 ± 0.5 kPa by the V705 valve operated through the EAOC-ASU system. Kpa; The argon column load FICA701 is controlled via EAOC-ASU software using valve V711 to maintain flow within the operator-defined target range. Since flow and pressure are interdependent, the EAOC-ASU system sets the pressure rating of PICA706 higher than the flow rating of FICA701. Valve V711 manages both flow and pressure control simultaneously, while valve V705 manages both pressure and flow control. Valve V766 is manually operated, opened to its full position in one go and maintained at 50%. For product liquid argon nitrogen analysis (AIAA717), valve V707 in the argon column evaporator is adjusted via EAOC-ASU system to maintain nitrogen content within the operator-defined target range of 0.5-1.2 ppm. The argon column internal pressure (PICAS704) is adjusted via EAOC-ASU system using valve V706 in the argon column condenser to maintain pressure within the operator-defined range of 16-22 ppm. Within the target kPa range, the nitrogen-side pressure of the argon tower condenser is automatically controlled at around 47 kPa by the V715 valve via PID control. The V766 valve is manually operated by the operator to open to the full position in one go and maintain a constant 100% opening. The V708 valve is automatically controlled by PID control according to the liquid level setting to ensure the stability of the LICA704 liquid level.

[0015] B. Automatic load change operation:

[0016] Load Reduction Operation: The operator reduces the load on the argon purification tower by the setpoint FICA701 flow rate; valve V711 is closed gradually according to the set flow rate of FICA701, reducing the flow rate and lowering the load on the argon purification tower while ensuring that the argon-side pressure PICA706 in the crude argon liquefaction unit does not decrease too much or too quickly; valve V705 is closed gradually according to the set flow rate of FICA701, while maintaining the argon-side pressure PICA706 at 21.5±0.5 kPa; the pressure of the argon purification tower PICAS704 and the nitrogen content analysis of the liquid argon product AIAA717 are controlled by the EAOC-ASU system using valves V706 and V707, always maintaining them between 16-22 kPa. Within the range of 0.5-1.2 ppm; Valves V766 and V751 are manually operated by the operator, opened to the full position in one go, and maintained at 50% and 100% opening respectively; The nitrogen side pressure of the crude argon liquefaction unit PICA702 is automatically controlled at 105 kPa by valve V716 using PID control; The nitrogen side pressure of the fine argon tower condenser is automatically controlled at around 47 kPa by valve V715 using PID control, and valve V708 is automatically controlled by PID control according to the liquid level setting to ensure stable liquid level;

[0017] Loading operation: The operator only needs to increase the setpoint of the FICA701 flow rate in the argon column load. All valves involved in the process will operate automatically until the FICA701 flow rate in the argon column reaches the set target value. Given the instability of the multivariate predictive control technology of the EAOC-ASU system under unsteady conditions, to ensure stable operation during the load change process, the rate of change of the FICA701 flow rate in the argon column load during the load change process must not exceed 10 m³ / s. 3 / h;

[0018] C. Automatic start-up and shutdown operation of the argon system:

[0019] The challenges of restarting the refined argon system after a shutdown lie in addressing the issues of high liquid feed vaporization rate during the initial startup phase, easy overpressure and increased pressure fluctuations within the refined argon tower, the inability of the EAOC-ASU system to guarantee stable pressure, and the unacceptable nitrogen content in the liquid argon product during the period from startup to normal operation. To address these challenges, the following strategies were implemented: V705 valve was pre-opened by 5%, V706 valve by 4%, and V707 valve by 6%. The nitrogen-side pressure PICA702 of the crude argon liquefaction unit was automatically controlled by PID control via valve V716 at 1... 0.05 kPa; The nitrogen-side pressure of the condenser in the argon tower is automatically controlled at 47 kPa by the PID control of valve V715. Valves V766 and V751 are manually operated by the operator, opened to the full position in one go, and maintained at 50% and 100% opening respectively. The operator sets the target value of the argon tower load FICA701 flow rate. The EAOC-ASU system controls the actions of valves V705, V706, V711, and V707, and the argon system is slowly loaded. During this period, the rate of change of the argon tower load FICA701 flow rate must not exceed 5 m / s. 3 / h; the step size of valve V707 is no greater than 0.001; the step size of valves V705 and V711 is no greater than 0.05. When valve V711 is opened to 25%, the EAOC-ASU system will use this as a trigger point to automatically restore the step size of the above valves to the normal step size of 0.15, so as to accelerate the argon column to reach the set target load. Valve V708 is automatically controlled according to the liquid level setting to ensure the stability of the LICA704 liquid level.

Claims

1. A method for automatic start-up, shutdown, and variable load control of an air separation and argon purification system, characterized in that... Follow these steps: A. Automatic Adjustment Operation under Steady-State: The nitrogen-side pressure PICA702 of the crude argon liquefaction unit is automatically controlled at 105 kPa by the V716 valve using PID control; the argon-side pressure PICA706 of the crude argon liquefaction unit is controlled at 21.5 ± 0.5 kPa by the V705 valve operated through the EAOC-ASU system. Kpa; The argon column load FICA701 is controlled via EAOC-ASU software using valve V711 to maintain flow within the operator-defined target range. Since flow and pressure are interdependent, the EAOC-ASU system sets the pressure rating of PICA706 higher than the flow rating of FICA701. Valve V711 manages both flow and pressure control simultaneously, while valve V705 manages both pressure and flow control. Valve V766 is manually operated, opened to its full position in one go and maintained at 50%. For product liquid argon nitrogen analysis (AIAA717), valve V707 in the argon column evaporator is adjusted via EAOC-ASU system to maintain nitrogen content within the operator-defined target range of 0.5-1.2 ppm. The argon column internal pressure (PICAS704) is adjusted via EAOC-ASU system using valve V706 in the argon column condenser to maintain pressure within the operator-defined range of 16-22 ppm. Within the target kPa range, the nitrogen-side pressure of the argon tower condenser is automatically controlled at around 47 kPa by the V715 valve via PID control. The V766 valve is manually operated by the operator to open to the full position in one go and maintain a constant 100% opening. The V708 valve is automatically controlled by PID control according to the liquid level setting to ensure the stability of the LICA704 liquid level. B. Automatic load change operation: Load reduction operation: The operator reduces the load on the argon purification tower by the FICA701 flow rate setpoint; valve V711 closes gradually according to the FICA701 flow rate setpoint to reduce the flow rate; valve V705 closes gradually according to the set step while maintaining the argon side pressure PICA706 at 21.5±0.5 kPa, taking into account the FICA701 flow rate; the argon purification tower pressure PICAS704 and the product liquid argon nitrogen content analysis AIAA717 are controlled by the EAOC-ASU system using valves V706 and V707, always maintaining the pressure between 16-22 kPa. Within the range of 0.5-1.2 ppm; Valves V766 and V751 are manually operated by the operator, opened to the full position in one go, and maintained at 50% and 100% opening respectively; The nitrogen side pressure of the crude argon liquefaction unit PICA702 is automatically controlled at 105 kPa by valve V716 using PID control; The nitrogen side pressure of the fine argon tower condenser is automatically controlled at around 47 kPa by valve V715 using PID control, and valve V708 is automatically controlled by PID control according to the liquid level setting to ensure stable liquid level; Load operation: only need to operate the staff to increase the argon tower load FICA701 flow setting value, the process involved in the valve are automatically action, until the argon tower load FICA701 reach the set target value; in view of the EAOC-ASU system multivariable predictive control technology in the non-steady state instability, to ensure the stability of the working condition of the variable load process, the variable load process of argon tower load FICA701 flow rate of change shall not be greater than 10 m 3 / h; C. Automatic start-up and shutdown operation of the argon system: Valve V705 is pre-opened by 5%, valve V706 by 4%, and valve V707 by 6%. The nitrogen-side pressure PICA702 of the crude argon liquefaction unit is automatically controlled at 105 kPa by valve V716 using PID control. The nitrogen-side pressure of the condenser in the refined argon tower is automatically controlled at 47 kPa by valve V715 using PID control. Valves V766 and V751 are manually operated by the operator, opened to their full positions in one go, and maintained at 50% and 100% opening respectively. The operator sets the target flow rate of the refined argon tower load FICA701. The EAOC-ASU system controls the actions of valves V705, V706, V711, and V707, and the refined argon system is slowly increased in load. During this period, the rate of change of the refined argon tower load FICA701 flow rate must not exceed 5 m / s. 3 / h; the step size of valve V707 is no greater than 0.001; the step size of valves V705 and V711 is no greater than 0.

05. When valve V711 is opened to 25%, the EAOC-ASU system will use this as a trigger point to automatically restore the step size of the above valves to the normal step size of 0.15, so as to accelerate the argon column to reach the set target load. Valve V708 is automatically controlled according to the liquid level setting to ensure the stability of the LICA704 liquid level.

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