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Tianjin Iron and Steel Co., Ltd. two sets of 28000m 3 / h air separation equipment, contracted by China Air Separation Equipment Co., Ltd., manufactured by Hangyang. The project was put into operation in September 2005 and the operational indicators are normal.
The automation control of two sets of 28000m 3 / h air separation equipment adopts the CS3000 system of Yokogawa. Automated design and control range, including circulating water system, instrument air compressor system, raw air filtration system, air compressor system, air pre-cooling system, refrigeration unit, molecular sieve purification system, supercharger system, expander system, fine Distillation column system, nitrogen press system, storage tank and pressurized vaporization system, pressure regulating station system and liquid product pressurized vaporization filling system. The entire air separation plant is controlled by the DCS system, which fully realizes the centralized control of the central control room, especially in the control of several imported compressor units, achieving good results. All high-voltage motors (10000 VAC) enable central control room start-up. The CS3000 system can fully meet the design requirements of the control system. The DCS system is stable and reliable.
1 DCS system configuration and network structure DCS system structure as shown.
1 1 DCS system configuration engineer station (CS3000 EWS) 1 unit; operation station (CS3000 HIS) 9 units, operator keyboard (AIP827 2) 9; control bus interface card (VF701) 10; dual process control station (AFS40D H4223/ 7 D82/ CH) 2 sets, double process control station (AFF50D H41201) 1 set; 2 sets of switches; various I/O card parts and terminal boards; software package.
1 2 DCS system network structure The CS3000 system has a three-level hierarchical network structure, which uses different networks, which effectively improves the communication efficiency and reduces the communication load. The network system provides a standard GSM clock system to ensure that each station's clock on the network bus is synchronized. The CS3000 system consists mainly of the operation station HIS, the engineering station EWS and the control station FCS.
(1) Operation station HIS: used to run operation monitoring and historical data records, display reports, and provide data services to upper computers. The operation station uses Windows XP as a general-purpose PC for the operating system.
(2) Engineer station EWS: used for design configuration and simulation debugging. The engineering station uses Windows Server 2003 as the general-purpose PC of the operating system.
(3) Control station FCS: used for process I/O signal processing, complete analog quantity acquisition, realize continuous control, sequence control and batch control, and complete real-time control function.
The system network includes Ethernet, V NET, and RIO buses. Ethernet is the transmission channel of information data between the operation station, the engineering station and the upper computer. It conforms to the IEEE 802 3 standard and is an open network of the system. The communication rate is 10Mb/sV NET for dual real-time control of operation monitoring and information exchange. The network adopts Token Passing as the token bus, which conforms to the IEEE 802 4 standard, the communication rate is 10Mb/s, and the maximum communication distance is 20km. The RIO bus is a dual real-time data transmission between the control station CPU and the remote I/O node. The communication bus has a communication rate of 2 Mb/s, and the length of the bus can be extended by the adapter and the optical fiber.
2 circulating water system controls two sets of 28000m 3 / h air separation equipment to share one set of circulating water system. The system consists of three pumps, which are driven by a 10kV high voltage motor. The normal operation mode is dual-use and one-off, that is, under normal conditions (two sets of air separation equipments are running simultaneously), two pumps are operated to provide circulating cooling water for two sets of air separation equipment; when the circulating water main pipe pressure is lower than 0 3MPa, The DCS system automatically activates the backup water pump to ensure a stable water supply to the circulating water system. When a single set of air separation equipment is operated and the circulating water consumption is small, it can also be used one by one, that is, one operation is normal, and one of the other two is in standby.
After listening to the user's specific requirements and understanding their operating habits, the configuration completed the control program of the pump house and passed the actual test to achieve the expected standby control requirements.
(1) When the circulating water system is started, any pump can be manually activated in the control room (the local knob is in the automatic! position).
(2) After starting a pump manually, if the pressure is normal, the second pump cannot be manually started (by logic control) to prevent overpressure. Only after starting a pump, if the pressure is still low, the second pump can be started manually.
(3) The standby pump can be started automatically (the local knob is in the automatic position, and the control mode in the DCS system is centralized). The electrical must be hot enough so that the backup pump can be started at any time. The operator should pay attention to monitoring the electrical allowable starting state of the standby water pump.
(4) It is more flexible in the choice of backup mode. It can be used one by one or two. The interface is simple and friendly, and it is easier to operate.
In addition, at the request of the user, the current indication of the pump motor is increased to allow the operator to directly monitor the pump load.
3 Compressor unit and expander system control The automatic control of the compressor unit plays an extremely important role in the overall design of the instrument control, because all units cancel the local PLC controller, which requires the transfer of PLC control functions to the DCS system. Controlled. The program in the PLC controller of the unit is the result of repeated trials and modifications by the machine manufacturer. The supplier will not give the program as a reference to the author, but only proposes its control requirements, which are required to be implemented in the DCS system configuration; and each unit The control requirements vary, and some unit control requirements are nearly demanding. The control programming process requires detailed thinking and does not allow for slight deviations.
The DCS system realizes all the control functions of the compressor unit. On the one hand, it saves a large amount of PLC purchase cost for the user; on the other hand, the control of the compressor unit is no longer a black box! This allows the user to clearly understand the control principle of the machine and to easily monitor and control the unit in the central control room.
During the commissioning process of the MAN_TURBO air compressor in Switzerland, the foreign commissioning personnel refused to drive again after completing the unit surge test. The reason is that the DCS system's anti-surge regulator scan speed and pressure transmitter response is too slow to meet the minimum time of 100ms. However, the author relies on the rich experience of using the DCS system to control the compressor, and believes that the control will not be a problem. After in-depth technical exchanges with the foreign personnel, finally, after adjusting the corresponding PID parameters, the air compressor realized a smooth automatic start and safe anti-surge control, achieving a win-win situation for the safety control and energy saving of the unit.
The supercharger is a two-stage compressor from ATLAS, Germany, which is extremely strict in terms of control. After fully studying its control requirements and taking into account the needs of specific air separation processes, all of its control requirements are implemented in the DCS configuration. As with the air compressor, fully automatic control is achieved. The operator is operating on several buttons during operation, greatly reducing the intensity of the operation, thereby reducing the possibility of misoperation. Especially in the automatic control input of each inlet guide vane and return valve, through in-depth consideration and repeated virtual test, the program design has achieved good results, the supercharger realizes smooth automatic start and safe anti-surge control.
The nitrogen press is a 5-stage compressor from Ingersoll Rand, Italy. Because the previous nitrogen press control was controlled by local PLC, after the DCS system was controlled, its control requirements were not clear, and the DCS configuration work encountered very much. Big difficulty. Finally, with the on-site commissioning staff, it also achieved good control results.
Through the design and commissioning of the compressor unit control system, some experience has been gained: in the anti-surge control, a fast transmitter should be used instead of a general transmitter; try to let the compressor unit bring its own surge detector. If not, a quick scan of the surge system must be considered when configuring the DCS.
3 1 The automatic control air compressor of the air compressor can be started in the local electric control cabinet or the central control room. If starting in the central control room, you must first turn the local start conversion knob to automatic. After receiving the electronic control to enable the instrument to start the air compressor signal, the operator will use the start air pressure in the air compressor start flow chart. Machine button to start the air compressor. When the motor allows the loading signal to arrive, the inlet guide vane of the air compressor will be at the starting position 0! Jump to a minimum opening of 10%. If within 20s, the inlet guide vane opening feedback is less than 8%, indicating that the inlet guide vane is not open to the light load opening, and the air compressor will interlock. While the vane jumps to 10% and the vane opening continues to be large by the climber, the vent solenoid is energized and the vent valve is closed from 100% by the downhill. When the exhaust pressure reaches the set value, the constant pressure controller is automatically adjusted, and the inlet guide vane is first in the automatic control state; when the inlet differential pressure value is less than the anti-surge control line, the anti-surge controller automatically inputs the cascade. The vent valve is in automatic control and the air compressor is automatically loaded. When the unit is running for a period of time under a small load and the preheating process is completed, the operator can modify the air compressor exhaust pressure setting value so that the air compressor operates at the rated pressure. At this point, the air compressor is started, and the operator can open the air valve V1100 to supply air to the air pre-cooling system. It should be noted that the air supply valve must be opened slowly and must be closed when closed. When the control of the air compressor is turned on automatically, the operator is strictly prohibited to put the constant pressure controller and anti-surge controller of the inlet guide vane into manual adjustment.
In addition, an anti-overpressure controller is also provided, which adjusts the output and the output of the anti-surge controller to perform superposition calculation, and acts on the vent valve to realize safety control. The motor overcurrent protection is also set, and the output of the regulation and the output of the constant voltage controller are subtracted. On the basis of the constant pressure control, the vane opening degree is reduced, and the compressor load is reduced. If the flow rate during the operation of the unit is less than the protection flow value, the vent valve opens quickly under the action of the anti-surge regulator, increasing the flow rate and causing the compressor to leave the surge condition.
In one of the following situations, the air compressor will be lightly loaded immediately: the exhaust pressure is super high; the air compressor flow is less than the surge flow, the unit surges; the operator forces the air compressor to light load through the emergency button; The cold system has failed. Air compressor light load action: the inlet guide vane is limited to 10%, and the vent valve is fully open.
After the fault is eliminated, the operator can automatically resume loading the air compressor through the recovery load button on the air compressor air circuit diagram, the same process as when starting.
In the auxiliary machine control, special attention should be paid to the automatic start control of the auxiliary oil pump. During the test of Tiangang, there was a dangerous situation that the auxiliary oil pump did not start after the air compressor stopped. It was later found that the changeover switch on the field electrical control cabinet was in the local position. It must be noted that this switch must be in the automatic position when driving normally. In future designs, the position information of this transfer switch should be fed back to the DCS system for unified monitoring.
In addition, in the tank heater logic, the electric heater can be started only when the oil circuit system is in a circulating state, otherwise the lubricating oil will deteriorate due to local overheating. Therefore, in the control logic, the lubricant manifold pressure control signal is added. If the lubricant manifold is not pressurized, it is not allowed to start the heater, regardless of whether the heater is controlled in place or in an automatic position.
3 2 The automatic control of the supercharger is started in the same way as the air compressor. When the motor allows the loading signal to arrive, the inlet guide vanes of the supercharger will be opened from the starting position 0 to a minimum opening of 25% (within 25 s).
The loading of the supercharger should be carried out step by step. First, the segment should be loaded. After the segment exhaust pressure reaches the design value, it can be loaded (segment. When the operator issues the segment loading command through the operation button, the downhill device will The return valve is closed from 100%. When the exhaust pressure reaches the set value, the section return valve pressure controller is automatically adjusted, and the return valve will be in automatic control state. At this time, the operator can open the air supply valve V401 and slow to the expander. As for the air supply, it should be noted that the V401 must be opened slowly and must be closed when it is closed.
Need to load (in the segment, the operator sends a load command, the downhill will (the segment return valve is closed from 100%. When the exhaust pressure rises to the set value of 5 8MPa, the controller is automatically adjusted, the return valve will be in Automatic control state. At this time, the operator can slowly supply air to the plate-fin heat exchanger. It should be noted that the air supply valve must be opened slowly and must be closed when closed.
After the compressor is loaded, the two-stage return valve will gradually close automatically under the action of the pressure controller as the air volume of the air separation system increases. when? When the segment return valve opening is less than 1%, ? The set value of the segment return valve controller is automatically increased by 0 1 MPa and used as an overpressure controller. When the segment return valve opening is less than 1%, (the set value of the segment return valve controller is automatically increased by 0 08 MPa, which is used as an overpressure controller. At the same time, the program automatically switches the inlet guide vane to the constant voltage controller PIC1636. (Set value 2 1MPa), PIC1637 (set value 5 9MPa) is put into automatic adjustment, and the load of the compressor is increased by continuing to adjust the inlet guide vanes of each section. In the automatic mode, the two-stage inlet guide vane constant pressure regulator The minimum output is 25% to prevent surge.
If the process gas volume is reduced, the direct reaction is an increase in pressure, at which point the inlet guide vanes will automatically close to stabilize the pressure. If the operating conditions change greatly, the pressure will continue to rise. When the return valve overpressure regulator setting is exceeded, the return valve will also be automatically opened by the full shutoff. If the return valve opening is greater than 5%, the inlet guide vanes will automatically be placed in the manual position to prevent adjustment instability due to simultaneous adjustment of the inlet vane and return valve; at the same time, the set value of the return valve regulator will be restored. To section 2 1MPa, (section 5 9MPa, to control the exhaust pressure in normal working conditions. At this time, the operator can manually close the small guide vanes to save energy.
The two-stage anti-surge control of the supercharger is constant flow control, that is: no matter how much opening of the vane, if the flow is less than the set value (by the surge test), it will act on the return valve adder, plus Large return valve opening to increase flow to prevent surge.
In addition, the section inlet pressure compensation controller PIC1631 is also set. If the suction pressure is lower than the set value 0 45MPa, will the controller act? Segment return valve adder, ? The segment return valve will be opened and opened. Set (segment inlet pressure compensation controller PIC1657, if (segment suction pressure is lower than the set value 20 MPa, the controller will act on (segment return valve adder, (the segment return valve will be enlarged). The motor over-current protection is set. If the high-selection value of the motor A, B, C phase current is higher than the set value, the motor over-current protector will act on the segment inlet guide vane subtractor, and the segment inlet guide vane will be closed. Small to reduce compressor load.
Encountered one of the following conditions, the supercharger (segment will be light load: supercharger section surge; supercharger section exhaust pressure is too high; % supercharger (segment surge; supercharger (segment row) The air pressure is super high;) The operator passes the forced light load on the flow chart (the segment button is lightly loaded.
Supercharger (segment light load action: the inlet guide vane is limited to 25% and the return valve is fully open.
In one of the following situations, the supercharged section will be lightly loaded: the supercharged section will surge; the supercharged section will have a high exhaust pressure; the operator will lightly load the HS1603 button on the button operation panel.
The light-loading action of the supercharged section: the inlet guide vane is limited to 25%, and the return valve is fully open, that is: the section is lightly loaded, (the section is lightly loaded at the same time; (the section is lightly loaded, and the section does not need light load.
After the fault is removed, the operator can automatically resume loading the booster in sequence by the recovery load button on the booster air circuit diagram. Segment and (segment, the process is the same as at startup).
3 3 About the local surge detection PLC In order to better protect the machine, the in-situ surge detection PLC that comes with the booster unit is used. Two PLCs are responsible for each? Segment and (segment surge detection protection. PLC includes the following card: power module, CPU processor module, configuration communication interface card, analog input card, digital input card and digital output card. Two PLCs are installed separately On the two local junction boxes of the supercharger.
When the compressor is allowed to load, the DCS system issues an instruction to activate both PLCs to work. If it is detected (configurable) within a certain period of time (configurable) that the pressure fluctuation exceeds the set value (configurable), that is, the unit is overwhelmed, the corresponding output channel of the digital output card of the PLC outputs an alarm. Interlocking is realized by DCS, the return valve is opened urgently, and the inlet guide vanes are limited to achieve the protection of the unit. After surge protection, if you want to reload, you need to use the PLC reset button on the booster startup flow chart to reset the fault.
If within a certain period of time (configurable), the PLC detects M times (configurable) surge, that is, it is judged that the surge protection is invalid, the corresponding output of the digital output card of the PLC is interlocked, and the motor is stopped urgently. According to the surge detection schematic diagram provided by ATLAS, its surge detection function is realized in DCS, and it has been verified during the test run, and the control technology of the compressor is a big progress.
In its control principle, the stack data structure is required because it needs to save the pressure data of the 3 cycles before the current scan cycle to calculate the pressure surge slope. However, the data structure of the stack is not provided in the DCS conventional control block. Finally, it is simple and convenient to implement the cyclic assignment of the BDSET 1L type point.
3 4 Expander Control During the commissioning of the engine, major changes were made to the machine side junction box of the expander. Re-adjust the indicator light on the front of the cabinet, keep two indicators: Allow start and run! . When the DCS determines that the expander is ready, the start indicator light is allowed to turn on, and the expander can be started at the DCS or the local cabinet. When the expander's emergency shut-off valve is open, the running indicator lights.
The booster end of the expander also realizes the automatic loading function. When the expander starts to load, the operator clicks the auto load button on the flow chart, and the downhill device closes the return valve from 100% when the exhaust pressure reaches When the value is set, the constant voltage controller is automatically adjusted by the program input.
If the expander overspeeds, it is automatically adjusted by the SICAS 430, and after adding the output of the anti-surge regulator FIC408, the large return valve is opened to control the rotation speed.
The set value of the surge end anti-surge regulator FIC 408 is obtained by a surge test. The PV value of the regulator is the calculated value, not the pressure value or the differential pressure value. It is calculated as: FIC408 PV = supercharged end exhaust pressure - booster end intake pressure booster end inlet constriction differential pressure if PV < SP (surge point parameter obtained by surge test), indicating increase The pressure end is close to the surge, the regulator acts on the return valve adder, and opens the large return valve to prevent the surge. If the operating conditions change drastically and PV is less than the surge protection point, the return valve will be fully opened to protect the machine.
Under the condition that the lubricating oil pressure is normal and the sealing gas pressure is normal, the defrosting button of the expander can be used to open the emergency shut-off valve of the expander and start defrosting. If the following fault occurs during the defrosting process, the interlock will be automatically interlocked and the emergency shut-off valve will be closed: the lubricating oil pressure is lower than normal; the sealing gas pressure is low; the rotating speed exceeds 500r min; the valve does not operate after the shut-off valve is energized for 2s.
If you want to stop the defrost process, you must place the defrost stop button in the stop position. It should be noted that during the defrosting process, the local emergency stop button and the central control room stop button do not work, they are only used for emergency stop during normal operation.
3 5 Nitrogen press automatically controls the nitrogen press to start the same way as the air compressor. When the motor allows the loading signal to arrive, the inlet butterfly valve of the nitrogen press will jump from the starting position of 8% to the minimum opening of 15%. While the climber continues to open the inlet butterfly valve, the vent valve is closed from 100% by the downhill. When the exhaust pressure reaches the set value, the inlet butterfly valve constant pressure controller is automatically adjusted, and the inlet butterfly valve will be in the automatic control state; when the exhaust pressure is less than the anti-surge control line, the vent valve controller is put into automatic adjustment, the vent valve Will be in automatic control state. The operator can then modify the pressure setpoint to operate the nitrogen press at the rated pressure. At this point, the nitrogen press is started, and the operator can open the air valve to supply air to the nitrogen pipe network. It should be noted that the air supply valve must be opened slowly and must be closed when closed. When the control of the nitrogen press is automatically turned on, the operator is strictly prohibited to put the constant pressure controller and the vent valve controller of the inlet guide vane into manual adjustment.
In addition, a current anti-surge controller is also provided. If the high value of the phase currents of the nitrogen compressors A, B, and C is less than the set value, the regulator output will act on the vent valve adder, and the vent valve will open. The motor overcurrent protection is also set. If the motor current is higher than the set value, the regulator output acts on the subtractor, and the inlet butterfly valve will be closed to reduce the compressor load. If the flow rate of the nitrogen press is greater than the set value of 20000 m 3 / h, the regulator output acts on the subtractor, which will close the small inlet butterfly valve to prevent affecting the operating conditions of the distillation column.
In one of the following situations, the nitrogen press will be lightly loaded: the exhaust pressure is super high; the nitrogen press is surged; the operator is forced to light load by the HS1503 forced nitrogen press. Nitrogen press light load action: inlet butterfly valve limit to 15%; vent valve fully open. After the fault is removed, the operator can automatically resume the loading of the nitrogen press through the recovery load button on the nitrogen compressor air circuit diagram, the same process as when starting. The problems encountered by Tiangang's nitrogen compressor control and its solutions: (1) The amount of nitrogen used in the steelmaking process fluctuates too much: the amount of nitrogen will change from 0 to 20000 m 3 / h in 1 min or from 20000 m 3 / h to 0. Because the nitrogen spherical tank is too small, only 400m 3 , it causes a large fluctuation of the nitrogen pressure machine working conditions. The inlet butterfly valve and the venting valve frequently operate, and the nitrogen pressure machine is easy to be out of adjustment. Finally, the operating conditions are stabilized by repeatedly adjusting the PID parameters, and the control of the nitrogen compressor is adapted to the fluctuation of the gas consumption.
(2) Control of the inlet butterfly valve: The change of the opening degree of the butterfly valve has a great influence on the operation of the nitrogen pressure machine, so the opening degree of the butterfly valve is limited, the maximum opening is 55%, and the minimum is 30%.
(3) Defects in engineering design: The flow orifice plate is not installed at the outlet of the nitrogen press, but is installed on the gas supply pipe, and cannot be used as the anti-surge of the unit, so the current is used for anti-surge.
(4) Insufficient current anti-surge: Since the motor current is converted by electronically controlled CT, there is error and large hysteresis, which is not suitable for anti-surge control of compressors that are sensitive to requirements.
4 Other system automatic control (1) Air pre-cooling system: The valve V1166 at the bottom of the air cooling tower is an on-off valve controlled by a solenoid valve. According to the requirements of Hangyang oxygen, the function is to open the control logic urgently when the liquid level of the air cooling tower is too high. In order to prevent molecular sieves from entering the water. Since the manual steam trap was cancelled during the design of the Hangyang design, during the test run, the operator requested that the valve be controlled by logic and manually controlled to switch the water to the air cooling tower after parking. After modifying the control logic, the process needs are met.
(2) Designed the automatic start of the instrument air compressor. When the air separation equipment is stopped and the instrument air main pipe pressure is lower than the set value, the DCS automatically starts the instrument air compressor to ensure the instrument gas supply of the storage tank and the pressure regulating station system.
(3) The return valve after the modification of the circulating liquid argon pump is controlled to the liquid level control instead of the pressure control.
(4) Considering the safety problem, the filling pump and the filling tank pump of the liquid storage tank system are changed from the central control room to the local starting.
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