Chemical automation and instrumentation from the transformation of PTA plant air compressor control system to talk about the improvement of the system Jin Bin (China Petroleum Liaoyang Petrochemical Company aromatics plant instrument workshop. Liaoyang 111003, Liaoning) control system technology upgrade to achieve PTA plant air compressor stability And reliable operation.

The PLC control system that has been in operation for about ten years has gradually entered the high-risk period of failure, but the sound components of the proprietary control board system that the original compressor manufacturer is supporting are no longer produced, which makes it more and more difficult to purchase, and the risk of control system operation is increasing. Enterprises are actively exploring the transformation of control systems based on actual production needs. Based on the actual situation on the spot, Liaoyang Petrochemical conducted in-depth research from the problems existing in the original system to the formulation and implementation. The modified control system is currently operating stably. The effect is good. It achieves the intended purpose and effect, and provides a strong guarantee for the smooth production of the device.

1PTA device air compressor control system introduction Air compressor unit structure as shown. The air compressor is the core set of the PTA unit, providing compressed air to the unit oxidation reactor. The unit is mainly composed of four parts: axial compressor, centrifugal compressor, exhaust gas turbine and synchronous motor. It is also equipped with a speed-increasing gearbox, lubricating oil system and inlet air filtration system. The control system adopts GE9070PLC and MOORE352 intelligent regulator. GE90~PLCCPU is single configuration, the startup program and interlock protection logic control of the unit, MOORE352 intelligent regulator is formed into axial flow, anti-surge of centrifugal compressor And the process control of the unit outlet pressure and exhaust turbine, the intelligent regulator communicates through the proprietary communication interface board and PLC; the temperature, displacement and vibration signals of the unit are detected by the input board developed by the manufacturer. Embedded in the PLC rack as its I/O input board, the human-machine interface is composed of a computer embedded in the PLC rack, which is used for data acquisition and display; and the control room DCS communication adopts RS485 mode, which is programmed by the PLC's coprocessor. .

Schematic diagram of air compressor unit Jin Bin talks about the improvement of the air compressor control system of the PTA device. With the increase of the operating system of the control system, the system gradually enters the aging period, especially the human-machine interface embedded in the computer has frequent faults. The co-processing board communicated with DCS is not working properly, the temperature, displacement and vibration plate developed by the manufacturer are no longer produced. The failure rate of MOORE352 intelligent regulator and PLC communication sometimes occurs, which brings the extreme operation of the control system. The big hidden dangers, using new advanced technology to transform it has become an inevitable choice.

2 Control system improvement technology introduction The control system used in this transformation is a new generation system developed by compressor manufacturers. The hardware adopts GE90J0PLC redundant system. Compared with the old system, the system is more open, the function is more complete, and the system reliability is further obtained. Improve; have a good man-machine interface, easier to operate; the new system integrates the unit's start sequence control, interlocking logic protection control, unit temperature, pressure process control and anti-surge control, eliminating the old system The communication problem of the manufacturer has many obvious advantages compared with the old system. The main performance comparison is shown in Table 1. The project redundant operation station control table 1 The new transformation system and the original system main performance comparison The modified control system adopts two separate racks. The CPUs are hot standby redundancy, and the input and output point cards participating in the anti-surge are connected to a plurality of ordinary industrial desktops through the Ethernet mode by using the racks as the hot standby redundancy mode, and the versatility is adopted by the Ethernet universal network card. The connection method is based on the human-machine interface developed by Windows XP. Support online diagnostics of the system, longer-term trends and event records. Support SOE event entry (can maintain the trend curve of two minutes before and after the stop, accurate to the second and minute trend, very conducive to the problem analysis using dual-rack CPU for each other in addition to the redundant standby control system In addition to the original start sequence control and interlocking logic protection control, the unit also completes the anti-surge control and temperature and pressure process control using the Genius bus mode. The system scans the I/O card faster, the system application The running cycle is shorter and DCS communication adopts GE's communication board, communicates through RS485 redundant mode, and runs stably to increase the fast logic relay function. The emergency stop button can ignore the operation of the PLC program, and the fast logic relay directly acts to make the unit safe. The state system adopts Genius I/O, no third-party I/O, more convenient configuration, more flexible system expansion, higher system stability, original control system, original CPU model does not support redundant mode, participate in anti-surge and process control. Both the input and output points enter the intelligent regulator, and the regulator hot standby mode cannot be implemented. A meter embedded on the VME bus of the PLC rack. Computer, poor versatility, high failure rate VME bus connection method based on DOS6.2.2 development of human-machine interface screen is less, does not support the online diagnosis of the control system, less trend and event records, does not support SOE event record The original control system of the original single-rack single CPU control system only completes the startup sequence control and interlocking logic protection control f anti-surge and process temperature and pressure control in the MOORE352 type intelligent regulator to complete the VM bus mode, plus the need The third-party equipment communicates, the scanning speed of the system is relatively slow, and the DCS communication is programmed by the GE coprocessor board. The communication is good or bad, and the reset communication is often required. The system does not use VMEI/O. The original system includes a third-party I. /O, such as vibration, displacement and RTD board, the system is not flexible, the configuration is more complicated. The transformation scheme of the control system uses the new generation GE9070PLC dual redundant system of the original compressor manufacturer as the upgrade scheme. The system hardware is as shown.

This transformation fully considers the risk that the CPU failure of the original system has caused CPU failure to the unit operation. Therefore, the two separate rack CPUs are used for mutual thermal redundancy, dual GBC dual bus redundancy, and the CPU and bus are implemented. All are redundant.

The system uses the third-party card and third-party interface card communication to bring the system to run unstable and the system expansion is not flexible and the sound is difficult to purchase.

The inlet guide vane of the 352 intelligent regulator and its anti-surge control, the pressure control of the centrifugal compressor for one and two stages and its two-stage anti-surge chemical automation and instrument control, exhaust gas turbine The temperature and pressure control are all placed in the PLC, making full use of the PLC resources, and at the same time solving the communication problem of MOORE regulator and PLC and its hardware aging, the failure rate is increasing year by year.

Although the redundancy method for powering the system has been considered, it is known from the problems encountered in many years of operation that the power supply to the field transmitter from the system does not take into account the redundancy mode, but only one way of power supply, there is a risk. This transformation has fully considered the 3 shown.

(After the parking of the two deuteration reactors, it can be opened after the manual device is stopped for a period of time.) The compressor pressure is high and the interlock is stopped. The power supply redundancy system for the field transmitter is solved. According to the operation experience and problems that have occurred in the field for many years, this transformation process has been carefully considered and discussed, and implemented in the system transformation, so that the problems existing in the original system have been fundamentally solved.

Optimize and adjust the second stage outlet pressure of the centrifugal compressor PIC-5101 control scheme (). Adjustment; section outlet pressure) ramp time, oxygen set the regulator to manual, and maintain the output value, the purpose is to stimulate the reaction force fluctuations and possible surge and optimization and adjust the centrifugal compressor two-stage outlet pressure PIC-5101 Control program Jin Bin from the transformation of the PTA device air compressor control system to talk about the improvement of the system technology PIC-5101 measurement point from the original PT-5101 (after the centrifugal two-stage check valve) to PT-5105 (centrifugal two Before the valve is reversed, that is, when the PV value of the regulator fluctuates due to pressure or the system is holding material, the regulator can quickly detect the compressor outlet pressure and can be quickly adjusted; change the original LSR-IDT ramp time of the PIC-5101 program to 10s. For 2S, the LC-MOP manual output value is changed from the original 5500 to 4500, that is, when the reactor is stopped, the opening of the anti-surge valve is manually opened to 55% of the opening to prevent pressure fluctuations and high pressure of the unit. Interlocking parking.

Increase the isolation measures of the system to improve the anti-interference ability of the system. The original system, whether it is AI, A or DI, D point field instrument power supply has a common problem at the positive end, specifically for the positive end of the AI/AO field instrument 24VDC common problem is when the 24VDC positive terminal has a virtual ground or grounding It affects the power supply of the entire field instrument. The display of the PLC is I/OFAULT, which affects the process control of the unit. When the CPU of the I/OFAULTPLC fails, the application stops running. For the common problem of the positive end of the DI/DO field instrument 110ACV, when the positive end of the 110ACV has a virtual ground or ground, the fuse is broken or the entire 110ACV voltage drops, causing the interlock point to operate and the machine to stop. This transformation uses MTL isolation barrier to increase system isolation measures. The virtual ground or grounding at the site is only a certain point (or one channel), which will not affect other points (or other channels) and improve the anti-interference ability of the system. , reducing the occurrence of unnecessary failures. The wiring pairs before and after the transformation are as shown.

The air compressor control system after the transformation of the final language solves the hidden dangers and problems of the original system, and the system is more open, and also improves the safety and reliability of the system. The modified system is stable in operation, and the control of the air compressor is more energy-saving, which plays a role in escorting the long-term stable operation of the device. This transformation has also accumulated experience for the transformation of other systems in the future, enriching and improving the professional knowledge.

(Continued from page 1186). After on-site testing, the central control room has realized centralized monitoring of the bridge crane, and the system is stable and effective, and can be quickly and accurately smashed into handling work, improving work efficiency.

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