Application of polyester industry S7400PLC control system in PTA air compressors Xia Yu, Li Yonghong (Urumqi Petrochemical Company, Urumqi, Xinjiang 830019, China) In the field of defects, using the field instrument, using Siemens' latest S7400PLC system to achieve interlock control, and update Displacement and vibration monitoring system. On the basis of analyzing the existing control technology, the PLC control system and fieldbus technology were analyzed and studied. The design idea of ​​the control system and the design ideas and system implementation of the hardware and software of the air compressor control system are discussed.
The PTA plant of Urumqi Petrochemical Company adopted the British ICI patent technology and was completed and put into operation in 1995. As the core equipment of the device, the air compressor has a complete control system design and a high degree of automation. The unit and the supporting control system are all produced by German DEMAG company. After long-term operation, the control system has many hidden dangers. This paper analyzes the process characteristics of the PTA unit air compressor and the original interlock control system, analyzes the existing problems, and implements the technical transformation through the S7400PLC system to realize the interlock control, which increases the stability of the control system and effectively reduces system error. The modified air compressor control system is stable in operation, high in safety and high in automation.
1 control system 11 air compressor process The air compressor in the PTA device is the key equipment of the PTA device, providing compressed air for the oxidation reaction. The air from the air intake port B1-167 is filtered through the inlet filter M1412 and then passed through the air. Press C1413A/B/C/D4 compression, and the condensate is cooled in the 4-stage compression valve via the 3-stage valve cooler E1417A/B/C. The air generated by the compressor of 1.80 MPa and 130 ° C enters the oxidation reactor D1-301 and the first crystallizer D1401 normally. When abnormal, part or all of the air is discharged to the atmosphere via the anti-surge valve FCV6615. If the air compressor fails, the oxidation unit will be shut down and shut down. Therefore, ensuring the smooth operation of the air compressor and reducing its failure rate have become the key to improving the production capacity and market competitiveness of the plants.
The process flow of the PTA unit air compressor is as shown.
Air compressor process 1.2 Control system conditions The air compressor used in the PTA unit is produced by DEMAG, Germany. It is a 4-stage compression, a 2-stage turbine assisted, powered by a motor, with a power of 4000 kW and a design four-stage outlet pressure of 2.25 MPa to provide compressed air for the PTA plant oxidation reactor.
This equipment is the key equipment of the PTA device, so the air compressor instrument interlock control system directly affects the operation of the air compressor.
The interlock control system is produced by DEMAG in Germany. It has been in operation for more than 10 years. The interlocking part adopts single equipment due to the aging of some components and the instrumentation of the interlocking. The operation and state changes of the air compressor are not recorded. The interlocking and alarm events of the parking are not recorded in order, and the first cause of the accident cannot be determined. The oxidation air compressor has been interlocked and stopped several times, causing the entire device to jump, which brings great hidden danger to the safe operation of the device. Therefore, the air compressor interlock system must be modified.
2 Determination of control schemes At present, PLC technology has been widely used in every aspect of industrial production systems, especially complex control loop systems. Air compressor-), female, Shanghainese, engaged in automatic control technology management and maintenance work.
Xia Yu, et al: S7400PLC control system in the PTA device air compressor application instrument interlock control system can also choose the appropriate PLC for optimal control.
2.1 Control system selection (1) System scale: This mainly refers to the number of I / O (input / output) points.
(2) Complexity: It includes a lot of content, such as the complexity of mathematical models, the complexity of batch problems, the availability of expert systems or other management functions with complex procedures, and the requirements of decision-making functions. It is generally believed that DCS is more suitable for more complex applications.
For example, DCS is still more suitable for analog control.
(5) Other factors: the service support of the seller, the difficulty of configuration, programming operation and training; development cycle, change, expansion requirements, etc. For a relatively simple system, the British vJLovuola recommended this principle of experience: (A * analog I / O points. D - switch I / O points) 256, you can choose the combination of PLC and DCS; The total control I/O point of the press is nearly 300, and most of them are switching quantities. Combining the above factors, the air compressor is most suitable for PLC system.
2.2 Control plan table, the display alarm table is a card type indicator. Now use the ST400PLC system as the main controller. Cancel all original conventional rack mounted instruments.
Changed to the Bentley 3500 system.
Point, increasing the trend to facilitate centralized monitoring of operators and training for process operations.
3 Implementation of the scheme (1) The original control cabinet adopts PLC as the main control instrument, and the display alarm table is a card type indicator. The vibration system uses the Bentley 3300 system to study and analyze the control strategy and application characteristics of the original control system of the air compressor and the defects in its use. The solution is determined to use the S7400PLC system as the main controller, and the vibration detection is the Bentley 3500 system.
Control strategy and application characteristics, as well as the implementation of internal interlocking and control of the system, hardware selection, configuration, system configuration, logic implementation and selection and application of communication protocols, and try to implement selection control and other functions.
The trend is to provide a basis for process operation. Research and analyze the interface technology between the TDC-3000DCS system and the S7400PLC system of the PTA device.
(4) After various aspects of analysis and research, the latest control system hardware and software design selected by the air compressor is selected from Siemens S7-W0HPLC control system. Siemens uses SCAUT (SIEMENSCOMPRESSORAUTOMATION) control on the compressor unit. The PROFIBUS bus is used as the communication protocol between the entire field device and the controller. The communication protocol between the field device control system and the distributed I/O is PROFIBUS~DP, and the I/O module connecting the control points selects the cheaper ET200 module. Using Siemens LCD color touch screen MP270 as the host computer, you can also use external PC as the host computer to realize unit running time and downtime display, machine phase display, speed display, temperature display, parameter modification, unit effective operation rate and output and material consumption. Statistics, fault alarms and history records; PLC and touch screen host computer exchange data through MPI communication protocol.
4 implementation effect to achieve air compressor control function, the system uses redundancy, to achieve PLCCPU redundancy, power redundancy, communication module and communication bus redundancy, host, slave can be switched without disturbance, module can be replaced online, reliability is significant Improvement, the amount of maintenance is significantly reduced, and the system failure rate is greatly reduced. The main advantages are as follows: the controller is connected, and the important process parameters, fault status and alarm information can be collected and displayed in real time. The important PID parameters can be adjusted, and the main motor and auxiliary equipment can be started/stopped to achieve optimal control of the unit.
(2) The operation and state changes of the air compressor are recorded. The interlocking and alarm events of the accident parking are recorded in sequence, which can quickly determine the first accident cause of parking, and provide basis for accident judgment, fault point determination and accident prevention.
(3) The system has powerful communication functions, supports multiple communication bus protocols, and has an open network structure for communication with its DCS. The air compressor S7-400PLC system data is introduced into the PTA device TDC-3000DCS system to configure the points and increase the trend. The data of the configured points can be remotely monitored in the control room even as far as the dispatch room.
(4) The vibration monitoring protection and anti-surge control system is relatively good in the polyester industry, which fully guarantees the smooth operation of the production and the protection of the unit's own equipment.
5 Conclusion With the continuous expansion of modern industrial production scale, while the development of DCS, intelligent regulators and PLCs are also developing rapidly, providing a broad prospect for optimizing industrial production system control. Through the optimization of the air compressor unit control system of the PTA plant of Urumqi Petrochemical Company, the selected S7400PLC system has passed the inspection of the production operation of the plant, which proves that the expected effect is achieved through this transformation, and the reliability of the system is improved, the maintenance volume is reduced, and the fault is reduced. The rate has been significantly reduced, ensuring the safe and reliable operation of the production equipment, indicating that the system can be successfully used in the PTA unit air compressor unit control system, providing a reference for the industry.
Due to the rapid increase in production capacity of PET products, structural adjustments are now taking place. China's polyester production capacity is rapidly expanding and is bringing greater impact to the market. In recent years, China's fiber industry, due to the development of low-cost countries in Asia, is worried about export growth difficulties, and the downstream fiber industry operating rate has declined. To this end, China's polyester industry is expected to decline the demand, will usher in the "production capacity elimination" and "industry restructuring" test.
In 2013~2014, at least a new polyester plant with an annual output of more than 4 million tons was put into production. The project with an annual output of 400,000 tons in Tongkun was successfully commissioned in January 2013. The annual production of 300,000 tons of Jiangsu Yingxiang Chemical Fiber has recently been approved by the National Development and Reform Commission. In addition, about 10 companies are under construction or are planning to start production of polyester filament equipment with an annual output of 300,000 to 400,000 tons.
On the other hand, according to the prediction of relevant personnel in the industry, the demand for PET products in 2013 is about 10%, polyester filaments are 12% ~ 13%, polyester staple fibers are 6% ~ 7%, PET bottles are sliced ​​10% ~ 12%. The film grew by 8% to 10%.
However, as the production capacity of various bio-fibers and the like expands, the choice of raw materials for downstream increases, and the demand for PET products cannot be as far as it has been. Therefore, relevant personnel in the industry pointed out that for the PET industry, it is necessary to focus on the elimination of old equipment. From 2003 to 2010, the total production capacity eliminated was 4.45 million tons, and 23.4 billion yuan of non-performing assets were eliminated. The assets of 35 billion yuan were activated due to acquisition and restructuring.
In 2013, the old equipment elimination requirement, the chemical fiber industry's goal is to increase from an annual output of 220,000 tons to 314,000 tons in 2012. However, the production capacity of China's chemical fiber exceeds 30 million tons, and it should be able to successfully complete the task.
(Wang Decheng contributed) Tianjin Petrochemical developed two new PET fiber products, Tianjin Petrochemical Company and Beijing Garment Institute jointly developed two kinds of multi-functional fine wool and composite functional polyester staple fiber. Recently, it passed the technical appraisal of Sinopec Group Company and obtained customers. Alike.
Tianjin Petrochemical New Product Development Workshop has a research and development production line based on multi-functional fiber, which can produce PET fine denier and various functional differentiated polyester staple fibers. They cooperated with Beijing Institute of Fashion Technology to process the process of preparing wool-like fibers by blending PET and PTT blending. The molecular structure was designed to produce the same properties as wool, strong stretch, elasticity and three-dimensional curl. Excellent fine-spun wool-like fiber. At the same time, the molecular structure design and the synergistic action of organic and inorganic modifiers are used to solve the problem of functional powder dispersion, and the polymerization rate, molecular mass, fiber supramolecular structure and morphological structure are controllable, and the production is realized. PET fiber and its fabric with moisture absorption-dehumidification, antistatic anti-UV, anti-pilling and composite function.
(Zheng Ninglai contributed)
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