Changzhou Chemical Industry School (21304) describes the composition, basic configuration, basic functions, major technical indicators, and performance of DCS.
1 The DCS decentralized control system (also called distributed control and distributed control system) is a high technology in the field of control. It integrates computer technology, communication technology, CRT display technology and process control technology, and adopts multi-layer polarization. The structural principles and design principles of decentralized control, centralized operation, hierarchical management, and self-governance separation have solved the drawbacks of computer control hazard concentration in the past, and the conventional analog instruments have a single function, are too scattered and inconvenient for human-machine contact. DCS's safety, reliability, general flexibility, excellent control and comprehensive management capabilities make it widely used in industrial control.
Our chemical training center lOOOt polyester production line is a dual-use device for production and teaching practice. In the selection of the control system, first, taking into account that DCS has a higher performance-cost ratio and its advanced technology, the market share is increasing day by day, and the second is that students should be exposed to advanced control equipment and master advanced control technologies. The need for future work. To this end, we have selected the FB-2000DCS decentralized control system developed by Zhejiang Weisheng Automation Co., Ltd., which was developed earlier in the country, mature in technology, reliable in quality and possessing a certain market share.
2lOOOt polyester production line DCS lOOOt Polyester production line automation technology is an important guarantee for safe and economical operation. The FB-2000DCS selected for this control system is the first distributed control system using fieldbus technology in China and adopts a hierarchical distributed intelligent architecture. It can be configured on-line and hot-swappable. It can guarantee the reliable operation of the system from the system structure compared to the traditional control system. It has advanced technology, reliable operation, functional and practical, friendly interface, convenient operation, and is suitable for various industries. Environment and scale, and have the capacity for upward compatibility.
3 System composition According to the technical characteristics and monitoring requirements of the PET polyester production line, the system adopts two levels of process control level and monitoring level, mainly consisting of a field control station and an operation station. The on-site control station is responsible for the production process control and data acquisition. The monitoring-level operation station is responsible for displaying various screens such as monitoring, alarm, control loop, various parameters, historical data, and statements, as well as data analysis, statistics, storage processing, and production scheduling management. . Field control stations and operating stations exchange data information via communication lines (see).
4 Basic configuration of the system 4.1 Operation station OPS CRT operation station 2 Field control station FCS 8-channel analog output terminal board 4.3 Industrial control software package 4.4 Field instrument PtlOO Platinum thermal resistance, digital display instrument, pressure, flow, level transmitter, Electromagnetic-pneumatic shut-off valve, pneumatic diaphragm control valve. 5 basic functions of the system According to the characteristics of PET polyester production process (charging * propeller, esterification, polycondensation, pelleting, drying, storage) and the control requirements of each production link, the control strategy of each part of the system is determined, and the configuration of the industrial control software Generate application programs, download them to process control stations, and implement the following functions.
5.1 Real-time control functions 5.1.1 Kettle temperature regulation The two-reaction Dad temperature closed-loop regulation system uses acetalization and polycondensation to regulate the heat balance of the jacket thermal oil flow control method. According to the process requirements, the system sets the temperature setpoint. The temperature signal is sent back to the kettle via the Boreothermic sensor. After comparison and calculation processing, the aperture of the pneumatic diaphragm control valve is adjusted to change the flow of the thermal oil and correct the balance. The temperature inside the kettle can be stabilized within a given range. The system has two manual/automatic adjustment methods.
5.1.2 Temperature adjustment of the top of the distillation tower The closed-loop temperature adjustment system of the top of the distillation tower of the esterification tank adopts circulating water cooling method. The system adjusts the cooling water flow according to the temperature setting value and the medium outlet temperature, and controls the tower top temperature. There are hand/automatic two adjustment methods.
5.1.3 Condensation kettle negative pressure regulation Polycondensation kettle negative pressure closed-loop regulation system, according to the negative pressure set value and the size of negative pressure within the father, adjust the opening of the vacuum bypass pneumatic diaphragm control valve, control the degree of vacuum in the kettle. There are hand/automatic two adjustment methods.
5.1.4 Speed ​​control of slurry pump and polycondensation stirring motor The two-motor speed control system adopts open-loop control mode. By changing the frequency setting value of the inverter through the DCS operation screen, the input current signal and output frequency of the inverter can be changed, thus controlling The speed of the motor.
5.2 Display and operation functions In addition to displaying the process flow chart with measurement points and the aforementioned various screens, the monitoring level CRT can also be operated at the operator level via the screen buttons!丨 Group gas-fired implementation device, 2 sets of frequency control, 4 sets of hand / automatic program control adjustment and start and stop of some motors. At the engineer level, the configuration of control strategies, the modification of the flow chart screens, and the control commands sent directly to the process control station can be used for production scheduling management.
5.3 Alarm function The CRT console is equipped with a flash alarm to remind the operator to deal with it in time.
5.4 Report Printing Function The printer configured by the monitoring level operator station can print various production reports.
5.5 Standby Meters and Manual Operation Functions The system's important process parameters are equipped with backup display instruments and actuator operators. Therefore, the system has an independent manual operation function. Even if the system host controller fails, the system can still work normally under manual operation.
5.6 Simulation function for production training In order to cooperate with students, a simulation laboratory is set up on the site. Ten simulation computers are connected to the system to monitor the production process in real time and simulate the operation of field devices. Students are familiar with the DCS control system (Continued from page 36). Page) Need to increase the problem of the device. Vendors have to consider whether they can allow more than one protection at a central location. On the other hand, Mills are also considering recommending that the UK adopt the arc fault arc extinguishers that must be followed in the installation of US installations in manufacturing.
Although conventional circuit breakers trip by overload or short circuit, they always ignore sparks generated by arc faults caused by low unstable current flowing. In low-voltage loops, such arcs can last for long periods of time, sometimes up to 5000*C, but they can cause cable insulation levels to fall and sparks in nearby materials.
The arc fault circuit arc extinguisher can discriminate the arc generated by the shaping current and voltage. If a series-parallel arc or arc-to-ground arc pattern is detected, it trips. This installation is mandatory for US implementation from January 2002 on new domestic installations. Although this description is only suitable for domestic installation and installation of suburban circuits with currents of 10-15A, it is also suitable for low-voltage circuit protection.
Another additional protection device, the transient overvoltage suppressor, has been available for many years. Major UK switchgear merchants and some mainland companies are accelerating their production. One is made in the US and the other is made in Australia.
Transient overvoltages are high-voltage pulse spikes. The worst part of this pulse is not only sustained for a few milliseconds, but can also result in equipment malfunction or severe damage. They are usually generated by lightning, and only 20% of the transient voltage is generated as a result of the discharge generated by opening and closing the high-voltage power line network. The rest is generated from internal power supplies such as load switches and normal equipment operation.
If there is no protection, direct lightning strikes can cause catastrophic damage, and even indirect impact can cause transient voltages to be induced in nearby cables. Even if external protection is provided, the internal residual transient voltage can affect the equipment unless secondary protection is provided on the branch distribution board. When triple protection is required to protect the equipment, it should be provided by the terminal distribution circuit.
There is no universally named device in the manufacturer to provide protection against transient overvoltages. According to their location in the power distribution system, these devices with different names are identified. Among them are instantaneous voltage pulse suppressors, pulse lightning protection, and pulse protection devices. And transient voltage protectors. Due to international differences, further confusion has arisen. For example, in Germany, transient voltage protectors conform to VDE and DIN standards. UK users will find four categories: Category A for low-voltage overhead lines; Category B for lightning protection of incoming power; Category C for prevention of internally generated transients. Overvoltage, while Class D is used for equipment protection for special projects. Class D equipment must be used with Class C; equipment manufactured in the United States that conforms to IEEE Standard C62.41 is classified by reversed-phase instructions and has only three areas.
Category C is outside the building, or on the main incoming line low voltage distribution board power supply side. Class B is in the power distribution system, between the load side and the outlet power supply side of the incoming distribution board or fuse, or the internal equipment and equipment cannot be fed from the wall outlet, or the branch distribution board has a series cable of 20m Class C equipment, or plug device or breaker with a series 20m cable class C equipment. Class A equipment that is explicitly operated as a plug device or side hole with a cable larger than 20 m.
Where there are UPS systems, it is not guaranteed that transient voltages are prevented. Although many suppliers include filters in the UPS system, they usually only meet the suppression of low voltage overvoltages and are not capable of resisting pulses from lightning surges. Many UPS systems have a bypass connection between operational faults and overvoltages, which requires the addition of a bypass pulse suppressor.
Systems, production operations and other training provide convenience.
6 Main Technical Specifications and Performance Process Parameters Detection Display and Alarm Accuracy Reactor Temperature Control Accuracy (Steady State) Polycondensation Kettle Negative Pressure Control Accuracy (Steady State) Polycondensation Kettle Roller Mixer Motor Variable Frequency Speed ​​Regulation Feed Pump Motor Variable Frequency Speed ​​Regulating Distillation Tower Top Temperature Control Accuracy (Steady State) Hand/Automatic Bumpless Switching System Self-diagnosis, Online Maintenance, Simulation 7 Conclusion After nearly two years of multi-batch production operation, the system has stable equipment performance, extremely low failure rate, and greatly reduced operations. The labor intensity of personnel improves production efficiency. As the system has excellent control performance and stability, product quality can be guaranteed, and good economic benefits are created. More importantly, it provides advanced production internship sites for school teaching and solves problems. The practical problem is that this type of dual-use device for production and education is a broadening of the school’s ideas for running schools. It is a new attempt. In May 2001, it was highly praised by the expert group and the leaders.
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