1 overview
Textile industry is an industry that processes natural fibers and manufactures processed chemical fibers. Spinning, weaving, printing and dyeing are the processes of processing natural fibers, which have poor continuity and low automation level, and are labor-intensive production processes. Chemical fiber production is the production process of manufacturing fibers, which is a multi-machine, long-flow, highly continuous and highly automated production process.
2 Development and present situation of chemical fiber automation
From the early 1960s to the mid-1970s, in the process of chemical fiber production in China, the electrical unit combination instrument and qdz were mainly used in a mixed way, and the control room was set as a unit for centralized control. Since the late 1970s, centralized control has been carried out with electrical instruments as the main body and workshops or devices as the unit, and distributed control system (DCS) has been adopted in large-scale chemical fiber projects. It was not until the late 1980s that mass flowmeters, intelligent transmitters, digital display and adjustment instruments were adopted, and online analytical instruments were used more. At present, DCS is basically used in new large and medium-sized chemical fiber projects.
Driven by imported projects, all field instruments and control systems used in chemical fiber production have basically reached the world advanced level in hardware. But there are two main problems:
1) The application level of DCS is low, which basically replaces the functions of conventional instruments.
2) In the newly-built large and medium-sized chemical fiber projects, more than 80% of instruments used are imported, and almost all DCS and PLC used are imported.
Therefore, how to improve the application level of DCS to improve economic benefits; In the selection of instruments, how to improve the localization rate, reduce investment and promote the long-distance development of automated stationery in China is an urgent problem to be solved.
3 ways to improve the application level of DCS
In the process of chemical fiber production, DCS has been widely used, but its functions are mainly simple PID control, cascade control, proportional control, parameter or status display, special optical alarm, remote operation and printing reports. , far from giving full play to the due role of district boards. The application level of DCS can be improved from the following aspects in the future.
1) Using the powerful and open communication function of DCS, the DCS in the whole plant can form a monitoring network and a comprehensive information network with management as the main function, so that it can provide a basis for optimizing height, management and leadership decision-making while carrying out real-time control, and create conditions for realizing comprehensive automation of enterprises.
2) Use the powerful operation function of DCS for soft measurement. In the process of chemical fiber production, some key time changes can not be measured directly, such as esterification degree and polymerization degree in synthetic fiber production; Maturity in viscose fiber production is an important index of intermediate product quality, which directly affects product quality. It is a process parameter that must be closely monitored and strictly controlled in the production process. Now it is determined by laboratory testing, which is not timely and often leads to many defective products. Using soft-sensing technology to measure these variables timely and effectively is of great significance to improve product quality. The difficulty lies in how to establish a soft sensor model. First of all, we should study the chemical or physical mechanism in the production process to determine the mathematical relationship between these unmeasurable variables and measurable variables, or establish a soft-sensing model through experimental statistical regression method, and then calculate and display the unmeasurable variables needed by DCS in real time according to the relevant measurable variables, so as to make the operation and monitoring intuitive and convenient, and then realize the process control or optimal management of these variables.
3) Advanced control and optimal control are carried out by using the powerful calculation function and control function of DCS. Chemical fiber production is generally a long process, strong continuity and strict control requirements. The quality of products is directly related to the composition of materials, the temperature and pressure in the equipment, and the residence time of materials in the equipment, and the stop time is related to the liquid level and material flow. In this continuous production process, how to make the relevant controllable variables react with the changes of controllable variables in a timely manner according to certain laws to ensure product quality and stable production. It is necessary to choose effective control schemes and advanced control methods according to different production characteristics, such as fuzzy control, adaptive control, predictive control and optimal control, which have achieved good results in petrochemical industry. Some academically mature technologies have not been well applied in skid-mounted production, which requires automation workers to implement advanced control and optimal control in view of production practice on the premise of in-depth study of process mechanism and thorough understanding of process, in order to obtain better economic benefits.
4. Improve quality, increase varieties and promote localization.
In large and medium-sized chemical fiber factories, most instruments are imported. The main reasons are: there is still a certain gap in quality between domestic instruments and imported instruments; Varieties can not fully meet the demand, especially some special instruments are not produced; Market management is not standardized, and there are factors such as inequality and competition.
4. 1 The instrument must be designed for users.
Should have high reliability, good environmental adaptability, easy to install, maintain and repair. For example, when the magnetic column level gauge is used in the tank farm of a factory, it often happens that some magnetic columns do not turn or the whole magnetic column does not move. Qiangguo will seal the whole magnetic column with plexiglass, which greatly improves its reliability and adaptability to the environment. Another example is that some field instruments do not have junction boxes, but use aviation sockets or leave a short cable, and some leave two short wires, which makes it difficult to connect field instruments, and the process connection specifications of field instruments are not uniform, which brings inconvenience to installation.
4.2 Improve the quality management system and improve product quality.
Automation instrument is a high-tech product, which must have advanced manufacturing technology and equipment, strict detection means, necessary special technology and perfect production management system to ensure product quality. At present, the production order of domestic instrument industry is chaotic. In some places, there are more than a dozen or even dozens of factories in a city that produce the same kind of instruments. Some small factories have poor production conditions, neither advanced production equipment nor strict management measures, and do not pay attention to product quality. Focus only on sales. These small factories should be rectified, and those with poor conditions should be closed or stopped; If conditions are good, we should unite and cooperate with other workers. The state should focus on supporting a number of domestic powerful enterprises, improve production conditions, improve the quality management system and improve product quality.
4.3 Introduce advanced technology and develop special instruments.
With the rapid development of science and technology, all walks of life have higher and higher requirements for automatic instruments, and more and more special instruments are needed. At present, the varieties and specifications of instruments in China can not meet the needs of users, especially the special instruments for various industries, which are generally unwilling to be developed because of high technical requirements and low consumption. For example, in the textile industry, it is used in the production of viscose fiber, such as porridge concentration meter, fiber hygrometer (measuring fiber moisture content), coagulation bath concentration meter, bleaching solution concentration meter, oil concentration meter and trace carbon disulfide analysis letter in the air; Polymer viscometer, ray level gauge, diaphragm pressure transmitter, high-speed rotating hot roller temperature detector, solid material switch valve in pneumatic conveying system, etc. Used in synthetic fiber production; Wool detector, textile defect detector and dye concentration meter are also used in the textile process. It is difficult to find products suitable for these instruments in China. There are similar situations in other industries. It is expected that the instrument research and development unit can absorb the world's advanced technology and conduct research and development in close connection with the actual situation to meet the needs of various industries.
4.4 Standardize the market competition mechanism and purify the domestic instrument market.
Although some domestic instruments are equivalent to imported instruments in terms of technology and product quality, their prices are cheaper than those of imported instruments, and their service quality is far higher than that of imported instruments, some users still spend a lot of foreign exchange to buy imported instruments because some foreign businessmen or agents have adopted some improper promotion methods, which have damaged the national interests. Therefore, it is necessary to further improve the bidding mechanism, purify the unequal competitive environment, encourage the use of domestic instruments and equip China's automated production lines with advanced domestic instruments.
5 Suggestions on the development of chemical fiber automation
With the rapid development of chemical fiber automation, higher requirements are put forward for automatic control. Field instruments are gradually developing in the direction of digitalization and intelligence, DCS is gradually developing in the direction of field bus control system, and single realization control is gradually developing in the direction of management and control integration. According to the development of skid-mounted automation in China, we should pay attention to the following points at present:
1) First of all, we should make good use of the existing DCS, popularize and apply more mature advanced control technologies on the basis of digesting and absorbing Jin Yang's advanced technologies, and organize the development and research of optimized control software in combination with the actual situation.
2) Recently, the function, reliability and openness of DCS developed in China have been roughly equivalent to those of foreign countries, and its price is only two-thirds of that of imported DCS, and it has been gradually popularized and applied in the State Council. For example, HS2000 of Beijing Hollysys Company and FB2000 of Zhejiang VIA Automation Company have sold nearly 100 sets. It should be first used in medium-sized chemical fiber projects to save foreign exchange and reduce investment.
3) In the textile and post-processing production process, according to its technical characteristics of many discrete points and strong time sequence, PLC should be mainly used.
4) Industrial PC should be widely used in the automatic control design of air conditioners, tank farms and public works (including air compression, air separation, refrigeration, heating, waste treatment, etc.). ) and some small and medium-sized projects. This is an effective measure to realize low-cost automation. metropolis
5) Pay close attention to the development trend of fieldbus. Fieldbus is a hot spot in the field of automation technology. It is expected that a complete field bus control system will be formed by 2000. We must keep abreast of the development trend and usage of the general site route at home and abroad in order to meet the needs of the rapid development of automation technology.