The automatic control of pulp and paper production has limited application in the past. It mainly focuses on the local simple instrument control of the pulping process and the electric drive control of the paper machine. A lot of control content is achieved through on-site manual adjustment. Since the reform and opening up, through the introduction of foreign advanced technology products, as well as the experience of automation control in related industries, automatic control has gradually been applied in papermaking production, and it is moving in the direction of centralized control of the entire plant. In recent years, many manufacturers have carried out technological transformations of self-control systems in key processes of the production process, such as cooking control, disc grinding control, slurry control, sizing flow control, paper machine drive, and multi-zone ventilation control of the dryer section of the paper machine (heat pump control ) and quantitative detection of water, etc., achieved significant results.

1.1 pulping process

The automatic control of the pulping process is mainly focused on the control of cooking, refining, mixing and beating. The main control parameters are: liquid level, temperature, pressure, flow and concentration. From the perspective of process control, on the one hand, logic and sequential control of the motor and solenoid valve in the production process are performed; on the other hand, process parameters are adjusted for various valves on the tank and process piping. In the pulping equipment, there are many monomer devices. Due to various reasons, there are not many mechatronic products in the pulping equipment body. A considerable part of the enterprises are generally not very automated in the pulping process. In recent years, the equipments such as disk grinding, pulp press and thermal dispersion have made great progress in automation control, and the equipment performance has been improved; more reforms in the proportioning of pulping and sizing have been made to improve and stabilize product quality. , achieved a certain effect.

The automatic control system of pulp production can be initially considered as a combination of the instrument control system and the relay logic control system. The secondary instrument is mainly used as a controller to perform single-loop or multi-loop automatic control. Many manufacturers have continued to use it so far, basically an independent, separate control. With the development of electronic technology, controllers using PLC as the mainstream product have been widely used since the 1980s. Since the original PLC controller was mainly controlled by logic and sequence, the PLC controller was used to perform interlocking and control of the motor and solenoid valve on the one hand; on the other hand, the secondary instrument was used as the controller to perform single-loop or multi-loop. Automatic adjustment control. Since the late 1980s, major changes have taken place in the functions and technical concepts of PLC controllers, appearing as the face of a process control system; and the ease of configuration and flexibility have been greatly improved with their capacity, speed, and The word length, cycle, etc. are used as indicators to form a series of products and thus have the ability to perform complex control. PLC controller has been widely used in the partial automatic control of pulp and paper production.

The appearance of new operating terminals and advances in CRT display technology, especially the enhancement of communication capabilities of PLC controllers, have made intelligent and dynamic man-machine interfaces increasingly used in critical control points for pulp production, such as steaming balls, Refining, mixing, and other parts of the system are equipped with liquid crystal or plasma display true color operation terminals on the charged site, which can be easily connected to the PLC and integrated into the operating system of the controller. The touch interface provides various real-time data in the user-specified refresh time, displays related status parameters, set values ​​and measured values, and displays configuration-related parameter graphics in digital form or bar graph format; at the same time, the touch interface is also With various operating functions, parameter setting and logic control can be performed. In order to clearly reflect the overall and local information of the production process in the control room, the upper computer is used to conduct centralized monitoring, operation and management of the production process. The operator can observe the status of the production process from different screens displayed on the display of the control room, and control the process parameters of the production process on a dedicated operation terminal or directly on the control display.

Pulp and paper production process, from the control point of view, is a multi-device coordinated linkage system, especially the direction of the company toward the large-scale development, the original backward control methods are increasingly unable to meet the requirements of production. This DCS came into being.

DCS, distributed control system, also known as distributed computer control system, is a new type of control technology that uses computer technology to centrally monitor, operate, manage, and decentralize the production process. It is infiltrated by computer technology, signal processing technology, measurement technology, communication network technology, CRT display technology and human-machine interface technology. The DCS distributed control system is structurally speaking, it separates the acquisition and control in multiple field control stations, and concentrates the operation and monitoring functions in one or more operation stations. It adopts standardized, modular and serialized products from the hardware. Each workstation on the system is connected through a network interface, and each workstation can operate completely independently. The system's real-time control network allows the sharing of system resources, online correction of system configuration and online maintenance. Its outstanding advantage is that the system hardware and software have flexible configuration and configuration capabilities. The openness of software is particularly prominent.

The DCS control system for the pulp and paper production process includes several sub-stage control systems such as wet preparation and continuous steaming, white water recovery, washing and bleaching, papermaking, dryer three-stage steam, sizing concentration, and QCS. Each control subsystem has both relative independence and interconnectedness. Therefore, the entire system adopts the method of decentralized control links and centralized data processing, that is, the DCS system of multi-operation stations. DCS connects the DCS of the workshop and each section to a network through the system bus. Each DCS subsystem consists of a basic I/O unit, a process master station, an operation station, an alarm station, an operation terminal, a display, an alarm printer, and a report printer, plus a detection instrument, an execution machine, and a control center at the production site. A complete papermaking production automation system. The system structure of DCS control system is generally divided into process control level, automation level and field level. The system hardware configuration is generally:

The industrial control computer as an operator station constitutes a host computer management system.

Large controllers form an automation center control system.

The operation display terminal serves as a human-machine interface on site.

Distributed remote control station as a control unit.

The process control level's operator interface uses industrial control computers and uses standard software and networks to implement process diagnostics, process monitoring, control, and information management. The standard display and operation window displays the process parameters of the process control point in real time. The operator can easily monitor the status of the equipment in real time through the dynamic screen, such as the level of the liquid level, the opening of the valve, the start and stop of the motor, etc.; at the same time, according to the The process flow of the section needs to control the equipment in time. There are two control methods for the control loop, namely automatic adjustment and manual adjustment. When the automatic manual rotary switch on the screen is clicked, the automatic manual mode can be switched. In the automatic state, the regulating circuit is controlled by the PLC and automatically adjusts the opening of the valve. At this point, if you click on the valve, a prompt window will appear indicating that it is in the automatic state and you cannot manually adjust the valve. If in the manual state, the operator can adjust the valve opening. Find abnormal events, make prompts, alarms and processing commands; and read and modify control parameters, remotely switch working status, fault diagnosis and report printing; also can save production reports and alarm information. The PC at the process control level, through the production management network, accepts the production data of the central PLC and transmits various types of production data and various types of production tasks to the operational management network. The control capability of the process control station is crucial. It is mainly measured by the capability, quantity, configuration convenience and flexibility of the control function block; the reliability and environmental adaptability of the process control station are equally important and can be made redundant. The reliability is higher, but the application in the paper production line is still rare. The main consideration is the reason for its performance-cost ratio.

The automation level uses high-performance, large-scale PLC controllers with single or multiple processors. The communication between automation level and process control level is realized by Industrial Ethernet. The communication with the field level is realized by the PROFIBUS-DP communication network. As part of the central control unit, the operating status of the field devices is controlled according to the process requirements. The coordinated control of the subsystems composed of the PLCs at each site is completed. At present, the more common configuration is to use a large controller to form an automation center control system, that is, a process control level. The system is easy to expand and has network communication capabilities; using a distributed architecture, the remote intelligent interface provides digital and analog I/O units of various voltages and protection levels that can be placed centrally or dispersedly installed on site. In order to facilitate the operation of personnel, and taking into account the needs of process engineers and control engineers, each station is equipped with a host monitoring computer. As an ordinary operator station, the operator can operate and control the field equipment through the host computer.

The field level is mainly connected to the fieldbus by standard system products.

(1) On-site operation panel. The operator panel is suitable for decentralized, device-related control and monitoring. Different drive and transmission groups can have standard graphical displays and the same operating procedures. On-site operation and display terminals display production data in real-time with dynamic graphics, and on-site operators can operate field devices through touch screens.

(2) Remote I/O station. The remote I/O station controls the PLC through the on-site control network, connects with the center, and exchanges various real-time information. Through I/O ports, intelligent control devices and transmitters are connected to implement the adjustment control. According to the layout of field devices, the distributed layout is used to respond to production events in real time on the spot, which greatly reduces the cable wiring from the site to the control room, making the production process control local and modular, which not only improves the system performance, The risk factor is reduced, and it is conducive to the expansion and maintenance of the system.

(3) Drive units, such as variable frequency controllers, control valves, etc.

The monitoring system is an important part of the DCS system. The characteristics of the process monitoring system used are suitable for rapid response to process events. The basic functions of the process monitoring system:

Graphic system: Through the configuration, it can form a rich and dynamic parameter control screen.

Informational alarms: capture process information and local events, group these in archives, and selectively extract them when needed, or transfer directly to relevant process screens to generate alarm information.

Production report: Provides a set of report system, which can conveniently generate the production report required by the user for historical data or real-time data combination.

Process Flow Chart: Dynamic display of the whole plant process flow enables operators to understand the operation status of the entire plant's various process segments for easy dispatch management.

Equipment operating status map: Dynamic display of the real-time operating status of the equipment in the factory, at any time to understand the plant equipment and production conditions.

Browsing system: In the server of the automation system, it should support the online browsing of 3 to 10 customers. In this way, the owner can browse the operation of the entire factory in the offices of some management or technical departments.

System self-diagnosis: The integrated control system should have a complete set of self-diagnosis function, which can automatically diagnose whether any part of the system is faulty during operation, and timely and accurately reflect the fault status and failure time in the monitoring software. Fault location and related information. After a failure of the system or process equipment, the I/O status should be returned to the state of the process requirements preset.

System operation authority: The entire monitoring system should have multiple operation levels. Each level should have its own user and password. It can prevent users from unauthorized access to display data and system functions, and has a very high safety and reliability.

1.2 Manufacturing Paper Process Automation of the papermaking process is prominently demonstrated in the drive control of the paper machine. Due to the change of paper types, the speed ratio of the paper machine changes greatly, the ratio of the pulp and the characteristics of different papers, etc., make the speed of the paper machine need to be adjusted in a wider range; at the same time, the fluctuation of the voltage, frequency and load of the power grid may also cause paper. The change of locomotive speed and the different heating temperature in each section of the drying section will cause the paper sheet to shrink longitudinally. Therefore, the paper machine transmission control system is required to be a stable, accurate, synchronous, and coordinated variable speed transmission system. The electric drive in the papermaking process is divided into fixed speed transmission and variable speed transmission. Fixed-speed transmission mainly includes pumps and stirring motors. Now for the control of high-power fixed-speed motors, the soft-start controller with good starting function has been gradually promoted. As the paper machine drive control adopts the form of multi-point subsection transmission almost without exception at present, objectively, it puts forward high requirements for the automatic control system, such as fast, accurate, stable and reliable; and because the paper machine drive is in production The special important position, the general configuration of the paper machine electrical transmission control is made up of bigger PLC control unit, vector type frequency conversion unit and production management computer. The use of PROFIBUS communication protocol to form an advanced fieldbus network, transmission of various production data, the implementation of production orders; control the operating status of each transmission point.

In recent years, foreign power transmission systems have generally adopted foreign import control devices, and the stability, dynamic response, and reliability of the drive system have been greatly improved. Its communication function is strong, with a variety of communication protocols; a wide range of parameters, can be applied to a variety of applications; can automatically test the load characteristics, to achieve the system's optimization;

Can automatically carry out load compensation through flux current control, perfect protection functions such as: over temperature, over voltage, under voltage, out of step, ground fault, etc.; such as torque control, tension control, coil diameter calculation, etc., can meet the paper industry The various special process requirements have caused fundamental changes to many problems that have plagued domestic manufacturers' analog control devices for a long time and improved the production efficiency. At present, the transmission system has transitioned from the initial analog control to the direction of full digital network communication. The latter has higher resolution and more precise control. At the same time, as a subsystem of the centralized control system of the whole plant, it is easy to connect with other relevant parts through the data network. Therefore, some famous brand high-end controllers are being applied more and more.

Different from the pulping process, the paper machine body equipment such as: headbox, calender, reel, cutter, rewinder, etc., the equipment body is equipped with a higher level of automation technology.

Practice has proved that, since the main drive system of paper machines has generally adopted digital drive devices, the control accuracy and the system's safety and reliability have been greatly improved, and it has been fully able to meet the needs of large-scale, high-speed development of paper machines. In addition, control of the sizing system, the steam condensate system, the vacuum system, the broke system, and the paint preparation system are also very important.

The QCS paper sheet quality inspection control system is a new type of high-tech product, and it is the most effective means for the paper machine to control the quality of the paper sheet. At present, foreign products occupy a major position, domestic research and development for many years, there is still a big gap with foreign products. At present, the application on large and medium-sized paper machines is still relatively common. It provides great help for monitoring the moisture content of paper sheets, mastering process parameters, and facilitating the control of product quality. However, due to various reasons, most of them have not achieved real closed-loop automatic control with sizing concentration and dryer temperature.

2.1 system control system takes the field bus as the core

It has become inevitable that automatic control systems have become more integrated and open. Factory automation requires stronger communication capabilities between various types of equipment and integration. FCS, the distributed automation system based on field bus, is emerging. The open structure will facilitate the data exchange with all control equipment systems and become a truly integrated, new system-wide automatic control system.

2.1.1 fully integrated automation thinking

With the rapid development of industrial automation modern control theory and computer technology, the industrial automation process control system can rapidly increase the amount of data exchange between the various levels of the system, which provides a basis for implementing a fully integrated automation control concept.

The idea of ​​Totally Integrated Automation is to use a system to complete the system that was originally matched by multiple systems to complete all functions. The application of this solution can greatly simplify the system structure and reduce a large number of interface components. The application of Totally Integrated Automation can overcome the boundary between the upper computer and the industrial controller, between continuous control and logic control, and between centralized and decentralized. At the same time, the Totally Integrated Automation solution can also provide a unified technical environment for all automation applications, including: unified data management, unified communications, unified configuration and editing software. Based on this environment, a variety of different technologies can be integrated under a user interface in a system with a global database.

2.1.2 Make Field Bus

Industrial control automation technology is an important means to guarantee the efficient and reliable operation of production. In the 1990s, the emergence and application of fieldbus control systems marked another leap in automation technology. The one-to-one link between traditional control system equipment is not only The increase of installation and maintenance costs also reduces the reliability of the system and brings security risks. Analog signal transmission limits the selection of transmission media and transmission structure, and the accuracy of the signal is affected. Therefore, it is very important for the factory to construct a reasonable LAN. Not only the characteristics and security of the communication network of the control system should be considered, but also the interconnection of the communication network with the original control system of the plant and the networking of the possible expansion of the production line. To achieve the purpose of data communication resources sharing.

Fieldbus is the core of a modern control system. It is essentially a digital communication protocol. It is a digital, fully decentralized, bidirectional transmission, multi-branch structure communication network that connects intelligent field devices and automation systems; it is at the forefront of industrial control automation. Status represents the direction of technological development.

Due to its high real-time performance and mature technology, the PROFIBUS field bus has been widely used throughout the world and is currently the most common domestic application. The PROFIBUS field bus is an open field bus based on the international standard EN50170. It is mainly used for on-site control and detection of the data exchange of the acquisition unit. It adopts the token scheduling principle for data communication and mainly includes a high-speed bus with a maximum baud rate of up to 12 Mbits. PROFIBUS-DP (H2) and intrinsically safe low-speed bus PROFIBUS-PA (H1) for the process. The perfect combination of DP and PA makes the PROFIBUS field bus superior to other field buses in terms of structure and performance. It is not only suitable for the communication between the automation system and the on-site signal unit, but also can be used to directly connect the transmitter, actuator, transmission and other on-site instruments and equipment with interfaces to collect, monitor and process the on-site signals. Twisted pair replaces the traditional large number of transmission cables.

2.1.3 System Meter (Bus Type Transmitter)

Since the control system has undergone new changes, in order to adapt to the requirements of the fieldbus control system, instruments and transmitters have evolved from analog and intelligent to fieldbus type. As a digital communication network, the fieldbus extends from the control room to the production site. In the past, point-to-point analog signal transmission was converted into multipoint, one-line serial digital transmission. In the field bus type transmitter, its superiority is obvious: The all-digital transmission, stability and accuracy are higher than the intelligent transmitter, in addition to maintaining the excellent measurement performance of the intelligent transmitter, but also increase the operation And control functions, embedded PID control, logic operation, arithmetic operation, accumulation and other modules, the user through the configuration software for any of these function modules call, to achieve the parameters of the site control.

Multivariable measurement is another feature of fieldbus type transmitters. One transmitter can measure multiple process variables at the same time. Since each fieldbus type transmitter is equipped with multiple sensing elements, it can simultaneously measure multiple process variables and transmit it via fieldbus. At present, the world's major instrument manufacturers have successively introduced fieldbus transmitters, and there are more than 60 certified transmitters.

In summary, the fieldbus transmitter is no longer a transmitter in the traditional sense. It is a field device that integrates transmission, control, and communication functions. The emergence of fieldbus transmitters will certainly bring new and revolutionary changes to the field of instrumentation and automation.

2.2 Extensiveness of Control Content and Specialization of Control Methods

The pulping and papermaking process is a continuous process. The automation control is based on the characteristics and requirements of the production process, realizing the whole process, real-time effective control and better service for the production process. Therefore, the control content will be further expanded and the control system will be controlled. The mode or method will be more in line with or close to the actual production, more original and professional. In terms of control methods, applications such as self-adaptive, self-diagnosis, and optimization are adopted. New advanced technological achievements such as fault-tolerance are adopted in the design of software. While enhancing system reliability, the equipment and process of pulp and paper production are combined. Actually, improving the actual effect of system control has become the goal of automation efforts.

According to the concept of decentralized control of the system, the system division of the production process will be more detailed and more unitized. With the constant progress of pulp and paper production equipment, the degree of automation of stand-alone ontology equipment will be improved, the level of control systems will be more distinct, and an automatic control structure that is independent of each other and the entire system will be formed. For example, the papermaking production automatic control system will be divided into process control DCS system, equipment control MCS system, quality control QCS system, paper break monitoring WMS system, paper disease monitoring WIS system, motor control center MCC, etc. and these systems will be integrated. In a larger network.

Wheat straw wet preparation and cooking sections have changed from batch cooking to continuous cooking in recent years. The use of DCS systems is more common in continuous cooking sections. Considering that the process of continuous steaming system is a high-temperature and high-pressure process and has certain risks, the development of the control system will firstly attach great importance to the safety and reliability of the system. In addition to the fault-tolerant technology used in the design of the software, the dual-CPU redundant The system should be considered; secondly, the control of the ratio of the grass volume of the pin drum meter to the flow rate of the “T” tube liquid added is the key to cooking. The control accuracy of the ratio during operation affects the quality of the product. The method of indirect detection of the amount of grass by the rotational speed ratio of the pin drum meter has a large error and needs to be improved; the pressure difference between the pulp removal and the discharge pressure of the descaler and the pressure screen should be effective Control to improve the effect of sand removal and screening; for double-roller or twin-wire presses, variable-speed control with double-point transmission and balanced load distribution will be promoted, making the concentration process easier to adjust; in the bleaching part, For the oxide bleaching agent entering the mixer, the flow rate should be automatically controlled; in the refining section, whether it is a single-disc mill, a double-disc mill or a conical mill, power control refining is used. The method of spacing is fully mature and is mainly constrained by the precision of the advance and retract drive mechanism. If a hydraulic drive system is used, the equipment quality will be significantly improved.

In the domestic waste paper pulping, thermal dispersion equipment only began to be applied. From the system point of view, the requirements for automatic control of the heat dispersion production line are relatively high. The control content includes temperature, pressure, position gap, etc. The control system needs to be further improved. .

Due to the development of high-yield and high-quality paper machine production, the requirements for slurry and concentration control of pulp have been continuously improved. Therefore, the adjustment and control of sizing concentration will be increasingly applied. The multi-section transmission in the papermaking process has achieved remarkable results in recent years with the use of variable frequency control technology, achieving continuous operation of the motor under constant long-term load, and the system's thermal stability is ideal. The transmission points of each subdivision should be in a hard speed characteristic. Since the paper sheet undergoes shrinkage when it is heated, a certain degree of softness is required in the calendering and take-up section. In addition to the dynamic speed compensation by installing a tension sensor, the medium and small paper machines Using the adaptive function block possessed by the vector-type frequency converter, according to the change of the output torque, adaptive adjustment through speed compensation, indirect tension control should be promoted to reduce the end of head and manual intervention.

However, the dynamic parameter optimization function of the drive is not fully utilized. When the load disturbance is encountered, the time for rapid suppression and adjustment is not yet adapted, especially in the case of large-scale high-speed paper machines where the bus voltage on the DC side of the inverter is too high. Therefore, the use of a common DC bus as the feeder system for each inverter will result in more applications.

Paper machine process control will be categorized as DCS systems: including sizing systems, steam condensate systems, vacuum systems, broke systems, and paint preparation systems. The process control content of the paper machine equipment body will be uniformly planned and called MCS. Flow rate and pressure of the headbox, circulation of lubricants, line pressure of the press section, shaking and movement of the net section, deflection of nets and blankets, hydraulic system of the calender, pneumatic system of the take-up section, etc. Based on the equipment body control system, centralized management.

The MCC motor control center will develop in the direction of intelligence. If conditions permit, it will abandon the mode of placing remote I/O in the MCC room. Each motor control unit can be regarded as an actuator under the control of the FCS system. If PROFIBUS P is used, each motor is a DP station.

The application of paper sheet quality control system QCS will be more extensive. To help improve quality, increase production, and reduce costs, in addition to the measurement and control of sheet weight and moisture, it also includes measurement and control of ash, thickness, whiteness, gloss, smoothness, transparency, and coating weight. . It is important that the QCS should achieve true closed-loop automation with relevant parameters such as sizing consistency and dryer temperature. For normal paper machines, longitudinal mass measurement and control are used; for large or special paper machines, lateral mass measurement and control are also added.

The WMS of the paper break monitoring system is rarely used in China at present. It uses the camera technology to monitor and record the paper where the paper machine is easily broken. When the paper break occurs, the system will automatically trace back the paper before it is stored in the camera. The paper break signal and related paper disease signal captured in the time zone will be synchronized with the production, allowing the technician to quickly determine the break area and the cause of the break. Paper disease monitoring system WIS for on-line inspection of paper diseases such as spots, holes, wrinkles, cracks, and streaks, and can be connected with the paper cutter to remove defective products. The inspection data is also used for quality management to determine the cause of the paper disease.

At present, the production process of pulp and paper making enterprises such as dryer surface temperature control, oven drying temperature continuous control, press roll line pressure control, sheet tension control, etc. are still carried out indirectly or manually. These need to be promoted and applied.

The pulping and papermaking process is a complex industrial process. It is also a highly technical work with high degree of uncertainty, non-linearity, correlation, large lag, and incomplete state. At present, the automation level of the domestic papermaking industry is still lagging behind. We should begin with the bottom-level automation of the optimization control of the production process. In the system configuration, the relevant technical personnel of the manufacturer should be fully aware of the hardware, software, and technical characteristics of the selected control system; in combination with the process equipment and its control requirements, the requirements of the management information system should be fully considered so that the entire plant can be controlled. The system forms a production management system that can communicate with each other and access each other. In order to enable the production and command department of the factory to grasp the production process and status of the whole plant more quickly and comprehensively, command and adjust the process operation parameters, and timely carry out production scheduling and optimization to serve the development of the company. It is believed that there will be a leap forward in the control of our country's pulp and paper automation and instrumentation in a relatively short period of time.