Abstract: This article describes the structure of the basic automation and transmission control system of the 120T converter in Jinan Iron and Steel Plant. It focuses on the advantages, accuracy, and stability of the integrated electrical, instrumentation, computer (EIC) control and network communication system and the transmission control system. The article also describes the practical application of the system in facilitating stable production.
Keywords: converter; basic automation; fieldbus; switch; main drive
Jinan Iron & Steel Co., Ltd.'s steelmaking plant has three 120t top-and-bottom combined blowing converters—Converters No. 1, No. 2, and No. 3. The entire automated control system is configured to be among the most advanced in China, integrating electrical, instrumentation, and electronic control (EIC) systems. It features a convenient, fast, and user-friendly human-machine interface (HMI) and integrated EIC network data communication, boasting high speed, large capacity, and open technical capabilities. The following section introduces the automated control system for the 120t converters at Jinan Iron & Steel's steelmaking plant from two aspects: basic automation and electrical drive.
1. Basic Automation
The converter basic automation system is the foundation for controlling the converter system. This system mainly includes an HMI operator station, PLC, instruments, frequency converters, and field control boxes. All components are connected via an industrial Ethernet ring network and a DeviceNet network to achieve control functions for the converter system.
1.1 Control System Structure and Characteristics
The control station uses Schneider Quantum PLC series, with the high-performance 53414 CPU from the 140CPU series. Remote stations utilize advanced fieldbus products (CRP series modules), and the programming software is Schneider Concept 2.6. The data communication network is a 100M high-speed fiber optic ring network centered on the German Hirschmann MICE series industrial fiber optic switches. Each control PLC is connected to the industrial Ethernet ring network via NOE Ethernet communication modules and shielded Category 5 twisted-pair cables. Remote operation boxes, consoles, and frequency converters for oxygen lances, tilting devices, and feeding devices are connected to their main PLC station via DeviceNet. The operation station uses a Siemens industrial computer with a Win2000+SP3 operating system, and the HMI monitoring software is Schneider Monitor Pro 7.2, connected to the industrial Ethernet via Ethernet cards and twisted-pair cables. The system has the following characteristics:
(1) The electrical, instrumentation and computer systems are connected by a network to realize the EIC three-electric integration.
(2) The electrical and instrumentation use the same control equipment, programming and control are unified, and communication is convenient on the same network, reducing communication hardware interfaces and reasonably sharing control functions; the electrical and instrumentation use the same operator station, simplifying and unifying operation, which is conducive to stable production.
(3) Remote station
Remote stations such as field control boxes and consoles adopt industrial fieldbus products, which greatly reduces the amount of design work and cable construction. Each box is connected through DeviceNet, which improves the reliability and ease of maintenance of the system.
1.2 Network Systems and Their Characteristics
The data communication network of the automation system of converters No. 1, No. 2 and No. 3 in Jinan Iron and Steel Plant is a 100M high-speed fiber optic ring network with the German Hirschmann MICE series industrial fiber optic switches as the core.
The Hirschmann MICE series switches offer flexible networking options, allowing for various functionalities to meet specific requirements whether integrated into control cabinets or distributed field operation boxes. They feature fanless cooling, redundant power supply, and HIPER-Ring support, achieving a high level of reliability. Modular structure is a key feature of the MICE series, consisting of a switch and several communication media modules. The switch includes all the functions of an industrial switch except for the network interface, while the media communication modules provide network interface functionality. This allows for customized equipment selection, avoiding wasted funds, and the modular structure also protects the user's investment. Furthermore, the MICE network switch offers multiple methods for managing the network system: a) accessing the MICE user interface via a V.24 serial port connection; b) accessing the user-friendly interface on the MICE from anywhere on the network via a web browser; c) centralized access to the SNMP agent on the MICE using SNMP management software such as HiVision.
1. Control methods and characteristics
There are 15 sets of PLC systems for converters, set up according to the principle of separate systems for each converter and common systems, so as to ensure that the normal operation of other converters is not affected in the event of maintenance or failure of one converter.
The basic operation of individual equipment is divided into two modes: automatic and manual, and the operation location can be either central or on-site. The system operation is divided into three modes: computer, automatic, and manual, with the operation location fixed at the central location. In the "computer" mode, the PLC receives data from the L2 level computer model and performs real-time control, including oxygen flow rate, bottom blowing gas type and flow rate, oxygen lance height, and by-product type and weight. In the "automatic" mode, the PLC automatically performs steelmaking according to the internally stored initial design plan. In the "manual" mode, the PLC controls steelmaking production based on manually set data.
Based on the characteristics of converter steelmaking production processes, three CRTs are configured per furnace in the central control room. During normal operation, the three CRTs monitor different functions, but they can serve as backups for each other in abnormal situations, and even a single CRT can complete the blowing operation. The main monitoring functions include top and bottom blowing, oxygen lance tilting, auxiliary raw material and ferroalloy feeding, gasification cooling flue gas purification, primary dust removal, and secondary dust removal. Operating stations are set up in the system charging room, blower room, and secondary dust removal room to monitor their respective equipment. For safety and to prevent misoperation, each converter operating station is designed as a dedicated station; that is, each station can only operate the equipment of its own furnace and cannot control other converter equipment. However, common equipment, except for the auxiliary raw material feeding system, can be operated from all furnaces.
The operation and monitoring of the equipment are mainly completed through the control station screen in the main control room. For the safety and convenience of production, a hardware control panel is set up, which is equipped with necessary operation switches, operation buttons, data display and emergency stop buttons for key equipment.
The PLC software development adopted a modular approach. Before programming, the PLC's memory and data blocks were planned, and the inter-station communication data area and HMI display data area were divided. Different types of programs used different organizational blocks for calling, such as the blowing clock, flow accumulation, and PID regulation using fixed-cycle calling. According to the process characteristics, multiple programming logics were used, such as statement list programming for process-level data processing and sequential function chart programming for bottom blowing control. Safety processing was performed on the operating data, such as checking the rationality of the set data and constraining the rate of change.
In terms of control functions, it achieves fully automated steelmaking through a "computer" approach. The system has the following main functions and features:
(1) Priority control of auxiliary raw materials and ferroalloys. The materials are fed according to the priority order specified in the "Booth Combination Setting Table", rather than according to the order of empty materials, in order to meet the control requirements of the converter process.
(2) Management of the inventory of the furnace top silo. The inventory of the furnace top silo is calculated based on the signals from the furnace top level gauge, level switch and feeding belt scale, and the drop is corrected in real time.
(3) Control of the state transition during blowing. Control oxygen flow rate, bottom blowing gas type and flow rate, oxygen lance position, auxiliary lance measurement, and auxiliary raw material type and input amount according to the blowing schedule and on-site equipment status.
(4) Automatic control of boiler drum water level. The boiler drum water level is adjusted by three-impulse or single-impulse according to the blowing period.
(5) The oxygen lance and tilting system are controlled by AC drive and equipped with an emergency backup power supply. This ensures the safety of the equipment in emergency situations.
(6) The auxiliary gun system also adopts AC drive control, is equipped with an emergency backup power supply, and uses the DIRC-5 computer system for data processing. It has the functions of measurement, carbon determination, and oxygen determination, and can use the TSO oxygen determination probe to measure and calculate the liquid level.
2. Electrical drive control
The steelmaking system is the central link in a steel plant. The control of the electrical drive equipment for converter tilting and oxygen lance lifting is crucial, as it has the most direct connection with the oxygen blowing system. The control speed and positioning accuracy of the electrical equipment directly affect the smelting cycle and oxygen blowing efficiency. Therefore, how to control the converter tilting equipment and how to automatically, quickly and accurately control the positions of the oxygen lance and auxiliary lance have become the key to improving steel output and quality.
2.1 Electrical drive and control method of converter tilting device
Electrical drives generally employ two forms: common branch bus and individual one-to-one drive. The individual one-to-one drive form offers advantages in terms of speed regulation and reliability. The No. 1, 2, and 3 converters in the No. 3 steelmaking plant of Jinan Iron and Steel Group use an individual one-to-one drive control method, employing Siemens SIMOVERT MASTERDRIVERS 6SE70 series three-phase AC vector control frequency converters. The control functions of this device include: encoder-based vector control for applications requiring highly precise torque and dynamic response; encoder-less vector control for simple applications such as water pumps and fans, and U/f control.
The four converter tilting motors are rigidly connected coaxially. If the output torque of the four motors is unbalanced, it will shorten the service life of the motors. Therefore, it is necessary to solve the load balancing problem of the four motors. A one-to-one transmission method can be adopted, with a "master-slave" configuration on the transmission device. The master drive device is identified, and a speed feedback signal is introduced through a pulse encoder. A common speed regulator is set up, and the input signal of the current regulator of the master drive is simultaneously output to the current regulators of the three slave devices. Since the input signals of the current regulators are the same, their outputs are also the same. Therefore, the four motors can be guaranteed to operate under equal loads, thus ensuring the stability and load balance of the operating equipment.
The four frequency converters are connected to the main PLC via DeviceNet. Each frequency converter receives control commands and speed settings through the network and transmits the operating status of the equipment to the main PLC. The four frequency converters are connected in a ring structure through SIMOLINK fiber optic network to realize the "one master and three slave" control concept and complete the data communication between the master and slave devices.
2. Electrical drive and automatic control of the oxygen lance
2.2.1 Electrical Drive
Each converter unit has two oxygen lance lifting mechanisms (Lance A and Lance B), equipped with two frequency converter control cabinets (Lance A control cabinet and Lance B control cabinet) and one braking control cabinet. One cabinet is used for the working lance, and the other is used as a spare lance. The frequency converters selected are SIMOVERT MASTERDRIVERS 6SE70 series three-phase AC vector control frequency converters.
The traditional design uses a "corresponding" control method, where the frequency converter for lance A controls the motor for lance A, and the frequency converter for lance B controls the motor for lance B. In the automatic control system for converters #1, #2, and #3, an "exchange" control method has been added to the two oxygen lance units. When the selector switch is set to "corresponding" control, the frequency converter for lance A still controls the motor for lance A, and the frequency converter for lance B still controls the motor for lance B. However, when the selector switch is set to "exchange" control, without switching the trolleys, the frequency converter for lance A can control the motor for lance B, and vice versa.
Oxygen lance "switching" control technology is a completely new control technology. During normal production, the frequency converters and lifting motors of the two oxygen lances can serve as backups for each other. Its key features are: in the event of a mechanical failure, the oxygen lance can be quickly switched electrically without moving the trolley; in the event of an electrical failure, normal control of the oxygen lance can be quickly restored without replacing the frequency converter or moving the trolley.
Furthermore, the oxygen lance braking control has been improved, perfecting the brake control of the oxygen lance motor. This achieves three-point interlocking control of the brake via inverter opening/closing, PLC program output, and inverter output, making the braking control technology more complete and the system safer, more stable, and more reliable. Key features include: when the inverter trips due to a fault, the braking output automatically engages the brake, ensuring equipment safety; when the PLC malfunctions, regardless of the inverter's operating state, the braking output remains in a brake-engaged state, absolutely guaranteeing that the equipment will not lose control, thus improving the reliability and safety of the control system. During normal production, if the inverter malfunctions due to internal or external wiring issues, the motor brake can be engaged via PLC output, ensuring the safety, reliability, and stability of the system and equipment.
2.2.2 Automatic control of oxygen lance
In the automatic control of top-blown oxygen converters, the correct height of the oxygen lance is a crucial factor. Employing advanced automatic oxygen blowing control technology to regulate the blowing point of the oxygen lance ensures it stops precisely at the required position for the process, achieving high positioning accuracy and thus better guaranteeing computer control and automation of the steelmaking process. The auxiliary lance, another important piece of equipment, measures the liquid level before the oxygen lance is lowered for blowing and takes temperature samples during the blowing cycle. It also has strict requirements for speed and position control. Their height and position control are essentially the same; the following section focuses on the control characteristics of the oxygen lance as an example.
(1) Position control
The vertical movement of the oxygen lance is measured by two absolute encoders that rotate coaxially with the electric rotary drum, converting the vertical position into a digital value. During normal production, one encoder is used as the primary encoder, while the other is compared to it as a calibration signal. An alarm is triggered when the deviation exceeds the set range, and an emergency stop is initiated if the deviation is too large.
During repeated up-and-down movements of the oxygen lance, sudden cumulative errors can occur in the numerical conversion of the digital zero-delay encoder. If not corrected, this will lead to a deviation between the oxygen lance's detected position and its actual position. To solve this problem, a correction point can be set at the oxygen lance's changing position. The operation cycle is roughly as follows: the actual height of the lance is pre-stored in the main PLC memory; each time the oxygen lance is moved to the changing position, this signal is read into the PLC, forcibly modifying the stored value of the actual oxygen lance height.
(2) Automatic rapid positioning control
In modern converter steelmaking, the oxygen lance automatically adjusts its position based on the amount of oxygen blown during the oxygen blowing process. The speed at which the oxygen lance adjusts its position directly affects the smelting cycle and the quality of the steel; therefore, it is desirable for the oxygen lance to stop accurately at the designated position as quickly as possible.
To address this issue, a closed-loop position control system can be employed. The deviation between the oxygen lance's set position and its actual position is used as a control signal, which is then converted into a speed command for the control transmission device. To shorten the oxygen lance's ascent and descent time, a higher speed is used when the deviation between the set value and the actual position is large. As the deviation decreases and reaches the set range, the control speed command decreases according to a pre-set function curve, ultimately bringing the oxygen lance to an accurate stop at the required position.
3. Conclusion
By assimilating and transplanting automation technologies from foreign steel plants, and combining them with the current specific conditions and process requirements of Jinan Iron and Steel Plant, the automatic control systems for converters No. 1, 2, and 3, developed using advanced contemporary technology and equipment, have raised the level of automatic control and production management of converters at Jinan Iron and Steel Plant to a new level, meeting the needs of future production and new technology development, production management, and information management.
