Abstract: This paper details the successful application of the Industrial IT automatic control system in the ironmaking process of Xuan Steel's No. 6 blast furnace, focusing on the system's hardware configuration, network communication, and functionalities. The paper demonstrates the system's rational structure, comprehensive functions, stable and reliable performance, and high control precision, thus meeting production requirements.
Keywords: ABB AC800F, hardware, communication, control
1. Introduction
In June 2008, a major overhaul was carried out on Xuan Steel's No. 6 blast furnace. Previously, the automatic control system used the ABB Industrial IT F2K system. To better meet production needs, the ABB Industrial IT AC800F DCS system was adopted. This system is stable, reliable, and has a low failure rate, integrating advanced control concepts, modern communication technology, and the latest developments in IT technology. Practice has proven that the AC800F DCS system has effectively achieved automatic control of the six furnace troughs, furnace top, and hot blast.
2. System Introduction
The AC800F system is a world-leading, all-in-one open system from ABB, integrating the advantages of traditional DCS and supporting multiple international fieldbus standards. It possesses the complex analog loop adjustment capabilities and user-friendly HMI of a DCS, while also boasting high-speed logic and sequential control performance comparable to high-end PLCs. The system can connect to conventional I/O, as well as remote I/O and various fieldbus devices such as Prlfibus, FF, CAN, and Modbus. The system offers high flexibility and excellent scalability, handling everything from small-scale production plant control to large-scale plant-wide integrated control, and even cross-plant management and control applications with ease. Upgraded to version V6.2 and higher, the system capacity reaches 140,800 I/Os. Future expansion can be achieved by adding I/O or fieldbus instruments directly to the existing system, facilitating future development.
The system comprises an operational level and a process level. The operational level includes traditional control functions such as operation and monitoring, archiving and information recording, trend and alarm functions, and loop and logic control functions. For ease of management, all functions can be executed in the corresponding process stations. The process level consists of one or more process stations, each composed of an AC800F CPU and expansion I/O units. The process station CPU can be configured as a redundant or non-redundant system. The system has various I/O modules that connect to various types of process signals in the field. The system provides two industrial buses: a process station bus for Pfofibus DP communication and an I/O bus for field I/O data communication, offering high security and strong data reliability. The DigiNet system bus is used for both the process and operational levels, and the communication transmission medium can be coaxial cable or optical fiber.
The system is equipped with multiple process stations and multiple operator stations: the engineering station uses an industrial PC, while the operator stations run on industrial PCs. The fully Chinese Digivis software package is based on the MS Windows IT platform, and its graphical user interface enhances the system's usability and operation. Furthermore, it can potentially improve the specifications of external devices such as monitors and printers to make system operation more convenient. The control system completes operation and monitoring on a single PC, and the system can be expanded to 100 operator stations and 100 process control stations.
3. Hardware structure and network connection of the automatic control system
This major overhaul involved a complete upgrade of the hardware, resulting in improvements in equipment automation, data acquisition, and communication. The structure and hardware diagram of the automatic control system are shown below:
3.1 Engineer Station ES
When the CBF application software is installed on a computer, that computer becomes an engineering station, which can be used for configuring automatic process-level control, configuring operator-level screens, recording and archiving screens, and performing process debugging. The system programming software generates a project file for each project. Although each controller allocates a certain amount of space as a data variable storage area, the system programming software uses only a global system variable table. Data exchange between operator stations and process stations is direct access. Variable modification and checking are also system-wide. The configuration of the system's process stations and operator stations is done using a single software package. This implements a system-wide database technology, namely "distributed storage, global management."
3.2 Process Control Station PS
The configuration of process equipment control, calculation (addition, subtraction, multiplication, division and logical operations), monitoring and trend acquisition are all completed under the process station. The hardware equipment of the process station includes AC800F and various modules.
According to process requirements, the entire control system is implemented by two process stations: the under-tank process station and the hot blast process station. The under-tank process station, located under the tank, is used for automatic control of under-tank and top-tank charging. The hot blast stove process station, located in the hot blast operator's room, is used for acquiring various instrument signals such as temperature, pressure, and flow rate from the hot blast stove and blast furnace. Both process stations use redundant AC800F controllers. The AC800F field controller is connected to an S800 I/O module, and communication between them uses the Profibus DP fieldbus protocol. The Profibus module (FI830) of the AC800F field controller is connected to the redundant connection module (RLM01) via a Profibus DP line, and then connected to the CI840 module. The CI840 is a standard Profibus-DP/DPV1 fully redundant communication interface. The CI840 achieves redundant connection through a matching TU847 base, ensuring reliable data communication. The following diagram shows the connection between the AC800F field controller and the S800 I/O station.
3.3 Operator Station OS
This system is used to monitor various process parameters, display production flow charts, trend charts, records, alarms, and other configurations. Two industrial control computers are installed below the blast furnace as operator stations for monitoring charging below and above. The main control room for the six furnaces also has two operator stations for monitoring the blast furnace's automatic control system status and setting charging lists. In the hot blast control room, one industrial control computer is installed as an operator station to monitor the status of the four hot blast stoves.
3.4 Communication Network
Communication between process stations, operator stations, and engineering stations is achieved through DigiNet S. Data communication employs a redundant fiber optic ring network, adhering to the industrial Ethernet TCP/IP protocol. Two industrial-grade fiber optic switches are installed at each node for redundancy, allowing automatic switching in case of switch failure at any node. The fiber optic ring network ensures that power outages, faults, or fiber optic cable interruptions at any node do not affect overall system communication, achieving complete redundancy of communication interfaces.
In this way, the communication between the nodes of the system connects the process stations, engineering stations, operator stations, and other hardware devices such as modules, forming a communication network for a distributed control system. See the diagram below.
4. Functions of the process station
4.1 Submerged Process Station
4.1.1 Loading from the bottom of the trough
The under-tank process station mainly controls the under-tank charging, blast furnace body charging, and communication. During this overhaul, the under-tank equipment underwent corresponding modifications. The number of weighing hoppers increased from 5 to 7. Hoppers 1 to 4 each have two vibrating screens, corresponding to 4 feeders; hoppers 5 to 7 each have one vibrating screen, with each hopper corresponding to 2 feeders. There are two coke hoppers, with a new feeder added to hopper 1. In addition, the equipment involved in automatic control includes the intermediate hopper, conveyor belts, return ore conveyor belts, main hoist, and return coke unit.
Bucket weighing: The feeders corresponding to the bucket weighing are all frequency converter controlled. Based on the ore type and weight input from the material list, the material is screened, and calculations are performed based on the flow rate and zero point, with compensation made accordingly.
Coke hopper: The material is screened according to the weight and selection of the material list.
Belt: The belt automatically starts at low speed based on the status of the intermediate bucket and the tipping plate, and then runs at high speed after 5 seconds.
Intermediate hopper: The material is fed into the furnace via the main belt and then into the furnace via the main hoist.
Main hoist: Based on the loading method, the type of material (coke or ore) is determined, and the coke or intermediate hopper gate is opened. The main hoist is started via frequency converter control, and high, medium, and low speeds are selected according to time during operation. To ensure the normal operation of the main hoist, two frequency converters are used, one in operation and one on standby.
Return conveyor belt: When the weighing hopper is empty and screening is required or when a vibrating screen is in operation, the return conveyor belt is started.
Coke return: Both east and west coke return systems are automatically activated. Depending on actual site needs, after starting the coke screen, there is an option to start one or both vehicles.
Soft water control: The expansion tank's pressurization valve and overflow valve are controlled, and the venting valve is also adjustable. Simultaneously, the expansion tank's liquid level and pressure are monitored.
The key components of the automatic control system under the tank include the breakdown of the material list, the operation of the prescription, the frequency conversion control during screening, and the automatic control of the main hoist and coke.
The decomposition and operation of the material list and the execution of the prescription extensively utilize Sequential Function Block Diagrams (SFC) and Function Block Diagrams (FBD) to initially set up the material list, determine the loading sequence of the delivered materials, and identify the location and quantity of coke and ore in the loading process, laying the foundation for screening and discharging operations. The interface also includes buttons such as "Programmable Control," "Batch Addition," "Batch Subtraction," and "Prescription Add One," enabling smooth switching and correction between manual and automatic modes.
The screening of each hopper is controlled by a frequency converter. Each hopper corresponds to two hoppers. To ensure the accuracy of screening, the two hoppers of the symmetrical hopper are controlled separately, and the output is controlled by a linearization block according to the weight. At the same time, a flow setting that can be adjusted by the operator is also added, laying the foundation for the most accurate screening.
The operation of the main hoist under the sump is extremely critical. To ensure normal operation, alarm screens were added to the program. In the control system, in addition to using signals for judgment, time control is also used as a condition, providing a dual protection function.
In coke control, automatic compensation for the coke hoppers is implemented. During the screening process, the data is compared with the previous screening, and any over- or under-screened portions are calculated as errors and carried over to the next screening, achieving the effect of "reducing over-screening and compensating for under-screening." While calculating coke error can ultimately achieve automatic coke compensation, if the error value is too large or too small, it will affect the calculation of the screening stop value, thus impacting the accuracy of screening. Therefore, the error must be zeroed out at certain times. In the operation screen below the hopper, there is a coke clearing error button, with error values for coke hoppers #1 and #2 displayed below. Clicking the button will zero out the error.
4.1.2 Blast Furnace Body Charging: The blast furnace top adopts a series-tank type bellless top charging device.
The furnace top process is divided into two parts: one is the transfer of furnace charge from the receiving hopper to the charging hopper, and the other is the transfer from the charging hopper to the blast furnace. When the furnace charge transfers from the receiving hopper to the charging hopper, after the discharge conditions are met, the venting valve is opened. After a 6-second delay, the upper sealing valve is opened, the shut-off valve is opened, and the venting valve is closed in sequence, transferring the furnace charge from the receiving hopper into the charging hopper. Whether the receiving hopper is empty can be determined by two conditions: one is that the shut-off valve is opened to its limit position for a 20-second delay, and the other is the weight of the receiving hopper. If the weight is less than 1.0t, it is empty. After emptying, the shut-off valve is closed, and the upper sealing valve is closed. At this point, the first part of the process ends, and the second part begins. For the transfer from the charging hopper to the blast furnace, after the corresponding discharge conditions are met, the probe is raised. After the probe is raised to zero, the lower sealing valve is opened, the rotary valve is turned, and the charge flow is started. At this point, the furnace charge is introduced into the blast furnace. After the charge hopper is emptied, the charge flow is opened wide and the equalizing valve is closed. The charge flow is opened wide once, then closed, and the lower valve is closed. The rotation stops, and the rotation stops, completing one cycle of charging from the top of the furnace.
Receiving hopper: Receives material from the winch and has a shut-off valve at the bottom. With the shut-off valve, top seal, and vent valve all in the closed position, if the receiving hopper is low on material, the winch can feed more material upwards. Once sufficient material is available, it is loaded into the storage tank via the shut-off valve and top seal.
Material Tank: Stores furnace feed, capable of holding one batch of ore or one batch of coke. An upper sealing valve is installed at the top of the hopper to seal off the gas inside the furnace in case of leakage. A lower sealing valve is located at the bottom of the hopper. When the hopper is empty and the receiving hopper is full: open the vent, open the upper sealing valve, open the shut-off valve, close the vent, and feed into the hopper. When the receiving hopper is empty, close the upper sealing valve and the shut-off valve, and equalize the pressure in the hopper. When the probe sends a signal to load into the furnace, open the lower sealing valve and simultaneously signal the chute to start rotating from the stop position.
Probe: Used to detect the depth of the material level inside the furnace. When the material level reaches the set value, the probe is raised, allowing the material hopper to release material into the furnace.
The chute (tilting) mechanism consists of a planetary reducer and an airtight box. This system enables the chute to rotate around the blast furnace centerline and change its tilt angle in the vertical plane. The tilt angle is driven by an AC servo controller. An absolute angle encoder is used for accurate chute positioning. Two position sensors (proximity switches) are installed at the two extreme tilt angles as safety interlocking and alarm devices.
Material flow: The speed of material flow into the blast furnace is adjusted by changing the valve angle (γ), which is used to synchronize with the tilting angle (α) and rotation (β) to achieve the required material flow for each layer.
Rotation: The rotation speed of the chute is controlled by a variable frequency motor to achieve the required number of revolutions of the chute on each ring as required by the process.
The key components of the automatic control system for the blast furnace body include:
Top pressure adjustment
During production, top pressure regulation is crucial because it affects furnace conditions and directly impacts output and coke ratio. In automatic control, the pressure at the furnace top is regulated by adjusting the degree of closure of the pressure regulating valve group. PID control is performed by comparing the setpoint SP of the top pressure with the progress value PV. To meet production requirements, the SP value has also been processed, adjusted according to different types of feed in the hopper and before and after feed discharging. Simultaneously, PV values are provided based on the actual values of the east and west top pressures, enhancing the accuracy of regulation.
Control of material flow, tilting, and rotation
The control of material flow, tilting, and rotation all employs encoders to count the feedback angles. To enhance the accuracy of angle finding, the base value and transformation ratio in the program can be modified. Furthermore, coke and ore are separated in the material flow feedback. During operation, if there is a deviation from the set angle finding, the output can be adjusted in the linearization block.
The furnace top solenoid valve can be switched between standby and active modes. The probe control allows for single-probe operation or dual-probe operation. For ease of operation, buttons have been added to the screen for selection.
Rotation failure alarm output
Signal monitoring of empty hopper and empty tank
4.2 Hot Air Process Station
The hot blast process station primarily implements automatic control of the hot blast stoves, including the switching of the four hot blast stoves, the display of valve positions for each regulating valve, the on/off status of other valves, and the display of valve limit positions, temperature, pressure, flow rate, and other values at various points. Simultaneously, it regulates the blast furnace top pressure and collects and monitors signals from various instruments within the blast furnace body.
4.2.1 Hot blast stove control
Each hot blast stove has three states: shut-off, combustion, and air supply. Each state is represented by a different color on the screen. The opening and closing limits of each valve on each hot blast stove are also displayed in different colors, and the process status during switching is represented by another color. Simultaneously, various instrument data are displayed numerically on the screen. This intuitive display method effectively illustrates the current furnace condition, greatly facilitating observation and operation for the operators.
The set values, process values, and valve position feedback values of each regulating valve can be displayed in the group screen. Moreover, the process value can be changed by setting the difference, so that the regulating valve can automatically open or close according to the difference.
Hot blast stoves play a crucial role in blast furnace ironmaking, and their success hinges on the correct and efficient operation during firing and blasting processes. This directly impacts the control of gas flow, air flow, burner temperature, and top pressure. Regulating valves are primarily used to control these flow, temperature, and pressure variations, and their success directly affects the blast furnace's performance. Control measures primarily involve adjusting gas pressure and blast temperature, as well as regulating the combustion air flow, gas flow, and burner temperature of each hot blast stove. Both automatic and manual modes are available to meet process requirements. Furthermore, current and monthly cumulative data on coal and cold air flow rates are also monitored.
The analog parameters such as gas flow rate, air flow rate, top pressure, and burner temperature of the four hot blast stoves in blast furnace No. 6 are all regulated by PID control valves. The automatic operation of the control valves is the guarantee for the stable operation of these parameters.
The automatic control principle of the control valve is as follows: The 4-20mA analog input signal from the control instrument is input to the analog input (DAI05) module of the process station. After AD conversion, it is compared with the valve position signal of the control valve in the computer. Based on the difference, a corresponding switching signal is output to drive the servo motor to rotate in the forward and reverse directions. After mechanical reduction, the motor drives the valve and outputs a 4-20mA analog signal for system display and tracking control. The control principle diagram is as follows:
Practice has proven that the requirements have been largely met, and the convenient and accurate adjustment function has been fully utilized. This makes the hot blast stove more stable and precise in the process of supplying hot blast to the blast furnace, providing a strong guarantee for ensuring the smooth operation of the blast furnace.
4.2.1 Body Signal Monitoring
The thermocouple signal from the main unit first passes through the process station, which uses the TRUCK BL67 series products. The thermocouple signal directly enters the BL67 analog module 2AI-TC, and then communicates with the AC800F via PROFIBUS-DP. The BL67 analog module can be freely plugged in and unplugged without disconnecting the field wiring, making it easy to maintain.
5. Conclusion
Currently, the system is operating normally. The DCS system provides an effective control method for achieving stable production, while also providing sufficient data support. The system has improved labor productivity, increased economic efficiency, and ensured blast furnace production. Production practice has proven that it operates reliably, stably, accurately, and efficiently, with a user-friendly interface, comprehensive protection functions, strong fault diagnosis capabilities, and easy system maintenance, resulting in significant social and economic benefits.
