Abstract: This paper introduces a novel baghouse dust collector control system based on the PROFIBUS fieldbus. Through process analysis and combined with actual field requirements, the system structure design and control functions of each subsystem are described in detail. The communication mechanism based on the PROFIBUS fieldbus enables faster and more secure information transmission. This paper also describes the configuration process of the lower-level control unit, operation panel, and communication. Actual operation results show that the system meets the design requirements, realizes the automation of the novel baghouse dust collector, reduces the dust content in flue gas, and greatly improves dust removal efficiency. Keywords: Profibus; Fieldbus; Jet Filter; Configuration Software Abstract: This paper introduces a new type of jet filter control system based on Profibus. By combining the requirements of actual circumstances with technical analysis, it expounds the system structure design and control function of the system. Based on the communication mechanism of Profibus, information data can be transferred more quickly and safely. This paper also elaborates on the configuration process of the control system, operation panel, and communication. Practical operation results indicate that the system fulfilled the design requirements, realized the automation of the new type of jet filter, and improved dedusting efficiency. Keywords: Profibus; Fieldbus; Jet Filter; Configuration Software 1 Introduction With the increasing demands for environmental protection, countries around the world have put forward increasingly stringent requirements for environmental protection. In China, not only have emission standards for smoke and dust been raised, but control over the emission of sulfur oxides has also been strengthened. Many boilers use low-sulfur coal to meet sulfur emission standards, which reduces sulfur emissions but also increases the resistivity of flue gas. This significantly reduces the efficiency of electrostatic precipitators (ESPs) based on 1960s and 70s technology, widely used in domestic industries, and makes them increasingly inadequate for modern environmental protection requirements. Therefore, a crucial issue facing environmental protection today is designing economical, energy-saving, and highly efficient new dust collection systems. Baghouse dust collectors have been widely recognized and adopted by these industrial sectors from the outset due to their advantages: dust collection efficiency unaffected by dust resistivity, low dust concentration, and absorption of sulfur oxides. In the long run, as environmental requirements become increasingly stringent, the superiority of baghouse dust collectors will become more apparent, leading to wider attention and application. Therefore, independently developing baghouse dust collection systems, especially control systems, suitable for Chinese industry has become an inevitable choice. 2. Process Introduction The new baghouse dust collector control system, according to process requirements, consists of a primary subsystem comprising the original flue gas temperature control system, dust collection chamber system, ash hopper system, and cleaning system. Separating from the primary control subsystem, it can be further divided into numerous secondary subsystems, such as the fan array system, pulse valve timing system, rotary arm system, flue gas damper system, bag filter system, and water spray valve system. Refer to Figure 1 for the specific process structure diagram. As can be seen from the process structure diagram, the bag filter dust collector control system is a comprehensive control system with numerous controlled objects, diverse control types, and complex control strategies. Such a control system has highly complex electrical equipment. Based on the maturity and openness of Profibus fieldbus technology, and considering cost, we designed and adopted Profibus fieldbus as the underlying field control bus for the new bag filter dust collector control system. Combined with distributed I/O boards, reliable data transmission can be ensured. The distributed I/O system is an intelligent system that will reduce the processing load of the control system. The I/O system will be able to perform functions such as scanning, data tuning, digital input and output, linearized thermocouple cold junction compensation, process point quality judgment, and engineering unit conversion. Each I/O board is connected to the Profibus bus through an interface. Simultaneously, the PLC on the bus will implement the control scheme. The bus is also equipped with a human-machine interface unit, allowing operators to perform on-site monitoring and manual control. [align=center] Figure 1 Process structure diagram of the new bag filter[/align] 3 System design The traditional control system scheme mostly adopts computer control system based on DCS technology to realize distributed automatic control and centralized monitoring. However, the DCS-based system has some important defects. On the one hand, the traditional DCS system is a self-enclosed distributed system, which makes it difficult to realize information interaction and sharing between equipment and between the system and the outside world, making the automation system an "information island"; on the other hand, the traditional DCS system uses one-to-one physical connection and analog signal transmission between the field bottom sensors and data acquisition devices, resulting in large-scale wiring, which brings great trouble to the field construction. At the same time, the anti-interference ability of signal transmission is also poor. Therefore, for the new bag filter system process, the traditional DCS is no longer able to meet its process and control requirements[3]. Profibus bus is a new type of fieldbus with a data transmission speed of up to 12Mb/s. It can undertake the communication tasks of field, control and monitoring, reduce system and engineering costs, and has a high cost performance. It is the ideal bus technology for realizing distributed and centralized control systems today. It has openness, operability, interchangeability and integrability, which greatly enhances the information inheritance capability at the field level and improves the reliability of the system. The Profibus network protocol is based on the seven-layer reference model of the OSI standard promulgated by ISO, only the third to sixth layers are simplified, and the standard adaptability is strong. In addition, its three modules (FMS, DP and PA) can adapt to different application objects and communication rate requirements, and have good openness. The Profibus fieldbus master station communicates with the slave station in a master-slave mode. There is a token protocol between each master station to determine the bus control right, and the number of nodes can reach 127[2]. The Siemens ET200M I/O system is used in this system. It is an I/O board system with optical isolation. It not only supports the distributed I/O configuration mode, providing the system with good scalability and flexibility, but can also be upgraded to the hot-swappable mode, so that the impact of module failure on the system is minimized. The main control PLC uses a Siemens S7-400 series CPU, with software development using the STEP 7 programming tool. Simultaneously, an OP270 human-machine interface panel is connected to the Profibus bus, working in conjunction with a monitoring system developed using ProTool, allowing operators to directly monitor and manually operate the baghouse dust collector system on-site. The DP/PA Link enables interconnection between Profibus DP and Profibus PA buses, allowing related sensors and actuators based on Profibus PA to access the fieldbus layer. The system bus structure schematic is shown in Figure 2. Furthermore, as an independently developed product, this system provides multiple interfaces for connection to the upper-level DCS. Through interfaces including Profibus DP, MPI, and various other interface modules, the DCS host can easily remotely monitor the baghouse dust collector, achieving a highly interactive and integrated multi-layered network structure. [align=center] Figure 2 Schematic diagram of network structure of bag filter[/align] 4 Description of system control function The bag filter system has a large structure and many devices. The process requires complex interlocking of electrical equipment and control system. To comprehensively control such a system, it is necessary to divide the entire control system in detail and coordinate each subsystem. While fulfilling the control needs of each subsystem, the overall process requirements are met [1]. The basic control structure of the bag filter can be divided into the following parts: 1) Control of all electrical equipment within the scope of the bag filter system; 2) I/O board is responsible for collecting field data and transmitting it to PLC for processing through Profibus fieldbus; 3) Group design concept, combining each electrical device in the subsystem into groups, and realizing safety interlocking between groups; 4) The control program and interlocking program of each group are completed by PLC; 5) The system has manual and automatic switching functions, and the operator realizes manual operation through the human machine operation panel. The most crucial component of a baghouse dust collector is the filter bag used to filter dust. Maximizing the lifespan of the filter bag is a key indicator of system success. Preventing filter bag blockage and ensuring normal system operation places high demands on the dust removal system. Therefore, selecting the correct and effective control scheme and strategy plays a vital role in the process's feasibility. The dust removal control system implements the following functions: fan control, rotary arm control, and the core pulse valve blowing system control; it also implements equipment interlock protection, fault handling, and alarm functions. The fan system provides the high-pressure air source required for pulse valve blowing. If the fan malfunctions, it cannot blow the filter bag at the predetermined frequency, causing filter bag blockage and ultimately system failure. To ensure normal system operation, the fan system adopts a one-in-one-out configuration, with 100% redundancy between the two fans under normal operation and normal dust removal conditions. When the operating fan malfunctions or the dust removal pressure is insufficient, the control system automatically activates the standby fan. The rotary arm system controls the rotary arms above the filter bags. Each rotary arm is driven by a small geared motor. When the rotary arm speed is too low or stops, it may continuously spray the same filter bag, greatly reducing its service life. To avoid this, the control system calculates and monitors the rotary arm speed in real time. When the rotary arm speed is too low, an alarm is issued to notify the operator to take appropriate measures. The pulse valve blowing system determines the blowing frequency, i.e., the blowing level, based on the pressure difference between the clean flue gas chamber and the original flue gas chamber, i.e., the pressure difference between the inside and outside of the filter bag. The blowing levels are divided into four levels according to process requirements: fast, standard, slow, and stop. Each level corresponds to a different pressure difference range. The specific blowing levels and their corresponding pressure difference ranges are submitted to the CPU in tabular form, and the operator can set and modify them on the control panel. When the pressure difference is high, it indicates that there is more dust attached to the filter bag, and the corresponding blowing frequency is also higher, and vice versa. The pulse valves operate in groups, with all valves in the system blowing according to a predetermined sequence and the set position determined at the start of each cycle. For ease of maintenance, individual pulse valves can enter or exit the cycle at any time (certain operating conditions must be met before a valve can enter the cycle), and manual blowing is permitted at any time. The dust collection chamber system mainly consists of an outlet baffle, an inlet baffle, an interlocking rotary arm, and a dust hopper. Each chamber is divided into two units. For the dust removal system to operate normally, all outlet and inlet baffles in each chamber must be fully open, and the rotary arms must be in operation. Each chamber has one inlet baffle for each of the two units, serving as the flue gas inlet. After cooling, the raw flue gas enters the chamber through the inlet baffle, passes through the filtration and isolation of the bag filter, and then enters the clean flue gas chamber. Finally, it is discharged into the atmosphere through the outlet baffle of the clean flue gas chamber. Each chamber has only one outlet baffle, shared by both units. Each unit has a dust hopper to collect the dust that falls off. When the dust level in the hopper exceeds the upper limit, the pulse valve will automatically stop operating via system interlocking. The raw flue gas temperature control system is implemented through a water spray device installed on the raw flue gas pipeline. Due to process requirements to prevent damage to the filter bags, the flue gas entering the dust collection chamber needs to have a stable temperature, and the moisture content in the flue gas also needs to be controlled. Based on these considerations, the raw flue gas temperature control of this system adopts self-learning fuzzy control technology. Since the temperature of the raw flue gas entering the bag filter system is a gradual variable, and the system needs to have good temperature sensitivity, we use the temperature derivative dT/dt as a prediction of temperature changes. In the program, we will not only collect the temperature T value of the current cycle, but also use the temperature change between two cycles divided by the cycle ΔT/C (cycle) to approximate dT/dt. This gives us a set of two data points (T, dT/dt) regarding time t and temperature T. Finally, a fuzzy control table is established, and intelligent control is achieved through fuzzy inference. Meanwhile, based on changes in different operating conditions, the fuzzy control table will continuously adjust through self-learning, achieving a unity of self-learning control and fuzzy control to meet system control requirements. 5 System Implementation According to the system's functional requirements, the system software is divided into a lower-level machine and a control panel. 1) Lower-level Machine Programming: This system uses the STEP7 programming tool配套 with the SIMATIC S7-400 CPU for hardware configuration, network configuration, parameter setting, I/O address setting, PLC program programming, and debugging. In STEP7, the user PLC program consists of organization blocks (OB), function blocks (FB, FC), and data blocks (DB). The organization block is the interface between the system operating program and the user program, determining the structure of the user program. The operating system uses the user-written organization block program to control the execution of the scan loop and interrupt program, as well as PLC startup and error handling, etc. The function block is the program block written by the user. The user writes programs for each subsystem through the function block. The function block provides powerful object-oriented functions, allowing the user to easily access it from outside the function block. Data blocks are data areas used to store variable data required when executing user programs, and can also be used to store data that needs to be communicated. 2) Operation Panel Screen Design The OP270 operation panel of this system is an integrated human-machine interface (HMI) system and a supervisory control and monitoring (SCADA) system. It is a product that combines Siemens' advanced technology in the field of process automation and Microsoft's powerful software functions. Its matching configuration software ProTool provides object-oriented functions, and various graphics libraries meet the needs of configuring different industrial control systems. In addition, it also has a fully open feature. Through the ProTool configuration software, the connection between the operation panel and the PLC can be easily established. It can directly use the variable table configured in STEP7, which greatly reduces engineering time and improves work efficiency. 3) Implementation Steps of Profibus DP Communication Configuration First, set the Profibus DP network parameters in the hardware configuration of STEP7. Set the network addresses for the CPU, operation panel, and I/O cards connected to the network. Note that the network addresses cannot be duplicated, and the configured communication network needs to be consistent with the hardware. Next, configure the variables in the STEP7 variable table. The configured variables will become global variables in the PLC program, accessible from the operator panel connected to the Profibus DP network. Then, launch ProTool, create a new ProTool project, and configure the system's CPU in the project window's controller manager. Set the Profibus DP network address and parameters, ensuring they match those configured in STEP7. Compile after confirming. Finally, the variables configured in the STEP7 variable table can be found through ProTool's variable manager, ensuring they share the same variable name and address. By connecting the variables that need communication and associating them with the corresponding configured controls, the connection between the operator panel's screen objects and field devices can be achieved. 6. Conclusion This system utilizes the currently popular Profibus fieldbus in industry, building a highly open and real-time network structure, fully realizing the comprehensive automation of the entire control system. Using Siemens' accompanying configuration software STEP7 and ProTool, PLC control functions are completed, generating human-machine interface screens, effectively unifying system automation control with operator on-site monitoring. Field commissioning showed that the new bag filter dust collector control system based on Profibus fieldbus has a reasonable control structure and excellent control performance. Combined with advanced control technology, it can improve dust removal efficiency, reduce operating costs, and greatly enhance the industrial application prospects of the new bag filter dust collector. References 1 Xie Jianying. Microcomputer Control Technology. Beijing: National Defense Industry Press, 2001 2 Zhou Ming. Fieldbus Control. Beijing: China Electric Power Press, 2001 3 Chen Dong, Xie Jianying, Chen Yinglin. Design of Dry Flue Gas Desulfurization Network Control System Based on Industrial Ethernet. Automation Instrumentation, 2005(3):46-48