"Informatization drives industrialization, and industrialization promotes informatization" is China's national policy. The informatization of petroleum and chemical enterprises is divided into three layers: the first layer is the basic automation layer of the production process, represented by PCS (Process Control System); the second layer is the production process operation optimization layer, represented by MES (Manufacturing Execution System); and the third layer is the production process management optimization layer, represented by ERP (Enterprise Resource Planning). This article focuses on the first layer (PCS) and discusses the application and development of DCS (Distributed Control System) and FCS (Field-bus Control System). 1. Application and Development of DCS Since its introduction in the 1970s, DCS has undergone several generations of technological changes and updates, and is now widely used in various industries, especially in petroleum and chemical enterprises. DCS is used in both technological transformation projects and new construction projects. In petroleum and chemical enterprises, there is a trend of gradually replacing conventional instrument control systems with DCS. The widespread application of DCS (Distributed Control System) stems from a series of characteristics and advantages: ① Decentralization: This refers to decentralized control, geographical distribution, equipment distribution, functional distribution, and hazard distribution. Modular hardware and software are concrete manifestations of decentralization. The aim is to disperse hazards, thereby improving system reliability and security. ② Centralization: This refers to centralized monitoring, operation, and management. Distributed devices are integrated into a unified whole using communication networks, and information is integrated across the entire system using distributed databases, achieving information sharing. Simultaneous monitoring, operation, and management can be performed from multiple operator stations. ③ Autonomy: This means that each device in the system can operate independently. Control stations autonomously perform input, calculation, control, and output; operator stations autonomously perform monitoring, operation, and management; and engineer stations can be configured online or offline. ④ Coordination: This means that devices in the system are interconnected via communication networks and databases, transmitting information and coordinating their work to achieve the overall system functionality. Decentralization and centralization, autonomy and coordination in DCS are not contradictory but complementary. ⑤ Flexibility and Scalability: The hardware adopts a modular structure, allowing for flexible configuration into small, medium, and large systems, and can be gradually expanded according to the company's development. The software adopts a modular structure, providing input, output, calculation, and control function blocks, which can be flexibly configured to form simple and complex control systems, and the control scheme can be modified at any time according to changes in the production process. ⑥ Reliability and Adaptability: The decentralized nature of the system brings reliability, and a series of redundancy technologies, hot-swappable technologies, fault diagnosis, and fault shielding technologies are adopted. High-performance components, advanced manufacturing processes, and anti-interference technologies enable the DCS to adapt to harsh working environments. ⑦ Advanced Technology and Inheritance: The hardware adopts advanced computers, communication networks, and human-machine interfaces; the software adopts advanced operating systems, databases, network management, and control languages; and the control algorithms adopt advanced control technologies such as adaptive, predictive, inference, and optimization. The DCS can be updated and replaced quickly, and its inheritance is reflected in the compatibility between new and old systems, which can bring better benefits to users. DCS (Distributed Control System) has continuously updated and developed along with the advancements in computer, control, network communication, configuration software, information integration, and database technologies, primarily reflected in the following aspects: ① Informatization: DCS has evolved from a single control system into a comprehensive information system integrating control and management. DCS provides an entire information channel from the production site to the workshop, from the factory to the company, and finally to the enterprise group, fully demonstrating the comprehensiveness, accuracy, and real-time nature of information. ② Integration: DCS has evolved from a single, closed system into one integrating various PLCs, industrial PCs, digital instruments and equipment. Even different models of DCS can be integrated and share information, providing end users with an integrated comprehensive system. ③ Intelligence: With the development and application of advanced control technologies such as artificial intelligence, expert systems, adaptive, predictive, and inference, DCS also integrates these new technologies to achieve advanced intelligent control functions. ④ Open Network: DCS has evolved from a single, closed network into an open network system. Through internet technology and an IE browser, users can access process screens, query data, manage scheduling, and direct production. The key to open networks is network security. Traditional DCS uses software firewalls, while modern DCS has both software and hardware firewalls to ensure both network security and openness, as well as real-time monitoring. For example, the control station of Honeywell's Experion PKSR300 uses hardware firewall technology. ⑤ Fault-Tolerant Ethernet (FTE): Traditional DCS uses two independent networks (A, B) for redundancy, with only one communication path between the two devices. Essentially, it operates on a single network, and in case of failure, the entire network switches (A to B or B to A), resulting in long switching times and low reliability. Modern DCS uses Fault-Tolerant Ethernet (FTE), as shown in Figure 1. In Figure 1, switches S1 to S6 are interconnected, with S1 and S2 being the upper layer and S3 to S6 the lower layer. Each device (D1 to D4) connects to two lower-layer switches simultaneously, and there are four communication paths between any two devices. Essentially, it operates on multiple networks. For example, the four communication paths between devices D1 and D4 are D1→S3→S1→S5→D4, D1→S3→S1→S2→S6→D4, D1→S4→S2→S1→S5→D4, and D1→S4→S2→S6→D4. In case of a fault, only the path needs to be switched, resulting in short switching time and high reliability. For example, Honeywell's Experion PKSR300 uses this FTE technology, with network bandwidth reaching 200Mbps between FTE device nodes and 1Gbps between switches. Figure 1 Fault-Tolerant Ethernet (FTE) ⑥ Wireless Network Technology: Supports handheld mobile wireless operating stations, integrating wireless and control technologies for on-site operation monitoring, fault handling, and instrument calibration, achieving seamless integration of operation and maintenance. For example, Honeywell's Experion PKSR300 uses this wireless network technology. ⑦ Digital Video Technology: This technology acquires on-site image information via cameras, processes the images using image recognition software, and immediately issues alarm signals upon detecting abnormal images. It features automatic recording and playback functions for easy accident analysis and integrates digital video technology with operation monitoring software. For example, Honeywell's Experion PKSR300 uses this digital video technology. ⑧ Advanced Control Station: The foundation of a DCS is the control station. To further improve the reliability, stability, and security of the control station and enhance its functionality, a series of advanced technologies are employed. For example, the control station adopts a baseboard-less modular structure, independent tilting vertical plug-in design, good heat dissipation, and convenient wiring and maintenance; it uses fault-tolerant Ethernet (FTE), a redundant hardware control firewall, redundant controllers, redundant I/O, redundant power supplies, and redundant fieldbus interfaces; it employs advanced predictive control algorithms, offering good robustness and parameter self-tuning capabilities. Honeywell's Experion PKSR300 control station is one example of such advanced control stations, as shown in Figure 2. Figure 2. Experion PKSR300 Control Station 2. Application and Development of FCS FCS is a new type of distributed network control system. It is both a field communication network system and a field automation system. As a field communication network system, it has open digital communication capabilities and can interconnect with various communication networks. As a field automation system, it uses various field instruments with input, output, calculation, control, and communication functions installed in the production site as nodes of the fieldbus, and directly forms distributed control loops on the fieldbus. FCS represents the current development direction of control technology and DCS, and has entered the stage of industrial application. People have various comments on FCS, some praising the new technology and others expressing confusion about the current situation. Despite the various opinions, the author believes that FCS and DCS coexist at present, with FCS as an important branch of DCS framework. The following are some personal views: ① The transformation of FCS: It not only transforms the traditional single-function analog instruments into integrated digital instruments; it also transforms the traditional DCS control station, distributing input, output, calculation, and control functions to fieldbus instruments, forming control loops on the fieldbus, and forming a fully digital and thoroughly distributed control system. ② Characteristics of FCS: FCS possesses seven key characteristics or advantages: system decentralization, system openness, product interoperability, environmental adaptability, ease of maintenance, system reliability, and economic efficiency. Some may object to the "economic efficiency," which is a normal and temporary phenomenon. This is because FCS has not yet entered the stage of large-scale application, and the price of fieldbus instruments and auxiliary equipment is relatively high. With the promotion and application of FCS, technological advancements, market competition, and natural selection, the economic benefits of FCS will become apparent. Looking back, DCS followed a similar path, and now people have fully accepted DCS. ③ Applications of FCS: A typical industrial application example is the Shanghai SECCO 900,000-ton/year ethylene project. The DCS uses Emerson's DeltaV system. In addition to conventional I/O modules, the control station is equipped with FF-H1 fieldbus modules. Each module's two interfaces constitute two FF-H1 bus segments, and each FF-H1 bus segment is designed for nine instruments (six in use and three as spares). This project utilizes 2473 FF-H1 fieldbus segments and 14375 FF-H1 fieldbus instruments, averaging 5.8 instruments per FF-H1 fieldbus segment. The FF-H1 fieldbus segments integrate fieldbus instruments from various manufacturers, including Emerson's temperature, pressure, and flow meters, E+H's radar level gauges and flow meters, ABB's valve positioners, ROTORK's electric motor controllers, and TYCO's electric motor controllers, ensuring consistency and interoperability among multiple products. ④ FCS Integration: In small-scale projects, the FCS operates as a self-contained system. In medium- and large-scale projects, the FCS and DCS control stations are integrated, generally using two integration methods. One is that the FF-H1 fieldbus module acts as a subordinate I/O module of the control station, such as Emerson's DeltaV system, as shown in Figure 3; the other is that the FF-H1 fieldbus module is independent, such as Honeywell's Experion PKSR300 system, as shown in Figure 4. The former, FF-H1, is attached to the controller, resulting in slow information transmission; the latter, FF-H1, is independent, with fast information transmission. In Figures 3 and 4, the Engineer Station (ES), Operator Station (OS), and Computer Station (CS) are DCS operation and monitoring layer devices. The control station contains redundant power supplies (P), controllers (C), fieldbus interfaces (H1), and various I/O modules. Figure 3: FCS and DCS Integration Part 1; Figure 4: FCS and DCS Integration Part 2. ⑤ FCS Development: The FF-H1 fieldbus communication rate is 31.25Kbps and does not support redundant buses; some have raised objections to these two points. It is encouraging that there are currently various fieldbuses available, including medium-speed and high-speed fieldbuses, and Industrial Ethernet (Ethernet) has entered the practical stage, extending from the high-level to the low-level, and is expected to achieve "E (Ethernet) to the bottom." FCS represents the direction of technological development; continuous improvement in application, leveraging its strengths and avoiding its weaknesses, will inevitably lead to a more perfect FCS. 3. Application of Advanced Control Technology According to the "Eleventh Five-Year Plan" for information technology development, the application penetration rate of advanced control technology in the process industry will reach over 70%. DCS and FCS provide the conditions for the application of advanced control technologies, with advanced control software integrated into the system as an optional component of DCS. Commonly used advanced control technologies include: ① Single-loop tuning technology: Single-loop PID control has always dominated process control, but its robustness is not ideal, showing significant shortcomings in processes with large time delays and strong disturbances. Therefore, single-loop model predictive control has been developed, automatically adjusting control parameters and suitable for processes with large time delays and strong disturbances. For example, the ProfitLoop single-input single-output (SISO) model predictive control algorithm in Honeywell's Experion PKSR300 system. ② Soft instrumentation technology: This is based on process mechanism models or statistical models to predict key product parameters online and incorporate these predicted parameters into online control of product quality. For example, Honeywell's ProfitGCC software package for switching between atmospheric and vacuum crude oil. ③ Multivariable Model Predictive Control Technology: This is the core technology of advanced control. First, the process model is identified, then process parameters and controlled variables are predicted and compared with the required target values. If there is a deviation, the optimal control variable is calculated, thus achieving multivariable control of the entire plant. Examples include Honeywell's RMPCT software package and Aspen Technology's DMC-plus software package. ④ Online Optimization Technology: This is based on process mechanism models and dynamic optimization technology to find the optimal operating point, and then achieve optimized operation through a multivariable controller. For example, Honeywell has developed dynamic optimization software based on ProfitOptimizer, ProfitBridge, and mechanism models, applied to ethylene and refining plants. ⑤ Performance Monitoring and Maintenance Technology: Advanced control has high initial efficiency. However, with increased operating time, changes in plant performance, model mismatch, and operational changes, the performance of advanced control decreases, and economic benefits decline accordingly. Therefore, developers have launched advanced control performance monitoring and maintenance tools to maintain the efficiency of advanced control. For example, Honeywell developed Scout software, and Aspen Technology developed AspenWatch software. The future development and application of DCS, FCS, and advanced control technologies will rely on the process industries, especially the petroleum and chemical industries, which will be at the forefront. Guided by the national policy of "informatization driving industrialization, and industrialization promoting informatization," the application and development of DCS, FCS, and advanced control technologies will undoubtedly usher in a golden age.