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The fertilizer plant of CNPC Lanzhou Petrochemical Company is equipped with 3 coal-fired boilers. Among them, Boiler C is a high-temperature and high-pressure, direct-fed natural circulation drum boiler with a rated output of 220 t/h; it was put into operation in May 1999. Since its commissioning, it has experienced over 200 shutdowns in total, with abnormal shutdowns accounting for more than 75% of them. Frequent stopping not only severely disrupts normal production, resulting in substantial economic losses and energy waste, but also causes varying degrees of damage to the boiler itself and related equipment. 1 Analysis of the boiler control system: The DCS is the Plantscape system from Honeywell in the United States, and it is used for data collection, process control, program logic management, trend recording, alarm handling, and monitoring as well as control of systems such as boilers and steam turbines. The coal feeding and pulverization system (abbreviated as Williams) is the C200 control system built into the mills manufactured by the American company Williams; it performs program-controlled monitoring functions for the coal mill, coal feeder, cold air dampers, hot air dampers, three outlet shut-off valves for the coal mill, cold air shut-off valves, hot air shut-off valves, as well as the seal fans connected to the coal mill and coal feeder. The Japanese Omron C-2000 programmable logic controller (PLC) carries out boiler safety protection and burner management functions (abbreviated as FSSS). The Japanese KMM programmable digital regulator is used to control Station 5 for temperature and pressure reduction. The 505E from WOODWARD in the United States, the Bentley 3300 system, and the MODICON TSX QUANTUM are used to monitor and control parameters such as speed and power, as well as the protection systems of steam turbines and steam-driven feedwater pumps. The 2 redundant servers in the control room are dedicated to functions such as data exchange for the Plantseape system and programming configuration maintenance, and are not used for operator operations. 3 Plantscape operation stations are used for the monitoring and control of the Plantscape system; 1 operation station that communicates with the Omron C-2000 PLC is used for FSSS monitoring; and 1 operation station that communicates with the Williams system is used for the monitoring and control of that system. In the early stages, due to lower configurations of the servers and operation stations as well as imperfect software, the Plantscape system experienced issues such as operation station crashes and communication disruptions. The original faults were resolved by replacing the servers, the models of the operation stations, and upgrading the Plantscape software. The Willimas system faces difficulties in maintenance and operation due to the lack of appropriate imported spare parts, as well as a insufficient understanding of its software and hardware. To date, the internal control principles of the Willimas system have not been fully understood, and there is still no qualitative or quantitative description of the interrelationships among the controlled parameters. When there are fluctuations in production (such as deterioration in the quality of coal used in boilers, abnormal conditions in the coal grinding process, or overshoot phenomena), the operators have extremely limited means of making adjustments; they are unable to make accurate and effective adjustments, and everything is controlled by the internal programs of the Willimas system, which makes it impossible to avoid shutting down the equipment. Control systems such as the Williams system, FSSS, and Plantscape system are independent of one another; they do not communicate with each other and carry out their own control functions. Relevant analog and switch signals are handled through hard wiring, resulting in insufficient sharing of information resources. Accident alarm information is incomplete, and there are contradictions in the accident alarm information provided by the DCS and the Williams system. Therefore, once a parking accident occurs, it is difficult to identify the true cause, and as a result, effective preventive measures cannot be taken. 2 Determination and implementation of the renovation plan: After a thorough analysis of the problems encountered with Boiler C and conducting in-depth investigations, it was decided to optimize and renovate the boiler control components of Boiler C, such as the Willimas system, the FSSS system, and the 5# temperature and pressure reduction station composed of KMM regulators; the remaining parts were left unchanged. Drawing on lessons from past experiences, the renovation did not involve expansion of the Plantscape system; instead, the DeltaV system from Emerson in the United States was adopted. The signals from the original Willimas system, FSSS system, and KMM controllers were integrated into the DeltaV system, which formed a single DeltaV control system that enabled unified timing and resource sharing. An additional SOE (Sequence of Event) card is installed in the control cabinet to generate alarms at the onset of an incident, facilitating the analysis of the reasons for shutdown. The control cabinets of the original FSSS control system and the desuperheating and pressure reduction station control system were removed, and a DeltaV 1# Controller (Node 1) cabinet was installed in their place; this cabinet is primarily responsible for controlling the original desuperheating and pressure reduction station as well as the coal grinder control system. The DeltaV 2# Controller (Node 2) cabinet is installed in the location of the original FSSS control cabinet, and it is primarily responsible for carrying out the control tasks of the original FSSS control system. The new DeltaV control system is equipped with 2 operator stations and 1 engineer station. Replace the original operator console, moving all the buttons and switches on that console to the vertical panel. The operators for the forced draft and exhaust fans, main feedwater, bypass feedwater, etc., on the original operator console were removed, and the corresponding Honywell Plantscape DCS I/O wiring and internal software were modified. 3 Characteristics and Configuration of the DeltaV System 3.1 Characteristics of the DeltaV System The DeltaV system features an open network architecture and OPC standards ； Data structure of the Foundation Fieldbus (FF) standard ； Modular structure design with plug-and-play functionality; the system hardware is automatically recognized, and all cards can be inserted or removed while the system is powered on, eliminating the need to shut down the system for operation and maintenance ； At the same time, the system can achieve true online scaling ； Conventional IO cards feature an 8-channel distributed design, with each channel isolated from the field, thereby fully reflecting the safety and reliability of distributed control. The DeltaV system consists of a redundant control network, operator stations, and control components. The boiler control room is equipped with 1 engineer station, 3 operator stations, and 2 controllers (Nodes). The engineer station houses the global database of the stored procedure control system, provides development tools for configuring system control strategies, and offers system diagnosis and equipment management (AMS) functions. The operator station runs the human-machine interface program to monitor the operation of the process control system, fault alarms, and historical trends. Engineer station software typically includes DeltaV software and other engineer station applications. Operation station software generally includes operation station software, control software, etc. The control network of the DeltaV system is a redundant Local Area Network (LAN) based on 10M/100M Ethernet. All nodes of the system (operation stations and controllers) are directly connected to the control network, without the need for any additional intermediate interface devices. A simple and flexible network structure can support local and remote operation stations as well as control devices. Both the workstations and controllers of the DeltaV system are equipped with redundant Ethernet ports. To ensure the reliability of the system and the proper execution of its functions, the control network is dedicated to the DeltaV system. Communication with other factory networks is achieved by using integrated workstations. Both the system controller and the control network adopt a redundant architecture, enabling automatic switching in the event of communication failures to ensure reliability of communication. 3.2 System Configuration The DeltaV system can be configured in various ways, such as through interactive dialog boxes in a browser, or via graphical configuration in the control scheme configuration studio. The DeltaV browser is the main navigation tool for system configuration. It uses one window to display the entire system, allowing direct access to any of its components. Through this interface similar to a Windows browser, it is possible to define the system components (such as areas, nodes, modules, and alarms), view the overall structure, and arrange the system. The DeltaV browser also provides a way to quickly add control modules to the database. The control module can be dragged from the module library to a factory area, and the module parameters that meet the application requirements can be defined. When inserting IO cards, intelligent field devices, or controllers into the system, the DeltaV browser uses its built-in automatic recognition function to establish the configuration, thereby greatly simplifying the configuration process. The control studio is used to create modules; it treats each module as a separate entity, allowing operations to be performed on specific modules without affecting other modules running within the same controller. It is a function that allows for the graphical configuration and modification of control schemes; it involves dragging the required functional modules from the module library into the module diagram and connecting them together to form module algorithms, or selecting appropriate control languages such as function block diagrams and sequential function charts to configure the system. A graphics studio uses graphic, text, data, and animation creation tools to configure high-resolution, real-time process flowcharts for operators. System operators monitor the process through the operator interface. 1) Configuration of the control scheme. For system control configuration, the DeltaV browser is first used to define the system’s structure: such as adding or removing workstations, activating controllers (by dragging a Decommission controller into the control network, the Plus workstation automatically assigns an IP address; the controller also requires a license), and the type and channels of IO cards are automatically identified once they are inserted ； Then the card attributes are configured, and the system is logically divided into plant areas: these can be physical locations of plants, or they can represent the main process control functions of a control system. Next, define modules using control studios: you can use the modules available in the DeltaV system library, or define your own modules using function blocks and sequential function blocks. The general control module represents process control devices such as valves, analog control loops, motors, isolation valves, fans, etc.; the module includes control algorithms, parameters, alarms, or other elements. Function blocks are primarily used for analog control, while sequential function blocks are a type of module mainly used to control the sequence of events over time. 2) Configuration of the operation graphics. The operation software in the DeltaV system uses Intellution’s IFIX software, which boasts powerful configuration capabilities; the Script language has been replaced by VBA (Visual Basic For Application), and Microsoft’s VBA development environment is integrated into it. By using IFIX’s workspace, it is possible to switch back and forth between the system configuration and the operating environment at any time (Ctrl+W), making system debugging very convenient and fast. The Intellution workspace environment can be customized to meet various requirements; IFIX development tools such as wizards and experts can be dragged into the workspace’s toolbox or toolbar, and custom-made tool buttons can also be added to it. 3) Configuration of alarms. This includes alarm priority, alarm type, alarm value, automatic confirmation of alarms, enabling/disabling of alarms, alarm name, and alarm information, etc. Alarm priorities can be defined globally in the DeltaV browser. For example, all alerts of the highest priority are displayed in red, flash and emit an alarm sound when unconfirmed. The alarm summary screen displays all unconfirmed alarms and their priorities. The system offers 12 alarm priorities ranging from 3 to 15, with 3 being the lowest and 15 the highest. The system comes pre-configured with four priority levels: LOG (3), ADVISORY (7), WARNING (11), and CRITICAL (15). In addition, users can define their own alarm priorities; other alarm parameters can be set in the control studio. The system’s alarm management function allows users to view and set whether alarms are allowed or prohibited, as well as the alarm thresholds and priorities. The conditional alarms of the DeltaV system are used to add time delays and allow/disable alarms, in order to reduce unnecessary alarms. 4) Historical trend configuration. First, define history data collection for the module and node parameters, activate the history subsystem, assign an area and nodes to the history system, then configure the process history view, and install the workstation. The history view can display real-time and historical data. 5) Bottoms. The DeltaV database stores all configuration data; it is possible to modify the configuration data in the database without affecting the operation of the controllers and workstations. After configuration, download that information to the controller and workstation. Any data can be installed in DeltaV Explore, such as a controller, setting data, I/O cards, or modules; independent modules can be installed in Control Studio. The operation screen can be applied and edited on any workstation in the DeltaV control network. The workstations of the DeltaV system have a synchronization function. In a DeltaV network, a workstation must ensure that the configuration data across the system is automatically distributed to all workstations, regardless of whether the information has been updated or not. If the setup data of the lower-level engineer station (Plus workstation) is changed, the system’s synchronization function will update all workstations to match the settings of the engineer station. For the lower-level workstation (non-Plus station), the system compares the screen data from this workstation with that from the engineer station; if a screen is selected for upload to the engineer station, the system will store that screen there. After uploading, it is downloaded to the workstations; the system settings and graphic data are automatically synchronized and distributed to all workstations. The engineer station and operator station use Emerson’s Windows XP and DeltaV 7.4 data software packages. Through the above configuration work, all the control functions of the coal feeding and pulverization system are implemented (pulverization system control, boiler fuel control, total air volume control for the coal mills, outlet temperature control for the coal mills, speed control of the main motors of the coal mills, speed control of the motors in the exhaust separators of the coal mills, speed control of the coal feeders, etc.), as well as the control functions of the desuperheating and depressurization stations. Additionally, the program control and alarm interlock protection functions of the Furnace Safety Supervision System (FSSS) (furnace purging, fuel tripping, sequential logic control systems, etc.), process flow diagrams, historical trend configurations, alarm information, and records – all of these are configured as well. Operators can monitor and control production from the control station. 4 Effects achieved after the control system renovation: After the renovation and commissioning of the boiler control system, the production unit operated smoothly. Unplanned shutdowns caused by issues with the control system were eliminated, and the difficulties associated with insufficient information for analyzing the causes of accidents were overcome. The SOE alarm messages enabled timely identification of the reasons for shutdowns. The DeltaV system provides operators with a user-friendly interface that enables easy and efficient monitoring and control of the parameters related to the boiler coal feeding and pulverization system, overcoming the issue in the original Willimns control system where most signals were processed only internally. By changing its operation method, and while retaining its control principle, the original closed-loop fully automatic control mode of the Williams system has been modified to offer three selectable operation modes under DCS control: cascade, automatic, and manual. Thoroughly resolve a series of constraints such as the unknown causes of previous malfunction-induced stops and system communication disruptions. The boiler has changed from a device with short cycle times (15–30 days) and unplanned shutdowns to one that now operates on a long cycle basis with stable performance. Before the renovation, over a period of 16 months from January 2004 to April 2005, the fertilizer plant’s boiler was shut down 36 times, of which 13 were planned shutdowns ； Shutdown 3 times due to fluctuations in the external power grid ； Shutdowns occurred 20 times due to process and equipment issues as well as control problems. Due to the aforementioned control system issues, it is not possible to determine the cause of the accident with accuracy. After the modification, the boiler operated continuously for 122 days (up to August 7, 2006). Over the 12-month period from July 2005 to July 2006, the boiler stopped operating 5 times, and the causes of these incidents were able to be accurately determined. This indicates that the bottleneck issue in the control system has been resolved, and the renovation was successful.