Solution

Atekon Technology Co., Ltd.

Auxiliary Control System Solutions for Thermal Power Plants

Release date:

2020-03-27

The auxiliary systems of a thermal power plant are an essential component, serving as a critical link in the overall operation of the plant. These systems primarily include the coal handling system, ash removal/sludge removal system, and chemical water treatment system—collectively referred to as "coal-ash-water." To enhance the control level and methods of the plant's auxiliary systems, while improving their operational safety and economic efficiency, and ultimately enabling unmanned local operation in the auxiliary workshops, thereby boosting labor productivity and elevating the plant's overall automation capabilities, thermal power plants typically implement centralized monitoring across the entire facility. Additionally, establishing a common auxiliary network lays a solid foundation for achieving comprehensive plant-wide monitoring (SIS).

Overview of Auxiliary Control Systems in Thermal Power Plants

The auxiliary control system of a thermal power plant is a critical component that ensures the stable operation of the generating unit, primarily comprising three core subsystems: water treatment control, ash and slag removal control, and coal handling process control.

1. Power Plant Water Treatment Control System
This system is responsible for monitoring processes such as boiler feedwater, condensate, circulating water, industrial wastewater, and unit drainage, and it utilizes PLC technology to achieve automated control. The system features functions like data acquisition, program start/stop, interruption management, and equipment operation, while also supporting automatic or semi-automatic chemical dosing, interlocked start/stop of sewage tank levels, seamless switching between pumps and fans, and low-level protection mechanisms. At the control room operator station, operators can view process flows, key parameters, and equipment statuses, along with receiving over-limit alarms, fault logging capabilities, and printing options. Additionally, the PLC system incorporates essential interlock protection logic to guarantee process safety.

2. Power Plant Ash and Slag Removal Control System
It is divided into two methods: water-flushing ash removal and pneumatic ash removal, featuring centralized monitoring, voice alarms, report management, and interface capabilities with the MIS system. The system enables fully automatic sequential control or remote manual operation via an LCD operator station, supporting operational modes such as step-by-step, skip-step, and interrupt operations. Ash removal air compressors, fluidizing air blowers, and other equipment are all integrated into the monitoring system, with a convenient switch between local and remote control options. Additionally, the system is seamlessly integrated with the DCS through redundant communication interfaces, allowing the central control room to remotely monitor and manage the entire ash removal system.

3. Coal Conveying Programmable Control System
The system is responsible for coal feeding, coal blending, and equipment safety interlocks, supporting program-based start/stop operations, interlock control, and automatic coal blending in the raw coal bunker. It features a three-way damper design to prevent blockages, as well as plow-type coal spreader control and voice-based fault alarm functionality. Operators can switch seamlessly among automatic, manual, and local control modes via a host computer. Additionally, the coal handling system integrates with broadcast paging and industrial TV systems, offering real-time monitoring of equipment operating hours, coal quantity reports, and instant fault displays. All operations are monitored and managed through the CRT display interface.

Solution

Through analysis and research of the aforementioned auxiliary control system, and guided by the principles of cost-effectiveness, stability, and comprehensive functionality, we have conceived and designed the following system solution.

 

Aoto
Network Diagram of the Auxiliary Control System for a Thermal Power Plant

 

1. System Architecture

The system employs three sets of NA400 series PLCs as control stations: the water treatment control station, the ash and slag removal control station, and the coal transportation programmable control station. Each control station is equipped with two Ethernet switches, which, together with two industrial Ethernet switches connected to the backbone network, form a redundant ring network. Additionally, each control station features both an engineer workstation and an operator workstation, while the central control room is outfitted with an engineer workstation, an operator workstation, and a redundant server.

2. Control System

The NA400 central processor features an Intel Pentium M chip and integrates two Ethernet TCP/IP communication interfaces, eliminating the need for separate communication modules, thereby reducing costs and simplifying network setup. Its modular design allows for easy installation and replacement, enabling flexible placement within the rack. Additionally, rack expansion can be achieved without requiring additional modules—simply connecting a single bus cable is enough to extend I/O capabilities.

The fully intelligent I/O design, combined with a range of safety and reliability features, ensures the system operates safely and dependably. The NA400 utilizes a fieldbus network, offering advantages such as fast communication speed, strong anti-interference capability, low cost, simple structure, and excellent real-time performance. Additionally, it boasts outstanding scalability, making it easy to achieve flexible module configurations—greatly enhancing its adaptability to diverse environmental and installation requirements. Moreover, the NA400 integrates all five programming languages defined by IEC 61131-3, along with a proprietary sequential control diagram language. These languages can seamlessly call upon each other within programs, enabling more flexible and convenient programming while effectively addressing the demands of various complex operational scenarios. Finally, the device is equipped with an Ethernet communication interface, allowing for remote programming and debugging. This feature enables the remote control center to modify on-site control processes and perform online maintenance, ensuring efficient and reliable operation even in distributed environments.

3. Network Structure

The entire auxiliary control network utilizes modular industrial switches, with the core network switches configured in a redundant setup. A multimode fiber-optic cable and industrial-grade switches are employed to establish an industrial Ethernet ring network. This unified network and software platform seamlessly interconnects the various auxiliary control systems, enabling centralized control of peripheral auxiliary systems. The entire auxiliary control network adopts a hybrid star-ring topology, using the Ethernet ring to link all auxiliary control systems while dividing the network into a core network and multiple sub-rings. Each auxiliary control system is connected to the core network in a star configuration, while the core network itself leverages advanced super-redundant ring technology. In the event of a failure at any point within the ring network, the system can automatically restore normal operation within 500 milliseconds. Additionally, with redundant switch configurations in place, the entire network achieves multi-point fault tolerance.

In this way, the entire auxiliary control network not only inherits the fast switching, safety, and reliability features of a ring network, but also integrates the multi-channel switching, convenient installation, and flexible scalability of a star network, thereby enhancing the system's reliability and real-time performance.

4. System Functions

The configuration software uses NA-control; its main functions are:

(1) Graphical interface: Maintain consistency with the operation interfaces of each subsystem and display the process flow of each subsystem.

(2) Real-time dynamic display: Provides real-time values and statuses of measurement points required for production operation monitoring;

(3) Trends: Provides real-time/historical trend display and printing functionality;

(4) Alarm System: Features a pop-up real-time alarm display and voice alert functionality, allowing for alarm acknowledgment and printing, as well as providing an alarm history log.

(5) Operation and Event Logging Function: Records real-time alarm information, alarm history, and application run lists in chronological order after system startup, facilitating easy querying and analysis by operators.

(6) Quick switching between the interfaces of each auxiliary subsystem;

(7) A unified system login interface, coupled with differentiated security levels and operational permissions, ensures the stable operation of the system.

The main interface of the auxiliary control system for the thermal power plant is shown in the figure below.

 

 

 

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