Design Of The Boiler Burner Control System Based On PLC

With the rapid development of modern industrial technology, the ratio of energy utilization has to meet more strict demands. As the key equipment to convert primary energy resources to secondary energy resources, the boiler develops with increasing control and management level. The burner, the essential and most energy-consuming part of boiler, requires an advanced burning control system to operate effectively at the optimized air-fuel ratio, so as to save the energy and protect the environment. This article, with the subject of burning control for five 75t/h gas/oil boilers used in the power station provided by some refining company, and with the efforts to improve the control method for the burner made by my company on the basis of current burning control theory study, provides with the control method for multi-fuel mixed burning, and the software and hardware platform for burning control system based on SIEMENS S7-300 PLC software redundant system. This article contains researches from the following four aspects: 1. The burning management system ( BMS ) based on SIEMENS S7-300PLC software redundant system has been worked out. The BMS, composed of redundant system, flame detecting system and ignition system, is mainly responsible for ignition, purge, flame detection, main fuel Valve ON/OFF, fuel switching management, and the detection and security for fault switching value, such as fuel oil pressure, fuel gas pressure, etc.2. In accordance with the project requirements,the design introduces a redundant hot standby control. In the event of controller or power failure, the system can automatically switch to the alternate controller,resume work from the breakpoint,achieve the seamless connection.3. According to the technological requirements, the controlled combustion system (CCS), has been designed out. It includes load control, steam pressure control, air-fuel ratio control and atomizing steam pressure control, etc.4. In order to achieve the ratio of air-fuel burner calculation, mixed burning, thermal switch, the article introduces the concept of the standard fuel quantity. We can set the quantity of a certain fuel as the standard, then compare the heating values of other fuels with that of the standard fuel, and make final calculations. In this way, the total quantity of the fuels coming into the system is converted into standard fuel quantity, and the total standard fuel quantity can be regarded as the quantity for only one fuel. The thermal test has proved that, by means of the curves for both standard fuel conversion and standard fuel-to-air ratio, either single-fuel burning or multi-fuel mixed burning, can achieve reasonable air-fuel ratio, which finally enables the boilers to work effectively and stably.