1 Introduction
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The low-pressure boiler of No. 4 converter of Jinan Iron and Steel Co., Ltd. shoulders the task of supplying vacuum for vacuuming to the rh refining system. Its normal operation is directly related to the smooth production of rh refining. The ignition system of the boiler is the key to the operation of the low-pressure boiler. Therefore, it is necessary to have a detailed understanding of the composition and principle of the ignition system of the low-pressure boiler, so that the daily maintenance work can be carried out smoothly.
2 The composition of the boiler ignition system
The ignition system of the No. 4 furnace of Jinan Iron and Steel Co., Ltd. is composed of nddh high-energy ignition device, ndhj-7 ultraviolet flame detector, ndlf fire detection cooling air system, ndtj igniter propulsion device and ndqf-1 electric quick-closing ball valve. Among them, high-energy ignition devices and ultraviolet flame detectors are particularly important. The ignition control section is an ndis ignition control system.
2.1 High-energy ignition device
The ignition system of the low-pressure boiler of No. 4 furnace of Jinan Iron and Steel Co., Ltd. adopts nddh type high-energy ignition device, which belongs to low-voltage capacitor discharge device. Its main structure consists of nddh high-energy igniter, nddz high-energy igniter and nddl high-voltage shielded ignition special cable (Figure 1).
Figure 1 nddh high-energy ignition device assembly diagram
The working principle is that the AC power frequency 220v is converted into a DC ripple current by boost rectification to charge the storage capacitor. When the capacitor is full, the discharge current is transmitted to the igniter's semiconductor nozzle through a discharge tube, a choke coil, a shielded cable, etc., forming a high-energy arc spark. When the ignition is stopped, the remaining charge on the capacitor is vented through the bleeder resistor (see Figure 2).
Figure 2 Electrical schematic of ddh high-energy ignition device
2.2 UV flame detector
The ndhj-7 UV flame detector can continuously detect the flame of various gas boilers for long-term safety monitoring of the boiler. The main structure consists of a probe and a processor. The probe and the processor are connected by a two-core twisted-pair shielded cable. The working principle is that the probe of the ndhj-7 ultraviolet flame detector is equipped with a quartz dustproof lens, and the light signal emitted by the flame is transmitted to the uv photosensitive tube at the tail of the probe, and the photoelectric conversion is completed by the uv photosensitive tube. The signal transmission between the probe and the processor adopts a current transmission mode to improve the anti-interference ability and is transmitted to the processor through the two-core twisted pair shielded cable. The processor processes the signal from the probe through the matching circuit, the Schmitt trigger, and the monostable trigger circuit, and performs the presence and absence of fire discrimination, and gives corresponding indications and outputs (see Figure 3).
Figure 3 block diagram of the working principle of the detector
3 ndis ignition control system
The ndis system is mainly used to control the ignition operation of the boiler ignition equipment. It can realize the automatic ignition of the boiler (accepting the program control ignition command of the centralized control room), and can also perform the single step operation on the ignition equipment, and feed back the working position and working condition signals of each unit equipment to the control room. The ndis system consists of a program-controlled ignition control cabinet (programmable controller plc control cabinet), an in-situ ignition control cabinet (relay control cabinet), a high-energy ignition device, a flame detection device, and a quick-shutdown valve. The block diagram of its control system is shown in Figure 4.
Figure 4 Schematic diagram of the ignition control system
3.1 main functions of the system
(1) Automatic or manual control of advancement and retreat of the propulsion actuator;
(2) Automatic or manual control of ignition of high energy ignition devices;
(3) Automatic or manual control to quickly cut off the purge, intake and cutoff of the valve;
(4) Automatic (control room) or manual (local) control mode switching;
(5) Operating condition indication.
3.2 system ignition process
The ndis ignition control system used in the ignition system of the low-pressure boiler of No. 4 furnace of Jinan Iron and Steel Co., Ltd. consists of a program control cabinet and a local control cabinet. Among them, the components in the control cabinet are Siemens s7300 series plc. Through different remote and local control methods, the ignition requirements under different conditions and requirements are realized. The system ignition process is shown in Figure 5.
Figure 5 system ignition flow chart
4 Conclusion
Through the analysis of the principle and composition of the ignition control system of the low-pressure boiler of No. 4 furnace of Jinan Iron and Steel Co., Ltd., the working principle and control flow of the core components of the boiler ignition system have a deeper understanding, which is conducive to the troubleshooting and maintenance work in the production process.
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