Detailed discussion on system structure of boiler burner

Detailed discussion on system structure of boiler burner
For a single dual-purpose oil and gas burner, it can be divided into five subsystems: fuel system, air supply system, ignition system, monitoring system, and electric control system according to the different functions realized by the system and burner structure.
1、 Fuel system.
1. The function of the fuel system is to ensure the fuel required for the combustion of the burner. The system mainly includes: oil pipe and joint, oil pump, solenoid valve, nozzle, and heavy oil preheater.
Oil pipe and connector: used for fuel delivery.
Oil pump: the mechanism that makes the oil form a certain pressure, and the output oil pressure is generally 10bar (1bar=1Kg/cm2).
On this basis, it can meet the atomization and fuel injection requirements, and can be divided into single-tube output and double-tube output. Some burner oil pumps are coaxial connected with fan motors, and some are driven by independent oil pump motors.
Solenoid valve: It is used to control the on-off of the oil circuit, generally two way valve and three way valve.
Nozzle: mainly used to atomize oil droplets. Injection angle (30 °, 45 °, 60 °, 80 °), injection mode (solid, hollow, semi-hollow) and injection quantity are the main parameters of the nozzle. The atomization effect is better with the nozzle with the same pressure and small injection quantity.
Heavy oil preheater: used to heat the heavy oil to a certain temperature, reduce the viscosity, and increase the atomization effect of the heavy oil. Its temperature control device is interlocked with the burner control circuit.
2. The fuel system of the gas burner includes: filter, pressure regulator, solenoid valve group, solenoid valve leakage detector, ignition solenoid valve group.
Filter: its function is to prevent impurities from entering the solenoid valve group and burner.
Pressure regulator: its main function is to reduce pressure and stabilize pressure. It is generally used in high-pressure gas supply system. Its inlet pressure shall not be less than 100mbar (1bar=1Kg/CM2).
Solenoid valve group: generally, it is composed of safety solenoid valve and main solenoid valve, which can be divided and integrated. Generally speaking, the integrated solenoid valve group is also composed of pressure stabilizing valve and filter. The safety solenoid valve is usually fast open and fast close. The general main solenoid valve is of two-stage type, and it can be divided into fast opening and fast closing and slow opening and fast closing.
Solenoid valve leakage detector: its function is to detect whether the solenoid valve group is closed tightly. Usually used on burners above 1400Kw.
Ignition solenoid valve group: generally, there are manual ball valves, pressure regulators and solenoid valves, which are mainly used for high-power burners.
2、 Air supply system.
The function of the air supply system is to input the air with a certain wind speed and volume into the combustion chamber. The main components include: shell, fan motor, fan impeller, gun fire pipe, damper controller, damper baffle, diffusion plate, etc.
Shell: It is the main part of the mounting bracket of the burner components and the fresh air inlet. According to the shape, it can be divided into box type and gun type. Most of the box type burners are covers with injection molding materials, and the power is generally small. Most of the high-power burners are split type, generally gun type. The shell is generally made of high-strength light alloy casting.
Fan motor: mainly provides power for the operation of fan impeller and high-pressure oil pump, and some burners use independent motors to provide power. Some small burners will use single-phase motors. The burners can only work normally by rotating in a specific direction.
Fan impeller: it can produce enough high air pressure, overcome the furnace resistance and chimney resistance, and blow enough air into the combustion chamber to meet the needs of combustion. The equipment is a cylindrical wheel equipped with blades with a certain angle of inclination. Its composition material is generally high-strength light alloy steel, and there are also injection molding products. Qualified fan impellers have good balance performance.
Air gun fire tube: it plays the role of guiding and stabilizing the air pressure, and is also a part of the air inlet channel. Generally, there is a shell flange connected with the furnace mouth. The constituent material is usually high-strength and heat-resistant alloy steel.
Damper controller: It is a driving device that controls the rotation of the damper baffle through mechanical linkage. Generally, there are two kinds of hydraulic drive controller and servo motor control. The former operates smoothly and is not prone to failure, while the latter control is accurate and the air volume is stable.
Damper: The main function is to adjust the air inlet volume of the air duct to control the air inlet volume. It is composed of injection molding and alloy. The injection molding baffle is generally composed of single piece, double piece and three pieces.
Diffusion plate (air conditioner): special structure can generate rotating air flow, help air and fuel fully mix, and also regulate secondary air.
3、 Ignition system.
The function of the ignition system is to ignite the mixture of air and fuel. Its main components are: ignition transformer, ignition electrode, and electric fire high-voltage cable.
Ignition transformer: It is a conversion element that produces high-voltage output, usually 2X5KV, 2X6, 2X7, and the output current is generally between 15 and 30 MA.
Ignition electrode: converts high voltage electric energy into light and heat in the form of arc discharge to ignite fuel, generally including single type and split type.
Electric fire high-voltage cable: its function is to transmit electric energy.
Fourth, monitoring system.
The function of the monitoring system is to ensure the safe operation of the burner. Its main components are flame monitor, pressure monitor, temperature monitor, etc.
Flame monitor: its main function is to monitor the formation of flame and generate signal alarm. There are three main types of flame detectors: photosensitive resistor, ultraviolet UV eye and ionization electrode.
(1) Photosensitive resistor: a kind of resistor is mainly used in light oil and heavy oil burners. Its function and working principle are as follows: three contacts are connected with the flame relay at a time. The resistance value of the photo resistor changes with the amount of light received by the device. The more light received, the smaller the resistance value. When the voltage at both ends is added to a certain value, the greater the current in the line. When the current reaches a certain value, the flame relay will start, Keep the burner working downward. If the photosensitive resistor cannot sense enough light, the flame relay will not work and the burner will stop working. Because the flame is not bright enough when the gas is burning, the photosensitive resistor is not suitable for the gas burner.
(2) Ionization electrode: mostly used for gas burner. The program controls the input of 220V voltage to the ignition transformer. One of the two output high-voltage lines is grounded, and the other is connected to the ignition electrode. The discharge between the electrode and the ground generates electric spark. When igniting the mixture of gas and air, the program controller supplies power to the ionization electrode. If there is no flame, the power on the electrode will stop. If there is a flame, the gas will be ionized by its own high temperature. The ion current will flow between the electrode, the flame and the combustion head, and the ion current will be rectified into direct current. It will reach the flame relay through the grounded burner shell to make it work, so as to ensure that the subsequent work of the burner can proceed smoothly. If the ionization electrode is grounded, the generated current is AC instead of DC, the flame relay will not work, and the program controller will be locked. In addition, in the same grounding circuit, both the ionization current and the ignition current pass through. Because the ignition current is far greater than the ionization current, when the two directions are opposite, the ionization current will be blocked by the ignition current. However, after the flame is generated, the burner is open. This defect can be compensated by the reverse input of the ignition transformer, because the reverse wiring causes ignition, and its AC direction rotates 180 °, and the resulting ignition current also rotates 180 °. The two currents have the same direction, thus overcoming the above defects. In addition, the flame in the ionization zone is unstable. It can also cause the flame when the burner is disconnected, which may be caused by the inappropriate air-gas ratio, which can be solved by adjusting the air volume or gas volume, or by the uneven distribution of air and gas in the combustion head, which can be solved by adjusting the position of the combustion head.
(3) Ultraviolet UV electric eye: usually used on dual-purpose oil and natural gas burners. This electric eye can only sense the ultraviolet light in the flame (spectral range 190~270 nm). The UV tube will not react to the flashing sunlight, ordinary light or furnace light substances in the furnace. The UV tube has a service life of about 10000 hours when the ambient temperature does not exceed 50 ℃. High ambient temperature has a great impact on battery life. If enough ultraviolet light is received by the ultraviolet light, an electric current will be generated and the machine or flame relay will turn it off. If the UV lamp runs out of power, even if there is no ultraviolet light, it will show the existence of ultraviolet light. In order to overcome this shortcoming, the program control will apply appropriate voltage at both ends of it before each opening. So even if the power is exhausted, its signal will only indicate that there is no flame, so the program controller will stop working immediately.
Pressure monitor: usually used for gas burners, mainly used for gas high pressure and low pressure monitoring, as well as air pressure monitoring. For example, steam boiler can also be used for steam pressure monitoring.
Temperature measuring device: mainly includes smoke temperature monitoring, oil (heavy oil) temperature monitoring, system water and medium water temperature monitoring and control, etc.
5、 Electric control system.
The electric control system is the command center and contact center of the above systems. The main control element is the program controller, which is equipped with different program controllers according to different burners. Their main difference is that the time of each program step is different.