Detailed discussion on the system structure of boiler burners

Detailed discussion on the system structure of boiler burners
For a single dual-purpose oil and gas burner, it can be divided into five subsystems based on the differences in system and burner structure functions: fuel system, air supply system, ignition system, monitoring system, and electrical control system.
1、 Fuel system.
1. The function of the fuel system is to ensure the fuel required for combustion of the burner. The system mainly includes: oil pipes and joints, oil pumps, solenoid valves, nozzles, and heavy oil preheaters.
Oil pipe and joint: used for transporting fuel.
Oil pump: a mechanism that creates a certain pressure on the oil, with an output oil pressure of generally 10 bar (1 bar=1Kg/cm2).
On this basis, it can meet the requirements of atomization and fuel injection, and is divided into single tube output and double tube output. Some burner oil pumps are coaxially connected to fan motors, while others are driven by independent oil pump motors.
Electromagnetic valve: used to control the opening and closing of oil circuits, usually a two-way valve and a three-way valve.
Nozzles: Their main function is to atomize oil droplets. The main parameters of the fuel nozzle are the injection angle (30 °, 45 °, 60 °, 80 °), injection method (solid, hollow, semi hollow), and injection quantity. Nozzles with the same pressure and less fuel injection have better atomization effects.
Heavy oil preheater: used to heat heavy oil to a certain temperature, reduce viscosity, and increase the atomization effect of heavy oil. Its temperature control device is interlocked with the burner control circuit.
2. The fuel system of a gas burner includes a filter, pressure regulator, solenoid valve group, solenoid valve leakage detector, and 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 systems, and its inlet pressure should not be less than 100mbar (1bar=1Kg/CM2).
Electromagnetic valve group: generally composed of safety solenoid valve and main solenoid valve, there are two types: split and integrated. Generally speaking, the integrated solenoid valve group also combines a regulator valve and a filter. Safety solenoid valves are usually fast opening and fast closing. The general main solenoid valve is a two-stage type and can be divided into fast opening and fast closing and slow opening and fast closing.
Electromagnetic valve leakage detector: Its function is to detect whether the electromagnetic valve group is tightly closed. Usually used on burners above 1400kW.
Ignition solenoid valve group: generally includes manual ball valves, regulators, and solenoid valves, mainly used for high-power burners.
2、 Air supply system.
The function of the air supply system is to input a certain amount of air with a certain wind speed and volume into the combustion chamber. The main components include: the shell, fan motor, fan impeller, gun barrel, air door controller, air door baffle, diffusion plate, etc.
Shell: It is the installation bracket for various components of the burner and the main component of the fresh air intake duct. According to their appearance, they can be divided into two types: box type and gun type. Box type burners are mostly equipped with injection molded material covers, and their power is generally small. High power burners are mostly split type, usually gun type. The composition material of the shell is generally high-strength lightweight alloy casting.
Fan motor: mainly provides power for the operation of the fan impeller and high-pressure oil pump, and some burners also use independent motors to provide power. Some small burners use single-phase motors, and the burner can only rotate in a specific direction to function properly.
Fan impeller: capable of generating sufficiently high wind pressure, overcoming furnace and chimney resistance, and blowing enough air into the combustion chamber to meet the needs of combustion. This equipment is a cylindrical wheel equipped with blades with a certain inclination angle. Its composition material is generally high-strength light alloy steel, and there are also injection molded products. Qualified fan impellers have good balance performance.
Wind gun barrel: It plays a role in guiding and stabilizing wind pressure, and is also a component of the air inlet channel. Generally, there is a shell flange connected to the furnace mouth. The constituent material is usually high-strength and heat-resistant alloy steel.
Air damper controller: It is a device that controls the rotation of the air damper baffle through a mechanical linkage. There are generally two types of control: hydraulic drive controller and servo motor control. The former operates smoothly and is not prone to malfunctions, while the latter has precise control and stable air volume.
Air damper: The main function is to adjust the intake air volume of the air duct to control the intake air volume. Its composition materials include injection molding and alloy, and injection molding baffles are generally composed of various combinations such as single piece, double piece, and three piece.
Diffuser disk (air regulator): A special structure can generate rotating airflow, help air and fuel mix thoroughly, and also regulate secondary air.
3、 Ignition system.
The function of the ignition system is to ignite a mixture of air and fuel, and its main components are: ignition transformer, ignition electrode, and high-voltage electric fire cable.
Igniter transformer: It is a conversion element that produces high voltage output, usually 2X5KV, 2X6, 2X7, and the output current is generally between 15-30MA.
Igniting electrode: converts high-voltage electrical energy into light and heat in the form of arc-shaped discharge to ignite fuel, generally available in single and split types.
Electric high voltage cable: Its function is to transport electrical energy.
Fourth, monitoring system.
The role of the monitoring system is to ensure the safe operation of the burner, and its main components include flame monitors, pressure monitors, temperature monitors, etc.
Flame monitor: Its main function is to monitor the formation of flames and generate signal alarms. There are three main types of flame detectors: photoresistors, UV eyes, and ionization electrodes.
(1) Photosensitive resistor: a type of resistor commonly used in light oil and heavy oil burners. Its function and working principle are as follows: a triple contact is connected to a flame relay, and the resistance of the photoelectric resistor changes with the amount of light received by the device. The more light received, the smaller the resistance. When the voltage at both ends is applied to a certain value, the greater the current in the circuit. When the current reaches a certain value, the flame relay will start, allowing the burner to continue working downwards. If the photoresistor does not feel enough light, the flame relay will not work and the burner will stop working. Due to the insufficient brightness of the flame during gas combustion, photoresistors are not suitable for use in gas burners.
(2) Ionizing electrode: commonly used in gas burners. 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 sparks. Ignite the mixture of gas and air, and the programmable 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, and the ion current will flow between the electrode, flame, and combustion head. The ion current is rectified into direct current and reaches the flame relay through the grounded burner shell to ensure the smooth operation of the subsequent combustion of the burner. If the ionization electrode is grounded, the generated current is AC instead of DC, the flame relay does not work, and the program controller is locked. In addition, in the same grounding circuit, both ionization current and ignition current pass through. As the ignition current is much greater than the ionization current, when the two directions are opposite, the ionization current will be blocked by the ignition current. But after the flame was generated, the burner broke circuit, and this defect can be compensated by reverse input of the ignition transformer, because reverse wiring causes ignition, and its AC direction rotates 180 °, resulting in a 180 ° rotation of the ignition current. 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 flames when the burner is disconnected, which may be due to an inappropriate air to gas ratio and can be solved by adjusting the air or gas volume. It may also be due to uneven distribution of air and gas inside the combustion head, which can be solved by adjusting the position of the combustion head to achieve uniformity.
(3) UV Eye: Usually used on dual-purpose burners for petroleum and natural gas, this type of eye can only perceive ultraviolet light in the flame (spectral range 190-270 nanometers). The UV tube does not react to the flickering sunlight, ordinary lights, or furnace light substances in the furnace. The UV tube has a lifespan of about 10000 hours in an ambient temperature not exceeding 50 ℃. Excessive ambient temperature has a significant impact on the lifespan of batteries. If a sufficient amount of ultraviolet light is received, an electric current will be generated, and the machine or flame relay will shut it off. If the UV lamp is fully charged, even without ultraviolet light, it will still display the presence of ultraviolet light. To overcome this disadvantage, before each opening, the program control will apply appropriate voltage to its two ends. Therefore, even if the battery is depleted, its signal only indicates that there is no flame, so the program controller immediately stops working.
Pressure monitor: usually used for gas burners, mainly for monitoring high and low pressure of gas, as well as wind pressure monitoring. If a burner is used for a steam boiler, steam pressure monitoring can also be performed.
Temperature measurement device: mainly includes smoke temperature monitoring, oil (heavy oil) temperature monitoring, system water and medium water temperature monitoring and control, etc.
5、 Electronic control system.
The electronic control system is the command center and communication center of the above systems, with the main control component being the programmable controller. Different programmable controllers are equipped according to different burners, and their main difference lies in the time of each program step.