Selection principle of fuel gas boiler burner
The selection of burners for oil-fired and gas-fired boilers should be based on the structural characteristics and performance requirements of the boiler body and fuel characteristics, combined with the user's operating conditions. As the combustion equipment of fuel oil and gas boilers, the main function of the burner is:
1) Provide the fuel oil or gas required by the boiler, and choose the oil atomization method for the oil fuel to increase the distance between fuel and air
Contact area. For gaseous fuel, the combustion method should also be selected.
2) Supply the air necessary for combustion to achieve full mixing of air and oil mist or gas to ensure complete combustion
3) Ensure rapid ignition and stable combustion.
4) Realize automatic control of program ignition and combustion process.
At present, the oil and gas burners used in small and medium-sized boilers mostly adopt an integrated structure, so people are used to calling them burners. As a fuel burner, it is mainly composed of a casing, a motor, a fan, a damper, a damper adjuster, an oil pump, a solenoid valve, an ignition device, a flame monitor, and a fuel injector. As a gas burner, it is mainly composed of a casing, a motor, a gas nozzle, a fan, a damper, a solenoid valve, an ignition device, and a flame detector. The motor is connected with the fan and the oil pump through a coupling, and when the motor rotates, it drives the fan and the oil pump to rotate together. The function of the fan is to send the air required for combustion into the furnace and generate a certain pressure. Adjusting the air door regulator can control the opening of the air inlet door to adjust the air intake. The role of the oil pump is to pressurize the fuel oil and provide energy for atomization. Control the solenoid valve switch to control the supply of fuel or gas. The number of oil nozzles or gas nozzles of small burners can be one or several, and they are controlled by different solenoid valves to achieve the purpose of staged combustion. The flame detector plays the role of safe ignition and flameout protection. In addition, each burner has a controller, and the ignition operation program of the burner is controlled through it. Although the working principle of the burner is roughly the same, and the structure is similar, but the performance of the burner produced by different structures or different manufacturers is very different, so the following aspects should be paid attention to when selecting the burner:1. Burner output Match with boiler capacity and boiler smoke wind resistance
Due to the compact structure and easy installation of the integrated burner, it does not need to be equipped with fans, oil pumps and other equipment, and has been widely used in small and medium-sized oil and gas boilers. Most boilers use positive pressure combustion and operation, that is, the intake air of the boiler is sent into the furnace by the fan of the burner, and the flue gas generated by the combustion is also blown out of the furnace and discharged into the atmosphere by the pressure head generated by the fan. At this time, if the back pressure of the selected burner is lower than the smoke wind resistance of the boiler system, the burner cannot blow the smoke out of the furnace, nor can it send air into the furnace, so that normal combustion cannot be guaranteed. However, there is a certain relationship between the back pressure of the burner and the thermal power (or fuel consumption) of the burner. When selecting the burner, it is necessary to consider not only the matching of the thermal power of the burner and the output of the boiler, but also the back pressure of the burner. Matching with the resistance of the flue gas system, both are indispensable. When selecting a burner, it should first be based on the type of fuel, such as kerosene, diesel, heavy oil, residual oil and waste oil for liquid fuels; city gas, natural gas, liquefied petroleum gas and biogas for gaseous fuels. The following characteristics of the fuel should be known:
1) Kerosene and diesel should have calorific value and density.
2) Heavy oil, residual oil and waste oil should have viscosity, calorific value, moisture, flash point, mechanical impurities, ash, freezing point and density.
3) Gas should have calorific value, gas supply pressure and density
In the case of mastering the characteristics of the fuel, first select a burner that can adapt to the fuel. Such as light oil burning heavy oil burner, residual oil burner or natural gas, petroleum liquefied gas burner, etc. Then roughly estimate the fuel consumption according to the calorific value of the fuel, so as to select the specific model of the burner
Fuel consumption B (kg/h or mh) can be estimated by the following formula
B=X3600Qnetvarn
In the formula, Q--the rated output of the boiler (kw). If it is a steam boiler, the calculation of Q is determined by the evaporation amount and the melting of steam; the low calorific value of fuel (kJ/kg) or (kJ/m') usually the net.v.ar calorific value of light diesel oil is about 42900kJ/kg; The calorific value of natural gas is generally 36000kJ/m; the calorific value of liquefied petroleum gas is about 92900kJ/m;
n one by one boiler efficiency. The thermal efficiency of oil-fired gas-fired boilers is generally around 90%. If there is no calorific value of fuel, the burner is selected, which can be determined by converting the output of the boiler into thermal power. However, each type of burner has a range of fuel or gas consumption. If the fuel consumption or gas consumption of the selected burner cannot meet the fuel consumption required by the boiler, the output of the boiler cannot be guaranteed at this time. .
The burners produced by each manufacturer should be accompanied by the burner operating characteristic curve shown in Figure 1 for users to use when selecting burners. As shown in Figure 1, the working point of the selected burner is A, then the corresponding fuel consumption GA; can meet the boiler fuel consumption requirements, and the combustion chamber back pressure HA: is enough to overcome the boiler smoke wind resistance, then the combustion The device can meet the working needs of the boiler. Otherwise, you have to choose again. In addition, the performance of the burner can also be seen through the operating characteristic curve. Generally speaking, the straighter the curve, the better the performance and the wider the scope of adaptation (the combustion chamber back pressure H will not drop significantly due to the increase of fuel consumption G).