Influence of gas pressure fluctuation on burner
With the increase or decrease of gas pressure, the jet flow of gas through the nozzle will also increase or decrease accordingly. Since the burner cannot detect this change, the combustion air of the blower remains unchanged, and the air-fuel ratio will inevitably fluctuate.
1、 Influence of gas pressure fluctuation on various aspects of burner
1. Influence of gas pressure fluctuation on burner thermal load.
The main function of the burner is to convert the chemical energy in the gas into heat energy. The heat load is a visual expression of the heat release rate and also the most important parameter of the burner. Its size directly affects the working efficiency of the burner. The burner thermal load under pressure drop is too small, and the heating process takes a long time, which affects the combustion effect; The excessive heat load of the burner under high pressure will cause excessive carbon monoxide in the flue gas, high flue gas temperature, low thermal efficiency, easy to burn out the burner and reduce the service life.
2. Influence of gas pressure fluctuation on combustion characteristics of burner.
The thermal load of the burner also determines the size of the burner structure. When the gas pressure exceeds the standard and the injection flow of the gas through the nozzle exceeds the standard, the primary air (premixed air) and secondary air (supplementary air around) required for combustion will be insufficient, the combustion will be incomplete, yellow flame and black smoke will appear, and the carbon monoxide content in the flue gas will increase significantly. Black smoke is an important factor leading to the increase of PM2.5. When the combustion condition continues to deteriorate, the environmental pollution increases sharply. When the gas supply pressure continues to increase or the damper is adjusted incorrectly, the flow rate of the gas volume in the combustion hole will be greater than the combustion speed, so that the flame leaves the edge of the fire hole is called flameout, and then develops into flameout.
3. Influence of gas pressure fluctuation on burner thermal efficiency.
It can be seen from the change of exhaust gas temperature that the higher the exhaust gas temperature is, the lower the heat utilization rate is, and the lower the thermal efficiency of the burner is.
2、 The consequence of air fuel ratio imbalance caused by gas pressure fluctuation.
1. Under-oxygen combustion: that is, the amount of fuel gas is greater than the amount of air required, the combustion is incomplete, the carbon monoxide content in the flue gas is greatly increased, and the loss of chemical incomplete combustion is also correspondingly increased. The ordinary mechanical blast burner has no self-detection ability for under-oxygen combustion.
2. Deactivation: if the gas supply pressure continues to increase, the gas flow speed in the burner exceeds the combustion speed, so that the flame leaves the edge of the fire hole, which is called misfire, and then develops into misfire. This will lead to flameout or unstable combustion, and even potential safety hazards. Ordinary mechanical air-blowing burners have their own high-pressure control function, which will automatically shut down for protection when the air pressure exceeds the limit.
3. Excessive air combustion: that is, the amount of fuel gas is less than the required amount of air, resulting in excessive amount of air, so that the excess cold air enters the furnace for heating. Therefore, the heat loss increases, and the general mechanical blast burner does not have the ability of self detection for under-oxygen combustion.
4. Flashback: If the air pressure continues to decrease or the damper adjustment cannot keep up, the gas flow velocity in the burner gas nozzle is lower than the combustion velocity, resulting in flame flashback and affecting the safe operation of the burner. General mechanical blast burner has low pressure control function. When the air pressure exceeds the limit value, it will automatically shut down for protection.
When the gas pressure fluctuation exceeds the pressure range required for normal operation of the burner, the flame shape will change. Excessive gas pressure will elongate the flame, increase the flame length, and make the combustible gas that is not completely burned contact the furnace wall. Because the thickness of furnace wall is low, it is generally lower than the ignition point of combustible gas. This part of incompletely burned gas will not burn because of low temperature, resulting in energy waste.