What are the Backfire of Burner and its Prevention Measures
What are the Backfire of the Burner and its Prevention Measures
For the burner, if the burning rate of the mixed gas is greater than the ejection rate, the flashback phenomenon will occur.
The burner that is difficult to de-ignite but easy to backfire on will not have a wide combustion range. For example, if the flame hole is relatively large, it is generally difficult to de-ignite, but it is easy to backfire, so it is difficult to handle. In order to prevent tempering, the following measures are usually taken.
① Make the flame hole small and deep (increase the number of flame holes when the flame hole load is constant), and reduce the combustion rate of the gas near the hole wall due to the cooling effect of the flame hole wall. Multi nozzle burners, Shepard-type burners, and Pylon-type burners all belong this way.
② If the heat received by the burner tip is transferred to the inside of the burner, the unburned mixed gas will be preheated by this heat. Therefore, ceramic materials with poor thermal conductivity are used to manufacture the burner tip, such as overheated burners and ceramic belt-type burners. In the slit-type radiant burner, the whole burner head outside the flame hole is covered with a layer of ceramic fiber [fiber cotton, fiberboard, thermal conductivity 0.13W/(m. C)], which can improve the thermal insulation effect.
③ Cool the burner tip at the distance from the furnace body. It is not only necessary to make the flame hole small and deep, but also to carry out water cooling or air cooling around the nozzle so that the cooling effect is greater. The burner tip is usually 10~25mm away from the furnace body. In principle, this method is also used when the premixed burner is used on the furnace.
④ For the nozzle with sleeve fire, because the sleeve fire backfires first, reduce the flame hole of the sleeve fire (the slit is less than 1mm) for cooling, so as to reduce the sleeve fire speed slightly, which is also beneficial to prevent the sleeve fire from falling off. For example, on Sheppard-type burners, the effect of preventing backfire can be improved by cooling the ignition burner with water.
⑤ When the primary air volume is reduced from 90% of the theoretical air volume to 70%, 50%, and 40%, the combustion rate will be reduced from 70cm/s to 50cm/s, 20cm/s, and 10cm/s. Therefore, the method of reducing the primary air volume and increasing the secondary air volume can be used to prevent backfire. There are many examples in this regard. When a premixed burner is used on the furnace, the primary air ratio shall be about 40% in principle.
⑥ If the injection speed is kept at a high level, there will be no flashback, but in this case, the adjustment range of combustion amount becomes narrow. The internal pressure of the cup-type radiant burner is usually above 25 mmH2O.
⑦ The most fundamental measure to prevent flashback is to use a nozzle mixing type burner (i.e. burning while mixing in the burner part, gas, and air).