What is tempering in a heating furnace?
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After checking information online, it is said that backfire in a heating furnace occurs when, during combustion, various factors such as oil in the fuel gas cause positive pressure to be generated inside the furnace chamber; this leads to the flame being ejected from the chamber, explosions occurring, or the refractory lining inside the furnace falling off. This phenomenon is known as backfire in a heating furnace. Another explanation for tempering in the heating furnace is that the mixture of gaseous fuel and premixed air flows out of the burner orifices at a speed slower than the speed of flame propagation, causing the flame to return inside the burner to continue burning. So, which of the two statements is correct? Or rather, the two statements are one statement, just expressed in different ways.
Phenomenon: A positive pressure is generated inside the furnace, causing the explosion-proof door to be pushed open; flames are ejected from the furnace, which can injure people due to backfire, or an explosion occurs inside the furnace, resulting in damage to the equipment. Reason: (1) A large amount of fuel oil is injected into the furnace, or a large amount of oil is carried in the gas ； (2) The opening degree of the flue baffle is too small, which reduces the furnace’s suction force and prevents the smoke from being expelled ； (3) The furnace is operating under overload, preventing the flue gas from being discharged in time ； (4) Backfire occurs during ignition at startup, mainly due to a faulty gas valve that allows gas to enter the furnace, or because if ignition fails the first time and the furnace is not thoroughly purged before attempting ignition again, this can lead to an explosion and backfire in the furnace. Prevention: (1) It is strictly prohibited to introduce large amounts of fuel into the furnace before ignition; oil must not be present in the gas ； (2) Determine the actual position of the flue dampers, and be careful not to close them completely or too tightly when adjusting them ； (3) It must not be operated under overload conditions; a negative pressure should always be maintained inside the furnace ； (4) Strengthen equipment management: gas valves that are not functioning properly should be replaced or repaired promptly, and flashback arrestors should also be checked regularly; any malfunctioning units should be replaced immediately ； (5) Before starting up and igniting, it is necessary to check whether the valves for gas and fuel oil are airtight; before each ignition, the combustible gases in the furnace must be purged with steam.
This post was last edited by sdwfsgyykai on 2018-11-17 at 14:09. In the first case, I have seen flash explosions occur when a furnace is reignited without proper purging after it had stopped burning; I have also encountered flash explosions caused by a large amount of combustible gas entering suddenly. If this is considered backflow, then it belongs to backflow within the furnace chamber. ——This is quite common; it’s nothing unusual. The second type of tempering involves fire entering the burner and fuel pipeline to burn, and I have personally experienced this once as well. ——This is relatively rare (and therefore quite shocking, as the fuel pipeline gets burned through in no time); after experiencing it once, my understanding of the minimum load requirement for the burner improved significantly.