What is furnace tempering?

Tempering occurs when the pressure in the inlet pipes of the combustion furnace or incinerator is lower than the pressure inside the furnace where combustion is taking place, causing the flame to flow back into the pipes. It is usually caused by a sudden cut-off of gas or improper operation; a flame arrester can be added.

The pressure inside the furnace is lower than that outside, causing the flame to flow from outside the furnace into it.

The pressure inside the combustion furnace is higher than that in the inlet pipe, which pushes the flame inside the furnace into the inlet pipe and causes backflow. Such devices generally require the installation of flame arresters to prevent accidents.

“\"Furnace\" tempering is common in gas or gas-producing furnaces. Harmful accidents that could cause explosions must be strictly prohibited. My understanding is that backfire in a gas generation furnace occurs due to negative pressure inside the furnace; if the furnace isn’t properly sealed, air from outside can enter the furnace, leading to backfire and potentially causing an explosion. Backfire in gas stoves is caused not only by negative pressure issues, but also by the fact that the gas pressure at the burner is not sufficient to overcome the resistance; as a result, air enters the burner, leading to backfire (this is the same principle behind backfire in gas welding). The flame arrester mentioned upstairs is used to \"extinguish the source of fire\" in order to prevent this problem from occurring. Gas equipment and pipelines require a positive pressure to be maintained. If there is still combustible gas inside a shut-down pipeline, backfire can occur during welding work during maintenance. It’s very dangerous. Ensuring sufficient positive pressure is key to preventing tempering accidents. GB6222-2006 provides detailed regulations.

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The pressure inside the combustion furnace is higher than that in the pipeline, which draws the flame from the furnace into the pipeline and causes backflow. Such devices generally require the installation of flame arresters to prevent accidents.

Tempering occurs when there is a positive pressure in the furnace, causing the flames to shoot out; this is generally an abnormal phenomenon. The solution lies in addressing the issues from a process perspective, and it is usually caused by the flue dampers being set too tightly or by an excessive load on the furnace!

I almost ended up with disfigured skin due to a backfire in the furnace; at that time, the instrument controlling the flue damper stopped working and it was closed completely. During the process of starting the furnace, I was at the explosion-proof door checking whether the third burner had ignited. The backfire caused the explosion-proof door to fly open, and hot sand sprayed onto my side face and neck, resulting in swollen skin. However, things returned to normal after treatment!

The phenomenon in which, when the fuel gas flow velocity is very low, the flame may propagate back into the combustion hole, causing combustion to occur inside the nozzle.

The fundamental reason for flashback is that the velocity of the gas stream ejected from the burner nozzle, which consists of a mixture of fuel gas and air, is lower than the speed at which the flame propagates; this causes the flame to flow back into the nozzle where it continues to burn. It can be seen from this that tempering only occurs in premixed or semi-premixed burners, and not in externally mixed burners. There are many possible reasons for tempering: 1. The furnace operates at a low load, the nozzle diameter is not properly designed, or the fuel gas holes are blocked, all of which result in the gas jet velocity being lower than the flame propagation speed. 2. Changes in the composition of the fuel gas result in different flame propagation speeds for various fuels; for example, hydrogen has the highest flame propagation speed, and premixed burners cannot be used in such cases. 3. Poor cooling at the burner nozzle causes the temperature of the premixed gas to rise, accelerating the flame propagation rate and leading to backfire. The way to avoid tempering is to do the opposite: find ways to increase the flow rate of the fuel-air mixture, and use nozzles with high thermal conductivity or heat-dissipating features in order to reduce the flame propagation speed.