Reasons for tempering in heating furnaces
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This post was last edited by liaifeng on 2018-8-11 at 11:20. What is the theoretical principle behind tempering in heating furnaces? What are the reasons for tempering, and how can it be prevented? Difference from de-oxidation, thank you
It’s likely that the positive pressure in the furnace is what causes tempering, and it’s even worse than undertempering
When the speed at which the mixture of air and gas flows out of the gas nozzle is lower than the flame propagation speed, the flame re-enters the burner to burn, a phenomenon known as backfire. It can cause knocking or stalling, and over time it may also damage the mixing chamber or lead to other accidents. A positive pressure in the furnace can easily lead to tempering. To prevent this, the outflow speed of the air-gas mixture must be greater than the flame propagation speed. When there is an adequate gas supply, adjusting the burner’s air damper or the butterfly valve on the air duct can prevent backfire.
It’s too narrow upstairs; we had a flashback incident once, and an operator suffered a burn on the face: L
Flame failure occurs when the gas pressure is too high, the gas composition is too lean, or the negative pressure in the furnace is too great, causing the fuel gas to burn away from the main burner. This can lead to unstable furnace temperatures and fluctuations in the temperature at the furnace outlet; when a large number of burners experience flame failure, it can result in the burners going out and explosions within the heating furnace.
Oil in natural gas can also cause backfire, right?
If the gas contains condensed oil, it can also cause backfire. In my opinion, it happens because the combustion volume of the condensed oil increases significantly, resulting in positive pressure in the furnace.
Backfire occurs when the concentration of combustible substances in the furnace reaches an explosive level; it can also be caused by a sudden increase in fuel supply, gas mixed with liquid, tripping of the blower and exhaust systems, or failure to restart the furnace after such tripping. Steadily adjusting the fuel amount, regularly checking the gas tank, and performing steam purging after the furnace is shut down can generally help avoid these issues. Flameout is an abnormal combustion condition in which excessive air flow or steam blows the base of the flame away from the burner.
It seems that what was said upstairs isn’t backfire; it’s deflagration. . . .
Backfire occurs when the flow rate of the air and gas mixture is very high, causing the fuel to ignite a distance away from the nozzle. During flameout, the flame burns unstably, resulting in its extinguishment. The supply of fuel and air should be reduced.
To put it more clearly, tempering means that the gas reaches its explosive concentration range at the nozzle; in effect, it is a small explosion. The explosive limit of gas is around 2.77%-14.2%. The reasons are as follows: 1. The pressure in the fuel gas system dropped suddenly. 2. When shutting down the fuel gas system, the air valve was not closed first. 3. In an emergency situation, the furnace was shut down by the operator in the control room