What is the appropriate flue gas exhaust temperature for a heating furnace?

With the current advances in technology, the temperature can be reduced to 120 degrees by using corrosion-resistant coatings on furnace tubes such as those in the convection section; it ultimately depends on the material composition of the furnace tubes in your plant. Generally, the corrosion threshold is considered to be 155 degrees!

The flue gas temperature mainly depends on the dew point temperature of the flue gas; too high a temperature results in significant heat losses and low thermal efficiency of the furnace； If it is too low, dew point corrosion is likely to occur; therefore, reducing the flue gas temperature should be done in such a way as to minimize the risk of low-temperature corrosion, and it cannot be reduced indefinitely. Personally, I think it’s better to keep it at 160 degrees.

It is related to the furnace structure: if exhaust occurs at the top, the lower the temperature, the better; if exhaust occurs at the bottom, the temperature must be higher than the dew point temperature.

It depends on the dew point temperature of the flue gas. During design, the wall temperature should be at least 20°C higher than the flue gas dew point temperature to prevent dew point corrosion. However, the wall temperature is generally not measured; therefore, during design, the exhaust temperature should be at least 42 degrees higher than the dew point temperature of the flue gas (an empirical value).

In my opinion, regenerative combustion technology (high-temperature air combustion technology) can effectively solve this problem: it enables high temperatures inside the furnace, yet does not require heat exchangers, resulting in lower exhaust gas temperatures. The heat exchange component of a regenerative burner is made of ceramic, so there is no need to worry about dew point corrosion. Its combustion mechanism is completely different from that of conventional combustion. Their burners always appear in pairs, one in operation and the other recovering sensible heat. A regenerative combustion furnace without a dedicated flue. Its smoke exhaust and air supply channels are opposite to each other. As the furnace temperature increases and the heat intensity rises, the following changes should be made: 1. In newly built heating furnaces, the convection section can be omitted to save on construction costs ； 2. The renovation of old furnaces should increase the material flow rate and reduce heating time ； 3. If the heating capacity remains unchanged, appropriately reduce the burner’s heating capacity. Currently, regenerative combustion technology is widely used in the steel industry. The energy-saving effect can reach over 70%. The technology development unit (can’t say it!) Avoid the appearance of advertising! ) It is currently not only the leader in China’s burner market but also the company with the highest market share in global regenerative combustion technology. The furnaces and kilns modified by them achieve an average energy-saving rate of over 30%! In the petrochemical industry, a few companies have already adopted this technology. But the company’s greatest aspiration with this technology is to completely transform the ethylene cracking furnace! If achieved, the heating cost of ethylene is expected to decrease by 30–50%. **Great importance is attached to this technology, which has been promoted in the energy-saving plans for certain industries under the 11th Five-Year Plan ； And it terminated the approval for that company’s plan to list abroad. Provide additional strong support in terms of funding and policies!