The role of exhaust gas temperature

Controlling the exhaust temperature at an appropriate level can effectively prevent sulfur-containing flue gases from causing corrosion below the dew point. Moreover, changes in the exhaust temperature allow one to assess the combustion conditions within the furnace as well as whether there are leaks in the heating tubes. An appropriate exhaust temperature is also a reflection of the heating furnace’s thermal efficiency

The exhaust temperature of the heating furnace directly reflects its thermal efficiency. A high flue gas temperature means that more heat is carried away by the flue gas, resulting in greater heat losses; this indicates that the heating furnace is not operating efficiently (under normal conditions, for every 10°C increase in flue gas temperature, flue gas losses increase by 0.5–0.8%). Therefore, from the perspective of the economic efficiency of furnace operation, it is desirable for this exhaust gas temperature to be as low as possible. However, if it is too low, as mentioned on the second floor, especially when it is below the dew point temperature of sulfur dioxide or nitrogen oxides present in the flue gas, it will cause acidic corrosion in the flue gas recovers of the heating furnace, thereby shortening the service life of these heat recovery devices. Therefore, it is advisable to maintain general control at no less than 130°C.

Generally speaking, the operating temperature of a heating furnace should be as low as possible, as lower temperatures help to reduce fuel consumption. However, given that the flue gases contain sulfur dioxide, sulfur trioxide, and water vapor, if the temperature is too low, sulfur trioxide reacts with water to form sulfuric acid, which condenses into a liquid at lower temperatures; this can lead to corrosion, known as dew point corrosion. Therefore, the temperature must be kept above the level at which dew point corrosion occurs, but it shouldn’t be too high either, in order to prevent abnormal fuel consumption.