Regarding the issue of flue gas emission temperature?

When boilers burn fuel with high sulfur content, high moisture content, and high ash content, low-temperature sticky ash is likely to form. This is because S + O₂ = SO₂, and SO₂ is further oxidized to SO₃. SO₃ combines with water vapor in the flue gas to form sulfuric acid vapor. Due to the low exhaust temperature of the air preheater and the low temperature of the cold air inlet, the tube wall temperature remains low. When this temperature falls below the dew point of sulfuric acid vapor, the vapor condenses on the tube walls, binding the ash present in the flue gas and resulting in low-temperature sticky ash; dew point corrosion also occurs as a consequence. 　　The dew point of flue gas depends on the sulfuric acid vapor present in it. The dew point of water vapor in flue gas is around 30–60 degrees, and condensation generally does not occur under these conditions. However, SO3 in the flue gas combines with water vapor to form sulfuric acid vapor, which significantly raises the dew point of the flue gas to 90–150 degrees. 　Prevention methods include: 1. Raising the wall temperature of the air preheater, that is, increasing the air inlet temperature, by using warm air heaters and hot air recirculation, etc. 2. Reduce the excess air coefficient to minimize air leakage. 3. Adding limestone to enhance soot blowing **There seems to be no regulations regarding this.

If a sulfur-free fuel such as natural gas is burned, can the flue gas emission temperature be below 170 degrees Celsius?

There is no requirement that it must be greater than 170 degrees. If there is no sulfur in the fuel, it can be controlled at 100 degrees. The key lies in the sulfur and hydrogen content in the fuel; these two values determine the dew point temperature. It is sufficient for the exhaust temperature to be higher than the dew point temperature.

It mainly involves checking the sulfur content in the fuel, then calculating the dew point temperature; thereafter, the flue gas temperature should be kept 20 degrees above that dew point temperature. If the temperature is too high, heat cannot be recovered, resulting in low furnace efficiency and energy waste; if the temperature is too low, it will cause equipment corrosion and lead to accidents. Generally, natural gas has a low sulfur content, allowing the flue gas temperature to be controlled at around 120 degrees.

This post was last edited by dongjiang1001 on 2011-9-15 09:26. The fuel used in the north currently contains less sulfur, so the exhaust temperature can be kept lower; I have seen many power plant boilers with an exhaust temperature of around 110 degrees, including those in 300MW units.

I heard that if the flue gas temperature rises, the thermal efficiency of the boiler will decrease! Some power plants deliberately reduce the exhaust gas temperature to an appropriate level (taking corrosion/dew point into account) in order to improve thermal efficiency!

That’s right; the higher the flue gas temperature, the more heat is carried away by the flue gases, and as a result, the thermal efficiency decreases.

1. Temperature setting: Natural gas also contains sulfur. The 170-degree requirement is aimed at addressing the issue of flue gas corrosion; if dew point corrosion occurs, it can quickly destroy the chimney! 2. The lower the temperature of the chimney, the better the heat recovery efficiency of the flue gases! Our goal is to minimize the dust temperature while ensuring that emissions meet the required standards!

This post was last edited by dongjiang1001 on 2011-9-15 09:27. Learned it*. Thank you all for the discussion.

Reply to 3# 70367706: The rare earth alloy cast products we manufacture, as well as the double-sided finned plate-type air preheaters, are resistant to corrosion caused by sulfuric acid dew points. The flue gas temperature can be reduced to between 120 degrees and 140 degrees, with a thermal efficiency of over 92%; their service life is around 10 years.