Dew point corrosion temperature
Thread Content
For dew point corrosion in the air preheater of a heating furnace, what range should the flue gas temperature be kept within to minimize dew point corrosion? At what temperatures is dew point corrosion relatively severe? Thank you
http://bbs.hcbbs.com/thread-708011-1-1.html
Dew point corrosion, also known as low-temperature dew point corrosion, occurs when fuel gases contain sulfur; upon combustion, sulfur dioxide is formed and further converted into sulfur trioxide. At high temperatures, this substance does not corrode metals. However, when the temperature drops below 400 degrees, it reacts with water vapor to form sulfuric acid vapor. As the temperature drops further, this vapor along with water vapor begins to condense on the surface of the furnace tubes, resulting in severe acid corrosion. It is easy to see that the higher the flue gas temperature, the less severe the dew point corrosion is. However, in actual production, the thermal efficiency of the heating furnace also needs to be taken into account; generally, the flue gas temperature is kept between 170 and 185 degrees. Corrosion should be most severe when the temperature is below 100 degrees.
The dew point corrosion temperature is related to the sulfur content of the fuel; the higher the sulfur content, the lower the dew point corrosion temperature. There are corresponding graphs in the equipment engineer’s manual; if you’re interested, you can take a look – it’s a good book.
Dew point corrosion is related to sulfur content; it is generally necessary to keep it above 150 degrees.
At atmospheric pressure: minimum temperature 135°
Reply to 5# jensen_xu: Dew point corrosion is mainly influenced by temperature; if the temperature is high enough and there is no liquid water, even high sulfur levels do not cause severe corrosion. It is mainly electrochemical corrosion; sulfur dioxide and sulfur trioxide, when in contact with water, turn into sulfate and sulfite ions, which corrode the metal.
The flue gas temperature of the heating furnace is controlled at around 130°C; if it falls below 95°C, dew point corrosion is likely to occur.
However, if steam soot blowers are used, dew point corrosion is a different matter; the high moisture content in steam increases the corrosion in the waste heat recovery system
Within the operating range of the heating furnace, lower temperatures increase the likelihood of dew point corrosion. We generally keep it between 140-160 degrees; the lower temperature is used to ensure the furnace’s thermal efficiency. According to the book, the sulfuric acid vapor that is formed condenses into a liquid state at lower temperatures, thereby corroding the equipment; water is not necessary for this process. The sulfurous acid that is formed does not condense at this temperature, so no corrosion occurs.
We generally keep the flue gas temperature of the catalytic waste heat boiler between 170 and 210, with 180 being the appropriate value.