[Q&A Question 303] 2017.11.17
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【Q&A Question 303】November 17, 2017: Why does flue gas suffer from low-temperature dew point corrosion? Answer: Ordinary fuel oils (gases) contain a small amount of sulfur. When sulfur burns, it produces SO2, which is further converted into SO3 in high-temperature flue gases. SO3 gas does not corrode tungsten; however, when the temperature drops below 400°C, it reacts with water vapor to form sulfuric acid vapor. As the temperature drops further, this sulfuric acid vapor and water vapor begin to condense on the surface of the low-temperature furnace tubes, causing severe acid corrosion, namely low-temperature dew point corrosion. (Unless otherwise specified, all questions and answers are based on hydrogenation units.) ) For management purposes, if you need to view content from a few days ago, please access it through the summary post below. 2017 Q&A Summary Thread (updates have begun) http://bbs.hcbbs.com/thread-1657793-1-1.html 2017 Daily Question Summary Thread (updates have begun) http://bbs.hcbbs.com/thread-1657794-1-1.html 2016 Q&A Summary Thread (updates completed) http://bbs.hcbbs.com/thread-1597792-1-1.html (Source: Haichuan Chemical Industry Forum)
S02 reacts with water to produce sulfuric acid, which causes corrosion
At low temperatures, nitrogen oxides and sulfides in the flue gas form acids, which corrode the flues
Flue gas dew point corrosion occurs because sulfur in the fuel is converted into SO2 and SO3 during combustion; when the outer surface temperature of the heat exchange surface is lower than the temperature of the flue gas, sulfuric acid mist droplets form on that surface, leading to corrosion of the heat exchange surface. When fuel burns, the hydrogen (H2) and oxygen (O2) in it combine to form water vapor (H2O), and since most burners use steam for atomization, the flue gases in the furnace contain a large amount of water vapor. Additionally, sulfur (S) in the fuel produces sulfur dioxide (SO2) upon combustion; a small amount of this SO2 is further oxidized to sulfur trioxide (SO3). Sulfur trioxide combines with water vapor in the flue gases to form sulfuric acid (H2SO4). The dew point of flue gas containing sulfuric acid vapor rises significantly; when the wall temperature of the heating surface is below this dew point, the sulfuric acid-containing vapor condenses on the heating surface to form a sulfuric acid-containing liquid, causing severe corrosion to the heating surface. Since it occurs on the heated surface at lower temperatures, it is called low-temperature corrosion.
Below the dew point, water condenses, acidic gases dissolve, leading to hydrogen-induced corrosion
When fuel burns, the hydrogen (H2) and oxygen (O2) in it combine to form water vapor (H2O), and since most burners use steam for atomization, the flue gases in the furnace contain a large amount of water vapor. Additionally, sulfur (S) in the fuel produces sulfur dioxide (SO2) upon combustion; a small amount of this SO2 is further oxidized to sulfur trioxide (SO3). Sulfur trioxide combines with water vapor in the flue gases to form sulfuric acid (H2SO4). The dew point of flue gas containing sulfuric acid vapor rises significantly; when the wall temperature of the heating surface is below this dew point, the sulfuric acid-containing vapor condenses on the heating surface to form a sulfuric acid-containing liquid, causing severe corrosion to the heating surface. Since it occurs on the heated surface at lower temperatures, it is called low-temperature corrosion. Since this type of corrosion occurs only after dew forms on the heated surface, it is also known as dew point corrosion.
Since sulfur in the fuel produces SO2 and SO3 during combustion, when the outer surface temperature of the heat exchange surface is lower than the dew point temperature of the flue gas, sulfuric acid mist droplets form on the heat exchange surface, leading to corrosion.
Sulfur dioxide, nitrogen oxides, carbon monoxide, and sulfur dioxide contained in flue gas combine with condensed water at temperatures below the dew point to form acidic substances that cause corrosion
When fuel burns, the hydrogen in it combines with oxygen to form water vapor, and since most burners use steam for atomization, the flue gases from the furnace contain a large amount of water vapor. Furthermore, sulfur in the fuel produces sulfur dioxide upon combustion; a small amount of this sulfur dioxide is further oxidized to sulfur trioxide. Sulfur trioxide combines with water vapor in the flue gases to form sulfuric acid. This results in a significant increase in the dew point of the flue gases containing sulfuric acid vapor. When the temperature of the heated surface is below this dew point, the vapor containing sulfuric acid will condense on the heated surface to form a liquid containing sulfuric acid, causing severe corrosion to the heated surface. Since it occurs on the heated surface at lower temperatures, it is called low-temperature corrosion. Since this type of corrosion occurs only after dew forms on the heated surface, it is also known as dew point corrosion.
Ordinary fuel oils (gases) contain a small amount of sulfur. When sulfur burns, it produces SO2, which is further converted into SO3 in high-temperature flue gases. SO3 gas does not corrode tungsten; however, when the temperature drops below 400°C, it reacts with water vapor to form sulfuric acid vapor. As the temperature falls further, this sulfuric acid vapor and water vapor begin to condense on the surface of the low-temperature furnace tubes, causing severe acid corrosion, namely low-temperature dew point corrosion.
Ordinary fuel oils (gases) contain a small amount of sulfur. When sulfur burns, it produces SO2, which is further converted into SO3 in high-temperature flue gases. SO3 gas does not corrode tungsten; however, when the temperature drops below 400°C, it reacts with water vapor to form sulfuric acid vapor. As the temperature falls further, this sulfuric acid vapor and water vapor begin to condense on the surface of the low-temperature furnace tubes, causing severe acid corrosion, namely low-temperature dew point corrosion.