How to address the corrosion of non-metallic materials caused by low-temperature, humid flue gas?
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We know that the low-temperature, humid flue gas from boilers causes severe corrosion to both metallic and non-metallic materials, and addressing this issue is quite complex. As shown in the flue for wet flue gas in the image below, the protective layer failed after being in use for over a year. The desulfurization tower of this system uses the ammonia-based desulfurization method; the flue gas after desulfurization passes through the flue and is then discharged into the atmosphere via a chimney. The flue gas after ammonia-based desulfurization has a high humidity, averaging around 15%. Such wet flue gas has a significant destructive effect on common special anti-corrosion coatings; coatings such as vinyl resin glass flake coatings and epoxy furan coatings lose their effectiveness after just one year of use. The crystalline form of corrosion products ((NH3)2SO4) in the flue has penetrated the outer wall, affecting its strength. The long-term operating temperature is around 90°C.
It is their responsibility as the design institute to address such issues.
The corrosion at the outlet of wet flue gas desulfurization is mainly caused by SO3 and Cl in the flue gas. Wet methods have a low efficiency in removing SO3, which also leads to an accumulation of Cl. Our company is planning to implement a dry + ammonia-based desulfurization method in a large thermal power plant; if successful, this approach can alleviate or resolve the corrosion problems associated with ammonia-based desulfurization
I would like to ask what the principle behind the crumbling of acid-resistant brick is.
Acid-resistant bricks crack and disintegrate. We know that such bricks have a high porosity and large individual pores; as a result, prolonged exposure to acidic environments leads to a decrease in their structural strength, eventual failure, and ultimately cracking and disintegration.
This issue is quite complex; first of all, accurate data on the flue gas conditions are needed, and it is also important to know whether diabase slabs have been used, as well as whether epoxy furan mortar was employed for construction. Or additional equipment can be used to cool it down to below 40–50°C, or even lower.
Wet desulfurization and denitration reduce SOx and NOx emissions, meeting the requirements for environmentally compliant discharges. However, emitting the treated flue gas at temperatures close to the dew point also introduces many new problems. A few years ago, when analyzing the causes of fog, experts suggested that the emission of flue gas with a high relative humidity resulting from wet desulfurization and denitration processes is also one of the important causes of fog.
At this temperature and under these operating conditions, phenolic resin mixed with graphite powder can be used; it offers high strength and improved corrosion resistance