Anti-corrosion plan for flue gas desulfurization and dust removal system in chimneys

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　The corrosion in flue gas desulfurization systems is primarily caused by acidic media formed from the condensation of high-temperature flue gases； Substances such as sulfuric acid, sulfurous acid, hydrochloric acid, and hydrates of nitrogen oxides have strong corrosivity. In addition, there are corrosion caused by chlorides and fluorides in the fuel, high-temperature corrosion, as well as erosion wear caused by solid particles and deposits. Furthermore, chimneys or flue pipes that discharge various treated and compliant waste gases at high altitudes also suffer from corrosion issues, and the mechanism of this corrosion is essentially the same as that in desulfurization and denitrification systems. Under the combined effect of these factors, the main forms of corrosion are as follows: 1. Chemical corrosion. Chemical corrosion is a type of uniform corrosion; corrosive substances in flue gas such as H2S, SOx, NOx, Cl-, F-, H+ 등 react chemically with metal materials at certain temperatures and humidity levels to form soluble salts, thereby gradually damaging the equipment. 　　2. Local corrosion: In desulfurization and dust removal systems, components are typically connected by welding, riveting, screws, etc., and gaps may occur in the connection areas. In chemical media, these gaps can easily lead to closed-cell corrosion; metal dissolution, that is, corrosion, occurs due to the lack of oxygen, high H+ levels, and high Cl- concentrations within these gaps. 　　3. Crystal corrosion: When an alkaline liquid absorbs SO2, soluble sulfates or sulfites are formed, and these substances penetrate into the capillaries of the anti-corrosion coating ； When the device is turned off, due to natural drying, this solution forms crystalline salts, accompanied by an increase in volume ； This causes internal stresses to develop within the anti-corrosion material, leading to peeling, pulverization, loosening, or cracking. Corrosion is more severe in environments with alternating dry and wet conditions. 　　4. Wear and corrosion: Flue gas contains a large amount of solid particles, such as dust that has not been removed or is not fully removed, as well as desulfurization by-products. There are numerous solid suspended particles in the fluid, and these particles rub against the surface of the equipment, continuously altering that surface and accelerating the wear process, which can lead to severe corrosion in extreme cases. 　　Requirements for anti-corrosion coatings in chimney and flue desulfurization and dust removal systems: 1. High adhesion, resistance to peeling, and long service life against corrosion. The anti-corrosion work for the entire desulfurization system is time-consuming and labor-intensive, and maintenance is difficult; therefore, it is required that the anti-corrosion materials have a long service life and a long maintenance-free period. 　　2. High requirements are placed on resistance to high temperatures, corrosion in humid and hot environments, and corrosion by acidic media; it is capable of withstanding the corrosion and erosion caused by high-temperature flue gases in acidic environments over the long term, as well as the dew-point corrosion caused by acidic gases. 　　3. It has good thermal shock resistance, enabling it to withstand the thermal fatigue caused by sudden fluctuations in flue gas temperature. Or failures in desulfurization equipment, which can lead to a sudden increase in temperature as a result of direct emission of flue gas; therefore, good resistance to temperature changes is required. 　　4. It has excellent waterproof and impermeable properties, capable of preventing further penetration of corrosive agents and protecting the substrate from erosion. 　　5. The coating has good mechanical properties, excellent wear resistance, and high strength; it can withstand erosion and wear caused by solid particles in fluids. 　　Performance advantages of Longyuan Naxin coating systems: A detailed analysis of corrosive environments leads to a more targeted formulation for these coating systems. The resins used in the film-forming layers, along with the functional fillers, work together to endow the coatings with excellent overall properties, including high density, water and oil repellency as well as self-cleaning capabilities, resistance to erosion and wear, tolerance to sulfuric acid exposure, resistance to strong oxidizing agents, and durability in high-temperature and humid conditions. 　　Recommended solutions for protection against corrosion caused by high-temperature flue gases. Solution structure: Paint name, thickness × number of coats, application rate in kg/㎡; Substrate preparation. Solution 1: Primer – High-temperature flue gas corrosion-resistant paint, 100μm × 20.3 coats; old coating removed, sandblasting to Sa2.5 standard. Topcoat – Polytetrafluoroethylene acid-resistant heavy-duty corrosion-resistant paint, 70μm × 20.2 coats. Application areas: Humid and hot environments with temperatures below 150℃, such as carbon steel chimneys, flues, pipes, scrubbers, acid and alkali tanks, etc. Solution 2: Primer – High-temperature flue gas corrosion-resistant paint, 100μm × 20.3 coats; old coating removed, sandblasting to Sa2.5 standard. Topcoat – Titanium nanocomposite heavy-duty corrosion-resistant paint, 70μm × 20.25 coats. Application areas: Humid and hot environments with temperatures below 250℃, such as desulfurization and denitrification systems, dust removal system equipment, etc. Option 3: Pretreatment – Polymer mortar repair is determined based on the specific conditions. Primer: Epoxy penetrating sealant, 30μm × 10.15; the old coating is removed via sandblasting or water jetting, followed by application of this primer. Intermediate coat: High-temperature flue gas corrosion-resistant coating, 100μm × 20.3. Topcoat: Polytetrafluoroethylene acid-resistant heavy-duty corrosion-resistant coating, 70μm × 20.2. Application areas: Corrosion protection for concrete chimneys and flues, as well as acid and alkali tanks, basins, and channels.