Sulfuric acid dew point corrosion control

Thread Content

1. Controlling Fuel Sulfur Content Sulfur compounds in fuel are the root cause of corrosion. The relationship between sulfur content and SO3 concentration in heavy oil is shown in Figure 8. The results show that when the sulfur content of the fuel is less than 1%, the dew point temperature decreases significantly as the sulfur content decreases. In terms of dew point,. It is generally believed that corrosion can be effectively controlled only when the sulfur content of fuel is less than 0.5% (weight ratio). 2． Additives used: Fuel additives include Mg(OH)2, ZnO, MgO, etc. After they are burned, they are dispersed in the ash, and harmful impurities such as V2O5 and Fe2O3 interact with them and are consumed, reducing the conversion rate of SO3. At the same time, the generated sulfuric acid is replaced to form neutral salt (MgSO4) and water, which slows down the corrosion of sulfuric acid. Another additive is to inject alkaline substances directly from the furnace to neutralize SO3 in the flue gas and reduce the generation of SO3, which is beneficial to lowering the dew point temperature of the flue gas. This type of additive oil is injected with ammonia, dolomite powder, magnesite ore powder, etc. 3． Increase metal surface temperature In the presence of SO3 and water vapor, metal surface temperature becomes an important factor affecting dew point corrosion. On the one hand, it can determine whether the conditions for dew point corrosion can form on the metal surface. On the other hand, it can also affect the concentration of condensed acid on the metal surface, further affecting the corrosion rate. Metal surface temperatures above the dew point destroy the formation of condensed acid. Therefore, increasing the metal surface temperature is one of the best ways to prevent acid dew point corrosion. 4． Reduce the moisture and oxygen content of the flue gas. The moisture content of the flue gas not only affects the dew point temperature, but also mainly affects the concentration of condensed sulfuric acid on the metal surface. At the same metal surface temperature, if the amount of steam is increased, the concentration of condensed sulfuric acid will decrease. Steam soot blowing can improve heat transfer, but it will also bring in water, diluting the concentration of condensed acid on the pipe wall, forming a corrosive environment in a dilute sulfuric acid state, and increasing the corrosion rate, so it should not be done too frequently. 5. Application of corrosion-resistant materials: Domestic ND steel, ND1 steel and other materials with strong corrosion resistance are used to make gas furnace pipes, which are more corrosion-resistant than low-carbon steel pipes and extend the service life of the equipment. During the corrosion process of ND steel, a passivation film containing Cr, Cu, Ti, Sb and other elements is formed on the surface to prevent corrosion. 6. Metal sintered coating Metal sintered coating technology is to bond nickel-based alloy to the metal surface and sinter it at high temperature to form a nickel-based alloy molten plating coating. Mainly used to solve the problem of sulfuric acid dew point corrosion in industrial heating furnaces, boiler convection chambers and air preheaters. 7. In order to solve the problem of sulfuric acid dew point corrosion in air preheaters, polymer corrosion-resistant paint is used. It is characterized by strong bonding with the steel surface, good temperature resistance, and excellent resistance to sulfuric acid dew point corrosion. It can be used as a special paint for air preheaters. 8. Other measures ⑴ When shutting down the furnace for dust cleaning, it needs to be cleaned carefully. Dust accumulation will reduce heat transfer efficiency, reduce the temperature of the metal surface of the pipe wall, and increase the possibility of dew point corrosion. At the same time, the unburned carbon in the dust has a catalytic effect on the generation process of sulfuric acid. It also has strong hygroscopic and moisture-fixing properties, and acts as a cathode in the dew point corrosion process, accelerating corrosion. ⑵Try to avoid running the waste heat boiler under low load conditions for a long time and shorten the running time at lower temperatures. In addition, since the finned tubes are prone to dust accumulation, it is necessary to strengthen the operation, turn on the soot blower regularly, remove the dust accumulation on the furnace tube in time, and reduce the sensitive parts that cause sulfuric acid dew point corrosion.