Ammonium bisulfate, the chemical formula is NH4HSO4, melting point 147, boiling point 490. Its colorless crystalline form makes it not have a significant color in its pure state, but it has a very high solubility, almost insoluble in ethanol, acetone and pyridine. WetAmmonium bisulfate is viscous, with ash absorption and adhesion; It has high moisture absorption and is easy to form ammonium bisulfate solution.
In aqueous solution, ammonium bisulfate can be ionized into bisulfate and ammonium ions. Bisulfate can continue to be almost completely ionized into hydronium ions and sulfate ions, a process that can be seen as a product of the neutralization of sulfuric acid by half of ammonia monohydrate. Therefore, the strong acidity of its aqueous solution is not accidental, but due to the ionization of ammonium bisulfate in aqueous solution. So,It is as acidic and corrosive as sulfuric acid.
nh4hso4→nh4++hso4-
hso4-+h2o→h3o+++so42-
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The active components in the catalyst in the SCR ammonia denitrification processV2O5 catalyzes the accelerated conversion of SO2 to SO3 in the gas phase, which then reacts with the escaping NH3 to form ammonium bisulfate.
v2o5+so2→v2o4+so3
2so2+o2+v2o4→2voso4
2voso4→v2o5+so2+so3
In the process of SNCR denitrification, although there is no catalyst to accelerate the transformation of SO2 to SO3, SO2 will still react with O2 to form SO3 under high temperature conditions, and finally react with the escaping NH3 in the high temperature environment to form ammonium bisulfate, which will cause corrosion to the subsequent equipment.
1. Block the air preheater.
The inlet gas temperature of the air preheater is about 200 300, the exhaust gas temperature is about 130 150, and the ammonium bisulfate in the flue gas is mainly in a liquid state. Research shows that whenWhen the concentration of SO3 in the flue gas is 2 3ppm and the ammonia escape is greater than 2ppm, the accumulation of ammonium bisulfate will occur in the air preheater. The blockage of the air preheater causes a series of follow-up problems, such as the increase of the inlet and outlet pressure difference, the increase of air leakage rate, the increase of the resistance of the air and smoke system, and the increase of fan current.
2. The dust collector corrodes and collects dust.
When there are more components of ammonium bisulfate adsorbed in the ash, the specific resistance value of the ash surface will be reduced, and it is easier to be captured by static electricity, while the liquid ammonium bisulfate is extremely viscous, easy to adhere to the plate, and difficult to remove by beating; It is also easy to cause the bag blockage of the bag filter.
3. Corrosive flue gas treatment equipment.
The corrosion of ammonium bisulfate is mainly concentrated in denitrification reactors, air preheaters, economizers, dust collectors and chimney flues and other medium and low temperature equipment. Due to the strong moisture absorption capacity and strong adhesion of ammonium bisulfate, the acidic corrosive medium in the flue gas is dissolved in the aqueous solution of ammonium bisulfate, resulting in acid water corrosion.
4. Reduce catalyst activity.
The high concentration of ammonia in the porous structure of the catalyst and the high catalytic activity temperature will lead to the reaction of NH3 and SO3 to form liquid ammonium bisulfate, which has strong adhesion and will adsorb the ash in the flue gas and cover the surface of the catalyst, resulting in a decrease in catalyst activity and denitrification efficiency.
In industrial production, in order to better solve the corrosion problem of ammonium bisulfate on equipment, some new anti-corrosion coating materials and technologies are also emerging. Such as: high temperature flue gas anticorrosive coatings, acid and alkali resistant anticorrosive coatings, electrostatic inorganic anticorrosive paints, etc., suitable anticorrosive coatings can be selected according to the actual working conditions.
In addition to this, a series of measures need to be taken to reduce the corrosive effect of ammonium bisulfate on equipment. For example, the operating temperature and pressure of the equipment can be strictly controlled to prevent ammonium bisulfate from decomposing into sulfuric acid and ammonia at high temperature and pressure, thereby reducing the corrosion rate. In addition, it is also essential to regularly overhaul and maintain the equipment to find and repair the corrosive parts in time.