monitoring sulphite in Boiler feed water
Recently I got confused why we are monitoring sulphite in Boiler feed water, then I found this useful information..!!
hashtagUseful information
-Sulfite (Sodium Sulfite Na2SO3) has unique properties which allow it to remove oxygen from water. The reaction of sulfite and oxygen creates sulfate.
Dissolved oxygen in boilers can cause rapid corrosion known as pitting. Pitting describes corrosion as the cause of holes to occur in the metal material. These holes can become deep and seriously damage the boiler system.
Direct or mechanical removal: Dissolved oxygen is accomplished through the use of a deaerator or by heating the water to a temperature above 80 Deg Celsius. Heating the water can be done with a preheater or sparge tube (Dearator) installed in the return system or the feed water tank. It removes less than 0.04mg/l.
Chemical removal: An oxygen scavenger is a chemical that consumes oxygen through an oxidation-reduction (redox) reaction. Sulfite is the most common type of this. Limit of sulphite to be maintained minimum 30 to 60 ppm.
2 N a 2 S O 3 + O 2 → 2 N a 2 S O 4.
(sulfate (SO4) which is a soluble salt that can be easily removed through boiler blowdown),
The dissolved oxygen content should be maintained at a minimum but at no time should it exceed 0.040 mg/l for drum pressure (0-450psi) 0.007 mg/l for drum pressure (451-900psi).
Fact: Low temperature feed water contains oxygen around 10Mg/L. High temperatures feed water contains 3Mg/L.
