Coagulation and Flocculation in Boiler Water

Coagulation and flocculation is the process to give coagulant and flocculants materials into boiler water by injection. Coagulation is the neutralization process of charges so the particles can be very close to one another. Flocculation is the unification process between particles that had been already much closed to one another so the particles will attract each other and form flock. Chemicals which are injected to reduce turbidity at inlet clarifier as follow:

1. Alum Sulfate (Al₂(SO₄) . 18 H₂O)

Alum sulfate serves to form clump of suspended particles in water. When alum is contacted with water then hydrolysis will occur which produces aluminum hydroxide and sulfuric acid. The addition of alum depends on water turbidity and flow rate. The following below is the reaction of alum sulfate:

Al₂(SO₄) . 18 H₂O + 6H₂O  → 2Al(OH)₃ + 3H₂SO₄ + 18H₂O

Al(OH)₃ in the form of colloidal will settle with other impurities and shipped with water while H₂SO₄ will result acidic water.

2. Caustic Soda (NaOH)

Caustic soda serves to neutralize the acid caused by reaction in previous process. Concentration of caustic soda is added depends on acidity of solution. pH expected between 6-8. The following below is the reaction of caustic soda:

H₂SO + 2NaOH → Na₂SO₄ + 2H₂O

3. Chlorine (Cl₂)

The addition of chlorine is intended to kill microorganisms in water, in addition it also prevent the growth of moss on clarifier wall which can interfere the next process.

4. Coagulant Aid (Polymer)

Coagulant aid serves to accelerate deposition process because the addition of this material will bind particles that had agglomerated before into bigger clumps (flock) so make it easier and faster to settle.