Boiler and FWG chemical dosing

FWG

Scale formation in freshwater generator can be controlled and minimized by continuous chemical treatment. 

Poly-sulphate compounds (like sodium poly-sulphate) with anti-foam is preferred by marine engineers and is extensively used on ships. Their trade name is different, like:

• Vaptreat (by “UNITOR”)
• Ameroyal (by “DREW CHEMICALS”)

These chemicals minimize calcium carbonate scale formation and possibility of foaming. the compound is nontoxic, no-acidic, and can be used in fresh water generator producing water for drinking purposes.

Boiler water test

.bwt  .boiler  water

Alkalinity test/ pH value:

(9.5~10.5) Sodium hydroxide is usually added to maintain alkaline condition. (200-700ppm)

Chloride level:

Regular testing of chloride ensures the monitoring of any seawater contamination and any leak from aux condenser. (60-200ppm)

Phosphate level: 

Sodium phosphate acts as water softener. They precipitate the scale forming compounds specially calcium sulphate from the boiler water to prevent scale deposit (30-50 ppm)

Conductivity/ hardness test:

Measured in micro siemens per cm. The reading determines the hardness of the water which is the TOTAL DISSOLVED SOLID (TDS)

Hydrazine level:

 Correct dosage prevents oxygen formation. Max 50 ppm

N₂H₄+O₂=2h₂O+N₂

Present chemicals used:

• Oxygen inhibitor
• Oxygen Control
• Oxygen scavenger

Standard Value for Boiler Water

Engine Cooling water Test:

pH value:

pH value should be kept at 7-8 at 25° C.

test cooling water every after 240 hours, add chemicals if pH value falls below 7.

If pH value goes over 10 , some amount of cooling water need to replaced.

Maintain pH value in alkaline range to prevent corrosive environment.

Nitrite (Anti-corrosive element):

Nitrite is used as an inhibitor to prevent corrosion in cooling systems. It promotes the formation of protective films on surfaces and inhibits corrosion by preventing oxygen-related corrosion. Nitrite levels should be checked frequently and treated with chemicals if levels are low. A common range for nitrite concentration is 500 to 1,500 ppm.

Keep nitrite value above 1500ppm.

Chloride content increasing:

→ Check possibility of seawater penetrating into cooling water.

→ Check the system which includes sea water, for example fresh water cooler cooled by sea water.

pH value decreasing or sulphate content increasing:

→ Check if cooling water is contaminated by exhaust gas.

→ Check cylinder head by hydraulic pressure test.