9 Gek Boi Hardness Salts
9 Gek Boi Hardness Salts
9 Gek Boi Hardness Salts
Auxiliary Boilers
Boiler Water Treatment Hardness Causing Salts
The hardness causing salts reduce heat transfer in boilers. The characteristics of these salts and
the treatment methods involved in their removal are explained in this document.
Alkaline salts
These are carbonates of calcium, magnesium and sodium. Their presence in water increases pH
value of water or the alkalinity.
These are bicarbonates of calcium and magnesium. Hardness is defined as the inability of water
to form lather easily in presence of temporary hardness. The hardness is removed on heating
the water. Bicarbonates get converted to carbonates and carbon dioxide is liberated.
When chlorides of calcium and magnesium get deposited, they are split into magnesium and
calcium hydroxide, accompanied by hydrochloric acid, which is corrosive. This reaction is
accelerated at high temperatures.
These are sulphates of calcium and magnesium. These salts deposit as a hard scale on the
heat transfer surfaces. Scales and deposits impede heat transfer. This results in overheating of
surfaces and subsequent failure.
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MEO Class IV - GEK
Auxiliary Boilers
Boiler Water Treatment Hardness Causing Salts
Harmless salts
These are the sulphates, chlorides and nitrates of sodium. Sodium chloride gets deposited at
high temperatures. Common salt gets deposited when the density is around 1225 to 225000
ppm. It becomes a chemically stable deposit.
Sodium sulphate does not form hard scale and deposits as a soft sludge. It can be kept in
suspension by the use of coagulants. Therefore, these salts are harmless.
Chloride salts
Fresh water contains small quantities of sodium chloride. Under boiler temperature and pressure
conditions, small quantity of sodium chloride in solution, does not deposit and is chemically
stable.
Large quantity of sodium chloride in the system creates problems. Sodium chloride enters the
boiler feed system as seawater via leaky condensers or priming evaporators of fresh water
generators.
Large amount of sodium chloride reacts with magnesium sulphate along with sodium chloride,
which is present in seawater and forms sulphate and magnesium chloride. The reaction is
accelerated at higher temperatures.
Treating the boiler water with standard chemicals involves removal of the temporary and
permanent hardness salts as non adherent sludge.
Primitive methods
Soda lime treatment and caustic soda treatment were primitive methods. Overdose leads
to caustic embrittlement. These treatments do not condition hardness salts into non adherent
sludge.
Adding phosphates convert the hardness salts into phosphate salts which can be conditioned
to non adherent sludge.
MARINE SOLUTIONS
Maritime leadership. All the way. 2008
2008 Teledata
Teledata MarineMarine
Solutions Solutions.
Ltd. All rights All
reserved. 2
MEO Class IV - GEK
Auxiliary Boilers
Boiler Water Treatment Hardness Causing Salts
Treatment by phosphates
When phosphates are added to the boiler water, it combines with calcium in boiler water to
form tri calcium phosphate Ca3(PO4)2. It precipitates as sludge, because its solubility is low.
The sludge can be kept in suspension by the use of coagulants. Phosphates also combine with
magnesium compounds to form tri magnesium phosphate Mg3(PO4)2, which also precipitates
as sludge and can be conditioned by the use of coagulants.
If requisite alkalinity is not achieved, some quantity of NaOH is added to the boiler water to
give the minimum required alkalinity.
However, when large quantity of oxygen is found, the source of air leakage should be
identified. It is an incorrect procedure to treat large quantity of oxygen with sodium sulphite,
because it will lead to high density levels, which is not desirable.
In high pressure water tube boilers, working at over 60 bar hydrazine is used for the removal
of oxygen. Since nitrogen is a gas, it does not form any salt on reaction.
N 2H 4 + O 2 --------> N2 + 2H2O
MARINE SOLUTIONS
Maritime leadership. All the way. 2008
2008 Teledata
Teledata MarineMarine
Solutions Solutions.
Ltd. All rights All
reserved. 3