Boiler Water Treatment Onboard
Hope you have read Ideal Boiler Water Properties & Boiler Water Tests . In this article we will discuss about boiler water treatments.
After doing boiler water tests we comes to know that the amount of excess compound or impurities in the system by matching with Ideal Boiler Water Properties.According to the result we will treat the water by adding suitable chemicals into the boiler water
Importance of boiler water treatment
>Low pH or dissolved oxygen in the water attacks the steel. This causes pitting or lowering the thickness of the steel tubes, leading to rupture of the boiler tubes.
>Water contains dissolved salts, which upon evaporation of water forms scales on the heat transfer surfaces.
>Flow assisted corrosion occurs in the carbon steel pipes due to the continuous removal of the protective oxide layer at high flows.
>Impurities carried over in the steam, causing deposits on turbine blades leading to reduced turbine efficiency, high vibrations, and blade failure.
>Silica at higher operating pressures volatilizes and carries over to the turbine blades.
Boiler water treatment parameters
Boiler water treatment mainly controls
>Alkalinity of boiler water
>Phosphate(controls magnesium and calcium sulphates)
>Dissolved Oxygen in boiler water
Alkalinity of boiler water can be controlled by adding Sodium Carbonate (Soda Ash) and
Sodium Hydroxide (Caustic Soda) in boiler water, reaction and effects are given below
>Sodium Carbonate (Soda Ash)
Reacts with non-alkaline hardness salts by either precipitating them, or
converting in to Sodium salts, which stay in solution.
Excess Sodium Carbonate remains in solution to provide an alkalinity to reduce corrosion.
Na2CO3+ CaSO4 → CaCO3+ Na2SO4
>Sodium Hydroxide (Caustic Soda)
Reacts with Magnesium Chloride producing a harmless precipitant and
Sodium Chloride, which remains in solution. It is not suitable for pre-mixing with other chemicals.
But can be used in conjunction with other chemical treatments.
The function of these chemicals is to prevent scale formation by precipitating the salts of
magnesium and calcium as a soft sludge.
>Disodium Phosphate
Dissolves in water and forms a neutral solution. Reacts with magnesium and
calcium sulphates and precipitates them as phosphates, or converts them to sodium salts,
which will remain in solution.
Na2HPO4+ MgSO4⇒ MgHPO4+ Na2SO4
>Trisodium Phosphate
Dissolves in water to produce disodium phosphate and sodium hydroxide, an alkaline solution.
Na3PO4 + H2O ⇒ Na2HPO4 + NaOH
Presence of oxygen in the boiler water will result in serious corrosion. To reduce the amount of oxygen present in the boiler water oxygen scavengers are used. Hydrazine or Sodium Sulphate are used as oxygen scavengers.even though sodium sulphate is discourage to use because it increases TDS of boiler water compared to hydrazine.
Hydrazine N2H4+ O2 → 2H2O + N2
Sodium Sulphate 2NaSO3+ O2 → 2NaSO4
Hope you have read Ideal Boiler Water Properties & Boiler Water Tests . In this article we will discuss about boiler water treatments.
After doing boiler water tests we comes to know that the amount of excess compound or impurities in the system by matching with Ideal Boiler Water Properties.According to the result we will treat the water by adding suitable chemicals into the boiler water
Importance of boiler water treatment
>Low pH or dissolved oxygen in the water attacks the steel. This causes pitting or lowering the thickness of the steel tubes, leading to rupture of the boiler tubes.
>Water contains dissolved salts, which upon evaporation of water forms scales on the heat transfer surfaces.
>Flow assisted corrosion occurs in the carbon steel pipes due to the continuous removal of the protective oxide layer at high flows.
>Impurities carried over in the steam, causing deposits on turbine blades leading to reduced turbine efficiency, high vibrations, and blade failure.
>Silica at higher operating pressures volatilizes and carries over to the turbine blades.
Boiler water treatment parameters
Boiler water treatment mainly controls
>Alkalinity of boiler water
>Phosphate(controls magnesium and calcium sulphates)
>Dissolved Oxygen in boiler water
- Alkalinity
Alkalinity of boiler water can be controlled by adding Sodium Carbonate (Soda Ash) and
Sodium Hydroxide (Caustic Soda) in boiler water, reaction and effects are given below
>Sodium Carbonate (Soda Ash)
Reacts with non-alkaline hardness salts by either precipitating them, or
converting in to Sodium salts, which stay in solution.
Excess Sodium Carbonate remains in solution to provide an alkalinity to reduce corrosion.
Na2CO3+ CaSO4 → CaCO3+ Na2SO4
>Sodium Hydroxide (Caustic Soda)
Reacts with Magnesium Chloride producing a harmless precipitant and
Sodium Chloride, which remains in solution. It is not suitable for pre-mixing with other chemicals.
But can be used in conjunction with other chemical treatments.
- Phosphate
The function of these chemicals is to prevent scale formation by precipitating the salts of
magnesium and calcium as a soft sludge.
>Disodium Phosphate
Dissolves in water and forms a neutral solution. Reacts with magnesium and
calcium sulphates and precipitates them as phosphates, or converts them to sodium salts,
which will remain in solution.
Na2HPO4+ MgSO4⇒ MgHPO4+ Na2SO4
>Trisodium Phosphate
Dissolves in water to produce disodium phosphate and sodium hydroxide, an alkaline solution.
Na3PO4 + H2O ⇒ Na2HPO4 + NaOH
- Dissolved Oxygen
Presence of oxygen in the boiler water will result in serious corrosion. To reduce the amount of oxygen present in the boiler water oxygen scavengers are used. Hydrazine or Sodium Sulphate are used as oxygen scavengers.even though sodium sulphate is discourage to use because it increases TDS of boiler water compared to hydrazine.
Hydrazine N2H4+ O2 → 2H2O + N2
Sodium Sulphate 2NaSO3+ O2 → 2NaSO4
Mr. Bijoy,
ReplyDeleteHi. I guess there's slight correction. Its sodium sulphite used as oxygen scavenger. And generally it is discouraged to use as it increases TDS of blr water and not that effective as hydrazine.
May be u can add this point. Thanks.
Himanshu Srivastava
thnkz for your kind information.....
DeleteHi,
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