Ideal Boiler Water Properties And Effects

In this article, we go through ideal  boiler water properties and the effects of varying chemical compound in it. It is very important to keep all the constituents should be maintained in their appropriate chemical range to keep the boiler water in ideal condition .
Must Read:>>Boiler Water Tests Onboard

Let's have look at the properties of boiler water

1. Ph --- For an ideal boiler water, PH is maintained between 10.5-11.5 ie alkaline
>> Controlling the PH of water is one of the important treatment in boiler water treatment 
>>PH is below 7 the solution is acidic and above 7 it's alkaline.
>>If either of the values increases, water will accordingly become acidic or alkaline, leading to detrimental effects caused due to acidic attack or caustic embrittlement. 

2.Oil and Fats--- For an Ideal boiler water, oil content should be nil

Lubricating oil may contaminate the feed system and it finally reaches on boiler tubes
>>This is done in order to prevent carbonization of oil and formation of scales due to boiler heat.
>>Proper care should be taken to minimize the oil-in-water emulsion
>>Effect is Corrosion and carbonization
>>If it stick on the boiler tubes which reduce the heat transfer there by reduce the boiler efficiency

3.Dissolved oxygen---For an Ideal boiler water, Dissolved oxygen is 0.04(before scavenger addition)

 >>Dissolved oxygen more corrosive than any other free gases in boiler water
>>So it is very important to remove dissolved oxygen from it.This can be done by adding additives such as hydrazine to water.

4. Hardness 

>>The main purpose of controlling hardness is to prevent scale formation building on the interior surface.This can be done by keeping hardness values low. 
>>In case layers of scales keeps on building inside the boiler, the insulation layer will reduce, which in turn will prevent the heating of water and generation of steam.This will lead to overheating and damage to the internal parts of the boiler, reducing the overall efficiency.

5. Chloride ion---Standard value of chloride ion is less than 300 mg Cl/l

>>The more the chloride ions, the more the scale formation.  
>> So it is better to keep the chloride low as much as possible
>>Formation of chloride ions can be done by controlling the amount and time of boiler blow down

6.Total Solids and electrical conductivity-----Conductivity (25°C) <2000 micromhos 

>>   The increase of total solids promotes deposition of scales in the boiler as well as in the equipment consuming steam due to carry over.
>>More amount of dissolved solids also leads to more scale formation and carrying over

7. P alkalinity--- P alkalinity in Boiler Water is between 50-300mg CaCO3/l.

  >>This is standard value of hydroxyl ion(OH) and carbonate ion (CO3) in water. The higher the value of P alkalinity, higher the probability of scales formation.
>>The conventional boiler water test finds only the presence of OH and half of CO3

8.Phosphate--- Standard value of Phosphate is 20-40 mg PO4/l.

>>Phosphates reacts with calcium and forms calcium phosphates, which is a major scale forming component 
>> Phosphates also contributes to the prevention of alkali corrosion and caustic embrittlement. 

Summary
Appearance----------------------- clear and free of mud
Chloride content------------------<100 ppm Cl
"P" alkalinity ----------------------100-150 ppm CaCO3
Total alkalinity---------------------<2 x "P" alkalinity
pH at 25°C --------------------------10.5-11.5
Hydrazine excess------------------- 0.2-0.5 ppm N2H4
Phosphate excess------------------- 20-50 ppm PO4
Specific gravity (20°C)-------------<1.003 kg/m3
Conductivity (25°C)----------------- <2000 micromhos
Oil content---------------------------- nil
  

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Ref:- brighthubengineering.com,Reeds general engineering knowledge