NEED FOR BOILER WATER TREATMENT

No water treatment or improper water treatment
Reduces the thermal efficiency of Boilers.
Reduces loading capacity of Boilers.
Reduces the availability of Boilers.
increases the maintenance cost of Boilers
Finally reduces the life of the Boilers.
A-Important water parameters
1. Hardness 
2. Alkalinity
3. pH
4. TDS
5. Silica
6. Suspended solids
7. Dissolved oxygen 
If there is a difference exists between an operating value and a target value, then 
decreasing or increasing blow down and adjusting chemical dosages will be done

1. Hardness
 •Total hardness is the combined concentration of dissolved calcium and magnesium salts. 
•Alkaline or temporary hardness is caused by bicarbonates, carbonates, or hydroxides. Bicarbonates that predominate in most natural waters are easily broken down when the temperature is raised. 
•Non-alkaline or permanent hardness is caused mainly by chlorides, sulfates, and nitrates.
•Water hardness is the most common contributor to boiler scaling
2. Alkalinity
•The extent to which a solution is alkaline (i.e., has a pH value greater than 7)
•It is a measure of its hydroxide (caustic), carbonate and bicarbonate, and hydroxides content. Expressed in terms of calcium carbonate content.  
•High Alkalinity also contributes to foaming and carryover in boilers.
3. pH  
•is a measure of a solution's acidity
•In water, small numbers of water molecules (H2O) will break apart or disassociate into hydrogen ions (H+) and hydroxide ions (OH-).
•
•Other compounds entering the water may react with these, leaving an imbalance in the numbers of hydrogen and hydroxide ions. 
•When more hydrogen ions react, more hydroxide ions are left in the solution, and the water is essential; when more hydroxide ions react, more hydrogen ions are left, and the water is acidic.
4. Total Dissolved Solids (TDS)
•The total dissolved solids (TDS) in water consist of inorganic salts and dissolved materials. 
•In natural waters, salts are chemical compounds comprised of
–Anions such as carbonates, chlorides, sulfates, and nitrates (primarily in groundwater), and
–Cations such as potassium (K), magnesium (Mg), calcium (Ca), and sodium (Na).
5. Silica
•Silica is found as dissolved silicate and in a suspended complex form.
•
•It can combine with other compounds to give scales that are strongly insulating and difficult to remove and cause high resistance to heat transfer

6. Suspended solids (SS) 
 / Turbidity•Turbidity is the amount of particulate matter that is suspended in water.
•Nephelometric Turbidity Units  
•Turbid include clay, silt, finely divided organic and inorganic matter, soluble 
organic compounds & organisms. Removed by coagulation, sedimentation, and filtration
7. Dissolved gases
•Oxygen and carbon dioxide are the most important. 
•Dissolved oxygen (DO) is an essential factor in determining the corrosiveness of water.
•The solubility of oxygen in water depends on temperature and pressure. 
•Dissolved carbon dioxide gives carbonic acid. Even this weak acid can lower the pH to values where the water becomes highly corrosive.
Corrosion
•Localized attack on metal can result in a forced shutdown. 
•Because boiler systems are constructed primarily of carbon steel and the heat transfer medium is water, the potential for corrosion is high. 
•Good water treatment aims to keep the pH within the safe range of pH 8.2 - 12.5, while the addition of oxygen scavengers prevents iron from being oxidized to ferric oxide or rust.

sugar plant equipment 

FEED WATER & BOILER WATER QUALITY

Keeping good feed water quality is very much crucial for the reliable operation of a Boiler.
Negligence in the maintenance of quality may prove a disaster to boiler life. 
The bad quality of feed water will cause fouling of the internal surface of pressure parts, causing their failure. 
HP & LP dosing system shall be operated to maintain boiler water quality.
A sampling of boiler water shall be carried out regularly to monitor its quality as recommended.
Boiler Water pH: It is recommended to keep boiler water pH between 9.5 to 10.5. 
Lower pH can cause disintegration of the magnetite layer, and higher pH can cause caustic corrosion.
Dissolved solids are required to be restricted to 100 ppm. 
In case of the TDS increases, there is a chance of deposition in tubes. These deposits will create a barrier to heat transfer and reduce the cooling of tubes. 
This can not only reduce boiler loading but can also lead to tube failures.
The DM water is recommended to have TDS less than 0.1 PPM. 
It is targeted to have DM water with no impurities. 
Pure water has TDS = 0 and pH = 7. 
For all practical purposes, DM water can best be produced from 0.02 to 0.1 TDS. 
This indicates an impurity level of 0.1 PPM continuously going to the boiler Drum. 
The water converts to steam, and these impurity elements start getting concentrated in the drum. 
To control the TDS level below 100 PPM, blow-downs are required to be given (CBD or IBD)
BOILER PRESERVATION PROCEDURE 
After the stoppage of the Boiler, cool the Boiler naturally and when drum pressure reaches 2 kg/cm2, open all vents.

Drain the Boiler completely by opening the drain valves of the water wall, economizer, and superheater headers.
Open drum maintenance hole doors and conduct a physical inspection of the condition of the drum surfaces.

Remove drum internals after putting good match marks for easy re-installation.

Clean the drums thoroughly and, if required, use a wire brush for cleaning purposes.

Boiler spare parts 

Flush the drum by feeding the water jet using a temporary hose.
Periodically analyze the Boiler water for pH and hydrazine, and whenever pH comes down below nine and hydrazine less than 100 ppm,  
Add pH booster and hydrazine to the Deaerator and repeat the above procedure.

Approx. 1-2 weeks before re-start of the Boiler, drain the complete system and carry out an internal inspection of boiler pressure parts. The decision for carrying out chemical cleaning prior to re-start of the Boiler will be taken based on the assessment of the condition of the internal surfaces of boiler tubes.
•Close the maintenance hole door, fill the Boiler upto the top of the drum and flush it once.
To prevent corrosion of the external surfaces of the pressure parts and internal surfaces of gas/air ducting, put silica gel bags (2 kg.) in the furnace and inside of ID, FD & SA ducting. Observe the color of the silica gel periodically, and when it gets dis-colored, 
Replace these bags with new ones.
Putting some Halogen lamps inside the Boiler (to raise the temperature above the surrounding ambient) helps to avoid condensation of atmospheric moisture and prevents corrosion of boiler surfaces.
NOTE : 
Boiler filling and pressurization can be done using transfer pumps and condensate storage tanks also in place of using a Deaerator feed tank and Boiler feed pump.

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