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Water Treatment
Boiler water treatment systems are used to handle many adverse conditions which are present due to the extreme temperature and pressures of boiler systems. A couple of these conditions are scale/deposits that form on the inside walls of piping and corrosive boiler feedwater. If these adverse conditions are left untreated, this could result in:
- Less efficient heat transfer
- Heat exchanger tube failures
- Higher pump head pressures
- Corrosion leading to pipe failure
All of these effects can impact the overall reliability & efficiency of the boiler system. One way to combat this is through the use of phosphates. Phosphate treatment is recommended if the following situations are present at your boiler location:
- Inability to frequently monitor piping of water system (infrequent shutdown/cleanouts)
- High quality feedwater is not available
- Low water treatment costs are necessary
Boiler Feedwater
A key to protecting the boiler system is to treat the boiler feedwater entering the system. Boiler feedwater can be protected from corrosive conditions through coordinated phosphate/pH control treatment. Phosphate buffers the boiler water, reducing the chance of large pH swings due to the development of caustic concentrations. In phosphate treatment, excess caustic combines with disodium phosphate to form trisodium phosphate. Therefore, adequate disodium phosphate must be available to combine with all of the free caustic in order to form trisodium phosphate. A slightly basic pH should be maintained in the boiler feedwater system. ASME suggests feed water to be kept at a pH of 8.3-10.5. Sodium phosphates help fulfill this requirement.
Boiler System
In the boiler system piping, scale can be formed by salts with low solubility. One of the worst types of scale buildup is calcium carbonate, commonly known as limestone. Scale buildup inhibits heat transfer, which in turn raises tube metal temperature resulting in potentially increased corrosive conditions.
Sodium Phosphates are often used in the system to prevent this build-up. When added at correct dosage levels the phosphate will react with the calcium carbonate and form Hydroxyapetite. Hydroxyapetite is softer than other deposits and will remain in suspension as long as it is kept in circulation. It can then be removed via routine blow down of the system.
Deposits, or sludge, arrives from the boiler water and enters the system as suspended solids. They can become attached to piping when boiler systems are drained at high temperatures. Once deposits are attached to the piping, they attract and bind additional solid particles found in the water. Sodium Hexametaphosphate is a scrubbing agent that can help remove these deposits.
Phosphates can be fed into the system in solution with other water conditioning chemicals. There are several water treatment companies which have specific programs that include phosphates for boiler water treatment.
Sodium Phosphates are often used in the system to prevent this build-up. When added at correct dosage levels the phosphate will react with the calcium carbonate and form Hydroxyapetite. Hydroxyapetite is softer than other deposits and will remain in suspension as long as it is kept in circulation. It can then be removed via routine blow down of the system.