FAQs on Boiler Water Treatment

1)  To prevent boiler scale
2)  To minimize corrosion to the feed water and steam & condensate system
3)  Improve boiler efficiency
4)  Reduce fuel, operating and maintenance costs
5)  Minimize maintenance and downtime

The most common scale is white in appearance and is from calcium carbonate that has precipitated from hard feed water. Hard water contains calcium and magnesium and minerals that are hard to wash. Silica scale is brittle and has a glassy appearance. The most common scale is white in appearance and is formed by calcium carbonate that has precipitated from hard feed water.

It is dissolved in the boiler water or precipitates out as part of the mobile sludge which is formed.

Initially maybe, but a scale-free boiler can be made leak-free by a good boiler smith. Minor leaks will be plugged by the tannin in the treatment. Also it should be remembered many leaks are actually caused by scale, which has led to localized overheating, or corrosions. Even a “traditional” boiler of riveted and expanded construction ought to be leak-free and PT will make sure no localized overheating or corrosion will ever occur to cause leaks.

Caustic embrittlement is a complex problem with multiple causes. The use of specific tannins have been shown to prevent it. Additionally leak-free boilers allow no opportunity for caustic embrittlement to occur.

History does not show the risk to be serious if simple maintenance and operating policies are followed.

It is not. Direct chemical treatment of boiler water can totally solve fouling, corrosion, caustic embrittlement and steam contamination problems. Line side treatments can only ease the problems of fouling and caustic embrittlement but can not deal with corrosion or steam contamination.

Any solids which would have formed mud’s or clays will either go into solution (due to the alkalinity) or will go into suspension in the boiler water. However those particles in suspension, again due to the alkalinity, form a totally mobile sludge which moves with the slightest water current, even when cold. It is not in any way adherent. Under high steam demand, and thus rapid boiler water circulation, this sludge fully mixes with the boiler water and appears as a brown colour in the gauge glasses.

No. Lead is rapidly eroded when alkalinities reach or exceed pH12. A number of alternatives are available:

a.  Lead/tin alloy plugs which give a 90+ day life and longer with copper electroplating on the water side.
b.  Copper electroplated (on the water side) pure lead plugs.
c.  Drop (button) plugs.

No. Lead is rapidly eroded when alkalinities reach or exceed pH12. An alternative must be used.

Only up to certain point. Experience shows it is important not to have leaking valves situated below the normal water level. Such valves seats and stems, when made of brass or bronze. It should ideally be substituted by stainless steel or other alkaline-resistant materials. Note ONLY the seat and stem need replacement. Erosion of the component body will be very slow indeed.
 
Doesn’t high alkalinity dissolve glass, i.e.: gauge glasses.
 
Silica is dissolved gradually by alkalinity. Correct maintenance policies based on inspection, on set days, in steam will prevent problems occurring with tubular glasses. It is best to use reflex glasses if possible. Failures of these flat glasses are virtually unheard. The ability to dissolve silica ensures silica scale does not form on boiler surfaces.

Because it leads to salts being deposited in the steam passages causing accelerated internal corrosion and hot spots (failed superheater elements, pipes etc). It leads to solids being carried to the valves and pistons acting as a grinding paste when mixed with liquids and it leads to contaminated and thus compromised lubrication. All these are equally true for any auxiliary item of equipment that use steam, e.g.: air pumps, generators etc.

They need not be! PT offers a 20+ year life from boiler tubes where regulation so allows. The lack of corrosions and thermal fatigue failures also, of course, extend to all other parts of the boiler. Corrosion prevention is just one part of the overall benefits available from using PT.

Pretreatment (PT) is no experiment. It is a fully developed water treatment based on highly successful previous treatments. It takes these further due to improvements in the understanding of various phenomena and the availability of more effective and relevant chemicals. It should also be remembered PT was developed for locomotives.

The high alkalinity created acts as a buffer to incoming water variation.

It is not. A pre-prepared chemical mix is added to the locomotive’s tank to treat the water on a regular basis. Long periods of standing without operation of any injectors will reduce the active antifoam concentration below safe levels. In such cases extra antifoam may be required depending on operating circumstances.

It is not. Only two boiler water parameters are to be measured and only a few remedies to incorrect conditions exist; these being blowdown and alkalinity regulation.

In application terms basically nothing. A treatment period will be seen as corrective if scale and corrosion are present in the boiler from previous use. Treatment in a boiler using PT from new or containing no scale or corrosion will be preventative. In these circumstances there is nothing from past incomplete treatments to correct.

These should be as clean as possible to start with. In time they will be descaled and corrosions will be prevented but it will be a slower process than in the boiler. New items will remain scale and corrosion free.

No problem! PT treated water should, where frost is not going to be a problem, be left in water tanks and boilers. It continues to work when a locomotive is not in use. Thus it is much better to leave tanks and boilers filled rather than in empty and so-called “dry” conditions.

A single drum program is referred to as a chemical mixture that contains all the boiler chemical components (sulfite, amine, phosphate/polymer, and alkalinity) in one container.

Phosphate and polymers are required in boilers to prevent the calcium and magnesium from precipitating to the boiler tubes. Theoretically, some calcium and magnesium will leak though the softener. The calcium and magnesium minerals attach themselves to the polymer or phosphate and are discharged either through surface blowdown or during bottom blow downs.

Sulfite is referred to as an oxygen scavenger. Sulfite is the most commonly used oxygen scavenger. It is used to eliminate or replace dissolved oxygen.

To calculate your return condensate percentage multiply 100 by 1 – (feedwater silica/makeup water silica)

Blowdown is the removal of the concentrated dissolved and suspended solids. By blowing down the water from the system, lower concentrated water dilutes the existing water in the boiler.

It depends on how many impurities you have in your feedwater. The goal is to determine what the limiting factor is (dissolved solids, alkalinity, silica, or iron) in your boiler water and set your blowdown setting at that limit. To determine the amount of blowdown percentage divide 1 by your concentration ratio and multiply by 100.

If your boiler water is red in appearance, it may be from a number of possible reasons. Some of the most common ones are:
 
1)  Inadequate levels of sulfite
2)  Over feeding alkalinity
3)  Condensate contamination
4)  Overfeeding an acidic sulfite product that depresses the boiler water pH
5)  Low alkalinity

If you have poor performing softeners, if your softeners are being by-passed, or if you do not have softeners or hard water is entering the boiler. Remember phosphates and polymers are only used as polishers to remove the minimal amounts of Calcium and magnesium that enter the boiler.
 
Your pre-treatment is designed to remove 95% of the calcium and magnesium. If you are using a straight phosphate program with no polymer, make sure to perform bottom blowdown twice a day. A phosphate chemical is designed to sink to the boiler bottom after the calcium and magnesium is attached.

A deaerator is mechanical way of removing dissolved oxygen from the water. There are different types of deaerators and multiple manufactures. Remember you still need to feed an oxygen scavenger to remove the dissolved oxygen that the deaerator does not remove.

There are two main categories of amines, neutralizing amines and filming amines. Neutralizing amines are the most common. Amines are designed to increase the condensate pH to minimize condensate corrosion. Make sure to check how your steam is being used. In some applications, there may be restrictions on using amines.

1)  Oxygen Pitting
2)  Short-Term Overheating
3)  Long-Term Overheating
4)  Caustic Gouging

The boiling point of water depends on pressure. At atmospheric pressure, water boils at 100°C. As pressure increases, the boiling point increases. At 22,000 kPa, where water is converted to steam, the boiler point is lowered.

Boiler feedwater is referred to as the water entering the boiler. It is a mixture of returned condensate and fresh make-up water.

Make-up water is referred to as the fresh water that is added to the feedwater tank.

One solution is to hire an outside company that specializes in acid cleaning. If scale is light, do not remove the scale, just make sure your softeners are functioning properly and use a polymer designed for gradual scale removal.

1)  Have a good operating softener
2)  Make sure the brine tanks is half filled with salt at all times
3)  Perform softener hardness and feedwater checks daily
4)  If using a phosphate chemical program, blowdown the boiler two times a day

If you plan on keeping your boiler idle for more than a month, dry lay-up is the preferred method. If the boiler needs to be readily available to service. Add additional sulfite and alkalinity (if you are using an acidic sulfite) to the boiler. Maintain at least 100ppm of sulfite and check sulfite residuals weekly. Also, it is important to ensure the boiler tubes stay fully in the water to prevent tube corrosion.

Drain, clean, allow time to dry, insert desiccant or hydrated lime to absorb the oxygen, and carefully seal the boiler to prevent air leaks. Inspect the desiccant or hydrated lime periodically.

For occasional low efficiency-clean the burner tips and fuel oil pumps filters, check for viscosity of fuel oil, burner tip holes and atomizing steam pressure.
 
For continuously low efficiency-check flame colour, if the colour of the flame is not bright golden yellow, combustion is poor. Take remedial measures mentioned as above and additionally check the following.
 
If stack temperature is high, there is soot deposition in the boiler. Stop the boiler and carry out cleaning of the boiler. Check water side deposition/scale formation. If scale formation is observed, plan for cleaning the boiler with appropriate method. Evaluate for installation of economizer and soot blowing frequency.

The reasons for heavy soot deposition are:
 
i)  Poor quality of fuel with higher ash content metals, high insolubility. Ensure the quality of fuel.
ii)  Poor combustion – improve the combustion by checking Atomizing Steam pressure by cleaning burner tip and fuel oil system filters and checking viscosity near burner tip.

i)  Monitor boiler water treatment. All volatile treatment is better than conventional treatment if there is techno-economical feasibility.
 ii)  Check water treatment process for seepage of Chloride, Silica, etc. Check TSP quality for Chloride content.
 iii)  Fine control of CBD with increased frequency of Blow down water will help in saving of energy & boiler water.