Optimising boiler efficiency using tried and tested water treatment techniques can deliver significant benefits to organisations and operators of industrial steam boiler installations. This expert guide has been prepared by the specialists at Water Treatment Services and looks at how improvements to water quality can benefit boiler plant safety, heat transfer and combustion efficiencies.

Why boiler water quality matters

The objectives for anyone operating an industrial steam boiler system should be safety first, followed by getting maximum efficiency from the heat transfer process, and achieving optimum combustion.

One of the ways of doing all this, and reducing the costs for ongoing maintenance, is for the water used in the boiler system to be treated using boiler water chemicals or specialist equipment (usually in the pre-treatment phase).

The quality of the water used in an industrial boiler can hugely affect the day-to-day operation, efficiency and long term performance of the system so it’s something where good management practices can make a real difference.

Optimising boiler efficiency

To get the most out of a steam boiler system there are a number of aspects which need to be given careful attention and these include:

Scale
Any hardness salts present in the water used to feed the boiler can result in the build-up of scale on internal surfaces, especially if the water isn’t properly treated to combat the effects of the hardness salts first.
The build-up of scale on the internal surfaces can reduce heat transfer efficiencies, it can mean increased downtime cleaning the boiler, or the development of hot spots inside the boiler which can cause damage or even premature failure.

Corrosion
If the boiler water contains excessive dissolved gases, then corrosion of the internal surfaces of the boiler or pipes is likely to occur.
The main culprit here is oxygen which can result in a range of corrosion issues if not dealt with correctly.

pH Control
If the pH value of the water is too acidic, the water will eat away at metal surfaces.
Too alkaline, and the water might cause excessive foaming or other issues.

Caustic Corrosion
Sodium hydroxide or caustic soda is commonly used to maintain or adjust pH levels in boilers – if this chemical reaches too high a concentration, it can cause localised caustic cracking or embrittlement.
This is most often a problem in older boilers which are rivetted together, but it’s not unknown in modern, welded boilers.

Effects of water impurities on boiler efficiency

If the water entering a boiler is impure, then these impurities can carry over into the steam produced and this can cause a number of operational issues including:

Control Valve Contamination
If contaminants build up on the surface of the control valves, then this could reduce capacity and affect the way the valves operate.

Heat Transfer Surfaces
Contamination of heat transfer surfaces can increase thermal resistance, which in turn reduces heat transfer properties and affects how efficiently the boiler system is operating.

Steam Trap
If the steam trap openings become restricted, this can eventually lead to the plant becoming waterlogged and output can be reduced.

What causes boiler water carryover?

Boiler water carryover tends to be caused when contaminants in the feed water get into the steam system… and it is usually caused by one of two factors:

Priming
Priming happens when water gets into the steam take-off because the water levels in the boiler are either too high, or because the boiler is being run at a lower pressure than it is designed to operate at.

Foaming
As the name suggests, foaming occurs when foam forms in the space between the top of the water level and the steam take-off.
If large quantities of foam form, the problems will be more severe.
Foaming can cause water to escape from the steam connection, making it difficult to measure water levels.
Foam can also stop level floats and other water level controls from working correctly.
Alarms might go off, and the boiler may stop firing completely, requiring a manual reset.

Foaming in more detail

Foaming in steam boiler systems is a common problem… it’s therefore a good idea to take a closer look at the composition of the foam itself so we understand how to control it better.

Surface Definition
If you think about the foam on the top of a pint of beer, the boundary layer separating the foam and beer are usually very well defined.
However, that’s not the case with boiling liquids… there could be small bubbles of steam at the bottom, and many larger bubbles at the top.

Agitation
Many modern businesses now use smaller sized steam boilers, with a smaller surface area.
This results in comparatively more steam being released from the water, and more foam being created on the surface of the water.

Water Hardness
Very hard water doesn’t create foam naturally.
However, in order to prevent the formation of scale, the feed water is typically treated with a boiler water softener.
The addition of a softener reduces the hardness which then allows the water to create a foam under the right conditions.

Colloidal Material
If other substances enter into the boiler water, they can also cause foaming.
These colloidal particles are typically very small and tend not to be trapped in a normal filter.
They can include organic matter, oils, fats, greases, and suspended solids.

How to deal with foaming in industrial steam boilers

There are a number of things that operators of industrial steam boilers can do to keep foaming to a minimum.

The most important aspect is to keep the boiler running as smoothly as possible, within its original design parameters.

If you allow large or rapid changes in boiler load, this can lead to very quick drops in pressure.

This can in turn mean the water in the boiler turns into steam very quickly, and can result in excessive foaming.

If you can’t avoid large changes in load then there are other things to consider.

Boiler water level controls can be refined if on – off is the only current setting.

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You may also consider adding in extra controls which won’t allow pressure to drop below a pre-set level, or which will bring pressure up to maximum before applying a load.

There are also controls which will bring the boiler online slowly, rather than very quickly.

Using water treatment chemicals to control water quality

Another option to control the formation of foam is to use special boiler water anti-foam chemicals which will help to control foaming by breaking down or disrupting the formation of bubbles before they become an issue.

These boiler anti-foams are effective under certain situations, but not when the foam is caused by the presence of solids suspended in the water.

The importance of safety

There are clear dangers from steam boilers overheating due to scaling and excessive corrosion.

If sludge, scale and foam are allowed to build up inside a boiler system they can reach dangerous levels if left unchecked.

This can sometimes fool boiler controls into giving false readings… and this can be an extremely dangerous situation for the system and people in the immediate vivinity.

Learn more about our expert boiler operator training courses

Treating boiler water for improved efficiency and performance

It is usually best to per-treat the water feeding a steam boiler externally, i.e. before it enters the boiler system itself.

The type of boiler water treatment process will vary, depending on the system and type of water but might include the use of:

Reverse Osmosis
Reverse osmosis is a process whereby water is forced through a very fine membrane layer to remove any particles and impurities.

Lime Softening
This type of softening process involves adding calcium hydroxide to the boiler water which then reacts with any calcium and magnesium in the water to form a solid sludge.
Once removed, the water becomes less alkaline.

Ion Exchange
Ion exchange is the most common way of treating water in shell boilers, so should be considered in greater detail.

Boiler water softening using ion exchange

There are three main methods of boiler water softening using ion exchange in shell boilers that are producing saturated steam and these are:

Base Exchange Water Softening

De-Alkalisation

De-Mineralisation

The ion exchange process uses a material which doesn’t dissolve in water, and for this type of application comes in the form of little resin beads sized between 0.5mm and 1mm in diameter which are packed into a bed inside a suitable container.

The ion-exchange beads absorb water, and inside the beads are ions which hold an opposite charge.

Base-exchange water softening

This is the least complex form of ion exchange as well as being the most used.

Firstly, the bed containing the resin beads is charged with a solution of salty water, the beads then absorb the sodium ions from the salt.

The water which needs to be softened is then pumped into the resin bed.

Calcium and magnesium ions from the water are taken into the beads, to be replaced with the sodium ions, which do not form scale deposits when the water passes into the boiler.

This process does not affect the levels of solids dissolved in the water or pH levels.

All that is happening is that one type of mineral ion (calcium or magnesium) in the water is being substituted with one that is not scale forming (sodium).

This method is cost effective, and with regular maintenance can be used over a number of years to treat the water.

It also works well in areas where hard water can be a problem.

If the water is particularly hard, then sometimes lime treatment is carried out first, to reduce the load on the resin beads.

Water softening using de-alkalisation

As discussed above, the downside to the base-exchange softening technique is that it leaves levels of both pH and total dissolved solids unaffected.

You can overcome this by controlling the water alkalinity in some other way, and this is usually done using a de-alkaliser chemical.

Water softening using de-mineralisation

The idea behind the de-mineralisation process is to remove all of the salts present in the boiler water.

It involves passing the boiler water through an exchange resin.

This process takes almost all the minerals out of the water, and the resulting water is very pure.

This process is most commonly used for very high pressure boilers, typically those found in power stations.

If the water being drawn into the steam boiler system contains high levels of minerals, then it won’t take long for any ion exchange units to become clogged-up, and this can increase operating costs significantly.

Sometimes, filtering or pre-treating the boiler water using some other method is carried out prior to the de-mineralisation process.

Running a de-mineralisation plant can also be very expensive, not just to construct but also as an ongoing running cost.

Water treatment for shell boilers

Most shell boilers can cope with relatively high levels of dissolved solids in the water, and because of this, water is usually softened using a base-exchange method.

If however the feed water has high levels of dissolved solids, there are a few things you could consider as a boiler pre-treatment process:

Using lime or soda which removes the alkalinity from the water by creating solid calcium carbonate or magnesium hydroxide, which can be easily filtered out of the water.
Running the water through a de-alkalisation plant to reduce the levels of dissolved solids in the water.

Managing water quality in water tube boilers

A water tube boiler often struggle to cope with high levels of Total Dissolved Solids (TDS) in the water, especially at higher pressures, and this is typically down to:

Water tube boilers having a smaller water surface area in the steam drum. This gives higher steam release rates.
This style of tube boiler often operates at a higher capacity, so even a small amount of blowdown in percentage terms can be significant.
These boilers also operate at pressures of up to 150 bar. At these high pressures, the blowdown water contains a lot more energy.

Higher pressure also means you will be dealing with higher temperatures, and that the materials from which the boiler is constructed will be under more stress… in some cases, they may be operating at their design limits.

Any contamination affecting heat transfer from the boiler water could cause overheating.

This style of boiler also usually involves a super-heater which has its own issues.

Carryover in the water can start to coat the inside of the tubes in the super-heater, and this can have potentially serious consequences.

Ensuring good water quality is essential when optimising boiler efficiency

Taking all of this into consideration, having techniques in place to achieve and maintain good boiler water quality is essential if you are interested in operating your boiler plant safely, optimising boiler efficiency from the heat transfer processes, and achieving optimum combustion.

To achieve these objectives it might be well worth investing in a well-designed boiler water treatment plant to ensure you get the most from your boiler performance.

Expert boiler water management solutions

Usually, the default choice is the introduction of either a reverse osmosis plant or de-mineralisation plant although each installation has its merits and should be carefully selected on a case-by-case basis.

Specialist industrial boiler management solutions

Water Treatment Services offer a comprehensive range of industrial water treatment solutions for the management and steam boiler systems. Our experts can help you optimise costs and operational efficiencies, reduce downtime, achieve water and energy savings, and increase plant reliability and safety.

With offices in London serving the South and South East England, Manchester (North West), Birmingham (Midlands), Bristol (South East England and Wales), Leeds (North and North East) and Glasgow (Scotland), supported by regional teams of specially trained technicians, in-field specialists and consultants we can offer professional, cost effective boiler water treatment and engineering services throughout the UK and Internationally.