Water treatment techniques to control scale in boilers
Scale formation on the internal surfaces of boilers and steam systems is a significant issue. If left untreated scale can build-up on the internal surfaces of pipework, boiler tubes and other heat transfer surfaces to act as an insulator and reduce boiler efficiencies significantly. It can also cause the boiler and pipework to overheat, and in extreme circumstances catastrophic failure can result.
Boiler scaling occurs when high temperatures reduce the solubility of calcium and magnesium salts commonly found in the feed water allowing them to precipitate out and on to internal surfaces.
To control boiler scale formation it is therefore important to pre-treat the feed water, removing as effectively as possible any hardness salts before they enter the boiler system. This can be achieved using a commercial water softener and specialist chemical scale inhibitors. Reverse osmosis (RO) equipment can also be considered for the pre-treatment of the boiler feed water.
To ensure the steam system is kept under full control at all times the quality of the boiler water should also be tested regularly to ensure the boiler water treatment programme is operating effectively and the correct water conditions are being maintained.
Corrosion control for steam boilers
The internal environments found within boilers and steam systems be extremely aggressive to the materials of construction and can cause a number of serious problems.
Corrosion is one such problem and if left untreated it can increase costs, reduce asset reliability and life-expectancy, and in the worst cases it can cause catastrophic failure.
The primary causes of corrosion in boiler systems are dissolved oxygen, acidity and excess alkalinity. The most common of these being oxygen associated corrosion which is caused by oxygen dissolved in the feed water entering the boiler system.
The oxygen contained in the water acts aggressively to create localised corrosion of the internal surfaces in the form of oxygen pitting. These corrosion pits are generally small but can sometimes grow, resulting in deep pinholes or pitting which if left to penetrate boiler tubes and other internal surfaces can affect their integrity and result in failure.
Effective boiler water treatment should be holistic in its approach and focus on the removal of dissolved oxygen from the feed water, whilst controlling both pH and alkalinity levels. This can be achieved through good system design, particularly feed-tank and condensate return arrangements) and the use of high performance boiler treatment technologies.
Boiler treatment and steam condensate corrosion
Managing condensate water quality in your steam generating system is important as if left untreated it can cause a number of serious issues including acid and oxygen corrosion. This can lead to the failure of the condensate return lines and other system components.
Problems arise in the condensate system when steam condenses. As it does so it absorbs carbon dioxide and oxygen from the atmosphere to create corrosive water conditions which can be detrimental to the boiler system, but particularly the condensate return lines, threaded joints and elbow components.
Oxygen corrosion acts aggressively on the internal condensate line surfaces to create localised pitting and potentially deeper pinholes. Pitting and pinholing can be controlled using boiler treatment chemicals such as oxygen scavengers including tannin, sulphite or DEHA.
The formation of carbonic acid in the system will lead to general corrosion throughout the boiler system and can be controlled using specialist steam volatile boiler treatment chemicals including film forming and neutralising amines, or by pre-treatment of the boiler water using reverse osmosis or de-alkalisation techniques.
Boiler blowdown
Boiler blowdown is an important component in the successful management of any steam generating system as it helps to remove accumulated sludge from the boiler, control levels of both suspended and total dissolved solids (TDS) and so maintain boiler efficiencies and overall steam purity.
It is also important to remember that boiler blowdown, while important should only be performed when required as it can be very energy inefficient.
Sludge deposition
The formation of boiler sludge occurs as the concentration of suspended solids, primarily from corrosion by-products and the deposition of solid hardness salts, increases in the system. If left unchecked the build-up of sludge can reduce heat transfer efficiencies and overall boiler performance.
Total dissolved solids (TDS)
As steam is generated in a boiler system water naturally evaporates and is lost to the atmosphere. As this occurs the concentration of Total Dissolved Solids in the remaining boiler water increases and can cause a number of problems including carryover and foaming.
Carryover (see below) can cause steam contamination issues whilst foaming can reduce the heat transfer efficiency of boiler tubes and lead to overheating and premature failure.
To prevent carryover and unwanted foaming it is therefore important to control TDS levels in the boiler water. This can be achieved by blowdown and the introduction of fresh, suitably pre-treated feed water.
Boiler water carryover
Carryover occurs when boiler water in its liquid form is “carried over” in to the gaseous steam. This can cause solids contamination of the steam and any process products it comes in to contact with. It can also result in damage to the boiler, steam system and other process equipment.
To prevent carryover and unwanted foaming it is therefore important to control the levels of contaminants in the boiler water (total dissolved solids). This can be achieved by blowdown and the introduction of pre-treated feed water.
Boiler water treatment training
The industrial and process water treatment specialists at Water Treatment Services have developed an extensive series of professional water and wastewater treatment training courses that includes WTS 0040 “Boiler Water Treatment & Steam Generation”.
This specialist boiler treatment training course comprises an intensive one day course designed for boiler plant operators, plant managers, maintenance and engineering contractors, water treatment specialists and those with responsibility for the operation and on-going maintenance of commercial and industrial boilers and steam generating plant… training courses →
Expert boiler water treatment services & technical support
Contact Water Treatment Services today to discuss your steam boiler requirements. We can provide expert advice and support regarding the maintenance, management and treatment of commercial and industrial boilers and steam generating systems to help you optimise costs and operational efficiencies, reduce downtime, achieve water and energy savings, maintain steam quality, 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 engineers, in-field specialists and technical experts we can offer reliable, cost effective boiler water treatment and engineering services throughout the UK and Ireland.
Contact us today for more information about our industry leading boiler solutions and how they can help you.
