According to Chris Paterson, managing director of Associated Energy Services (AES), specialist operations and maintenance service provider to the steam and boiler sector, poor boiler water treatment is the primary cause of poor boiler performance. He says that not all water is created equal, and that there is a lot more to water treatment than ensuring it appears clean. Unfortunately, this is where many companies are tempted to cut costs. Correctly treated boiler water is an integral part of preventive maintenance, ultimately ensuring boiler safety and operational and energy efficiency.
A drop in water standards
Poor infrastructure has reduced municipal water quality, while increased costs persuaded many companies to switch to alternative streams - such as borehole water and stored rainwater - creating a whole new set of challenges. “Each of these streams has different properties, and hardness levels and total dissolved solids (TDS) need to be considered. Borehole water should be analysed, and the iron and silica content monitored. Water from alternative sources used in boilers should be thoroughly tested periodically, checking the variability of contaminants, and if need be, appropriate treatment equipment and technology can be designed and installed,” says operations director, Ray Lund.
According to Lund, the quality of water going into a boiler has two direct impacts: first on its life expectancy, and secondly, on its heat transfer capacity and efficiency. “Corrosive water damages internal boiler surfaces,” he explains. “It can cause pitting of the surface material. This often results in boilers having to be downgraded to operate at lower pressures because the material has been compromised or even scrapped.”
Clarifying boiler water treatment
Lund explains that calcium and magnesium form a hard scale which adheres to surfaces. This limits the transfer of heat from the fire side of the boiler to the water side, making it inefficient when it comes to the production of steam. Paterson warns: “Poor water treatment damages boilers over long periods. Water treatment needs to be done correctly and consistently, every single day.”
At the beginning of the process, solids are removed via different forms of filtration. Plants with very high TDS might require the installation of a reverse osmosis plant, which can be a very effective energy saver as it requires fewer blowdowns of the boiler to clean it out. “Typically with municipal water supply the TDS is low, so we proceed directly to a softener. There are some areas in the country where the water is very hard. We look at various technologies to identify the most cost-effective way in which to manage this over the long term,” says Lund.
pH control is crucial, and should remain within the right parameters to facilitate the formation of a protective layer on the internal surfaces of the boiler. It is vital to remove as much oxygen as possible before water enters a boiler as it prevents oxygen pitting, which increase the risk of equipment failures.
One significant issue stemming from inadequate water treatment is foaming, which leads to liquids being carried from the boiler instead of just hot gas into the steam piping network. This can result in water hammer—an effect where pockets of water move at the same velocity as the heated gas. When these pockets reach pipe bends, they can cause serious damage. Furthermore, foaming can interfere with the accurate measurement of water levels. This means there could be little or no water in the boiler, even when indicators suggest otherwise, leading to overheating or even a potential explosion.
The last resort: tipping the ‘scales’
According to Lund, when scale has built up to the point where the equipment is at risk and efficiencies are compromised, clients have two options: using an online descalant or using a difficult and expensive offline acid wash, which essentially ‘pickles’ the boiler.
It can take up to four days to acid wash a boiler and the cost of the chemicals, as well as neutralising and disposing of the resulting acid effluent, can have a very negative financial impact. Boilers requiring repairs after this acid wash process will further add to the overall cost.
“Years of poor boiler water treatment can really add up, with negative operational and financial consequences. With our performance guarantee to clients in mind, we do as much as we can to ensure that all AES clients are aware of potential water quality concerns and the related risks, allowing for timeous preventive action to be taken if required,” Paterson concludes.
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