Water Conditioning

Steam boilers are used in industrial areas, residences, and workplaces for heating, sterilization, obtaining hot water, and pressure. Supplying water obtained from the mains directly to the steam boiler can lead to various problems, primarily corrosion and scaling. The operating efficiency of a boiler, the purity of the steam it produces, and the life of the boiler are directly proportional to the purity of the water put into it rather than its manufacturing quality. Therefore, boiler feed water is of great importance.

Why is Water Conditioning Necessary? Encountered Problems

High levels of calcium and magnesium in the boiler feed water cause scaling on the inner surface of the boiler and in the pipes over time. This thickening scale layer reduces heat conduction, the heat given to the boiler goes to nature through the chimney, and the boiler efficiency drops significantly. In addition, since heat conduction is reduced, the temperature of the boiler plates rises, decreasing the life of the metal and therefore the life of the boiler.

Corrosion is caused by oxygen and carbon dioxide in the water. High levels of "HCO3" (bicarbonate) ions in the feed water cause carbon dioxide (CO2) gas formation inside the boiler; this gas dissolves in the condensate, forming carbonic acid (H2CO3). This lowers the pH of the condensate water, causing corrosion and frequent puncturing in the condensate pipes. Furthermore, foaming in the boiler causes minerals to pass into the steam line, deteriorating the purity of the steam and damaging the processes. To reduce these problems, hot water blowdown is performed, but this causes heat loss and significantly reduces the operating efficiency of the boiler.

Boiler Feed Water and Boiler Water Quality Standards

Even if a boiler is fed with very high-quality water, the water quality inside the boiler does not remain the same because the evaporating water is pure, and the minerals entering with the feed water do not evaporate. As a result, mineral concentrations increase, raising the conductivity of the boiler water. Therefore, the boiler water must be treated with "chemicals" and concentration values must be kept under control by blowdowns. The required properties for steam boilers with an operating pressure of up to 20 bar are as follows:

Desired Quality for Feed Water (Up to 20 Bar)

• Conductivity: Low.
• Total Hardness: Less than 0.1 °Fr.
• Oil amount: Less than 2 mg/l.
• Oxygen: Less than 0.05 mg/l.
• Total Iron: Less than 0.05 mg/l.
• Chloride: As low as possible.
• Total Carbon dioxide: Less than 20 mg/l.
• pH Value: Between 7.0 - 9.5.
• Suspended Solids: As low as possible.

Permissible Practical Values for Boiler Water (Blowdown Water)

• Total Hardness: 0.0 °Fr.
• Conductivity: Maximum 6000 microsiemens/cm.
• pH: 9.5 - 11.5.
• Alkalinity: Maximum 700 mg/l.
• Silicate: Maximum 125 mg/l.
• Total Iron (Fe): 10 mg/l.
• Chloride: As low as possible.
• Dissolved Oxygen: 0 mg/l.
• Suspended Solids: 300 mg/l.

Water Conditioning and Chemical Controls (EN 12953-10 Standards)

The supply of feed water and boiler water must comply with the EN 12953-10 standards. Conditioning is necessary to minimize corrosion by optimizing the pH value, to stabilize hardness to prevent scaling, and to promote the formation of protective oxide layers. For this purpose, inorganic maintenance agents like sodium and potassium hydroxide, sodium phosphate, sodium sulfite, and hydrazine, as well as organic-based agents, can be used.

Note: Hydroxide and bicarbonate do not exist together. P= Phenolphthalein Alkalinity, M= Methyl Orange Alkalinity.