Special Consideration for Silica in High Pressure Boilers

Silica is an impurity commonly found in water and it requires special consideration in case of very high pressure boilers. Silica (SiO2) is present in natural water sources such as rivers, lakes, and groundwater. It is also introduced into the water through treatment processes such as reverse osmosis and ion exchange. While silica is generally harmless in low-pressure boilers, it can cause significant issues in high-pressure boilers.

1. Formation of Silica Scale
When water is heated in high-pressure boilers, the solubility of silica decreases, leading to the formation of silica scale. This scale can deposit on the internal surfaces of the boiler, including the heat transfer surfaces and tubes. The accumulation of silica scale reduces heat transfer efficiency, increases fuel consumption, and can ultimately lead to overheating and failure of the boiler.

2. Corrosion
Silica scale can also lead to localized corrosion in high-pressure boilers. The accumulation of silica on the metal surfaces creates an uneven surface, promoting the formation of localized corrosion cells. This can result in pitting corrosion, stress corrosion cracking, and other forms of corrosion, which can weaken the boiler components and compromise their integrity.

3. Foaming and Carryover
Another issue associated with high levels of silica in water is foaming and carryover. Silica can contribute to the formation of foam in the boiler water, which can lead to carryover of water droplets into the steam. This carryover can cause damage to downstream equipment, such as turbines and steam lines, and reduce the overall efficiency of the system.

4. Prevention and Treatment
To prevent the problems associated with silica in high-pressure boilers, special consideration needs to be given to its control. This can be achieved through various methods, including:

- Pretreatment of water: Implementing proper water treatment processes such as coagulation, sedimentation, filtration, and ion exchange can help remove silica from the water before it enters the boiler.
- Blowdown: Regular and controlled blowdown of the boiler helps to remove the concentrated silica and other impurities from the boiler water, preventing their buildup.
- Monitoring and testing: Regular monitoring and testing of the silica levels in the boiler water can help identify any deviations from the acceptable limits and allow for appropriate corrective actions to be taken.
- pH adjustment: Maintaining the proper pH level in the boiler water can also help control silica solubility and prevent its deposition as scale.

In conclusion, silica impurities in water require special consideration in high-pressure boilers due to the potential for scale formation, corrosion, foaming, and carryover. Proper pretreatment, blowdown, monitoring, and pH adjustment are essential to prevent these issues and ensure the efficient and safe operation of high-pressure boilers.