Collided Silica Effect on Boiler Water Treatment

Abstract

Silica contamination in boiler water systems is a persistent challenge that affects operational reliability, heat transfer efficiency, and overall plant performance. Collided silica—finely dispersed, weakly ionized, and often colloidal in nature—poses unique difficulties because conventional ion-exchange and precipitation techniques fail to remove it effectively. This paper explores the behaviour of collided silica in high-pressure boiler systems, its mechanisms of deposition, analytical challenges, and treatment strategies. In-depth discussion is provided on the physicochemical characteristics of collided silica, its tendency to pass through filtration systems, and its role in turbine blade scaling. The paper concludes with recommended monitoring methods and integrated treatment solutions suitable for modern industrial boilers.

Introduction

Silica exists in water in reactive and colloidal (collided) forms, with colloidal silica being the most problematic for high-pressure boilers due to its extremely fine size (1–100 nm), non-ionic nature, and stability. It can bypass standard filtration, volatilize with steam, and deposit in superheater tubes and turbines, causing scaling, reduced heat transfer, turbine efficiency loss, and increased maintenance.

Measurement Challenges: Standard silica tests detect mainly reactive silica, underestimating colloidal content. Accurate detection requires high-temperature digestion, ultrafiltration, coagulation, or specialized analysers.

Treatment Methods: Effective removal strategies include:

• Coagulation/flocculation to agglomerate silica for filtration

• Ultrafiltration (UF) + Reverse Osmosis (RO) for high-purity feedwater

• Lime softening for moderate-pressure systems

• Internal chemical treatments (dispersants, phosphates) to prevent deposition
  Ion exchange alone is largely ineffective against colloidal silica.

Monitoring and Control: Best practices include continuous silica monitoring, high-temperature digestion tests, UF-RO pretreatment, maintaining feedwater pH, controlled boiler loads, and optimized blowdown to reduce scaling and ensure reliable boiler operation.

Conclusion

Collided silica is one of the most challenging contaminants in boiler water treatment due to its small particle size, non-ionic nature, and ability to bypass conventional removal methods. Its presence contributes significantly to boiler tube scaling and turbine deposits, directly affecting plant efficiency and operational reliability. Effective control requires a combination of advanced monitoring, membrane-based separation, coagulation, and proper chemical conditioning. Understanding the behaviour and treatment of collided silica is therefore essential for maintaining high-purity steam and ensuring sustainable boiler performance.

References

[1] Betz Handbook of Industrial Water Conditioning, Eighth Edition, George E. Bonilla, Betz Laboratories. [2] Boiler Water Treatment Principles and Practice, Colin Frayne, Chemical Publishing Co. [3] Water Treatment for Industrial and Power Applications, N. Manivasakam, Chemical Publishing House. [4] Steam: Its Generation and Use, Babcock & Wilcox Company, 42nd Edition.

Copyright

Copyright © 2026 Deepak Shankhdhar. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.