Understanding Silica and Alkalinity; ASME Consensus for Industrial Steam Production

January 12, 2022

Author; E. S. Beardwood, 2021 International Water Conference, Paper IWC-21-28, Engineers’ of Western Pennsylvania,


Silica present as an impurity in waters used for the production of steam have resulted in both water side deposition in steam generators and steam/condensate fouling within turbines. A brief review of the history of silica deposition/fouling and its control will be provided. The suggested boiler water silica limits in the new ASME booklet; “Consensus on Operating Practices for the Control of Feedwater and Boiler Water Chemistry in Modern Industrial Boilers” , and their derivation will be discussed. The elements comprising total steam purity as well as a procedure for estimating the silica contribution will be disclosed. The effects of silica volatility and prediction methods will be provided. This then allows one to determine the steam generation system operational control range set points required to meet the silica steam purity specification associated with a particular turbine and its duty. Emphasis on the methodology used to avoid silica deposits within steam generators and fouling of steam turbines will be outlined. To illustrate the process; an example calculation is provided in the paper.