Case Study: Saving Costs By Monitoring Silica In Boiler Feedwater

The high efficiency steam turbines in power plants face corrosion, erosion and depositing problems. Several factors contribute in the growing deposition problem. These problems can be minimized or controlled by keeping a close watch on the feed water quality parameters, such as pH, DO, conductivity and silica concentrations.

Although not a source of corrosion, silica can form extremely hard and dense scales in the boiler and turbines, lowering heat transfer efficiency as well as increasing the risk of mechanical failure such as turbine blade malfunction. This can result in expensive repairs or replacement of the turbine. Thus silica is an important control parameter that is monitored. Dissolved silica becomes weakly ionised, and is difficult to detect by conductivity measurement. Dedicated silica analysers are required to obtain accurate measurement. Silica in the condensate can be an indication of entrainment problems or condenser leakage.

Stamolys CA71SI is a compact photometric analysis sytem for the silicate measurement in ultrapure water and boiler feed water. By installing a Stamolys CA71 SI, the content of silicate can be determined and controlled. The standard limit for boiler feed water is 0.02 ppm silicic acid. For injection and boiler water, the standard limits are pressure dependent. For example, at an operation pressure of 986 psi, the concentration of silicic acid in boiler water must not exceed 10 ppb.