What is the impact of silica in boiler feedwater, and what treatment processes are used to remove it?

Silica in boiler feedwater can have a significant negative impact on boiler system performance and reliability. Silica tends to form hard, insulating scales on boiler tubes and turbine blades, reducing heat transfer efficiency and potentially causing overheating and tube failures. Silica scale is particularly problematic because it is difficult to remove chemically. In turbines, silica deposits can reduce turbine efficiency and capacity. The solubility of silica increases with temperature and pressure, so it can vaporize in the boiler and then deposit on cooler turbine surfaces. Several treatment processes are used to remove silica from boiler feedwater. One common method is ion exchange, where the water is passed through resin beds that selectively remove silica ions. Strong base anion exchange resins are typically used for silica removal. Another effective method is reverse osmosis (RO), which uses a semi-permeable membrane to filter out silica along with other dissolved solids. RO is particularly effective for removing colloidal silica, which is difficult to remove with ion exchange alone. Coagulation and filtration can also be used as a pretreatment step to remove suspended solids and some colloidal silica before ion exchange or RO. In this process, chemicals are added to the water to cause small particles to clump together, forming larger particles that can be easily filtered out. Regular monitoring of silica levels in the boiler feedwater and condensate is crucial to ensure that the treatment processes are functioning effectively and to prevent silica-related problems.