Silica in Boiler Water

Ordinary Silica is insoluble in water.  But when silica combines with other materials such as lime and soda, it can form scales which are very difficult to remove.  Soda and lime are used in softening units. 

Use of silica based lubricants in the thermal plant as well can also result in silica entering the boiler water.  Another source is the presence of unreacted silicon in the feed water. 

If silica is not removed in time, it forms deposits in the turbine nozzles and change the direction of the steam.  The velocities and pressure drops are changed inside the turbine resulting in reduced efficiency.  Uneven nozzle flow can result in torsional vibration due to uneven loading of the blades.  This can result in vibrations. 

Silica deposits in the boiler are difficult to remove.  They equipment has to be dismantled and physically cleaned.  Blasting aluminium oxide on the surface is also a method used in the removal of silica deposits.