Steam Washing in boilers refers to the "washing" of the steam with fresh water or steam with condensate. The objective of steam water is to remove the impurities in steam such as silica. Silica in steam is mostly in the vapor state. Silica can deposit in the blades of turbines and affect the efficiency and the operation.
When water which is at a colder temperature than steam is sprayed on the steam, the silica condenses and gets carried away by the water.
The washing is usually carried in many stages for better efficiency.
