Two Methods of Boiler Blowdown

In previous posts on this site we have discussed blowdown and how to properly blowdown your boiler.  Did you know that there are different kinds of boiler blowdown?  In this series of posts we will explain each and why they are both important.

During the process of generating steam, suspended solids and dissolved solids build up in the boiler water of steam boilers.  Removing these contaminants by “bottom blowing” and “surface blowing” boilers is necessary to prevent deposition of suspended solids on heat transfer surfaces and to prevent boiler water carryover issues due to high dissolved solids.

Why are two different methods of boiler blowdown necessary? Bottom blowdown is used to remove suspended solids such as those formed by calcium and magnesium salts, iron, copper, phosphorus and silica.  Surface blowdown or surface 'skimming' is used to remove dissolved solids such as sodium, potassium, chloride and soluble calcium, magnesium, phosphate and silica that concentrate up in the boiler water as steam is generated.

Stay tuned as we examine these two methods of boiler blowdown in the next several blogs.