Continuous Blowdown - Continued

The solids content of boiler water is measured in terms of Total Dissolved Solids (TDS). A common unit for TDS is “parts per million.” To get an idea about the dissolved solids, you can take a sample of boiler water and boil it off in a crucible. After the water boils off, solids will be left behind as residue. At this time you will be able to weigh the residue and calculate the value for TDS. You must have realized that it is very cumbersome process. In the industry we use a far simpler method to measure the TDS.

Presence of dissolved solids increases the electrical conductivity of the boiler water. There is a direct relationship between these two terms: TDS and conductivity. Conductivity, on the other hand is very easy to measure by using simple conductivity probes. Therefore, in the industry we measure conductivity to get an idea about the boiler water TDS.

The common unit for measurement of conductivity is micro-mhos.

To maintain the TDS within acceptable limits, we continuously discharge a small portion of the boiler water to sewer. The lost water is made up by the feedwater which has very low concentration of solids.