As we discussed in the blog, learning how to control dissolved solids in your boiler system by surface blowdown can save time and money. Today we will look at how a typical surface blowdown system works.
Surface blowdown systems typically consist of a pipe entering the upper section of the boiler approximately 6 inches below the boiler water surface. This may be in a steam drum in a water tube boiler or the upper steaming portion of a firetube boiler. This pipe needs to remain below the water level at all times when the boiler is operating. The flow of boiler water from the "skimmer" pipe is controlled using a special pressure rated "needle" valve or flow throttling valve designed for this purpose. Some of these "skimmer" valves have built in micrometers so that the valve setting can be monitored and adjusted precisely. Operators simply adjust this valve to maintain the recommended boiler water dissolved solids level. This may be an adequate method of controlling dissolved solids in a boiler that is operated at a steady load. However, because most boilers operate with a fluctuating steam load, controlling dissolved solids with a needle valve becomes impractical because of the frequent adjustments that are needed. In these situations, automatic blowdown controllers are recommended. We will cover the advantages of using these controllers in next week's blog which will end our series on Boiler Blowdown.