WHY PROVIDE IBD IN BOILER.Intermittent blowdown is taken from the bottom of the steam drum and is used to keep it sludge-free during operation. Continuous Blow Down (CBD) removes suspended salts , where as Intermittent Blow Down (IBD) removes dissolved salts.
The highest concentration of contaminates and suspended salts are at the surface that is a phenomenon of boiling anything (think of the scum that forms in a pot when boiling potatoes). This must be removed to prevent carrying over into the superheater (if it is equipped with one) or the header.
We had an issue with our superheater tubes plugging and rupturing every 6 months... we tried everything... couldn't figure out why. Turned out the Boilermakers had added a double elbow on the CBD line so they could swing it out of their way when they entered the boiler rather that having to remove it. They forgot to swing it back when the exited... the CBD line was drawing from the bottom of the drum, It should be located about ~2" below the surface. Remember the CBD line is also normally where the boiler water is sampled for TDS you want to sample near the surface where the TDS is at its highest.
30 окт 2024
