Intermittent blowdown
Intermittent blowdown, as the name suggests, is the blowdown performed at frequent intervals. The general rule is to do the blowdown for 2 minutes in 8 hours.
This method requires increases in the feedwater input to the boiler. Feedpumps of large size may be required for this method.
With each blowdown, a significant amount of energy is lost.
Continuous blowdown
Continuous blowdown involves a steady discharge of concentrated boiler water and its replacement by a constant input of feed water. TDS and steam purity are maintained at a given load.

The heat lost during continuous blowdown can be recovered by blowing it into a flash tank and generating flash steam.
The blowdown which leaves the flash tank will still have heat which can be recovered. This is done by using a heat exchanger to heat the make-up water.
Package blowdown heat recovery systems which can be customized are available.
Benefits of blowdown control
The benefits of blowdown control are
- Reduced cost of pretreatment.
- The quantity of makeup water required is less.
- The maintenance downtime is less.
- The boiler life is increased.
- The amount of chemicals to treat the water is less.