Types of Blowdown in Boilers

Two types of blowdown can be carried out in boilers. They are,

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.

Once the discharge rate of the blowdown and the feed rate are set, it requires no operator intervention.

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.

Posted by: Electrotechnik