NB-27: A Guide for Blowoff or Blowdown Vessels

Guide to Blowoff Vessels

The treatment of boiler feedwater is an integral part of boiler operation, used to control scaling, corrosion, and deposits. Boiler feedwater treatment often leads to the formation of solid particles that are initially suspended in the boiler water. Solids concentrated in boiler water tend to promote foaming and scaling with a resultant loss of heat transfer which may result in overheating of the boiler tubes. Solids also may settle to the bottom of the boiler to form sludge. “Blowing off” part of the boiler water is a means of removing solids from the water while controlling boiler water levels. (It is common for the terms “blowdown” and “blowoff” to be used interchangeably.)

The primary function of the blowoff system is to provide a safe means of controlling boiler blowoff water. This includes reduction in both pressure and temperature to limits acceptable for safe discharge into a sewer, drain system, or other area. The usual practice, therefore, is to discharge the water into a vented vessel where it may be allowed to cool, or mixed with cold water to reduce the temperature and pressure to acceptable discharge levels.

The National Board of Boiler and Pressure Vessel Inspectors issued this Guide for Blowoff Vessels. The publication is intended to provide design information and guidance for boiler blowoff systems.

It does not address details for all possible arrangements of boiler blowoff equipment. If the design of boiler blowoff equipment is not covered in this publication, guidance should be obtained from both a competent engineering firm and the inspection authority of the jurisdiction in which the equipment is to be installed.

If you have further questions, contact the team at Campbell-Sevey




NB-27: A Guide for Blowoff or Blowdown Vessels