Suspended solids entering boilers through feed water will remain behind when steam is generated. After a while the concentration of solids makes the operation of the boiler unsatisfactory
Dissolved solids and particles entering a boiler through the make-up water will remain behind when steam is generated. During operation the concentration of solids builds up and finally a concentration level is reached where operation of the boiler becomes impossible.
If solids are not purged from the boiler they can lead to
- Scale formation
Chemical treatments and continuous surface blowdowns are commonly used to eliminate solids at the same rate as they are added from make up water.
- short frequent blowdowns are more effective in removing boiler water sludge than
- a one, long, infrequent blowdown
Note that blowdown tanks are required by the Uniform Plumbing Code (UPC)1) and Uniform Mechanical Code (UMC)1) Codes on any hi-pressure installations exceeding 15 psig.
1) The International Association of Plumbing and Mechanical Officials (IAPMO) develops the Uniform Plumbing Code (UPC) which is widely adopted in western United States.
Due to high pressure and temperature in the boiler water a large amount of flash steam will be generated during blowdown. BE AWARE that the hot water and flash steam are DANGEROUS. Care must be taken during design, construction and operation.
Manual blowdowns are accomplished through tapings at the bottom of the boiler where solids settled are removed. With manual blowdowns water level control devices and cutoff devices are kept clean of any solids interfering with their operation.
All steam boilers requires manual blowdowns even if they are supplied with automatic continuous blowdown systems or not.
Automatic Continuous Blowdown
A continuous blowdown system use a calibrated valve and a blowdown tap near the boiler water surface. Water is continuously taken from the top of the boiler at a predetermined rate.