750-211 (revised 2009)
Promethean Boilers, Model 4WI Manual
3-11
3.7 — Blowdown: Steam Boiler
Brooks authorized representative. In extreme cases, it may be necessary to resort to acid cleaning. Professional
advice is recommended if acid cleaning is required.
The inspections will indicate the effectiveness of the feedwater treatment. The effectiveness of treatment, the water
conditions, and the amount of fresh water make-up required are all factors to be considered in establishing fre-
quency of future pressure vessel washouts. Contact your local Cleaver-Brooks authorized representative for more
information.
3.7 — Blowdown: Steam Boiler
Boiler water blowdown is the removal of some of the concentrated water from the pressure vessel and its replace-
ment with feedwater so that the lowering of concentration of dissolved solids in the boiler water occurs.
Dissolved solids are brought in by the feedwater even though the water may be treated prior to use through exter-
nal processes that are designed to remove unwanted substances which contribute to scale and deposit formations.
However, none of the processes can remove all substances. Regardless of their efficiency, some dissolved solids will
be present in the boiler feedwater.
Dissolved solids become less soluble in the high temperature of the boiler water and tend to accumulate on heating
surfaces. Therefore blowdown and internal chemical treatment are required to prevent the solids from forming
harmful scale and sludge.
Scale has a low heat transfer value and acts as an insulation barrier. Scale retards heat transfer, which not only
results in lower operating efficiency, and consequently higher fuel consumption, but equally important, can cause
overheating of boiler metal. Overheating of boiler metal can result in tube failures or other pressure vessel metal
damage and lead to boiler downtime and costly repairs.
Scale is caused primarily by calcium and magnesium salts, silica and oil. Any calcium and magnesium salts in the
boiler water are generally precipitated by the use of sodium phosphate, along with organic materials, to maintain the
precipitates or “sludge” in a fluid form. The solids such as sodium salts and suspended dirt do not readily form
scale. But as the boiler water boils off as relatively pure steam, the remaining water is thickened with the solids. If
the concentration is permitted to accumulate, the sludge will build possibly causing overheating of the metal.
Therefore, we must control the amounts of totally dissolved solids (TDS) and sludge and so so in the following
ways.
3.7.1 — Types of Blowdown
The two principal types of blowdown are intermittent manual blowdown and continuous blowdown.
3.7.1.1 — Intermittent Manual Bottom Blowdown
Manual or sludge blowdown is necessary for the operation of the boiler regardless of whether or not continuous
TDS blowdown is employed.
The blowdown tappings are located at the bottom or lowest part of the boiler in order to rid the sludge in the lower
part of the vessel.
Summary of Contents for 4WI
Page 46: ...Burner Operation and Control 2 22 750 211 revised 2009 Promethean Boilers Model 4WI Manual...
Page 62: ...Waterside Care and Requirements 3 16 750 211 revised 2009 Promethean Boilers Model 4WI Manual...
Page 70: ...Sequence of Operation 4 8 750 211 revised 2009 Promethean Boilers Model 4WI Manual...
Page 114: ...Adjustment Procedures 6 28 750 211 revised 2009 Promethean Boilers Model 4WI Manual...
