DRAFT BOILER/FEEDWATER GUIDELINES - The National Board of ...

3.5 Solids
3.4.2.2 Soft scale is usually found in hot water heating boilers and system.
In has the appearance of thick, black or brown sludge and forms in the
boiler tubes, on the boiler shell and throughout the heating system.
3.4.3 Scale can be removed by mechanical or chemical means. The boiler
manufacturer’s recommendations should be followed when removing scale from a
boiler.
3.5.1 Solids cause many problems throughout the entire boiler system. External
pretreatment include; filtering, softening, and dealkalizing. Those solids which
remain after external pretreatment can be treated internally with a variety of
treatment chemicals.
3.5.2 At least two conditions should be controlled with internal treatment. First,
the boiler water should be maintained at pH 11; this may require an addition of
alkali if the water is not soft. Secondly, a chemical called a sludge conditioner
can be added to treat the solids so that they drop out (precipitate). Finally, these
treated solids then must be removed from the boiler by blowdown.
3.5.3 Dissolved solids in the water are soluble and cannot be seen; dissolved
solids are measured with a conductivity meter in micromhos/cm (µmhos/cm) or
measured in Total Dissolved Solids (TDS) in ppm. The boiler manufacturer’s
recommendation for the specific conductance or TDS should be followed.
3.5.3.1 The following are examples of TDS in water:
Lake water has approximately 180 ppm of dissolved solids;
1,000,000 pounds of this water will contain approximately 180
pounds of solids; a 100 hp boiler vaporizing 3,450 pounds of this
as make-up water would leave behind 0.62 pounds of solids.
Well water can have as high as 1,250 ppm of dissolved solids;
1,000,000 pounds of this water will have 1,250 pounds of solids; a
100 hp boiler vaporizing 3,450 pounds of this as make-up water
could leave 4.3 pounds of solids behind.
3.5.4 Suspended solids are insoluble and are measured in Total Suspended Solids
(TSS). Suspended solids refer to small solid particles which remain in suspension in the
boiler water.
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