Page 20 - Boiler plant and distribution system optimization manual

Boiler Plant Orientation 5

Because the smaller boiler tubes in the water gins. As this occurs there is a condition where tube
tube design can be bent rather easily, numerous metal temperatures begin to peak, approaching
boiler designs have evolved. These designs have their highest operating temperature. Although de-
been named according to the letter of the alphabet signers and manufacturers have compensated for
they resemble. For example there is the “A” type this phenomena in their designs, it is useful to un-
[Figure 1.5] with one larger upper steam drum derstand this condition with regard to boiler tube
and two lower drums or headers resembling the
letter A. The “D” [Figure 1.6] and “0” [Figure 1.7]
types are other examples this convention for clas-
sifying water tube designs.
Early boiler designs utilized a large percent-
age of brickwork in the combustion zone to aid
stable combustion by reflecting energy back into
the wood, coal and oil fires from glowing brick-
work. Modern boiler designs have very little
brickwork by comparison, usually only around
the burner throat in wall fired utility and large in-
dustrial units.
The nomenclature for water tube boiler de-
sign is quite simple. Like a house they have floor
tubes, wall tubes (front, side and back) and roof
tubes.
Figure 1.8 illustrates factors concerning boil-
ing in a typical boiler tube. At low heat flux levels,
small bubbles are formed referred to as nucleate
boiling. As the heat flux Increases more of the tube
is occupied by steam bubbles until film boiling be-
Figure 1.6—A “D” type boiler.

Figure 1.5—An “A” Type boiler. Figure 1.7—An “O” type boiler.