Figure 4-4.—Generating tubes and furnace area.
Figure 4-5.—Natural circulation (accelerated type).
nine times the volume. The smaller the diameter
of the tube, the higher is the ratio of absorption
surface to the volume of water.
times the surface area of a 1-inch tube but
shown are almost vertical. The greater the incline,
the greater the acceleration.
Normally, only one row of tubes leads
from the steam drum to the sidewall header.
These are the sidewall (water wall) tubes. Their
function is to cool and protect the side wall of
the furnace.
So far, we have assembled the drums, header,
downcomers, and generating tubes. Before going
any further with the assembly, let us trace the path
of the water through the boiler.
As the water is heated, it becomes less dense,
and steam is formed in the tubes. The water in
the steam drum is much cooler than the steam and
has greater density. As the hotter water and steam
rise through the generating tubes, the cooler more
dense water drops through the downcomers to the
water drum and headers. The arrows in figure 4-5
show the circulation path of the water as it leaves
the steam drum and returns to the steam drum
as steam. Notice that the caption under figure 4-5
states that it is an accelerated type. This is
indicated by the inclination of the tubes. The tubes
So far, we have learned how the steam is
formed in a boiler. Next, let’s find out what
happens to the steam once it returns to the steam
drum from the generating tubes.
INTERNAL FITTINGS
Components of the steam drum area are
known as INTERNAL FITTINGS. The internal
fittings we will discuss are the feedwater
distribution, the chemical injection, and the steam
and water separator. This equipment is used to
direct the flow of steam and water within the
steam drum and the desuperheaters, which are
located either in the steam drum or the water
drum. We will also discuss the economize in this
section. This component is not considered an
internal fitting, but its role is important to the
function of the steam drum.
The design
drum’s internal
and arrangement of a steam
fittings will vary somewhat from
4-7
