transfer zones may be designed for downflow of water.
e.
The generator shall be designed for equalization of water flow
through the tube circuits. Radiant and convective heating
surfaces shall be arranged for series water flow to insure uniform
flow distribution and temperature rise. Flow shall be
proportioned to the heat input to prevent formation of steam in
any tubes or headers to the extent that flow distribution becomes
unbalanced. Distribution of flow may be controlled by limiting
the number of flow paths in parallel, or by using restrictors
(orifices), when required, in each group of parallel flow paths to
increase pressure drop and to insure that all groups have the same
pressure drop.
2.1.4.5
Spreader Stoker Units
Spreader stoker units with continuous or intermittent automatic mechanical
ash discharge grates shall have a maximum loading of 2206 kW/square meter
700,000 Btuh/square foot of grate area. The traveling grate type shall
have a maximum loading of 1,419 kW/square meter 450,000 Btuh/square foot of
grate area.
2.1.4.6
Underfeed Dumping Grate Units
Underfeed dumping grate units shall have a maximum loading per square meter
square foot of grate of 1,419 kW 450,000 Btuh, assuming a 10 percent
maximum ash content and 1200 degrees C 2200 degrees F minimum ash softening
temperature. The area shall not include side dumping areas.
2.1.4.7
Effective Radiant Heating Surface
Effective radiant heating surface is defined as the heat exchange surface
within the furnace boundaries which is directly exposed to radiant heat of
the flame on one side and to the medium being heated on the other. This
surface includes plain or finned tubes and headers and plain surfaces which
may be bare, metal covered, or metallic core covered. Refractory lined
surfaces shall not be counted. The surface shall be measured on the side
receiving heat. Computations of effective radiant heating surfaces shall
be based on the following:
a.
Bare, metal covered, or metallic core covered tubes and headers -
the projected area, external diameter times length, of the tube or
header.
b.
Extended surfaces, metal and metallic surfaces extending from the
tubes or headers - 80 percent of the flat projected area, except
metal blocks not integral with tubes or headers; extended surfaces
less than 6.4 mm 1/4 inch thick or more than 32 mm 1-1/4 inches
long; that portion of the extended surface which is more than one
tube or header radius from the tube or header from which it
extends, are not included.
c.
Furnace exit tubes - the projected area of those portions of the
first two rows of exit tubes receiving radiant heat from the fire.
2.1.4.8
Furnace Volume
Furnace volume is defined as the cubical volume between the top of the
grate and the first plane of entry into, or between, the tubes. If screen
SECTION 15555A
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