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Full text of "The Flow Of Gases In Furnaces"

DESIGN OF HOT-BLAST STOVES                       303

Mm. of
Water

Column

Upward pressure in combustion chamber........................ +26.20

Upward pressure in checkerwork............................... -f 24.60

Difference or positive pressure acting at chimney valve............  -f- 1.60

Draft depression at chimney valve..............................   38.00

Draft depression at chimney valve due to stack will therefore be. . .   36.40
Upward pressure in checker....................................   -f-24.60

Draft depression in dome of stove due to chimney................   11.80

Upward pressure in combustion chamber........................  +26.20

Making a draft depression at the burner available to draw in the air
required for combustion.....................................    38.00

Professor Groume-Grjimailo has suggested that combustion
conditions in the two-pass Cowper stove may be improved by
springing an arch across the chamber with an opening proportioned
to retard the flow of the gases to such an extent that combustion
occurs in the chamber. The location of the arch will be fixed
by the amount of gas burned and the time required for combustion.
Two seconds may be allowed for combustion, which will be very
rapid under incandescent chamber conditions, with good mixing.
The size of the chamber and the port may be arrived at as follows:

Chamber volume = 25.67 X 2 = 51 m3 34,
Height of chamber = 51.34 -r- 3.79 = 13 m 60.

It is necessary to provide an opening in the arch over the top of
the combustion chamber which will permit the waste gases to
escape and yet restrict their flow sufficiently to supply time for
the completion of combustion. The area of this opening may be
determined by the use of Yesmann's formula, as follows:

in which Q = the quantity of gas flowing, in cubic meters per
second; for the case in hand, Qi2oo= 25 m3 67;
H=the head at the orifice or the vertical distance from
the orifice to the lower free surface of the gases;
for the case in hand 77 = 13 m 60;
2g = gravitational constant = 2 X9.81 = 19.62;