DESIGN OF OPEN-HEARTH FURNACES 287
water), therefore the pressure to be supplied from the gas main
will be
9.817-4.236 = 5kg581
0.22 in of water
The chimney draft required for removing the waste gases from
the heating chamber will be
Gas on Waste Gas
Draft required at flue junction .................
26 kg 442
Draft required for port velocity ...............................
13 kg 940
Draft in inches of water column
40 kg 382 1 60
The total draft at the base of stack or waste-heat boiler inlet will be
40.382+0.228 + 1.520 = 42 kg 130 per m2
42 mm 413 of water
1.67 in of water
The height of the chimney will be based upon the assumption
that the furnace will be workable by natural draft with the waste-
heat boiler out of service. The temperature of the waste gases
at the base of the stack will be 630° C. (1166° F.) and the volume
of the waste gases 42 m3 29 (1494 cu ft) per second at this tempera-
ture. The area of the chimney may be fixed by assuming a
desired velocity of 10 m 00 (32.7 ft) per second. A velocity head
of 5 m 10 (16.7 ft) will be required to impress this velocity upon
the gases. The area of the stack may be approximated by the
following formula: _____
Qt =
in which Q* = the volume of gases flowing per second; for the case
in hand, this is 42 m3 29;
H = the head at the base of the stack, assumed as 5 m 10;
2g = gravitational constant = 2X9.81 = 19.62;