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DESIGN OF OPEN-HEARTH FURNACES

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THE DESIGN OF OPEN-HEARTH FURNACES

Design computations for an open-hearth furnace do not require
any large amount of mathematical knowledge, for the principles
involved are comparatively simple. As in all other engineering
and chemical propositions, it is necessary to effect a compromise
between a number of different requirements and co-ordinate them
in the right manner to secure a desired result. All of the different
elements of the problem are closely interrelated, and changes and
modifications at one point necessitate carrying a corresponding
modification through the entire system which it affects.

In order to establish a point of departure, it has been assumed
that a furnace having a nominal capacity of 100 tons is to be
designed, that it is to be fired with producer gas, and that the
actual hearth area will be 650 sq ft. The computations will be
limited to those required to establish the design lines. Certain
factors may bp more or less arbitrarily fixed without regard to
current practice or whether they are desirable or not, merely
for the purpose of furnishing a working base, the purpose of the
computation being to illustrate the formulas used and their
application.

The reactions in the open hearth are well known. Their main
effect, as far as the flue gases are concerned, is an increase in C02
and in the moisture content, the latter in the first part of the
heat, and the former during the boil and after the limestone is
added. The fuel consumption will vary with the furnace, the
method of working, etc. Ranging from 220 kg (485 Ib) per ton,
using molten pig, up to 350 kg (770 Ib) per ton and higher. The
fuel consumption is not uniform during each furnace cycle, from
charge to charge, but varies about as follows:

Percentage of . Cycle (Time)
	Percentage of Fuel Consumed

63.00
	76.00

17.00
	15.20

14.00
	8.40

1.00 5.00
	0.40


	

100.00
	100,00