The Flow Of Gases In Furnaces

46 APPLICATION OF THE LAWS OF HYDRAULICS

the heat released, therefore, serves to heat the ingots and to
maintain the hot gases at a high temperature. If the flames, that
is to say, the mixture of combustible gases and air, in which the
reaction is taking place, impinge against the cold ingots, a deposit
of soot will be formed, and carbon, carbon monoxide and hydrogen
will pass off unburned through the waste gas port. It is evident
that such a method is not advantageous, as it is necessary for
combustion to occur in the heating chamber in order that the heat
may be utilized. From this effect it is evident that the flaming
gases should not be cooled while the reaction of combustion is
taking place or until it has been completed. On the contrary,
if the reactions of combustion are very nearly completed, the hot
gases produced may be cooled very rapidly.

The Lyswa furnace has a large firebox, allowing the producer
gas to mix perfectly with the secondary air. On the other hand,
1 0 | in the " N " furnace there is a very small firebox with very poor

| I mixing of the producer gas and the secondary air. The flaming

; ' gases from this firebox are forced directly down upon the ingots

I ; without any precautions; the production of soot is inevitable.

If It is for this reason that these gases sweep along under the roof,

I f' from the strangulation which is located immediately over the

bridge wall, to obtain a better mixture; and from this point on the
velocity of the gases is increased, thus diminishing the thickness
of the layer of gases below the arch. As a result of these condi-
tions, the furnace works very poorly.(1)

A furnace at the Zavertse works, where the height from the
hearth to the roof is only 350 mm, will serve as an example of a
continuous reheating furnace with a very low roof. This furnace
gives off enormous quantities of smoke when coal is placed in the
firebox. There is no flame in the heating chamber and the heat
there is not sufficient to ignite the gaseous products which are
given off in great volume by the fresh charge of coal as it is distilled
on the fire.

Continuous reheating furnaces, therefore, will not work well
with low roofs; on the other hand, the fuel consumption increases
very rapidly as the roof is raised. From Yesmann's formula it
can be deduced that

(1) The formation of soot by the cooling down of the flaming gases is partic-
I ularly noticeable in open-hearth furnaces working with a charge of cold pig.