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Full text of "The Flow Of Gases In Furnaces"

APPLICATION  OF THE LAWS OF  HYDROSTATICS         21
Boetius and Bichcrou have utilized this method of firing in a
furnace invented by them and bearing their names.
When many of the various existing types of furnaces, such as
the continuous furnaces, Siemens furnaces, brick kilns, etc., an;
analyzed, it will be noted that their construction is such as to
preclude, in reality, the draft action of the chimney in drawing
in outside air and to limit the action of the chimney to the removal
of the waste gases. The drawing in of the cold outside air would
have an injurious effect upon the working of the; furnace, par-
ticularly in the case of brick kilns. Those furnaces, therefore,
constitute a perfect illustration of the fundamental principle of
the method in which metallurgical furnaces operate. It is well
known that the pressure of the hot gases in the; heating chamber
of such furnaces is practically equal to the pressure of the atmos-
phere. The gases coining from the; firebox and the supply of
secondary air, if such is necessary for the operation of the furnace,
enter the heating chamber under a pressure head which may br
measured by the difference in level between the grate bars and
the hearth of the furnace. The chimney for a metallurgical
furnace should be designed to provide for the removal from the
heating chamber of the burned gases, but it should riot, in addi-
tion, provide any further draft depression. On the; contrary, it is
always desirable that there should be a slight positive pressure1
in the heating chamber of metallurgical f urnacos.
(6) Hydrostatic Pressure within Metallurgical Furnaces and
their Flues.1. All revcrberatory furnaces comprise a chamber
of some fixed height filled with incandescent gases. Ai, each
point in the interior of this chamber there will be a different
pressure, according to the height of the point. Therefore, in
a reheating furnace, having working doors with a height of
700 mm, with a pressure equal to that of the; atmosphere acting
at the hearth level, there; will be a pressure +0 mm 728 of water,
at the level of the top of the door, as has been shown previously
on page 13.
This pressure, in excess of that of the atmosphere, causes, as
is well known, the formation of a great aureole or " sting " of
flame due to the hot gases which escape through the crevices at
the top of the door. In order to diminish the loss of gases through
these crevices, the following means may be employed. By a slight
increase in the chimney draft, the level at which the pressure in