Weekly Arizona journal-miner., 1904-06-08
THE BRETHERT0Ns
HOT BLAST SYSTEM
Continued from page 2.

mace, JDeQ Suulcleul uelsHOulO De uset
}, in order to save the necessary sulphur
e for making a proper grade of matte
t With hot blast, a cool top and care
) full feeding, a more uniform grade Of
), matte is made than it has ever beer
= possible to make by the use of the
r cold blast. At the same time, there
is less loss of precious metals by VIOLA
tilizatiOn.
The advantages of a hot blast over
cold blast are in the improved chem
ical conditions, economy of fuel, and
9 the greater capacity of the furnace.
Where the blast is heated without any
expense, every degree of heat so Oh
tanned is saving of a percentage of
coke needed for fuel in the working
of the furnace. As matter of fact,
the saving goes beyond that point, be
cause the cold blast chills the charge
, at the point of contact in the furnace
, from each one of the tuyeres, thus re
ducing the activity of the coke fur
nished. and imposing an increased de-
mand on it.
This chilling action reduces the ca
pacity of the furnace in proportion to
the area occupied by the chilled por-
tions, and near the nozzle of each
tuyere will be found large surface of
the charge chilled below the fusing
point by the action of the cold blast,
which with hot blast. would be kept
active. This proportion cuts q ma
terial figure, so that the use of the
hot blast in that direction alone is a
decided advantage. As p matter of
fact, it has been found In the practical
working of furnaces on large scale
that it is advantageous to heat the
blast by separate ovens, where the
expense for fuel in operating these
ovens was more than double the saw
ing of the fuel in the furnace charge,
II was found that the increased ca
pacity of the furnace, and the i'm
proved chemical conditions which
resulted in bringing about a more
thorough fusion of the ore, more than
compensated for tine extra cost of the
| fuel to heat the air. This fact hav-
! ing been demonstrated on a large
scale, one can see how much advan-
tage it will be in the cost of operat- |
| ing and furnace if the air can be heated |
automatically without cost. Realizing !
the field for the improvement in that |
direction several inventions have been !
| brought out to accomplish that end. !
Most of those l have seen utilized the |
heat escaping from the fumes OF the
furnace by means of coils of pipe, |
at some distance above the feed floor |
of the furnace. Where a furnace is /
prapertly fed and properly operated
so as to prevent volatilization of the
precious metals, there should be very
little heat above the fed floor, so
that to utilize the invention it is nee
essary to keep a strong blast running
through the entire charge of the fur
mace, igniting the free atoms of sui
phur and the coke on the top of the
charge. This causes a heavy loss
by volatilization where the ore con-
tains any tellurides, lead or other
volatile substances, and destroys a
great portion of the fuel heat before
the charge reaches the oxidizing por
ton of the furnace. In other cases,
attempts have been made to use the
waste heat escaping from the Stag,
but this has been taken in such a way
that the fumes from the Stag were
driven back into the furnace again,
furnishing an impure blast with a
great portion of the free oxygen al
ready removed.
The object of my researches has
been to secure a hot blast which would
furnish the air heated to a sufficient
degree of heat to prevent chilling, at
the same time increasing the capacity
of the furnace and minimizing the
use of fuel; and to accomplish this
without any additional cost for oper
alton. This l have been able to do by
what is known as the Bretherton hot
blast apparatus. In constructing
this apparatus 1 have kept in mind
the principal features required for its
successful operation, doing away
with the back pressure on the flower so
that the volume of air would not be
minimized, taking the heat from the
escaping heat of the hot Stag by build
ing an oven around the foTehearth,
the oven having fiues passing through
it for the escaping fumes of the Stag
and augmenting the heat acquired in
that manner somewhat by using set
of air jackets above the water jackets
around the furnace, the air having a
continuous passage from the blower
to the tuyeres. In this way | have
been able to keep the top of the fur
mace cool, so as to prevent volatiliza-
ton.
The first and most important item !
to consider when heating the air blast /
is that it in no way interferes with |
the regular working of the blower as
the blast passes through the blower |
cold. All calculations as to the !
amount of blast required and used |
can be based on the regular volume |
handled by the blower, the same as
when using cold blast. 1t is custom
airy to calculate the amount of blast |
furnished by the tables sent out by |
the manufacturers to the different
blowers. In this way, the amount Of
free oxygen sent into the blast fur
mace, whether heated or cold, can be
calculated, provided there is no OBJ
struction to the free passage of the
air through the heating apparatus.
/ 1t is therefore necessary that the area
| of the heating box shall be larger than
| the inlet where the cold blast enters.
so that no back pressure is created.
The outlet of this heating box should
be made with nearly double the ca
pacity of the inlet.
e