After this the heat is still further
utilized by passing it under the boilers for the generation of steam,
and the heat lost in the gases, when they finally escape, is very
small. In a blast furnace the carbon is at first burned only to
carbonic oxide, and the products of combustion issue mainly in this
form from the top of the furnace. Then a portion of the heat resulting
from the subsequent burning of these gases is pretty well utilized in
making steam to supply the power required about the works, but the
rest of the gas can only be utilized for heating the blast, and here
there is an enormous waste, the amount of heat returned to the furnace
by the heated blast being very small in proportion to the amount
generated by the burning of that portion of carbonic oxide expended in
heating it, and the gases escape from both the hot-blast and the
boilers at a high temperature.
In the direct process under consideration the fuel burned is more
completely utilized than in the puddling process, to which the cast
iron from the blast furnace is subjected to convert it into wrought
iron.
The economy claimed for this process, over the blast furnace and
puddling practice for the production of wrought iron, is that nearly
all the fuel used in the puddling operation is saved, and that with
about the same amount of fuel used in the blast furnace to produce a
ton of pig iron, a ton of wrought iron blooms can be made.
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