THE ECONOMY OF SMELTING.
Instead of altering the form and increasing the body of the furnace, a better plan is to prepare the ore for a more rapid and complete deoxidization and carbonization; and this can be done with much economy by a simple process.
The objection to an increase in the height of stacks, to the increase in area, and the pulverization of the materials used, is the strangulation of the draft, or the obstruc tion to the free escape of the vapors of combustion ; but this is provided for, while the preparation is completed by the following process : All ores should be torrefied in kilns before going into the furnace ; and this can be done at a very trifling expense with the waste coal of the anthracite mines, if proper provisions are made for the purpose. The cost of this operation in kilns with waste coal is not over ten cents per ton, while that of torrefaction in the furnace, by our pre sent process, is not less than one dollar per ton of iron produced at present prices.
When the ore is thus prepared, the deoxidization and carbonization are rapid, and though the ore may pack more closely in the furnace and obstruct the draft to a cer tain extent, the furnace-stack may be much less in elevation, and better results be obtained, than in the high furnaces where the torrefaction is carried on at the expense of the production of iron.
In Wales, where iron is made cheaper than in any other part of the world, this pre paration of the ores is always carefully performed; and we may also practise it with equal economy here.
But it is not proposed that the improvement should stop at this point, since still greater economy can be effected by carrying the preparatory process The most refractory and massive ores after torrefaction become friable and easily pulverized : they are therefore readily reduced to a powder by the stamping or rolling process. In this condition they are mixed with a sufficient amount of fine coal or car
bon dust, to absorb the oxides of the ores and carbonize the iron. In fact, enough carbon in the shape of powdered anthracite may be added to complete the fusion as well as the preparation. To the pulverized ore and coal is then added a sufficient quantity of lime to insure adhesion and for flux : the mass is then made into a stiff mortar, and subse quently into blocks by hand or machinery.
This process may seem elaborate and costly; hut from the burning of the ore to the formation of the blocks ready for the furnace, not over twenty-five cents per ton need be expended in labor, if the proper apparatus and machinery are provided.
It can always be made convenient to dump the ores at the top of the calcining kilns, while the elevation of the calcined ores to the top of the pulverizing and preparing establishment—something like our anthracite coal-breakers, but less extensive—can be done by the ordinary means. From this elevation the pulverized ores, coal, and lime descend to the mixing-troughs, and from them to the compressing machines, where the compound is formed into blocks solid enough for handling, and from whence they are conveyed by self-acting elevators to the top of the furnace, to be stacked and dried for use.
By this mode one ton of waste coal, such as 's now refused and is a constant trouble and expense to our coal-miners, would be of more service than two tons of the best anthracite ,lump as now used in our blast-furnaces.