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Art. VII.- On the Construction of Blast-furnaces for the Smelt
ing of Iron with Anthracite ; by S. S. HALDEMAN, of Columbia, Penn.*
THE occurrence of inexhaustible strata of anthracite coal in Pennsylvania, has attracted the attention of miners and practical men generally, to its use in smelting iron. With charcoal, this process requires a peculiar location, and a large capital, to be invested in extensive woodland tracts, which are generally mountainous, and consequently cheaper, being unfitted for agriculture. This renders the construction of the necessary roads difficult, and transportation expensive. The number of workmen employed in wood-cutting, coaling, and hauling, is large, and the expense of horses and wagons, forms a considerable item. Charcoal being a soft, porous material, much of it is wasted in transportation and handling, and large sheds are required to store and keep it dry. These various contingencies require the general manager to have industry, judgment, and good business habits. In using anthracite, the exact expense of the fuel is known, the transportation being by railways or canals extending to most of the mines, and if the furnace is placed near such public works, there will be but little waste of coal in its final transportation. There is but little waste in the transportation of ore, which is of course common to both kinds of fuel.
The earlier attempts at smelting iron with anthracite in the ordinary furnace, failed so completely, that it was by some deemed impossible to accomplish it; while others, looking to a different construction for a solution of the problem, devised various structures, more remarkable for ingenuity than utility ; later experiments having proved that no such modifications are necessary, except perhaps a higher inclination of the bosh and a less contracted tunnel-head.
Incandescent anthracite has the peculiarity of being rapidly extinguished when struck with a blast of cold air, the loss of heat from this source exceeding that resulting from combustion ; and although this phenomenon does not take place when the temperature exceeds a certain point, the vast accession of cold air in a blast furnace, may be sufficient under slightly unfavorable conditions, to produce it at any time. Hence a hot blast, which is economical when charcoal is used, becomes an essential element of success with anthracite; and its temperature should not be less than is sufficient to smelt a slip of lead opposed to a jet of it near the twiers. Anthracite being a very dense and concentrated fuel, the amount of air thrown in must be much greater than when charcoal is used. Success, therefore, depends upon the quantity as well as upon the temperature of the blast.
* The figures given in connection with this article, represent the structure of the Chikiswalungo Tron Furnace, at Columbia, owned by Messrs. Haldeman.-Eds.
The necessary amount of oxygen can be secured only by means of the proper machinery, and a certain velocity of the blast; and in consequence of this fact, the false opinion that the effect depends merely upon the velocity or sharpness of the jet, is universally maintained. In consequence of this view, the exit pipe is reduced to a small size, and the quantity secured by increased velocity under a high pressure ; which causes much of the blast to be lost, as among the multitude of joints to be made air-tight, it is impossible to secure them all. Besides this, the machinery is liable to injury from the great and unnecessary strain upon it.
The stack or main structure of a blast furnace, is a quadrangular pyramid, the lower portion of which has an arched passage through the middle of each side, leaving four large piers of masonry. Three of these passages (A, fig. 1) are named twier-arches. The junction of these arches forms an open square about one-third the diameter of the stack, in which the hearth, (which requires renewal from time to time,) is built up with large cut stones of siliceous conglomerate or sandstone. Near the top of the hearth, the inner portion of the four arches is closed by forming a square with eight large sows or iron beams, four of which are shown in section at S in fig. 2, their position nearly corresponding with the dotted square in fig. 1. The dotted circle in fig. 1, indicates the internal face of the fire-brick lining (1, fig. 2) at its widest part, and also the top of the bosh,* (b, fig. 1, 2.) The lining being circular and the lower portion a square, the former is supported upon four plates (9) of such a form as to close the angles of the latter, and at the head of the furnace it is continued in an ordinary brickwork chimney, (z, fig. 3,) leaving one or two large vacant spaces for the purpose of filling. The chief use of this chimney is to protect the workmen from the heat.
The two posterior piers have a circular passage (fig. 1, 2, g) for the admission of the blast pipe, p, which descends from the hotoven (o, fig. 3) at the head of the stack. This passage is sometimes continued through the front piers, which renders the front or working arch, cooler, and gives more ready access to the twiers. The blast pipe is carried by appropriate branches to the posterior, and lateral twiers, t, t, t, fig. 1, the former being seen in longitudinal_and one of the latter in transverse section, at t in fig. 2.
To prevent the twier from being destroyed by contact with the fire of the hearth, it is made of an interior and exterior cone of wrought iron, with a stream of water circulating between
* This word is from the German word böschung, a slope.
them. The twier receives the nozzle, and this the belly-pipe, which is attached to the terminal upright portion of the blastpipe, called the ball-and-socket joint from having a connexion of this kind. Behind this, at k, there is a small aperture, to insert an iron rod to detach any slag that may cling to the twier. As the smelted materials within the hearth frequently rise above the twiers, it is evident that, in case the blast should be accidentally checked, they would flow into the blast-pipe. To prevent this, a valve (v, fig. 2,) is interposed, which is kept open by the blast, but falls the moment the pressure is removed.
The cavity of the hearth, (Hh, fig. 1, 2) where the metal is reduced and retained, bears a very small proportion to the size of the stack. In the figures, which are drawn to a scale of one-eighth
of an inch to a foot, it is two feet wide, and five and a half feet long, but enlarges upwards in a slight degree. The back and front of the hearth are separated by a partial partition called the temp, (m, fig. 1, 2,) made of fire-bricks, and which does not extend to the bottom of the hearth. The horizontal dotted line, (h, fig. 2) shows the level to which the smelted materials can rise
before running over the dam-stone (d) at c, where the cinder will escape first, being the lightest, whilst the smelted iron occupies the bottom. To prevent the fluid matter from being forced out by the blast, clay is rammed beneath the temp, around the twiers, and upon the surface, at h, where it is retained by heavy iron plates, which are raised every few hours, to allow the cinder to run off along the level of the top of the dust-plate c, i, whilst the metal is run off every twelve hours, at the lower level of d, through an aperture at the bottom of the dam-stone. The dam-stone is defended in front by a large iron dam-plate (de, fig. 1) against which the dust-plate c, i, rests. The lower edge of the latter rests upon the ground, which is raised to about the level of the bottom of the hearth d, e.
Explanation of Figs. 1, 2. A, twier arches. e, tapping place. k, twier key. 9, square of the hearth. B, bosh.
f, fues for boilers. 1, lining. ", space for loam. b, greatest diameter. g, passage.
m, temp. 8, sows. c, cinder run.
Hh, hearth. n, sconsh'n. t, twiers. d, dam-stone & plate. i, dust-plate. p, blast-pipe. 0, valve in blast-pipe.
Fig. 2 would represent a transverse section of the stack, if the left half were symmetrical with the right. In this case the temp m, and the open space in front of it, would be filled with stone to the bottom of the hearth, and e would represent the place of exit for the iron.
The bosh BB, fig. 2, (shaded vertically,) resembles a large funnel, except that its termination at H, fig. 1, 2, is square. It is built of fire bricks, except its lower portion in front, where, in consequence of the open temp arch (m), a large stone (n) called the sconsh'n, is laid across the front portion of the hearth. The inclination of the bosh is seen to be at a higher angle than when charcoal is used; but it may vary considerably without affecting the result. When in blast a few months, the bosh increases in steepness from the abrasion of its surface, and the hearth partakes of this enlargement; so that instead of being a parallelogram, it assumes an oval form. The enlargement of the hearth continues until its walls become so thin, that the radiation of the heat will prevent the inner portion from melting away any further; and in case the temperature diminishes, the inside will be protected by a coating of slag. I have known a furnace to be in successful action, when the hearth had been so much enlarged as to have the middle portion of the inmost back sow (s, fig. 2) melted away, permitting the blast to escape until the aperture was closed with tenacious clay. In this case the under surface of the sow was in contact with a brick wall usually built beneath, as an additional barrier to the escape of the heat.
Towards the head of the furnace, there are three equidistant apertures (f, fig. 2) to admit the waste flame, first under the boilers, then through a return flue in them into the hot oven, which is placed in part upon the top of the stack posteriorly and laterally. When a separate engine is employed, the oven is placed upon the front side of the top, and the flame passes into it by a single aperture.
The boilers are in this case three in number, twenty-six feet long, forty-five inches in diameter, with a return flue eighteen inches in diameter. They are represented at w wo, in fig. 3, where the course of the flame is represented by the arrows leaving the outlet of the flues in the stack, and passing beneath and through the boilers into the hot-oven o, which has one or two high chimneys to secure a proper draft. For the purpose of exhibiting the position of the boilers, a part only of the brickwork which supports and encloses them is represented in the figure, and the minor details of construction are omitted. Figure (3) is an elevation and partial section of the right side of fig. 1, 2, showing a twier arch, with the aperture for the admission of the blast, the parapet upon the top, and the chimney (z) around the tunnelhead. The engine is placed upon the ground on this side, the