────────────────────────────┬──────────────────────────────────────
│ B.F. NO. 3—NIGHT SHIFT.
│ Typical Green Ore Charges.
├───────┬───────┬───────┬───────┬──────
│ I. │ II. │ III. │ IV. │
────────────────────────────┼───────┼───────┼───────┼───────┼──────
│ Lbs. │ Lbs. │ Lbs. │ Lbs. │
Coke, │ 180 │ 240 │ 240 │ 400 │ ..
Ore A., │ 5,000 │ .. │ .. │ .. │ ..
Ore B., │ .. │ 5,000 │ .. │ .. │ ..
Ore C., │ .. │ .. │ 5,000 │ .. │ ..
Slag, │ .. │ .. │ .. │ 4,000 │ ..
Lime rock, │ .. │ .. │ .. │ .. │ ..
Green ore (low grade) matte,│ .. │ .. │ .. │ .. │ ..
Flue-dust, │ .. │ .. │ .. │ .. │ ..
Quartz (for flux), │ 950 │ .. │ .. │ .. │ ..
────────────────────────────┼───────┼───────┼───────┼───────┼──────
Total weight of charge, │ 6,130 │ 5,240 │ 5,240 │ 4,400 │ ..
────────────────────────────┼───────┼───────┼───────┼───────┼──────
│ No. of│ No. of│ No. of│ No. of│ Total
_Hours of Charging_— │Charges│Charges│Charges│Charges│per Hr
6–7, │ 2 │ 2 │ .. │ .. │ 4
7–8, │ 2 │ .. │ 2 │ 2 │ 6
8–9, │ 2 │ 2 │ .. │ .. │ 4
9–10, │ 2, 2 │ .. │ 2, 2 │ .. │ 8
10–11, │ .. │ 2 │ .. │ 2 │ 4
11–12, │ 2 │ .. │ 2 │ .. │ 4
12–1, │ 2, 2 │ 2 │ .. │ .. │ 6
1–2, │ 2 │ .. │ 2 │ 2 │ 6
2–3, │ 2 │ 2 │ .. │ .. │ 4
3–4, │ 2 │ .. │ 2 │ .. │ 4
4–5, │ 2 │ .. │ .. │ 2 │ 4
5–6, │ 2, 2 │ 2 │ 2 │ .. │ 8
────────────────────────────┼───────┼───────┼───────┼───────┼──────
Total No. of charges daily,│ 28 │ 12 │ 14 │ 8 │ 62
────────────────────────────┴───────┴───────┴───────┴───────┴──────
─────────────────────┬───────────────────────────────────────────────
│ B.F. NO. 5—DAY SHIFT.
│ Typical Concentrating Charges.
├───────────────────┬──────────┬─────────┬──────
│ I. │ II. │ III. │
─────────────────────┼───────────────────┼──────────┼─────────┼──────
│ Lbs. │ Lbs. │ Lbs. │
Coke, │ 150 │ 400 │extra 700│ ..
Ore A., │ .. │ .. │ .. │ ..
Ore B., │ .. │ .. │ .. │ ..
Ore C., │ .. │ .. │ .. │ ..
Slag, │ .. │ 4,000 │ .. │ ..
Lime rock, │ 700 │ .. │ .. │ ..
Green ore (low grade)│ │ │ │
matte, │ 3,500 │ .. │ .. │ ..
Flue-dust, │ .. │ .. │ .. │ ..
Quartz (for flux), │ 1,050 │ .. │ .. │ ..
─────────────────────┼───────────────────┼──────────┼─────────┼──────
Total weight of │ │ │ │
charge, │ 5,400 │ 4,400 │ 700 │ ..
─────────────────────┼───────────────────┼──────────┼─────────┼──────
│ No. of │ No. of │ │Total
_Hours of Charging_— │ Charges │ Charges │ │per Hr
6–7, │2, 2, 2, 2, 2, 2, 2│ .. │ .. │ 14
7–8, │ 2, 2, 2, 2 │ 2 │ .. │ 10
8–9, │ 2, 2, 2, 2, 2 │ .. │ .. │ 10
9–10, │ 2, 2, 2, 2, 2 │ .. │ .. │ 10
10–11, │ 2, 2 │2, 2, 2, 2│ .. │ 12
11–12, │ 2, 2, 2, 2, 2 │ .. │ .. │ 10
12–1, │ 2, 2, 2, 2, 2 │ .. │ .. │ 10
1–2, │ 2, 2, 2, 2, 2 │ .. │ .. │ 10
2–3, │ 2, 2, 2 │ 2,2 │ .. │ 10
3–4, │ 2, 2, 2, 2, 2, 2 │ .. │ .. │ 12
4–5, │ 2, 2, 2, 2, 2 │ .. │ .. │ 10
5–6, │ 2, 2, 2 │2, 2, 2, 2│ .. │ 14
─────────────────────┼───────────────────┼──────────┼─────────┼──────
Total No. of charges│ │ │ │
daily, │ 120 │ 12 │ .. │132
─────────────────────┴───────────────────┴──────────┴─────────┴──────
It will be observed that the concentrating furnace works twice as
quickly as the green ore matting furnace, and hence one furnace only
is required for the concentration of the matte product from two of the
matting furnaces.
The Isabella smelter comprises two furnaces of moderate size, 17
feet by 3 feet 4 inches at the tuyeres, having a joint capacity of
500 to 600 tons daily. The furnaces are about 9 feet high, and are
water-cooled. Air at only 20 to 30 ozs. pressure is supplied through
3-inch tuyeres. The smelting scheme is somewhat analogous to that
adopted at Copperhill, the first smelting producing a 20 per cent.
copper matte from the 2 per cent. ore, whilst the re-concentration
results in a converter-grade matte assaying 50 per cent. The coke
proportions are somewhat similar to those used at Copperhill, being 5·0
per cent. for the first smelting, and 3·5 per cent. for the second. The
furnace management at this small plant is exceedingly efficient, and
the campaigns are long, it being claimed that the furnace operations
have never had to be completely stopped on account of crusting or
gobbing. This is held to be due to the results of special care in
feeding and charge distribution, the ingenious Freeland charger already
described being used. The charge is kept low (6 to 8 feet above the
tuyeres), and is evenly red hot all through. The slags assay 35 to 36
per cent. silica, 38·8 per cent. iron, and 8·0 per cent. lime—with
moderate copper losses. The annual output is equivalent to about 3,000
tons of metallic copper. An acid-making plant is also attached to these
works.
=The Manufacture of Sulphuric Acid from Pyritic Furnace Gases.=—Modern
legislative requirements make severe demands upon the managements of
smelter-works where sulphury ores are dealt with, by reason of the
disastrous effects of the sulphurous gases upon the conditions of life
generally in the vicinity. In other cases, litigation by neighbouring
farmers and others impose restrictions on the amount and character of
the gases which the smelters are allowed to emit from their furnace
stacks. So serious has the problem become that several smelters have
had to cease operations altogether, others have been mulcted in
enormous costs by law suits, by claims for compensation, or by the
installation of plant and processes which they have been compelled to
adopt for dealing with the gases. These matters have become subjects of
historical importance in the development of smelter practice.
As has been the case in analogous circumstances elsewhere, when
interference with the uncontrolled dispersion of then-considered waste
products has often proved of ultimate benefit and a source of much
profit to their producers, the enforced treatment of highly sulphurous
furnace gases has in several instances resulted in considerable gain to
the copper smelters.
Among the methods which are at present economically practicable for
dealing with the smelter gases, those of dilution, and of utilisation
for acid manufacture are the most important.
The considerations which decide the best course of treatment depend on
the numerous economic and local factors which are always of such prime
importance in connection with industrial undertakings demanding large
capital outlay. The installation of a plant for making sulphuric acid
from the gases largely depends on—
(_a_) The technical factor as to whether the composition
of the gases is suitable for the making of acid.
(_b_) The economic factor as to whether such acid can
be put upon the market on a satisfactory basis.
(_a_) For the successful operation of acid-making plant, as at present
developed, it is necessary that the proportions of sulphur dioxide in
the gases shall not fall below a certain minimum, and further, that
the gases shall not contain more than certain limiting proportions
of other interfering constituents, such as, for instance, CO_{2}. It
is for this reason that the blast furnace operating the true pyritic
process furnishes gases of the type most suitable for acid manufacture,
since by this process the sulphur-dioxide is obtained in the gases in
the most concentrated and the least contaminated form possible under
smelting conditions. Even under these circumstances the gases are not
in the least of an ideal composition for treatment, owing to their
dilution with nitrogen, etc., and the development of the acid-making
plants and processes adopted for the successful utilisation of copper
blast-furnace gases furnishes a record covering many years of very
slow and costly experiment, marked by many preliminary failures and
disappointments. These difficulties have now been overcome, as the
working of the successful plants attached to both of the Tennessee
copper smelters affords conclusive proof, and the sulphur which
formerly cost money to dissipate by roasting, now not only acts as
fuel, but furnishes a very profitable bye-product.
The requirements for the gases are chiefly the presence of sufficient
SO_{2} and oxygen, and of as little CO_{2} as possible—factors which
depend largely on the proportions of sulphide in the charge. The
gas for the acid plant must be supplied in regular and continuous
amount, at a specific temperature, and this calls for special care
in the smelting operation, furnace manipulation and blast supply,
supplementary air admission, etc.
About 3·5 to 4 per cent. of SO_{2} in the gases delivered at the
chambers is the minimum proportion for satisfactory working; CO_{2}
should not exceed about 5 per cent., and about 6·0 per cent. or more of
oxygen is also necessary.
(_b_) In addition to the capital charges involved in the acid-making
installation and the costs of adapting the furnace plant and operations
to the process, the problem of putting the acid upon the market on a
satisfactory economic basis is important, particularly in view of the
competition from other sources. The districts which offer a consuming
area for the large and regular supply of acid from the smelters are
not unlimited in number, and are probably readily accessible to other
sources. In view of the costs of production, the distance of the
smelter from the market is a serious consideration, since freight
charges on sulphuric acid are high, involving special regulations with
respect to the form of car and conditions of traffic, and they may
readily exceed all possible profits resulting from the sale of the
product.
In Tennessee the companies were forced to install acid plants. That
at Copperhill is the largest in the world; commenced in 1906, acid
manufacture began about two years later, after much experimenting, and
further units have gradually been added. The plant now includes two
Glover towers, 30 feet across and 50 feet high, 64 cooling chambers
about 11 feet × 11 feet × 70 feet high, eight cooling chambers 11
feet × 24 feet × 70 feet high, twelve old chambers 50 feet × 50 feet
× 70 feet, six new chambers 50 feet × 50 feet × 75 feet, eight new
chambers 23 feet × 50 feet × 80 feet, eight Gay-Lussac towers, with
complementary tanks, etc.—producing at the rate of 168,000 tons of 60°
B. acid per annum.
The Ducktown Company’s plant was installed in record time, and, like
the Copperhill plant, comprises elaborate dust chambers and flues,
with Glover and Gay-Lussac towers of special design and construction,
and enormous acid-making chambers with complex valves and fittings.
The plant is designed to produce about 160 tons of 60° B. acid daily.
The analysis of the gases supplied to the towers varied during the
early working of the plant; under fairly normal conditions the average
analysis of the gases delivered is SO_{2} 3·5 per cent., CO_{2} 3·5
per cent., SO_{3} trace; the oxygen in the mixture being about 8·0 per
cent. The temperature is also apt to vary. Full details on these points
are not yet available for general service.
The management of both companies have been successful in obtaining
particularly satisfactory contracts for the purchase of their acid by
fertiliser corporations.
References.
Peters, E. D., “Principles” and “Practice of Copper Smelting.”
_Blast-furnace Manipulation._
Shelby, Geo. F., “Alumina in Blast-Furnace Slags.”
_Eng. and Min. Journ._, 1908.
Offerhaus, C., “Copper Blast-Furnace Smelting at Anaconda.”
_Eng. and Min. Journ._, 1908, Aug. 7, pp. 243–250.
Sackett, B. L., “The Granby Smelter Equipment.”
_Mines and Minerals_, 1910, April, p. 524.
“Operations of the Tennessee Copper Company.”
_Official Annual Reports of the General Manage.r_
Walker, A. L., “The Metallurgy of Copper in 1910.”
_Eng. and Min. Journ._, 1911, Jan. 7, p. 39.
Austin, L. S., “Review of Metallurgy in 1910.”
_Met. and Chem. Ind._, 1911, Jan. 11, p. 40.
Rice, Claude T., “Handling Copper Smelting Gases.”
_Eng. and Min. Journ._, 1911, Mar. 25, p. 614.
“Cottrell’s Fume Smelter.” _Min. and Scient. Press_,
Aug. 26, Sept. 2, 1911.
Herrick, R. L., “Boston and Montana Co.’s Smelter at Great Falls.”
_Mines and Minerals_, 1909, Dec., p. 257.
Harvard, F. T., “Condensation of Fume and Neutralisation of
Furnace Gases.” _Bull. Amer. Inst. Min. Eng._,
No. 44, 1910, Aug.
“Mineral Industry.” Annual.
_Pyritic Smelting._
Holway, John, “A new Application of Bessemer’s Method of
Rapid Oxidation, by which Sulphides are utilised for Fuel.”
_Journ. Society of Arts_, Feb. 1879.
Rickard, T. A., “Pyrite Smelting.”
Sticht, Robert, “Ueber das Wesens des Pyrites Verfahrens.”
_Metallurgie_, Nov. 22, Dec. 8, 1906.
Wintle and Alabaster, “Pyritic Smelting.”
_Trans. Inst. Min. and Met._, 1906, vol. xv., p. 269.
Nicholls, F. S., “Pyrite Smelting in Tilt Cove, Newfoundland.”
_Eng. and Min. Journ._, 1908, Sept. 5, p. 462.
Wright, L. T., 44 “Pyritic Smelting without Coke.”
_Min. and Scient. Press_, 1906, Sept. 29.
_Sulphuric Acid Manufacture._
Falding, F. J., and Channing, J. P.,
“Pyrite Smelting and Sulphuric Acid Manufacture.”
_Eng. and Min. Journ._, 1910, Sept. 17, p. 555.
Freeland, W. H., and Renwick, C. W.,
“Smeltery Smoke as a Source of Sulphuric Acid.”
_Eng. and Min. Journ._, 1910, May 28, p. 1116.