By B.H. THWAITE.
In order to approximately ascertain the relative reducing action of
water gas, carbon monoxide, and superheated steam on iron ore, the
author decided to have carried out the following experiments, which were
conducted by Mr. Carl J. Sandahl, of Stockholm, who also carried out the
analyses. The ore used was from Bilbao, and known as the Ruby Mine, and
was a good average hematite. The carbonaceous material was the Trimsaran
South Wales anthracite, and contained about 90 per cent. of carbon.
A small experimental furnace was constructed of the form shown by
illustration, about 4 ft. 6 in. high and 2 ft. 3 in. wide at the base,
and gradually swelling to 2 ft. 9 in. at the top, built entirely of
fireclay bricks. Two refractory tubes, 2 in. square internally, and the
height of the furnace, were used for the double purpose of producing the
gas and reducing the ore.
The end of the lower tube rested on a fireclay ladle nozzle, and was
properly jointed with fireclay; through this nozzle the steam or air was
supplied to the inside of the refractory tubes. In each experiment the
ore and fuel were raised to the temperature "of from 1,800 to 2,200 deg.
Fahr." by means of an external fire of anthracite. Great care was taken
to prevent the contact of the solid carbonaceous fuel with the ore. In
each experiment in which steam was used, the latter was supplied at a
temperature equivalent to 35 lb. to the square inch.
The air for producing the carbon monoxide (CO) gas was used at the
temperature of the atmosphere. As near as possible, the same conditions
were obtained in each experiment, and the equivalent weight of air was
sent through the carbon to generate the same weight of CO as that
generated when steam was used for the production of water gas.
[Illustration]
_First Experiment, Steam (per se)_.--Both tubes, A and B, were filled
with ore broken to the size of nuts. The tube, A, was heated to about
2,000 deg. Fahr., the upper one to about 1,500 deg.
NOTE.--In this experiment, part of the steam was dissociated in passing
through the turned-up end of the steam supply pipe, which became very
hot, and the steam would form with the iron the magnetic oxide
(Fe_{3}O_{4}). The reduction would doubtless be due to this
dissociation. The pieces of ore found on lowest end of the tube, A, were
dark colored and semi-fused; part of one of these pieces was crushed
fine, and tested; see column I. The remainder of these black pieces was
mixed with the rest of the ore contained in tube, A, and ground and
tested; see column II. The ore in upper tube was all broken up together
and tested; see column III. When finely crushed, the color of No. I. was
bluish black; No. II., a shade darker red; No. III., a little darker
than the natural color of the ore. The analyses gave:
-----------------------------+---------+---------+---------
| I. | II. | III.
+---------+---------+---------
|per cent.|per cent.|per cent.
Ferric oxide (Fe_{2}O_{3}). | 68.55 | 76.47 | 84.81
Ferrous oxide (FeO). | 16.20 | 9.50 | 1.50
+---------+---------+---------
Total. | 84.75 | 85.97 | 86.31
+---------+---------+---------
Calculated: | | |
Ferric oxide (Fe_{2}O_{3}). | 32.55 | 55.36 | 81.47
Magnetic oxide (Fe_{3}O_{4}).| 52.20 | 30.61 | 4.84
Ferrous oxide (FeO). | | |
+---------+---------+---------
Total. | 84.75 | 85.97 | 86.31
+---------+---------+---------
Percentage of total
oxygen reduced. | 6.93 | 4.02 | 1.07
Metallic iron. | 60.59 | 60.92 | 60.54
-----------------------------+---------+---------+---------
_Second Experiment, Water Gas_.--The tube, A, was filled with small
pieces of anthracite, and heated until all the volatile matter had been
expelled. The tube, B, was then placed in tube, A, the joint being made
with fireclay, and to prevent the steam from carrying small particles of
solid carbon into ore in the upper tube, the anthracite was divided from
the ore by means of a piece of fine wire gauze. The steam at a pressure
of about 35 lb. to the square inch was passed through the anthracite.
The tube, A, was heated to white heat, the tube, B, at its lower end to
bright red, the top to cherry red.
------------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+
Experiment. | 1st. | 2d. | 3d. |
------------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+
Number. | I. | II. | III.| I. | II. | III.| IV. | I. | II. | III.|
------------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+
Total Iron. |60.59|60.92|60.54|65.24|61.71|61.93|57.23|59.73|57.93|55.54|
------------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+
Iron occurring as
------------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+
FeO. |12.60| 7.39| 1.17|46.98|18.59| 4.03| 0.84|29.45| 2.69| 1.12
Fe_{2}O_{3} |47.99|53.33|59.37|18.26|43.12|57.90|56.39|30.28|55.24|54.42
------------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+
Per cent. of Oxides. |
------------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+
FeO. |16.20| 9.50| 1.50|60.40|23.90| 5.18| 1.08|37.86| 3.46| 1.44
Fe_{2}O_{3}. |68.55|76.47|84.81|26.08|61.60|82.71|80.55|43.26|78.91|77.74
Total. |84.75|85.97|86.31|86.48|85.50|87.89|81.63|81.12|82.37|79.18
------------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+
Oxygen in Ore.
------------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+
Before experiment.|25.97|26.10|26.05|27.96|26.45|26.54|24.52|25.60|24.81|23.80
After experiment. |24.16|25.05|25.77|21.24|23.79|25.96|24.40|21.39|24.44|23.64
Difference. | 1.81| 1.05| 0.28| 6.72| 2.66| 0.58| 0.12| 4.21| 0.37| 0.16
------------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+
Per cent. of oxygen reduced.
------------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+
oxygen reduced. | 6.93| 4.02| 1.07|24.03|10.02| 2.18| 0.49|16.44| 1.49| 0.42
------------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+
Degree of Oxidation of the Ore after the Experiment.
------------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+
FeO. | ... | ... | ... |84.66| ... | ... | ... |18.40| ... | ... |
Fe_{3}O_{4}. |52.20|30.61| 4.84|37.82|77.01|28.12| 3.88|62.72|11.14| 4.64|
Fe_{2}O_{3}. |32.55|55.36|81.47| ... | 8.49|59.77|77.75| ... |71.23|74.54|
Total. |84.75|85.97|85.97|85.97|85.97|85.97|85.97|85.97|85.97|85.97|
------------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+
------------------+-----------------+-----------------------+-----------------+
The ore having | | | |
been exposed to | Steam. | Water gas. | Carbon monoxide.|
------------------+-----------------+-----------------------+-----------------+
_Four Samples were Tested_.--I. The bottom layer, 1¼ in. thick; the
color of ore quite black, with small particles of reduced spongy
metallic iron. II. Layer above I., 4¼ in. thick; the color was also
black, but showed a little purple tint. III. Layer above II., 5 in.
thick; purple red color. IV. Layer above III., ore a red color. The
analyses gave:
-----------------------------+---------+---------+---------+---------
| I. | II. | III. | IV.
+---------+---------+---------+---------
|per cent.|per cent.|per cent.|per cent.
Ferric oxide (Fe_{2}O_{3}). | 26.08 | 61.60 | 82.71 | 80.55
Ferrous oxide (FeO). | 60.40 | 23.90 | 5.18 | 1.08
+---------+---------+---------+---------
Total. | 86.48 | 85.50 | 87.89 | 81.63
+---------+---------+---------+---------
Calculated: | | | |
Ferric oxide (Fe_{2}O_{3}). | ... | 8.49 | 59.77 | 77.75
Magnetic oxide (Fe_{3}O_{4}).| 37.82 | 77.01 | 28.12 | 3.88
Ferrous oxide (FeO). | 48.66 | | |
+---------+---------+---------+---------
Total. | 86.48 | 85.41 | 87.89 | 81.63
+---------+---------+---------+---------
Percentage of total
oxygen reduced. | 24.03 | 10.02 | 2.26 | 0.49
Metallic iron. | 65.24 | 61.71 | 61.93 | 57.23
-----------------------------+---------+---------+---------+---------
NOTE.--All the carbon dioxide (CO_{2}) occurring in the ore as calcic
carbonate was expelled.
_Third Experiment, Carbon monoxide_ (CO).--The tube A was filled with
anthracite in the manner described for the second experiment, and heated
to drive off the volatile matter, before the ore was placed in the upper
tube, B, and the anthracite was divided from the ore by means of a piece
of fine wire gauze. The lower tube, A, was heated to the temperature of
white heat, the upper one, B, to a temperature of bright red. I. Layer,
1 in. thick from the bottom; ore dark brownish colored. II. Layer 4 in.
thick above I.; ore reddish brown. III. Layer 11 in. thick above II.;
ore red color. The analyses gave:
-----------------------------+---------+---------+---------
| I. | II. | III.
+---------+---------+---------
|per cent.|per cent.|per cent.
Ferric oxide (Fe_{2}O_{3}). | 43.26 | 78.91 | 77.74
Ferrous oxide (FeO). | 37.86 | 3.46 | 1.44
+---------+---------+---------
Total. | 81.12 | 82.37 | 79.18
+---------+---------+---------
Calculated: | | |
Ferric oxide (Fe_{2}O_{3}). | ... | 71.23 | 74.54
Magnetic oxide (Fe_{3}O_{4}).| 62.72 | 11.14 | 4.64
Ferrous oxide (FeO). | 18.40 | |
+---------+---------+---------
Total. | 81.12 | 82.37 | 79.18
+---------+---------+---------
Percentage of total
oxygen reduced. | 16.44 | 1.49 | 0.42
Metallic iron. | 59.73 | 57.93 | 55.54
-----------------------------+---------+---------+---------
NOTE.--The carbon monoxide (CO) had failed to remove from the ore the
carbon dioxide existing as calcic carbonate. The summary of experiments
in the following table appears to show that the water gas is a more
powerful reducing agent than CO in proportion to the ratio of as
4.21 x 100
4.21 : 6.72, or ------------ = 52 per cent.
72
Mr. B.D. Healey, Assoc. M. Inst. C.E., and the author are just now
constructing large experimental plant in which water gas will be used as
the reducing agent. This plant would have been at work before this but
for some defects in the valvular arrangements, which will be entirely
removed in the new modifications of the plant.
* * * * *