Shaft Furnaces.—The finished product from the Huntington-Heberlein blast-converters is of a porous character, and already contains a part of the flux materials (such as limestone, silica and iron) which are required for the shaft-furnace charge. It is just these two characteristics of the roasted product (its porous nature, on the one hand, leading to its more perfect reduction by the furnace gases; and, on the other hand, the admixture of fluxes in the molten condition, resulting in a more complete utilization of the temperature), which, together with its higher lead and lower zinc content, determine its ready fusibility. If we further consider that it is possible in the new process to make the total charge of the shaft furnace richer in lead than formerly (two-thirds of the total charge as against one-third), and that a higher blast pressure can be used without danger, it follows immediately that the capacity of a shaft furnace is much greater by the new process than by the old method of working. The daily production of the shaft furnaces on the old and the new process is as shown in the table given herewith:
| Type of Shaft Furnace | Character of Charge | Charge per Day, Tons | Work-lead Produced per Day, Tons |
|---|---|---|---|
| Low-pressure Blast | |||
| 3 tuyeres | Gray slag from reverberatory furnaces and sintered concentrate | 36 | 6 to 7 |
| 8 tuyeres | ” | 36 to 38 | 6 to 8 |
| 3 tuyeres | Roasted product of Huntington-Heberlein process | 36 | 11 to 12 |
| High-pressure Blast | |||
| 8 tuyeres | ” | 65 to 72 | 24 to 26 |
| 15 tuyeres | ” | 270 | 90 to 100 |
It should be noted that the figure given for the furnace with 15 tuyeres represents the average for 1904; this average is lowered by the circumstance that during this period there was frequently a deficiency of roasted material, and the furnace had to work with low-pressure blast. A truer impression can be gained from the month of March, 1905, for instance, during which time this furnace worked under normal conditions; the results are as follows:
The average for March, 1905, was: Ore charged, 8,269.715 tons; coke, 652.441 tons; total, 8,922.156 tons. Or, in 24 hours: Ore charged, 266.765 tons; coke, 21.046 tons; total, 287.811 tons. The production of work-lead was 3,133.245 tons, or 101.069 tons per day.
The maximum production of roasted ore was 210 tons, on June 30, 1905, when the total charge was: Ore, 327.38 tons; coke, 25.2 tons; total, 352.58 tons. The quantity of work-lead produced on that day was 120.695 tons, while the largest quantity previously produced in one day was 124.86 tons. It should also be mentioned that the lead tenor of the slag is almost invariably below 1 per cent.; it usually lies between 0.3 and 0.5 per cent.
As in the case of the roasting furnaces, the productive capacity of the shaft furnace also comes out clearly if we figure the number of furnaces required, on the basis of an annual consumption of 50,000 tons of ore. If we consider 1 ton of the roasted material as equivalent to 1 ton of ore (which is about right in the case of the Huntington-Heberlein material, but is rather a high estimate in the case of the product of the sintering furnace), then, in the old process (where one-third of the charge was lead-bearing material), 12 tons could be smelted daily. There would therefore be needed at least:
50,000 ÷ (12 × 300) = 14 three-tuyere shaft furnaces.
Since, as already mentioned, the lead-bearing part of the charge constitutes two-thirds of the whole in the Huntington-Heberlein process, the number of shaft furnaces of different types, as compared with the foregoing, would figure out:
3-tuyere shaft furnace, with product of sintering furnace, 50,000 ÷ (12 ×
300) = 14 furnaces;
3-tuyere shaft furnace, with product of Huntington-Heberlein furnace,
50,000 ÷ (24 × 300) = 7 furnaces;
8-tuyere shaft furnace, with product of Huntington-Heberlein furnace,
50,000 ÷ (48 × 300) = 3.4 (say 4) furnaces;
15-tuyere shaft furnace, with product of Huntington-Heberlein furnace,
50,000 ÷ (180 × 300) = 1 furnace.
Running regularly and without interruption, the large shaft furnace is therefore fully capable of coping with the Huntington-Heberlein roasted material at the present rate of production.