At several smelters, blast furnaces have been equipped with hot-blast “tops” for the purpose of preheating the air supply, the air-heating pipes being exposed to the gases in the upper portions of the furnace. The Giroux blast-heating device has been installed on furnaces at smelters in Mexico and Arizona, whilst at others in the same localities, the Mitchell system of baffle passages has been successfully used. The Kiddie system of running the blast pipes through the dust chambers has been tried at Tyee, B.C. The advantages of thus utilising the heat of waste gases have generally, however, been found to be more than balanced by the extra costs involved.
Efforts have been made to use the heat contained in molten slag for warming the air, but owing to the low conducting power of these materials, and the difficulty of bringing extended surfaces in close contact, the method has not proved itself very efficient. Blast is occasionally warmed by passing the air through tunnels in which bogies of molten slag are allowed to remain for some time.
When methods of utilising waste heat from the furnace products fail, the fuel-heated iron pipe-stove is generally employed. Since the temperatures required are comparatively low, and the margin of profit involved by the use of hot blast is usually small, the use of the cheapest class of fuel available is imperative; but many classes of fuel unsuitable for other purposes may find useful application for this work.
The stove is of the usual
cast-iron pipe form, designed to give the maximum exposing surface, suitably strengthened and protected from direct action of the fire. Much valuable information on the advantages, disadvantages, and appliances for blast heating was afforded by the smeltermen who contributed to the symposium on “Pyrite Smelting,” which Rickard edited for the Engineering and Mining Journal.
References.
Mathewson, E. P., “The Development of the Modern Blast Furnace.” Eng. and Min. Journ., May 27, 1911, p. 1057.
Wright, Lewis T., “Metal Losses in Copper Slags.” Bulletin Amer. Inst. Min. Eng., 1909, Sept., No. 33, p. 817.
Shelby, Geo. F., “Cananea Blast Furnaces.” Engineering and Mining Journal, April 25th, 1908.