Technological Aspects of Low Shaft Furnace Process

Abstract

WHILE the primary object of the low shaft furnace is to produce commercial grades of pig from iron-ore and fuel unsuitable for smelting in the conventional blast furnace, there is a wide diversity ill the design of the furnace, all of which are characterised only by the shortness of the shaft and the smallr.ess of one of the horizontal dimensions. Low shaft furnaces of circular,rectangular and oval hearths and with double rows of tuff tires have been tried. In the construction of the furnace, width is gove-rned by the ability of the blast to penetrate to the centre with minimum dust losses and for this reason a rectangular or oval cross-section is preferred. The height of the charge in the low shaft furnace seldom exceeds 16 ft. This low height widens the choice of ratio materials. The burden may, therefore, consist of friable ores and ore fines and fuels like small coke, non-coking coal, carbonised lignite briquette, or similar fuels of an inferior grade both from the point of view of physical strength and heating value, the cost of which compared to blast furnace coke is very low and which are available in abundance. The reduction of height causes the burden in a low shaft furnace to descend in 2 to 4 hours compared to 8 to 12 hours in a conventional blast furnace. With the shorter throughput time, the time of reaction afforded in the low shaft furnace becomes 1/3 to 1/5 of that in a blast furnace. It is, therefore, obvious that a suitable burden prepartion is necessary.Uniform distribution of the burden, reducibility of iron-ore, intimacy- of cotact between the oxide and the reductant on which the reaction time depends are to be taken into consideration for deci-ding the size and shape of the furnace. The height and the cross-section can be adjusted to meet the demands of the raw materials. But once the design has been worked for a particular set of conditions, treatment of raw materials widely varying in analyses, may not be economical.The low shaft furnace differs from the conventional blast furnace not only in design but also in the smelting operation. The raw materials smelted in the, blast furnace are somewhat similar in nature but those in the low shaft furnace vary eon-iderably