Reading Week 4
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Blast furnace, a vertical shaft furnace that produces liquid metals by the reaction of a flow of air introduced under pressure into the bottom of the furnace with a mixture of metallic ore, coke, and flux fed into the top. Blast furnaces are used to produce pig iron from iron ore for subsequent processing into steel, and they are also employed in processing lead, copper, and other metals. Rapid combustion is maintained by the current of air under pressure.
A zinc-lead blast furnace and lead-splash condenser.
Encyclopædia Britannica, Inc.
Blast furnaces produce pig iron from iron ore by the reducing action of carbon (supplied as coke) at a high temperature in the presence of a fluxing agent such as limestone. Ironmaking blast furnaces consist of several zones: a crucible-shaped hearth at the bottom of the furnace; an intermediate zone called a bosh between the hearth and the stack; a vertical shaft (the stack) that extends from the bosh to the top of the furnace; and the furnace top, which contains a mechanism for charging the furnace. The furnace charge, or burden, of iron-bearing materials (e.g., iron-ore pellets and sinter), coke, and flux (e.g., limestone) descends through the shaft, where it is preheated and reacts with ascending reducing gases to produce liquid iron and slag that accumulate in the hearth. Air that has been preheated to temperatures from 900° to 1,250° C (1,650° and 2,300° F), together with injected fuel such as oil or natural gas, is blown into the furnace through multiple tuyeres (nozzles) located around the circumference of the furnace near the top of the hearth; these nozzles may number from 12 to as many as 40 on large furnaces. The preheated air is, in turn, supplied from a bustle pipe, a large-diameter pipe encircling the furnace. The preheated air reacts vigorously with the preheated coke, resulting in both the formation of the reducing gas (carbon monoxide) that rises through the furnace, and a very high temperature of about 1,650° C (3,000° F) that produces the liquid iron and slag.
Schematic diagram of modern blast furnace (right) and hot-blast stove (left).
Encyclopædia Britannica, Inc.
The bosh is the hottest part of the furnace because of its close proximity to the reaction between air and coke. Molten iron accumulates in the hearth, which has a taphole to draw off the molten iron and, higher up, a slag hole to remove the mixture of impurities and flux. The hearth and bosh are thick-walled structures lined with carbon-type refractory blocks, while the stack is lined with high-quality fireclay brick to protect the furnace shell. To keep these refractory materials from burning out, plates, staves, or sprays for circulating cool water are built into them.
Retrieved from: https://www.britannica.com/technology/blast-furnaceAssessment 1: Explain a zinc-lead blast furnace and lead-splash condenser working process (Picture1)
Assessment 2: Describe the diagram of modern blast furnace and hot blast stove. (Picture2)