The blast furnace (BF) has a vertical cylindrical structure externally covered with a shell of thick steel plate and internally lined with refractories. The refractory structure is cooled by water-cooled metal components called staves, which are embedded between the shell and the refractories. The furnace body is composed of (i) the shaft, which tapers outward from the top, (ii) the belly, which is a straight cylinder, (iii) the bosh, which tapers inward toward its bottom and is located immediately under the belly, and (iv) the hearth, at the bottom of the furnace. The shaft, belly, and bosh are usually lined with chamotte brick and silicon-carbide brick, and the hearth is lined with carbon brick. Depending on the size of the furnace, the side wall of the hearth is radially fitted with some 20 to 40 of water-cooled copper tuyeres, which are used to inject the hot blast into the furnace from the hot stoves through the hot-blast main and bustle pipes. Tapholes for discharging hot metal and cinder notches for discharging slag are also installed in the hearth section. The largest BFs at present are about 80m in total height, with a furnace body height of about 35m and a maximum internal diameter of about 16m, and have an internal volume of about 5,200m3. A furnace of this size can produce approximately 10,000 tons of hot metal a day. All BFs have auxiliary equipment such as (i) belt conveyors for transporting raw materials (ore and coke) to the furnace top, (ii) hoppers for temporarily storing these raw materials, (iii) a bell-type or bell-less-type device for charging the raw materials into the furnace with appropriate distribution in the radial direction, (iv) hot stoves for heating the blast, (v) blowers for feeding the blast, and (vi) equipment for dust removal, and recovering and storing the gas from the furnace top. Blast furnaces in which pulverized coal is injected from the tuyeres (PCI = pulverized-coal injection) are provided with equipment for pulverizing the coal and feeding it under pressure. With bell-type charging equipment, the raw materials enter the furnace through the gap created by moving down a small inverted bell. This bell closes and a larger bell (big-end-down) opens to allow material to fall into the shaft below. With bell-less charging equipment, the raw materials are dropped into the furnace through a rotating chute. The hot stove is a cylindrical furnace about 12m in diameter and some 55m in height, and has a chamber filled with checkered silica bricks. The hot stove is a type of heat exchanger in which the heat produced by combustion of the BF gas is stored in the checker-work chamber, after which cold air is blown through the hot checker-work to produce the preheated hot air blast to the furnace. Two or more stoves are operated on alternate cycles, providing a continuous source of hot blast to the furnace. A BF is usually operated with a furnace-top pressure of about 250 kilopascals. To recover the energy from the large volume of high-pressure exhaust gas, the BF is equipped, after dust removal, with a top-pressure recovery turbine (TRT), for generating electric power by utilizing the pressure difference between the furnace-top and gas storing holder.