The state of the hearth is evaluated by visual inspection of the tuyere regions and the composition and distribution of the hot metal and the slag. To date, there have been few attempts to mount pyrometers at the inspection holes of the tuyeres and thermocouples at the end of the tuyeres. Therefore, in the absence of continuous information on the processes in the tuyere regions and the mechanics of coke motion in the hearth, it is hard for technologists to form clear ideas regarding the state of the hearth. It has long been assumed that the combustion zone ventilated by the blast is a source of high-temperature reducing gas. The dimensions of the zone are related to the furnace processes and parameters. Therefore, the extent of the coke combustion is regularly inspected manually, by introducing an iron probe through the tuyere inspection hole until it encounters a dense batch layer. The gas composition was first investigated by Ebelmann in 1844, at charcoal- and coke-fired coke furnaces in France. In 1892, Van-Vloten studied the combustion in a coke-fired German blast furnace with a hearth diameter of 3 m. In the USA, the first data on the gas composition in the tuyere region was obtained by Pirrot and Kean in 1922. In 1927, Lennings undertook more thorough study of the combustion zone in a 525-m~3 German furnace, with a blast temperature of 600-700 deg C. In the Soviet Union, the study of combustion underwent extensive development in the 1930s. Experimental data obtained by I. Z. Kozlovich, D. V. Efremov, N. I. Krasavtsev, N. N. Kruglov, Z. I. Nekrasov, and L. M. Tsylev formed the basis for evaluating the influence of the blast parameters and the coke quality on what was then regarded as the most important characteristic of furnace operation: the extent of the tuyere region. Generalization of these data [1] led to the characterization of the coke consumption as the layer-by-layer combustion of coke fuel.
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