Furnace, Two-Bath

a steel-making unit consisting of two baths, in which the heat of gases formed when oxygen is blown through the molten metal in one of the baths is used in the second bath, where they heat the cold charge.

After the charge in the second bath is sufficiently heated, molten pig iron is poured into this bath and the blowing of oxygen through the bath is started. The resulting gases now pass through appropriately set gate valves and enter the first bath. At this point the first bath has been emptied of metal and has already received a new cold charge. The proposal to use a two-bath method, in order to utilize the heat of waste gases in steel-smelting units, was made as early as 1904. However, the realization of this idea became possible only during the 1960’s, when the metallurgical usage of oxygen as an oxidizer became widespread. The “blow-through” with oxygen significantly increases the content of carbon monoxide in the gases vented from the bath. The “afterburning” of carbon monoxide (completion or combustion) increases the efficiency of heating the charge. The output of the two-bath furnace is two to four times that of the Martin (open-hearth) furnace, and the fuel consumption is ten to 15 times less for the two-bath furnace. In the USSR the annual output of two-bath furnaces operating in the scrap-ore process, with a pig iron content in the charge of 60–70 percent, exceeded 1 million tons (1970).