Open hearth steelmaking

The high calcium limestone and dolomite should both be high in calcium plus magnesium carbonate content and low in silica and phosphorous (Table 11.4 [11.2]). They should be resistant to decrepitation on heating, and produce limes which are strong enough to resist being crushed in the blast furnace. 

The open hearth steelmaking process was invented in 1863 and up to the early 1960s was the principal means of producing steel in the U.S.A. and the U.K. [11.2]. Since then, it has been displaced by the basic oxygen steelmaking processes (see sections 27.4 and 27.5). 

Originally, the process was operated with a molten acid slag, which only permitted the removal of Si, Mn and C. Small amounts of limestone were often added towards the end of the refining process to produce a boil , caused by the calcination of the limestone and the evolution of carbon dioxide, but the amounts were insufficient to affect significantly the chemistry of the slag. 

Subsequently, the furnace was operated with a molten basic slag, which enabled the removal of P and S. Limestone, or a mixture of 80 to 90 % of limestone and 10 to 20 % of quicklime, were added to give a basicity (CaO- Si02) of 2.5 to 3. Typically this required about 25 kg of limestone per tonne of hot metal [11.4, 11.5]. Limestone with low silica and sulfur contents and a particle size of up to 250 mm was preferred. 

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G. Derge, ed., Basic Open-Hearth Steelmaking, 3rd ed., AIME, Warrendale, Pa., 1964. 

Bertrand Thiel A variation of the Basic Open Hearth steelmaking process, suitable for ores rich in silicon and phosphorus. Two hearths are used by varying the quantities of hme added to each it is possible to concentrate most of the silicon and phosphoms in the slag from the first. Developed by E. Bertrand and O. Thiel at Kladno, Bohemia, in 1894 subsequently adopted at Hoesch, Germany (hence the alternative name for the process). 

Opened fullerenes, 12 232 Open-end spinning, cotton yarn, 8 17 Open-head drums, 18 8 Open-hearth furnace, 12 320 21 408 Open-hearth steelmaking process, 16 150-151... 

Chipman, J. In Basic open Hearth Steelmaking. The American Institute of Mining and Metallurgical Engineers, S. 571. New York 1951. 

The BOS process replaced the Bessemer and open hearth steelmaking processes during the 1960 s and caused some major changes in both the steel and lime industries [27.1, 27.2]. The process is currently used for 70% of the world s steel production, with most of the remainder being in electric arc furnaces (EAF). The main processes in iron and steelmaking are illustrated in Fig. 27.1. 

The various steelmaking processes were all eventually supplanted (3,4). The first of the newer techniques was the historic pneumatic or Bessemer process, introduced in 1856. Shortiy thereafter, the regenerative-type furnace, known in the 1900s as the open-hearth furnace, was developed in the United... 

Kingdom. Adapted to steelmaking, the open-hearth process was the principal method for producing steel throughout the world until 1970. As of this writing (1996), it is stiU used in China and the CIS. 

Electric-Arc Furnace. The electric-arc furnace is by far the most popular electric steelmaking furnace. The carbon arc was discovered by Sir Humphry Davy in 1800, but it had no practical appHcation in steelmaking until Sir William Siemens of open-hearth fame constmcted, operated, and patented furnaces operating on both direct- and indirect-arc principles in 1878. At that early date, the avadabiHty of electric power was limited and very expensive. Furthermore, carbon electrodes of the quaHty to carry sufficient current for steel melting had not been developed (see Furnaces, electric). 

Basic oxygen furnaces (BOFs) have largely replaced open hearth furnaces for steelmaking. A water-cooled oxygen lance is used to blow high-purity oxygen into the molten metal bath. This causes violent agitation and rapid oxidation of the carbon, impurities, and some of the iron. The reaction is exothermic, and an entire heat cycle requires only 30-50 min. The atmospheric emissions from the BOF process are listed in Table 30-16. 

Acid Open Hearth The original version of the Open Hearth process for steelmaking in which the hearth is made of a silica refractory. The process does not remove phosphoms or sulfur, the acid impurities in the iron, so the raw materials must be relatively free from these. Pioneered by C. W. Siemens and F. M. E. and P. Martin at Sireuil, France, in 1864. 

Ajax An oxygen steelmaking process in which the oxygen is injected into an open hearth furnace through water-cooled lances. Used at the Appleby-Frodingham steelworks, UK. 

Basic Open Hearth A version of the Open Hearth process for steelmaking in which the hearth is made from calcined dolomite (calcium and magnesium oxides). The sulfur and phosphorus impurities in the raw materials are converted to basic slag, which is separated from the molten steel. First operated in 1882 at Alexandrovsky, near St. Petersburg, Russia, and at Le Creusot, France. It was the major steelmaking process in the world in the first half of the 20th century. See Thomas. 

Chenot An early steelmaking process. Iron ore was first reduced to sponge iron this was mixed with charcoal, manganese, and resin and compressed into small blocks. These blocks were then melted as in the Crucible process. Invented by A. Chenot in France in 1846 and operated on a small scale in Sheffield in the 1860s, but abandoned after the introduction of the Open Hearth process. 

Talbot A semi-continuous steelmaking process which combines the Bessemer and Open Hearth processes. Molten pig iron from a Bessemer converter is poured into an Open Hearth furnace containing fresh ore and lime. Impurities in the pig iron oxidize and enter the slag. The process improves the yield of steel and the throughput of the plant. Introduced by B. Talbot at Pencoed, PA, in 1900 and subsequently adopted in Europe. 

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