HISTORY OF TECHNOLOGY IIOT-BLAST STOVES -- 120 YEARS A. G. Romanenko

In 1977, 120 years had elapsed since the Englishman Edward Alfred Cowper took out his patent on a hot-blast stove for blast furnaces. Cowper was born on Dec. 19, 1819, the son of a professor at the Royal College of Engineering Science. He entered the office of G. Breitwein at the age of 14, where his natural gifts and technical intuition enabled him to show his inventive capabilities even during the years of apprenticeship: in 1841 he invented detonator signals to stop trains in case of fog. In 1848, Cowper entered the engineering office of Fox and IIenderson. Here he showed himself to be a capable designer, having worked up the design for a railroad station entrance hall with a span of 215 feet (65.6 m), which was regarded as an extraordinary structure at the time. Later Cowper opened his own office and began to develop apparatus for heating the blast for blast furnaces. He also worked on improvements to marine engines. Discoveries and inventions do not occur in a vacuum; thus, the previous history of blast heating began long before Cowper patented his hot-blast stove. Seddeger had stated his opinion that the blast should be heated as early as 1799, and Leichs confirmed his proposal by experiments in 1812-1822. At the time, however, they did not receive due recognitiOn from metallurgists. In 1828, the Englishman James Neilson obtained a licence for the use of heated blast. In spite of its relatively low temperature (only 150~ the hot blast improved blast furnace operation appreciably: the temperature of the iron and the slag increased and the latter became more fluid, and fuel consumption was reduced. In 1831, blast heating was increased to 300-400~ at the Calder Works (Scotland), making it possible to replace coke by coal. The blast was heated in iron boxes or in cast-iron pipes passing through a coal-fired stove. In 1834, Faber du Faur heated the blast feed pipes at the Sainerhutte Works (Germany), making use of sensible heat from the blast-furnace gas. The hot-blast stove was installed on the furnace top, which made charging difficult. The installation was not readily accessible for servicing, and was therefore not widely used. In 1835-1836, a hot blast was being used at many plants in England, France, and Germany . In Russia, blast heating was tested in 1836 in the Urals in blast furnaces at the Vyksa Plant. However, the Urals furnaces continued to run on a cold blast until the 1870s, and air-heating devices were installed at State plants at Verkhnyaya Tura and Kushva only in 1870. The box-type and tubular stoves had a short life and did not raise the blast temperature appreciably. The first Cowper hot-blast stove, with checkerwork made from bricks laid in staggered rows (of the same type as the Friedrich Siemens regenerators), was not free from substantial faults. The checkerwork was heated by combustion products from coal burned in an external stove. Heating of the Checkerwork by the ascending gas flow was uneven. The sections close to the inlet port let through more gas and heated up more quickly; the draft increased here, and this increased the inflow of gas still more and intensified the heating of the nearer bricks in the checkerwork. The opposite occurred during the descent of the current of air to be heated. An improved hot-blast stove appeared in 1860. In it, Cowper used a gas burner and a special combustion chamber to heat the checkerwork. He replaced Siemens' checkerwork by his own, with straight channels. The combustion products now descended through the checkerwork and the heat flux improved. The power of the hot-blast stove increased: it became possible to heat the blast to 600~ Hot-blast stoves designed by the Englishman Thomas Whitwell appeared in 1869. In these the checkerwork was replaced by brick partitions. Not knowing the laws of heat transfer, Translated from Metallurg, No. 2, pp. 44-45, February, 1978.

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9 1978 Plenum Publishing Corporation

Whitwell tried to make better use of the heat by making the route followed by the gas as long as possible. Resistance to the passage of the gas flow increased as a result of the many changes in direction. At first, Whitwell's units were widely used in England and on the continent. There were supporters of both systems among blast furnace men up to the end of t h e 1880s. Both inventors must be given their due: each of them spent his whole life in improving his hot-blast stove. However, Cowper's hot-blast stoves had obvious advantages. A hundred years ago~ his units had an internal diameter of 7.9 m, an overall height of 13 m, a checkerwork height of 8 m, and an effective brickwork mass of 240 tons; 180 m s of air pe r minute were heated to 700~ the unit. There were 21.5 kg of brick for each cubic meter of air passing through per hour. The Whitwell unit would heat only i00 m s of blast per minute with the same blast temperature and effective brickwork mass. The Cowper hot-blast stoves began to drive out their competitors, and in 1883, the number of Cowper stoves throughout the world had risen to 360. In one of his papers on blast heating, Cowper mentions that he had been awarded a bonus: sixpense for each ton of pig iron produced using his equipment. There were substantial improvements to the hot-blast stove equipment in the south of Russia, where ferrous metallurgy had begun to develop rapidly in the 1870s. The blast furnaces at the southern plants were equipped with Cowper hot-blast stoves. At the ten major plants in the South in 1913, the specific hot-blast stove surface was 119.7 m 2 per ton of daily output, or 58.3 m s per m 3 of furnace volume. By virtue of its high level of blast heating (700-900~ one of the largest furnaces in Europe, blast furnace No. 6 at the South Russia Plant of the Bryansk Company (now the Petrovskii Dnepropetrovsk Plant), operated with a coke consumption ratio of not more than 1 (a good figure for the time). The furnace had three hot-blast stoves 30 m high and 7 m in diameter, each with a heating surface of 7176 m 2. The constant striving for increased blast furnace output and more economical operation made it essential to increase the hot-blast stove heating surface and to improve the stove equipment. In fairness it must be said that Cowper had the soundest ideas for further improvements to his units. For example, he suggested the installation of gas burners operating with not more than 13% excess air and water-cooling for the hot-blast valve (put into practice many years later, after Cowper's death, which occurred on June 9, 1893). The most numerous and varied ferent checker brick shapes (some cells. This prompted one English hot-blast stoves lies in learning

changes made were to the checkerwork. Many dozens of difextremely fanciful) and sizes were tested in forming the engineer to say not without irony: "The art of building to make holes in bricks."

The shape and position of the combustion chambers were altered many times. The consumption chamber occupies about a third of the hot-blast stove cross section, reducing the area and volume of the checkerwork accordingly. It was thought that the combustion chamber could be dispensed with, by igniting the gas below the dome. Difficulties in servicing the burners and hot-blast valves and sweating of the eheckerwork (due to combustion of gas within it) prevented the extensive use of these stoves. After the Second World War, hot-blast stoves with a remote combustion chamber were built for blast furnaces 4 and 5 at the Petrovskii Metallurgical Plant following proposals by K. A.

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Oleinikov and I. K. Kotov. The volume and surface of the checkerwork increased substantially, with no change in the external dimensions of the hot-blast stove. Intensification of stove operation with increased brickwork temperature made it essential to use brick with higher refractoriness: hard-burned Dinas, and high-alumina and chrome-magnesite brick, making it possible to raise the blast temperature to 1400~ The introduction of automatic burners, the capacity of which in terms of air reaches 200,000 m 3, is a significant improvement in hot-blast stove equipment. The almost universally adopted automatic control of hot-blast stoves provides for maintenance of the required heating conditions and the necessary sequence of valve operations when the units are switched from gas to air and back. During the 120 years of their existence, Cowper hot-blast stoves (while retaining their general layout) have altered beyond all recognition in their dimensions, power, and the arrangement of individual subassemblies and equipment. Up to the present time, Russian and Soviet engineers have laid great stress on improving hot-blast stove design. Unique blast furnaces, with an annual capacity of s o m e 4 m i l l i o n tons of pig iron, the largest in the world, have been built in the Soviet Union. Their ancillary equipment includes exemplary hot-blast stoves. However, even the most modern hotblast units have potential for further improvement. As regards the blast-furnace process, there are no limitations as to blast temperature, and the search in this area is continuing.

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