blast(redirected from blast off)
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blasting, supplying air or other gases in industrial heat engineering plants in order to ensure or intensify the physicochemical processes taking place in them. The gas is compressed and supplied by means of blowers and compressors. There are two types of blast: cold blast, in which ordinary air is supplied, and hot blast, in which air is preheated to 1100°-1200°C. The substitution of a hot blast for a cold blast in metallurgy has increased the productivity of furnaces.
Blasts with a constant moisture content, which eliminates the adverse effect of moisture variations in ordinary air on smelting conditions, appeared in the 1940’s. Blasts enriched with oxygen to increase the rate of the smelting process began to be widely used in the 1960’s. The highest blast flow rate is characteristic of blast furnaces in which the average amount of gas supplied is 2 m3/min per cu m of furnace working volume (in modern blast furnaces, 6,000–7,000 m3/min, under a pressure of 0.3–0.5 meganewtons per sq m [MN/m2]). The simultaneous supply to the furnace of oxygen-enriched air and of natural gas not only increases the productivity but also reduces the consumption of coke. An oxygen blast supplied from above at a pressure of 0.9–1.5 MN/m2 and a rate of 300–800 m3/min is used in converter production.
ii. The characteristic instantaneous rise in pressure followed by a sudden decrease that results from this movement, differentiated from less-rapid pressure changes.