INCREASING

T H E S E R V I C E L I F E OF H O T - B L A S T

MAINS

(UDC 669.162.222.004.5) I.V.

Kotel'nikov

and A.A.

Berdnik,

Ii'ich Zhdanovskii Plant Translated from Metallurg, No. 4, p. 13, April, 1964

With the blowing of natural gas in the blast furnaces of our plant, the hot blast temperature has increased from 850-870 to 950*C, and in one furnace to 1000~ However, blowouts have become more frequent in the hot-blast mains. The low service life of the main led to a decrease in the blast temperature, and consequently to a decrease in the efficiency of using natural gas. The output of the furnaces also dropped owing to downtimes for repair of the mains and the drop in gas pressure under the bell. For example, the downtimes for the shop to eliminate blowouts in the hot blast mains in 1960 was 20 h (not counting the slow- down times). Blowouts were most frequently observed on the bustle pipe owing to formation of cracks in the casting at overheated spots, at places where the goosenecks are welded to the bustle pipe, and at places where the pipes of the hotblast valves are connected to the hot-blast main as a result of the formation of the cracks in the casing. The control of blowouts in the hot-blast main mainly reduced m a careful periodic examination of the mains in order to detect in time over-heating of the casings, to delivery of fire-clay solution under pressure to these places, and to patching of the cracks. However, these measures could not radically solve the problem of increasing the service life of the hot-blast main. The results of observations showed that the chief cause for the low service life of the hot-blast main was the pronounced thermal fluctuations of the refractory brickwork of the mains when blowing in file blast furnace after prolonged shutdowns-mainly to replace the charging apparatus, Owing to their low service life, furnaces were shut down for replacing the charging apparatus every 8-10 months for 40-60 h. In this case the refractory brickwork of the hot-blast main cooled to a temperature of the order of 50-70~ When blowing in the furnace the hot-blast temperature was set at 500-600~ and within 10-16 h reached the operating temperature, 900-950~ (figure, curve a). The high starting hot-blast temperature and also the rapid elevation of temperature from the starting to the operating destroyed the solidity of the refractory brickwork of the hot-blast main; cracks occurred which were later sites of blowouts. To increase the service life of the hot-blast main, it was proposed to set the starting blast temperature at 200~ after prolonged shutdowns of the furnace and to raise it to the operating temperature in 24 h. Curve b in the figure shows the proposed temperature regime which was followed while blowing in the same furnace after replacing the charging a apparatus in July 1961.

1000

p

goo 800

9

7oa 6aa 500

The new temperature regime made it possible to reduce considerably the initial thermal load on the brickwork of the hot-blast main.

9

E~ *003o0-

2oa

2 # 6 8 10 12 10 16 18 20 22 2it T i m e from start of blowing, h

Temperature regime schedule when blowing in a furnace after replacing the charging apparatus.

164

Calculations showed that at a starting hot-blast temperature of 500~ 1 m 2 of the surface of the main accumulates in 1 h about 13000 kcal of heat, and at 200"C the quantity of heat accumulated by the brickwork drops to 3000 kcal, i.e., 1/4 as much, which of course appreciably improves the operating conditions of the brickwork when blowing in the furnace.

As resuk of using the new temperature regime when the furnaces are being blown in, the downtimes of the furnaces owing to blowouts in the hot-blast main have virtually been eliminated. Moreover, it was possible (along with other measures for increasing the hot-blast temperature) to raise and stably maintain the blast temperature within 950-1000"C.

165