CAST IRON METHODS

OF I N C R E A S I N G

THE HOT

A. A. S h o k u l , I. M. P e f t i e v , V, A. C h e r n y s h e v , a n d N. N.

BLAST

TEMPERATURE UDC 669.162.23

Temnokhud

The solution of problems associated with the improvement of stoves at this plant began as earIy as 1959 in connection with the use of natural gas and the need to improve the quality of the pig iron produced. At present, when the blast furnaces operate at a combined blast there are no technical limitations to a further increase in the hot blast temperature. It must therefore be maintained constant at the upper limit in order to utilize fully the stove capacity. Control of the blast furnace by varying the hot blast temperature is not economic since a more advantageous method for e l i m i n a t i n g temporary heating of furnaces is the use of a humidified blast. An increase in the hot blast temperature to 1100~ and over was achieved in blast furnaces by the c o m m i s i o n ing of new and the improvement of existing stoves, the improvement of hot blast ducts, the development of new high-temperature tuyeres, automation of the furnace, and by the discontinuation of the use of hot blast as a means of controlling the blast furnace. Two stoves were built in 1959-1965: one for the No. 4 blast furnace in 1959 and the other for No. 3 blast furnace in 1961. The construction of a further stove for No. 5 blast furnace is in progress. Thus, each blast furnace has four stoves.

.^

,+39100

/ @"

',II'',I_I',I

'JIl

II II II It II I111 II I1 II It i l II I1 II

A a

Fig. 1. Stove top (a) before and (b) after the reconstruction.

Azovstal' Plant. Translated from Metallurg, No. 2, pp. 3-5, February, 1968.

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'1

Class B fireclay, item 6-45 bricks .,~r

--)/f.

Class A fire clay, " ~ t ~ 72 bK

Class B fireclay, i t e m ~ ~ l ~ 38-73 bricks item 3-20 bricks

~. /

Class A fireclay, 8 bricks; brickitem}8 7

4

~

na bricks i t e m ~ k ~ 3-36 bricks, ~ item 39-34 bricks

High-quality brick, item 38-48 bricks; it 39-13 bricks

~

j / / ~ / ~

~//,e~/ J

Fig. 2. Hot blast duct (a) before and (b) after modification. TABLE 1. Change in Total and Specific Heating Surface of Stoves from 1958 to 1965 Specific heating No. of Total heating surface, mZ/m a blast surface, m z furnace 1 2 3 4 5 6

Total

1958

1965

79731 63810 72280 56130 94380 II0000 476331

86254 81880 81210 89100 94380 llO00O 542824

1958 64,6 51,7 55,6 43,6 62,4 64,0 57,8

1965 70,0 66,3 62,5 668,5 2,4 64,0 65,5.

In 1959-1966 22 major overhauls and 10 medium repairs were carried out on stoves. During the major overhauls of five of these stoves their height was increased by 6 m which increased the heating surface of each stove by 5572 m 2. Firebrick containing 4 5 % alumina was used in the top part of nine stoves while six stoves were lined by brick containing 62% alumina. In ten stoves the two- and three-stage checkerwork was replaced by a single-stage checker with a cell size of 45 x 45 ram. Only four stoves will have 60 • 60 mm checker.

The design of the top part of the lining (Fig. 1) was altered in three stoves; this eliminated damage sustained by the checker at the point where the dome joins the circular wall of the shell and in addition prevents burning of the shell The domes of two stoves were for the first time insulated by slag wool; this considerably reduces the heat loss from the stove top. In 14 stoves the Frein gas burners were replaced by the high-output IZTM units with an output of 4800 ma/h. The construction of new stoves and the improvement of existing ones considerably increased the total and specific heating area (Table 1). This also increased the blast temperature on average to 1096~ and reduced coke consumption (Table 2). The increase in blast temperature resulted in a deterioration of the working conditions of blast ducts and air tuyeres and in a shortening of their service life. For this reason the hot blast ducts were improved during the general overhauls (Fig. 2). In addition, intensive work was carried out on the development of high-temperature air tuyeres. At present Nos. 2, 3, 4, and 5 blast furnaces have hot blast ducts lined with 2.5 instead of 2 layers of a brick containing 45% alumina while at Nos. 1 and 6 three layers are used. Before 1961 the blast furnaces had screened air tuyeres; in 1961 the tuyeres were redesigned and received a foam-fireclay lining with cooled flanges while in 1963 designers suggested the use of a tuyere lining made from a refractory material packed into special frames. This material has the following composition: 80% alumina powder and 20% sand mixed with 5% suifite-alcohol grains and 12% water. This lining resists a blast temperature of 1200~ Tuyere failure is now very rare, and then only when they are filled with slag after an emergency stoppage of the furnace or when the cooling water feed piping fails. From 1964 onwards the fireclay material has also been used for bends and spherical joints. The automation of all stoves reduced the switching time and improved heating.

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TABLE 2. Changes in the Hot Blast Temperature and Coke Consumption from 1958 to 1966 No. ofblast fumace I 2 3 4 5 6

Years 1958 1959 1960 1961 1969 1963 1964 1965 1966 827 783 783 841 817 -812

758 749 847 813 896 954 838

957 830 899 905 922 962 914

989 981 989 994 990 974 982 934 957 994 963 1021 966 961 935 987 970 970 991 998 995 1013 1040 1035 978 980 984 995

Total coke consumption, kg/t.on of 831 855" 752 725 plg Iron

705

679

673

lOOt 1037 1078 1120 1033 941 1036

1051 1108 1100 1151 1087 1048 1096

672

637

* The increase is due to the start of the production of cast iron. When working at 1100-1150~ heating of the shell was observed at the point where the cylindrical part and the dome join at the combustion chamber side near the duct connections, gas burners, and manholes. The time needed for running repairs increased and stove campaign decreased (e.g., at the No. 6 blast furnace working at a hot-blast temperature of 1050-1070~ stove campaign was 6 years). In addition, the service life of stoves is c o n siderably affected by alkali deposits in the top part of the checkerwork when the furnace operates "to draft." The presence of alkali chemicals in firebrick markedly lowers its melting point and this results in the melting of the checker in its upper part. The brick in the upper rows of the checker were 7-8% alkali while the alkali content in a new checker is only 0.6-1.0%. In order to e l i m i n a t e the heating of the shell over the height of the stove and in the dome region a 113 m m thick insulation lining was moved nearer to the shell. Between the shell and the insulation lining a gap of 100-120 m m was provided which was subsequently filled with granulated slag. In this case the stove wall and the insulation brick layer are not connected and this eliminates any possibility of damage to the insulation layer when the stove shell height changes. The insulation layer of the dome rests on the stove wall and the dome lining (Fig. lb). For this reason, when the lining expands it does not damage the insulation layer of the dome. Such dome linings eliminate the need for the use of a m e t a l ring at the dome-base. In order to reduce heat losses the dome is insulated with mineral wool. In order to avoid the heating of the shell in the region of the hot-air duct gas burner connections they are lined with refractory bricks: three layers in the connection and in the wall region without interconnecting the layers in order to e l i m i n a t e failure of bricks during the displacements of the wall in the vertical direction when the stoves are in operation. In addition, in this region the stove wall is lined close to the shell leaving a gap which is filled with a 40-50 m m thick asbestos layer. The organization of stove repair has also been improved in recent years. A general overhaul is carried out in 30-35 days instead of previous 60 days; this has been made possible by the following measures: 1) all necessary materials are delivered to the stove before the repair starts; 2) two fans are mounted for ventilation and cooling of the dome space; and 3) a new method is used for blasting operation for which the partition wall is removed at a height of 4-5 m from the top and several horizontal holes measuring 300 x 300 or 400 x 400 m m are made, Because of the shortened service life of stoves they must be repaired during the operation of blast furnaces and this considerably reduces the furnace output and increases coke consumption (this applies in particular to the blast furnaces with three stoves). For example, during the repair of the stove of No. 5 blast furnace in March 1965 the hot blast temperature decreased from 1050 to 700~ This increased the coke consumption by 12% and correspondingly reduced the blast furnace output. This supports once again the need to have four stoves for each blast furnace. To increase the hot blast temperature to 1200~ the following measures must be taken: 1) the general overhauls must be used to increase the stove height; 2) the combustion chamber, dome, and 50% of the upper portion of the checker should be lined with a higha l u m i n a brick containing 62% alumina;

64

3) the dome temperature shonld be increased to 1380~

and the gas exit temperature to 450~

4) during the blast furnace stoppages needed to r e p l a c e equipment damaged by heat the furnace must be run "to draft," bypassing the stoves; this requires the installation of a special pipe in the region of the circular air duct; 5) additional thermocouples should be installed in stoves to measure the temperature distribution over the chamber height; and 6) a fourth stove should be built for the blast furnaces with three stoves.

65