Metallurgist, Vol. 50, Nos. 9–10, 2006
ENERGY CONSERVATION IN THE SINTER PLANT OF THE SEVERSTAL’ COMPANY
M. S. Tabakov,1 M. A. Gurkin,1 V. P. Nevraev,1 T. V. Detkova,1 V. A. Kobelev,2 and V. M. Kurkin3
UDC 622.785.5:669.012.48
Results are presented from a study of the operation of sinter plants operated by the Severstal’ company when finely crushed iron-ore concentrates are used in the charge. The company decided to modernize the equipment used for primary mixing, moistening, and balling of the charges in sinter plants Nos. 2 and 3. Preliminary estimates indicate that the cost of this improvement should be recovered in three years.
The iron content of the crude ore processed at mining-concentration combines in Russia decreases every year. To avoid a deterioration in the quality of the concentrate produced from the ore, such plants are subjecting the ore to greater comminution during the beneficiation process. However, the introduction of fine-grained concentrate into the charge used for sintering places new special requirements on the operations of batching, mixing, moistening, and balling the charge. The equipment available for mixing, moistening, and balling at sinter plants that were built several decades ago is not adequate to obtain a charge of the necessary granulometric composition. The required degree of mixing of the materials is not achieved in the mixers that are employed (usually drum-type mixers used for the primary mixing operation). Also, the nozzles that are usually in use do not provide for uniform moistening of the charge, and the balling equipment does not provide the necessary degree of balling. In 2003, a laboratory test produced sinter with improved hot and cold strength and a 23% reduction in solid fuel consumption (compared to the base sinter). During the production of experimental batches of the sinter, the charge was mixed for 3 min, uniformly moistened, and balled for 6 min; the combined duration of the mixing and balling operations was 2–3 times greater than in the existing production practice. The homogeneous, gas-permeable charge that was obtained made it possible to reduce solid fuel consumption and obtain sinter with improved metallurgical properties. In 2004, sinter shop No. 2 at the Severstal’ plant conducted commercial trials on a sintering machine and halved the amount of charge materials introduced into the primary mixer. Here, the relative yield of sinter increased 2.6%, the consumption of solid fuel decreased 5%, and sintering-machine speed increased 10%. The strength of the sinter increased slightly, and the productivity of the sintering machines as a group also rose. The use of fine-grained iron-ore concentrate in the sintering charge requires an increase in the charge’s relative moisture content and an improvement in the efficiency of the balling operation. It is known that a film of water 9–16 nm thick (the exact thickness depending on the temperature) forms on the surface of the particles comprising the components of the charge when they are moistened. Calculations show that a 16% increase in the content of finely crushed Kursk Magnetic Anomaly (KMA) concentrates at Severstal’ requires a 1–1.5% increase in moisture content. 1
Severstal’ OAO. Ural Institute of Metals. 3 SPbÉK NPO. 2
Translated from Metallurg, No. 10, pp. 39–41, October, 2006.
506
0026-0894/06/0910-0506 ©2006 Springer Science+Business Media, Inc.
TABLE 1. Parameters of the Sintering Operation for Sintering Machine No. 11 (AKM-312)
Date
July 15 July 16 July 19 August 2 August 3 August 4
Amount in the charge, tons/h
Balling-drum
Charge cons-
speed, rpm
umption, tons/h
Sintering-machine Amount of coke in Yield of usable
recycled sinter
limestone
coke fines
speed, m/min
the top layer, tons/h
sinter, tons/h
x1
x2
x3
x4
x5
x6
x7
x8
5.0
442
331.7
80.2
27.5
3.1
1.2
327
5.0
461
332.8
81.7
27.9
3.2
1.5
298.5
4.5
438.9
337.2
71.8
27.5
3.0
2.2
295.9
4.5
454.9
328.2
70.8
27.9
3.0
2.4
320.6
4.0
486.8
331.7
81.9
33.6
2.9
1.1
271.4
4.0
468.2
347.2
80.3
35.1
3.1
1.6
281.5
6.0
484.8
335.3
69.4
29.6
3.3
2.1
481
6.0
490.2
357.6
70.6
33.6
3.3
1.9
453
5.5
490.6
337.7
67
34.9
3.2
0.9
479
5.5
490.9
339.7
70.8
36
3.2
2.5
464
5.0
470.4
359.5
75.5
36.5
3.3
2.1
344
5.0
471.1
377.8
71.2
36
3.3
2.1
389
To analyze the performance of the balling drums in sinter plants Nos. 2 and 3, investigators used the method of calculation devised by V. I. Korotich and compared the specified process parameters with their actual values. Under the test conditions and normal production conditions at the Severstal’ Metallurgical Combine, the optimum parameters for the (2.8 × 8 m) balling drums in plant No. 2 are 0.2° for the inclination of the drum axis and 7.5 rpm for drum speed; the corresponding optimum parameters for the (3.2 × 12.5 m) balling drums in plant No. 3 are 1.2° and 7.5 rpm. Tests performed on the drum in plant No. 2 under the new operating conditions showed an increase in the degree of balling of the sintering charge from 31.2 to 37.2% with a decrease in the drum angle from 1.5 to 0.75°. Increasing the speed of rotation of the drum also proved effective. The results of study of the operation of (3.2 × 12.5 m) balling drums in plant No. 3 at different speeds (rpm) are shown below: 4.5 6.0 Charge load on the sintering machine, tons/h 534.46 540.6 Output of usable sinter, tons/h 218.6 231.2 Relative yield of sinter, % 40.9 42.8 Consumption of coke fines in the charge, kg/ton 62.26 61.4 Drum strength, +5 mm, % 74.4 75.3 Abradability, –0.5 mm, % 4.4 4.5 It follows from the above data that an increase in the speed of the balling drum is accompanied by an increase in the relative yield of sinter and the charge load on the sintering machine and a decrease in the consumption of solid fuel. To determine the accuracy of our predictions of the sintering operation, we constructed a multivariate model of sintering machine No. 11 (AKM-312) for different balling conditions (drum speed was varied from 4 to 6 rpm). Table 1 shows the process parameters used to construct the model. The dependence of the output of usable sinter on the speed of the balling drum (Fig. 1) shows that an increase in drum speed is accompanied by an increase in the ballability and gas permeability of the charge, an improvement in the indices of the sintering operation, and a substantial decrease in the amount of product requring re-sintering. All this has led to a significant boost in the productivity of the sintering machine. 507
Output of usable sinter, tons/h 500
400
300 y = 108.87x – 177.22 200
4
5 6 Drum speed, rpm; K = 0.9
Fig. 1. Dependence of the yield of usable sinter on the speed of the balling drum.
Sintering-machine speed, m/min 3.3 3.2
3.1 3 y = 0.16x + 2.3583 2.9 4
5 6 Drum speed, rpm; K = 0.78
Fig. 2. Dependence of the speed of the sintering machine on the speed of the balling drum.
The correlation between the yield of usable sinter and the speed of the balling drum is determined by the equation y = 108.87x – 177.22,
(1)
where y is the yield of usable sinter, tons/h; x is the speed of the drum, rpm. The correlation coefficient K for Eq. (1) is equal to 0.9. The speed of the sintering machine also depends appreciably on the speed of the balling drum (Fig. 2). The equation linking the speed of the sintering machine and drum speed has the form y1 = 0.16x1 – 2.3583,
(2)
where y1 is the speed of the sintering machine, m/min; x1 is the speed of the balling drum, rpm. The correlation coefficient K1 for Eq. (2) is 0.78. The multivariate model that we constructed from production data (see Table 1) and used to determine the output of usable sinter has the form y = –147.935 + 68.02x1 + 1.25x2 – 5.28x3 – 7.19x4, (3) where y is the yield of usable sinter, tons/h; x1 is the speed of the balling drum, rpm; x2 is the charging rate, tons/h; x3 is the amount of limestone in the charge, tons/h; x4 is the speed of the sintering machine, m/min. 508
500
Yield of usable sinter, tons/h
Actual Calculated
400
300
200 1
2
3
4
5
6 7 8 9 10 11 12 No. of experiment, K = 0.98
Fig. 3. Actual and calculated values of the yield of usable sinter.
We will compare actual values of sinter output with values calculated from model (3). The regression coefficient is 0.98, the determination index is 0.96, and the standard deviation of the actual values of sinter output from the calculated data is 16 tons/h or 4.4%. It follows from these results (see Fig. 3) that the yield of usable sinter calculated from the multivariate model closely agrees with the actual value. This means that it is possible to predict the course of the sintering operation and, thus, to also control it. The results obtained from scientific research done on the given topic in 2003–2004 was used as the basis for modernizing the mixers and balling drums in sinter plants Nos. 2 and 3 at Severstal’. The upgrades made to the primary mixers and drums accomplished the following: • an increase in the capacity of the sintering machines; • the installation of high-speed mixers that make the charge up to 90–95% homogeneous; • optimization of the moistening and balling of the charge, ensuring that the degree of balling achieved is at least 50–60%; • automation of the production operations that are involved. Conclusions. Laboratory studies have shown that it is possible to perform the sintering operation in an energy-efficient manner. The studies also made it possible to more accurately identify the factors that affect energy conservation in this operation. Factory tests have demonstrated that operating conditions can be changed in such a way as to conserve energy during sintering. The results obtained from the laboratory and factory tests were used to make the decision to modernize the equipment employed by sinter plants Nos. 2 and 3 at Severstal’ to mix, moisten, and ball the sintering charge. According to preliminary calculations, the cost of the modernization should be recovered in three years.
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