TOTEM Co Ltd.

 

Experience of Operating a Rotary Charging Unit (RCU) at the Bhilai Steel Plant

 

Dr.(Tech) B.M. Boranbaev, Dr.(Tech) B.L. Zhurakovskiy, V.N. Vakulin, Yu. M. Glazer
TOTEM Co.Ltd.
3-rd Mytischinskaya str., 16, block 60, Moscow, 129626, Russia
Tel.: +7(495)6316209
Fax: +7(495)6314777
E-mail: totem@totem-engineering.com
Sulaiman Ahmed
Bhilai Steel Plant (SAIL), Bhilai-490001(C.G.), India
Tel.: +91(778)2221024
Fax: +91(778)2222890
E-mail: sulaimanahmed@sail-bhilaisteel.com

 

Key words: Blast furnace, Rotary charging unit, Burden distribution, Performance, Maintenance

 

INTRODUCTION

Blast Furnace No.3 of 1033m3 useful volume of Bhilai Steel Plant, India was equipped with Rotary Charging Unit (RCU) during Category I Repair of the Blast Furnace and commissioned on 15.07.1998. This paper contains a detailed analysis of many year performance of RCU, which gives every reason to draw a conclusion that this apparatus has a substantial edge over the chargers of other designs.

THE SALIENT FEATURES OF THE ROTARY CHARGING UNIT

RCU represents a new type of top charging equipment having a 5-vane Rotary Distributor of burden materials as the main working part, which ensures a multi-stream and multi-layer distribution of burden materials on the stock profile of the furnace top. The Rotary Distributor has a flexible and highly efficient control of burden material distribution across the radius of the furnace top by way of changing the speed and direction of rotation of the Rotor. Technological capabilities of RCU in regard with the formation of the optimum stock profile and distribution of ore/coke ratio across the furnace radius are much wider and versatile than that of the conventional Double-Bell, as well as that of Chute Bell-less Top charging equipment (BLT).

The Lower Bell of RCU is set free from performing the function of burden distribution, which allows downsizing of its diameter and shifting the bell from the zone of direct thermal and abrasive attack of dust-laden gas flow. Simultaneously, the Rotary Distributor acts as an efficient protecting shield for the Lower Bell. Therefore, the Lower Bell operates under much more favorable conditions compared to the conventional Big Bell. As a result of the abovementioned, the service life of the Lower Bell of RCU is several times longer than that of the conventional Two-bell unit.

RCU discharges the burden materials into the blast furnace in five wide streams. It should be stressed that the period of discharge of one charge with the help of RCU is 2-3 times shorter than the dumping time of the Chute BLT. Therefore, RCU ensures a higher furnace charging rate and, hence, a higher throughput capacity of the charging system as a whole.

Due to the fact that the burden materials are discharged into the furnace in five wide streams simultaneously, a closed ring of burden materials on the stock surface is formed within 1/5 revolution of the Rotor. While discharging a single charge to the intermediate or peripheral areas of the furnace top, the Rotor forms 30 50 closed rings, which is 3 6 times more than one can achieve using Chute BLT. Due to the above feature, the Rotary Distributor has much higher averaging capabilities.

The Rotary Distributor reduces the mean circular non-uniformity of distribution in regard with material weight by 2.6 times and the variation in particle size distribution is reduced by 4.2 times compared to chute BLT as proved during special model tests 1.

The Rotor creates a smooth and soft discharge of the material into the furnace while it rotates and this neither deforms (shears) the underlying material, nor it results in any kind of uncontrolled deformation of the stock profile, which takes place in case of Two Bell systems and the Chute BLT.

Wear of the liner plates of the Rotor is much less intensive than that of the BLT chute lining and it does not have any adverse effect on the quality of material distribution. Usage of liner plates made of special heat resistant cast iron, separation of material flow into five streams and quite a slow velocity of material flow along the vanes of the Rotor guarantees high wear resistance of the lining and ensures minimum 4 years of continuous operation up to reline of wear plates.

Technical solutions incorporated in the design of RCU (protection of main parts from abrasive and thermal attack of the furnace gases, oil cooling of the Gearbox housing and of the support unit, Nitrogen cooling of the Rotor Shaft and Gearbox chamber etc.) ensure a long service life and reliable operation. RCU continues performing even at elevated top gas temperatures up to 5000C and at short-term peak temperatures up to 9000C.

INSTALLATION OF RCU ON BLAST FURNACE No.3, BSP

The BF dome part, the Skip Bridge, Skip Hoist, Bell drives and semi-clean gas lines for inter-bell pressure equalizing of Blast Furnace No.3 of BSP were retained without any changes when the existing bell system was replaced with RCU.

The RCU parts and units have been manufactured in Russia (Rotor and Angular Gearbox) and India (the rest of RCU) as per the detail design drawings and under the technical supervision by "TOTEM" (Moscow).

TOTEM Engineers were rendering technical supervision of equipment installation and adjustment of the automatic control system of RCU operation before commissioning. They have developed and incorporated the software based on physical modeling for various modes of blast furnace charging applicable to the actual operational conditions. Manuals have been prepared for the operation and maintenance of the mechanical equipment and automation & instrumentation as well as for the technological modes of charging. Theoretical & practical training of the personnel has been carried out. Comprehensive study of burden distribution upon the stock profile has been performed prior to the blast furnace blow-in.

TOTEM specialists have taken an active part in the blast furnace blow-in, helped developing the optimal technology for the blast furnace process and achieving the blast furnace Performance Guarantee indices using RCU 2.

After 2 years and 9 months of continuous operation, Blast Furnace No.3 has been blown down by the end of April 2001 because of unsatisfactory condition of the hot stoves. The blast furnace has been blown-in again after repair of the stoves in the middle of March, 2003 after 23 months of shutdown. Duration of the RCU operation totaled 61.5 months by August 2005 i.e. more than 5 years. Presently, RCU is in satisfactory condition and is still operated.

OVERVIEW OF BLAST FURNACE DEPARTMENT OF BSP

The Blast Furnace Department consists of seven blast furnaces (Ref. to Table I), four Pig Casting Machines, two Ladle Repair Shops, Tap Hole Mass Preparation Shop, Mechanical Shop, Coal Dust Injection Unit for BF No.6 & BF No.7 and a Pilot Plant for injection of Coal Tar in BF No.2 & BF No.3.

Table I Design features of BSP Blast Furnaces

Parameter description

BF

1

2

3

4

5

6

7

Useful volume, 3

1085*)

1085*)

1085*)

1719

1719

1719

2000

Working Volume, 3

935

935

935

1480

1480

1480

1740

Number of Cast Houses

1

1

1

1

1

1

2

Number of Iron Notches

1

1

1

2

2

2

2

Number of Slag Notches

1

1

1

-

-

-

-

Number of Tuyeres

14

14

14

18

18

18

20

Number of Hot Stoves

3

3

3

4

4

3
(Hoogovens)

4

Type of top Charging Equipment

Two-bell

Two-bell

RCU

BLT, single bin

BLT, single bin

BLT, single bin

BLT, double bin

Number of Cast House SGP

-

-

-

1

1

1

2

*) Useful volume of Blast Furnaces 1 3 was enhanced from 1033 3 to 1085 3 during Category I Capital Repair

All blast furnaces are equipped with conveyorized raw material supply to the skips, sinter screening facilities with fines return conveyors, as well as automatic charging, weighing and monitoring of the charged iron bearing materials and coke. Blast Furnaces No.5, 6 & 7 are equipped with iron ore screening facilities to screen out +40 & -10mm.

Blast Furnaces No.4 7 are equipped with radial Overburden Probes (4 nos. each) for radial top gas temperature monitoring. Hydraulic Mud Guns are used in BF-5, BF-6 & BF-7 for Tap Hole closing and Pneumatic Tap Hole Drilling Machines for the cast opening.

Initially, ramming Runner Mass was used for Cast House Runner making in BF-1, BF-2 & BF-3 and the throughput of the runners was about 5 7 thousand tones of hot metal. Since 2000, a castable runner mass comprising of high alumina and silicon carbide mixture is used for runner making and the runner hot metal throughput became 50 60 thousand tons. Castable heat resistant masses are used in BF-4, BF-5, BF-6 & BF-7, the throughput of which is up to 150 200 thousand tons of hot metal.

Screening of coke in BF No.1 ? 3 is performed with the help of screens with lower mesh of 20mm O. BF-4 lower screen mesh is made of wire mesh with 20 x 20mm square cells, while BF-5 ? BF-7 are having screens with round holes of O 28 .

Oxygen enrichment of blast to a moderate level (0.1 2.0%) was initially practiced in BF-4, BF-5, BF-6 & BF-7 only. Since 2004, oxygen enrichment was also incorporated in BF-2 & BF-3 after commissioning of Coal Tar Injection Unit.
Blast Furnaces of Bhilai Steel Plant operate under specific burden material conditions characterized by a high ash coke (16-17%) used along with high alumina iron ore, which impart an elevated content of Al2O3 to the slag to the extent of 17 20%.

A combination of sinter from Sinter Plant No.1 (70 80%) & Sinter Plant No.3 (20 30%) along with 0-60 mm iron ore is used in BF-1 ? 3. Because of obsolete design and worn out machinery of Sinter Plant No.1, the quality of sinter is characterized by unstable chemistry and particle size distribution.
Sized & screened lump ore of 10-40mm is used in larger blast furnaces (BF No.4 ? 7), SP III sinter in BF 4 & BF 5, while SP II sinter is used in BF 6 & BF 7.

Small quantities of manganese ore, LD slag and limestone are used for burden correction in all blast furnaces.
Blast Furnaces No.1 3 get 75 80% coke from Coke Oven Batteries No.1 ? 4, which have almost exhausted their service life and the rest 20 25% coke is supplied from the Open Coke Yard. BF 4 & BF 5 are using coke from the newly repaired Batteries No.5 & 6, while BF 6 & BF 7 are supplied with coke from Batteries No. 7 & 8.
Nut coke of +15mm is used in all blast furnaces. It is added to sinter to the sinter conveyors while sinter is filled in BF bunkers.

Coal dust of 10-11% ash and 29-32% volatile matter is injected in the Tuyeres of BF-6 & BF-7. Coal Tar produced by Chemical Recovery Plant and having 1.10 1.20g/cm3 density, 6 9% moisture and 76 78% Carbon content is injected as a coke substitute in BF 2 & BF 3.

It can be concluded from the abovementioned that smaller blast furnaces (BF No.1 - 3) are equipped with inferior facilities compared to that of larger furnaces and they operate under poorer burden conditions compared to larger blast furnaces (BF No.4 - 7). The smaller furnaces are supplied with unscreened iron ore, unstable and poor quality sinter from worn out SP I and low quality coke from threadbare Batteries No.1 - 4. The smaller blast furnaces are also featured by lower blast temperatures and lower top gas pressure.

EVALUATION OF THE EFFICIENCY OF THE RCU OPERATION IN BF 3
COMPARED TO OTHER TYPES OF TOP CHARGING EQUIPMENT

Blast furnaces of Bhilai Steel Plant are equipped with three different types of top charging units (Ref. to Table I): BF 1 & BF 2 retained the conventional two bell charging equipment, Rotary Charging Unit is installed in BF 3, while BF 4, 5, 6 & 7 are equipped with Paul Wurth BLT supplied to BSP from 1987 to 1992.

An in-depth and exhaustive analysis of the performance indices of all blast furnaces within a considerably long period, i.e. during three financial years of 2000 2001 (a year of BF 3 operation before it was put down for reserve), 2003 2004 (when BF 3 was re-commissioned) and 2004 2005, has been carried out in order to verify the efficiency of the RCU performance.

The Annual Performance Indices based on the official operational data of the Plant are presented in Tables II IV within the abovementioned period and separately for each financial year. The difference in the specific productivity and total fuel rate between Blast furnaces No. 1, 2, 4 - 7 and similar indices of BF 3 (the actual & adjusted to similar operating conditions) are presented in the abovementioned Tables.

In order to avoid subjective factors, the annual hot metal production of each blast furnace has been calculated using Fe balance based on the records of statistical data on the specific consumption of burden materials and the content of Fe in the materials. Adjustment of the performance indices of blast furnaces to comparable conditions has been carried out by means of factor-wise correction of the specific productivity and specific coke rate in accordance with calculated standard coefficients presented in Table V. The actual performance indices of Blast Furnace No.3 were taken as a reference in order to adjust the indices of other blast furnaces to a comparable status.

Table II Performance Indices of the Blast Furnaces of Bhilai Steel Plant in 2000-2001
(BF-6 is down for reserve)


Parameters

BF-1

BF-2

BF-3
(reference)

BF-4

BF-5

BF-7

Hot metal output, t/day
Working time, days/annum
Specific prod-ty, actual, t/m3/day (Pact.) *)
dPact. (actual), % of reference
Hot metal output, adjusted, t/day
Spec. Prod-ty, adjusted t/m3/day (Padj.) *)
dPadj. (adjusted), % of reference
Coke rate, dry, g/THM
Nut coke rate, dry, g/THM
Pitch rate, g/THM
Total fuel rate, actual, (act), g/THM
dact (actual), % of reference
Coke rate, adjusted, g/THM
Total fuel rate, adjusted. (adj.), g/THM
dadj. (adjusted), % of reference
Iron ore rate, g/THM
Sinter rate, g/THM
LD slag rate, g/THM
Mn ore rate, g/THM
Limestone rate, g/THM
Fe content in burden, %
Sinter content in burden, %
-5 mm in burden, %
Blast:
Temperature, 0
2 content, %
Pressure, Atm.exc.
Top pressure, Atm.exc.
Hot metal composition, %: Si
Mn
S
Slag basicity, CaO/SiO2
Al2O3 content in slag, %
Coke properties: , %
10, %
+80 , %
Downtime, %
Non-dry casts, %
Off-rod, %

1544.1
280.3
1.651
-3.11
1522.0
1.628
- 4.46
515.4
33.6
0.3
549.3
2.56
528.6
562.5
5.02
818.8
860.7
29.6
22.2
1.6
56.10
49.7
7.9

950
21.0
1.75
0.67
0.71
0.58
0.031
0.97
18.39
17.0
8.2
7.7
2.81
7.9
0.54

1322.7
221.9
1.415
-16.96
1360.1
1.455
- 14.61
512.5
31.9
0.1
544.5
1.66
518.6
550.6
2.80
906.5
750.5
7. 7
10.4
8.5
57.78
44.8
8.0

943
21.0
1.41
0.37
1.05
0.37
0.031
0.97
19.87
17.0
8.2
7.7
4.13
12.7
0.86

1593.8
343.5
1.704
0.00
1593.8
1.704
0.00
501.9
33.7
-
535.6
0.00
501.9
535.6
0.00
826.8
854.1
16.1
18.2
8.0
56.52
49.8
7.9

887
21.0
1.74
0.68
0.71
0.56
0.033
0.98
18.22
17.0
8.2
7.7
2.41
10.0
0.61

2244.5
354.8
1.516
-11.03
2188.1
1.478
- 13.26
544.3
28.5
-
572.8
6.94
558.1
586.6
9.52
755.2
915.0
18.2
23.3
6.6
56.42
53.4
7.7

944
21.17
1.85
0.74
0.71
0.63
0.030
0.95
18.61
17.2
8.2
7.8
2.75
7.1
0.83

2287.8
350.4
1.546
-9.27
2129.7
1.439
- 15.55
564.0
25.6
-
589.6
10.08
589.1
614.7
14.77
695.5
979.1
7.4
19.6
5.4
57.04
57.3
7.7

925
21.48
1.97
0.85
0.70
0.58
0.029
0.94
18.51
17.2
8.2
7.8
2.01
5.4
0.44

3171.3
354.0
1.822
6.92
2892.4
1.662
- 2.46
543.6
28.6
0.5
572.7
6.93
586.2
615.3
14.88
589.5
1112.8
-
27.6
0.9
56.07
64.3
7.5

962
21.12
2.43
1.27
0.63
0.56
0.028
0.96
18.28
17.2
8.2
7.2
3.08
3.1
0.18

Total Efficiency Factor
(dPact. - dadj.), % f reference 2

-9.48

-17.41

0.00

-22.78

-30.32

-17.34

*) as per working volume

Table III Performance Indices of Blast Furnaces in 2003-2004


Parameters

BF-1

BF-2

BF-3
(reference)

BF-4

BF-5

BF-6

BF-7

Hot metal output, t/day
Working time, days/annum
Specific prod-ty, actual, /3/day (Pact.) *)
dPact. (actual), % of reference
Hot metal output, adjusted, t/day
Spec. prod-ty, adjusted t/m3/day (Padj.) *)
dPadj. (adjusted), % of reference
Coke rate, dry g/THM
Nut coke rate, dry, g/THM
Coal dust rate, g/THM
Total fuel rate, actual, (act), g/THM
dact (actual), % of reference
Coke rate, adjusted, g/THM
Total fuel rate, adjusted. (adj.), g/THM
dadj. (adjusted), % of reference
Iron ore rate, g/THM
Sinter rate, g/THM
LD slag rate, g/THM
Mn ore rate, g/THM
Limestone rate, g/THM
itanium ore rate, g/THM
Mill scale rate, g/THM
Fe content in burden, %
Sinter content in burden, %
-5 mm in burden, %
Blast:
Temperature, 0
2 content, %
Pressure, Atm.exc.
Top pressure, Atm.exc.
Hot metal composition, %: Si
Mn
S
Slag basicity, CaO/SiO2
Al2O3 content in slag, %
Coke properties: , %
10, %
+80 , %
Downtime, %
Non-dry casts, %
Off-rod, %

1738.8
288.46
1.860
- 5.87
1770.2
1.893
- 4.20
539.9
21.1
-
561.0
6.63
528.2
549.3
4.41
685.3
981.6
5.3
12.5
12.9
1.6
-
57.33
58.9
8,07

949
21.0
1.80
0.65
0.65
0.24
0.033
0.98
19.03
16.2
8.3
7.7
2.97
9.1
0.61

1552.3
82.04
1.660
- 15.99
1624.6
1.738
- 12.04
536.1
27.1
-
563.2
7.05
531.9
559.0
6.25
581.7
1084.9
0.5
5.6
10.1
0.3
0.4
57.71
65.1
7,86

925
21.0
1.74
0.64
0.77
0.17
0.032
0.97
18.98
16.2
8.3
7.7
8.83
2.5
0.63

1847.2
354.83
1.976
0.00
1847.2
1.976
0.00
507.9
18.2
-
526.1
0.00
507.9
526.1
0.00
680
991.0
2.5
3.8
8.9
-
0.5
57.71
59.3
8,06

948
21.0
1.82
0.68
0.68
0.14
0.030
0.98
19.32
16.2
8.3
7.7
4.20
9.0
0.73

2288.1
343.58
1.546
- 21.76
2179.5
1.473
- 25.46
509.1
24.4
-
533.5
1.41
510.3
534.7
1.63
659.7
986.8
6.0
14.3
12.9
-
2.6
57.87
59.9
7,82

904
21.55
1.90
0.87
0.65
0.27
0.030
0.96
19.04
16.2
8.2
7.4
2.06
2.8
0.74

2263.5
359.5
1.529
- 22.62
2011.4
1.359
- 31.22
510.5
21.4
-
531.9
1.10
535.7
557.1
5.89
638.0
1013.0
1.7
13.3
6.3
0.3
0.2
57.93
61.4
7,60

976
21.78
2.08
0.92
0.63
0.38
0.030
0.94
18.88
16.2
8.2
7.4
1.47
1.3
0.06

2548.3
353.58
1.722
- 12.85
2181.0
1.474
- 25.40
437.5
24.8
65.7
528.0
0.36
471.5
562.0
6.82
659.0
994.8
3.6
2.0
5.5
2.5
-
58.51
60.1
8,18

1034
22.66
2.04
0.86
0.63
0.13
0.030
0.98
18.92
16.2
8.2
7.2
1.73
1.5
0.2

3298.3
354.96
1.896
- 4.05
2867.1
1.648
- 16.60
509.1
41.2
-
550.3
4.60
543.6
584.8
11.16
606.6
1078.2
0.4
5.3
0.9
1.0
-
58.15
64.0
7,59

946
21.21
2.40
1.29
0.66
0.19
0.027
0.98
18.77
16.2
8.2
7.2
3.02
0.5
0.01

Total Efficiency Factor
(dPact. - dadj.), % f reference

-8.61

-18.29

0.00

-27.09

-37.11

-32.22

-27.76

*) as per working volume

Table IV Performance Indices of Blast Furnaces in 2004-2005
(BF-4 is down for reserve)


Parameters

BF-1

BF-2

BF-3
(reference)

BF-5

BF-6

BF-7

Hot metal output, t/day
Working time, days/annum
Specific prod-ty, actual, t/m3/day (Pact.)
dPact. (actual), % of reference
Hot metal output, adjusted, t/day
Spec. prod-ty, adjusted t/m3/day (Padj.) *)
dPadj. (adjusted), % of reference
Coke rate, dry g/THM
Nut coke rate, dry, g/THM
Coal Tar rate, g/
Coal dust rate, g/THM
Total fuel rate, actual, (act), g/THM
dact (actual), % of reference
Coke rate, adjusted, g/THM
Total fuel rate, adjusted. (adj.), g/THM
dadj. (adjusted), % of reference
Iron ore rate, g/THM
Sinter rate, g/THM
LD slag rate, g/THM
Mn ore rate, g/THM
Limestone rate, g/THM
Mill scale rate, g/THM
i ore rate, g/THM
Metallic Iron rate, g/THM
Fe content in burden, %
Sinter content in burden, %
-5 mm in burden,%
Blast: Temperature, 0
2 content, %
Pressure, Atm.exc.
Top pressure, Atm. exc.
Hot metal composition, %: Si
Mn
S
Slag basicity, CaO/SiO2
Al2O3 content in slag, %
Coke properties: , %
10, %
+80 , %
Downtime, %
Non-dry casts, %
Off-rod, %

1555.1
197.1
1.663
- 18.84
1624.3
1.737
- 15.23
562.1
22.1
-
-
584.2
9.89
539.3
561.4
5.61
527.3
1131.7
1.9
10.3
5.0
-
-
-
58.01
68.3
7,50
753
21.0
1.82
0.67
0.74
0.26
0.027
0.97
18.73
16.9
8.41
8.04
1.2
3.24
0.28

1724.5
357.3
1.844
- 10.00
1697.1
1.815
- 11.42
528.1
19.3
7.9
-
555.3
4.46
540.6
567.8
6.81
575.5
1070.8
0.8
10.6
3.6
9.5
-
3.9
58.29
65.0
7,66
939
22.26
1.81
0.67
0.74
0.34
0.032
0.98
18.78
16.9
8.41
8.04
1.79
2.68
0.4

1916.0
351.5
2.049
0.00
1916.0
2.049
0.00
501.6
18.6
11.4
-
531.6
0.00
501.6
531.6
0.00
562.8
1104.9
1.5
8.9
3.0
15.4
8.7
-
57.12
66.2
7,51
928
22.61
1.8
0.71
0.78
0.25
0.032
0.97
19.10
16.75
8.28
7.75
1.61
6.19
0.57

2243.3
356.9
1.516
- 26.01
2091.1
1.413
- 31.04
523.4
21.7
-
-
545.1
2.54
556.5
578.2
8.77
495.7
1160.9
1.4
8.1
2.7
3.6
0.3
-
57.88
70.2
7,66
975
21.97
2.04
0.89
0.63
0.32
0.032
0.96
18.56
16.75
8.28
7.75
0.88
1.53
0.08

2621.7
353.6
1.771
- 13.57
2427.8
1.640
- 19.96
460.1
22.9
-
74.9
557.9
4.95
499.5
597.3
12.36
564.9
1085.1
1.9
0.6
8.9
0.1
1.9
-
58.49
65.8
7,68
1041
22.51
2.02
0.76
0.66
0.14
0.031
0.99
18.69
16.8
8.35
7.41
1.99
1.87
0.04

3109.3
355.2
1.787
- 12.79
3006.3
1.728
- 15.67
511.7
26.1
-
11.9
549.7
3.4
546.6
584.6
9.97
519.1
1143.9
0.3
1.6
0.6
-
0.2
-
58.42
68.8
7,68
954
21.3
2.17
1.05
0.71
0.15
0.028
0.98
18.79
16.8
8.35
7.41
4.78
1.71
0.02

Total Efficiency Factor
(dPact. - dadj.), % f reference

-20.84

-18.23

0.00

-39.81

-32.32

-25.64

*) as per working volume


Table V Impact of Technological factors on the productivity and coke rate of blast furnace


Description of Factor

Variation of factor

Variation of indices, %

BF productivity

Specific coke rate

Hot Blast Temperature,

100

2

3,3

Top Gas Pressure, Atm. exc

0,1

1,1

0,5

Fe content in burden, %

1

2

1,8

Raw Limestone rate, g/THM

10

0,5

0,5

5 in burden, %

1

1

0,8

+ 80 in coke, %

10

2

2

Coke ash content, %

1

2

2

10 of coke, %

1

3

2,5

Oxygen enrichment of blast, %

1

2

-

Si content in hot metal, %

0,1

1,2

1,2

Mn content in hot metal, %

0,1

0,3

0,3

Number of non-dry casts, %

1

0,3

0,2

Off-rod, %

1

0,1

0,2

Downtime, %

1

1

-

It is evident from Tables II IV that the specific productivity of Blast Furnace No. 3 within the above considered period of operation is higher and the specific fuel rate is lower compared to the other blast furnaces of the Shop both as per the actual and adjusted indices. The only exclusion is a high actual specific productivity of BF 7 in 2000 2001. However, the adjusted specific productivity indices of BF 7 for the above period are lower than that of BF 3.

It should be noted that BF 3 performs more efficiently when compared to either BF-1 & 2, which are of the same volume and operate under similar burden conditions, as well as to BF 4 ? 7, which are better equipped and are operated with better burden materials.

The above mentioned performance indices of all blast furnaces are presented in the Figure 1 in the form of bar graphs for a more convincing comparison.

The analysis of the performance results present a strong evidence that Blast Furnace No.3 equipped with Rotary Charging Unit operates with far better indices of specific productivity and fuel rate within an extended period of time (more than five years till date) compared to the other blast furnaces of the Shop. On certain occasions, the differences in the adjusted parameters amount to 15% in regard with the specific fuel rate and 30% in the specific productivity.

A significant and recurrent advantage of BF-3 in comparison with the other blast furnaces of the Shop can be explained only through fundamental differences in the technology of blast furnace charging by means of different types of charging equipment.

The most modest and conservative estimate shows that replacement of the conventional double bell system with RCU ensures not less than 5 % reduction in the specific coke rate with a simultaneous 6?8% blast furnace productivity enhancement.

Tentative estimation shows also that under BSP operational conditions and prevailing international BF coke prices about $250?300/ton, the payback period for the RCU investment due to coke saving only would not exceed 1 year, while taking into account the furnace specific productivity enhancement and reduction in maintenance & repair of the charging equipment, the actual return-on-investment period becomes less than 6 months.

On the basis of the comprehensive comparative analysis of the performance indices of Blast Furnaces of Bhilai Steel Plant, it can be concluded that RCU has an edge over both the conventional bell charging and chute BLT systems. Due to its specific design and technical features, RCU ensures a much higher quality of burden material distribution over the BF top, which results in a considerable coke rate reduction and productivity enhancement of the blast furnace.

It should be noted that a similar conclusion has been made on the basis of the analysis of the long-term performance data of Rotary Charging Unit in BF 1 & BF 2 of West Siberia Steel Works in Russia 3.

2000-2001 Performance

2003-2004 Performance

2004-2005 Performance

Figure 1 Comparison of adjusted annual performance indices

of Blast Furnaces of Bhilai Steel Plant

COMPARATIVE ESTIMATE OF MAINTENANCE AND REPAIR EXPENDITURES
FOR DIFFERENT TYPES OF TOP CHARGING EQUIPMENT OF BHILAI STEEL PLANT

Two-Bell Top Equipment

The performance of blast furnaces 1 & 2 within 10 years before the stoppage of each of the furnaces for the last Capital Repair was scrutinized in order to find out the service life of Two-bell system.

7 Capital Repairs have been carried out in BF-1 within 10 years, including four Category-III Repairs, two Category-II Repairs and one Category-I Repair. The average service life of the Top charging equipment calculated against the working time of the blast furnace totaled to 13.7 months. BF-2 has also undergone through 7 Capital Repairs within the same period, including five Category-III Repairs and two Category-II Repairs. The average service life of the Top charging unit turned out to be 13.3 months.

The average service life of the Top charging units for both blast furnaces was 13.5 months and duration of the shutdown for Category III Repair was 3.4 days.

The tentative estimate shows that within 5 years of operation of blast furnaces with Two-Bell system under BSP conditions, a certain investment is required for the maintenance and repair (procurement of new equipment, refurbishment of worn out equipment, dismantling & erection activities, compensation of production losses and over-consumption of coke during furnace shutdown and start-up), which makes about 70 80% of the cost of RCU.

BLT with Chute Distributor

In accordance with the Modernization Programme of Blast Furnace Shop, Bell-less Top Charging Units were installed as follows: BF-7 on 30.08.1987, BF-4 on 08.12.1989, BF-6 on 30.11.1990 and BF5 on 27.07.1992.

Table VI shows the data on the repairs carried out in these furnaces since the installation of BLT.


Table VI Capital Repairs in BSP Blast Furnaces


BF

Capital Repairs

Average Time of

Category-III Repair

Category-II Repair

Total

Inter-repair period, years

Category-III Repair, days

BF-4

2

2

4

3.5

3.5

BF-5

3

2

5

1.9

3.5

BF-6

2

2

4

3

3.5

BF-7

7

2

9

1.8

5.7


As per the reference data 4, the service life of parts of BLT was:
- Chute - service life varies from 1.5 to 2.0 years. Replacement of the chute can be performed only during the furnace shutdown with
top gas ignition within 27-30 hours;
- Silicon Rubber Seal of Gas Seal Valves service life is one year and 6-hour shutdown is required for the replacement.
As per the BSP Blast Furnace Shop data service life of BLT parts was:
- Upper Bank of Valves: Gas Sealing Valve 2 years (Indigenous valve 6?8 months); Material Gate 1 year. Replacement time
of the Valve Unit 12 hours;
- Lower Bank of Valves: Gas Sealing Valve 1 year (Indigenous make valve - 6 months); Material Gate 6 months. Replacement
time of the valve unit takes 72 hours during blast furnace shutdown with top gas ignition;
- Discharge Funnel of Two-bin BLT: service life 2 years.
If we assume that the average life of the replaceable parts of BLT is 2 years, then 2.5 repairs for the replacement of those parts will be required within 5 years of operation. A tentative estimate of expenditures required for the maintenance and repairs of BLT is commensurable with the cost of RCU. The actual expenditures for BLT will be higher due to shorter service life of certain units of BLT.

Rotary Charging Unit (RCU)

No repair whatsoever has been performed on the Rotary Charging Unit within five years of operation of BF-3 with RCU. Maintenance of RCU consisted only of visual inspection, checking of gas sealing of the contact surfaces of the bells (once in a quarter), routine (1-2 times a month) oil make-up filling of angular gearbox oil lubrication system. Oil consumption is ~ 600 l/annum.

Initially, RCU receiving funnel was supplied with the revolving distributor drive. As proved by the practical work, an intermittent operation of RCU with revolving receiving funnel did not have any influence on the circumferential distribution of burden materials and furnace performance indices. As a result, the revolving distributor drive has been turned out of operation in 2000.

A comprehensive inspection of all parts and units of RCU has been carried out in January 2003 (after 2.75 years of continuous operation of RCU) during the furnace shutdown. The following observations have been made during the above inspection:

- Liner Plates and cell-type self-lining of the receiving and guide funnels were in good condition and no visible wear was observed;
- Wear resistant plates of Upper & Lower Bells were in good condition, no local wear of the surface of Bells has been noticed;
- Liner plates and cell-type self-lining of the Intermediate Hopper were in good condition without visible traces of wear;
- The condition of wear resistant lining of the Angular Gearbox Chamber top cover and Support Beams was satisfactory, no chipping of hard-facing or presence of naked spots was found.
- The status of the cell lining and liner plates of Discharge funnel was also good and no wear was observed;
- Liner plates of the discharge surface of the vanes made of wear resistant cast iron were found in satisfactory condition, wear was not more than 1-5%; no deformation of the vanes was observed while rotating the Rotor; a steel rope was found wound around the shaft of the Rotor.
- No noise or abnormal beat inside the Angular Gearbox was observed while rotating the Rotor.
During the 5th year of operation of RCU, a slight gas leakage was observed through the contact surface of the Upper Bell, which was eliminated by means of turning the Bell by 1800.
High service life of RCU can be, first of all, explained by the design features of the parts and units of the RCU 5 and low temperature (~ 100 0 ) in the area of Lower Bell.
Since no repair of RCU has been carried out and not a single part of it was replaced within 5 years of operation, the total expenditure for maintenance of RCU within that period was by the order lower of that of Double-bell and Chute BLT.

 

SUMMARY

1. The results of the comparative analysis of the performance indices of blast furnaces of Bhilai Steel Plant in 2000-2001, 2003-2004 and 2004-2005 leaves no room for any doubt that Blast Furnace No. 3, which is equipped with TOTEM Top Rotary Charging Unit, operates with much better techno-economical parameters in terms of fuel rate and specific productivity compared to all other blast furnaces of the Shop within an extended period of five years of operation.

On the basis of the results obtained through the comprehensive study, it can be concluded that Rotary Charging Unit has obvious advantages in comparison both to conventional Two Bell Top and Chute BLT. By the virtue of its design and technological features, RCU ensures a higher quality of burden distribution on the BF top, which results in a significant coke rate reduction and blast furnace productivity enhancement.

2. Tentative estimate of expenditures for the maintenance and repair of Two-bell units and Chute BLT reveals that within 5 years of operation these expenditures are commensurable with the cost of RCU. High service life of RCU can be testified by the fact that no repair of the unit has been carried out and not a single part of it was replaced within 5 years of operation of BF-3 with RCU. The total expenditure for maintenance and repair of RCU is substantially less than that of Two-bell and Chute units.

3. Under BSP operational conditions and prevailing international BF coke prices ($250?300 /ton), the payback period for the RCU investment due to coke saving only would not exceed one year, while taking into account the furnace specific productivity enhancement as well as reduction in maintenance & repair of the charging equipment, the actual return-on-investment period becomes less than 6 months.

 

REFERENSES

1. B.M.Boranbaev, S. K.Nosov, A. N.Lavrik, "New concept of blast furnace charging",
XXXII Seminar on Ore Reduction and Raw Materials, Vila Velha-ES-ABM, Brasil, November, 2002, pages 371-385.

2. B.M.Boranbaev, V.N.Vakulin et al., "Running of the blast furnace in with the use of the rotary charging unit",
Steel, No.10, 1999, pages 11 16.

3. A.F.Avtsinov, S.F.Bugaev et al., "Efficiency of the rotary charging unit as used on the West Siberia
Steel Works blast furnaces", Bulletin of the "Chermetinformatsiya" Institute, No.2, 2002, pages 35-40.

4. T.Damodaran, S. K.Jain, R. K.Gopal, T.Jayachandran, "Maintenance strategy for BLT equipment", Bhilai Steel Plant (SAIL),
Mover,Vol. 1, October, 1998, pages 34-44.

5. TOTEM, "Rotary Charging Unit", Steel, No.11, 1998, pages 15 17.

Up

 

 

TOTEM Co Ltd.

""