Operating efficiency of
Rotary Charging Unit
as
Used on Blast Furnaces at the West Siberia Steel Works.
A.F.Avtsinov,
B.M.Boranbayev, V.N.Vakoulin, V.V.Gaydouk, M.F.Maryasov
West Siberia Steel
Works, Totem Co. Ltd.
3rd Mytischinskaya
Str., 16, block 60, 6th floor, Moscow, 129626, Russia
Tel.:
+7(495)631-62-09, Fax:
+7(495)631-47-77
E-mail:
totem@totem-engineering.com
Key words: Rotary
Charging Unit, Blast Furnace
As of late, there
has been a growing interest among ironmakers in Russia and abroad
towards the performance of the Rotary Charging Unit (RCU), used on
blast furnaces, which has lead to the necessity to analyse once
again its efficiency at the West Siberia Steel Works, both at the
time of it being commissioned and what it is nowadays. The experts
from WSSW and Totem Co. Ltd have carried out such an analysis
jointly.
RCU is an
up-to-date charging device of new generation, with its salient
feature being its rotating distributor of burden, which is located
inside the furnace and designed as a five vane rotating propeller.
The general view of RCU is given in Figure 1.
RCU consists of the
following main parts: guiding funnels to guide stock as it goes from
skips to the receiving funnel; upper bell, transfer hopper/ lock
with a gas isolator, which receives stock before it is sent into the
furnace; lower bell; angular gearbox for the rotor drive; vane
rotor. The charging process is controlled automatically through a
specific automatic control system called “Rotor”.
Burden is distributed throughout the top span by
varying speed and spinning direction of the rotor. Depending on the
speed, the bulk of stock is lain and the burden ridge is formed at
various distances from the furnace central line. As it happens the
ridge can be shifted from one annular zone to another, smoothly
without sharp changes in profile, which makes it possible to vary
ore/coke ratio along the furnace radius in the same smooth way.
Owing to 5 vanes, one revolution of the rotor would make 5 layers of
stock in the top. One discharged portion of stock makes 30 to 40
layers, on the average. Such a practice ensures a high degree of
circular distribution uniformity and averaging of burden in terms of
chemistry and size as it is being discharged into the furnace.
The first RCU,
which had been fabricated by the Chief Mechanic Division of the WSSW,
was installed on blast furnace No.2 (2000 m3) in June
1989, at the time of 3rd category capital repair. In the first RCU
design, in addition to the above-said components, there was a
provision of a revolving burden distributor.
Prior
to the erection of RCU a research had been carried out, using a RCU
1:25 scale model and full-size model, to look into the burden
distribution pattern in the top. Another research was carried out
with the help of RCU in the top before blow-in, again to check the
distribution pattern. A comparison of the results, obtained from the
physical models and the furnace before blow-in showed adequacy of
the data generated by all tests for the distribution of burden along
the top radius. This fact made it much simpler to plan later new
promising modes of charging operations, on the basis of preliminary
data, obtained from a small RCU physical model [1].

Fig.1. Blast
Furnace with RCU
It was found out by research that the most
flexible control of the desired distribution of burden along the top
radius could be achieved by a separate discharge of ore-bearing
material and coke, using, in most cases, the ring-wise pattern of
charging.
After blow-in
and further blowing the modes of charging practice had been
streamlined and specified, taking into account their impact upon the
heat main indices (furnace productivity and specific coke rate).
Also, main criteria for adjusting modes of charging practice were
specified, like pressure drop along the furnace height, distribution
of carbon dioxide along the top radius, utilisation of chemical and
thermal energy of gas
[2].
Table 1 shows a
comparison of main operating indices of blast furnace No.2 during
the base period (1st half of 1989), when a typical
two-bell apparatus was used, and trial periods after the
installation of RCU, in August-December 1989, respectively.
Table1. Basic performance indices of BF No.2
(2000 m3) at WSSW, after replacing 2-bell apparatus with
RCU
Indices |
Base
1st half
1989 |
Aug.
1989 |
Sep.
1989 |
Oct.
1989 |
Nov.
1989 |
Dec.
1989 |
Design |
2-bell |
RCU |
RCU |
RCU |
RCU |
RCU |
Output |
|
|
|
|
|
|
Actual t/day |
4404 |
4667 |
4727 |
4634 |
4665 |
4800 |
Adjusted t/day |
|
4739 |
4761 |
4798 |
4862 |
4799 |
D
P % |
|
7.6 |
8.1 |
8.9 |
10.4 |
9.0 |
Coke rate Actual kg/t |
431.9 |
418.8 |
417.4 |
416.5 |
422.2 |
414.0 |
Adjusted kg/t |
|
401.3 |
406.1 |
408.8 |
415.8 |
413.5 |
D
C % |
|
- 7.10 |
-5.97 |
-5.30 |
-3.73 |
-4.30 |
Natural gas rate m3/t |
102.6 |
97.3 |
90.7 |
100.9 |
101.0 |
91.5 |
O2 in blast % |
28.9 |
29.1 |
28.8 |
28.7 |
28.2 |
28.0 |
Fe in burden % |
57.05 |
56.50 |
56.84 |
56.20 |
56.32 |
57.37 |
Ore/coke ratio t/t |
3.9 |
4.08 |
4.08 |
4.13 |
4.05 |
4.11 |
Blast rate m3/min |
3501 |
3438 |
3426 |
3566 |
3546 |
3666 |
Blast temperature
°
C |
1145 |
1145 |
1129 |
1135 |
1132 |
1139 |
Blast moisture g/m3 |
5.5 |
12.5 |
7.1 |
5.6 |
3.0 |
2.6 |
Pressure drop atm (pos) |
1.48 |
1.53 |
1.54 |
1.53 |
1.52 |
1.50 |
CO utilisation % |
45.10 |
45.73 |
45.71 |
45.62 |
45.47 |
45.66 |
Si in hot metal % |
0.66 |
0.66 |
0.63 |
0.66 |
0.67 |
0.72 |
Mn in hot metal % |
0.60 |
0.57 |
0.53 |
0.58 |
0.57 |
0.56 |
Top pressure atm (pos) |
1.61 |
1.56 |
1.54 |
1.53 |
1.55 |
1.58 |
Top gas temperature
°
C |
167 |
160 |
152 |
155 |
157 |
154 |
Downtime %
Slag basicity CaO/SiO2
Slag basicity CaO+MgO/SiO2 |
0.86
0.91
1.23 |
0.60
0.92
1.23 |
0.75
0.93
1.24 |
0.89
0.94
1.24 |
0.82
0.95
1.23 |
0.0
0.92
1.22 |
Coke grade Ac %
M40 %
M10 % |
10.0
69.8
7.2 |
10.0
69.8
7.7 |
10.1
70.7
7.3 |
9.9
70.3
7.4 |
10.2
70.4
7.4 |
10.0
72.4
7.3 |
CO2 content %
Points along top radius 1
2
3
4
5
6 |
14.0
-
21.6
-
-
16.6 |
18.6
22.2
23.6
22.3
20.0
8.4 |
19.0
22.8
24.0
22.9
20.6
10.6 |
18.0
22.1
22.9
22.1
19.8
11.1 |
19.4
22.3
22.4
21.8
19.5
6.9 |
17.5
21.3
22.9
22.6
20.3
9.7 |
Аs analysis
of the furnace performance showed, thanks to RCU, in the trial
periods it became possible to redistribute ore-coke ratio and gas
flow respectively along the top radius. CO2 content in
gas in periphery went up from 14.0 to 17.5 - 19.4%, while in the
centre it went down from 16.6 to 6.9 - 11.1%. A more uniform
distribution of ore bearing material in the peripheral and central
zones of the top and appearance of the central gas vent due to a
more concentrated discharge of coke all these helped to make the gas
flow more even throughout the whole span of the top, furnace run
steadier and utilisation of flew gas better. The utilisation rate of
CO went up from 45.1 to 45.47 - 45.73%, while the temperature of top
gas went down by 7 - 13
°
C.
Table 2. Basic performance indices of blast
furnace No.1 (3000 m3), WSSW, as a two-bell apparatus was replaced
with RCU
Indices |
Base 1st
quarter, 1991 |
April 1992 |
May 1992 |
June 1992 |
Design |
2-bell |
RCU |
RCU |
RCU |
Output actual
t/day
adjusted, t/day |
5452
|
5535
5892 |
5967
5723 |
6052
5884 |
D
P % |
|
8.1 |
4.97 |
7.9 |
Coke rate actual, kg/t
adjusted kg/t
D
C % |
446.6
|
423.2
416.2
-6.8 |
425.9
412.4
-7.65 |
430.6
420.4
-5.87 |
Natural gas rate, m3/t |
96.0 |
84.7 |
82.1 |
88.4 |
O2 in blast, % |
27.6 |
25.0 |
27.9 |
26.7 |
Fe in burden, % |
57.35 |
57.07 |
56.3 |
57.0 |
Ore/coke ratio, t/t |
3.78 |
3.97 |
4.02 |
3.91 |
Blast temperature,
°C |
1152 |
1165 |
1147 |
1130 |
Blast moisture, g/m3 |
2.0 |
2.5 |
8.3 |
15.7 |
Pressure drop, atm (pos) |
1.50 |
1.69 |
1.80 |
1.71 |
Top pressure, atm (pos) |
1.50 |
1.45 |
1.66 |
1.62 |
CO utilisation rate, % |
45.23 |
45.66 |
45.85 |
45.57 |
Top gas temperature,
°C |
184 |
178 |
179 |
180 |
Si in hot metal, % |
0.75 |
0.72 |
0.70 |
0.69 |
Mn in hot metal, % |
0.47 |
0.56 |
0.61 |
0.61 |
Downtime, % |
2.99 |
3.29 |
0.63 |
0.55 |
Coke grade Ac
M40
%
M10
% |
10.2
71.8
7.3 |
10.2
72.3
7.5 |
10.4
72.9
7.5 |
10.4
73.3
7.6 |
CO2 content, along the radius,
% |
|
|
|
|
periphery |
15.4 |
18.0 |
19.2 |
16.2 |
middle |
24.2 |
23.5 |
22.9 |
22.2 |
centre |
16.0 |
12.5 |
12.0 |
7.3 |
Having reduced the
heat indices to similar conditions, the following results were
obtained: furnace productivity in the trial periods had been
increased by 7.6 - 10.4% (by 8.8% as average), the specific coke
rate has been decreased, as compared with the base period, by 3.37 -
7.1% (by 5.28% as average). It should be also noted that during
period No.2, on some dates, when smelting conditions happened to be
quite favourable, the output of hot metal would go up to 5200 - 5500
t/day.
In 1991, a
charger with revolving burden distributor of improved design was
erected on blast furnace No.1 (3000 m3 useful volume).
The RCU on BF-1, which is still in operation, has two guiding
funnels and upgraded rotating distributor of burden with a 34 m3 funnel which can accommodate two skips. The interbell space of 63 m3
can hold four skiploads. In practice, burden is charged in two-skip
separate (one coke, one ore) portions, though sometimes in mixed
halfportions
[3].
It should be noted
that as of late the rotating burden distributors of blast furnaces
No.1 and No.2 have been put out of operation. As a long-lasting
practice proved, their performance does not exert practically any
effect upon the circular uniformity of distribution. This inference
has been substantiated by trials on the RCU physical models.
Table 2 shows the
main indices of blast furnace No.1 performance in the base period (1st quarter of 1991) when a typical two-bell apparatus was in use, and
during trial periods (April, May and June, 1992) when RCU was
mounted on the furnace. It should be noted that due to a slump in
the steel products market, the run of the furnaces in 1991-1992 had
been somehow put under restraint.
As can be seen from
Table 2, in the trial periods, when RCU was in use, the furnace
productivity, as adjusted to similar smelting conditions, went up by
4.97- 8.1% (by 7.0% average), and an adjusted coke rate went down by
5.87-7.65% (by 6.8% average). Similarly to blast furnace No.2, a
research had been carried out on BF No.1 with the aim of finding
rational charging procedures, capable of additional loading of ore
bearing material to the periphery of the top, stretching of the
ridge in the central part of radius and unloading of stock from the
central zone. As RCU was used, CO2 content in the
periphery increased from 15.4 to 16.2 - 19.2%, in the middle point
of radius it decreased by 0.7 - 2.0% and in the centre decreased
from 16.0 to 7.3 -12.5%.
Thanks to RCU, the
run of the furnace became steadier, the furnace became less
susceptible to poor quality of coke and ore bearing material.
The Chief Mechanic Division also fabricated RCU
for BF No.1 at the WSSW. All in all, 4 RCUs had been fabricated: 2
for BF No.2 and 2 for BF No.1.
The first RCU of BF
No.2 was taken off during scheduled capital reline work after 15
months of performance, to inspect the condition of components and
parts. The lining of vanes and other elements of the Unit and
contact surfaces of the bells were found in a satisfactory
condition. RCU-1 and RCU-2 on BF No.2 had been operated by turns for
11 years altogether, with the campaign being extended up to 23-25
months. And during that period there were no sign of a sizeable wear
on the contact surfaces of bells and cups, lining of the receiving
funnels, gas isolator and rotor. There has been no repair of the
rotors during the period of their performance, except for
replacement of some lining plates on vanes that happened to be
slightly eroded.
RCU-3 and RCU-4 on BF No.1 are also in a
satisfactory condition after 9 years of service (also by turns).
Some lining plates on the vanes have been also replaced.
Nowadays all
chargers on BF No.1 and BF No.2 are in a satisfactory condition,
still in operation. For the sake of comparison, a two-bell apparatus
with valves is being used on blast furnace No.3. Its service life is
1.5 years. When taken off, all members of this apparatus are to be
reclaimed: old facing from big and small bells, big and small bells
funnels, cups and valves is to be removed. After that the revolving
burden distributor and valves mechanisms are reconditioned and bells
and cups are hard-faced with expensive material and undergo
grinding. Sometimes it is necessary to repair or replace big and
small bells rods. Cost of the reconditioning of a typical two-bell
apparatus (without valves), with allowance to its service life
reduced to 1 year, is likely to be even higher.
It would be
interesting to look into the comparison of performance of two
similar blast furnaces at the WSSW (BF No.1 and 3000m3 BF
No.3), that are equipped with different chargers. On blast furnace
No.1 a circular and radial distribution of burden is carried out
with the help of RCU, whereby burden is laid at fixed radii in 9
annular zones of the top. On blast furnace No.3 the distribution of
burden is controlled by movable throat armours in accordance with
the preset charging cycle, with some separate charges like CC¯¯OO,
when ore halfportions are loaded into the periphery and coke
portions into the furnace central line zone.
Table 3. Performance indices of blast furnaces
No.1 and No.3, WSSW, in October-December 2000, as adjusted to
similar smelting conditions
Indices |
Unit |
BF No.3 |
BF No.1 |
Volume |
m3 |
3000 |
3000 |
Design |
|
2-bell, valves |
RCU |
Output |
t/day |
6355 |
6710 |
DP |
% |
|
5.58 |
Coke rate |
kg/t |
435.8 |
416.8 |
DC |
% |
|
- 4.36 |
Natural gas rate |
m3/t |
86.3 |
89.7 |
O rate |
m3/t |
104.9 |
103.2 |
O2 in blast |
% |
27.30 |
27.35 |
Fe in burden |
% |
55.94 |
56.06 |
Blast temperature |
º C |
1156 |
1163 |
Blast moisture |
g/m3 |
11.6 |
13.1 |
Pressure drop |
atm |
1.69 |
1.73 |
Top pressure |
atm (pos) |
1.37 |
1.68 |
CO utilisation rate |
% |
45.27 |
45.69 |
Si in hot metal |
% |
0.49 |
0.48 |
Downtime |
% |
0.8 |
0.7 |
Slag basicity CaO/SiO2 |
|
1.05 |
1.04 |
Slag basicity CaO+MgO/SiO2 |
|
1.30 |
1.30 |
Tuyeres replacement (including burnt-out
ones) |
number |
12/5 |
14/3 |
Tap time |
% |
98.6 |
99.1 |
Coke grade moisture
ash
CSR
CRI |
%
%
%
% |
0.0
10.8
62.7
30.5 |
1.1
11.1
60.3
33.5 |
CO distribution along top radius |
|
|
|
periphery |
% |
20.2 |
20.6 |
middle |
% |
23.3 |
24.9 |
centre |
% |
12.7 |
10.5 |
The blast furnaces are in a satisfactory
condition, practically similar ore bearing material is smelted in
them. During the year 2000, bituminous lump coal from Bacha colliery
(grade SSPK) was used as a substitute of coke in burden. The yearly
average rate of it amounted to 8.8 kg/t of hot metal.
The furnaces are fed with different grades of
coke: for BF No.1 it is +35 mm wet quenched coke from quite worn-out
batteries No.No.3, 5 and 6, for BF No.3 its is dry quenched +35 mm
coke from a new battery No.7, of better quality.
As was found out earlier, when BF No.1 was
switched over to dry quenched coke from battery No.7, the furnace
productivity would go up by 3.0%, and specific coke rate would go
down by 3.7%.
To compare the
performance efficiency of the furnaces quite an extended period of 4
months was chosen (October - December, 2000), which was
characterised by a high output, without failures, going haywire and
long downtime. Table 3 shows basic techno- economics of BF No.3 and
BF No.1 performance.
As can be seen from
this Table, the adjusted productivity of furnace No.1 with RCU is
higher than that of blast furnace No.3 by 5.58% (relative), and the
adjusted coke rate is lower by 4.36% (relative).
A long-lasting
experience of operation with various chargers shows that:
-
In case of BF No.1 with RCU, it is possible, if
required, to arrange a developed central gas flow with reduced CO2 content in the furnace centre down to 0 and to make even ore/coke
ratio in the central and peripheral zones of the top, with lowering
the peripheral gas temperature down to 100‑150 °C.
The variation of temperature of the peripheral gas in the furnace
circumference from the mean value is 50‑80° C,
which gives evidence of a high degree of burden circular
distribution uniformity. The furnace features a considerable reserve
in making its run steady and is less susceptible to a worse size
distribution in burden. Sour pellets that are used in burden (as of
late, their rate has been increased to 25-30%) are charged with the
help of RCU into the top radius span and into the furnace central
zone thus preventing them from contacting the stack lining. As a
result, there have been no cases observed when fusible ferriferrous
scull would be built up and then removed. This may help to increase
the service life of stacks.
-
On BF No.3 with a two-bell apparatus and movable
throat armours, the burden distribution can be controlled when the
stock line has been lowered to 2.1 - 2.3 meters. The variation of
the peripheral gas temperature along the furnace circumference is
much bigger and comes to 180-220 °C,
from the mean value. Attempts to level up the circular distribution
of stock with the help of combined actions by movable throat armours
and revolving distributor, which operates in the automatic mode of
control over gas flow, turned out to be not efficient enough. The
furnace is operated with additionally loaded centre and is
susceptible to a worsening quality of burden stock. The charged
low-basicity pellets would go to the peripheral zone of the top,
which results in the build-up of fusible ferriferrous scull on the
stack walls. Scull peel-off and the circular non-uniformity of gas
flow distribution would be conducive to disabilities in heating the
hearth. This is corroborated by a greater variation of silicon in
hot metal, as compared with BF No.1, in the period of the 4th
quarter of 2000.
|
Hot metal share, % |
|
BF No.1 |
BF No.3 |
Si in hot metal below 0.35% |
3.7 |
4.7 |
Si within 0.35-0.65% |
93.9 |
90.9 |
Si more than 0.65% |
2.4 |
4.4 |
The advantage of RCU is quite obvious and
therefore a decision has been made at the WSSW to replace the
existing charger on blast furnace No.3 with a RCU.
INFERENCES
1. The experience
of using RCU on 2 blast furnaces during 9-11 years proves high
dependability of its members and components, a small scope of needed
maintenance and repair.
2. RCU helps to
improve ironmaking indices. As was found out by research, thanks to
RCU the productivity of BF No.2 has increased by 7.89% and specific
coke rate decreased by 4.86%. On blast furnace No.1 its productivity
has increased by 7.0% and coke rate decreased by 6.8%.
3. As comparison of BF No.1 and BF No.3
performance in 2000 shows, in case of BF No.1 with RCU, as compared
with BF No.3 with movable throat armours, the adjusted productivity
has increased by 5.58% and adjusted coke rate decreased by 4.36%.
4. In view of the
obviously better cut of RCU above others, a decision has been made
to replace the existing apparatus on BF No.3 with a RCU. The
preparatory activities have been already started.
REFERENCES
1. G.V.Abramin, B.M.Boranbayev, A.V.Koshelnikov,
D.Y.Yankovky. Stahl No.3, 1999, p.p. 1 - 3.
2. S.F.Bougayev et al, Chornaya Metallourgiya,
NTI Bulletin 1992, No.8, p.p. 19-20
3.
S.F.Bougayev, A.A.Antonov, I.I.Basalayev Stahl, 1997, No.6, p.p.
19-22
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