Pergamon
SPECIFIC
Energy Vol. 20, No. 12, pp. 1247-1250, 1995
Copyright 0 1995 Elsevier Science Ltd
Printed in Great Britain. All rights reserved
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ENERGY CONSUMPTION
IN THE STEEL INDUSTRY
A. K. BHAKTAVATSALAM and RATNA CHOUDHURYj’
Centre
for Energy Studies, Indian Institute of Technology, Hauz Khas, New Delhi-I 10 016, India
(Received 9 February 1995)
Abstract-The
specific energy consumption in the Indian steel industry is high compared to that
in advanced countries. Data for four integrated steel plants in India have been analysed. The coals
used are of much inferior quality. Experiments were conducted for selective removal of silica in
coal. Theoretical analysis was performed of the effect of demineralisationon the specific energy
consumption (SEC) in an integrated steel plant (BP).
1. INTRODUCTION
Steel production involves many heating, cooling, melting and solidification cycles. The SEC in integrated plants is computed according to a standardized methodology prescribed by the International Iron
and Steel Institute (IISI). The SECs of Indian steel plants range from 8 to 12 Gcal/tcs (giga calories
per tonne of crude steel), whereas those of developed countries range from 4 to 6 Gcal/tcs.’ Figure 1
shows the SECs for different countries and also the world average for 4 decades starting in 1950. The
data comparisons may be biased for the following reasons: (i) outside of India, energy consumption
in facilities such as oxygen plant, coke ovens etc. may not be accounted for because these supplies are
purchased. (ii) The values 4-6 Gcal/tcs are averages which include the use of electric arc furnaces for
steel making, whereas 8-12 Gcal/tcs for India applies only to ISPS.~
cl
Japan
+ Austria
.
W. Germany
*
x U.K.
India
A U.S.A.
0 World
1960
1970
1980
YCU
Fig. 1.
tTo
SECs for selected countries and the World.
whom all correspondence should he addressed.
1247
1990
1248
A. K. Bhaktavatsalam
and Ratna Choudhury
Table 1. Energy consumption
Parameter
Steel production
(1 O3 mt)
Amounts
Coking coal 910” mt)
Boiler coal ( IO7 mt)
Purchased power (10’ mWh)
Fuel oil (10’ kl)
Energy inputs (106 Gcal)
Coking coal
Boiler coal
Purchased
power
Fuel oil
patterns in Indian ISPs.
BSP
DSP
RSP
BSL
4028
618
1148
3712
4239
798
1051
25
1124
291
264
11
1682
1115
342
68
3890
1699
702
90
29.1
(80%)
4.0
(11%)
3.2
(8.5%)
0.2
11.2
(83%)
1.3
(10%)
11.3
(69%)
(2::)
26.1
(72%)
7.1
(20%)
(0.5%)
Total
36.5
$4
1.0
(6%)
0.7
(Fi)
13.4
(4%)
16.3
(622)
0.8
(2%)
36.1
2. THE INDIAN STEEL INDUSTRY
There are seven integrated steel plants in India. Data pertaining to four plants under The Steel Authority of India Limited (SAIL) located at Bhilai (BSP), Durgapur (DSP), Rourkela (RSP), and Bokaro
(BSL) have been analysed. Table 1 shows production and energy inputs for these plants.3 The primary
energy inputs into ISPs are coking coal, steam coal for use in boilers, liquid petroleum fuels, and
purchased electricity. Table 1 shows that coking coal and boiler coals account for more than 90% of
the total energy input. Figure 2 is a pie chart of the average energy inputs.
Indian coals generally have high ash contents from 15 to 55%.4 The average ash contents of Indian
coking coals are 20-25%, while those of foreign coals are less than 10%. The SEC of an ISP is mainly
determined by the coke rate in making iron, where the coke rate (in kg of coke consumed per mt of
pig iron produced) is directly related to the ash content. More than 50% of the ash content is silica5
(Table 2).
3. EXPERIMENTAL
STUDIES
Proximate analyses of the Nagpur coal used for experiments are presented in Table 3. The coal was
first treated for 100 hours with 25% (w/w) aqueous ammonia solution under ambient conditions without
Coking
____________
____-__-___
______-_____
-_-_-_-_-_-_-_-_-_-_-_-_-_-_----___--_-_------_________--m-m-_---__-___-____-_---mm-____________________
_____-__-____-______--___-___________-_-_---______-____________--_______________-_------___-__---__________--_________--__---------__________-__-______---________________-_------_______ --__---______-_
___-___-___--__---__----____________________~~~~
________________--__-----_-_----_-___________
-_----__-__
_-____--__--------_________
___-__-___- _-__
--___---___---------____________
--__--___-_
_-___---__--______-___
____________
-____-_---__
___________
_---------mm__---w-v-__---m-m___-___-__--__---________
---_---_
________
coal 75.8 %
Fuel oil 1.8 %
purchased
Boiler
coal
15.5 %
Fig. 2. Energy supplies used for Indian ISPs.
power
6.9 %
1249
Specific energy consumption in the steel industry
Table 2. Typical mineral contents (%) of coals.
Compound
India
Australia
Canada
S. Africa
SiOz
A&O,
TiO,
FezOX
CaO
57.0
27.0
I .6
10.0
1.7
0.63
0.35
0.35
0.81
0.56
59.0
28.5
3.6
53.0
30.5
49.0
30.1
4.8
3.9
0.4
0.9
0.7
-
6.9
5.5
1.3
0.8
0.7
-
2.5
3.6
MgO
Na,O
K,O
Fe&
SO,
Table 3. Proximate
Sample/treatment
Original coal
(Western coal fields)
Ammonia-treated
coal
CaF,-H,SO,-treated
coal
HCI-treatment of CaF,H,SO,-treated
coal
-
1.35
0.75
0.65
1.6
0.9
analyses
-
of Nagpur coals.
% Ash
% Moisture
% Volatile
matter
% Fixed carbon
32.9
28.5
44.4
5.6
5.6
5.6
23.1
23.1
26.7
38.4
42.8
23.3
9.6
5.6
30.6
54.2
or agitation. Next, this treated coal was reacted with mixtures of concentrated H2S04 and CaF2
stirring
at 350°C and atmospheric pressure. The treated coal was then washed with HCl and Hz0 to neutral pH.
4. REACTION
MECHANISM
A study of chemical reactions of silicon compounds shows that silica can easily be converted6 to
SiF,, which is a colourless gas with b.p. = -101°C. Since HF is highly corrosive, the reaction was
designed to generate HF in situ so that it is consumed as soon as it is produced. The reactions
involved are:
CaF, + H2S04 SiOz + 4 HF Combining
CaSO, + 2 HF,
(1)
SiF, + 2 HZO.
(2)
Eqs. ( 1) and (2),
2CaF2 + 2HzS04 + SiO, -
CaSO, was then removed
by boiling
2CaS0,
+ SiF, + 2Hz0.
the treated coal with dilute HCl to convert CaSO, to CaC&.’
5. RESULTS
AND DISCUSSION
(i) Coal is the major energy input into an integrated steel plant (over 90%) and the poor quality
of Indian coals is the primary reason for high SECs in Indian ISPs. (ii) Chemical techniques may be
employed to demineralise Western coals. (iii) The ash content was first reduced to 28.5% from 32.9%
by using NH3 treatment and subsequently
to 9.6% by in situ HF treatment and HCl washing.
(iv) Theoretical analyses show that a reduction of coal ash content from 20 to 10% reduces the SEC
by over 5%. (v) A computer model which calculates the overall SEC based on energy input and
output at every stage of the steel-making process was developed and may be obtained on request from
the authors.
1250
A. K. Bhaktavatsalam and Ratna Choudhmy
REFERENCES
1. “Statistics on Energy in the Steel Industry ( 1990 Update),” International Iron and Steel Institute, Brussels
( 1990).
2. “Energy Conservation in SAIL,” Research & Development Centre for Iron and Steel, Ranchi (1988).
3. “Annual Statistics of BSP, DSP, RSP and BSL,” Steel Authority of India Limited, Lodi Road, New Delhi,
India ( 1993).
4. R. Choudhury and A. K. Bhaktavatsalam, in Proc of National Systems Co& Roorkee, India (1992).
5. Background papers for the International Conference on Environmentally Sound Coal Technologies UNCSTD,
Madras, India (1992).
6. W. Radamacher and A. Hovernath, BrennstofSchemie 40, 97 (1959).
7. R. Choudhury and A. K. Bhaktavatsalam, in Proc. of the National Seminar on Clean Coal Technology, Indian
Institute of Chemical Technology, Hyderabad, India (1994).