Experience of Using 100% Imported Coal for
Coke Making in Bhilai Steel Plant
B.C.Mandal , M.K.Solanki , J.Arjun Prasad, J.Dey, B.Phuse, P.Jha,
Satya Prakash, G. S.Venkata Subramanian
Abstract
Coking coal is an invaluable natural resource for Iron and Steel Industries not only in terms of
producing good quality metallurgical coke for BOF process for hot metal production, but also in
terms of availability. World-wide efforts are being made to restrict its usage and take maximum
benefit with minimum usage by retrofitting advanced technology like PBCC, stamp charging, usage
of inert, coke breeze, etc. Indian steel industry is badly affected due to its inferior coal characteristics
in terms of high ash content, inferior coking properties, heterogeneous petrographic make up and
poor amenability to washing. Moreover, low prime coking coal reserve and uncertainty in supply,
compels Indian steel makers to import coking coal from different sources to cope up growing
demand of hot metal.
In the year 1979, Bhilai Steel Plant, a subsidiary of Steel Authority of India Limited, started to use
imported coking coal to the tune of 15% with indigenous Prime Coking Coal, Medium Coking Coal
and Blend-able coal to study its compatibility with indigenous coal and impact on coke oven battery
health. Under the present circumstances, considering the cost of blend optimization, coal availability
and impact on oven health, usage of 78-80% of imported coal with 22-20% of indigenous coking
coal is established in coal blend.
But in the middle of 2014, with non-availability of indigenous coal, BSP was left with the option of
having to use 100% imported coal for some time. With no prior experience of using 100% imported
coal, it became an unknown journey in terms of oven wall pressure and operational difficulties.
With its 56 years of experience in coke making, BSP coke plant managed the situation reasonably
well by deploying various combinations of imported hard coal from Australia, USA and New
Zealand and soft coal from Australia and New. Thus an unprecedented opportunity was available to
us to experiment with what we had at hand. Some interesting and notable improvements in terms of
hot and cold strength of coke were observed with due acknowledgement from the customer as well.
This paper throws light on the experience of using 100% imported coal for coke making in the
existing coke oven batteries of different age mix.
Introduction:
Bhilai Steel Plant, a flag ship unit of Steel Authority of India Limited (SAIL), is located at
central India in the close vicinity of huge deposits of iron ore, Limestone and Dolomite in the
state of Chhattisgarh. Hot metal and steel production started in a formal way in 1959 through
coke dependent BF-BOF route. The blast furnace is a counter current packed bed chemical
reactor in which ferrous and coke descend and are preheated by hot gases rising from the
raceway combustion zone infront of the tuyeres where coke and injectants undergo
combustion reactions deriving oxygen from the hot blast. Below the inner edge of the
cohesive zone, coke is the only solid material in the blast furnace, playing three major roles:
 A fuel providing the energy required for endothermic chemical reactions and for
melting of iron and slag
 A reductant by providing reducing gases for iron oxide reduction
 A permeable grid providing for passage of liquids and gases in the furnace,
particularly in the lower part of the furnace
Coke manufacture at BSP started with the commissioning of its 1st Coke Oven Battery on 31st
January 1959; subsequently two more Batteries added under 1 MT stage. 5 more similar
batteries came under 2.5 MT stage and two 7 M tall batteries came in 4MT stage. The third 7
MT tall battery marked the beginning of 7 MT stage. Presently seven 4.3 Meter tall batteries
and two 7.0 tall batteries are in working. One 4.3 Meter tall battery and one 7.0 tall battery
are under repair.
BACKGROUND:
India is bestowed with huge amount of coal reserve. But only about 17% of coal reserve is
proved to be coking coal. High mineral content, poor caking and coking properties, wide
fluctuation in quality parameters forced Indian coke makers to search for alternate sources of
good coking coals in place of indigenous coals, for coke making. Moreover, coal washing in
terms of ash reduction is not very effective, with the added disadvantage of escalating cost of
production, in India. These situations led Indian coke makers to produce the coke of
requisite quality by importing coals and judiciously incorporating maximum quantity of
inferior indigenous coking coals.
Considering the present circumstances, like BF productivity, volume of production, quality
and compatibility, social and political obligation, demand and supply gap, competitive cost of
production, existing infrastructure of coke making and other logistics, usage of about 80% of
imported coal in the coal blend has been established with numerous industrial trials.
BSP coke plant has witnessed many upswings and down trends s in quality parameters as
well as in the receipt of right quantity and right quality of coking coal grades (both
indigenous and imported).
PHYLOSOPHY OF COAL BLENDING:
Two basic parameters of coal i.e., coking and caking properties play key roles in determining
the coke quality. Out of these, coking properties play the vital role in producing coke of
desired quality. The prime factors that determine coking properties are ash, volatile matter,
fluidity, reactive contents(%virtinite) and rank.
Keeping the coal ash content to the minimum possible extent is the most significant
parameter in coke manufacture. Coal ash affects the caking/coking properties of coals and in
turn the strength of coke This unwanted constituent affects coke rate, slag volume, fluxes
required and productivity of Blast Furnace.
Fluidity of a coal which denotes formation of a semi-solid stage(plastic stage) on
carbonization at a certain temperature softening to the maximum and then re-solidification
with increasing temperature is an important parameter for coke making(coal blending).
Softening of coal and its re-solidification does two important things. Firstly it allows volatiles
to pass thus controlling the coking process and secondly enabling encompassing non-fluid
part (inert rich coaly part) during re-solidification thus forming and strengthening the coke
matrix. It can be seen that a fluidity of 200-1000 ddpm is the optimal range of blend for coke
making.
Reactive content (% of vitrinite, semi vitrinite and part of exinite) is very important as it can
be considered as a cementing part where as organic inert (inertinite) can be considered as
stone chips and inorganic inert (mineral matter) as sand on the same idea of making a mortar
for construction.
Volatile matter is one of most important parameter to classify the coals and an indirect
indicator of the maturity of the coal. During coal carbonizing, VM is driven off as
combustible gases like H2, CO, CH4 and other Hydro carbons as well as tar vapours and other
incombustible gases as water vapour and CO2. In the course of coal carbonization the plastic
layers swell, as a result of gas evolution and push the sides of charge against the heating
walls. Thus the charge exerts pressure against the wall. Normally coal blend containing 2226% depicts good coking behavior. Blend having below 22% VM gives lesser shrinkage
and causes difficulty in oven pushing and blend having higher VM% , causes higher wall
pressure and produces weak structured coke with higher porosity.
No individual coal inherently posses all the properties required for quality coke making.
However a deficiency of particular property in any coal can often be supplemented by
blending it with another compatible coal since many of the coal properties, like ash content,
FSI,LTGK, petrography analysis of different coal are additive in nature..
Objective behind a blend preparation rests on keeping the quality parameters within the
following range: Ash 13%,VM 22-26%,FSI 4-6%, Fluidity min 200-1000ddpm, vitrinite %
min 45 and rank min 1.1.
USUAGE OF 100% IMPORTED COAL IN COAL BLEND:
Process of coal blend preparation starts from averaging of coal at stock yard, reclaiming it into Silos,
discharging of coal at pre-set rate through Automatic Proportioning Device from Silos to make coal
blend. It passes through hammer crushers to ensure uniform crushing and fed to coal tower of
Battery and subsequently it is charged in coking chamber for coke making.
In Bhilai steel plant, coal blend is prepared from Indigenous coal named as Prime coking coal
(PCC),Medium coking coal(MCC) and imported coal consisting of hard and soft coal. There are 3
types of hard coal i.e Hard1, Hard2, Hard3 and soft coal (S1) used at BSP and corresponding
quality parameters have been shown in Fig No 1 & 2. BSP is having two stock yards. Stock Yard -1
which feeds coal blend to six 4.3 tall batteries and one 7.0 tall battery is called Blend 1 and Stock
Yard -2 feeds coal blend to two 4.3 tall batteries and two 7.0 tall batteries is called Blend -2.
Coal Quality
Hard-1 Hard-2 Hard-3
Ash, %db
Soft
PCC
MCC
9.4
8.5
5.1
9.4
18.7
33.4
VM, %db
Petrographic
Analysis
27.6
26.6
28.2
24.9
28.5
25.8
Vitrinite
67.5
66.9
93.6
54.8
40.0
31.9
Semi-vitrinite
0.9
0.4
0.0
0.0
2.0
0.0
Exinite
3.4
4.2
0.8
1.3
3.5
7.4
22.7
23.5
2.6
38.4
37.1
40.5
5.5
5.0
3.0
5.5
17.4
20.2
100.0
100.0
100.0
100.0
100.0
100.0
28.2
28.5
5.6
43.9
54.5
60.7
Inertinite
Mineral Matter
Total
Total Inerts
Fig 1
Coal Quality
Hard-1 Hard-2 Hard-3
Gieseler Fluidity
Initial softening
temp. C,
(1ddpm)
Maximum
fluidity temp., C
Solidification
Temperature
Plastic Range
Maxi. Fluidity,
ddpm
Soft
PCC
MCC
403.0
411.0
421.0
424.0
402.0
414.0
445.0
447.0
451.0
451.0
459.0
441.0
484.0
486.0
475.0
475.0
492.0
468.0
81.0
75.0
54.0
51.0
90.0
54.0
627.0
393.0
7.0
16.0
149.0
44.0
Fig 2
Coke making process uses different coals in blend, blend preparation facilities, battery and
coke handling facilities. Based upon several years of coke making experiences regarding the
in-built discrepancies in installed facilities in coke oven batteries, battery operating
parameters and working environment, for a specific set of blend composition, to a large
extent coke quality is predicted. Any deviation in coke quality is taken care of by adjusting
input coal constituents in coal blend. When limitation is imposed in the choice of input coal
blend, it becomes a challenge to sustain required coke quality, battery health and other
operational parameters and this happened to Bhilai Steel Plant.
From the beginning of the year 2014, supply of indigenous coals- both Prime and Medium
coking coals to Bhilai Steel Plant showed a downward trend due to some problems in Coal
Mines and subsequently in the month of May 2014, the indigenous coal stock depleted to
zero level. Hence, BSP was left with no choice but to use 100% imported coking coal.
It became difficult to keep the coal blend as usual. Therefore, imported coal in blend was
increased from a level of 78-80 % to 85, 89, 91 and 100%. This was a challenging task to
increase the % of imported coal while maintaining the other operational parameter like
shrinkage, pushing amperage at normal level.
BSP’s Quality Performance with respect to usage of imported coal in 2013-14
100 % Imported coal in Blend
(19.05.2014 to 27.05.2014)
1.0
Coal analysis at Plant end:%
%
%
Fluidity
Micro
%
Plant end Ash
VM
FSI
Mositure
(ddpm)
Fines (%)
Sulphur
AUS-H
9.2
22.5
6.0
8.2
-
23.9
-
USA
8.1
25.2
6.0
8.3
1794
29.1
-
NZL
4.9
27.5
4.0
8.6
-
35.5
-
SOFT
2.0
8.9
25.9
3.5
8.1
-
8.5
-
Coal Blend composition (%) – (CHP-I & CPP-II):
BLEND RATIO
Aust.
PCC
MCC
Hard
Composition
0
New
Soft
Total
Zeland
Coal
Imported
7
18
100
USA
0
58
17
3.0 Coal Blend Quality:
%
%
%
Coal Quality
Crushing Index
Fluidity
-3.2mm
- 0.5mm
(ddpm)
LTGK
FSI
Moisture
Ash
VM
CHP-I
8.2
8.8
24.5
5.0-6.0
82.4
41.3
335
G-4&6
CPP-II
8.2
8.8
24.5
5.5-6.5
83.4
41.5
869
G-4
OVER ALL SHOP
8.2
8.8
24.5
5.0-6.5
83.0
41.4
602
G-4&6
4.0 Coke Quality at Coke Sorting plants(CSP)
Coke
%
Coke Quality
Moisture
Ash
M-40
M-10
CRI
CSR
Sulphur
Porosity
CSP-I
3.9
12.4
80.8
6.9
22.7
64.6
0.54
43.9
CSP-II
4.0
12.2
79.8
7.4
22.1
65.3
0.55
41.0
CSP-III
4.9
12.2
80.4
7.3
22.5
65.0
0.55
42.2
OVER ALL
4.3
12.2
80.3
7.3
22.3
65.1
0.55
42.4
5.0 BATTERY OBSERVATION:-
DATE
Control Vertical
Temperature
Coking
Pushing
Gas
QI
P/S
C/S
Time
Index
make
20.05.14
1239
1269
21.03
1.13
149.0
21.05.14
1236
1270
20.93
1.13
151.8
22.05.14
1238
1272
20.91
1.13
153.5
23.05.14
1241
1272
20.65
1.13
153.0
24.05.14
1237
1270
20.35
1.14
154.5
25.05.14
1232
1267
20.23
1.15
151.7
26.05.14
1239
1272
20.32
1.16
150.2
27.05.14
1236
1272
20.35
1.16
149.5
7.3
AVG
1237
1271
20.60
1.14
151.7
7.5
BATTERY OBSERVATION
100 % Imported
Before
After
Batt.no.
FST
%
shrinkage
FST
%
shrinkage
1
868
5.65
853
5.48
2
814
5.75
844
5.45
3
846
6.63
845
3.45
4
906
3.62
904
4.14
5
900
5.00
911
4.80
6
901
4.70
890
4.90
8
837
6.40
8.32
6.15
10
783
5.72
791
5.90
Norm
850±25
6 % max
850±25
6 % max
7.6
6.0 Operational observation with use of 100 % Imported coal
(i) Its handling
: Normal
(ii) Pushing amperage : Normal
(iii) Coke shrinkage etc. : Normal
(iv) Any other comment : All batteries working normal
PERIOD
16-25 Mar-14
T.IMP.
81
PCC
8
20-27 May-14
100
0
COAL BLEND
MCC
AUS-H
11
55
0
58
PERIOD
16-25 Mar-14
ASH
12.0
COAL BLEND
VM
-3.2 mm
23.9
81.8
20-27 May-14
8.9
24.5
USA-H
13
NZL-H
7
AUS-S
6
NZL-S
-
17
7
9
9
- 0.5 mm
39.0
MOIST.
4.5
ASH
15.7
BF COKE
M40
M10
77.5
7.9
41.4
4.3
12.2
80.3
83.0
PERIOD
16-25 Mar-14
MOIST.
4.5
ASH
15.7
BF COKE
M40
M10
77.5
7.9
20-27 May-14
4.3
12.2
80.3
7.3
QI
7.3
Pushing
CRI
23.0
CSR
64.5
5.8
1.18
22.3
65.1
7.5
1.14
Index
Usage of Indian and Imported coals at various compositions in BSP
PCC
(Prime
Coking)
MCC
(Medium
Coking)
Indian
component
%
Hard-1
(Australia
Hard)
Hard-2
(USA)
Hard-3
(Newzealand)
Soft
Imported
component
%
Total
%
1
4
11
15
58
14
7
6
85
100
2
0
11
11
58
17
7
7
89
100
3
0
9
9
58
17
7
9
91
100
4
0
0
0
58
17
7
18
100
100
Sl
CRI
23.0
22.3
Results and discussions:
Parameters
Effect on coal
Coke Ash (Avg)
Q.I.
Effect on Coke
M10
CSR
Imported Coal Usage
100 %
12.10
7.60
81 %
15.59
4.80
Peaked at 91% then decreased reaching the minimum at 100 %
Increased with corresponding increase in imported coal %, but decreased in the
89 to 91% imported coal usage zone; subsequently started increasing attaining
the maximum at 100 % imported coal
At 100 % - CSR 65.3
Conclusion:
On increasing the imported coal percentage, the observations are as follows
 Coke ash decreased (by 22.38 %)
 Fixed carbon increased
 Q.I increased
 +80 fraction and -25 fraction decreased
 Coke quality like M10 and CSR increase with imported coal % but during blend design one
must check the compatibility of different coals, otherwise in spite of increase in imported
coal %, Coke quality shows downward trends.
 Hard –II is compatible with Soft-I coal
 MCC and Soft are compatible with Hard-2 for certain % range