Nonrecovery and Heat recovery
cokemaking technology
10
Hardarshan S. Valia
Coal Science Inc., Highland, IN, United States
Chapter Outline
10.1
10.2
10.3
Introduction 263
Heat recovery coke plant and operation 265
Coke quality from nonrecovery heat recovery coke plants 269
10.3.1
10.3.2
10.3.3
10.3.4
Coke quality from SunCoke IHCC plant 269
Coke quality slot versus heat recovery 271
Coke quality from other facilities 275
Coke quality from stamp-charged versus nonestamp-charged blends 276
10.4
10.5
Performance of SunCoke’s IHCC coke at the blast furnace 278
Heating and draft control strategy for a nonrecovery heat recovery
battery 280
10.6 Environmental advantages 284
10.7 Cost benefits 285
10.8 Future research 287
10.9 Concluding remarks 287
Acknowledgments 289
References 289
10.1
Introduction
Simple and effective technologies generally survive the test of time and are not relegated into spaces reserved for near extinction. Such has been the case with nonrecovery (NR) technology, which was the prevalent method of cokemaking in early 19th
century. Versions ranged from simple beehives (domes similar in shape as the original
coal piles) to rectangular box types (facilitating easy coke push via door lifting) to
advanced NR ovens (with sole flue heating and a waste gas common tunnel). Some
versions recovered heat to dry coal, others recovered tar by making gas pass through
a tank of water. The historical progression from simple beehive to advanced NR is well
documented in the literature (Eisenhut et al., 1991; Kobus, 2017; Miller, 1967). A leap
frog advancement incurred in the late 20th century, whereby waste heat was recovered
for power generation (Ellis et al., 1999). This version helped imprint the name heat
New Trends in Coal Conversion. https://doi.org/10.1016/B978-0-08-102201-6.00010-8
Copyright © 2019 Elsevier Ltd. All rights reserved.
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recovery (HR) in cokemaking vocabulary. In this chapter, the NR and HR processes
will be used together because the basic theory of carbonization is the same. The
carbonization of coal takes place in horizontally placed box-type ovens operating under negative pressure, allowing air to be drawn into the coking chamber where it helps
combust generating gases. The partially combusted gases are fed into sole flue where
residual combustibles are fully combusted and the waste gases are then fed into a common tunnel finally exiting through a waste heat stack (Fig. 10.1). In HR, there is a
waste gas boiler and turbine before it reaches the waste heat stack. There is another
version of the NR/HR version, where box-type horizontally placed ovens are replaced
by a narrow slot-type vertical oven called vertical HR cokemaking, which still operates
under negative pressure but the coking is done in the absence of air and heat is provided by raw gases combusted with air in the adjoining flues (Fig. 10.2).
However, the early 20th century saw a phenomenal rise in the slot oven byproduct coke plant because of the innumerable use of by-products in accelerating
a nation’s growth. During this period, the NR cokemaking went through a rapid
decline. After suffering near demise, the renewed interest in NR/HR technology is
mainly ascribed due to its inherent environmental friendly characteristics. The
improved environmental controls in NR/HR cokemaking is due to the fact that (1)
the oven is operating under negative pressure; that is, it is under suction so leakage
is eliminated; (2) volatiles produced are combusted with influx of air, thereby eliminating volatile organic compounds (VOCs) before they are formed; and (3)
Typical non-recovery gas circulation system
Air ports
Combustion air
Combustion
chamber
Off gas
Waste
gas
Coal bed
Sole flues
Oven tunnel
Isolation
damper
Common tunnel
Figure 10.1 Flow chart of heat transfer in a nonrecovery coke plant.
Reproduced with permission from Ellis, A. and Valia, H., 2008. Non-Recovery operating
practices from around the world. In: AISTech Conference Proceedings, Pittsburgh, PA, USA,
vol. 1, pp. 61e78. © 2008 AISTech.
Nonrecovery and Heat recovery cokemaking technology
265
Combustion air
Draft stack
Raw coke gas
Vertical heating walls
Coking chamber
Waste gas
boiler
Combusted waste gas
Spent waste gas
Figure 10.2 Gas flow through a vertical heat recovery coke plant.
elimination of wastewater and hazardous waste generation that is associated with byproduct plants. These environmental features have allowed NR/HR cokemaking
technology to earn a special status in the US Clean Air Act, thereby paving the
way for dominance of HR in the United States. Various versions of NR/HR ovens
are operating in the United States, China, India, Brazil, Colombia, Peru, Mexico,
and Argentina. It should be noted that Australia had the distinction of operating
and maintaining more than 100 years of advanced type of NR batteries (earliest
one to adopt sole flue heating), but now all the plants in Australia have been shut
down. Valia (2013) described in detail many plants in operation from various parts
of the world. The characteristics of some selected plants have also been reported in
the literature (Madias and de Cordova, 2011; Xiobing, 2010).
This chapter will cover the following aspects: HR coke plant description, coke quality and coal usability, performance in the blast furnace (BF), heating and draft control
methodology, environmental advantages, cost benefits, and future research.
10.2
Heat recovery coke plant and operation
US Environmental Protection Agency (EPA) Clean Air Act Amendments of 1990
acknowledged SunCoke’s Jewell-Thompson-designed NR coke oven batteries as a
standard for reducing coke oven emissions and listed it as Maximum Achievable Control Technology for cokemaking (Allen, 2001). Thus new coke plants that begin
construction have to meet similar emission standards. Inland Steel Company
(now ArcelorMittal) took the lead in accepting this new technology (Carmichael,
1998) instead of buying coke for its No. 7 BF from a contract plant located in another
266
New Trends in Coal Conversion
state. March 20, 1998 was a historical day as SunCoke HR coke design was the first
state-of-the-art HR plant commissioned at an integrated steel facility (Ellis et al.,
1999). SunCoke built and owned the plant next to No. 7 BF at its Indiana Harbor facility and called it IHCC coke plant. The SunCoke battery at IHCC, along with waste
heat boilers, is shown in Fig. 10.3.
HEAT RECOVERY, SUN - INDIANA HARBOR COKE COMPANY
Figure 10.3 Startup of the first heat recovery battery at Suncoke’s IHCC coke plant.
Photo courtesy of SunCoke. © SunCoke.
However, it should also be noted here that an equally important landmark event in
coke oven emission reduction took place in China in the year 2001, where a drive to
reduce carbon emissions started for Chinese Township and Village Enterprises
(TVEs). Shanxi Xinggao Energy Company started a 6-year international project under
the TVE program launched by the Global Environment Facility, the United Nations
Industrial Development Organization, The United Nations Development Programme,
and the Chinese Ministry of Agriculture (Chung, 2007). The resultant HR coke plant in
2002 by Shanxi Xinggao Energy Company at Gaoping City is a model example of
clean, low-emission coke plant site with aesthetics (Fig. 10.4). The author had a chance
to visit the facility and was impressed by the plant site and found it to be true to its
touting as the “Demonstration Enterprises of energy saving and emission reduction
for countryside enterprises in China.”
Because all new greenfield coke plants built in the United States are of SunCoke HR
type, it is important to know its history. The basic oven unit of SunCoke HR plant is
based on Jewell-Thompson oven design. It should be noted here that the JewellThompson coke plant, built in 1962 in Vansant, Virginia, was the only NR coke plant
existing in the United States, and the ovens were constructed using the Mitchell NR
oven design. However, new modifications with regard to charging through the door
and better sole flue design were made in 1966, and the ovens were called
Jewell-Thompson NR ovens. By 1990, with further modifications in sole flue heating
aided by computer control with operator interface, they were able to attaining the
Nonrecovery and Heat recovery cokemaking technology
267
Figure 10.4 Heat recovery coke plant, Shanxi Xinggao Energy Company, Gaoping, China.
equalization of coking from top and bottom, resulting in production of consistently
high-quality coke (Knoerzer et al., 1991). Thereafter, Jewell Coke and Coke Company, a subsidiary of Sun Coal Company, announced an engineering study for an
HR with power generation for a one million ton per year coke production facility
(Knoerzer and Cekela, 1992).
Because SunCoke IHCC coke plant was the first HR coke plant adopted at an integrated steel mill, a great deal of research was done on coke quality so that the BF
performance and productivity was not hampered. Hence, the operation and results
from this facility will be described in detail. The design of the Jewell-Thompson
oven, used at IHCC, is shown in Fig. 10.5.
The coke facility is comprised of 4 batteries, 67 ovens per battery (total 268
ovens), with 4 waste heat boilers on each battery (Westbrook, 1998). The details
of its design and operating parameters are as follows: width, 4572 mm; height,
2438.4 mm; length, 13,716 mm; coal height, 1016e1143 mm; coal weight,
36.3e40.8 metric ton; gross coking time, 48 h. The plant produces 1.2 million
tons of screened coke and 75 MW of electricity. The coal charge is fed via a moving belt conveyor into each oven by lifting the pusher side door. This type of gravity charging is unique to SunCoke; others, in a similar situation, use gravity
charging from top or stamp-charged coal cake from the side (Agarwalla et al.,
2005). After the charging, the doors are closed and the air ports on the doors are
opened. The coal is exposed to the heat from the combustion chamber, and the volatiles produced are combusted from the air inflow arriving through open air ports.
The combustion thus results in providing radiant heat from the top. The combusted
gases then pass through downcomers into the sole flues where gases go through
several passes where residual combustibles are fully combusted via airflow introduction at select places in the sole flue region. In this way, the coal bed bottom
is heated via conduction of heat through sole flue area. Thus, the coking process
268
New Trends in Coal Conversion
Uptake
damper
Waste heat tunnel
Uptakes
Crown
Lintel
Buckstays
Oven floor
Sole flues
Downcomer
intake
Update
intake
Downcomer
Exit to sole flues
Castable slab
8″ Airspace
Foundation
*Doors and sole flue dampers not shown
Figure 10.5 Suncoke’s Jewell-Thompson oven design.
Drawing courtesy of SunCoke. © SunCoke.
proceeds from top of the bed downward and from bottom of bed upward, resulting
in meeting of the plastic layer placed horizontally in the center of the bed. The
waste gases from the sole flue exit into a common tunnel through uptakes controlled
via an uptake damper. The damper helps regulate oven pressure, thereby helping
regulate coking rate. The waste gases then move into a waste heat boiler (4 boilers
per battery) at 954 C and exit the boiler at 200 C, producing about 120 kg/s of
steam. The steam generated is then fed into a steam turbine, resulting in typical production of 75 MW of electricity. The spent gases are drawn into lime spray scrubbers for sulfur removal. Thereafter, the waste gases enter the baghouse and then exit
out through the stack (Westbrook, 1998).
In subsequent NR/HR coke plant construction, SunCoke moved the HR steam
generator from the rooftop and erected it on the ground. In the author’s opinion,
some of the HR coke plants in other parts of the world, except with slight modifications, are similar in design to SunCoke. However, per the author’s knowledge, none
of the others place boilers on the oven roof.
As mentioned earlier, there is another version of HR cokemaking called vertical
HR/NR cokemaking. It originated in China in the year 2002. The ovens are designed
as slot types stacked together, where carbonization takes place in a vertical coking
chamber and the raw gases are fed into adjoining combustion chambers where they
are combusted with incoming air. This version addresses two drawbacks commonly
noted with horizontal HR ovens. First, the coke yield in vertical HR is higher because
heat transfer takes place via conduction through refractory oven walls. Second, it
covers less area than the horizontal HR batteries. There are 10 vertical HR coke plants
in China, and 1 plant has also been constructed in India. Plant description and operating sites are described in detail in a presentation by Xiobing (2010).
Nonrecovery and Heat recovery cokemaking technology
10.3
269
Coke quality from nonrecovery heat recovery coke
plants
Because coke is produced from various types of NR/HR coke plants with different
plant sizes and varying operating variables and blend compositions, this section of
coke quality will be in four subsections as follows:
•
•
•
•
Coke quality
Coke quality
Coke quality
Coke quality
from SunCoke IHCC
slot versus HR
from other facilities
from stamp-charged versus nonestamp-charged blends
10.3.1 Coke quality from SunCoke IHCC plant
Because this was the first HR coke plant at an integrated steel works, it set the baseline
for coke quality for noncompacted charge. It should be noted that the plant was
commissioned in March 1998, which started by using coal blends of high-volatile matter (HVM) rank that was similar to that used at one slot oven by-product battery of domestic origin (Valia, 2002). The blend design for startup was made keeping in mind to
get maximum power generation. However, later the blend rank was increased so as to
lower the volume of waste gas passing through the sole flue. Thus, five blend changes
were made by a successive increase in rank culminating to low-volatile matter (LVM)
rank by the end of the year 2000, which is the type of blend adopted for use in successive years. All these changes were made by testing the blends in six commercial ovens
at an IHCC HR facility. The coal and coke quality related to six blends, from six commercial oven tests, are shown in Table 10.1. The cold and hot strength properties are
superior. The point to note here is that despite change in coal from HVM blend (31.7%
VM, daf) to LVM blend (24.0% VM, daf), the coke strength properties remain high
and meet all contract specifications for the large BF of Ispat Inland (now ArcelorMittal). The coke quality specifications for the Ispat Inland BF are specified in the literature (Valia, 2018).
One example of coke strength after reaction (CSR) variation with rank in Fig. 10.6
shows that all blends produced CSR above the BF contract specification of 65, emphasizing that this process can accommodate a wide range of coals and especially lower
cost high-volatile coals and still produce superior quality coke. Conventional slot oven
by-product cokemaking using coals from US CSR decreases with increasing coal rank
in the medium-volatile and low-volatile rank range. This trend was also observed in the
six blend tests (Fig. 10.6).
All of these cokes contain varying amounts of pyrolytic carbon formed due to
cracking of the volatiles passing through a thicker bed of semicoke at higher temperature with a longer passage time. Arendt et al. (2001) also found that HR coke from
IHCC has pyrolytic carbon nearly twice as high as in the slot oven and attributed it
as one of the reasons for higher CSR. In an interesting experiment by the same authors,
they removed pyrolytic carbon from the coke fingers collected from a slot oven and ran
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New Trends in Coal Conversion
Table 10.1 Coke quality associated with blend changes at Suncoke’s IHCC heat recovery
coke facility
1998
Start
Year
1998
End
1999
Start
1999
End
2000
Start
2000
End
Coal/Coke properties
Rom (%)
1.11
1.15
1.18
1.42
1.38
1.34
Volatile matter
(wt% daf)
31.7
30.8
29
24
24.8
24.2
CSR
71
71
71
67
69
66
CRI
19
20
21
20
21
22
M40
85
88
85
87
87
85
M10
6.3
5.8
5.5
6.6
5.8
6.2
Micum slope
0.55
0.48
0.57
0.47
0.51
0.65
Pyrolytic
carbon (%)
2.6
0.6
4.5
1.2
2.8
2.4
CRI, coke reactivity index; CSR, coke strength after reactivity.
75
CSR
70
65
60
22
24
26
28
30
32
Volatile matter (wt% daf)
2000 end
1998 start
Figure 10.6 Coke strength after reaction (CSR) variation of six blends varying in rank from
high volatile matter to low volatile matter in the period 1998e2000.
a CSR test on it. The results were compared with the original coke with pyrolytic carbon in it. The results indicate that removal of pyrolytic carbon resulted in a drop in
CSR from 70.0% to 67.2% and coke reactivity index (CRI) increased from 16.8%
to 19.5%.
Shigeno and Evans (1999) and Vandazande (1983) attribute carbon deposition to
an improvement in CSR and CRI when methane gas is cracked in the hot coke bed.
Furthermore, with regard to CSR variation within the IHCC HR oven, Nyathi et al.
Nonrecovery and Heat recovery cokemaking technology
271
(2016) studied coke fingers from the central part of the oven and noted that bottom
coke had higher CSR (av. 61.8) and top coke had lower CSR (av. 58.1). However,
the bottom coke had lower carbon form and crystallinity but better porosity and pore
structure, whereas the top coke had better carbon form and crystallinity but poorer
porosity and pore structure. So, faster heating and better plastic range in the upper
part of the coke bed although helped carbon form and crystallinity, unrestricted
swelling into the free space above caused an increase in the surface area, resulting
in lower CSR.
In terms of cold strength properties, particular attention should be paid to the
Micum slope (an index of abrasion resistance). Unlike M40/M10, which are measured
for a total drum revolution of 100, the Micum slope is measured for a series of
increasing drum revolutions supposedly trying to represent coke abrasion descending
over a larger height. The lower numbers achieved here point to a possibility of less
fines generation as coke descends in the BF; in other words, when all things are equal,
better BF performance can be expected.
Carbonization of such a high rank blend in a by-product slot oven would have
created wall pressure problems damaging the oven walls, whereas in HR coke oven,
the coal is able to expand upward in the free space above the bed. However, the expansiveness of blend should be checked so as not to impact coke strength negatively.
Because of flexibility of coal rank, SunCoke has been able to run blends with many
components at high frequency, specifically during scarcity of coal supply, without
resorting to pilot oven testing.
SunCoke has proven usage of pulverized coal injection (25%), petroleum coke
(10%), semicoking coal (25%) at their facilities (Quanci and Perkins, 2017). SunCoke
selects its blends from a coal data base, with constraint inputs, by using a sequential
quadratic programming method (Perkins et al., 2012). Such a procedure is limited
by a number of coals in the data base for each plant. Tiwari et al. (2013) proposed a
coefficient named composite coking potential of coal/coal blend calculated from
coal properties (chemical, rheological, petrographic), which in turn is correlated
with the coking properties. Again, such a prediction model is only valid for the range
of coals investigated in the study and the carbonizing conditions.
10.3.2 Coke quality slot versus heat recovery
Because before the IHCC startup, the coke used at the BF was from slot oven byproduct battery, it was decided to compare how the similar blends behave in slot versus
HR (Valia, 2002). To assess the difference in coke quality, an HVM blend and an
LVM blend were chosen. The HVM blend was a startup blend called HVM-B blend
and was carbonized in SunCoke’s NR facility at Vansant for use at IHCC as the startup
blend. At the same time, the HVM-B blend was also carbonized at a pilot slot oven
facility. Similarly, the LVM represented by the IHCC-1999 year-end blend was
carbonized in the IHCC HR facility and also in the pilot slot oven facility. The results
are shown in Table 10.2 and Fig. 10.7e10.12.
As compared with the slot oven coke, the HR coke shows higher pyrolytic carbon
content for both HVM and LVM ranked blends (Fig. 10.7). However, the pyrolytic
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New Trends in Coal Conversion
Table 10.2 Coke quality for two blends of different ranks carbonized in heat recovery
(HR) and slot ovens
Coal blend
HVM-B blend start up
LVM-1999 blend year end
Oven type
HR
Slot
HR
Slot
Isotropic (%)
1.5
1.4
6.7
2.3
Granular (%)
31.8
32.3
19.5
13.6
Acicular þ ligular (%)
40.9
39.7
49.4
62.1
Mosaic size index
3.2
3.2
3.7
3.9
Total inerts (%)
21
24
23
22
Pyrolytic carbon (%)
4.5
2.8
1.1
0.6
Porosity (%)
53
ND
53
50
Apparent specific gravity
0.97
0.90
0.90
0.93
Coke VM (wt% db)
0.52
0.58
0.22
0.63
Coal reflectance (%)
1.09
e
1.42
e
Coal VM (wt% db)
29.54
e
22.45
e
Stability
62.2
58.5
64.0
62.0
Hardness
69.7
68.3
70.0
71.0
CSR
72.0
61.2
66.7
65.0
CRI
20.2
24.9
20.4
27.6
Texture/Structure
Coalecoke properties
Coke strength properties
CRI, coke reactivity index; CSR, coke strength after reaction; HVM, high volatile matter; LVM, low volatile matter; VM,
volatile matter.
Reproduced with permission from Valia, H., 2002. Coal blend rank changes and resultant coke quality from IHCC heat
recovery coke making. In: Proceedings of ISS-AIME Ironmaking Conference, Nashville, USA, vol. 61, pp. 419e426.
© 2002 ISS-AISTech.
carbon content for the LVM blend is lower because of the amount and kind of volatile matter evolved during the process. In terms of carbon form, the mosaic size index does not show any change in slot or HR cokes from the HVM blend (Fig. 10.8).
However, the coke produced in the slot-type oven from the LVM blend shows
marked changes in carbon form; acicular and ligular carbon forms increase at the
expense of isotropic and granular carbon forms (Fig. 10.9). This is due to the fact
that the LVM coal blend expands and exerts higher wall pressure when carbonized
in a slot-type oven, which would result in formation of larger carbon crystallites at
the expense of smaller crystallites. An increase in anisotropy when carbonized under
higher pressure has been reported in the literature for slot oven conditions (Patrick
Nonrecovery and Heat recovery cokemaking technology
273
Carbonization in heat recovery vs . slot oven
Pyrolytic carbon %
Heat recovery
5.0
Slot
4.5
4.0
2.8
3.0
2.0
1.1
1.0
0.6
0.0
LVM blend
HVM blend
Figure 10.7 Pyrolytic carbon of cokes from high volatile matter (HVM) and low volatile matter
(LVM) blends in heat recovery versus slot oven.
Carbonization in heat recovery vs. slot oven
Heat recovery
Slot
Mosaic size index
5.0
4.0
3.7
3.2
3.9
3.2
3.0
2.0
1.0
0.0
HVM blend
LVM blend
Figure 10.8 Mosaic size index for cokes from high volatile matter (HVM) and low volatile
matter (LVM) blends in heat recovery versus slot oven.
Carbonization in heat recovery vs. slot oven
Heat recovery
Slot
Carbon forms %
70.0
62.1
60.0
49.4
50.0
40.0
30.0
19.5
20.0
10.0
0.0
13.6
6.7
2.3
Isotropic
Granular
LVM blend
Acicular & ligular
Figure 10.9 Carbon form components for cokes from high volatile matter (HVM) and low
volatile matter (LVM) blends in heat recovery versus slot oven.
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New Trends in Coal Conversion
Carbonization in heat recovery vs. slot oven
Apparent specific gravity
Heat recovery
1.0
Slot
0.97
1.0
0.9
0.93
0.9
0.9
0.9
0.9
0.9
0.9
HVM blend
LVM blend
Figure 10.10 Apparent specific gravity for cokes from high volatile matter (HVM) and low
volatile matter (LVM) blends in heat recovery versus slot oven.
Carbonization in heat recovery vs. slot oven
Slot
Heat recovery
74.0
72.0
72.0
70.0
68.0
66.7
CSR
66.0
65.0
64.0
62.0
61.2
60.0
58.0
56.0
54.0
HVM blend
LVM blend
Figure 10.11 Coke strength after reaction (CSR) for cokes from high volatile matter (HVM)
and low volatile matter (LVM) blends in heat recovery versus slot oven.
et al., 1989). As a result of this, there is an increase in apparent specific gravity
(Fig. 10.10) and a decrease in porosity (Table 10.2) for the coke produced from
the slot oven from the LVM blend.
In terms of coke strength properties, the most dramatic change takes place in the
CSR of the coke from the HVM blend (Fig. 10.11). Compared with the slot oven
coke, the HR coke shows about 11 points increase in CSR. Also, the cold strength
properties either show improvements or are steady (Table 10.2; Fig. 10.12).
Nonrecovery and Heat recovery cokemaking technology
275
Carbonization in heat recovery vs. slot oven
Heat recovery
Stability
65.0
64.0
63.0
62.0
61.0
60.0
59.0
58.0
Slot
64.0
62.2
62.0
58.5
57.0
56.0
55.0
HVM blend
LVM blend
Figure 10.12 Stability for cokes from high volatile matter (HVM) and low volatile matter
(LVM) blends in heat recovery versus slot oven.
However, for the LVM blend, except for CRI, one does not see much improvement
whether carbonized in slot or HR ovens. These findings are significant for countries
that have abundance of high-volatile coal, which is of lower cost than the lowvolatile coals. The improvements in HR coke are ascribed to higher temperature,
combined with uniform spatial temperature distribution, slow coking rate, and higher
soak time. Nyathi et al. (2017) also reported that slot oven coke has slightly lower
CSR than HR coke for one particular blend. They ascribed it to unfavorable pore
structure, less developed carbon structures, and shorter coking time. However, their
study of selected coke fingers revealed that slot oven coke was noticeably more homogenous than HR coke.
10.3.3 Coke quality from other facilities
Because there are many NR and HR coke plants operating in other parts of the world,
such as China, India, Vietnam, Brazil, Peru, Colombia, Mexico, Argentina, one
would like to know generalized coke quality produced from those facilities. It should
be noted that these plants vary in terms of size, design, operating parameters, and
charging parameters. Many of the plants use stamp charging methodology, where
coal blend is stamped so as to increase the bulk density of the charge. Table 10.3
shows coke quality from four selected coke plants representing HR (nonstamped
and stamped) and NR (nonstamped and stamped). As can be seen, the coke quality
is generally good and reflects variations in coal blend compositions, oven designs,
and operating practices. Although the Colombian coke produced was somewhat
lower in quality, the author, however, found the coal blend to be superior and discerned the cause to the variability in battery operating conditions, which could be
remedied with minor adjustments.
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New Trends in Coal Conversion
Table 10.3 Coke quality examples from various coke plants from different regions
Technology
Heat recovery
Nonrecovery
Charging
Nonstamped
Stamped
Nonstamped
Stamped
Country
United States
China
Colombia
India
M40
87
86
80
88
M10
6.6
6.6
8.4
5.9
CSR
67
62
62
63
CRI
20
n/a
19
23
CRI, coke reactivity index; CSR, coke strength after reaction.
10.3.4
Coke quality from stamp-charged versus
nonestamp-charged blends
Many NR/HR plants worldwide are equipped with stamp charging mechanism
(Madias and de Cordova, 2013). In stamp charging, a coal cake is made outside the
oven via stamping with hammers or compaction via vibration with or without
compression plates. It is worth mentioning that a minority of plants were known to
do stamping inside the oven (Yan and Song, 2000). The stamping forces movement
of finer particles into the interparticle voids and is helped by moisture that acts as a
lubricant. The resultant cake possesses high density and high mechanical stability.
The coal cake density of about or greater than 1100 kg/m3 is achieved with approximately 8%e10% moisture. Kuyumcu and Sander (2014) indicated that stamp ability
(densification) depends on coal rank, ash content, and particle size and developed an
equation to predict stamp ability and also a methodology to predict cake stability for a
given cake height.
Because the coke quality is significantly affected by stamping, it is necessary to
address this aspect of coking in some detail. According to Eisenhut (1991), the
use of stamp charging in cokemaking dates back to approximately 1880. A
need for stamping in cokemaking arose so as to incorporate a higher amount of
lower quality noncaking coals. Because compaction brings particles together,
there is increasing density of the coal cake, facilitating a uniform thermal gradient
during carbonization. This results in better wetting and bonding of the particles
during the plastic stage. The net effect is improvement in coke quality. Besides
improved coke quality and ability to use lower quality noncaking coals, other benefits include increase in coke productivity per oven and decrease in charging
emissions.
One example of the effect of stamping from an Indian NR coke plant is worth
mentioning. In this plant, the same blend is sent to two batteries; one is stamp
charged, whereas the other is gravity charged (nonstamped). The results for two
blends of different ranks are presented in Table 10.4. It is evident that the blend
with 26% volatile matter shows the greatest improvement in CSR, M40 and M10,
Nonrecovery and Heat recovery cokemaking technology
277
Table 10.4 Stamp-charged versus nonestamped-charged nonrecovery
coke quality at one Indian nonrecovery plant
Charging
Stamped
Nonstamped
D
Blend 1: VM, 26 wt%
CSR
57
42
15
M40
86.5
78
8.5
M10
6
14
10
Blend 2: VM, 20 wt%
CSR
65
59
6
M40
86
83
3
M10
6.5
11
4.5
CSR, coke strength after reaction; VM, volatile matter.
whereas lower improvement (still significantly high) is seen when the blend rank
increases to VM of 20%. This was further exemplified in a paper by Choudhury
et al. (2009), wherein a CSR improvement by 27 points was reported (Table 10.5).
As one can see, the reason for the improvement is attributed to the growth of
binder carbon form at the expense of a drop in isotropic and incipient carbon.
Isotropic carbon forms are more reactive to CO2; higher carbon form improves
resistance to CO2 gasification (Chiu, 1982; Koba and Ida, 1980; Marsh, 1982)
Thus higher ranked, better quality coal blends that show less improvement is
also reported by others in the literature (Veit and D’Lima, 2002; Wright et al.,
2005). The best example of use of high amount of noncoking coal in stamp
charging is the use of about 35% of anthracite (9.3% daf VM; 0-Y value; 0-G
Caking Index) in Chinese HR facilities (Pin, 2005). Such a blend is reported to
produce high-quality coke with the following coke properties: 62% CSR;
85.6% M40; 6.6% M10.
Table 10.5 Experiment showing effect of stamped versus nonstamped coke for
nonrecovery cokemaking
Coke
quality
CSR
M40
M10
Isotropic
carbon
Incipient
carbon
Binder
carbon
Nonstamped
36
75
18
3.4
5.3
68.7
Stamped
63
79
12
0.8
1.1
73.3
CSR, coke strength after reaction
Reproduced with permission from Choudhury, N., Boral, P., Ranjan, R., Yadav, R., Pramanik, T., Hazra, S., 2009. Effect of
stamp charging on coke micro texture vis-a-vis coke properties. In: Proceedings of the SAIL Conference on Coking Coal
and Coke Making e Challenges and Opportunities, Ranchi, India. © 2009 SAIL.
278
New Trends in Coal Conversion
During the blend design for the startup of IHCC HR plant, one of the blend trials at
SunCoke’s Vansant NR facility contained 12% of noncoking coal (mean maximum
vitrinite reflectance, 0.63%). It produced extremely high CSR of 70 (Valia, 2006).
However, Prachetan Kumar et al. (2007) reported use of 25% noncoking coal in
stamped charged oven that produced CSR of 65; thereafter a further increase in the
amount of noncoking coal to 30% resulted in a drop in CSR to 63.
Valia et al. (2004) reported super strength coke from NR stamped charged coke battery of the Shanxi province of China with the following coke strength properties:
Stability 70; hardness 70; CSR 70 and called such coke as “super strength
cokedSSC777.” To the author’s knowledge, such high strength numbers for all three
strength parameters above 70 are not found in any other coke plant outside of Shanxi,
China.
These unusual values above 70 are ascribed due to a combination of compaction,
operating variables (very long coking and soaking time), and high quality-high
fluidity-LVM coals from the Shanxi region.
10.4
Performance of SunCoke’s IHCC coke at the blast
furnace
SunCoke’s IHCC coke was transported by conveyor belt to Ispat Inland (now ArcelorMittal) No. 7 BF. Because the BF used purchased domestic slot-oven coke, the transition to IHCC HR coke was monitored carefully. It should be noted that the No. 7 BF
is a large one (13.7 m hearth with 3749 m3 working volume). The coke quality measurements at No. 7 BF stock house for both cokes along with expected effects are
shown in Table 10.6. In other words, expect lesser degradation. It should be noted
that the quality data is different than that measured at the IHCC screening station. A
comparison of coke quality of SunCoke at the screening station versus at No. 7 BF
stock line shows a drop in coke size-coke ash-coke sulfur (degradation effect) but
an increase in stability-M40-CSR (fissure reduction) and no change in hardnessM10 values, suggesting good wetting and bonding (Valia, 2001). The results of the
No. 7 BF coke transition, covering a span of about two and half years, are summarized
as follows:
•
•
•
BF performance was good with sustained high levels of productivity.
Improved hot metal quality.
Improved furnace efficiency and permeability.
For details, one is referred to papers by Dutler et al. (2001) and Knorr et al. (2000).
These improvements happened despite large changes in blend composition made at
IHCC, starting with HVM blend going into an LVM blend. By the way, the HVM
startup blend was similar in composition to that used for the production of purchased
domestic slot oven coke.
It is also interesting to note that before the introduction of IHCC coke, No.7 BF
was using stamped NR coke from Shanxi as a second coke along with the domestic
Nonrecovery and Heat recovery cokemaking technology
279
Table 10.6 Expected coke behavior in No. 7 blast furnace (BF) stock line
a
Slot oven
coke
IHCC heat
recovery (HR)
coke
Expected HR coke
behavior at No. 7 BF
Mean size (mm)
45
47
Larger coke @ raceway
Stability/M40
60/84
64/85
Larger coke @ raceway
Hardness/M10/Micum
slope
67.7/7.4/0.70
71.6/3.0/0.57
Lesser fines @ raceway
Coke strength after
reaction
62
70
Larger coke and lesser
fines @ raceway
Reaction at 1200 C (%)
via SBF testa
10.67
10.09
Similar to slot coke for
reduction potential
coke reacted under changing temperature and gas composition to simulate passage through BFdsee text for details.
slot-oven coke, and its introduction, because of extremely superior coke quality,
created several operational problems (Chaubal and Valia, 2003). The Shanxi
stamped NR coke had coke strength values as follows: stability, 72; hardness, 73;
CSR, 69; CRI, 22; M40, 90; M10, 4.8; and Micum slope, 0.27. On the other
hand, the values for slot oven coke were as follows: stability, 60; hardness, 67;
CSR, 62; CRI, 24; M40, 84; M10, 7.4; and Micum slope, 0.70. In addition, the
Shanxi stamped NR coke was characterized by thicker cell walls (180 mm vs.
127 mm), lower porosity (43% vs. 48%), higher pyrolytic carbon (2.0% vs. 0.7%),
and higher inerts (32% vs. 21%). The superior coke properties for Shanxi NR
coke are due to coal properties, high compaction of the charge, and very long coking
time and soak time. Too understand degradation of such high-quality, dense coke,
two kinds of tests were done at Ispat Inland, as follows: a) laboratory studies on
various reactivity tests that simulate blast furnace (SBF) conditions and b)
coke degradation study via tuyere core sampling (for SBF test procedures, refer to
Chaubal and Valia, 2003). The laboratory studies were carried out in the following
three areas: (1) intrinsic reactivity tests, (2) reaction with hot blast, and (3) reaction
in CO/CO2 atmosphere. The test results from Chaubal and Valia (2003) can be summarized as follows: (1) intrinsically, the start of rapid reaction, whether in air or at
60%COe40%CO2, is indistinguishable for the two cokes, (2) activation energy was
almost identical for both cokes; reaction rate with hot blasts were similar, and (3)
under changing temperature and gas composition (that is, SBF condition), similarsized coke pieces reacted in identical fashion. Thus, the reaction rates of stamped
charged NR coke are similar to a typical slot-oven coke; this is contrary to markedly
different reactivity measured in the CSR test.
On the other hand, the tuyere sampling results indicated that the change in cell wall
thickness for stamp-charged NR coke is higher than for the slot oven coke, suggesting
that the stamp-charged NR coke is much more reactive than otherwise suggested by
280
New Trends in Coal Conversion
the CSR test. The probable cause may be the higher reactivity of high inert content
(32% inerts) exposed via degradation. However, still at the tuyere level, the NR
coke is characterized by higher cell wall thickness, suggesting it should maintain
strength and size beneficial to BF operation. For more details, the reader is referred
to the paper by Chaubal and Valia (2003). As indicated earlier, the dense coke from
Sanjia created BF operational problem. It had apparent specific gravity (ASG) greater
than 1.1. Valia and Ambry (2009) devised a procedure whereby coal was compacted in
Sanjia NR ovens so that the coke resulted in ASG of 1.05, which was then successfully
used at the BFs.
10.5
Heating and draft control strategy for a
nonrecovery heat recovery battery
Operating an NR/HR battery is a lot simpler than a slot by-product battery. Because
NR/HR operates under a negative pressure, a well-developed draft control and heating
strategy is the key for the success of the operation. It should be noted that as compared
with slot oven cokemaking, the carbonization in NR/HR cokemaking differs in
following aspects (Wei-Kao and Valia, 1998):
a. The flame is located at the upper part of the charge, providing heat and generating gases but
not impairing the reducing atmosphere at locations where coke is made.
b. The generating gas needs to be only partially oxidized directly above coal/coke mass, but
fully combusted in sole flues beneath the hearth floors. Thus, the radiant heat transfer
from the top and conduction of heat from the sole floor should facilitate in placing the plastic
layer junction equidistant within the coke mass, resulting in uniform coke quality.
c. Convective mass transfer of oxidizing gases (O2, CO2, and H2O) into coal being carbonized
below needs to be minimized.
d. Upward expansion of coal mass in open free space under the crown need to be minimized for
better coke quality.
The key is the radiant heat transfer from the top of coal bed and conduction of heat
from the sole flue should facilitate in placing the plastic layer junction equidistant
within the coke mass, resulting in uniform coke quality. SunCoke has perfected this
(Fig. 10.13), and it is a showcase of optimum heating and operating conditions. The
author has seen quite installations where the outline of the centerline appears skewed.
In one case, a U-shaped centerline suggests that the waste gas as it descends from the
two sides of the oven walls into the sole flue is losing the heating value.
As the gas evolution varies with the progress of carbonization of a charge, equidistant placement of plastic layer is best achieved via adopting a proper damper control
methodology at the door, sole flue, and uptake dampers. It should be noted that the
design of the sole flue passes and sole flue gas exit through uptake damper play a
very critical role not only in creating desired draft but also not to affect sole flue refractory and uptake damper refractory to get damaged from high temperatures. Enough hot
gases are needed to be held in the sole for the necessary heat transfer to the coal bed.
Attention should be paid to the number of baffles and the size and number of flow
Nonrecovery and Heat recovery cokemaking technology
281
Figure 10.13 Equidistant placement of plastic layer in Suncoke’s nonrecovery coke bed.
Photo Courtesy of SunCoke. © SunCoke.
passageways in the sole so as to maintain the correct flow and right draft conditions.
Air dampers in the sole flue are usually located at the beginning and end of the sole
flue. Most plants follow similar overall designs. Some plants place uptake dampers
not in the oven but outside in castable blocks that control gas flow into the tunnel;
the tunnel is placed away from the ovens (Ellis and Valia, 2008). Others maintained
homogenous and constant sole flue temperatures (up to 1300 C) by providing eight
air intake adjustable ports for secondary air (Wright et al., 2002).
As mentioned earlier, gas evolution is high in the beginning of the carbonization
cycle and decreases as the coking proceeds. Thus draft demand varies with time and
damper openings (at both the air vent and uptake isolation damper) are constantly
adjusted over the period of a coking cycle. Regardless of charge weight, coking
time, and battery design, the gas flow profile over the period of one coking cycle
can be divided into four zones. Gas flow zones for a coking cycle of 48 h are shown
in Fig. 10.14, and the damper positions corresponding to those four zones are shown in
Table 10.7 (Ellis and Valia, 2008).
Zone I
Zone III
Zone IV
Gas flow rate
Zone II
0
8
12
24
Time (h)
42
48
Figure 10.14 Four gas flow zones during one coking cycle of 48 h.
Reproduced with permission from Ellis and Valia (2008). © 2008 AISTech.
282
New Trends in Coal Conversion
Table 10.7 Damper openings and heating strategies for the four gas flow zones
Isolation
damper
Air port
damper
Gas flow condition
100% Open
100% Open
High flow
80%e40%
Open
100%e20%
Open
Declining flow
Zone IIIb
40% Open
20% Open
Steady-state moderate
c
100% Shut
100% Shut
Slight flow, almost coked; plastic
layers collapse, begins soaking state
Area
Zone I
a
Zone II
Zone IV
Max flow and all points open;
Steady-state coke rate, longest duration of operation, minimum adjustment required;
Soak zone and zero emissions evolving from the bed.
Reproduced with permission from Ellis, A., Valia H., 2008. Non-Recovery operating practices from around the world.
In: AISTech Conference Proceedings, Pittsburgh, PA, USA, vol. 1, pp. 61e78. © 2008 AISTech.
a
b
c
Ellis and Valia (2008) describe gas flow zones and damper positioning strategy for
a 48-h coking cycle as follows:
•
•
•
•
Zone I begins from the time when the coal is charged, resulting in massive release of gas and
its exodus into sole flue, reaching maximum flow at about 6e8 h.
In Zone II, as plastic layers are being formed, the gas evacuation continues but at lower rate.
Zone III is characterized by a steady-state gas flow reaching to the near end of the coking
cycle.
In Zone IV, the plastic layers meet and collapse and the last vestiges of gases exist from the
semicoke bed.
To maintain desired draft conditions in the gas flow zones, specific damper control
practices are followed and are listed in Table 10.7.
•
•
•
•
In Zone I, air ports in the door and wall are completely open so as to allow maximum draft.
The aim is to combust majority of the volatiles in the combustion chamber and not in the sole
flue so as to not damage the floor and sole flue passageway. The air port at the sole flue helps
combust the residual combustibles before it exits through the common tunnel. Good combustibles on the sole floor must be between 2% and 3%.
In Zone II, the gas flow begins to decrease and dampers start closing to various degrees with
time so as to control the combustibles and the excess oxygen (combustibles less than 3% and
oxygen less than 6%).
In Zone III, steady state is within reach so very little change is made once the dampers are
positioned.
In Zone IV, semicoke has been formed and soaking time has begun so all dampers are
fully closed, oven doors are covered with heat-resistant fabric, and the oven is sealed
so no air enters the oven. This will prevent burning of coke and help maintain the
coke yield.
In the author’s experience, yield loss through burning in NR/HR cokemaking is
generally found to be between 2% and 4%. However, Chati et al. (2010) report a
Nonrecovery and Heat recovery cokemaking technology
283
3000
1650
2500
1372
2000
1094
1500
816
1000
538
Temperature (°C)
Temperature (F)
process of coating the upper surface of compacted coal cake with a desulfurizing agent
with an aim to reduce SO2, which Sesa Goa claims helps increase coke yield with
burning loss less than 1%; they also claim that the inorganic components report to fines
during coke pushing.
The heating profile during a coking cycle is a direct result of damper control strategy. SunCoke has published various examples of heating profiles for its NR and HR
coke facilities (Knoerzer et al., 1991; Walker, 1996). Fig. 10.15 is a typical temperature profile published by SunCoke for a 48-h coking cycle (Barkdoll, 2001). Temperature is monitored at crown and at sole flue. Crown temperature is maintained at a
narrow range through damper adjustments. Sole flue temperature shows a peak with
initial gas evolution and drops as the coking progresses closely following the gas
flow profile of Fig. 10.14. Thus understanding the zone heating practice via damper
control is the key to temperature control and must be optimized for the successful operation of a battery.
It should be mentioned that in preparation of the HR batteries at IHCC, an attempt
was made to follow coking mechanism of a coal bed charged in one Jewell-Thompson
NR oven at Vansant, Virginia. The work involved thermal profiling (using infrared imaging) and video imaging (using standard video camera). Images were taken on the
coke bed surface from all three dampers on the pusher side door, each damper covering
a small area with 45,000 points scanning along two-thirds of the length from the pusher
side door. The measurements were made on the coal bed through the three air ports on
the pusher side door. The highlight of the study can be summed up as follows: In a 48h coking cycle, the thermal profiling via infrared imaging for one oven for the higher
Crown
500
260
Sole flue
0
–18
0
4
8
12 16 20 24 28 32 36 40 44 48
Time (h)
Figure 10.15 Heating profile for a 48-h coking cycle.
Reproduced with permission from Barkdoll, M.P., 2001. Consistent coke quality from Suncoke
Company’s heat recovery coke making technology. In: Proceedings of the ABM 1st
International Ironmaking Meeting, Belo Horizonte, Brazil. © 2001 ABM.
284
New Trends in Coal Conversion
VM blend showed average coke bed temperature of 1244 C and also the last peaks for
the coke bed arriving at 42 h followed by rapid temperature drop, thereby allowing
coke to go through 6 h of soak time. It is the higher coke temperature, large soak
time coupled with longer coking time and thicker coal bed that led to production of
superior coke quality at Vansant as well as later at the startup of the HR battery at
IHCC (Ellis et al., 1999; Valia, 2000).
One-dimensional time-dependent mathematical models for the HR/NR cokemaking
process has been published by Buczynski (2016a,b,c,d) in a series of four papers. First,
a carbonization model was developed for a compact charge. It predicts temperature distribution, composition (as a fraction of coke carbon, ash, moisture), and structural properties (porosity, density) of the coke bed as a fraction of time and position in the bed;
for coal pyrolysis, they used the Merrick model (Merrick, 1983). This work, coupled
with the coal pyrolysis model, was then followed up for gas flow through downcomers
to sole flue, resulting in predicting flow rate, temperature, and composition of gas. With
knowledge of gas temperature and wall temperature, areas of refractory damage in sole
flue walls could be identified, whereby action could be taken to mitigate it via changing
the operating variable. The study also predicted an amount of energy released and its
disposition. These models were subsequently validated at a commercial facility that
uses compacted coal blend (1100 kg/m3) with 60 h of coking time.
10.6
Environmental advantages
Operation under negative pressure allows air intake that facilitates combustion of hydrocarbons before the VOCs are formed. The negative pressure also helps prevent air
emissions from the doors. The gases leaving the boiler pass through a SO2 scrubber
and then to the baghouse and exit through the waste gas stack. The other major advantage is that by-products are not generated because only waste heat gases leave the common tunnel. This eliminates the generation of wastewater effluents (such as from
ammonia liquor and from other chemicals) or hazardous solid wastes (such as from
tar decanter sludge, tar tank bottoms, other process sump, tank, and vessel bottoms,
coke oven gas (COG) line fouling, and biotreatment plant sludge). The only water
used is for coke quenching. However, one does encounter emissions during coal
handling, oven charging (as it takes about 8 min of coal charging via conveyor [minimal if stamped coal cake is used]), coke pushing, coke quenching, coke handling, or
during cases of venting through emergency stack when boilers are out of service. SunCoke process does produce solid waste at the SO2 scrubber.
Allen (2001) reported a detailed account of emission measurements for SunCoke
facility and comparisons with by-product facility. His findings on the charging and
oven criteria and hazardous air pollutant (HAP) emissions from a HR and byproduct facility charging 1,000,000 metric tons of coal are shown in Fig. 10.16 and
10.17.
Allen (2001) states: These graphs were derived using EPA’s July 2001 Draft AP42, Section 12.2 estimates of Post-NESHAP data emissions for the by-product process
and for the HR process with typical controls. Fig. 10.16 shows the HR criteria
Nonrecovery and Heat recovery cokemaking technology
285
Criteria pollutants, charging and ovens
1,000.000 tonnes coal carbonized per year
900
821
800
728
Emission (tonnes/yr)
700
600
500
460
400
372
355
300
200
100
63
25
22
87
87
48
45
0
SO2
NOx
CO
VOC
TSP
PM10
Pollutant
Sun heat recovery technology
Byproduct technology ovens
Figure 10.16 Charging and oven emissions for SunCoke heat recovery coke technology. TSP,
total suspended particles; VOC, volatile organic compounds.
Reproduced with permission from Allen, C.P., 2001. Environmental comparison Suncoke
Company’s heat recovery coke technology and competing technologies. In: Proceedings of
the AISE Annual Convention, Cleveland, USA. © 2001 AISE-AISTech.
emissions of SO2, NOx, CO, and VOCs are lower, whereas total suspended particles
(TSP) and PM10 are higher. Sun’s HR ovens utilize good combustion practices, long
residence time (over 6 s), high temperatures (over 1000 C), turbulence, and sufficient
oxygen to destroy HAPs within the ovens, producing the very low emission rates
shown on Fig. 10.17.
Towsey et al. (2010) reported that if one considers coke plant as part of the steel
plant complex, then the HR option has a smaller footprint than the slot by-product
option.
10.7
Cost benefits
There is lack of cost figures in the literature but NR/HR processes claim to incur lower
operating and maintenance costs. This is attributed to simpler design and ease of operation of the battery. SunCoke, in the year 2001 (Barkdoll, 2001), did publish the actual
capital cost data for a 1.35 million tpy fully operational plant from the ground up as
follows:
•
•
•
•
Coke oven facility (complete)d190.00 million US dollars
Coal handling/blending (complete)d35.00 million US dollars
Energy facility (complete)d140.00 million US dollars
Total capitald365.00 million US dollars
286
New Trends in Coal Conversion
HAP pollutants, charging and ovens
1,000,000 tonnes coal carbonized per year
160
155.08
140
Emission (tonnes/yr)
120
ND = Not detected
100
80
60
48.45
40
16.72
20
7.23
0
0.26
Benzene
ND
Ethylene
ND
ND
3.62
Heavy
Hydrogen Sulfide
hydrocarbons
ND
0.15
Methane
3.28
4.07
0.26
Naphthalene
Toluene
0.09
0.01
Xylene
Pollutant
Sun heat recovery technology
Byproduct technology ovens
Figure 10.17 Hazardous air pollutants (HAPs) in charging and ovens for SunCoke heat
recovery coke technology.
Reproduced with permission from Allen, C.P., 2001. Environmental comparison Suncoke
Company’s heat recovery coke technology and competing technologies. In: Proceedings of
the AISE Annual Convention, Cleveland, USA. © 2001 AISE-AISTech.
Towsey et al. (2010) did a detailed economic study on the selection of choice of HR
versus by-product coke plant technologies for placement within a steel plant. They
selected the following two cases: Case 1 of HR with high power generation and
Case 2 of by-product with gas for usage in the steel plant. They stated, “In Case 1
due to the lack of available electricity from the grid and reliance on an expensive alternative fuel source, fuel oil required to generate electricity, the HR coke plant was
preferred whereas in Case 2, when both electricity and natural gas were available at
a low cost, the by-product plant was shown to be the preferred option, although sensitivity analysis showed that increase in electricity and gas prices could change the
outcome.” Their study clearly showed that in Case 1, although the HR had a higher
CAPEX, the net present value and the region of interest (ROI) over a 20-year period
was better because of lower operating cost. In Case 2, the by-product plant had lower
CAPEX and better net present value and a better ROI; however, the results are too sensitive to price changes in electricity and natural gas price, but the lower environmental
footprint plus cost ratio comparison indicated HR even with lower ROI was a better
sustainable plant.
Quanci and Perkins (2017) suggested a synergy of 50% coke supply via HR and
another 50% via by-product coke plant. The idea that fuels this synergy is that a
by-product coke plant can supply enough gas for a steel plant and meeting 50%
Nonrecovery and Heat recovery cokemaking technology
287
coke needs of its BF. The other 50% of its coke needs can then be fulfilled via HR
coke plant, which can then also supply steel mill’s need for steam and power. This
becomes more attractive when natural gas or power is not easily available to the
steel mill; and if natural gas is available only at low cost, it can then fulfill the steel
mill’s gas needs, whereas the entire coke need is then fulfilled via HR coke plant.
Other factors that need to be considered are HR that has a larger plant footprint than
a by-product plant so paucity of land could also be hindrance. Similarly, areas that
depend on coal-derived by-products because of scarcity of petroleum could also be
a hindrance for HR cokemaking. But at the end, the technology that will survive the
competition is the one that is least harmful to the environment.
10.8
Future research
There are clear differences between conventional slot by-product cokemaking and
NR/HR cokemaking. The differences arise because the fundamental carbonization
mechanisms are different and variable parameters exist for NR/HR ovens that do
not exist in conventional coke ovens. Hence, the need of the hour is to fully understand the carbonization mechanism of NR/HR cokemaking and thereafter, identify
factors that affect coke quality, productivity, heat transfer, coke oven deterioration,
and emissions; the same goes for the HR power generator part of the facility. Thereafter, quantify the effects of raw material input and operating variables on the product
output. All these steps are necessary to optimize productivity (for both coke and power), increase yield, minimize emission, and reduce cost. In other words, all rules of
thumb for by-product cokemaking relationships that were established (evolved) over
a research and development (R&D) span of 100 years need to be developed at a
faster rate for HR cokemaking. Also, modifications such as vertical HR, coupled
with a coal gasifier that produces gas for steel mill consumption, should be explored.
Also of interest could be synergy of power from HR with coal-based direct-reduced
iron/basic oxygen furnace/electric arc furnace, a scenario as suggested by Jansen and
Cameron (2012). Enormous tasks lie ahead for R&D in HR cokemaking. The need of
the hour demands that the coke and steel companies put high priority on R&D in the
field of NR HR cokemaking so as to fulfill the mission of “high quality at lowest cost
operation.”
10.9
Concluding remarks
The rise of HR and NR cokemaking technology in recent years has triggered increased
emphasis in understanding the coking process associated with this technology. The
highlights of research activities spanning over a few decades can be summarized as
follows:
a. The NR/HR technology, because of operating under negative pressure and partially oxidizing
environment, results in significantly different air emissions and no hazardous solid waste,
288
b.
c.
d.
e.
f.
g.
h.
i.
New Trends in Coal Conversion
hence inherently providing a smaller environmental footprint than the slot by-product cokemaking. However, the choice of heat or by-product plant site selection will be based on many
regional need factors, but ultimately, the technology that will survive the competition/future
is the one that is least harmful to the environment.
The process can use coal blends from a wide range of coal ranks (HVM content
blend to LVM content blend) and still produce coke of superior hot and cold strength
properties.
For a comparable coal rank, it produces coke of higher cold and hot strength than that produced from slot by-product oven. The most dramatic change was noted for a particular HVM
content noncompacted blend, where CSR improved by about 11 points when the blend was
carbonized in HR versus in slot oven. These findings are significant for countries with abundance of HVM content coals. Further coupling the process with compaction allows use of
significantly higher amounts of noncoking coals.
In a 48-h coking cycle, the thermal profiling via infrared imaging for one oven for the higher
VM blend showed average coke bed temperature of 1244 C and also the last peaks for the
coke bed arriving at 42 h followed by rapid temperature drop. Thus higher coke temperature,
large soak time coupled with longer coking time and thicker coal bed led to production of
superior coke quality.
Literature work, although a limited study, shows coke fingers taken from the center of the
oven having higher CSR at bottom and lower CSR on the top coke bed attributed to more
dependence on structural parameters rather than carbon form and crystallinity.
Literature work also shows significant work being done in developing models with regard to
blend selection prediction and one-dimensional models for understanding the mechanism of
carbonization utilizing mass and energy balance.
The results of the BF coke transition from domestic purchased slot oven coke to SunCoke
IHCC HR coke, covering a span of about two and half years indicated that the BF performance was good with sustained high levels of productivity, improved hot metal quality,
and improved furnace efficiency and permeability.
Further studies of stamped NR coke from Shanxi China that was used in BF with the domestic purchased slot oven coke suggested that although the two cokes had wide differences in
coke strength properties, under simulated BF conditions, the reaction rates of stamped
charged NR coke are similar to the slot-oven coke; this is contrary to markedly different reactivity measured in the CSR test. Furthermore, the degradation studies on core samples
obtained via tuyere core sampling during the time of using the two cokes indicated that
the change in cell wall thickness for stamp charged NR coke is higher than for the slot
oven coke. This indicated that the stamp-charged NR coke is much more reactive than otherwise suggested by the CSR test. The probable cause may be the higher reactivity of high inert
content of Shanxi coke that were exposed via degradation. However, still at the tuyere level,
the NR coke is characterized by higher cell wall thickness, suggesting it should maintain
strength and size beneficial to BF operation.
Vigorous future research efforts is needed in modeling plus in understanding operating variables so that the process can be optimized for even smaller environmental footprint, better
oven efficiency, better coke quality, wider use of noncoking coals all aiming toward production of higher quality coke at lower cost. Thereafter, similar efforts are needed to be carried
on first to understand coke behavior under SBF conditions in the laboratory, followed by
understanding the degradation behavior of the HR coke inside the BF and its effect on BF
productivity and stability.
Nonrecovery and Heat recovery cokemaking technology
289
Acknowledgments
Much of the writing is reproduced from part of a cokemaking course that author delivered at
McMaster University, Hamilton, Canada and author is thankful to McMaster University for
granting permission to publish it. The author would also like to thank ArcelorMittal USA and
SunCoke management for supporting the research work done during author’s professional career
days at ArcelorMittal USA R&D laboratory. And gratitude is extended to colleagues who helped
in carrying the research work, laboratory tests, and plant trials at ArcelorMittal and at SunCoke.
References
Agarwalla, A., Agarwalla, A., Valia, H., 2005. High quality coke from non-recovery BLA coke
plant, Mithapur, India. In: AISTech Conference Proceedings, Charlotte, North Carolina,
USA.
Allen, C.P., 2001. Environmental comparison Suncoke Company’s heat recovery coke technology and competing technologies. In: Proceedings of the AISE Annual Convention,
Cleveland, USA.
Arendt, P., Kuhl, H., Huhn, F., Strunk, J., Stoppa, H., Louis, G., Steller, M., 2001. Cracking
reactions in coke ovens and their importance for coke quality. Cokemaking International 1,
61e64.
Barkdoll, M.P., 2001. Consistent coke quality from Suncoke Company’s heat recovery coke
making technology. In: Proceedings of the ABM 1st International Ironmaking Meeting,
Belo Horizonte, Brazil.
Buczynski, R., Weber, R., Kim, E., Schwoppe, 2016a. One-dimensional model of heat-recovery,
non-recovery coke ovens, Part I: General description and hydraulic network sub-model.
Fuel 181, 1097e1114.
Buczynski, R., Weber, R., Kim, E., Schwoppe, 2016b. One-dimensional model of heatrecovery, non-recovery coke ovens, Part II: coking bed sub-model. Fuel 181, 1115e1131.
Buczynski, R., Weber, R., Kim, E., Schwoppe, 2016c. One-dimensional model of heat-recovery,
non-recovery coke ovens, Part III: upper oven, down comers and sole flues. Fuel 181,
1132e1150.
Buczynski, R., Weber, R., Kim, E., Schwoppe, 2016d. One-dimensional model of heatrecovery, non-recovery coke ovens, Part IV: Numerical simulations of the industrial
plant. Fuel 181, 1151e1161.
Carmichael, K., 1998. Heat recovery cokemaking: minimizing environmental impact. In: Proceedings of Environmental Innovations in the Metal Industry for the 21st Century, Air and
Waste Management Association, March 30, 1998.
Chati, H., Kamat, G., D’Lima, P., Kim, Y., 2010. Reduction of Sulfur containing gases during
conversion of coal in to metallurgical coke. U.S. Patent No. 7731821, June 8, 2010.
Chaubal, P., Valia, H., 2003. Studies on blast furnace coke degradation e a case study with low
reactivity stamped charged beehive coke. In: Proceedings of 3rd ICSTI-METEC Congress,
International Conference on Science and Technology of Ironmaking, D€
usseldorf, Germany,
pp. 202e207.
Chiu, Y.F., 1982. Study of coke petrography and factors affecting coke reactivity. Ironmaking
and Steelmaking 9, 193e199.
290
New Trends in Coal Conversion
Choudhury, N., Boral, P., Ranjan, R., Yadav, R., Pramanik, T., Hazra, S., 2009. Effect of stamp
charging on coke micro texture vis-a-vis coke properties. In: Proceedings of the SAIL
Conference on Coking Coal and Coke Making e Challenges and Opportunities, Ranchi,
India.
Chung, W.U., 2007. Green Turns to Gold. http://www.chinadaily.com.cn/cndy/2007-05/31/
content_883838.htm.
Dutler, M., Carter, W., Chaubal, P., Knorr, E., Moore, J., Valia, H., Zuke, D., 2001.
Experience with heat recovery coke use at Ispat Inland No. 7 BF. In: Proceedings of
ISS-AIME Ironmaking Conference, Iron and Steel Society, Baltimore, USA, vol. 60,
pp. 129e139.
Eisenhut, W., Rohde, W., Orywal, F., Huhn, F., 1991. From beehive to Jumbo Coking
Reactor e history and future of coke making. In: Proceedings of the ISS-AIME Ironmaking
Conference, Washington DC, USA, vol. 50, pp. 15e26.
Ellis, A., Schuett, K., Thorley, T., Valia, H., 1999. Heat recovery coke making at Indiana Harbor
Coke Company e an historic event for the steel industry. In: Proceedings of the ISS-AIME
Ironmaking Conference, Chicago, USA, vol. 58, p. 173.
Ellis, A., Valia, H., 2008. Non-Recovery operating practices from around the world. In: AISTech Conference Proceedings, Pittsburgh, PA, USA, vol. 1, pp. 61e78.
Jansen, M., Cameron, I., 2012. Combining new coke and ironmaking technologies to reduce the
carbon footprint in the production of steel. In: AISTech Conference Proceedings, Atlanta,
GA, USA, vol. 1, pp. 267e275.
Knorr, E., Carter, W., Chaubal, P., Moore, J., Ranade, M., Valia, H., Zuke, D., 2000. Transition
of Ispat Inland’s No. 7 blast furnace from conventional to heat recovery coke. In: Proceedings of 4th European Coke and Ironmaking Congress, ATS, Paris, France, vol. 1,
pp. 231e236.
Koba, K., Ida, S., 1980. Gasification reactivities of metallurgical cokes with CO2, steam and
their mixtures. Fuel 59 (1), 59e63.
Kobus, K., 2017. The history of coke making [Teaching part]. In: 8th Cokemaking Course,
McMaster University, Hamilton, Canada, pp. 1e1/1-53.
Knoerzer, J., Ellis, C., Pruitt, C., 1991. The design and operation of Jewell new non recovery
coke oven batteries. In: Proceedings of the 50th ISS-AIME Ironmaking Conference,
Washington DC, USA, vol. 50, pp. 191e196.
Knoerzer, J., Cekela, V., 1992. Jewell Thompson non recovery coke making with heat recovery
and power generation. In: Proceedings of the 2nd International Cokemaking Congress,
Institute of Materials, London, UK.
Kuyumcu, H., Sander, S., 2014. Stamped and pressed coal cakes for carbonization in by-product
and heat-recovery coke ovens. Fuel 121, 48e56.
Madias, J., de Cordova, M., 2011. Non recovery/Heat Recovery coke making: a review of recent
developments. In: AISTech Conference Proceedings, Indianapolis, USA, vol. I,
pp. 235e251.
Madias, J., de Cordova, M., 2013. A review on stamped charging of coals. In: AISTech Conference Proceedings, Pittsburgh, USA, vol. I, pp. 253e262.
Marsh, H., 1982. Metallurgical coke: formation, structure and properties. In: Proceedings of ISSAIME Ironmaking Conference, Warrendale, USA, vol. 41, pp. 2e11.
Miller, J.W., 1967. Non-recovery coke ovens. Journal of Metals (JOM) 19 (6), 74e77.
Merrick, D., 1983. Mathematical model of the thermal decomposition of coal 1. The evolution of
volatile matter. Fuel 62, 534e539.
Nyathi, M.S., Kruse, R., Mastalerz, M., Bish, D.L., 2016. Nature and origin of coke quality
variation in heat recovery coke making technology. Fuel 176, 11e19.
Nonrecovery and Heat recovery cokemaking technology
291
Nyathi, M.S., Kruse, R., Mastalerz, M., Bish, D.L., 2017. Investigation of coke quality variation
between heat-recovery and byproduct cokemaking technology. Energy & Fuels 31 (2),
2087e2094.
Patrick, J., Green, P., Thomas, K., Walker, A., 1989. The influence of pressure on the development of optical anisotropy during carbonization of coal. Fuel 68, 149e154.
Perkins, J., Molnar, W., King, V., Quanci, Q., 2012. Coal blend optimization for a horizontal
heat recovery coke plant. In: Proceedings of MetCoke World Summit, Pittsburgh, PA,
USA, Smithers.
Pin, Z., 2005. The advantages of heat recovery stamping coking technology in the aspect of
expanding coking coal resources. In: Proceedings of the SAIL Conference on Coking Coal
and Cokemaking - Challenges and Opportunities, Ranchi, India.
Prachetan Kumar, P., Vinoo, D.S., Yadav, U.S., Ghosh, S., Lal, J.P.N., 2007. Optimization of
coal blend and bulk density for coke ovens by vibro-compacting technique non-recovery
ovens. Ironmaking and Steelmaking 34 (5), 431e436.
Quanci, J., Perkins, J., 2017. Recent trends in coke making heat recovery processes [Teaching
part]. In: 9th Cokemaking Course, McMaster University, Hamilton, Canada, pp. 9e1/9-15.
Shigeno, Y., Evans, J., 1999. Infiltration of metallurgical coke by thermal decomposition of
methane and its effect on CSR through microporous structure changes. In: Proceedings of
ISS-AIME Ironmaking Conference, Chicago, USA, vol. 58, pp. 257e267.
Tiwari, H., Banerjee, P., Saxena, V., 2013. A novel technique for assessing the coking potential
of coals/coal blends for non-recovery coke making process, Fuel 107, 615e622.
Towsey, P., Cameron, I., Gordon, Y., 2010. Comparison of byproduct and heat recovery
cokemaking technologies. In: AISTech Conference Proceedings, Pittsburgh, USA, vol. 1,
pp. 333e338.
Valia, H., 2000. The comparison of coke quality from a by-product (USA), a non-recovery
(China), and a heat recovery coke plant (USA). In: Proceedings of the 4th European
Coke and Ironmaking Congress, ATS, Paris, France, vol. 1, pp. 148e156.
Valia, H., 2001. Coke breakage behavior of heat recovery coke. In: Proceedings of 3rd IAS
Ironmaking Seminar, Buenos Aires, Argentina, pp. 11e14.
Valia, H., 2002. Coal blend rank changes and resultant coke quality from IHCC heat recovery
coke making. In: Proceedings of ISS-AIME Ironmaking Conference, Nashville, USA, vol.
61, pp. 419e426.
Valia, H., Yan, J., Song, W., 2004. Production of super strength coke from non-recovery
cokemaking at Shanxi Sanjia, Jixiu, Shanxi Province China. In: AISTech Conference
Proceedings, Nashville, USA, vol. 1, pp. 633e636.
Valia, H., 2006. Coal cost reduction using low rank coals, Iron and Steel Technology. March
1e6.
Valia, H., Ambry, W., 2009. Method for producing blast furnace coke through coal compaction
in a non-recovery oven. U.S. Patent 7611609, November 3, 2009.
Valia, H., 2013. Coke production utilizing non recovery/heat recovery technology, [Teaching
part]. In: The 7th Cokemaking Course, McMaster University, Hamilton, Canada.
Valia, H., 2018. Web Site of American Iron & Steel Institute. www.steel.org. Learning Center,
How Steel is made, Coke Production.
Vandazande, J., 1983. Effect of pyrolytic carbon on coke properties. In: Proceedings of the 16th
Biennial Conference on Carbon, American Chemical Society, San Diego, USA.
Veit, G., D’Lima, P.F.X., 2002. Combining stamp charging with the heat recovery process. Steel
Technology, July-August 24e29.
Walker, D., 1996. High CSR coke from non-recovery coke making process. In: Proceedings of
the 3rd International Cokemaking Congress, Ghent, Belgium.
292
New Trends in Coal Conversion
Wei-Kao, L., Valia, H., 1998. Hearth-type furnaces for ironmaking and coke making with better
environmental protection. In: International Symposium on Global Environment and Iron &
Steel Industry Proc., Chinese Society of Metals & United Nations Environment Program,
Beijing, China, pp. 185e190.
Westbrook, R., 1998. Heat Recovery Cokemaking at Suncoke Company. In: AISTech Conference Proceedings, Pittsburgh, USA.
Wright, R., Kochanski, U., Platts, M., 2002. Start up and operating experience of new non recovery coke ovens at the Illawara coke Company, coal Cliff, New South Wales, Australia.
In: ISS-AIME Ironmaking Conference Proceedings, Nashville, USA, vol. 61,
pp. 327e338.
Wright, R., Sch€ucker, F., Kim, R., 2005. Compacting of coal for heat recovery ovens. In:
Proceedings of 5th Cokemaking and Ironmaking Congress, ECIC, Stockholm, Sweden, pp.
TU2:2-1-TU2, pp. 2e13.
Xiobing, Z., 2010. Vertical heat recovery coke ovens (VHRCO). In: Proceedings of the Metcoke
World Summit, Pittsburgh, USA, Intertech Pira.
Yan, J., Song, W., 2000. Coke making into the 21st century-environmental protection efforts at
Shanxi Sanjia coal Chemistry Company Ltd. In: Proceedings of ISS-AIME Ironmaking
Conference, Pittsburgh, USA, vol. 59, pp. 285e291.