REENGINEERING BLUESCOPE STEEL'S PORT KEMBLA SINTER PLANT FOR HIGH PRODUCTIVITY AND REDUCED STEELWORKS GREENHOUSE EMISSIONS
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REENGINEERING BLUESCOPE STEEL’S PORT KEMBLA
SINTER PLANT FOR HIGH PRODUCTIVITY AND REDUCED
STEELWORKS GREENHOUSE EMISSIONS
N. Di Giorgio, D. Brace, A. Bennett, K. Wijekulasuriya
BlueScope Steel Australia New Zealand Steel Manufacturing Business:
PO Box 1854 Wollongong 2500
nick.digiorgio@bluescopesteel.com
ABSTRACT
Maximising the amount of highly reducible sinter in blast furnace feed is crucial to
minimising blast furnace fuel rate; the chief source of CO2 emissions at an integrated
steel plant.
As part of the ongoing drive to improve process capability and reduce operating cost,
BlueScope Steel in late 2009 upgraded the sintering capacity at its Port Kembla
steelworks. The business case for upgrading the sinter plant was based on replacing high
cost imported pellets with an increased amount of locally sintered iron ore. However the
need to substantially re-engineer the plant presented the opportunity to build a lower
carbon footprint into the Port Kembla steelworks as a whole through increased sinter
make and to potentially lower the greenhouse intensity of the sinter plant itself through
measures aimed at further increasing sinter plant productivity.
Following commissioning of the upgraded sinter plant there has been an ongoing
challenge to achieve design sinter production rates. It was found that high rates of
goethitic ores in the sinter feed was detrimental to sinter plant productivity. However a
previously undocumented relationship was found to exist between increased Goethitic
ore content of the sintered ore blend and decreased blast furnace fuel rate. Overcoming
decreased sintering productivity due to high goethitic ore rates represents an opportunity
to lower steel plant greenhouse impact by lowering blast furnace fuel rate.
The paper outlines the measures implemented to increase the sinter plant productivity in
the context of high Goethite rate, and the correspondence between the observed
increased sintering productivity and reduced sinter plant CO2 intensity. The newer
technologies implemented within the scope of the sinter plant upgrade, that could
further lower greenhouse intensity are described. Possible technologies that could be
applied to reduce sinter plant greenhouse emissions in the longer term are also outlined.
OVERVIEW
Blast Furnace Sinter Burden, Fuel Rate and CO2 emissions
BlueScope Steel’s Port Kembla works supplies in excess of 5Mt per annum of high
grade flat steel products. The steel shop is supplied by iron from two modern blast
furnaces: No.5, which was relined in 2009 to a fourth campaign inner volume of
3427m3 and No. 6, a 3208m3 furnace commissioned in 1996 which has to date produced
in excess of 37.5 Mt of iron.N. Di Giorgio, D. Brace, A. Bennett, K. Wijekulasuriya
At normal production levels, the Port Kembla plant emits in excess of 10 million tonnes
of CO2 equivalent per annum (National Greenhouse and Energy Reporting 2010) of
which approximately 80% is due to the blast furnace iron making process, while the
sintering process contributes approximately 10%. The blast furnaces use a combination
of pulverised coal injection (PCI) and coke to supply the carbon required for heat and
reduction of iron oxides. Minimising blast furnace fuel requirement is therefore central
to minimising CO2 intensity of an integrated steel plant.
15000 90
Average Daily Ironmake (t)
14000 85
13000 80
Burden Sinter %
12000 75
11000 70
10000 65
9000 60
8000 55
7000 50
1982 1987 1992 1997 2002 2007
Year
Daily Ironmake (t) Burden Sinter %
Fig.1 Port Kembla average daily Blast Furnace iron production and sinter percentage in
blast furnace burdens 1982 – 2011. No 5 Blast Furnace was relined in 1991 and 2009.
45 18000
43
Daily Sinter Production (t)
17000
Productivity (t/ m2/ d)
41
16000
39
37 15000
35 14000
33 13000
31
12000
29
27 11000
25 10000
1982 1987 1992 1997 2002 2007
Year
Productivity Daily Sinter Production (t)
Fig. 2 Port Kembla average daily sinter production and productivity (t/m2/day) 1983-
2011. The sinter plant was enlarged during 2009.
2N. Di Giorgio, D. Brace, A. Bennett, K. Wijekulasuriya
A major determinant of blast furnace fuel rate is ferrous burden reducibility; the greater
the rate and extent of reduction to Fe under standard test conditions (ISO Standard
7215), the more reducible the burden. Of the three types of ferrous burden charged to
blast furnaces, namely sinter, pellets and lump iron ore, sinter is the most reducible. It is
also the least costly. Integrated steel makers have known for some time that using sinter
in place of lump ore and pellets can decrease blast furnace fuel rate.
The ability to maximise sinter feed to the blast furnaces is therefore vital to integrated
steel plant operation to minimise blast furnace fuel costs, associated greenhouse
intensity and ferrous feed cost.
From multiple linear regression analysis of long term blast furnace operating data it is
observed, after correcting for other known influences on fuel rate (e.g slag rate) that
• +1% Blast Furnace Sinter burden = -0.4 kg/t Fuel Rate,
From a steel plant operating viewpoint, lower greenhouse gas emissions and lower fuel
rate are the same objective. The large and increasing fraction of steel plant operating
cost related to carbon fuels has driven significant reductions in both blast furnace and, to
a lesser degree, sinter plant fuel rate over many years. Blast Furnace Fuel Rates are
typically of the order of 500 kg/t. The scope for further blast furnace fuel rate
reductions, though small in percentage terms, represent significant tonnages of CO2.
Conversely, even large percentage reductions of sinter plant CO2 emissions represent
small CO2 tonnages when compared to blast furnace operation.
As such increased sinter productivity is likely to produce a net fuel rate and CO2
emission benefit even if sinter plant emissions rise with increased sinter make.
The Port Kembla furnaces have operated with a sinter based burden supplied by a single
sinter plant supplemented by purchased pellets and lump ore. The Port Kembla 3DL
sinter plant was first commissioned in 1975 to supply sinter requirements for a then 3.8
million tonne steel make with a strand length and area of 84m and 420m2 respectively.
As iron make increased, the fraction of sinter in the blast furnace burden decreased over
time (Fig.1), with the shortfall being supplemented by increased amounts of lump iron
ore, expensive imported pellets and party offset by increasing sinter plant productivity
(Fig. 2).
Despite the primary Ironmaking focus at Port Kembla having been blast furnace
productivity, the sinter plant productive capability was significantly increased with the
introduction of burnt lime in the late 1980’s. Despite its age, the sinter plant has
achieved productivity well above international norms.
Blast Furnace PCI operation
Both blast furnaces were converted to the use of PCI in 2002. While this was done to
decrease operating cost through the replacement of a portion of expensive coke with
cheaper PCI coals, high PCI Blast Furnace operation offers the opportunity to increase
productivity and hence decrease fuel rate. In addition, the PCI grinding and drying plant
is less energy intensive than coke ovens.
Obstacles to achieving the targeted PCI rate of 150 kg/t-HM have proven formidable
chiefly due to blast furnace lower zone permeability issues driven by unique coke
3N. Di Giorgio, D. Brace, A. Bennett, K. Wijekulasuriya
quality challenges. However the amount and nature of sinter is also important in
maximising PCI. A key factor in the improvement of PCI injection was a change in
sintering philosophy in 2005 (Fig. 3) aimed at increasing the sinter hot strength, and in
turn the ability of the blast furnaces to accept higher PCI rates. This involved increasing
sinter FeO by increasing heat input to the strand. Part of the extra energy requirement
for this would be supplied by operating at ignition gas rates above those needed for
ignition alone. This approach places significant demands on the ignition and –
especially- cooling capabilities of the sinter plant. These considerations influenced the
nature of the sinter plant upgrade.
180 8.5
Blast Furnace 6 PCI Rate (kg/ t)
160 8
140 7.5
Sinter FeO (%)
120
7
100
6.5
80
6
60
40 5.5
20 5
0 4.5
01/ 01/ 04 19/ 07/ 04 04/ 02/ 05 23/ 08/ 05 11/ 03/ 06 27/ 09/ 06
BF6 PCI Rate (kg/ t) Sinter FeO (%)
Fig.3 No. 6 Blast Furnace PCI rate, sinter FeO, 2004 – 2006. Sinter FeO target was
increased in 2005 to enable sustained higher PCI rate operation.
Sinter Plant Performance 2003 to 2009
The focus of capital expenditure at the Port Kembla sinter plant prior to 2009 was in
areas of environmental impact. In 2003, a Sumitomo Heavy Industries (SHI) secondary
Waste Gas Cleaning Plant (WGCP) was built at a cost of $93 Million to remove SOx,
NOx, Volatile Organic Compounds (VOC’s) and any dust not captured by the
precipitators. As a statutory licence condition, the WGCP is without the ability to be
bypassed, as similar plants elsewhere can be. This creates the possibility of blockages in
the char system limiting sinter plant productivity.
After the commissioning of the WGCP sinter productivity became regularly limited by
permeability of the activated char beds in the five adsorbers.
From plant observation and process analysis it was found that alkali chlorides were
largely responsible for blockages in the char beds causing production limitations in the
period 2003 to 2008. These findings matched those reported by Kobayashi et al. (1980).
The chief source of chlorides (more than 64% of the total) was found to be a particular
Australian hematite used in the sinter blend. The significant reduction of chloride load
in sinter feed with the removal of this high chloride ore in late 2008 resulted in a
4N. Di Giorgio, D. Brace, A. Bennett, K. Wijekulasuriya
significant reduction in differential pressure across the activated char adsorbers (Fig. 4).
This has been taken as confirmation that alkali chlorides, together with the age and
condition of the precipitators, were in fact causing blockages in the char adsorbers. This
has alleviated a major cause of reduced sinter make at Port Kembla.
25 4.5
4
High Chloride Ore (%)
20 3.5
3
15
2.5
2
10
1.5
5 1
0.5
0 0
26/ 09/ 03 07/ 02/ 05 22/ 06/ 06 04/ 11/ 07 18/ 03/ 09 31/ 07/ 10
High Chloride Ore (%)
Booster Outlet Pressure (kPa)
Waste Gas Flow Nm3/ h (* 1000000)
Fig. 4. High chloride ore % in blend, pressure and flow to WGCP
2003 – 2010. Permeability improved with high chloride ore removed from blend.
Ore Preparation Upgrade Project (OPUP) 2009
The 2009 reline of No. 5 Blast Furnace presented the opportunity to upgrade the sinter
plant & in turn lower operating cost and fuel rate by supplying more sinter to the
furnaces. Known internally as OPUP, the Ore Preparation Upgrade Project involved the
expenditure of approximately $140 Million to increase sinter make from 5.5Mt-annum
to 6.6Mt-annum.
Existing strand width and main fans were retained, but the strand was lengthened from
84 to 96 m to increase the grate area from 420 to 480m2. The strand was lengthened
rather than widened, despite the higher capital cost, so that the original hot screen
feeders could be removed and a full height cooler filling chute installed. This enabled
minimisation of lateral segregation in the cooler pans, which had not been possible with
the previous low height chute, as well as a reduced maintenance workload. To enable
increased bed height, the strand sideplates were increased from 500mm to 700mm.
The added cooling capacity required for higher sinter FeO levels was achieved through
significantly improving the permeability of sinter on the cooler. This was done by
widening the cooler, coupled with the improved size segregation mentioned previously,
and the addition of a fourth cooler fan.
An entirely new ignition furnace replaced the existing line burner. It is unusual in that it
uses four burner rows instead of one, and so can be operated in various combinations to
condition the strand prior to ignition, ignite the strand and sustain ignition. This offers
considerable flexibility in both the profile and total amount of ignition heat that can be
presented to the strand. Another difference is the use of Natural Gas instead of Coke
Ovens Gas as fuel for the ignition furnace.
5N. Di Giorgio, D. Brace, A. Bennett, K. Wijekulasuriya
The ageing strand feeder was replaced with a POSCO-designed feed unit with the ability
to improve particle size segregation for increased through-thickness permeability in the
sinter bed, and to minimise lateral size segregation across the strand. This in turn makes
burn – through at the end of the sintering strands more uniform, in turn improving
productivity through the minimisation of return fines. Lastly the electrostatic
precipitators were rebuilt after thirty years of service to include a fourth zone and
minimise the particulate load to the WGCP.
Sinter Plant Performance Post-Upgrade
The sinter plant upgrade was justified on the basis of increased sinter productivity at a
rate of 40.5 t/m2/d at 93% availability. Plant operating data showed that such
productivities could be achieved. The operating data in Fig. 6 shows periods of
operation at or above the intended target for short periods. That sinter plant productivity
was generally below this target in the years leading to the upgrade was mainly due to the
age and condition of the sinter plant coupled with periods of high WGCP permeability
resistance, and underpinned the need for a larger, more modern sinter plant.
Sintering Fundamentals
Sinter plants are relatively simple in concept. Granulated iron ore fines are mixed with
suitably sized coke and fluxes, ignited under suction on a moving grate. The speed of
the strand is adjusted to ensure the “burn through point” is at the end of the strand. This
is achieved in practice by controlling the temperature of the waste gas into the
precipitators within a narrow band.
However fundamental sinter productivity (P) considerations, as outlined by Loo (1993)
re-expressed as a mass balance in equation 1, reveal some of the complexity behind the
simple concept.
42
Sinter Productivity Upgrade Target 40.5
40
38
36
34
Degraded Machine condition
and Waste Gas Cleaning Plant permeability prior to
32 Sinter plant upgrade
Global median productivity 37 t/m3/d
30
17/11/2003 17/11/2004 17/11/2005 17/11/2006 17/11/2007 17/11/2008 17/11/2009 17/11/2010
Fig. 5 Sinter plant productivity 2003 – 2011, blended bed average basis. Post upgrade
period circled.
6N. Di Giorgio, D. Brace, A. Bennett, K. Wijekulasuriya
P= (1-LOI) ρ (1-%H2O) (1-ε) H(L/T) W/(1+ CRF) (1)
Where LOI denotes Loss on Ignition being either CO2 or chemically combined water,
%H2O is “free” (not LOI) moisture, ρ denotes feed particle density, ε denotes bed
voidage.
The terms H(L/T)W refer to bed height, strand speed and strand width respectively.
Over a fixed time the product of the three is “sintered volume”. At fixed length it relates
to “flame front speed”. CRF denotes the recirculating cold return fines load.
Essentially productivity is maximised by minimising the ignition loss in the feed
materials, maximising the density of the feed materials, minimising the granulation
moisture requirement and maximising the flame front speed. Contradictions arise and
need to be managed between, say, the need for a high flame front speed and low CRF
rate on the one hand, and the fact that increased flame front speed generally increases
CRF. Similarly high productivity requires a permeable bed which calls for more, not
less, voidage.
Viewed from another perspective the Flame Front Speed (FFS) is fundamental to
sintering productivity, as described in equation 2 below, outlined by Blaskett (1958)
using data published by Voice and Wild (1956).
hg W
FFS = (2)
hc (1 − ε )
Where hg denotes the heat available from the gas stream, W denotes the waste gas rate,
hc, denotes the heat requirement of the solid stream.
OPUP
Goethite 1
High Chloride
Hematite 2
Hematite 1
Sth American
Hematite 1
Hematite Goethite blend Goethite 2 Sth American Hematite 2 Sth American Hematite 3
Fig. 6 Sintering ore blended bed makeup through 2010 compared to planned post
upgrade “OPUP” blend (LHS Column)
7N. Di Giorgio, D. Brace, A. Bennett, K. Wijekulasuriya
Essentially flame front speed is the ratio of the heat available from the gas stream to the
heat required by the solid stream. For the flame front to progress through the bed
“equality of heat capacity between gas and solid is required” (Ball et al. 1973) or
restated, increasing the available heat in the gas stream increases driving force for the
progress of the flame front, with a higher waste gas rate implying a higher flame front
speed. However permeability considerations as outlined by Ergun (1952) indicate that
increased waste gas rate, all else being equal, will result in higher local gas velocities
and increased pressure drop. As such, considering both equations (1) and (2), if the
specific waste gas rate is increased due to increase ignition losses in the charged blend a
lower flame front speed will result unless heat input and voidage are increased.
Sinter productivity challenges & responses
Figs. 2 and 5 show sinter plant productivity falling short of the expected rate in the post
OPUP period. The main reasons for this were found to be related to the change in iron
ore blend in use compared to that assumed during the preparation of feasibility studies
in 2005. At Port Kembla, iron ores are blended in beds of approximately 220,000 tonnes
and consumed by the sinter machine over approximately 20 days. Fig. 6 shows both the
difference between the planned blend ( the “OPUP” blend) and what actually prevailed
in the period following start up of the upgraded sinter machine, on a blended bed basis.
The difference between the planned and actual blends, as well as the apparent large
bed-to-bed variation was driven by rapid change in iron ore supply circumstances
driven by high demand for iron ore worldwide. This lead to the use of Goethitic ores in
place of the Hematites, at rates well above previous experience. The magnitude and pace
of change in blend makeup, and the degradation of quality of the individual ores, were
in sharp contrast to the incremental changes that had prevailed over many years.
Coupled with newly upgraded equipment the Port Kembla sinter plant was in a new and
unexpected operating regime.
115
110
Relative CO2 (% of aim)
105
100
95
90
85
Dec-10
Oct-10
Aug-10
Apr-10
Apr-11
Jan-10
Feb-10
May-10
Sep-10
Nov-10
Jan-11
Feb-11
Mar-10
Jun-10
Jul-10
Mar-11
Relative CO2 Equivalent 100%
Fig. 7 Sinter CO2 intensity relative to aim January 2010 – April 2011
(includes process fuels and electricity).
8N. Di Giorgio, D. Brace, A. Bennett, K. Wijekulasuriya
Numerous changes were made to the sintering process to increase productivity in the
face of these challenges. These changes and the corresponding process response are
outlined in Table 1, which groups daily sinter plant operating data from the period
August 2010 to March 2011; the period over which the major process adjustments were
made. Data is grouped by sinter plant productivity, with days of abnormal operation
removed. The correspondence between increasing productivity and decreased waste gas
rate stemming from reduced LOI, brought about by ore blend and waste material rate
adjustments are apparent in Table 1. Increases in limestone size, coke size and
favourable changes in iron ore sizing resulted in decreased permeability resistance
through the sinter bed and increased flame front speed. The rate of cold return fines
decreased despite increased flame front speed. This was partly achieved through
adjustments to fluxing rate and a lower sinter Al2O3 (not shown) resulting from the ore
blend adjustments. Decreased ultrafine coke fraction improved green feed permeability
and combustion efficiency. This is consistent with previously published literature [Loo
(1991), Peters et al. (1990) Ball et al. (1973)].
These changes, which target sintering fundamentals as outlined in equations 1 and 2,
simultaneously resulted in increased sinter plant productivity and decreased sinter plant
CO2 intensity as seen in Table 1 and Fig. 7. Moreover, it was shown that sinter plant
productivity at or above 39 t/m2/day - a figure well above the international norm of 37 –
can be achieved with 45% Goethite in the blend and, importantly, a lower fuel
requirement.
9N. Di Giorgio, D. Brace, A. Bennett, K. Wijekulasuriya
Table 1. Sinter plant process changes daily data August 2010 – March 2011
>32- >34.5- >36- >37.5-
Productivity t/m2/d 34.5 36 37.5 39 >=39 Aim 40.5
days 15 58 63 39 13
Sintered volume (m3) (strand
speed*time*w*h) 15276 16053 16737 17138 17368 16070
Net Waste Gas Rate (Nm3/t) 1795 1723 1691 1648 1599 1543
Coke & Anthracite rate (kg/t) 57.7 56.7 55.7 54.3 53.8
Sinter plant process fuel CO2 (kg-CO2/t-
sinter)* 192 190 187 182 180
Permeability Resistance 33.6 33.5 32.3 31.6 31
Flame Front Speed (mm/min) 21.5 22.4 23.2 23.9 24.3 24.5
Cold Return Fines (%) 34.1 33.6 33.7 32.8 31.2 27
South American Hematites (%) 14 14.2 15.5 16.9 18.4
Hematite 1 (%) 15.2 16.2 16.2 16.4 14.9
Goethitic Ore 1 (%) 40.1 38.8 39.7 43 45
Hematite/Goethite blend (%) 11.3 7.9 5 1.7 -
Sth American Hematite 1 LOI (%) 2.2 2.1 2 1.9 1.8
Hematite 1 LOI (%) 3.1 3.1 2.9 2.8 2.8
Virgin Ore Weighted LOI (%) 5.25 5.27 5.17 5.09 4.94 4.28
Waste Material Rate (wet % ) 0.94 0.97 0.9 0.47 0.44
Ore feed LOI (%) 6.91 6.81 6.69 6.34 6.3 6.0
Blend Mean Size (mm) 3.67 3.25 3.36 3.36 3.64 3.55 min
Blend %+250micron- 1mm 13.7 13.5 13.2 13.2 12.8 13.6 max
Blend ratio -250/+1mm 0.32 0.31 0.3 0.32 0.25 0.3 max
Blend %-63 Micron 11.1 10.7 10.9 12 9.6 13 max
Limestone % +4mm 7.6 7.1 9.8 15.6 15.8
Limestone % -125 Micron 17.9 18.3 17.3 15.8 15.2
Coke % +4 mm 13.7 12.7 14.4 16.9 21.3
Coke % -250 Micron 21.4 20.6 20.2 19.3 17
*Natural Gas, Coke and Anthracite:
Ore blend and sinter plant performance
The ore blend characteristics are fundamental to the sintering process. Fig. 8 shows both
the particle (true) density of ores in the blend, and the LOI of the ores as functions of
typical Fe content. It is clear that higher grade ores are denser and contribute less waste
gas per tonne than lower grade ores. This effect was the main process cause of the
productivity shortfall at the newly upgraded sinter plant. From 2004 the quantity of
goethite in the blend had been gradually increased. The rate of Goethite use further
increased to offset decreased rates of Hematite ore brought about by alumina, alkali
chloride content, cost and other supply constraints. Goethite 1 is an Australian ore that
offers the benefits of low alumina and phosphorus required by the blast furnaces and
10N. Di Giorgio, D. Brace, A. Bennett, K. Wijekulasuriya
steelmaking shop. Fig. 9 shows the sinter plant productivity response to increasing
amounts of Goethite 1 and the corresponding increase in weighted ore LOI. The effect
of partially reversing this trend is apparent in Table 1. It is also apparent that the
“sintered volume” required to achieve a given sinter productivity is higher than that
assumed in the plant design, reflecting the lower density of the current ore blend.
5.1
Sth American Hematite 1
4.9
Sth American Hematite 3
4.7 Hematite 1
4.5
High Chloride Ore
Density
4.3
Goethite/Hematite
4.1
3.9
Goethitic 1
3.7
3.5
%Fe
10.0
Goethite 1
9.0
8.0
7.0
Ignition Loss (wt%)
6.0
Goethite / Hematite
5.0
4.0
Hematite 1
3.0
High Chloride Ore
2.0
Sth American Hematite 3
1.0
Sth American Hematite 1
0.0
57 58 59 60 61 62 63 64 65 66
%Fe
Fig 8 Ignition Loss (waste gas rate) and Particle Density t/m3 of various iron
ores as a function of typical Fe content (Density Data C/- Dr. D. Maldonado
BlueScope Steel).
Burnt lime is used in many sinter plants worldwide to increase productivity by
improving on-strand permeability. Fig. 10 shows the rate of burnt lime consumption at
Port Kembla since it’s introduction in the late 1980’s. Compared with recent experience
at comparable sinter plants the burnt lime rate at Port Kembla is low, and represents an
opportunity to offset the detrimental productivity impact of Goethitic ores, however the
current burnt lime rate represents the full productive capability of the supplier.
11N. Di Giorgio, D. Brace, A. Bennett, K. Wijekulasuriya
% Goethite 1 Virgin Ore Blend Weighted LOI
60 6.5
% Goethite 1 in sintering blend
55
Weighted Virgin Ore LOI (%)
6
50
5.5
45
5
40
4.5
35
4
30
25 3.5
20 3
1/
4211/ 200315/ 03/ 200528/ 07/ 200610/ 12/ 200723/ 04/ 20095/ 09/ 2010
41
Sinter Productivity (t/ m2/ d)
40
39
38
37
36
35
34
33
32
1/ 11/ 03 15/ 3/ 05 28/ 7/ 06 10/ 12/ 07 23/ 4/ 09 5/ 9/ 10
Sinter Productivity
Fig. 9 Goethite 1 percentage in sintering blend, weighted average Iron Ore LOI
and corresponding sinter plant productivity 2003 – 2011
14
12
10
8
6
4
2
0
1981 1986 1991 1996 2001 2006 2011
Burnt Lime Rate (kg/ t)
Fig 10. Burnt lime rate (kg/t-sinter) at the Port Kembla Sinter Plant 1989 – 2011.
Burnt lime feed rate has been at the limit of the feeding system since 2007.
Typical burnt lime rate for comparable plants is 15 – 20 kg/t-sinter.
12N. Di Giorgio, D. Brace, A. Bennett, K. Wijekulasuriya
Sinter reducibility, Goethitic ores and Blast Furnace Fuel Rate.
While high goethite rate is detrimental to sinter productivity, it is also known to be
beneficial for sinter reducibility [Loo (1991)]. Fig. 11 shows sinter reducibility at Port
Kembla, determined by the standard test, as a function of the amount of Goethite 1 in
the blend. This plot corresponds to the time period from 2004 shown in Fig. 8.
69
68
67
Sinter Reducibility (%)
66
65
64
63
62
61
60
59
58
20 25 30 35 40 45 50 55 60
%Goethite 1 in sintering blend
Fig. 11 Sinter reducibility as a function of Goethite 1 content in the sintering blend
2003 – 2011 blended bed (~20 day) average basis.
As part of the analysis that yielded the relationship between sinter burden and blast
furnace fuel rate, mentioned previously in the present work, it was also found that for a
given amount of sinter in blast furnace feed
• + 1% “Goethite 1” in sintering blend = -0.15 kg/t Blast Furnace Fuel Rate
While such a relationship is not unexpected given the relationship in Fig. 10, and
previous findings by Loo (1991) a direct relationship between an individual ore type in
the sinter and blast furnace fuel rate performance has not previously been documented.
Moreover multiple linear regression analysis showed, somewhat surprisingly, that
correlation between Goethite 1 in sinter and blast furnace fuel rate was stronger and of
higher confidence than the correlation between sinter reducibility and blast furnace fuel
rate. This means that different sinters with similar physical standard reducibility test
results may in fact respond very differently in the blast furnace due to the mineralogy of
the ores they were made from.
This finding is highly significant. It means that the goals of maximising both the
reducibility and the amount of sinter are in conflict with each other. However the
present work shows that overcoming productivity impediments associated with the use
of Goethite can yield an additional blast furnace fuel rate benefit beyond that accruing
from the use of more sinter alone.
Present challenges and future opportunities.
The largest opportunity to decrease fuel rate on the upgraded sinter machine, and with it
greenhouse emissions, is by making full use the natural gas capability of the new
13N. Di Giorgio, D. Brace, A. Bennett, K. Wijekulasuriya
ignition furnace. At the time of writing, the natural gas rate is approximately 50GJ/t-
sinter, or little over half of the available natural gas capability. Analysis of fuel
consumption data shortly after commissioning showed that increasing the natural gas
rate could permit decreases in solid fuel rate at a replacement ratio of 1.7:1 joules
coke/joule gas at constant sinter FeO. This equates to a decrease in solid fuel rate of up
to 2.4 kg/t-sinter or about 4% of current sinter machine solid fuel requirement.
The ability to increase natural gas above current levels is presently limited by the need
to fully optimise solid fuel size distribution and through-thickness placement on the
sinter strand with the upgraded feeder. It has been found that the sinter plant solid fuel
rate is sensitive to the settings of the new feeder, with lower solid fuel rates being
associated with improved uniformity of lateral material placement. Lower solid fuel
rates are also associated with a shallower charging angle on the lower feed plate that is
the departure point for material directly on to the strand. The mechanism for this is
thought to be more even placement of solid fuel and fluxes through the thickness of the
bed.
Increased sinter productivity through the addition of sugar or molasses (Loo 1995) to
granulation water was successfully tested at Port Kembla in short term plant trials in the
1990’s. However sugar is costly and molasses had negative environmental
consequences. With the subsequent installation and successful de-bottlenecking of the
Waste Gas Cleaning Plant, and limitations to burnt lime supply, revisiting the use of
sugars as sintering accelerants to supplement burnt lime and decrease granulation water
load is opportune. These materials also afford the advantage of being renewable
substitutes for some of the solid fuel.
In the longer term, more extensive use of renewable biomass derived products, as
outlined by Dell’ Amico et al. (2004), Lovel et al. (2005) and Mathieson et al. (2011),
warrant vigorous exploration.
CONCLUSIONS
Maximising the amount of highly reducible sinter in the blast furnace feed is a key part
of decreasing operating cost and CO2 emissions at an integrated steel plant. Measures
taken to maintain and enhance sinter plant productivity fundamentally assist these
objectives.
The Port Kembla sinter plant was upgraded in 2009 from 420 to 480 m2 to enable
production of sinter at a rate in excess of 40.5 t/m2/d. The major cause of initial
productivity shortfalls post upgrade was the requirement to use more goethitic ore than
originally planned owing to iron ore supply constraints. The negative effects of this were
identified, and successfully offset through means directed at fundamentally improving
sintering permeability and flame front speed; measures which also decreased sinter plant
CO2 intensity.
A previously undocumented relationship was found between the extent of Goethite used
in making sinter and blast furnace fuel rate. This relationship was found to be stronger
than the relationship between sinter reducibility as measured in standard tests and Blast
Furnace fuel rate further highlighting the value in offsetting negative sintering
productivity due to Goethite.
14N. Di Giorgio, D. Brace, A. Bennett, K. Wijekulasuriya
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BRIEF BIOGRAPHY OF PRESENTER
Nicholas Di Giorgio BE Eng Materials (Hons) MSc (UNSW) is a Senior Development
Engineer in Ironmaking Technology at BlueScope Steel’s Port Kembla Steelworks. He
has extensive experience in Process Operation, Process Analysis and Improvement in
the Blast Furnace and Sinter plant realms having driven numerous improvements &
undertaken extensive plant based Research in the areas of blast furnace operation, iron
and slag product quality, blast furnace and sinter plant productivity, fuel consumption,
Blast Furnace PCI capability, the impact and nature of carbonaceous and ferrous raw
materials and Ironmaking Greenhouse impact.
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