ISIJ International, Vol. 51 (2011), No. 6, pp. 913–921
Development of Secondary-fuel Injection Technology for Energy
Reduction in the Iron Ore Sintering Process
Nobuyuki OYAMA,1) Yuji IWAMI,1) Tetsuya YAMAMOTO,1) Satoshi MACHIDA,1) Takahide HIGUCHI,1)
Hideaki SATO,1) Michitaka SATO,1) Kanji TAKEDA,1) Yoshinori WATANABE,2) Masakata SHIMIZU3)
and Koki NISHIOKA3)
1) Steel Research Laboratory, JFE Steel Corp., 1 Kokan-cho, Fukuyama, 721-8510 Japan.
2) East Japan Works (Keihin), JFE Steel Corp., 1-1 Ogishima, Kawasaki-ku Kawasaki, 210-0868 Japan.
3) Department of Material Science and Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, 819-0395 Japan.
(Received on November 26, 2010; accepted on March 22, 2011)
JFE Steel Corporation developed the hydrogen-based gas fuel injection technology for sintering
machines to improve sinter quality without increasing coke breeze ratio. With the technology, it is possible
to extend the temperature zone between 1 200°C and 1 400°C by injecting the gaseous fuel from the top
surface of the sintering machine as a partial substitute for coke breeze. Theoretical and experimental
studies were carried out to verify the effect of the gaseous-fuel injection technology on pore structure in
the sinter cake with the X-ray CT scanner and sintering pot test.
It is important to hold the temperature between 1 200°C and 1 400°C in order to produce high strength
and high reducibility sinter. The liquid phase ratio can be increased with extending the proper temperature
zone by applying the gaseous fuel injection technology. The increase in liquid phase ratio promotes the
combination of pores (1–5 mm) and sinter strength is improved. At the same time, the pores over 5 mm
growth are promoted and the permeability is improved in the sintering bed. Moreover, the low-temperature sintering process depresses the iron ore self-densification. Micro pores under 1 μ m remain in
unmelted ores and improve sinter reducibility. As a result, the technology enables to improve the pore
structure in the sinter cake and sinter quality.
The technology was put into commercial operation at Keihin No. 1 sinter plant in January 2009 and
stable operation has continued up to the present. As a result, the energy efficiency in the sintering process is greatly improved, and it has been achieved to reduce CO2 emissions by a maximum of approximately 60 000 t/year at Keihin No. 1 sinter plant.
KEY WORDS: sinter; sintering; gaseous fuel; temperature distribution; pore structure; pressure drop.
1.
between 1 200°C and 1 400°C to produce high strength sinter. Generally when coke breeze ratio increases, the sinter
strength improves, because sinter mixtures are melted
enough. If coke breeze ratio increases excessively, the sinter
strength decreases by the generation of glassy silicate with
over melting.
In the past, various technologies have been proposed, in
order to improve the sinter yield without increasing BAR.
For example, it was reported that the main exhaust gas recirculation system in sintering machines decreases the cooling
rate with its sensible heat.4–8) In these previous reports, it
was pointed the sinter productivity decrease with the lower
O2 concentration and higher humidity in the main exhaust
gas.9–13) On the other hand, the preheated air injection
methods were suggested.14–17) It is difficult to control the
temperature zone over 1 200°C, because the preheating air
temperature was low between 150°C and 450°C. It also
deteriorated the permeability with the increase in actual
velocity. Therefore each technology is not widely applied to
sintering machines for these reasons.
It’s difficult to achieve the sinter strength and reducibility
Introduction
In recent years, the reduction of CO2 emissions has
become an urgent issue in the steel industry as countermeasure against global warming. Approximately 60% of the
steel industry emissions are generated in the sintering and
blast furnace processes.1) Therefore the reduction of coke
breeze rate used in sintering (hereinafter, bonding agent rate,
BAR) and the carbonaceous materials rate used in the blast
furnace (hereinafter, reducing agent rate, RAR) has been
strongly required.2)
It is widely known that the improvement of sinter strength
and reducibility is an effective method for reducing BAR
and RAR.3) In other words, if the sinter strength is
improved, the generation ratio of return fine decrease and
the BAR can be reduced. If the sinter reducibility is
improved, it becomes possible to reduce RAR in the blast
furnace. Accordingly, it is important to produce the high
strength and high reducibility sinter for reduction of CO2
emissions in ironmaking process.
The temperature in the sintering bed must be kept
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ISIJ International, Vol. 51 (2011), No. 6
simultaneously with conventional technologies.18) That is to
say, high strength and dense structure is inferior in reducibility, high reducibility and porous structure is inferior in
strength.
Then the hydrogen-based gaseous fuel (hereinafter, gaseous fuel) injection technology was developed and applied
successfully to sintering machine at Keihin No. 1 sinter
plant in JFE Steel Corporation. The technology enables to
produce high strength sinter without increasing coke breeze
ratio by changing the heating/cooling rate in the sintering
process.
The fundamental research was carried out at the laboratory scale to clarify the effect of gaseous fuel injection on
the temperature distribution, pressure drop and the pore
structure in the sinter cake. Operational tests were also performed at commercial plant to verify the principle of the
technology.
2.
holes, which were installed at intervals of 100 mm height.
Table 1 shows the blending ratio of the sinter mixture
used in the experiments. Table 2 shows the chemical compositions of iron ores. In the experiments, Ore A is a dense
iron ore from South America and Ore B is a porous iron ore
from Australia.
The limestone, silica sand, return fine, and coke breeze
were obtained by sampling at the commercial plant. The
blending ratio of the limestone and silica sand were adjusted
to obtain a SiO2 content of 4.8 mass% and basicity (CaO/
SiO2) of 1.9 in the sinter, and the return fine ratio was set at
20 mass%.
Table 3 shows the experimental conditions in the sintering pot test. LNG, propane gas and CO gas were used as gaseous fuels. When the LNG concentration was set at 7/10 or
more of the lean flammable limit (4.8 vol%),19) that is, at 3.4
vol% or more, it was found that the LNG burned before
injection into the sintering bed, thus it could not be used in
controlling the temperature distribution. In addition, when
the LNG concentration was set more than 1/10 of the lean
flammable limit concentration, it was found that the
improvement effects were saturated. Based on the preliminary experiments results, the gaseous fuel concentrations
were set at 0.4 vol% (LNG), 0.2 vol% (propane gas) and 1.2
vol% (CO gas) with the suction air volume for the improvement effect and safety. The experiment was performed at
coke breeze ratio of 5.0 mass% with the total all sinter mixture as a standard. When the LNG injected with coke breeze
ratio of 5.0 mass%, the over melting was caused and the
sinter strength was decreased. Therefore coke breeze ratio
was reduced 0.4 mass%, equivalent to the injected LNG in
combustion heat. Here, the combustion heat of coke breeze
is higher heating value of 27.1 MJ/kg measured according
to JIS M 881420) and LNG is lower heating value of 41.6
MJ/Nm3 measured according to JIS K 2301.21) The average
of suction air volume was 1.5 m3/min measured with the orifice flowmeter located above the sintering pot.
Sinter product was defined as sinter with a size of 5 mm
or larger when the sinter cake was dropped once from a 2
m height after sintering tests. Here, sinter yield was calculated by the net weight of the sinter product divided by the
total sinter cake. Sintering time was defined as the time from
ignition until the exhaust gas reached its maximum temperature. Sinter productivity was calculated from the sinter
product weight and sintering time.
In the laboratory experiment, shatter strength was measured according to JIS M 8711 (Test method for determination of shatter strength of iron ore sinter). The degree of
Experimental Method
2.1.
Measurement Method of Temperature Distribution in Sintering Bed
Figure 1 shows the measurement method for the temperature in the sintering bed. In order to observe the combustion conditions, the laboratory sintering test was performed
with the transparent quartz glass pot (300 mm φ × 400 mm
height). After charging all sinter mixture (approximately 42
kg/charge) into the pot and igniting it, liquefied natural gas
(hereinafter, LNG; CH4/C2H6/C3H8 = 89/5/6 vol%) and air
were begun to inject from the top surface at 60 s after ignition. LNG injection was continued for all sintering time. In
all cases, the sintering test was performed at the constant
suction pressure of 6.9 kPa and the hearth layer thickness of
20 mm height. The observation of the combustion/melting
zone was performed using a video camera and an infrared
thermography. In addition, R type sheathed thermocouples
(1.6 mm φ × 200 mm length) were used to correct the temperature distribution acquired by the thermography, and to
measure holding time over 1 200°C in the sintering bed. The
three thermocouples were inserted 150 mm into the pot side
Table 2.
Chemical composition of iron ores.
(mass%)
Fig. 1.
Table 1.
Measurement method for the temperature and pressure
dropin the sintering bed.
Blending ratio of sinter mixture used in the experiments.
(mass%)
© 2011 ISIJ
Blending ore
66.1
Silica sand
1.4
Limestone
12.5
Return fine
20.0
Material
T.Fe
FeO
SiO2
Al2O3
CaO
MgO
L.O.I.
Ore A
66.14
0.07
1.26
1.31
0.03
0.06
1.41
Ore B
58.15
0.36
5.39
1.43
0.33
0.13
10.40
Table 3.
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Experimental conditions in the sintering pot test.
All coke method
LNG injection method
Coke (mass%)
5.0
4.6
LNG (vol%)
0.0
0.4
ISIJ International, Vol. 51 (2011), No. 6
was set at 0.4 vol% (relative to the suction air volume) and
the LNG was begun to inject from a nozzle located above
the sintering bed at 180 s after ignition. The other sintering
conditions, photographic conditions by the X-ray CT
scanner and the image analysis method were the same as the
previous report.29) The branch width, branch number, etc.
were quantified with the X-ray CT images. The pore over 1
mm area ratio was calculated from these values.
In addition, the pore size distribution was measured with
a mercury porosimeter. The samples were screened in
4.0–6.7 mm to fit on cell size, and measured 3 times with
each condition.
reduction (hereinafter, JIS-RI) was measured according to
JIS M 8713 and reduction disintegration index (hereinafter,
JIS-RDI) was measured according to JIS M 8720.
2.2.
Measurement Method of Pressure Drop in Sintering Bed
As shown in Fig. 1, the pressure drop in the sintering bed
was measured with the steel pot (300 mm φ × 400 mm
height), based on the method proposed by Shibata et al.22)
In addition, the temperature was measured to classify into
each sintering reaction stage. The pressure probes (stainless
steel tubes, outer diameter of 6 mm × inner diameter of 4
mm) were inserted 150 mm into the pot side holes, which
were installed at intervals of 100 mm height, and the pressure drop was measured at a constant gas volume of 1.0
Nm3/min measured by the orifice flowmeter. Based on the
observation with the quartz glass pot, the red-hot region
thickness was approximately 30 mm. Therefore the pressure
probes were also inserted at 200 mm height and 230 mm
height position from top surface to measure the pressure
drop in the melting zone.
2.4.
Experimental Method at Commercial Sintering
Machine
In order to quantify the effects of the technology on the
commercial sintering operation, the operational tests were
conducted at Keihin No. 1 sinter plant, based on the laboratory experimental results.
Table 4 shows the experimental conditions in the operational tests. The LNG injection rate was set at 250 Nm3/h
(0.5 Nm3/t-s, increase in heat quantity: 20 MJ/t-s), the coke
breeze ratio was decreased from 5.3 mass% to 5.0 mass%
(decrease in heat quality: 80 MJ/t-s). Therefore the reduced
heat amount was equivalent to approximately 4 times as
large as the injected LNG heat amount. The LNG injection
part was set at the initial 1/3 length of the sintering machine,
where the flame front existed in the upper layer. The sinter
strength of the upper layer tends to be weaker than that of
the lower layer.
The blending conditions for sinter mixture were held constant. The granulation moisture was set at 7.6 mass% and the
bed height was set at 650 mm. The pallet speed was adjusted
so that the BTP (burn through point; end point of sintering)
was constant in the operational test. The tests were performed for approximately 4 days, and conducted a total of 5
times at each experimental condition. In these tests, tumble
strength was measured according to JIS M 8712.
Moreover, R type sheathed thermocouples (3.2 mm φ ×
1 000 mm length) were inserted 500 mm into the sintering
bed through the holes installed in the sidewall. The effect of
gaseous fuel injection method on the temperature distribution was quantified in the sintering machine.
One sintering pallet was sampled. Approximately 300 kg
of sinter product was taken from 6 locations in the center/
side parts and upper/lower layer. The tumble strength and
reducibility were measured for the each sample.
2.3.
Observation Method of Pore Structure with X-ray
CT Scanner
The pore structure have major effects on the sinter quality
and permeability in the sintering bed,23–25) because the pores
in the sinter cake are simultaneously structural defects and
also function as air passages. In more detail, the pores over
5 mm improved the permeability in the sintering bed25) and
the pores (1–5 mm) deteriorated sinter strength.26) Although,
there were various theories27,28) for the diameter of micro
pores to improve JIS-RI, the diameter was defined under 1
μ m in these research. Therefore the sintering tests were performed with a X-ray CT scanner29) to observe the changes
of the pore structure in the sinter cake directly, which had
been remodeled to enable the LNG injection. Figure 2
shows the schematic diagram of the X-ray CT scanner for
sintering tests.
The X-ray tube voltage was 130 kV, the tube current was
200 mA, and it took 2.8 s to photograph one cross-sectional
image. The CT images were expressed using CT values in
which water was defined as 0 and air as –1 000. The threshold
CT value for pores and solid parts was defined as 200. The
resolution of the CT images was 1 mm.
First, the sinter mixtures were charged into a carbon test
pot (100 mm φ × 100 mm height), and the suction gas volume was set at 0.2 Nm3/min measured by the pitot tube
flowmeter located under the pot. The LNG concentration
Table 4.
Experimental conditions of the operational test.
All coke method
LNG injection method
Bonding agent ratio
in raw mixture (mass%)
5.3
5.0
LNG (Nm3/h)
0
250
3.
Experimental Results
3.1.
Fig. 2.
Changes of Temperature Distribution in Sintering
Bed and Sintering Characteristics by Gaseous Fuel
Injection Method
Figure 3 shows the comparison of the sinter productivity
Schematic diagram of hot stage X-ray CT scanner for sintering test.
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ISIJ International, Vol. 51 (2011), No. 6
Coke 5.0 mass%
(All coke method)
Coke4.6 mass% and
LNG0.4 vol%
(LNG injection method)
Sintering time (min.)
16.0
16.7
Sinter yield (%)
69.0
72.8 (+3.8)
1.56
1.64 (+0.8)
Macroscopic
image of
red-hot region
with quartz glass pot
2
Productivity (t/h·m )
Fig. 3.
Fig. 4.
Shatter index (%)
70.7
72.9 (+2.2)
JIS-RDI (mass%)
36.1
28.3 (–7.8)
JIS-RI (%)
64.5
70.4 (+5.9)
Comparison of the sinter productivity and quality between the call coke method and the LNG injection method.
Change in pressure drop during sintering at the each position.
and quality between the all coke method and the LNG injection method. From Fig. 3, the image showed the red-hot
region, in which it was considered that the combustion/
melting zone existed, in the middle layer. It confirmed that
the red-hot region was greatly expanded by the LNG injection method. The red-hot region was also expanded in the
all layer of the sintering bed.
On the other hand, the sinter strength improved and the
generation ratio of return fine decreased remarkably, while
the sintering time was almost the same. Although JIS-RI and
JIS-RDI normally tended to be inversely related to sinter
strength, the both properties improved with the LNG injection method.
In the propane gas case and CO gas case, the improvement effect was almost the same as LNG case.
Changes of Pressure Drop in the Sintering Bed by
Gaseous Fuel Injection Method
Figure 4 shows the changes in pressure drop during sintering. With the all coke method and the LNG injection
method, the pressure drop reached its maximum value in
480–540 s after ignition. At 500 s after ignition, the pressure
drop reached its maximum value and its difference was
Fig. 5.
Change of pressure drop in each zone during sintering by
LNG injection at 500 s after ignition.
Fig. 6.
Change in the operational result and quality with the LNG
injection method in comparison with all coke method.
3.2.
© 2011 ISIJ
remarkable between the all coke method and LNG injection
method. Therefore the pressure drops of both conditions
were compared to investigate the effect of the gaseous fuel
injection method at 500 s.
The sintering bed was classified into 4 zones (sinter cake
zone, melting zone, combustion zone, wet zone) and the
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ISIJ International, Vol. 51 (2011), No. 6
Coke 4.6 mass%
and LNG 0.4 vol%
(LNG injection method)
Coke 5.0 mass%
(All coke method)
Video
Thermography
Video
Thermography
Combustion
conditions
during sintering
Fig. 7.
Effect of the gaseous fuel injection method on temperature distribution measured by the thermography at 250 s
after ignition.
thickness of each zone was determined with the temperature
distribution based on the method proposed by Shibata et
al.22)
Figure 5 shows the changes of pressure drop in each zone
by gaseous fuel injection method at 500 s after ignition. In
this figure, no remarkable difference was observed in the
wet zone with the both methods. The LNG injection method
decreased the pressure drop in the combustion/melting zone
by 32% in comparison with the all coke method. As a result,
the LNG injection method decreased the pressure drop in
the whole sintering bed by 15% in comparison with the all
coke method.
Fig. 8.
Change of Commercial Operation by Gaseous Fuel
Injection Method at Keihin No. 1 Sinter Plant
Figure 6 shows the changes in the operational result and
quality between LNG injection method and all coke method.
In this figure, the tumble strength increased by approximately 1% with the same sinter production in the LNG injection
method. And the bonding agent ratio was reduced with the
increase in the sinter strength. Bonding agent ratio was
reduced by 0.3 mass% with the total blending iron ores and
CO2 emissions were reduced by a maximum of approximately 60 000 t/year at Keihin No. 1 sinter plant. JIS-RI also
gradually increased, and finally, 4% improvement effect was
confirmed. The same effects were confirmed in the other 4
operational tests.
The temperature distribution measured by the thermography in the sintering bed at 600 s after ignition.
3.3.
4.
CH430) composing approximately 90% of LNG.
Figure 8 shows the temperature distribution measured by
the thermography in the sintering bed at 600 s after ignition.
From these results, the temperature zone over 1 200°C was
narrow, and the maximum temperature was over 1 400°C in
the all coke method. In contrast, the maximum temperature
decreased, but the temperature zone over 1 200°C was
greatly expanded with the gaseous fuel injection method.
Moreover the holding time over 1 200°C measured by the
thermocouples was extended from 144 s to 376 s at 200 mm
height from the top surface. From this figure, it was considered that the gaseous fuel burned above the coke breeze
combustion position with the temperature 650–750°C.
Therefore the temperature zone over 1 200°C was expanded
in upper direction with the low cooling rate by the combustion positions difference.
Authors have developed a mathematical model for the
temperature distribution in the sintering bed to clarify the
principles of the gaseous fuel injection method. At first, the
basic state was prescribed with differential equations based
on the conservation laws of mass, enthalpy and momentum.
In the mathematical model, combustion of coke breeze,31–33)
resolution of CaCO3,34) evaporation-condensation of water35)
were considered as the main reactions during sintering.
Moreover, the combustion rate of CH4 gas was installed into
the mathematical model to calculate the temperature distribution with the gaseous fuel injection method.
Figure 9 shows the effect of the gaseous fuel injection
Discussion
4.1.
Mechanism for the Expansion of Temperature
Zone between 1 200°C and 1 400°C in the Sintering
Bed with Gaseous Fuel Injection Method
Figure 7 shows the effect of the gaseous fuel injection
method on temperature distribution measured by the
infrared thermography at 250 s after ignition. In this figure,
the temperature zone over 1 200°C was expanded in upper
direction with the gaseous fuel injection. The combustion
positions of the LNG and coke breeze were different in the
direction of bed height, because the gaseous fuel was
injected from top surface and burned before reaching at the
coke breeze combustion position with the temperature 650–
750°C. Here the temperature was the ignition temperature of
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ISIJ International, Vol. 51 (2011), No. 6
combustion/melting zone.25) At the same time, the combination of the pores (1–5 mm) improved the sinter strength.26)
Figure 12 shows the changes in the branch width for each
condition. From this figure, the branch width began to
increase simultaneously with the sintering reaction and stop
increasing before the completion of the sintering reaction.
The growth rate of branch width was accelerated with the
LNG injection method, and the final branch width was also
30% larger. Although the increase in coke breeze content
also promoted the branch width growth and the branch width
increased by 16%, which is smaller than that with LNG
injection method. Though the maximum temperature
increased, the holding time over 1 200°C extended little with
the increase in coke breeze ratio. As a result, the increase in
coke breeze ratio increased the liquid phase ratio little and it
had small effect on the growth rate of pore over 1 mm.
method on the temperature distribution with the mathematical model at 600 s after ignition. These results were in good
agreement with the experimental results of these studies.
According to these calculation results, the temperature zone
over 1 400°C existed with the all coke method but in contrast the maximum temperature was held under 1 400°C and
the temperature zone over 1 200°C expanded with the gaseous fuel injection method. Moreover it was confirmed that
the gaseous fuel burned above the coke breeze combustion
position with the temperature 650–750°C in Fig. 9.
4.2.
Mechanism for the Improvement of Sinter Strength and Decrease in Pressure Drop with Gaseous
Fuel Injection Method
As shown in Fig. 3, the LNG injection method improved
the sinter strength. From Fig. 5, the pressure drop in the
combustion/melting zone was decrease remarkably. The
sintering test with the X-ray CT scanner was performed to
clarify the mechanism for the improvement in sinter
strength and the decrease in pressure drop.
Figure 10 shows the comparison of X-ray CT image in
sinter cake between the all coke method and the gaseous
fuel injection method. In this figure, the solid parts are
shown in white and the pore over 1 mm in black. Figure 11
shows the comparison of pore over 1 mm area ratio calculated from the X-ray CT images. From these results, the
pore over 5 mm increased and the pore (1–5 mm) decreased
by the gaseous fuel injection method in comparison with the
all coke method. The extension of the holding time over
1 200°C increased liquid phase ratio.36) As a result, the
increase in liquid phase ratio promoted the combination of
pores (1–5 mm) and increased penetrated pores over 5 mm
as air passages. Therefore the pressure drop decreases in the
4.3.
Mechanism for the Improvement of Reducibility
with Gaseous Fuel Injection Method
To investigate sinter reducibility, an analysis was performed with the reduction rate equation37,38) based on oneinterface un-reacted core model in consideration of the
Fig. 11.
Fig. 9.
Comparison of pore (1–5 mm, over 5 mm) area rate calculated from the X-ray CT images.
Effect of the gaseous fuel injection method on the temperature distribution with the mathematical model at 600 s after
ignition.
Coke 5.0 mass%
Coke 4.6 mass% and
LNG 0.4 vol%
CT images
of sinter cake
Fig. 10.
Comparison of X-ray CT image of sinter cake between
all coke method and LNG injection method.
© 2011 ISIJ
Fig. 12.
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Change in branch width for each condition with time.
ISIJ International, Vol. 51 (2011), No. 6
following three stages: chemical reaction resistance at the
un-reacted core, diffusion resistance through the reduced
shell and mass transfer resistance through the gas film
around the sinter particle.
The reduction test was performed with the sinter products
obtained in the pot test. The shape of sinter products was
non-spherical and the diameter was 19–21 mm. The reduction temperature was set at 900°C and reduction gas composition was set in CO (30%)– N2.
r (3f 2 − 2f 3 ) (3f − 3f 2 + f 3 )
(Cb − Ce)t
f
+ 0
=
+
r0 ⋅ a 0
kc ⋅ (1+1/K)
6 ⋅ De
3 ⋅ kf
.......................................... (1)
f =1–
Fig. 13.
Comparison of chemical reaction rate constant and effective diffusivitybetween the all coke method and the LNG
injection method.
Fig. 14.
Change in pore size distribution measured by a mercury
porosimeter.
(1–R)1/3 .............................. (2)
Cb: CO gas concentration (mol/m3),
Ce: CO equilibrium concentration (mol/m3),
t : time (s)
r0 : Spherical equivalent diameter (m),
a0 : O2 concentration in sinter (mol/m3),
kc : Chemical reaction rate constant (m/s)
K : Fe–FeO equilibrium constant (–),39)
De: Effective diffusivity (m2/s),
kf : Gas film coefficient of mass transfer (m/s)
R : Reduction rate (–),
f : Relative thickness of reduced layer (–)
In this analysis, kf was calculated from Ranz-Marshall
equation,40) and the equilibrium value for wustite to iron was
used as the equilibrium constant. The chemical reaction rate
constant in the reduction reaction and the coefficient of
effective diffusivity in a particle were obtained from the
mixed-control plot proposed by Murayama et al.37,38). We
analyzed the reduction rate range above 33% for the CO
reduction of wustite to iron.41)
Figure 13 shows the comparison of chemical reaction
rate constant and effective diffusivity between the all coke
method and the LNG injection method. In this figure, the
JIS-RI contour line substituted the prescribed reduction rate
and reduction time (180 min) for Eqs. (1) and (2). From this
figure, although the chemical reaction rate constant changed
slightly in the LNG injection method in comparison with the
all coke method, effective diffusivity increased remarkably.
The kc value and the De value obtained in the study differed
slightly from the value reported by Murayama et al.,37,38)
because the sinter samples had lots of variability on the
shape, porosity and other factors.
Figure 14 shows the change in the pore size distribution
measured by the mercury porosimeter with LNG injection
method. From this figure, with the LNG injection method,
the sinter contained a large number of micro pores under 1
μ m in comparison with the all coke method. As shown in
Fig. 6, the BAR was decreased with the LNG injection
method and the maximum temperature decreased. As a
result, the iron ore self-densification42) was depressed and a
large number of micro pores under 1 μ m remained in
unmelted ores with the gaseous fuel injection method as
shown in Fig. 14. JIS-RI was improved with a larger number
of micro pores under 1 μ m remained in unmelted ores by
the LNG injection method.27,28)
4.4.
Effect of Gaseous Fuel Injection Method on Operational Result at Commercial Plant
At first, the effect of the gaseous fuel injection on the
temperature distribution was evaluated at Keihin No. 1
sinter plant. Figure 15(a) shows the temperature distribution
in the upper layer, while Fig. 15(b) shows that in the lower
layer. As shown in Fig. 15(a), although the upper layer generally tends to get low heat, the holding time over 1 200°C
was extended from 134 s to 258 s without the maximum
temperature rising by 1/3 zone the LNG injection method.
Although the lower layer tends to overheat, Fig. 15(b)
shows that the maximum temperature decreased from
1 437°C to 1 370°C with the 1/3 zone LNG injection method. The decrease in the maximum temperature was caused
by the decrease in bonding agent ratio in 0.3 mass% with the
total blending iron ores. Therefore the sinter strength at the
upper weak layer was improved by the LNG injection and
JIS-RI at the lower layer was improved by the decrease in
bonding agent ratio as described section 4.2 and 4.3.
A sintering pallet was sampled and the tumble strength
and reducibility were measured for the each sample to verify
the improvement effects. Figure 16 shows the effects of
LNG injection method on sinter strength and reducibility at
each sampling position. The 1/3 zone LNG injection method
improved the sinter strength in the upper layer and JIS-RI
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© 2011 ISIJ
ISIJ International, Vol. 51 (2011), No. 6
Fig. 15.
Effects of LNG injection method on temperature distribution at Keihin No. 1 sinter plant.
Table 5.
Heat input
Operational result
Comparison of heat balance and quality of sintered ores at Keihin No.1 sinter plant.
All coke method
LNG injection method
Combustion heat of coke-oven gas
(MJ/t-s)
39
39
Combustion heat of coke breeze
(MJ/t-s)
1 505
1 420
Combustion heat of LNG
(MJ/t-s)
0
22
Total
(MJ/t-s)
1 544
1 481
Tumble index
(mass%)
68
69
JIS-RI
(mass%)
63
67
(t-s/h)
500
500
Production
comparison with the all coke method. Here, the combustion
heat of coke oven gas is 17.6 MJ/Nm3, coke breeze is 27.1
MJ/kg and LNG is 41.6 MJ/Nm3. However the unit heat
consumption decreased with the LNG injection method, it
was possible to improve by 1% in tumble strength and 4%
in JIS-RI in comparison with the all coke method at the
same sinter production.
The several times of operational tests were carried out at
the commercial sintering machine and confirmed the principle of the technology.
5.
Fig. 16.
A fundamental study was carried out in the laboratory
experiment to confirm the effect of the gaseous fuel injection technology on the temperature distribution, pressure
drop and the pore structure in the sinter cake. The effects of
the technology were also quantified by performing operational tests at the commercial plant.
The following conclusions were obtained as a result of
the research.
(1) The temperature zone over 1 200°C was expanded
in upper direction without increasing the maximum temperature in the sintering bed with the gaseous fuel injection
method, because the gaseous fuel was injected from top surface and burned before reach at the coke breeze combustion
position with the temperature 650–750°C.
(2) The gaseous fuel injection technology promoted the
pore (1–5 mm) combination and the pore over 5 mm growth
by increasing the liquid phase ratio. As a result, the decrease
in the number of pores (1–5 mm) improved sinter strength
and the increase in the number of penetrated pores over 5
mm improved permeability in the sintering bed.
Effects of LNG injection method on sinter strength and
reducibility at each sampling position.
in the lower layer.
The temperature distribution with the LNG injection
method was considered to be the ‘low-temperature sintering
process’36) in which the maximum temperature was not
greatly increased and the holding time over 1 200°C was
extended.
Table 5 shows the comparison of heat balance and sinter
quality at Keihin No. 1 sinter plant between the LNG injection method and the all coke method. In the calculation for
the heat balance, the heat inputs consisted of the combustion
heat of the coke oven gas in the ignition furnace, the combustion heat of the coke breeze and the injected LNG. From
this Table, the unit heat consumption decreased by approximately 60 MJ/t-sinter with the LNG injection method in
© 2011 ISIJ
Conclusion
920
ISIJ International, Vol. 51 (2011), No. 6
(3) The bonding agent ratio was decreased with the gaseous fuel injection method, and the maximum temperature
decreased in the sintering bed. As a result, the iron ore selfdensification was depressed and the large number of micro
pores under 1 μ m remained in unmelted ores with the gaseous fuel injection method. This also improved reducibility.
(4) The gaseous fuel injection technology enabled to
produce the high strength and high reducibility sinter while
maintaining the same level of sinter production at commercial plant. Moreover it has achieved to decrease bonding
agent ratio by 0.3 mass% with the total blending iron ores
and reduce CO2 emissions by a maximum of approximately
60 000 t/year at Keihin No. 1 sinter plant.
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