Development of injection of reduction gas into the blast ... - klimazwei

Development of injection of reduction gas
into the blast furnace shaft
Joachim Buchwalder 1 , Jörg Mernitz 1 , Günter Harp 2 , Michael, Hensmann 2 ,
Christian Reuther 3 and Manfred Schingnitz 3
1 Arcelor Eisenhüttenstadt GmbH, Werkstrasse 1, 15890 Eisenhüttenstadt Germany
2 Betriebsforschungsinstitut VDEh-Institut für angewandte Forschung GmbH
Sohnstrasse 65, 40237 Düsseldorf, Germany
3 Siemens Fuel Gasification Technology GmbH, Halsbrücker Str. 34, 09599 Freiberg, Germany
Abstract
The injection of hot reducing gas into the shaft was investigated at Arcelor
Eisenhüttenstadt. The blast furnace No. 1 (BF 1) was modified for the
investigations with additional tuyeres at the BF shaft and the installation of hot gas
generators (HGG). The hot reducing gas was generated by partial oxidation of
natural gas with oxygen within 4 HGG and injected into a fourth of the total BF
cross-section. First CFD calculations for prediction of expected penetration depth
were carried out. The penetration depth during experimental reduction gas injection
was determined by He tracing tests. The reduction degree of the burden material
was determined by core drilling exercises and analysis of the core material.
The investigation shows, that the gas injection into the shaft seems to be a key
technology to raise the use of additional reductants for the blast furnace process
and to become more flexible in reductant application.
Key words: Blast furnace, CO2-emission, injection, partial oxidation, reducing
agent, reducing gas.
1. Introduction
The coke consumption of the BF-process has been minimized by optimization of
burden technique and application of additional reductant injection through the
tuyeres. The minimum consumption of reducing agents with the best-availabletechnology
(BAT) was calculated with a complex BF calculation model by Schmöle
and Lüngen [1] to 300 kg/tHM coke and 174 kg/tHm pulverized coal. The reductant
consumption as well as the specific productivity has reached nearly the technical
process limits. New concepts for lowering the reductant consumption and the CO2emission
are announced under the term “nitrogen free BF-Process” and “plasma
heated BF-Process” [2-4]. Those concepts need greater process modifications.
At Arcelor Eisenhüttenstadt process modification with injection of hot reducing gas
into the shaft is investigated. The aim is to increase the degree of indirect reduction
of the burden by injection of reducing gas into the shaft within the thermal reserve
zone and lowering the specific reducing gas amount generated at normal tuyere
level. The BF 1 was modified for the investigations with additional tuyeres at the BF
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upper belly area and the installation of so called hot gas generators (HGG) for the
production and injection of hot reducing gas.
2. BF-Process with injection of hot reducing gas
Several theoretical and operational stages were carried out for the modification of
the BF-process. The procedure of investigation is listed as follows.
� definition of the required consumption of the reducing gas (equilibrium
calculations)
� CFD calculation for determination of expectable penetration depth of the
reducing gas into the BF-shaft
� energy and mass balance calculations for BF operation with injection of hot
reducing gas
� technical development of HGG
� implementation and commissioning of HGG at BF 1
� operational trials at BF 1 with injection of hot reducing gas
� optimisation of the injection of hot reducing gas into the BF shaft
The injection of hot reducing gas was carried out at BF 1 (Arcelor
Eisenhüttenstadt) (figure 1) with a av. production of about 1,600 tHM/d.
Figure 1: BF 1 at Arcelor Eisenhüttenstadt
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The operating data of BF 1 at Arcelor Eisenhüttenstadt are shown in table 1. In
addition to the usual reductant coke with a consumption of 377 kg/tHM oil and
plastics are injected with a total amount of 85 kg/tHM. The BF is operated with a
nominal blast flow rate of 71,000 m 3 /tHM, a blast pressure of 1.9 bar (abs.), and an
oxygen content of approx. 24 % in the blast.
hot metal:
av. production [tHM/d] 1,576
hot metal temperature [°C] 1,423
reducing agents:
dry coke rate [kg/tHm] 377
oil [kg/tHM] 16
plastics [kg/tHM] 67
blast:
blast flow rate [m 3 /h] 71,000
blast pressure [bar] 1.9
blast humidity [g/m 3 ] 13.3
blast temperature [°C] 1,086
oxygen content of blast [%] 23.6
slag:
spec. slag amount [kg/tHM] 215
slag basicity (CaO/SiO2) 1.13
Table 1: operating data of BF 1 at Arcelor Eisenhüttenstadt
To minimize the investment costs for reducing gas generation for the operational
scale trials the reducing gas was generated by partial oxidation of natural gas with
oxygen within so called hot gas generators (HGG).
Figure 2 shows a schematic diagram of the HGG developed by Siemens Fuel
Gasification Technology. The HGG is designed for a maximum production of
reducing gas of about 2,400 m³/h.
Figure 2: Schematic diagram of the HGG
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Oxygen is fed concentrically to the natural gas. At the tip of the HGG the ignition
equipment is installed. The flame monitoring is done by a wave length sensitive
detector at the rear side of the HGG. The central tube of the flame detector is
cleaned with nitrogen as purge gas. The head of the HGG is hemispherical
designed for the direct connection to the blast tuyere installed at the shaft shell. It
is cooled with the available process water. The total length of the HGG is below 1.0
m. The distance from the tip of the HGG to the inner side of the BF-shaft is approx.
0.3 m.
Figure 3 shows one HGG installed 5.35 m above the tuyere level.
Figure 3: HGG installed at the shaft of BF 1
Every HGG is supplied with gas and oxygen independently. The HGG operation is
remote controlled by the control room personal.
For the operational trials 4 HGG were installed within a fourth of the total BF crosssection.
They are placed in the middle between the underlying tuyeres. The axial
and transversal section of the modified BF 1 is shown in figure 4 and figure 5.
One temperature and gas probe with a length of 0.5 m is located 1.2 m above
HGG 10. An above burden probe equipped with 6 channels for temperature
measurement and gas sampling is installed at the top of the shaft in the middle of
HGG 10 and 11. An additional above burden probe with also 6 channels for
temperature measurement is installed at the opposite site.
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Figure 4: axial section of the modified BF 1.
Figure 5: transversal section of the modified BF 1.
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3. Results of theoretical approach
For a first determination of penetration depth CFD calculations were carried out by
using the commercial FLUENT software. The calculated percentage of reducing
gas in the shaft for an injection velocity of about 170 m/s is shown in figure 6 as an
example. In a distance of 790 mm from the shaft wall the percentage of reducing
gas decreases to 50 %.
Figure 6: calculated percentage of reducing gas in the shaft
Table 2 shows the results of thermochemical equilibrium calculations for the
product gas formed by partial oxidation of natural gas with oxygen. The resulting
ratio between H2 and CO amounts approx. 2. The reducing gas contains about 5.6
% of total oxidised components CO2 and H2O.
set points:
reducing gas flow [Nm 3 /h) 2,400
reducing gas temperature [°C] 900
input:
natural gas flow [Nm 3 /h] 800
oyxgen flow [Nm 3 /h] 470
reducing gas composition:
H2 [Vol.-%] 61.7
CO [Vol.-%] 31.8
CO2 [Vol.-%] 1.5
CH4 [Vol.-%] 0.5
N2 [Vol.-%] 0.4
H2O [Vol.-%] 4.1
Table 2: results of thermochemical equilibrium calculations for the product gas
4. Operational results and obtained experience
After commissioning the 4 HGG at BF 1 a trial period of approx. 6,500 h was
started. The penetration depth of the injected hot reducing gas into the shaft was
measured by He-tracing experiments by using the natural He-content of the
injected natural gas (250 to 300 ppm). During reducing gas injection gas sampling
is done via 6 channel above burden probe at the top of the shaft (27.3 m above BF
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floor). The sampled gas was cleaned and subsequent detected with a process
mass spectrometer on the components CO, CO2, H2, CH4, N2 and He. The period
for scanning all 6 sampling points was fixed to 6 min. Selected results of the radial
gas analyses are shown in the figures 7 and 8.
Figure 7: selected results of the radial gas analyses for normal BF operation
Figure 8: selected results of the radial gas analyses for BF operation
with reducing gas injection (700 m 3 /h natural gas, 385 m 3 /h oxygen)
As expected the radial He concentration for normal BF operation is nearly
constant. Under conditions with reducing gas injection into the shaft the measured
maximum He concentration is 20 ppm at 0.25 m off the shaft wall. The value
decreases with raised distance to the shaft wall. The influence of reducing gas
injection is perceptible up to a distance of 2 m from the shaft wall. The raised CH4
concentration near the shaft wall is an indication for incomplete CH4 conversion.
The CH4 conversion ranges between 80 and 90 %. The gas utilization (ETA CO)
decreases in the direction to the middle of the BF shaft as a result of high
percentage of coke in the centre of the shaft showing no difference to normal
operation.
The progress of burden material reduction is determined by core drilling exercises
(figure 9) and analysis of the core material. Parts of the samples contain massive
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metallic iron. Its presence above the cohesive zone is a definite indication for high
reduction work in accordance with the injected hot reducing gas.
Figure 9: HGG tuyere opened for core drilling
5. Conclusion
The injection of hot gas into the BF shaft was successfully executed in operational
trials at BF 1 at Arcelor Eisenhüttenstadt. The penetration depth of the hot reducing
gas into the BF shaft has been evaluated theoretical by CFD calculation and
experimental by He-tracing investigations. The progress of burden material
reduction was determined by core drilling exercises and analysis of the core m
aterial.
The investigations show, that the shaft gas injection seems to be a key technology
to raise the use of additional reductants for the blast furnace process and to
become more flexible in reductant application.
6. Acknowledgement
This work has been financially supported by the BMBF (Bundesministerium für
Bildung und Forschung) under FKZ 01 LK 0401, 01 LK 0402, 01 LK 0403. The
authors wish to thank the BMBF for the financial assistance.
The authors are responsible for the contents of this paper.
7. References
[1] Schmöle, P. and Lüngen, H. B.: Roheisenerzeugung im Hochofen unter
ökologischer Betrachtungsweise. Stahl und Eisen 124 (2004) Nr.5, s.27-34
[2] Steiler, J. M. and Hanrot, F.: Present state and innovative issues for
ironmaking. Science and technology of innovative ironmaking for aiming at
energy half consumption. Tokio, 27./28.11.2003
[3] Birat, J. P., Hanrot, F. and Danloy, G.: CO2 mitigation technologies in the
steel industry: a benchmark study based on process calculations. Scanmet
II, Lulea, 6.6/9.6. 2004
[4] Danloy, G., Korthas, B. Hanrot. F. and van der Stel, J.: Challenges of new
blast furnace process development aiming at reducing CO2 emission.
Symp. scrap substitutes and alternative ironmaking, Baltimore
31.10./4.11.2004
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