Effect of blast furnace burden water content on the blast ... · and blast furnace burden consist...
Transcript of Effect of blast furnace burden water content on the blast ... · and blast furnace burden consist...
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Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012
Effect of blast furnace burden
water content on the blast
furnace gas
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MEBF-Material Efficient Blast
Furnace (FIMECC -project)
• Commissioned study for Ruukki
Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012
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Content
• Introduction
• The water-gas shift reaction (WGSR)
• Experimental determination of critical temperature
for the WGSR in the blast furnace (BF) conditions
• Temperature profile of the BF shaft
• Experimental studies for water component
evaporation from BF burden
• Estimation for the effect of the burden water
content on the BF gas
Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012
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Introduction
• Up flowing gas in the BF shaft consist ~20 % CO
and blast furnace burden consist evaporating
water (H2O), which provides premises for the
water-gas shift reaction
(CO(g)+H2O(g)↔H2(g)+CO2(g)) to occur at
elevated temperatures in the BF shaft
• The composition of BF gas can change through
the WGSR and affect the heat value of the BF gas
• In this study the possible effect of burden water
content on the BF gas was investigated
Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012
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• The WGSR is an exothermic reversible
chemical reaction in which CO(g) and
H2O(g) converts to CO2(g) and H2(g)
(forward WGSR, ΔH= -41.1 kJ/mol)
• The WGSR is widely used in the production
of hydrogen in fuel processing industry
• Several catalysts have been investigated
and proposed for the WGSR
Water-gas shift reaction (WGSR)
(CO(g)+H2O(g)↔H2(g)+CO2(g))
Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012
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Water-gas shift reaction (WGSR)
(CO(g)+H2O(g)↔H2(g)+CO2(g))
• The WGSR has its ∆G=0 at 823 °C where
the direction of the reaction changes
(Callaghan 2009)
Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012
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Water-gas shift reaction (WGSR)
(CO(g)+H2O(g)↔H2(g)+CO2(g))
• Reaction equlibrium constant Keq becomes
unfavorable at higher temperatures for the
reaction products (exothermic reaction)
(Callaghan 2009) Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012
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Water-gas shift reaction (WGSR)
(CO(g)+H2O(g)↔H2(g)+CO2(g))
• The WGSR is commonly conducted in
multiple adiabatic stages at two temperature
ranges in the fuel processing industry to
obtain higher conversions:
- At 150-300 °C with copper based catalyst
- At 350-600 °C with magnetite (Fe3O4)-
chromia catalyst
• In terms of BF conditions the magnetite-
chromia catalyst is relevant
Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012
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Layer furnace used in the experiments
Inlet gas
Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012
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Critical temperature of the WGSR
in the BF conditions
• Empty layer furnace
- The WGSR was observed at about 500 °C
Gas feed:
50 % N2
42 % CO
8 % H2O
Flow rate:
15 l/min
Furnace heating:
3 °C/min to 700 °C
Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012
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Critical temperature of the WGSR
in the BF conditions
• Hematite pellet layer
- The WGSR was observed at 400-450 °C simultaneously with hematite to magnetite reduction
Gas feed:
50 % N2
17 % CO
25 % CO2
8 % H2O
Flow rate:
15 l/min
Furnace heating:
3 °C/min to 500 °C, where kept for 2 h
Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012
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Critical temperature of the WGSR
in the BF conditions
• Magnetite pellet layer (pre-reduced hematite)
- The WGSR was observed at 350-400 °C
- Magnetite clearly catalyzes the reaction
Gas feed:
50 % N2
17 % CO
25 % CO2
8 % H2O
Flow rate:
15 l/min
Furnace heating:
3 °C/min to 500 °C, where kept for 2 h
Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012
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Gas balance in the layer furnace
• 2 h time of magnetite pellet layer exp. at 500 °C
- Gas mixture converts quickly to thermodynamically balanced composition in presence of magnetite catalyst in the furnace tube
Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012
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Water components in BF burden
• Burden (pellets and briquettes) include water
components in different forms: basic moisture
(H2O), water of crystallization (•H2O) and as
hydroxides (-OH), which are usually bound in
the cement ingredients of briquettes
• Evaporation of different water components
from burden occurs at different times and
temperatures as the burden descends in the
BF shaft
Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012
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Effect of burden water content on
the BF shaft temperature profile
• Temperature profile of BF shaft as water content of burden is on normal level
• Temperature profile of BF shaft with high burden water content
(Bailly et al. 1999) Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012
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BF shaft temperature profile
• Heating rates of BF shaft
with normal water content
level in the burden were
used in the laboratory
experiments to determine
the required times to
vaporize water
components
• Experimental results
were compared to a BF
shaft temperature profile
in literature
• Temperature profile of BF shaft on wall, mid radius and center sections on normal burden water content level
(European Commission report 2004)
Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012
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Moisture evaporation from a
single pellet
• Various heating experiments were made for single pellets to determine water evaporation times
• According to the results of the experiments single pellets are not expected to contain any moisture at 350 °C
• DSC/TGA graph of a wet pellet heated up 2 °C/min in air
Water evaporation ends at 104.7 °C
Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012
Evaporation mechanisms:
- Heating of material
- Steady evaporation stage. High evaporation rate from the surface of the pellet
- Lower evaporation rate at the end as the last amount of water evaporates from the inner parts of the pellet
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Moisture evaporation from a
pellet layer
• Water vapor condensation on the upper gas analysis measurement spots disturbed the measurement -> no reliable results were obtained from the pellet layer drying experiments
• 25 cm wet pellet layer was heated 5 °C/min in 30 l/min gas flow
Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012
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Water component evaporation
from cement of briquette
• DSC/TGA graph of rapid cement sample (Pisilä 2009)
- Basic moisture (H2O) evaporation at 90- 110 °C
- Water of crystallization (•H2O) is removed at under 250 °C
- At 450-500 °C decomposition of calciumhydroxides cause 3.6 % decrease in the mass of the sample (according to theory the decomposition of portlandite Ca(OH) 2 → CaO + H2O) -> water is released! Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012
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Summary of experimental results for WGSR
occurrence and for water content
evaporation in the BF conditions
• In hematite pellet layer WGSR was observed at 400-
450 °C temperature range simultaneously with hematite
to magnetite reduction
• In magnetite pellet layer WGSR was observed at 350-
400 °C temperature range
• Burden is not expected to contain moisture (H2O) at
350 °C temperature on normal water content level
• Water released from calciumhydroxides in briquettes at
450-500 °C may change the BF gas composition
according to the critical temperature determinations
made for the WGSR
Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012
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Effect of burden water content on
the BF gas composition
• If all water content released from calciumhydroxides
at 450-500 °C is expected to change the composition
of BF gas through WGSR, the BF gas composition
will change as follows:
N2 43.42 % → 43.42 %
CO 22.78 % → 22.75 %
CO2 22.43 % → 22.45 %
H2 6.83 % → 6.85 %
H2O 4.55 % → 4.53 %
Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012
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Effect of burden water content on
the BF gas heat value
• By assuming 100 % oxidation to occur the water
content released from cement at 450-500 °C will
decrease the heat value of BF gas by 0.4 kJ/Nm3
according to calculations made with HSC Chemistry
• Decresing effect to the heat value is caused by the
greater heat energy obtained from burning of CO
compared to H2. i.e. at 200 °C:
• CO(g)+0.5O2(g)=CO2(g), ∆H=-283.592 kJ/mol
• H2(g)+0.5O2(g)=H2O(g), ∆H=-243.508 kJ/mol
Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012
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Effect of burden water content on
the BF gas heat value
• In reality conditions such as the prevailing gas
atmosphere and presence/absence of catalyst in the
location where the water vapor is released at 450-500
°C will have crucial significance on the water vapor
reaction behavior
• It was shown that in presence of catalyst
thermodynamically unbalanced gas composition can
convert rapidly through WGSR to a thermodynamically
balance composition
• With high burden water content the situation is different
as wet burden can confront up flowing very hot gas
Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012
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Thank you!
Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012
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References:
• Kinetics and Catalysis of the Water-Gas-Shift Reaction: A
microkinetic and Graph Theoretic Approach. Callaghan C. 2006.
Doctoral thesis.
• A new measuring device for the Simultaneous Evaluation of Heat
Pattern and Gas utilization Pattern in the shaft of a Blast furnace.
Bailly J.L., Picard M. Succurro A., Rouge, M. ja Reboul J.L. 1999.
• Critical review of existing procedures for the characterization of the
metallurgical properties of blast furnace burden material at
conditions of high injection rates. Technical steel research. European
Commission report 2004.
• Sekundäärisistä raaka-aineista valmistetun masuunibriketin
ominaisuudet. Sauli Pisilä 2009. Master’s thesis.
Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012