Effect of burden content on the

Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012

MEBF-Material Efficient Blast Furnace (FIMECC -project)

• Commissioned study for Ruukki

Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012

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

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

Water-gas shift reaction (WGSR)

(CO(g)+H2O(g)↔H2(g)+CO2(g))

• 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 in processing industry • Several catalysts have been investigated and proposed for the WGSR

Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012

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

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)

Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012 (Callaghan 2009)

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

Layer furnace used in the experiments

Inlet gas

Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012

Critical temperature of the WGSR in the BF conditions

• Empty layer furnace

Gas feed: Furnace heating: 3 °C/min to 700 °C 50 % N2 42 % CO

8 % H2O Flow rate: 15 l/min

- The WGSR was observed at about 500 °C

Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012

Critical temperature of the WGSR in the BF conditions

• Hematite pellet layer

Gas feed: Furnace heating: 50 % N 3 °C/min to 500 °C, 2 where kept for 2 h 17 % CO

25 % CO2 8 % H2O Flow rate: 15 l/min

- The WGSR was observed at 400-450 °C simultaneously with hematite to magnetite reduction Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012

Critical temperature of the WGSR in the BF conditions

• Magnetite pellet layer (pre-reduced hematite)

Gas feed: Furnace heating: 50 % N 3 °C/min to 500 °C, 2 where kept for 2 h 17 % CO

25 % CO2 8 % H2O Flow rate: 15 l/min

- The WGSR was observed at 350-400 °C - Magnetite clearly catalyzes the reaction Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012

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

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

Effect of burden water content on the BF shaft temperature profile

• Temperature profile of BF shaft as • Temperature profile of BF shaft with water content of burden is on normal high burden water content level

Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012 (Bailly et al. 1999)

BF shaft temperature profile

• Heating rates of BF shaft • Temperature profile of BF shaft on wall, mid with normal water content radius and center sections on normal burden level in the burden were water content level 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 (European Commission report 2004)

Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012

Moisture evaporation from a single pellet • DSC/TGA graph of a wet pellet heated up 2 °C/min in air

Evaporation mechanisms: Water evaporation - Heating of material ends at 104.7 °C - 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 • 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 Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012

Moisture evaporation from a pellet layer

• 25 cm wet pellet layer was heated 5 °C/min in 30 l/min gas flow

• Water vapor condensation on the upper gas analysis measurement spots disturbed the measurement -> no reliable results were obtained from the pellet layer drying experiments

Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012

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

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

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

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

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

Thank you!

Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012

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