Effect of blast furnace burden water content on the blast ... · PDF fileEffect of blast...

Lab. Of Process Metallurgy, Antti Kemppainen, 29.5.2012

Effect of blast furnace burden

water content on the blast

furnace gas

MEBF-Material Efficient Blast

Furnace (FIMECC -project)

• Commissioned study for Ruukki


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


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


• 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))




• The WGSR has its ∆G=0 at 823 °C where

the direction of the reaction changes

(Callaghan 2009)




• 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



• 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


Layer furnace used in the experiments

Inlet gas


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




• 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




• 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


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


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


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

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)


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


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

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


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



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 %



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



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


Thank you!


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.


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