sponge iron TCE NMD

CONSULTING ENGINEERS LIMITED

CHALLENGES IN SPONGE IRON

MAKING USING ROTARY KILNS Asaman Prasad Patnaik, Dr M D Maheshwari,

Jitendra Nath Rath & Raghunath V Deshpande

TATA CONSULTING ENGINEERS LIMITED


OUTLINE OF PRESENTATION


1. Introduction

2. Present Technological Options in DRI Making

a. Gas Based DRI Making

b. Coal Based DRI Making

3. Factors affecting Productivity & Emission

4. Cleaner Technology Options -Opportunities & Challenges

a. Using Low Grade Coal

b. Using Coal Bed Methane

5. Conclusions

6. Acknowledgement


INTRODUCTION


In Direct Reduction route, Ore is reduced at a temperature of 900-1050 oC, in

the solid state (below the melting point) by :

Carbon Monoxide (Coal Based).

Or

Hydrogen & Carbon Monoxide (Gas Based)

The reducing gas, diffuses through the pores of the ore, reacts to reduce the

ore. As the ore is reduced, the porosity increases. Hence, it is called as

Sponge Iron.

DRI is produced as a result of removal of oxygen from the iron ore, and

hence has a higher porosity and is reactive with atmospheric air.

The gaunge (SiO2 and Al2O3 etc) present in the ore is not removed and

remain as such in the product (unlike in case of hot metal making where the

gaunge is separated as Slag)



Reduction Reactions:

First, Haematite is reduced to Magnetite:

3Fe2O3 + H2 = 2Fe3O4 + H2O

3Fe2O3 + CO = 2Fe3O4 + CO2

Then, Magnetite is reduced to Wustite:

Fe3O4 + H2 = 3 FeO + H2O

Fe3O4 + CO = 3 FeO + CO2

Most of the Wustite (FeO) is reduced to Iron (Fe):

FeO + H2 = Fe + H2O

FeO + CO = Fe + CO2

Carburisation Reactions:

3Fe + CO + H2 = Fe3C + H2O

3Fe + CH4 = Fe3C + 2H2


PRESENT TECHNOLOGICAL OPTIONS IN DRI MAKING


COAL BASED DRI UPTO 0.15

MTPA GAS BASED DRI 0.20 MTPA TO 2.0 MTPA


GAS BASED DRI MAKING


• MIDREX and HYL processes using a Shaft furnace.

• Uses Natural Gas. Can also use Synthesis Gas from Coal

Gasification

• The CO and H2 required for reduction produced by reforming of

Natural Gas in a Reformer (MIDREX or Hyl III) or by direct

injection of Natural Gas into the shaft furnace (HYLZR).

Steam Reforming (MIDREX/HYL):

CH4 + H2O = CO + 3 H2

CO2 Reforming (MIDREX):

CH4 + CO2 = 2 CO + 2 H2

• The gas based processes have a higher annual capacity ranging

from 0.2 MTPA (minimod) to 2.5 MTPA (Super Megamod).

• Product can be cold DRI/ hot DRI/ Hot Briquetted Iron (HBI)


COAL BASED DRI MAKING


• Uses Rotary Kiln

• Use Coal as the fuel & reductant

• At a bed temp of about 1050 oC.

• Air flow into the kiln:

• Radial Air -Using a series of radial ports (ACCAR/OSIL process)

• Axial Air – Using Axial Air Fans (Lurgi Process etc)

• Standard sizes of economic importance are 300 / 350 TPD (100000

TPA) and 450 / 500 TPD (150000 TPA) modules

• Coal is charged from both feed end as well as discharge end

• Limestone or Dolomite is added to remove sulphur from DRI

• DRI is separated from non-magnetics like ash and char and

bagged.


AXIAL AIR PROCESS


Variation of GasTemp along Length in Axial air Kiln

0

200

400

600

800

1000

1200

1400

0 10 20 30 40 50 60 70 80 90

Length from Feed End

Tem

p

Air tubes for Air

AXIAL AIR KILN WITH AIR TUBES

Axial Air

AXIAL AIR TUBE.exe


RADIAL AIR PROCESS


Gas Temperature along the length of a radial air Kiln

-

200

400

600

800

1,000

1,200

1,400

0 10 20 30 40 50 60 70 80

Length from FE

Te

mp

Ported Section for air to kiln

PORTED KILN OF OSIL PROCESS

Radial Air

PORT AIR DISTRIBUTION SYSTEM.exe


RADIAL AIR PROCESS


Rotary Kiln

Air Manifold with 8

no of Fans

Port Air Distribution System



FACTORS AFFECTING PRODUCTIVITY & POLLUTION

Iron Ore Coal

Design

Spec.

Being Used Design

Spec.

Being Used

Fe T 65% min 60 % - 63% FC (dry) 45 % min 30% -36%

SiO2 +

AL2O3

5% max More Ash (dry) 29-31 % 34-40%

LOI 1- 1.5% 3- 4% Volatile

Matter (dry)

24-26% 28-30%

Tumbling

Index

88% min. 75- 80% Cal Value

kCal/kg

5500-6000 4500-5000



AFFECT ON PRODUCTIVITY


ENVIRIONMENTAL IMPACT


ORE AND COAL AS PER DESIGN SPECIFICATION

Material IN per t MATERIAL OUT per t

Ore 1.50 DRI 1.00 Coal 1.02 Char 0.25

Dolomite 0.03 Dust 0.15 Accretion 0.01

Loss in process and to gas 1.15

Unaccountable 0.00

Total 2.55 Total 2.55

SPEC ENERGY CONS.* Gcal/ t 4.6-4.8 CO2 EMMISSION** t/ t DRI 2.2

INFERIOR QUALITY ORE AND COAL


Ore 1.67 DRI 1.00

Coal 1.44 Char 0.26

Dolomite 0.04 Dust 0.51

Accretion 0.02


Unaccountable 0.00


SPEC ENERGY CONS.* Gcal/ t 5.2-5.5

CO2 EMMISSION** t/ t DRI 2.8

*After taking credit for WHR Power generation.

** Process related GHG emission including power consumption and credit for WHR

Power


CLEANER TECHNOLOGY OPTIONS -OPPORTUNITIES &

CHALLENGES


CONCERN AREAS

• Natural Gas availability limited to western India.

• Restriction in supply of Natural Gas for DRI Making

• Pollution Aspects in Rotary Kiln process

OPPORUNITIES

• Availability of Non-coking Coal Resources

- Beneficiation

- Coal Gasification

• Availability of Coal Bed Methane

CHALLENGES

• Use of Synthesis Gas from Coal in Rotary Kiln/ Shaft Furnace

• Use of CBM in Rotary Kiln/ Shaft Furnace


CLEANER TECHNOLOGY OPTIONS –COAL

BENEFICIATION


INFERIOR QUALITY ORE AND BENEF. COAL


Ore 1.67 DRI 1.00

Coal 1.28 Char 0.26

Dolomite 0.04 Dust 0.36

Accretion 0.01


Unaccountable 0.00


SPEC ENERGY CONS.* Gcal/ t DRI 4.95

CO2 EMMISSION* * t/ t DRI 2.50

• With coal beneficiation reduction in ash

upto 10% possible.

• Productivity improves by 7.5%.

• Reduction in dust generation by 25%

• Reduction in Sp Energy Cons by 10%.

• Reduction in CO2 emission by 2%

*After taking credit for WHR Power

generation.

** Process related GHG emission including

power consumption and credit for WHR

Power


CLEANER TECHNOLOGY OPTIONS –USE OF SYNTHESIS

GAS


• Synthesis Gas Obtained by Coal Gasification.

• Most Suitable is Entrained Bed (Shell, GE, Conoco Phillips) or Fixed Bed Dry Bottom

type (SASOL Lurgi)

Gas Composition : CO : 32%, H2 : 52%, CH4: 12%, CO2: 3%

Gas Quality (H2 + CO/ H2O + CO2) More than 10.

H2/CO ratio All acceptable. (> 0.5 prefered)

Shaft Furnace Rotary Kiln

Syn Gas requirement

Nm3/t 600 1100

Spec Energy Consumption

Gcal/ t DRI 5.25* 5.99*+

CO2 emission*** t/ t DRI 0.10 1.05

• Considering Coal Gasification also. + After taking credit for WHR Power generation.

** Process related GHG emission including power consumption and credit for WHR

Power


CLEANER TECHNOLOGY OPTIONS –USE OF CBM


• CBM contains about 96-98% Methane.

• CBM can be used as an alternative to Natural Gas.

• CBM availability in Asansol Coal belt in West Bengal is promising

Shaft Furnace Rotary Kiln

CBM requirement Nm3/t 250 400

Spec Energy Consumption

Gcal/ t DRI 2.75 3.35

CO2 emission t/ t DRI 0.55 0.95


GASEOUS REDUCTION IN ROTARY KILNS


• Use of natural gas in a ported

(radial air type) Rotary Kiln

(80% gas and 20% oil) has

been established by a pilot

plant at Niagra Falls, Ontario,

Canada (1960s).

• A 233,000 TPA Commercial

Plant was also set up by

ACCAR at Sudbury, Ontario

using 80% Natural Gas and

20% HSD (1973).




MIDREX PROCESS



MIDREX PROCESS


Shaft Furnace is at 1 bar g pressure .

Module Capacity : 0.5 MTPA ( 5m dia) to 2.5 MTPA

I : Reduction :

• Ore/ Pellet charged through a proportioning hopper at top.

• Dynamic seal legs at top and bottom of the furnace.

• Reduction Gas (called as Reformed Gas) at 850-900 oC is introduced at

bustle at the bottom of reduction zone.

H2: 56-61%, CO : 33-38% balance H2O & CO

H2/CO ratio : 1.5 to 1.8:1, H2+CO/H2O+CO2 : 10 to 12:1

• Natural Gas is also injected at the bottom of cooling zone (conical section)

for carburization and quenching.

• Cooling gas is re-circulated through a scrubber – compressor.

• The hot product can be briquetted/ hot discharged/ cooled as cold DRI.

• Top Gas leaving furnace at 400 oC(contains 90% CO2 & H2O) is sent to a

Scrubber. Around 2/3rd of Top Gas is recycled as process gas (used in

reforming) and the rest as fuel in reformer.


MIDREX PROCESS


II : Reforming

• Reformer is a refractory lined furnace containing alloy steel tubes with Ni-Fe

Catalyst.

• Process Gas is compressed to 2 bar g and mixed with Natural Gas (feed

gas mixture) and preheated in a Recuperator and sent to Reformer.

• Preheated Air is used to burn Fuel Natural Gas to maintain the temperature

at 950oC.

• Reforming is carried out by CO2 and Steam present in the process gas.

• Reformed Gas is sent to the Shaft Furnace.

III: Heat Recovery

• Sensible heat is recovered from Reformer Flue Gas to preheat Feed Gas

mixture, and combustion air in the Recuperator.


HYL III Process



HYL PROCESS


Shaft Furnace is at 6-10 bar g pressure .

Module Capacity : 0.2 MTPA ( 2.5m dia) to 2.5 MTPA (6.5 m)

I : Reduction :

• Ore/ Pellet charged through four pressurised bins with charging legs with

hydraulically operated valves

• Production rate controlled by discharge rotary valve at bottom.

• Reduction Gas (Called as Process Gas) at 900-950 oC passes through a

refractory lined transfer line where O2 (for partial combustion) is injected and

then introduced at the bottom of reduction zone.

H2: 56-61%, CO : 33-38% balance H2O & CO

H2/CO ratio : 1.8 to 2.5:1, H2+CO/H2O+CO2 : 10 to 12:1

• Natural Gas is also injected for carburization and quenching.

• Cooling gas is re-circulated through a scrubber – compressor.

• The hot product can be briquetted/ hot discharged/ cooled as cold DRI.


Top Gas Recuperator (energy recovered as Steam) and then Scrubber.


HYL PROCESS


II : Process Gas System:


Top Gas Recuperator (energy recovered as Steam) and then Scrubber.

• Steam generated is used in regeneration of absorbent in CO2 absorption

system.

• Water generated during reduction is removed in scrubbing.

• Process Gas is then sent to PG Compressor followed by PG aftercooler.

Then to CO2 absorption system.

• After removal of CO2. the Process Gas is sent to PG Heater and mixed with

reformed gas and sent back to shaft furnace.

III: Reforming:

• Natural Gas is reformed using excess steam.

• After reforming the excess steam is removed by cooling.

• The reformed gas is sent to the Process Gas Heater.

IV: PG Heater

• The recycled Process Gas and the reformed gas is heated to 900-950 oC

and sent to the reactor.


HYL ZR PROCESS


Desulphurisation of Natural Gas is not required.


SYNTHESIS GAS IN SHAFT FURNACES


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sponge iron TCE NMD