DRI Lumps
Specification
|
Characteristics |
Requirement
Achieving in Mono Steel |
|
% Non-magnetic |
1.0 Max. |
|
% Metallic Fe |
81 Min. |
|
% Total Fe |
91 Min. |
|
Metallization |
88 Min. |
|
% Phosphorous |
0.05
Max. |
|
% Sulphur |
0.03% |
|
% Carbon |
0.3 Max. |
|
% Sio2+ Al2O3
|
5 Max. |
Applications
»
DRI Lumps is one of the most important and the
basic raw materials required for the production of various
steel/iron based products like
TMT bars, Middle Steel Billets etc.
» DRI Lumps is
a part–substitute for steel scrap used for manufacturing steel
by electrical arc furnaces and induction furnaces.
» Steel melting scrap is
primarily required for using as a feed material in all mini
steel plant that use this scrap for melting in electric arc
furnace/induction furnace to manufacture steel.
» DRI Lumps is
also good suitable material for using as a coolant in LD
converters of the Integrated Steel Plants.
Size: A
grade Lumps 5-20 mm
A grade
Fines 0-6 mm (+6 mm 5% Max.)
Production Process
ROTARY KILN PROCESS
This process has essentially been designed to carry out
reduction using solid reductants like non-metallurgical coal. A
long, slightly inclined, slowly rotating kiln is employed to
carry out the reduction. The charge is fed from the higher level
and it travels under gravity, aided by rotating motion through
several heating zones. The reduced charge comes out from the
other end of the kiln and passes through a continuous cooling
cooler without coming in contact with atmospheric air.
The reduced and cooled product is screened and the oversized are
subjected to magnetic separation to obtain clean, and sized
DRI Lumps while the
non-magnetic oversized portion as well as the undersized are
re-circulated through the charge. In a country like India, which
does not posses adequate natural gas and abundant non-coking
coal bed, the rotary kiln process is the obvious choice for
producing DRI Lumps from their own grade iron ores.
PROCESS SELECTED
The Rotary Kiln process is a well-established process for
production of coal based DRI Lumps. The process, in general,
salient features of the various rotary kiln processes available
now for commercial exploitation, and the process selected are
discussed in this chapter.
In this process a refractory lined Rotary Kiln of 42 Mtr long is
used for reduction of iron ore in solid state. The kiln is
mounted with a slope of 2.5% down words from the feed end to the
discharge end. A central burner located at the discharge end is
used for initial heating of the kiln.
Sized iron ore is continuously fed into the kiln along with
coal, which has dual role of fuel as well as reductant. Small
quantities of lime stone/dolomite are added to scavenge the
sulphur from the coal.
A number of air tubes are provided along the length of the kiln.
The desired temperature profile is maintained by controlling the
volume of combustion air through these tubes. Air is introduced
through these tubes axially in the free space over charge.
The rotary kiln is broadly divided into two zones namely, the
pre-heating zone and the reduction zone. The pre-heating zone
extends over 40 to 50 percent of the length of the kiln. In this
zone, the moisture in the charge is driven off, and the volatile
matter in the coal, liberating over a temperature range of 600
to 800 degree centigrade, is burnt with the combustion air
supplied through the air tubes in the free space above the
charge. Heat from the combustion raises the temperature of the
lining and the bed surface.
As the kiln rotates, the lining transfers the heat to the
charge. Charge material, pre-heated to about 1000 ˚C enters the
reduction zone. Temperature of the order of 1050 to 1100 ˚C is
maintained in the reduction zone, which is the appropriate
temperature for solid-state reduction of iron oxide to metallic
iron.
The reduced product is discharged into a rotary cooler along
with coal ash, calcinated limestone and residual char, where
they are cooled to below 100˚ C indirectly by spraying water on
the outer surface of rotary cooler.
The product is then screened and magnetically classified.
RAW MATERIALS
GENERAL
The major Raw Materials required for production of
DRI Lumps
by the rotary kiln process are: sized graded iron ore and
Non-Coking coal. Blast furnace grade limestone, in small
quantities, is also required to scavenge the sulphur. This
chapter deals with the Annual requirement, Quality consideration
and Sources of supply of the Raw Materials
QUALITY REQUIREMENTS OF RAW MATERIALS:-
IRON ORE
Unlike in the gas based shaft furnace process, for production of
DRI Lumps the rotary kiln based processes can operate with 100
percent sized lump ore, a cheaper fees stock. Therefore, it is
envisaged to use sized lump ore. The quality requirements of
iron ore, and the sources of its supply for the plant are
discussed below.
The quality requirement of lump ore for DRI Lumps production
can be classified into:-
Physical requirements:-
Strength and granulometry are the two important physical
requirements. The ore should be hard, and posses high strength.
The optimum tumbler strength of the ore should be 80 percent
minimum. Depending on the reducibility, closely calibrated ores
in the size range of 5 to 18 mm generally used.
Metallurgical requirements:-
The ore should be highly reducible, thermally stable and have a
low tendency for sticking and disintegration during heating and
reduction.
Chemical requirements:--
Apart from the removal of oxygen, no other major chemical change
takes place in direct reduction. The gangue material in DRI
Lumps, originating from iron ore, namely, silica and alumina and
the sulphur and phosphorous contents adversely affect the
economics in subsequent steel making operation. Therefore, the
ore should be high in iron content and low in gangue,
CHEMICAL COMPOSITION PERCENTAGE MIX
Fe (Total) 65% (Minimum)
Si O2 + Al2O3 5% (Maximum)
Sulphur 0.01% (Maximum)
Phosphorous. 0.06% (Maximum)
Moisture. 2% (Maximum)
Size. 5 – 18 mm.
COAL
Non-coking coal is generally used as reductant in the rotary
kiln process. Other reductants such as anthracite and lignite
can also be used.
CHEMICAL COMPOSITION PERCENTAGE MIX
Fixed Carbon. 40% to 55%
Volatile matter. 25% to 30%
Ash 15% to 20%
The major quality requirements of coal for DRI Lumps
production are-
Non-coking characteristics
Low ash content
Low sulphur content
Good reactivity
High ash fusion temperature
Medium volatile matter
1). Non-coking character:-
Non-coking coal is required in DRI Lumps production, since the
coking reaction leads to formation of rings inside the kiln.
Practically permissible caking index is 3 maximum for rotary
kiln operations.
2) Low ash contents:-
High ash leads to under utilization of the kiln volume available
for reduction. It also increases the consumption of fixed
carbon, since additional energy is consumed in heating the inert
ash mass to reaction temperature. An ash content of 30 percent
maximum is the practicable limit for normal operation.
3) Low sulphur content:-
To control the sulphur in DRI Lumps, the sulphur in coal
should be one percent maximum.
4) Good reactivity:-
An important step in solid state reduction is the boudward
reaction, whereby carbon dioxide generated from burning of coal
reacts with coal to regenerate carbon monoxide, the coal,
therefore, should posses sufficient “reactivity” so that the
bounded reaction proceeds at sufficient rate. Bituminous and
sub-bituminous coal exhibits very good reactivity suitable for
production of DRI Lumps.
5) Ash fusion temperature:-
Coals with low ash fusion temperature leads to sticky mass, and
consequent unstable kiln operation by forming accretions inside
the kiln, and reducing the reduction rate by formation of slag
layer on surface of the ore. Hence coals with ash fusion
temperature above 1150˚C Are desirable for rotary kiln
operation. Ash fusion temperature is governed by its chemistry.
Coal with as of high sulphur trioxide equivalent, low silica
ratio and high alkali ratio has lower eutectic temperatures, and
hence is not desirable.
6) Volatile matter:-
Coals with optimum volatile content are required for coal based
rotary kiln process. Coal with very low volatile matter result
in very low reactivity of char, and thus give rise to poorly metallised product. Very high volatile coals, though they yield
highly reactive char, are also not preferred. Generally for
rotary kiln process volatile matter should be in the range of 28
to 32 percent.
Volatile matter 26-28 26-28 31 28 31
Ash 23-24 32 24 16 7
Moisture 8-15 8-15 8-15 8-15 8-15
Sulphur 0.60 0.60 0.60 0.60 0.60
heating
value kcal/kg
5500 5200 3500/4500 4500/
5500
4500
LIMESTONE
Blast Furnace grade limestone is used as a de-sulphuriser in the
production of DRI Lumps. Typical specification of limestone is
given below –
CHEMICAL COMPOSITION PERCENTAGE MIX
MgO 20% (Minimum)
CaO 28% (Maximum)
L.O.I. Remainder
PRODUCT
GENERAL
The product to be manufactured under the envisaged project is
DRI Lumps OR DIRECTLY REDUCED IRON (DRI). It is the single
most important raw material in basic steel manufacturing
produces, especially by the furnace route DRI Lumps or direct
reduced iron, is a high ferrous charge material and is used as a
substitute for scrap as the prime raw material in the Electric
Arc Furnace/Induction Furnace during the process of manufacture
of iron and steel. It can be produced both iron the lumps and
pellet from or in a compacted and briquetted form known as hot
briquetted iron.
The product propose to be manufactured by the proposed project
shall conform to the various Industry and Organizational
Standards.
The present project is being set up for the manufacture of
30,000 metric tons per annum of DRI Lumps Lumps and Fines.
DRI Lumps is on the rise due to two primary reasons.
Firstly, with an improvement in the steel scenario, there has
been a growth in the use Electric Arc Furnace/Induction method
of producing steel which requires the use of good quality scrap,
and; Secondly, due to the shortfall in the supply of good
quality scrap generation.
Apart from making the secondary steel sector less vulnerable to
fluctuations in the international scrap prices by reducing
dependence on imports, increased domestic production of DRI
Lumps and the consequent reduction of scrap imports have led to
substantial savings in foreign exchange.
The induction Furnace/Electric Arc Furnace method of
manufacturing iron & steel, allows flexibility in the charge
mix, amounts to reduced electricity consumption and decreased
refractory electrode consumption, which has resulted in the
manufacture of international quality steel. Since, India has
rich reserves of coal, and the technology for manufacturing
DRI Lumps is rawer. DRI Lumps production seems to have
bright future.
PRODUCT SPECIFICATIONS
DRI Lumps (Direct reduced iron) is produced by the iron
reduction process in which metallic iron is produced at a
temperature range of 700°C to 1000°C which is much below its
melting point. The typical reduction reactions are give below:-
1) Fe2 O3 + 3C = 2Fe + 3Co
2) Fe2 O 3 + 3Co = 2Fe + 3Co2
3) Fe2 O3 + H2 = 2Fe + 2H2O
The product from the process is a solid material generally in
the form of a geometric shape containing metallic iron, iron
oxide, iron carbide and some impurities. The chemical
composition of DRI Lumps is as under:-
Chemical Composition of DRI Lumps
Fe (Total) 92%
Fe (Metal) 83%
Metallisation 90%
Carbon 0.15%
Sulphur 0.025%
Phosphorous 0.050%
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