Tuesday, 23 August 2016
Wednesday, 10 August 2016
Some of Required Properties Of Iron Ore for Sponge Iron Operation.
Iron, along with its generic products, is
currently the most widely utilised metal in the various sectors of the world’s
economy. Many factors contribute to this, ranging from the good mechanical
properties it possesses to the low cost associated with its production. Iron is
mainly produced through two methods; the blast furnace, BF, route (pig iron),
and the direct reduction, DR, route (sponge iron).
Iron ore can be used directly in its natural form as a raw
material for processing iron or it can be upgraded through beneficiation before
it’s charged into the BF or DR furnaces. The feedstock is evaluated for
physical and metallurgical properties. Physical properties give an indication
of the material behaviour during handling and descent in the furnace.
Metallurgical properties on the other hand indicate the materials’ behaviour
during the reduction process. In selecting iron ore for iron and steel
industries, some of the properties which need to be considered include (i) tumbler,
abrasion and shatter indices, (ii) porosity, (iii) chemical composition, (iv)
loss on ignition, (v) reduction behavior, and (vi) thermal degradation.
The
strength and resistance of the iron ore to degradation (Physical Properties) is
represented by Tumbler Index, Abrasion Index, Shatter Index and Thermal
Degradation Index as well
as their apparent porosity.
(i) Tumbler Index
(i) Tumbler Index
The Tumbler Index is a relative measure of the resistance of
the material to breakage or degradation by impact.
(ii) Abrasion Index:
(ii) Abrasion Index:
It is a relative measure the degradation of iron ore by
abrasion. The Tumbler Index and Abrasion Index are determined in a tumbler test
apparatus as per the Bureau of Indian Standard No. IS:6495 .
A tumble strength test
measures two mechanisms of feedstock degradation, that is, the Tumble Index
(TI) and the Abrasion Index (AI). It was carried out following the
International Standard ISO 3271:1995(E) for determination of Tumble Strength
for iron ore . Precisely, a 15 kg test block sample was tumbled in a circular
drum rotating at 25 rpm for 200 revolutions. Subsequently, the ore was screened
and fractions +6.3 mm and −0.5 mm were obtained. The percentage of the
fractions in proportion to the feed weight is the value of the TI (+6.3 mm) and
AI (−0.5 mm). The test was repeated four times and the average values for these
tests represent the final TI and AI data.
(iii) Shatter Index
It is a measure of resistance to free fall of the material .
it is determined by the quantity of material which after being tested , retains
a size over specified dimension. This test can be carried out as per Bureau Of
Indian Standard No.IS:9963.
For estimation of a Shatter
Index, a dried lump iron ore sample (10 kg) of size −40 + 10 mm was dropped 4
times from a height of 2 m onto a cast iron floor (0.5 × 0.5 × 0.03 m).
Thereafter, the iron ore was screened and the shatter index expressed as the
wt% passing through a 5 mm sized screen (i.e., −5 mm fraction).
(iv) Thermal Degradation Index:
It is a measure of the tendency of the iron ore bearing
materials to undergo size degradation as a result of either thermal shock or
reduction or both .The term decrepitation or low temperature breakdown (LTB)
are also used in place of degradation in technical literature.
(v)
The apparent
porosity
It was determined using the GeoPyc 1360
pycnometer. A quantity of helium was placed in the sample chamber and its
volume was measured. Thereafter, a 2.0 g iron ore piece was placed in the
chamber together with the helium gas and the equipment registered the new
volume values. The difference in the new and original helium volume gave the
sample’s envelope and skeletal volumes. The difference in the envelope and
skeletal volumes indicates the percentage of porosity of the sample.
Sunday, 7 August 2016
Process Description and flow diagram of Coal Based DRI Plant
Process Description and flow diagram of Coal Based DRI Plant
Description of Sponge Iron Manufacturing Process
Most of the
plants in India use DRI process—a solid state direct reduction process by which
iron ore is reduced to sponge without phase change. Raw material
mix-iron ore, dolomite and coal are fed to one end of rotary Kiln as well as some fine coal also fed from discharge end and product
sponge iron along with char is taken out from the other end.
Apart from this,
primary and secondary airs are supplied to the Kiln to initiate the combustion
and reaction processes. The reaction takes place at high temp (1050˚C to
1065˚C). Coal plays a dual role in the Kiln. Part of coal is used as fuel to
supply the desired heat so as to take the raw materials to the desired temp.
But main role of coal is to supply carbon in the reduction process. Dolomite is
used as sulphur scavenger which finally comes out with the char. Char contains
ash of coal and other impurities of iron ore.
The reactions inside the kiln are
given below
C + O2 = CO2
CO2 + C = 2CO
3Fe2O3 + CO = 2Fe3O4 + CO2
Fe3O4 +
CO = 3FeO + CO2
FeO + CO = Fe (product) + CO2
Plants in India use wide variety
of raw material and coal which has direct bearing on the process. Again some
plants don’t use iron ore directly. They make iron pellets before feeding it to
rotary kiln.
Few highlighting points of
the selected plant are given below to understand the process better:
• Other
than oxides of Fe, iron ore also contains impurities like gangue material,
sulphur, phosphorous and moisture. The quality of ore is determined by the iron
percentage as it has direct bearing on the yield. The best quality feed has the
following characteristics
- Fe (total): 65% or more;
- LOI 1%
- SiO2 + Al2O3 (Gangue material): 5%
- Sulphur: 0.01%
- Phosphorous: 0.05%
- Moisture: 1%
- Size: 3 - 18 mm (no crushing required, can be fed to kiln directly)
• As mentioned earlier Dolomite is used
here as sulphur scavenger—it doesn’t have any role in the main stoichiometric
reaction. Dolomite typically contains MgO (20%), CaO (28%) and acid soluble
(7%). The size of dolomite is 2 - 8 mm hence no crushing is required.
• The
reducing agent is here non-coking coal. Coal size is 0-22 mm hence it requires
crushing before feeding into kiln. the good quality should be as bellow to get better result.
| Coal Properties | Indian Coal | South African |
| Coal Fixed Carbon % | 43 | 55 |
| Volatile Matter % | 31 | 30 |
| Moisture | 8 | 12 |
| Ash | 26 | 15 |
| GCV (Kcal/Kg) | 5360 | 6540 |
Because of the huge length of the kiln and to maintain the
temperature profile, 45-55% coal is injected from the discharge end.
• Sponge iron
produced by the process will be the high grade which contains 80% Fe, 12% FeO and 8%
gangue material. After separation of sponge iron in the magnetic screen/pulley,
the remains are collected as char. Char has good amount of fixed carbon (25% -
30%) and moderate GCV (2500 - 2600 Kcal/Kg). Char is sold outside as low grade
fuel which is subsequently used in brick kiln or large boiler. Out of the total
kiln discharge, 15% to 20% is the char generation.
Saturday, 6 August 2016
What is DRI (Direct Reduced Iron)
Direct-reduced
iron (DRI), also called Sponge iron, is produced from direct reduction Iron (in the form of lumps, pellets or fines) by a
reducing gas produced from natural
gas or coal. ‘Reduced iron’ derives its name from
the chemical change that iron ore undergoes when it is heated in a furnace at
high temperatures in the presence of hydrocarbon-rich gasses. Direct reduction refers
to processes which reduce iron oxides to metallic iron below the melting point of iron. The product of such solid state processes are called direct
reduced iron. The reducing gas is a mixture of gasses, primarily hydrogen (H2) and carbon monoxide (CO). The process temperature is typically 800
to 1050 °C.
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