OBJECT OF THE INVENTION:
The present invention relates to process for making briquettes utilizing iron
making and steel making waste as a charge material for blast furnace.
BACKGROUND OF THE INVENTION:
The Blast furnace process of iron making is the first step in producing steel
from iron oxide. Despite the speed at which the good quality iron ore and
coking coal reserves in the world in general and in India in particular are
being exhausted and development of alternate route of iron making for
ultimate conversion to steel are becoming more and more adopted, blast
furnace route has not lost its importance and would probably remain the
same at least next five decades.
The blast furnace works on a counter current principle, the descending solid
charges meeting the ascending hot gases. In the production of Iron, iron
ore, sinters, coke and fluxes lime stone/and or dolomite are charged in to
the furnace. The resulting process produces carbon monoxide which
reduces the iron ore to molten iron. The ore is directly reduced by the
carbon in the coke and indirectly by the carbon oxide. The proportion of
direct and indirect reduction greatly influences the process in term of the
quality of the hot metal and economy. The end product of the blast furnace
process is hot metal and slag along with the blast furnace gas of high
calorific value.
It is important to note that the art of slag making is the art of iron making.
The slag must have the affinity for absorbing impurities i.e. gangue from the
charge along with other deleterious impurities which affect the quality of hot
metal. The blast furnace slag is essentially a low melting compound consists
of silica, alumina, calcia and magnesia. The other minor constituents of slag
depends on the quality of ore which includes Manganese oxide, sulphur,
phosphorous and compound thereof. It is essential to know the behavior of
the slag in term of chemical composition, their eutectic and ability to react
and trap the minor impurities.. Also the slag should be free flowing at the
operating temperature with high slag metal separation with out entrapping
metal. The slag generated should have a low fusion temperature so that at
the furnace operating temperature a high available super heat will increase
the kinetics of chemical reaction and will ensure better slag metal
separation from both physical and chemical point of view. In this regard
many investigations have been carried out to study effect of compositional
variation on the onset of slag melting and its flow ability. However, behavior
of a single constituent in a multicomponent system is complex and different
in different circumstances.
The cohesive zone in a blast furnace is bound by the softening line at the top
end and melting line at its bottom end acts as a gas distributor in the blast
furnace. The blast furnace being basically a counter current process, the
distribution of gas as influenced by the gas-semi liquid/gas-liquid
permeability greatly affects the BF operation particularly influencing the
productivity, hot metal quality, coke consumption as well as reducing agent.
The continuous increasing demand on iron and steel with high productivity
in Blast furnace demands good quality of iron ore having Fe content >62%.
Good quality of ore are gradually depleting world over, particularly in India.
This demands utilization of alternate iron bearing material. Huge quantities
of iron bearing dust are generated from iron making and steel making units.
Apart from these dust large quantity of mining dust are generated from iron
ore mines.
The present invention relates to utilization of these aforementioned wastes
along with coke waste from coke oven for making briquettes. These
briquettes have not only good green strength but also shows excellent
strength up to softening temperature. This provides excellent permeability
which narrow down the cohesive zone of the blast furnace.
This optimization of slag not only improves the metal quality by reducing the
silicon content in hot metal but also improves the fuel efficiency by
decreasing the gap between the onset of melting and flow ability of slag
imparting better permeability resulting in reduction of coke consumption.
According to present invention there is provided a Process for making
briquettes utilizing iron making and steel making waste as a charge material
for blast furnace which comprises making briquettes by stiff extrusion
method consisting of dust of iron making or steel making or iron ore fines
or any combination thereof with or without fluxing material and/ or fines of
coking industries characterise in that the percentage of iron ore fines is not
less than 5% or more than 100%, iron making dust is not less than 5% or
more than 100%, steel making dust is not less than 5% or more than 100%
and the coke fines is not less than 5% or more than 30% adding to the same
binding material and/ or plasticizer such as herein described.
Process as claimed in claim 1 wherein plasticizer and binding materials are
selected such as bentonite or activated bentonite or any known plasticizer
the percentage of which is not less than 0.5% or more than 3% and lime
containing binder may be ordinary Portland cement or Portland slag cement
or pozzolana cement as binder and percentage of which is not less than
2.5% or more than 15%.
The briquettes are made by stiff extrusion with pressure and under vacuum.
The slag must have the affinity for absorbing impurities i.e. gangue from the
charge along with other deleterious impurities which affect the quality of hot
metal the blast furnace slag is essentially a low melting compound consists
of silica, alumina, calcia and magnesia.
The other minor constituents of slag depends on the quality of starting
material which may include Manganese oxide, sulphur, phosphorous and
compound thereof.
The slag is free flowing at the operating temperature with high slag metal
separation with out entrapping metal. The slag generated is having a low
fusion temperature so that at the furnace operating temperature a high
available super heat will increase the kinetics of chemical reaction and will
ensure better slag metal separation from both physical and chemical point
of view.
The fines of industrial waste like blast furnace dust, LD converter dust, blue
dust in different proportion with the addition of plasticizer and binders, is
thoroughly mixed in a mixer to attain optimum homogenisation.
Fragmentation of densified charge mix is being performed by extrusion
through the die with single or multiple holes of regular form having diameter
of 35-40 mm and length 20 mm to 100 mm the briquettes are air dried
before charging in to blast furnace wholly or with addition of sized iron ore.
Presently burden of blast furnace consists of sinter (iron ore with size
greater than 3mm with lime stone/dolomite, coke) coke and lime
stone/dolomite. This involves very high grade ore. Apart from this during
mining of ore blue dust are generated. Also during crushing of iron ore lot of
dust is generated which is remained unutilised and creates ecological
problem. During iron making and steel making dust are generated which is
a potential hazard to the plant and creates ecological problem.
WE SHALL NOW DESCRIBE THE POSITION IN INDIA:
India is producing around 68 million tons of crude steel. Out of total
production near about 40% is produced through conventional route (BF-
BOF Route). Increased indirect reduction and decreased thermal load help
to decrease coke rate. Several measures have been taken to achieve that
like using pre-fluxed agglomerates, increased blast temperature, fuel
injection and so on. Also several methods like high top pressure, humidified
and oxygenated blast have been adopted to increase productivity by
increasing coke through put. The Bhilai and Bokaro blast furnace with high
top pressure have shown a smooth furnace operation and almost 80%
decreases in silicon content of the hot metal. Because of these measures
remarkable changes have taken place in key performance indices like
productivity, fuel rate, campaign life and hot metal silicon level in last 30-40
years. Present coke consumption in Indian blast furnace has come down to
525-650kg/ton of hot metal from more than 800kg/ ton of hot metal.
Obtaining uniformly permeable burden inside the furnace and proper
softening and melting characteristic of burden are prerequisite for smooth
furnace operation and quality hot metal. The present charge material as a
source of iron for blast furnace is sinter or super fluxed sinter along with
iron ore which demand good quality of ore or iron ore fines. During
operation of blast furnace around 10% of blast furnace dust are generated
which remains as waste. Apart form this during steel making process
through LD converter or any other route also generates iron bearing dust
which also does not find any utilization and thrown as waste. Apart from
this, huge quantities of iron ore dust are generated during mining/crushing.
WE SHALL NOW DESCRIBE THE POSITION IN OTHER COUNTRIES
THROUGHOUT THE WORLD EXCEPT INDIA:
Around 1500 million ton of crude steel is produced worldwide. In spite of the
development of electric steelmaking, Blast furnace-Oxygen steel making is
still the major route. Near about 56% of steel is produced by this route. Lot
of innovation are made in order to have smooth furnace operation which can
improve overall productivity of furnaces. The average coke consumption has
come down to as low as 350-550kg/ton of liquid metal. Y.S.Lee and his
group from Korea are evaluating the effect of different parameters like
basicity and FeO content on viscosity of blast furnace slag. Viscosity of
blast furnace slag plays an important role in controlling gas permeability,
heat transfer and the reduction of SiO2 and FeO and thereby affect the
operation efficiency of blast furnace M A Jitang of Sweden is engaged in
studying the feasibility of injection of flux from tuyeres in order to optimise
slag formation. In order to improve performance indices of blast furnace, one
of the important measures is to optimise slag characteristic with respect to
its melting characteristics and fluidity, at the same time ensuring slag has
an adequate desulphurisation and alkali removal capacity. Brazil, Australia,
Russia has huge reserves of good quality of ore and feeding to major steel
producers of the world. Iron ore fines are beneficiated and used as a source
of feed material after pelletisation. Still dust generated from Iron making or
steel making units are remaining unutilised.
TECHNICAL FIELD:
This invention relates to the development of briquettes from iron making
and steel making waste with the addition of the binder which does not
require any heat treatment prior to charging in the blast furnace. The
briquettes are charged wholly or partially with the addition of sized iron ore
which does not disintegrate even up to 1400°C. Presently burden of blast
furnace consists of sinter (iron ore with size greater than 3mm with lime
stone/ dolomite, coke) coke and lime stone/dolomite. This involves very high
grade ore. Apart from this during mining of ore blue dust are generated. Also
during crushing of iron ore lot of dust is generated which is remained
unutilised and creates ecological problem. During iron making and steel
making dust are generated which is a potential hazard to the plant and
creates ecological problem.
SUMMARY OF THE PRESENT INVENTION:
The present invention revolves around developing the practical way involving
fine fraction of industrial waste like dust from iron making and steel
making, iron ore fines as well as fines of coke industries in the metallurgical
processing by means of briquetting. The essence of the concept is that the
fine fraction raw materials are not only given a new form with a required size
but also the briquettes obtain new qualitative characteristics. This process
involves mixing thoroughly the iron bearing fines with carbon containing
fines with the addition of plasticizer and binders and loading the mix into
the agglomerating aggregates. Extrusion is being performed by high
pressure with simultaneous degassing by vacuum application. The densified
charge mix is extruded through the die with single or multiple holes of
regular form having diameter 5-50mm and length 20mm to 100mm.
Briquettes are made with stiff extrusion which generates briquettes of a
given configuration and chemical properties, mechanical and hot strength
which maintains operational characteristics for distant transportation.
These briquettes are now charge material for the blast furnace after drying
at around 50-60°C along with coke and limestone/dolomite with or with out
sized iron ore. These briquettes do not crumble even at 1400°C and
maintain the bed permeability which makes the process energy efficient.
THE DISTINCTIVE FEATURES OF THE PRESENT TECHNOLOGY:
- High economic efficiency
- Total waste utilisation
- Ecological safety
- Reduced coke consumption
ADVANTAGES OF THE PRESENT TECHNOLOGY:
A. utilisation of different waste of metallurgical industries
B. Predicted and controlled strength of the briquettes
C. Produce briquettes of various configuration and weight.
D. Mineral binding agent which provides high hot strength even at
1400°C
E. Short production cycle of the briquettes
F. Low temperature treatment of the briquettes( Less than 50°C)
WE SHALL NOW DESCRIBE THE PRESENT INVENTION WITH
REFERENCE ACCOMPANYING DRAWINGS WHICH ARE GIVEN BY WAY
OF ILLUSTRATIONS BUT DO NOT RESTRICT THE SCOPE OF
INVENTION:
Figure 1 is briquettes as such
Figure 2 is briquettes after firing at 950 degree Celsius_ 2hrs
Figure 3 is iron pellets after fired at 1000 degree Celsius _2 hrs
Figure 4 is iron pellets after fired at 1100 degree Celsius _2 hrs
Figure 5 is iron pellets after fired at 1200 degree Celsius _2 hrs
Figure 6 is iron pellets after fired at 1300 degree Celsius __2 hrs
Figure 7 is iron pellets after fired at 1400 degree Celsius _2 hrs
Figure 8 is iron pellets after fired at 1500 degree Celsius _2 hrs
Figure 9 X200 Briquettes after firing at 950°C/2 hours
Figure 10 Briquettes after firing at 1000°C/2hours
Figure 11 X200 briquettes after firing at 1100°C
Figure 12 X200 after firing at 1200°C
Figure 13 X200 after firing at 1300°C
Figure 14 X200 After firing at 1400°C
Analysis of briquettes fired at different temperatures by X-ray diffracto
meter
The briquettes are fired at different temperature in reducing atmosphere.
The firing conditions are as under.
The briquettes are put inside a magnetite cylinder having diameter 150mm
and length 500mm. The briquettes are put along with coke breeze in
alternative layers. The bottom of the cylinder is plugged with perforated
blocks at a distance of 70mm from the bottom.Afetr filling the briquettes and
coke breeze the top of the cylinder is plugged with another perforated
blocks. Air is supplied at a pressure of 0.5kg/cm2 with a flow of around 5
litres /min through a hole in the bottom part of the cylinder. The whole set
up is fired in a electrically heated raising hearth furnace at different
temperature for 2 hours.
Phase analysis
Phase analysis is done by XRD with Copper target and nickel filter. The
results are as shown in of the accompanying drsiwngs;
Microscopic analysis
Microscopic analysis is done under reflected light in an universal microscope.
Photomicrographs after firing at different temperatures are given in Fig 9, 10, 11, 12, 13 & 14
Microscopic analysis is in close agreement with phase analysis by XRD. Secondary hematite
is formed during cooling. With the increase in firing temperature metallization increases.
Microscopic analysis reveals calcium ferrite appears as the first fluxing agent.
Degree of metallization by chemical method
Degree of metallization is studied after firing briquettes at different temperature and
compared with iron ore. The results are as under.
We CLAIM:-
1. Process for making briquettes utilizing iron making and steel making
waste as a charge material for blast furnace which comprises making
briquettes by stiff extrusion method consisting of dust of iron making
or steel making or iron ore fines, or any combination thereof, with or
without fluxing material and/ or fines of coking industries
characterise in that the percentage of iron ore fines is not less than
5% or more than 100%, iron making dust is not less than 5% or more
than 100%, steel making dust is not less than 5% or more than 100%
and the coke fines is not less than 5% or more than 30% adding to the
same binding material and/ or plasticizer such as herein described.
2 Process as claimed in claim 1 wherein plasticizer and binding
materials are selected such as bentonite or activated bentonite or any
known plasticizer the percentage of which is not less than 0.5% or
more than 3% and lime containing binder may be ordinary Portland
cement or Portland slag cement or pozzolana cement as binder and
percentage of which is not less than 2.5% or more than 15%.
3. Process as claimed in claim 1 wherein binder may be ordinary
Portland cement or Portland slag cement or pozzolana cement as
binder and percentage of which is not less than 2.5% or more than
15%.
4. Process as claimed in claim 1 wherein mixes are prepared and the
briquettes are made by stiff extrusion under vacuum and pressure.
5. Process as claimed in Claim 1 and 2 wherein slag must have the
affinity for absorbing impurities i.e. gangue from the charge along with
other deleterious impurities which affect the quality of hot metal the
blast furnace slag is essentially a low melting compound consists of
silica, alumina, calcia and magnesia.
6. Process as claimed in any of claims 1 to 5 wherein the other minor
constituents of slag depends on the quality of input which includes
Manganese oxide, sulphur, phosphorous and compound thereof.
7. Process as claimed in any of claims 1 to 6 wherein the slag is free
flowing at the operating temperature with high slag metal separation
with out entrapping metal. The slag generated is having a low fusion
temperature so that at the furnace operating temperature a high
available super heat will increase the kinetics of chemical reaction and
will ensure better slag metal separation from both physical and
chemical point of view.
8. Process as claimed in any of claims 1 to 7 wherein the bed
permeability is not impaired in cohesive zone due to high hot strength
of the briquettes.
9. Process as claimed in any of claims 1 to 8 wherein the optimization of
slag not only improves the metal quality by reducing the silicon
content in hot metal but also improves the fuel efficiency by
decreasing the gap between the onset of melting and flow ability of
slag imparting better permeability resulting in reduction of coke
consumption.
10. Process as claimed in any of claims 1 to 9 wherein the fines of
industrial waste like blast furnace dust or LD converter dust or iron
ore dust or any combination with the addition of binders with or
without plasticizer, is thoroughly mixed in a mixer to attain optimum
homogenisation, extrusion is performed by stiff extrusion technique
for the formation of briquettes by pressure with simultaneous
degassing the charge under vacuum. Fragmentation of densified
charge mix is being performed by extrusion through the die with
single or multiple holes of regular form having diameter of 5-50 mm
and length 10 mm to 100 mm the briquettes are air dried before
charging in to blast furnace wholly or with addition of sized iron ore/
pallets/ sinter.

ABSTRACT

Process for making briquettes utilizing iron making and steel making
waste as a charge material for blast furnace which comprises making
briquettes by stiff extrusion method consisting of dust of iron making or
steel making or iron ore fines, or any combination thereof, with or without
fluxing material and/ or fines of coking industries characterise in that the
percentage of iron ore fines is not less than 5% or more than 100%, iron
making dust is not less than 5% or more than 100%, steel making dust is
not less than 5% or more than 100% and the coke fines is not less than 5%
or more than 30% adding to the same binding material and/ or plasticizer