|Title of Invention||
AN ECOFRIENDLY, ENERGY EFFICIENT METHOD OF STEEL PRODUCTION FROM IRON ORE EMPLOYING LOW GRADE COAL
|Abstract||Heretofore low grade coal had hardly any metallurgical or other industrial applications. With depletion of coal reserve with high carbon content, attention was given to low grade coal but gainful mode of utilization was not forthcoming. The present invention has made a considerable advancement in this field and provides an eco-friendly, energy efficient method of steel production from iron ore employing low-grade coal, wherein (a) iron ore mixed with low-grade non-coking coal and flux are charged into a rotary reactor to produce sponge iron; (b) sponge iron thus produced is fed into an iron-smelting unit to which is added carbon and flux for removal of impurities, residual reduction and carburization; (c) transferring the molten mass to steel making unit with additional sponge iron for production of crude steel and (d) subjecting the crude steel to refinement in refining vessel or vessels to give rise to refined steel, characterized in that the Fixed Carbon Content of the low-grade non-coking coal may be as low as 15% by wt and the waste! combustible gases, waste coal fines and char generated in the course of sponge iron production is utilized for power generation, simultaneously ensuring trapping of fines in suitable receptacles to ensure substantial prevention of environmental pollution.|
|Full Text||The present invention relates to an eco-friendly, energy
efficient method of steel production from iron ore employing low
grade non-coking coal. More particularly, this invention
pertains to steel production using low grade non-coking coal with
fixed carbon content as low as 15% by weight to heat iron ore and
limestone/dolomite in a reactor under reducing conditions to
remove oxygen and sulphur from iron ore. The product called
sponge iron is then smelted together with fluxes in a furnace
using power generated from waste energy recovered from the sponge
iron plants and remove impurities like silica and alumina. This
molten iron together with additional sponge iron is then melted
and refined in a steel making furnace and further refined in a
refining furnace as necessary to make steel to meet quality
requirements for the steel products.
Procedures for steel making hitherto followed are based
mainly on reductive extraction of iron from iron ore like haematite
or magnetite or a mixture of both (Fe2O3/Fe3O4), attended with
removal of impurities like alumina (N2O3) and silica (SiO2).
Steel making is essentially two-step process, namely, iron ore to
metallic iron and then iron to steel.
Different routes of iron steel making practised till date
may be enunciated as follow :
a) In one route, oxygen is removed from iron ore without
melting it using either non-coking coal/coal gas or
natural gas. Removal of oxygen from the ore makes it
porus and the product is called sponge iron. This
sponge iron is then melted to remove other impurities
like alumina and silica in an electric steel making
vessel to make Steel, which may be further refined in
a refining vessel.
b) In another route, oxygen and impurities like alumina
and silica are removed by melting iron ore together
with coke and limestone in a iron making furnace e.g.
Blast Furnace where oxygen is removed as a gas when
carbon combines with oxygen while lime form limestone
combines with alumina and silica to from a slag which
floats over the molten iron and is removed by skimming.
The molten iron is then taken to a steel making
converter to make steel, by removing excess carbon,
phosphorous, silicon etc. by blowing oxygen. Further
refinement may be carried out in a refining vessel.
c) In yet another route, molten iron from Blast Furnace
and Sponge iron are melted together in an electric
furnace to make steel and may be further refined in
a refining vessel.
d) Several other processes are either under
development or are in commercial operation using
iron ore lumps or fines and high grade low-ash
non-coking coal together with oxygen to produce
molten iron as an alternate to the Blast Furnace route
in an effort to remove dependence on coke and thereby
on coking coal, reserves of which are only a fraction
of the reserves of non-coking coals in the world. The
molten iron is then taken to a steel making converter
and to a refining vessel for further refining as
The aforesaid routes of steel making may be represented by
means of flow sheet diagrams as shown in Figs. 1, 2, 3 and 4 of
the accompanying drawings.
These steel-making procedures invariably suffer from
drawbacks which are enunmerated in a tabular form as shown
CONVENTIONAL METHODS DRAWBACKS
a) Electric Steel making : Lower yield and higher energy
using primarily Sponge consumption; consequent cost
b) Converter steel using Blast : Dependence on coking coals,
Furnace Hot Metal higher costs.
c) Electric steel using partly : Dependence on high grade
Blast Furnace Hot Metal and coking coals, higher costs,
d) Converter steel using smelter : Dependence on high quality
based Hot Metal non-coking coals.
The present invention attempts to overcome the shortcomings
stated above and provide a viable alternative route for steel
The principal object of this invention is to provide an eco-
friendy, energy-effective method of steel production.
A further object of this invention is to provide a method of
steel production wherein there is used low-grade non-coking coal
with as low as 15% carbon-content and ash content as high as 40%.
Thuselliminating the need to use coking coal and traditional
A still further object of this inention is to provide a
method of steel production wherein the waste gases and waste coal
generated in the course of production of sponge iron is employed
for generation of steam which in turn is used for producing
electricity in a power plant.
Another object of this invention is to provide a method
of steel production which ensures substantial elimination of
dust/fines emission to prevent environmental pollution.
Yet another object of this invention is to provide a method
of steel production which employs a mixture of hot metal and
sponge iron produced in the smelting unit not being a Blast
Furnace (e.g. Submerged Arc Furnace) before being sent to steel
making and/or refining unit.
The foregoing objects are achieved by the present invention
which provides an eco-friendly, energy efficient method of steel
production from iron ore employing low-grade coal, wherein -
(a) iron ore mixed with low-grade non-coking coal and flux
are charged into a sponge iron plant to remove bulk of
the oxygen and sulphur;
(b) sponge iron thus produced is fed into an iron-smelting
unit to which coke and further amounts of flux are
added for removal of other impurities, residual
reduction and carburisation etc;
(c) the molten metal is then processed further in a
steel making unit together with additional sponge
for production of crude steel;
(d) the crude steel is refined in a refining vessel to
produce refined steel,
characterized in that the low-grade non-coking coal may have
carbon-content as low as 15% by wt. and waste gases and waste coal
fines/char generated in the course of sponge-iron production is utilised
for power generation, simultaneously ensuring trapping of fines
in suitable receptacles to ensure substantial prevention of
The overall procedure of the subject invention has been
represented by the flow-sheet diagram as shown in Fig.5 of the
drawings and the sequential steps of the process are given below.
1. PRODUCTION OF SPONGE IRON
Coal based sponge iron is produced using sized iron ore,
together with sized coal heated in a rotary kiln under reducing
atmosphere through controlled distribution of air and coal. The
kiln is rotated at a controlled speed to ensure adequate reduc-
tion time to achieve the desired degree of oxygen removal from
iron ore. The chemical reactions are represented by the following
Fe2O3 + C = 2 FeO + CO
FeO + CO = Fe + CO2
CO2 + C = 2 CO
C + O2 = CO2
CO2 + C = 2 CO
The chemical reactions are either exothermic or endothermic
and therefore require close process control to limit incidence of
The energy content in waste process gases are recovered in
a waste heat recovery boiler before releasing the same to environment
through a full stack. The steam at high temperature and pressure
is utilized to generate electricity which subsequently is used in
Coal based sponge iron is also produced by using reducing
gasses such as those produced during gasification of coal,
either in a rotary kiln or in a shaft furnace.The degree of
metallization usually exceeds 90%. Coal based sponge iron has a
typical composition as follows with a very low carbon content.
Metallic Fe : 82%
FeO : 12%
Silica, Alumina and other impurities : 6%
Typical range of composition of ore and coal used are given
Iron ore : Fe : 63-66%
Silica + Alumina : 4-6%
Non-coking coal : Fixed carbon : 15-40%
Ash : 25-45%
2. COAL BENEFICATION
The use of low carbon and high ash coal as feed is
beneficiated to reduce ash content to less than 30% and increase
fixed carbon content.
3. POWER GENERATION
Electric power is generated using waste energy recovered
from the off gases as well as from the waste coal fines and
coal char generated as process by-products in the iron and
steel plants which can meet nearly the entire electric energy
requirement of the plant. Grid support is typically taken to meet
power surges required during arcing etc. and to meet emergency
needs. Total power generation is approximately 1000 KWH per tonne
of sponge production.
Step-11 : PRODUCTION OF MOLTEN IRON
Sponge iron is smelted in an iron smelting furnace in
presence of fluxes to remove alumina/ silica and other impurities
as slag. The molten metal is carburized by using a carbon source
such as petroleum coke, nut coke etc.
Step-Ill : STEEL MAKING
(i) Molten iron is converted into steel in a steel making
vessel using either nearly 100% liquid iron or a mix
of liquid iron and sponge iron. The steel making
vessel will have the necessary features required for
(ii) Further refining can be done in a refining furnace with
or without power to meet quality requirements of the
end products. Further refining processes include,
inter alia, ladle refining, vaccuum degassing, etc.
DEGREE OF PURITY OF PRODUCT
The process envisages the provision of steel refining
vessel e.g. Laddie Refining Furnace together with vacuum
degassing when required by the product specification. This
ensures cleanliness of the product through argon purging,
deoxidation through Si-Al killing and further of entrapped
gasses by vacuum degassing as necessary.
The process is eco-friendly. The sulphur in coal is removed
by using dolomite/limestone in the sponge iron kiln. Lime reacts
with sulphur to make calcium sulphide, which together with charred
remains of coal are removed by magnetic separation after sponge
iron along with the wastes is cooled in a cooler.
NCL generation is reduced by use of relatively low
temperature processes. For example, the sponge iron process
operates at around 1000°C.
CO2 generation is comparable to the standard BF + BOF route.
The process utilizes waste energy recovered from Sponge
iron making, liquid iron making, as well as steel making for
heating as well as electric power generation.
To sum up, the present invention is concerned with a method
of making steel capable of using even low quality non-coking coal
for production of sponge iron, smelting part or all of sponge
into hot metal in an iron making furnace, and using hot metal
itself or in admixture with more sponge in a steel making furnace
to make steel. Thereafter the steel is refined in a refining
vessel as desired or necessary. The result is attainment of a
higher metallic field a lower cost of production, as well as a
low energy consumption and a cleaner environment with
substantial prevention of emission of greenhouse gases.
SUMMARY OF ADVANTAGES/DISADVANTAGES
The following table summarizes the advantages/disadvantages
of the new method compared to Blast Furnace and Basic Oxygen
converter route of steel making from iron ore treated as the
of iron Total energy
emission Cost of
BF + BOF 100 100 100 100
New Method >101 The principle used for calculating energy consumption is
based on guidelines of IPCC 2006, an international body. (Inter
Government Panel for Climate Change).
Additional modifications and improvements of the present
invention may also be apparent to those skilled in the art.
Thus, the particular combination of parts/steps described and
illustrated herein is intended to represent only one aspect/
embodiment of the present invention, and is not intended to
serve as limitations of alternative features within the spirit
and scope of the invention.
Dated this 12th day of February, 2008.
|Indian Patent Application Number||235/KOL/2008|
|PG Journal Number||02/2012|
|Date of Filing||12-Feb-2008|
|Name of Patentee||ORISSA SPONGE IRON & STEEL LIMITED|
|Applicant Address||CHATTERJEE INTERNATIONAL CENTRE, 11TH FLOOR, 33A, JAWAHARLAL NEHRU ROAD, KOLKATA|
|PCT International Classification Number||C21B13/00|
|PCT International Application Number||N/A|
|PCT International Filing date|