Sponge Iron Manufacturing
Sponge Iron Manufacturing
Sponge Iron Manufacturing
1. Sponge Iron is iron ore reduced directly in solid state using coal gas,
natrual gas or coal as reductants and is also known as Directly Reduced
Iron (DRI). The need for development and commercialisation of
sponge iron manufacturing process arose in late 50's when Electric Arc
Furnaces (EAFs) engaged in manufacturing steel started facing
problems of availability of scrap of desired quality, the traditional
source of their iron metallics. The DRI processes soon became popular
and since the inception of first DRI plant in 1957 in Mexico, there has
been a continuous growth of this industry in last three decades. This is
evident from the steep rise in world DRI production during the past
three decades. India, entered the sponge iron industry only in 1980,
when the coal based DRI plant of Sponge Iron India Limited (SIIL)
was commissioned at Kothagudem, in Andhra Pradesh.
2. The reasons for the tremendous growth of the sponge iron industry
world over could be attributed to the advantages of using sponge iron
in electric arc furnaces, partly substituting scrap, the conventional
charge to the furnaces. Further, the use of sponge iron in other steel
manufacturing processes has also been well proven. The advantages of
sponge iron use in EAFs are summarised below:-
Uniform known composition
Low levels of residuals/tramp elements
Capability to maintain phosphorous level in steel within 0.002%
Maintenance of sulphur in steel by its removal in sponge
manufacture.
Low content of dissolved gases
Uniform size and higher bulk density as compared to scrap
Capability of forming protective cover of foamy slag in the bath
Lower refining requirements of steel produced
Potential of sensible heat recovery from waste gases
Possibility of producing variety of steels
(iii)
Basic Oxygen Furnaces (BOFs), Induction Furnaces (IFs) and Cupolas.
There are a few disadvantages of the use of sponge iron in the arc
furnaces such as lower liquid metal yield, lower metallisation, lower
carbon content in sponge iron produced in coal based plants, gangue
content of the sponge iron resulting in additional requirement of
electrical energy in its melting and higher meltdown time. However, an
ever widening gap between the demand and availability of scrap
clearly indicates a bright future for the sponge iron industry.
(iv)
SPONGE IRON
(v)
Technologies using carbon monoxide as reductant
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reformer gas is recovered and used elsewhere in the process. For
the reduction, the reducing reformed gas is mixed with lean
reformed gas from the reactor after removal of its CO2 content,
preheated and used in shaft kiln reactor for reducing iron oxides.
The product sponge iron is cooled by counter current cooling
gas in cooling section from where the cooled product is removed
continuously.
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Raw Material ; Direct reduction processes are very sensitive to
chemical and physical characteristics of raw materials used in the
process. Iron ore or pellets, reductant natural gas or non-coking coal
and limestone/dolomite are the main raw materials. For the successful
operations the process licensors of DR technology have specified the
characteristics of the raw materials to be used in the process. The
quality requirements of the raw materials in general are:
Iron Ore : Lumps or pellets with high iron content, low gangue content,
good mechanical strength, readily reducible and of non decrepitating
variety.
Natural Gas and Non-coking Coal : These are the reductants in the
process. The characteristic desired for non-coking coal are that the
non-coking coals should have high fixed carbon content and high
volatiles content. Ash, sulphur and moisture in coal should be low.
The ash fusion point of coal is required to be high. The coal should be
highly reactive and should have low coking and swelling indices.
(viii)
Boiler feed water system
Inert gas generation system
Raw materials and product handling systems
Instrumentation and control system
12. The basic capital equipment required for the coal based processes is:
14. As far as gas based plants are concerned, the design and manufacture
of non-proprietary items, except for the critical items like process gas
compressors and briquetting machines can be done indigenously. As
indicated by MECON, some proprietary items can also be
manufactured indigenously based on basic design from the proprietors.
In respect of coal based plant, capability has been developed in the
country for manufacturing almost 100% of equipment required for
plants upto capacity of 1,00,000 TPA sponge iron.
(ix)
15. The capital investment made by existing DRI plants is summarised
below:
16. The existing coal based sponge iron units in the country include the
plants of SIIL, OSIL, IPITATA, BSIL AND SISCL. The total installed
capacity of the existing coal based plants is 5.85 lakh TPA. The gas
based plant of Essar Gujnarat based on Midrex technology having a
capacity of 8.8 lakh TPA comprises two modules. The first module
was commissioned in March '90 while the second was commissioned
in July 1990. Most of the existing plants have plans to expand their
capacities. The additional planned capacity of existing coal based
plants is 5.2 lakh TPA while EGL's plant is planned to have an
additional capacity of 7.2 lakh TPA. Grasim Industries, Goldstar, Ispat
Group, Bharat Forge, Usha Rectifier, Jindal and Mukand are some of
the other companies having proposals for putting up large capacity new
plants. Thus, the installed capacity of sponge iron at present including
that of EGL plant is 14.65 lakh TPA. The capacity is likely to go over
6.6 million TPA by 1994-95.
17. Sponge Iron India Limited : SIIL selected SL/RN DR technology for
their plant. They absorbed the imported technology through R&D
efforts carried out in course of overcoming some of the initial
problems in their first unit of 30,000 TPA installed in 1980. Beside
this SIIL were also able to carry out number of innovations in process
and equipment design to improve productivity and product quality and
to reduce raw material consumption levels. This enabled them to
engineer, erect and commission their second D.R. kiln in 1985. Today
SIIL is equipped with all the R&D facilities for testing of raw
materials and an Engineering Division capable of providing complete
services for design, erection and commissioning of coal based DR
plants.
(xi)
Plant SIIL OSIL IPITATA BSIL SISCL
Production:
Period 1989-90 1987-88 1988-89 (15 1990-91 No commer-
months) (7 months) cial pro-
duction
Tonnage 52930 89000 68937* 71.300
Cap. Utili- 88.0 65.9 61.0 81.0
sation %
Av. Metalli- 90+2 90 90 91-92
sation %
Consumption /ton of DRI
Iron ore t 1.90-1.95 1.45 1.54-1.77 95% yield
NC Coal t 1.50-1.55 1.1 to 1.15 1.20-1.53 0.45 CFix/Fe
ratio
Water Cum 10.0 7.0 7.0
Power kwh 155-170 141 140 80
*Since August '90, production higher than rated capacity
18. Orissa Sponge Iron Limited : The OSIL plant is based on ACCAR
technology of Allis Chalmers Corporation of USA. The technology
uses non-coking coal and HSD. The installed capacity of plant was
150,000 TPA. During the initial years of operation, OSIL faced a
number of problems in plant operations, but with dedicated research
and development, they have been able to solve many of the problems
and in the process, were successful in absorbing the technology. The
main problems faced were the accretion or ring formation in the kiln,
poor metallisation of the product and higher coal consumption.
OSIL were successful in overcoming the problem of accretion and poor
metallisation by controlling the raw material feed and the temperature
profile of the kiln. For reducing the high consumption of coal, OSIL
modified their coal feeding system by introduction of coal slinging
from the kiln discharge end and achieved the desired results.
19. Ipitata Sponge Iron Limited : Ipitaita is the first plant where
indigenously developed direct reduction technology was put on
commercial scale. The plant was commissioned in 1986 and since then
there had been a number of problems in the plant operations. The main
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problem faced was continuous failure of kiln refractories. With
continued efforts for improvisation and technical assistance from
Lurgi, Ipitata were able to overcome all the problems. Presently,
Ipitata is achieving production levels of more than the rated capacity
indicating that the TDR technology has now been fully proven.
20. Bihar Sponge Iron Limited : BSIL plant at Chandil, Bihar is based on
SL/RN technology of Lurgi, GmbH, West Germany. The plant was
commissioned in April 1989 and during the first year of operations,
there were no major problems in respect of the process and the desired
quality of the product was obtained. During the current year, the plant
is operating with capacity utilisation of over 80%. BSIL technical
personnel have been fully trained and have absorbed the imported
technology.
21. Sunflag Iron & Steel Company Limited : The plant belonging to
SISCL has an installed capacity of 1,50,000 tonne per annum and is
based on CODIR process. The plant production is planned to be used
in the Company's own downstream EAF facility. The plant was started
in August 1989. The plant operations are yet to be stabilised. Constant
efforts are being made to adapt the technology to local conditions
especially those of highly variable quality of the raw materials.
22. Since, the development of DR. processes in late 50's. there had been
tremendous growth of sponge iron industry all over the world. The
process licensors have utilised their long operating experience to
remove the initial technical lecunae and brought the technologies to
near perfection. Through constant research and development work,
many improvements in technologies have also been brought about,
such as :
(xiii)
Iron (HBI) has opened new avenues to DRI like oxygen steel
making and foundaries. Many of the Midrex plants also have
achieved capacity utilisation of over 100%.
iv) SL/RN technology of Lurgi GmbH is the most favoured coal
based technology and 31 units at 10 different places with a
total annual installed capacity of over 4.8 million tonne are
operating on this technology.
23. The other coal based processes, namely CODIR process of Krupp
MDH. DRC process of Davy Mckee, ACCAR process of Allis
Chalmers/Boliden and indigenously developed TDR technology have
only limited commercial application. Out of these, CODIR process,
which had only one plant to its credit in South Africa, has some
commercial success recently. SISCL's plant based on this technology
has just been commissiosned and two more plants are under
construction and would be ready in 1991 and 1992 respectively. Only
one plant each is operating on DRC (Scaw Metals, S.A.), ACCAR
(OSIL, India) and TDR (Ipitata, India) processes. Jindal Strips
Limited are installing plant based on their recently developed coal
based technology.
24. Most of the available DR technologies both the coal based and gas
based have been so far imported in the country. The gas based
plants on imported technology have been commissioned recently but
the plants based on solid reductant technologies have been erected,
commissioned and operated for quite some time and the plant operators
had good opportunity of technology absorption. They have been able
to overcome the technological problems in the initial stages and bring
about certain improvements in the operations. Sponge Iron India
Limited, the first entrants in the sponge iron field, have also
engineered, erected and commissioned the second DRI unit and with
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this experience they are offering technology and engineering services
for setting up coal based DRI plants up to 30,000 TPA capacity with
98% indigenous equipment.
25. Indigenously developed TDR process have now been proven and the
technology is available for setting up of plants up to 90,000 TPA
capacity. Indigenously developed technology of Jindal Strips Limited
is being adopted at their Rigarh plant in M.P. Jindals are also using
100% indigenously manufactured equipment. The capacity of each of
the two units being installed is 100,000 TPA. This indicates that there
are no technological gaps in respect of coal based technologies
especially for the plants of capacity up to 100,000 TPA DRI. As
regards the gas based plants, the reforming of natural gas with steam is
not new to Indian industry and the knowhow for engineering, erection
and commissioning of the same is available in the country. But
technology for gas reforming by reactor top gas used in Midrex
process is not available in the country.
(xv)
based Midrex technology, though commissioned recently, has
achieved rated capacity in a short time.
27. The following recommendations are made to ensure the desired growth
of the industry:-
i) Adopting indigenously available technologies for settingg up of
coal based DRI plants.
ii) For gas based, technology may have to be imported. In that case
negotiations may be held for maximum indigenisation of the
equipment and time bound arrangements of technology transfer.
(xvi)