Iron Making Technology: ITMK3

Introduction

In 2006, India produced 50 million tonnes of crude steel and was ranked the 5 th

largest steel producer in the world. The industry is growing very fast and in all likelihood India will attain the 2nd place, next to China, by the middle of the next decade. The National Steel Policy, 2005 projected a production of 110 million tonnes by 2019-20. Subsequent estimates however, reveal that India’s production would surpass this projection. According to a recent analysis in the Ministry of Steel, it is found that the 100 million tonnes mark would be achieved much earlier, by 2011-12 itself. Going by this expansion mode, India’s production by 2020 is projected at around 200 million tonnes. A closer look at the world steel production reveals that there is an upward trend in the production of steel by Electric Furnace route. The contribution of this route has increased from 20 per cent in 1980, 28 per cent in 1990 to 32 per cent in 2006. In tandem with the world trend, the contribution of electric furnace is also increasing in India and the percentage contribution of electric route was approximately 50 per cent in 2006-07. From the assessment of the process routes of the upcoming steel plants, it is noticed that the share of electric steel production would remain in the range of 45-50 per cent in 2011-12 and beyond.

One of the major constraints of the Indian steel industry, particularly the electric furnace industry, is the availability as well as cost of metallics. Barring two units, which are dependent on hot metal, all other units use solid metallics viz. scrap and direct reduced iron (DRI), commonly called, sponge iron. Domestic generation and availability of steel melting scrap is limited and hence substantial quantity, 1.5-3 million tonnes, is imported annually. The silver lining however is, the fact that India is well placed in the production of DRI. During the last consecutive three years, India has been the largest producer of sponge iron. The actual production in 2006-07 was 16 million tonnes, which is likely to grow to over 25 million tonnes by 2011-12. The industry however, needs to address the following issues to ensure its growth undeterred: Limited availability of iron ore lumps/pellets, which is essential input in gas

based, or coal based DRI plants. Limited availability of non-coking coal of required specification/grade, and Limited availability and high price of natural gas.

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These constraints together with the present trend to use clean tramp free inputs for high quality steel production have led to development of certain alternate inputs to meet the raw material related challenges for electric steel making. Additionally, quality related issues like low metallization and high gangue content, particularly in coal based DRI, and associated higher energy consumption in steel making are significant and needs to be addressed to. Yet another issue is the environmental emission and waste disposal. In the face of these constraints, the steel industry in general and the electric steel making industry in particular needs alternative solutions to sustain its growth both in the short term and long term perspective. Hot metal produced in conventional blast furnace appears as one of the appropriate solutions. However, in view of constraints like scarce availability and high cost of coke/coking coal, requirement of lumpy iron ore or agglomerated fines etc., the newly developed smelting reduction technologies like COREX, FINEX, HI-smelt etc for production of hot metal are gathering attention. Yet another technology, which appears promising in light of growing demand for metallics particularly by the electric furnace industry, is the ITmk3 technology, product of which is called iron nuggets. This technology is not dependent on lumpy ore or conventional pellets and its economic capacity suit well with the mini steel mills.ITmk3 Technology

ITmk3 is pronounced as “Eye-Tee Mark Three” and stands for “Iron Making Technology Mark Three”. It is a unique technology developed and owned by Kobe Steel Limited, Japan for smelting iron ore fines using non-coking coal to produce premium grade iron in the form of nuggets. Unlike traditional technologies of iron making, ITmk3 represents a revolutionary change in the way iron is made as also the product quality. In effect, it may be considered as a new source of iron particularly, for electric steel making.

The Process:The heart of the ITmk3 process is the Rotary Hearth Furnace (RHF) where iron ore fines is reduces and smelted using pulverized coal. The process flow sheet below depicts various units and sub-units used in the ITmk3 process:

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The steps of iron ore reduction and smelting in the ITmk3 process are given below:

Iron ore fines, Flux and pulverized coal are mixed in a mixer.

Mixed inputs are converted into carbon composite green pellets in a pelletizer.

Pellets are dried at a temperature of around 180 deg. C using preheated air which is heated by exhaust gas of the furnace.

In the RHF, the carbon bearing composite pellets are gradually heated up using natural gas. The smelting reduction process involving reduction and smelting takes place in stages. In the last zone, the temperature is raised to 1350-1450 degree centigrade, thereby melting the iron and its easy separation from the gangue in the form of slag.

The following reactions takes place when the carbon composites pellets are heated to the reaction temperature:

FexOy +y CO=x Fe +y CO2 CO2+C=2CO C(s)=C{carburised)

Fe(s) = Fe(molten)

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The series of reactions are completed in around 10 minutes. To begin with (after approx. 3 minutes), pellets are converted into DRI with unreacted core which later ( after 5 minutes) convert into a dense metallic iron shell containing molten slag and large void space. Immediately thereafter, the metallic iron melts and starts separating out from slag and by around 9 minutes, there is complete separation of iron and slag.

In the last two minutes of the process of the RHF, the molten iron and slag are cooled which further cooling in the cooler follows. The solidified iron nuggets are separated from the slag with the help of a magnetic separator.

The sensible heat of the off gas from the RHF is substantially recovered by a recuperator thereby heating the air for combustion of natural gas used in the process. The hot air is also utilized for drying the green pellets.

Raw Material and other inputs

The three main inputs are iron ore fines, coal and fluxes. Generally, pellet feed grade iron ore fines are used as it is and sinter feed ores is ground to the pellet feed grade. Coal is ground to minus 200 mesh over 80%. Coal is the reductant for conversion of iron ore into iron and also serves as the main source of heat. The quality and quantity of flux is determined based on the nature of iron ore and coal. Besides coal, natural gas is another heat source, which is burnt in the RHF to heat up the pellets. In place of natural gas, furnace oil could also be used in the process.

Product Characteristics

The quality of Iron nuggets depends on the quality of iron ore and coal used in the process. However, typically, iron nuggets are highly metalized product containing over 97% metallic iron with very low phosphorous. A typical composition of nuggets is given in the table below:

ELEMENT % COMPOSITIONMetallic Iron(Fe) +97Carbon(C) 2-2.5Sulphur(S) 0.07-0.10Phosphorus(P) 0.01-0.02

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Unlike blast furnace where phosphorous removal is minimal; in ITmk3 process, phosphorous removal is substantial leading to a very low content of phosphorous in iron nuggets. This is mainly because of shorter reaction time, essentially around 6 minutes, and iron and slag are separated after 2 minutes cooling time. In other words, the operation does not reach equilibrium to allow phosphorous to transfer to the metal. It has in fact been established in one of the experimental study of the ITmk3 demonstration plant that if iron and slag are allowed to stay together longer, phosphorous content of metal was much higher.

Evolution of ITmk3 Process

The ITmk3 process is the result of extensive research and investigations over several years since 1996 which are enumerated below:

The concepts were tested using iron ore and coal from different sources.

In 1999, a pilot plant of capacity 3000 tonnes per annum (Diameter: 3 M and Hearth Width 0.8 M) was constructed in 1999 at Kakogawa Works of Kobe Steel, Japan to prove the process concept. Iron nuggets were successfully produced and a large number of trials were conducted using various types of iron ore and coal during 1999-2000.

Based on the successful results, a limited company namely, Mesabi Nugget, LLC ( MNC) was incorporated at Minnesota, USA in September, 2001 to construct and operate a Pilot Demonstration Plant (PDP). This was a joint venture effort of Iron Units LLC, a subsidiary of Cleveland-Cliffs Inc, Ferrometrics Inc, Kobe Iron Nuggets LLC, a subsidiary of Kobe Steel, USA and Ferrous Resources LLC a subsidiary of Steel Dynamics Inc, The state of Minnesota provided the construction cost and the operation cost of the Mesabi Nuggets Project was supported by the US Department of Energy. The 25,000 TPA Pilot Demonstration Plant (Diameter: 12 M and Hearth Width: 2 M) was commissioned in May, 2003 with a total capital cost of US$ 16 million and iron nuggets were produced on 24th May, 2003. After the start-up, the PDP was operated for 230 days with shortest campaign of 38 days and the longest of 81 days and produced 9500 tonnes of iron nuggets. The nuggets were supplied to Steel Dynamics Inc, USA for

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conversion into steel in its Electric Arc Furnace. During this campaign, a wide variety of iron ore and coal were tested and economics were studied.

Encouraged by the successful operation of the PDP, Mesabi Nugets, LLC is now setting up a 5,00,000 TPA (Diameter: 60 M and Hearth Width: 7.6 M) large scale demonstration plant/commercial scale plant at Minnesota, USA.

Kobe Steel is further exploring setting up of such commercial plants in Ukraine and Russia as well as India.

Techno-economic analysis of ITmk3 Technology

The process is simple with a single stage furnace operation requiring less energy, capital and operating & maintenance cost as compared to conventional BF iron making, avoiding thereby coke oven, sinter/pellet plant… The process is also flexible permitting use of a wide variety of iron ore and non-coking coal. The product quality having less gangue and more carbon is superior to DRI. The nuggets could be directly charged into electric arc furnace or basic oxygen furnace as a pure iron source instead of scrap or pig iron. The physical and chemical characteristics of nuggets help in easy handling, efficient melting, energy saving and higher productivity. The process is unique in that nearly all the chemical energy of the ingredients foil fuel is consumed and no gas credit is exported from the RHF. This is an important difference from that of blast furnace process or even the alternate iron making processes. As a result, energy consumption for production of nuggets adopting ITmk3 technology is much lower. The process is more environment-friendly and emits much less Green House Gases or Particulate Matters when compared to conventional iron-steel making processes.

The estimated investment cost of the Large Scale Demonstration /Commercial plant is US$ 150 million. In other words, the specific investment cost works out to US$ 300 per tonne of installed capacity, which appear attractive as compared to conventional blast furnace or DRI plants of equivalent capacity. However, based on presently available information and knowledge, it is apparently clear that benefits of lower investment and lower operating cost of ITmk3 technology would get eroded if scale of operation crosses the million tonne limit, when conventional processes would become more economical.

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Relevance of ITmk3 in India

India is blessed with large reserves of iron ore and is the fourth largest iron ore producing country in the world. However, over 60% of its total production are fines. Due to limited agglomeration capacity, indigenous utilization of iron ore fines is limited and therefore, substantial portion, nearly 80% of total, is exported. Besides, there are problems of utilization of tailings. ITmk3 provides a unique opportunity for the iron ore producers in India for adding value to such iron ore fines for utilization in Electric furnaces as well as basic oxygen furnaces as partial substitute of scrap and pig iron. Attracted by the features of the ITmk3 technology, several iron ore companies have already signed MOUs with Kobe Steel Ltd and Tokyo Boeki Development Ltd. (TBDL), Japan. Further, Mukand Ltd, Mumbai has signed an MOU with Kobe Steel Ltd. to be an exclusive licence contractor to set up ITmk3 plants in India. However, all these MOUs are at preliminary stage and the entrepreneurs are watching further developments towards commercial exploitation of the technology and results thereof.

During the laboratory investigation, pilot plant as well as pilot demonstration plant stage, a variety of iron ore (Fe: 62-68%) from Brazil, Chile, Australia and South Africa and coal (Ash: 8 –10%) from Canada, USA and South Africa as well as low volatile coke breeze have been tested to evolve best operating practices and economics of operation. However, no Indian iron ore or coal has been tested. Most of the Indian non-coking coal are of high ash and low fixed carbon and therefore, may not be suitable for this process. Impurities in iron ore adversely affect the operation and economics of ITmk3 process almost similar to that of blast furnace. Laboratory investigations are therefore, required to establish the suitability and economics of operation of ITmk3 process using low or medium grade Indian ore abundantly available in India. Alternately, the ores need to be beneficiated to produce suitable concentrate for the process. To resolve this problem, Kobe Steel is planning to take up laboratory investigation of Indian ore in collaboration with Mukand Ltd.

Conclusion

ITmk3 is a newly developed technology conceptualised in the 90’s. Within this short span of time, it has created its impact amongst the entrepreneurs and iron

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ore miners in India and abroad. It is a flexible, economical and environment-friendly process, which enables utilization of iron ore fines and non-coking coal without going in for calibrated lumpy or agglomerated fines and expensive coke as used in conventional blast furnace route. The process is thus promising and if proven commercially, for which efforts are already on; it may be an ideal vehicle for iron ore mining companies and others to convert iron ore fines to value added nuggets, an ideal feedstock for electric steel making as well as the basic oxygen furnaces. However, much will depend on the results of the commercial plant under installation in Minnesota and adaptability of the technology to Indian raw material particularly, non-coking coal.

Acknowledgements

The author deeply acknowledges the help and support of Dr. Takuya Negami, Director (Engineering) and Advisor, Kobe Steel Ltd., Japan and Mr. Takeshi Ue, President & CEO TBDL, Japan. The views and opinions expressed in this article are strictly of the author and not of the organization of his Employment

References

1. State-of-the Art Clean Technologies ( SOACT) for Steel making Handbook of Asia Pacific Partnership on Clean Development & Climate.

2. Mesabi Nugget- The New Age of Iron: by Jaffrey A. Hansen, MNC, Minnesota, USA.

3. Evolution of Ironmaking Technology: by Takuya Negami, Director ( Engg) & Advisor, Kobe Steel Ltd, Japan.

4. Development of ITmk3 Process: by Hidetoshi Tanaka, Isao Kobayashi, Osam Tsuge, Shoichi Kikuchi, Koji Tokuda and Shuzo Ito, Kobe Steel Engineering Company, Japan.

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