Iron Making in Mini Blast Furnace (MBF)

The Blast Furnace ironmaking process had, until recently, been the unchallenged method of making hot metal on a large scale. Till 1990, the blast furnace route of ironmaking had about 97% (527mt) share of global iron production. Since then many other alternative processes of iron making have arisen e.g., Shaft Furnace DR processes (MIDREX, HyL), Rotary Kiln DR processes (SL/RN, CODIR, TDR), and recently the COREX Smelting Reduction process. The Mini Blast Furnace (MBF) is the most proven technology, as revealed by one recent global iron production data. While gas-based as well as coal-based DRI production routes produced 2.7% of total iron production in 1990 - 1991, the corresponding share held by MBF, operating mainly in Brazil, China and India, was 3.4%.

Mini Blast Furnaces (MBFs) are ideally suited to small scale operations. A Mini Blast Furnace (MBF), which can be viewed as is a miniature version of conventional large blast furnace, also has a few additional characteristic features known for their simplicity and economy. Since MBFs are small (working volume ranges between 100 - 370 m³ corresponding to production capacities of hot metal between 60000 - 200000 tpa) blast furnaces, the technology involved is not only well proven, but also very sophisticated. Smaller scales of operation allows the use of inferior grade coke and iron ore (sinter usage is difficult). Mini blast furnaces are becoming increasingly as an economic and reliable source of iron for foundries as well as for forward integration with steelmaking units in EAF / EOF (and sometimes even small BOF) based steel plants.

The products from mini blast furnaces are of the same quality as that of normal Blast Furnaces and are free of tramp elements - this is of particular advantage in steel making in mini steel plants. Use of 40 - 45% hot metal in EAF (Electric Arc Furnace) charge has thus become standard practice, which has helped to reduce the power consumption in Electric Arc Furnaces to 380 - 400 kwh/t liquid steel from 550 - 600 kwh/t. At the same time, sine the hot blast temperature in MBFs is lower than normal blast furnaces and the specific heat loss is more, the coke rate tends to be 100 - 150 kg/thm higher.

The biggest limitation of mini blast furnaces is that coal injection is normally difficult and the higher specific heat requirement has to be met entirely by coke (normally purchased from external sources).

In India, with the recent increasing demand of pig iron and steel, mini blats furnace technology has proliferated. Kalinga Iron Works is successfully operating three small blast furnaces with volumes less than 100m³ each, an MBF of 175m³ capacities was commissioned in Goa in 1992 and nine more mini blast furnaces with installed capacity of 0.80 Mtpa of foundry pig iron and 0.10 Mtpa of basic grade are already operational. These units are spread all over the country. If this trend continues, which is more likely to happen, Mini Blast Furnace Technology would play an increasingly important role in the rapid and wide spread growth of iron and steel making capacity in this country.

Brazil has a large hot metal production through mini blast furnaces which use charcoal as a reducer and an energy source. These companies are not integrated and their final product is pig iron. The growth in this sector started in Brazil in the early 1970's as a result of the availability of cheap and good quality raw materials (native wood charcoal and granulated iron ore). In addition, the return of the investment in the construction of Mini Blast Furnace was very fast. Nowadays, this sector is consolidated and has a fundamental role in the national and international iron and steelmaking sector since Brazil is a major supplier of primary iron.

Plant availability as well as the perfection achieved in technology, made Mini Blast Furnaces a well accepted iron making route in China. The situation in India could be similar in future. Presently, about one fifth of China’s total iron production is through about 55 - 60 MBFs. The furnaces in China use metallurgical coke, and the coke rates vary between 500 - 630 kg/thm. Extensive innovations have been introduced in the Chinese Mini Blast Furnaces including:

• Injection of pulverized anthracite to the extent of 60 kg/thm, to bring down the coke rate by about 40 - 50 kg/thm.
• Heat recovery from stove waste gas at 250-300^OC for increasing the hot blast temperature by about 80^OC.
• Incorporation of self-preheating process stoves, enabling the generation of hot blast with a temperature of more than 1200^OC.
• Dry cleaning of furnace gas.

According to a published report some typical characteristics of raw materials used in Chinese Mini Blast Furnaces (MBFs) are given below:

Chemical Analysis (%)	Iron Ore	Sinter
Fe	40-45	53-54
FeO	--	11-12
CaO	8	10.5-12
SiO2	13-14	8.5-9
Al2O3	2	---
MgO	1	2.5
S	0.03-0.04	0.03-0.04
P	0.02	---
Tumbler index, %	81-82
Basicity	1.2-1.4

A typical range of iron oxide feed done in Chinese MBF is as follows:

Size (mm)	Percent
+70	2
-70, +60	2
-60, +40	8
-40, +25	12
-25, +10	49
-10, +5	20
-5	7

The coke characteristics used in China are:

Ash = 13.5 - 14.0

V.M. = 1.1 - 1.4

Sulphur = 0.25 - 0.75

Moisture = 7.5 - 8.0

M10 index = 17

M40 index = 75

Size = 25 - 60 mm

Development of FINEX Process and Steel Plants with FINEX in Operation

In the present article we give a brief data about how the FINEX process evolved from COREX technology, FINEX plants were started and subsequent developments and changes brought in those FINEX plants with their effects besides, the steel plants with FINEX process in operation (existing & upcoming FINEX Plants). Also Read: 

FINEX® Process, smelting reduction technology of iron making - Features, Merits and Limitations     

Development of FINEX Process and FINEX Plants

The FINEX is the latest addition and an optimized fine-ore smelting reduction (SR) process of iron making developed by POSCO that can be considered as an offshoot of COREX technology. In December 1992, POSCO and Primetals Technologies signed a cooperation agreement for the joint development of the FINEX Process. The first FINEX plant with a pilot scale production was started on November 14th 1995. In 2002 POSCO converted one the existing COREX plant into FINEX F-0.6M demonstration plant with a nominal capacity of 0.6 MTPA hot metal production, which commenced operation in May 2003. In July 2014, POSCO stopped the operation of this plant and at present it is in the final stage of agreement with an Indian steel maker for its reinstallation in India (discussed  under Upcoming FINEX plant in India).

Having successful results and following optimization of equipment and process parameters, POSCO decided to install the industrial FINEX F-1.5M Plant (1.5 MTPA production capacity). The work was started to build the first commercial FINEX F-1.5M plant by POSCO in August 2004 which finally commenced operation in April 2007.

Based on the successful results of the F-1.5M FINEX Plant, POSCO and Primetals Technologies decided to further develop F-2.0M FINEX plant with an annual hot metal production capacity of 2 MTPA. The job was started by POSCO In 2011 to build the first FINEX F-2.0M and the plant has been successfully put into operation in January 2014 and according to POSCO, the F-2M FINEX plant produced 1.5 million tons of hot metal in the first 11 months.

Modifications made in the F-2M FINEX Plant with their achievements

The design of the third generation F-2M FINEX plant is characterized by a simplified plant concept resulting in decreased construction weights compared to the F-1.5M concept. Besides others, following major changes in its design are attributed to its achievement: 

• Pneumatic ore charging to the fluidized bed reactors including a 3-stage fluidized bed reactor system resulting in a decreased building height of more than 30%
• Simplified system configuration in the hot compacting system and implementation of dry de-dusting equipment
• Elimination of HCI bin and related top gas system in the melter gasifier tower
• Installation of a centre charging system for hot HCI and coal, allowing for homogeneous charging of feed materials to the melter gasifier. The distribution on the char bed surface is realized via a dynamic gimbal distributor.

These modifications helped in reducing overall construction weight of the FINEX F-2.0M plant by approx. 9% and required no larger space in the plant layout. After start-up in January 2014, operation optimization and facility stabilization, the productivity of the F-2.0M plant achieved its target value of 5760 t/d in April 2014. Since then operation targets are achieved and operational optimization is under progress to further optimize coal consumption.

Due to improvements in equipment and operational skills, a target availability of greater than 95% could be achieved in the first few months of operation.

Upcoming FINEX Plants in India

POSCO and USPL

In Aug’15 POSCO signed a memorandum with Uttam Steel and Power Limited (USPL) to set up 3 MTPA integrated steel plant in Maharashtra (India) at an envisaged investment of nearly ₹ 20,000 crore (Approximately 3.07 Billion USD). The proposed project at Satarda in Maharashtra’s Sindhudurg district in India is based on POSCO’s patented Finex process. For complete details please refer to our article POSCO signs MOU with Uttam Steel and Power Limited (USPL) to set up a 3 MTPA Integrated Steel Plant at Satarda, India

POSCO and MESCO 

Earlier in this year Mideast Integrated Steel Limited, the flagship company of Mesco Group, India signed a memorandum with South Korean steel maker POSCO to use FINEX technology at its Kalinganagar plant in Jajpur district of Odisha (India). The first FINEX plant of POSCO which they ceased operating since July 2014, is to be transferred to MESCO. This project is part of the USD 700 million first phase steel expansion project to take Mesco Steel's capacity to 2 million tonnes. Presently, Mesco Steel operates two blast furnaces in its plant at Kalinganagar. The company has its own iron ore mine in Roida Barbil region of Keonjhar District in Odisha and another iron ore mining lease at Malangtoli in Odisha. In this month both Posco and Mesco have agreed for next meeting in November this year to discuss the modalities for transfer of Finex technology. After that, the process of dismantling of Posco's Finex plant in Korea and its subsequent installation at Mesco premises would take off. The Finex plant during operation would need a running 100 Mw captive power plant (CPP) and an oxygen plant of 1,000 tonne per day (tpd) capacity. Finex process is expected to cut hot metal production cost for Mesco by Rs 2000-2500 per tonne.

Available FINEX Modules

Different sizes of FINEX modules and capacity made available by POSCO to meet specific requirements of the customers are:

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Steel Plants with COREX Process in Operation: A Quick Review

This article presents a quick review about some of the steel plants with COREX process in operation especially, as how these COREX plants were started and subsequent developments and changes brought in those COREX plants. Because of its techno-commercial and ecological advantages the COREX Process, besides the FINEX technology, is the only industrially accepted alternative to the blast furnace route for the production of hot metal. Current COREX pre-projects also indicate an existing demand for the “by-product” COREX gas for power generation and for the production of DRI. You may also like to read: COREX Process ofIron Making - its Merits and Demerits

Steel Plants with COREX Process in Operation  

ArcelorMittal Steel, Saldanha Works, South Africa   

An Integrated Compact Mill (ICM), based on a COREX C-2000 plant and the Midrex DR plant was started up in mid 1999 at ArcelorMittal Steel South Africa (Saldanha Steel), situated near the west coast of South Africa. It is operated with mainly indigenous iron ores comprising SISHEN lump ore (80 - 100%), CVRD pellets (0 - 20%) and indigenous coal from the VAN DIJKSDRIFT and GROOTELUK coal districts. COREX gas from the plant is used for the production of DRI in the adjacent DR plant using a MIDREX shaft furnace and a LINDE Vacuum Pressure swing Absorption plant (VPSA). Both the hot metal from COREX plant and direct reduced iron (DRI) are processed to high quality steel in a twin-shell EAF, followed by thin slab casting and direct rolling in the hot strip mill to produce high quality hot rolled coils (HRC). It is only steel mill in the world to have successfully combined the Corex / Midrex process into a continuous chain - replacing the need for coke ovens and blast furnaces, and making the plant a world leader in emission control and environmental management.

Plant highlights / developments:

• The COREX plant operation is based on approx. 80% local lump ore charging.
• Typical annual production for the COREX / MIDREX DR plant combination is 700,000 t/a HM and 700,000 t/a DRI.
• Compared to other ArcelorMittal steel plants, this steel works is within the plants with the lowest production cost.

JSW Steel, Toranagallu Works, Bellary, Karnataka, India

Considering the importance of environment protection, resource conservation and sustainable development in India, JSW Steel (formerly, Jindal Vijaynagar Steel Ltd) opted for COREX technology (COREX + BOF route) for its integrated iron making project. JSW Steel (India) has two COREX C-2000 and one combined COREX gas based MIDREXTM DR plant. Start-up of COREX C-2000 plant Module 01 and 02 took place in 1999 and in 2001 respectively. This process allowed greater flexibility of operation as well as use of non-coking coals as a primary fuel and raw materials of less stringent quality. Some of the special features of COREX hot metal are high temperature (1480 - 1510^OC), low sulphur, low nitrogen and least amount of impurities. This has proved to be more eco-friendly as compared to the conventional blast furnace route due to the exclusion of sinter plant and coke ovens. Recycling of the most of the metallurgical wastes such as coke fines, mill scale, iron ore fines, LD slag, Limestone and Dolomite fines etc. are done as a COREX burden feedstock.   

Plant highlights / developments:

• In 2014 a COREX gas based 1.2 million t/a MIDREX DR plant was successfully added to produce Hot DRI. 
• COREX gas from both modules is partly used for Hot DRI production which is subsequently transferred to a new adjacent EAF steel plant via a hot transport system. The remaining export gas is still used for internal steel works use, the pelletizing plant and the power plant for co-firing.
• A recovery in excess of 95% of COREX slag could be done through slag granulation plant and is used in the manufacture of cement.
• Jindal’s COREX plant has been able to surpass its rated capacity by more than 20 - 25%, producing quality hot metal for steelmaking.
• During the relining in 2012 and 2013 an Arial Gas Distribution System was introduced in the reduction shaft of each COREX module. As a result of new developments (more even gas distribution, less burden weight on the DRI screws, more even flow of the material through the reduction shaft, etc.) an improvement of the process itself could be achieved: (a) Improved gas distribution, (b) Lower dp over the reduction shaft (c) Significant increase in Shaft Lifetime - the time from one shaft cleaning to the next shaft cleaning that occurred at JSW Steel on a regular basis has now been elongated to more than one year.

POSCO, Pohang Works, Republic of Korea

This COREX plant, POSCO (COREX C-2000 – Capacity: 0.8 Mtpa), started in 1995 adjacent to five existing blast furnaces. The COREX gas was utilized for power generation. In parallel with the signature for the COREX plant contract in December 1992, POSCO and PRIMETALS started working together for the development of the FINEX process of iron making.

Further developments:

• In 2002 the COREX plant of POSCO, Pohang Works was converted into the FINEX F-0.6M.
• Demonstration Plant with a nominal capacity of 2000 t/d commenced operation in 2003.
• In July 2014 the operation was stopped and currently it is under investigation to relocate the plant to India.

Baosteel Group, China

The first industrial COREX C-3000 of 1.5 MTPA capacities was built at the new steel works of Baosteel in Luojing at the outskirts of Shanghai. It was the largest COREX process plant in the world which successfully generated hot metal on November 8th 2007. The plant started-up in November, 2007. The contract for a second COREX C-3000 plant (COREX Module 2) was signed in December 2007 and started-up successfully in March 2011. Both Corex plants for Baosteel in Shanghai were supplied by Siemens Metals Technologies. Module 02 was more advanced as compared to COREX Module 01 which subsequently resulted in a successful performance guarantees test shortly after start-up where all agreed performance parameters were achieved and even exceeded. A significant increase in Shaft Lifetime was achieved by BAOSTEEL COREX plant module 02 where no shaft cleaning was necessary during its operation time of 1.5 years.

Further developments:

• Due to declining prices for heavy plate and as part of a strategic realignment of production in the Shanghai area, Baosteel decided to cease steel production in the Luojing Works and dismantle the individual steelmaking installations, including the two COREX plants. It rebuilt the dismantled installations in various Chinese steel works. The COREX Module 01 has been transferred to Bayi Iron & Steel Co Limited in the Xinjiang Province, a steelmaker belonging to the Baosteel Group.
• The COREX plant at Bayi Steel will allow local coal to be used, which are significantly cheaper in Xinjiang area.
• COREX gas can be used as a fuel gas in the downstream facilities to generate electricity or for the production of direct-reduced iron in a region that has almost no resources of natural gas.

Essar Hazira Ltd. India

Essar Hazira Ltd. relocated the two COREX plants (C-2000) from former Hanbo, Korea to their steelworks in Hazira, near Surat in Gujarat, India. The first plant has been started-up successfully in August 2011. Start-up of the second plant took place in December 2011. The COREX gas is mainly utilized at the existing MIDREX DR Modules to minimize natural gas consumption and for internal heating purposes.

COREX Process of Iron Making - its Merits and Demerits

COREX Process and Technology of Ironmaking

The COREX technology is a cost efficient, environmentally friendly and industrially accomplished alternative to the blast furnace route for the production of hot metal from iron ore and coal. By fulfilling more stringent ecological regulations by law, utilization of low-cost, highly available low grade raw materials including fines, the COREX process has been accepted as a commercially proven technology for present and future iron making process. The COREX process was created by Siemens VAI and was elevated to industrial maturity by PRIMETALS. Primetals Technologies Limited, is a London (UK) based engineering and plant construction company established in 2015 by a joint venture of Siemens VAI Metals Technologies and Japan’s Mitsubishi Hitachi Metals Machinery (MHMM).

In a nutshell, COREX is a coal based SR (smelting reduction) process of making hot metal or pig iron by direct use of non-coking coal. The outputs can be used either by integrated mills or EAF (electric arc furnace) mills. The process gasifies non-coking coal in a smelting reactor, which also produces liquid iron. The gasified coal is then fed into a shaft furnace to remove oxygen from iron ore lumps, pellets or sinter and finally, this direct reduced iron (DRI) is fed to the smelting reactor. Compared with the traditional iron making process via the blast furnace route, the COREX process differs since non coking coal can be directly used for ore reduction and melting work, eliminating the need for coking plants. The use of lump ore or pellets also dispenses with the need for sinter plants.

Read: Steel Plants with COREX Process in Operation: A Quick Review 

Some Merits and Demerits of COREX Process

=> Conducive to production of high end and special steel required for sophisticated industrial and scientific applications with minimum damage to the environment at various stages of steel making and mining.

=> Unlike the conventional Blast furnace route for production of hot metal, it can accept high alkali containing ores without any build up inside the reactor.

=> It takes only half an hour to stop the plant and only four hours to restart it.

=> Specific melting capacity is higher than that in Blast Furnace; productivity around 3.5 t/m³/d can be achieved.

=> In 2009 Siemens first completed a life cycle assessment for pig iron production, looking at both conventional production in a blast furnace and the more environmentally friendly COREX and FINEX processes. Siemens claimed the COREX and FINEX processes can substantially reduce pollutant emissions when compared to traditional steel production, with its blast furnace and coking and sintering facilities.

=> The iron content of the feed should not be less than 50% as otherwise the slag volume produced will be too high.

=> As is the case in blast furnaces, over 90% of the phosphorous input reports to the hot metal. So, the phosphorous content of ore and coal should be as low as possible.

=> There are also reports that the COREX process cannot be operated without some amount of coke along with non-coking coal - at least around 10% of coke is required in the total reductant charge.

=> As far as coal is concerned, the non-coking coals having too high volatile matter (VM) or too low fixed carbon (FC) cannot be used in corex process of iron making.

=> The heat transfer plays a crucial role in the overall efficiency of the COREX process. This being a two stage process, i.e. reduction and smelting taking place in two separate units, post combustion of the gas generated in the smelting unit provides the heat to melt the DRI produced in the reduction unit. This calls for high heat transfer efficiency.

=> Unless the net export gas from any Corex plant (extent of generation around 1650 Nm³/thm) can be utilized, the process will not be economical. Because of many peripheral requirements, the total cost of a Corex project can be relatively high.   

=> The export gas generated in Corex technology can be used as a fuel gas in the downstream facilities to generate electricity or for the production of direct reduced iron in a region that has almost no resources of natural gas.

=> COREX plant emissions contain only insignificant amounts of NOx, SO2, dust, phenols, sulphides, and ammonium. Emission values are already far below the maximum values allowed by future standards. Also, waste-water emissions from the COREX process are far lower than those in the conventional blast-furnace route. These environmental features are key reasons for the attractiveness of the COREX process.

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