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

28-June-2020
What is FINEX ?

The FINEX is the latest addition and an optimized fine-ore smelting reduction (SR) iron making process based on the direct use of the coal and iron ore fines. FINEX Process is a fluidized bed based process using ore fines instead using iron ore lumps and pellets. This is a process with great potential with regard to productivity and the low cost production of hot metal.

In 1992, POSCO and VAI, Austria signed an agreement to work together for a joint development of the FINEX Process. And accordingly, FINEX process was developed jointly by POSCO, Korea and Primetals Technologies to provide the iron making sector with the capability of producing (hot metal) at a reduced cost, lesser environmental pollutions and more flexibility in terms of operation and the choice of raw materials. Primetals Technologies Limited, is a joint venture of Siemens VAI Metals Technologies and Japan’s Mitsubishi Hitachi Metals Machinery (MHMM).

The present article contains about:

• What is Finex process
• Benefits or Merits of this technology
• Some limitations or disadvantages of Finex technology

To know more about the Steel plants with FINEX process in operation as how these FINEX plants were started and subsequent developments and changes brought in those FINEX plants, read: 

Development of FINEX Process and Steel Plants with FINEX in Operation

Fig: FINEX Technology (Flowsheet)

FINEX Process of Iron Making - An Overview

In the FINEX process the iron production is carried out in two separate Process steps. In a series of fluidized bed reactors, fine-grained iron oxides are reduced to direct-reduced iron, compacted and then transported to a melter gasifier. Coal and coal briquettes charged to the melter gasifier are gasified, providing the necessary energy for melting in addition to the reduction gas. Fine ore and additives (limestone and dolomite) are dried and then charged to a 3 or 4 stage fluidized bed system where the iron ores are progressively reduced in counter current flow with the reducing gas to fine DRI and the fine additives are partly calcined.

Reactors R4 and R3 are primarily used to preheat the ore fines to the reduction temperature, which can be adjusted by partial combustion of the off-gas (export gas) from R2. In R2 the fine ore is pre-reduced to reduction degree (RD) of about 30%. At the end of the production in R1, the final reduction to DRI takes place (RD about 90%). Operational pressure in R1 to R4 is approximately 4 - 5 bars. The fine DRI is compacted and then charged in the form of Hot Compacted Iron (HCI) into the melter gasifier. So, before charging to the melter gasifier unit of the FINEX unit, this material is compacted in a hot briquetting press to give hot compacted iron (HCI) since the melter gasifier cannot use fine material (to ensure permeability in the bed). Non-coking coal (lumpy and / or briquetted fines) is charged from the top of the melter gasifier, dried and degassed in the upper char bed area and finally the degassed coal (char) is gasified with pure oxygen which is blown in at the tuyere zone of the melter gasifier bed. The gasification supplies the energy required for the metallurgical reactions and for the melting of HCI and coal ash to hot metal and slag. Pulverized coal injection (PCI) system is provided to inject fine coal via the oxygen tuyeres. The gas generated in the melter gasifier of the FINEX unit is used to reduce the ore in the reactors preceding the melter gasifier. The generated FINEX off-gas is a highly valuable product and can be further used in power generation or heating processes. The DRI is charged in the melter gasifier in hot condition, where it is melted, fully reduced and carburized to hot metal. The hot metal and slag produced in the melter gasifier is frequently tapped from the hearth similar to the blast furnace and COREX operations. Also refer COREX Process of Iron Making - its Merits and Demerits.

FINEX Process - Merits and Benefits

In many respects FINEX process can be considered as an offshoot of COREX process and hence, bear the various advantages of the COREX and more as outlined below -  

Flexibility in Raw Materials

• No blending of ore & coal. Rather direct utilization of coal.
• Use of Low-grade ore & low-ranked coal. Integration of the coal briquetting technology increases the range of suitable coal blends for the FINEX application. Utilization of 100% coal briquettes offers the possibility to mix different coal qualities for the generation of coal briquettes.

Easy & Flexible Operation

• Independent control of reduction & melting processes
• Easy & hassle-free operational control

Environmental Friendliness

• Far less emission of SOx, NOx, phenols, sulphides, ammonia & dust because the FINEX process does not need sinter plant and the coke oven battery which are the actual sources of emission in a conventional blast furnace route.
• Applicability to the CO₂ sequestration.

Cost Competitiveness

• Lower cost in both capital investment & operation as compared to the blast furnace route, keeping the quality of the hot metal same.
• According to POSCO, the capital cost & operating cost of FINEX process are less than by 20 and 15 percent respectively of that of Blast Furnace route. 
• Need much less land as compared to conventional BF complex.
• Similar to the Corex export gas, FINEX export gas (with calorific value of 5,500 – 6,250 kJ/m3 STP) can be used to substitute natural gas, oil, coke and coal for metallurgical applications and power generations etc. Depending on the composition of coal and the decision whether gas recycling is applied or not, the amount and the composition of the export gas can vary within definite limits.

Limitations (Demerits) of FINEX Process

As said FINEX, COREX, HISMELT are the latest alternative methods for producing liquid iron (Hot Metal) through Smelting Reduction (SR) process. Some of the limitations (disadvantages) are -

• Ease of obtaining FINEX technology is uncertain though POSCO has started to extend it.
• Both COREX and FINEX processes need a large amount of oxygen.
• The major criteria for an initial evaluation of coals or coal blends for the FINEX Process are: 1. Fix carbon content at a minimum of 55%, 2. Ash content up to 25%, 3.Volatile content lower than 35%, 4. Sulphur content lower than 1%
• Additional to these qualities the coal must have a good thermal stability to ensure the formation of a stable char bed in the melter gasifier. 

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HYL III and SL/RN - The two widely accepted Direct Reduction (DR) Processes of ironmaking

10-Oct-2009

Direct Reduced Iron (DRI) is obtained by reducing lumps as well as fines of iron ore in solid state at a relatively low temperature of around 1000^OC. A large number of DR processes are available today. SL/RN and HYL are two such DR processes. While HYL is a batch-type gas based process and uses a countercurrent shaft-furnace, the SL/RN process utilizes rotary kiln to reduce lump ore, pellets and sand iron with coal. Here we will discuss about some key features, including advantages and disadvantages of these two DR processes.

HYL III

Fig: HYL III Process Scheme

The HYL process was developed in Mexico and was the forerunner of the HYL III direct reduction technology. In HYL I process, a mixture of gases containing about 89% of reducing compounds is used. Each reduction module in HYL plant consists of four units - three “in line” and the fourth in “turn around” mode. The principal change made over HYL I in HYL III was the modification of the four fixed bed reactors by a single moving bed reactor, utilizing the same gas reforming plant, auxiliary equipment and quenching towers.  Actually HYL III technology is characterized by its wide flexibility for adapting to special needs, depending on available reducing gases, energy use and melt-shop requirements. Use of spent gases from direct ironmaking processes, coal gasification, energy optimization in DR plants and technology developments aimed to improve EAF productivity have been the objective of HYL. Some distinctive features of HYL III process are:

Fig: HYL III - COREX Off-Gas Process Scheme

=> The H₂/CO of the reformed gas is 3, the temperature is about 930^OC, the inside pressure of the countercurrent shaft-furnace is 450 kilopascals and the energy required for the reduction is basically the same as in the MIDREX process.

=> The selective elimination of H₂O and CO₂ from the reducing gas circuit allows maximum recycle of the reducing gases to the reduction reactor. Hence, the reducing gas make-up and the process natural gas consumption are minimized.

=> The reducing gas generation and the reduction sections of a HYL III unit are independent from an operational point of view. This feature offers important flexibility for adapting to different reducing gas sources. The process schemes based on use of alternative reducing gases from different sources and other DR/ Ironmaking sources have been proven in HYL III plants. Such alternate sources of reducing gas can be -

• Coal gasification processes.
• Coke oven gas.
• Gases from Hydrocarbon gasification.
• Partially spent gases from another DR plant.
• COREX off-gases.

=> High pressure operation (4 atmospheres or more) enables the effective control of process conditions, with smaller equipment size for gas handling and lower energy requirements (9.0 - 10.0 GJ/t).

=> The process is much flexible as far as raw material use is concerned - while it operates best with 100% pellets, even 100% lump ore of a suitable type has been used, but it is suggested to use a mixture of pellets and lump ores.   

=> This technology offers the unique flexibility to produce three different product forms depending on the specific requirements of each user - Cold DRI, HBI and HYTEMP iron. Metallization can be controlled up to 95% and Carbon content 5.0%.

=> When combined with COREX off-gas as a source of reducing gas, the HYL III DR plant offers high productivity using available spent gas and benefits in steel production using HYTEMP® iron together with hot metal in EOF/BOF based steel mills.

=> The HYL III process features the flexibility of generating electric power, taking advantage of high pressure steam produced in the natural gas-steam reforming unit which can be used in a turbo generator or in a set of turbines, at a high generation capacity.

According a data of recent past, around 11 million tones of direct reduced iron (DRI) was produced in 2003 by this process in India, Grasim’s HYL plant at Raigad (Orissa) produced 0.75 million tones of HBI.     

SL/RN

SL/RN is the most widely accepted coal based DR process. It was jointly developed by Stelco, Lurgi Chemie, Republic Steel Company and National Lead Corporation in 1964. In this process, the materials charged into the kiln gravitate towards the discharge end during which they are progressively heated to the temperature of reduction of around 1000 - 1100^OC. The product discharged from the kiln is cooled in an extremely cooled rotary cooler around 100^OC before being subjected to magnetic separation to separate sponge iron from coal ash and char. Waste gases leaving the kiln at the inlet end pass through a dust chamber and a post combustion chamber, before being cooled and cleaned in electrostatic precipitators, scrubbers or bag filters. In SL/RN technology the clean gases can be used in waste heat boilers to recover the sensible heat and the steam generated can be utilized for heating purpose or for electric power generation. Some distinctive features of SL/RN process include:

=> Flexibility with regard to the type of iron bearing materials which can be used such as lump ore, pellets, ilmanite, iron sands and steel plant wastes.

=> Use of a wide variety of solid fuels ranging from anthracite to lignite and charcoal.

=> Improved heating of the charge by submerged air injection in pre-heating zone of the kiln. This process suffers, however, from relatively big heat loss and facility size.

=> SL/RN technology provides optimized coal injection facilities at the discharge end of the kiln.

=> Waste gas conditioning by controlled post combustion followed by power generation (the power generated is more than the requirement of the plant).

The original SL/RN process has been modified in a variety of ways, particularly in India where rotary kiln DR technology has been widely applied.            

MIDREX - The Most Widely accepted Direct Reduction (DR) Process of Ironmaking

2-Oct-2009

Midrex the most widely accepted direct reduction (DR) process of ironmaking in the world was developed by Midland Ross Corporation of Cleveland, USA in 1967 , has the following distinctive features:

Recommended Natural Gas Composition for MIDREX Plants

Components	Vol %	Effects
CH4 C2H6 C3H8 C4H10 +C4 (Hydrocarbon) CO2 N2 S	75 - 100 0 - 25 0 - 4 0 - 2 0 - 0.5 20 max 20 max 20 ppm. (max Wt.)	-- -- Above 4% C3H8, water vapour content should be increased. -- Above 20% CO2, export fuel is produced. For every 10% of N2, fuel consumption increases by 2%. Above 20 ppm, carbon deposition on catalyst.

MIDREX Process - Some Features

=> It allows the production of highly metalized DRI (exceeding 92%, see adjacent Table showing typical composition of Midrex DRI) and the carbon content of can be controlled in the range of about 1.0 - 2.0%.

=> Although originally developed for use with high grade pellets, the Midrex shaft furnace is now able to use some amount of lump ores. Optimum process conditions are often obtained by mixing 30-50% of an appropriate type of lump ore with high grade pellets. See adjacent Table showing Physical Characteristics of Pellets and Lump Ores used in the MIDREX Process.  

=> Fuel utilization in Midrex process has steadily decreased from an average of 12.5 - 14 GJ/t of DRI to 9.5 - 10.5 GJ/t. This improvement in energy efficiency has been the result of higher reduction temperatures, enrichment of reduction gas with methane, utilization of in-situ reforming, and pre-heating of the process gas utilizing waste heat from the reformer.

=> Following the advent of in-situ reforming, oxygen carriers from an external source are now not required in the production of reformed gas. Therefore, the investment cost and operating costs of Midrex units have been reduced.

=> The DRI produced is relatively active towards re-oxidation, particularly when moisture is present. Hence it must be deactivated if it is to be stored or transported over a long distance.    

Physical Characteristics of Oxide Feeds

(Pellets and Lump Ores) used in the MIDREX Plants

	Pellets	Lump Ores
Screen analysis (wt %) 50 - 31.75 mm 31.75 - 6.3 mm + 15 mm 8 - 15 mm – 8 mm – 6.3 mm Bulk Density (t/m3) Compressive Strength (kg/pellet) ISO Tumbler Test (wt%) + 6.3 mm – 0.5 mm	-- -- 10% max 85% max 5% max -- 2.0 - 2.1 270 min 95% min 4% max	5% max. 93% max. -- -- -- 7% max 2.0 - 2.6 -- -- --

Typical Product Composition of Midrex DRI

Content	Wt %
Fe (total) Fe (metallic) Metallization SiO2 Al2O3 CaO MgO S P	92 -93 84 - 88 93 - 95 2.0 - 3.5 0.5 - 1.5 0.2 - 1.6 0.3 - 1.1 0.005 - 0.015 0.02 - 0.04

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ROMELT - Another No Coke Alternative Smelting Reduction (SR) Process of Ironmaking

19-Nov-2009
ROMELT - The Process

This process was developed by the Moscow Institute of Steel and Alloys (MISA) in the mid-eighties to produce liquid iron from iron-bearing ores (lumps and fines) as well as waste iron oxides generated in an integrated plant using non-coking coal and oxygen. ROMELT is the only single stage SR process.

Unlike COREX and most other SR processes, the strength of this process is that it is a single stage concept. That is why ROMELT is a robust and simple process, which is also very much environment-friendly, since it operates under a slight negative pressure. As a result the area around a ROMELT plant is extremely clean. However, the process has a few inherent weaknesses being a single stage process, it uses large amounts of coal (1.3 - 1.5 t/thm) as well as oxygen (1100 - 1200 Nm³/thm) and it generates a very rich exit gas, which has to be utilized effectively e.g. in power generation to meet the demand of oxygen plant to make the hot metal production economic.        

ROMELT Process - The Advantages

=> This process can accept iron ore in a wide range of sizes (0 - 20 mm) without any pre-treatment. This would allow operating units to use slimes and other iron-bearing wastes which can be a big advantage for many reasons.

=> Non-cocking coals of size 0 - 20 mm with moisture content less than 10% are acceptable for this process. Although it is preferable to restrict the VM content of the coal up to 20%, higher VM coals can also be used. Then, no separate coal preparation is required.

=> The ROMELT process is capable of achieving fairly high degrees of post-combustion (even more than 70%) of the melter gas (primarily CO and H₂) before it leaves the reactor, thus ensuring satisfactory utilization of energy even though it is a single stage process.

=> The quality of ROMELT iron is excellent - Carbon 4%, Silicon 0.6%, Manganese 0.05%, Sulphur 0.04% and temperature 1400 - 1450^OC. The process offers particular advantage  in terms of phosphorous in hot metal because in the ROMELT process, instead of 100% phosphorous going to metal (as is the case in Blast furnace), only 60% phosphorous is reported to be in the hot metal while 30% goes to the slag, and 10% forms a part of exit gas.

=> Small scale production of 200000 to 1000000 tpa of hot metal is possible along with flexibility in production. The capacity of the rectangular ROMELT reactor (productivity in the range of 0.95 t/m² of hearth area) is limited by the penetration of oxygen from the side-wall tuyeres into the bath. Thus, ROMELT unit may be ideal for supplying hot metal in EAF based mini steel plants.

=> The specific investment in a ROMELT plant is not likely to be as high as in many other SR processes because the equipment is simple and easy to operate. For the same reason, the plant availability should be high.

What is FASTMET Process of Ironmaking ?

11-Sept-2009
Fastmet – The Process Concept and References  

This is a direct reduction process using a Rotary Hearth Furnace (RHF) which was derived from the work done in USA by Midland Ross and Surface Combustion, in the ‘Heat Fast’ process, treated in 1960s. It is a solid reductant based process in which iron ore concentrate, pulverized coal and a binder are mixed together and pelletized. The resulting green pellets are fed either to a drier or directly to a rotary hearth furnace where the pellets are heated to 1250 - 1400^OC and reduced to metallic iron. Burners and post-combustion the CO evolved provide the heat required to raise the pellets to the reduction temperature.

The first commercial Fastmet plant was commissioned at the Hirohata Works No.1 of Nippon Steel in April, 2000 and Hirohata Works No.2 in February, 2005 with material processing capacities of 190000 tpa each plant. The second plant established was Kobe’s Steel’s Kakogawa Works started from April, 2001 having a material processing capacity of 16000 tpa.  The Fastmet process has allowed the Kakogawa Works to achieve a zero emission rating of steel mill waste. Waste utilization is the principal application of the Fastmet process in Japan.       

FASTMET Process - Flowchart

Advantages of Fastmet

Some of the advantages of Fastmet process as have been reported are summarized as follows:

=> A wide variety of iron ore as well as steel mill wastes including BF dust, BF Sludge, BOF dust, Sinter dust, EAF dust, mill scale, and etc. can be used as the oxide feed.

=> Elimination of waste disposal cost and landfill liability as wastes is changed to a quality source of iron (DRI).

=> Recovery of Zinc contained in wastes (Zn deriving from scrap) which can be sold to zinc producer. Zinc removal: 95% or higher.

=> A wide variety of energy sources can be utilized including natural gas, LPG, coke oven gas, heavy oil, coke breeze and carbon bearing wastes or pulverized non-coking coal.

=> The short reduction time of less than 12 minutes enables easy plant starting and shut-down, and quick adjustment of production rate.

=> Reclamation of carbon is possible. Carbon contained in dusts will be used as reductant. The carbon content of DRI can be adjusted as per the customer’s requirement.

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