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Showing posts with label Smelting Reduction. Show all posts
Showing posts with label Smelting Reduction. Show all posts

COREX Process of Iron Making - its Merits and Demerits

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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.
COREX Process of Iron Making
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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ZERO Waste Steel Shop - The Most Innovative Metallurgical Process

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28-Nov-2009

The ongoing boom in the iron and steel industry combined with scarcity in raw material supply, their availability has caused a dramatic increase of prices for raw materials and steel roducts. The whole chain of production from front-end side of iron making up to the finishing stage of steel products has to be observed and optimized continuously by introducing highly efficient new technologies, tools, and emission and residue free, environment-friendly processes for production of high value steel products. Among the various innovative iron making processes like Midrex, COREX®, FINEX®, Finmet, Fastmet, Romelt, Primus etc.

ZEWA (Zero Waste) is one such process. Here we are going to discuss in brief about the background and some features of ZEWA process.ZEWA (Zero Waste) is a new metallurgical process which converts blends of industrial waste materials and residues into hot metal and mineral products such as Hydraulic Binders for cement production, metallurgical powders for desulphurization practices and materials suitable for road construction. ZEWA (Zero Waste) process involves high temperature smelting reduction (SR) operations which are carried out in a specially designed, electrically operated reactor.
A demonstration plant with all necessary auxiliary facilities was erected at the Vitkovice Steel Works in the Czech Republic. An earlier report says that it took eleven test campaigns to prove the technical and economical feasibility of the process with respect to the generation of hot metal and useful mineral products from the residues of carbon and stainless steel production.
ZEWA (Zero Waste) Process - A Background
The basis for the development of the ZEWA (Zero Waste) process was laid at the Central Recherche Metallurgique (Center for Metallurgical Research) in Belgium where a laboratory scale smelting reduction process was developed to convert various residues from Steel Plants into valuable metallic and mineral products. Pilot plant tests using a hollow electrode for the pneumatic injection of residue materials into a furnace were then conducted by CRM, MSFOS (Sweden) and FEhS (German Research Institute) in the framework of the IBPM (Internal By-product Melting) project.
In 2000, Voest Alpine (VAI) teamed up with CRM and a large consortium of partners as part of a multi-national project team supported by the European Union. A process concept based on the previously tested pneumatic injection of residue materials into a furnace via an injection lance was chosen. The partnership within this so-called “Fifth Framework Programme” is as follows:
=> From the steel industry; CRM (project coordinator), VAI, ARCELOR, and Vitkovice Research team.
=> From the cement industry; LAFARGE
=> From the car dismantling industry; the Belgian SME Comestsambre.
=> From the coal industry; the ICPC (Institute for Chemical Processing of Coal, Poland)
This project works with a goal of developing a viable technology for the so-called ZEWA (from Zero-Waste) process and to test it on a demonstration scale. The main task to be carried out was thus the design and erection of a dedicated pilot plant, the performance of the pilot test campaigns and the final evaluation of the ZEWA as the basis for commercialization.   
The Principal of ZEWA (Zero Waste) Process
The ZEWA (Zero Waste) process is based on smelting reduction of suitable blends of basic and acidic residue materials from industrial production as follows:
=> From the steel industry basic steel making slags and dusts, and silica containing residues from scrap handling (mixtures of glass and plastics) in EAF plants;
=> Complementary acidic residues from another industrial sectors, such as fly ash from coal-fired power plants, automotive shredder residues (ASR) or bottom ash from urban incinerators (BI ash).
The main products are the refined slag (or mineral product) with targeted chemical composition, and hot metal or metal product to be recycled for steel production. For the smelting reduction (SR) process carbon based reductant (coke, anthracite, coal etc.) are added to the blend of residue materials. Depending on the raw material and the mineral product, small quantities of stronger reductants like ferro-silicon, or additives such as lime or bauxite, may also be added when necessary. Process dust with high zinc content is recovered in an off gas filtering unit. Targeted mineral products are a Portland clinker substitute for use in cement production and metallurgical powders for use in secondary steel refining units.       
ZEWA (Zero Waste) - The Process Technology
The smelting reduction in ZEWA or Zero Waste process is done in an electrically heated ladle-type furnace which is equipped to allow for top charging of liquid steel making slag and coarse solid materials into the foamy slag bath, and also for the deep pneumatic injection of powdery materials into the hot metal with a lance. Coarse solid materials like solid slags are charged by gravity, via a fibro-feeder or by a chute. Injected powdery materials are mainly steel making dusts, fly ash and reductants. Other features of the ladle include bottom stirring (to enhance mixing and reaction kinetics) and post combustion in the upper part of the slag bath (to recover chemical heat through the partial combustion of the CO from the reduction reactions). The ZEWA (Zero Waste) process technology is quite flexible with regards to the input materials, firstly because it allows for the charging of the liquid slag, and secondly because it can cope with highly variable charging ratios of liquid slag, coarse solids and powdery materials. Dry dusts can be directly used as a raw material. Sludges and other residue materials require only drying and micro granulation. No pelletization or briquetting is necessary, thus reducing the material pre-treatment costs substantially. Because of the filtering effect of thick foamy slag bath, ZEWA technology is also very efficient in terms of lowering dust emissions. Moreover, due to the low thermal losses by radiation from the arc and the metal bath, ZEWA process is very effective in lowering the energy consumption too.             

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

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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 - 1450OC. 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.