Introduction
Technology plays a pivotal role in moulding the future of a machine and thereby an industry. And when technology is linked with science, the value adds on. Although, both link each other in some way or the other, they differ too. The purpo of technology differs from that of science. As Dr. Amit Chatterjee of Tata Steel, one of India’s eminent steel technologist, aptly mentions the objective of since is to obtain general and publishable knowledge. In economic terms, its findings become public property. Technology, on the other hand, focud on opportunities, specific problems or group of problems. The solution of such problems often yields proprietary knowledge that many have considerable value. The owners of such intellectual property will only share this ast on commercial terms. Steel technologies have emerged massively during the last four decades for the production of value-added steel products in a cost-effective manner with environmentally free process. Many new technologies have been developed in the areas of iron making, steelmaking, casting and rolling. An outline of the major developments in emerging technologies are prented below : a) Blast Furnace. The blast furnace route produces about 63 per cent of
crude steel in the world. Continuous developments have taken place in blast furnace process technology as well as in the design and engineering aspects. Furnace size has gone up from around 2000 m3 (inner volume) to over 5000m3 and productivities of 2.5 t/m3/day to 3t /m3/day have been achieved in developed countries. PW bell-less rotating chute system for burden distribution is now widely adopted. Mathematical models and instrumentation have been developed to predict stock line profiles and measure the effect of changes in the distribution pattern. With good hearth conditions, improved refractories, optimal cooling increa the heat-flux rates in the lower part of the furnace and judicious gas flow distribution in the central and peripheral regions, it has been possible to increa the campaign life to as high as 15 years. By controlling heat loss, increasing the thermal flow ratio and reducing temperature in the vicinity of the raceway by steam or water injection through the buyers, it has been possible to produce hot metal with less than 0.20 per cent silicon.
Reduction of coke consumption in blast furnace
雪罗隐The following major technologies have helped reduce coke consumption in blast furnaces :
(i) Oxygen Enrichment Significant reduction fuel rate in modern Blast Furnaces along with oxygen enrichment has led to a reduction in fuel consumption per tonne of hotmetal. Oxygented BFs are operated with 60-100 per cent in the blast. (ii) Coal Dust Injection (CID) in blast furnaces has helped reduce coke consumption by more than 15 per cent coke is itlf produced through energy intensive process and its consumption, therefore, has a cascading effect on energy consumption. With right amount of oxygen enrichment (up to 3.5 percent) and stable raw material characteristics, coal can be injected up to 130-140 kg / thm. (iii) Coal Tar Injection in blast furnace to the extent of 40 Kg / thm to 45 Kg / thm can save about 60 Kg / thm of coke in BFs. (iv) Stamp charged coke the adoption of stamp charging technology at Tata Steel has made significant contribution towards coke rode and productivity in blast furnaces. The CSR values, which in top charging were below 60, incread to over 65 in stamp charging. (v) The favorable impact of stamp charging technology in coke quality, has, in turn, had a positive effect on operation. BF productivity was incread to 2 tonnes / m3 / day due to coke produced by stamp charging.
Increasing the efficiency of BF operation
In the developed world, major trends in improvement of blast furnace productivity, incread life of refractory lining and lowering of energy consumption are obrved in the following areas : In areas in hot blast temperature from 11500c to 13500c coupled with coolent injection. • High top pressure up to 1.5 2.5 Kg / cm2 Extensive u of thermal and pressure proving of a BF by the u of over / under burden probes, vertical pressure probes, thermocouples all around the furnace to monitors refractory wear. Clo circuit high pressure stake cooling system to take care of excessive heat flux of a fast driving furnace. Automation in BF control to precily predict the behavior of a blast furnace and to ensure timely corrective measures to be taken. Better cast hou practice such as cast hou slag granulation, multiple tap hou with automatic drilling machine, tilting / rocking rummers and improved cast hou lay out. Belt conveyor charging system to replace the conventional skip system. Covered cast hours runners with liquid pool system U of superior refractory material of ling of BFs coupled with under-hearth cooling of refractory padhearth Part replacement of coke by injecting non-coking coal through the blast furnac
e tuyers. Some of the above methods have already been in operation in the Indian steel plants.
Iron making process eliminating the B. F. route
Brief outlines of some major iron making proce eliminating the blast furnace route are mentioned below : (i) Corex process In VAI’s Corex process all metallurgical work is carried out in two parate process the reduction shaft and the melter gasifier. Non-coking coal directly enters the dome of the melter gasifier through a lock hopper system and is converted to char at 1100-11500c. Environmentally undesirable by – products like tar, phenols and poly cyclic hydrocarbons are immediately dissociated are therefore not relead to the environment. Oxygen is blown into the melter gasifier and upon gasification with the coal, an excellent reduction gas is generated consisting of 95 per cent CO + H2 and approx. 3 per cent Co2. Following its exit from the melter gasifier, the gas is cooled to the required has temperature between 800 and 8500 Co. After degusting in a hot gas cyclone, the gas is fed to the reduction shaft, where the burden, consisting of any desired combination of lump ores, pellets or sinter, is converted to DRI.
宋宁宗Following extraction from the reduction shaft by means of specially designed screw conveyers, the DRI 1 drops into the melter gasifier where it is melted. The tapping producer, tapping temperature as well as the further processing of the hotmetal is the same as with the blast furnace hot metal. Export Gas – The top gas from the reduction shaft has a net calorific value of about 7,000 KJ / Nm3. Following scrubbing, this expert gas can be ud for wide variety of heating, drying, metallurgical, chemical and power generation purpos. The export gas from a COREX C-2000 module, would not only produce 0.8 mtpy of hotmetal, but also generate the required 50,000 Nm3/h process gas as well as approx. 115 MW of exportable electrical energy.中国大尺度电影
(ii) Midrex Process The miderx process converts iron oxide to DRI in a vertical shaft furnace. This is accomplished as the iron oxide flows downwards through the shaft furnace by gravity, counter current to hot reducing gas which are rising through the shaft furnace. The hot refusing gas react with the iron oxide in the upper zone of the shaft furnace, stripping away the chemically bound oxygen. The reduced DRI descends to the lower of the shaft furnace from which is continuously discharged. In the lower zone,
the DRI can be cooled to 500C or it can be discharged hot at 7000C directly to an adjacent EAF via the miderx Hotlink TM system. The spent reducing gas (called top gas) exit the top of the shaft furnace and are scrubbed and cooled to remove entrained particulates and to conden most of the water vapour. The top gas at this point contains too much C02 for direct reu in the shaft furnace. In a conventional Midrex plant, the gas is recycled through the Midrex Reformer. However, when a gasifier is involved, the top gas pass through a vacuum pressure swing adsorption system (VPSA) to remove most of the CO2 before being mixed with fresh synthesis gas and recycled back to the shaft furnace. The synthesis gas from the gasification plant and the recycled top gas from the VPSA system are at ambient temperature and must be heated to 9000C which is the target reducing has temperature. To minimize power consumption in the EAF, the MIDREX Hotlink TM system could be ud to ‘hot charge’ a significant portion of the DRI directly into an adjacent EAF. It is estimated that hot charging via the Midrex Hotlink system can save 140 k Wh/tonne in the steel mill.
(iii) Conarc Process The converter ARC furnace technology or the CONARC process dev
eloped by SMS-Demag combines the advantages of converter and EAF. The process utilizes liquid hot metal in the charge – mix of EAF along with DRI and solid scrap. Each vesl of the twin shell initially act as a converter, blowing oxygen into the molten iron and is then charged with scrap and there after operated as a conventional EAF for melting and refinishing. The vesl is ud as a converter, while the other operates as an EAF melting unit which increa both flexibility and productivity of operation. The Conare process reduces energy consumption from 600 k Wh / tonne in the conventional process to less than 300 kWh / tonne. The oxygen blowing top lance can be ud with highest efficiency, when hot metal and sponge iron are the main output. In this ca, the energy consumption is less than 200 kWh/tonne. (iv) Romelt Process Romelt process was developed by Moscow Institute of Steel and Alloy in 1985. The important features of the Romelt Process are : (a) This is a single stage smelting process where liquid iron is produced in a molten slag metal bath reactor using non-coking coal and oxygen.
(b) The process requires minimum preparation of raw materials with no limitations on size range or moisture content. (c) A wide range of iron bearing materials including lump ore, 红烧狮子头
防溺水教育ore fines, pellets and ferrous waste generated in the steel plant can be re-ud. (d) There is no need for coke ovens or sintering plants. (e) Oxygen is ud as the primary gasification medium. (f) The unit is simple in a design and environmentally friendly as compared to the conventional routes. (g) Post combustion of primary bath gas and transfering the resultant heat back to the bath is the principal driving force of the process. The capital cost for installing the Romelt process is lower compared to similar process like COREX due to its being a less sophisticated plant. In comparison to BF iron making, the Romelt process cost is 15 per cent lower and the capital cost is 40 per cent lower. (v) Hismelt process This process us iron ore fines and low cost steaming coal. The process is capable of producing iron. Units of better quality than pig iron and a material that can be tailor made to suit the individual mini mill requirements. Hismelt process is likely to be more suitable for EAF steelmaking than other iron units such as DRI. (vi) Fastmet process In the Fastmet process, iron ore fines or steel mill waste is mixed with pulverd coal or other sold carbon bearing materials and formed into pellets. The pellets are fed into a doughmut-shaped rotary hearth furnace (RHF) and heated to 13500C. Und
同样的爱er high heat, the pulverized coal acts as a reductant and burns off the oxygen in the iron ore, leaving pellets with a high iron content.
Feature of the Fastmet Process
(a) Raw material flexibility The process can handle a wide variety of raw materials, including iron ore fines or iron bearing wastes. Reductants can be pulverized coal, coke braze or other carbon-bearing wastes which are easily available. (b) High productivity The Fastmet process loads the RHF with only one or two layers of pellets which leads to more uniform heating and reduction and conquently to high productivity and metalisation. (c) Uniform DRI quality One or two layer arrangement of pellets in the RHF also leads to more uniformity in product quality. (d) High zinc recovery By designing the Fastmet RHF for minimal carry over to the off gas system, high zinc dust can be recovered. (vii) Finex Process Posco of Korea and the Rearch Institute of Science and Technology (RIST) of VAI, Austria has completed a smelting reduction plant bad on this process at POSCO’s Pohang Works. The plant is bad on fluidized bed technology with a daily production capacity initially of 150 tonnes bad on fine ore and non-coking coal.
The finex process has been developed to enable production of high quality hot metal in a cost effective and environmentally free manner. (vii) Finmet Process The process us iron ore fines with a grain size of less than 12mm which is dried to flow freely through storage bins. This is done in a fluidized bed dryers where the ore is heated up to 1000C which reduces free water content to 1-2 per cent. Fluidid bed reactors are inter connected with gas and soild transfer lines. Ore fines flow downwards by gravity from upper to lower most reactory while reducing gas flows upwards in a counter current direction. The fine ore is heated in the first reactor to 400-5000C by partially spent reducing gas. The ore flows downwards through next reactors of the rious and the degree of metallisation continually increa at each step due to the reaction with progressively reacher reducing gas. In the final lowermost reactor (usually the fourth) a temperature of 8000C prevails.
The hot DRI fines are transported by a pneumatic lift system to the briquetting area into an insulated bin. From there, the fines flow by gravity into double roll briquetting machines where they are compacted. (ix) HYL III The Process consists of a reforming an给孤独
d reducing ction. Natural gas is steam reformed to obtain a hydrogen rich reducing gas which reacts with the iron ore lumps and pellets in the reactor at a temperature of 9300C. Hot DRI is discharged at a temperature of 7000C. The hot DRI is either briquetted to form HBI or Cooled as cold DRI. Since gaous reducant is ud, the HBI and DRI produced by this process is very clean and of high quality. (x) Redsmelt process It is basically a two step smelt reduction process where in the first step, reduction of carbon containing green pellets takes place in a rotary hearth furnace converting the iron oxide into highly metallid sponge iron. This step us iron ore fines and ground coal mixed and pelletid into lf reducing green pellets which is procesd in the rotary reduction furnace (RRF). In the cond step of the process, hot sponge iron is charged into a submerged arc furnace(SAF) whole characteristic is to melt the sponge iron into a higher layer of generic slag, parating the iron from the gangue and ash components. The products of this process line are hot metal as well as low iron containing slag suitable for u in starter of the art applications. The production cost of hotmetal in Redsmelt process is lower than that for high grade scrapor HBI. In EAF steelmaking its inherent low energy
consumption saves up to 120 kWh per tonne of steel at a supply of about one third of the charge. Many more modern process are coming up for production of high quality iron in a environment friendly manner requiring low to moderate cost in minimills. Some of the are : (a) ECO ARC developed by NKK, Japan (b) New scrap Recycling (NSR) process developed by NKK, Japan (c) Plasma Fired Cupola (PFC) developed by WEC, USA (d) Technored process developed by CAEMI, Brazil (e) DIOS developed by NKK, Japan and Cicored, Hyl4m, comet process etc.
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