Let's think about how ferrous methods have been developed. The iron ore was originally smelted in this kind of bloomery to produce a porous mass of iron and slag which is called bloom. A mixture of ore and charcoal would be poured into a hot bloomery containing an already burning charcoal fire. And then, air from bellows would be blown into the bottom of the furnace to feed the fire, and increase the temperature. Inside the furnace, carbon monoxide actually from the burning charcoal reduces the iron oxides in the ore to metallic iron, without melting the ore. This eventually forms a bloom of iron and slag, then taken out of the furnaces. Only bloomeries were relatively small, smelting less than 1 kg of iron with each firing. Progressively, large bloomeries were constructed in the late 14th century with a capacity of about 15 kg on average. The use of water wheels to power the bellows allowed the bloomery to become larger and hotter. And then average bloom size quickly rose to 300 kg, where they levelled off until the demise until the demise of the bloomeries. The bloom produced is repeatedly hammered to remove as much slag as possible, which is known as shingling. The remaining iron can then be forged into wrought iron containing very low carbon amount. The wrought iron so produced through the laborious, time-consuming process is a malleable but fairly soft alloy. Because they contain very low carbon amount. The bloomery type furnaces typically produced iron products ranging from very low carbon iron to steel containing about 0.2 to 1.5% carbon. The master smith had to select bits of low carbon iron and carburize them to make a steel. When applied to a non-carburized bloom, this pound, fold and weld process resulted in a more homogeneous product and removed much of the slag. At very high temperatures, a radical change takes place. The iron begins to absorb carbon rapidly, and the iron starts to melt, since the higher carbon content lowers the iron melting point. The result is cast iron, which contains around 4.5% carbon. This high proportion of carbon makes cast iron hard and brittle; it cannot be forged at any temperature. The pig iron was produced by blast furnaces, first used by the Chinese in the 6th century BC but more widely used in Europe during the middle Ages, increased the production of cast iron. Blast furnaces produce pig iron; which is about which is an alloy of approximately iron and carbon of around 4.5% carbon. If the process of steelmaking begins with pig iron instead of wrought iron here. The challenge is to remove a sufficient amount of carbon to get it to be 0.2 to 2% for steel. Then let��s look at how iron and steel, produced from pig iron using coal instead of charcoal. Early iron smelting used charcoal as both the reducing agent and heat source. By the 18th century, the availability of wood for making charcoal was limiting the expansion of iron production. In the early 17th century, it was attempted produce pig iron using coal in the place of charcoal, but the product was refused because of its bad quality due to sulfur. This indicates a lot of the sulfur was generated from coal which was absorbed by liquid iron. The breakthrough in the production of iron with coal came about in 1709 when coke a kind of contraction of "coalcake" was used for iron smelting. The next innovation was done by British metallurgist Sir Henry Bessemer in 1856. He designed what he called a converter large pear shaped receptacle with holes at the bottom to allow the injection of compressed air. Bessemer filled it with molten iron here blew compressed air through the molten metal, and found that the pig iron was indeed emptied of carbon and silicon in just a few minutes; moreover, instead of freezing up from the blast of cold air, the metal became even hotter and so remained molten. However, one shortcoming of the initial Bessemer process was that it did not remove phosphorus from the pig iron. As you know, phosphorus makes steel excessively brittle. Most of phosphorus was generated from iron ore founded all over the world. Exactly 20 years later, Sidney Gilchrist Thomas, discovered in 1876 that adding a basic material such as limestone draws the phosphorus from the pig iron into slag. This is normally called basic Bessemer process, sometimes Thomas process. This crucial discovery enabled iron ore from many regions of the world to be used for Bessemer converter which in turn led to skyrocketing production of steel like this. On the other hand, another steelmaking process was developed in Germany. The usual open, that is the usual usually called the open hearth process This process used pig iron ore and scrap. It became known as the Siemens-Martin process. The process allowed closer control over the composition of the steel; also, a substantial quantity of scrap could be included in the charge. This process has this kind of a characteristics unlike the Bessemer converter which makes steel in one volcanic rush, the open hearth process takes hours and allows for periodic laboratory testing of the molten steel so that the steel can be made to the precise specifications. The open hearth process also allows for the production of larger batches of steel than the Bessemer process and the recycling of steel scrap. Because of these advantages, by 1900, the open hearth process had largely replaced the Bessemer process. And then another innovative, steel making process was developed around 1950's, that is the Basic oxygen furnace(BOF). The basic oxygen furnace is a refined version of the Bessemer converter, which replaced the blowing of air with blowing oxygen was commercialized in 1952-1953 in Linz-Donawitz, Austria. It lances oxygen above the steel, reducing the amount of nitrogen uptake into the steel. Blowing oxygen through the molten pig iron lowers the carbon content of the alloy and change it into steel. The vast majority of steel manufactured currently in the world is produced using BOF. So, therefore we can summarize this way, there base oxygen furnace brought us a very innovative steelmaking process which can deal with pig iron, steel scrap as well as feeding materials to turn them into a steel product. Then let��s look at lets closer look at another steelmaking process which is electric arc furnace (EAF). Electric arc furnace was designed to pass an electric current through charged materials. Through the 3 electrode resulting in exothermic oxidation and temperatures up to 1800 degrees C, more than sufficient to heat steel production. The use of EAF's allow steel to be mad from a 100% scrap metal feedstock. This greatly reduces the energy required to make steel when compared with primary steelmaking from ores. Another benefit is flexibility of electric arc furnaces, while blast furnaces cannot vary their production by much and remain in operation for years at a time, EAF can be rapidly started and stopped, allowing the steel mill to vary production according to their demands. Although steelmaking arc furnaces generally use scrap steel as their primary feedstock, if hot metal from blast furnace or direct reduced iron is available economically, these can also be used as furnace feed. However, there have been great efforts to develop alternative ironmaking process to cope with some environmentally sensitive measures and to cope with scarcity of high quality iron ore and cooking coals. They are smelting reduction technology and direct reduction technologies. Smelting reduction technology produce liquid iron and provide it to BOF process and EAF process. On the other hand, direct reduction technology produces solid state DRI and which is produced to transported to electric arc furnace. Let's look at the characteristics of directly reduced iron. Direct- reduced iron is called sponge iron is produced from the direct reduction of iron ore in the form of lumps or pellets or fines to iron by reducing gas produced from natural gas or coal. Direct reduction refers to processes which reduce iron oxides to metallic iron at a temperature below the melting point of iron. This process was mastered by our ancestors already several thousand years ago. The product in such a solid state are called direct reduced iron. The reducing gas is a mixture of gases, primarily hydrogen and carbon monoxide. The process temperature is typically 800 to 1050 degrees C. The direct reduction process is comparatively energy efficient. Steel made using DRI requires a significantly less fuel DRI is most commonly made into steel using electric arc furnaces. Two representative DRI are producing processes MIDREX and HyL process which are quite popular the among petroleum producing company because the natural gas is utilized to reduce iron oxide. Then, let's look at close factors that make DRI economical. DRI has about the same iron content as pig iron, typically 90-94% total iron, so it is excellent feedstock for the electric furnaces because the scrap has a lot of impurities called tramp elements. And then hot-briquetted iron is normally manufactured because it is a competitive form of DRI designed for easy shopping, handling, and storage. On the other hand, hot direct reduced iron, is produced by not cooling, before discharging from the reduction furnace, that is immediately transported to a waiting electric arc furnaces and charged, thereby saving energies. Let's look at talk about smelting reduction process. Smelting reduction technology is a coal- based ironmaking process. The product of coal is avoided which require no coking plant. In this process agglomeration of iron ore is avoided which does not require sinter plant. The process involves both solid- state reduction and smelting. That's why some people define smelting reduction process in terms of their separate treatment of iron in pre-reduction furnace and melting furnaces. The process exploits the principle of coal gasification in a molten iron bat in terms of oxygen blowing. The one representative process of smelting reduction process is COREX process. The COREX process consists of 2 main parts a Reduction Shaft here and Melter-Gasifier here. The main reason for the COREX process are iron ore, non-coking coal, and oxygen. Unlike the blast furnace the COREX process uses not air but oxygen. The second smelting reduction process is FINEX process which was developed by Siemens and POSCO as an innovative methodology in way molten iron is produced directly using iron or fines and non-coking coal. The main benefits of the FINEX process include process efficiency, lower environmental impact, process simplification in terms of the pre- reduction in fluidized-bed reactors and the melting of DRI powdered DRI in melted gas fires. Another smelting reduction process is Hlsarna process. This smelting process is a process for primary steelmaking where iron ores are processed almost directly into steel. Actually, this process is optimal combination of blast furnace ironmaking and BOF steelmaking. So this is process based around a new type of blast furnace called cyclone converter process here which makes it possible to skip the process of manufacturing pig iron that is necessary for BOF process.
