The Modern Processes for Steel Making - Essay Example

aSteel Making The report presents comprehensive discussion on the different process used in making of steel as determined by the different raw materials available for use, and the technological feasibility that ensures maximum production at the least cost possible. The processes that include Basic Oxygen Steelmaking, Electric ar Furnace and Electric Induction Furnace will be discussed. The relevant environment-related challenges will equally be addressed. Date: ID: Word Count: 2293 Introduction Steel is among the most important products with a wide range of usage in the world. The steel industry has undergone gradual changes in its processes over time. The process of steel making process involves producing steel from either the ferrous scrap or from iron. During the steel making practice, there is the removal of excessive impurities, among which are silicon, nitrogen, carbon and phosphorous from raw iron, together with other elements of alloy like nickel, vanadium, chromium and manganese, for the production of different steel grades (Mohammed, Stephen, and Seetharaman 1566). The limitation of dissolved gases that include oxygen and nitrogen, as well as all other impurities entrained within steel is important for enhancing the product quality cast from the initial liquid state. Two important processes are involved in steel making; the electric arc furnace, and Basic Oxygen Steelmaking (BOS). The latter uses scrap steel and blast-based liquid pig-iron as the major feed materials, whereas the former makes use of the direct reduced iron or the scrap steel (Mao, Pan, Pang, and Chai 67). The oxygen steel making is exclusively fueled by the reaction’s exothermic nature within the vessels, while the electric arc furnace (EAF) process makes use of the electric energy for melting of the solid scrap material. Introduction of additional chemical energy for EAF processes has enhanced the evolution of the process to almost equal the technological expertise involved in oxygen steel making. The modern processes for steel making can be classified as primary or secondary. The primary steel making generally entails the conversion of liquid iron from an original steel scrap and blast furnace to steel by the melting of scrap, or basic oxygen steel making, and the use of direct reduced iron within the electric arc furnace (Seiji, Yoshiyuki, and Masuro 13). The secondary process of steel making, however, entails the refinery of crude steel prior to casting, and this involves numerous operations in the ladles. The addition of alloying agents occurs during the secondary metallurgy process, together with lowering of dissolved gases within steel. The process also facilitates removal of inclusions or general chemical alteration to ensure production of steel with high quality following the casting (Naiyang, and Joseph 224). The Basic Oxygen Steelmaking (BOS) Process The basic oxygen steel making method is among the primary steel making techniques, where molten pig iron that is rich in carbon is converted into steel. The oxygen is blown into the molten pig iron in order to reduce the content of iron in the alloy as well as changing it into steel, a process referred to as ‘basic’, owing to the chemical integrity of manganese and calcium oxide refractories, which form the lining of the vessels in order to withstand the corrosive nature and high temperatures of slag and molten metal within the vessel (Mohammed, Stephen, and Seetharaman 1568). The BOS process of steel making constitutes of an approximate 60 percent of the total crude steel output in the world, hence making it the dominant technology for steel making. This technology varies from the EAF due to the self-sufficiency or autogenous nature of the BOS in energy. The major raw materials for use in the BOSare hot metal in liquid form from blast furnace with the rest being the steel scrap (Mao, Pan, Pang, and Chai 69). All these are then charged into the vessel of Basic Oxygen Furnace (BOF), with oxygen eventually blown at extremely high velocity into the BOF. The oxygen oxidizes silicon and carbon elements in the hot metal, and these release high heat quantities that melt the scrap (Seiji, Yoshiyuki, and Masuro 15). Oxidation of manganese, iron and phosphorous results in less contribution of energy. On the other hand, the carbon monoxide post combustion during its exit from the vessel results in transmission of heat back into the bath. The BOS product is the molten steel that has definite chemical analysis at between 2900°F-3000°F. There could be a further refining of the same during the secondary process of refining, or could be directly sent to the continuous caster for solidification into the semi-finished shapes like slabs, billets and blooms (Naiyang, and Joseph 226). The Basic, which is the refractory lining of magnesia (MgO), wears out as a result of contact with slag that is basic and hot. The popularity of the use of this process in steel making, which was initially referred to as Linz and Donawitz (LD) process, has grown markedly in the recent days hence revolutionizing the entire technology for making of steel (Mohammed, Stephen, and Seetharaman 1570). The basic oxygen converter, which is basic in nature, has a pear-shape, together oxygen lance that is positioned concentrically. In addition, the shell made of steel is lined with refractories that are basic in nature. The ferro-alloys, scrap, fluxes, as well as the hot metal get charged down through via th throat and into the converter. The figure showing BOF Vessel in operation Positions (Mohammed, Stephen, and Seetharaman 1566). Figure for molten steel ladle leading to the ladle metallurgical plant (Naiyang, and Joseph 226) Electric Arc Furnace (EAF) Direct arc electric furnace applications are also common in the steel making processes. This method involves the use of three electrodes, which are often made of graphite, which are positioned on cup or bowl-shaped hearth, acting as stores or containers for molten slag and metal (Mao, Pan, Pang, and Chai 72). The electric current is let to pass through the electrodes with arcs struck between the charge and the electrodes. The heating process occurs by both convention and radiation from the arcs, and to a lower degree, due to the electric current passing through them. Figure for the EAF process (Yuanyuan, and Shixin 1042) The general plant construction includes making of electric arc furnace that is constituted by three phases, added to three graphite or carbon electrodes. The constituents of the furnace are largely a robust steel shell on the outer side with a circular cross section, and also has a bottom with a dish-shape, together with a roof ring that supports the refractory roof, which is slightly dome-shaped (Naiyang, and Joseph 228). The roof is made of three holes that are placed symmetrically at around the centerline, and located at the apices of the equilateral triangle, which provides a way for the electrode entrance into the furnace. The furnace is essentially made of the steel shell with a circular cross-section, together with a removable ring on the roof and a dish-shaped bottom, with all of these offering support to the refractory roof with a domed shape (Naiyang, and Joseph 224). The electrodes get low and high as controlled by the hydraulic ram or motor, hence controlling the power level reaching the furnace. Figure for Scheme of an Electric Arc Furnace (Naiyang, and Joseph 224) Recycled scrap from of steel is an ideal source of raw material that is eventually used in EAF. Upon completion of scrap loading in EAF, there is the lowering of electrodes past roofs that are retractable EAF at scrap metal charge. The transfer of electricity occurs from an electrode to a scrap metal charge, and comes back to the other electrode. The heat for use in scrap metal charge melting develops as a result of the metal resistance to the flow of high level electricity, together with the resultant heat from the arc (Seiji, Yoshiyuki, and Masuro 15). The melting process is sped up by the injected oxygen into the EAF, and there could be the addition of alloys and fluxes into the EAF at the completion of the melt cycle, or at the ladle following the taping of EAF in order to establish the chemistry behind the steel heat. The molten steel is eventually tapped to a ladle from the EAF. Eventually, the ladle is pushed to the metallurgy refining station (LMF). The steel heat is verified when the ladle reaches the LMF for the purpose of determining whether or not a proper alloy addition was done during heat taping. Additional alloys together with fluxes could be added at LMF when necessary. The chemistry of the heat of steel as well as temperature homogenization is fulfilled when the inert gas is bubbled via the ladle (Mao, Pan, Pang, and Chai 74). When the LMF treatment is completed, the ladle is eventually sent to the operation of continuous casting. The strand casting or continuous casting operation leads to the production of beam blanks, billets, as well as the profiles with near-net shapes. The half-finished products are then used in rolling mills for the production of structural shapes. For instance, the molten steel is often poured through a nozzle that is slide gate controlled on the lower side of the ladle to form tundish. Tundish is used as a reservoir and works to release the steel in molten form in a continuous stream via a series nozzle within its base. The outflow of steel is at a relatively steady rate and is drained into the oscillating mold. The interior part of the hollow oscillating mold bears internal dimensions that correspond to the thickness and width of the beam blanks, billets, as well as the near-net shape profiles that are cast. These molds are then held within the water cooled jackets, which direct the flow of water around the external walls of the mold. As the solidification of the metal surface begins, there is the formation of a thin skin at the external edges. As the freezing operation continues, there is a continuous movement of the metal in the mold downwards during the up and down oscillation of the mold, in order to prevent sticking of the metal (Mao, Pan, Pang, and Chai 77). The solidification of the metal occurs towards the center of the skin from outside throughout the process. Upon the solidification of the metal, the beam blanks, billets, and the near-net profiles are cut into certain lengths and could be directly charged to the rolling mill. Electric Induction Furnace (IF) Apart from the use of electricity in arcing, the same can be employed in solid charge melting by induction, the same way it is done in the induction furnaces. Therefore, an electricity induction furnace is important in the steel plant since it facilitates the production of high quality steels, especially the stainless steel produced from the stainless steel scrap (Naiyang, and Joseph 224). Application of induction melting furnaces became popular after the installation of these furnaces, which could then produce stainless steel. The induction furnace chemistry behind melting cheminstry can be regulated by addition of mill scale into the bath, containing oxide carbon following the melting of a high-quality steel scrap. The use of the sponge iron, especially the finer ones with between 1 and 3 mm sizes, in the furnaces has equally enabled the manufacture of pencil ingots without tramp elements (Yuanyuan, and Shixin 1040). This means up to 40 percent of the sponge iron can be used in making high-quality steel. Environmental Issues The steel making processes are associated with various environmental challenges, which must be dealt with in order to ensure a safe environment for humans and other organisms. Among notable challenges experience at BOS plants is capturing and removing contaminants within primary off gas that is dirty and hot, coming from converters. In addition, there are secondary emissions, which are linked to tapping and charging of furnaces. There is the challenge of emission control, particularly that originating from ancillary operations like hot metal transfer, operations of ladle metallurgy, or desulfurization. The plant must also be able to recycle and dispose all the sludges and oxide dusts collected, as well as the slag disposition. Within the US, the majority of the systems for handling primary gas for BOF have been designed for generation of steam for the plant from water cooled hood that serving primary systems. Almost half of all the systems are designed for open combustion and excess air is normally induced at the hood mouth to facilitate complete combustion of the carbon monoxide (Seiji, Yoshiyuki, and Masuro 18). The gases are eventually cooled and then cleaned using dry electrostatic presipitators or the use of wet scrubber. The rest of the systems in he US are suppressed combustions, in which gases are dealt with while in uncombusted state before they are cleaned in wet scrubbers, and later discharged after ignition (Yuanyuan, and Shixin 1042). The gases cleaned in these plants must comply with the set standards in line with the EPA levels of particulate matter. Secondary fugitive emissions linked with the tapping and charging of the vessels for BOF, or the escaping emissions from the hood when oxygen is blown could be captured using exhaust systems that serve the high canopy or local hoods that are located in the shop trusses. On the other hand, ancillary operations that include desulfurization, the hot metal transfer stations, as well as the operations of ladle metallurgy are used for fabric filtering in the exhausts of the local hood system. The particulate matter that is captured from this primary system, which could exist as wet scrubber sludge, as well as dry dusts originating from precipitators, ought to undergo processing before they are recycled. However, the sludge originating from the wet scrubber demand extra step of drying. As opposed to the dust from EAF, the sludge or dust from BOF does not constitute part of the listed hazardous wastes. Work Cited Kasahara, Seiji, Inagaki, Yoshiyuki, and Ogawa, Masuro. Process flow sheet evaluation of a nuclear hydrogen steelmaking plant applying very high temperature reactors for efficient steel production with less CO2 emissions. Nuclear Engineering & Design, 271(2014):11-19 Kun Mao, Quan-Ke Pan, Xinfu Pang, and Tianyou Chai. An effective Lagrangian relaxation approach for rescheduling a steelmaking-continuous casting process. Control Engineering Practice, 30(2014):67-77 Ma, Naiyang, and Houser, Joseph. Recycling of steelmaking slag fines by weak magnetic separation coupled with selective particle size screening. Journal of Cleaner Production, 82 (2014):221-231 Tan, Yuanyuan, and Liu, Shixin. Models and optimisation approaches for scheduling steelmaking–refining–continuous casting production under variable electricity price. International Journal of Production Research, 52.4(2014):1032-1049 Tayeb, Mohammed, Spooner, Stephen, and Sridhar, Seetharaman. Phosphorus: The Noose of Sustainability and Renewability in Steelmaking. JOM: The Journal of The Minerals, Metals & Materials Society (TMS), 66.9(2014):1565-1571 Read More