Paper Example on Steel Manufacturing: Raw Materials and Production Routes

The essential raw materials required in steel manufacturing include iron ore, coal, limestone or coke, and recycled steel. In steelmaking production, there are two significant routes involved with their respective inputs, namely;

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The integrated course which based on the blast furnace and the basic oxygen furnace, and takes up limestone, iron ore, coal and recycled steel as the raw materials. For instance, to produce 1000 kilograms of crude steel, this particular route consumes 300kg of limestone, 1400kg of iron ore, 800kg of coal, and 120kg of recycled steel.

The electric arc furnace route which uses direct reduced iron and recycled steel and electricity on a primary basis before other raw materials such as coal being added up. For example, using this route, to produce 1000kg of crude steel, 880kg of recycled steel is combined with varying amounts of other inputs such as 16 kg of coal and 64kg of limestone.

The consumption of raw material again depends on the final product and quality required by the customer. The consumption of raw material given above is commonly used to manufacture the standard grade steel almost by all the steel manufacturing industries.

Iron ore

Approximately 98 per cent of mined iron ore is used to produce steel. Iron ore is the most critical input in the manufacturing of steel, which is the backbone of maintaining a robust industrial standard or base. Putting in consideration availability of naturally-occurring impurities, 60 to 65 per cent high-grade pure content can be extracted from the ores, hence making iron one of the most dominant metallic elements in the earth crust.

Coal and Coke

Coal is an essential raw material in steel production, used as energy input in the form of solid fuels to yield electricity and heat in the presence of oxygen by combustion. Coal is derived from iron oxides by using carbon as a reducing agent. Coal also play vital role in maintaining carbon dioxide and carbon monoxide level in the chemical composition in the production of steel or casting. On the other hand, coke as an input in steelmaking is to reduce iron ores to a hot metal with carbon.

Recycled steel

Through its durability and recyclability characteristic, steel can be infinitely reused as an input in steel production inform of scrap. About its magnetic properties, iron can be easily separated from waste materials, enhancing high recovery rates and environmental conservation through avoided landfills. Therefore recycled steel saves on energy and raw materials as it can be easily converted to new steel.

Stages involved in the Steel making process

The overall process in steelmaking from the introduction of inputs that is coal, iron ore, coke, and recycled steel to steel finished products involve several stages, namely modern iron making, conversion of steel, basic oxygen steelmaking, electric arc furnace, secondary steel making, and casting steel. These processes include:

Modern iron making

The first step involved is that iron ore is mixed with coke, which acts as a reducing agent. It is then heated to form a sinter. Sintering is an essential part of the entire iron manufacturing process in the blast furnace because it reduces waste and yields an efficient raw material for iron production. Different grades of coal are stored and blended before transfer to coke ovens. It's then introduced to coke ovens, where coal is heated to form coke. Coke is then removed from the oven and cooled before being used in the blast furnace. Coal gas produced during carbonization of coal in the coke ovens is collected to be used as fuel energy in the manufacturing process whereas tar, benzoyl and sulfur, which are the by-products, are extracted from further refining. Therefore, recycling the gas in this way makes an essential contribution to the thermal efficiency of the entire process.

Input materials that are coal, ore, resin & hardener, pig-iron, bentonite, sinter, bauxite and limestone are fed into the upper part of the blast furnace whereas hot blast air that maybe oxygen-enriched if introduced through the nozzles in the bottom part of the furnace. The purpose of the blast air is to provide additional heat and minimize coke needs. The blast then distributes the heat in the furnace to extremely high temperatures which in turn melts out the iron in the ore and sinter into a pool of hot and molten metal that settles in the bottom part of the furnace. The purpose of limestone is to combine with the impurities and molten rock from the iron ore and sinter forming a liquid slag that floats on top of the hot metal due to its lighter density. The main feeds at the top of the furnace act as a valve to prevent the escape of gas that's collected via large-bore pipes to a gas cleaning plant.

The significance of iron manufacturing is that the process is continuous since when enough amount of hot metal is accumulated, it is tapped off into ladles for steel making. Similarly, the molten slag is also tapped off at regular intervals via different tap holes, and at the same time, raw materials are continued being charged at the top of the blast furnace. The continuous process is determined by the life span of the furnace, which takes about ten years to deteriorate and hence at such a state, the furnace is relined.

Conversion of steel

The original feed material for steel making is either hot molten metal from the blast furnace, steel scrap or the mixture of both the steel scrap and the hot metal. With regards to the process and the type of steel needed, the materials used are determined by the proportional requirements of the process invested. Generally, steel is referred to as iron with most carbon removed to make it enhance its strength in terms of toughness and flexibility. Steel is separated with its various grades, with each grade characterized by specific chemical composition and individual properties attached to the requirements of different applications.

Basic oxygen steelmaking

In the BOS, hot metal from the blast furnace and steel scrap is used as the primary inputs. Modern converters will take charge of up to 350tons of the feed materials and convert it to steel in about 15 minutes. To eliminate unwanted elements and carbon from the molten charge, high purity is blown on the metal under high pressure as well as water-cooled oxygen is lowered into the converter. Oxidation reactions that take place in the converter yield heat while the temperature of the metal is managed by the amount of the scrap introduced, (Kuang, X.M., et al, 2017, pp. 147-158). The carbon monoxide gas, which is the by-product of the oxidation reactions, can be collected and after cleaning reused as fuel. While the high purity oxygen is blown over the molten charge, lime is added as a flux to remove other impurities in the form of a floating slag. The amounts of scrap, metal and lime flux are taken in account to ensure that the correct steel temperature and composition is attained. Injection of argon, nitrogen or carbon dioxide gases through the base of the modern furnace aid in the refining process. After refining, samples are taken to check on temperatures and composition, after which the converter is slanted at an angle and steel is tapped to the spoon. After all the steel has been tapped, the converter is turned upside down to collect residual lime slag into the slag ladle into slag cooling pond. In the pond, slag is processed further to reclaim any material that can be recycled.

Electric arc furnace

In the EAF, the first material is only cold scrap metal. Initially, compared to all other process involved in steel making, this is a more precise one in terms of composition control hence mainly used in making of high-quality steel such as steel for the production of machine tools, automobile engines parts and spring steel. Presently, electric arc furnace is also used in the manufacture of a wide range of steels such as stainless grades and alloys as well as some special carbon and low-alloy steels. To meet customer demand, modern electric furnaces can yield up to 150 tons of steel in a single melt. EAF is made of a circular path with a rotatable roof, via which three graphite electrodes can be raised or lowered. As the process began, electrodes are withdrawn, and the roof is moved clear to charge the steel scrap into the furnace. The after charging, the roof is swung back, and electrodes lowered into the furnace. Then a powerful electric current is passed through the charge to form an arc, and the heat produced melts the steel scrap. Fluxes of both fluorspar and lime are the introduced and oxygen is then blown into the melt; thus, the impurities in the metal combine with the lime flux to form liquid slag. Samples are then collected and analysed to check on composition, and also when the exact composition and temperature has been attained the furnace faster tapped into the ladle. In this stage, customer specification can be met by adding alloys during tapping.

Secondary steelmaking

In secondary steel making, customer specification is met since molten metal tapped into the ladle from the BOS furnace or EAF is given one or more treatments as per the grade of steel required. The further refining treatments include wire injection, ladle stirring with argon, vacuum degassing and ladle arc heating, and they improve homogenization of temperature and composition. This allows careful trimming to more accurate and exact compositions, removal of dangerous and unwanted gases such as hydrogen.

Casting steel

Casting steel is a very crucial process in steel manufacturing since it produces finished products from molten steel. First, the molten steel has to solidify and be formed into standard or semi-finished casting products available in varied shapes termed as billets, blooms, or slabs. These particular shapes were generated by pouring molten steel material into ingot moulds which are then placed in soaking pits which ensures the uniform temperature is attained before being channeled to the primary mills, where rolling is done to needed shapes. The moulds are made of two parts one is called drag and the other is called cope. In between drag and cope there is mould which is exact shape of the final product which is needed.

Continuous casting

In this process, molten steel is directly poured into the casting machine to generated billets, blooms, or slabs. This process promotes efficiency since it eliminates the need for primary and intermediate rolling mills, use of ingot moulds, and soaking pits. Continuous casting also increases the production of good product from a particularly given weight of steel and processes steel into a semi-finished form that's closer to that of finished products. In this process, a vessel of steel with its mouth covered by an insulating lid to reduce heat loss undergoes a sequence of casting without stopping the machine, hence saving on costs incurred. Before casting operation, a gas-tight refractory tube is installed on the outer part of the nozzle to prevent liquid steel from absorbing excessive oxygen and nitrogen from the atmosphere. After molten steel is solidified, steel is then drawn from the bottom of the mould via a curved pattern which supports rolls and water sprays until its occurs as a solid steel slab discharge from the machine, its automatically cut into the lengths as needed. Presently, continuous casting is widely employed in steel manufacturing industries as it saves on costs and its efficiency in the production of the more precise composition of steel thus high quality, in comparison to initial casting steelmaking.

Increased competitiveness in the steel industry in terms of energy conservation. literally steel making is regarded one of the most energy dependent process. Many kinds of researc...