Process Fans in Iron and Steel Industry

Steel in industries is manufactured in two ways, traditionally by using raw materials like iron ore, coal and limestone in blast furnace or by recycling the material using electric arc furnaces. The first process involves making of molten iron using the raw materials iron ore, coke (pure form of carbon obtained by heating and driving off impurities of coal) and lime in blast furnace. Then it is further followed by combining varying amounts of steel scrap with molten iron in Basic Oxygen Furnace (BOS). The second method requires no raw materials and reuses the existing steel scrap to produce steel in an Electric arc furnace. Both these production processes require several centrifugal fans for drying & heating ore pellets, handling the undersized dust particles, removing and cleaning waste gases, providing combustion air to burn coke, exhausting waste by-products, cooling the product to remove heat etc.

Pelletizing FansPelletizing is a process that involves mixing very finely ground particles of iron ore fines of size less than 200mesh with additives like bentonite and then shaping them in to oval/spherical lumps of 8-16mm in diameter by a pelletizer and hardening the balls by firing with a fuel. It is the process of converting iron ore fines into "uniformed sized iron ore pellets" that can be charged directly into a blast furnace. The process of pelletization requires several industrial centrifugal fans to supply process air for drying, preheating, indurating and cooling. Particularly, the fans used here should be capable of handling both low level and high level heat produced during the process. For instance, if we consider indurating section where the pellets get dried and heated for hardening, centrifugal fans used in the process have to handle air of different temperatures in updraft drying zone to remove moisture from the pellet bed and to supply downdraft drying air for heating up the pellets.

Sinter Plant FansThe process of sintering is basically a pre-treatment process step during iron making to produce charge material called sinter for the blast furnace from iron ore fines and also from metallurgical wastes (collected dusts, sludge and mill scale etc.).The principle of sintering involves the heating of iron ore fines along with flux and coke fines or coal to produce a semi-molten mass that solidifies into porous pieces of sinter with the size and strength characteristics necessary for feeding into the blast furnace. It is basically an agglomeration process achieved through combustion. Sintering plants use several centrifugal fan types like forced draught combustion air fans to support the combustion, induced draught waste gas fans to draw the gases off through dust removal system, cooling fans to cool the hot sintered product, hot air fans to recover heat from the hot sintered product and return it to the process, and several other fans for exhaust and dedusting.

Basic Oxygen Furnace FansBasic oxygen process is one of the main processes in steel making where pure oxygen is supplied to the blast furnace iron and scrap of steel to produce crude steel. Before charging the iron to blast furnace converter, pretreatment of the metal is done to reduce sulphur, silicon and phosphorous. As the reaction takes place, the process also produces large amount of gas (called converter gas) at high temperatures containing mixture of combustible waste gases of carbon monoxide (CO), carbon dioxide (CO2) and nitrogen (N2).To avoid pollution and keep the production environment clean, there is a need to remove dust & waste gases by drawing them through a dust removal system or wet scrubber. Here the mechanism of induced draft air is typically used for waste gas exhaust. Also the gas coming out of the converter is normally of high temperatures and requires cooling using cooler exhaust fans before the gas is sent to dry precipitators. The cooler exhaust fans are primarily used to maintain the thermal balance of the furnace.

Electric Arc Furnace (EAF) FansThis is secondary method in steel making where high current electric arcs are used to melt the steel scrap to produce steel. Oxygen and coal powder are injected into the hot liquid metal to accelerate the formation of slag. Due to the high content of impurities in the metal scrap, the dust generated during the process can contain hazardous waste which can be dangerous to working environment. The particles of EAF fume extraction can contain emissions of vapors, fine dust and solid particles. Also there is another potential issue for larger industrial installations. Since the process is dependent on high power electric arcs, the temperatures are relatively high near the furnace and within the manufacturing unit. So there is a need to regulate the temperatures and keep the work atmosphere safe. To control the volume and temperatures of waste gases and maintain ambience in the working environment, centrifugal fans of different types are employed for cooling and waste gas reduction.

Apart from the above fan equipment, other centrifugal fan types such as coke oven fans, combustion air fans, booster and exhauster fans and several others are used in steel making applications.

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