Raw material for ironmaking process, the iron ore and the coal. They obtained from mines. They are not directly used for ironmaking process. They should be pretreated so in ironmaking plant, there are two pre-treatment plant. One is a coke plant the other is sinter plant. Let's first look at coke. What we can get from mine is called coal. Coal is natural form of carbonaceous materials. This contains a certain number of volatile materials inside such as moistures. In order to be effectively used for ironmaking process this coal needs to be treated in coke oven to transform into coke. So this is coke produced from coal. The coke is of course the source of reduction of iron ore by providing carbon to iron ore and when it burns, and it also generates a lot of heat. So heat energy required for ironmaking process is supplied by this coke and this is a source for carbon of hot metal. When iron is reduced from iron ore, first it could be a solid state. But by dissolving carbon from coke, the melting temperature of iron lowers and could become a molten state so that's why, we could get the hot metal in liquid form and coke has certain level of mechanical strength. Since this coke and iron ore are stayed inside blast furnace layer by layer, coke and iron must sustain a certain amount of weight. So this coke could be a source of the internal structure of blast furnace burden, and from the coal it contains certain amount of impurities like sulfur and some volatile melt like Alkalis. So if we could lower amount of suffer in Alkalis in coke then this is much preferred. Next, the iron ore, iron ore is also put into blast furnace layer by layer with coke. So it should sustain some burden inside blast furnace. If it could use lump type ore, then it may be okay but in these days the lump ore has been consumed and the available ore is very fine powder type. So these ore is first brought into sinter plants and it under goes some agglomeration process Then we could produce sinter or pellets. Having this Agglomeration process, it could improve the permeability of this sinter and it allows better gas solid contact so the Boudouard''s reaction we produce CO gas and CO should react with iron ore. Certain level of permeability should be available if we use just fine powder type ore then permeability will be very very low and having this type of sinter we could reduce coke consumption rate but increase reduction rate. And just fine ore is used then this powder will be blown out of the blast furnace by gas but having sinter it could be prevented and of course, the fine ores are much less expensive than the lump type ore. And when sinter is made not only iron ore powder is used but, also certain type of flux is added. So sinter is composed of iron oxide and some other flux, this is put into blast furnace so this process effectively used. Why do we use flux inside? Iron ore and coke contains certain level of impurities called gangue and ash. The gangue is typically composed of silica and alumina. Once ore and coke react together then iron is produced and carbon is disappeared in forms of gas then just this impurities are remained. This silica- alumina melts and forms molten silicate or molten alumino silicate, we call this as slag. This slag has this kind of network structure inside. Having this network structure lowers fluidity, in other words slag has high viscosity, because of this mass transfer inside blast furnace becomes lower. In order to improve mass transfer or in order to make this slag more fluid, we need to add some flux, this is limestone providing calcium oxide from calcium carbonate. This could lower viscosity by breaking this point in several places so that network structure becomes in smaller size by doing this the fluidity of slags becomes improved. Also at the same time the provided flux CaO is effective in removal of sulfur available in coke by this reaction. Lime reacts with sulfur to form calcium sulfide and calcium sulfide absorbed into slag. Finding its way, sulfur available in coke and absorbed in hot metal could be exerted out of hot metal into slag. Then now let's look at sequence of ironmaking process. This is scaled out figure of iron making plant. First, we have raw materials, iron ore and some blocks here and cokes. These are delivered through this route and charged into blast furnace from top position. At the same time, the heated air from hot stoves is delivered through this route called tuyeres from bottom side of blast furnace. Temperature of this heated air is about 1150 degrees celsius. This air moves upward and raw material moves downward and they react together. So this is typical of current reactors. The heated air burns the carbon in the fuel gas to form carbon dioxide and this carbon dioxide react with coke to form carbon monoxide. Then this carbon monoxide removes oxygen from iron ore, in this way iron ore is reduced and iron is produced. Reduced iron melts by dissolving carbon from coke and it actually falls down to bottom of this blast furnace called hearth. At the same time, the ash and gangue materials combined with the flux added to this system and it also absorbs impurities and they form slag. Slag is also falling down to bottom of this vessel. The density of slag is lower than density of hot metal. Slag stays over hot metal. Then this how metal is tapped and slag is also drained out. The raw materials, ore, flux and coke, they continuously delivered into blast furnace and hot air is also continuously delivered into blast furnace. Reacted gas moves upward and it is collected again to be recycled. Whole these processes are continuously repeated. Let's look at what's happening inside blast furnace. This chemical figure shows inside temperature level of blast furnace. Temperature could be increased up to 2,600K is quite high. What is delivered into this system? We actually charge coke ore and some other types of ore. Lump type ore or pellet type ores as raw material. At the same time, we provide air which is heated around these temperatures. Then they react together inside furnace. As a result we produce hot metal and slag as by-product and reacted gas leaves out of the system and it is recycled. Now let's compare temperature of blasted hot air and the exit scale. When gas leaves out of blast furnace it's temperature was lowered significantly. It means the heat energy contained in hot air is efficiently left inside blast furnace and it leaves as a cool, cold gas. This means that this blast furnace is very effective reactor in terms of energy saving. Required energy is provided by self inside blast furnace and it could increase temperature up to or over 2000k. And as a result, we could produce hot metal and slag. The time required to for this process, we call tap to tap time. It's about five to six hours, it means when you put raw materials here after five to six hours it came out as a hot metal and depending on size of this blast furnace, the producing capacity is also dependent. The capacity and tap time and the number shown in slide are just an example. It varies from blast furnace to blast furnace even in one ironmaking plant because this is just an illustration purpose. Inside blast furnace, now let's look at reaction. We have ore and coke to this coke we blast hot air with fuel. They form carbon dioxide gas and comes out as gas reacted coke to form CO gas. This CO gas moves. This pours inside coke and it arrives at ore to react with ore. Then, ore in the form of Fe2O3 or Fe3O4, they react with CO gas to form a reduced form. From Fe2O3 to Fe3O4 or to FeO. This FeO finally reacts with CO gas to form reduced Fe and carbon dioxide gas. Again the process of carbon dioxide gas is converted into carbon monoxide gas through Boudouard's reaction. And through this reaction, calculation occurs but at the same time heat energy is involved. Carbon in the fuel gas react with oxygen in hot air, it becomes CO2 gas. This produces a lot of heat so this is the heat energy used inside blast furnace and requires for ironmaking reactions. So the blast furnace does not require any external device to heat inside but all the heat energy is produced by itself so this is quite effective. As a result of the ironmaking process, we could get hot metal and slag. The hot metal contains certain level of carbon, sulfur, silicon, manganese, and phosphorus. Depending ore used, we may have titanium or some other type elements. This will be sent to steelmaking plant.
