Download Ironmaking Material Balance: Ore Consumption, Slag Composition, and Air Requirements and more Study notes Materials Physics in PDF only on Docsity! Lecture 28: Materials Balance in Iron making Introduction Illustration Key words: Ironmaking, reduction of iron oxide, material balance Introduction The blast furnace is essentially a continuous counter‐current reactor in which the descending chargeis heated and reacted with ascending gases, derived from combustion of carbon at the tuyere. The charge consists of iron sinter/pellets +coke and limestone. During descent, iron oxide is reduced to FeO and limestone decomposed to CaO and CO2. The combustion of coke at the tuyere level with air raises the temperature in between 1800 to 2100 , and melts slag and metal. The reduction of FeO to Fe and the melting of iron and formation of hot metal and slag begin once the charge descends to the bosh region. The following reduction reactions occur: SiO 2C Si 2CO MnO C Mn CO P O 5C 2P 5CO FeO C Fe CO The gases consisting mainly of CO and N and some H , derived from moisture of blast, ascends through the charge. Heat transfer occurs as the gas rising upward and simultaneously reduction of wustile to Fe occurs.The CO so produced quickly reacts with C and produces CO CO C 2CO Further reaction between CO and higher oxides of iron will produce CO which accumulates in the ascending gases. The content of CO increases with the decomposition of CaCO CaCO CaO CO . at about 950 . The exit gas may contain CO CO⁄ ratio close to one and leaves the furnace at about 500‐600K. It may also be noted that the reduction of FeO to Fe occurs both by carbon (called direct reduction) and CO (called indirect reduction) Illustration Let me illustrate material balance through a problem Consider a blast furnace which is charged with iron ore coke and flux of the following composition: Iron ore (weight %): Fe2 O3 =78, SiO2 ‐8.4, MnO = 0.6, Al2O3=5.0, P2O5 = 1.7MgO = 1.2 and H2O=5.1 Coke (weight %): C=88, SiO2 =9, Al2O3 =1 and H2O = 2 Flue : Ca CO3=96 %, Mg CO3 =2% and SiO2 =2% Pig iron analyses weigh percent % Fe 92.7, C 4 Si 2, P 0.9 and Mn 0.4 The coke rate is 900kg/ton of pig iron. (Modern blast furnace operates with much lower coke rate) During smelting 99.5% of Fe is reduced and 0.5% is slagged. The CO/CO2 ratio in the top gas is 2/1 Calculate a) Weight of iron ore b) Weight and composition of slag c) Volume of air required d) Volume and% composition of exit gas. Solution: Fe balance: (0.995).(Fein iron ore) =Fe in pig iron Let x kg iron ore 0.995 0.78 927 (a) Weight of slag: Slag consists of FeO, SiO , Al O , MgO, P O , CaO Si in slag Si in ore Si in coke Si in limestone Si in pig iron 88.65kg 3.166 kg moes SiO in slag 189.97 kg Al O in slag 0.05 1706 900 0.01
