Swelling Behaviour of Cement-bonded Briquettes-proposed Model

Abstract

The cement-bonded agglomeration process is an alternative to the traditional balling-sintering process for recycling iron-rich by-products generated in iron and steel plants back to the blast furnaces. It has been observed that, under certain conditions, the briquettes containing pellet-fines show a tendency to swell catastrophically when reduced. This swelling is dependent upon a number of factors like: reducing temperature, composition of briquettes, particle size of raw material, amount of cement and composition of reducing gas. The SEM and optical micrographs do not show the formation of iron whiskers as the cause of swelling; instead, the swelling is due to the movement of reduced iron particles away from each other. It has been proposed that the swelling takes place in three steps: (a) fragmentation of weak pellet-fines particles during reduction to wustite; (b) formation of liquid slag due to reaction between CaO, MgO, FeO, SiO 2 and Al 2 O 3 ; (c) generation of high gas pressure due to formation and subsequent oxidation of metastable iron carbide.

Novel Approach Towards Biomass Lignin Utilization in Ironmaking Blast Furnace

“…At 850°C, the iron oxides are reduced to metallic iron. At 1 100°C, the metallic iron became the dominant phase in the reduced samples beside slag (CaO, CaSiO 4 and CaMgSiO 4 ). The intensity of metallic iron in lignin samples (R3) is higher than that in reference sample (R1) which confirms the positive impact of lignin on the reduction rate of iron oxides.…”

“…[1][2][3] Under normal conditions cement is used as a binder to give the proper mechanical strength of the briquettes and then it goes to slag during the production of hot metal. [4][5][6] Coke and coal are the main sources of fuel and reducing agent in the blast furnace, at the same time they are responsible for the main fossil CO 2 emission in steel industry. Intensive work is being done to mitigate the CO 2 emissions in steel industry by partial substitution of fossil fuels (coal and coke) with renewable source of energy such as biomass.…”

Dynamic and Isothermal Reduction Swelling Behaviour of Olivine and Acid Iron Ore Pellets under Simulated Blast Furnace Shaft Conditions

“…Swelling can be categorized into normal swelling, up to 20% in volume, [1][2][3][4][5] and abnormal, i.e. catastrophic swelling, which may exceed 400% in volume at worst.…”

“…2) Various operating parameters such as firing time, rate of reduction, reduction temperature, reduction time, reducing gas atmosphere, partial pressure of reducing gases, total flow rate, impurities in the reducing gas and isothermal/nonisothermal reduction, and pellet properties such as porosity, basicity and gangue content, have been reported to affect the swelling of different pellet types used in blast furnaces. [1][2][3][4][5][6][7] Some authors 10,11) have reported the existence of a critical rate of reduction at which the swelling index of an iron oxide pellet reaches its maximum value. In addition, sulphur 6,22,23,25) and potassium 22) in the reducing atmosphere have been associated with the swelling of pellets.…”

Effects of Firing and Reduction Conditions on Swelling and Iron Whisker Formation during the Reduction of Iron Oxide Compact

“…Singh and Bjorkman [23][24][25] studied the effect of reduction conditions on the swelling behavior of cement-bonded briquettes. It was observed that, under certain conditions, the briquettes containing fines generated from pellets during handling show a tendency to swell catastrophically when reduced at 900-1 000°C using CO.…”