Abstract
Thermogravimetric analysis of recycling dust (RD) from the melter gasifier of COREX, coke1 (C-1), coke2 (C-2) and coal char (CC) under 70% oxygen atmosphere was carried out using thermal balance. The chemical composition and physical structure of the samples were investigated. The characteristic temperatures and comprehensive combustion characteristic indexes were calculated and kinetic parameters during the combustion process were calculated as well using a distributed activation energy model (DAEM). The results show that the carbon in the recycling dust originates from unconsumed CC and coke fines, and the average stacking height of carbon in RD is larger than that of C-1, C-2 and CC. The conversion curves of RD are different from those of C-1, C-2 and CC, and there are two peaks in the RD conversion rate curves. The combustion profiles of RD moves to a higher temperature zone with increasing heating rates. The average activation energies of their combustion process for RD, C-1, C-2 and CC range from 191.84 kJ/mol to 128.31 kJ/mol. The activation energy for recycling dust increases as the fractional conversion increases, but the value for C-1, C-2 and CC decreases with increasing conversion, indicating different combustion mechanisms.
Highlights
The COREX process, an alternative iron-making technology, is independent on coking coal to meet the environmental and source requirements, and it has been successfully applied in China, India, South Africa and South Korea [1,2]
The results show that carbon in the recycling dust (RD) mainly originates from unconsumed fine coke produced in the moving bed or hearth and unconsumed pulverized coal burnt in the dome
Combustible components decrease with increasing fractional conversion, and the reaction difficulty tends to increase gradually, which is the main reason that the activation energy of RD increases with conversion increasing
Summary
The COREX process, an alternative iron-making technology, is independent on coking coal to meet the environmental and source requirements, and it has been successfully applied in China, India, South Africa and South Korea [1,2]. Two COREX-3000 processes, the melting rate of which aims to reach approximate 150 t/h, were introduced in 2007 and 2011 in China, respectively. For the sake of taking advantage of low iron costs, one of the COREX-3000 processes was entirely moved to XinJiang, a large region with abundant sources of low rank coal and iron ore. The COREX process can be studied according to the investigations by Wu et al [3,4]. It consists of two reactors: the prereduction shaft furnace and the melter gasifier. The raw materials, i.e., lump ore, pellet, coke and fluxes, are continuously charged into the shaft furnace, while large amounts of coke and lump coal are charged into the melter gasifier. The reducing gas at about 1223 K is introduced through the bustle and moves in a countercurrent direction to the top of the shaft furnace
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