Zhanxia Di

Influence of microwave heating on the microstructures of iron ore pellets with coal during reduction

Iron ore oxidised pellets as the burden of blast furnace present many advantages, such as uniform size, high iron grade and high physical strength. A comparison of the iron ore oxidised pellets with coal (out-proportioning) by conventional heating and microwave heating was carried out in this paper. Microstructure transformations during reduction process were investigated by optical microscopy and scanning electron microscope with energy dispersive spectrometry analysis. Micro-hardness of metallic iron phase formed in the reduction was tested with digital micro-hardness tester. The influences of microwave heating on reduction degree, morphology, iron phase and gangues were investigated, respectively. The results show that reduction time can be greatly shortened by microwave heating even at lower temperatures. The fine cracks generated, as the pellets were heated by microwave, were irradiated due to the selectivity of microwave heating. Densification of the metallic iron phase and the separation of the iron and gangues were both found to be enhanced by microwave heating.

Mechanism of Selective Desulphurization in Iron Ore Sintering Process by Adding Urea

Abstract Iron ore sintering is an important part during the ironmaking process, and a large amount of SO2 is also generated. Our previous research shows that it is an effective way to reduce SO2 content of flue gas by adding urea to a special sintering material zone position. In this paper, the mechanism of selective desulphurization by adding urea during the iron ore sintering was carried out. The results show that 88.14 % desulphurization rate was obtained with the addition of 0.05 % urea particles at 100 mm height from the feed bottom. During the sintering process, when drying zone reached the added position of urea, large amounts of NH3 were generated by urea decomposition, and then reacted with SO2 to produce (NH4)2SO4 in the wetting zone. With the accumulated desulphurization reactions during the sintering, the low SO2 emission in the flue gas was achieved. Moreover, the addition of urea in the bottom zone avoided the ammonia present in the sintering ore and promoted the urea utilization efficiency.

Assimilation Behavior of Calcium Ferrite and Calcium Diferrite with Sintered Al2O3 and MgO

In this study, the assimilation behaviors between calcium ferrite (CF), calcium diferrite (CF2) and sintered Al2O3, and MgO were explored by an improved sessile drop technique, and the interfacial microstructure was discussed. The results indicated that the apparent contact angles of CF slag on Al2O3 and MgO substrate were 15.7 and 5.5 deg, and the apparent contact angles of CF2 slag on Al2O3 and MgO substrate were 17.9 and 7.2 deg, respectively. Namely, CF and CF2 slag were wetting well with Al2O3 and MgO substrate. The dissolution of Al2O3 substrate into the CF and CF2 slag was found to be the driving force of the wetting process. For the CF-MgO and CF2-MgO substrate systems, CaO contrarily distributed with MgO after wetting. For the CF-MgO system, after wetting, the slag was composed of CF and C2F, and most of the Fe2O3 permeated into substrate and formed two permeating layers.

A pilot-scale study of selective desulfurization via urea addition in iron ore sintering

The iron ore sintering process is the main source of SO2 emissions in the iron and steel industry. In our previous research, we proposed a novel technology for reducing SO2 emissions in the flue gas in the iron ore sintering process by adding urea at a given distance from the sintering grate bar. In this paper, a pilot-scale experiment was carried out in a commercial sintering plant. The results showed that, compared to the SO2 concentration in flue gas without urea addition, the SO2 concentration decreased substantially from 694.2 to 108.0 mg/m3 when 0.10wt% urea was added. NH3 decomposed by urea reacted with SO2 to produce (NH4)2SO4, decreasing the SO2 concentration in the flue gas.

Sticking behaviour and mechanism of iron ore pellets in COREX pre-reduction shaft furnace

ABSTRACT COREX is a clean process releasing lower pollution and consuming fewer cokes than the blast furnace process. However, serious sticking phenomenon often occurs in COREX shaft furnace, causing many problems to the normal operation. In this study, the loading reduction experiments of iron ore pellets were carried out under the simulating COREX reducing conditions. The influence of temperature and H2 content in the syngas on the sticking behaviour of the pellets was observed by scanning electron microscope, energy-dispersive spectrometer and X-ray diffraction. The results indicated that the sticking index increased from 6.7 to 90.43%, when the temperature increased from 750 to 950°C. The main composition of sticking material was metallic iron, and the sticking behaviour depended upon the amount and morphology of precipitated iron on the pellets’ surface. The sticking mechanism was the interpenetrating diffusion mechanism of iron atoms between the adjacent pellets.

Preparation of Direct Reduction Sponge Iron (DRI) Using Pyrite Cinder Containing Nonferrous Metals

Abstract Pyrite cinder is a solid waste generated by the sulfuric acid industry and is considered environmentally hazardous. It contains abundant iron, such as Fe2O3 and Fe3O4, and nonferrous metals, such as zinc, lead and copper. In order to try and recycle this material as a source of Fe units, preparation of direct reduction iron (DRI) using pyrite cinder was investigated by coal-based grate rotary kiln process. This process includes chloridizing and reduction roasting. The results show that 97 % lead was removed after the chloridizing process. Copper was only detached in chloridizing process with the removal rate of 78.49 %. Furthermore, the removal of zinc was carried out in both chloridizing and reduction process, and the removal rate of 96.76 % was achieved after reduction roasting. The final product representing a metallization degree of 93.36 % with compressive strength of 1,198 N/pellet was obtained after the oxidized pellets were reduced at 1,050 °C for 80 min.