Light burning magnesium ball sintering and reducing magnesium, the benefit is more beautiful

In recent years, the iron and steel industry is facing a severe situation, and the cost of iron has increased sharply, and the quality of iron ore has been deteriorating. In order to stabilize the sinter quality and reduce the cost of ironmaking production at the same time, Jingtang company of Shougang, after a series of basic studies, finally realized the sintering of natural magnesium. The sinter grade, strength, grain size, metallurgical property and droplet performance were improved, and considerable economic benefits were created.

Light burning magnesium balls have obvious advantages in reducing magnesium

As the main burden of blast furnaces in the Asia Pacific region, sinter generally accounts for more than 60% of the blast furnace structure. Magnesium melting agents such as dolomite and serpentine are usually added to increase the MgO content in blast furnace slag to improve the fluidity and desulphurization capacity of the slag and to adapt to the high Al2O3 mass fraction in the slag.

Sintering is the main source of MgO for blast furnace slag, and its MgO content is limited by the requirement of blast furnace slag and the operation habit of blast furnace. The content of MgO in blast furnace slag of Japan and Korea is controlled at 3%~5% level, and most of them are above 7% in China. By this effect, the MgO content of the sinter in Japan new iron, South Korea Pohang light Yang and the modern iron making sinter is at the level of 0.7%~1.2%, while the MgO content of the sinter in China is mostly above 1.6%, and the high is even above 3%. Even some researchers believe that the higher MgO content in sintering is beneficial to the improvement of sinter quality.

In recent years, a large number of domestic light burned magnesia ball sintering researchers have called for light magnesia ball sintering and magnesium reduction, and Shougang Jingtang has been at the forefront of practice. The project group carried out a series of MgO laboratory studies on sintering process heat balance calculation, sintering basic characteristics test and high temperature confocal in-situ observation, ore phase research, sintering cup test and comprehensive furnace drop performance test.

The study found that:

Magnesium reduction helps to improve sinter grade, helps to develop high quality calcium ferrite and improve sinter reduction. Reducing the MgO by 0.5% can increase the TFe content of sinter by more than 0.3%. Under the background of the deterioration of imported ore fines, the magnesia also shows the value of actively protecting sinter grade. The improvement of sinter grade will help to form more high-quality bonding phase - acicular calcium ferrite, which is beneficial to improving sinter index and reducibility.

Magnesium reduction helps to reduce the heat consumption of flux, thereby increasing the effective heat of sintering. Magnesium containing flux can decompose heat consumption during sintering process and reduce the ratio of magnesium containing flux to save energy and improve sinter quality. The MgO content of sinter is reduced by 0.5 percentage points, and the single consumption of magnesium flux is reduced by 14kg/t sinter. The decomposition heat loss of the sintering process is reduced by about 1%, which is equivalent to increasing the effective heat of the sintering process by 1%, which is beneficial to the improvement of the granularity composition of sinter.

Magnesium reduction helps to improve liquid fluidity and enhance sintering bonding effect. The basic characteristics of sintering and the high temperature confocal equipment test showed that after the MgO content decreased from 2.3% to 0.3%, the liquid liquidity index increased from 0.7 to 1.9. Compared with the MgO containing scheme, the solution in situ found that the solution without MgO had the highest liquid flow velocity. The improvement of sinter liquid fluidity enhances the bonding effect and is beneficial to the improvement of sinter size composition.

Sintering magnesium reduction combined with pellet magnesium extraction improves the droplet performance of the composite burden on the basis of ensuring the stability of the blast furnace slag system. The droplet performance test shows that after the transition from 0.7%MgO of sinter 1.9%MgO+ pellet to 1.7%MgO of sinter 1.5%MgO+ pellet, the droplet range is reduced from 64 to 59 C, and the maximum pressure difference is reduced from 1910Pa to 1590Pa, and the S characteristic value of the comprehensive furnace material is finally reduced from 122.2kPa to 93.8kPa.

Benefit from industrial practice

Basic research shows that the advantage of magnesia ball sintering is magnesium reduction. In November 2012, the Shougang Jingtang pellet produced magnesia pellets, which provided conditions for sintering magnesium reduction. In February 2013, the researchers began to reduce the MgO industrial test in the sinter of Shougang. The following results were obtained: the content of sinter MgO decreased from 1.8% to 1.5%, and the sinter grade increased from 55.95% to 56.48% in combination with the structure adjustment of the ore powder. After September 2013, the magnesium containing flux was basically stopped in the Beijing Tangshan, Shougang. After reducing magnesium, the improvement of sintering index is obvious: the proportion of <10mm in sinter is reduced from 20.28% to 17.85%, the reducibility is increased from 80.15% to 84.7%, the droplet performance of sinter is significantly improved, and the S characteristic value of sinter is reduced from 262kPa to 87kPa. In recent years, the main indicators of Shougang Jingtang sinter are shown in the schedule.

After more than one year of industrial practice, the MgO content of the sinter in Beijing Tangshan sinter in 2014 has been stabilized at the level of 1.4%~1.5%. It is at the lowest level in the large sinter plant in China, and further reaches 1.35% in October 2014.

The following is a comparison of the MgO content between the sintering plant of the Jingtang sintering plant and the international sintering plant. Compared with some advanced international factories and mines, although the MgO content of Jingtan sintering plant in Shougang Group is still a little high, it is a natural magnesia sinter with no magnesium flux.

According to statistics, the annual benefit of sintering magnesium reduction in Shougang Jingtang reaches 8 million 125 thousand yuan. In October 2014, after expert appraisal, the research and practice of sintering magnesium reduction in Shougang Jingtang reached the leading level in China.

Experts believe that the successful practice of sintering magnesium reduction in Shougang Jingtang has great application prospects in China. Two kinds of application schemes can be considered as follows: one is to reduce the MgO content in the blast furnace slag by reducing the MgO content of the sinter ore, to contribute to the blast furnace fine material, and two to reduce the mixture ratio of the sintered magnesium flux and to add the suitable magnesium containing additives in the pellets - to transfer the MgO content of the sinter to the pellet. In the process of producing low magnesium sinter and Gao Meiqiu