CO2 injection improves the high-temperature performances of Cr-bearing vanadia-titania magnetite smelting in blast furnace

https://doi.org/10.1016/j.jcou.2020.101363Get rights and content

Highlights

  • CO2 can be used in vanadia-titania magnetite ironmaking.

  • CO2 injection helps to reduce coke consumption and CO2 emissions.

  • CO2 improves the softening-melting-dripping performances to be better.

  • CO2 injection helps to reduce the generation of titanium carbonitride.

Abstract

The effects of CO2 injection on the high-temperature metallurgical performance of Cr-bearing vanadia-titania magnetite (CVTM) in blast furnace (BF) smelting were investigated. The dry air or O2-enriched air is not necessarily suitable for any blast furnace production, and CO2-containing high-temperature energy-carried gas (CHEG) also can be an alternative injection gas with lower cost and pollution. This kind of CHEG can be blast furnace gas, basic oxygen furnace gas, coke oven gas, sintering gas and rotary kiln gas and so on, which contained high sensible heat and CO2, H2 and CO. Injecting CHEG into the blast furnace can replace air injection to achieve the heat balance in the cohesive zone and raceway. The calculated boundary injection ratio of CO2 is approximately 15.3%, and the experimental optimal CO2 injection ratio is about 10∼20%. CO2 injection benefits the blast furnace operation, the permeability of cohesive zone, recovery ratio of Cr and V. With increasing injected content of CO2, the temperature range of softening zone [T40-T4] and melting-dripping zone [Td-Ts] decrease almost 20℃, and the dripping ratio increases from 62.36% to 69.76%, the recovery of V increases from 32.75% to 47.96%, and the recovery of Cr increases from 42.35% to 64.41%. The CO2 injection affects the melting temperature of the high-titanium slags to be higher and the maximum temperature difference can reach 45℃, which is beneficial to the slag stability and separation of slag-iron and restrain the over-deduction of titania to TiN upon the slag-coke interface with lower N2.

Introduction

China’s steel production has now exceeded one billion tons per year, and its CO2 emissions are also considerable. One of the sources where CO2 has not been well treated is ironmaking and steelmaking production [[1], [2], [3], [4], [5], [6], [7], [8], [9], [10]]. In the smelting process of general blast furnaces, air or oxygen-enriched air preheated by hot blast stoves is injected into the raceway through the tuyeres, and burns with coke to produce the reducing gas CO and the heat required for element reduction, and CO2 is emitted as a pollution production. However, this kind of by-product gas called energy-carried gas contains high sensible heat and chemical energy. At present, there are many studies on comprehensive utilization of these kind of productions, such as combustion for power generation, heating, carbon capture, spraying in steelmaking and production of chemical products [[11], [12], [13], [14], [15], [16], [17], [18], [19], [20]]. Many researchers have studied the energy utilization potential of CO2 in steel companies, and we are committed to reusing this by-product furnace gas into the ironmaking and steelmaking process, and it is vital to grasp the influences of CO2 on production [21,22].

As a special resource, chromium-containing vanadia-titania magnetite (CVTM) contains not only Fe, V, and Ti, but also scarce Cr resources. It has extremely high strategic and comprehensive utilization value. Since the 1960s, a production process for the comprehensive utilization of vanadia-titania magnetite based on blast furnace pyrometallurgical technology has been formed in China, from which the three major resources of Fe, V and Ti can be recovered at the same time. How to use the blast furnace process to recover Fe, V, Ti, Cr, Sc and other resources from Cr-bearing vanadia-titania magnetite to the maximum and efficiently is still an important development direction for future scientific research and industrial practice [[23], [24], [25]].

It is generally believed that although N2 in the injected air occupies a large proportion, it does not participate in the blast furnace reaction. However, in the smelting process of CVTM, N2 will participate in the over-reduction reaction of TiO2 to produce titanium nitride TiN and titanium carbonitride Ti (Cx, Ny), which will cause the viscosity of the slag to increase sharply. It also produces a series of phenomena that are not conducive to blast furnace production, such as difficult separation of slag and iron, foamed slag, and slag stagnation [[23], [24], [25], [26], [27], [28], [29], [30]]. At the same time, the O2-enriched air injection used in the general blast furnace will also get a higher hearth temperature, which promotes the formation of titanium carbonitride, accelerates the loss of coke, increases the smelting cost and increases refractory linings wear.

Therefore, we propose that CO2 injection is to achieve the effect of "sensible heat and chemical cooling", thereby reducing the generation of titanium nitride and reducing the coke ratio. CO2-containing high-temperature energy-carried gas (CHEG) is a kind of alternative by-product gas containing CO, H2, CO2, lower N2 and high sensible heat, such as blast furnace gas, basic oxygen furnace gas, coke oven gas, sintering gas and rotary kiln gas and so on.

The high-temperature properties in the ironmaking process include the gas permeability, reducibility, shrinkage and expansion of the charge, the fluidity, viscosity, melting point, surficial tension and interfacial tension of the molten slag and molten iron. Whether the ironmaking process is operating normally can almost be judged by these indicators. Therefore, the effect of CO2 injection on the high-temperature properties of Cr-bearing vanadia-titania magnetite smelting in the blast furnace were investigated in this study. And the CO2 injection provides the feasibility for achieving CO2 ironmaking in Cr-bearing vanadia-titania magnetite blast furnace.

Section snippets

Methods and samples

The CO, CO2 and N2 are mixed and preheated as a simulated CHEG, and injected into the reduction equipment of the simulated blast furnace. The influence of CO2 on the reduction process can be reflected by recording the softening-melting-dripping process of the samples. Among them, the experimental samples are consistent with the actual blast furnace production. The experimental samples were prepared with high Cr-bearing vanadia-titania magnetite (HCVTM) and mixed with the pellet and sinter as

Calculation of regional heat balance in high-temperature zone of blast furnace

The heat demand and heat transfer of various parts in the blast furnace are very different, so it is more meaningful to calculate according to the regional heat balance algorithm. The reason why the high temperature zone of the blast furnace is determined as the calculation object is because the blast gas as the main heat source of the blast furnace has a significant impact on the regional heat balance, which also determines whether the blast furnace production goes forward or not [23,24,31].

Conclusions

As compared with general blast furnace smelting, the regional heat balance, shrinking-softening-melting-dripping behavior, recovery of V and Cr, melting performance of Cr-bearing vanadia-titania magnetite in blast furnace smelting with CO2-containing high-temperature energy-carried gas injection were investigated. From the obtained results, the following conclusions have been drawn.

  • (1)

    According to the calculation of the heat balance in the high temperature zone of the CVTM blast furnace, it is

CRediT authorship contribution statement

Hanlin Song: Data curation, Formal analysis, Visualization, Writing - original draft, Writing - review & editing. Jinpeng Zhang: Data curation, Software, Writing - review & editing. Gongjin Cheng: . Songtao Yang: . Xiangxin Xue: Conceptualization, Funding acquisition, Investigation, Project administration, Resources, Supervision.

Declaration of Competing Interest

The authors report no declarations of interest.

Acknowledgments

The research was financially supported by the National Natural Science Foundation of China (Grant No. 51674084, No.21908020, and No.U1908226), and special thanks are due to the instrumental or data analysis from Analytical and Testing Center, Northeastern University.

References (40)

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