Research progress on the principle and industrial application of hydrogen metallurgy

Hydrogen energy is regarded as the most promising clean energy in the 21st century and will play an important role in the future energy structure reform. Around the goal of achieving zero greenhouse gas emissions, many countries have promoted the utilization of hydrogen energy as a national strategy, and hydrogen technology research and development has become a hot spot. Hydrogen metallurgy is in the field of metallurgy with hydrogen instead of carbon reduction, hydrogen metallurgical reduction process and carbon reduction ratio has different characteristics, in the application of hydrogen metallurgy, iron ore direct reduction and blast furnace coal injection technology in the application of hydrogen energy has made progress. Although there have been many studies on hydrogen reduction of iron oxides, it is still unable to give an exact and reasonable explanation for some reaction behaviors, and it needs in-depth systematic analysis, research and summary to provide theoretical support for the application of hydrogen metallurgy. Combining with the technical accumulation of direct reduction and hydrogen reduction utilization in blast furnace process, the rational application of hydrogen metallurgy principles is emphasized from the aspects of hydrogen metallurgy thermodynamics, kinetics and engineering, hoping to explore the methods and paths to further improve the reduction capacity, efficiency, rate and industrial application of hydrogen metallurgy.

1 Basic research of hydrogen metallurgy

According to the basic theory of metallurgical reaction process, the development of hydrogen metallurgy technology must be designed according to meet the thermodynamic, kinetic and engineering principles of hydrogen metallurgy. Thermodynamics determines the direction, equilibrium conditions and limits of metallurgical reaction processes, kinetics discusses the rate, mechanism and limiting links of metallurgical processes, and engineering studies the macroscopic transfer law, unit operation and reactor characteristics of metallurgical processes. The three are organically combined to develop the maximum output conditions and parameters that can be achieved by hydrogen metallurgy process, find out the method to control and improve the reaction rate efficiency, improve the system problems existing in the operation process, and achieve the purpose of engineering popularization and application.

1.1 Put forward the concept of hydrogen metallurgy

The definition of hydrogen metallurgy is based on the concept of carbon metallurgy. Carbon metallurgy is the representative development mode of iron and steel industry, and the basic smelting formula is Fe2O3+3CO=2Fe+3CO2; The reducing agent is carbon, and the product is carbon dioxide. The basic reaction formula of hydrogen metallurgy: Fe2O3+3H2=2Fe+3H2O; The reducing agent is hydrogen, the end product is water, and the carbon dioxide emissions are zero. Carbon has always been the most important reducing agent in the steel industry, and it also causes a large amount of carbon dioxide emissions [1]. Non-carbon metallurgy is a metallurgical process that does not use carbon-containing substances as fuels and does not use carbon-containing media as reducing agents. Hydrogen is an excellent reducing agent and clean fuel. Research on hydrogen metallurgy technology, which replaces carbon with hydrogen as reducing agent and energy source, can change the environmental status of the iron and steel industry and is the most favorable choice for the development of low-carbon economy, which will bring hope for the sustainable development of the metallurgical industry [2].

1.2 Hydrogen metallurgy thermodynamics

According to the Fe-O-H system equilibrium diagram, below the critical temperature (about 570℃), the order of Fe2O3 reduction by H2 is Fe2O3-Fe3O4-Fe. Above the critical temperature, the order of reduction of Fe2O3 by H2 is Fe2O3-Fe3O4-Feo-Fe. The thermodynamics of hydrogen reduction in the reaction process includes two process routes: low temperature reduction and high temperature melting reduction [3]. In the process of hydrogen direct reduction of iron ore at low temperature, the raw material needs to be preheated due to heat absorption, and the multi-stage fluidized bed is often used for reduction to make up for the shortcomings of low temperature drop and low gas utilization rate. The high temperature molten hydrogen reduction process of iron ore is to inject hydrogen or hydrogen-rich gas into the lower part of the molten reduction furnace, by controlling the carbon combustion rate, and using hydrogen to replace part of carbon as a reducing agent, reduce the heat load required for carbon reduction, and achieve the purpose of accelerating the reduction speed and reducing carbon consumption.

(1) Low temperature reduction reaction includes:

FeO(s)+H2(g)=Fe(s)+H2O(g)

ΔG0=23430-16.16T (1)

FeO(s)+CO(g)=Fe(s)+CO2(g)

ΔG0=-17883+21.08T (2)

FeO(s)+C=Fe(s)+CO(g)

ΔG0=147904-150.22T (3)

(2) high-temperature reduction reaction includes:

(FeO)+CO(s)=[Fe]+CO2(g)

ΔG0=-35421+32.47T (4)

(FeO)+H2(g)=[Fe]+H2O(g)

ΔG0=5892-4.77T (5)

(FeO)+C=[Fe]+CO(g)