Research progress on the principle and industrial application of hydrogen metallurgy

2.3 Domestic hydrogen metallurgy technology development

China's hydrogen metallurgy process research started late, iron and steel enterprises in recent years began to layout the field of hydrogen metallurgy, its typical hydrogen metallurgy projects are shown in Table 3[11]. In the steel industry facing the situation of capacity reduction, structural adjustment and transformation, the cooperation between the hydrogen energy industry and steel enterprises can form a complementary win-win effect. The utilization of hydrogen energy can help iron and steel enterprises to achieve energy saving and emission reduction, industrial extension and transformation, and iron and steel enterprises can provide more and more large-scale industrialization demonstrations for the hydrogen energy industry.

2.4 Hydrogen preparation technology

The development of hydrogen energy is based on the large-scale production of hydrogen by hydrogen-containing compounds. Hydrogen production methods mainly include electrolytic water hydrogen production, fossil fuel hydrogen production and biomass hydrogen production. Hydrogen must be compressed, transported, stored and transferred before reaching the end user. Large-scale production, storage and transportation of hydrogen depend on technological progress and infrastructure construction, which is a difficulty in the development of hydrogen energy industry [12].

The traditional hydrogen production methods are fossil energy reforming and water electrolysis. Hydrogen production from fossil energy reforming is to mix fossil fuel with water vapor, generate hydrogen and carbon dioxide under catalytic action, and produce high purity hydrogen through pressure swing adsorption and membrane separation evaporation. Hydrogen production by electrolysis is a pair of electrodes with an intermediate diaphragm immersed in an electrolyte, and the electricity is applied to decompose the water into hydrogen and oxygen. The production of hydrogen from fossil fuels and electrolytic water emits a lot of carbon dioxide, and this high-carbon hydrogen is called "gray hydrogen" or "black hydrogen". The actual process of hydrogen production is low carbonization, and the acquisition of low-carbon "blue hydrogen" and zero-carbon "green hydrogen" in the sense of the whole life cycle needs to increase carbon capture and storage in the fossil fuel hydrogen production system, or directly use the electricity produced by non-fossil fuels for electrolytic hydrogen production. "Fossil fuel hydrogen production + carbon capture and storage" is a short and medium term low-carbon hydrogen production transition mode, long-term non-fossil fuel power generation electrolytic hydrogen production will gradually become the main low-carbon hydrogen production mode.

Biomass is an abundant renewable resource on earth, and the technology of rapid pyrolysis of biomass to produce bio-oil has been developed rapidly in recent years. Bio-oil can be reformed with water vapor to produce hydrogen, which provides a new way to produce hydrogen from biomass. Due to the low energy density of biomass, the industrial technology of direct hydrogen production needs to be further developed.

3 Direction of industrialization and promotion of hydrogen metallurgy

3.1 Expansion of hydrogen energy in traditional metallurgical processes

(1) Recycling of gas from the top of the blast furnace. The core of the blast furnace top gas recycling process is to remove dust, purify and decarbonize the blast furnace top gas, inject the reducing components (CO and H2) into the tuyre or furnace body, return to the furnace to participate in iron oxide reduction, and use CO and H2 to further improve the blast furnace index, reduce energy consumption and reduce CO2 emissions.

(2) Blast furnace injection of hydrogen-containing substances. The hydrogen rich medium of blast furnace injection mainly includes natural gas, coke oven gas, waste plastics, and used tires [13]. After blast furnace injection of hydrogen-containing substances, hydrogen participates in iron ore reduction, strengthens the adaptability of blast furnace to raw fuel, and realizes the diversification of blast furnace functions, which has practical significance for energy saving and emission reduction of iron and steel industry. The main component of natural gas is CH4, which is sprayed into blast furnace tuyere together with oxygen-rich hot air to reduce the coke ratio of blast furnace. Some blast furnaces in North America and Russia inject natural gas, and the injection volume is 40~110kg/t. Coke oven gas is the product of waste gas after chemical production recovery and purification. There are cases that coke oven gas injected into blast furnace can reduce the coke ratio of blast furnace to less than 200kg/t.

Plastic is a petrochemical product, and blowing old plastic can not only control "white pollution", but also realize the comprehensive utilization of resources. Waste plastics are used in blast furnaces, including sorting, crushing, granulation and other aspects, replacing some pulverized coal from the tuyere into the blast furnace, the maximum injection volume has reached 60kg/t, and the theoretical maximum injection volume of waste plastics is 200kg/t; The processes that need to be improved include plastic granulation and dechlorination treatment.