Development and Progress of Hydrogen Metallurgy

International Journal of Minerals, Metallurgy and Materials Accepted manuscript, https://doi.org/10.1007/s12613-020-2021-4 © University of Science and Technology Beijing and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Development and Progress of Hydrogen Metallurgy

Jue Tang1*), Man-sheng Chu2*), Feng Li1), Cong Feng1), Zheng-gen Liu1), Yu-sheng Zhou1)

1) School of Ferrous Metallurgy, Northeastern University, Shenyang 110819, China.

2) State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110819, China.

Corresponding author: Jue Tang, [email protected]；Man-sheng Chu, [email protected]

Abstract: Hydrogen metallurgy was a technology that taking hydrogen as the reduction agent instead of

carbon to reduce CO2 emission, which is beneficial to promote the sustainable development of steel

industry. Lots of main projects of hydrogen metallurgy have been proceeded and planed, such as H2 reduction ironmaking in Japan, ULCORED and Hydrogen-based steel making in Europe, hydrogen Flash

TM Ironmaking Technology in the US, HYBRIT in Nordic, Midrex H2 , H2FUTURE of Voestalpine,

SALCOS Project of Salzgitter. The hydrogen-rich BF with COG injection is typical in China. AnSteel,

XuSteel, and BenSteel have carried out the industrial tests in running blast furnaces. And the pilot plant of coal gasification-gas based shaft furnace with an annual output of 10,000 t DRI was under construction.

The reducing gas of 57%H2 and 38%CO was prepared by ENDE method. The life cycle assessment of the coal gasification-gas based shaft furnace-electric furnace short process (30%DRI+70% scrap) was carried out with 1 t molten steel as the functional unit. It was found that the total energy consumption per ton steel

was 263.67 kgce, and the CO2 emission per ton steel was 829.89 kg, which was superior to the traditional

BF-converter process. Considering the domestic materials and fuels, the developing production and storage of hydrogen, the characteristics of hydrogen reduction, it was more suitable to develop hydrogen-rich shaft furnace in China, and the production and storage of hydrogen with an economic and large-scale industrialization would promote the further development of full hydrogen shaft furnace. Key words: hydrogen; hydrogen metallurgy; blast furnace; gas-based shaft furnace; low-carbon

1 Introduction

According to IEA, the global energy-related CO2 emissions totaled 3.31 billion tons in 2018, which increased by 1.7% compared with the previous year and reached the highest level on record. China, the US,

Europe and India accounted for more than 60% of the world's total CO2 emissions, which were 9481 Mt,

4888 Mt, 3956 Mt and 2999 Mt respectively [1]. In recent years, as for the global energy consumption and

CO2 emissions, industry accounted for 33% and 40% respectively. CO2 emissions from steel industry accounted for a high proportion of about 33.8% of industrial emissions [2].

To combat global warming, the Paris Agreement was adopted in 2015. Its main goal was to limit the rise in global average temperature to less than 2℃ this century and to keep the global temperature rise to less than 1.5℃ above pre-industrial level. Countries around the world signed the agreement and put forward plans to reduce carbon emission. In 2016, China had launched 10 low-carbon demonstration zones,

100 mitigation projects and 1,000 training opportunities for climate change, with a view to reduce CO2 emission per unit of GDP by 60-65% by 2030 [3-5]. And in 2017, the carbon emission trading system had been launched in China [2]. The steel industry was the main target for that new trading system, and the

mandatory CO2 emission reduction would force the steel enterprises to develop low-carbon technology.

Based on the global warming and energy transformation, the governments had attached great importance to developing and utilizing the carbon-free or low-carbon energy. Hydrogen energy, with its diverse source, low-carbon emission, high efficiency, and wide application range, was regarded as the most promising clean energy in the 21st century and had been listed in the national energy strategic deployment by many countries [6,7]. Xu Kuangdi put forward the idea of achieving the reduction of iron ore by hydrogen in 1999 [8], and then he further put forward the idea of hydrogen metallurgy in 2002 [9]. In 2018, Gan Yong pointed out that 21st century was the era of hydrogen, and hydrogen metallurgy was the process that water

was generated by hydrogen reduction instead of carbon reduction, with no emission and extremely fast reaction rate [10]. At present, the hydrogen metallurgy mainly included blast furnace (BF) ironmaking with adding hydrogen and production of direct reduction iron (DRI) by hydrogen [11-16]. The following topics including the development and progress of hydrogen metallurgy abroad and in China, and the challenges and opportunities of hydrogen metallurgy were systematically discussed in this work.

2 Development and progress of hydrogen metallurgy abroad

2.1 Hydrogen metallurgy in Asia

2.1.1 H2 Reduction ironmaking in Japan

The route of the COURSE50 project was shown in Fig 1, involving two main technologies of

hydrogen-rich reduction and CO2 capture and recovery from BF exhaust to achieve the CO2 emission. The former was based on the reforming technology of coke oven gas (COG) and water and the novel coking

technology to make coke with a high strength and a high reactivity. The latter was on the base of CO2 efficient absorption technology to utilize the waste heat. Through the experimental BF of 12 m3 with a productivity of 35 tons/d built by Nippon Steel, the project emission reduction target was confirmed as: 10%

reducing by hydrogen reduction ironmaking, and 20% reducing by CO2 recovery, so as to achieve the overall emission reduction target of 30% [17,18].

Hydrogen reduction ironmaking was a method that replaced part of coke with hydrogen to reduce CO2

emissions during BF process. From 2014 to 2016, the first stage of experimental BF operation with H2 injection was carried out. It was indicated that the carbon emission reduced by 9.4% compared with that of

non-H2 injection. Due to the small density of H2 and the hydrogen reduction accompanied by endothermic

reactions, the adjustable position in the stack and raceway of BF and the preheating of H2 before injection were conducted to ensure the maximum reduction performance and stable inner temperature respectively.

In the second stage, an expanded test would be carried out to gradually simulate the practical BF of

3 4000-5000 m . The first BF was expected to be operated with H2 reduction by 2030 and the technology would be available around Japan by 2050. In addition, the COURSE50 project had also developed the technology for producing hydrogen from COG. When COG left the carbonization chamber, the temperature reached 800℃, which could make full use of its sensible heat to achieve the catalytic cracking of tar and

hydrocarbon substances to produce H2. The specific technical route was described in Fig 2. At present, the

industrial trial of this technology had been completed. Through this modification, the H2 content of COG increased from 55% to 63-67%，and the gas volume was to be double. [20].

Sinter BF gas without CO2 CO2 separation BF gas equipment Coke

Hot metal Slag Other CO2 Improvement of coke Unused waste heat recovery

Increase of hydrogen Utilization of CO2 capture, separation concentration in COG unused waste heat and recovery

Hydrogen reduction

Technology to decrease Technology to CO2 capture, CO2 emissions separation and recovery

Fig. 1. Route of the COURSE50 project

Hydrogen concentration: 55%→63-67% Gas volume: to be double Enriched H2 (derived from Catalytic chemical reaction field sensible heat) Coke ex: CH4+H2O→3H2+CO COG COG H2 sensible heat H2 (water vapor) Waste heat Hydrocarbons Hydrocarbons (Sensible heat) (methane, etc.) (methane, etc.) CO, etc CO, etc

H2 reduction COG H2 enrichment COG H : 65% of iron 2 (dried gas) ore H2

Enriched H2 H2 reduction process flow H2 enrichment concept (converted from tar and light oil)

Fig. 2. Process of H2 enrichment from COG

According to the report on the 12th CSM Steel Congress by Akihiko Inoue who was the vice president of Nippon Steel Co., the roadmap for super innovative technologies development by JISF (Japan Iron and

Steel Federation) was given as Fig 3. COURSE50 was just the first step. Actually, a series of relevant

hydrogen metallurgy technologies, such as H2 reduction in BF (internal H2 and external H2), H2 reduction without BF, CCS, and CCU, had been undertaken or planned in Japan [20].

Development of technologies specific to iron and steel sector 2010 2020 2030 2040 2050 2100

COURSE50 H2 reduction in BF (internal H2) R&D Introduction Super COURSE50 H2 reduction in BF (external H2) R&D

H2 reaction ironmaking H2 reduction without using BF R&D Introduction

CCS Recovery of CO2 from BF gas, etc. R&D Introduction

CCU Adding value to CO2 from steel plant R&D Introduction

Development of common fundamental technologies for society Zero-emission electricity Zero-emission electricity though R&D Introduction nuclear, renew ables, etc. Carbon-free H Low cost, large quantity production 2 R&D Introduction with nuclear and renew ables, etc. CCS/CCU Cheap storage, location, adding R&D Introduction value, etc.

Fig. 3. Roadmap for super innovative technologies development by JISF

2.1.2 H2 metallurgy projects in Korea

The hydrogen reduction ironmaking was developed through the public-private cooperation in Korea.

There are three steps: starting the trial operation in test furnace from 2025; putting into production in two

BFs from 2030, the CO2 emission decreased by 1.6%; achieving the complete hydrogen reduction

[40] ironmaking in twelve BFs will be by 2040, the CO2 emission decreased by 8.7% .

2.2 Hydrogen metallurgy in Europe

2.2.1 ULCORED and Hydrogen-based steel making in ULCOS project

ULCOS (Ultra Low CO2 Steel Making) was an ultra-low CO2 steelmaking project jointly initiated by

15 European countries and 48 enterprises, aiming at achieving 50% or more reduction in CO2 emission.

The overall route was shown in Fig 4. The triangular matrix showed that the consumption reduction of reducing agent and fuel could be realized by three possibilities of carbon, hydrogen and electricity. Also, this ternary figure demonstrated all existing energy structures, where coal was close to carbon on the

carbon-hydrogen line, natural gas (NG) was near to hydrogen and H2 was produced by electrolysis of water on the hydrogen-electricity line. There were four processes mainly promoted in ULCOS, including Top-gas recycling of BF (TGR-BF), direct reduction (ULCORED), smelting reduction (HISARNA), electrolytic iron ore process (ULCOWIN/ULCOLYSIS), and hydrogen-based steel making [21].

Existing Technology Carbon New Technology

Coke CO2 capture and storage Coal Decarbonizing

Use of C from Syngas sustainable Plasm in BF biomass Electric Arc Furnace Natural gas Natural prereduction gas Electrolysis

H2 prereduction H2 Electricity

Hydrogen H2 by electrolysis of H2O Electrons

Fig. 4. Route of ULCOS

During the ULCORED process, the traditional reducing agent of coke was replaced by coal-gasification gas or NG, and the consumption of NG could be cut down by the means of top gas recycling and gas preheating. In addition, the application of NG with partial oxidation was beneficial to omit the coke oven and the reforming equipment to greatly reduce the investment. The route of ULCORED was shown as Fig 5. Taking the ULCORED with NG as an example, the charge was loaded from the top of shaft furnace, and both the exhaust after purification and NG were mixed and injected into the shaft furnace

to react with the iron-bearing burden. The tail gas of the new process only contained CO2 which could be stored through CCS. Compared with the average emission from BF in Europe, the ULCORED process

[22-24] combined with CCS technology could reduce CO2 emission by 70% .

Hydrogen-based steelmaking was a hydrogen ironmaking technology with H2 as a reducing agent. H2 was made form electrolyzing water, and the tail gas was only water. The overall process was shown in Fig 6.

Carbon emission of shaft furnace was negligible, and taking the carbon emission generated by electric

power into account, the CO2 emission during whole process was only 300 kg per ton crude steel, reducing by 84% compared with that of 1850 kg per ton crude steel from traditional BF process [22-24].

CO2 removal Excess gas for external users

CO2 storage Gas cleaning

Coal gasification

DRI cooler Dust and sulphur removal DRI Hot or cool

Oxygen Green field Brown field （a）ULCORED with coal-gasification gas

Filter

Multi-Cyclone Shifter

CO CO 2 2 scrubber

Heat-Exchanger

DRI-Rea

Natural gas

Gas-generation

DRI-cooler

（b）ULCORED of NG Fig. 5. Route of ULCORED

Electricity Lump iron ore Iron ore pellets

Water electrolysis Direct H 2 reduction in

H2O shaft furnace

C-free Electric arc furnace DRI steelmaking Liquid steel

Hot Continuous rolled Hot rolling casting coil

Fig. 6. Hydrogen-based Steel Making in ULCOS project

2.2.2 H2FUTURE of Voestalpine

In 2017, H2FUTURE project initiated by Voestalpine had aimed to reduce CO2 emissions from steel production by developing a breakthrough technology to replace coke with hydrogen, with the ultimate goal

of reducing CO2 emissions by 80% till 2050. The hydrogen industry chain of H2FUTURE was shown in

Fig 7. The project would build the largest hydrogen reduction pilot plant around the world [25, 26].

Clean energy Electricity Transmission technology: solar, wind network and hydrogen power Power Power Power supply supply

H Water Electrolysis 2 Water Electrolysis Hydrogen Fuel Cell Hydrogen Fuel Cell

Fig. 7. Hydrogen energy industry chain of H2FUTURE

2.2.3 SALCOS Project of Salzgitter

In 2019, SALCOS Project (Salzgitter Low CO2 Steelmaking) was proposed by Salzgitter and Tenova

to take hydrogen as the reducing agent of ironmaking to reduce CO2 emissions, aiming at gradually transform the conventional and carbon-intensive BF-convert process to DRI-electric arc furnace process and realizing the multi-purpose utilization of surplus hydrogen. The assumption of SALCOS project was shown in Fig 8. GrInHy (Green Industrial Hydrogen) 1.0 was started in 2016, where the reversible electrolysis process was used to produce hydrogen and oxygen and the excess hydrogen was stored.

Subsequently, GrInHy 2.0 was started in 2019. The remarkable feature of GrInHy2.0 project was the use of waste heat from steel plant to produce water vapor which was applied to generate electricity from green renewable energy, and then hydrogen was produced by high-temperature electrolysis of water. Hydrogen could be used in both DRI production and later processes of steel production, such as the reducing gas for

cold rolling annealing [27-29].

Hot metal

Coke Crude steel Electricity BF Converter H2 O2 Iron ore pellet Scrap Crude steel

Electrolytic hydrogen production electric arc Natural gas DRI furnace Direct reduction

Fig. 8. Assumption of SALCOS project

2.2.4 Replace coal with hydrogen project of ThyssenKrupp Stahl AG

Replacing coal with hydrogen project of ThyssenKrupp Stahl AG was that coal was replaced with

hydrogen as the reducing agent in BF to reduce or completely avoid CO2 emissions in steel production. In the initial, hydrogen was injected to the No. 9 BF through one tuyere in Duisburg Steel plant and gradually

expanded to all the 28 tuyeres. The three other BFs would realize the technology by 2022. By then, the CO2 emission from steel production the technology was expected to reduce by about 20% [30].

2.2.5 COG injection system for ROGESA blast furnaces

ROGESA Roheisengesellschaft Saar mbH (ROGESA) has awarded Paul Wurth to design and supply

COG injection systems for the blast furnaces No. 4 and No. 5 located in Dillingen/Saar, Germany. COG will partially replace both pulverized coal and metallurgical coke as reducing agents in the BF process, contributing to reducing the carbon intensity in the BF as well as the carbon footprint during the overall ironmaking process. This application will be the bold step toward the hydrogen based ironmaking in the future. As the project schedule, COG injection will start in summer 2020 at half of the number of tuyeres of

[31] No. 5 BF and with the aim to permanent injection at all tuyeres of both furnaces by the end of 2020 .

2.3 Hydrogen flash ironmaking technology in the United States

The novel Flash Ironmaking Technology (FIT) was the method that reducing iron concentrate to DRI

with a high metallization rate under the suspension state. The reducing gas could be H2, CH4, etc. This process was developed on the base of the iron ore resources in the US where 60% of iron ore was taconite with the small particle size less than 25-38 µm. It was the direct use of iron oxide concentrates without pelletizing or sintering. The schematic diagram of FIT was given as Fig 9 [32].

At present, the University of Utah had carried out the large-scale tests with a shaft furnace inner diameter of 20.3 cm and the length of 244 cm based on FIT, using the iron concentrate from ArcelorMittal and Ternium. It was shown that the reduction degree of 90-99% could be rapidly obtained within 1-7 s at

1200-1400℃, and the reduction degree depended on the excess coefficient of hydrogen. The comparisons

of energy consumption between BF process and FIT using H2, CH4 and coal by mathematical calculation were listed in Table 1. As seen, the energy consumption of FIT was remarkably lower than that of BF

process. And as for 1 t iron, the CO2 emissions were 71 kg, 650 kg and 1145 kg respectively corresponding

to using FIT of H2, CH4 and coal, while the emission of conventional BF was as high as 1671 kg. Even if

[33, 34] coal was used as fuel, the CO2 emission of FIT was significantly lower than that of BF process .

Slurry H2O, CO2

Heat recovery Water vapor removal CO2 removal Recycled H2, CO Scrubber Waste heat boiler

O2 CH or H Heat exchanger 4 2 Iron ore concentrate +Flux Off-gas

(H2, H2O, CO, CO2)

Flash Uptake shaft External heating External heating (if needed) (if needed)

Ironmaking Steelmaking

Steel

Slag

O2 +CH4, H2, or Coal O2 Fig. 9. Schematic diagram of FIT

Table 1. The comparison of energy consumption between BF process and FIT using H2, CH4 and coal

BF Using H2 Using CH4 Using coal

GJ/tHM GJ/tHM GJ/tHM GJ/tHM

Energy required (feed at 25°C to products)

1) Enthalpy of iron-oxide reduction (25°C) 2.09 -0.31 -0.61 1.73

2) Sensible heat of molten Fe (1600°C) 1.36 1.36 1.36 1.36

3) Slag making -0.21 -0.15 -0.15 -0.21

4) Sensible heat of slag (1600°C) 0.46 0.32 0.32 0.46

5) SiO2 reduction 0.09 - - -

6) Limestone (CaCO3) decomposition 0.42 0.29 0.29 0.42

7) Carbon in pig iron 1.65 - - -

8) Heat loss and unaccounted-for amounts 2.6 2.6 2.6 2.6 (assumed the same for all processes)

9) Sensible heat of offgas (90°C) 0.25 0.25 0.21 0.20

Sub-Total

Heating value of feed used as Reductant 5.37 7.70 8.00 5.67

Total for Iron oxide reduction 14.07 12.06 12.02 12.23

Preparation

1)Pelletizing 2.87 - - -

2) Sintering 0.62 - - -

3) Coking 1.93 - - -

Sub-Total for preparation 5.42

Total for molten hot metal making 19.49 12.06 12.02 12.23

2.4 HYBRIT in Nordic

In 2016, Swedish steel company (SSAB), Vattenfall and Swedish mining company (LKAB) co-founded a non-fossil energy project called HYBRIT (Hydrogen Breakthrough Ironmaking Technology),.

The core concept of this project was the direct reduction by hydrogen made from electrolyzing water. And

[35-38] it was expected to reduce the CO2 emissions by 10% in Sweden and 7% in Finland .

The comparison of technology route between HYBRIT and BF process was shown in Fig 10. This new process was similar to the existing direct reduction shaft furnace but with 100% hydrogen as the

reducing agent. Base on the Swedish raw material and production data, thes comparison of CO2 emission and energy consumption for one ton between HYBRIT and BF was described in Fig 11. As for BF, the

main processes including pelletizing, coking, ironmaking and steelmaking were considered. The CO2 emission, fossil energy consumption, and electric power consumption were 1600 kg, 5231 kWh and 235 kWh respectively, and the total energy consumption was 5466 kWh. As for HYBRIT, the main processes pelletizing, hydrogen production, direct reduction by hydrogen and electric furnace were taken into account.

The CO2 emission, BIO energy consumption, fossil energy consumption and electricity consumption are respectively 25 kg, 560 kWh, 42 kWh and 3488 kWh, and the total energy consumption including is 4090

kWh. Compared with the BF process, the CO2 emission decreased 1575 kg, decreased by 98.44%, and the energy consumption decreased 1,356 kWh, decreased by 25.17%. In addition, it was worth mentioning that

10% reduction of CO2 emission in Sweden would lead to a 15 kWh increase in power consumption, which could be achieved by wind power and solar power generation. Meanwhile, three pilot plants would be built, including a hydrogen production-hydrogen direct reduction-steelmaking plant in Lulea, a non-fossil pellet plant in Malmberg and Lulea, and a hydrogen storage plant in Lulea [35-38].

Blast furnace route HYBRIT route

Iron ore concentrate Fossil fuels Non-fossil fuels Coal Iron ore Pelletizing Iron ore pellet pellet Coke plant

Coke

co2 Electricity Ironmaking H2 plant Hot blast Cool oxygen H2 H2 storage

Hot DRI metal Steelmaking Scrap Oxygen

co2

Crude steel

Fig. 10. Comparisons of technology route between HYBRIT and BF process

Fossil Emission CO2 1600 kg 5

1140 kg 160 kg 40 kg 220 kg 1 Output 2 1 ton crude steel 3 4

Pellet plant Coke plant H2 direct reduction Electric arc furnace Continuous casting 81 3860 1290 kWh kWh 40 kWh kg

Lime making O2 plant

Coal 5150 Oil Electricity Energy carriers 81 kWh kWh 235 kWh Principal system description. Numbers do not reflect a specific production site or time period. All number per ton crude steel. （a）BF process

CO2 Fossil Emission 25 kg 5

5 kg 1 2 3 4 Output 1 ton crude steel

Pellet plant H2 plant H2 direct reduction Electric arc furnace Continuous casting

80 2633 322 494 42 380 kWh kWh kWh kWh kWh kWh 20kg

BIO Coal Electricity Energy carriers 560 kWh 42 kWh 3488 kWh All number per ton crude steel （b）HYBRIT

Fig. 11. CO2 emission and energy consumption for one ton between BF (a) and HYBRIT (b)

2.5 Direct reduction technology by hydrogen-rich gas

As early as the mid-20th century, the technology of direct reduction by hydrogen-rich gas had been industrialized. At present, the running shaft furnaces were mostly based on the MIDREX and HYL processes by using NG, coal and oil gasification gas. In order to ensure that the high-temperature alloy furnace tube would not be corroded and to prevent iron ore pellet from sticking, the hydrogen content in the reducing gas was high to 55%-80% [39]. The Midrex HBI plant, belonged to Voestalpine with an annual capacity of 2 million tons, had been established in 2017. Nucor invested $750 million to build the first native HYL DRI plant in Louisiana in 2013, with an annual capacity of 2.5 million tons [40].

Taking Midrex as an example, the content of H2 and CO in the reducing gas was generally about 55%

and 36% respectively (H2/CO was about 1.50). The H2/CO in the FMO MIDREX plant in Venezuela was

3.3-3.8 due to the reforming technology of steam. Some shaft furnaces used coal gasification technology to

obtain reducing gas with the H2/CO of 0.37-0.38. Therefore, the Midrex had been successfully applied to

produce DRI at the H2/CO of 0.37-3.8 shown in Fig 12. On this basis, it was possible to develop the Midrex

with pure hydrogen (Midrex-H2™) with the route shown in Fig 13, which eliminated the reforming process and heated hydrogen directly to the required temperature. It was worth mentioning that the content of

hydrogen in the reducing gas was about 90% in the practical production and the rest was CO, CO2, H2O

and CH4, which was mainly to control the appropriate furnace temperature and ensure the carburization of

DRI [41]. In 2019, ArcelorMittal had announced that it had commissioned Midrex Technologies to design a demonstration plant at its Hamburg site to produce steel with hydrogen. And it was to demonstrate in

Hamburg the large-scale production and use of DRI made with 100% hydrogen as the reductant. In the coming years, the demonstration plant will produce about 100,000 tons of DRI per year–initially with grey hydrogen sourced from natural gas. Once the green hydrogen from renewable energy sources was available in sufficient quantities and at an economical cost, hydrogen production could come from wind farms off the coast of Northern Germany. The plant will be the world’s first DRI production plant powered by hydrogen on an industrial scale [42].

Iron ore Process gas NG Top gas scrubber compressor

Main air blower

NG+O2 Flue gas

NG H2 Feed gas HDRI Combustion air

Fig. 12. Route of Midrex

Iron ore H2 (make up) Process gas Top gas scrubber compressor

Reducing gas

O2 Flue gas Energy

Recuperator (optional)

Combustion air HDRI

Fig. 13. Route of MIDREX-H2™

3 Development and progress of hydrogen metallurgy in China

With the increase of CO2 emission reduction pressure, the hydrogen reduction technology has received much attention. The utilizations of hydrogen during BF and direct reduction processes had been discussed and started in China. And the fundamental conditions for both the hydrogen production from nuclear energy and hydrogen metallurgy were available in China.

3.1 Development of hydrogen-rich BF in China

BF ironmaking had been the core of energy saving and CO2 reduction in steel industry. Hydrogen-rich reduction was one of the feasible technologies for low-carbon ironmaking. The practice of hydrogen-rich

BF in China was mainly to inject hydrogen-rich gas into blast furnace, such as COG and NG.

As early as the 1960s, the test of BF operation with COG injection was carried out in Ben Steel. Under the COG injection rate of 82 m3/tHM, the productivity increased by 10.8%, the coke ratio decreased by

3~10%, the temperature of BF was stable, the phenomena of collapse burden and suspended burden were enhanced, and the condition of BF was improved. In addition, combining with the experience of injecting

COG into BF of Ben Steel, An Steel also proceeded the No. 9 BF operation with COG injection in 1964,

and for 1 m3 of COG injection, 0.6 ~ 0.7 kg of coke could be saved. And in 2012, An Steel had started the

COG injection in No. 1 BF in Bayuquan. It was estimated that the annual economic benefit was about 100

[43] million yuan and the annual reduction of CO2 emission was about 650,000 tons .

3.2 Development of hydrogen metallurgy direct reduction in China

The world development trend of DRI showed that the gas-based shaft furnace process was an effective way to rapidly expand DRI. Since the end of the 20th century, China had carried out gas-based shaft furnace direct reduction researches, such as the industrial test of BL coal gasification-shaft furnace process of BAO Steel, the semi-industrial test of coal gasification-shaft furnace process of Hengdi plant, the

COG-shaft furnace of Zhongjin Mining, etc..

With the development of coal gasification in chemical industry and the progress of shaft furnace direct reduction, the coal gasification-shaft furnace has attracted much attention. Considering the domestic energy structure, China was not suitable for large-scale development of gas-based direct reduction technology due to the shortage and high price of oil and NG. However, it was rich in coal resource, especially the reserve of non-coking coal resource was large. The combination of coal gasification and direct reduction was the main development direction for the steel industry in China. Moreover, the reducing gas generated from coal

gasification technology was H2-riched with the H2 content of about 60%. Therefore, the coal gasification-shaft furnace process was the important part of hydrogen metallurgy.

3.2.1 Key integration technologies of coal gasification-shaft furnace

The key integration technologies of coal gasification-shaft furnace process mainly included the technology of iron concentrate dressing, the preparation and optimization of special oxidized pellets using for gas-based shaft furnace, the reasonable selection of coal gasification technology, the control technology of gas-based reduction, and the improvement technology of energy utilization.

As reported in Han’s work, the economic production of high-grade iron concentration with a total Fe

more than 70.5%, a content of SiO2 less than 2.0% through grinding and magnetic separation based on the

most magnetite resources in China [44], which could be directly to prepare the excellent oxidized pellets.

According to Chu’s research, it was found that the oxidized pellet with excellent metallurgical properties could be obtained by optimizing the use of additives and improving the technological parameters of drying, preheating, and oxidation roasting. The comparisons between the performances of the pellet prepared from the domestic iron concentrate and HYL indexes were listed in Table 2. As seen, its performances could meet the requirements of HYL process. Meanwhile, the shaft furnace with a high temperature and a high content of hydrogen was adopted. Through controlling the reduction process, the

qualified DRI with a metalized rate not less than 92% and a content of SiO2 not more than 3% could be obtained. In addition, based on the comprehensive considerations of the equipment characteristics, the technical and economic indexes and the investment, the comprehensive weighted scoring method was applied to evaluate the rational selection of coal gasification technologies. It was suggested that the fluidized bed method with the advantages of low investment, low oxygen consumption and high production efficiency seemed a proper choice. Furthermore, the hot delivery together with the top gas recycling would enhance the energy utilization of gas-based shaft furnace [45].

Table 2. Comparisons between the performances of the pellet prepared from domestic iron concentrate and HYL indexes

Items Jilin Shanxi Liaoning HYL index TFe/% 67.30 67.90 68.36 As high as possible Chemical FeO/% 0.10 0.19 0.19 ≯1.0 composition SiO2/% 2.65 1.72 2.11 ≯3.0 CS*/N 3276 2985 2598 ≮2000 Physical （GB/T 14201） properties Drum strength /% T=94.5 T=94.4 T=94.7 T≮93 （GB/T 8209） A=4.5 A=4.4 A=4.7 A≯6

RDI+6.3=87.5 RDI+6.3=95.7 RDI+6.3=80.0 RDI*/% Metallurgical RDI+3.15=91.4 RDI+3.15=97.0 RDI+3.15=84.2 - （GB/T 13242） properties RDI-0.5=6.5 RDI-0.5=2.4 RDI-0.5=6.5 Reduction degree/% 72.83 75.71 69.90 -

（GB/T 13241） RSI*/% 18.70 16.78 17.73 ≯20 （GB/T 13240） Note: CS- Compressive strength; RDI- Reduction degradation index; RSI- Reduction swelling index

3.2.2 Development of coal gasification-gas based shaft furnace pilot plant co-built by Northeastern

University and Liaoning Huaxin

In 2018, Lliaoning Iron and Steel Generic Technology Innovation Center was established by

Northeastern University and Liaoning Huaxin. It was aimed to build a national demonstration of low-carbon ironmaking and high-quality steelmaking based on the short process of hydrogen metallurgy.

The coal gasification-shaft furnace with an annual DRI of 10,000 tons was the important content of this project. The main route was shown in Fig 14.

The Ende method was adopted to accomplish coal-gasification. It was required that the raw coal was none or weakly cohesive, the content of ash was less than 25-30%, the chemical activity was good. Taking the Huolinghe coal as raw material, the main components of clean gas obtained by Ende method were listed

in Table 3. The contents of H2, CO and CH4 are 57%, 38% and 2% respectively. According to the material and energy balances, one Ende furnace with a gas production capacity of 5000 m3/h would be adopted.

1-Crude gas of coal gasification; 2-Crude gas after desulfuration; 3-Pressed top gas; 4-Purified gas; 5-Heat exchange gas;

6-Input gas; 7-Hot top gas; 8-Tog gas after cleaning and drying; 9-Heating gas for heat furnace; 10-Cooling NG; 11-O2;

12-N2; 13-Tail gas after SPA; 14-Exhaust after combustion; 15-Combustion air Fig. 14. Coal gasification-gas based shaft furnace of Northeastern University and Liaoning Huaxin

According to the production requirements, the effective gas flow, the reduction temperature, the utilization coefficient of shaft furnace and the charging of burden, the key parameters such as proper shaft diameter, stack angle, the height of reduction part, transitional part, and cooling part were all calculated.

The shaft furnace with the independent intellectual property right was developed. The three-dimensional model and final assembly diagram of this gas-based shaft furnace were shown in Fig 15. Based on the domestic raw materials, firstly the multi-field and multi-phase coupling simulations of reducing gas flow, reduction process, burden movement, temperature field were carried out. The distribution of solid phase

during the gas-based reduction (Fe2O3→Fe3O4→FeO→Fe) was shown in Fig 16. Secondly, the process models of each unit including coal gasification, pelletizing, gas-based reduction, electric furnace smelting were established. The material balance and exergy balance of shaft furnace were seen in as shown in Table

3 and Table 4, respectively. The most exergy input was the chemical exergy of reducing gas, and the exergy of top gas accounted for 57% of the output. Therefore, the improvement of the utilization of top gas was the

key to enhance the energy utilization of gas-based shaft furnace. Finally, GaBi 7.3 software was used to conduct an overall life cycle assessment (LCA) of the coal gasification-shaft furnace -electric furnace process (30% DRI+70% scrap) with 1 ton molten steel as the functional unit. It was showed that the overall environmental impact of this system was 1.83E-11, and the three types of environmental impact that contributed the most were given as follows: GWP100 (48.39%), POCP (39.86%) and EP (7.24%). The key processes that have the greatest impact on the environment were electric furnace, heating and coal-gasification. Under these conditions for per ton steel, the total energy consumption was 263.67 kgce

and the CO2 emission was 829.89 kg, which were both superior to the traditional BF process.

Fig. 15. Three-dimensional models and final assembly diagram of this gas-based shaft furnace

Fig. 16. solid phase distribution during the reduction process (Fe2O3→Fe3O4→FeO→Fe)

Table 3. Material balance of shaft furnace

Items Gas-base shaft furnace Pellet/kg 1377.85 Input Reducing gas/kg 647.88 ∑/kg 2025.73 DRI/kg 1000.00

Top gas/kg 1011.95 Output Ash/kg 13.78

∑/kg 2025.73

Table 4. Exergy balance of shaft furnace Items Exergy /MJ Ratio/% Pellet chemical Ex* 21.39 0.11% Reducing gas physic Ex 1182.92 6.34% Input Reducing gas chemical Ex 17446.37 93.54% ∑ 18650.69 100.00% DRI physic Ex 186.29 1.00% DRI chemical Ex 6161.96 33.04% Ash physic Ex 1.69 0.01% Ash chemical Ex 0.21 0.00% Output Top gas physic Ex 469.36 2.52% Top gas chemical Ex 10730.26 57.53% Heat loss Ex 130.23 0.70% Inner loss Ex 970.69 5.20% ∑ 18650.69 100.00% Note: Ex-Exergy

4 Challenges and opportunities of hydrogen metallurgy

4.1 Production and storage of hydrogen

The key of hydrogen production was economy and low carbon. At present, it mainly applied the fossil energy to produce hydrogen, which accounted for more than 95% of hydrogen in the world. But the large

amount of CO2 would be generated by this technology. In the long run, the technologies based on solar energy, wind energy, water energy, marine energy and geothermal energy would become the important resources supplement for hydrogen production to realize zero-carbon emission. The conversion efficiency

of these technologies was still relatively low, but the hydrogen production from solar energy had been used as a temporary and supplementary way of hydrogen refueling in Europe and Japan. With the improvement of CCS technology, the combination of hydrogen production from coal gasification and CCS technology would find a new way to cleanly and efficiently utilize the coal resources, and it was also the development direction of coal-based and low-carbon hydrogen production [46, 47].

Hydrogen storage technology was the restrictive step to efficiently utilize hydrogen. Currently, the hydrogen storage methods mainly included: gaseous storage with a high pressure, cryogenic and liquefied storage, organic and liquid storage, porous material storage, etc.. For the large-scale storage and transportation of hydrogen energy, although many technologies had been developed, the most feasible technologies in industry were high-pressure gaseous storage and cryogenic liquefied storage[46, 47].

4.2 Problems of gas-based shaft furnace with pure hydrogen

Shaft furnace with pure hydrogen was the important development direction of hydrogen metallurgy, which had been achieved the industrial production as early as the 1980s in Western Europe. Although many authoritative metallurgical experts had emphasized the benefits of hydrogen metallurgy, the technology and economy of pure hydrogen shaft furnace were still needed to be considered and discussed.

Firstly, there was no carbon source in the shaft furnace, and it was impossible to realize the complementation and transformation of heat and the recycling of substances. In the pure hydrogen shaft furnace, there are three strong endothermic reactions were given as follows.

Fe2O3+3H2=2Fe+3H2O （1）

Fe3O4+4H2=3Fe +4H2O （2）

FeO+H2=Fe+H2O （3）

Therefore, a large amount of heat was absorbed and the inner temperature at the bulk material layer became cool rapidly, which delayed the reduction reactions those need to consume much heat and

worsened the gas utilization rate. To maintain the preferred productivity, the amount of hydrogen as a heat carrier was required to increase. For example, the pressure at the top was 0.4 MPa, the amount of hydrogen with a temperature of 900℃ should be at least of 2600 m3/tDRI to meet the heat demand of shaft furnace reduction. If the supplement of hydrogen remained unchanged, the DRI output would be one-third less than that of the current, leading to the great increase of DRI cost.

Secondly, the specific gravity of hydrogen was small, and the volume density of hydrogen was only

1/20 of that of CO, CO2 and H2O. As a result, the entering hydrogen would escape to the top rapidly.

Compared with the mixed reducing gas, the path and direction of hydrogen in the furnace changed so quickly that hydrogen could not stay in the high temperature zone at the bottom part of shaft furnace to complete the task of reducing iron ore pellets. Theoretically, the DRI product could also reach the designed index by maintaining the entering hydrogen with a pressure above 1 MPa and a temperature above 1000℃.

However, hydrogen was an extremely flammable and explosive, and the shaft furnace needed a high efficiency and long-term stable production. If the shaft furnace system was allowed to work for a long time under the ultimate conditions of high temperature and high pressure, the safety cannot be guaranteed, which was not in line with the goal of metallurgical process design.

Thirdly, hydrogen was expensive. Hydrogen was a secondary energy with high cost at present. DRI production in the pure hydrogen shaft furnace was difficult to be profitable and commercial. Moreover, the costs of pure hydrogen shaft furnace, including equipment, investment and maintenance, was nearly twice as high as the current coal gasification-gas based shaft furnace. Among the running shaft furnaces of

MIDREX, HYL, PERED, there was also a small amount of CO. The exothermic reactions and endothermic reactions were carried out simultaneously in the different parts of furnace, which greatly improved the heat exchange and the thermodynamics and dynamics conditions of heat and mass transfer in the shaft furnace.

In a word, there were many factors those affected the direct reduction rate and the production

efficiency, such as the proportion of hydrogen, temperature, pressure, gas utilization rate, residence time of iron ore, heat transfer, mass transfer, shaft furnace design and so on. Based on the abundant coal resources, the developed coal gasification technology, and the production and storage technology of hydrogen needed to be improved, if obeying the law of countercurrent reduction shaft furnace, following the reliable, stable, efficient and energy saving introduction, promoting the advantages of rapid reaction rate and mass transfer speed, making full use of the existing mature industrialization of shaft furnace design and production operation experience, improving the key equipment, optimizing the process parameters of shaft furnace reduction, playing the advantages of hydrogen-rich shaft furnace, achieving the proper capacity and the lowest energy consumption, the hydrogen-rich shaft furnace was much easier to be successful compared with the pure hydrogen shaft furnace in China. Moreover, the development and practice of zero-emission , economic and large-scale hydrogen production based on solar energy, wind energy, water energy, marine energy and geothermal energy, together with the development and industrialization of hydrogen storage device and technology, would be conducive to realize the pure hydrogen metallurgy.

5 Conclusions

(1) Hydrogen metallurgy applied hydrogen instead of carbon as the reducing agent to cut down CO2 emission and to promote the green and sustainable development of iron and steel industry. There were

several hydrogen metallurgy projects or methods abroad mainly given as follows: H2 reduction ironmaking in Japan, ULCORED and Hydrogen-based steel making in Europe, hydrogen Flash Ironmaking Technology

TM in the US, HYBRIT in Nordic, Midrex H2 , H2FUTURE of Voestalpine, SALCOS Project of Salzgitter, replace coal with hydrogen project of ThyssenKrupp Stahl AG.

(2) COG injection was typical among the BF hydrogen-rich smelting processes in China. Some Steel plants, such as Ben Steel, An Steel, and Mei Steel, had conducted the BF operation with COG injection and

gained some positive effects. Under the COG injection rate of 82 m3/tHM in Ben Steel, the productivity increased by 10.8%, the coke ratio decreased by 3~10%, and the condition of BF was improved.

(3) The key technologies of coal gasification-shaft furnace process, including the iron concentrate dressing, the preparation of special oxidized pellets for gas-based shaft furnace, the reasonable coal gasification technology, the control technology of gas-based reduction, and the improvement technology of energy utilization, were available in China. The pilot plant for coal gasification- gas based shaft furnace

with an annual DRI output of 10,000 tons was under construction. The reducing gas of 57% H2 and 38%

CO was prepared by Ende method. With 1 ton electric furnace steel as a functional unit, the LCA of the coal gasification-gas based shaft furnace-electric furnace short process was conducted. It was resulted that three types of environmental impact that contributed the most were as follows: GWP100 (48.39%), POCP

(39.86%) and EP (7.24%). Under these conditions for per ton steel, the total energy consumption for was

263.67 kgce and the CO2 emission was 829.89 kg, which were both superior to the traditional BF process.

(4) Considering that the equipment and technology of hydrogen production and storage were still to be improved, the endothermic reduction reaction by hydrogen would reduce the temperature of shaft furnace, the specific gravity of hydrogen was small, the cost of hydrogen production was high, it was more suitable to develop hydrogen-rich shaft furnace under the conditions of raw materials and fuels in China. And the large-scale, zero-emission, and economic industrialization of hydrogen production and storage would promote the further development of full hydrogen shaft furnace.

Acknowledge

The authors are especially grateful to National Natural Science Foundation of China (No. 51904063),

Fundamental Research Funds for the Central Universities (No. N172503016, No. N172502005, No.

N172506011) and China Postdoctoral Science Foundation (No. 2018M640259)

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中图分类号 TF56

二级学科钢铁冶金