# Technical and environmental assessment of new green iron production strategies using hydrogen

A. Skaf, L. Tiruta-Barna, A. Ahmadi

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A. Skaf, L. Tiruta-Barna, A. Ahmadi. Technical and environmental assessment of new green iron production strategies using hydrogen. 2025. hal-05388893

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# Technical and environmental assessment of new green iron production strategies using hydrogen

A. Skafá, L. Tiruta-Barnaª, A. Ahmadiª

ª TBI, Université de Toulouse, CNRS, INRAE, INSA 135 Avenue de Rangueil, 31077, France

## Abstract

In order to assess the decarbonization potential and overall environmental benefits of new reduction pathways in the ironmaking industry, using hydrogen to produce Direct Reduced Iron (DRI), a coupled approach combining process simulation for rigorous technical and energy evaluation of iron ore conversion and Life Cycle Assessment (LCA) for environmental assessment was developed and extended to two alternative renewable heating strategies: (i) electric gas heating and (ii) solar reactor heating. The entire hydrogen-based ironmaking process, including conversion in a shaft reactor, gas and solid heating, gas recycling, and electrolysis, was therefore simulated. The hydrogen-based reduction of iron ores in the shaft reactor was modelled using a rigorous reactor model describing the reduction of multi-layer iron ore pellets in countercurrent gas-solid moving beds, with the particularity of representing the dual influence of particle size and temperature on conversion. The remainder of the process including gas recycling and hydrogen production, was simulated using ProSim software. The hydrogen-based green ironmaking scenarios were then compared to MIDREX NG, a leading natural gas-based reduction technology. Hydrogen-based scenarios, powered by the French electricity mix, reduce carbon footprints by 53% for electric gas heating and 57% for solar reactor heating, potentially reaching 82% (-0.79 $kg_{CO_2-eq}/kg_{DRI}$) with low-carbon electricity (hydro, nuclear). Compared to MIDREX NG, the energy requirements of both hydrogen-based scenarios are primarily determined by the use of electricity for hydrogen production, illustrating the importance of hydrogen production for the assessment of future hydrogen-based green ironmaking.
# 1. Introduction

To achieve net-zero global carbon emissions by 2050, the iron and steel industry must be decarbonized [1], [2]. With the iron and steel sector contributing approximately 7% of global greenhouse gas emissions, reducing these emissions is critical to achieving climate goals. As a result, the iron and steel industry, like the rest of the economy, must dramatically reduce its emissions [3], [4]. The Blast Furnace-Basic Oxygen Furnace (BF-BOF) route, which is widely used to produce primary steel, has a very high emissions intensity of 1.6-2.2 $t_{CO2-eq}/t_{steel}$ because it primarily uses coke as an energy source and reducing agent [5], [6]. According to previous studies, the widely used BF-BOF route requires extremely high temperatures of up to 2000°C, making it difficult to decarbonize [6] [7]. Currently, natural gas-based direct reduction (NG-DRI) is the only other established process in use. Despite having a lower emissions intensity than BF, NG-DRI is not widely used because natural gas is typically not as affordable as coke [8]. Up to 60% of emissions can be reduced by retrofitting BF-BOF with post combustion carbon capture and storage (BF-BOF-CCS); however, this reduction is still insufficient to meet long-term targets [9], [10]. The BF-BOF-CCS and NG-DRI-CCS retrofits emit $1 \text{ kg}_{\text{CO2-eq}} \cdot \text{kg}_{\text{steel}}^{-1}$ and $0.3 \text{ kg}_{\text{CO2-eq}} \cdot \text{kg}_{\text{DRI}}^{-1}$, respectively, demonstrating that fossil-based routes continue to generate significant emissions even with CCS [11]. Incomplete $CO_2$ capture in the flue gas stream and, in the case of the BF-BOF route, additional uncaptured emissions from the coking process are the main causes of these residual emissions. Therefore, switching to new technologies is the only way to achieve a significant reduction of $CO_2$ in primary steel production. The main strategy is electrification [9]. In this context, the most promising technologies are: iron ore electrolysis and hydrogen-based direct reduction ($H_2$-DRI) [12] [7].

Operating hydrogen-based direct reduction with hydrogen from renewable electricity can virtually eliminate $CO_2$ emissions [13]. Because $H_2$-DRI can be adapted from existing NG-DRI technology, it is often considered the most appropriate technology for the near future. A combination of hydrogen and natural gas can be used to power direct reduction furnaces. Therefore, once sufficient hydrogen is available, DRI (Direct Reduced Iron) allows a switch from natural gas to hydrogen in the same furnaces [14]. Iron ore electrolysis is a less developed but directly electrified technology. It avoids the conversion
losses that occur in the production of hydrogen in the case of H₂-DRI by using electricity to reduce iron ore [9]. Numerous previous studies have examined the individual emissions reduction potential of various technologies [15], [16], [17]. Only a few of these have considered the innovative H₂-DRI technology [14], [18], [19]. These literature studies primarily evaluate the technical feasibility and energy performance of H₂-DRI based on the material and energy flows within the reactor and the overall process equipment. These assessments focus on the direct operational performance of the process without considering the complete life cycle implications of the process. Energy consumption is estimated based on mass and energy flows without detailed modeling, feasibility analysis of reduction or technical assessments of the entire process. Emissions are typically calculated based on the electricity consumed during the process and do not account for upstream or downstream impacts such as raw material extraction, energy production, or end-of-life considerations.

The integration of process modeling with Life Cycle Assessment (LCA) is central to the eco-design of industrial processes [20], [21]. This combined approach enables a comprehensive assessment of environmental impacts by considering both the operational performance and the broader life cycle implications of a process. A multi-level, multi-fidelity process modeling structure that includes detailed representations of unit operations and their configurations is essential. Such models, when scaled to an industrial scale, provide material and energy inventories that serve as inputs to the LCA study [22]. This integration facilitates the assessment of environmental impacts associated with raw material extraction, energy production, transportation, and waste treatment, thereby supporting informed decision making in process design and optimization [23].

In this study, we apply this integrated process modeling and LCA approach to evaluate the technical and environmental performance of the H₂-DRI process. Since H₂-DRI has not yet been implemented on an industrial scale, this methodology allows us to assess its feasibility by rigorously modelling the iron ore reduction with hydrogen [24] and then to quantify process inventories and to assess the energy performance by simulating the different unit operations involved in the entire process. This study evaluates and compares two variants of the H₂-DRI ironmaking process with the conventional NG-DRI ironmaking route. The first variant, relies entirely on electrification, using renewable electricity for both hydrogen production via electrolysis and electric gas heating as the main heating strategy for the
reduction process. The second also uses renewable electricity for hydrogen production, but employs
concentrated solar energy to heat the reactor, based on lab-scale proof of concept [25].

The results of this study can provide insights for decision-makers on the most efficient technological pathways to minimize CO₂ emissions in the iron industry. They also highlight the implications for the energy system and infrastructure requirements, particularly regarding hydrogen and electricity demand, along with the necessary adaptations in industrial processes to support the transition to hydrogen-based ironmaking.

**2. Materials and methods**

**2.1 Process description and modelling for industrial scale hydrogen-based ironmaking with
renewable heating**

The shift to renewable hydrogen as a reducing agent for ironmaking eliminates the formation of carbon dioxide as a coproduct in the shaft furnace, since the hydrogen reduces iron ore to metallic iron while generating only water vapor. In contrast to the MIDREX process, which relies on a reformer unit to convert natural gas into syngas (a mixture of CO and H₂), the use of pure hydrogen simplifies the gas circuit and eliminates emissions from natural gas combustion and reforming.

However, the implementation of a hydrogen-based direct reduction process requires significant
rethinking of the entire flowsheet. The use of hydrogen introduces new technical challenges related to
hydrogen production, storage, and handling at high flow rates and pressures. In addition, since the
reduction of iron ore remains a highly endothermic process, alternative heating strategies must be
considered. While traditional processes recover heat from combustion gases or use fossil fuels directly
for heating, a hydrogen-based route must rely on electric heating or renewable thermal sources such as
concentrated solar energy and electrical heating. Efficient gas recirculation and heat recovery systems
are also essential to maintain energy efficiency and minimize operational costs. These requirements
highlight the need for a complete redesign of process integration, control, and thermal management
strategies in the H₂-DRI route, making it not just a substitution of the reducing agent but a comprehensive
reengineering of the process to align with future climate-neutral goals.
Despite the shift to low-carbon technologies, the shaft reactor remains central in these green scenarios due to its high efficiency, proven industrial scalability, and compatibility with both syngas and hydrogen as reducing agents. Retaining this core equipment allows for a smoother technological transition by leveraging existing infrastructure while adapting it to renewable energy sources. Moreover, its counter-current gas-solid flow configuration enables efficient mass and heat transfer, which is essential for maintaining high metallization rates and overall process performance in hydrogen-based reduction.

These considerations result in two green hydrogen-based reduction scenarios with alternative heating strategies, further detailed in the following sections: (i) H₂-based ironmaking with electric gas heating (“H₂ DRI ELECTRIC”, Figure 1a) and (ii) H₂-based ironmaking with solar reactor heating (“H₂ DRI SOLAR”, Figure 1b).

Although hydrogen combustion could technically be employed to supply the required process heat, it was not included in this study, as the focus is on two specific renewable heat integration pathways (electric gas heating and solar reactor heating) that do not require further use of energy intensive reducing gas for heating. Previous analyses (Rosner et al. 2023) [26] indicate that hydrogen-based heating for gas preheating would increase the total hydrogen demand by less than 20%, but would also raise the overall energy use and cost due to the energy-intensive nature of hydrogen production.

Note that the process flow diagrams in Figure 1 are based on a medium-size industrial scale ironmaking plant, with a production capacity of 126 t.h⁻¹ of direct reduced iron from hematite pellets, requiring 6 t.h⁻¹ of pure hydrogen. The reactor operates with a hydrogen feed of 36 t.h⁻¹ and a solid pellet feed of 180 t.h⁻¹ (Figure 1). The reactor operates at 2 bar, while other operating conditions such as gas inlet temperatures and heating requirements are established and discussed in Sections 3.1.a and 3.1.b.

The main reactor characteristics are summarized in Table 1, and the following temperature-dependent stoichiometries are considered:

$$3\text{Fe}_2\text{O}_3(\text{s}) + \text{H}_2(\text{g}) \leftrightarrow 2\text{Fe}_3\text{O}_4(\text{s}) + 3\text{H}_2\text{O}(\text{g}) \quad \text{(Rx1)}$$

$$\text{Fe}_3\text{O}_4(\text{s}) + 4\text{H}_2(\text{g}) \leftrightarrow 3\text{FeO}(\text{s}) + \text{H}_2\text{O}(\text{g}) \quad \text{T>570°C} \quad \text{(Rx2)}$$

$$\text{FeO}(\text{s}) + \text{H}_2(\text{g}) \leftrightarrow \text{Fe}(\text{s}) + 4\text{H}_2\text{O}(\text{g}) \quad \text{T>570°C} \quad \text{(Rx3)}$$

$$\text{Fe}_3\text{O}_4(\text{s}) + 4\text{H}_2(\text{g}) \leftrightarrow 3\text{Fe}(\text{s}) + 4\text{H}_2\text{O}(\text{g}) \quad \text{T \le 570°C} \quad \text{(Rx4)}$$
In both scenarios, hydrogen is provided from water electrolysis using alkaline type electrolyzer operating at 80°C, composed of 80 cells connected in series, each with an active surface area of 2.7m².

The choice of alkaline electrolysis is due to its lower investment cost [27] and approved field validity for industrial application in the HYBRIT [28] hydrogen iron ore reduction pilot project in Sweden.

Water removal is performed by cooling with a water flow at 10°C. To improve process water footprint, the condensate leaving the condenser (stream 8, Figure 1) is recycled to the electrolyzer, reducing the amount of water needed to produce hydrogen. Moreover, as the oxygen flowrate produced (stream 4) by electrolysis on an industrial level is not neglectable, the produced oxygen is further liquefied through a series of cooling and compression steps up to 25 bars, allowing valorization despite additional energy consumption required.

To compensate for the pressure drop in the gas/solid reactor, a compressor is placed downstream of the reactor to restore the operating pressure of 2 bar in the reactor (Table 1).

<table><caption>Table 1. Main characteristics of the shaft reactor used for hydrogen-based ironmaking.</caption><thead><tr><th colspan="2">Reactor</th></tr></thead><tbody><tr><td>Reactor geometry</td><td>Cylindrical</td></tr><tr><td>Height (m)</td><td>6</td></tr><tr><td>Radius (m)</td><td>3</td></tr><tr><td>Type of iron ore pellets</td><td>Hematite</td></tr><tr><td>Shape of pellets</td><td>Spherical pellets</td></tr><tr><td>Pellets diameter (mm)</td><td>10</td></tr><tr><td>Pellet porosity</td><td>0.33</td></tr><tr><td>Bed porosity</td><td>0.45</td></tr><tr><td>Operating pressure (bar)</td><td>2</td></tr><tr><td>Hydrogen feed flow (t.h<sup>-1</sup>)</td><td>36</td></tr><tr><td>Solid injected flow (t.h<sup>-1</sup>)</td><td>180</td></tr><tr><td>Iron production (t.h<sup>-1</sup>)</td><td>126</td></tr></tbody></table>
<figure><img src="image_2.png" /><figcaption>(a)</figcaption></figure>
<figure><img src="image_3.png" /><figcaption>Figure 1. Process flow diagram for H₂-based ironmaking: (a) with electric gas heating (“H₂ DRI ELECTRIC”), (b) with solar reactor heating (“H₂ DRI SOLAR”) (gas recycling, heat recovery and hydrogen production are simulated by ProSim software and shaft reactor is modeled in Python [24])</figcaption></figure>

a) Hydrogen-based Ironmaking with electric gas heating (H₂ DRI ELECTRIC)

The Figure 1a shows the flow diagram of the scenario “H₂ DRI ELECTRIC” with electric gas heating.
Initially, hematite pellets of 10mm diameter enter the vertical-axis cylindrical reactor, where reduction
takes place with almost pure hydrogen injected at the bottom of the reactor with 2% molar fraction of
water vapor resulting from the electrolysis. The gas leaving the reactor (stream 6) is a mixture of excess
unreacted hydrogen and water vapor. It is then cooled in a heat exchanger before being routed to a
condenser to remove the water. The remaining hydrogen is then combined with a new stream of make-
up hydrogen (stream 5) recirculated in the heat exchanger for heat recovery and preheated before
reaching the desired inlet gas temperature in the electric gas heating device. For “H₂ DRI ELECTRIC”
scenario, an efficient electrical gas heater using heating resistors with direct contact is considered, compatible with gas compositions and temperatures corresponding to the direct reduction of iron ore with hydrogen, with an approved efficiency of 95% by MIDREX for 10 to 15 years of plant operation [29].

As illustrated in Figure 1a, the simulation of the entire “H₂ DRI ELECTRIC” process is carried out by coupling the simulation of hydrogen production and gas recirculation process using ProSim software with the modelling of hydrogen-based reduction of iron ores in a shaft reactor using a rigorous 1D reactor model describing the reduction of multi-layer iron ore pellets in countercurrent gas-solid moving beds, with the particularity of representing the dual influence of particle size and temperature on conversion [24]. Note that the ProSim simulation in Figure 1a involves gas recycling, heat recovery from gas, water removal by condensation and hydrogen production through electrolysis.

The reactor model describes the reduction kinetics at the pellet scale and the transient transport in the reactor based on the general convective-diffusive transport equation involving mass and energy balance differential equations as well as the pressure drop and the continuity equation. This formulation is summarized in the set of equations (Eq.1-6), which correspond to a counter-current gas-solid reactor, assuming plug flow at constant bed porosity with temperature and size dependent kinetics for the chemical reactions involved.

The pellet model is based on the concept of a multilayer shrinking core, in which chemical reactions progress layer by layer, considering transfer, diffusion and reaction phenomena. The rigorous modelling of reduction at the pellet scale coupled with the reactor transient model provides a more reliable assessment of reduction feasibility under non-isothermal conditions [24].

The results are presented at steady state to illustrate reduction performance and thermal efficiency under a stable operating regime. However, the reactor was implemented as a dynamic model to (1) enable future studies under intermittent renewable-energy supply and (2) avoid possible numerical convergence issues that can arise when solving large spatially discretized algebraic systems directly at steady state.

$$ \frac{\partial \varepsilon_b C_{g,i}}{\partial t} = - \frac{\partial}{\partial z} (\varepsilon_b u_g C_{g,i}) + \frac{\partial}{\partial z} \left( D_a \frac{\partial \varepsilon_b C_{g,i}}{\partial z} \right) + S_i (1 - \varepsilon_b) \quad i \in \text{gas species} \quad (1) $$
$$ \frac{\partial c_{s,j}}{\partial t} = \frac{\partial}{\partial z}(u_s c_{s,j}) + S_j \quad j \in \text{solid species} \qquad (2) $$

$$ \rho_g c_{pg} \varepsilon_b \frac{\partial T_g}{\partial t} = - \rho_g c_{pg} \varepsilon_b u_g \frac{\partial T_g}{\partial z} + \frac{\partial}{\partial z} \left( \varepsilon_b \lambda_g \frac{\partial T_g}{\partial z} \right) + a_g h (T_s - T_g) \qquad (3) $$

$$ \rho_s c_{ps} \frac{\partial T_s}{\partial t} = \rho_s c_{ps} u_s \frac{\partial T_s}{\partial z} + \frac{\partial}{\partial z} \left( \lambda_{eff} \frac{\partial T_s}{\partial z} \right) + \frac{a_g h}{(1 - \varepsilon_b)} (T_g - T_s) + \sum_{k=1}^{n} R_k (-\Delta_r H_k) \qquad (4) $$

$$ \frac{\partial \varepsilon_b c_{g,t}}{\partial t} = - \frac{\partial}{\partial z} (\varepsilon_b \cdot u_g \cdot c_{g,t}) + S(1 - \varepsilon_b) \qquad (5) $$

$$ \frac{-\partial P}{\partial z} = 150 \frac{(1 - \varepsilon_b)^2 \mu_g \cdot \hat{u}_g}{\varepsilon_b^3 d_p^2} + 1.75 \frac{(1 - \varepsilon_b) \rho_g \hat{u}_g^2}{\varepsilon_b^3 d_p} \qquad (6) $$

## b) Hydrogen-based Ironmaking with solar heating of the reactor (H₂ DRI SOLAR)

The second scenario proposes applying the heating directly to the reactor, while the gas entering the reactor is only preheated via gas recirculation and heat recovery in the exchanger (Figure 1b). It should be noted that, apart from the difference in heating mode, all other unit operations are identical to those in the “H₂ DRI ELECTRIC” scenario. This includes the hydrogen recycle loop, water removal in the condenser and the addition of a make-up hydrogen stream to compensate for the amount of hydrogen consumed in the reactor.

It is worth noting that the reactor heating can be provided by a variety of technologies. Among these technologies, the most widespread are concentrated solar heating and microwave heating. Concentrated solar heating is a technology that uses a solar field to collect solar energy, then a concentrator to generate high temperatures suitable for thermochemical reactions. This emerging technology could be relevant in the context of decarbonization, as it makes use of a renewable and abundant source of solar energy [30].

On the other hand, microwave heating provides deep uniform heating with lower heat losses compared to heterogeneous surface heating. Nevertheless, the potential for hot spots and material compatibility issues are among its limitations as it relies on the direct interaction of electromagnetic waves with the absorbing material [31]. Since the absorption of electromagnetic waves decreases with the formation of
reflective metallic iron during the reduction in the reactor, microwave heating alone cannot ensure the complete conversion of iron ore to metallic iron. For this reason, only concentrated solar energy is used as the heating strategy.

The Figure 2 illustrates the reactor heating using concentrated solar energy in “H₂ DRI SOLAR” scenario, where the heating zone is located over one meter of the reactor height at the bottom. The energy required for the reaction is supplied by a system of heliostats that reflect and concentrate the solar energy onto this zone.

<figure><img src="image_4.png" /><figcaption>Figure 2. Schematic representation of the gas/solid countercurrent reactor coupled by concentrated solar heating.</figcaption></figure>

As illustrated in Figure 1b, the overall simulation of “H₂ DRI SOLAR”, including hydrogen production and gas recycling, is carried out using ProSim software while the modelling of shaft reactor with concentrated solar heating is handled using the same reactor model. The energy balance of the solid
phase is modified in Eq 7 to account for heating of the solid phase using the concentrated solar energy introduced at the cavity on the bottom of the reactor (Figure 2).

$$ \rho_s c_{ps} \frac{\partial T_s}{\partial t} = \rho_s c_{ps} u_s \frac{\partial T_s}{\partial z} + \frac{\partial}{\partial z} \left( \lambda_{eff} \frac{\partial T_s}{\partial z} \right) + \frac{a_g}{(1 - \varepsilon_b)} h(T_g - T_s) + \sum_{k=1}^{n} R_k(-\Delta_r H_k) + \hat{Q}_{react} \quad (7) $$

with the heating applied to the dedicated zone $\hat{Q}_{react} \neq 0$ for $1m < h < 2m$, where the heating power in the reactor per unit reactor volume is expressed in W.m⁻³.

## 2.2 Conventional natural gas-based Ironmaking (MIDREX NG)

To enable energy and environmental comparisons to be made, the “MIDREX NG” process was chosen as the benchmark as it is widely used for iron ore direct reduction and accounts for around 80% of the world’s direct reduced iron [32].

The “MIDREX NG” process is based on two main operating units: the shaft furnace, where the iron oxide is reduced, and the reformer, which produces the reducing gas (Figure 3). A heat recovery and production system improve the entire process. The iron oxide is introduced at the top of the furnace while being heated. It is reduced by an upward flow of reducing gases (H₂ and CO), which removes oxygen from iron oxides to form iron, generating water vapor and carbon dioxide. The furnace top gas (stream 3) is first partially dehydrated by removing water (stream 4) and then recycled: one part is used as fuel (stream 6), and another part is mixed with fresh natural gas to feed the reformer (stream 11). The latter contains catalyst-filled tubes placed in a refractory combustion chamber. The heat supplied enables the natural gas and CO₂ to be converted into syngas (88-92% H₂ and CO on a dry basis) (stream 21), which is then used as the reducing gas in the furnace. A special feature of the “MIDREX NG” scenario is the recycling of CO₂ into the reformer, thus avoiding its disposal. Heat is generated by the combustion of natural gas at several points in the system, and a heat recovery circuit improves the overall efficiency as part of the sensible heat of the flue gases is recovered to preheat the combustion air (stream 8) and the fresh natural gas (stream 12). After these two stages of heat recovery, the remaining hot flue gas is
vented through the ejector stack, where pressurized air is injected to entrain and safely expel it to the
atmosphere.

The simulation of the global process uses data from an industrial reactor at Contrecoeur (ArcelorMittal
Canada [33]). This reactor operates under specific conditions, including a production rate of 119 t.h⁻¹
and iron oxide feed containing 97% hematite with a particle size of 15 mm and 3% dolomite at an initial
temperature of -10°C. The reducing gas entering the furnace at 900°C consists mainly of H₂ (50%) and
CO (33%) with traces of CH₄, H₂O, CO₂ and N₂. The reactor operates with a pressure of 2 bar. The
simulation of the entire “MIDREX NG” process was carried out using ProSim software to assess the
conversion, process inventories, and the energy performance of this conventional fossil-based scenario.

<figure><img src="image_5.png" /><figcaption>Figure 3. Flowsheet description of MIDREX NG process.</figcaption></figure>

## 2.3 Environmental and technical assessment of scenarios

### 2.3.1 Life Cycle Assessment (LCA)

The Life Cycle Assessment (LCA), as defined by the ISO 14040/44 standards [34], is a widely
recognized methodology for evaluating the environmental impacts of products or processes throughout
their entire life cycle. It involves four main phases: defining the goal and scope, compiling the Life
Cycle Inventory (LCI), performing the Life Cycle Impact Assessment (LCIA), and interpreting the
results. This approach allows for a comprehensive quantification of resource use and emissions, as well
as their associated impacts on human health, ecosystems, and resource depletion.

The function of the process is to produce iron from iron ore pellets and reducing gas. The functional unit
is therefore defined as the production of one kilogram of DRI. A 50-year plant lifetime was assumed,
reflecting the typical service life of industrial ironmaking facilities. This duration is used for the
calculation of infrastructure impacts, while equipment with shorter lifetimes—such as electrolyzers and
heliostats (25 years)—are accounted for by adjusting their replacement frequency within this timeframe.

A cradle-to-gate life cycle approach was applied, covering the extraction of raw materials to the
production of iron as shown in Figure 4. The foreground system (Figure 4) includes all main inputs and
processes required up to the production of direct reduced iron (DRI). For the hydrogen-based routes,
this covers the upstream production of hydrogen, including electricity generation, water treatment for
electrolysis, and operation of the electrolyzer. Additional inputs such as cooling water, iron ore pellets,
and infrastructure materials (electrolyzer, heliostats, reactor) are also included. For the benchmark NG-
DRI process, natural gas supply and use in the reformer and combustion chamber are considered.
Outputs include DRI as the functional product, direct process emissions, and oxygen as a co-product in
the H₂-based routes. The plants were considered to be located in France. Transport by sea of iron pellets
from one of the main producer countries (Canada, 5000 km) is included.

The ReCiPe Midpoint H assessment method was chosen, as it is one of the most recent and is frequently
used in steel industry [35]. This method covers a large panel of environmental issues translated in 18
impact categories. The use of the complete set of categories prevents neglecting unexpected impacts.

For example, land use is considered by ReCiPe, which is particularly relevant in our study, as a solar
field is required to produce heat using concentrated solar energy. The LCA model was implemented in
Umberto 11 software with the Ecoinvent 3.9 database. The attributional modeling system was used with
system expansion (subtraction) for the co-products in the foreground system.
<figure><img src="image_6.png" /><figcaption>Figure 4. System boundaries for the three scenarios studied: “H₂ DRI ELECTRIC”, “H₂ DRI SOLAR”, and “MIDREX NG”.</figcaption></figure>

### 2.3.2 Technical performance indicators

In addition to environmental impacts, several technical performance indicators were also considered to assess the feasibility and relevance of new green ironmaking pathways. These include the overall conversion of iron ore to metallic iron and the required height of reduction in the reactor to assess the feasibility and intensification potential of the process. Two other performance indicators considered are the specific energy consumption (kWh.kg<sub>DRI</sub><sup>-1</sup>) and the annual energy cost (€/kg<sub>DRI</sub>), which evaluate the process efficiency and the potential economic implications of green ironmaking compared to the conventional NG-DRI route.

## 3. Results and discussions

### 3.1 Simulation results and indications on process design for H₂-based ironmaking scenarios

#### a) H₂-based ironmaking with electric gas heating (H₂ DRI ELECTRIC)

Based on the reactor model described in Section 2.1 and the process flow diagram in Figure 1a, a series of parametric studies examines the influence of gas inlet temperature on conversion in the shaft reactor.
The Figure 5a shows the conversion profile in the reactor at different temperatures. Below 700°C, very long reactors heights are needed to achieve 99% conversion. For example, at 600°C, nearly 99% conversion is obtained within 6m of an adiabatic reactor. Therefore, for the simulation of “H₂ DRI ELECTRIC” scenario, a gas inlet temperature of 700°C was selected together with reactor characteristics given in Table 1 and Section 2.1, where the complete set of operating conditions are provided in Table A.1 (Supplementary Information).

Figure 5b shows the trade-off between the reactor length and the gas heating demand as a function of the gas input temperature. As the temperature increases, the required height for reduction decreases significantly, while the gas heating demand rises due to the higher thermal energy input needed. For the selected gas inlet temperature of 700 °C, a reactor height of approximately 2 m is sufficient to achieve complete reduction, with an energy requirement of 45 MW.

Figure 5c illustrates the evolution of gas and solid temperatures, as well as the overall conversion, along the height of the reactor. The results show that the iron ore is fully converted to metallic iron with the selected favorable gas inlet temperature of 700°C, with good heat exchange between the gas and solid phases under nonisothermal operating conditions.

<figure><img src="image_7.png" /><figcaption>(a)</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>(b)</figcaption></figure>
<figure><img src="image_9.png" /><figcaption>Figure 5. (a) Effect of the inlet gas temperature on the conversion of iron ore to metal iron using hydrogen in reactor; (b) Trade-off between the energy demand and the required height for reduction as a function of the inlet gas temperature; (c) Temperature of gas and solid phases as well as the overall conversion along the reactor height for “H₂ DRI ELECTRIC” process considering an inlet gas temperature of 700°C.</figcaption></figure>

Table 2 shows the process-specific breakdown of electricity consumption. The electrolyzer is the main source of energy consumption, accounting for about 87% of the total energy required by the system. Hydrogen heating also makes a significant contribution, although to a lesser extent. On the other hand, the energy consumption associated with gas compression and pumping operations remains relatively low in comparison. This analysis highlights the predominant impact of water electrolysis on the overall energy consumption of the process and underlines the importance of enhancing this stage to improve energy efficiency. The results of the current model are in the range of values reported in the literature [19], [36], suggesting consistency with existing studies. The oxygen produced from electrolysis was assumed to undergo three cycles of compression and cooling up to 25 bar and 123 K for liquefaction. The additional electricity required for oxygen purification and liquefaction was directly added to the total electricity consumption of the electrolyzer system. This approach ensures that all associated energy requirements are consistently included in the overall power demand. The values are consistent with reported data for large-scale electrolysis plants (250–500 MW), where oxygen liquefaction and
purification require 11.9–23.8 MW, corresponding to an increase of approximately 4% in total electricity
consumption [37].

b) H₂-based ironmaking with solar reactor heating (H₂ DRI SOLAR)

For the hydrogen-based reduction with solar reactor heating (Figure 1b), a series of parametric studies
was carried out to analyze the effect of the concentrated solar power on the conversion in the reactor.
The parametric study indicated that a reactor heating power of 45 MW is required to achieve complete
conversion of iron oxide to metallic iron within the complete process, while the conversion remains at
66% and 98% for a reactor heating power of 30 MW and 40 MW, respectively, as shown in Figure 6a.
Therefore, an absorbed heating power of 45 MW was selected, using the same reactor characteristics as
those in Section 2.1 and Table 1, with the complete set of operating conditions reported in Table A.2
(Supplementary Information).

The Figure 6b shows the gas and solid temperature profiles, along with the overall conversion of iron oxides considering a reactor heating power of 45 MW. A rapid rise in temperature under the effect of concentrated solar heating is observed between 1 and 2 meters of the reactor height. In this zone, the temperature of the solid phase is higher than that of the gas phase due to the direct absorption of solar radiation by the solid phase, whereas at the reactor top, the opposite trend reflects dominant heat transfer from gas to solid. Unlike the previous scenario with electric gas heating, thermal equilibrium between phases is not attained throughout the reactor.

<figure><img src="image_10.png" /></figure>
<figure><img src="image_11.png" /><figcaption>Figure 6. (a) Effect of absorbed heating power input on the conversion of iron ore to metal iron using pure hydrogen in reactor; (b) Temperature of gas and solid phases as well as overall conversion along the reactor height for “H₂ DRI SOLAR” process considering a reactor heating power of 45 MW.</figcaption></figure>

In the case of concentrated solar heating, due to the various losses inherent in the process, the required incident solar power ($P_{solar}$) is higher than the heating power absorbed by the reactor ($P_{reactor}$) and can be determined from the global efficiency of the solar field and concentration systems ($\tau_{solar}$) as expressed in equation 8.

$$P_{solar} = \frac{P_{reactor}}{\tau_{solar}} \qquad (8)$$

The estimation of the required incident solar energy is also necessary to determine the solar field area and the number of heliostats, and consequently to quantify the infrastructure that must be included in the Life Cycle Assessment. The solar concentrating system is a central tower configuration, as this is the most suitable technology for large-scale applications [38]. The cavity is located at the top of the tower, where the solar radiation, reflected by the field of heliostats, is concentrated. The global efficiency ($\tau_{solar}$) considers multiple factors, including losses in the heliostat field (such as atmospheric
absorption, shadowing, cosine effects, and guidance errors), imperfections in concentration, and radiation losses. Here, a practical approach following Rodat et al. [39] is applied, resulting in an estimated global efficiency of 67%, meaning that 67% of the incident solar radiation captured by the field of heliostats is transmitted and absorbed by the reactor.

Table 2 shows the energy consumption per equipment, as well as the total energy consumption for the “H₂ DRI SOLAR” process. The power consumption of the electrolyzer is similar to that of the previous scenario with electric gas heating. Overall, the total power consumption is quite similar, with the main difference being the required incident solar energy. This is due to the higher efficiency of electrical heating (95%) compared to solar heating (67%), which requires a higher incident power input to achieve the same reduction performance.

### c) Conventional natural gas-based Ironmaking (MIDREX NG)

The energy consumption of the MIDREX NG process is presented in Table 2, based on the simulation of the process shown in Figure 3, for which the complete set of operating conditions is provided in Table A.3 (Supplementary Information). The ratio of natural gas required per DRI produced is 164.4 kg.t<sub>DRI</sub><sup>-1</sup> which is comparable to data from the literature : 182.8 kg.t<sub>DRI</sub><sup>-1</sup> (Nduagu et al, 2022 [15]), 159.8 kg.t<sub>DRI</sub><sup>-1</sup> (Sarkar et al, 2018 [40]).

The total energy consumption is calculated from the total natural gas consumption in the process and its lower heating value, and the electricity consumption needed for gas compression and water pumping. According to Nduagu et al. [15], an electricity consumption of 120 kWh.t<sub>DRI</sub><sup>-1</sup> should be considered for the various parts of the process.

<table><caption>Table 2. Energy consumption per unit operation for the three scenarios studied: “H₂ DRI ELECTRIC”, “H₂ DRI SOLAR”, and “MIDREX NG”.</caption><thead><tr><th>Energy demand by type (MW)</th></tr></thead></table>
<table><thead><tr><th></th><th>Electricity for<br>electrolyzer</th><th>Electricity<br>for gas<br>heating</th><th>Required incident<br>solar power</th><th>Energy for<br>reforming<br>(Natural gas use)</th><th>Electricity for pump,<br>compressor and<br>auxiliaries</th></tr></thead><tbody><tr><td>H<sub>2</sub> DRI ELECTRIC</td><td>363</td><td>47</td><td>-</td><td>-</td><td>6</td></tr><tr><td>H<sub>2</sub> DRI SOLAR</td><td>363</td><td>-</td><td>67</td><td>-</td><td>6</td></tr><tr><td>MIDREX NG</td><td>-</td><td>-</td><td>-</td><td>300</td><td>14</td></tr></tbody></table>

## 3.2 Environmental assessment of hydrogen-based ironmaking

### 3.2.1 Building of Life Cycle Inventories (LCI) for the 3 scenarios studied

The inventory for the foreground system, i.e. material and energy consumption and production, was built using the simulation results, i.e. material and energy consumptions and emissions. The inventory results (detailed in section B of the Supplementary Information) for the three scenarios studied are presented in Table 3, where the values are expressed per kg of DRI produced.

<table><caption>Table 3. Life cycle inventories for the three studied scenarios: “H<sub>2</sub> DRI ELECTRIC”, “H<sub>2</sub> DRI SOLAR”, and “MIDREX NG”.</caption><thead><tr><th>Inventory</th><th>MIDREX NG</th><th>H<sub>2</sub> DRI ELECTRIC</th><th>H<sub>2</sub> DRI SOLAR</th><th>Unit</th><th>Ecoinvent database 3.9</th><th>Inventory data source/Reference</th></tr></thead><tbody><tr><td>Reactor infrastructure</td><td>-</td><td>-</td><td>-</td><td>Unit</td><td>market for blast furnace [GLO]</td><td>Derived from Ecoinvent v3.9 dataset, normalized per kg of DRI (value not disclosed due to licensing)</td></tr><tr><td>Eletrolyzer infrastructure</td><td>-</td><td>1.63×10<sup>-4</sup></td><td>4.89×10<sup>-4</sup></td><td>Unit</td><td>-</td><td>[41]</td></tr><tr><td>Heliostats infrastructure</td><td>-</td><td>-</td><td>2.9×10<sup>-4</sup></td><td>kg</td><td>flat glass production, coated [RER]</td><td>Solar power calculation- this work</td></tr><tr><td>Avoided liquid oxygen</td><td>-</td><td>-0.39</td><td>-0.39</td><td>kg</td><td>market for oxygen, liquid [RER]</td><td>Simulation results-this work</td></tr></tbody></table>
<table><tr><td>Iron ore pellet</td><td>1.33</td><td>1.43</td><td>1.43</td><td>kg</td><td>iron pellet production [CA-QC]</td><td>Simulation results-this work</td></tr><tr><td>Dolomite</td><td>0.05</td><td>-</td><td>-</td><td>kg</td><td>dolomite production [RER]</td><td>Simulation results-this work</td></tr><tr><td>Transportation</td><td>6.650</td><td>7.15</td><td>7.15</td><td>ton*km</td><td>Transport, freight, sea, container ship (GLO, transport, freight, sea, container ship)</td><td>Based on an average sea distance of 5000 km between France and Canada</td></tr><tr><td>H₂ input requirements</td><td>-</td><td>0.06</td><td>0.06</td><td>kg</td><td>-</td><td>Simulation results-this work</td></tr><tr><td>Natural gas</td><td>0.25</td><td>-</td><td>-</td><td>m³</td><td>market for natural gas, low pressure [FR]</td><td>Simulation results-this work</td></tr><tr><td>Electricity</td><td>0.12</td><td>3.3</td><td>2.9</td><td>kWh</td><td>market for electricity, high voltage [FR]</td><td>Simulation results-this work</td></tr><tr><td>Cooling water</td><td>229</td><td>342</td><td>257</td><td>kg</td><td>market for water, completely softened [RER]</td><td>Simulation results-this work</td></tr><tr><td>Water for electrolyzer</td><td>-</td><td>0.71</td><td>0.8</td><td>kg</td><td>market for water, ultrapure [RER]</td><td>Simulation results-this work</td></tr><tr><td>Direct emissions</td><td>0.44</td><td>-</td><td>-</td><td>kg</td><td>Carbon dioxide, fossil</td><td>Simulation results-this work</td></tr></table>

### 3.2.2 Life cycle impact assessment: hydrogen-based vs natural gas-based ironmaking

Figure 7 shows the results for each ReCiPe midpoint impact category, normalized to the maximum value for each impact category. The analysis of the environmental impacts of the different scenarios shows that no single scenario systematically stands out as the most virtuous for all the indicators studied, each scenario has advantages and disadvantages depending on the environmental impact considered. In terms of water depletion, the “H₂ DRI ELECTRIC” and “H₂ DRI SOLAR” scenarios have a higher footprint. This is due to the water consumption associated with cooling and hydrogen production. On the other hand, in terms of fossil depletion, the “MIDREX NG” process based on natural gas has the highest impact. With regard to metal depletion, the impacts are relatively similar for the three scenarios as they all use iron ore as raw material. However, there is a slight difference for the “MIDREX NG” process due to the inclusion of dolomite in the raw material mix, which may affect the relative consumption of mineral resources.
In terms of land occupation, the “H₂ DRI SOLAR” scenario is clearly the most impactful. This difference is mainly due to the need for a dedicated solar field for concentrating solar radiation and the oversizing of installations to compensate for the reduced operating period compared to other technologies.

<figure><img src="image_12.png" /><figcaption>Figure 7. Results of ReCiPe midpoint environmental impacts for the three scenarios studied: “H₂ DRI ELECTRIC”, “H₂ DRI SOLAR”, and “MIDREX NG”.</figcaption></figure>

In the following analysis, only the climate change impact (GWP100) is detailed for clarity. Details are presented in the supplementary information for the other impacts (Figures C.1-17, Supplementary Information). Figure 8 shows the contribution of the different processes to the impact: infrastructure, total process electricity consumption, ultrapure water production for electrolysis, transportation, water treatment for cooling, iron ore pellet production, avoided impact of liquid oxygen production, natural gas and dolomite consumption in “MIDREX NG”.
The comparative analysis of the three ironmaking scenarios with French mix electricity shows significant differences in terms of climate change impact, expressed in kgCO2-eq/kgDRI. As expected, the “MIDREX NG” process has the highest carbon footprint (1.01 kgCO2-eq/kgDRI). This is mainly due to direct emissions from the combustion of natural gas to produce heat. Conversely, the hydrogen-based scenarios show a marked reduction in emissions, with 0.49 kgCO2-eq/kgDRI for the all-electric variant and 0.46 kgCO2-eq/kgDRI for the solar energy variant, a reduction of 53% and 57% respectively compared to “MIDREX NG”. The use of solar energy allows a further improvement by replacing electricity with a renewable thermal heat source, reducing the dependency on the electricity mix and resulting in lower emissions. However, due to the oversizing required to ensure annual productivity similar to other scenarios, the impact of infrastructure becomes more significant and can no longer be neglected in the overall analysis. Iron ore pelletization is a major contributor to emissions in all scenarios, underlining the importance of this stage in the overall carbon footprint of the process. Transportation of iron pellets, as considered in this work (Canada – France), contributes with 7% to 14% of the impact in “MIDREX NG” and in the other two scenarios, respectively. It should also be noted that the recovery of oxygen from electrolysis is a prerequisite for reducing the process footprint. Indeed, without this recovery, the results would be 0.68 and 0.65 kgCO2-eq/kgDRI and the emissions reduction compared to “MIDREX NG” would only be 32% and 36%.
<figure><img src="image_13.png" /><figcaption>Figure 8. Comparative analysis of climate change impact for the three scenarios studied: “H₂ DRI ELECTRIC”, “H₂ DRI SOLAR”, and “MIDREX NG”.</figcaption></figure>

The carbon footprint of electrified iron ore reduction processes is highly dependent on the source of electricity used for water electrolysis and heating. To assess the influence of this variable, different types of electricity, ranging from highly fossil -based to the French electricity mix and to renewable and low carbon electricity have been compared to “MIDREX NG” process in Figure 9. To derive these results, only the electricity mix was changed in the LCA models, all other LCI components were kept unchanged. The hydrogen-based scenarios show significant impact reductions depending on the source of electricity used. Sources using hydropower or nuclear power have the lowest emissions, at around 0.16 kgCO₂-eq/kgDRI. The use of renewable energy sources reduces emissions by almost 83% compared to “MIDREX NG”, confirming their essential role in the transition to green iron production.
The “H₂ DRI SOLAR” process is characterized by solar reactor heating, which reduces dependence on electricity for this function. This difference is observed when the electricity mix is used. On the other hand, when the electricity comes from renewable or low-carbon sources, the emissions associated with electricity become low, making both processes similar in environmental impacts, and reduced almost to the impact of iron oxide pellet production.

Since India is the leading producer of DRI and Iran the world's second largest producer [42], it is important to evaluate the potential emissions reduction of the electrified process in these contexts. However, as shown in Figure 9, the Indian electricity mix primarily relies on coal, resulting in a high carbon footprint (4.4 kgCO₂-eq/kgDRI for “H₂ DRI ELECTRIC” and 3.8 kgCO₂-eq/kgDRI for “H₂ DRI SOLAR”). In contrast, Iran's electricity grid is mainly fueled by natural gas, leading to a carbon footprint of 2.5 kgCO₂-eq/kgDRI for “H₂ DRI ELECTRIC” and 2.1 kgCO₂-eq/kgDRI for “H₂ DRI SOLAR”. Although lower than the values observed for India, these results remain significantly higher than those obtained with low-carbon electricity mixes (e.g., nuclear or hydroelectricity). Together, these findings highlight a key limitation: while electrification can be a viable environmental solution in countries with low-emission electricity grids, its benefits are significantly reduced in regions where electricity generation is still heavily dependent on fossil fuels, underscoring the necessity of decarbonizing power production to fully leverage the environmental advantages of hydrogen-based ironmaking.
<figure><img src="image_14.png" /><figcaption>Figure 9. Comparison of the climate change impact of the three scenarios according to the type of electricity used.</figcaption></figure>

### 3.3 Multicriteria analysis and assessment of hydrogen-based ironmaking

Table 4 presents a multi-criteria analysis of three DRI production scenarios. The “H₂ DRI ELECTRIC” scenario relies entirely on electricity, used to produce both the hydrogen and the heat, with a total consumption of 3.3 kWh/kgDRI and a carbon footprint of 0.49 kgCO₂-eq/kgDRI. The “H₂ DRI SOLAR” scenario combines electricity for electrolysis and concentrated solar energy for reactor heating, slightly reducing the carbon footprint to 0.46 kgCO₂-eq/kgDRI for an electricity consumption of 2.9 kWh/kgDRI and a solar power required of 0.5 kWh/kgDRI. Despite its environmental advantage, the technological complexity of solar reactor heating limits its economic gains, with an estimated cost of €0.37/kgDRI, slightly lower than that of electric heating (€0.40/kgDRI), but potentially offset by higher capital and operational challenges. Details on the economic estimation are presented in the Supplementary
Information (Section D). By comparison, the natural gas-based “MIDREX NG” process has the lowest energy consumption (2.4 kWh/kgDRI) and the lowest energy cost (€0.32/kgDRI), but at the cost of a much higher carbon footprint (1.01 kgCO2-eq/kgDRI). In addition, the reactor height required for complete reduction is significantly lower in the hydrogen-based scenarios (1-2 m) than in the MIDREX process (9 m), revealing a marked potential for process intensification in H2-based ironmaking.

It should be noted, however, that the feasibility of the “H₂ DRI SOLAR” scenario is strongly influenced by the intermittency of solar energy. Seasonal fluctuations and daily variations in solar radiation could limit the ability to maintain continuous reactor operation, particularly at night or during periods of insufficient sunlight. For instance, for summer 2024 in France, peak DNI around 900–1000 W/m² was likely reached at noon on clear days in the South, and about 700–900 W/m² in central and northern regions. In winter 2024, clear-sky noon maxima were about 200–400 W/m² in the South and 100–300 W/m² further north, with much lower values under cloud cover. These estimates are consistent with long-term climatological data from the Global Solar Atlas (Solargis). To address this limitation, the process could be coupled with thermal storage systems to ensure continuous operation, or designed as a hybrid configuration in which gas heating compensates for periods without sufficient solar input.

Conventionally, in DRI processes the reducing gas is heated rather than the solid phase. The solar-based route requires more advanced assessments and the integration of solutions such as thermal storage or hybrid heating [43] to ensure production continuity before it can be evaluated on the same basis.

Addressing these challenges represents a main focus of our future research interests.

Overall, green hydrogen-based ironmaking enables significant decarbonization, particularly “H₂ DRI ELECTRIC”, which appears to be an effective compromise between environmental performance, operational simplicity and energy cost under continuous production conditions.
<table><caption>Table 4. Multicriteria assessment of new green hydrogen-based ironmaking pathways compared to conventional natural gas-based process.</caption><thead><tr><th>Scenario</th><th>GWP100 impact (kgCO2-eq/kgDRI)</th><th>Energy consumption (kWh/kgDRI)</th><th>Energy cost (€/kgDRI)</th><th>Required reactor height for reduction (m)</th></tr></thead><tbody><tr><td>"H<sub>2</sub> DRI ELECTRIC"</td><td>0.49</td><td>Electricity: 3.3</td><td>0.40</td><td>2</td></tr><tr><td>"H<sub>2</sub> DRI SOLAR"</td><td>0.46</td><td>Electricity: 2.9<br>Solar power: 0.5</td><td>0.37</td><td>1</td></tr><tr><td>"MIDREX NG"</td><td>1.01</td><td>Natural gas <sup>(1)</sup>: 2.3<br>Electricity: 0.1</td><td>0.32</td><td>9</td></tr></tbody></table>

### 3.4 Impact of key energy parameters on process performance

For the H₂-DRI process, which has not yet been commercialized, the level of uncertainty is higher than for the NG-DRI process due to the lack of industrial process parameters and operational data. As shown in Table 2, the energy consumption in the H₂-DRI process is mainly driven by the electricity demand of the electrolyzer. In our study, an electrolyzer efficiency of 90% was assumed, resulting in an electricity consumption of 363 MW. If an industrial electrolyzer operates at a lower efficiency of 80%, the electricity consumption would increase to 408 MW, leading to a total GWP impact of 0.52 kgCO₂-eq/kgDRI for "H₂ DRI ELECTRIC" and 0.49 kgCO₂-eq/kgDRI for "H₂ DRI SOLAR", using the French mix electricity grid.

Another parameter influencing the results is the efficiency of the electrical gas heater. Although an efficiency of 95% is reported by MIDREX, lower values are possible. In our study, an efficiency of 95% corresponds to an electricity consumption of 47 MW. If the efficiency were reduced to 80%, the

<footnote>(1) reforming</footnote>
electricity demand would increase to about 56 MW, leading to slightly higher CO₂ emissions (from 0.49 to 0.5 kgCO₂-eq/kgDRI, for “H₂ DRI ELECTRIC”).

For H₂ DRI routes, the reactor was considered as adiabatic. In conventional industrial shaft furnaces, heat losses are typically on the order of ~15%. However, our work explores an intensified reactor concept with a significantly reduced length (approximately one-sixth of conventional designs) and enhanced insulation, both of which substantially reduce lateral heat loss. In this context, the adiabatic assumption is justified, as it reflects design improvements specific to hydrogen operation. If thermal losses are considered, they would increase the thermal energy demand. For the H₂ DRI ELECTRIC process, such losses would directly increase the electricity consumption of the gas heater, while for the H₂ DRI SOLAR process they would reduce the overall solar efficiency ($\tau_{solar}$, Eq. (8)) and thus require higher incident solar power. For example, assuming reactor thermal losses of 20%, the electricity demand of the gas heater would rise from 47 MW to 56 MW, while the required incident solar power would increase from 67 MW to 85 MW ($\tau_{solar}$ from 0.67 to 0.53).

## 4. Conclusions

This study presents a comparative assessment of two hydrogen-based ironmaking routes that employ different heating strategies - electric gas heating and solar reactor heating - against the conventional natural gas-based MIDREX process. Through comprehensive simulations, the study identified favorable configurations and operating conditions to ensure complete iron ore conversion and effectively evaluate the H₂-based alternatives.

The results show that hydrogen-based reduction pathways offer a significantly lower environmental impact compared to natural gas-based processes. These methods also hold promise for process intensification, particularly through reducing shaft reactor size, assuming that renewable energy and hydrogen production infrastructure can be scaled accordingly.

On average, hydrogen-based ironmaking could reduce CO₂ emissions by 50-80%, depending on the carbon intensity of the electricity used, since hydrogen production is the primary energy consumer in both scenarios. The electric gas heating route is technically preferable when low-carbon electricity is available, as it offers greater robustness and easier implementation. In contrast, solar reactor heating
currently faces challenges related to land use and the intermittency of solar energy, which limit its scalability and reliability. Additionally, iron pellet production was found to contribute significantly to environmental impacts, emitting around 0.23 kgCO2-eq/kgDRI. Decarbonizing this step could further advance the industry toward carbon-free ironmaking.

The lack of industrial validation for H₂-based DRI processes, the simplified representation of solar operation, and the limited scope of the economic assessment represent important limitations of this study. The solar-heated DRI process was analyzed under idealized solar conditions; intermittency effects and potential mitigation strategies, such as thermal storage or hybrid heating, were discussed qualitatively but not simulated quantitatively. In addition, the economic analysis was restricted to energy-related costs (electricity, hydrogen, and natural gas), without considering capital and installation costs for key equipment such as the electrolyzer and solar field. These aspects could affect the comparison with the conventional natural gas-based ironmaking route, as well as the selection of the most suitable hydrogen-based process variant between solar and electrical heating. Future work should extend the analysis to the full steelmaking chain, including the electric arc furnace, to enable a more comprehensive assessment of hydrogen-based steel production systems.

## Acknowledgments

This work was funded by the French National Research Agency (ANR) under the grant ANR-20-CE05-0008-01 METASOL (Solar iron metallurgy based on renewable or bio-sourced reducers).
## Notations

<table><tr><td>a<sub>g</sub></td><td>specific surface of bed</td></tr><tr><td>c<sub>p<sub>s</sub></sub>, c<sub>p<sub>g</sub></sub></td><td>molar specific heat of solid and gas phases [J mol<sup>-1</sup> K<sup>-1</sup>]</td></tr><tr><td>C<sub>g,i</sub></td><td>gas molar concentration [mol m<sup>-3</sup>]</td></tr><tr><td>C<sub>s,i</sub></td><td>solid molar concentration [mol m<sup>-3</sup>]</td></tr><tr><td>D<sub>a</sub></td><td>axial dispersion coefficient [m<sup>2</sup> s<sup>-1</sup>]</td></tr><tr><td>d<sub>p</sub></td><td>pellet diameter [m]</td></tr><tr><td>S<sub>i</sub>, S<sub>j</sub></td><td>Source term [mol m<sup>-3</sup> s<sup>-1</sup>]</td></tr><tr><td>&Delta;<sub>r</sub>H</td><td>enthalpy of reaction [J mol<sup>-1</sup>]</td></tr><tr><td>h</td><td>heat transfer coefficient [W m<sup>-2</sup> K<sup>-1</sup>]</td></tr><tr><td>&lambda;<sub>eff</sub></td><td>effective thermal conductivity [W.m<sup>-1</sup>.K<sup>-1</sup>]</td></tr><tr><td>&lambda;<sub>g</sub></td><td>gas phase thermal conductivity [W.m<sup>-1</sup>.K<sup>-1</sup>]</td></tr><tr><td>R</td><td>reaction rate [mol m<sup>-3</sup> s<sup>-1</sup>]</td></tr><tr><td>&rho;<sub>s</sub>, &rho;<sub>g</sub></td><td>density of the solid phase and gas phase [kg.m<sup>-3</sup>]</td></tr><tr><td>T<sub>s</sub>, T<sub>g</sub></td><td>temperature of solid and gas phases [K]</td></tr><tr><td>t</td><td>time [s]</td></tr><tr><td>u<sub>s</sub>, u<sub>g</sub></td><td>velocity of solid and gas phases [m.s<sup>-1</sup>]</td></tr><tr><td>z</td><td>height [m]</td></tr><tr><td>&epsilon;<sub>b</sub></td><td>bed porosity</td></tr><tr><td>P</td><td>gas pressure [Pa]</td></tr><tr><td>&mu;<sub>g</sub></td><td>gas dynamic viscosity [Pa.s]</td></tr><tr><td>&tau;</td><td>efficiency</td></tr><tr><td>ALOP</td><td>Agricultural land occupation</td></tr><tr><td>FDP</td><td>Fossil depletion</td></tr><tr><td>FEP</td><td>Freshwater eutrophication</td></tr><tr><td>FETPinf</td><td>Freshwater ecotoxicity</td></tr></table>
<table><tr><td>GWP</td><td>Climate change</td></tr><tr><td>HTPinf</td><td>Human toxicity</td></tr><tr><td>IRP_HE</td><td>Ionising radiation</td></tr><tr><td>MDP</td><td>Metal depletion</td></tr><tr><td>MEP</td><td>Marine eutrophication</td></tr><tr><td>METPinf</td><td>Marine ecotoxicity</td></tr><tr><td>NLTP</td><td>Natural land transformation</td></tr><tr><td>ODPinf</td><td>Ozone depletion</td></tr><tr><td>PMFP</td><td>Particulate matter formation</td></tr><tr><td>POFP</td><td>Photochemical oxidant formation</td></tr><tr><td>TAP100</td><td>Terrestrial acidification</td></tr><tr><td>TETPinf</td><td>Terrestrial ecotoxicity</td></tr><tr><td>ULOP</td><td>Urban land occupation</td></tr><tr><td>WDP</td><td>Water depletion</td></tr></table>
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# Supplementary data

## Technical and environmental assessment of new green iron production strategies using hydrogen

A. Skafa, L. Tiruta-Barna, A. Ahmadi

a TBI, Université de Toulouse, CNRS, INRAE, INSA 135 Avenue de Rangueil, 31077, France

### Notations

<table><tr><td>ALOP</td><td>Agricultural land occupation</td></tr><tr><td>FDP</td><td>Fossil depletion</td></tr><tr><td>FEP</td><td>Freshwater eutrophication</td></tr><tr><td>FETPinf</td><td>Freshwater ecotoxicity</td></tr><tr><td>GWP</td><td>Climate change</td></tr><tr><td>HTPinf</td><td>Human toxicity</td></tr><tr><td>IRP_HE</td><td>Ionising radiation</td></tr><tr><td>MDP</td><td>Metal depletion</td></tr><tr><td>MEP</td><td>Marine eutrophication</td></tr><tr><td>METPinf</td><td>Marine ecotoxicity</td></tr><tr><td>NLTP</td><td>Natural land transformation</td></tr><tr><td>ODPinf</td><td>Ozone depletion</td></tr><tr><td>PMFP</td><td>Particulate matter formation</td></tr><tr><td>POFP</td><td>Photochemical oxidant formation</td></tr><tr><td>TAP100</td><td>Terrestrial acidification</td></tr><tr><td>TETPinf</td><td>Terrestrial ecotoxicity</td></tr><tr><td>ULOP</td><td>Urban land occupation</td></tr><tr><td>WDP</td><td>Water depletion</td></tr></table>
## A. Operating conditions tables

<table><caption>Table A.1 Operating conditions of “H₂ DRI ELECTRIC” process.</caption><thead><tr><th rowspan="2">Stream</th><th rowspan="2">Temperature</th><th rowspan="2">Pressure</th><th colspan="6">Mass flowrate</th></tr><tr><th>K</th><th>bar</th><th colspan="5">kg.s<sup>-1</sup></th></tr><tr><th></th><th></th><th></th><th>Hematite</th><th>DRI</th><th>Hydrogen</th><th>Water vapor</th><th>Water</th><th>Oxygen</th></tr></thead><tbody><tr><td>1</td><td>298</td><td>-</td><td>50</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>2</td><td>973</td><td>-</td><td>-</td><td>35</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>3</td><td>298</td><td>1</td><td>-</td><td>-</td><td>-</td><td>-</td><td>42.8</td><td>-</td></tr><tr><td>4</td><td>123</td><td>25</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>13.6</td></tr><tr><td>5</td><td>298</td><td>1</td><td>-</td><td>-</td><td>1.7</td><td>0.5</td><td>-</td><td>-</td></tr><tr><td>6</td><td>674</td><td>1.8</td><td>-</td><td>-</td><td>8.28</td><td>19.56</td><td>-</td><td>-</td></tr><tr><td>7</td><td>346</td><td>1.8</td><td>-</td><td>-</td><td>8.28</td><td>19.56</td><td>-</td><td>-</td></tr><tr><td>8</td><td>298</td><td>1.8</td><td>-</td><td>-</td><td>-</td><td>-</td><td>18</td><td>-</td></tr><tr><td>9</td><td>298</td><td>1.8</td><td>-</td><td>-</td><td>8.28</td><td>1.52</td><td>-</td><td>-</td></tr><tr><td>10</td><td>314</td><td>2</td><td>-</td><td>-</td><td>8.28</td><td>1.52</td><td>-</td><td>-</td></tr><tr><td>11</td><td>312</td><td>2</td><td>-</td><td>-</td><td>10</td><td>2</td><td>-</td><td>-</td></tr><tr><td>12</td><td>667</td><td>2</td><td>-</td><td>-</td><td>10</td><td>2</td><td>-</td><td>-</td></tr><tr><td>13</td><td>973</td><td>2</td><td>-</td><td>-</td><td>10</td><td>2</td><td>-</td><td>-</td></tr><tr><td>14</td><td>283</td><td>1</td><td>-</td><td>-</td><td>-</td><td>-</td><td>12000</td><td>-</td></tr><tr><td>15</td><td>283</td><td>2</td><td>-</td><td>-</td><td>-</td><td>-</td><td>12000</td><td>-</td></tr><tr><td>16</td><td>284</td><td>2</td><td>-</td><td>-</td><td>-</td><td>-</td><td>12000</td><td>-</td></tr><tr><td>17</td><td>298</td><td>1</td><td>-</td><td>-</td><td>-</td><td>-</td><td>24.8</td><td>-</td></tr></tbody></table>

<table><caption>Table A.2 Operating conditions of “H₂ DRI SOLAR” process.</caption><thead><tr><th rowspan="2">Stream</th><th rowspan="2">Temperature</th><th rowspan="2">Pressure</th><th colspan="6">Mass flowrate</th></tr><tr><th>K</th><th>bar</th><th colspan="5">kg.s<sup>-1</sup></th></tr><tr><th></th><th></th><th></th><th>Hematite</th><th>DRI</th><th>Hydrogen</th><th>Water vapor</th><th>Water</th><th>Oxygen</th></tr></thead><tbody><tr><td>1</td><td>298</td><td>-</td><td>50</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>2</td><td>748</td><td>-</td><td>-</td><td>35</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>3</td><td>298</td><td>1</td><td>-</td><td>-</td><td>-</td><td>-</td><td>42.8</td><td>-</td></tr><tr><td>4</td><td>123</td><td>25</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>13.6</td></tr><tr><td>5</td><td>298</td><td>1</td><td>-</td><td>-</td><td>1.7</td><td>0.5</td><td>-</td><td>-</td></tr><tr><td>6</td><td>755</td><td>1.8</td><td>-</td><td>-</td><td>8.3</td><td>17.3</td><td>-</td><td>-</td></tr></tbody></table>
<table><caption>Table A.3 Operating conditions of “MIDREX NG” process.</caption><tr><td>7</td><td>345</td><td>1.8</td><td>-</td><td>-</td><td>8.3</td><td>17.3</td><td>-</td><td>-</td></tr><tr><td>8</td><td>298</td><td>1.8</td><td>-</td><td>-</td><td>-</td><td>-</td><td>16</td><td>-</td></tr><tr><td>9</td><td>298</td><td>1.8</td><td>-</td><td>-</td><td>8.3</td><td>1.36</td><td>-</td><td>-</td></tr><tr><td>10</td><td>301</td><td>2</td><td>-</td><td>-</td><td>8.3</td><td>1.36</td><td>-</td><td>-</td></tr><tr><td>11</td><td>301</td><td>2</td><td>-</td><td>-</td><td>10</td><td>1.86</td><td>-</td><td>-</td></tr><tr><td>12</td><td>748</td><td>2</td><td>-</td><td>-</td><td>10</td><td>1.86</td><td>-</td><td>-</td></tr><tr><td>13</td><td>283</td><td>1</td><td>-</td><td>-</td><td>-</td><td>-</td><td>9000</td><td>-</td></tr><tr><td>14</td><td>283</td><td>2</td><td>-</td><td>-</td><td>-</td><td>-</td><td>9000</td><td>-</td></tr><tr><td>15</td><td>284</td><td>2</td><td>-</td><td>-</td><td>-</td><td>-</td><td>9000</td><td>-</td></tr><tr><td>16</td><td>298</td><td>1</td><td>-</td><td>-</td><td>-</td><td>-</td><td>26.8</td><td>-</td></tr></table>

<table><thead><tr><th rowspan="3">Flux</th><th rowspan="3">Temperature</th><th colspan="10">Pressure</th><th colspan="10">Mass flowrate</th></tr><tr><th colspan="10">K bar</th><th colspan="10">kg.s<sup>-1</sup></th></tr><tr><th>Hematite</th><th>DRI</th><th>Hydrogen</th><th>Water vapor</th><th>Water</th><th>Carbon monoxyde</th><th>Carbon dioxyde</th><th>Methane</th><th>Oxygen</th><th>Nitrogen</th></tr></thead><tbody><tr><td>1</td><td>263</td><td>-</td><td>45</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>2</td><td>1230</td><td>-</td><td>-</td><td>33</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>3</td><td>555</td><td>2</td><td>-</td><td>-</td><td>2</td><td>8</td><td>-</td><td>13.1</td><td>16.3</td><td>3.17</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>4</td><td>325</td><td>2</td><td>-</td><td>-</td><td>-</td><td>-</td><td>5.3</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>5</td><td>325</td><td>2</td><td>-</td><td>-</td><td>2</td><td>2.7</td><td>-</td><td>13.1</td><td>16.3</td><td>3.17</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>6</td><td>325</td><td>2</td><td>-</td><td>-</td><td>0.6</td><td>0.84</td><td>-</td><td>4.2</td><td>5.2</td><td>1</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>7</td><td>298</td><td>2</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>8</td><td>998</td><td>2</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>9</td><td>298</td><td>2</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>10</td><td>325</td><td>2</td><td>-</td><td>-</td><td>1.4</td><td>1.86</td><td>-</td><td>8.9</td><td>11.1</td><td>2.17</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>11</td><td>320</td><td>2</td><td>-</td><td>-</td><td>1.4</td><td>1.86</td><td>-</td><td>8.9</td><td>11.1</td><td>7.57</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>12</td><td>438</td><td>2</td><td>-</td><td>-</td><td>1.4</td><td>1.86</td><td>-</td><td>8.9</td><td>11.1</td><td>7.57</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>13</td><td>1473</td><td>2</td><td>-</td><td>-</td><td>-</td><td>8.8</td><td>-</td><td>-</td><td>14.6</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>14</td><td>1043</td><td>2</td><td>-</td><td>-</td><td>-</td><td>8.8</td><td>-</td><td>-</td><td>14.6</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>15</td><td>955</td><td>2</td><td>-</td><td>-</td><td>-</td><td>8.8</td><td>-</td><td>-</td><td>14.6</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>16</td><td>400</td><td>2</td><td>-</td><td>-</td><td>-</td><td>8.8</td><td>-</td><td>-</td><td>14.6</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>17</td><td>298</td><td>2</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>18</td><td>353</td><td>2</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>19</td><td>283</td><td>2</td><td>-</td><td>-</td><td>-</td><td>-</td><td>7559</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>20</td><td>284</td><td>2</td><td>-</td><td>-</td><td>-</td><td>-</td><td>7559</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>21</td><td>1230</td><td>2</td><td>-</td><td>-</td><td>2.17</td><td>1.6</td><td>-</td><td>20</td><td>2.57</td><td>4.3</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr></tbody></table>
## B. Life cycle inventories

The data for the energy production, raw materials, and transportation were taken from ecoinvent database and considered in the background system. The French electricity mix was considered, consisting of 64% nuclear power, 11% hydroelectricity, 10% wind power in 2023, and a limited share of fossil fuels and other sources like biomass [1].

The construction of infrastructure, including the shaft furnace, the electrolyzer (details in Table B.1, supplementary information), and the heliostats required for concentrated solar energy, has also been considered as shown in the Table 4. In the absence of specific data on reactors and their infrastructure, the methodological approach adopted is to assume, for the sake of simplicity, the blast furnace infrastructure for all reactors used in the three scenarios. This approach is intended to ensure consistency in the analysis while facilitating comparative studies.

Detailed data on the alkaline electrolyzer infrastructure is taken from [2] and presented in Table B.1. Noting that the production of 1 MJ of hydrogen requires approximately $2.16×10^{-5}$ stack unit of electrolyzer. For the solar concentrator, the required solar power of 67 MW implies a field of heliostats with 67 000 m² of mirrors to reflect the solar radiation. In addition, the production of iron ore pellets is based on three main stages: extraction, concentration and palletization, as reported in Wang's study [3]. In ecoinvent, the activity "Iron pellet production" includes all the above-mentioned steps.

The water used for the electrolyzer must be ultrapure to ensure the absence of impurities that could damage the electrodes or reduce process efficiency [4]. The cooling water used in the process is softened, which limits scaling and corrosion of the equipment [5].

In terms of direct emissions, CO₂ emissions are generated in the “MIDREX NG” process due to the combustion of natural gas. The water electrolysis produces a large amount of oxygen, which can either be released into the atmosphere or valorized. Its valorization as liquefied oxygen has been considered, making it a co-product.

In terms of infrastructure and equipment, the “H₂ DRI SOLAR” process requires a larger infrastructure and more associated equipment than the other scenarios. Solar energy needs to operate at higher flowrates for a short period of time to achieve the same annual productivity as conventional technologies, which operate almost all year round. In France, the average duration of sunshine is around
7 hours and 15 minutes per day, which limits the operating time of “H₂ DRI SOLAR” process. By comparison, the “H₂ DRI ELECTRIC” and “MIDREX NG” processes could operate for approximately 22 hours per day. To achieve equivalent production capacity, the solar process therefore requires three operating plants in parallel, significantly increasing infrastructure requirements.

<table><caption>Table B.1 Alkaline electrolyzer manufacturing process for one stack unit.</caption><thead><tr><th>Inventory</th><th>Stack unit</th><th>Unit</th><th>Ecoinvent database 3.9</th></tr></thead><tbody><tr><td>Unalloyed steel</td><td>33.3</td><td>kg</td><td>market for steel, unalloyed [GLO]</td></tr><tr><td>Copper</td><td>1.33</td><td>kg</td><td>market for copper-rich materials [GLO]</td></tr><tr><td>Nikel</td><td>12.66</td><td>kg</td><td>market for nickel concentrate, 7% Ni [RoW]</td></tr><tr><td>Aluminium</td><td>0.30</td><td>kg</td><td>market for aluminium collector foil, for Li-ion battery [GLO]</td></tr><tr><td>Carbon monoxide</td><td>0.1</td><td>kg</td><td>market for carbon monoxide [RER]</td></tr><tr><td>Zirconium oxide</td><td>0.733</td><td>kg</td><td>market for zirconium oxide [GLO]</td></tr><tr><td>Polyphenelene sulfide</td><td>0.227</td><td>kg</td><td>market for polyphenylene sulfide [GLO]</td></tr><tr><td>Polysulfones</td><td>0.173</td><td>kg</td><td>market for polysulfone [GLO]</td></tr><tr><td>N-Methyl-2-pyrrolidone</td><td>0.867</td><td>kg</td><td>market for N-methyl-2-pyrrolidone [GLO]</td></tr><tr><td>Polytetrafluoroethylene</td><td>0.05</td><td>kg</td><td>market for tetrafluoroethylene [GLO]</td></tr><tr><td>Graphite</td><td>0.287</td><td>kg</td><td>market for graphite [GLO]</td></tr><tr><td>Acrylonitrile butadiene styrene</td><td>0.1</td><td>kg</td><td>market for acrylonitrile-butadiene-styrene copolymer [GLO]</td></tr><tr><td>Lubricating oil</td><td>3.20×10<sup>-4</sup></td><td>kg</td><td>market for lubricating oil [RER]</td></tr><tr><td>Aniline</td><td>3.27×10<sup>-2</sup></td><td>kg</td><td>market for aniline [RER]</td></tr><tr><td>Acetic anhydride</td><td>3.60×10<sup>-2</sup></td><td>kg</td><td>market for acetic anhydride [GLO]</td></tr><tr><td>Terephthalic acid</td><td>5.87×10<sup>-2</sup></td><td>kg</td><td>market for purified terephthalic acid [GLO]</td></tr><tr><td>Nitric acid</td><td>2.20×10<sup>-2</sup></td><td>kg</td><td>market for nitric acid, without water, in 50% solution state [RER w/o RU]</td></tr><tr><td>Hydrochloric acid</td><td>8.67×10<sup>-2</sup></td><td>kg</td><td>market for hydrochloric acid, without water, in 30% solution state [RER]</td></tr><tr><td>Electricity</td><td>6.6×10<sup>-3</sup></td><td>kWh</td><td>market for electricity, medium voltage [FR]</td></tr></tbody></table>
### C. ReCiPe Midpoint H impacts figures

<figure><img src="image_15.png" /><figcaption>Figure C.1 Comparative analysis of WDP impact for the three scenarios studied: “H₂ DRI ELECTRIC”, “H₂ DRI SOLAR”, and “MIDREX NG”.</figcaption></figure>
<figure><img src="image_16.png" /></figure>

<figure><img src="image_17.png" /></figure>

<figure><img src="image_18.png" /><figcaption>Figure C.2 Comparative analysis of ULOP impact for the three scenarios studied: “H₂ DRI ELECTRIC”, “H₂ DRI SOLAR”, and “MIDREX NG”.</figcaption></figure>

<figure><img src="image_19.png" /></figure>

<figure><img src="image_20.png" /></figure>

<figure><img src="image_21.png" /><figcaption>Figure C.3 Comparative analysis of TETPinf impact for the three scenarios studied: “H₂ DRI ELECTRIC”, “H₂ DRI SOLAR”, and “MIDREX NG”.</figcaption></figure>
<figure><img src="image_22.png" /><figcaption>Figure C.4 Comparative analysis of TAP100 impact for the three scenarios studied: “H₂ DRI ELECTRIC”, “H₂ DRI SOLAR”, and “MIDREX NG”.</figcaption></figure>

<figure><img src="image_23.png" /><figcaption>Figure C.5 Comparative analysis of POFP impact for the three scenarios studied: “H₂ DRI ELECTRIC”, “H₂ DRI SOLAR”, and “MIDREX NG”.</figcaption></figure>
<figure><img src="image_24.png" /></figure>

<figure><img src="image_25.png" /></figure>

<figure><img src="image_26.png" /><figcaption>Figure C.6 Comparative analysis of PMFP impact for the three scenarios studied: “H₂ DRI ELECTRIC”, “H₂ DRI SOLAR”, and “MIDREX NG”.</figcaption></figure>

<figure><img src="image_27.png" /></figure>

<figure><img src="image_28.png" /></figure>

<figure><img src="image_29.png" /><figcaption>Figure C.7 Comparative analysis of ODPinf impact for the three scenarios studied: “H₂ DRI ELECTRIC”, “H₂ DRI SOLAR”, and “MIDREX NG”.</figcaption></figure>
<figure><img src="image_30.png" /></figure>

<figure><img src="image_31.png" /></figure>

<figure><img src="image_32.png" /><figcaption>Figure C.8 Comparative analysis of NLTP impact for the three scenarios studied: “H₂ DRI ELECTRIC”, “H₂ DRI SOLAR”, and “MIDREX NG”.</figcaption></figure>

<figure><img src="image_33.png" /></figure>

<figure><img src="image_34.png" /></figure>

<figure><img src="image_35.png" /><figcaption>Figure C.9 Comparative analysis of METPinf impact for the three scenarios studied: “H₂ DRI ELECTRIC”, “H₂ DRI SOLAR”, and “MIDREX NG”.</figcaption></figure>
<figure><img src="image_36.png" /></figure>

<figure><img src="image_37.png" /></figure>

<figure><img src="image_38.png" /><figcaption>Figure C.10 Comparative analysis of MEP impact for the three scenarios studied: “H₂ DRI ELECTRIC”, “H₂ DRI SOLAR”, and “MIDREX NG”.</figcaption></figure>

<figure><img src="image_39.png" /></figure>

<figure><img src="image_40.png" /></figure>

<figure><img src="image_41.png" /><figcaption>Figure C.11 Comparative analysis of MDP impact for the three scenarios studied: “H₂ DRI ELECTRIC”, “H₂ DRI SOLAR”, and “MIDREX NG”.</figcaption></figure>
<figure><img src="image_42.png" /></figure>

<figure><img src="image_43.png" /></figure>

<figure><img src="image_44.png" /><figcaption>Figure C.12 Comparative analysis of IRP_HE impact for the three scenarios studied: “H₂ DRI ELECTRIC”, “H₂ DRI SOLAR”, and “MIDREX NG”.</figcaption></figure>

<figure><img src="image_45.png" /></figure>

<figure><img src="image_46.png" /></figure>

<figure><img src="image_47.png" /><figcaption>Figure C.13 Comparative analysis of HTPinf impact for the three scenarios studied: “H₂ DRI ELECTRIC”, “H₂ DRI SOLAR”, and “MIDREX NG”.</figcaption></figure>
<figure><img src="image_48.png" /><figcaption>Figure C.14 Comparative analysis of FETPinf impact for the three scenarios studied: “H₂ DRI ELECTRIC”, “H₂ DRI SOLAR”, and “MIDREX NG”.</figcaption></figure>

<figure><img src="image_49.png" /><figcaption>Figure C.15 Comparative analysis of FEP impact for the three scenarios studied: “H₂ DRI ELECTRIC”, “H₂ DRI SOLAR”, and “MIDREX NG”.</figcaption></figure>
<figure><img src="image_50.png" /></figure>

<figure><img src="image_51.png" /><figcaption>Figure C.16 Comparative analysis of FDP impact for the three scenarios studied: “H₂ DRI ELECTRIC”, “H₂ DRI SOLAR”, and “MIDREX NG”.</figcaption></figure>

<figure><img src="image_52.png" /></figure>

<figure><img src="image_53.png" /><figcaption>Figure C.17 Comparative analysis of ALOP impact for the three scenarios studied: “H₂ DRI ELECTRIC”, “H₂ DRI SOLAR”, and “MIDREX NG”.</figcaption></figure>
## D. Energy cost analysis

The cost analysis is based on the French market. The cost of electricity is assumed to be that of nuclear power, which dominates the mix electricity in France, accounting for 64% of electricity production. The cost of solar thermal energy is often estimated on the basis of the conversion efficiency between heat and electricity produced using the concentrated solar power technology, assuming that the cost of solar thermal energy is about one third of the cost of electricity produced by solar power. However, this remains an approximation and further studies and research are needed for a more accurate determination.

The corresponding energy costs [6], expressed in euros per kilowatt-hour (€/kWh), are presented in Table D.1.

<table><caption>Table D.1 Energy costs per type of energy.</caption><thead><tr><td></td><td>Price (€/kWh)</td></tr></thead><tbody><tr><td>Electricity</td><td>0.120</td></tr><tr><td>Natural gas</td><td>0.129</td></tr><tr><td>Solar energy</td><td>0.040</td></tr></tbody></table>
References

[1] « France - Countries & Regions », IEA. Consulté le: 2 avril 2025. [En ligne]. Disponible sur :
https://www.iea.org/countries/france/emissions

[2] X. Wei et al., « Comparative life cycle analysis of electrolyzer technologies for hydrogen production: Manufacturing and operations », *Joule*, vol. 8, n° 12, p. 3347-3372, déc. 2024, doi: 10.1016/j.joule.2024.09.007.

[3] T. Wang, « Novel iron ore direct reduction process using biomass », phdthesis, Université de Lorraine, 2022. Consulté le: 2 avril 2025. [En ligne]. Disponible sur: https://hal.univ-lorraine.fr/tel-04128333

[4] D. Amiruddin, D. Mahajan, D. Fang, W. Wang, P. Wang, et B. S. Hsiao, « A Facile Ultrapure Water Production Method for Electrolysis via Multilayered Photovoltaic/Membrane Distillation », *Energies*, vol. 16, n° 15, Art. n° 15, janv. 2023, doi: 10.3390/en16155765.

[5] G. Tomberlin, J. Dean, et M. Deru, « Continuous Monitoring and Partial Water Softening for Cooling Tower Water Treatment », National Renewable Energy Lab. (NREL), Golden, CO (United States), NREL/TP-7A40-76756, oct. 2020. doi: 10.2172/1710165.

[6] « Hausse de 11,7 % du prix repère de vente de gaz naturel en juillet ». Consulté le: 9 mai 2025.
[En ligne]. Disponible sur: https://www.service-public.fr/particuliers/actualites/A16833