Refractory Brick Heat Battery

Thermal Energy Storage ("TES") systems have evolved from ancient refractory materials used in kilns and furnaces to advanced, grid-scale solutions critical for industrial decarbonization and renewable energy integration. Modern TES technologies, including firebrick and molten salt systems, offer high-temperature, low-cost, and modular storage options that outperform conventional batteries in cost and temperature range, enabling direct replacement of fossil-fueled industrial heat. Key innovations focus on material sustainability, system flexibility, and integration with existing infrastructure, while technical challenges remain in material durability, heat transfer efficiency, and system control. Non-technical barriers include market adoption, financial incentives, and regulatory frameworks, all of which are crucial for widespread deployment. Overall, TES is positioned as a pivotal technology for achieving deep decarbonization in heavy industry and enhancing grid flexibility.

The history of heat storage systems spans ancient practices utilizing refractory materials through modern innovations aimed at grid-scale energy transition.

Ancient and Traditional Uses

The fundamental concept of TES can be traced back to ancient times, primarily through the use of refractory materials. Refractory bricks are bricks that can withstand high temperatures without structural damage and have been used for thousands of years to insulate kilns, furnaces, and other hot enclosures. Firebricks are a type of refractory brick that can be composed to store heat or insulate the bricks that store the heat. In the 19th century, refractory bricks, specifically silico-aluminous bricks, were utilized in copper smelting furnaces in Atacama, Chile. Modern TES development began with building heating and cooling in the early 1900s. However, the concept itself can be traced back to the early 19th century with the invention of the ice box in 1803.

Mid-20th Century Industrial and Domestic Firebrick Storage

The technology found widespread use in industrial processes and residential applications for electricity load shifting in the mid-20th century. Firebricks have been used extensively in industry, primarily as heat recuperators and regenerators to transfer heat between gases and recover heat that would otherwise be lost. Regenerators are heat interchangers that store heat from high-temperature flue gas for 20–30 minutes, then use it to preheat air for combustion. This application was used in glass making and steel making. In open-hearth steel production, historical large-scale use involved two recuperators alternating to store heat and provide high-temperature air, often operating with a temperature difference exceeding 1,000°C between cold and hot conditions. Firebrick heat storage became popular in Britain in the 1960s. This surge was motivated by utility companies needing to smooth electricity demand due to large quantities of excess electricity being generated overnight by continuously running base-load power stations (70% coal and 10% nuclear). By 1973, there was 150,000 MWh of firebrick heat storage capacity across Britain and Germany. The prevalence of these domestic systems declined sharply in the 1980s due to changes in the structure of electricity generation. In the early 2010s, the technology saw continued small-scale deployment, such as in 2013 when VCharge installed 15 MWh of firebrick heat storage capacity across 200 homes in eastern Pennsylvania.

Late 20th Century Molten Salt and Concentrating Solar Power

Molten salt thermal energy storage became a key technology for large-scale energy storage in the context of power generation. Modern TES development for power generation began with concentrating solar thermal technologies in the late 1970s. Molten salt systems utilize solar salt as the storage medium. It was first demonstrated in commercial Concentrating Solar Power ("CSP") power plants during the 1990s. The first CSP plant using a molten salt tank TES system was the Solar Electric Generating Station I, built in the USA in 1984 (decommissioned in 1999). It had 13.8 MW capacity and 3 hours of storage. In 2008, the Andasol 1 plant in Spain was commissioned as the first large-scale application of this technology, achieving a storage capacity of 375 MWh. By the end of 2021, approximately 27,500 MWh of TES using molten salt tanks was installed worldwide.

21st Century Electrified and Advanced Thermal Storage

Recent developments have focused on high-temperature solid media and coupling TES with renewable electricity (Electric-Thermal Energy Storage, "ETES"). Sensible heat storage ("SHS") is the most mature and commercialized storage type. Latent heat storage ("LHS") has only been applied to large-scale projects in the last three to five years, while thermochemical storage ("TCS") is still generally at a low maturity level. The concept of Firebrick Resistance-Heated Energy Storage** **("FIRES") was developed to store low-priced electricity as high-temperature heat, specifically for industrial heat or peak electricity production. The intended scale for FIRES is significantly larger than historical applications, targeting hundreds of MWh and peak temperatures up to 1800°C Even before 2018, firebricks storing 10 MWh of heat were deployed in China for commercial complexes and district heating projects. The recent commercialization of firebricks suggests a potential large-scale solution for addressing industrial process heat emissions. The development of sensible heat storage, whether using molten salts or solid materials like firebricks and sand, has consistently moved towards achieving higher temperatures and lower costs, driven by the need to integrate intermittent renewable energy sources and decarbonize heavy industry. This evolution mirrors the strategic shift required globally, moving away from systems constrained by geography (like pumped hydro) or high cost (like conventional batteries) towards versatile, high-capacity TES systems.

Thermal Storage Medium

The thermal storage mechanism refers to the physical or chemical processes utilized to capture, store, and later release energy in the form of heat. TES technologies are broadly categorized into three main types based on how the energy is stored: Sensible Heat Storage, Latent Heat Storage, and Thermochemical Energy Storage.

Sensible Heat Storage Sensible Heat Storage is the most commercially mature and widely deployed TES technology.

Core Mechanism SHS stores thermal energy by raising the temperature of a storage medium (liquid or solid) without causing a phase change in the material. The total amount of thermal energy stored in a sensible heat medium is proportional to its mass, specific heat capacity, and the change in temperature. Storage media selected for SHS, such as firebricks, typically have high specific heats, high densities, and high melting points.

Solid Media (Firebricks and Particles) Solid media SHS systems, like those utilizing firebricks or particles, are capable of operating at very high temperatures. Heat is added to the solid medium, increasing its temperature. This charging can occur via several methods. Electricity can be converted to heat using metallic electric-resistance heaters connected to the firebricks or integrated into ducts near the storage medium. The heat generated by the coils is then typically dissipated to the solid medium by forced convection and conduction. Direct Resistance Heating ("DRH") is an innovation where electrically conductive firebricks function as both the heating element and the thermal storage medium. Electricity runs directly through the bricks, heating them by the Joule effect (volumetric heat generation). This approach eliminates the temperature drop between the heating element and the brick because the brick itself is the heat source. Particle Heating is when low-cost off-peak electricity is used by a particle heater to heat large volumes of solid particles (e.g., silica sand) to high temperatures. The stored thermal energy is recovered on demand through: Convective Heat Transfer: Hot air or recycled gas is blown through channels or gaps in the hot solid media (firebricks or packed beds), absorbing heat via forced convection to produce low-to-high-temperature air. The air flow is designed to minimize temperature gradients and ensure uniform heating. Direct Contact Heat Transfer (Particles): In particle-based systems, hot particles are gravity-fed through a Pressurized Fluidized Bed Heat Exchanger ("PFB HX") where they engage in direct air/particle contact counterflow heat transfer. This direct contact eliminates traditional heat transfer surfaces, allowing the air to be heated to a temperature near the particle temperature to drive a power cycle. Radiation: Heat may also be obtained from the emission of infrared radiation directly from the red-hot bricks.

Liquid Media (Molten Salts) Molten salt systems store sensible heat and have been widely used, particularly in CSP plants. These systems traditionally use a dual-tank configuration: a "cold" tank (e.g., around 290°C) and a "hot" tank (e.g., up to 565°C for solar salt). Molten salts ("MS"), such as solar salt, act as both the heat transfer fluid ("HTF") and the storage medium. They circulate between the two tanks, facilitating the storage (charging) and retrieval (discharging) of thermal energy. The design often incorporates internal circulation rings or ejectors to promote circulation and mixing within the tanks to maintain a homogeneous temperature profile, which is crucial in the cold tank to prevent thermal stratification and cold spots near the salt's freezing point (e.g., 220°C). SHS is like filling a conventional reservoir (tank) by simply increasing the water level (temperature). The more volume (mass) or the higher the walls (specific heat capacity), the more water you can store for every foot the level rises. You release the water by opening the gate and letting it flow out.

Latent Heat Storage Latent TES units utilize a Phase Change Material ("PCM") to store energy associated with a phase transition. The material stores or releases a relatively large amount of energy, known as latent heat, during its phase change (typically melting or solidifying) at a relatively constant temperature range. This mechanism provides a high energy density, as both sensible heat (temperature rise) and latent heat contribute to the overall stored capacity. LHS is particularly effective when the application requires energy delivery within a limited temperature difference. Materials include ice/water, paraffin wax, and salt hydrates. This is like converting the water in the reservoir to ice. You store a vast amount of energy (latent heat) during the phase change (freezing) without a huge change in temperature. When you need the energy back, you thaw the ice; you get a large release of energy at a near-constant temperature point (the melting point).

Thermochemical Energy Storage TCES is the least developed technology among the three main types. TCES stores energy in the form of reaction heat by using reversible endo- and exothermic chemical reactions, such as sorption, chemical looping, and salt hydration. TCES offers high energy density and crucially, the charged material can often be stored at room temperature with minimal heat loss, making it promising for long-duration or seasonal storage applications. TCES is like using the energy to chemically separate two components (like hydrogen and oxygen) and storing those components in separate, sealed containers. You can store them indefinitely at room temperature with no loss. When you need the energy back, you recombine the components (the reaction) to release the original energy as heat.

Charging Mechanism

The charging mechanism for TES systems, particularly modern high-temperature solutions, involves transferring energy (usually electricity or high-grade heat) into the storage medium to raise its thermal energy content.

Direct Resistance Heating (DRH) / Joule Heating This is an advanced electrical charging mechanism where the storage material itself acts as the heating element, converting electricity directly into heat.

External Electric Resistance Heating (Conventional) This method involves converting electricity to heat using separate heating elements, which then transfer that heat to the storage medium. Systems like Rondo Energy’s Heat Battery or smaller-scale prototypes use external heating elements. Nichrome heating coils/wires are commonly used as resistive electric heaters. These coils are installed within an air duct adjacent to the firebrick assembly. The coils heat up using electricity according to Joule’s Law. Axial fans or blowers ensure constant airflow and heat distribution (forced convection). The heated air or gas passes through channels or gaps in the firebricks, transferring the heat to the solid media. Rondo's system charges through electric heating elements embedded within the TES bricks, primarily via radiative heating. No air flow is needed during charging, though limited flows might be introduced to improve heat transfer and thermal distribution.

Other Charging Mechanisms TES systems outside the electrified solid media sphere utilize different energy inputs. In CSP plants, the molten salts (which serve as both the heat transfer fluid and storage medium) are charged by collecting thermal energy from solar radiation concentrated by parabolic trough collectors or heliostats. The thermal energy collected by the heat transfer fluid is then transported to the molten salt storage tanks, raising the salt temperature. Some commercial solid media TES units offer flexibility by being charged either thermally via embedded HTF pipes or electrically via embedded resistive electric heaters. Some emerging TES technologies (often referred to as Carnot Batteries or pumped heat storage) use a heat pump cycle during charging to capture low-grade heat from a cold TES and upgrade it to a higher temperature, transferring it to the hot TES. This approach offers higher charging efficiencies than simple resistive electric heaters

Heat Retention and Insulation Architecture

The architecture for heat retention and insulation in modern TES systems, particularly those using solid media like firebricks and particles, is critical for minimizing heat loss and ensuring the system can reliably discharge high-temperature heat over extended periods. This architecture involves selecting appropriate low-conductivity materials, arranging the heat-storing media strategically, and designing containment structures to manage both temperature and mechanical stress.

Architecture for Solid Media Storage (Firebricks and Particles) The common goal for firebrick and particle TES systems is to store heat (sensible heat) by raising the temperature of a solid medium, and the insulation architecture is designed to minimize thermal losses through conduction, convection, and radiation.

Core Components and Material Selection The insulation architecture relies on using materials with opposing functions: dense, high-heat-capacity materials for storage and light, low-thermal-conductivity materials for insulation. The materials chosen for storing heat must have a high specific heat and high density so they can absorb a large amount of energy with little temperature increase, along with high melting points to withstand high temperatures. Firebricks (refractory bricks) are commonly made of ceramic materials containing combinations of alumina, silica, magnesia, and chromia. Examples include alumina and magnesia due to their specific heat and density characteristics. The insulating layers must also withstand high temperatures but possess low thermal conductivities to prevent rapid heat loss to the outside. Silica is regularly used in insulating firebricks because it has a low thermal conductivity. Common types of insulating firebricks include alumina silicate bricks and calcium silicate bricks. Insulating Firebricks are often used to surround the heat-storing firebricks. Rockwool board insulation is used for external containment due to its high thermal performance, non-combustibility, and low thermal conductivity.

Structural and Containment Design The storage medium is housed within an enclosure designed to maintain structural integrity under high temperatures while preserving thermal energy. The refractory bricks or particles are surrounded by conventional insulation and often a steel container to further reduce heat loss and accommodate thermal expansion of the firebrick. In particle storage systems, the particles are held in insulated concrete silos. The silo uses concrete with internal layers of refractory insulation liners. In large-scale silo designs, the containment wall consists of multiple layers to keep the outer concrete wall below its thermal allowance. An inner lining of strong refractory material provides erosion resistance. Multiple insulation layers follow, typically including low-density refractory layer, calcium silicate, and the outer concrete wall. Specialized installation is required, especially in high-temperature environments. For tall silos, large refractory blocks can be fabricated and stacked to form a modular insulation layer.

Airflow and Heat Transfer Management The internal arrangement of the firebricks is designed to optimize both charging efficiency and heat retention. Firebricks are organized in a pattern that allows air to flow through channels. The use of static solid media (such as particles in a silo) creates a self-insulating layer that reduces thermal conduction during the storage period. This is a major advantage over liquid storage media where free convection can induce mixing and cause greater heat loss. The efficacy of the insulation and architecture is quantified by the heat loss rate. For the Rondo RHB300 heat battery, the assumed daily heat loss rate is 1% per day, attributed to insulating the firebricks and recycling air during heat delivery.

Architecture for Liquid Media Storage (Molten Salts) In systems using molten salts, insulation architecture is focused on managing the immense weight, preventing the salt from freezing, and minimizing thermal stratification and heat loss from the containment vessel. The foundation is a critical, multi-layered component that supports the tank's massive weight and must endure temperature fluctuations. Typical layers include: a bottom layer of fine sand, a wide layer of insulating refractory bricks or expanded clay, a layer of insulating material, such as glass foam or ceramic fiber, a thick layer of reinforced concrete. The reinforced concrete layer of the foundation often includes an air- or water-cooling system consisting of horizontal tubes embedded within the concrete. This is necessary to avoid high temperatures that would compromise the concrete’s structural integrity. Temperature sensors are incorporated to measure the foundation's temperature and confirm safe values. Since molten salts have a high freezing point, maintaining a homogeneous temperature profile is crucial to prevent "cold spots" that could cause solidification. The design incorporates internal circulation rings or ejectors within the salt tanks to induce circulation flow and facilitate thorough mixing, thus homogenizing temperatures and safeguarding against undesirable thermal variations. Because the high working temperature causes significant thermal expansion of the metal tank structure, the insulation design must account for this. There must be an overlap of the insulation so that when the metal structure expands, there is no gap or opening between the tank body and the outside.

Heat Discharge and Integration with Industrial Processes

The process of heat discharge and integration with industrial processes involves retrieving stored thermal energy from the storage medium and delivering it to industrial facilities, often in the form of hot air or steam, to replace heat generated by burning fossil fuels. This process varies based on the type of TES system used, primarily solid media (like firebricks or particles) or liquid media (like molten salts).

Heat Discharge Mechanism (Retrieval) The discharge mechanism converts the stored thermal energy back into a usable form of heat (thermal energy) or electricity (bidirectional systems).

Solid Media (Firebricks and Particles) Discharge Solid sensible heat storage systems (like firebricks or silica sand) rely on forced heat transfer, typically convection, to extract energy. Convective Heat Transfer (Firebricks): Heat is drawn from the firebricks on demand by passing ambient or recycled air through channels or gaps in the hot bricks. This process yields low-to-high-temperature air. The axial flow fans force heated air through the channels in the firebrick matrix, distributing thermal energy evenly and ensuring the air stream absorbs heat via forced convection. Heat may also be obtained from the emission of infrared radiation directly from the red-hot bricks. For industrial applications that require constant power output, the airflow intake needs to be varied or increased over time to counteract the natural cooling down of the TES. This strategy balances the energy depletion rate with the flow rate to sustain power delivery.

Molten Salt Discharge In molten salt systems (primarily used for CSP), discharge involves thermal energy conversion. The molten salts are circulated from the hot tank to a steam generator. The hot molten salts transfers heat to a Rankine power cycle or steam generator, producing steam that drives a turbine to produce electricity. The cooled MS is then sent back to the cold tank to be reheated.

Integration with Industrial Processes The discharged heat is designed to replace fossil fuel combustion in industrial manufacturing, addressing the high heat demand in sectors like cement, steel, and ceramics.

Direct Heat Use for Manufacturing TES is primarily used to provide continuous, low-cost heat directly for industrial processes. Discharging heat in the form of high-temperature air or steam allows industries to replace energy generated by burning coal, oil, fossil gas, or biomass continuously. TES systems target a wide range of industrial heat needs:

• Temperatures of 1,300°C to 1,800°C are needed for Ordinary Portland Cement ("OPC) and lime production.
• Temperatures of 1,000°C to 1,500°C are necessary for glass, fused silica, and traditional iron and steel making.
• Lower temperatures 100°C to 500°C are needed for mineral production and chemical manufacturing.

Heat Delivery and Efficiency If the hot air discharged from the TES is hotter than the furnace requirements, it is mixed with cold air. If the discharged air is cooler than needed, it can be supplemented by burning natural gas (in hybrid systems) or utilized in a lower-temperature process. TES systems can be integrated into existing infrastructure, such as continuous billet reheating furnaces, to capture industrial waste heat** **("IWH") in the form of flue gas (e.g., at 650°C to 850°C. A refractory-lined bypass duct diverts a controlled fraction of the exhaust gas through the brick matrix. The heat released from the bricks then flows continuously to pre-heat combustion air or the material itself, requiring minimal change to the existing furnace hardware. The aim is to maintain a high heat retention duration proving feasibility for next-day thermal reuse.

Integrating TES for Grid Stability and Flexibility TES allows industrial users to employ demand response by shifting heat production loads to off-peak periods when excess renewable electricity is available. The ability of industry to cut peak electric loads is a motivator for utilities to incentivize this load shifting. The capacity of firebrick storage is sized so that its maximum discharge rate equals the annual-average industrial process heat demand subject to storage. The process of heat discharge acts as a highly efficient, low-cost bridge, enabling continuous operation of high-temperature industrial processes using intermittent renewable electricity.

Modern versions of TES systems are innovating over incumbent technologies (such as conventional lithium-ion batteries and traditional fossil-fueled heating) primarily by achieving drastically lower costs, reaching significantly higher temperatures, and enabling deep system integration with renewable energy sources for industrial decarbonization and grid flexibility.

Cost Reduction and Material Sustainability

A fundamental innovation across various modern TES platforms is the replacement of expensive electrochemical storage components with low-cost, abundant thermal storage media. The use of modern firebricks to store industrial process heat can substantially reduce the overall need for other electricity storage like battery energy storage systems ("BESS") and green hydrogen storage. New solid media systems prioritize abundant, non-critical materials. Firebricks are made from common materials (such as alumina, silica, magnesia, and chromia). This approach avoids the reliance on mined materials and rare-earth minerals common in other commercial energy storage systems.

High-Temperature Capability and Direct Heating

Modern TES systems, especially those using solid media, are achieving temperatures far beyond conventional thermal storage limits, addressing the critical need for decarbonizing high-temperature industrial processes. These temperatures are necessary for hard-to-abate industries like cement and steel manufacturing.

Enhanced System Design and Flexibility

Modern TES innovations focus heavily on making the systems modular, highly efficient, and easily integrable into existing power and industrial infrastructure. Companies like Rondo Energy, EnergyNest, and Caldera offer modular, containerized solutions that can be scaled from MWh to GWh capacity. Rondo Energy announced plans for a large-scale manufacturing plant with an annual production capacity of 90 GWh. Innovations in molten salt systems focus on overcoming the drawbacks of conventional two-tank systems (like high freezing points, corrosion, and cost). Development of single-tank thermocline storage is underway to replace dual-tank systems, which has the potential to significantly reduce storage block cost. New systems are using high-stability salts, such as high-temperature molten sodium hydroxide-based salts. Emerging solid media technologies (like moving-particle and packed-bed TES) offer siting flexibility and the potential to be placed at retired fossil-fueled thermal power plants. This approach allows for the reuse of decommissioned assets, leveraging existing steam turbines, cooling systems, and generators to minimize capital investment and achieve a competitive energy storage cost.

Deployment challenges for TES systems, particularly modern high-temperature solutions, span technical complexities related to material properties and system integration, as well as non-technical hurdles concerning market mechanisms, policy support, and infrastructure readiness.

Technical and Operational Challenges Technical challenges primarily revolve around material durability at extreme temperatures, heat transfer efficiency, and the development of robust control systems.

Material and Durability Issues While SHS using firebricks and solid particles is highly stable, emerging technologies face material-related hurdles.

• Graphite Vaporization: Graphite, a potential firebrick material, slowly vaporizes when heated to 2,400°C
• Thermochemical Storage: TCES systems face a key challenge in the degradation of media performance with long-term cycling.
• Phase Change Materials: Latent heat storage materials can suffer from severe supercooling, phase separation, and corrosion, although this technology has only recently been applied to large-scale projects.
• Solid Media Abrasion: For moving-particle systems, the effect of solid media transportation on the degradation of the media and the system containment is not well characterized.
• High-Temperature Component Development: The transportation and storage of high-temperature heat transfer and storage media require affordable, long-lived materials and equipment rated for high temperatures. Existing materials and equipment, such as high-temperature alloys, pumps, and lifts, must be further developed for improved operational lives.
• Thermal and Mechanical Stress: High power capacity electrical heating, necessary for rapid charging when intermittent renewable electricity is available, induces large thermal gradients and thermomechanical stress within heating elements that can lead to premature failure. Corrosion of high-power heater elements must also be assessed when exposed to oxygen or reactive media.

System Control and Performance Consistency A critical technical challenge is the need for control strategies and hardware to maintain a consistent delivery temperature to industrial processes. As thermal reserves are depleted, control strategy and delivery techniques must be improved for commercial deployment. Key technical challenges for TES technologies include control mechanisms and the necessity of increased durability and stability of materials, and overall device/system reliability. TES applications used for power to heat to power require specific technical challenges related to the fast dynamic performances needed to provide grid services or enable demand response. The performance of TES systems can vary depending on transient assumptions, highlighting the importance of transient models that can simulate annual operations for a holistic understanding of performance. For industrial process heat applications, the efficiency of heat transfer to the industrial process needs to be improved to reduce the volumetric footprint.

Challenges in Specific Technologies While mature, molten salt systems still show challenges in implementation and operation. Failure modes include corrosion (which increases with temperature and can be localized or mechanically assisted), thermal shock (caused by large temperature gradients), and managing thermal expansions. There is no single unified regulation for the mechanical design of molten salt tanks, leading to potential safety, efficiency, and consistency issues in the thermal storage industry. In packed-bed TES where gaseous heat transfer fluid flows through granular material, the pressure drop of the air can represent an issue, potentially reducing overall efficiency. Additionally, auxiliary power consumption associated with fans or blowers may represent a relevant share of the total costs. The controllability and flowability of particles must be addressed, and innovative solutions are needed to convey and monitor the movement of hot particles. The main challenges include the cost and availability of the PCM and the scalability of the TES unit at high temperatures.

Non-Technical and Policy Challenges Deployment is also hampered by the current market structure, regulatory gaps, and financial barriers.

Financial and Market Adoption Barriers The use of combustion heating is deeply ingrained in industrial facilities globally, and little incentive currently exists for businesses to invest large amounts of capital in firebricks until existing combustion heaters are naturally retired. As such, incentives and policies are likely needed to affect a transition to firebricks in the necessary timeframe. TES integration in buildings faces a key barrier: it is difficult to be cost-effective compared to alternatives (e.g., electrochemical batteries) when low-cost, easy-access natural gas and coal resources are available. The lack of utility tariffs and incentives is the top barrier for TES deployment in buildings. Building owners are unlikely to invest capital without incentives, and utilities are not convinced to subsidize without user data. A potential solution is an improvement of the business cases and novel approaches to produce revenues from TES units are crucial to foster innovation. Examples include 'storage as a service' business models.

Policy and Regulatory Framework Combining low-cost TES technologies and renewable inputs requires the development of regulatory frameworks and standards to become economical. The standardization and certification aspects are very important, such as the possibility to transport, store, and handle heat at high temperature. Scaling up innovations in TES requires the capability to develop a First of a Kind ("FOAK") demonstration plant that can increase the trust of investors and enable sufficient fundraising to scale up production. Firebricks primarily address combustion for industrial heat (about 90% of applications). However, they do not address emissions from chemical reactions during the manufacturing of steel and cement, which require other solutions like green hydrogen or alternative processes.