HYL I & HYL III: Key Hydrogen-Based Steelmaking Processes and Technologies

Definition and Basic Concept

HYL I and HYL III are advanced direct reduction processes used in steelmaking to produce sponge iron (also known as direct reduced iron, DRI). These processes involve the reduction of iron ore pellets or lump ore using a reducing gas, primarily composed of hydrogen and carbon monoxide, at elevated temperatures in a shaft furnace. The primary purpose of these processes is to produce high-quality, metallic iron that can be directly used in electric arc furnaces (EAF) or integrated steelmaking routes, thereby reducing reliance on blast furnace operations.

Positioned within the overall steel manufacturing chain, HYL I and HYL III serve as key primary reduction steps that convert raw iron ore into a form suitable for melting and refining. They are typically situated upstream of electric arc furnace (EAF) or basic oxygen furnace (BOF) steelmaking, providing a flexible, energy-efficient alternative to traditional blast furnace routes. Their role is crucial in enabling more sustainable, energy-efficient steel production with lower emissions.

Technical Design and Operation

Core Technology

The core engineering principle behind HYL processes is the direct reduction of iron ore using a reducing gas mixture at high temperatures, typically between 800°C and 1050°C. The process relies on the thermodynamic favorability of reducing iron oxides to metallic iron in a controlled environment, minimizing carbon consumption and emissions.

Key technological components include the shaft furnace, where reduction occurs, and the gas generation and recycling systems. The shaft furnace is a vertical, cylindrical vessel lined with refractory materials to withstand high temperatures and corrosive gases. The process begins with the introduction of iron ore pellets or lump ore at the top of the shaft, along with a reducing gas mixture supplied from gas generators.

The reducing gas, primarily composed of hydrogen and carbon monoxide, is produced on-site via reforming or gasification of natural gas or other hydrocarbons. This gas is preheated and injected into the shaft furnace, flowing counter-current to the ore movement. As the ore descends, it reacts with the reducing gases, gradually losing oxygen and transforming into sponge iron. The reduced material is extracted from the bottom of the shaft, cooled, and prepared for subsequent steelmaking steps.

Process Parameters

Critical process variables include temperature, reducing gas composition, pressure, and residence time. Typical operating temperatures range from 850°C to 1050°C, optimized for efficient reduction without sintering or melting.

The reducing gas composition generally contains 70-85% hydrogen and carbon monoxide, with the balance being inert gases like nitrogen. Gas flow rates are adjusted to ensure complete reduction within the residence time, usually between 20 to 60 minutes depending on the process design.

Pressure conditions are usually atmospheric or slightly pressurized (up to 2 bar), influencing reaction kinetics and gas utilization efficiency. Maintaining optimal temperature and gas composition is vital for achieving high metallization rates (> 90%) and minimizing energy consumption.

Control systems employ advanced sensors and automation to monitor temperature, gas composition, pressure, and material flow. Real-time data acquisition enables dynamic adjustments, ensuring stable operation and consistent product quality.

Equipment Configuration

Typical HYL installations feature a vertical shaft furnace with a diameter ranging from 3 to 6 meters and a height of 20 to 50 meters, depending on capacity. The furnace is equipped with a series of tuyeres or gas injectors distributed along its height to ensure uniform gas distribution.

The gas generation units, often reformers or gasifiers, are located adjacent to the shaft furnace, providing the reducing gas continuously. Auxiliary systems include preheaters for the ore, cooling systems for the sponge iron, and dust collection equipment to control emissions.

Design variations have evolved from early HYL I configurations to more advanced HYL III systems, which incorporate improved gas recycling, automation, and energy recovery features. Modern plants also integrate environmental control units such as scrubbers and filters to meet emission standards.

Process Chemistry and Metallurgy

Chemical Reactions

The primary chemical reactions involve the reduction of iron oxides (Fe₂O₃, Fe₃O₄, FeO) to metallic iron (Fe). The main reactions are:

• Fe₂O₃ + 3H₂ → 2Fe + 3H₂O
• Fe₃O₄ + 4H₂ → 3Fe + 4H₂O
• FeO + H₂ → Fe + H₂O

Similarly, carbon monoxide reduces iron oxides:

• Fe₂O₃ + 3CO → 2Fe + 3CO₂
• Fe₃O₄ + 4CO → 3Fe + 4CO₂
• FeO + CO → Fe + CO₂

These reactions are thermodynamically favored at high temperatures, with the reduction proceeding via gas-solid interactions. The process is kinetically controlled, with reaction rates influenced by temperature, gas composition, and ore particle size.

Reaction products include metallic sponge iron and gaseous byproducts such as water vapor (H₂O) and carbon dioxide (CO₂). The management of these gases is critical for process efficiency and environmental compliance.

Metallurgical Transformations

During reduction, iron oxides undergo phase transformations from hematite (Fe₂O₃) or magnetite (Fe₃O₄) to magnetite, then to wüstite (FeO), and finally to metallic iron. Microstructurally, the process involves the formation of porous sponge iron with a high surface area, facilitating further reduction.

The microstructure evolves from dense oxide particles to porous metallic iron, which influences the mechanical properties and melting behavior of the final product. Proper control of reduction conditions ensures minimal formation of slag inclusions or unreacted oxides, resulting in high metallization degrees (> 90%).

Material Interactions

Interactions between the metallic iron, residual slag, refractory lining, and atmosphere are complex. Iron ore particles can react with slag constituents, potentially leading to contamination or degradation of refractory materials.

Gases like CO and H₂ can diffuse through the ore bed, facilitating reduction but also causing potential corrosion of furnace linings if not properly managed. To control unwanted interactions, process parameters are optimized to maintain stable temperature zones, and refractory materials are selected for high corrosion resistance.

Gas cleaning systems remove dust, sulfur compounds, and other impurities from off-gases, preventing environmental pollution and equipment corrosion.

Process Flow and Integration

Input Materials

The primary input is iron ore in pellet or lump form, with high iron content (typically > 60%) and low impurities. The ore must be adequately prepared, with uniform size and moisture content, to ensure consistent reduction.

Reforming gases are generated on-site from natural gas or other hydrocarbons, with specifications including high purity and controlled composition. Auxiliary materials include fluxes or binders, if necessary, for pellet formation.

Input quality directly impacts reduction efficiency, metallization degree, and final sponge iron quality. Impurities like sulfur or phosphorus can adversely affect downstream processes and product properties.

Process Sequence

The operational sequence begins with raw material preparation, including crushing, pelletizing, and drying. The prepared ore is fed into the top of the shaft furnace.

Simultaneously, reducing gas is produced and preheated before injection. The ore moves downward by gravity, reacting with the gas mixture as it descends. Reduction occurs progressively, with the highest temperature and reduction degree near the furnace bottom.

The sponge iron is discharged from the bottom, cooled, and transported for further processing. The off-gases are collected, cleaned, and recycled or utilized for energy recovery.

Typical cycle times range from 20 to 60 minutes per batch, with continuous operation in modern plants. Production rates depend on furnace size and feed rate, often reaching several hundred thousand tons annually.

Integration Points

HYL processes are integrated with upstream raw material handling and downstream steelmaking units. The sponge iron produced feeds directly into electric arc furnaces or is combined with other iron sources.

Material flows include ore delivery, gas generation, reduction, and product handling. Information flows involve process control data, quality monitoring, and operational feedback.

Buffer systems like stockyards or intermediate storage silos ensure steady feed rates and accommodate fluctuations. Efficient integration minimizes downtime and optimizes overall plant productivity.

Operational Performance and Control

Performance Parameter	Typical Range	Influencing Factors	Control Methods
Metallization Degree	85-95%	Gas composition, temperature, residence time	Real-time gas analysis, temperature sensors, automated control systems
Gas Utilization Efficiency	70-85%	Gas flow rates, ore porosity	Flow meters, pressure sensors, process automation
Reduction Rate	90-98%	Temperature, gas composition, ore size	Continuous monitoring, process modeling
Energy Consumption	3500-4500 kWh/t Fe	Furnace design, gas efficiency	Energy meters, process optimization algorithms

Operational parameters directly influence product quality, particularly metallization and impurity levels. Maintaining stable conditions ensures consistent sponge iron quality.

Real-time process monitoring employs gas analyzers, temperature sensors, and control systems to adjust parameters dynamically. Optimization strategies include advanced process control (APC) and predictive maintenance to maximize efficiency and minimize costs.

Equipment and Maintenance

Major Components

The shaft furnace is the core equipment, constructed from high-temperature refractory-lined steel, designed to withstand thermal and chemical stresses. Gas generators, such as reformers or gasifiers, are equipped with burners, reactors, and heat exchangers, often made from corrosion-resistant alloys.

Dust collection systems, including electrostatic precipitators or bag filters, are critical for environmental compliance. Cooling systems for sponge iron and off-gas handling units are also essential.

Wear parts include refractory linings, tuyeres, gas injectors, and dust filters, with typical service lives ranging from 3 to 10 years depending on operating conditions.

Maintenance Requirements

Routine maintenance involves refractory inspection and replacement, calibration of sensors, and cleaning of dust collection systems. Scheduled shutdowns are necessary for refractory relining and equipment upgrades.

Predictive maintenance employs vibration analysis, thermal imaging, and gas analysis to detect early signs of wear or failure. Condition monitoring extends equipment lifespan and reduces unplanned outages.

Major repairs include refractory rebuilding, component replacement, and system overhauls, often scheduled during planned shutdowns to minimize production impact.

Operational Challenges

Common operational issues include refractory degradation, gas leaks, uneven reduction zones, and dust buildup. Troubleshooting involves systematic inspection, process data analysis, and simulation.

Diagnostic approaches include gas composition monitoring, temperature profiling, and refractory integrity assessments. Emergency procedures involve rapid shutdown, gas venting, and safety system activation to prevent accidents.

Product Quality and Defects

Quality Characteristics

Key quality parameters include metallization degree, carbon content, impurity levels (sulfur, phosphorus), and physical properties like porosity and microstructure. Testing involves chemical analysis, metallography, and mechanical testing.

Inspection methods include X-ray fluorescence (XRF), optical microscopy, and hardness testing. Quality classification systems categorize sponge iron based on metallization, impurity levels, and physical characteristics.

Common Defects

Typical defects include unreacted oxides, excessive porosity, contamination with slag inclusions, and uneven reduction. These defects can compromise downstream melting behavior and final steel properties.

Defect formation mechanisms involve incomplete reduction, temperature fluctuations, or material contamination. Prevention strategies include process parameter optimization, feedstock quality control, and equipment maintenance.

Remediation involves reprocessing or blending to achieve desired specifications, along with process adjustments to prevent recurrence.

Continuous Improvement

Methodologies for process optimization include Six Sigma, Lean manufacturing, and statistical process control (SPC). These tools help identify variability sources and implement corrective actions.

Case studies demonstrate improvements such as increased metallization rates, reduced energy consumption, and lower impurity levels through process tuning and equipment upgrades.

Energy and Resource Considerations

Energy Requirements

HYL processes consume approximately 3500-4500 kWh per ton of sponge iron, primarily for gas generation, furnace operation, and auxiliary systems. Energy efficiency measures include waste heat recovery, process insulation, and optimized gas flow.

Emerging technologies focus on integrating renewable energy sources, such as green hydrogen, to reduce carbon footprint. Use of waste heat for power generation further enhances energy utilization.

Resource Consumption

Raw materials include iron ore, natural gas, and auxiliary chemicals. Water consumption is minimized through closed-loop cooling systems. Recycling of off-gases and dust reduces resource wastage.

Resource efficiency strategies involve optimizing ore preparation, recovering heat and gases, and implementing waste recycling. Techniques like slag valorization and dust reuse contribute to sustainability.

Environmental Impact

The process generates emissions such as CO₂, NOₓ, SO₂, and dust. Solid wastes include slag and dust, which can be processed into construction materials or other products.

Environmental control technologies include scrubbers, electrostatic precipitators, and gas cleaning systems. Compliance with regulations requires continuous monitoring, reporting, and adoption of best practices for emission reduction.

Economic Aspects

Capital Investment

Initial capital costs for HYL plants vary from $200 to $400 per ton of annual capacity, depending on plant size, technology level, and regional factors. Major costs include furnace construction, gas generation units, and pollution control systems.

Investment evaluation employs metrics like net present value (NPV), internal rate of return (IRR), and payback period, considering market demand and technological risks.

Operating Costs

Operating expenses encompass energy, raw materials, labor, maintenance, and consumables. Energy costs typically account for 40-50% of total operating costs.

Cost optimization involves process automation, energy recovery, and supply chain management. Benchmarking against industry standards helps identify areas for efficiency gains.

Economic trade-offs include balancing higher capital expenditure for advanced control systems against long-term savings in energy and maintenance.

Market Considerations

The HYL process enhances product competitiveness by enabling high-quality sponge iron with lower emissions and energy consumption. Market requirements for sustainability and low-carbon steel drive process improvements.

Economic cycles influence investment decisions, with increased demand during steel shortages or technological shifts favoring direct reduction methods. Flexibility and scalability of HYL plants make them attractive in diverse market conditions.

Historical Development and Future Trends

Evolution History

The HYL process was developed in the 1960s by the HYL company, pioneering the direct reduction of iron ore using natural gas. Early versions, like HYL I, focused on simple shaft furnace designs.

Subsequent innovations introduced in HYL III included improved gas recycling, automation, and environmental controls, significantly enhancing efficiency and environmental performance. Market forces, such as the need for cleaner steelmaking, propelled continuous development.

Current State of Technology

Today, HYL processes are mature, with numerous operational plants worldwide, especially in regions with abundant natural gas. Variations exist in plant size, gas generation methods, and integration with steelmaking facilities.

Benchmark plants achieve metallization degrees exceeding 95%, with energy consumption at the lower end of the range. The technology is considered reliable, with ongoing improvements in automation and environmental management.

Emerging Developments

Future innovations focus on integrating renewable hydrogen produced via electrolysis, aiming for zero-carbon reduction. Digitalization and Industry 4.0 concepts are being applied to optimize process control, predictive maintenance, and data analytics.

Research is exploring alternative feedstocks, such as biomass-derived gases, and advanced refractory materials to extend equipment lifespan. The development of hybrid processes combining direct reduction with electric arc furnace recycling is also underway, promising further sustainability gains.

Health, Safety, and Environmental Aspects

Safety Hazards

Primary safety risks include high-temperature operations, gas leaks, and dust explosions. The presence of combustible gases like hydrogen and carbon monoxide necessitates rigorous leak detection and ventilation systems.

Accident prevention measures involve safety interlocks, gas detection alarms, and protective barriers. Emergency shutdown procedures include rapid gas venting and fire suppression systems.

Occupational Health Considerations

Workers face exposure to dust, gases, and high noise levels. Dust inhalation can cause respiratory issues, while gases pose toxicity risks.

Monitoring involves continuous air quality sampling, personal protective equipment (PPE) such as respirators, and regular health surveillance. Long-term health programs track occupational exposure effects and implement corrective measures.

Environmental Compliance

Regulations mandate emission limits for CO₂, SO₂, NOₓ, and particulate matter. Continuous emission monitoring systems (CEMS) are employed to ensure compliance.

Best practices include installing scrubbers, filters, and gas cleaning units, along with waste heat recovery systems. Regular environmental audits and reporting are essential for regulatory adherence and corporate sustainability commitments.