Detailed Process of High-Carbon Ferromanganese Smelting in Submerged Arc Furnaces

Detailed Process of High-Carbon Ferromanganese Smelting in Submerged Arc Furnaces

High-carbon ferromanganese (HC FeMn) is an important alloying element in steel production, mainly used for deoxidation and increasing the manganese content in steel. Its production relies on precise operation of submerged arc furnaces to ensure high yield, reduce manganese volatilization loss, save energy, and improve raw material utilization. This article provides a detailed explanation of furnace process operations, covering furnace design, raw material preparation, charging strategies, furnace condition management, as well as tapping and slag handling.

1. Furnace Design and Refractory Materials

The production of HC FeMn mainly depends on submerged arc furnace (SAF) smelting. Based on production scale and capacity requirements, SAFs can be classified as small, medium, or large. Furnace type selection not only affects output and energy consumption, but also directly impacts raw material heating efficiency, refractory lifespan, and manganese volatilization losses.

1.1 Refractory Materials and Performance Requirements

Furnace linings are usually constructed with high-density carbon bricks, whose performance directly affects furnace lifespan and smelting efficiency. The main characteristics of high-density carbon bricks are:

High-temperature resistance: Able to withstand temperatures over 1500°C in the melting zone while maintaining structural stability.

Chemical stability: Resistant to corrosion in high-carbon reducing atmospheres and slag environments, reducing lining wear.

Thermal conductivity: Appropriate thermal conductivity ensures uniform heat distribution, reducing local overheating and heat loss.

Mechanical strength: Resistant to crushing under the weight of the charge and internal furnace pressure, ensuring long operational cycles.

In practice, different parts of the lining are selected based on heat exposure and chemical corrosion intensity, using bricks of different density and hardness to optimize durability and cost. For example, the furnace bottom and areas around electrodes use high-strength, wear-resistant bricks, while the upper furnace walls use materials with lower thermal expansion coefficients to reduce thermal stress cracking.

1.2 Electrode Arrangement and Current Distribution

Three-phase or multi-phase electrode arrangements are commonly used to ensure uniform current distribution, forming a stable melting-zone temperature. Electrode arrangement significantly affects charge melting and reduction reactions:

Uniform melting: Properly arranged electrodes allow uniform heating of the charge, reducing local overheating or cold zones.

Control of melt pool depth: By adjusting electrode spacing and immersion depth, the depth of the melt pool can be controlled, optimizing heat exchange.

Reduced electrical energy loss: Balanced current lowers local resistance, improving overall energy efficiency.

Additionally, multi-phase electrode arrangements help cope with large furnace capacity production, improving thermal load management, production continuity, and smelting stability.

1.3 Furnace Structure Design

Different furnace structures are crucial for smelting efficiency and furnace gas control:

Enclosed SAF: Equipped with a sealed top and charging pipe, maintaining slightly positive pressure (0–400 Pa) to prevent air ingress and stabilize furnace gas composition. The sealed structure also effectively reduces manganese volatilization and furnace gas heat loss.

Open-top SAF: Offers flexible operation but requires control of charge height and charging strategies to manage gas escape and heat loss.

Furnace design must also consider thermal expansion, structural strength, and operational convenience. Enclosed tops facilitate gas monitoring and safety valve installation, enhancing operational safety.

1.4 Integrated Impact of Furnace Type and Refractory Selection

Reasonable furnace type and refractory material selection directly influence:

Thermal efficiency: Optimizing lining thermal conductivity and furnace structure reduces heat loss and improves electrical energy utilization.

Lining lifespan: High-temperature and chemically resistant linings reduce shutdown frequency for maintenance, enhancing continuous production.

Manganese volatilization: Enclosed furnace design combined with heat-resistant linings effectively reduces high-temperature manganese loss, improving smelting yield and economic benefits.

Furnace design and lining material selection are key technical factors for efficient, stable, and safe HC FeMn smelting, directly affecting production capacity, energy consumption, and product quality.

2. Raw Material Preparation and Charging Strategy

The production quality and capacity of HC FeMn heavily depend on raw material preparation and precise charging strategy. Proper raw material composition not only determines smelting thermal efficiency but also affects manganese recovery, charge melting uniformity, and refractory lifespan.

2.1 Raw Material Composition and Properties

Main furnace materials include coke, manganese ore, and fluxes. The physical properties and chemical composition of each material significantly influence smelting performance:

Coke: Provides reducing agent and furnace heat energy; major carbon source in the furnace.

Requirements: uniform particle size, low moisture, moderate ash content. Uniform size ensures good permeability and avoids local oxidation; low moisture reduces water vapor generation, lowering heat loss and manganese volatilization.

Manganese ore: Supplies the main manganese element, reduced at high temperature to produce HC FeMn.

Requirements: high grade, uniform particle size, low impurity content. Oversized or undersized particles affect melting uniformity, reduction rate, and charge flowability.

Fluxes (lime, dolomite, etc.): Adjust slag properties including fluidity, viscosity, and basicity.

Technical significance: good slag fluidity promotes manganese recovery, reduces iron loss, improves slag-metal separation, and ensures smooth tapping.

2.2 Charging Sequence and Method

Scientific charging sequence ensures smelting stability and output:

Weighing order: Typically coke → manganese ore → flux. Coke, as fuel base, should be evenly distributed first, followed by manganese ore, with flux added last to adjust slag properties.

Charging methods:

Small SAFs: manual charging, flexible operation but requires uniform piling to prevent collapse.

Medium and large SAFs: use hopper and charging pipe for continuous mechanized feeding, ensuring charge height and uniformity.

Enclosed SAF: charging pipe penetrates the charge layer, remaining filled with material; molten charge gradually descends into the furnace, forming a stable charge layer.

This operation reduces errors, improves continuous production efficiency, and maintains stable furnace gas composition and pressure.

2.3 Technical Operation Points

Particle size control: Uniform coke and manganese ore improve charge permeability and reduction efficiency.

Batch charging: Avoids charge collapse, local overheating, or unmelted zones, reducing manganese volatilization.

Charge surface monitoring: Strict control of charge height and morphology ensures uniform gas rise, optimizes heat exchange, and reduces heat loss.

Raw material moisture control: High-moisture materials generate water vapor, reducing reducing gas concentration and increasing manganese volatilization; thus, raw materials must be dried.

Proper raw material preparation and scientific charging strategy are core to high-efficiency, stable SAF HC FeMn production. By controlling raw material quality, particle size, moisture content, and charging methods, manganese recovery can be significantly improved, energy consumption reduced, and uniform melting and smooth tapping ensured.

3. Charge Bed Formation and Surface Management

Charge bed shape and surface management are crucial for smelting efficiency, product quality, and refractory life. Reasonable bed shape optimizes internal heat distribution, increases reduction efficiency, and reduces manganese volatilization and energy loss.

3.1 Charge Bed Shape Requirements

Conical piles: Around electrodes, charge should be piled in cones of appropriate height. This promotes uniform charge layers, ensuring uniform gas rise and full heating and reduction of each layer.

Surface height control: Excessive height hinders gas penetration, forming cold zones; too low causes local overheating and uneven lining heating. Proper height ensures uniform melting, reducing caking and local burn loss.

3.2 Impact of Pile Shape on Smelting

Heat exchange efficiency: Conical structure increases contact area between charge and rising gas, improving heat absorption and reduction rate.

Reduce manganese volatilization: Uniform bed and appropriate shape lower local high temperatures, reducing high-temperature manganese oxidation and volatilization.

Prevent caking and collapse: Proper shape controls charge descent, reducing local accumulation or collapse, stabilizing the melt zone.

3.3 Surface Management Operation Points

Frequent, small additions: Add small amounts of charge in batches to prevent collapse or uneven melting.

Post-tapping or collapse handling: Restabilize the charge before adding new material for consistent surface.

Poking and stirring: Regularly use iron rods or mechanical mixers to remove caked layers, prevent trapped gas pockets that increase manganese volatilization or charge expansion.

Observation and adjustment: Operators monitor height, uniformity, and temperature, adjusting charging position and speed to maintain stability.

3.4 Advanced Management Techniques

Zoned charging:For medium and large SAFs, adjust charging amount based on temperature distribution and layer thickness.

Bed shape optimization: Minor adjustments guide gas flow, optimizing heating and overall thermal efficiency.

Integration with gas monitoring: Adjust bed height and shape according to gas flow, pressure, and composition for dynamic control, ensuring stable smelting.

Proper bed formation and surface management ensure uniform melting, efficient reduction, reduced manganese volatilization, decreased heat loss, refractory protection, and safe operation. Through frequent small additions, regular stirring, and dynamic monitoring, SAF can achieve high yield, low consumption, and stable HC FeMn production.

4. Furnace Gas Flow and Reaction Control

During HC FeMn SAF smelting, furnace gas flow and chemical composition are key factors affecting manganese ore reduction efficiency, charge melting uniformity, and manganese loss. Proper gas management ensures stable furnace temperature, significantly improves manganese recovery, and reduces energy consumption.

4.1 Furnace Gas Composition and Function

The furnace gas mainly consists of carbon monoxide (CO), carbon dioxide (CO₂), hydrogen (H₂), and a small amount of oxygen (O₂):

Carbon monoxide (CO): Primary reducing agent, reduces MnO to Mn.

Hydrogen (H₂): Auxiliary reducing gas, accelerates reduction reactions; excessive H₂ may cause local combustion and temperature unevenness.

Oxygen (O₂): Excess O₂ in the furnace promotes manganese oxidation, increasing volatilization and lowering molten iron quality.

Carbon dioxide (CO₂): Main by-product gas, affecting the reducing atmosphere balance, adjustable through furnace temperature and charge layer management.

By controlling gas composition, manganese reduction rate can be optimized, oxidation losses minimized, and furnace thermal efficiency improved.

4.2 Pressure Control in Enclosed SAF

Micro-positive pressure operation: Enclosed SAFs maintain furnace pressure between 0–400 Pa.

Benefits: Prevents air ingress, reduces oxygen entry, minimizes manganese oxidation and volatilization. Maintains stable gas flow, ensuring uniform heating and avoiding cold or overheated zones.

Risks of improper pressure:

Excessive positive pressure may damage the top seal and cause gas leakage.

Negative pressure may draw in air, increasing oxygen content, causing local combustion or furnace explosions.

4.3 Uniform Gas Release and Charge Surface Management

Even gas release from the charge surface:

Ensures full heating of the charge and efficient manganese ore reduction.

Prevents caking and formation of needle-shaped gas pores, reducing manganese volatilization.

Maintains charge descent rate and melt zone stability.

Uneven gas distribution can create local overheating or underheating (“dead zones”), reducing production efficiency and increasing lining wear.

4.4 Gas Control and Operational Strategy

Dynamic gas monitoring: Real-time CO, H₂, and O₂ measurements allow adjustment of charging speed, charge height, and flux ratio to maintain reducing atmosphere stability.

Charge-gas coordination: Bed height and shape influence gas flow rate and direction; uniform surface with appropriate gas pressure ensures full-layer heating and efficient reduction.

Manganese loss reduction: Controlling gas composition, pressure, and charge surface shape effectively lowers high-temperature oxidation and improves HC FeMn yield and economic efficiency.

4.5 Advanced Optimization Recommendations

Zoned airflow control: In medium and large SAFs, adjusting layer thickness and bed shape optimizes gas velocity and composition in different zones.

Integration with temperature monitoring: Combine melt pool temperature, gas flow, and composition monitoring to dynamically adjust charging and flux addition, achieving coordinated control of gas, charge, and temperature.

Furnace gas flow and reaction control directly affect manganese reduction efficiency, furnace temperature stability, and manganese loss. Through micro-positive pressure operation, uniform bed formation, gas composition monitoring, and dynamic charging, SAF can achieve high-yield, low-consumption, stable, and safe HC FeMn smelting.

5. Tapping and Slag Handling

Tapping and slag handling are crucial for manganese recovery, energy efficiency, and resource utilization. Proper practices ensure molten iron quality, extend lining life, reduce production cost, and support green metallurgy.

5.1 Slag Retention Method

Principle: Iron and slag have different densities and can be separated via slag and tapping ports. The slag retention method keeps part of the slag until molten iron reaches required temperature and composition, then taps the iron for efficient separation.

Advantages:

Improved manganese recovery: More thorough iron-slag separation reduces Mn loss.

Reduced power consumption: Optimized melt zone temperature and slag-metal ratio lower unnecessary energy input.

Simplified pre-tapping operation: Reduces manual intervention, improves production continuity and safety.

5.2 Casting Methods

After tapping, molten HC FeMn can be cast via direct or indirect methods:

Direct casting: Molten iron flows via long troughs into casting beds, breaking into standard blocks naturally or mechanically.

Advantage: Simple operation, continuous output, low equipment investment.

Requirement: Ensure flat casting bed and smooth trough to avoid splashing or local overheating.

Indirect casting: Molten iron flows into steel ladles and then into molds via belt or ring-type casting machines.

Advantage: Accurate block size and shape control, suitable for medium and large continuous production.

Requirement: Strict control of pouring temperature, flow rate, and mold filling to prevent gas pores or crystallization defects.

5.3 Slag Handling and Resource Utilization

Slag properties: Rich in oxides with certain basicity and stability.

Recycling: Quenched slag can be reused for:

Road base or concrete aggregates.

Construction materials or industrial fillers.

Environmental significance: Slag recycling reduces waste treatment cost, supports green metallurgy, minimizes environmental pollution, and enables resource circularity.

5.4 Operational Points and Optimization

Confirm melt iron temperature and composition before tapping to ensure product quality.

Keep slag and tapping ports clear to prevent clogging or iron inclusion in slag.

For large SAFs, staged slag removal and split tapping improve smelting efficiency and safety.

Through scientific slag retention, proper casting, and slag resource utilization, HC FeMn production achieves high manganese recovery, energy saving, safe and stable operation, and supports green metallurgy and sustainable resource use.

6. Furnace Monitoring and Safety Operations

Furnace monitoring and safety operations are essential for efficient, stable, and safe HC FeMn production. SAF operation depends not only on raw material and process design but also on real-time monitoring of key parameters such as charge surface, gas, and current.

6.1 Normal Operation Indicators of Open-Top SAF

Open-top SAF offers flexible operation but relies on operator judgment. Normal indicators include:

Good charge permeability: Even and loose charge layers ensure uniform gas rise and full heating and reduction.

Uniform short yellow flames: Indicate uniform heating and complete reduction reactions.

No charge collapse or flash fire: Stable melt zone without local collapse or violent flame.

Electrode and current state: Balanced three-phase current and stable electrode immersion prevent local overheating or electrode burnout.

Smooth slag and iron flow: Clear slag-metal separation ensures full melt zone and smooth tapping.

These indicators help detect issues such as surface compaction, local cold zones, or uneven melting.

6.2 Normal Operation Indicators of Enclosed SAF

Enclosed SAF uses sealed top and charging pipe to control furnace pressure and gas composition. Normal indicators include:

Stable internal pressure: Micro-positive pressure (0–400 Pa) prevents air ingress and ensures gas composition stability.

Normal gas composition: H₂ <8%, O₂ <3%, maintaining stable manganese ore reduction atmosphere.

Warning of anomalies: Pressure abnormalities or seal damage can allow air ingress, causing gas oxidation, local combustion, or explosion risks.

Stable operation depends on continuous charging, charge surface height control, and gas pressure management.

6.3 Safety Operation Considerations

SAF operations involve high temperature, high current, and high energy density; strict safety protocols are essential:

Charging pipe operation: Continuous and stable charging avoids sudden surface drop or collapse.

Tapping operation: Follow standard procedures; ensure temperature and composition compliance; maintain smooth trough to prevent splashing.

Slag handling: Discharge in steps to avoid hot slag impact; monitor flow and level in large SAFs to prevent accidents.

Gas and temperature monitoring: Real-time monitoring allows early detection of anomalies; for enclosed SAF, address seal failure or abnormal pressure immediately to avoid air ingress and explosion risk.

6.4 Advanced Management and Optimization

Regular inspection: Check electrodes, charging pipes, slag ports, and lining; address abnormalities promptly.

Dynamic adjustment: Adjust charging and surface height based on gas composition and melt status to optimize smelting efficiency.

Safety training: Operators should be trained on high temperature, electrical, and gas safety to respond to emergencies quickly.

Safe and stable SAF operation relies on real-time monitoring, surface management, gas control, and strict operational procedures. Proper monitoring, optimized charging and tapping, and routine inspections ensure high-yield, low-consumption, safe, and environmentally friendly smelting.

7. Summary 

Efficient and stable HC FeMn SAF operation depends on scientific process design and strict operational management. From furnace design and refractory selection to raw material preparation, surface management, gas control, and tapping/slag handling, every step directly affects output, energy consumption, and product quality.

Key process optimizations include:

Precise raw material preparation: Correct ratios of coke, manganese ore, and flux ensure full melting, uniform reactions, and controlled slag properties.

Optimized charging and surface management: Batch, uniform charging with optimized bed shape ensures good permeability and uniform heating, reducing manganese volatilization.

Gas control and reaction management: Precise control of gas flow, pressure, and composition maintains proper reduction atmosphere and maximizes manganese recovery.

Safe tapping and slag handling: Standardized procedures ensure product quality, operational safety, and slag recycling for green metallurgy.

High manganese recovery and energy savings: Optimized charge structure, charging strategy, and melt zone temperature maximize Mn utilization and minimize loss.

Stable furnace operation: Real-time monitoring of current, charge surface, gas pressure, and temperature reduces risks and extends lining lifespan.

Modern HC FeMn SAF production achieves high yield, low energy consumption, and sustainability, providing high-quality alloying materials, reducing environmental impact, and maintaining global competitiveness.