Industrial furnaces: Impact of biofuels and fuel switching

Industrial furnaces are undergoing a transformation driven by decarbonization, energy volatility, and new regulatory requirements. The use of industrial biofuels and fuel switching strategies is no longer experimental; they are operational decisions that affect industrial combustion, mechanical integrity, and thermal efficiency. However, changing fuels involves modifying flame conditions, heat transfer, emissions, and the metallurgical behavior of equipment. Understanding these changes is essential to reduce carbon emissions without compromising safety, reliability, or operational performance.

The energy transition in industrial furnaces

Industrial furnaces consume large amounts of thermal energy in sectors such as refining, petrochemicals, power generation, cement, steelmaking, and manufacturing. As a result, they represent a significant source of greenhouse gas emissions.

The pressure to reduce carbon emissions has driven the adoption of alternatives such as biodiesel, biogas, renewable oils, hydrogen blends, and synthetic fuels. In this context, fuel switching consists of partially or fully replacing the original fuel with another one with lower environmental impact.

Although the concept seems simple, flame behavior and heat transfer can change drastically. A furnace designed for natural gas will not respond the same way when using biogas or hydrogen-enriched blends. Likewise, a system originally designed for fuel oil may experience significant variations when operating with biodiesel or renewable fuels.

The energy transition requires simultaneous evaluation of thermal performance, operational safety, materials, mechanical integrity, and environmental compliance.

What changes in a furnace when using biofuels?

One of the main effects of using industrial biofuels in industrial furnaces occurs in combustion dynamics and the thermal profile of the equipment.

Variation in heating value

Many biofuels have a lower heating value than traditional fossil fuels. This may generate:

• Higher volumetric fuel consumption
• Changes in flame length
• Temperature variations in radiant chambers
• Increased cold or hot zones
• Alterations in heat distribution

The result can directly affect thermal efficiency and process stability.

What changes in combustion, flame, and heat transfer

The chemical composition of the new fuel modifies fundamental industrial combustion parameters:

• Air–fuel ratio
• Flame speed
• Adiabatic temperature
• Soot formation
• NOx and CO emissions
• Thermal radiation

For furnaces operating with heavy liquid fuels, the transition to renewable fuels may reduce carbon deposit formation. However, some biofuels generate less radiant flames, reducing heat transfer by radiation.

Changes in heat transfer can lead to localized overheating or efficiency losses in tubes and radiant coils.

In petrochemical and refining processes, these variations may alter tube metal skin temperature, increasing metallurgical risks and accelerating damage mechanisms.

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Fuel switching and combustion behavior

Fuel switching modifies the thermal and aerodynamic balance of the combustion system. Therefore, before implementing a fuel change, it is essential to conduct thermal engineering studies and operational simulations considering:

Flame stability changes

Flame behavior may vary significantly depending on the fuel used.

For example:

• Hydrogen has high combustion speed
• Biogas has lower heating value
• Some liquid biofuels present different atomization behavior

These conditions may cause:

• Flame instability
• Flame backflow
• Flashback
• Incomplete combustion
• Increased vibration
• Excessive CO formation

When the system is not properly adjusted, emissions in furnaces may increase instead of decreasing.

Emissions and environmental performance

One of the main objectives of fuel switching is to reduce carbon emissions. However, real reduction depends on multiple variables:

• Fuel quality
• Combustion efficiency
• Burner configuration
• Excess air
• Furnace control system

In some cases, CO₂ emissions decrease, but NOx emissions increase due to higher flame temperatures.

Environmental behavior must be evaluated through integrated combustion analysis and continuous gas monitoring.

Modern industrial furnaces integrate online analyzers to measure:

• CO₂
• O₂
• NOx
• CO
• Unburned hydrocarbons

This information allows optimization of industrial combustion and maintenance of proper thermal efficiency levels.

What technical risks does fuel switching involve?

The most important risks associated with fuel switching in industrial furnaces include:

Tube overheating

Changes in thermal radiation may generate localized temperature increases in radiant and process tubes.

This may cause:

• Accelerated creep
• High-temperature oxidation
• Carburization
• Thermal fatigue
• Loss of mechanical strength

Operational instability

Flame variations may cause:

• Burner shutdowns
• Thermal oscillations
• Pressure surges
• Refractory damage

Corrosion and deposits

Some industrial biofuels contain contaminants or oxygenated compounds that promote:

• High-temperature corrosion
• Deposit formation
• Tube fouling
• Chemical attack in injection systems

Increased emissions

Poor calibration can increase furnace emissions, affecting environmental compliance.

What adjustments does an industrial furnace require?

Safe fuel switching implementation requires technical and operational modifications.

Burner adaptation for the energy transition

Depending on the fuel, the following may be required:

• New nozzles
• Atomization systems
• Mixer modifications
• Air control systems
• Flashback protection systems
• Specialized flame sensors

Control and automation adjustments

Control systems must be recalibrated to respond to new combustion conditions.

This includes:

• Excess air control
• Fuel–air ratio
• Safety alarms
• Gas instrumentation
• Interlock logic

Incorrect adjustment may compromise thermal efficiency and increase operational risks.

Metallurgical and mechanical assessment

Before implementing fuel switching, it is necessary to analyze:

• Design temperature
• Metallurgical conditions
• Remaining thickness
• Weld integrity
• Material compatibility

Thermal profiles may vary significantly after fuel switching, especially with hydrogen blends.

Integrity monitoring in industrial furnaces

Monitoring tube integrity in industrial furnaces is essential during and after the energy transition.

Common inspection techniques include:

• Conventional ultrasonic testing
• Corrosion mapping
• Laser profilometry
• Metallographic replicas
• Infrared thermography
• Creep measurement
• Remote visual inspection

Tube metal skin temperature must be continuously monitored to detect overheating zones.

In many cases, post-fuel-switching thermal behavior requires adjustments in inspection frequency and RBI strategies.

Fuel switching and thermal efficiency

The relationship between fuel switching and thermal efficiency depends on furnace design and combustion quality.

A successful fuel change may result in:

• Lower energy consumption
• Reduced thermal losses
• Improved operational control
• Less soot formation
• Reduced corrective maintenance

However, when the transition is performed without proper thermal analysis, efficiency may significantly deteriorate.

In some cases, furnaces converted to biogas experience reduced thermal capacity due to lower fuel heating value.

Therefore, CFD (Computational Fluid Dynamics) studies and thermal simulations are key tools to validate expected performance.

Regulatory compliance and API standards

Compliance with API standards in fuel switching processes is essential to ensure safety and operational reliability.

Key related standards include:

• API STD 560: Design
• API 556: Instrumentation and control
• API 573: Inspection of fired heaters
• API 579-1/ASME FFS-1: Fitness for Service
• API 580 and API 581: RBI

Fuel switching may also require updated HAZOP, SIL, and process risk studies.

Economic impact of fuel switching

Energy transition in industrial furnaces is not only driven by environmental factors. Economic considerations are also critical:

• Fuel costs
• Carbon taxes
• Environmental penalties
• Energy availability
• Regulatory incentives

In regions with fuel restrictions or emission taxes, industrial biofuels may offer competitive advantages.

However, initial investment may include:

• Burner replacement
• Instrumentation modifications
• New safety systems
• Thermal studies
• Material upgrades

Lifecycle cost and operational risk must be considered in economic analysis.

Digitalization and intelligent monitoring

Digital transformation improves the operation of industrial furnaces undergoing fuel switching.

Current systems include:

• Smart sensors
• Predictive monitoring
• Combustion analytics
• Artificial intelligence
• Digital twins

These tools enable real-time detection of thermal deviations, optimization of industrial combustion, prediction of flame behavior, deposit formation, and metallurgical degradation.

Future perspectives of industrial furnaces

Decarbonization will continue driving technological development to reduce carbon emissions in industrial furnaces.

Future trends include:

• Hydrogen blends
• Synthetic fuels
• Hybrid systems
• Partial electrification
• Ultra-low NOx burners
• Carbon capture systems

However, each energy transition must be technically evaluated to avoid compromising mechanical integrity and operational reliability.

The real challenge is not only changing the fuel, but maintaining safety, thermal stability, and productivity under new operating conditions.

Conclusions

Industrial furnaces are undergoing an energy transition where fuel switching and industrial biofuels offer opportunities to reduce carbon emissions and improve sustainability. However, fuel changes modify industrial combustion, heat transfer, and mechanical integrity. Associated risks include overheating, flame instability, corrosion, and changes in furnace emissions. Successful transition requires burner adaptation, continuous monitoring, metallurgical analysis, and regulatory compliance to preserve thermal efficiency, safety, and operational reliability.

References

1. American Petroleum Institute. (2024). API Standard 560: Fired Heaters for General Refinery Service (5th ed.). API Publishing Services.
2. American Petroleum Institute. (2023). API Recommended Practice 573: Inspection of Fired Boilers and Heaters (4th ed.). API Publishing Services.
3. American Petroleum Institute. (2021). API Recommended Practice 556: Instrumentation, Control, and Protective Systems for Gas Fired Heaters (4th ed.). API Publishing Services.
4. National Fire Protection Association. (2023). NFPA 86: Standard for Ovens and Furnaces. NFPA.
5. American Petroleum Institute & ASME. (2021). API Recommended Practice 579-1/ASME FFS-1: Fitness-for-Service (3rd ed.).