Techniques of Coal Burner Stability in Tangentially Fired Boiler

Tangentially Fired Boiler Furnace

  • Tangentially fired boilers are commonly used in large power plants for their efficiency and ability to handle various fuel types, including coal.
  • These boilers are designed with burners located at the corners of the furnace, firing tangentially towards an imaginary circle in the center of the furnace.
  • This setup creates a swirling fireball, promoting thorough mixing of fuel and air, enhancing combustion efficiency, and reducing emissions.
  • Here’s a detailed look at the key features, benefits, and techniques to ensure the stability and efficiency of tangentially fired boiler furnaces:

Key Features

  1. Burner Arrangement:
    • Corner Burners: Burners are placed at the four corners of the furnace.
    • Tangential Firing: The burners are angled tangentially to an imaginary circle, creating a rotating fireball in the center of the furnace.
  2. Swirl Burners:
    • Swirl Vanes: These impart a swirling motion to the air-fuel mixture, enhancing mixing and flame stability.
  3. Air Supply Stages:
    • Primary Air: Transports pulverized coal to the burners.
    • Secondary Air: Provides additional oxygen for combustion.
    • Tertiary and Overfire Air: Further enhances combustion efficiency and controls NOx emissions.
Tangentially fired boiler with burner arrangement
Tangentially fired boiler with burner arrangement

Advantages 

  1. Efficient Combustion:
    • The swirling fireball ensures thorough mixing of fuel and air, leading to more complete combustion.
  2. Uniform Heat Distribution:
    • The tangential firing pattern results in a more uniform temperature distribution in the furnace, reducing thermal stresses on the boiler walls.
  3. Reduced Emissions:
    • Better mixing and staged combustion help in reducing NOx emissions.
  4. Flexibility:
    • Capable of burning a wide range of coal qualities and other fuels.

Techniques for Enhancing Stability and Efficiency

  1. Optimized Burner Design:
    • Ensure that the burners and swirl vanes are designed to promote thorough mixing and stable flame formation.
    • Maintain proper alignment and angle of the burners for optimal tangential firing.
  2. Air-Fuel Ratio Control:
    • Use advanced control systems to dynamically adjust air and fuel flow rates, ensuring optimal combustion conditions.
    • Regularly tune the combustion system to maintain the ideal air-fuel ratio.
  3. Advanced Monitoring Systems:
    • Install infrared cameras and flame scanners to monitor flame shape, intensity, and stability in real-time.
    • Use data from these monitoring systems to make automatic adjustments to the combustion process.
  4. Regular Maintenance:
    • Keep burners, nozzles, and air registers clean to prevent blockages and ensure consistent air and fuel flow.
    • Inspect and maintain the furnace refractory lining to prevent heat loss and ensure proper combustion temperatures.
  5. Fuel Quality Management:
    • Ensure consistent coal particle size, moisture content, and calorific value to maintain stable combustion.
    • Use coal blending techniques to achieve a more uniform fuel quality.
  6. Combustion Tuning:
    • Regularly tune the combustion system to optimize air-fuel ratios and burner performance.
    • Adjust burner angles and air registers to control the shape and stability of the flame.
  7. Emissions Control:
    • Implement low-NOx burner technologies and overfire air systems to reduce NOx emissions and enhance combustion stability.
  8. Preheated Air Supply:
    • Preheat combustion air to improve fuel ignition and combustion stability.

Techniques for Coal burner stability 

  • Achieving stability in coal burners, particularly in tangentially fired boilers, requires a combination of proper design, operation, and maintenance practices.
  • Here are several techniques to enhance and maintain coal burner stability:

Optimized Burner Design

  • Tangential Firing Configuration: Burners arranged tangentially to an imaginary circle in the furnace create a vortex of combustion gases, promoting thorough mixing and stable flames.
  • Swirl Burners: Incorporate swirl vanes to impart a rotational motion to the air and fuel mixture, enhancing mixing and flame stability.
  • Staged Air Supply: Utilize primary, secondary, and tertiary air supplies to control combustion stages, reducing NOx formation and improving stability.

Air-Fuel Ratio Control

  • Balanced Air Distribution: Ensure that primary, secondary, and tertiary air flows are correctly proportioned to achieve complete combustion.
  • Dynamic Air-Fuel Adjustment: Use advanced control systems to continuously adjust air and fuel flow rates based on real-time combustion conditions.

Fuel Quality Management

  • Consistent Fuel Supply: Ensure coal supplied to the burners has consistent size, moisture content, and calorific value.
  • Coal Blending: Blend different grades of coal to achieve a more uniform fuel quality, which can enhance combustion stability.

Combustion Tuning

  • Regular Tuning: Periodically tune burners and the overall combustion system to optimize air-fuel ratios and burner performance.
  • Flame Shape Adjustment: Adjust burner angles and air registers to control the shape and stability of the flame.
  • Regular Cleaning: Keep burners, nozzles, and air registers clean to prevent blockages and ensure consistent air and fuel flow.
  • Furnace Inspection: Regularly inspect and maintain the furnace refractory lining to prevent heat loss and maintain proper combustion temperatures.
  • Component Replacement: Replace worn or damaged burner components promptly to maintain performance.

Emissions Control

  • Low-NOx Burners: Implement low-NOx burner technologies that reduce nitrogen oxide emissions while maintaining stable combustion.
  • Overfire Air Systems: Use overfire air systems to further reduce NOx emissions and enhance combustion stability by promoting complete burnout of fuel particles.

Air and Fuel Preheating

  • Preheated Air: Preheat combustion air to improve fuel ignition and combustion stability.
  • Coal Drying: Use drying techniques to reduce coal moisture content, enhancing combustion efficiency and stability.

 

Combustion stability Techniques in Industrial Burners
Combustion Stability Techniques in Industrial Burners

Key Factors Influencing Burner Stability

  • Stability in coal burners, particularly for tangentially fired boilers, is crucial for ensuring efficient combustion, minimizing emissions, and maintaining reliable operation.
  • Here are some key aspects that contribute to the stability of coal burners in tangentially fired boilers
  1. Fuel Quality:
    • Coal Particle Size: Uniform and appropriate particle size ensures better mixing and combustion.
    • Moisture Content: Low moisture content is preferred as high moisture can lead to incomplete combustion and instability.
    • Calorific Value: Consistent calorific value helps maintain steady combustion.
  2. Air-Fuel Ratio:
    • Primary Air Flow: Adequate primary air is required for transporting and initial mixing of the coal particles.
    • Secondary Air Flow: Proper secondary air distribution ensures complete combustion and flame stability.
    • Tertiary and Overfire Air: These are used to control emissions and further stabilize the combustion process.
  3. Burner Configuration:
    • Tangential Firing: Burners are arranged tangentially to an imaginary circle in the furnace. This configuration helps create a rotational flow, promoting thorough mixing and stable flame.
    • Swirl Burners: These induce a swirling motion to the air and fuel mixture, enhancing mixing and flame stability.
  4. Furnace Design:
    • Size and Shape: The furnace should be appropriately sized to provide sufficient residence time for complete combustion.
    • Refractory Lining: Proper insulation helps maintain high temperatures necessary for stable combustion.
  5. Operational Parameters:
    • Load Conditions: Burners must be able to operate stably across a range of load conditions.
    • Start-Up and Shutdown Procedures: Proper procedures help prevent instability during transitions.
    • Control Systems: Advanced control systems can adjust air and fuel flow dynamically to maintain stability.
  6. Flame Monitoring:
    • Infrared Cameras: These can detect flame shape and intensity, providing data for adjustments.
    • Flame Scanners: Used to monitor flame presence and stability, ensuring safe operation.
Combustion Stability Curves
Combustion Stability Curves

Enhancing Stability in Tangentially Fired Boilers

  1. Optimized Burner Design:
    • Burners should be designed to ensure even distribution of air and fuel, preventing local hotspots or unburned regions.
    • Swirl vanes or other flow control devices can be used to enhance mixing and stability.
  2. Regular Maintenance:
    • Ensuring that burners, nozzles, and air registers are clean and in good condition helps maintain consistent operation.
    • Inspecting and maintaining the furnace refractory lining to prevent heat loss and ensure proper combustion temperatures.
  3. Combustion Tuning:
    • Regular tuning of the combustion system helps optimize air-fuel ratios, improving efficiency and stability.
    • Adjusting burner angles and air registers to ensure proper mixing and flame shape.
  4. Advanced Control Systems:
    • Implementing advanced control systems that use real-time data to adjust air and fuel flow can significantly enhance stability.
    • Using predictive maintenance tools to identify and address potential issues before they affect stability.

Conclusion

  • Stability in coal burners for tangentially fired boilers is achieved through a combination of high-quality fuel, proper air-fuel ratios, optimized burner design, and advanced control systems.
  • Regular maintenance and tuning are essential to maintain efficient and stable combustion, which is crucial for the reliable operation of tangentially fired boilers
  • .Achieving and maintaining coal burner stability in tangentially fired boilers requires a multifaceted approach.
  • By combining optimized burner design, precise air-fuel ratio control, advanced monitoring systems, regular maintenance, and proper operational practices, you can ensure stable and efficient combustion.

Reference

  1. Shinji et al, Development of Low-Volatile Coal Firing Burner (2008)
  2. Xu et al., Quantitative Assessment of Burner Flame Stability through Digital Image Processing, (2022)
  3.  Power Magazine, Low NOx Burner in Power Plant, May (2007)
  4. YU et al, Numerical Simulation of Tangentially Fired Boiler (2019)
  5. Tian et al, Effect of Vertical Title Angle on PC Tangentially Fired Boiler 700 MW  (2015)

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