Combustion Efficiency for Various Fuels and its Industrial Applications

What is Combustion Efficiency (CE)?

Definition

  • Combustion efficiency quantifies how well fuel is burned to produce heat.
  • It is a measure of how effectively a combustion process converts the chemical energy in a fuel into usable thermal energy.
  • It is expressed as a percentage and represents the ratio of the useful energy obtained from the combustion process to the total energy potential of the fuel.
  • The ideal combustion process would result in the complete conversion of the fuel into heat, water, and carbon dioxide.
  • However, in real-world scenarios, achieving 100% combustion efficiency is challenging due to various factors such as incomplete combustion, heat losses, and the formation of by-products like carbon monoxide and unburned hydrocarbons.
Combustion Efficiency with species across the flame
Combustion Efficiency with species across the flame

Formula

  • The combustion efficiency (η) is often calculated using the formula:

                      η =  (1−Unburned Fuel in Flue Gas /Total Fuel Input)×100

 

  • Here, the unburned fuel in the flue gas represents the portion of the fuel that did not undergo combustion.
  • The higher the combustion efficiency, the better the system is at converting fuel into usable energy while minimizing waste products.
Thermal radiation in biomass combustion
Thermal radiation in biomass combustion

Combustion Efficiency for Various Fuels and its Industrial Applications

  • The combustion efficiency of various fuels plays a crucial role in industrial applications, impacting energy efficiency, environmental performance, and overall operational costs.
  • Additionally, combined heat and power (CHP) systems, which capture and utilize waste heat, are widely employed to improve overall energy efficiency in various industrial processes
  • Here’s a breakdown of combustion efficiency for different fuels and their industrial applications:

Hydrogen

  • Hydrogen has the potential for high combustion efficiency since its combustion product is mainly water vapor.
  • However, practical challenges, such as storage and transportation, need to be addressed for widespread use.
  • Industrial Applications:
    • Being explored for use in various industries, including manufacturing and transportation, as a clean energy carrier.
    • Hydrogen’s application is found in fired heaters and boilers using raw fuel gases that contain more than 60% hydrogen

Natural Gas:

  • Combustion Efficiency: Natural gas
    • Its  high combustion efficiency, often exceeding 90%.
  • Industrial Applications:
    • Widely used in industrial boilers, furnaces, and combined heat and power (CHP) systems.
    • Natural gas is a popular choice in industries such as manufacturing, chemical processing, and power generation.
    • Natural gas like PNG, LPG, and CNG have been used for domestic cooking and automobiles
Natural Gas Burner Bunsen Flame
Natural Gas Burner Bunsen Flame

Diesel Fuel:

  • Combustion Efficiency: Diesel engines generally exhibit high combustion efficiency, especially in industrial applications like power generation and transportation.
  • Industrial Applications: Commonly used in industrial backup generators, transportation (trucks, ships, locomotives), and off-road equipment.

Coal:

  • Combustion Efficiency: Combustion efficiency for coal can vary, with older coal-fired power plants typically having lower efficiency compared to newer, more advanced technologies.
  • Industrial Applications: Historically used in power plants for electricity generation, as well as in various industries for process heat. Transitioning to cleaner technologies due to environmental concerns.
Coal Combustion Processes
Coal Combustion Processes – Devolatization and volatile matters

Biomass:

  • Combustion Efficiency:
    • It is highly dependent on the type of biomass and combustion system.
    • Advanced biomass boilers and combined heat and power (CHP) systems can achieve good efficiency.
  • Industrial Applications:
    • Used in industries such as pulp and paper, food processing, and bioenergy production.
    • Biomass is often employed for both heating and power generation.
steps in biomass combustion process
Basic Steps in the Biomass Combustion Process

Propane:

    • Combustion Efficiency: Propane has a high combustion efficiency.
    • Industrial Applications: Used in industrial processes, heating applications, and as a fuel for vehicles. Propane is often chosen for its clean-burning properties and ease of storage and transportation.

Methane (Biogas):

    • Combustion Efficiency: Combustion efficiency for methane (biogas) is generally high.
    • Industrial Applications:
      • Used in industries with access to biogas sources, such as wastewater treatment plants, landfills, and agricultural operations.
      • Biogas is a renewable energy source derived from organic waste
Methane gas combustion reaction in combustion chamber
Methane gas combustion reaction in combustion chamber

How to improve CE?

  • Improving combustion efficiency is crucial for several reasons, including energy conservation, reducing environmental emissions, and optimizing the performance of combustion-based systems such as boilers, furnaces, engines, and power plants.
  • Engineers and researchers employ various techniques to enhance combustion efficiency, such as optimizing air-fuel ratios, improving burner designs, and implementing advanced control systems.
  • Improving combustion efficiency involves optimizing the combustion process to achieve better energy utilization and reduce waste. Here are several ways to enhance combustion efficiency:

Selection of  Optimize Air-Fuel Ratio

  • Ensure the correct air-fuel ratio for combustion. Too much or too little air can lead to inefficiencies.
  • Utilize oxygen sensors and combustion analyzers to monitor and adjust the air-fuel mixture in real time.
Effect of excess air on combustion Efficiency

Effect of excess air on combustion efficiency

  • Excess air in combustion refers to the amount of air supplied to the combustion process beyond the theoretically required amount for complete combustion.
  • While some amount of excess air is often necessary for practical combustion applications, excessive levels can have significant effects on combustion efficiency
    • Incomplete Combustion:
      • Too much excess air can lead to incomplete combustion. This occurs when the quantity of oxygen available is more than what is required for the complete oxidation of the fuel.
      • Incomplete combustion results in the production of unburned fuel, carbon monoxide (CO), and other harmful pollutants. This not only reduces combustion efficiency but also increases emissions.
    • Reduced Flame Temperature:
      • Excessive air can lower the flame temperature by diluting the concentration of reactants.
      • Lower flame temperatures reduce the efficiency of heat transfer to the working fluid (e.g., water or air), impacting the overall thermal efficiency of the combustion process.
    • Increased Heat Losses:
      • Additional air introduced into the combustion process can lead to increased convective and radiative heat losses.
      • Higher heat losses mean less heat is transferred to the intended application (e.g., a boiler or engine), resulting in reduced overall efficiency.
    • Wasted Energy:
      • The energy required to heat excess air contributes to wasted energy and reduces the effective utilization of the fuel’s energy content.
      • This wasted energy increases operational costs and decreases the overall efficiency of the combustion system.
    • Higher Nitrogen Oxide (NOx) Emissions:
      • Excess air can contribute to elevated temperatures, leading to increased nitrogen oxide (NOx) formation during combustion.
      • NOx emissions are a major concern due to their environmental impact and contribution to air pollution.
  • It’s important to note that the optimal level of excess air can vary depending on the type of fuel, combustion system design, and operational conditions.
  • Regular monitoring, tuning, and control of the air-fuel ratio based on combustion analysis can help maintain optimal combustion efficiency while minimizing emissions and energy losses.
  • Advanced control systems and combustion modeling, such as Computational Fluid Dynamics (CFD), can also aid in achieving and maintaining the desired air-fuel ratio for efficient combustion

Regular Maintenance:

  • Perform routine maintenance on combustion equipment to ensure clean and properly functioning burners.
  • Clean and inspect burners, nozzles, and heat exchangers regularly to remove any deposits that can affect efficiency.

Prevent Heat Loss:

  • Insulate combustion equipment to minimize heat losses and improve thermal efficiency.
  • Seal air leaks in combustion chambers and duct work to prevent the escape of hot gases.

Use High-Efficiency Equipment:

    • Upgrade to modern, high-efficiency burners and combustion systems.
    • Consider investing in advanced technologies, such as condensing boilers or combined heat and power (CHP) systems, which capture and utilize waste heat.

Implement Combustion Controls:

    • Use advanced control systems to optimize combustion parameters in real time.
    • Incorporate variable speed drives and modulation controls to match the combustion output with the load requirements.

Monitor and Tune Systems:

  • Regularly monitor combustion processes using sensors and instrumentation.
  • Conduct periodic tuning of combustion systems to ensure optimal performance under different operating conditions.

Install Flue Gas Heat Recovery:

  • Capture and utilize waste heat from flue gases through heat recovery systems.
  • Implement economizers or air preheaters to preheat combustion air using the recovered heat.

Consider Alternative Fuels:

  • Explore the use of alternative and renewable fuels that may have higher combustion efficiency or lower environmental impact.
  • Evaluate the feasibility of using biofuels, hydrogen, or other clean energy sources.

Training on Basics of Combustion

  • Ensure operators and maintenance personnel are well-trained in the proper operation and maintenance of combustion equipment.
  • Provide ongoing education about energy-efficient practices and the importance of combustion optimization.
CFD modelling of turbulent combustion
CFD modeling of
turbulent combustion

CFD Modeling to Improve Combustion Efficiency

  • Computational Fluid Dynamics (CFD) modeling is a powerful tool used to optimize combustion processes and improve combustion efficiency in various applications.
  • Here’s how CFD modeling can contribute to enhancing combustion efficiency:

Understanding Combustion Physics:

    • CFD simulations provide insights into the complex fluid flow, heat transfer, and chemical reactions occurring during combustion.
    • By modeling the fundamental physics of combustion, and its modeling helps engineers understand combustion dynamics and identify areas for improvement.

Optimizing Combustion Chamber Design:

  • CFD allows engineers to analyze different combustion chamber geometries, burner configurations, and fuel injection strategies virtually.
  • By simulating various design iterations, engineers can identify the most efficient combustion chamber layout to promote better mixing, minimize heat losses, and enhance combustion stability.

Improving Fuel-Air Mixing:

  • Efficient fuel-air mixing is critical for achieving complete combustion and minimizing emissions.
  • CFD modeling helps optimize burner designs and airflow patterns to ensure thorough mixing of fuel and oxidizer, thereby improving combustion efficiency.

Gas Burner - Venturi effect uded for mixing of fuels

Reducing Pollutant Emissions:

  • CFD simulations enable the prediction of pollutant formation mechanisms, such as nitrogen oxides (NOx) and carbon monoxide (CO), during combustion.
  • By understanding the factors influencing emission formation, engineers can develop strategies to reduce pollutant emissions while maintaining high combustion efficiency.

Optimizing Turbulence and Combustion Kinetics:

  • Turbulent flow plays a significant role in promoting mixing and enhancing combustion efficiency.
  • CFD models can incorporate turbulent flow simulations and detailed chemical kinetics to predict combustion performance accurately.
  • By optimizing turbulence parameters and combustion kinetics, engineers can improve combustion efficiency and reduce fuel consumption.

Analyzing Heat Transfer and Thermal Management:

    • CFD simulations help assess heat transfer mechanisms within combustion systems and optimize thermal management strategies.
    • Engineers can identify areas of high heat transfer and implement measures to recover waste heat and improve overall energy efficiency.

Validating Experimental Data:

    • CFD models can be validated against experimental data obtained from combustion test rigs or real-world installations.
    • By comparing simulation results with experimental measurements, engineers can verify the accuracy of the CFD model and gain confidence in its predictive capabilities.

Iterative Design and Optimization:

    • CFD modeling enables engineers to perform iterative design and optimization studies quickly and cost-effectively.
    • By systematically exploring design parameters and operating conditions, engineers can identify optimal configurations that maximize combustion efficiency and minimize environmental impact.

Summary

  • Optimizing combustion efficiency in industrial settings is crucial for minimizing energy waste and reducing emissions.
  • Industries often invest in advanced combustion technologies, control systems, and regular maintenance to enhance efficiency and comply with environmental regulations
  • CFD modeling serves as a valuable tool for improving combustion efficiency by providing detailed insights into the underlying processes
  • optimizing system design, and guiding engineering decisions towards more sustainable and efficient combustion solutions.

 

References

  1. Science Direct, Overview of Combustion Efficiency
  2. The US. Dept. Energy, Boiler combustion Efficiency Calculation
  3. Control System, Combustion efficiency Calculations

Leave a Comment