Efficiency and Performance Impacts of Fuel Switching from Coal to Natural Gas in Radiant Furnaces

Strategic Insights -

When transitioning from coal to natural gas as a fuel source in radiant furnaces, several efficiency and performance impacts are observed. These changes are primarily driven by differences in the characteristics of the two fuels, including moisture content, heating value, and flue gas composition. According to the Kentucky Public Service Commission, switching from coal to natural gas typically results in a 5% decrease in efficiency due to the elimination of energy required to operate coal-specific aux equipment.

Key Takeaways:

  • Minor losses, such as heat of ash and CO and NOx formation losses, are not controlled directly by the layout of the furnace, resulting in no significant efficiency difference between wall and T-fired designs.
  • The most notable efficiency impact of fuel switching is the reduction of around 5% efficiency, which is generally offset by changes to the overall plant heat rate.
  • The radiant heat transfer and furnace exit gas temperature (FEGT) are affected by the flue gas emissivity, wall emissivity, and temperatures of flue gas and walls.
  • The presence of soot particles in coal flames, which have a high emissivity, results in a higher radiant heat transfer compared to natural gas firing with grey-body emissivity.
  • The increase in surface radiant heat absorption due to the elimination of ash deposits on boiler surfaces can act to reduce FEGT.
  • The overall gas temperatures in the various regions of the furnace are dependent on the fuel type, with coal firing requiring 20% or more excess air and natural gas firing requiring only approximately 10% excess air.

Statistics:

  • The efficiency decrease when transitioning from coal to natural gas is typically around 5%.
  • The elimination of energy required to operate coal-specific aux equipment offsets the 5% efficiency decrease.
  • The radiant heat transfer is primarily a function of flue gas emissivity, with coal flames having a high emissivity due to soot particles and natural gas firing having a grey-body emissivity.
  • The furnace exit gas temperature (FEGT) is affected by the radiant heat transfer and surface emissivity, with the presence of ash deposits and changes in flue gas composition impacting the overall performance of the furnace.

Sources:

  • Kentucky Public Service Commission document 2.3.5.