Key weather-related factors affecting burner performance include: 

  • Temperature fluctuations that alter heater draft and combustion air properties
  • Humidity levels that affect oxygen concentration in the combustion air
  • Barometric pressure changes that influence air density and fuel-air mixing
  • Elevation differences that alter available oxygen and heater draft requirements

Understanding how these conditions impact burner operation helps maintain efficiency and prevent combustion-related issues. 

Effect on Operations 

Fluctuations in Excess Oxygen and Heater Efficiency 

  • As ambient conditions change, the amount of excess oxygen in the flue gas will increase or decrease.
  • Changes in oxygen levels can cause:
    • Flame impingement on tubes, leading to high tube metal temperatures.
    • Flame instability, increasing the risk of flame lift-off or flameout.
    • Higher or lower emissions, affecting compliance with NOx and CO regulations.
    • Reduced heater efficiency, requiring additional tuning to maintain performance.

Impact on Heater Draft 

  • Heater draft is influenced by both firebox temperature and ambient air temperature.
  • A decrease in ambient temperature increases draft, while warmer conditions reduce draft.
  • Rain and cold weather can cool the stack, further reducing draft and requiring adjustments.

Changes in Air Density and Oxygen Content 

  • Standard atmospheric air at 60°F, 0% humidity, and 14.7 psi contains 21% oxygen by volume.
  • At 80°F and 80% humidity, oxygen content drops to 20%, reducing available combustion oxygen.
  • This reduction can lower excess oxygen in the flue gas from 3% to 2.2%, translating to a decrease from 15% excess air to 10% excess air.
  • Lower oxygen levels can affect burner efficiency and emissions, requiring adjustments to maintain proper combustion.

Impact on NOx Emissions 

  • Cooler, dry air can lead to increased NOx levels, as lower humidity results in higher flame temperatures.
  • NOx emissions may fluctuate seasonally, requiring monitoring and adjustments.

Effect of Elevation on Burner Performance 

  • Atmospheric pressure decreases with elevation, affecting air density and oxygen availability.
  • A heater designed for Houston, Texas would require 20% more draft to operate at the same excess air level in Cody, Wyoming, where atmospheric pressure is 12.2 psi compared to 14.7 psi at sea level.
  • Higher elevations require additional draft adjustments to maintain proper combustion conditions.

Corrective and Preventive Actions 

Monitor Oxygen and Draft Levels Continuously 

  • Use an accurate oxygen analyzer and draft sampling system to monitor changes in combustion air.
  • The oxygen probe and draft tube should be located at the top of the radiant firebox, as this is the key control point for both excess oxygen and heater draft.

Plan Ahead for Seasonal Changes 

  • During warmer months, the heater may require additional air and more draft to achieve the same process duty.
  • Anticipate changes in weather and adjust burner air registers and stack dampers accordingly.

Adjust Stack Damper and Air Registers as Needed 

  • If excess oxygen levels are normally 2% with -0.1 inches of draft at the arch, consider increasing them to 3% oxygen and -0.2 inches of draft before a major temperature or humidity change.
  • These adjustments help compensate for reduced oxygen content and density variations in the incoming air.
  • Once ambient conditions stabilize, fine-tune the heater for optimal efficiency and emissions performance.

Summary 

Ambient weather conditions play a significant role in burner performance, heater draft, and emissions levels. Monitoring and adjusting for temperature, humidity, and atmospheric pressure changes ensures consistent heater efficiency and reliable combustion. 

To maintain stable operation: 

  • Use oxygen analyzers and draft gauges to track changing conditions.
  • Adjust stack dampers and burner air registers proactively before seasonal shifts.
  • Account for higher elevation requirements by increasing draft to maintain proper excess air levels.
  • Expect NOx fluctuations with humidity and temperature changes, requiring ongoing monitoring and tuning.

For expert assistance in burner tuning, emissions management, and seasonal adjustments, contact our experts.