Burner.wiki

Burner Types by Emission Control

Environmental regulations (such as MCPD in Europe or SCAQMD in California) strictly limit Nitrogen Oxide (NOx) emissions. Burners are categorized by their ability to suppress thermal NOx formation.

1. Standard Burners

  • NOx Levels: Typically 100 - 200 mg/Nm³ (Natural Gas).
  • Technology: Simple diffusion flame. High peak flame temperatures (>1600°C) cause nitrogen in the air to react with oxygen, forming thermal NOx.
  • Status: Obsolete in regulated markets; still used in regions with lax environmental laws.

2. Low NOx Burners (LNB)

  • NOx Levels: Typically < 80 mg/Nm³ or < 60 mg/Nm³ (Europe Class 3).
  • Technology:
    • Air Staging: Air is supplied in two streams (primary and secondary). This creates a fuel-rich primary zone (too little O2 for NOx) and a fuel-lean secondary zone (too cool for NOx).
    • Fuel Staging: Fuel is injected at different points to create a similar effect.
    • Internal Flue Gas Recirculation (iFGR): The burner head geometry induces furnace gases to mix with the flame, lowering the temperature.

Solutions

The standard choice for most new industrial boilers in Europe and China. Good balance of cost and performance.

3. Ultra-Low NOx Burners (ULNB)

  • NOx Levels: < 30 mg/Nm³ (Standard) or < 9 ppm (< 18 mg/Nm³).
  • Technology:
    • External Flue Gas Recirculation (FGR): A pipe ducts exhaust gas from the stack back into the burner air intake (typically 10-20% volume). This inert gas acts as a heat sink, drastically reducing flame temperature.
    • Fiber Mesh / Surface Combustion: Gas and air premix and burn on the surface of a metal fiber mesh. The flame is short, blue, and very cool, producing minimal NOx.
    • Steam Injection: Steam is injected into the flame to cool it (common in oil firing).

Solutions

Required in California (SCAQMD), Beijing, and other strict air quality control districts.

  • Trade-offs: ULNBs often have lower turndown ratios (e.g., 3:1 or 4:1) and require higher electrical power (larger fan motors) to push the FGR.

4. SCR Systems (Post-Combustion)

While not a burner type, Selective Catalytic Reduction (SCR) is the next step when burners alone cannot meet limits (e.g., < 5 mg/Nm³).

  • Process: Ammonia or Urea is injected into the exhaust stream, passing through a catalyst to convert NOx into N2 and water.
  • Application: Large power plants and waste-to-energy facilities.