Low NOx combustion concepts

1
Low NOx combustion concepts

• Lean burning
• DLN (Dry, low NOx)
• Key issues turndown, combustion instability,
  blowoff, flashback (in higher H2 applications)
• LPP (Lean, premixed, prevaporized)
• Key issues same as above, autoignition
• Rich burning
• RQL (rich burn, quick quench, lean burn)
• Key issues soot, quench mixers
• Catalytic
• Low temperature catalytic combustion
• Key issues cost, catalyst durability

1000
100
NOx
10
1
1.5
1.0
0.5
1000
100
NOx
10
1
1.5
1.0
0.5
Equivalence ratio
2
Combustor ConfigurationsRich burn, quick quench,
lean burn (RQL)

• Rich head end
• Mixture quickly mixed with excess air
• Lean burn downstream
• Realized to some extent in many conventional
  combustors
• Intensive development by PW

Fuel
High NOx Route
Lean zone
Rich zone
Air
1000
Quench zone
100
NOx
10
Low NOx Route
1
Source A. Lefebvre, Gas Turbine Combustion
1.5
1.0
0.5
Equivalence ratio
3
Combustor ConfigurationsGround based -
Nonpremixed

• Water/steam injection used for NOx control

Source A. Lefebvre, Gas Turbine Combustion
4
Combustor ConfigurationsGround Based - Dry, Low
NOx (DLN) Systems

• Premixed operation
• If liquid fueled, must prevaporize fuel (lean,
  premixed, prevaporized, LPP)
• Almost all air goes through front end of
  combustor for fuel lean operation little
  available for cooling
• Multiple nozzles required for turndown

Source A. Lefebvre, Gas Turbine Combustion
5
Emissions

• NOx Reactions with nitrogen in air and/or fuel
• CO Incomplete or rich combustion
• UHC Incomplete combustion
• SOx sulfur in fuel (jet fuel, coal)
• Particulates (soot, smoke)
• CO2? Major project of hydrocarbon combustion

Source A. Lefebvre, Gas Turbine Combustion
6
Pollutant Trends, CO

• Rich flames large amounts formed due to
  insufficient oxygen to react fuel to CO2
• Lean flames incomplete combustion
• Low power, low temperature operation

From A. Kendrick, et al, ASME-GT-2000-0008
Source A. Lefebvre, Gas Turbine Combustion
7
Pollutant Trends, NOx

• Primarily formed at high temperatures (gt1800 K),
  due to reaction of atmospheric oxygen and
  nitrogen
• Water/steam injection used to cool flame in
  nonpremixed combustors
• Fuel lean operation to minimize flame temperature
  is a standard strategy in DLN combustors

Source A. Lefebvre, Gas Turbine Combustion
8
Pollutant Trends, Particulates

• Manifested as visible smoke
• Due to carbon particles
• Minimization requires eliminating fuel rich
  pockets, fuel/air premixing