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Low NOx combustion concepts

Low NOx combustion concepts. Lean burning DLN (Dry, low NOx) Key issues: turndown, combustion instability, blowoff, flashback (in higher H 2 applications) LPP (Lean, premixed, prevaporized) Key issues: same as above, autoignition Rich burning RQL (rich burn, quick quench, lean burn)

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Low NOx combustion concepts

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  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 0.5 1.0 1000 100 NOx 10 1 1.5 0.5 1.0 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 P&W 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 0.5 1.0 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 (>1800 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

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