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Gas Turbine Combustion Systems

Gas Turbine Combustion Systems. Recap Problem solutions. Ideal case: T2 = 579 K, T4 = 699 K, Wc = 280.6 kJ/kg, Wt = 654 kJ/kg, BWR = 0.43, =0.48 Actual case: T2’ = 624.7 K, T4’ = 579.2 K, Wc = 326.3 kJ/kg, Wt = 582.1 kJ/kg, BWR = 0.56, =0.35 Recuperator case: T5 = 741.57 K, =0.42.

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Gas Turbine Combustion Systems

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  1. Gas Turbine Combustion Systems

  2. Recap • Problem solutions Ideal case: T2 = 579 K, T4 = 699 K, Wc = 280.6 kJ/kg, Wt = 654 kJ/kg, BWR = 0.43, =0.48 Actual case: T2’ = 624.7 K, T4’ = 579.2 K, Wc = 326.3 kJ/kg, Wt = 582.1 kJ/kg, BWR = 0.56, =0.35 Recuperator case: T5 = 741.57 K, =0.42 • Effect of Pr

  3. Role of Combustor

  4. Main Job of the Combustor • Raise the temperature of the compressed air to the highest value the turbine can handle, with the smallest hot spots possible and within the prescribed radial profile.

  5. Annular Combustor

  6. Combustor Configurations MULTIPLE CANS TUBO-ANNULAR ANNULAR

  7. Combustor Types - can annular • CAN-ANNULAR: multiple, single burners (“cans”) evenly spaced around the rotor shaft. • Less efficient, more complex (more parts), expensive, easier to field replace

  8. Combustor Types : Can or Silo Combustor

  9. Combustor Types -Annular Combustor Combustor Liner Injector shaft • ANNULAR: toroidal, single assembly burner where rotor shaft passes through the center • aerodynamic, compact, inexpensive, harder to field replace

  10. Factors for the selection of configuration • Cooling challenges • Pressure loss • Temperature profile • Development Cost • Manufacturing cost • Testing facility • Maintainability in the field • Achieving low NOx with catalytic methods

  11. The fuel injector • Used to introduce fuel into the combustion chamber. • Can be for single or dual fuel • Fuel can be mixed with combustion air either… • in the combustor (standard combustion system) • pre-mixed prior to entering combustor ( lean pre-mix, DLN (dry-low-Nox), DLE (dry low emissions), SoLoNOx) Dry-Low-NOx injector Pre-Mix Barrel Standard injector Conventional vs Lean premixed system injector

  12. GAS FUEL WATER LIQUID FUEL MIDDLE SWIRLER (Atomizing) AIR MIXING LIP GAS LIQUID CENTRAL SWIRLER (Atomizing) AIR CENTRAL SWIRLER(Radial Flow) OUTER SWIRLER Typical Dual Fuel Injector

  13. Flame stabilization Low pressure region

  14. Combustion efficiency Denominator can be estimated as Heating Value When combustion reactions take place, the chemical bonds between the elements of the fuel/oxidant molecules are broken and new chemical bonds between the fuel and oxidant atoms are established. The difference in bond energies between the reactant and product bonds is released as the heat of the reaction.

  15. Heat of Combustion

  16. Combustor Design Criteria • Reliable Ignition • Proper fuel/air mixing w/ excess available air • Sufficient transient chemical reaction time • Good Combustion/flame Stability • High Combustion Efficiency • Low Smoke • Satisfactory Emissions Levels • Minimum Pressure Loss • Satisfactory Exit Temperature Profile • Low Oscillations • Combustion of wide range of fuels • Life

  17. Caution • Systems not (always) adiabatic • Heat Loss • Gas Compositions Change • Gas Composition not known or incomplete

  18. Why is Combustor Design so Challenging? Many different phenomena to consider: • Aerodynamics • Hydrodynamics • Chemical Reactions • Heat Transfer • Mechanical Durability

  19. Some Combustion fundamentals • Equivalence ratio, Air/Fuel ratio • Diffusion flame and premixed flame • Laminar flame and turbulent flames • Flamespeed • Autoignition Delay times • Adiabtaic flame temperature • Heat of combustion • Heat of vaporization • Liquid fuel atomization • Flame stabilization • Flash back, blow out, flammability limits

  20. Some definitions Equivalence ratio or Air/Fuel ratio Measure of mixture richness or lean-ness CxHy + a (O2 + 3.76 N2) → x CO2 + (y/2) H2O + 3.76a N2 a = (x+y/4) Do calculations for Methane

  21. Some definitions Flame A flame is a self-sustaining propagation of a localized combustion zone at subsonic velocities. Flame speed Flame speed is the rate at which an observer riding with the flame would experience the unburnt mixture approaching the flame. Flows in the gas turbine combustors are turbulent, hence turbulent flame speeds are relevant. Flashback Flashback occurs when the flame travels upstream wherever partially premixed fluid elements have residence times longer than the chemical reaction times, for instance in wall boundary layers or wake regions. Blowout Flame blowout can occur if the flame speed through the burning front is less than the local bulk fuel velocity. To maintain flame stability at a point the velocity of the fuel-oxidizer mixture must be within the flame-propagation speed to prevent blowout. Autoignition delay time Autoignition delay time is defined as the time interval between the creation of a combustible mixture and the onset of flame

  22. Some definitions Flammability Limits A fuel-oxidizer mixture is only flammable within a limited range of compositions. The most relevant for safety purposes is the lower flammability limit, which indicates the fuel vapor concentration that should not be exceeded, in order to avoid any explosion hazard. Heat of formation The standard enthalpy of formation "standard heat of formation" of a compound is the change of enthalpy that accompanies the formation of 1 mole of a substance in its standard state from its constituent elements in their standard states (the most stable form of the element at 1 bar of pressure and the specified temperature, usually 298.15 K or 25 degrees Celsius). Its symbol is ΔHfO. Adiabatic Flame Temperature Adiabatic flame temperature is defined as the equilibrium temperature attained on completely reacting fuel / air mixture without any heat loss.

  23. Combustion Chemistry

  24. H H H H O O O + C + Energy H H O O O O O H C H + => Methane Oxygen Water Carbon Dioxide CH4 + 2O2 => 2H20 + CO2 + Energy Good OK? Very Good Combustion Reactions Desired Exothermic

  25. In reality combustion chemistry is a complex system IMPORTANT ELEMENTARY STEPS : 1. Fuel attack by radicals 2. H+O2→OH+O 3. OH+H2 →H2O+H 4. H+O2+M→HO2+M 5. OH+CO→CO2+H • Types of elementary reactions • Initiation • Chain propagation or branching • Termination

  26. An example from my Ph.D. thesis for ethanol flames PARTIALLY PREMIXED FLAME NONPREMIXED FLAME (XF=0.3, plug-flow strain rate 100 1/s) (φ = 2.3, plug-flow strain rate 100 1/s) C2H5OH + 3 O2 → CO2 + H2O + Heat ?

  27. PARTIALLY PREMIXED FLAME N2/3 O2 H2O C2H5OH CO CO2 H2

  28. PARTIALLY PREMIXED FLAME T C2H2+C2H4 CH4 NO*100 C2H6 • Peak Concentrations of • Soot Precursors 16000 ppm • NOx 40 ppm • Acetaldehyde 5000 ppm • Ketene 1600 ppm

  29. NONPREMIXED FLAME C2H5OH N2/3 O2 H2O CO2 H2 CO

  30. NONPREMIXED FLAME T C2H2+C2H4 CH4 NO*200 C2H6 • Peak Concentrations of • Soot Precursors 20000 ppm • NOx 25 ppm • Acetaldehyde 4000 ppm • Ketene 700 ppm

  31. FUEL CONSUMPTION ROUTES Soot precursor aldehyde soot/GHG prompt NOx Partially Premixed Flame, P = 1 atm, Φ = 2.3, Plug-flow strain rate = 100 1/s

  32. CHEMICAL-KINETIC MECHANISM A Sample from San Diego Mech !ETHANOL (C2H5OH) REACTIONS 1. C2H5OH(+M) = CH3 + CH2OH(+M) 5.0E+15 0.0 82000 (This study) LOW /3E+16 0.0 58000/ TROE/ 0.5 1E-30 1E+30 / H2/2.00/ H2O/6.00/ CO/1.50/ CO2/2.00/ CH4/2.00/ AR/ .70/ 2. C2H5OH(+M) <=> C2H4 + H2O(+M) 8.0E+13 0.0 65000 (This study) LOW /1E+17 0.0 54000/ TROE/ 0.5 1E-30 1E+30 / H2/2.00/ H2O/6.00/ CO/1.50/ CO2/2.00/ CH4/2.00/ AR/ .70/ 3. C2H5OH + OH <=> CH2CH2OH + H2O 1.81E+11 0.4 717.0 (Li) 4. C2H5OH + OH <=> CH3CHOH + H2O 3.09E+10 0.5 -380.0 (Li) 5. C2H5OH + OH <=> CH3CH2O + H2O 1.05E+10 0.8 717.0 (Li) 6. C2H5OH + H <=> CH2CH2OH + H2 1.9E+07 1.8 5100.0 (Li) 7. C2H5OH + H <=> CH3CHOH + H2 2.58E+07 1.6 2830.0 (Marinov) 8. C2H5OH + H <=> CH3CH2O + H2 1.5E+07 1.6 3040.0 (Marinov) 9. C2H5OH + O <=> CH2CH2OH + OH 9.41E+07 1.7 5460.0 (Marinov) 10. C2H5OH + O <=> CH3CHOH + OH 1.88E+07 1.9 1820.0 (Marinov) 11. C2H5OH + O <=> CH3CH2O + OH 1.58E+07 2.0 4450.0 (Marinov) 12. C2H5OH + CH3 <=> CH2CH2OH + CH4 2.19E+02 3.2 9620.0 (Marinov) 13. C2H5OH + CH3 <=> CH3CHOH + CH4 7.28E+02 3.0 7950.0 (Marinov) 14. C2H5OH + CH3 <=> CH3CH2O + CH4 1.45E+02 3.0 7650.0 (Marinov) 15. C2H5OH + HO2 <=> CH3CHOH + H2O2 8.2E+03 2.5 10800.0 (Marinov) 16. C2H5OH + HO2 <=> CH2CH2OH + H2O2 2.43E+04 2.5 15800.0 (Li) 17. C2H5OH + HO2 <=> CH3CH2O + H2O2 3.8E+12 0.0 24000.0 (Li) Initiation/ Fuel Pyrolysis step H abstraction Initiation Reaction and Radicals Attack on Fuel molecule

  33. A Sample from San Diego Mech 18. C2H4+OH<=>CH2CH2OH 2.41E+11 0.0 -2380.0 (Li) 19. C2H5+HO2<=>CH3CH2O+OH 4.0E+13 0.0 0.0 (Li) 20. CH3CH2O+M<=>CH3CHO+H+M 5.6E+34 -5.9 25300.0 (Li) H2/2.00/ H2O/6.00/ CO/1.50/ CO2/2.00/ CH4/2.00/ AR/ .70/ (This study) 21. CH3CH2O+M<=>CH3+CH2O+M 5.35E+37 -7.0 23800.0 (Li) H2/2.00/ H2O/6.00/ CO/1.50/ CO2/2.00/ CH4/2.00/ AR/ .70/ (This study) 22. CH3CH2O+O2<=>CH3CHO+HO2 4.0E+10 0.0 1100.0 (Marinov) 23. CH3CH2O+CO<=>C2H5+CO2 4.68E+02 3.2 5380.0 (Marinov) 24. CH3CH2O+H<=>CH3+CH2OH 3.0E+13 0.0 0.0 (Marinov) 25. CH3CH2O+H<=>C2H4+H2O 3.0E+13 0.0 0.0 (Marinov) 26. CH3CH2O+OH<=>CH3CHO+H2O 1.0E+13 0.0 0.0 (Marinov) 27. CH3CHOH+O2<=>CH3CHO+HO2 4.82E+13 0.0 5020.0 (Li) 28. CH3CHOH+O<=>CH3CHO+OH 1.0E+14 0.0 0.0 (Marinov) 29. CH3CHOH+H<=>C2H4+H2O 3.0E+13 0.0 0.0 (Marinov) 30. CH3CHOH+H<=>CH3+CH2OH 3.0E+13 0.0 0.0 (Marinov) 31. CH3CHOH+HO2<=>CH3CHO+OH+OH 4.0E+13 0.0 0.0 (Marinov) 32. CH3CHOH+OH<=>CH3CHO+H2O 5.0E+12 0.0 0.0 (Marinov) 33. CH3CHOH+M<=>CH3CHO+H+M 1.0E+14 0.0 25000.0 (Marinov) H2/2.00/ H2O/6.00/ CO/1.50/ CO2/2.00/ CH4/2.00/ AR/ .70/ (This study) Hydorxy-ethyl and Ethoxy radical consumption Consumption of hydroxy-ethyl and ethoxy radical formed by H abstraction

  34. A Sample from San Diego Mech 34. CH3CHO<=>CH3+HCO 7.0E+15 0.0 81700.0 (Baulch et al.) 35. CH3CO(+M)<=>CH3+CO(+M) 3.0E+12 0.0 16700.0 (Warnatz) LOW / 1.2E+15 0.0 12500.0/ H2/2.00/ H2O/6.00/ CO/1.50/ CO2/2.00/ CH4/2.00/ AR/ .70/ (This study) 36. CH3CHO+OH<=>CH3CO+H2O 3.37E+12 0.0 -620.0 (Atkinson et al.) 37. CH3CHO+OH<=>CH2CHO+H2O 3.37E+11 0.0 -620.0 (Li) 38. CH3CHO+O<=>CH3CO+OH 1.77E+18 -1.9 2980.0 (Marinov) 39. CH3CHO+O<=>CH2CHO+OH 3.72E+13 -0.2 3560.0 (Marinov) 40. CH3CHO+H<=>CH3CO+H2 4.66E+13 -0.3 2990.0 (Marinov) 41. CH3CHO+H<=>CH2CHO+H2 1.85E+12 0.4 5360.0 (Marinov) 42. CH3CHO+CH3<=>CH3CO+CH4 3.9E-07 5.8 2200.0 (Marinov) 43. CH3CHO+CH3<=>CH2CHO+CH4 2.45E+01 3.1 5730.0 (Marinov) 44. CH3CHO+HO2<=>CH3CO+H2O2 3.60E+19 -2.2 14000.0 (Marinov) 45. CH3CHO+HO2<=>CH2CHO+H2O2 2.32E+11 0.4 14900.0 (Marinov) 46. CH3CHO+O2<=>CH3CO+HO2 1.0E+14 0.0 42200.0 (Marinov) 47. CH2CHO+H=CH3+HCO 5.0E+13 0.0 0.0 (Marinov) 48. CH2CHO+H=CH2CO+H2 2.0E+13 0.0 0.0 (Marinov) 49. CH2CHO+O=CH2O+HCO 1.0E+14 0.0 0.0 (Marinov) 50. CH2CHO+OH=CH2CO+H2O 3.0E+13 0.0 0.0 (Marinov) 51. CH2CHO+O2=CH2O+CO+OH 3.0E+10 0.0 0.0 (Marinov) 52. CH2CHO+CH3=C2H5+CO+H 4.9E+14 -0.5 0.0 (Marinov) 53. CH2CHO+HO2=CH2O+HCO+OH 7.0E+12 0.0 0.0 (Marinov) 54. CH2CHO+HO2=CH3CHO+O2 3.0E+12 0.0 0.0 (Marinov) 55. CH2CHO=CH3+CO 1.17E+43 -9.8 43800.0 (Marinov) Acetaldehyde Vinoxy radical San Diego Mech: http://maeweb.ucsd.edu/~combustion/cermech/

  35. Egolfopoulos (1992) Ethanol Autoignition Delay Times and Laminar Flame Speeds

  36. Combustion Process

  37. Combustion Concepts 70% AIRFLOW 30% 3600°F Conventional Same Turbine Inlet Temp FUEL FUEL Lean-Premixed 2800°F 60% 40% AIRFLOW

  38. Mars Engine Configuration SoLoNOx Conventional • Modifications to Combustion / Controls Systems • Remainder of Engine Unchanged

  39. SoLoNOx 18.0 in. 14.5 in. Conventional Conventional vs SoLoNOx Combustion Systems

  40. Conventional Lean Premixed Lean Limit FLAME TEMPERATURE Part Load Gas Prod. Turbine Inlet Lean Rich FUEL / AIR RATIO Low NOx Combustion

  41. Desired Operating Range CO and UHC NOx Emissions Stoichio- Metric Mixture Lean Rich Fuel/Air Ratio Combustion System Emissions Characteristics

  42. DILUTION AIR PRIMARY ZONE SECONDARY ZONE DILUTION ZONE

  43. Combustion air/fuel flow Fuel T5 Thermocouple injector

  44. Annular Combustor Design Centerline Gas Temperature Temperature Average combustor exit temperature Axial distance

  45. Radial Profile Tip Turbine Blade Root

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