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(Paper #GT-2002-30414)

RAI Conference Center Amsterdam, Holland June 3-6, 2002. F. BOZZA, M.C. CAMERETTI, R. TUCCILLO Dept. of Mechanical Engineering (DIME) University of Naples “Federico II”, ITALY. The Employment of Hydrogenated Fuels From Natural Gas Reforming: Gas Turbine and Combustion Analysis.

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(Paper #GT-2002-30414)

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  1. RAI Conference Center Amsterdam, Holland June 3-6, 2002 F. BOZZA, M.C. CAMERETTI, R. TUCCILLODept. of Mechanical Engineering (DIME) University of Naples “Federico II”, ITALY The Employment of Hydrogenated Fuels From Natural Gas Reforming: Gas Turbine and Combustion Analysis (Paper #GT-2002-30414)

  2. ASME Turbo Expo 2002, Paper #GT-2002-30414 Bozza, et al., DIME, Napoli, The Employment of Hydrogenated Fuels ... Pag.2 Introduction • The University of Naples has been involved in a research project related to the reduction of CO2 emission in Gas Turbine based power plants • Several solutions have been proposed in current literature. Many of them have been analyzed by means of 1st and 2nd-Law based thermodynamicapproaches • Methods for CO2 abatement: • Separation from exhausts by chemical or physical absorption • Recycled or Semi-closed cycles, with CO2 as working fluid • Fuel Decarbonization prior to combustion (reforming): • Partial Oxidation • Steam Reforming • Auto-Thermal Reforming (combination of previous two) • Shift Reactions

  3. ASME Turbo Expo 2002, Paper #GT-2002-30414 Bozza, et al., DIME, Napoli, The Employment of Hydrogenated Fuels ... Pag.3 Introduction • Apart from the advantages and drawbacks of each proposal: • Each solution requires modification in the plant configuration, which can induce large variations in component operation • In the case of decarbonization, the reformed fuel composition and the varied LHV can affect the reaction process in the existing combustor • Thermodynamic analyses cannot account for those effects • Our contribution in the research project was then to perform a more accurate analysis of the Low-CO2 power plant, through: • Thermodynamic analysis of the plant, as a preliminary step • Matching analysis of the several components, by employing the performance maps of the existing turbomachines • CFD analysis of the combustor, supplied with both the natural gas and the decarbonized fuel

  4. ASME Turbo Expo 2002, Paper #GT-2002-30414 Bozza, et al., DIME, Napoli, The Employment of Hydrogenated Fuels ... Pag.4 Background • Decarbonization through Partial Oxidation was analyzed in a previous paper at the same conference (ASME 2001-GT-0066) • Flows through the oxider were simply synthe-sized with literature derived ratios, to obtain: • Air extraction flow for Nat.Gas reforming • Decarb. Fuel flow feedingtheCombustor • A water intercooled / recuperated cycle was alsoconsidered Constant Data

  5. ASME Turbo Expo 2002, Paper #GT-2002-30414 -184.47 Bozza, et al., DIME, Napoli, The Employment of Hydrogenated Fuels ... Pag.5 Background Detailed equilibrium calculations of Partial Oxidation and shift reactions lead to a ~50% H2-N2, Low-LHV Decarbonized Fuel, as in ASME 2000-GT-0163 by Lozza and Chiesa: CO2 and NOX Emission are both reduced but GT efficiency also decreases of about 7-8%

  6. ASME Turbo Expo 2002, Paper #GT-2002-30414 Bozza, et al., DIME, Napoli, The Employment of Hydrogenated Fuels ... Pag.6 Objectives • Alternative Solution: Decarbonization through Steam Reforming (a minor GT efficiency decrease is expected) • Refinement of the analysis: • Mass and Energy Flows through the reformer are now directly evaluated in the whole GT operating range • Different reforming conditions (Temp., Steam/NG ratio, etc.) can be now analyzed: • Higher Reformer Temp. More complete decarboniz. Higher H2 content  Higher NOX • A CO2-NOXtrade-off exists

  7. ASME Turbo Expo 2002, Paper #GT-2002-30414 Bozza, et al., DIME, Napoli, The Employment of Hydrogenated Fuels ... Pag.7 GT with Steam Reforming Steam is mainly produced by the heat released by the “Shift 1” reactor Additional steam (if required) is produced in a conventional HRSG High Temp. level in the reformer is maintained by GT exhaust flow Additional heat is providedbyburning a fraction of the DF fuel The remaining fraction is then compressed and injected in the existing GT combustor

  8. ASME Turbo Expo 2002, Paper #GT-2002-30414 Bozza, et al., DIME, Napoli, The Employment of Hydrogenated Fuels ... Pag.8 GT with Steam Reforming A typical industrial GT (PGT25) is considered in the example of a CO2 removal strategy for an existing power plant Variation on GT load conditions impact on heat and steam required in the reforming section Is the energy conversion system self-sustainable in each operating condition? What about performance and emissions?

  9. ASME Turbo Expo 2002, Paper #GT-2002-30414 Bozza, et al., DIME, Napoli, The Employment of Hydrogenated Fuels ... Pag.9 Thermodynamic and Matching Analyses • Main features of the methodology: • Access to the compressor performance map and direct mean-line analysis of both HP and LP turbines provides cycle parameters for thermodynamic analysis • Accurate evaluation of various fluid properties (Janaf Tables) • Estimation of turbine cooling flow requirements and cooled expansion patternfor an assigned metal blade temperature • Integration of the reforming process with the GT operation • Inclusion of a reliable thermo-kinetic procedure for the computation of theThermal NO emission, accounting for: • Overall residence time inside the combustor • Air flow rate distribution in the various combustor zones • Thermo-chemical conditions of the reacting mixture

  10. Matching Analysis ASME Turbo Expo 2002, Paper #GT-2002-30414 Running Lines Pressure Ratio NG DF 500 DF 700 NG DF 500 DF 700 Turb. Inlet Temp., K Pressure Ratio Air Flow Rate, kg/s Natural Gas Flow, kg/s Bozza, et al., DIME, Napoli, The Employment of Hydrogenated Fuels ... Pag.10 Quite overlapping Running Lines (6500 LP turbinespeed) are obtained when varying the reforming temperature Cycle Parameters are only slightly affected, especially at low load

  11. ASME Turbo Expo 2002, Paper #GT-2002-30414 NG DF 500 DF 700 NG DF 500 DF 700 GT Mech. Output, kW 2nd Law 1st Law Efficiency Natural Gas Flow, kg/s Natural Gas Flow, kg/s Bozza, et al., DIME, Napoli, The Employment of Hydrogenated Fuels ... Pag.11 Matching Analysis Slightly better operation is found for DF 500 at high load More relevant variations (4-8%) are computed for 2nd Law Efficiency at each load, for both DF 500 and DF 700

  12. ASME Turbo Expo 2002, Paper #GT-2002-30414 NG DF 500 DF 700 DF 500 Fuel Flow, kg/s DF 700 Natural Gas Flow, kg/s Bozza, et al., DIME, Napoli, The Employment of Hydrogenated Fuels ... Pag.12 Matching Analysis 500 C reformer temperature requires small afterburning Nat. Gas Total DF produced Reformer Inj. DF GT injected DF This low-temperature combustion penalizes DF7002nd Law Effic.

  13. ASME Turbo Expo 2002, Paper #GT-2002-30414 Total Steam Flow required for NG reforming (NG/Steam=3.095) Additional HRSG Steam Fuel Flow, kg/s Shift1 Steam DF 500 Shift1 Steam DF 700 Cooler Steam CoolerSteam Natural Gas Flow, kg/s Bozza, et al., DIME, Napoli, The Employment of Hydrogenated Fuels ... Pag.13 Matching Analysis 500 C reformer temp. requires additional HRSG Steam A lower exergy flow remains then available in the exhaust gas This explains DF500 2nd Law Efficiency decrease

  14. Matching Analysis ASME Turbo Expo 2002, Paper #GT-2002-30414 DF700 EINO DF500 NG NG DF500 EICO2 DF700 Bozza, et al., DIME, Napoli, The Employment of Hydrogenated Fuels ... Pag.14 Existing turbo-machineryadapt well to the new fuels Limited 1st Law Efficiency Drop(only at low load) Relevant 2nd Law Efficiency drop (at each load) NOX-CO2 Trade-Off

  15. ASME Turbo Expo 2002, Paper #GT-2002-30414 Bozza, et al., DIME, Napoli, The Employment of Hydrogenated Fuels ... Pag.15 CFD Analysis • Second question to be answered: • Can the ‘existing’ Combustor be supplied with the large H2 contents in the Decarb. Fuel? What about Combustion Efficiency and NO emission? • A CFD analysis is required. Main features of the CFD analysis: • The KIVA3 code (Unsteady N-S eqs. ALE method) is employed • An accurate 3D geometrical representation of both combustion chamber, liner and dilution holes is available • Annular type chamber: only a 12° 3D periodical sector needs to be meshed and solved (30 air swirlers and 30 fuel injectors)

  16. ASME Turbo Expo 2002, Paper #GT-2002-30414 Bozza, et al., DIME, Napoli, The Employment of Hydrogenated Fuels ... Pag.16 CFD Analysis CAD Output of the 12° periodical sector Numerical Mesh: (ICEM code) 60000 nodes Liner, Secondary and Dilution holes layout

  17. ASME Turbo Expo 2002, Paper #GT-2002-30414 Bozza, et al., DIME, Napoli, The Employment of Hydrogenated Fuels ... Pag.17 CFD AnalysisBoundary Conditions • Main features of the methodology (cont’d): • Intake flow surface and flow areas are of the ‘continuous inflow’ type; outlet section is a ‘continuous outflow’ boundary • Operating points at constant natural gas input, as derived by the previous matching procedure, provide the total inlet pressure and temperatures, and the static outlet pressure • Inlet air and fuel flow velocities are computed in agreement with input datafrom matching analyses • The existing swirlers are replaced by a swirled intake air (constant flow angle: 60°). The same average velocity of the fuel jet (full cone, 30°) was assumed for both NG and DF fuel. Nozzle flow areas are accordingly scaled

  18. ASME Turbo Expo 2002, Paper #GT-2002-30414 Two-step eqs. for Methane (NG) oxidation: One-step eq. for Hydrogen(DF) oxidation: Bozza, et al., DIME, Napoli, The Employment of Hydrogenated Fuels ... Pag.18 CFD Analysis Sub-Models • Main features of the methodology (cont’d): • Turbulence model: classical - approach • Kinetic mechanism for fuel combustion:

  19. ASME Turbo Expo 2002, Paper #GT-2002-30414 Bozza, et al., DIME, Napoli, The Employment of Hydrogenated Fuels ... Pag.19 CFD Analysis Sub-Models • Main features of the methodology (cont’d): Kinetically controlled reaction rate: Turbulent mixing-controlled reaction rate: (Magnussen Model) Actual reaction rate: Thermal NO formation model: simultaneous solution (predictor-corrector scheme) of the kinetic equations of the extended Zel’dovich mechanism

  20. Temperature, K (exit section) ASME Turbo Expo 2002, Paper #GT-2002-30414 Thermal NO, ppm (exit section) Steady Solutions DF700 DF500 NG DF 500 DF 700 NG Computational Cycle Computational Cycle Bozza, et al., DIME, Napoli, The Employment of Hydrogenated Fuels ... Pag.20 CFD Analysis Convergence History Time-marching computation Higher temperatures and NO levels with DF Fuels

  21. ASME Turbo Expo 2002, Paper #GT-2002-30414 Max Temp. (A) (C) (B) Mean Temperature Combustor NG DF 500 DF 700 (B) (C) (A) Axial Distance, cm Bozza, et al., DIME, Napoli, The Employment of Hydrogenated Fuels ... Pag.21 CFD Analysis (A)Sharp temperature rise inside primary zone (B)Combustion completion sustained by secondary air supply (C)Flame extinguishment due to dilution air flow

  22. ASME Turbo Expo 2002, Paper #GT-2002-30414 1st secondary holes Inlet Section 2nd dilution holes Meridional plane Bozza, et al., DIME, Napoli, The Employment of Hydrogenated Fuels ... Pag.22 CFD Analysis • Gas flow field in the combustor (Natural Gas): Liner

  23. ASME Turbo Expo 2002, Paper #GT-2002-30414 NG DF500 DF700 Bozza, et al., DIME, Napoli, The Employment of Hydrogenated Fuels ... Pag.23 CFD Analysis T, K Temp. distribution in the meridional plane Higher temperature zones are localized at the periphery of the fuel jet and inside flame plume in the DF 700

  24. ASME Turbo Expo 2002, Paper #GT-2002-30414 NO, ppm NG DF700 Bozza, et al., DIME, Napoli, The Employment of Hydrogenated Fuels ... Pag.24 CFD Analysis Meridional Plane NO distribution:NO levels are consistent with both local temperatures peaks previously shown andthe air presence at the interface between secondary and the dilution zones

  25. ASME Turbo Expo 2002, Paper #GT-2002-30414 Bozza, et al., DIME, Napoli, The Employment of Hydrogenated Fuels ... Pag.25 CFD Analysis Exit Plane distributions Temperature, K NO Emission, ppm NG DF700 higher NO and temperature non-uniformities are detectable with DF 700

  26. ASME Turbo Expo 2002, Paper #GT-2002-30414 3D - CFD Combustor analysis Thermodynamic and component matching approach Integrated Procedure Bozza, et al., DIME, Napoli, The Employment of Hydrogenated Fuels ... Pag.26 Conclusion • The influence on Gas Turbine performance and emission of systems for CO2 abatement was analyzed in the whole GT operating range, by means of: • The results presented have shown that: • The existing plant components (turbomachinery and combustor) adapt well to high H2 contents decarbonized fuels • Thermal efficiency and overall mechanical outputof the GT power plant are not strongly affected (cont’d)

  27. ASME Turbo Expo 2002, Paper #GT-2002-30414 Bozza, et al., DIME, Napoli, The Employment of Hydrogenated Fuels ... Pag.27 Conclusion • Results (cont’d): • A decay in thermal efficiency is expected in gas-steam combined cycles, due to the estimated2nd law efficiency decrease (4-8% in the whole operating range) • The plant operation equipped with the steam reforming devices is almost self-sustained by an energetic point of view • The effect of an increasing reforming temperature emphasizes the typical trade-off between the CO2 reduction and the rise in thermal NO. This seems to be the most challenging problem for a practical utilization of strongly hydrogenated fuels Thanks for the Attention

  28. ASME Turbo Expo 2002, Paper #GT-2002-30414 Bozza, et al., DIME, Napoli, The Employment of Hydrogenated Fuels ... Pag.28

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