APPLICATION OF AN LES BASED CFD CODE TO SIMULATE COAL AND BIOMASS COMBUSTION IN GENERAL REACTOR CONFIGURATIONS A. Suo-Anttila, J. D. Smith, and L.D. Berg, SAS, Inc. and J.P. Goldring, RJM International 9th European Conference on Industrial Furnaces and Boilers Estoril, Portugal www.cenertec.pt/infub April 26-29, 2011
Slide 2 OUTLINE • Introduction • LES Based Code Background • Code Validation and Application • Plant Burner Simulation • Observations and Conclusions 4/28/2011 9th European Conference on Industrial Furnaces and Boilers Estoril, Portugal
Slide 3 SAS/RJM Capabilities • Site survey and testing to quantify plant performance • Analyze and Recommend “Best” NOx abatement strategies – Over Fire Air (OFA) – Burners Out of Service (BOOS) – Low NOx Burners – SCR and SNCR systems – CFD modeling to identify “minimum cost” strategy • Combustion air supply – CFD model complex ductwork to balance flow – Physical modeling to “fix” flow/particle mal-distribution • Coal blending analysis • Fuel conversion analysis • Multi-fuel modeling of combustion systems – natural gas, refinery gases, landfill gases, #2 & #6 fuel oil, bio-oil, sub- bituminous/bituminous/lignite coals, bio-mass 4/28/2011 9th European Conference on Industrial Furnaces and Boilers Estoril, Portugal
Slide 4 Code Background: General Comments • Transient conservation equations with radiative heat transfer and combustion chemistry • Considers soot formation and other multi-phase systems using Eulerian/Eulerian formulation • Accurately assess different operation scenarios (wind, flow rate, fuel type, surroundings) • Reasonable CPU time requirements on “standard” workstation • Trade offs for “Engineering” Approach – Sacrifice generality (large fires only) in favor of quick turnaround with quantitative accuracy – Reaction rates and radiation heat transfer models apply best to optically thick fires – Models intended to make predictions “good-enough” for industrial use – Model validation for each application to establish accuracy of results 4/28/2011 9th European Conference on Industrial Furnaces and Boilers Estoril, Portugal
Slide 5 Gas Combustion Model * • Variant of Said et al. (1997) turbulent flame model • Relevant Species (model includes relevant reactions) F = Fuel Vapor (from evaporation or flare tip) O2 = Oxygen PC = H 2 0(v) + CO 2 C = Radiating Carbon Soot IS = Radiating Intermediate Species • Eddy dissipation effects and local equivalence ratio effects • Reactions based on Arrhenius kinetics C and T A determined for all reactions * Coal combustion Model follows same outline but includes more reaction parameters 4/28/2011 9th European Conference on Industrial Furnaces and Boilers Estoril, Portugal
Slide 6 EBU-Finite Rate Combustion Formulation • Arrhenius rate model – Consumption of primary reactant increases on reactants mass fraction f Ri and temperature T in volume – Coefficients C and Activation Temperatures (T A ) determined for all reactions Where: A k = Pre-exponential Factor X 1 = Natural Gas Mol Frac X 2 = O2 Mol Frac E a = Activation Temperature T = Local Gas Temperature b, c, d = Global Exponents 4/28/2011 9th European Conference on Industrial Furnaces and Boilers Estoril, Portugal
Slide 7 Radiation Inside Large Fires • High soot volume fractions make large fires non-transparent (optically thick) which causes flame to radiate as a cloud (radiatively diffuse) • Fire volume defined where product-of-combustion (f pc ) mass fraction is greater than user specified minimum fraction (f min ), usually 6% or (f pc > f min ) • Flame edge (f flame edge ) where products of combustion volume fraction = minimum volume fraction Calculated flame surfaces from 3 time steps from validation against test 4/28/2011 9th European Conference on Industrial Furnaces and Boilers Estoril, Portugal
Slide 8 Code Validation - Test Facility Details 18.28 m 6.09 m 3.66 m 3.66 m 1 2 3 4 5 6 7 8 • 18.9 m diameter JP8 fuel pool LE L C R RE • Pipe suspended 0.6m above leeside Thermocouple Ring Locations of pool • Pipe axis perpendicular to Culvert Pipe predominant wind • Wind speed and direction measured 18.9-m diameter 2 and 10 m above the ground on two fuel pool upwind poles x θ z 30 m 30 m Predominant Wind Direction Southwest South Anemometer Anemometer Pole Pole 9th European Conference on Industrial Furnaces and Boilers Estoril, Portugal 4/28/2011
Slide 9 Model Validation: Computational Domain • 60 m square base; 15 m high • 16,500 elements, highly refined near pipe • Each pipe grid linked to 1-D conduction module (see next slide) L X = 60 m N X = 31 Y L Z = 60 m N Z = 28 X Z Wind direction L Y = 15 m N Y = 19 Pool Location Pipe 9th European Conference on Industrial Furnaces and Boilers Estoril, Portugal 4/28/2011
Slide 10 Code Validation –Predicted vs Measured Top Top 1700 1700 Predicted Data 1500 1500 Wind Top Lee Top 1300 Wind Top Lee Top 1300 1100 1100 900 900 700 700 500 left end 500 left Wind 300 Leeward Wind 300 Leeward middle right Left End right end Left Center Right Right End Wind Bot Lee Bot Wind Bot Lee Bot Bottom Bottom • Coolest near the top, hottest on leeside: caused by flame tilt and downstream recirculation zone • Nearly uniform at each axial position • Predicted max temperature closer to ground than measured data 9th European Conference on Industrial Furnaces and Boilers Estoril, Portugal 4/28/2011
Slide 11 Applications of C3d: Elevated Flare Ignition • Nominal Firing Rate = 350 Tons Per Hour (TPH) • Max Firing Rate – 1350 TPH • Mostly Natural Gas (Mwt = 18) • Experienced Pressure Wave during ignition • Conducted Tests to quantify ignition phenomena: − Microphones used to measure pressure wave − High Speed Video used to capture flame during ignition • Test results reported elsewhere (summarized below) • Test video shows ignition behavior 9th European Conference on Industrial Furnaces and Boilers Estoril, Portugal 4/28/2011
Slide 12 Coal/Biomass Validation Test • Primary Inlet – Coal flow = 2.835e-3 kg/sec – Air flow = 6.228e-3 kg/sec – Gas Temperature = 300 K • Secondary Inlet (co-annulus) – Air flow = 0.019 kg/sec – Gas Temperature = 589 K • Reactor – Refractory lined – Flanged sections (20 cm ID x 30 cm long • Outlet – Constricted/cooled exit – Assume Constant pressure in model to allow unrestricted exit of particles/gases 4/28/2011 9th European Conference on Industrial Furnaces and Boilers Estoril, Portugal
Slide 13 Test Reactor Geometry and Mesh Model assumptions: Computational grid size & cell number Turbulence model (zero equation and one-equation LES) Numerical upwind and central differencing using TVD scheme Hydrostatic pressure on outlet boundary (allow free exit of particles/gases) Initial Primary gas temperature and composition set to 300 K air 4/28/2011 9th European Conference on Industrial Furnaces and Boilers Estoril, Portugal
Slide 14 Coal Combustion Reaction Model • Reaction Coefficient selected as providing “best” fit to Combustion Data from ASAY Case • 8 Reactions involving 11 Species Considered: – Fine Particles ( FCP ) – Coarse Particles ( CCP ) – Volatile Organic Hydrocarbons from the devolatilization process ( VOC ) – Partially Devolatilized Fine Particles ( PDFP ) – Partially Devolatilized Coarse Particles ( PDCP ) – Soot Particles ( Soot) – Fine Char Particles ( FP char ) – Coarse Char Particles ( CP char ) – Ash ( Ash ) – Oxygen ( O2 ) – Products of Combustion ( PC ) 4/28/2011 9th European Conference on Industrial Furnaces and Boilers Estoril, Portugal
Slide 15 Coal/Biomass Combustion Mechanism (1) 1-Fine Coal Particles ( FCP ) undergo fast devolatilization: 1.0 FCP 0.5 VOC + 0.5 PDFP Activation temperature = 12,581 K; Pre-exponential coefficient = 1.0e11 sec -1 2-Partially Devolatilized Fine Coal Particles ( PDFP ) undergo slow devolatilization: 0.5 PDFP 0.2 VOC + 0.3 FP char Activation temperature = 12,581 K; Pre-exponential coefficient = 1.0e7 sec -1 3-Fine Char Particle ( FP char ) combustion uses global combustion form: 0.3 FP char + 0.72 O2 0.7 PC + 0.05 Ash Activation temperature = 7,337 K; Pre-exponential coefficient = 1.4e7 sec -1 ; Oxygen exponent = 0.5, Char particle exponent = 0.33; Temperature exponent = 0.6 4-Coarse Coal Particles (CCP) undergo fast devolatilization: 1.0 CCP 0.2 VOC + 0.8 PDCP Activation temperature = 12,581 K; Pre-exponential coefficient = 1.0e8 sec -1 . 4/28/2011 9th European Conference on Industrial Furnaces and Boilers
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