1st Oxy-fuel Combustion Conference, Cottbus, Germany - 09 / 09/ 09 Ig itio Cha acte istics of Si gle Ignition Characteristics of Single Coal Particles in Air (O2 /N2) and Oxy‐‐Fuel (O2 /CO Oxy / 2) Environments Zeenathul Farida Gani | T.F. Wall | Liza K. Elliot | Y.Liu | B.Moghtaderi Department of Chemical Engineering, The University of Newcastle, Callaghan, NSW 2308, Australia Priority Research Centre for Energy gy Outline 2 Introduction Hypothesis and Objectives Experimental Details Single Particle Flame Sheet Model Results Conclusions Priority Research Centre for Energy Oxy--fuel Combustion Technology Oxy 3 Recirculated Flue Gas (RFG) Steam to Turbine Steam to Turbine O2 from ASU Secondary Air Boiler Coal + Primary Air N2, CO2 , H2O Flue Gas Water in CO2 H2O Secondary RFG C l+ Coal Primary RFG Air Combustion Boiler Flue Gas Water in Oxy-fuel Combustion Combustion atmosphere – O2 and RFG (primarily CO2) Thermo‐physical properties of N Th h i l ti f N2 and CO d CO2 • • Specific heat capacity 1.6 times higher for CO2 Mass diffusivity Mass diffusivity 20% lower in CO2 Molina and Shaddix, Proceedings of Combustion Institute (31) 2007 Priority Research Centre for Energy Coal Particle Ignition g - Theory y Ignition Mechanism Volatile Flame volatiles homogeneous combustion CO2, H2O O2 coal coal particle heterogeneous combustion O2 4 CO2, H2O 1. Homogeneous Homogeneous Ignition Ignition ‐ Gas Phase oxidation 2. Heterogeneous Ignition ‐ Surface Oxidation S f O id i Devolatilization O2 I iti Ignition studies involve t di i l Measurement of minimum gas temperature (Tg) or time (ti) at which ignition occurs Tg and t d ti are usually accompanied by a measurable indicator which could be ll i db bl i di t hi h ld b 1. a rapid mass loss ( TGA) 2. monitoring the exit gas composition 3 Visual changes Light flash (common indicator in single particle experiment) 3. Visual changes – Light flash (common indicator in single particle experiment) Priority Research Centre for Energy Hypothesis yp & Objective j 5 Hypothesis “The ignition and devolatilization of coal particles in oxy-fuel (O2/CO2) environment are different from the conventional air (O2/N2)nenvironment. The differences in the bulk gas (N2 and CO2) properties have a major contribution towards the difference in ignition and devolatilization in O2/CO2 conditions. conditions.” Objectives • To develop a fundamental understanding on the ignition characteristics of To develop a fundamental understanding on the ignition characteristics of single coal particles in oxy‐fuel (O2/CO2) environment • To establish the differences in the ignition characteristics of single particles in air (O2/N2) and oxy‐fuel (O2/CO2) conditions • To measure and compare the particle temperatures under air (O2/N2) and oxy‐fuel (O2/CO2) conditions and to obtain the kinetic parameters oxy‐fuel (O ) conditions and to obtain the kinetic parameters Priority Research Centre for Energy Experimental SetupSetup- Entrained Flow Reactor with ith Optical diagnostics 6 Fibre Optic Cable Fibre Optic Cable Spectral Response 300‐ 800 nm VIS/NIR High Voltage supply High Voltage supply Lens US SB 2000+ Spectrometer Photo Multiplier Tube Cooling water out Cooling water in Cooling water outCooling water in Quartz Chimney Quartz Chimney y Char Combustion Region Char Combustion Region Trigger Amplifier Oxidizer in Oxidizer in Pulse Fuel in Fuel in Amplifier Timer Generator Trigger 0.00.001 Computer with Computer with Data Aquisition Data Aquisition Lens Volatile Combustion Region g Volatile Combustion Region Heating Region Heating Region Fuel in Fuel in Particle Detector Particle Detector CH4/H2 CH4/H2 O2/N2 or O2/CO2 O2/N2 or O2/CO2 P l i dC lP i l Pulverised Coal Particles Pulverised coal particles from Fluidised Bed Feeder from Fluidised Bed Feeder Priority Research Centre for Energy Coal Properties & Experimental conditions 7 Coals studied Parameter Condition 1. Sub‐Bituminous coal Particle size +180 ‐212 μm 2. Lignite Furnace Temperature 1550 oK Furnace gas CH4 ,H2 , O2 ,N2 / CO2 Carrier gas g N2 / CO2 Total flow rate 40 lpm Oxygen concentration in N2/CO2 10% to 50% v/v basis Coal Properties Wt % air dried basis Sub‐Bitum Lignite Proximate Analysis Moisture 8.0 11.1 A h Ash 19 7 19.7 54 5.4 Volatile Matter 25.6 47.8 Fixed Carbon 46.5 35.7 Carbon 57.03 56.3 Hydrogen 3.25 4.16 Spectrometer experiments – Coal & Prepared Char Temperature ‐ 1550 K O2 level – 10, 21, 30, 50% in N2/ CO2 Nitrogen 0.84 0.55 Prepared char – epa e c a Char prepared in DTF at 1200 K C a p epa e i a 00 Sulphur 0.17 0.96 Oxygen 10.81 21.43 Ultimate Analysis Ultimate Analysis PMT experiments ‐ Coal Temperature ‐ 1550 K O2 level – 10, 21, 30, 50% in N2/ CO2 Priority Research Centre for Energy Single g Particle Flame Sheet Model Heat of Reaction Gas (O2/N2) or (O2/CO2) Conductive Conductive Heat transfer Combustion Products Coal Particle rp Tp Radiative Heat transfer Particle heat up Devolatilization O2 volatiles 8 Char burnout rf εp =1 Schematic of flame sheet model Flame Sheet Priority Research Centre for Energy 9 RESULTS Priority Research Centre for Energy PMT Experiments 10 5 Intenssity 4 Volatile Combustion Time Char Burnout Time 3 Sub‐bituminous 180‐212 um 21% O2(O2/N2) 2 1 0 0 50 100 150 200 250 300 350 400 Residence Time (ms) Example of energy trace obtained using a Photomultiplier tube Priority Research Centre for Energy PMT Experiments 4 11 Volatile Combustion Time Char Burnout Time Intensiity 3 2 Sub‐bituminous 180‐212 um 50% O2 (O2/N2) 1 0 250 275 300 325 350 Residence Time (ms) Example of energy trace obtained using a Photomultiplier tube Priority Research Centre for Energy 160 80 40 80 Char Burnout Time (ms Ai Air 60 120 20 40 Lignite 180-212 um Lignite 180-212 um 0 0 0 0 10 10 20 30 40 50 20 30 40 50 Oxygen Concentration (%) Oxygen Concentration (%) 60 12 180 Air Oxy Oxy Model - Air Model - Oxy Char Burrnout Time (mss) Devolat ilization Time ((ms) Devolatiilization Time (ms) Devolatilization & Char Burnout Time – Lignite 60 100 AirAir Oxy Oxy 13575 Model - Air 9050 Model - Oxy 4525 0 0 Lignite 180-212 Lignite 180-212 umum 0 0 20 30 40 1010 20 30 40 5050 60 60 Oxygen Concentration (%) O Oxygen C Concentration t ti (%) •Devolatilization and char burnout decreases with increasing O2 concentration. •Devolatilization and char burnout decreases with increasing O concentration • Devolatilization and char burnout takes longer in the presence of CO2 Priority Research Centre for Energy 120 60 Char out Char burno Burno outTime Time(ms) (ms) Devolatilizaation Time (ms)) Devolatilizati ion Time(ms) Devolatilization & Char Burnout Ti Time – Sub S Subb-Bituminous Bit i Coal C l Air Oxy Air Oxy ModelAir 90 40 Model- Oxy 60 20 30 Sub-Bitum 180-212 Sub-Bitum 180-212umum 0 0 0 0 1010 2020 30 30 40 40 Oxygen OxygenConcentration Concentration(%) (%) 50 50 60 60 13 150 300 120 Air Oxy Oxy 90 200 Model - Air M d l - Oxy Model O 60 100 30 00 Air Sub-Bitum180-212 180-212um um Sub-Bitum 00 10 10 20 20 30 40 50 30 40 50 Oxygen Concentration (%) 60 60 •Devolatilization and char burnout decreases with increasing O2 concentration. • Devolatilization and char burnout takes longer in the presence of CO2 Priority Research Centre for Energy Spectrometer Experiment – Coal Particle Spectra 14 1250 1250 Intens sity Inten nsity Volatile combustion 1150 1150 Char combustion 1050 1050 Sub bituminous 180 Sub-bituminous 180-212 212 um in 21% O2 950 950 400 400 500 500 600 700 800 600 700 800 Wavelength g ((nm) Wavelength (nm)) 900 900 1000 1000 Spectra collection of a burning coal particle Priority Research Centre for Energy Spectrometer Experiment – Intensity Profile 15 Inteensity 100 75 800 nm 700 nm 50 25 0 100 150 200 250 Residence Time (ms) Intensity profile (wavelength 700 nm & 800 nm) yp ( g ) Priority Research Centre for Energy Temperature p measurement Energy emitted by a grey body Energy emitted by a grey body λ ε λ λ 5 [ exp ( C I λ1 ε λ1 I λ 2 ε λ2 ε λ1 ελ 2 1 1 2 / λT )1 ] e ( C2 / λ2 T ) 1 λ2 ( C / λ T ) 2 1 1 λ1 e 5 16 3500 Tempeerature (K) I C (grey (g y body y assumption) p ) 3000 2500 550/700 2000 600/700 650/750 1500 700/800 1000 100 120 140 160 180 200 Residence Time (ms) Calculated two color temperature (grey body assumption) Grey body assumption ‐ wide variation in temperature with different wavelength combination Priority Research Centre for Energy Comparison – Coal & Prepared Char Spectra 1200 1150 1150 1100 1100 1200 Sub-bitum Sub-bitum coal coal180-212 180-212 um um Char spectra Intennsity In ntensity In ntensity 1250 1200 1050 1050 1000 1000 400 400 17 Sub-bitum prepared char 180-212 um Sub-bituminous 180-212 um Prepared char 21% O2 1150 1100 1050 500 500 600 700 800 600 700 800 Wavelength Wavelength (nm) (nm) Coal 900 900 1000 400 500 600 700 Wavelength (nm) 800 900 Prepared Char Emission intensity during char oxidation is higher for coal than prepared char E i i i i d i h id i i hi h f l h d h Priority Research Centre for Energy Volatile burning g intensity y Inteensity 6 18 Sub-bituminous coal 180-212 micron in 21% O2 Air (O2/N2) Oxy (O2/CO2) 4 2 0 0 10 20 30 40 Residence Time (ms) 50 Volatile burning intensity Emission intensity during volatile combustion is higher in air (O2/N2) than in oxy(O2/CO2) Priority Research Centre for Energy Char burning g intensity y Sub-bituminous 180-212 um 21% O2 3 Sub-bituminous 180-212 um 21% O2 3 Air (O2/N2) Oxy (O2/CO2) 2 IIntensity IIntensity Air (O2/N2) 19 1 Oxy (O2/CO2) 2 1 ` 0 0 50 100 150 R id Residence Time Ti (ms) ( ) Char burning intensity of coal 200 50 100 150 200 Residence Time (ms) Char burning intensity of prepared Char Emission intensity during char oxidation is higher in air (O E i i i i d i h id i i hi h i i (O2/N2) than in oxy(O ) h i (O2/CO2) Emission intensity during char oxidation is higher for coal than prepared char Priority Research Centre for Energy Conclusion 20 Devolatilization occurs faster with higher oxygen concentration in both air (O2/N2) and oxy‐fuel (O2/CO2)conditions. This is attributed to higher oxygen flux Devolatilization and char burnout times are longer in (O2/CO2) environment than in (O2/N2) . This can be explained by the the higher heat capacity of CO2 and lower mass diffusivity in CO y 2 The predicted trends using the single particle model are in good agreement with the measured combustion time data The measured emission intensities during volatile oxidation are higher in air (O2/N2) than oxy‐fuel (O2/CO2) conditions The measured emission intensities during char oxidation are higher for coal The measured emission intensities during char oxidation are higher for coal compared to prepared char in both air and oxy conditions Priority Research Centre for Energy Acknowledgements g 21 Dr. Ron Roberts – University of Newcastle MS. Jennifer Martin, Dr. Jianglong Yu, Mr. Renu Kumar, Mr.Rohan Dr. Christopher Shaddix – Sandia National Laboratory Dr. Alejandro Molina – j Universidad National De Colombia Dr. Yiannis A. Levendis – North‐eastern University Dr Carlos Romera Lehigh University Dr. Carlos Romera ‐ Lehigh University Priority Research Centre for Energy 22 THANK YOU THANK YOU Priority Research Centre for Energy Char burning g intensity y 3 23 Sub-bituminous 180-212 micron in 21% O2 Inten nsity Coal 2 P Prepared d char h 1 0 30 50 70 90 110 Residence Time (ms) 130 Priority Research Centre for Energy 24 3000 3000 T e m p e ra tu r e ( K ) T e m p e ra tu r e ( K ) 3500 550/700 2500 600/700 650/750 2000 700/800 1500 2500 550/700 2000 600/700 650/750 700/800 1000 1500 120 130 140 Residence Time (ms) 150 160 140 150 160 170 180 190 200 Residence Time (ms) Priority Research Centre for Energy 25 2700 Temperature (K)) T Temperature (K)) T 2900 2800 550/700 2700 2600 2550 600/700 2500 150 160 170 180 190 Residence Time (ms) 200 150 160 170 180 190 Residence Time (ms) 200 2400 Temperrature (K) 2300 Temperaature (K) 2650 2250 650/750 2350 2300 700/800 2250 2200 2200 150 160 170 180 190 Residence Time (ms) 200 150 160 170 180 190 Residence R id Time Ti (ms) ( ) 200 Priority Research Centre for Energy 26 3000 Te emperature (K K) 2500 2000 1500 1000 550/700 500 615/715 700/800 800/900 850/950 0 320 330 340 350 360 370 380 390 Time (ms) Priority Research Centre for Energy 27 Energy trace obtained using a Photomultiplier tube Priority Research Centre for Energy PMT Experiments p 28 Energ gy Intensiity (a.u) 6 4 2 0 0 50 100 150 200 250 300 350 400 Residence Time (ms) Energy trace obtained using a Photomultiplier tube Priority Research Centre for Energy 900 800 800 700 700 600 600 Intensity Counts 900 500 400 300 Lignite 180‐212 um‐ Air 10 200 500 400 300 Lignite 180‐212 um‐ Air20 Lignite 180‐212 um‐ 200 100 100 0 0 0 200 400 600 800 1000 1200 0 200 400 Wavelength (nm) 600 800 1000 1200 Wavelength (nm) 1000 1400 900 1200 800 1000 Intensity Counts 700 Intensity Counts Intensity Counts 29 600 500 400 300 800 600 400 Lignite 180‐212 um‐ Air 30 200 Lignite 180‐212 um‐ Air 50 200 100 0 0 200 400 600 Wavelength (nm) 800 1000 1200 0 0 200 400 600 800 1000 1200 Wavelength (nm) Priority Research Centre for Energy Single Particle Flame Sheet Model Governing Equations 30 1. Devolatilization rate equation dV k (V * V ) dt where E k A exp RT p 2. Flame Sheet Radius . rf m v (n s ) (n s ) y O2 , 4 C DO2 ln1 s 3. Energy Balance for flame sheet . m v H Qc Q out Qc Q in Qrad Q d f w Qrad Q d f p Priority Research Centre for Energy Single Particle Flame Sheet Model Governing Equations 31 4. Energy Balance for a single coal particle - Devolatilization 4.1 Without flame sheet (attached flame condition) m pC dT p pp dt Qcon g p Qrad w p Q Q endo dev 4 2 With fl 4.2 flame sheet h t (flame (fl lift-off lift ff condition) diti ) m pC dT p pp dt Qcon f p Qrad w p Qrad f p Q endo 5. Energy Balance for a single coal particle (during char combustion) m pC dT p pp dt Qcong p Qrad w p Q comb Priority Research Centre for Energy 32 A- Frequency factor (s-1) C -Total molar concentration (moles/m3) Cpp- Specific heat capacity of coal particle (J/kg/K) DO2 -Diffusivityy of O2 in the bulk g gas ((m2 / s)) E -Activation Energy (J/kg) FC -Fixed carbon as measured by Proximate analysis (kg/kg) H -Heat of volatile combustion (J/kg) K -Rate constant (s-1) Mp-Particle mass (kg) mv -Volatile release rate (kg/s) n -kmoles of oxygen required per kg of volatiles on the flame sheet or on the particle surface (kmoles/kg) Q -Ratio of total volatile yield to the proximate volatile matter No unit Priority Research Centre for Energy 33 Q endo- Heat of Pyrolysis (J) QCin -Convective heat transfer from the flame to the particle (J) Qcomb -Heat of char combustion (J) ( ) Qconf-p- Conductive heat transfer between the flame and the particle (J) Qcong-p -Conductive heat transfer between the gas and the particle (J) QCout -Convective heat transfer from the flame to the gas (J) Qdev -Heat of volatile combustion (J) Qgasf -Heat absorbed during gasification reaction (J) Q df Radiative Qradf-pR di ti h heatt ttransfer f b between t th the fl flame and d th the particle ti l (J) Qradf-w -Radiative heat transfer between the flame and the wall (J) Qradw-p -Radiative heat transfer between the wall and the particle (J) R -Universal gas constant (J/kg/K) r f -Flame sheet radius from the centre of the particle (m) rp -Particle Particle diameter (m) S-kmoles of product generated per kg of volatiles on the flame sheet or the particle surface (kmoles/kg) Tf -Temperature of the flame front (K) Tg- Temperature of the ambient gas (K) Tp- Partice Temperature (K) Tw- Wall temperature (K) V* -Ultimate volatile yield (kg/kg) VM -Volatile matter content as measured by Proximate analysis (kg/kg) yO2, α- Mole fraction of oxygen in the ambient gas No unit Priority Research Centre for Energy Coal particle Spectra 4000 3000 2000 1000 400 500 600 700 800 900 Energy Inteensity (Raw w) Energy In ntensity (Raw w) 34 1500 1250 1000 400 Wavelength (nm) 600 800 200 Energy yIntensity (Corrrected) Energyy Intensity (Corrrected) Wavelength (nm) 150 100 50 0 400 600 800 Wavelength (nm) Spectra obtained for a sub‐bituminous coal particle (180‐212 um) 50 25 0 500 600 700 800 Wavelength (nm) Priority Research Centre for Energy 35 Priority Research Centre for Energy Spectrometer p – USB 2000+ 36 Multi wavelength Pyrometer Microcontroller based Spectrometer Spectral Range ‐ 300 ‐ 1100 nm (VIS/NIR) Resolution ‐ 0.35 nm Response Time ‐ 1ms ‐ 60 sec Detector ‐ CCD array Grating – 600 lines/mm Priority Research Centre for Energy Spectrometer p calibration 37 80000 Lamp file data 60000 Measured 8 40000 4 20000 0 0 0 Tungsten Halogen Lamp (radiometrically calibrated) 12 Spectral Outp put (uw/cm2/mm m) Intensity C Count Lamp Spectrum 200 400 600 800 1000 1200 Wavelength (nm) Intensity from calibration lamp file at λ CorrectionFactor (A ) λ Actual int ensity measured from the lamp by the spectrometer at λ I c I m X A Iλc -Corrected Intensity I λm - Measured Intensity Aλ Relative Grating Efficiency - Correction Factor Corrected Intensity (Iλc) = Measured Intensity (Iλm) X Correction Fact Priority Research Centre for Energy 38 Composition % N2 10 N2 21 N2 30 N2 50 CO2 10 CO2 21 CO2 30 CO2 50 CO2 2. 8 2. 8 2. 8 2. 8 70.5 59.8 51.4 31.5 H2O 14 3 14. 3 14 3 14. 3 14 3 14. 3 14 3 14. 3 19 4 19.4 19 2 19.2 18 5 18.5 18 5 18.5 N2 72. 9 62. 0 52. 8 32. 8 ‐‐ ‐‐ ‐‐ ‐‐ O2 10. 0 20. 9 30. 1 50. 1 10.1 21.0 30.1 50.0 Priority Research Centre for Energy
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