Comparison of Flame Stability under Air and Oxy-Fuel Conditions for an Aerodynamically Stabilized Pulverized Coal Swirl Flame Martin Habermehl, Johannes Hees, Diego Zabrodiec, Reinhold Kneer 40 th International Technical Conference on Clean Coal & Fuel Systems, May 31 st – June 4 th , 2015, Clearwater, Florida
Introduction Different „modes“ of coal combustion: Air Oxy-fuel (21 vol.-% O 2 ) Oxy-fuel (25 vol.-% O 2 ) • What determines the stability of air and oxy-fuel flames? • Possible parameters: flow velocities, momentum flows, oxygen concentrations, etc. etc. • Investigation of flame stability conducted Page 2 Comparison of Flame Stability under Air and Oxy-Fuel Conditions for an Aerodynamically Stabilized Pulverized Coal Swirl Flame | Martin Habermehl | 40 th International Technical Conference on Clean Coal & Fuel Systems | 2015, May 31 st – June 4 th | Clearwater, FL, USA
Experimental Setup: Combustion chamber Ø400 mm Displaceable burner port Coal 2100 mm Observation ports (4x) 4200 mm Combustion chamber Gas mixer Air supply Flue gas quench CO 2 (Carbon dioxide) Flue exit to the stack O 2 (Oxygen) Page 3 Comparison of Flame Stability under Air and Oxy-Fuel Conditions for an Aerodynamically Stabilized Pulverized Coal Swirl Flame | Martin Habermehl | 40 th International Technical Conference on Clean Coal & Fuel Systems | 2015, May 31 st – June 4 th | Clearwater, FL, USA
Experimental Setup: Measurement techniques Flue gas analytics: CO content Ø400 mm • Flue gas analyzer installed at the stack 2100 mm • Measurement of CO concentration (dry) by non- 4200 mm Refrigerant type dryer dispersive infrared spectrography (NDIR) • CO concentration used as an NO CO indicator for stable combustion O 2 CO 2 (low values stable combustion) Flue gas analyzer (NDUV/NDIR) Page 4 Comparison of Flame Stability under Air and Oxy-Fuel Conditions for an Aerodynamically Stabilized Pulverized Coal Swirl Flame | Martin Habermehl | 40 th International Technical Conference on Clean Coal & Fuel Systems | 2015, May 31 st – June 4 th | Clearwater, FL, USA
Experimental Setup: Measurement techniques Investigation of OH* chemiluminescence Optical access • Detection of UV radiation window emitted by excited OH* radicals at approx. 307 nm CCD camera & • Indication of zones with high intensifier reaction rates and heat release • Mapping of flame structures • Investigation of the entire flame: Placing the burner at different height positions UV filter Recording multiple images and ( λ =307 nm, Δλ =10 nm) average them Recording Generate one system chemiluminescence map of the entire flame by composing the averaged images Page 5 Comparison of Flame Stability under Air and Oxy-Fuel Conditions for an Aerodynamically Stabilized Pulverized Coal Swirl Flame | Martin Habermehl | 40 th International Technical Conference on Clean Coal & Fuel Systems | 2015, May 31 st – June 4 th | Clearwater, FL, USA
Experimental Setup: Measurement techniques Laser Doppler Velocimetry Ar Ion Laser • Coal particles used as tracer Measurement Transmission Receiver particles volume optics optics • Measurement of axial and tangential mean flow velocity components by two laser beam pairs of different wavelengths • Positioning of the measurement volume: Radial position adjusted by traversing a horizontally displaceable rack for the optics Horizontally displaceable rack Axial position adjusted by traversing the burner Evaluation and • Only axial velocity components recording system considered in this study Page 6 Comparison of Flame Stability under Air and Oxy-Fuel Conditions for an Aerodynamically Stabilized Pulverized Coal Swirl Flame | Martin Habermehl | 40 th International Technical Conference on Clean Coal & Fuel Systems | 2015, May 31 st – June 4 th | Clearwater, FL, USA
Experimental Setup: Swirl Burner Oxy-3 P S S T T Sta Sta P – Primary flow: coal dust + carrier gas S – Secondary flow, swirled T – Tertiary flow Sta – Staging flow Page 7 Comparison of Flame Stability under Air and Oxy-Fuel Conditions for an Aerodynamically Stabilized Pulverized Coal Swirl Flame | Martin Habermehl | 40 th International Technical Conference on Clean Coal & Fuel Systems | 2015, May 31 st – June 4 th | Clearwater, FL, USA
Very schematic sketch of design flame shape Conical dispersing swirl Internal recirculation combustion zone backflow Page 8 Comparison of Flame Stability under Air and Oxy-Fuel Conditions for an Aerodynamically Stabilized Pulverized Coal Swirl Flame | Martin Habermehl | 40 th International Technical Conference on Clean Coal & Fuel Systems | 2015, May 31 st – June 4 th | Clearwater, FL, USA
Settings and Investigated Cases Local Oxygen Ratio at Burner vicinity • Parameter characterizing the near burner flow field: Local oxygen ratio λ local : 𝜇 𝑚𝑝𝑑𝑏𝑚 = 𝑛 𝑃2,𝑢𝑠𝑝𝑣ℎ 𝑐𝑣𝑠𝑜𝑓𝑠 𝑛 𝑃2,𝑠𝑓𝑟𝑣𝑗𝑠𝑓𝑒 • Takes only the flows through the burner into account • Remaining oxygen provided by staging flow • Influenced by the Oxygen content x O2 and the molar mass M Oxydizer of the oxidizer 𝑁 𝑃2 ⋅ 𝑛 𝑃𝑦𝑧𝑒𝑗𝑡𝑓𝑠 𝑢𝑠𝑝𝑣ℎ 𝑐𝑣𝑠𝑜𝑓𝑠 𝜇 𝑚𝑝𝑑𝑏𝑚 = 𝑦 𝑃2 ⋅ 𝑁 𝑃𝑦𝑧𝑒𝑗𝑡𝑓𝑠 𝑛 𝑃2 • Applied values: λ local = 0.6; 0.8; 1.0 Page 9 Comparison of Flame Stability under Air and Oxy-Fuel Conditions for an Aerodynamically Stabilized Pulverized Coal Swirl Flame | Martin Habermehl | 40 th International Technical Conference on Clean Coal & Fuel Systems | 2015, May 31 st – June 4 th | Clearwater, FL, USA
Settings and Investigated Cases Oxidizer Composition Normalized total momentum • Investigated Oxidizer Compositions: flow through the burner „Reference“ case with air (21 vol. -% O 2 ) (AIR) λ local AIR OXY-21 OXY-25 Oxy-fuel case with 21 vol.-% O 2 and 79 vol.-% CO 2 1.0 1.000 1.438 1.003 (OXY-21) 0.8 0.640 0.920 0.642 Oxy-fuel case with 25 vol.-% O 2 and 75 vol.-% CO 2 0.6 0.360 0.518 0.361 (OXY-25) • Reasoning for these parameters: OXY-21: Same volumetric flow rates, velocities and O 2 content as for the AIR case OXY-25: Same momentum flow rates P as for the AIR case 2 𝑛 𝑄 = 𝑛 ⋅ 𝑤 = 𝜍⋅𝐵 𝑑𝑠𝑝𝑡𝑡 Page 10 Comparison of Flame Stability under Air and Oxy-Fuel Conditions for an Aerodynamically Stabilized Pulverized Coal Swirl Flame | Martin Habermehl | 40 th International Technical Conference on Clean Coal & Fuel Systems | 2015, May 31 st – June 4 th | Clearwater, FL, USA
Observations and Results Stability assessment from flue gas analytics • Stable combustion: Low values of CO concentration within the flue gas (single digit range) Continuous and stable trend of the CO concentration • Instable combustion: Raised and fluctuating values of CO concentration within the flue gas (100 – 200 ppm) Sporadic distinct CO concentration overshoots λ local AIR OXY-21 OXY-25 1.0 stable stable stable 0.8 stable stable Stable 0.6 instable stable instable Page 11 Comparison of Flame Stability under Air and Oxy-Fuel Conditions for an Aerodynamically Stabilized Pulverized Coal Swirl Flame | Martin Habermehl | 40 th International Technical Conference on Clean Coal & Fuel Systems | 2015, May 31 st – June 4 th | Clearwater, FL, USA
Observations and Results Intensity maps of OH* chemiluminescence emissions for AIR (relative intensity units) • Main reaction • Cylindrical zone attached vortex instead to the burner of conical quarl expanding swirl • Conical shape of the reaction zone identifiable • Significantly • Prolonged increased flame for length of the decreased reaction zone local oxygen ratio Page 12 Comparison of Flame Stability under Air and Oxy-Fuel Conditions for an Aerodynamically Stabilized Pulverized Coal Swirl Flame | Martin Habermehl | 40 th International Technical Conference on Clean Coal & Fuel Systems | 2015, May 31 st – June 4 th | Clearwater, FL, USA
Observations and Results Mean axial velocities measured by LDV for AIR No recirculation backflow at Internal recirculation x = 100 mm backflow No extending swirl Extending conical swirl region Page 13 Comparison of Flame Stability under Air and Oxy-Fuel Conditions for an Aerodynamically Stabilized Pulverized Coal Swirl Flame | Martin Habermehl | 40 th International Technical Conference on Clean Coal & Fuel Systems | 2015, May 31 st – June 4 th | Clearwater, FL, USA
Observations and Results Intensity maps of OH* chemiluminescence emissions for OXY-25 (relative intensity units) • Main reaction • Change of zone attached flame structure to the burner very similar to quarl the air case • Conical shape of the reaction zone identifiable • Reaction zone size increased compared to AIR Page 14 Comparison of Flame Stability under Air and Oxy-Fuel Conditions for an Aerodynamically Stabilized Pulverized Coal Swirl Flame | Martin Habermehl | 40 th International Technical Conference on Clean Coal & Fuel Systems | 2015, May 31 st – June 4 th | Clearwater, FL, USA
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