Advanced Monitoring and Characterisation of Combustion Flames

Transcription

1 20 th Annual Meeting and Meetings of the Combustion and Advance Power Generation Divisions, University of Leeds, 22 nd April, 2009 Advanced Monitoring and Characterisation of Combustion Flames >1609 >1588 >1566 >1545 >1523 >1501 >1480 >1458 >1437 >1415 a b c d Dr G Lu and Prof Y Yan Department of Electronics, University of Kent, UK

2 Outline Introduction 2D flame imaging 3D flame imaging Concluding remarks 2

3 Introduction Advanced monitoring of combustion flames plays an important role in the in-depth understanding of energy conversion and pollutant formation processes and subsequent combustion optimisation. Current practice of flame monitoring is limited to indicate whether the flame is present or absent for safety purpose only. Conventional flame detector (Source: DURAG) Coal-fired boiler (Source: DTI) Flames (Source: DTI) 3

4 Introduction Advanced techniques are required to provide reliable, non-intrusive and continuous monitoring of combustion flames. Substantial research has been carried out at the University of Kent to develop a vision based technology for 2D/3D monitoring and characterisation of combustion flames. This presentation presents an overview of recent developments in the 2D and 3D flame imaging techniques. 4

5 Typical coal-fired flames 1.0 MW th 0.75 MW th (Flame images taken on a 1MW th CTF, E.ON, UK) 5

6 Flame characterisation through 2D imaging Remote computer Image acquisition & processing unit Camera housing Optical probe Video signals Cooling water/air Water Jacket Flame Flame characteristics Flame images Size/shape, Ignition point Luminous intensity, Uniformity Temperature Flame assessment Fuel/air inputs Emissions Other data Oscillation frequency Computational modelling Recommendation to Combustion optimisation 6

7 2D flame imaging industrial trials Cooli ng syste m Burner Combustion Chamber 0.5MW th CTF, RWE npower 90 MW th CTF, Doosan Babcock 1MW th CTF, E.ON UK 3MW th coal-fired CTF, Cerchar, France 7

8 Determination of flame geometric and luminous parameters Geometric and luminous parameters - Ignition point: Ip - Spreading angle: α s - Brightness: B f - Non- uniformity: N uf Techniques used Ip min - Edge detection - Pattern recognition -etc Burner axis Ip max Flame α s 8

9 Example results -- Tests on a 1MW th CTF, EON (UK) Flame images and the ignition point for variable furnace load. 0.8MW 0.9MW 1.1MW 1.0MW Ignition point (mm) Max Mean Min Furnace load (MW) Ignition area (%) Furnace load (MW) 9

10 Determination of flame temperature The two-colour method- The temperature is determined from flame radiation intensities at two wavelengths based on the Planck s radiation law. Spectral radiance of a blackbody (Wien s radiation law) Spectral radiance of particles C M λ T ε 1 (, ) = λ 5 λ e C 2 λt The two-colour method Emissivity of particles Spectral radiance of a blackbody for selected temperatures T=f(λ 1, λ 2, M 1, M 2 ) 10

11 Determination of flame temperature Sensing arrangement Objective Beam splitter Filter Ocular Imaging sensor λ 1 λ 2 Flame Prism Image at λ 1 Image at λ 2 T=f(λ 1, λ 2, G 1, G 2 ) Temp ( C) >1609 >1588 >1566 >1545 >1523 >1501 >1480 >1458 >1437 >1415 Temperature distribution 11

12 Example results -- Tests on a 1MW th CTF, E.ON (UK) Temperature profiles of a coal-fired flame for variable furnace load. 0.8MWth 0.9MWth Temp ( C) >1609 >1588 >1566 >1545 >1523 >1501 >1480 >1458 >1437 >1415 Temperature ( C) Max Min Mean Furnace load (MW) 1.0MWth 1.1MWth Temperature variation Temperature profiles 12

13 Example results -- Tests on a 3MW th CTF (France) Comparison of flame temperature profiles obtained by the imaging system and by a thermocouple. Flame image Temperature from imaging system Radical coordinate (mm) mm Temp ( C) Temperature from thermocouple from 44 measuring points (Source: Cerchar, France). ~1.1m Measuring lines ~1.5m Location of measurement points 13

14 Determination of oscillation frequency Oscillatory (flickering) characteristic of a flame is reflected by the dynamic alternating components (AC) superimposed on the steady state (DC) or brightness level. The oscillation signal is reconstructed from the luminous intensity of pixels within flame images. Quantified frequency is the weighted average of the power spectra over the whole measuring range, i.e., 0-180Hz. Flame 5 0 FFT Burner Root Middle Camera Time (Sec) Power (X10 7 ) Frequency (Hz) 14

15 Example results -- Tests on a 1MWth CTF, EON (UK) Flame oscillation frequency for variable furnace load 25 Variation of the oscillation frequency MW th Flicker (Hz) Root Middle Furnace load (MW) MW th 15

16 3D flame monitoring and characterisation through imaging A flame is a 3D flow field. To fully reveal the dynamic nature of the flame, 3D monitoring and characterisation techniques are required. 16

17 3D flame geometric model Camera z Contour extraction Mesh generation Pseudo-colouring Flame y x 17

18 3D tomographic reconstruction of the flame luminosity Mirrors /lenses Flame Reconstruction Algorithm Filtered Back Projection Algebraic Reconstruction Technique Reconstructed grey-scale cross-sections Camera

19 3D tomographic reconstruction of the flame luminosity Gas flame images Longitudinal-section reconstruction Cross-section reconstruction 19

20 3D tomographic reconstruction of the flame temperature Image acquisition & digitisation Image 1 (for λ 1 ) Grey level reconstruction Temperature calculation (Two-colour method) Image 2 (for λ 2 ) Grey level reconstruction Data presentation Flame

21 3D tomographic reconstruction of the flame temperature A gas flame image Flame temperature distribution Flame height (mm) Temp ( C)

22 3D tomographic reconstruction of a coal flame 粉煤火焰三维灰度重构 a b c d A coal flame image Cross-section reconstruction 22

23 Concluding remarks Digital imaging provides a viable approach to on-line 2D/3D monitoring and characterisation of combustion flames. Prototype systems have been evaluated on laboratory- and industrialscale combustion test facilities. The test results have proven their effectiveness and operability. Work is being undertaken to, study flame stability and burner condition monitoring under biomass/coal co-firing and oxyfuel combustion conditions (EPSRC projects) study the internal structure of a flame under a wide range of conditions (EPSRC projects) Scale up the 2D prototype systems for the installation on full-scale coal fired boilers (BCURA Project B95). The flame imaging techniques are being extended to other applications such as gas turbine combustors and blast furnaces. 23

24 Acknowledgements The following organisations are acknowledged for their support for the flame imaging work at Kent: EPSRC BCURA DIUS/TSB RWE npower E.ON Doosan Babcock Energy Alstom Power EDF Energy Spectus Energy PCME

25 System calibration The imaging system is calibrated using a standard temperature source - blackbody furnaces at NPL. Images of the blackbody furnace nm, 1400 C 700nm, 1400 C Temp ( C) λ 1 λ 2 632nm, 1300 C 700nm, 1300 C Grey-level Calibration curve (1/500sec, Iris 11) 25