Measurement and Modeling of Particle Radiation in Coal Flames

Abstract

This work aims at developing a methodology that can provide information of in-flame particle radiation in industrial-scale flames. The method is based on a combination of experimental and modeling work. The experiments have been performed in the high-temperature zone of a 77 kW th swirling lignite flame. Spectral radiation, total radiative intensity, gas temperature, and gas composition were measured, and the radiative intensity in the furnace was modeled with an axisymmetric cylindrical radiation model using Mie theory for the particle properties and a statistical narrow-band model for the gas properties. The in-flame particle radiation was measured with a Fourier transform infrared (FTIR) spectrometer connected to a watercooled probe via fiber optics. In the cross-section of the flame investigated, the particles were found to be the dominating source of radiation. Apart from giving information about particle radiation and temperature, the methodology can also provide estimates of the amount of soot radiation and the maximum contribution from soot radiation compared to the total particle radiation. In the center position in the flame, the maximum contribution from soot radiation was estimated to be less than 40% of the particle radiation. As a validation of the methodology, the modeled total radiative intensity was compared to the total intensity measured with a narrow angle radiometer and the agreement in the results was good, supporting the validity of the used approach.

Particle composition and size distribution in coal flames – The influence on radiative heat transfer

“…The average diameter of the fuel in Ref. [19] was 40 lm (54 lm in this study) but no significant difference was noticed in the results using the two fuel batches. Gas temperature was measured with a suction pyrometer and the gas concentration was analysed with standard gas analysers and with an FTIR analyser.…”

“…In this work measurements were performed in the high temperature part of the flame, 384 mm downstream from the burner, with a measured peak gas temperature of approximately 1250°C in the centre position. The radiative intensity was measured against a cold background with a Narrow Angle Radiometer, and the results and measurement procedure from the investigated cross-section of the lignite flame have been presented previously [19]. The average diameter of the fuel in Ref.…”

“…The modelling approach has been developed and used in previous works at Chalmers [19,26], and a short description follows below.…”

“…The discrete transfer method is used to calculate the intensity field in the absorbing, emitting and scattering media with consideration of a difference in temperature between the gas and particles [19]. Spectral variations of the radiative properties of the gas and particles are accounted for and the particles are assumed to scatter isotropically.…”

“…In previous works at Chalmers a 100 kW th oxy-fuel test facility has been used in studies related to large scale combustion of solid fuels [17][18][19][20]. In one of these studies [19] a methodology based on combined measurements with a FTIR system and detailed radiation modelling was used to estimate the amount of particles and the particle temperature in a lignite flame similar to the one examined here. It was concluded that coal particles dominated the radiative heat transfer in the investigated cross-section of the flame with only a minor contribution from soot.…”