491 / 2018-09-09 10:34:25

Experimental Investigation on Temporal Release of K from Single Biomass Pellet Combustion by Flame Emission Spectroscopy

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In this paper, the temporal release behaviour of potassium (K) during the combustion of the single biomass pellet was in-situ investigated by Flame Emission Spectroscopy (FES). Two kinds of biomass, rice husk and camphorwood, with different volatile matter (16.2%, 87.93%) and potassium content (1.8%, 7.99%) were used in this study. The experiments were performed on a Hencken flat flame burner. The biomass pellets with controlled moisture content (10%, 20%) were burned at 10 mm height above the burner, and a spectrometer was used to collect the emission spectrum of biomass pellets flame, as shown in Fig.1. Based on the multi-wavelength spectral analysis method, the spectral intensity (Ik) of K was measured from the visible spectrum, while the temperature (T) and thermal radiation (Q) were calculated from the visible and near-infrared spectrum. According to the theory of FES, the spectral intensity of K is proportional to the concentration of gas phase potassium in the flame. The integral of the spectral intensity of K during the whole combustion process (Ik,total), which may represent the total release amount of K, was calculated.

Fig.1 Experimental setup Fig.2 Typical flames of biomass pellets
Fig.2 shows the typical flames of biomass pellets. Fig.3 shows the release of K would be influenced by the moisture content, especially camphorwood during the char combustion, and rice husk during devolatilization, on account of the water evaporation, as well as temperature (T) and thermal radiation (Q). From Fig.4, the spectral intensity (Ik) of K from camphorwood appears two peaks, while only one peak for rice husk during devolatilization, and whose release duration would be longer with higher volatile content. What’s more, the release amount (Ik, total) of K from rice husk was evidently less than the camphorwood pellet due to the lower initial content of K. With the increase of the moisture content, the release amount of K during combustion was found to increase. These results proved the FES technique is feasible for in-situ monitoring the combustion of biomass.