BIOMASS-COAL FLAME MONITORING BY DIGITAL IMAGE PROCESSING IN A SEMI-INDUSTRIAL COMBUSTION PILOT PLANT

摘要

Co-firing of biomass with coal is a widely adopted strategy in order to reduce CO2 emissions in electricity generation. Among the adverse effects of biomass addition, problems derived from ash deposition in heat exchanger surfaces, leading to fouling, slagging and corrosion, have been reported and attracted special interest in recent years. However, literature concerning the influence of biomass on flame structure and combustion behaviour is scarcer. Flame monitoring by means of digital imaging allows a complete description of the flame structure and provides a fundamental tool to optimise combustion processes. In the present work, a flame monitoring system has been implemented in a 500 kWth PF pilot swirl burner. The system is based on a high-speed CCD (charge-coupled device) camera that captures image sequences, which contain the spatial-temporal attributes of the flame. The objective is to extract such attributes, mainly the flame oscillation frequency from the estimation of the flicker frequency (weighted average of power spectral density - PSD). A test program has been conducted, aimed at investigating relevant parameters, such as primary air ratio, air excess and swirl number, as well as the impact of different percentages of biomass substitution, which may influence combustion behaviour. First results about optical parameters of the flame, oscillation frequency (flicker) and its correlation with some operational conditions and emissions are presented.