EFFECTS OF O_2 PARTIAL PRESSURE ON FLAME STABILITY IN OXY-COAL COMBUSTION

摘要

Oxy-fuel combustion of pulverized coal is one of the few technologies that may allow CO_2 sequestration technologies to be applied to existing coal-fired boilers. One issue of interest is to understand and predict the effects of near burner zone environment consisting of O_2 and CO_2 (instead of N_2). The purpose of this research is to better understand and to scale the effect of partial pressure of O_2 and CO_2, which becomes another degree of freedom, on coal jet ignition and flame stability. A novel methodology is developed to quantify the flame stability and flame length by introducing an image processing technique. Ultimately the experiment will provide data for simulation validation studies that can be used to predict how air fired combustors may be retrofitted to oxy-coal. Specifically the objective is to explore effects of the partial pressure of O_2 and CO_2 on coal jet flame stability, which is quantified by stand-off distance, the distance between burner tip and the base of the detached flame. The experiments are carried on in a 100 kW pilot-scale laboratory furnace outfitted with a coaxial burner (primary jet in the center pipe and secondary stream in the annular sleeve, no swirl, type 0 turbulent flame) and arrays of electrically-heated panels in the burner zone in order to control variations in near-burner heat loss. Currently no flue gas recirculation is introduced to provide a nearly pure CO_2 stream. Instead, fresh, one-through CO_2 and O_2 streams are introduced to the burner. The furnace also has visual access to the burner zone through quartz windows, which allows for optical measurements. A special CMOS sensor based camera, which is more sensitive to the near infrared wavelength(responsivity: 1.4 V/lux-sec (550nm)), is applied to capture Type 0 axial turbulent diffusion flame shape for the use of statistical studies of stand-off distance at different operational parameters, such as systematic variations of partial oxygen pressure in both transport and secondary oxidant stream. Statistical analysis is used to scale the effect of oxygen partial pressure in both transport and secondary stream on coal jet ignition and flame stability. Ultimately the statistics help to generate probability density function (PDF), which can be used to evaluate the experiment accuracy, reproducibility and to do model validation.