390 / 2018-08-15 17:16:43

Experimental Study on Ignition Characteristics of Single Sewage Sludge Particle in Enriched-O2 Atmospheres

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In recent years, the sewage sludge and coal co-combustion for generating electricity is considered to be an effective method of the sewage sludge treatment. Owning to the significantly difference of the combustion characteristics of sewage sludge and coal, sewage sludge and coal co-combustion is prone to the combustion instability. This paper proposes the oxygen-enhanced combustion method to increase the stability of sewage sludge and coal co-combustion and the sludge blending ratio. Therefore, the study of the ignition mechanism of a sewage sludge particle under enriched-O2 atmospheres is the basic research of the oxygen-enhanced co-combustion of sewage sludge and coal. The ignition characteristics of single sludge particles (45-106μm, 106-180μm 180-250μm) were conducted in the concentration range of O2 from 21% to 70% in N2 in this work. The experiment was carried out in a drop tube furnace with the furnace wall temperature of 1273K. The ignition process of the single sludge particle was recorded using a high-speed camera with 1000 fps. Because of the high ash content, the radiation was enhanced during the sewage sludge ignition process, thus the radiant energy analysis technology was used to analysis the ignition mechanism of the sewage sludge. The results show that the flame surround the sludge particle during the ignition process, and the flame area does not increase evidently while the radiation energy of the particle increases obviously with the proceeding of the ignition process. The phenomenon indicates that the volatile and char are simultaneously ignited, that is to say, the sludge particle ignites hetero-homogeneously. As the O2 mole fraction increased, the phenomenon that flame area and luminance sharply increase several milliseconds after the ignition has been observed. The reason for it is that the existing of high O2 concentration intensifies the combustion of the sludge particle and results in the radical increase of the temperature of the sludge particle, and then，causes the quick release and combustion of the volatile. The results revealed that oxygen-enhanced combustion could reduce the gap of combustion characteristics between sewage sludge and coal and improve the combustion stability of the co-combustion of sewage sludge and coal.