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Abstract
This study presents the effects of acoustics on the primary yields of pyrolytic reactions of black liquor (a spent liquid from pulping processes in pulp and paper manufacturing) solid particles in an entrained flow reactor at gas temperatures between 400-700°C with flow rates of 5-20 SLPM. The particle sizes were around 125 μm. The acoustic intensities were 151 dB and frequencies were from 300-1000 Hz. At a gas temperature of 550°C, char yield was reduced by 10° and CO and CO2 gas yields were increased by about 50-400% and 50-800% respectively, with acoustics under various particle reaction (residence) times. The results of char and gas yields also show that the acoustic effects were more enhanced at the initial particle heat-up period. The fact that acoustics selectively enhanced the two endothermic reactions, organic carbon reduction, and inorganic (carbonate) carbon formation indicates that acoustics increased the heat transfer from the surrounding gas to the particles. SEM analysis of the char surfaces revealed that particles swelled much more and large bubbles were formed at the particle surface when particle were pyrolyzed with acoustic fields, further verifying the enhanced heat and mass transfer between the particle surfaces and the surrounding gas. At a gas temperature of 400°C, char, CO, and CO2 yields were unchanged with acoustics due to a temperature too low for progression of tar secondary reactions. At a gas temperature of 700°C, CO2 yield increased by 30-80% with an acoustic field; whereas, CO and char yields were about the same, indicating that a critical heat and/or mass transfer rate has been achieved with or without acoustics and that secondary cracking of reactive tar functional groups forming CO2 is more likely than is polymerization into char.