Pyrolysis of Black Liquor in a HIgh-Intesity Acoustic Field, 1998 International Chemical Recovery Conference Proceedings

This study presents the effects of acoustics on the product yields and swelling of soda-AQ black liquor (a spent liquid from pulping processes in pulp and paper manufacturing) solid particles pyrolyzed in an entrained flow reactor at gas temperatures between 400-700°C. Particle diameters were 106-125 pm. The acoustic amplitudes were 151 dB and frequencies were 300-1000 Hz. Nitrogen gas flow through the reactor was 5-20 slpm. At 400°C, acoustics did not affect char or CO and CO2 yields due to too low temperature for progression of tar secondary reactions. At 550°C, char yield was reduced by 10% and CO and CO2 gas yields were increased by 40-500% and 40-l000%, respectively, with an acoustic field under various particle reaction (residence) times. At 700°C, CO2 yield increased by 30-80% with an acoustic field, whereas CO and char yields were about the same. The results of char and gas yield also show that acoustic effects were more enhanced during the initial particle heatup period. The fact that acoustics selectively enhanced the two slightly endothermic reactions, organic carbon reduction and inorganic (carbonate) carbon formation, indicates that acoustics increased the heat transfer from the surrounding gas to the particles. The fact that acoustics most significantly increased CO2 yield and reduced char yield at 550°C, at which reactive tars may undergo secondary cracking to form CO2 or polymerize into char unless the tar can escape, indicates that acoustics enhanced the transport of reactive tar species away from the pyrolyzing particle. At a higher temperature (700°C), lack of reduction of char yield with acoustics indicates that secondary cracking of reactive tars to form CO2 is much more favored than is polymerization into char. SEM analysis of the char surfaces revealed that particles swelled much more and large bubbles were formed at the particle surface when particles were pyrolyzed with acoustic fields, further verifying the enhanced heat and mass transfer between the particle surfaces and the surrounding gas.