Experimental Investigation of Reaction Confinement Effects on Coke Yield in Coal Pyrolysis

Abstract

The pyrolysis of agglomerating coal was analyzed by thermogravimetric analysis (TGA) coupled to microgas chromatography (μGC) to determine the effects of reactor confinement on solid product yield, tar evolution, and gas composition. The primary volatile products generated from pyrolysis are studied using two TGA crucibles with height to width aspect ratios of 0.11:1.0 and 2.0:1.0 for heating rates of 1, 3, and 10 K min −1 . Mass balances were determined from measurements of the solid residual, gaseous flow rates, and tar products captured via glass impingers. The measurements resulted in mass balance closures greater than 99%. The higher aspect ratio confinement provided a zone where the residence time of volatile species was extended to 0.35 s from 0.04 s for the low aspect ratio confinement. The extended residence time was found to increase the solid yield by 0.6−5.7% for the low and mid ranged volatile material coals by secondary tar reactions which form coke. There was a trend of increasing solid yield with a decreasing heating rate because of the shorter residence time of the released volatile material at the higher heating rates. A decrease in tar production by 2.1−2.5% was observed in the higher aspect ratio confinement. The differences in product evolution between the two confinements were determined to be due to reactions occurring in the range of 783−848 K, which produce hydrogen, methane, and coke. In the confinement of higher aspect ratio, hydrogen production increased by 10% and 30% for low and mid VM coals, respectively, along with a 40% increase in methane production for both coals. The higher productions of methane, hydrogen, and solid residual between 820 and 1100 K for increased residence time of 0.27−0.35 s are due to demethylation and recombination reactions during the formation of char from recondensed tar products.

A Comparative Study on the Performance of Direct Carbon Solid Oxide Fuel Cells Powered with Different Rank Coals

“…Subsequently, some aliphatic chains and aromatic rings are broken down to form hydrogen and small molecular alkanes, accompanied by highly active hydrogen and atomic free radical fragments. Finally, the pyrolysis reaction gradually decelerates, and the polycondensation reaction occurs to form tar and semicoke. , Examining Figure , HLH shows the lowest initial thermal decomposition temperature, whereas TX shows the highest. In the environmental stabilization stage, the weight of the sample is essentially stable, suggesting that the pyrolysis reaction of coal is completed.…”

“…Finally, the pyrolysis reaction gradually decelerates, and the polycondensation reaction occurs to form tar and semicoke. 24,25 Examining Figure 3, HLH shows the lowest initial thermal decomposition temperature, whereas TX shows the highest. In the environmental stabilization stage, the weight of the sample is essentially stable, suggesting that the pyrolysis reaction of coal is completed.…”

Investigating Secondary Pyrolysis Reactions of Coal Tar via Mass Spectrometry Techniques

“…The experimental setup was described in detail in previous works. 19,20 The hot volatile pyrolysis products were transferred via a 1 / 4 in. passivated stainless-steel tube heated to 275 °C.…”

“…It has recently been shown via thermogravimetry and high-frequency gas chromatography that the residence time of pyrolysis tar in the solid−gas interface of the reacting solid can be systematically altered by changing the height and cross-sectional area of the reaction confinement. 19 It was demonstrated that increasing the residence times of tar within the solid−gas interface will increase tar cracking, leading to more hydrogen, methane, and solid carbon and decreasing tar production by 2.1−2.5 wt %. 19 The present work shows a set of experiments investigating the secondary tar cracking reactions in high-temperature pyrolysis environments by analyzing the change in tar composition as a result of the extended residence time.…”

“…19 It was demonstrated that increasing the residence times of tar within the solid−gas interface will increase tar cracking, leading to more hydrogen, methane, and solid carbon and decreasing tar production by 2.1−2.5 wt %. 19 The present work shows a set of experiments investigating the secondary tar cracking reactions in high-temperature pyrolysis environments by analyzing the change in tar composition as a result of the extended residence time. In this work, the tar product generated at varying residence times in a pyrolysis environment was analyzed using GC−MS and laser desorption/ ionization−time-of-flight mass spectrometry (LDI−TOF).…”