Effects of Heating Rate and Ion-Exchangeable Cations on the Pyrolysis Yields from a Victorian Brown Coal

Abstract

A Victorian low-rank coal (Loy Yang) was acid-washed and ion-exchanged with Na and Ca to prepare the H-form, Na-form, and Ca-form coal samples. Two more H-form samples were also prepared by rewashing the Na-form and Ca-form samples with acid. These coal samples were pyrolyzed in a wire-mesh reactor where the secondary reactions of the evolved volatiles were minimized. The ion-exchanged coal samples were found to give very different tar yields from those of the raw coal samples. While the tar yields from the pyrolysis of the raw and H-form coal samples were observed to be very sensitive to changes in heating rate, the tar yields from the Ca-form and Na-form samples showed little heating rate sensitivity. Unlike higher rank coals studied previously, the tar yields from the pyrolysis of the raw coal and the H-form coal samples at 600 °C were found to increase much more than the corresponding increases in the total volatile yields as the heating rate was increased from 1 to 2000 K s -1 . Reexchanging Na in the Na-form sample and Ca in the Ca-form sample with H confirmed the effects of Na and Ca but also suggested that the irreversible structural changes taking place during ion-exchange, possibly including the loss of humic materials and the physical reconfiguration of the macromolecular network, should also be considered to ascertain the effects of ion-exchangeable cations during pyrolysis. The heating rate sensitivity of pyrolysis yields is believed to be at least partly related to the presence of carboxyl/carboxylate groups and other bulky substitution groups in the coal as well as the rapid pressure buildup within the particles. The major roles of ion-exchangeable cations during pyrolysis are also discussed in the paper.

Changes in nascent char structure during the gasification of low-rank coals in CO2

“…The sample preparation of two coals can be found elsewhere [14,30]. Briefly, "as mined" coal was dried 100 at low temperature (< 35 °C).…”

“…A wire-mesh reactor (WMR) that was frequently used in the investigation of primary pyrolysis [28][29][30][31] and gasification [32,33] can provide a wide range of heating rate from 0.1 to 5000 K s -1 and high time resolution (increment of 10 ms). It is very suitable for the production of nascent char with even milliseconds holding at a pre-set peak temperature.…”

The Effect of Rice Straw Gasification Temperature on the Release and Occurrence Modes of Na and K in a Fluidized Bed

“…The O-Na+ group is difficult to decompose due to the strong electron adsorption [16]. Second, part of the Na may also have combined with the char matrix to form a stable cross-linked structure [42,43]. These two forms of Na attach on the char stably, but there is no enough energy to break the keys to evaporate Na in this experiment.…”

Toward Low-Temperature Coal Gasification: Experimental and Numerical Studies of Thermochemical Coal Conversion Considering the Interactions between Volatiles and Char Particles

“…4. Under our conditions, it is assumed that the coal sample has already been converted into tar, carbon gases, char, and soot by primary pyrolysis at the top non-isothermal zone of the DTR (at 500-900 °C) (Jamil et al, 2004;Sathe et al, 1999). The carbon conversion reactions in the isothermal zone of the DTR were simulated, and the feedstock was lumped into tar, carbon gases, char, and soot derived from the primary pyrolysis of the coal.…”