Rapid Gasification of Nascent Char in Steam Atmosphere during the Pyrolysis of Na- and Ca-Ion-Exchanged Brown Coals in a Drop-Tube Reactor

Abstract

Several recent studies on in situ steam gasification of coal suggest a possibility of extremely fast steam gasification of char from rapid pyrolysis of pulverized brown coal. The unprecedented rate of char steam gasification can be achieved by exposing nascent char, that is, after tar evolution (temperature range >600°C), but before devolatilization (<900°C), to steam in the presence of Na and/or Ca dispersed in/on the char. In this study, we conducted rapid pyrolysis experiments using ion-exchanged Loy Yang brown coal samples, that is, H-form coal with Na/Ca contents <0.001 wt %, Na-form coal with Na content = 2.8 wt % and Ca-form coal with Ca content=3.2 wt %. These samples were pyrolyzed in an atmospheric drop-tube reactor at a temperature of 900°C, inlet steam concentration of 50 vol. %, and a particle residence times of 2.8 s. The char yields from the pyrolysis of Na-form and Ca-form coals were as low as 12 and 33% on the respective coal carbon bases, and accounted for only 18 and 53% of the char yields from the full devolatilization of the respective coals at 900°C. In addition, the pyrolysis also consumed as much as 0.7-1.1 mol of H 2 O per mol of coal C. On the other hand, the nascent char from the H-form coal allowed carbon deposition from the nascent tar, resulting in a char yield as high as 115% of that from the full devolatilization. The chars from the Na-form and Ca-form coals also acted as catalysts for steam reforming of tar, which was evidenced by significant negative synergistic effects of blending of H-form coal with Na-form coal or Ca-form coal on the tar and soot yields.

Production and characterisation of activated carbon and carbon nanotubes from potato peel waste and their application in heavy metal removal.

“…Pyrolysis is a process which involves heating matter in an inert atmosphere to produce useful products, with the product properties depending upon various factors (Adam et al 2013, Lago et al 2018, Mašek et al 2009. One of which is the chemical composition of the original biomass.…”

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

“…Bayarsaikhan et al (2005) found that the inherent Na + and Ca 2+ species increased the initial gasification rate of the nascent char under a steam atmosphere by more than 80 % in a drop-tube/fixed-bed reactor system. Mašek et al (2009) reported that catalytic steam gasification proceeded extensively even under conditions in which the gasification of the unloaded coal was retarded by coexisting tarry compounds and char. In addition, higher AAEM contents have also been shown to be favorable for maintaining the coking activity of the char, promoting the in situ steam reforming of tar over the char surface.…”

Modeling of gas/particle flow in coal conversion with a drop tube reactor using a lumped kinetic model accounting volatiles–char interaction

“…The gas flow rate was carefully adjusted to maintain a constant gas residence time in the isothermal zone under the different experimental conditions. Detailed descriptions of the experimental setup and procedure are given elsewhere [15,27,28]. The experimental conditions used to investigate the effects of residence time, reaction temperature, steam partial pressure, and solid hold-up on the conversion characteristics of the coal samples in the DTR are provided in Table 1.…”