Effects of Pyrolysis Atmosphere and Temperature on Coal Char Characteristics and Gasification Reactivity

Abstract

Coal chars are usually produced under complex atmospheres in industrial production. However, most of the research about char characteristics and gasification reactivity uses the coal char samples prepared under an inert atmosphere. In this study, the influences of the pyrolysis atmosphere and temperature on coal char characteristics and gasification reactivity were investigated. A Shanxi bituminous coal was pyrolyzed in a bubbling fluidized bed to produce char samples. A mixture of hydrogen (H2), carbon dioxide (CO2), carbon monoxide (CO), and methane (CH4) was used as simulated pyrolysis gas (SPG). The coal was pyrolyzed in the SPG and N2 atmospheres, respectively. SEM, Raman spectroscopy, and FTIR spectroscopy were used to study the influences of the pyrolysis atmosphere and temperature on the coal char characteristics. The char–H2O and char–CO2 gasification reactivities were measured by using a modified thermogravimetric analysis (TGA) system. The experimental results indicate that the SPG atmosphere has no obvious influence on the coal char morphology, but it has significant influences on the carbon structures and surface chemical groups. The SPG char samples have lower gasification reactivity. The disproportionation reaction of CO, the decomposition reaction of CH4, and the loss of oxygen‐containing structures induced by H2 lead to a higher‐ordered degree of char, and the graphite generated from the disproportionation reaction and the decomposition reaction can decrease the specific surface area of the coal char. These two reasons result in the lower gasification reactivity of SPG char.

Effect of particle size on the pyrolysis process of low‐rank coal: Assessment of structural evolution by N2 adsorption, Raman, X‐ray diffraction, and Fourier transform infrared

“…[3][4][5][6] The pyrolysis process of coal is influenced by many factors, such as the type of coal, differences in the degree of coalification, coal sample size, moisture, petrographic composition and minerals, atmosphere, temperature, heating rate of the pyrolysis process, and pressure. [7][8][9][10][11][12][13] The pyrolysis process has a large effect on the structure of coal coke. Huo et al 14 investigated the effect of particle size on the structure of char prepared by pyrolysis of Inner Mongolian lignite using X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET), and the results showed that the specific surface area and graphitization of char decreased as the particle size increased.…”

“…The pyrolysis process of coal is influenced by many factors, such as the type of coal, differences in the degree of coalification, coal sample size, moisture, petrographic composition and minerals, atmosphere, temperature, heating rate of the pyrolysis process, and pressure 7–13 . The pyrolysis process has a large effect on the structure of coal coke.…”

Kinetic and thermodynamic investigations of CO2 gasification of coal chars prepared via conventional and microwave pyrolysis

“…Char-CO 2 reactivity is greatly affected by char characteristics, which are determined mainly by coal pyrolysis conditions, of which the pyrolysis temperature is the most important parameter (Wang et al 2016b). Microwave heating can produce rapid, volumetric, selective, noncontact heating of coal by directly converting electromagnetic energy into thermal energy (Parvez et al 2019).…”

Thermodynamic and economic analyses of a novel coal pyrolysis–gasification–combustion staged conversion utilization polygeneration system

“…However, the char gasification experiments in a circulating fluidized bed (CFB) indicate that the molar fraction of CO 2 of syngas is very high, so a large amount of char is actually combusted during the gasification process . Because the graphitized carbon in char has low reactivity and is much harder to gasify than the disordered carbon, the high CO 2 molar fraction of syngas increases the cost of gas cleaning and the difficulty of H 2 separation. The char combustion during complete gasification also consumes O 2 , and the O 2 produced by an air separation unit (ASU) is very expensive.…”