Laboratory Study on Gasification Reactivity of Coals and Petcokes in CO₂/Steam at High Temperatures

Abstract

The gasification reactivity of 13 carbonaceous materials in CO 2 or in steam was studied in the temperature range 1000−1600 °C. The gasification reaction was carried out in a drop-in-fixed-bed reactor under atmospheric pressure. The gasifying agent fed into the reactor either as pure gas or as 36% volumetric concentration in argon with a total gas flow rate of 500 mL/min. The test samples included different rank coals, petcokes, and graphites. The raw materials were used to eliminate the problem related to char prepreparation. The dynamic profiles of gasification rate were used to compare the gasification behaviors for different samples. The physicochemical characteristics of chars were evaluated by scanning electron microscopy and N 2 adsorption method. The experimental results reveal that the difference in gasification reactivity among samples decreases as the temperature increases and is not distinguishable for most coals at 1600 °C. However, the temperature is still critical for gasification of petcokes and some high-rank coals at high temperature. The gasification reactivity of petcokes is 2−9 times lower than that of coals at 1600°C. The kinetic analysis reveals that the temperature dependence of reactivity varies with the type of materials. It is interested to find that, in the temperature range 1400−1600 °C, the gasification reactivity in CO 2 is higher than that in steam for coals but not for petcokes. From the views of the reaction thermodynamics, the gas diffusion difficulty, and the catalytic effect, the high temperature is favorable to the CO 2 -gasification. The effect of AAEMs (alkali and alkaline earth metals) should be a key factor. The content of AAEMs is apparent in coals but limited in petcokes. The Arrhenius plots reveal that the gasification mechanism may be altered around 1200 °C for most of coals. The petcokes are appeared with the most compact physical structure and the least gasification reactivity. Either the shrinking core model (SCM) or the volume reaction model (VRM) is suitable for most of the samples and conditions but not suitable for the petcokes. A diffusion term associated with the carbon structure may be needed for modelling the gasification behaviors of the petcoke-like materials.

CO2 gasification of biogenic fuels in a dual fluidized bed reactor system

“…The cold gas efficiency as well as the CO 2 conversion rate were both decreased with increasing moisture content and particle size. [22] Another researcher, Ren et al, considered the gasification temperature as the most significant parameter which affects the gasification reactivity of char and controls the gasification rate [23]. These findings and hypothesis were used for comparison with the generated results within this publication.…”

Pore Development During CO2 and Steam Activation of a Spent Tyre Pyrolysis Char

“…Some studies found 97 that steam activation generated activated carbons with narrower pore size distribution and larger 98 surface area and total pore volume than CO2 activation [23,27,32], which was believed to be caused 99 by higher activation rates in char-steam [20,33,34]. However, the activation rate of char also heavily depends on the activation temperature and concentration of the activation agent, regardless of which activation agent is used [35][36][37][38]. So far, very few literature reports have examined the effects of the concentration of the activation agent on the development of pore structure during the activation process, although it has been demonstrated to play a significant role in activation [35,37].…”

“…However, the activation rate of char also heavily depends on the activation temperature and concentration of the activation agent, regardless of which activation agent is used [35][36][37][38]. So far, very few literature reports have examined the effects of the concentration of the activation agent on the development of pore structure during the activation process, although it has been demonstrated to play a significant role in activation [35,37]. Literature reports on the effect of the concentration of activation agent are relatively few.…”

Gasification Kinetics of Bituminous Coal Char in the Mixture of CO2, H2O, CO, and H2

“…Many researchers [21][22][23][24] have devised reaction models of char-carbon dioxide (CO 2 ) and char-water vapor (H 2 O) separately to explore the coal gasification reaction mechanism. The kinetics of both char-CO 2 and char-H 2 O gasification have also been studied in detail [25][26][27][28]. However, these studies, carried out in systems with a sole gasifying agent, could hardly be applied in systems where the mixtures of carbon dioxide, water vapor, carbon monoxide (CO), and hydrogen (H 2 ) usually serve as gasifying agents in actual industry.…”