Carbon Conversion Of Char Research Articles

Experimental study on the reaction kinetics of char combustion in a pressurized O2/H2O atmosphere

Pressurized O2/H2O combustion is a potential CCS technology. In this study, a pressurized horizontal furnace was used to prepare pyrolysis char under pressurized inert atmosphere, and then a pressurized drop tube furnace was used to carry out char combustion under pressurized O2/H2O atmosphere (5% O2, 20% H2O) at the same pressure and temperature as the pyrolysis process. The carbon conversion of char under different pressures (0.4/0.7/1.0 MPa), temperatures (900/950/1000 °C), and residence time (1.38/2.76/4.14 s) was studied by proximate analysis. The random pore model was used to calculate reaction kinetic parameters of char combustion at different pressures. The results show that when the pressure increased from 0.4 MPa to 0.7 MPa, the carbon conversion increased significantly, with the increment reaching up to 9.90 percentage points. The marginal diminishing effect became significant when the pressure was greater than 0.7 MPa. The reaction activation energy and pre-exponential factor at 0.4/0.7/1.0 MPa were 66.53/66.29/35.79 kJ/mol and 20.54/36.84/1.69 s−1, respectively.

Steam Gasification of Caking Bituminous Coal using Composite Bimetallic Catalyst

The catalytic steam gasification of Yanzhou (YZ) bituminous coal char loading with K2CO3 and CaO was studied in a fixed bed with 20 mm in inner diameter. The influence of K2CO3 on caking properties of Yanzhou bituminous coal was investigated. The relationship between carbon conversion and reaction time and catalyst loading amount of Yanzhou coal char was measured from 700 to 850°C. The effects of reaction temperature and catalyst loading amount on molar yield of the gasification gas were studied. The influence of catalyst on the microstructure of the YZ coal char was determined. The results show that K2CO3 had significant effects of caking destruction and catalytic gasification on YZ coal. The carbon conversion of YZ coal char increased with the increase of gasification temperature and K2CO3 loading amount. The addition of CaO could improve the carbon conversion of char and promoted the generation of gasification gas to some extent. The molar yield of gasification gas increased with the increase of gasification temperature, and H2 increased the most. The 002 peak of YZ coal char became lower and wider, and moved towards the lower position with the addition of K2CO3 and thus decrease the graphitization trend.

A study of the effect of H2O on char oxidation during O2/H2O combustion using reactive dynamic simulation

In present work, the effect of H2O on the oxidation of char during O2/H2O combustion is investigated by reactive molecular dynamics simulation (ReaxFF MD). The simulation results show that H2O promotes the overall carbon conversion of char, which is consistent with the experimental results. By analyzing the distribution of H2 yield, the contributions of the char-H2O gasification reaction to the overall carbon conversion at different temperatures are quantitatively determined. The activation energy of char-H2O gasification reaction obtained from ReaxFF MD simulations is 199 kJ/mol. The contributions of the oxidation reactions to the overall carbon conversion in O2/H2O combustion are also obtained. The results show that the carbon oxidation is enhanced by the reactivity of H2O. The effect mechanism of H2O on char oxidation is revealed by analyzing the distributions of OH radicals·H2O significantly increases the concentration of OH radicals through the reaction of H2O with O radicals. Then, the contribution of H2O to the oxidation rate of char at different char conversions in O2/H2O combustion is quantitatively determined based on the assumption that char oxidation and char gasification reactions occur at separate active carbon sites. Finally, the effect of H2O concentration on the contribution of H2O to the oxidation rate of char is investigated. The results show that the oxidation rate contributed by H2O is enhanced with increasing H2O concentration.

CFD-Based Modeling of Kraft Char Beds • Part 2: A Study on the Effects of Droplet Size and Bed Shape on Bed Processes

This is the second of two papers. The first paper presented the char bed burning model used in this work. In this paper, the effects of liquor droplet size and bed shape on kraft char bed processes and lower furnace combustion are studied using a computational fluid dynamics (CFD)-based furnace model. The simulations show that droplet size affects not only the amount of in-flight conversion and the amount of combustible material reaching the bed, but also to what degree char carbon conversion in the char bed is due to direct oxidation or gasification. Droplet size also affects char bed burning indirectly through bed shape. Char bed shape affects the degree to which combustion air jets impinge on the bed surface, increasing carbon conversion by direct oxidation. In addition, changes in bed shape over time affect char bed processes. The results suggest that when a char bed starts to grow, the local carbon input to the bed could increase with bed height. In addition, carbon conversion decreases in locations of air jet impingement if the bed shape is not maintained.