CO2 Gasification Of Coke Research Articles

Coke evolution during the air- and oxy-firing regeneration of a spent Ni/ZnO sulfur adsorbent

Reactive adsorption desulfurization (RADS) is an effective desulfurization technology in refineries to reduce the sulfur contents in oil products. To ameliorate the desulfurization technology, the evolution of coke was first studied in the air-firing regeneration of a typical spent Ni/ZnO sulfur adsorbent used in RADS. Efforts were made to elaborate the conversion of carbon and sulfur during the oxy-firing regeneration of the spent adsorbent to test the possibility of applying that carbon capture technology – oxy-fuel combustion to the sulfur adsorbent regeneration. A lab-scale drop-tube furnace was employed to conduct the combustion experiments; and the speciation of carbon and sulfur in the regenerated adsorbents was characterized by advanced techniques including near-edge X-ray absorption fine structure (NEXAFS), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). The catalytic role of metals (Ni/Zn) in the coke combustion was also verified by acid leaching and temperature-programmed oxidation (TPO) experiments. It has been founded that the carbonaceous materials deposited on the adsorbent comprise five groups, including polyaromatic and graphitic carbon with a fraction of around 27 mol% of the entire carbon, and the other groups which are mostly light aliphatic compounds and oxygen-containing functional groups. During the air-firing regeneration process, most of the light coke species were oxidized into oxygenated intermediates and then desorbed as CO and CO2, with a small portion being polymerized into heavy molecules. Oxy-firing regeneration was verified to improve the efficiency of coke combustion due to the metal-catalyzed CO2 gasification reaction and improved the sulfur conversion under the oxygen-lean condition such as 3 vol% O2 in CO2. The carbon conversion increased from 23% in 3%O2/N2 to 31% in 3%O2/CO2 at 510 ℃. In the meantime, the sulfur conversion was also increased from 50% to 57% at 750 ℃, which is probably due to that the CO2 gasification of coke alleviated the competition of oxygen between carbon and sulfur.

Interaction of vitrinites in similar middle-rank coals during coking process

Interaction of vitrinites in coals during coking process has effect on the properties of the coke. The evaluation of the vitrinites interaction is of great significance of coal blending and coke quality prediction. Vitrinites separated from the similar middle-rank coals in Tangshan (TS) and Ewirgol (EW) are mixed with ratio of 0:1, 1:3, 1:1, 3:1, 1:0 to prepare cokes. The characteristics of coke-CO2 gasification were studied to evaluate the interaction of vitrinites during coking process. The results show that the maximum reaction rate (rmax) and the comprehensive gasification index (Gc) of cokes have negative quadratic linear relationships with the content of TS vitrinite, and the difference between the experimental and theoretical gasification reactivity of cokes indicates the interaction of EW and TS vitrinites in the coking process. An interaction index (δ) based on the gasification reactivity of cokes is proposed to characterize the degree of interaction between the two kinds of vitrinites in coking process, and the interaction index based on Gc is 6.9%. Also, XRD and Raman spectroscopy analysis results show that the microcrystalline structure parameters (n and fa) have a negative linear relationship with Gc, and the Raman parameter AD1+D2+D3+D4/AG has a positive quadratic linear relationship with Gc, the Raman parameter AG/AAll has a negative quadratic linear relationship with Gc. TS vitrinite in coal blending can enhance the graphite characteristics in the coke and increase the order degree of carbon structure in the coke, which improve the resistance of CO2 erosion for the cokes.

ReaxFF MD simulations of petroleum coke CO2 gasification examining the S/N removal mechanisms and CO/CO2 reactivity

High S content (>4 wt%) petroleum coke (petcoke) are used as fuel but are also potential gasification feedstocks (commonly achieved with CO2). Petcoke S and N heteroatoms are in thermally stable structures and thus will contribute to the gasification process during consumption. Here, the removal and transformation of S and N from a petcoke atomistic representation during CO2 gasification were explored via the reactive force field (ReaxFF) NVT simulations. Pyrolysis, reducing, and oxidizing conditions were examined at 3000 K for 250 ps. Under these conditions the slow pyrolysis and slower gasification processes overlap, thus both contribute to the overall gasification behavior. The S/N transformations were: thiophenic-S → COS, C1-2S → CnOnS, COnS → H1-2S, SO2; with pyrrolic and pyridinic N → CON, CN, NO1-2 → C1-2O1-2N, COnN, HNO1-2 → HCN, HNO1-2, NO1-3 (0 < n < 5). The ReaxFF simulations captured the Boudouard reaction with one O atom in CO2 bonding with a C atom then the O-C bond in CO2 breaks after producing CO. The petcoke C atom that bonded with the O atom is then removed producing the second CO molecule. Reactive molecular dynamic simulations such as these are helpful in capturing both the structural diversity (scale challenge) and the complexity of the interactions to elucidate contributions to coke consumption.

Effects of magnesium compounds on the gasification of petroleum coke

The magnesium compounds are used as catalysts for petroleum coke-CO2 gasification. The effect of catalyst type, catalyst addition amount and gasification temperature on petroleum coke-CO2 gasification is studied by using thermogravimetric analyzer. It is shown that the catalytic activity of MgCl2 is higher than other magnesium catalyst. The catalytic activity of the catalyst increases with the increase of temperature. At the same temperature, the time required for complete gasification of petroleum coke decreases with the increase of catalyst dosage. There is a limit to the amount of catalyst added, and the best amount of magnesium chloride is 5%.

Effects of MgCl2 on the gasification kinetics of petroleum coke

ABSTRACTMgCl2 is used as catalysts for petroleum coke-CO2 gasification. The effect of catalyst addition amount and gasification temperature on petroleum coke-CO2 gasification is studied by using thermogravimetric analyzer. It is shown that magnesium chloride has a catalytic effect on petroleum coke gasification. At the same temperature, the time required for complete gasification of petroleum coke decreases with the increase of catalyst dosage. There is a limit to the amount of catalyst added, and the best amount of magnesium chloride is 5%. The kinetics model of petroleum coke catalytic gasification is described by using the homogeneous model, the shrinkage model, and the Gaussian model, respectively. Compared with the gasification reaction activation energy calculated by the conversion method. It is shown that the shrinkage model can better describe the dynamic characteristics of petroleum coke catalytic gasification.

Effect of SiO2 on loss of catalysis of inherent metallic species in CO2 gasification of coke from lignite

Inherent metallic species retained by coal char or coke, such as Na and Ca, behave as catalysts in gasification. The char/coke normally contains inherent SiO2, which can react with the inherent catalysts to form silicates, resulting in catalyst deactivation over the range of pyrolysis, carbonization and gasification, and thereby reducing the char/coke reactivity. The present authors simulated the inherent catalyst deactivation experimentally by blending a Victorian lignite with SiO2, briquetting the SiO2/lignite blend, carbonizing the briquette, and then gasifying the coke with CO2. The kinetic analysis of the gasification employed a comprehensive model, which assumed progress in parallel of non-catalytic and catalytic gasification. The model quantitatively described the measured kinetics of the coke gasification with different SiO2 contents over a range of coke conversion up to 99.9%. The kinetic analysis revealed that the SiO2 deactivated substantial and entire portions of the most active catalyst and its precursor, respectively, before the gasification (i.e., during the carbonization). The catalyst deactivation also occurred during the gasification, but mainly following a self-deactivation mechanism that involved no silicates formation.

Effect of Iron Species and Calcium Hydroxide on High-Sulfur Petroleum Coke CO2 Gasification

The effect of iron species on petroleum coke CO2 gasification was studied in the present work. The effects of the temperature (1173–1673 K), the catalyst types, catalyst loading (ranging from 0 to 5 wt %), and composition during the gasification of petroleum coke CO2 were discussed. The catalytic gasification residue of petroleum coke was identified by X-ray diffraction (XRD). The XRD result shows that the iron species exist as Fe3C at the initial stage of gasification. Then, most Fe3C is transformed into reduced iron Fe0; subsequently, some of these species are oxidized to FeO, Fe2O3, and Fe3O4, while some of which quickly reacted with S in petroleum coke to form stable FeS, leading to catalyst deactivation. The changes during gasification are discussed in terms of the oxygen-transfer mechanism. It is clearly demonstrated that there exists a significant synergistic effect between calcium hydroxide and iron species during petroleum coke gasification. The random pore model is suitable to describe catalytic...

The Effect of Metallic Iron Particle on Coke-Matrix after Coke CO2 Gasification Reaction

In order to prevent pulverization and fracture of metallurgical coke, control of gasification reaction part in coke lump and embrittlement behavior is important. Addition of catalyst particle is an effective and a simple method for enhancement of the CO2 gasification reactivity. However, the effect of the catalyst particle on coke-matrix and gasification part of coke lump after gasification reaction has not been investigated. In this study, the effect of iron particles on coke-matrix state after gasification reaction is investigated experimentally. Coke-matrix vanishing is evaluated by spatial distribution of lump porosity and microscopic observation. Elastic modulus of coke-matrix is evaluated by nano-indentation method. Coke lumps with and without iron-particles (ferrous coke and formed coke, respectively) were used. These coke lumps were gasified by CO2-containing gas. Reaction temperature was set at 1173 K. Reaction gas compositions were set at 100/0 and 50/50 in ratio of CO2/CO. In each reaction gas composition, in ferrous coke, a decrease in the elastic modulus of coke-matrix with progress of gasification is smaller than that in formed coke and coke-matrix vanishing occurred. It is suggested that the iron particle promotes gasification reaction of coke-matrix selectively around itself (and coke-matrix in that part is rapidly vanished). It is also suggested that this reaction mechanism maintains elastic modulus of coke-matrix because of the local rapid gasification reaction around the iron particle.