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Baking is the most costly and critical process in anode preparation, and the study from the microscopic scale is conducive to the optimisation of anode baking process. In this research, a hybrid simulation method of reactive force field molecular dynamics (ReaxFF-MD) and force-biased Monte Carlo (fbMC) was proposed to understand the interaction mechanism between coal tar pitch (CTP) and calcined petroleum coke (CPC) during kneading and baking processes, and to explore the optimal ratio of CTP from the molecular scale. Results showed that the CTP content of 14 wt.% was beneficial for anode production. The mechanism of anode coking behaviour at high temperatures was also analyzed. The carbonisation of CTP during high-temperature baking broke the carbon rings and formed straight chains, exposing active carbon atoms that can bond with the remaining layers. As the high-temperature simulation progresses, the carbon chains at the bonding sites became increasingly cyclized and aromatised, which made the layered structure of the baked block similar to that of graphite. The generation of various volatile hydrocarbons during the baking process was observed, namely CH4, C2H4, C2H2, C2H6, and C3H6. This work provides theoretical basis for process optimisation. [ABSTRACT FROM AUTHOR]

High-sulfur petroleum coke (petcoke) is generally used as fuel in industries, but the S and N in petcoke will damage the environment during the combustion process. Gasification of petcoke could reduce pollution from S/N-containing compounds. Supercritical water gasification (SCWG) is a new direction with good potential because of its high activity and accelerated reaction characteristics. This work used the reactive molecular dynamics (ReaxFF) simulation to explore the removal and conversion mechanisms of S and N during the SCWG of petcoke. The simulation results showed increasing the pressure and temperature could improve the desulfurization speed. S removal began with the conversion of thiophene-S into C1–4S (mainly C2S) or COS, followed by the conversion into H1–2S in the presence of a large number of hydrogen atoms. The removal of N began with the conversion of pyrrole/pyridine-N into C1–3N(mainly CN). Then, CHON and CON were successively formed. The behaviour of S/N in SCWG could be summarised as follows: thiophene-S → CxS + H → HS + H → H2S, thiophene-S → CxOS + H → CHOS, pyrrole/pyridine-N → CxN/HCxN → CN → CHON → CON, H2N → HON. [ABSTRACT FROM AUTHOR]

Abstract Green petroleum coke (petcoke) is used as a feedstock for raw carbon material or as a fuel. Petcoke with high sulfur (S) content (>4 wt%) is typically restricted to fuel use unless extensive S removal is successful. Here, the S removal mechanisms during both pyrolysis and combustion were explored using the Reactive Force Field (ReaxFF) MD approach. A structural representation (C 1648 H 772 O 59 N 24 S 47) of a green Qingdao petcoke was generated coupling high-resolution transmission electron microscopy lattice fringe image analysis and analytical data. This structure was consistent with elemental, aromaticity (FT-IR), the pair correlation function (XRD), and functional group (S, O, and N from XPS) data. The ReaxFF pyrolysis simulation produced gas and tar yields of 44.7 and 11.0 wt% at 3000 K after 250 ps of simulation. The combustion simulation on the same initial structure was performed in an O 2 environment. During the pyrolysis simulation, the first-step for S-removal was thiophenic sulfur conversion to C 1–4 S (mostly C 2 S), COS, or CNS. The heteroatom pyrolysis overlapped, for this structure, at these conditions. However, for the combustion simulation earlier conversion of thiophenic sulfur to COS was observed. No N S containing structures occurred in this O-rich environment, as pyrrolic and pyridinic N quickly oxidized into CON or NO compounds. The S transformation during combustion can be summarized by COS → CO 2 S → CO 3 S → CO 4 S. The H atoms reacted with S-containing gases like COS/C 2 S/CNS producing HS and H 2 S rather than with the coke-S. [ABSTRACT FROM AUTHOR]

Petroleum coke (petcoke) contains high carbon and low ash qualities, but often with an undesirably high sulfur content. High-temperature (>1000 K) calcination produces a coke, suitable for many industrial uses, with an acceptable S content. Here the sulfur removal behavior during high-temperature pyrolysis was evaluated by combining high-temperature thermogravimetric analysis with product gas mass spectrometry (TG-MS), and reactive molecular dynamics (ReaxFF) simulations. From the TG-MS data the pyrolysis temperature of >1000 K significantly affected the S rejection. Three petcokes under 1273–1773 K in six different particle sizes (≤6 mm) were pyrolyzed to determine the desulfurization initiation temperature and desulfurization extent. A non-uniform behavior across the particle size ranges was obtained. Six Qingdao petcoke samples with cut sizes of <0.038, 0.07–0.05, 0.11–0.09, 0.25–0.15, 1.18–0.88, and 5.00–6.00 mm all achieved a similar desulfurization extent (∼80%) at >1673 K. However, considerable variability was shown in larger particles (1.18–0.88 and 5.00–6.00 mm) for Qingdao, Zhenhai, and Qilu petcoke between 1473 and 1773 K. The products included water (presumably from coke quench, 350–410 K), volatiles (430–550 K), CO 2 and H 2 (>800 K, mainly), CO and SO 2 (>1200 K, mainly), and trace quantities of CS 2 (>1400 K). The stable sulfur-containing products of this petcoke during high-temperature pyrolysis were SO 2 and trace amounts of CS 2 . However, COS and H 2 S pyrolysis products were absent or below the detection limits. The pyrolysis behavior was explored using ReaxFF on a macromolecular petcoke structure with the S atoms in thiophene-like functional groups. The mechanism of S loss, under the simulation conditions, involved molecular rearrangement and thermolysis into intermediate states (C 2 S and CNS) and COS. These were explored for 250 ps for 3000, 3500, and 4000 K with the constant volume/temperature (NVT) ensemble. The sulfur removal transformation during pyrolysis is generally followed: thiophene sulfur → COS, C 2 S, or CNS → HS → SO 2 or CS 2 . [ABSTRACT FROM AUTHOR]

Structural features of a green Qingdao petroleum coke (produced at ∼ 500 °C) were investigated by image analysis of high-resolution transmission electron micrographs, XRD, and matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS). The fringe length distribution was comprised mostly of fringes <20 Å, with a peak at 5–7 Å. The MALDI-TOF MS data also indicated an abundance of low molecular weight material 250–300 Da. The coke had considerable preferential orientation within the field of view of the micrograph. However, the degree of ordering was poor with fringe stacking occurring for ∼20% for the fringes, with a mean of 2.11 fringes. XRD also indicated low ordering as expected for a lower quality, low temperature coke. The poor nanostructure-level order was a result of small fringe lengths, with curvature (present in 42% of the fringe) likely contributing. It is thus a partially ordered system, with order varying over length scales. An image-guided construction strategy capable of controlling the degree of order (utilizing Fringe3D and Vol3D) was used to construct an atomistic structural representation (C 3717 H 1830 N 54 O 134 S 109 ) incorporating many experimental parameters. The structure was comprised of preferentially orientated molecules, but with the observed limited stacking, incorporating both curvature frequency and extent. [ABSTRACT FROM AUTHOR]

A real-time mathematical model for the two-dimensional temperature field of petroleum coke calcination in vertical shaft calciner was developed based on computational fluid dynamics. In the modeling process, the petroleum coke discharging process was described by the solid viscous flow, the dynamic heat flux boundary condition was adopted to specify the heat transfer between the flue wall and the gas in the flue, and the Arrhenius equation was used to characterize the pyrolysis process of petroleum coke. The model was validated with both measurement data and data from the literature. The effects of discharge rate per pot, volatile content of green coke, and excess air coefficient on the temperature field of the vertical shaft calciner were investigated with the use of the developed model. The following reasonable operating conditions were obtained: the discharge rate per pot should be less than 90 kg/h, the volatile content of green coke should be in the range of 9-11%, and the excess air coefficient should be in the range of 1.10-1.20. In this work, the governing equations were discretized by using the finite volume method, and the discrete linear equations were solved by using sparse matrix package UMFPACK. The model calculating process takes about less than 15 s. Therefore, the model is beneficial in realizing real-time online temperature detection of petroleum coke calcination in a vertical shaft calciner. [ABSTRACT FROM AUTHOR]

The aim of this work was to establish a mathematical model for the analysis of calcining process of petroleum coke in a 24-pot calciner via computational fluid dynamics (CFD) numerical simulation method. The model can be divided into two main parts (1) heterogeneous reacting flow of petroleum coke calcination in the pot was simulated using a two-fluid model approach where the gas and solid phase are treated as a continuous phases; and (2) the standard turbulence equations combined with the finite rate/eddy-dissipation combustion model and discrete ordinates model were solved for the turbulent gas reacting flow in the flue. The model of the calcining process was implemented in ANSYS Fluent 15.0 (commercial CFD software) and validated by industrial production data. After the validation research, the model has been applied to inspect the distribution features of the temperature field in the furnace, the concentration field of residual moisture and volatiles in the petroleum coke, and the vector velocity field of gas and solid phases. This research can provide a theoretical basis for optimizing the structure and improving the automatic control level of a pot calciner. [ABSTRACT FROM AUTHOR]

• The CO 2 gasification mechanism of petcoke was investigated via ReaxFF simulations. • The S/N removals and transformations from petcoke were investigated. • Boudouard reaction was captured and disassembled into two step reactions. High S content (>4 wt%) petroleum coke (petcoke) are used as fuel but are also potential gasification feedstocks (commonly achieved with CO 2). 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 CO 2 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, C 1-2 S → C n O n S, CO n S → H 1-2 S, SO 2 ; with pyrrolic and pyridinic N → CON, CN, NO 1-2 → C 1-2 O 1-2 N, CO n N, HNO 1-2 → HCN, HNO 1-2 , NO 1-3 (0 < n < 5). The ReaxFF simulations captured the Boudouard reaction with one O atom in CO 2 bonding with a C atom then the O-C bond in CO 2 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. [ABSTRACT FROM AUTHOR]

In this study, for the purpose of substituting part of petroleum coke with low ash anthracite to prepare carbon anode used in aluminum electrolysis, the effects of high-temperature pyrolysis on the structure and properties of coal char and petroleum coke were studied at the temperature range of 1000 °C–1600 °C. Results showed that the carbon crystallite structure of coal char and petroleum coke became more ordered with the increase of the temperature. However, the graphitization degree of coal char was lower than that of petroleum coke at the same pyrolysis temperature. The Brunauer-Emmett-Teller (BET) surface area of coal char decreased with the increase of temperature, whereas the BET surface area of petroleum coke decreased first and then increased. The increase of pyrolysis temperature generally inhibited the gasification reactivity of coal char, whereas the gasification reactivity of petroleum coke was inhibited first and then promoted. Moreover, the increase of pyrolysis temperature led to the rapid decrease of powder resistivity of coal char and petroleum coke. In particular, the powder resistivity of coal char was significantly higher than that of petroleum coke at the same pyrolysis temperature. Additionally, the real density of coal char and petroleum coke showed a different trend with the increase of temperature. Specifically, the real density of the former decreased, whereas that of the latter increased. The causes of the above observations were also discussed. Overall, this study provides further understanding about the differences between coal char and petroleum coke, which will facilitate the preparation of carbon anode from the mixture of coal char and petroleum coke. [ABSTRACT FROM AUTHOR]

[Display omitted] • Summarized equations could predict the features value at given temperatures. • Microstructural features transformation was quantified via HRTEM analysis method. • Features variation fitted well with the Logistic regression model above 873 K. • Trace metals were considered in the calcined coke modeling process. • Multi-scale atomistic models capture actual microstructural features data. Calcined petroleum coke is a high-quality precursor for graphitic electrodes, and the heating temperature is an essential parameter for the key calcination process. Microstructural features (including lattice fringes length, stacking, orientation, and curvature) transformation at various temperature stages and multi-scale atomistic representations of the calcined coke were investigated by combining HRTEM lattice fringes analysis, XRD, XPS, XRF, mathematical function fittings, computational scripts, molecular dynamics relaxation, and DFT calculation. In the temperature range of 289 to 1873 K, the average lattice fringe length, total stacking frequency, 45° contribution, and curved fringe length frequency changed from 7.36 to 12.03 Å, 10.26 % to 50.63 %, 44.91 % to 98.71 %, and 58.74 % to 36.13 %, respectively. The variation patterns of most microstructure features fitted well with the quadratic function pattern in the temperature range of 298 to 873 K and the Logistic regression model in the temperature range of 873 to 1873 K. The trends of the fitted curves indicated that the microstructure of the calcined coke evolved to slight disorder below 873 K and significant order above 873 K. The mathematical equations of the fitted curves could reliably predict the value of the features at a given temperature stage. The typical molecular-scale (∼70 atoms) models, lattice-scale (3990 atoms) 3D model, and nano-scale (31909 atoms) 3D model of the calcined coke were constructed via the image-guided construction strategy with controllable order degree (utilizing Fringe3D and Packmol). The model data of the H/C ratio, functional groups proportion, trace metals content, true density, and structural features were similar to experimental data. The calculated FT-IR and XRD spectra validated the aromaticity and order degree of the representations. [ABSTRACT FROM AUTHOR]