Distribution Of Gaseous Products Research Articles

Study on detailed reaction pathways of sulfur-containing alkali lignin during supercritical water gasification for hydrogen production

This work was focused on the evolution process of alkali lignin with a macromolecular structure in supercritical water gasification reactions. Using Quantum chemistry calculations and molecular dynamics simulations, the effects of different factors on the reaction process were studied, and the detailed pathways of main products were obtained. The results indicate that the presence of sulfur significantly inhibits the pyrolysis behavior of alkali lignin macromolecular structures. Sulfur significantly impacts the morphology of the intermediate molecular fragments of products containing 5–10 carbon atoms. Sulfur also has a significant inhibitory effect on the ring opening reaction of the benzene ring. Still, its effect on the final gas product distribution is not significant from a microscopic perspective. In addition, high temperature has a significant impact on improving the gasification efficiency of alkali lignin, while the scale of the reaction system has no significant effect on the distribution of gas products. This study will provide theoretical guidance for further improving the supercritical water gasification efficiency of lignin.

Decomposition behavior of supercritical ethylene under ultra-high temperature and ultra-high pressure

The gas-phase raw materials in many industrial scenarios currently exist in the reactor in a supercritical state. Unlike gas phase molecules, the supercritical molecules usually exhibited dynamic motion patterns in the system, which made them more susceptible to decomposition. Previous researches mainly focused on low-temperature and low-pressure systems, and few research on decomposition behavior of supercritical molecules under ultra-high temperature and ultra-high pressure were studied. This study focused on the decomposition behavior of supercritical ethylene under ultra-high temperature and ultra-high pressure, the effect of triggering conditions on supercritical ethylene decomposition was investigated. In addition, the temperature and pressure change curves during ethylene decomposition were analyzed to obtain evolution time nodes to determine energy accumulation in supercritical states. Moreover, the gas product distribution and derived explosive carbon were characterized for better evaluating the consequences of supercritical ethylene decomposition. This article aimed to provide theoretical basis and data guidance for energy utilization and conversion in ethylene supercritical systems.

Catalytic upgrading of Naomaohu coal pyrolysis volatiles over CaO catalyst

Catalytic upgrading of coal pyrolysis volatiles is one the promising way to achieve high quality tar and gas. In this study, catalytic upgrading of volatiles from Naomaohu (NMH) coal pyrolysis has been conducted in a two-stage fixed bed reactor using CaO as catalyst. The aim of this work was to investigate the catalytic effect of CaO on the gas and liquid product distribution, as well as the variations in gas and coal tar components. Simulated distillation and GC-MS analysis has been used to understand the distribution of tar component. On the one hand, CaO exhibits selective cleavage of large molecules, such as long-chain esters, leading to the production of aromatics through the processes of dehydrocyclization and aromatization. CaO has the ability to stabilize free radicals that are generated during the cleavage of large molecules, thereby promoting the formation of light aromatic hydrocarbons. Consequently, the light tar fraction (boiling point <360 °C) increased from 64.4 % to 74.6 %, while the heavy tar fraction (boiling point＞360 °C) decreased from 35.6 % to 25.4 % in the pyrolysis tar. The compounds with long ester chains in the tar composition decreased by 24.4 %. The content of light components, such as benzenes, naphthalene, and phenols, increased significantly with the increasing catalytic temperature. Specifically, the content of benzenes, naphthalene, and phenols increased by 11.83 %, 17.73 %, and 4.41 % respectively at the coal to CaO ratio of 1/0.5 and the catalytic temperature of 600 °C. On the other hand, the CaO absorbs the CO2 pyrolysis gas leading to an elevation in the concentration of CH4 and H2 in the pyrolysis gas. The concentration of CO2 decreased from 37.9 % to 16.58 % compared to without the catalyst while the concentrations of H2 and CH4 increased to 26.24 % and 31.15 % at the catalytic temperature of 450 °C. The CO2 absorption ratio reached a maximum value of 97.16 % at a coal to CaO ratio of 1/2. These findings suggest that the CaO catalyst beneficial both for improving the tar and gas quality.

Experimental and numerical investigation on the pyrolysis of oil shale particles in a bubbling fluidized bed

The efficient utilization of oil shale resource is beneficial to environment and the resource diversity. In this work, a bubbling fluidized bed (BFB) reactor was first used to pyrolyze Huadian oil shale experimentally, mainly focusing on the influence of fluidization flow rates. The yield of shale oil, char and non-condensable gas varies little at different fluidization flow rates, but the components in shale oil are different due to the secondary cracking, such as the fractions and species of aliphatic hydrocarbons, aromatic hydrocarbons and non-hydrocarbons. Then, the dense discrete phase model (DDPM) was used to track the trajectories of oil shale particles with different diameters in a bubbling fluidized bed. Population balance model (PBM) coupled Eulerian model was used to well describe the bubbling status of bed materials to characterize the hydrodynamic behaviors. Furthermore, a segmented kinetic model was compiled by UDF module to illuminate the pyrolysis of oil shale particles. The multi-phase reactive flow modeling clearly indicated the distribution of oil shale particles and gaseous products in BFB reactor, as well as pyrolysis time and the secondary cracking at different fluidization flow rates. In summary, this work provides a reference basis for complete pyrolysis of oil shale particles in a bubbling fluidized bed and generating shale oil with high yield and good quality.

Efficacy of initiators on fuel conversion, heat sink, and coke propensity of hydrocarbon fuel under supercritical environment

The investigation includes the cracking characteristics of a multi-component hydrocarbon fuel with a boiling range of 149–224 °C under supercritical environments. The impact of reactor pressure and the influence of initiators on cracking characteristics, such as fuel conversion, coke deposition, gas and liquid product distribution pattern, and heat sink capacities, of the fuel are examined explicitly. The fuel conversion improved by 70.8% as the reactor pressure increased from 2.5 MPa to 5.5 MPa at 650 °C. However, the coke deposition also increased by 55% for the corresponding pressure range. A decrease in the olefin-to-alkane ratio with pressure signifies the possibility of a reduction in unimolecular decomposition reactions and an increase in bimolecular reactions. The efficacy of two initiators, namely triethylamine (TEA) and di-tert-butyl peroxide (DTBP), on heat sinks and coke deposition was also examined. Between the two initiators, the nitrogen-based TEA initiator showed better performance in terms of fuel conversion and coke deposition rate, and the oxygen-based DTBP offered better heat sink capacity. About 22% increment in endothermicity was obtained with 1 wt% DTBP loading at 650 °C under 5.5 MPa pressure.

Effect of Fe and its oxides on steam gasification mechanism of lignin using ReaxFF molecular dynamics simulations

Lignin is an important biomass component and its gasification process has been extensively studied. Iron is widely found in nature, and the corresponding iron-based catalysts have been heavily used in the study of various systems. The advantages are that it is inexpensive and not easy to pollute the environment, and it can also be extracted from the system and reused. However, studies on the effect of iron and its oxides on the steam gasification of lignin are limited, most studies have focused on supercritical water gasification. In this study, the effects of Fe and its oxides on the steam gasification process of lignin dimers were simulated using reactive force field (Reaxff) molecular dynamics (MD). By analyzing the gas products and the evolution of the structures. It was found that low valence Fe greatly improved the efficiency of lignin steam gasification, while higher valence iron oxides were significantly less effective. There were also significant differences in the distribution of gas products for different valence states of Fe. Low-valent Fe greatly improves the yield of combustible gases such as H2 and CO, while high-valent Fe is better at generating CO2. Carbon accumulation occurs on the surface of the catalyst, which reduces the catalytic effect. By comparing the effects of different temperatures on the steam gasification of lignin, it was found that increasing the temperature accelerates the decomposition process of lignin, and that the steam gasification of lignin has a critical temperature at which the yield of the main gaseous products of lignin is the highest.

Pyrolytic characteristics of abutilon stalk waste using TG-FTIR, Py-GC/MS, and artificial neural networks: Kinetics, thermodynamics, and gaseous products distribution

The physicochemical properties of abutilon stalk (ABUS) were investigated to assess its suitability for pyrolytic conversion into bioenergy and bio-based chemicals based on kinetic triplet state, thermodynamic parameters, decomposition mechanisms and product distributions. The pyrolysis behavior of ABUS was studied using a thermogravimetric analyzer at five heating rates in a nitrogen atmosphere. The Gaussian deconvolution function indicated that the pyrolysis process of ABUS can be successfully modeled as four parallel devolatilization events (R2 > 0.99), divided into the devolatilization of pseudo drying (PO-D), hemicellulose (PO-H), cellulose (PO-C), and lignin (PO-L), respectively. The average apparent activation energies were 34.89 kJ/mol for PO-D, 163.02 kJ/mol for PO-H, 169.55 kJ/mol for PO-C, and 107.51 kJ/mol for PO-L using four model-free methods (Ozawa-Flynn-Wall, Kissinger-Akahira-Sunose, Starink, and Tang). The pyrolysis process was accurately predicted using diffusional, power law, geometrical contraction, and order-based reaction mechanism models. Thermal degradation process for each devolatilization event was successfully reconstructed using combined kinetics (R2 > 0.96), providing a useful theoretical basis and mathematical model for predicting the pyrolysis behavior of ABUS. The volatile products produced by ABUS pyrolysis were characterized using an integrated TGA-FTIR and Py-GC/MS system, confirming the proportion of high-energy compounds (benzenes, phenols, ketones, alcohols, aldehydes, acids, esters, hydrocarbons and their derivatives, N-heterocyclic substances, and N-containing compounds) and gas emission levels (CO > CH4 > C-O > H2O > CO2 > CO > C-O(H) > HCN > NH3 > SO2). Artificial neural network (ANN) was used to predict the pyrolysis behaviors of ABUS, and the best ANN model was ANN (5 *11 *1) with high R2 of 0.99998. Based on the kinetics, thermodynamics, and gaseous products distribution, ABUS has great application potential as raw material for bioenergy production.

Synergistic effect mechanism of biomass ash-derived K-Ca-Si catalytic system on syngas production and reactivity characteristics of high-sulfur petroleum coke gasification

In this study, three typical biomass ash (BA) components, KCl, CaCO3 and SiO2, are selected as model compounds to construct BA-based key ternary component system for petroleum coke (PC) gasification. Gas product analysis was conducted using gas chromatography to study the influence of different catalysts on the gas product distribution, gas yield and carbon conversion of PC gasification, and clarify the synergistic effects of binary and ternary components in K-Ca-Si catalytic system. In addition, electron scanning microscopy (SEM) and Raman techniques are used to characterize the physicochemical structure of gasification semi-char to reveal the synergistic mechanism of K-Ca-Si system. The results show that the yield of different gases is ordered as H2 > CO > CO2 and the increment of H2 yield, CO yield, syngas yield and carbon conversion in K-Ca-Si catalytic system is 43.41 mmol/g, 26.67 mmol/g, 80.37 mmol/g and 0.49, compared with single PC gasification, respectively. By comparing the theoretical and actual value of gas yield and carbon conversion, it is found that there are synergistic catalytic effects for K-Ca-Si ternary catalyst, but Si will inhibit the activity of K and Ca. Coupled with SEM and Raman analysis, synergistic mechanism of ternary catalytic system can be revealed. KCl and CaCO3 reduce the graphitization degree of semi-char by reacting with carbon matrix, and CaCO3 can stimulate the pore structure development of semi-char, which accelerate reaction between KCl and carbon matrix to form intermediate active sites, thus favoring gasification reaction and exhibiting a synergistic effect. SiO2, on the other hand, will combine with KCl and CaCO3 to form inert silicates, resulting in the deactivation of KCl and CaCO3. It could be concluded that for high K-high Ca-low Si ternary catalytic system, KCl and CaCO3 would still show a synergistic effect due to higher CaCO3 content than SiO2.

Raw hydrocarbons base of the republic of Uzbekistan - growth and production structure

The article considers the existing, actual raw material base of hydrocarbon raw materials of the Republic of Uzbekistan. Brief information is given on the number of discovered oil and gas fields, their distribution in the oil and gas regions of the republic, according to the degree of development, the type of fluids and the size of the reserves. Share participation of initial total resources in the context of oil and gas bearing regions is shown. Information is presented on the results of exploration work of two time periods - before 1991 and from 1991 to the present, where the growth rates of reserves of industrial categories for the first and second stages and the distribution of cumulative oil and gas production are considered. From the above data, it can be seen that the main increase in hydrocarbon reserves in the Republic of Uzbekistan was due to the discovery of unique and large fields in terms of hydrocarbon reserves. Based on the results of the analysis of the actual material, a con-clusion was made, indicating the high potential of the subsoil of the Republic of Uzbekistan and the feasibility of conducting exploration work in the long term, given the presence of significant forecast hydrocarbon resources. Keywords: field; oil; gas; hydrocarbons; reserves; oil and gas potential; initial total resources.

New insights into brominated epoxy resin type WPCBs pyrolysis mechanisms: Integrated experimental and DFT simulation studies

Pyrolysis is a recycling technology for waste circuit boards (WPCBs) with a wide range of applications. In this research, the brominated epoxy resin (BER) type WPCBs were taken as the research object, and the optimal pyrolysis process parameters were determined. Combined with experiments and density functional theory (DFT) calculations, the pyrolysis gaseous generation pattern and product distribution of BER type WPCBs were analyzed, and the generation mechanism of phenol, bromide and other pyrolysis products was investigated in depth. The results of the study showed that the pyrolysis rate of WPCBs exceeded 95 % under optimal reaction conditions. In the initial phase of the pyrolysis of WPCBs, the BER's CO bonds and a portion of Ph-Br bonds will be broken, leading to the production of intermediates such propylene oxide, bisphenol A, isopropyl alcohol, tetrabromobisphenol A and HBr. Among them, propylene oxide can generate ethylene oxide through free radical reaction. In the second stage, intermediates such as bisphenol A undergo homolytic cleavage and radical addition to form phenols, bromides, alcohols, ketones and other pyrolysis products.

Optimization of gas extraction of producing wells to increase the efficiency of condensate production

The article discusses ways to increase the efficiency of condensate production due to the optimal distribution of gas flows between producing wells. For a large number of wells, the solution of this problem becomes nontrivial and requires special methods of nonlinear optimization. The main aim of research is obtaining accurate solutions to the problem of optimizing condensate production using direct dependencies between gas and condensate production. The minimum set of reliable field information has been determined, which allows solving the problem of optimal distribution of gas production between wells at the maximum condensate flow rate. An optimization problem is formulated for this model. The conditions under which the initial problem is divided into a system of optimization subtasks for subgroups of wells are considered. By the method of pairwise optimization, analytical expressions were found for optimal ratios of gas flow rates in a group of wells. Based on the expressions obtained, an algorithm has been developed for the exact solution of the problem of short-term optimization of the well operation mode.

Atmospheric impact of 2-methylpentanal emissions: kinetics, photochemistry, and formation of secondary pollutants

Abstract. The tropospheric fate of 2-methylpentanal (2MP) has been investigated in this work. First, the photochemistry of 2MP under simulated solar conditions was investigated by determining the UV absorption cross sections (220–360 nm) and the effective photolysis quantum yield in the UV solar actinic region (λ &gt; 290 nm). The photolysis rate coefficient in that region was estimated using a radiative transfer model. Photolysis products were identified by Fourier transform infrared (FTIR) spectroscopy. Secondly, a kinetic study of the chlorine (Cl) and hydroxyl (OH) reactions of 2MP was also performed at 298 K and as a function of temperature (263–353 K), respectively. For the Cl reaction, a relative kinetic method was used in a smog chamber coupled to FTIR spectroscopy, whereas for the OH reaction, the pulsed laser photolysis (PLP) with laser-induced fluorescence (LIF) technique was employed. The estimated lifetime of 2MP depends on the location, the season, and the time of the day. Under mild–strong irradiation conditions, UV photolysis of 2MP may compete with its OH reaction in a mid-latitude inland urban atmosphere, while Cl reaction dominates in mid-latitude coastal urban areas at dawn. Finally, the gaseous product distribution of the Cl and OH reactions was measured in a smog chamber as well as the formation of secondary organic aerosols (SOAs) in the Cl reaction and its size distribution (diameter between 5.6 and 560 nm). The implications for air quality are discussed based on the observed products.

Experimental study on the mechanism of water on heat sink variation in catalytic partial steam reforming of supercritical n-decane

Regenerative cooling is an effective method for heat management of hypersonic vehicles and faces a problem of insufficient cooling capacity under higher flight Mach number. Water-assisted hydrocarbon fuels thermal conversion can effectively increase heat absorption and inhibit carbon deposition. The mechanism of water on the variation of heat sink is unclear. In this study, experimental study was conducted to investigate the effect of different water contents, pressure and mass flow rates on the variation of heat sink and the distribution of gaseous products in a continuous experimental system. The results show that catalytic partial steam reforming reaction consists of catalytic steam reforming and catalytic thermal cracking in the low temperature stage (T＜490 ℃), and non-catalytic thermal cracking is activated and gradually dominate in the high temperature stage (T＞490 ℃). The contribution of water to total heat sink is mainly caused by physical heat sink. Increasing mass flow rate mainly suppress the cracking reaction in the high temperature section by reducing reaction residence time. The flow rate has little effect on the chemical reaction equilibrium. Higher pressure has little effect on heat sink, but accelerates carbon deposition by promoting the formation of olefin products.

Syngas Production from Protective Face Masks through Pyrolysis/Steam Gasification

The COVID-19 pandemic has caused a heavy expansion of plastic pollution due to the extensive use of personal protective equipment (PPE) worldwide. To avoid problems related to the entrance of these wastes into the environment, proper management of the disposal is required. Here, the steam gasification/pyrolysis technique offers a reliable solution for the utilization of such wastes via chemical recycling into value-added products. The aim was to estimate the effect of thermo-chemical conversion temperature and steam-to-carbon ratio on the distribution of gaseous products obtained during non-catalytic steam gasification of 3-ply face masks and KN95 respirators in a fluidized bed reactor. Experimental results have revealed that the process temperature has a major influence on the composition of gases evolved. The production of syngas was significantly induced by temperature elevation from 700 °C to 800 °C. The highest molar concentration of H2 gases synthesized from both types of face masks was estimated at 800 °C with the steam-to-carbon ratio varying from 0 to 2. A similar trend of production was also determined for CO gases. Therefore, investigated thermochemical conversion process is a feasible route for the conversion of used face masks to valuable a product such as syngas.

Hydrogen production through two-stage sorption-enhanced biomass gasification: process design and thermodynamic analysis

This study presents process design and thermodynamic analysis of hydrogen production through a novel two-stage sorption-enhanced gasification (SEG) process. The SEG process integrates decoupled gasification with calcium looping to convert solid fuels such as biomass. The proposed two-stage SEG process employs a fluidized bed gasifier and a countercurrent moving bed reformer. The first stage involves high-temperature sorption-enhanced gasification in a fluidized bed. Then the product gas from the first stage undergoes sorption-enhanced reforming at relatively lower temperatures to further improve the hydrogen purity. This study employs an autothermal multistage model based on Gibbs free energy minimization to analyze and optimize the calcium looping ratio, steam-to-carbon ratio and feed temperatures of the moving bed reformer. The product gas distribution and temperature profile along the moving bed are discussed. Under optimal conditions, the two-stage SEG process can directly produce 99% H2 (dry basis), and the overall energy efficiency of the two-stage SEG is 58.7%, which is nearly 10% higher than the conventional process. Therefore, two-stage sorption-enhanced biomass gasification shows the potential to significantly improve green hydrogen production.

Numerical analysis of the distribution of combustion products from methane explosions in a full-scale tunnel using all-speed CFD code GASFLOW-MPI

ABSTRACT Methane explosions are among the main hazards in coal mines. Shock waves from methane explosions can cause damage near the explosion site, and combustion products can spread along the tunnel to locations far from the explosion source and endanger the lives and health of personnel. Therefore, the study of the propagation patterns of methane explosion shock waves and the distribution of high-temperature combustion products in tunnels. has significance for emergency decision-making in the event of methane explosions in a mine. This study uses the 3D Computational Fluid Dynamics (CFD) program GASFLOW-MPI, which models the one-step methane combustion mechanism with the addition of a heat transfer model. The methane explosion process is simulated and reproduced at the Lake Lynn Experimental Mine (LLEM) to analyze the process of gas deflagration. The results reveal that the overpressure in the tunnel after the methane explosion oscillates and decays with time. Gaseous products of the explosion “expand and compress” and flow back and forth in accordance with the oscillation of overpressure. The maximum expansion ratio of the CO2 concentration isosurfaces of 0.5% in the heat transfer simulation is 6.21, whereas the volume expansion ratio is 3.78 once the flow field stabilizes. The distribution of combustion products along the alleyway exhibits a Gaussian decay trend. The range of gaseous product distribution and temperature fields in the adiabatic tunnel is significantly higher than that in the heat transfer simulations, thus indicating that heat loss significantly influences the temperature characteristics and distribution pattern of combustion products in the full-scale tunnel.

Utilization of PET (waste) via hydrothermal co–gasification with sorghum for hydrogen rich gas production

In this study, the applicability of hydrothermal biomass co–gasification for utilizing polyethylene terephthalate (PET) based waste was investigated. For this purpose, hydrogen rich gas production was realised by hydrothermal co–gasification of sorghum biomass with virgin and waste PET mixtures at 500 °C, and the gasification performances were compared. The feedstock/water ratio (%, w/v) was significantly effective on the gasification process in terms of gas yields, gas, and liquid product distributions. Synergistic effects were observed in hydrogen formation in co–gasification of PET and sorghum. The amount of hydrogen obtained from the co–gasification of PET and sorghum was 4.0 mol H2/kg feed higher than the sum of total amount of hydrogen obtained from the individual gasification of PET and sorghum. GC/MS analysis showed that liquid contents were also affected from experimental conditions. The use of catalysts increased the gasification and carbon conversion yields regardless of the type. Although KOH was the most effective single catalyst on hydrogen yield, the catalyst combinations were more effective with promoted activities in terms of hydrogen yields and CO2 capture. Hydrogen yield, which was 12.9 mol H2/kg feed without catalyst, increased to 31.0 (±0.9) mol H2/kg in the presence of K2CO3/CaO catalyst combination for virgin PET/sorghum mixtures and 28.1 (±0.3) mol for PET waste plastics/sorghum mixtures. For the PET waste plastics/sorghum mixtures with the binary catalyst combinations (K2CO3/CaO and KOH/CaO), the CO2 mole fractions of the product gas mixtures were below 1% and the hydrogen contents of the obtained gas mixtures were above 90%. The results of the study show that pet–based plastic wastes can be effectively utilized to produce hydrogen rich gas, by co–gasification with biomass.

Insight into gaseous product distribution of cross-linked polyethylene pyrolysis using ReaxFF MD simulation and TG-MS

Cross-linked polyethylene (XLPE) has been widely used as the insulation material of power cables due to the great electrical and thermal properties. However, the material deteriorated when subjected to excessive thermal stress, leading to performance reduction and even failure of the cables. In this paper, we proposed a novel thermal fault detection method in power cables by exploring the gaseous product distribution of XLPE pyrolysis. Firstly, the gas generation characteristics of the XLPE pyrolysis was investigated using large scale ReaxFF molecular dynamics simulation. The simulation results showed that the major gaseous products included H2, CH4, C2H6, C2H4, C2H2, CO. The pyrolysis kinetics as well as the formation mechanism of the gases was illustrated using the real-time trajectory obtained by molecular dynamic calculation. Furthermore, the influence of temperature on the gas product distribution was characterized. Higher temperature increased the yield of H2, C2H4, C2H2, but decreased that of CH4. The yield of C2H6 and CO almost kept constant as temperature changing. The influencing mechanism of temperature was reasonably explained by the proposed gas formation mechanism. On the basis of investigation on XLPE pyrolysis, a three ratios technique was proposed for the detection of thermal faults in power cables. Finally, the chemical composition of the gas product was validated by thermogravimetric and mass spectrometric simultaneous experiment. The experimental results exhibited good agreement with the numeric simulation.

Analysis and distribution of volatile gases from catalytic pyrolysis of Sulcis low-rank coal

Catalytic pyrolysis of Sulcis low-rank coal over naturally occurring olivine, and home-made 15 wt%Ni/γ-Al2O3 catalyst was conducted for the upgrading of coal pyrolysis volatile gases in the temperature range ambient-900 °C under atmospheric pressure. Raw coal and mixtures of coal-additive (90:10 wt%) were slowly heated in temperature programmed mode using a laboratory-scale quartz furnace coupled in parallel to Fourier transform infrared (FTIR) spectrometer and GC chromatograph for quantitative analysis of flue gas. Coal pyrolysis with and without additives was also conducted by TG/DTG/DSC analysis at different heating rate (β = 15, 20, 30 °Cmin−1). DSC results clearly indicated some extra exothermic events during catalytic coal pyrolysis. Quantitative gaseous products distribution with temperature showed yields significantly and selectively improved with additives. Generally, more CO and CO2 were emitted under catalytic coal pyrolysis. Meanwhile, nickel catalyst exerted a marked positive effect on H2 yield overall in the temperature range 400–500 °C. The light hydrocarbons such as methane, ethane, propane and n-hexane substantially remaining unchanged, whereas a remarkable increase of emitted ethene was originated from catalytic pyrolysis. A deeper SO2 evolution was observed over olivine, whereas the N-containing compounds (NH3, NOx) were also modified in catalytic pyrolysis. Formaldehyde was also monitored, which represents a fragment originating from polycyclic aromatic side chains. Reaction kinetic study by a model-free isoconversional method indicated a complex multiple-step mechanism of coal pyrolysis, exception made for conversion values between 5% and 50% where a single-step reaction path was operating. The calculated average Ea and the pre-exponential factor were markedly reduced by the presence of additives. Meanwhile the compensation effect was also existing.

Numerical simulation of uranium tetrafluoride fluorination in a multistage spouted bed using the improved CFD-DEM chemical reaction model

A CFD-DEM reaction coupling model was established to simulate UF4 fluorination process, in which heat and mass transfer, heterogeneous chemical reaction, and particle shrinkage model were considered. The gas behavior was described by the conservation laws of mass, momentum, and energy. The solid phase is modeled with the discrete element method, considering the gas–solid interphase force, contact force, heat transfer, and chemical reaction models based on the discretized surface. Each particle can be individually tracked and associated with specific physical properties. The proposed CFD-DEM reaction coupling model based on particle shrinking reaction model with discretized surface was validated by the experimental and literature results at first. Then a multistage conical spouted bed was proposed and the process of UF4 fluoridation reaction in it was investigated. The fluidization characteristics and the concentration distribution of gaseous products in the spouted bed with an extended gas velocity range were obtained and analyzed. In addition, the effects of different parameters, such as superficial gas velocity, temperature, fluorine concentration, on fluoridation rate and the fluorine conversion rate were investigated based on the proposed CFD-DEM reaction coupling model. The results obtained in this work are beneficial for method development of the chemical reaction simulation research in particle scale using the CFD-DEM model, and useful for operation and equipment parameters design of the uranium tetrafluoride fluorinate industrial process in the future.