Devolatilization Region Research Articles

Catalytic decarboxylation of crude oil in a fixed-bed pyrolysis reactor

This study focused on using titanium dioxide (TiO2) as a catalyst to decarboxylate crude oil from the Imo oil field in Nigeria. The TiO2 catalyst was characterised using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and thermogravimetric analysis (TGA). XRD investigation identified rutile-TiO2 as the primary crystalline phase, with important diffraction peaks matching the ASTM standard for rutile. SEM showed extensive agglomerations of TiO2 particles, whereas FT-IR detected surface functional groups such as hydroxyl, carbonyl, and aromatic. TGA identified three separate weight-loss stages, the biggest of which occurred in the devolatilization region, accounting for around 84%. The catalytic decarboxylation process revealed a considerable decrease in the total acid number (TAN) of the crude oil as the temperature increased, reaching a TAN of 0.28 mg KOH g⁻1 at 300 °C, with 96.35% decarboxylation. The TiO2-catalyzed process outperformed thermal cracking alone, resulting in less oxygenated functional groups and increased oil quality. These findings show that rutile-TiO2 can be an excellent catalyst for decarboxylation in crude oil refining.

A new 2.5‐D twin screw extruder melting model with comparisons to data

AbstractMany polymers are processed and compounded in co‐rotating, fully intermeshing twin screw extruders. A typical compounding process consists of multiple unit operations including feed introduction, solids transport, transitioning from the conveying zone to the kneading block melting zone, melting, a downstream feed zone, a mixing zone, a devolatilization region, and a pressure generating discharge section. This paper will focus on the kneading block melting zone which typically includes a reverse pitch element so the kneaders remain full. Mechanisms for flow and energy input to pellets in kneading elements, including friction heating, pellet compression, energy diffusion, and viscous dissipation to form a melt phase: followed by viscous dissipation in a solid pellet/melt slurry, and heat transfer; are developed and implemented in a novel melting model. The model is validated with extrusion measurements and visualizations using low density polyethylene (LDPE). The predictions of the model are also compared with a classical set of experiments using high density polyethylene (HDPE). This paper describes the physics and engineering concepts that the authors feel are inherent in the melting section of the twin screw extruder where a large pressure peak is calculated using the friction and compression of the polymer pellets. The modeled increase in pellet bulk/surface temperature is due to the inclusion of four energy sources, pellet compression, thermal diffusion, friction energy dissipation, and viscous energy dissipation. This combined thermal dynamics based melting model results in a novel melting protocol. The melting mechanisms are coupled to flow regimes in the kneading blocks as melting progresses. The effects of throughput, Q, and screw rotation speed, N, are also examined.Highlights Novel 2.5D melting model for corotating, intermeshing twin‐screw extruders. Energy for melting; friction, deformation, diffusion, and viscous dissipation. The model helps elucidate mechanisms during melting in a twin‐screw extruder.

New 2.5‐Dtwin screw extruder model for the feed section of a co‐rotating twin screw extruder with comparisons to data

AbstractMany polymers are processed and compounded in co‐rotating, fully intermeshing twin screw (TS) extruders. The typical compounding process consists of multiple unit operations including feed introduction, conveying solids away from the feed zone, transitioning from the conveying zone to the kneading block (KB) melting zone, melting, a downstream feed zone, a downstream mixing zone, a devolatilization region, and a pressure generating discharge section. This paper will focus on the first of these unit operations, the conveying of pellets in a partially filled screw leading to compaction and pressure generation in the full screw channel prior to the KB melting zone. Mechanisms for pellet conveying, for heating the polymer pellets, and for developing pressure at the end of the solids conveying screw elements are first presented for low‐density polyethylene (LDPE). The predictions of the model are also compared with a classical set of experiments on high‐density polyethylene (HDPE). The model is then tested using published characteristics of a polyamide‐type polymer. This paper focuses on the physics and engineering concepts that are inherent in the feed section of the TS extruder where the pressure is calculated using the friction of the polymer pellets. The effects of throughput,Q, at a constant rotation speed,N, are examined. Low and highQ/Nratios have significantly different axial pressure profiles.

Thermal degradation characteristics, kinetic and thermodynamic analyses of date palm surface fibers at different heating rates

The potential of the least-exploited date pam waste was presented as feedstock for bio-oil production. The surface fibers of the date palm are widely available as waste material in the Gulf region, the Middle East, and Africa. Chemical composition analysis and physiochemical characterization showed that surface fibers are valuable feedstock for energy production. Surface fibers were analyzed thermogravimetrically at different heating rates (10, 20, and 30 °C /min) in an inert atmosphere. Decomposition was carried out in three stages: dehydration, devolatilization, and solid combustion. Kinetic analysis was performed on the devolatilization region using the Coats–Redfern model–fitting method using twenty–one reaction mechanisms from four different solid-state reaction mechanisms. Two diffusion models: one–way transport (g(x) = α2) and Valensi equation (g(x) = α+(1-α) × ln(1-α)) showed the highest regression coefficient (R2) with the experimental data. The activation energy (Ea) and the pre-exponential factor (A) was estimated to be 91.40 kJ/mol and 1.59 × 103 –29.39 × 103 min−1, respectively. The kinetic parameters were found to be dependent on the heating rate. The surface fibers' thermodynamic parameters ΔH, ΔG, and ΔS were 80–97, 151–164, and −0.17- −0.18 kJ/mol, respectively. This indicates that the pyrolysis of surface fibers is endothermal and not spontaneous. Since there is not much experimental work on the pyrolysis of surface fibers available in the literature, the reported results are crucial for designing the pyrolysis process.

Non-gray gas and particle radiation in a pulverized coal jet flame

In pulverized coal combustion, the participating radiative media includes gas, soot, and coal/char particles; a fundamental understanding of their radiation behavior is essential for the prediction of radiation heat transfer and control of radiation in the furnace. In this study, the individual contributions of gas, soot, and coal particles to the total radiation were examined based on the large eddy simulation of the CRIEPI pulverized coal jet flame. The radiation transfer equation was solved using the discrete ordinate method with state-of-the-art non-gray radiative property models of multi-phase media. The full spectrum correlated k-distributions (FSCK) model was used to calculate the radiative property of the gas-soot mixture. A burnout-based particle radiative property model was applied for coal/char particles. The results showed that the predicted spatial distributions of coal particles, tar, and soot were in good agreement with the experimental data. The gray gas radiation model predicted temperatures approximately 50 K lower in this flame, and the peak soot volume fraction was predicted at approximately 22% lower. For the laboratory scale burner under examination, the individual radiative contributions of gas, soot, and coal/char were found to be 35%, 40%, and 25%, respectively, so that it was necessary to consider all components for accurate prediction. Moreover, these contribution ratios varied with the flame position. Because of the high particle concentration, the individual contribution of coal/char particles accounted for up to 65% in the devolatilization region. Soot radiation played an important role in the pulverized coal flame. In the region where the ensemble-averaged soot volume fraction reached the maximum of 2.7 ppm, the individual contribution of soot was 50% of the total radiation, which accounted for 70% of the total particles (soot and char) radiation.

Study of the kinetic behaviour of biomass and coal during oxyfuel co-combustion

In this study, the thermogravimetric analysis (TGA) method has been used to evaluate the kinetic behavior of biomass, coal and its blends during oxyfuel co-combustion. The thermogravimetric results have been evaluated by the Coats–Redfern method and validated by Criado's method. TG and DTG curves indicate that as the oxygen concentration increases the ignition and burn out temperatures approach a lower temperature region. The combustion characteristic index shows that biomass to coal blends of 28% and 40% respectively can achieve enhanced combustion up to 60% oxygen enrichment. In the devolatilization region, the activation energies for coal and blends reduce while in the char oxidation region, they increase with rise in oxygen concentration. Biomass, however, indicates slightly different combustion characteristic of being degraded in a single step and its activation energies increase with rise in oxygen concentration. It is demonstrated in this work that oxygen enrichment has more positive combustion effect on coal than biomass. At 20% oxygen enrichment, 28% and 40% blends indicate activation energy of 132.8 and 125.5 kJ·mol−1 respectively which are lower than coal at 148.1 kJ·mol−1 but higher than biomass at 81.5 kJ·mol−1 demonstrating synergistic effect of fuel blending. Also, at char combustion step, an increase in activation energy for 28% blend is found to be 0.36 kJ·mol−1 per rise in oxygen concentration which is higher than in 40% blend at 0.28 kJ·mol−1.

Combustion behaviors of wood pellet fuel and its co-firing with different coals

Biomass resources, which are carbon-neutral and sustainable, may help to address climate change and reduce greenhouse gas emissions. This study was performed to examine the effects of wood pellet (WP) particle size, environmental conditions (stoichiometric ratio; SR), and blending ratio on the combustion characteristics of single fuels and blends using a thermogravimetric analyzer and drop tube furnace (DTF). The results indicate that WP demonstrated a higher mass reduction in the devolatilization region and a faster reaction rate compared with coal. Blends tested in the analyzer showed the expected profiles for devolatilization and char oxidation without the presence of non-additive effects. However, the DTF results showed that simultaneous reactive and non-reactive phenomena occurred with increasing biomass-blending ratios. When WP fuel containing fine particles ( 600 μm) showed that unburned carbon (UBC) increased owing to slower reactivity. WP fuel containing particles of 400 μm or less in size demonstrated superior UBC performance, indicating that biomass-coal blends were significantly affected by blending ratio, particle size, and the surrounding environment.

Thermal decomposition study and pyrolysis kinetics of coal and agricultural residues under non-isothermal conditions

In this work thermal decomposition along with pyrolysis kinetics of two coals namely Chamalang Coal (CC) and Dukki Coal (DC) and four agricultural residues i.e. Rice Husk (RH), Corn Husk (CH), Sunflower Disc (SD) and Falsa Stick (FS) were investigated under non-isothermal conditions. Four different parameters were used to evaluate the reactivity of fuels. These were peak temperature, average rate of weight loss, maximum rate of weight loss and pyrolysis factor. All these parameters were evaluated at four heating rates 10, 20, 30 and 40 °C/min. The average rates of weight loss were found higher in devolatilization region compared with char formation region of degradation. It was found from reactivity analysis that the fuels could be ranked in following order of reactivity CH > FS > RH > SD > DC > CC. It was observed that increasing heating rate shifted the reaction zone to higher temperature and increased the peak temperatures, rate of average and maximum weight loss that increased the reactivity and pyrolysis factor. Coals showed low reactivities and high activation energies compared to agricultural residues. The activation energy has been estimated using Friedman differential isoconversional model and it was found that the activation energy varied with fractional conversion. The estimated average values of activation energy (kJ/mol) for CC, DC, RH, CH, SD, and FS were found to be 134.54, 129.81, 109.43, 98.24, 113.25, and 103.64 respectively.

Pyrolysis characteristics of Turkish lignites in N2 and CO2 environments

ABSTRACTPyrolysis characteristics and kinetic parameters of two Turkish lignites having different ash contents (Orhaneli as low ash and Soma as high ash sample) were studied under N2 and CO2 atmospheres by means of thermogravimetric analysis. The isoconversional kinetic methods of Flynn‒Wall‒​Ozawa, Kissinger‒​Akahira‒​Sunose, and Friedman were employed to estimate the activation energy and pre-exponential factors. The experiments were conducted at four different heating rates of 5, 10, 15, and 20°C/min within the temperature range of 50‒​950ºC. The obtained results indicated that changing the pyrolysis ambient had no significant effect on the devolatilization region up to 700°C. The char formation region in N2 atmosphere was due to the CaCO3 decomposition and was more significant for Soma lignite due to its high ash content. However, in CO2 atmosphere, the gasification reaction took place at temperatures higher than 700°C. The decomposition process of CaCO3 in CO2 atmosphere was hampered up to temperatures higher than 900°C. The estimated activation energies were found to have approximately similar trends under different atmospheres. For Orhaneli lignite, the average activation energy values were higher in CO2 environment. However, for Soma lignite due to decomposition of CaCO3, the activation energy values were higher in N2 atmosphere. The mean uncertainty values were assessed for the activation energy values obtained for all test cases.

Pulverized coal particle ignition in a combustion environment with a reducing-to-oxidizing transition

A reducing-to-oxidizing (RO) environment is characteristic of what a coal particle experiences in the near-burner region of pulverized coal (pc) furnaces. The RO environment can influence early-stage coal combustion processes such as ignition, aerosol formation, and char burnout. However, fundamental studies have focused on either oxidizing conditions (mimicking the post-flame region) or reducing conditions (mimicking the devolatilization region). The effect of this RO environment on early-stage coal combustion has, until now, not been considered. Here, the role of this reducing-to-oxidizing environment on single-particle ignition is evaluated. Powder River Basin (PRB) sub-bituminous coal was used, with a particle size of 125–149 μm and two nominal gas temperatures of 1300 K and 1800 K. The experimental findings for purely-oxidizing conditions with 20 vol% oxygen are compared with those of reducing-to-oxidizing environment. Single particles were tracked using high speed, high resolution videography. Emission intensities of the particles were used to evaluate the prevailing ignition modes, and to determine the characteristic ignition and induction times in both oxidizing and reducing-to-oxidizing environments. Experimental findings show that homogeneous-to-heterogeneous mode of ignition is prevalent for purely oxidizing conditions for both nominal gas temperatures of 1300 K and 1800 K. However, hetero-homogeneous ignition is favored in reducing-to-oxidizing environment at 1800 K and heterogeneous ignition at 1300 K gas flame temperature. The reducing-to-oxidizing environment leads to longer ignition delay times of about 20% and 40% on average for 1300 K and 1800 K nominal gas temperatures respectively but shorter induction times than those of oxidizing condition. The results show that ignition behavior in a reducing-to-oxidizing post-flame environments can be quite different from those in oxidizing environments.

Pyrolysis behavior of biomass with different Ca-based additives

CaO is an important catalyst in biomass gasification and pyrolysis. However, CaO can stem from many precursors. And, the effect between different precursors has still not been studied. Calcined natural limestone, natural dolomite, calcium oxide, calcium carbonate, calcium acetate, and calcium propionate were used to investigate their pyrolysis reactivity of biomass (peanut shells and pine sawdust) at high temperature (>800 °C). Experiments were conducted using a thermogravimetric apparatus and a fixed-bed pyrolysis system. Pine sawdust displayed higher pyrolysis reactivity than peanut shells. During pyrolysis, Ca-based additives fixed carbon dioxide mainly in the temperature range of 300–700 °C. By addition of Ca-based additives, the concentrations of hydrogen and carbon monoxide were increased and the concentrations of methane and carbon dioxide (over 18 vol%) were decreased. De-carbonation started around 700 °C. The emission of CO2 by de-carbonation promoted the reduction of char by the Boudouard reaction and methane by the dry reforming reaction. The total pyrolysis conversion decreased as PI-Dol > PI-CaA > PI-Lime > PI-Ca > PI-CaP > PI Raw > PI-CaC. The excellent pyrolysis reactivity of biomass in the presence of calcined calcium acetate can be ascribed to its preeminent physical structure. Addition of Ca-based additives increased the activation energy of the main devolatilization region. The activation energy of biomass with calcined natural dolomite, about 110 kJ mol−1, was much lower than that of other Ca-based additives studied at high temperatures. Pyrolysis of the pure biomass sample can be simply hypothesized as a first order reaction, but it varied significantly with the addition of additives.

The Physicochemical Characterization of a Newly Explored Thar Coal Resource

The samples of Thar coalfield were characterized using a thermogravimetric analyzer, atomic absorption spectrophotometer, X-ray diffractometer, Fourier transform infrared spectra, and scanning electron microscopy-energy dispersive x-ray spectroscopy analysis. The samples were ranked as lignite and subbituminous according to American Society for Testing and Materials standard classification. Differential thermogravimetric analysis results specified chemical reactivity of coal at the primary devolatilization region (257–412°C) and secondary devolatilization region (741–900°C). The minerals identified were quartz, kaolinite, dikite, halloysite, gold copper indium, graphite hydrogen nitrate, and magnesium vanadium molybdenum oxide. X-ray diffraction study confirmed the presence of mineral constituents as indicated by microscopic investigation. Fourier transform infrared spectra identified C=C aromatic groups at 1,500–1,700 cm−1 as maturity indicator and 2,800–3,000 cm−1 and 2,300 cm−1 as aliphatic stretching regions. The peaks of quartz and kaolinite were observed at 900–1,100 cm−1. Strong correlations between mineral matter-SiO2 (r 2 = 0.808) and Al2O3-SiO2 (r 2 = 0.957) indicates Al and Si as the dominant inorganic components. Cluster analysis appeared as an additional tool for coal ranking based on their physicochemical properties.

Thermal degradation behavior and kinetic analysis of spruce glucomannan and its methylated derivatives

The thermal degradation behavior and kinetics of spruce glucomannan (SGM) and its methylated derivatives were investigated using thermogravimetric analysis to characterize its temperature-dependent changes for use in specific applications. The results were compared with those obtained for commercial konjac glucomannan (KGM). The SGM and the KGM exhibited two overlapping peaks from 200 to 375°C, which correspond to the intensive devolatilization of more than 59% of the total weight. Differences in the pyrolysis-product distributions and thermal stabilities appeared as a result of the different chemical compositions and molecular weights of the two GMs. The Friedman and Flynn-Wall-Ozawa isoconversional methods and the Coats–Redfern were adopted to determine the kinetic triplet of the intensive devolatilization region. Both GMs can be modeled using a complex mechanism that involves both a Dn-type and an Fn-type reaction. The comparative study of partially methylated GM indicated higher homogeneity and thermal resistance for the material with the higher degree of substitution.

연료의 물리적 특성과 직접탄소연료전지의 연료극 반응성에 관한 연구

The effect of physical properties of coal fuels and carbon particle on performance of DCFC (Direct Carbon Fuel Cell) was investigated. Shenhua and Adaro were selected as coal fuel and carbon particle was used for comparing with coal. The Ultimate, proximate, SEM, XRD, and BET analysis of samples were conducted. The component of char was more important than that of raw coal because the operating temperature of reactor is higher than devolatilization region of coal. The surface area and volume of pores affected significantly the performance of the system than content of fixed carbon or char rates. The performance of DCFC with carbon particle was in proportional to working temperature.

Some aspects of changes in the macromolecular structure of coals in relation to thermoplastic properties

The development of coal thermoplasticity during the primary devolatilization region is critical in determining coke structures. The solvent swelling technique was used to study the changes in macromolecular structure of four coals of different rank (902 to 203 in the British Coal classification scheme) during carbonization to temperatures up to 600°C. The results were compared with the thermoplastic characteristics of the coals. The dilatometric and gas permeability properties are discussed in terms of changes in macromolecular structure. The study of the macromolecular structure provides new insight into the development of thermoplasticity and coke structure.

Combustion behaviour of pulverized coal particles in a high temperature and high oxygen concentration atmosphere

The combustion of pulverized coal particles in a high temperature and high oxygen concentration atmosphere was studied experimentally using a laminar flow furnace. Some peculiar phenomena were observed during the early stages of coal particle combustion. It was shown that particle rotation occurred in the devolatilization region and rotation frequency reached 3000–5000 cycles s −1. Also, thermal cracking occurred during devolatilization. These findings suggest that these phenomena were induced by the evolution of volatile matter, and that char combustion occurred simultaneously in the devolatilization region under a high temperature and high oxygen concentration atmosphere. A model to explain the mechanism of char ignition during devolatilization is presented.

New ignition phenomenon in coal combustion

A reducing-to-oxidizing (RO) environment is characteristic of what a coal particle experiences in the near-burner region of pulverized coal (pc) furnaces. The RO environment can influence early-stage coal combustion processes such as ignition, aerosol formation, and char burnout. However, fundamental studies have focused on either oxidizing conditions (mimicking the post-flame region) or reducing conditions (mimicking the devolatilization region). The effect of this RO environment on early-stage coal combustion has, until now, not been considered. Here, the role of this reducing-to-oxidizing environment on single-particle ignition is evaluated. Powder River Basin (PRB) sub-bituminous coal was used, with a particle size of 125–149 μm and two nominal gas temperatures of 1300 K and 1800 K. The experimental findings for purely-oxidizing conditions with 20 vol% oxygen are compared with those of reducing-to-oxidizing environment. Single particles were tracked using high speed, high resolution videography. Emission intensities of the particles were used to evaluate the prevailing ignition modes, and to determine the characteristic ignition and induction times in both oxidizing and reducing-to-oxidizing environments. Experimental findings show that homogeneous-to-heterogeneous mode of ignition is prevalent for purely oxidizing conditions for both nominal gas temperatures of 1300 K and 1800 K. However, hetero-homogeneous ignition is favored in reducing-to-oxidizing environment at 1800 K and heterogeneous ignition at 1300 K gas flame temperature. The reducing-to-oxidizing environment leads to longer ignition delay times of about 20% and 40% on average for 1300 K and 1800 K nominal gas temperatures respectively but shorter induction times than those of oxidizing condition. The results show that ignition behavior in a reducing-to-oxidizing post-flame environments can be quite different from those in oxidizing environments.

Formation and behavior of submicron fly ash in pulverized coal combustion furnace

In this study, the formation mechanism and the behavior of submicron fly ash (SFA) (larger than 0.1 μm) in the industrial type pulverized-coal combustion furnace was examined experimentally by using two different models of furnace: a turbulent furnace, which was designed to realize practical combustion conditions, and a small, laminar flow furnace. Observations were made by an electron micrograph, x-ray microanalysis, and infrared spectroscopic analysis of the submicron particles sampled from the furnace, and measurements of the concentration distribution of the suspended and coagulated SFA were carried out. Both the electron micrographs and the infrared spectroscopic analysis showed that the submicron particles sampled near the concentration peak in the furnace closely resembled raw coal. The major components (aluminum, silicon, calcium, and iron) in the ash contained in the submicron raw coal fragment was compared with the SFA sampled at the flue for six different coals. The composition of the SFA was mostly compared to that of the raw coal fragment. There was no silicon condensation in these coals, with one exception. The measured concentration distribution of the SFA in the furnace showed that its peak concentration level in the furnace was two or three times higher than that calculated from the SFA content in coal, assuming that no formation or extinction of the SFA occurs in the region of coal combustion. From these results, we concluded that approximately half of the SFA in the furnace is simply carried over from the submicron coal fragment originally contained (3.5–9.5 wt%) in the pulverized raw coal, and that the remaining SFA is newly formed in the furnace through the breakup of larger coal particles in the devolatilization region. However, the breakup ratio was dependent on the primary air velocity at the burner exit. The percentage of the submicron coal fragment originally contained in the pulverized raw coal that became suspended in the furnace was estimated to be less than 10 wt% under actual flow conditions. The effect of the submicron coal fragment in the pulverized raw coal on the emission of suspended SFA was clearly shown using a small laminar furnace.

The thermal decomposition of pulverized coal particles

The physical, thermal, and chemical behavior of pulverized coal particles during thermal decomposition are examined for five coal types and two particle sizes for one of the bituminous coals. Particles were injected axially into a lean (35% excess air) methane/air flat flame with a nominal peak temperature of 1750°K. The significant events observed are classified by three time scales. Particles heat to the gas temperature in less than 10 msec, devolatilization occurs between 10 and 75 msec and, under the appropriate conditions, large soot particles are formed WRS and grow for times exceeding 75 msec. The events that accompany devolatilization are dependent upon coal type and particle size. For large bituminous particles (ca., 80 μm) a significant volatile fraction is ejected from the particle as a jet. This volatile jet reacts close to the particle producing a trail of small solid particles. The local heat released during the reaction of the volatiles, in combination with heterogeneous oxidation, increases the particle, temperature and raises it above that of the bulk gas stream. At later times, large soot structures, are formed which are attributed to the agglomeration of small, homogeneously formed soot on the volatile trail structures. Small bituminous particles (ca., 40 μm) burn with a higher intensity (i.e., higher temperature and more rapidly) with few trails and do not produce soot structures probably because of the more diffuse nature of the devolatilization process. Other ranks of coal exhibit different physical, thermal, and chemical behavior. For example, neither the lignites nor the anthracite produce volatile trials. Further, the particle temperature for the lignites is only slightly shifted above the bulk gas temperature in the devolatilization region while anthracite takes 50 msec to reach the bulk gas temperature level. This is attributable to the relatively low heat content of the volatiles in the former case and the low volatile content in the latter. The impact of the above observations on the formation of fuel NO is discussed.