Gasification Reactivity Of Char Research Articles

Direct Liquefaction of South African Vitrinite- and Inertinite-Rich Coal Fines.

In this investigation, coal fines enriched with inertinite were used for direct liquefaction experiments. For comparison, a vitrinite-rich coal typically utilized in coal-to-liquid processes was also employed. To assess the impact of mineral matter content, demineralization was used to remove most of the inorganic constituents. The findings revealed that the inertinite-rich coal exhibited lower liquefaction conversions due to a reduced proportion of reactive macerals and elevated levels of inorganic mineral matter. These conversion values exhibited a strong correlation with the quantity of reactive macerals present in the parent coals. For the inertinite-rich coal, the presence of inorganic mineral matter impeded the liquefaction process but facilitated the CO2 gasification reactions of the derived chars. To evaluate their potential in gasification processes, CO2 gasification experiments were conducted and the reactivities and apparent gasification activation energies of both coal chars, liquefaction residue chars, and preasphaltene and asphaltene (PAA) chars were calculated. These calculations were carried out using the random pore model (RPM) and volumetric reaction model (VRM). The chemistry, reactivity, and kinetics of residue gasification conversion are not thoroughly understood, yet they hold significant importance in optimizing syngas production within gasification processes. The findings from this work highlight significant differences in liquefaction conversion values, product distribution, and composition. These differences are influenced by factors such as maceral composition, inorganic mineral matter content, hydrogen-donor capabilities of the solvent, and liquefaction reaction temperatures. Additionally, these variables affect the CO2 gasification reactivity of liquefaction solid residue chars.

Highly Efficient Transformation of Tar Model Compounds into Hydrogen by a Ni-Co Alloy Nanocatalyst During Tar Steam Reforming.

Hydrogen (H2) production from coal and biomass gasification was considered a long-term and viable way to solve energy crises and global warming. Tar, generated as a hazardous byproduct, limited its large-scale applications by clogging and corroding gasification equipment. Although catalytic steam reforming technology was used to convert tar into H2, catalyst deactivation restricted its applicability. A novel nanocatalyst was first synthesized by the modified sol-gel method using activated biochar as the support, nickel (Ni) as the active component, and cobalt (Co) as the promoter for converting tar into H2. The results indicated that a high H2 yield of 263.84 g H2/kg TMCs (Tar Model Compounds) and TMC conversion of almost 100% were obtained over 6% Ni-4% Co/char, with more than 30% increase in hydrogen yield compared to traditional catalysts. Moreover, 6% Ni-4% Co/char exhibited excellent resistance to carbon deposition by removing the nucleation sites for graphite formation, forming stable Ni-Co alloy, and promoting the char gasification reaction; resistance to oxidation deactivation due to the high oxygen affinity of Co and reduction of the oxidized nickel by H2 and CO; resistance to sintering deactivation by strengthened interaction between Ni and Co, high specific surface area (920.61 m2/g), and high dispersion (7.3%) of Ni nanoparticles. This work provided a novel nanocatalyst with significant potential for long-term practical applications in the in situ conversion of tar into H2 during steam reforming.

Integrated process for simulation of gasification and chemical looping hydrogen production using Artificial Neural Network and machine learning validation

A significant driver of global warming is fast growth in greenhouse gas (GHG) generated by energy-producing areas. Converting biomass into useful products, chemical looping gasification is an appropriate route. Using integrated steam gasification technology that utilizes a chemical looping method to produce hydrogen. Mn-, Ni-, and Ca-based materials are the three types of oxygen carriers (OC), and they are utilized. This process offers the syngas, in the greatest quality and quantity, which is a key factor. We consider that the optimum gasifier temperature is 1100 °C. The steam-to-biomass ratio is 0.95, if the steam is further increased then the char gasification reaction starts moving in the reverse direction. In this process, 736.629 MW of power is produced when only natural gas and air are used in the combustion chamber and if we add hydrogen, power is increased up to 16 MW. To predict syngas composition and the S/B ratio, machine learning modeling using Artificial Neural Networks (ANN) algorithms are applied and compared, Bayesian Regularization and Scaled Conjugate gradient proves to be the best ANN model for validating and comparing with process model, demonstrating its accuracy and potential for optimizing biomass gasification processes as high as up-to 0.99 R2 value.

Some new insights into the kinetic compensation effect in different diffusion-controlled domain for char-CO2 gasification

The CO2 gasification reaction of lignite and coffee char are conducted at 1098–1173 K and 0.025–0.1 MPa CO2 via thermogravimetry analysis (TGA). The calculation methods of the activation energy and pre-exponential factor are further compared and analyzed. The activation energy and pre-exponential factor in the chemical-controlled domain, the external diffusion-controlled domain and the bed diffusion-controlled domain are measured to investigate the relationship between the kinetic compensation effect and mass transfer limitations. Results reveal that the normalized power-law rate equation can provide reliable kinetic parameters due to PCO2n ≠ constant (PCO2n represents the partial pressure term) at different temperatures and f(X) ≠ constant (f(X) represents the mechanism function term) at different char conversion. In the chemical-controlled or the external diffusion-controlled domains, coffee grounds char (CGC) and lignite char (LC) exhibit similar activation energies and pre-exponential factors in the char conversion range of 0.2–0.8. In the bed diffusion-controlled domain, the activation energy and pre-exponential factor increase and then decrease during the reaction process. An evident kinetic compensation effect was observed between E and ln(A0) throughout the conversion process with bed diffusion and among data from experiments with and without diffusional limitations, showing its dependence on mass transfer limitations.

Catalytic performance of activated lignite chars on biomass tar cracking

The tar problems are the major obstacle to developing the biomass pyrolysis technology. The coal chars derived from in situ pyrolysis and/or partially gasification are a promising alternative tar cracking catalyst with great industrial application potential because of its cheap and easily available characteristics. This work investigated the application of lignite chars as catalysts for biomass tar decomposition. Raw lignite char was further gasified with CO2 for 5min (GC5) and 15min (GC15) and used as tar cracking catalysts. Effects of pyrolysis temperature, char/biomass mass ratio, and pore structure of char on the pyrolysis tar removal were studied. The results showed that increasing pyrolysis temperature and char/biomass mass ratio would promote tar decomposition. When using GC15 as catalyst, tar yield was as low as 0.10 wt% at the temperature of 850°C and the mass ratio of 2. Gasification treatment increased the specific surface area of raw char from 284.1 to 342.7 m2/g (GC5) and 435.6 m2/g (GC15). Comparing the catalytic activity of lignite chars with commercial activated carbon demonstrated that mesopores were more influential than micropores in tar removal. In addition, water produced during biomass pyrolysis could in situ contribute to tar reforming and char gasification reactions. The results obtained in this study suggested that a cheaper coal char-based catalyst with excellent performance for biomass tar cracking could be achieved by combining with a coal gasification process and optimizing gasification conditions.

Comparative study on the effects of heating rate on char gasification behaviors by thermogravimetric analyzer and high-temperature stage microscope under non-isothermal condition

Understanding the intrinsic gasification reactivity and kinetics of coal char is vital in the process optimization, reactor design, and scaling of industrial gasifiers. Thermogravimetric analyzer (TGA) and visual high-temperature stage microscope (HTSM) were developed to investigate the mass loss and morphological evolution of coal char under non-isothermal conditions at different heating rates of 2.5, 5, and 10 °C/min, respectively. The gasification reactivity and kinetics obtained from different systems were comprehensively compared with the consideration of heating rate. Results showed that the consumption of carbon matrix and sintering could be responsible for the appearance of two reaction rate peaks in the rapid reaction stage in the HTSM experiments. As the heating rate increased from 2.5 to 10 °C/min, the limitation of heat and mass transfer and shortened residence time were conducive to the increase of observed reactivity and characteristic temperatures. Also, more serious diffusion and limitation could be responsible for the lower reactivity monitored by TGA and the difference in increasing amplitude of characteristic temperatures. Kissinger-Akahira-Sunosen (KAS) iso-conversional method was efficiently proposed to predict the gasification process. The activation energy varied with the carbon conversion, and then the average activation energies determined by TGA and HTSM were 191.51 and 199.01 kJ/mol, respectively. The evidence proved powerfully that the results close to the intrinsic behaviors could be provided by HTSM due to lower diffusion and limitation from heat and mass transfer.

Thermochemical conversion characteristics of biosolid samples from a wastewater treatment plant in Brisbane, Australia

Environmental context Biosolids are nutrient-rich organic materials. They can be used as fertiliser and solid amendments in agriculture if treated according to regulatory requirements. If farming applications of biosolids decline due to potential pollution from their heavy metal content, an alternative to traditional methods of biosolid disposal is required. In this context, thermal processing of biosolids is an economically and environmentally suitable option to convert large quantities of biosolids into useful energy. Rationale Due to more stringent environmental regulations and frequently required long-distance transportation, the traditional disposal of biosolids from wastewater treatment plants in landfills and farms is becoming unsustainable. A potentially economical and environmental option is the thermochemical conversion of biosolids into energy and value-added products. This paper describes the chemical composition and energy content of a representative biosolid sample collected from a major wastewater-treatment plant in Queensland, Australia. Methodology The thermochemical behaviour and compositional changes in biosolids were investigated under a wide range of pyrolysis and gasification conditions using a horizontal tube furnace (HTF), a fixed-bed reactor and a thermogravimetric analyser (TGA). In terms of practical application of by-products, we describe mineral matter transformations in char and ashes during pyrolysis and volatilisation as well as under different gasification conditions. Results HTF experiments revealed that at pyrolysis below 800°C, mainly organic species were released, while losses of inorganic elements (phosphorus, magnesium and zinc) occurred at higher temperatures. In-situ gasification behaviour of biosolid chars in the TGA reactor showed that the gasification reaction of biosolid chars occurred rapidly at temperatures above 720°C, regardless of the pyrolysis temperatures at which those chars were produced. Mineral matter transformations began at temperatures above 600°C, and mainly involved the transformation of amorphous phases into crystalline oxide and phosphide forms. Under gasification conditions, all crystalline phases appeared as different phosphates and alumino-silicates. Discussion The methods described here provide different options for the disposal of biosolids from wastewater by adjusting and optimising thermochemical conversion processes.

Effect of fresh bed materials on alkali release and thermogravimetric behavior during straw gasification

Alkali-associated problems are key issues for the efficient use of straw that is available as a major renewable energy resource worldwide. The effects of six bed materials commonly used in fluidized bed reactors on straw pyrolysis and char gasification were evaluated using online monitoring of alkali release and thermogravimetric analysis. Scanning electron microscopy with energy dispersive spectroscopy was used to determine the elemental composition of the char surface. In the straw pyrolysis stage, alkali release is reduced by the addition of dolomite and silica due to alkali adsorption on the bed materials, and enhanced by the addition of alumina because of its high sodium content. In the char gasification stage, silica, sea sand, olivine, and ilmenite reduce the char reactivity and alkali release, which is attributed to transfer of Si and Ti from the bed materials to the char and reaction with alkali to form stable and catalytically inactive compounds. Alumina also reduces the char conversion rate by transfer of Al to the char and formation of K-Al-Si and Ca-Al-Si compounds, while alkali release from the straw and alumina blend remains high due to the high Na content in alumina. Dolomite initially appears to increase the char gasification reactivity, but the results are affected by conversion of volatile matter that deposited on the dolomite in the straw pyrolysis stage. Dolomite also significantly increases the alkali release, which is attributed to Ca reactions with aluminosilicate compounds that allow potassium to remain in volatile form. Fresh bed materials are concluded to have significant effects on straw conversion depending on their chemical composition, and the results can contribute to the understanding required for efficient use of straw in commercial applications of biomass thermochemical conversion.

Investigation on the influence of inherent AAEMs on gasification reactivity of solid digestate char

Char reactivity usually determines the overall efficiency of the entire gasification process, while the presence of the alkali and alkaline earth metals (AAEMs) has a catalytic effect on char gasification. In this study, the influence of inherent AAEMs in the gasification behaviour of char was investigated. The char sample was prepared through the pyrolysis of solid digestate derived from anaerobic co-digestion of silage and dairy cattle slurry. The raw char and HCl-washed char were characterized by elemental analyzer, ICP-OES, SEM and XRD to explore their structural changes. HCl-char loses weight in the temperature range of 440–620 °C, and the weight loss percentage is significantly higher than that of char. Ash content of char is reduced by half after a pickling process. AAEMs are largely removed after char acid pickling, resulting in an increase in activation energy of the gasification reaction and a decrease in gasification reactivity, resulting in the gasification reaction time of HCl-char longer than char. Water-soluble AAEM and ion-exchange AAEM affect the evolution of carbon structure, which directly lead to char reactivity during the gasification reaction. As the carbon is consumed, the carbon microcrystalline structure of the residual carbon tends to be ordered, resulting in fewer active free carbon sites for the gasification reaction. Kinetic analysis showed that the loss and deactivation of AAEMs after char acid washing increased the average activation energy Ea by 115.76 KJ/mol compared with the original char.

Evaluation of Pyrolysis Reactivity, Kinetics, and Gasification Reactivity of Corn Cobs after Torrefaction Pretreatment

To reveal the effect of torrefaction pretreatment on pyrolysis and gasification reactivity of biomass, corn cob was first subjected to torrefaction pretreatment in a fixed-bed reactor at various reaction temperatures. The pyrolysis reactivity, kinetics, and gasification reactivity of torrefied corn cob were systematically assessed by various methods, proving that torrefaction pretreatment has a substantial influence on the physicochemical properties of corn cobs. The O/C and H/C molar ratios of corn cobs considerably drop with the increasing torrefaction temperature, and their higher heat-ing value (HHV) and energy density rise as well. It is found that torrefaction improves the pyrolysis reactivity of corn cobs because hemicellulose degradation is more severe than cellulose degradation during torrefaction, resulting in an increase in the percentage of cellulose in torrefied corn cobs. However, the severe depolymerization, polycondensation, and carbonization reaction during torre-faction of corn cobs at 280–300 °C can lead to a significant decline in the pyrolysis reactivity of corn cobs. Torrefaction pretreatment increases the pyrolysis activation energy of corn cobs, in addition to decreasing the char gasification reactivity of corn cob. The average char gasification reactivity of corn cobs drops when torrefaction severity increases. The passivation of active sites on the char surface may cause condensation and carbonation reactions of corn cobs during torrefaction. These findings provide new sights into the reasonable design of efficient torrefaction methods for appli-cation prior to pyrolysis and gasification of biomass.

Analysis of model dimensionality, particle shrinkage, boundary layer reactions on particle-scale modelling of biomass char conversion under pulverized fuel combustion conditions

In this work, the effects of model dimensionality, particle shrinkage, and boundary layer reactions on particle-scale modelling of biomass char conversion under pulverized fuel combustion conditions have been analysed by using six models: zero-dimensional models with constant particle size (0D_Cons) or shrinking particle size (0D_SPM), one-dimensional models with/without considering particle shrinkage (1D_Cons/1D_SPM), and 1D_Cons and 1D_SPM with considering boundary layer reactions (1D_Cons_BH and 1D_SPM_BH). A comparison with existing experimental data shows that the 1D_SPM_BH model with consideration of intra-particle heat and mass transfer, particle shrinkage, and boundary layer reactions is an appropriate model to describe biomass char conversion over a wide range of conditions. The 0D_Cons model is a good approximation for the conditions of small particle size (< 1 mm) at 1273–1473 K, but overestimates the char conversion rate for larger biomass char particle or at high temperatures (regime III). The 0D_SPM model gives a reasonable prediction on char conversion time but predicts a larger contribution of reaction between char and O2 as compared to the 1D_SPM_BH model. The consideration of intra-particle heat and mass transfer in particle-scale modelling (1D_Cons and 1D_SPM) is beneficial to improving the model prediction of char conversion time and the contributions of char oxidation and gasification reactions. The boundary layer reactions have a significant effect on the prediction of char conversion for large particles (> 1 mm) and high temperatures (> 1473 K). An implication for the selection of a particle-scale model in CFD modelling is also given.

Insight into the internal relevance of three-phase products in supercritical water gasification of coal

• Internal relevance of three-phase products of coal gasification was investigated. • Insight into the formation mechanism of products in the micro dimension. • Solid-liquid reaction model in coal particle surface was established. • Control steps for decreasing the irreversibility of reaction process was summarized. Supercritical water gasification (SCWG) is a promising technology for coal utilization and has attracted more attentions. This paper is aimed to obtain coal gasification behavior and the internal relevance of products from the perspective of micro level. Evolution characteristics of three-phase products were employed in high heating rate batch reactor. As a result, removal of functional groups in solid particles led to the decrease of the gasification reactivity of char (R coal > R 20s > R 60s > R 100s > R 1200s ). The hydrogen bonds formed by water forced the coal structure decomposition, in which the CO and CO 2 gas were generated from the deetherization and decarboxylation reaction. H 2 and CH 4 primarily came from the collision of free radicals and polycondensation reaction. Liquid intermediate components were detected by high-performance liquid chromatography quantitatively. The content of phenol and naphthalene was up to 280.8 ppm and 3647.4 ppm, and the mutual conversion mechanism of organic matters and polycyclic aromatic hydrocarbons (PAHs) was represented. Effectively controlling the ring growth of PAHs and the polycondensation of solid fragments is the primary goal to inhibit char formation, which is of great significance to decrease the irreversibility of chemical reaction process and realize the large-scale industrial production.

In-situ study on structure evolution and gasification reactivity of biomass char with K and Ca catalysts at carbon dioxide atmosphere

The structural evolution and gasification reactivity of biochar prepared from the pyrolysis of wheat straw were investigated by in-situ Raman spectroscopy and thermogravimetric analysis. The Raman spectra consisted of a combination of four Lorentzian bands (D1, D2, D4, G) and one Gaussian band (D3) in the first-order region. The experimental results showed that the addition of catalysts or the presence of ash could improve the CO2 gasification reactivity of biochar and result in a larger ID1/IG ratio and a lower IG/IALL ratio, meaning that the carbon structure was less ordered, and there were also more active sites such as amorphous carbon and cross-linked structures; Ca-based catalysts and K-based catalysts changed the evolution of biochar structure in a different way in CO2 atmosphere, the ID3/ID1 of Ca-based biochar was close to the value of non-catalyst biochar and decreased slowly, indicating that the Ca-based catalysts can stabilize the aromatic rings, while the IG/IALL of K-based biochar decreases significantly and the ID3/ID1 increased significantly, indicating the increase of carbon structure defects and the cracking of large aromatic rings in bio-char into small ones; a scheme of K and Ca reaction with biochar in CO2 gasification process was proposed.

Effect of Char Temperature on CO2 Gasification of High Ash Coal and Biomass

AbstractInformation on comparative gasification reactivity of high temperature chars in CO2 with high ash coal (C), sawdust (SD) and rice husk (RH) under identical condition is important for clean energy development drive particularly in countries like India, where energy matrix is dominated by coal and introduction of larger quantity of biomass in energy‐mix is attracting global interests. Therefore, TGA‐studies on char‐gasification reactivity using CO2 as a gasifying agent were performed at temperatures 850–1000 °C. In case of coal and RH‐chars, CO2 reactivity found to increase with increasing the BET surface area and reverse trend was observed with SD‐chars. Both the biomass‐chars showed increased specific micro pore surface area with increasing char preparation temperature through t‐plot analysis, still keeping unusual behavior of CO2 reactivity of SD‐char unexplained. The estimations indicating the presence of catalytically active alkali and alkaline earth metals in substantial quantity is only important criteria found to explain the decreasing trend of gasification reactivity of SD‐char prepared at various temperatures despite the increase in surface area. Catalytic activity of the components decreases with the rise in char preparation temperature. Kinetic analysis reveal that activation energy values of SD‐chars varied in the range123–182 kJ mole−1, whereas those for coal‐ and RH‐chars remained in the range 204–214 kJ mole−1.

Comparative investigation on gasification performances of co-pyrolytic char from bio-oil distillation sludge and rapeseed cake: Decomposition, kinetic, structural and prediction characteristics

The formation of bio-oil distillation sludge (DS) severely hampers the clean and continuous operation of biomass refinery system in terms of corroding the equipment and hazarding to human health, and thus the effective degradation and further disposal of DS is in accordance with the contaminant management and cleaner production. In this study, we proposed a co-pyrolysis strategy to optimize the gasification reactivity of DS to realize rapidly and efficiently converting DS into syngas. The co-pyrolysis feedstocks were DS and rapeseed cake (RC) under the carbonization temperatures of 800 °C and 1000 °C, followed by being gasified at 850–950 °C to estimate the gasification characteristics and kinetics. The results indicated the gasification reactivity of RC char was markedly higher than that of DS char, thereby with the potential to facilitate biochar reactivity of DS. The co-pyrolytic char reactivity obtained at temperature of 800 °C was enhanced with the elevated RC ratio but was all lower than that of mono-pyrolysis char, whereas the gasification reactivity of biochar pyrolyzed in 1000 °C was continuously strengthened as the DS ratio decreased from 100 % to 0. The kinetic results also indicated the apparent activation energy were increased with adding more proportion of DS, which resulted in a higher energy barrier to initialize the gasification reaction. The carbon arrangement was a critical key factor to modify the biochar reactivities, from which the large amounts of amorphous carbons and defects were promoted the biochar reactivity of RC char, whereas the ordered arrangement of crystallites for DS char was scarcely conducive to the diffusion effects of gasifying agents in carbon atoms and further diminishing the gasification reactivity. Furthermore, machine learning (ML) algorithm was for the first time adopted to simulate the co-gasification characteristics as a function of reaction time and blend ratios, and presented a higher consistency with experimental data, indicating the potential value of ML in predicting the co-gasification behaviors. Our findings can provide a feasible strategy to recover DS waste in a clean and efficient pathway, and layer a foundation for further perfecting the biomass refinery system to match the upstream production with downstream waste processing.

Detailed kinetic analysis and modelling of the dry gasification reaction of olive kernel and lignite coal chars

The dry gasification process of solid fuels is a promising pathway to mitigate and utilize captured CO2 emissions toward syngas generation with tailored composition for several downstream energy conversion and chemical production processes. In the present work, comprehensive kinetic analysis and reaction modelling studies were carried out for olive kernel and lignite coal chars gasification reaction using pure CO2 as gasifying agent. Chars reactivity and kinetics of the gasification reactions were thoroughly examined by thermogravimetric analysis at three different heating rates and correlated with their physicochemical properties. The reactivity of olive kernel char, as determined by the mean gasification reactivity and the comprehensive gasification characteristic index, S, was almost three times higher compared to that of the lignite coal char. It was disclosed that the fixed carbon content and alkali index (AI) have a major impact on the reactivity of chars. The activation energy, Ea, estimated by three different model-free kinetic methods was ranged between 140 and 170 kJ/mol and 250–350 kJ/mol for the olive kernel and lignite coal chars, respectively. The activation energy values for the lignite coal char significantly varied with carbon conversion degree, whereas this was not the case for olive kernel char, where the activation energy remained essentially unmodified throughout the whole carbon conversion range. Finally, the combined Malek and Coats-Rendfrem method was applied to unravel the mechanism of chars-CO2 gasification reaction. It was found that the olive kernel char-CO2 gasification can be described with a 2D-diffusion mechanism function (D2) whereas the lignite coal char-CO2 gasification follows a second order chemical reaction mechanism function (F2).

Comprehensive effects of different inorganic elements on initial biomass char-CO2 gasification reactivity in micro fluidised bed reactor: Theoretical modeling and experiment analysis

In this study, a theoretical model of biomass char gasification reactivity was developed, focusing on the catalytic effect of inorganic elements on the char gasification process. A comparison with previous research results shows that the catalytic ability of K in a fixed bed reactor is stronger than that of Ca, while the catalytic ability of Ca in a fluidised bed reactor is stronger than that of K. The migration and transformation of K and Ca in a fixed bed reactor and fluidised bed reactor are compared. In the fluidised bed reactor, a larger proportion of Ca is transformed into an ion-exchanged state than K, which is contrary to the experimental results in the fixed bed reactor. Then, according to the equivalent-volumetric impregnation method, the saturated loading ratio of K was determined to be 35%, and the full catalytic ratio of K was determined experimentally. Finally, eight typical biomass char samples were selected to perform experiments at different temperatures in the micro fluidised bed reactor to determine the char gasification reactivity, and the results were compared with the calculated values of the model. Results show that the model can effectively predict the char gasification reactivity both in trend and accuracy.

Kinetic Studies on the Steam Gasification of Chars Derived from Coals by Different Isoconversional Methods

Previous studies have successfully assessed the extent to which a kinetic model accurately represents a specific reaction mechanism by comparing the kinetic parameters derived from the kinetic model to those obtained using isoconversional methods. However, this approach remains underdeveloped for the important steam gasification reaction of char. This study addresses this issue by conducting a series of steam-assisted char gasification tests, using thermogravimetric analysis at five different heating rates. The results indicate that the carbon conversion ratio of the char gasification reaction increases with the increasing heating rate. The activation energies of the reaction process are determined with different carbon conversion ratios using three isoconversional methods, including the Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose, and Starink methods. The gasification mechanism is also analyzed using model-fitting methods with a wide variety of carbon conversion models, and the accuracies of the models are evaluated, firstly, by comparing the obtained goodness of fit values of the models with the experimental results, and, secondly, by comparing the obtained activation energies with those derived using the isoconversional methods. The goodness of fit results and the results of the comparisons between the activation energies obtained using the various models with the isoconversional values demonstrate that the three-dimensional Avrami–Erofeev model best represents the steam gasification char reaction, where the difference between the two activation energy values is only 0.70 KJ.mol−1. The reliability of the proposed approach for evaluating the applicability of a given kinetic model to the steam gasification reaction of char is tested by comparing the results obtained for char samples derived from three different bituminous coal sources.

Physico-Chemical Structure and Gasification Performance of Co-Pyrolytic Char Produced by the Pyrolysis of Polyvinyl Chloride Blends with Two Rank Coals.

Co-pyrolysis of waste plastics and coal has been considered to be an environmentally friendly and scalable waste treatment technology. This study investigated the influence of polyvinyl chloride (PVC) on the physico-chemical structure and gasification performance of co-pyrolytic char with lignite (PZ) and bituminous (SM) coal. The structure characteristics were explored by applying an X-ray diffractometer and a specific surface area analyzer. The quantitative analysis on the influence of PVC on pore characteristics and carbon microcrystal structure was conducted by the fractal theory and deconvolution method. The gasification performance was explored using a thermogravimetric analyzer. When the PZ blending ratio was larger than 50%, the specific surface area of PVCPZ chars enlarged significantly due to the increment of mesopores. Nevertheless, the effect of SM on the pore structure was not pronounced, and the specific surface area of PVCSM chars was as small as PVC char. A higher PZ blending ratio benefited the formation of mesopores with an aperture smaller than 10 nm for PVCPZ chars, whereas SM had little influence on pore diameter distributions of PVCSM chars attributed to the remarkable coating effects. The values of fractal dimension of co-pyrolytic char were larger than PVC char, revealing that the adjunction of coal increased the pore surface coarseness and improved the complicacy of the pore structure. Quantitative analysis on XRD spectra indicated that the disorder extent of the carbon structure was improved because of coal addition, and the influence of lignite on the disorder degree of the carbon structure was more significant. The gasification reaction of co-pyrolytic char showed significant synergistic effects, resulting in the improvement of gasification performance.

Insight into the relationship between CO2 gasification characteristics and char structure of biomass

Biomass gasification consists of three thermochemical stages: drying, pyrolysis, and char gasification, of which char gasification is the rate-limiting step. This study compared the char structure of biomass components (cellulose, hemicellulose, lignin, starch, and pectin) and revealed its quantitative relationship with the CO2 gasification reaction rate. Gasification experiments were performed in a self-built macro-thermogravimetric analyzer (Macro-TGA), and the char was characterized by proximate analysis, ultimate analysis, Fourier transform infrared (FTIR) spectroscopy, N2 adsorption/desorption isotherm, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The char gasification starting temperature from low to high was pectin ≈ starch < lignin < xylan. SEM revealed that the cellulose and starch chars had larger block structures. According to the FTIR results, the hydroxyl groups in the char enhanced the reactivity of char gasification. C–C/C=C was the dominant functional group in char, and O-containing groups, especially C–O, positively affected char gasification reactivity. It was found that the relationship between the gasification mass loss rate r and the char structure was r = 0.384 × surface area0.12 × ash content0.24. This study helps understand the relationship between biomass char gasification and its structure.