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[Display omitted] • Washed and unwashed P. oceanica wastes were pyrolyzed using TG-MS. • Its natural detrital inorganic matter affects its pyrolysis substantially. • O release and HCOOH formation were probably promoted by AAEMs and Fe 2 O 3. • SO 2 /HCl release decreases, due to carbonates and alkali metal chloride presence. • Depending on the purpose, the interest of P. oceanica washing should be studied. Significant quantities of Posidonia oceanica deposit on some beaches and coastlines every year, which generates high costs associated with the disposal of this waste. Pyrolysis may be an adequate way for its valorization. However, it would imply to know how the process takes place and if the removal of its natural detrital inorganic matter (epiphytes, marine salt and sand) is necessary, which are the objectives of this research. Pyrolysis by thermogravimetry-mass spectrometry was carried out on both the washed and unwashed samples. During this waste pyrolysis, the following occurs: (i) the high alkali metal chloride content promotes fragmentation reactions of carbohydrates and O formation, which increases HCOOH intensities at temperatures between 250 and 360 °C; (ii) from 500 °C to 650 °C, Fe 2 O 3 and decomposition of carbonates seem to be involved in reactions that produce O release and steam and CO 2 reforming of hydrocarbons and oxygenated organic compounds with H 2 generation; (iii) from 650 °C to 750 °C, Fe 2 O 3 , high alkali metal content and carbonate decomposition generate char gasification, an increase in O release, SO 2 capture and HCOOH formation. In general, the abundance of inorganic matter (chlorides, carbonates, etc.) minimizes the release of various compounds during pyrolysis, including SO 2 and HCl, while increasing HCOOH production. Thus, this high content of inorganic matter may represent an advantage for its pyrolysis, producing value-added chemical products with a reduced environmental impact. Therefore, this study may be the starting point for defining the optimal pyrolysis conditions for this waste valorisation. [ABSTRACT FROM AUTHOR]

For a gasification process, the char-CO2 gasification is the controlling step worthwhile to be deeply investigated. The article chosen corn stalk (CS), poplar sawdust (PS) and bagasse residue (BR) as the typical waste species derived from agricultural, forestal and industrial sources. The char-CO2 gasification behavior, reaction kinetics and carbon structure were studied to reveal the intrinsic factors determining the reaction kinetics. Generally, the carbon conversion and maximum conversion rate were influenced by the feedstocks species and char preparation temperatures, as influenced by ash proportion, potassium content in ash and carbon structure of char. The char-CO2 reaction for CS was subject more to the catalytic effect of alkali compositions, while pore structure affected more the gasification reaction for PS char. The isoconversional kinetic analysis indicated that the gasification reaction became stable at carbon conversion of 0.5. Subsequently, sectionalized kinetic parameters were calculated for the initial gasification temperature to the temperature reaching 50% conversion. The result showed that high initial gasification temperature increased the char-CO2 gasification barrier to hardly start the reaction but accelerate the reaction rate. The carbon structure analyses further clarified that the reaction activation energy was highly related to the microcrystalline structure of carbon, while the reaction rate was more determined by carbon pore structure.

The rate of conversion during gasification of char particles depends on the type of reagents, the concentration of reactants, and reactor temperature, among many other parameters; however, the overall conversion depends on the residence time distribution (RTD) of the particles in the reactor. The objective of the present work is to investigate the influence of gasifying agents, their concentration, and reactor wall temperature on the RTD of the char particles. The aim also includes studying the effect of mean residence time on the overall char conversion during gasification of Victorian brown coal in an entrained flow reactor. Two gasifying reagents, namely, CO2 and H2O, are selected in the present study. A discrete particle model (DPM) is coupled with computational fluid dynamics (CFD) to simulate the solid phase dynamics. Gasification is modelled using a lumped approach. The mean residence time of the solid char particles, determined using three different methods, is observed to increase with the CO2 concentration and wall temperature but decrease in the H2O environment. The longer residence time leads to higher overall char conversion in a CO2 environment despite the higher reactivity of H2O compared to CO2 as a gasifying reagent. [ABSTRACT FROM AUTHOR]

• Conducted a numerical study on co-firing biomass with coal in a pressurized combustor. • Quantititively assessed the reaction pathways of coal and biomass inside the furnace. • Analized NOx evolution in pressurized oxy-fuel combustion. As the next evolution in oxy-fuel combustion technology, pressurized oxy-combustion (POC) can potentially improve the process efficiency and economics. Biomass combustion is considered to be nearly CO 2 neutral, and thus, a negative CO 2 balance can be achieved by co-firing biomass in an oxy-fuel combustion process. However, this concept has not yet been demonstrated for the POC system. To address this need, and validate the feasibility of co-firing under these conditions, simulation investigations are conducted based on a pressurized pilot-scale facility. The influences of biomass co-firing ratio on the combustion characteristics and pollutant emissions are estimated. It is evident from the results that the diffusion flame formed by the fuel-oxidant reaction has a good fullness within the furnace, with the maximum flame temperature under each condition not exceeding 1950 K. Biomass typically contains higher moisture and volatile mass fractions compared to coal, leading to a lower temperature around the fuel inlet. In the POC scenario, char gasification plays a prominent role in the process of char consumption. In 100 % coal and 100 % biomass cases, the char consumption caused by the gasification reaches 80 % and 69 % respectively. The predicted NOx emissions in 0 %Bio, 50 %Bio, and 100 %Bio cases are no more than 10 ppm. Furthermore, NOx reduction by volatile and char is quantitatively estimated. The employed low equivalence ratio, coupled with the enhanced NOx reduction by volatile and char can be applied to account for the low NOx emissions in the POC system. This investigation is to provide a comprehensive assessment regarding the combustion and pollutant emissions within the pilot-scale pressurized oxy-combustor during co-firing biomass with coal. [ABSTRACT FROM AUTHOR]

In this work, the influence of KCl concentration on the gasification characteristics of lignite coal char between 800–1100 °C is studied through the experiments of temperature programmed gasification and isothermal gasification using a thermogravimetric analyzer. The gasification kinetics, characteristic parameters, and the reaction mechanism of catalytic gasification is explored using the random pore model (RPM). In view of temperature programmed gasification, the gasification rate of coal char is relatively slow when the temperature is below 700 °C, and only when the temperature is higher than 700 °C, the gasification starts to accelerate. Results show that with the existence of a catalyst, the temperature required for gasification reaction is reduced and the gasification reaction rate is increased. Furthermore, the higher concentration of KCl leads to the shorter half reaction time, the higher gasification rate, and the stronger catalysis. In addition, the activation energy of AW-char (the char from acid-washed coal) is the highest, while the activation energy and the energy level required for the gasification reaction are reduced by adding KCl. Based on the analysis of the catalytic mechanism, it is found that the unified mechanism of catalytic gasification of alkali and alkaline earth metals is applicable for the KCl catalysis on coal char gasification. [ABSTRACT FROM AUTHOR]

This study evaluates the potential to produce phosphorus (P)-rich fertilizer substrates with high plant availability as well as carbon (C)-rich biochar with soil enhancement properties in a single slow-pyrolysis plant. Campaign-based production or co-production of soil enhancers and fertilizer substrates may increase the potential societal value of slow pyrolysis plants. The assessment focus on conventional slow pyrolysis operated at 600 °C to produce biochar from various substrates as well as two options for post-process char treatments—char oxidation at 550 °C and char steam gasification at 800 °C, as a potential way to improve substrate fertilizer value. Four P-rich biomass residues including municipal sewage sludge (SS), biogas fiber (BF), cattle manure (CM), and poultry manure (PM) as well as two C-rich biomasses: wood chips (WC) and wheat straw (WS), were tested. Production yields of biochar and ash from char oxidation and steam gasification were compared and the materials were characterized to be used as soil enhancers and P-fertilizers through direct analysis and soil incubation studies with two different agricultural soils. All thermal treatments increased the concentration of the plant nutrients P, potassium and magnesium in the resulting biochar and ashes compared to the dry biomass. At the same time, concentrations of nitrogen and sulfur were reduced. The dry biomasses generally increased the amount of available P in the soils to a greater extent than biochar or ashes at an application rate of 80 mg P/kg soil. The P-rich biochar and ash made from BF, CM and PM had higher P fertilizer values than those made from SS. In terms of thermal processes, pyrolysis with subsequent char steam gasification was found to be the best option for high P availability in both soils, except for operation on SS where the oxidized char gave the best results. The C-rich biochars made from wood and wheat straw both showed potential for improving soil properties including soil organic matter (SOM) content, cation exchange capacity (CEC) and water holding capacity (WHC). The study shows that campaign operation of slow pyrolysis with the option for char steam gasification is a viable option for producing fertilizer substrates with high levels of plant available P as well as biochar with substantial soil enhancing properties on a single plant. In addition, results also indicate that direct co-pyrolysis of P-rich substrates—especially BF and CM, with any of the two tested C-rich substrates—without subsequent char treatment may be a sufficiently well integrated option for combined soil fertility and soil P fertilization management. [ABSTRACT FROM AUTHOR]

Gasification is an effective approach to consume the excess production capacity of coke. The effects of lignite and Fe/red mud oxides on the steam gasification of coke were investigated in this study. Results show that the addition of lignite as an active substance exhibited a significant positive effect on the improvement of coke reactivity, and the volume content of syngas including H 2 , CO and CH 4 reached to the values ranging from 82.24% to 89.46%. With the employment of lignite addition, free active OH radicals were formed, accompanying by an increase in surface area values and a decrease in carbon ordering degree of the coke, which are all benefit for improving the reactivity of coke with steam. The introduction of Fe4RM6 oxides further promoted the carbon conversion with a value of 99.61% of coke/lignite mixtures, which is significantly higher than that of 65.46% of pure coke gasification at a time of 150 min. The Fe4RM6 oxides presented a good performance after five gasification cycles. • The presence of lignite/Fe4RM6 significantly improved the x of coke reacted with H 2 O. • The addition of lignite produced free active OH radicals during coke-H 2 O reaction. • The addition of lignite decreased the carbon ordering degree of the gasified coke. • The low-cost Fe4RM6 oxides presented a good performance after five cycles. [ABSTRACT FROM AUTHOR]

[Display omitted] • Char-Gaseous reaction inhibition due to H 2 evolution in packed bed established. • Nonlinear inhibition: over 75 % occurs within initial 20 % of bed height. • FTIR confirms H 2 -induced inhibition, shifting char bonds from C–OH to C–H. • Inhibition can be overcome by adjusting gas phase concentration and temperature. • Oxy-Steam gasification efficiency can be improved from this research. Previous research on Char reactions with gas phase compounds under micro-thermogravimetry systems shows that hydrogen inhibits heterogeneous char reactions. However, its impact on larger gasification systems with evolving hydrogen profiles remains largely unexplored. This study examines a macro-scale wood char bed to understand the influence of in situ evolving hydrogen on char reactions. When subjected to a specific steam flux, carbon conversion and pore morphology changes are mainly confined to the bed's upstream, with the downstream char retaining its original characteristics. Numerical investigations reveal over 75 % of species production and consumption occurs within the initial 20 % of bed height. Fourier-transform infrared spectroscopy confirms hydrogen-induced inhibition in downstream segments, showing a shift from C–OH to C–H bonds. Particle-scale analysis indicates significantly higher rates of hydrogen diffusion and adsorption compared to H 2 O , impeding downstream C + H 2 O reactions. Increased temperature, higher reactant concentrations, or reduced residence time can overcome this inhibition, enhancing conversion rates. These findings are critical for optimizing steam-to-biomass ratios in oxy-steam gasification systems for generating hydrogen-rich syngas. [ABSTRACT FROM AUTHOR]

Char conversion is a complex phenomenon that involves not only heterogeneous reactions but also external and internal heat and mass transfer. Reactor-scale simulations often use a point-particle approach (PP approach) as sub-models for char conversion because of its low computational cost. Despite a number of simplifications involved in the PP approach, there are very few studies that systematically investigate the inaccuracies of the PP approach. This study aims to compare and identify when and why the PP approach deviates from resolved-particle simulations (RP approach). Simulations have been carried out for CO 2 gasification of a char particle under zone II conditions (i.e., pore diffusion control) using both PP and RP approaches. Results showed significant deviations between the two approaches for the effectiveness factor, gas compositions, particle temperature, and particle diameter. The most significant sources of inaccuracies in the PP approach are negligence of the non-uniform temperature inside the particle and the inability to accurately model external heat transfer. Under the conditions with low effectiveness factors, the errors of intra-particle processes were dominant while the errors of external processes became dominant when effectiveness factors were close to unity. Because it assumes uniform internal temperature, the models applying the PP approach always predict higher effectiveness factors than the RP approach, despite its accurate estimation of intra-particle mass diffusion effects. As a consequence, the PP approach failed to predict the particle size changes accurately. Meanwhile, no conventional term for external heat transfer could explain the inaccuracy, indicating the importance of other sources of errors such as 2D/3D asymmetry or penetration of external flows inside the particles. • Char gasification models with resolved- (RP) and point-particle (PP) approaches. • Inaccuracies of the PP highlighted by comparing two approaches. • Profound consequence of neglecting internal temperature distribution. • Intrinsic errors identified including internal Stefan flows and 2D/3D asymmetry. [ABSTRACT FROM AUTHOR]

To explore the feasibility of converting oxy-fuel combustion flue gas into valuable syngas through char gasification process, the reactivity of three types of char (bituminous coal char, biochar, and waste char) were experimentally studied under atmospheric pressure in a fixed-bed reactor. The effects of flue gas flow rate and temperature, CO 2 /H 2 O/O 2 ratio, char types on the char gasification characteristics were mainly investigated. It was found that when the flue gas temperature is 1200 °C or even higher, no matter which char is used, >90% CO 2 conversion rate can be reached in line with the Boudouard equilibrium. The reactivity of biochar-H 2 O is relatively higher than that of waste char-H 2 O. Besides, 5% oxygen ratio in CO 2 /H 2 O mixture is preferred to promote the gasification reaction to some degree. It is important to balance the fixed carbon conversion rate and CO/H 2 yield in syngas to decide the optimum residence time of char. Overall, it is a novel way of CO 2 reduction and waste resources utilization. • It is feasible to recover waste heat from oxy-fuel combustion furnaces through char gasification process. • The reactivity of coal char, biochar and waste char are experimentally studied. • Some oxygen added in CO 2 /H 2 O mixture can promote the gasification reaction. • The fixed carbon conversion rate and CO/H 2 yield should be balanced to decide the optimum residence time of char. • It is a novel technology contributing to CO 2 reduction and waste resources utilization. [ABSTRACT FROM AUTHOR]

Coal O2/CO2 combustion is a promising carbon capture and storage technology for coal-fired power plant. Char consumption rate prediction is essential for the boiler design, but challenging for O2/CO2 combustion since char reaction behavior within dual reactive gas media is complex. There is also a doubt of whether or not the O2 reaction and CO2 reaction occur independently, whereby the overall rate would be simply additive, or the two reactions compete for the same char actives, in which case the rate prediction could be more complicated. Here, the competitive behavior for O2 and CO2 reactions of char active sites was investigated via thermogravimetric approach, with a focus on the effect of temperature and inherent mineral composition. For char combustion within O2/CO2 environment with molar fractions of 30/70, the contribution of O2 to char consumption is the same as the O2 reaction alone. However, as being out-competed by O2, only 37% CO2 could occupy char active sites and react. Consequently, the overall char reaction rate within O2/CO2 is only 83% of the sum of that for individual gases at 900 °C. With increasing temperature, this ratio becomes even smaller, as the contribution of CO2 that being out-competed (to the sum of individual gases) is larger. With increasing O2 fraction, it occupied more active sites, thus further inhibiting CO2 reaction. The inherent alkali and alkaline earth metal provides the char with more active sites, thus muting the competition and inhibition for CO2 gasification. [ABSTRACT FROM AUTHOR]

Gasification models of a char particle based on the true porous structure are essential for the accurate simulation of gasifiers, and pore-scale study might provide important information for the development of the porous char particle gasification models. In this paper, a numerical study was conducted on the gasification of a single-pore char particle in supercritical water, and the emphasis was put on the gasification process inside the pore with the effects of surrounding fluid, pore structure and pore position considered. The results showed that the gasification in a pore was quite affected by pore diffusion. The increase in temperature and particle Reynolds number promoted the gasification in the pore, and convection mainly enhanced the heat transfer but had limited promotion on mass transfer in kinetically controlled regime. Increasing pore length and decreasing pore diameter caused the increase in diffusion resistance and the former had more obvious effects. However, the decreased pore diameter increased the specific surface area and benefited the whole char conversion. The pore position affected the species distribution inside the pore for non-diffusive gasification, and the impact was limited in kinetically controlled regime. Finally, study in this work will be further extended to the gasification of the porous char particle. [ABSTRACT FROM AUTHOR]

As an emerging clean coal combustion technology, Moderate or Intense Low-Oxygen Dilution (MILD) combustion or oxy-fuel combustion, compared with traditional coal combustion, has many advantages. However, compared with MILD combustion and oxy-fuel combustion, MILD-oxy combustion is believed more attractive. In this work, MILD-oxy combustion characteristics with oxygen concentrations from 10% to 50% are studied numerically. The results show that within a certain range, increasing the oxygen concentration is in favor of MILD-oxy combustion performance close to that of MILD-air combustion. When the oxygen concentration is higher enough, the momentum reduced by the increase of oxygen concentration has a great influence on the furnace temperature. With the increase of oxygen concentration, the radiation heat transfer is enhanced and the convective heat transfer is weakened. The increase of oxygen concentration can promote the occurrence of char gasification reaction with CO 2. In addition, MILD-oxy combustion has a large impact on CO emission. • Characteristics of the coal MILD-oxy combustion are simulated for 10%-50%O 2. • Reducing O 2 can improve MILD performance, but increasing O 2 can reduce CO emission. • The peak temperature during coal combustion increases with the O 2 concentration. • Increasing O 2 concentration can promote the char gasification with CO 2 and H 2 O. • For coal MILD-oxy combustion, CO emission is not negligible. [ABSTRACT FROM AUTHOR]

Alkali ceramics are well-known high temperature CO 2 sorbents in forms of zirconates or orthosilicates with catalytic tar cracking ability prior to or after carbonation. In this study, Li 2 ZrO 3 , Li 4 SiO 4 , and Na 2 ZrO 3 were selected as catalyst-sorbent bifunctional materials to enhance the pyrolysis of sawdust. This study investigated the synergy between the alkali metal bifunctional materials under pyrolytic conditions. The weight loss data and gas yield trends in the temperature between 200 and 800 °C demonstrated a combined catalytic process and gas-solid reaction. A metal carbonate phase was formed after the reaction of capturing CO 2. The CO 2 capture promoted H 2 production because of Le Chatelier principle and the formation of carbonate phase assisted tar cracking reactions. H 2 production increased from 5.73 mmol g−1 to 8.87 mmol g−1, 15.85 mmol g−1, and 13.67 mmol g−1 in the presence of Li 2 ZrO 3 , Li 4 SiO 4 , and Na 2 ZrO 3 , respectively. At temperatures around 700 °C, CO was released due to secondary cracking reaction and the Boudouard reaction of CO 2 released from the sorbents. Overall, the alkali ceramics present the catalyst-sorbent bifunctional activity for enhancing H 2 production during biomass pyrolysis. Image 100066 • Bifunctional catalyst-sorbent activity of alkali ceramics was investigated. • Alkali ceramics were active in catalytic and chemisorption activities of pyrolysis. • Presence of alkali ceramics increased H 2 yield by two-fold. • At 700 °C alkali ceramics participated in gasification of char. [ABSTRACT FROM AUTHOR]

The high concentration of CO 2 and low concentration of O 2 at relatively low temperatures of 1123-1223 K are typical reactive atmospheres in the fuel reactor of a chemical looping with oxygen uncoupling (CLOU) unit. Char within this environment can be converted via lean-O 2 oxidation and/or rich-CO 2 gasification. Conventional models, which either considered the oxidation only or considered the oxidation and gasification contributions independently by simply adding the two individual conversion rates together, seem arbitrary. Therefore, it is necessary to quantitatively explore the contributions of the oxidation and the gasification reactions as well as their interactions in CLOU conditions through more detailed particle-resolved simulations. In this work, a single particle model which described a spherical reacting porous particle with its reacting boundary layer was developed to investigate the conversion characteristics of pulverized coal char in lean-O 2 and/or rich-CO 2 conditions (analogous CLOU conditions). The heterogeneous reaction kinetics developed by Tilghman and Mitchell [35] and the simplified GRI-Mech 3.0 gas-phase reaction kinetics were adopted. It was found that the char conversion rate in CLOU conditions could be basically modeled as the sum of the full oxidation consumption rate and the partial gasification consumption rate, i.e. r mix = φ 1 r gasi + r oxid. The interactions between the oxidation and gasification reactions were elaborated in two aspects: on the one side, the oxidation of coal char in CLOU conditions is within the weak zone II burning region, where the oxidation reaction only happens peripherally and is nearly unaffected by the high concentration of CO 2 ; on the other side, the gasification reaction within the external layer of the coal char particle is inhibited by the oxidation reaction, consequently the gasification reaction only happens inside the coal char particle where O 2 cannot penetrate into. Based on these understandings, a correlation between the coefficient, φ 1 , and the effectiveness factor of the oxidation reaction, η , was proposed to describe the overall char conversion rate in CLOU conditions. Through fitting the simulation results under typical CLOU conditions, the quantitative relationship between φ 1 and η was finally attained. [ABSTRACT FROM AUTHOR]

Considering the endothermic process accompanied by the ash melt and the effect of the ash melt on char particle structure, a fusion gasification model for a single char particle is established. Model predictions and experimental data show that the decreasing trend of the porosity caused by the melt and aggregation of ash is well represented in the model. Compared with the predicted results without consideration of ash fusion, the accuracy is improved obviously. Based on the model, the fusion gasification characteristics of the char are investigated. The results show that when particle size is less than 0.4 mm, the fusion gasification process is more sensitive to the effect of the ash fusion. With the particle size increases from 0.4 mm to 1 mm, the char conversion rate increases by about 5% at 1573 K and 1673 K, while the char conversion rate increases by only about 1% at 1773 K. Unlabelled Image • A fusion gasification model for a char particle is established. • The final particle size increases with the gasification temperature. • Ash fusion obviously affects the gasification process for char less than 0.4 mm. [ABSTRACT FROM AUTHOR]

Supercritical water gasification of coal is a clean and efficient method for coal utilization which can convert coal into H 2 and CO 2 . In order to further reduce costs, a novel two-step cascade utilization method was proposed in this study: conducting traditional pyrolysis first and then gasifying the pyrolysis char in supercritical water. The influences of different pyrolysis operating parameters on gaseous products and char gasification in supercritical water were investigated. Quartz tube reactors were used to ensure the complete collection of gaseous products in pyrolysis process. The experimental results showed that both carbon and hydrogen conversion efficiency increased with temperature, and the increasing trend became not obvious after reaction for 5 min. The thermo-gravimetric curves showed that volatilization removal process was completed at the pyrolysis time of 5 min and higher pyrolysis temperatures were beneficial to the subsequent gasification process. The result also showed that residual weight was 15%–20% of the initial weight. Hydroxyl radicals kept stable during pyrolysis process with the absorption peak intensity increasing first and then decreasing, and mineral substance disintegrated gradually as time increased. As pyrolysis temperature increased, the peak of C C double bonds decreased, turning into stable functional groups and carbonyl group increased. Dispersive pores occurred at the surface of coal as residence time increased with particle size decreasing, specific surface area and reactivity increasing. The results might be used for the design of a cascade utilization system based on coal gasification in supercritical water. [ABSTRACT FROM AUTHOR]

The measurement of char gasification reactivity and kinetic parameters by TGA is generally complicated with mass transfer limitations. There is a reactant gas concentration gradient in the stagnant gas region between the mouth of the TGA crucible and the surface of the char bed because of gas consumption by the sample. The counter-diffusions between the reactant and product gases occur in this stagnant region. The Maxwell-Stefan equation has been used to estimate the distribution of gas concentration in the stagnant gas region. However, there is some uncertainty associated with semi-empirical gas diffusion coefficients used in the equation. In this study, we propose a new method to estimate the distribution of CO 2 concentration in the stagnant gas region during CO 2 gasification of coal char in TGA. The external effectiveness factors obtained in this way were in a reasonably good agreement with the value obtained by the traditional method widely used in literature. [ABSTRACT FROM AUTHOR]

The CO 2 gasification reactions of biomass char in granulated BFS (blast furnace slag) were isothermally investigated using a thermogravimetric analyzer with the temperature ranging from 1173 K to 1323 K. The effects of temperature, biomass type and granulated BFS on the kinetic characterizations of CO 2 gasification of biomass char were illuminated. The kinetic mechanism models and parameters were obtained through a novel two-step calculation method. The results indicated that the CO 2 gasification reactivity of biomass char as conversion and gasification index increased with the increase of temperature and it could be promoted through granulated BFS. The CO 2 gasification reactivity of CS (cornstalk) char with lower alkali index was lower than that of PS (peanut shell) char. The A 4 model (Avrami-Erofeev (m = 4) model) and A 3 model (Avrami-Erofeev (m = 3) model) were demonstrated as the best appropriate models for CO 2 gasification of CS char and PS char, respectively. The gasification activation energy of CS char ranging from 155.08 to 160.48 kJ/mol was higher than that of PS char whether with or without granulated BFS. Granulated BFS could decrease the activation energy of CO 2 gasification of char at any biomass type. [ABSTRACT FROM AUTHOR]

Reaction mechanism takes place in char gasification was tested by kinetic studies. A modified kinetic model (thin reaction zone model) was developed to evaluate the mechanisms controlling the process of gasification. The model was compared to the experimental data of char gasification using steam as gasification agent. The gasification was carried out at 600-800∘C for 60 min. The model assuming the mass transfer of steam through the ash layer controls the reaction rate work well. The average error at operating temperatures of 600, 700, and 800∘C was 2.89, 1.75, and 3.26% respectively. [ABSTRACT FROM AUTHOR]

A multi-stage fluidized bed (MSFB) by configuring the distributor with an overflow standpipe between its neighboring stages was developed to couple the powder coal pyrolysis with its resultant char gasification for co-production of tar and syngas. This work succeeded in the smooth operation of MSFB for coal staged conversion. The three modes of coupling pyrolysis and gasification in terms of the one-stage, two-stage and three-stage bed characterized by temperature drop from the bottom up were investigated to evaluate the quality of the liquid and gas products. Coupling low- and mid-temperature tandem coal pyrolysis with high-temperature char gasification in the MSFB improved the quality of tar and syngas. The obtained tar yield was over 80% of the Gray-King assay tar yield and its light tar fraction (boiling point <360 °C) was as high as 70–80% in the MSFB. Syngas with CH 4 content of 5.2 vol.% was produced that was suitable for SNG production. Inside the reactor, the flow direction of pyrolysis volatiles toward the temperature drop avoided the deep secondary reaction of tar. Syngas and steam from the bottom gasification section could contribute to the formation of light tar and CH 4 by affecting the top coal pyrolysis. A comparison with the typical pyrolysis processes suggested that the MSFB process had its own advantages in treating powder coal to produce the high-quality tar and syngas. [ABSTRACT FROM AUTHOR]

The CO 2 gasification reaction of lignite and coffee char are conducted at 1098–1173 K and 0.025–0.1 MPa CO 2 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 P C O 2 n ≠ constant (P C O 2 n 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(A 0) throughout the conversion process with bed diffusion and among data from experiments with and without diffusional limitations, showing its dependence on mass transfer limitations. [ABSTRACT FROM AUTHOR]

• Non-uniform distributed Stefan flow leads obvious variations on C dp and C p under different reaction temperatures. • Strong endothermic effect of heterogeneous reactions enhances the heat transfer of the sphere surface. • Increasing the relative content of gaseous H 2 O leads the higher heterogeneous reaction rate. • Ash layer leads larger drag, while inhibits the heat transfer and heterogeneous reaction rate. Based on PR-DNS (Particle Resolve-Direct Numerical Simulation) method, the gasification process of a single spherical char particle moving in high-temperature supercritical CO 2 /gaseous H 2 O atmosphere at 9 MPa is conducted, and related mechanism on the reaction-affected drag of the sphere, flow field and interphase thermal as well as mass transfer near sphere surface is presented. The reaction temperature and Re (Reynolds number) of the fluid flowing over the sphere are variable within the range of 1273.15–1673.15 K and 10–200, respectively. The mass decomposition source on the sphere surface (Stefan flow), reaction heat, heat radiation between fluid species and char, porous inert ash layer and variations on physical properties of fluid mixture near the sphere surface are taken into account, while the Pseudo-Steady-State approach is employed for handling the particle shrinking. The results indicate that the higher reaction temperature leads the smaller drag coefficient, while enhances the performance of heat transfer compared with that of non-reactive cases. Due to the relative strength between convective heat transfer and endothermic effect of heterogeneous reaction, variation laws of temperature on the sphere surface vs. Re differs from each other under different reaction temperatures. Higher temperature and lower Re leads the higher surface Damköhler numbers, which indicates that the heterogeneous reactions in gasification process have normal characteristic of reactions in the kinetically-controlled regime. Porous inert ash layer increases resistance to flow as well as diffusion of species, and the variations in relative concentration of fluid reactants can also result in varied influences on above variables. [ABSTRACT FROM AUTHOR]

Biochar, as an important renewable and carbon-natural energy, shows plentiful prospects to be used in the ironmaking industry. In this study, the effect of iron ore content and temperature on the reduction of iron ore-biochar pellets in nitrogen atmosphere were investigated. Results indicated that with the decrease of carbon to iron ratio, the iron ore indirect reduction was promoted more than char conversion which resulted in an decrease value of CO:CO 2 . Pellets reduction at 900 °C found that 60% iron ore in pellet exhibited considerable carbon conversion and the highest iron ore reduction amount. With the increase of reaction temperature, the char gasification reaction was promoted prior to the iron ore reduction, resulting in an increase of CO:CO 2 ratio. The wustite and metallic Fe gradually increased, while hematite and magnetite gradually decreased, with the increase of temperature. Kinetics study found that carbon conversion was controlled by one-dimensional diffusion, while the iron phase reduction reaction was controlled by three-dimensional diffusion, and the increasing activation energy as the reaction proceeded restricted the iron reduction process. The intrinsic reaction behavior, thermal kinetics, and technical analysis may guide the application of bioenergy in the ironmaking industry. [ABSTRACT FROM AUTHOR]

This work, performed in the context of Gaya project, focuses on the characterization and modelling of the effect of the pyrolysis heating rate on the steam gasification of char from woodchips. An experimental work was performed based on thermogravimetry and solid characterization of char samples prepared under different conditions. The results showed that gasification apparent reactivity increased with the increase of heating rate. The faster chemical kinetics of char prepared under high heating rate could be related to its higher catalytic inorganic content together with a more reactive carbonaceous structure. The increase of heating rate favours porosity development and the enlargement of pores, which would have a positive effect on gasification reaction rate by enhancing gas diffusion within the solid. The effect of heating rate on char gasification was included in a model previously developed, by correlating the chemical kinetics, particle density and diffusion rate to the char yield, which was selected as a suitable indicator of the heating rate. The new version of the model, considering the variability of heating rate during char formation, was validated through accurate predictions of the experimental results. [ABSTRACT FROM AUTHOR]

The gasification mechanism of char in the mixture of H 2 O, CO 2 , H 2 and CO is controversial for a long time, and the reasons leading to different results of validation experiments of gasification mechanism are yet not clear. In this study, the specific surface area (SSA) and ash of char are assumed to be the possible reasons leading to the controversial results. The large-SSA char, the small-SSA char, and the ash-free char were prepared for validation experiments. The gasification experiments were performed in the mixture of H 2 O, CO 2 , H 2 and CO using a modified TGA system. The experimental results indicate that SSA and ash really have significant effects on char gasification mechanism. The gasification mechanism of large-SSA char is close to the separate active sites assumption, while the gasification mechanism of small-SSA char is close to the common active sites assumption. The gasification mechanism will transition from the separate active sites assumption to common active sites assumption if the ash is removed from the large-SSA char, and will become closer to the separate active sites assumption again if Na is loaded to the ash-free char. Therefore, for char gasification in the mixture of H 2 O, CO 2 , H 2 and CO, the separate and common active sites assumptions are two extreme situations of the same gasification mechanism. Finally, a unified model was proposed based on this char gasification mechanism. This model is applicable to the char samples that have different specific surface areas and ash contents. [ABSTRACT FROM AUTHOR]

A high temperature stage microscope to investigate the temperature effect caused by particle size on char gasification is applied in this study. Experiments were carried out with different particle sizes for raw chars and chars on molten slag surface, respectively. Heat transfer models were built for the raw char of two temperature distributions and char particle on molten slag, respectively. Results showed that reaction layer temperature of raw char decreased in the reaction dominant while char on molten slag had higher temperature. Temperature difference between two distributions increased with the initial particle size, indicating the temperature effect on large particles was obvious. Shrinking core model was applied and modified herein coupled with the modification of reaction layer temperature and reaction area. Model prediction and experimental data showed good agreements of carbon conversion and reactivity index for raw char and char on molten slag, respectively. © 2016 American Institute of Chemical Engineers AIChE J, 63: 716-724, 2017 [ABSTRACT FROM AUTHOR]

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Based on percolation theory, the discrete model of char particle gasification with structure evolution under various distinct regimes was developed. Initial structure of individual char particle was modeled as a simple cubic lattice consisting of a large number of small sites. Sites arranged in the char lattice were randomly classified as either carbon, ash, or macropore, depending upon the proximate analysis data and the porosity of coal char. Suggested model was used to study the effects of structure parameter and reaction condition on the gasification reactivity and the evolution of char structure. Simulation results showed that under external diffusion controlled regime, the gasification rate decreased as reaction advanced for char particles with lower porosity (porosity < 0.15), and the gasification rate vs. conversion curves exhibited maxima for large char particles with higher porosity (porosity > 0.15). Besides, the particle sizes of coal char decreased slowly in the early stage of gasification, and then they decreased slightly fast. The gasification reaction of fine coal chars under the external diffusion controlled region could inhibit the particle fragmentation and reduce the formation of fine ash particles to a certain degree. [ABSTRACT FROM AUTHOR]

The present study aims to understand the phenomenology of char gasification by monitoring the chemical, structural and textural char characteristics through the gasification reaction. Chars from beech wood were gasified under 20%H 2 O, 20%CO 2 and 20%H 2 O + 20%CO 2 in N 2 at 900° C. The gasification reactions were stopped at 20%, 50% and 70% of char conversion. The char properties were analysed by different analytical techniques such as temperature programmed desorption coupled to mass spectrometry, Raman spectroscopy, Scanning Electron Microscopy, N 2 manometry and X-ray Fluorescence. These analyses provide valuable information on the unfolding of the gasification reactions with H 2 O, CO 2 and their mixtures. In particular, it is noted that H 2 O and CO 2 gasification reactions follow different pathways. Moreover, during mixed atmosphere, despite that the char reactivity can be fairly expressed by summing the two individual reactivities, this apparent additivity appears to be the result of several competitions and synergies between H 2 O and CO 2 reactions. [ABSTRACT FROM AUTHOR]

A pseudo-steady state model of reaction and diffusion has been constructed to model the non-isothermal gasification of single char particles by CO 2 . The model uses a Cylindrical Pore Interpolation Model for intraparticle mass transfer, Ergun’s Langmuir–Hinshelwood equation for the intrinsic rate of gasification, an experimentally determined function f ( X ) for the pore evolution as a function of the conversion X , the Stefan–Maxwell equations to describe external mass transfer and the equation of energy for energy balance. Experiments were conducted to measure rates and extent of conversion, at various temperature and for various particle sizes, of lignite char and the less reactive activated carbon. The simulation results have been compared with experimental measurements, with excellent agreement being obtained. The results show that for the gasification of chars, the experimentally determined function f ( X ) predicts the rate of reaction of particles of various sizes well, all being at the same temperature. However, for the CO 2 gasification of char particles, at least, an f ( X ) evaluated at one temperature does not predict experimental measurements well at other temperatures, possibly because there are contributions from multiple types of active sites within the particles. However, multiple sites are also not reflected in most published pore models. [ABSTRACT FROM AUTHOR]

While the operational conditions of a fluidized bed are known to influence the fuel axial mixing, the effect of the resulting axial location of the fuel particles on the char gasification rate remains unexplored. In this work, a laboratory-scale bubbling fluidized bed was used to investigate how the gasification rate of biomass char was influenced by the fuel axial location (during pyrolysis and char gasification), the pyrolysis atmosphere, the fuel size, and the fuel concentration. When pyrolysis at the bed surface was followed by char gasification inside the dense bed the char gasification rate was up to 2-fold lower than the other combinations of the fuel axial location, which held similar rates. Cooling the char after pyrolysis decreased the char gasification rate in all cases studied. The gasification rate increased when the fuel particle size was decreased, and its dependence on the degree of char conversion was also affected. Thus, the operational conditions of a fluidized bed reactor, through modified fuel axial mixing, can influence the char gasification rate. Furthermore, experimental determination of reactivity data in laboratory-scale systems must account for the axial location of the fuel at the desired end-scale, using similar fuel particle sizes. [ABSTRACT FROM AUTHOR]

• Reaction-front of oil sludge and palm kernel shell mixtures was assessed. • Higher values of flame front velocity were obtained as airflow increased. • Reactor operation tended to combustion regime as the equivalence ratio was raised. • Adsorption/desorption curves of char obtained were performed. • Char pore structure was composed mainly of micropore and mesopores. A reaction-front assessment and char characterization of a mixture of oil sludge and palm kernel shell in a fixed-bed reverse-downdraft gasifier using air as the oxidizing agent has been performed. The investigation was focused on assessing the effect of airflow (from 30 up to 60 L/min) on the reaction front as well as on the characterization of char derived from the thermochemical treatment. The thermochemical conversion process was described by output parameters such as fuel consumption rate, flame front velocity (V ff), maximum process temperature (T max), air–fuel equivalence ratio, and char yield. The char was characterized regarding its surface structure by determining Brunauer, Emmett, and Teller (BET) surface area, pore volume, and pore size distribution. The results demonstrated that as the airflow rate increased from 30 to 60 L/min, V ff and T max augmented from 4.36 to 6.49 mm/min, and from 967 to 1090 °C, respectively, as the process approached a combustion regime. In parallel, the char yield decreased from 13.4 to 4.5 % for the same airflow range due to the higher temperatures, which favors oxidation reactions. The char characterization showed that the BET surface area reached a maximum value of 269.8 m2/g at 50 L/min and subsequently decreased, which was attributed to the thermal deformation of the pore structure as the process temperature increased. Furthermore, pore size distribution showed that the char was mainly composed of micropores. Besides providing useful information related to the operation of gasifiers and char production, this analysis is particularly relevant for solutions aimed at mitigating environmental impacts, as it involves renewable sources and energy recovery. [ABSTRACT FROM AUTHOR]

The effect of inherent minerals in coal on gasification in H 2 O and CO 2 mixtures was investigated, and the synergistic effect was explained. First, low-temperature ash that has the same state as the inherent minerals in raw coal was prepared by low-temperature ashing with an oxygen plasma at 150 °C. The minerals were identified by X-ray diffraction. Then, the coal was successively demineralized with deionized water, HCl, HF, and HCl/HF. Char gasification reactivities of the successively demineralized coals with different mixtures of H 2 O and CO 2 were investigated using a thermogravimetric analyzer at 800 °C. The gasification reactivity closely correlated with the Ca content in successively demineralized coals. The calcite present in coal catalyzes the gasification reaction, causing the synergistic effect. [ABSTRACT FROM AUTHOR]

In the present study, the pyrolysis process under dynamic conditions of swine manure solids collected from rearing farm was investigated. Tested type of biomass feedstock was analyzed from the point of view of technological exploitation in order to obtain the highest possible quality and yields of bio-oil and bio-char. Furthermore, char gasification process was also examined. It was found that pyrolysis process can be described by parallel independent two-portion process model (PI-TPPM), which includes two processing state of the system (marked by processes # 1 and # 2), where process # 1 can be attributed to decomposition processes of hemicelluloses and fats/proteins, while process # 2 corresponds to pyrolyses of cellulose and lignin. Also, it was found that liquid and gas yields increase with an increase in heating rate, while approximately 40% of heavy oil yield is achieved by proposed experimental setup, which have been attained the satisfactory results for a good support in industrial extraction procedures. It was found that results associated with the presence of high reactivity at highest heating rate can be attributed to the highly porous structures formed, as we approach to the fast pyrolysis conditions. [ABSTRACT FROM AUTHOR]

Despite the huge literature on biomass char gasification with CO 2 or H 2 O, ambiguity still hovers over the issue of char gasification in complex atmospheres. Gas alternation gasification experiments, in which the reacting gas is changed during the reaction, were performed with CO 2 /H 2 O at 900 °C for small (200 μm) and large (13 mm) Low Heating Rate (LHR) beech wood char particles to assess the potential influences that CO 2 and H 2 O can have on each other during the char gasification reaction. The results showed no influence of a first gasification atmosphere on the char reactivity under the second one. The char reactivity to a specific gas at a certain conversion level was the same as if the gasification reaction was operated from the beginning with the same atmosphere composition. The purpose of this paper is to bring understanding keys to this lack of influence of previous gasification conditions on the char reactivity. Characterization of the chars throughout the conversion by measuring the total surface area and the active surface area was first performed. Then a transport limitation analysis based on the Thiele modulus was considered. It was concluded that the two gasses develop different porosities in the char, however, the Thiele modeling results and active surface area analysis indicate respectively that gasses diffuse preferentially in large macro-pores and that the concentration of active sites evolves similarly during both gasification reactions. This similarity in the diffusion mechanism as well as in the evolution of the concentration of active sites could be a plausible explanation for the only-dependent conversion reactivity observed in the gas alternation gasification experiments. [ABSTRACT FROM AUTHOR]

Char is the solid product of coal pyrolysis and its utilization is closely related to the scale of coal pyrolysis and tar processing. Char gasification is a promising choice for char utilization as it can provide hydrogen, which is needed for tar hydrogenation and chemical synthesis. However, reliable and mature coal char gasification technology has not yet been developed. The fluidized bed has been adopted as a gasifier in many studies, and its gasification temperature is relatively low. In this work, the feasibility of char gasification using a fluidized bed has been studied. A pyrolyzed bituminous coal char was gasified in a mixture of O2 and steam using a circulating fluidized bed. The height of the fluidized bed is 2360 mm and the inner diameter is 66 mm. The reactor is made of Ni-Cd alloy steel, and a loopseal was used for solid circulation. In the experiments, the gasification temperature was varied between 870 and 900 °C, and the effects of O2/char and steam/char mass ratios on the gasification results were analyzed. The volume fraction of combustible gas, dry gas yield, carbon conversion, and lower heating value of the best case were 43.92 %, 1.64 Nm3 kg−1, 0.85, and 5.17 MJ N m−3, respectively. In addition, a simple model and a complex model were established by using Aspen Plus software. The two models were used to simulate char gasification, and the simulation results were validated with the experimental results. The results indicated that the complex model is more accurate than the simple model and is more suitable to simulate char gasification in a circulating fluidized bed. [ABSTRACT FROM AUTHOR]

Char particles of high ash Indian coal with different sizes are produced using thermogravimetric method at different heating rates. Particle diameter and porosity changes during devolatilization significantly affect char gasification rates. The effect of coal particle size on char production under various heating rates is reviewed. Char gasification is affected by operating conditions such as reaction temperature, char production method, and particle size in addition to chemical composition and physical structure of char. The measurements of the steam and CO 2 gasification rate of the produced chars are performed by an isothermal thermo-gravimetric analysis at the temperatures of 900, 950, and 1000 °C under ambient pressure conditions. It is found that the reactivity of char gasification is increased along with heating rate of char. Three kinetic models are applied to describe the varying conversion rate: volumetric model, grain model, and random pore model. The activation energy of the gasification is varied based on the char generation method and particle sizes. The activation energy is varying from 122 to 177 kJ mol −1 for steam gasification and 130 to 214 kJ mol −1 for CO 2 gasification to different sized char particles. The effect of char heating rate on gasification is more pronounced in the activation energies of smaller sized particles. [ABSTRACT FROM AUTHOR]

Char particles of high ash Turkish coal of two sizes were produced by pyrolysis in an atmospheric pressure thermo-gravimetric apparatus using 3 heating rates (100 K/min, 500 K/min and 800 K/min). It is observed that the particle size (for particles between 0.8 and 3 mm) did not change the pyrolysis process results. Char gasification rates in CO 2 , steam and mixture of CO 2 + steam are investigated in the same TGA system over the temperature range of 850–950 °C. The pyrolysis heating rate for char formation is observed to have a marked influence on the subsequent gasification reactivity of the char. The results indicate that the char produced from high heating rates show improved gasification rates. Smaller particles exhibit higher char–CO 2 and char–steam gasification rates. Increasing the temperature from 850 to 950 °C, leads to a significant reduction of the time required for 50% char conversion both for small and large particles. The maximum reaction rate is shifted to higher conversion degrees when the chars are produced from high heating rates. The gasification rate of char–H 2 O strongly depends on the H 2 O partial pressure. Gasification rates in CO 2 ambiance are much lower than those in steam. For CO 2 –steam blended ambiance, no obvious CO 2 inhibition effect is observed. But this topic requires more investigation. Kinetic parameters of the char particles are estimated using three different kinetic models. The obtained activation energies for char gasification essentially depend on the particle size and the three kinetic models give very close activation energy values for all the tested conditions. [ABSTRACT FROM AUTHOR]

Alkali metals inherent in black liquor (BL) have strong catalytic activity during gasification. A catalytic co-gasification process based on BL with pyrolysis oil (PO) has the potential to be a part of efficient and fuel-flexible biofuel production systems. The objective of the paper is to investigate how adding PO into BL alters fuel conversion under gasification conditions. First, the conversion times of single fuel droplet were observed in a flat flame burner under different conditions. Fuel conversion times of PO/BL mixtures were significantly lower than PO and comparable to BL. Initial droplet size (300–1500 μm) was the main variable affecting devolatilization, indicating control by external heat transfer. Char oxidation was affected by droplet size and the surrounding gas composition. Then, the intrinsic reactivity of char gasification was measured in an isothermal thermogravimetric analyser at T = 993–1133 K under the flow of CO 2 –N 2 mixtures. All the BL-based samples (100% BL, 20% PO/80% BL, and 30% PO/70% BL on mass basis) showed very high char conversion. Conversion rate of char gasification for PO/BL mixtures was comparable to that of pure BL although the fraction of alkali metal in char decreased because of mixing. The reactivities of BL and BL/PO chars were higher than the literature values for solid biomass and coal chars by several orders of magnitude. The combined results suggest that fuel mixtures containing up to 30% of PO on mass basis may be feasible in existing BL gasification technology. [ABSTRACT FROM AUTHOR]

This study, performed in the context of GAYA project, focuses on the development of a simple predictive model about steam gasification of char from woodchips fast pyrolysis. A semi-empirical model was developed through experiments in a macro thermogravimetric analyzer which owns the peculiar ability of fast heating, as well as to deal with macro-size particles and higher mass loads compared to conventional TGA. The experimental results show that gasification is controlled by chemical kinetics and internal transfer phenomena. During gasification, char particles can be considered as isothermal in a given range of temperatures and particle sizes, more likely for low values. The gasification model was based on the effectiveness factor, which involves the chemical kinetics and diffusion rate. The chemical kinetics were expressed by a classical Arrhenius law, whereas empirical expressions from mathematical fitting of the experimental data were established for the diffusion coefficient and surface function. The diffusion coefficient from this work is suspected to probably include supplementary rate limiting phenomena, apart from steam porous diffusion, such as H 2 inhibition and/or the decrease of temperature within char particles because of the endothermic character of gasification. The model globally predicts with accuracy the gasification rate in typical operating conditions of a fluidized bed reactor. For its simplicity and reliability, this approach can be used for the modelling of char gasification in the conditions of interest. [ABSTRACT FROM AUTHOR]

The char-CO gasification reactions in isothermal and pressurized conditions were studied kinetically by high-pressure thermo-gravimetric analyzer, and the primary objective of this paper was to study the effects of pressure, temperature and char rank on the intrinsic reaction kinetics of the char-CO gasification by the Langmuir-Hinshelwood model. The results indicated that the order of reactivity sequence at the same temperature and pressure was Char A > Char B > Char C (Char A from subbituminous coal, and Char B and C from bituminous coals). With the increase in the pressure and temperature, both the intrinsic reaction rate at the same carbon conversion and the carbon conversion efficiency at the same reaction time increased. The results also showed that the gasification rate experienced an initially slow increase, followed by a rapid increase, and finally a decrease corresponding to the increase in the carbon conversion efficiency. It implied that the Langmuir-Hinshelwood model was incompatible to thorough presentation of the complete conversion of the char-CO gasification, but was well agreeable to the intrinsic reaction kinetics of char-CO gasification when the carbon conversion efficiency was low at the initial stage of the carbon conversion (0-0.6). Based on this, the intrinsic reaction kinetic models of the selected char samples were built. [ABSTRACT FROM AUTHOR]

The gasification of carbonaceous char into synthesis gas species presents a viable thermochemical conversion pathway of both fossil fuel-based and biomass-based solid fuels. Observations of these synthesis gas species—particularly hydrogen—inhibiting gasification rates have been documented for decades. Finite-rate surface kinetic reaction mechanisms that can be applied to a variety of reactor models and conditions are needed, particularly those which describe gasification inhibition. To quantify the effects of hydrogen inhibition reactions in gasification conditions, existing surface kinetic mechanisms were employed in simulations and compared with experimental data available in the literature. A computationally inexpensive method to model the surface chemistry in simple gasification reactors is utilized in this study—where appropriate, these experiments in the literature were simulated as perfectly stirred reactors. When used in comparison with kinetically controlled experiments, this method can readily facilitate the identification of missing reaction steps in surface mechanisms. Results reveal the inability of current surface mechanisms in predicting experimentally observed inhibition trends. Modeling the inhibition with an adsorption–desorption pair of reactions based on a combination of theoretical and empirical considerations was found to improve the overall model when these reactions were appended to a current surface mechanism. Reasonable agreement with experimental data is found with regard to the kinetics of carbon gasification reactions in the inhibiting presence of hydrogen. [ABSTRACT FROM AUTHOR]

• CO 2 gasification of Ca-rich lignite and coffee char are conducted via TGA. • Calcium deactivation leads to the increase of the activation energy. • Calcium deactivation could be eliminated by adjusting CO 2 pressure at various temperatures. CO 2 gasification of calcium-rich lignite and coffee char are conducted via thermogravimetry analysis (TGA) at 1098–1173 K and 0.025–0.1 MPa CO 2. The effects of calcium deactivation on determining the activation energy are assessed in detail. Results reveal that the calcium deactivation increases the value of the activation energy. The activation energies of the lignite char (LC) and coffee grounds char (CGC) with Ca deactivation are significantly increased compared with those of CGC and LC without Ca deactivation, and the relative errors are between 4.5% and 23.4%. To measure the activation energy without Ca deactivation in char-CO 2 gasification, the lower CO 2 pressures and higher temperatures should be selected according to the equilibrium regularity of CO 2 over CaCO 3. [ABSTRACT FROM AUTHOR]