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The CO2 gasification of pine and birch charcoals was studied by thermogravimetric analysis (TGA) at CO2 partial pressures of 51 and 101 kPa. Linear and stepwise heating programs were employed to increase the information content of the experimental data sets. Low sample masses were used because of the high enthalpy change. Seven experiments with dif...
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... However, the mass transfer limitation is a crucial disadvantage of TGA. It can be assumed that the mass transfer does not significantly affect kinetic evaluation if the reaction temperature is below 1000 C. 13,14 Such temperatures are significantly below the operating conditions. As a result, the overall conversion time requires several minutes or even hours, that is, several orders of magnitude above the real process, which features conversion times in the order of several seconds. ...
Solid fuel conversion in a pressurized drop‐tube reactor is studied in detail using a three‐dimensional computational fluid dynamics (CFD) model. The main focus is on analyzing individual particle trajectories and residence times, as these data are crucial for the precise experimental estimation of heterogeneous reaction kinetics. The numerical results were substantiated by radioactive tracer measurements carried out in different operating conditions. The numerical results reveal a complex gas flow that is affected by buoyancy due to a non‐homogeneous temperature distribution, which has a strong affect on the trajectories of particular particle size fractions. In this case, empirical residence time correlations for particles, as commonly used for the evaluation of heterogeneous kinetic measurements, lose their validity since the assumption of a plug flow is no longer valid. It can be shown that if CFD‐assisted data evaluation is used, a significant improvement in the measured heterogeneous reaction kinetics is feasible.
... However, and despite the consumption of CO by this pathway, they still found no decrease in the formation of CO, thus suggesting that CaO addition promotes decarbonylation reactions during biomass pyrolysis. Furthermore, different studies have clearly highlighted increases of CO yields at high temperatures [85,135,173], which can be traced to different mechanisms, including the catalytic cracking of phenols (a process well documented in the case of coal [156,208]), the dissociation of diaryl ether [209] and the Boudouard reaction (C + CO 2 = 2CO), which results from the interaction between the CO 2 released from the decomposition of CaCO 3 with the carbon in pyrolysis char [210]. With respect to this last route, it is important to note that CaCO 3 as well as Ca(OH) 2 can be formed at low temperatures due to the absorption of the CO 2 and H 2 O molecules released during the pyrolysis by CaO [85,203]. ...
Alongside the development of pyrolysis processes aimed at converting solid biomass into upgraded biofuels and biochemicals, interest has been growing in the analysis of the catalytic effects induced by inherent or externally added alkali and alkaline earth metals (AAEMs). These AAEMs greatly affect the thermal conversion of biomass, although their effects are only partly understood. Furthermore, while coal currently plays a major role in global energy demand, its massive use in a carbon-constrained world has prompted the need to identify alternative and carbon-neutral energy sources. In this context, the co-pyrolysis of biomass with coal has been shown to be a promising way to support the transition from fossil to renewable energy carriers. Because AAEMs can significantly impact such a co-processing approach, there is therefore the need for a firm understanding of their catalytic role. Consequently, and to examine and summarize the main research advances that have been made in this field, the present review first covers a description of the main properties of lignocellulosic biomass and coal, along with their decomposition processes. It then focuses on AAEM catalysts and on their impact on pyrolysis reaction pathways and kinetics. In terms of highlights, the review illustrates that the presence of inherent or impregnated AAEMs shifts the decomposition of biomass to lower temperatures while increasing the char and gas yields at the expense of bio-oil. Moreover, these effects depend significantly on the nature of the catalyst considered and on the way it is mixed with biomass. As examples, potassium tends to favor the production of low molecular weight compounds and gaseous species, magnesium promotes dehydration reactions, whereas calcium and magnesium oxides allow to upgrade volatiles by deoxygenation and deacidification. A discussion of pyrolysis reaction mechanisms is also proposed by reviewing the different pathways involved in the decomposition of the main components of biomass and coal, noting that the emphasis is particularly on the changes induced by AAEM catalysts. The synergistic effects between coal and biomass which are likely to enhance the co-pyrolysis process are then discussed. Eventually, a comprehensive reaction pathway is proposed to better explain the important role played by AAEM catalysts during primary and secondary pyrolysis reactions.
... kJ/ mol. Activation energies reported by various other studies were 125−217 kJ/mol [197], 159−251 kJ/mol [186], 183−263 kJ/mol [189], 180−307 kJ/mol [176], 262−263 kJ/mol [179], 125 kJ/mol [198]. ...
... Khalil et al. [179] used TGA experiments to determine the kinetics of the gasification of pine and birch charcoal in a fluidized bed gasifier. A power law kinetics approximation was used to model the gasification kinetics, which accurately modelled the dependence upon the char conversion. ...
... The activation energy of the gasification step proved to be a fairly constant quantity: all trials and evaluations resulted in values of 262−263 kJ/mol for this study. However, as mentioned earlier, this activation energy was not consistent throughout all studies, therefore, it is possible that the 262−263 kJ/mol is only consistent for the experimental conditions used by Khalil et al. [179]. There are a number of other aspects that can affect the kinetics of the gasification process, including the pressure and temperature. ...
... When the reaction gas environment is CO 2 [12] or oxy-fuel combustion which is mainly composed of O 2 and CO 2 . The CO 2 -char gasification reaction has been studied by various researchers [13][14][15][16][17] is a chief reaction in the biomass thermal decomposition, especially in the high temperature zone. The most important CO 2 -char gasification reaction is the Boudouad reaction Eq. ...
This study investigates the thermal and kinetic analysis of six diverse biomass fuels, in order to provide valuable information for power and energy generation. Pyrolytic, combustion and kinetic analyses of barley straw, miscanthus, waste wood, wheat straw, short rotation coppicing (SRC) willow and wood pellet were examined by non-isothermal thermogravimetry analyser (TGA), differential thermogravimetric (DTG) and differential scanning calorimetry (DSC) techniques. Biomass fuels were thermally degraded under N2, air, CO2 and the selected oxy-fuel (30% O2/70% CO2) reaction environments. The thermal degradation under inert N2 and CO2 atmospheres showed an almost identical rate of weight loss (R), reactivity (RM × 103) and activation energy (Ea) profiles. Similar profiles for R, RM and Ea were observed for the environments under air (21% O2/79% N2) and the oxy-fuel combustion. Results indicated that the thermal decomposition rate for biomass fuels in an oxidising condition was faster than in an inert atmosphere, favourable effect on thermal degradation of biomass fuels was observed when oxygen content increased from 21 to 30%. Higher activation energies with lower reactivity were observed for the biomass fuels that have low cellulosic contents as compared to the other fuels. Regression analysis confirmed that the reaction order 0.5 modelled fitted well for all biomass samples. All these findings will provide valuable information and promote the advancement of future researches in this field.
... The standard method of measuring these rates is via thermogravimetric analysis (TGA) under inert and oxidizing conditions, whereby a small sample of the feedstock (5-15 mg typically) is heated at a certain rate while simultaneously recording mass, time and temperature. TGA is used extensively to study the kinetic parameters of gasification of biomass with CO 2 as a function of mass loss [9][10][11]. TGA can be considered to be a fixed reactor technique with a relatively low heating rate compared to larger scale systems where biomass is added directly to the reactor at the reaction temperature so the particle heating rate is significantly greater. ...
This paper is an experimental study of the kinetics of gasification of olive kernel by using a thermogravimetric fluidized bed reactor technique. Gasification of ‘as received’ and torrefied olive kernels were investigated in a lab-scale bubbling fluidized bed gasifier, operating at up to 3.2 kg/h. The effect of bed temperature between 550 and 750 °C in 50 °C increments on the gasification product gas at mass-based equivalence ratios of 0.15 and 0.2 was studied. To explore the potential of torrefied biomass, the gasification results were compared to that of the ‘as received’ biomass. The product gas from torrefied biomass produced higher H2, CO and CH4 concentrations at identical oxidant flow rates in addition to higher cold gas efficiency and higher product gas heating value. The influence of equivalence ratio in gasification was also investigated at reactor temperatures of 750 °C and five equivalence ratios (0.15, 0.2, 0.25, 0.3, and 0.35). The results revealed that the torrefied biomass has the highest HHV at an equivalence ratio of 0.2 with a value of 6.09 MJ/Nm³, while ‘as received’ biomass 4.72 MJ/Nm³. Kinetic experiments under isothermal conditions were performed for the gasification of the materials in continuous mode. A mass balance model was successfully used to provide the capability of separately determining the rate constant of the reactions taking place. The kinetic parameters were calculated by a first order reaction model giving activation energies for ‘as received’ olive kernels of 84 kJ/mol and for torrefied olive kernels of 106 kJ/mol.
... 16−19 More importantly, the use of CO 2 offers the flexibility to adjust syngas composition for various downstream applications and contributes to greater environmental and economical benefits for the entire process. 19−21 Much effort has therefore been made to investigate biomass gasification in CO 2 atmosphere, 22−24 such as kinetic study, 16,23,24 gasification reactivity, 12,18,25 and characteristics. 12,26,27 The effects of operating parameters, such as temperature, pressure, and heating rate, on the CO 2 gasification of petroleum coke, coal, and biomass had also been reported. ...
... Liliedahl et al. [29] Khalil et al. [60], Alvarez et al. [61] ...
In this work, stem wood and branches and tops of Norwegian spruce and birch were carbonized at different pressures, producing charcoals of which the CO2 gasification reactivity was studied by means of a thermogravimetric analyzer operated isothermally at 850 °C. The results reveal that the gasification reaction rates of charcoals produced under higher pressures was lower than those produced at the atmospheric pressure. Clear correlations between the CO2 gasification reactivity of the charcoals and their fuel and chemical properties, including the catalytic effect of the inorganic matter, were observed. The semi-empirical power law kinetic model described well the gasification behavior with high fit quality. The activation energy was found to be within 140–160 kJ/mol, whereas the reaction order varied in the range of 0.4–0.6.
... In addition, the activation energy of the lignin-like component is in all cases slightly lower than that of lignin, being around 50 kJ/mol on average. For the second step, char gasification, the activation energy of three samples is within 260e290 kJ/mol, which is also in agreement with the literature [62,63]. For example, according to Khalil at al., the activation energy of the CO 2 gasification of chars derived from birch and pine is about 262 kJ/mol [63]. ...
... For the second step, char gasification, the activation energy of three samples is within 260e290 kJ/mol, which is also in agreement with the literature [62,63]. For example, according to Khalil at al., the activation energy of the CO 2 gasification of chars derived from birch and pine is about 262 kJ/mol [63]. It is worthwhile to note that the activation energy reported in the literature for the biomass char gasification varies widely from 99 to 318 kJ/mol [26,64]. ...
CO2 gasification of torrefied forest residues (birch and spruce branches) was investigated by means of a thermogravimetric analyser operated non-isothermally (400–1273 K) and isothermally (1123 K) under the kinetic regime, followed by kinetic analyses assuming different models. For the non-isothermal gasification, the distributed activation energy model (DAEM) with four or five pseudo-components was assumed. It is found that the severity level of torrefaction had great influences on gasification behaviour as well as devolatilization step. The activation energy of non-isothermal gasification step of three samples varied in the range of 260–290 kJ/mol. The char reactivity decreased with increased torrefaction temperature. For the isothermal gasification, the random pore model (RPM), shrinking core model (SCM), and homogeneous model (HM) were tested. The result has confirmed the trend of decrease in char reactivity with increased torrefaction temperature observed from the non-isothermal gasification. However, different trends in char reactivity due to different wood types were observed by the two methods of gasification.
... It is less corrosive than steam and can be used to adjust syngas composition for different downstream applications [8]. In the past few decades, much research had been carried out on biomass gasification using CO 2 as a gasifying agent [5,7,[9][10][11][12]. These research were mainly focused on the kinetics [5,9,11,12], gasification reactivity [7,10,13,14] and gasification characteristics [14][15][16] in general. ...
... In the past few decades, much research had been carried out on biomass gasification using CO 2 as a gasifying agent [5,7,[9][10][11][12]. These research were mainly focused on the kinetics [5,9,11,12], gasification reactivity [7,10,13,14] and gasification characteristics [14][15][16] in general. In spite of the huge potential of utilizing CO 2 in coal and biomass gasification, limited effort has been made to understand the interactions between coal and different types of biomass during co-gasification. ...
In order to evaluate the feasibility of using CO2 as a gasifying agent in the conversion of carbonaceous materials to syngas, gasification characteristics of coal, a suite of waste carbonaceous materials, and their blends were studied by using a thermogravimetric analyser (TGA). The results showed that CO2 gasification of polystyrene completed at 470 °C, which was lower than those of other carbonaceous materials. This behaviour was attributed to the high volatile content coupled with its unique thermal degradation properties. It was found that the initial decomposition temperature of blends decreased with the increasing amount of waste carbonaceous materials in the blends. In this study, results demonstrated that CO2 co-gasification process was enhanced as a direct consequence of interactions between coal and carbonaceous materials in the blends. The intensity and temperature of occurrence of these interactions were influenced by the chemical properties and composition of the carbonaceous materials in the blends. The strongest interactions were observed in coal/polystyrene blend at the devolatilisation stage as indicated by the highest value of Root Mean Square Interaction Index (RMSII), which was due to the highly reactive nature of polystyrene. On the other hand, coal/oat straw blend showed the highest interactions at char gasification stage. The catalytic effect of alkali metals and other minerals in oat straw, such as CaO, K2O, and Fe2O3, contributed to these strong interactions. The overall CO2 gasification of coal was enhanced via the addition of polystyrene and oat straw.
... In other words, the reaction rate is not linear with respect to the partial pressure of the gasifying agent. Reaction orders for coal char gasification and biomass char gasification have been reported in the literature [7][8][9][10]. However, no studies on the effect of partial pressure on the reaction rate have been reported in the open literature for co-gasification of coal and biomass blended char. ...
This short communication reports the results of an experimental study that is an expansion of two previous studies (Jeong et al., 2014, 2015). In this study, mixtures of coal and biomass with different mass ratios were co-gasified with CO2 or H2O. Five different partial pressure conditions between 0.2 and 0.6 bar were tested for both gasifying agents. Random pore model was used to interpret the carbon conversion data. Pre-exponential factors and reaction orders of CO2 and H2O gasifications were determined using the Arrhenius equation and activation energies obtained in the two previous studies.
