Non-isothermal Thermogravimetric Method Research Articles

Co-combustion behavior and catalytic mechanism of high CaO/SiO2 biomass mixed with anthracite for blast furnace injection: Experiment, modeling and DFT investigation

The physical and chemical properties of apricot tree (AT), corncob (CC), and anthracite (CC) were systematically analyzed. Their combustion behaviors and blends were examined using a non-isothermal thermogravimetric method, which revealed the catalytic mechanism of biomass mineral composition in the combustion process. The presence of high CaO content resulted in better combustibility, particularly with an addition ratio of more than 50 % AT, which enhanced anthracite combustion. Kinetic analysis indicated that the random pore model had a better fit than the volume reaction model. At 75 % addition of AT and CC, the lowest apparent activation energies were observed, with values of 100.5 kJ/mol and 110.23 kJ/mol, respectively. Density functional theory calculations demonstrated that the presence of CaO caused reconfiguration in the coal's molecular structure, making it easier for aliphatic chains attached to six-membered rings to detach. The co-combustion process and catalytic combustion mechanism of biomass and coal were discussed, highlighting CaO's ability to remove oxygen-containing functional groups and aliphatic chains, while facilitating O2 diffusion within the molecular structure. Conversely, SiO2 tended to generate silicates, leading to the deactivation of CaO's catalytic effect.

A combined analysis of the drying and decomposition kinetics of wood pyrolysis using non-isothermal thermogravimetric methods

In this paper, we evaluate the pyrolysis of wood biomass as a combination of drying and thermal decomposition via the Page and modified Page models for drying kinetics as well as the Friedman and Vyazovkin methods for solid-state decomposition kinetics. This approach was applied to data obtained from thermogravimetric analysis of three wood species (spruce, pine, and birch) at 5, 20, and 30 K/min temperature programs.According to the Page model, the average activation energies for spruce, pine, and birch wood between 30 and 150 °C were 12.87 ± 1.08, 13.32 ± 0.48, and 11.61 ± 0.59 kJ/mol, respectively. While all activation energies fell between 11.0 and 14.5 kJ/mol, the modified Page model predicted slightly higher energies, with an average absolute difference of 6.4% from Page's predictions. The activation energies and pre-exponential factors predicted by both models were lower at low heating rates, with the pre-exponential factor yielding significantly large differences between 5 and 30 K/min. These results showed that drying kinetics were significantly affected by heating rates. In addition, the goodness-of-fit analysis revealed that both models were reasonably accurate when predicting wood drying kinetics.For the analysis of solid-state decomposition kinetics, a comparison of Friedman's linear differential method (FR) and Vyazovkin's nonlinear integral method (NLN-INT) was conducted at temperatures higher than 150 °C. In contrast to the NLN-INT method, the FR method predicted activation energies slightly higher, with an average absolute difference of about 8.4%. Evaluation of the relative errors revealed that both the FR and NLN-INT methods performed similarly. However, the Friedman (FR) method provided a reasonable fit to multistep decomposition kinetics through the simultaneous estimation of activation energies and pre-exponential factors. Nevertheless, the activation energies estimated by both the FR and NLN-INT methods were unreliable at conversions of α < 0.15 and α > 0.85. Validation of the kinetic results was conducted with differential thermogravimetric data at a heating rate of 5 K/min.

Investigation on co-combustion behavior and kinetic analysis of bamboo char/waste plastics (PVC) hydrochar

The combustion properties of bamboo char (BC), PVC hydrochar and blends were studied by non-isothermal thermogravimetric method. The high carbon structure order and ash content of BC are the main reasons for its poor combustion performance. Blending with PC can effectively improve its combustion performance, and there is an obvious negative synergistic effect between PC and BC, which is most obvious when the content of PC is 40%. The accuracy of fitting degree of RPM model is better than that of VM model, the activation energies (E) of BC and PC are 102.1 kJ/mol and 60.9 kJ/mol, respectively. Finally, a coupling process of fuel preparation and blast furnace injection was proposed, and the environmental and economic benefits were calculated. The total cost can be reduced by 29.18 CNY/T, carbon emissions can be reduced by 73.16 KG/T, and the maximum proportion of PVC hydrochar is only 40%.

Effect of sample mass on the apparent Arrhenius parameters observed for the thermal dehydration of sodium carbonate monohydrate

The dynamics of the thermal dehydration of sodium carbonate monohydrate was investigated using isothermal and non-isothermal thermogravimetric methods for sample masses between 1 and 10 mg in a 70 μl alumina cell. The apparent activation energy determined from isothermal measurements changed from 70 kJ mol−1 for 10 mg samples to 115 kJ mol−1 for 1 mg samples when the data was fit using the AE-2 mechanism. Fitting non-isothermal data using the Starink method produced apparent activation energies were constant within experimental error for 0.05 < α < 0.6 then decreased rapidly for α > 0.6 indicating there were at least two steps in the dehydration mechanism. The values found for 0.05 < α < 0.6 also depended on the sample mass and were 112, 105, and 100 kJ mol−1 for 1, 5 and 10 mg samples respectively. The experimental uncertainty in each of these measurements is ± 5 kJ mol−1. The Arrhenius parameters found for the dehydration reaction by extrapolating the isothermal reaction rates to zero mass where it was assumed that the rehydration reaction was not contributing to the dynamics were Ed = 116 ± 5 kJ mol−1 and Ad = 1.7 ± 0.9 * 1015 s−1. Since the activation energy determined is less than the value of 130 kJ mol−1 obtained using the thermochemical approach these values could still include a contribution from the rehydration reaction and represent a lower bound for these parameters. Using these values and other measured thermodynamic quantities gives Er = 57 ± 5 kJ mol−1 and Ar = 1.3 ± 0.9 * 107 s−1 for the rehydration reaction. This investigation clearly shows that self-generated atmospheres may affect the measured dynamics for a reversible reaction and should be considered when doing the analysis.

Intrinsic combustion kinetics of rapid-pyrolysis Zhundong coal char

Driven by the demand for accurate intrinsic kinetics for the prediction of the combustion rate of purely fired Zhundong coal (ZDC) in a slag tapping boiler, the surface activation function (SAF) and intrinsic kinetic parameters of two types of rapid-pyrolysis ZDC chars were revealed via the isothermal and nonisothermal thermogravimetric analysis methods. The isothermal kinetic results show that the activation energy (E), reaction order and SAF of these two chars were the same, at 146 kJ/mol, 0.78 and X0.44 (1 – X)−0.48, respectively. Therefore, the difference in the intrinsic reaction rate between these two chars was caused only by the different pre-exponential factors, which are mainly influenced by the specific surface area and catalytic elements in char ash. Nonisothermal kinetic parameters were obtained via the isothermal model-fitting method (ISOM), thereby using the isothermal SAF to fit the nonisothermal data at different heating rates (βs). The results indicate that the E values of the two chars were 148.95 ± 3.12 kJ/mol and 146.16 ± 1.66 kJ/mol, indicating that β has little influence on E. These measured values are consistent with the isothermal E values, so the ISOM is suitable for the determination of the nonisothermal kinetics of rapid-pyrolysis char combustion.

Co-Combustion of Food Solid Wastes and Pulverized Coal for Blast Furnace Injection: Characteristics, Kinetics, and Superiority

The combustion characteristics and kinetics of food solid wastes (FSW), pulverized coal (PC), and their mixtures were studied by a non-isothermal thermogravimetric method. In the co-combustion of FSW and PC, with the increase in FSW content in the mixture, the initial decomposition temperature, burnout temperature, and ignition temperature of the mixture decreased, and the flammability index and comprehensive combustion characteristic index gradually increased. The co-combustion of FSW and PC showed an inhibitory effect in the devolatilization stage but exhibited a combustion-promoting effect in the fixed carbon combustion stage. The interaction between FSW and PC while co-combusting them appeared to be dominated by thermal effects. On one hand, FSW combusted first and released heat that was partially absorbed by the PC, which hence suppressed the devolatilization stage of the co-combustion process. On the other hand, the PC absorbed the heat released by the combustion of the FSW, which increased the combustion rate of the PC in the fixed carbon combustion stage of the co-combustion process. The activation energy of the devolatilization stage and the fixed carbon combustion stage of the co-combustion process was calculated to be 34.16–74.52 kJ/mol and 15.04–36.15 kJ/mol, respectively. In general, the combustion performance of FSW is better than that of PC. The mixed injection of FSW and PC can improve the overall combustion efficiency and reduce CO2 emissions in the iron-making process.

Thermogravimetric Devolatilization Behavior of Agricultural Residue for Generation of Syngas

Abstract The thermal degradation characteristics of eucalyptus, pearl millet cob, and corncob were investigated using the nonisothermal thermogravimetric method. This investigation was performed to carry out the thermochemical conversion for obtaining syngas. Thermogravimetric (TG) and differential thermogravimetric (DTG) analyses were carried out to understand thermal devolatilization behavior and estimation of various thermophysical properties of the biomasses. The degradation behavior was analyzed in the light of lignocellulosic composition that was found to have a definitive influence on degradation outcomes. The TG analysis has been utilized to obtain the proximate analysis of biomass. Activation energy using the Flynn-Wall-Ozawa method has been estimated and found to be 201, 150, and 68 kJ/mol for eucalyptus, pearl millet cob, and corncob, respectively. The TG analysis and activation energy together indicated that corncob is easiest for thermochemical conversion among the three biomasses. The TG curve also confirms the same.

Determinación de los parámetros cinéticos de la pirolisis de la biomasa lignocelulosica

Over the past decades, interest in renewable energy and the environment has grown considerably, with a significant effort being made in the field of energy efficiency, the creation of sustainable technologies and the reduction of the carbon footprint. Therefore, the use of biomass in an economical and efficient way is of interest, and its study and analysis becomes necessary. In this work, kinetic parameters such as activation energy (Ea) and preexponential factor (A) were determined for apple residues using the non-isothermal thermogravimetric method and treating the data obtained under the models mathematicians of the differential method and the maximum speed method, and additionally performing the activation energy distribution. The calculation of the activation energy helped to see the way in which thermal decomposition takes place (if there are one or more processes and in what range of conversions they occur), through the characteristic kinetic constants provided by the kinetic models, allowed to identify the gaseous species emitted by the material, and thus study the processes through which such decomposition occurs

Investigation of synergy and inhibition effects during co-gasification of tire char and biomass in CO2 environment

This study investigates the co-gasification of tire char (TC), as a low-quality side-product of scrap tire pyrolysis, and rambutan peel (RP). The objective of this study was to comprehend any synergistic/antagonistic effects during the co-gasification of TC/RP. For this, co-gasification of TC and RP (85:15, 70:30, 50:50, 30:70, and 15:85 wt% of TC:RP) was conducted in CO2 environment by non-isothermal thermogravimetric method. The samples were heated (15 K/min) under N2 to 923 K and then under CO2 to 1400 K. Comparison of the observed and theoretical results indicated the incidence of antagonism in blends with high proportion of TC (e.g., 85%TC–15%RP and 70%TC–30%RP), possibly attributing to the high content of acid oxides (SO3 (30.1%) and SiO2 (24.8%)) in the TC-ash which could inhibit the gasification by formation of inactive silicates in the presence of alkali/alkaline earth metal-rich biomass. In blends with higher content of biomass (e.g., 30%TC–70%RP and 15%TC–85%RP), the actual gasification rates were higher than the theoretically predicted ones showing the presence of a synergism associated with the natural catalysts (K2O (40.6%) and CaO (42.3%)) in RP-ash. Activation energy and thermodynamic studies confirmed the profound effect of biomass on enhancing the reactivity of TC in reaction with CO2. These promoting effects of biomass were associated with its considerably higher alkali index (133.4) than tire (5.6), its less graphitic structure with more structural defects, and imperfections compared with TC. According to the results, the inherently low reactivity of TC in gasification can be accelerated by co-feeding of biomass with TC.

Determination of a Complete Conversion Model for Gasification of Lignite Char

The conversion of solid fuels via gasification is a viable method to produce valuable fuels and chemicals or electricity while also offering the option of carbon capture. Fluidized bed gasifiers are most suitable for abundantly available low-rank coal. The design of these gasifiers requires well-developed kinetic models of gasification. Numerous studies deal with single aspects of char gasification, like influence of gas compositions or pre-treatment. Nevertheless, no unified theory for the gasification mechanisms exists that is able to explain the reaction rate over the full range of possible temperatures, gas compositions, carbon conversion, etc. This study aims to demonstrate a rigorous methodology to provide a complete char gasification model for all conditions in a fluidized bed gasifier for one specific fuel. The non-isothermal thermogravimetric method was applied to steam and CO2 gasification from 500 °C to 1100 °C. The inhibiting effect of product gases H2 and CO was taken into account. All measurements were evaluated for their accuracy with the Allan variance. Two reaction models (i.e., Arrhenius and Langmuir–Hinshelwood) and four conversion models (i.e., volumetric model, grain model, random pore model and Johnson model) were fitted to the measurement results and assessed depending on their coefficient of determination. The results for the chosen char show that the Langmuir–Hinshelwood reaction model together with the Johnson conversion model is most suitable to describe the char conversion for both steam and CO2 gasification of the tested lignite. The coefficient of determination is 98% and 95%, respectively.

Determination of a Complete Conversion Model for Gasification of Lignite Char

The conversion of solid fuels via gasification is a viable method to produce valuable fuels and chemicals or electricity while also offering the option of carbon capture. Fluidized bed gasifiers are most suitable for abundantly available low-rank coal. The design of these gasifiers requires well-developed kinetic models of gasification. Numerous studies deal with single aspects of char gasification, like influence of gas compositions or pre-treatment. Nevertheless, no unified theory for the gasification mechanisms exists that is able to explain the reaction rate over the full range of possible temperatures, gas compositions, carbon conversion, etc. This study aims to demonstrate a rigorous methodology to provide a complete char gasification model for all conditions in a fluidized bed gasifier for one specific fuel. The non-isothermal thermogravimetric method was applied to steam and CO2 gasification from 500 °C to 1100 °C. The inhibiting effect of product gases H2 and CO was taken into account. All measurements were evaluated for their accuracy with the Allan variance. Two reaction models (i.e., Arrhenius and Langmuir–Hinshelwood) and four conversion models (i.e., volumetric model, grain model, random pore model and Johnson model) were fitted to the measurement results and assessed depending on their coefficient of determination. The results for the chosen char show that the Langmuir–Hinshelwood reaction model together with the Johnson conversion model is most suitable to describe the char conversion for both steam and CO2 gasification of the tested lignite. The coefficient of determination is 98% and 95%, respectively.

Analysis of Coal Spontaneous Combustion by Thermodynamic Methods

ABSTRACT In order to better determine the spontaneous combustion tendency of coal, two types of heating rate methods, namely, single and multi-scan methods, commonly used in the field of spontaneous coal combustion are summarized based on a thermal analysis kinetics method. The single scanning rate method mainly included the Coats–Redfern, Achar, universal equation, MacCallum–Tanner, Madhusudanan–Krishnan–Ninan, and non-isothermal thermogravimetric and differential scanning calorimetric methods. The multi-scan rate method mainly included the Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose, Starink, and Friedman methods. For each of these methods, their respective theoretical basis, advantages, and disadvantages were described. In addition, the Popesc and Malek methods were used to determine the optimal reaction kinetic model. In view of the compensation effect, the invariable activation energy E inv and the pre-exponential factor lnAinv at different heating rates were determined. For each method, the oxygen weight gain stage of Shaanxi bituminous coal was selected as an example interpretation.

The oxidation behavior of ZrB2–ZrC composite nanofibers fabricated by electrospinning and carbothermal reduction

In this paper, ZrB2–ZrC composite nanofibers were prepared by electrospinning method followed by carbothermal reduction process. Nanofibers with ZrC content of 15, 35 and 50 wt%, respectively, were obtained by varying the n(B)/n(Zr) molar ratio. The oxidation resistance of fabricated nanofibers was investigated by the non-isothermal thermogravimetric method. The effect of ZrC content on the oxidation resistance of ZrB2–ZrC composite nanofibers was analyzed systematically. The Kissinger method was used to calculate the oxidative activation energy (E) of the fibers with different ZrC content. The results show that the E values of fiber with n(B)/n(Zr) equal to 2.5, 3.5 and 4 are 219, 362 and 275 kJ/mol. Among the prepared fibers, the fiber with n(B)/n(Zr) of 3.5 has the highest oxidative activation energy and the best oxidation resistance.

Co-combustion of coal and carbonaceous wastes: thermogravimetric analysis

ABSTRACTThe co-combustion characteristics of coal, two types of carbonaceous wastes (HDPE and scrap tire) and their blends were investigated in this study via a non-isothermal thermogravimetric method. The temperature indices and burnout index were used to evaluate the combustion performance of fuel. Strong synergistic effect emerged between carbonaceous wastes and coal, which showed the enhancement effect on devolatilization and the inhibition effect on char oxidation for the mixtures of coal and scrap tire while the opposite result for the mixtures of coal and HDPE. However, the addition of HDPE into coals can promote the release of volatile in advance. Moreover, the shape of TGA curves and the strength of the synergistic effect was different when carbonaceous wastes blending with different ranks of coal, which related to the combustion temperature zone and volatile content of coal.

Synergistic effects and kinetics analysis of biochar with semi-coke during CO2 co-gasification

It is well-known that there is an interaction between biomass and coal in co-gasification process. In this paper, gasification of semi-coke (SC) and soybean straw char (SS) and their blends were carried out using non-isothermal thermogravimetric method. Interaction between SS and SC during co-gasification was investigated and synergy factors were calculated at different conversion stage. In order to explore whether the physical and chemical structure features have an effect on interaction, surface area analyzer, XRF and Raman spectrometer were adopted to determine the porous properties, ordering degree and ash composition for blends. The results show that the changes of porous properties and ordering degree for blends follow a linear law. The correlation expressions linking char characteristics to char reactivities indicate that the degree of graphitization is the main reason influencing the gasification reactivity. The interaction exhibits a negative synergetic effect at low conversion stage and a positive synergetic effect at high conversion stage. In addition, there are significant synergistic effects in the co-gasification of 75%SC/25%SS. Similar conclusions about synergetic effect are also observed from the kinetics data calculated by three kinetic models.

Kinetics of microwave radiation pulverized coal combustion based on non-isothermal thermogravimetric analysis

ABSTRACT The combustion characteristics of Yangquan (YQ) and Yungang (YG) coal samples before and after exposure to microwave radiation were studied using the non-isothermal thermogravimetric method, and the combustion rules of pulverized coal before and after microwave exposure to radiation were investigated. The results show that after microwave modification the ignition temperature (T i), burnout temperature (T j) and the temperature of maximum combustion rate (T k) of coal sample were all reduced about 10-20°C and the burnout time was shortened by 1–2 min, indicating that the provided treatment effectively improved the combustion performance of the pulverized coal. The characteristic indices C and S of the modified coal samples increased at a high heating rate (20°C/min), which suggests that the microwave modification has a stronger effect on the combustion performance of coal samples at high heating rates. As per the FT-IR spectrum curve, the absorption peak intensity of the higher activity group in the coal sample increased significantly after microwave modification. A comprehensive VR model was employed to model the kinetics of the coal combustion process. The resultant model had a correlation coefficient (R 2) of above 0.999 and root means square error (RMSE) of less than 0.018%, which indicating that the combustion behavior of the pulverized coal can be well described using the VR model. The activation energies E 1 and E 2 of M-YQ and M-YG modified via microwave treatment were decreased by 3.12 kJ·mol−1, 1.02 kJ·mol−1, 4.55 kJ·mol−1, and 8.14 kJ·mol−1 respectively, which further demonstrates that the microwave radiation can effectively accelerate reaction rate of the coal combustion per unit time.

Effect of pore structure on CO2 gasification reactivity of biomass chars under high-temperature pyrolysis

The CO2 gasification reactivity of pine sawdust chars (PS char) obtained from the different high-temperature pyrolysis is studied based on non-isothermal thermogravimetric method. Results show that the order of gasification reactivity is PS char-1073 > PS char-1273 > PS char-1473. Under the effect of high-temperature pyrolysis, the surface structure of biomass char is gradually destroyed and the pore structure parameters of specific surface area, total pore volume and average pore diameter increase. By means of the N2 adsorption-desorption isotherms, it is seen that biomass char has more micro- and mesoporous at higher pyrolysis temperature. Besides, the PS char-1073 mostly has rich closed cylinder pores and parallel plate pores, and the PS char-1273 and PS char-1473 have plentiful open cylinder pores and parallel plate pores. An increase of pyrolysis temperature contributes to the development of porosity and improves diffusion path, which promotes the gasification reactivity. But, its effect on the decline of active site hinders the gasification reactivity. What's more, the kinetic model of distributed activation energy model (DAEM) is applied to calculate activation energy and pre-exponential factor with the integral and differential methods. The calculation results of integral method is more accurate and precise because the differential method is more sensitive than integral method for experimental noise. There is a compensation effect in the CO2 gasification process.

Combustion characteristics and kinetics of different food solid wastes treatment by blast furnace

Food Solid wastes (FSWs) can provide energy for blast furnace through combustion. The combustion characteristics and kinetics of waste meat (WM), waste steamed bread (WSB), waste rice (WR), waste vegetables (WV) and their mixture were studied by the non-isothermal thermogravimetric method. The combustion of FSWs could be divided into two stages: volatiles released and fixed carbon combustion. The first stage was all very intense, while the second stage was different. The fixed carbon combustion was prominent for WM and WV. The order of ignition point was the WV < WM < WR < WSB < coal. However, the order of burnout capacity was WV > WSB > WR > WM > coal. FSWs have a better combustion performance than coal and are better suited for blast furnace injection. The single waste promoted each other at the mixture combustion, ignition point was improved. The combustion activation energy of FSWs was far lower than the coal. The volatiles released were third-order chemical reactions for FSWs. Fixed carbon combustion of WSB and WR was the first order reaction, but that of WM, WV and their four mixture was cylindrical symmetry phase boundary reaction.

Investigation of synergism and kinetic analysis during CO2 co-gasification of scrap tire char and agro-wastes

Tire char (TC), the by-product of waste tire pyrolysis, suffers from low reactivity in CO2 gasification reaction due to high content of acid oxides in its ash and its graphitic structure, with low degree of structural conformations. To address this limitation, TC was co-gasified with several biomass residues including cattle manure (CM), palm empty fruit bunch (EFB), almond shell (AS) and rubber seed shell (RSS). The CO2 gasification reactivity of the TC/biomass blends was investigated at different heating rates by non-isothermal thermogravimetric method. Results signified the incidence of synergy during CO2 gasification of TC/biomass blends where the reactivities of blends were superior to that of individual TC. This was attributed to the inherent alkali and/or alkaline earth metals of biomass fuels acting as natural catalysts to enhance the gasification rate of TC. Several isoconversional kinetic methods also confirmed the occurrence of synergism in blends where the activation energy of all blends in CO2 gasification reaction was lower than sole TC (238 kJ/mol), with TC/CM blend (172 kJ/mol) leading other combinations. Thermodynamic studies also revealed that blending of TC with biomass was effective to improve the reaction rate of TC with CO2 and favorability of the reaction.

Catalytic CO2 gasification of rubber seed shell-derived hydrochar: reactivity and kinetic studies.

In this study, hydrothermal carbonization (HTC) of a biomass was used as a means to improve the physicochemical properties of rubber seed shell (RSS) and enhance its reactivity in the char-CO2 gasification reaction, known as the Boudouard reaction (C + CO2 ↔ 2CO). Hydrochar samples were developed by hydrothermal treatment of RSS, without separating the solid residue from the liquid product, at 433, 473, 513, and 553K under autogenous pressure. The CO2 gasification reactivity of the developed hydrochars was then investigated at different heating rates (5, 10, 20, and 30K/min) by the non-isothermal thermogravimetric method. The hydrochars revealed higher reactivity and improved gasification characteristics compared to the untreated biomass, while the hydrochar which was filtered from the liquid slurry showed lower reactivity compared to the untreated biomass. This was due to the chemical and structural evolutions of the biomass during hydrothermal treatment as indicated by various analyses. The gasification reactivity of the hydrochar was substantially enhanced by introduction of a catalyst (NaNO3) during HTC. Kinetic analysis of the char-CO2 gasification reaction was carried out by applying Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS), and Starink isoconversional methods, and thermodynamic parameters were also determined. The activation energy of the Na-loaded RSS hydrochar in CO2 gasification (120-154kJ/mol) was considerably lower than that of the untreated biomass (153-172kJ/mol). Thermodynamic studies also confirmed the promoting effect of hydrothermal treatment and catalyst impregnation on enhancement of reactivity of the virgin biomass and reduction of gasification temperature.