Macro Thermogravimetric Analyzer Research Articles

Assessment of the use of biochar from the slow pyrolysis of walnut and almond shells as an energy carrier

ABSTRACT This study explores the energy applications and combustion kinetics of biochar produced from walnut and almond shells through pyrolysis. Using macro-thermogravimetric analysis at heating rates of 10, 15, and 20 K min−1, a multi-step mechanism involving two parallel reactions was used to model thermal decomposition. Bioenergy indices revealed that walnut shell-based biochar (WSB) produced at 773 K and 873 K displayed superior biofuel potential due to its high energy density and low ash content, while almond shell-based biochar (ASB) at 673 K demonstrated the best overall bioenergy performance. Among the tested heating rates, 15 K min−1 provided optimal results for ignition, combustion, and burnout indices, with WSB showing the highest overall combustion performance. Kinetic analysis using the Coats-Redfern method demonstrated the highest R2 values and minimized RMSE and SSE. The activation energy for the first pseudo-component ranged from 54.91 to 129.84 kJ mol−1 for ASB and from 61.71 to 141.85 kJ mol−1 for WSB. For the second pseudo-component, the activation energy ranged from 25.21 to 159.32 kJ mol−1 for ASB and 25.63 to 96.25 kJ mol−1 for WSB. These findings emphasize the potential of WSB and ASB biochar for bioenergy applications, with WSB exhibiting the best combustion characteristics.

Experimental and kinetic study of PET pyrolysis under fast and slow heating rates using a visualized Macro TGA

A visualized macro thermogravimetric analyzer was utilized to gather data on sample weight, temperature, and image signals of centimeter-scale PET. The PET was subjected to both fast (above 300 K/min) and slow (below 25 K/min) heating rates. The experimental findings revealed that weight loss mainly occurred at different temperature ranges under fast (above 610 °C) and slow (400–520 °C) heating rates. The isoconversional method (ICM) and the distributed activation energy model (DAEM), both assuming single-step reactions, were employed separately to predict the conversion and rate of PET pyrolysis. However, the prediction error was considerable. To address this issue, a discrete distributed activation energy model (DDAEM) was developed, incorporating both single-step and double-step parallel reactions. The DDAEM yielded a prediction error within 10 %, which is better than ICM and DDAEM. Furthermore, all three models (ICM, DAEM, and DDAEM) indicated significant discrepancies in activation energies between fast and slow heating rates.

Influence of Temperature in the Thermo-Chemical Decomposition of Below-Stoichiometric RDF Char—A Macro TGA Study

Due to the energy crisis that some countries are facing nowadays, the gasification process appears to be a good alternative to produce some energy from solid materials. Increasingly, gasification involves using wastes as a solid fuel, making the process green and reusing some materials that otherwise could end up in a landfill. However, the process of finding the best gasification parameters of a sample can be very expensive and time-consuming. In this sense, a refuse-derived fuel (RDF) char produced from an original RDF under 30 min at 400 °C was tested on a small-scale reactor using macro thermogravimetric analysis (TGA), as presented in this paper. The goal was to study and evaluate the devolatilization and residual carbon rate of the sample under several conditions and, at the same time, quantify and analyze the released gas. In the first round of tests, 5, 10, and 20 g of samples were tested at 750 °C with an excess of air coefficient (λ) = 0 and 0.2. It was possible to conclude that the lower the mass, the higher the devolatilization rate. The λ only had an influence on the devolatilization rate with a 20 g sample. Regarding the gas, CO, CO2, and H2 had no variation in the sample mass in contrast to CH4, which increased with the increase in the sample mass. The second round of tests was performed with samples of 10 g of mass at temperatures of 700, 800, and 900 °C and λ values of 0.15, 0.2, and 0.25. The tests indicated that the temperature influenced the devolatilization rate but not the residual carbon combustion rate. Regarding the gas composition, CH4, CO2, and CO followed the same trend, decreasing the concentration with the increase in temperature; in contrast, H2 increased in concentration with an increase in temperature. The heating value of the gas followed the same behavior as CH4.

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

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

Study of the memory effect of PCDD/F during the combustion of several biomasses in a moving grate boiler.

The objective of this work was to study the influence of temperature on the PCDD/Fs behavior stored in biomass ashes issued from an automatic pilot-scale wood boiler. A mixture of these ashes with a dioxin mass ratio dry based of 5.9 μg kg-1 was used for thermal treatment at temperatures ranging between 200 and 500°C. First tests were carried out in a macro thermogravimetric analysis instrument while a couple of other tests were carried out in a quartz-lined crossed fixed-bed reactor. These treated ashes were afterwards analyzed and their dioxin mass ratio was determined. Results obtained from these both experiments are radically different: ashes treated in macro-TGA contain 18 times more PCDD/Fs than the initial non-treated ashes while those from the reactor have 84% less of PCDD/Fs. Ninety-one percent of stored PCDD/Fs in the initial ashes were eliminated after 1h at 400°C in crossed fixed-bed reactor. Macro-TGA experiments are a representation of what happens during the shutdown and cooling phase of the boiler, some areas reaching temperatures for which the formation of PCDD/Fs is optimal. Without cleaning the boiler, a memory effect on further tests is observed.

Measurement and Importance of Volatile Matter in Coals and Biofuels

Abstract Volatile matter values for solid fuels are used to assess their burning rates and, thus, provide a basis for the buying and selling of these fuels. The major factors that affect volatile matter yields are the type of fuel, moisture contents, and the heating rates used in the tests. This paper reports the results of experiments designed to improve the reliability and application of test methods for the determination of volatile matter in various solid fuels. The macro thermogravimetric analysis studies described herein include the rapid drying of analysis samples of coal and the effect on volatile matter yields, the heating of various chars at high temperatures to reach a state of constancy, the measuring of decomposition moisture, an “elusive” constituent in coal, and the cocombustion of coals and other solid fuels. The presence of residual moisture and decomposition moisture in the coal during the volatile matter tests increases the measured volatile matter yields even though the residual moisture has been factored out. The rates of heating solid fuels during volatile matter tests affect the volatile matter yields because of the presence of different types of moisture in the fuel that are released at different temperatures. The heating rates used in volatile matter tests affect the type of compounds released and the total volatile matter yields of coals and biofuels. The experiments reported in this paper were instrumental in the decision of ASTM Committee D05 on Coal and Coke to recently revise the classic volatile matter standard test method D3175 to change the temperature for drying sparking coals from 600°C to 107°C. The role volatile matter plays in the combustion of fuel blends is discussed in this article.

Macro Thermogravimetric Analyzers: Versatile and Underutilized Analytical Instruments

Abstract Thermogravimetric analysis (TGA) is an analytical technique in which changes in physical and chemical properties of materials are measured as a function of temperature or time or both. TGA is commonly used to determine selected characteristics of materials that exhibit either mass loss, or gain, because of decomposition, oxidation, reduction, or loss of volatile material, such as moisture. Common applications of TGA are materials characterization through analysis of characteristic decomposition patterns and determination of combustible materials and combustion residues from a sample. Macro thermogravimetric analyzer (macro TGA) systems that use gram-size samples have been used for almost four decades for routine laboratory measurements, especially those measurements that monitor industrial processes. The larger sample sizes allow more accurate mass measurements for characterization of materials. Larger sample sizes also reduce the effects of uneven particle sizes and uneven distribution of properties between particles. Macro TGAs are automatic multi-sample analyzers with a multi-position sample carousel. Widespread use of these systems has led to the development of at least four ASTM International standard test methods that use macro TGAs. Other standard test methods using macro TGAs are in the process of being developed by ASTM International. Some other countries have developed, or are in the process of developing, standard test methods that use macro TGA instrumentation.

Upgraded pongamia pod via torrefaction for the production of bioenergy

Torrefaction can be used to reduce the oxygen content of biomass and improve the feedstock properties for thermochemical conversion. Pongamia (Millettia pinnata), a leguminous, oil-seed bearing tree, is a potential resource for sustainable aviation fuel production due to the high oil content of its seeds. The present work investigates thermochemical pretreatment of pongamia processing residues, i.e. pods. Torrefaction tests were performed with both a fixed bed reactor and a macro thermogravimetric analyzer (TGA) under nitrogen atmospheres. The effects of process conditions on feedstock properties relevant to thermochemical conversion technologies, proximate and ultimate composition, heating value, and Hardgrove grindability index (HGI), were measured. The chemical structure, reactivity, and changes in elemental composition of the torrefied materials were also investigated. The mass and energy yields decreased 43% and 25%, respectively, from the mildest (165 °C) to the most severe (281 °C) torrefaction conditions, while the energy densification index increased from 1.15 to 1.68. The HGIs of pods torrefied at temperatures >215 °C were found to equal or exceed the HGI of a reference bituminous coal sample. A LECO model TGA801 macro-TGA with a sample loading capacity of ~95 g was also used to torrefy pongamia pods. Products from the LECO and the fixed bed reactor were comparable, and the macro-TGA was demonstrated to be a useful fast screening tool to study effects of process parameters.

Kinetic analysis and thermodynamics properties of air/steam gasification of agricultural waste

The air/steam gasification of wood sawdust (SD), plum and olive pits (PP, OP) bio-wastes was studied using macro-thermogravimetric analysis at three heating rates (5, 10, 15 K/min). Three stages were identified during gasification process: water vaporization; de-volatilization and char gasification. The experimental data were analysed by applying five model-free methods: Flynn-Wall-Ozawa (FWO), Distributed Activation Energy Model (DAEM), Friedman, Starink, and Kissinger-Akahira-Sunose (KAS), to evaluate the gasification kinetic parameters. The FWO method exhibited the best fit to the experimental results. The pre-exponential factor was estimated using the Kissinger’s expression. The average apparent activation energy (E) for the char-gasification step was found to be 218.27 (SD), 143.70 (PP) and 87.89 kJ mol−1 (OP). The pre-exponential factors were 6.93 1023 (SD), 5.10 1014 (PP), and 3.71 1009 s−1 (OP).A kinetic model to predict the CO release during the bio-waste decomposition was also proposed and validated. The E values for global release of CO were 87.34 (SD), 67.19 (PP), and 133.23 kJ mol−1 (OP). In addition, the thermodynamic parameters ΔS, ΔH and ΔG were calculated from the FWO method. The positive values of ΔH evidenced the global endothermicity of the gasification process over the whole range of the conversion degree.The average ΔG values were 130.53 (SD), 148.17 (PP) and 132.91 kJ mol−1 (OP). The average ΔS and ΔG values, together with the Arrhenius kinetic coefficient showed that the reactivity for gasification decreased in the following order: SD > OP > PP. The results are in good agreement with previously reported data.

Non-isothermal drying of bio-wastes: Kinetic analysis and determination of effective moisture diffusivity

A macro-thermogravimetric analysis (macro-TGA) was applied to analyse the non-isothermal drying of different bio-wastes (quince solid waste, grape marc and pumpkin shell from different enterprises located in San Juan Province, Argentina). The experimental data were obtained at three heating rates (5, 10 and 15 K/min) and two different initial moisture contents (30 and 50% w/w). These data were fitted using the Coats-Redfern and Sharp methods. The D2 model showed the best fitting for all experiments when using the Coats-Redfern method. It is assumed that drying occurs on the solid boundary. The predicted Ea values ranged from 43.60 to 64.50 kJ/mol for the three bio-wastes under the different experimental conditions. The Ea value slightly increases with the increase in heating rate because the wastes require more energy to undergo drying.Deff increases moderately with temperature at the beginning of the dehydration process; then, this increasing behaviour is significant due to the loss of continuous moisture channels. Otherwise, Deff increases with the initial moisture content, showing that the humidity of the samples did not reach the saturation content.

Comparative investigation on thermal decomposition of powdered and pelletized biomasses: Thermal conversion characteristics and apparent kinetics

In this work, the thermal degradation behaviors of two kinds of biomasses (pinewood and rice husk) with powder and pellet under three oxygen concentrations were investigated by a self-designed macro-thermogravimetric analyzer. An obvious hysteresis of thermal degradation of biomass pellets was observed under three conditions. The maximum activation energy of biomass pellets was significantly greater than that of biomass powders, while their average activation energies were almost equal based on distributed activation energy model. For the oxygen-rich combustion, the comprehensive combustion character index of powdered and pelletized biomasses ranged from 3.92 × 10−7 to 5.16 × 10−7%2·min−2·°C−3 and from 1.82 × 10−7 to 1.91 × 10−7%2·min−2·°C−3, respectively. Furthermore, the derived biochar of powdered biomass has a higher caloricity than that of pelletized biomass during combustion by TG-DSC analysis. The performances of thermal degradation observed by macro-thermogravimetric analyzer could factually reveal the influence of mass and heat transfer on the thermochemical conversion of powdered and pelletized biomasses.

Torrefaction of Maize Residue Pellets with Dry Flue Gas

In this work, maize residue pellets were torrefied in a macro thermogravimetric analyzer with simulated dry flue gas from mixing of CO2 and N2. The effects of temperature (220–300 °C), residence time (10–40 min), and the presence of CO2 (0–18% v/v) in the reacting gas were investigated on products’ yields, distribution, and torrefied pellet properties such as higher heating value (HHV), elemental composition (C, H, O, N, S, K, and Cl), grindability, and moisture uptake ability. Temperature and residence time were found to affect the distribution of products’ yield and the properties of torrefied pellets considerably. In comparison with the untreated biomass pellets, the torrefied pellets appeared to have improved HHV and grindability but reduced moisture uptake ability. In the presence of CO2, the Boudouard reaction caused slight reductions in the C content and HHV of the torrefied pellets. Changes in torrefaction conditions did not prove to have a statistically significant effect on S, K, and Cl contents of the torrefied biomass materials.

Comparative investigation on thermal degradation of flue-cured tobacco with different particle sizes by a macro-thermogravimetric analyzer and their apparent kinetics based on distributed activation energy model

The particle size was an important factor that can affect the thermal degradation behavior of biomass during thermochemical conversion. In this work, the thermal degradation behavior of flue-cured tobacco with different particle sizes for thermochemical conversion was investigated by a self-designed macro-thermogravimetric analyzer (macro-TGA) under inert and oxidative conditions. During pyrolysis and combustion, the thermal degradation behavior could be described by a four-stage and five-stage mass loss reaction, respectively. At the second mass loss stage, for six cut tobaccos, the mass loss rate increased with the decrease in particle size during pyrolysis and combustion. In addition, the combustion character index of cut tobaccos ranging from 3.0480 × 10−7 to 4.4825 × 10−7%2 min−2 °C−3 also increased with the decrease in particle size. Furthermore, the mass change data recorded by the macro-TGA were used to estimate the kinetic parameters, such as the apparent activation energy and the pre-exponential factor, based on distributed activation energy model. For the thermochemical conversion of tobacco materials, it was found that the apparent activation energy increased with the increase in conversion rate for pyrolysis reaction under inert condition, while the apparent activation energy reached a maximum within a certain conversion rate in the middle of combustion reaction under oxidative condition. As well, the kinetic compensation effect was evaluated by the equation $$\ln A = \varphi \times E + \psi$$. The investigation on thermal degradation and apparent kinetics of tobacco revealed the effect of particle size on thermochemical conversion, which can provide a reference for building a more accurate cigarette combustion model.

Experimental and modeling study of potassium catalyzed gasification of woody char pellet with CO2

Understanding the catalytic effect of potassium on CO2 gasification of biochar can help clarify the complex catalytic conversion mechanism of biochar. In this study, effects of temperature and KOH content on conversion performance and reaction kinetics of gasification of biochar pellet were investigated by using a macro-thermogravimetric analysis (MTGA) unit. Results showed that the increase of gasification temperature and KOH content promoted the conversion of biochar pellet and enhanced the gasification rate (dX/dt). With the reaction proceeded, dX/dt increased initially then decreased, and reached the peak values at X of about 0.15–0.40. A faster expansion of pore structure at both higher temperature and higher KOH content would contribute to the shift of peak values to lower X. Phase boundary-controlled model fitted well to the gasification of biochar pellet with added KOH at 750 and 800 °C, while the possible melting of K species at 850 °C would change the gasification reaction to phase change model. The inferred catalytic role of K in pellet gasification is that it reduced the activation energy and increased the active sites for carbon to react with CO2, and the activation energy was reduced with the increase in K content (0–20 wt. %).

Moisture and Heating Rate Effects on Volatile Matter Yields for Coals

Abstract Currently there are two ASTM standard test methods used around the world for the determination of volatile matter in coal. ASTM D3175, Standard Test Method for Volatile Matter in the Analysis Sample of Coal and Coke, was first published as ASTM D22-16, Laboratory Sampling and Analysis of Coal, in 1916 and uses a minimum volume vertical furnace. ASTM D7582, Standard Test Methods for Proximate Analysis of Coal and Coke by Macro Thermogravimetric Analysis, uses a macro thermogravimetric analyzer (TGA) system. Macro TGA systems use samples that are one gram or larger, whereas micro TGA systems use only milligram-size samples. In both test methods, the furnaces are heated to a final temperature of 950°C and include a seven-minute hold time before final mass measurements. For nearly four decades, fuel scientists have tried to reconcile the differences between the coal volatile matter yields obtained using either a preheated (950°C) minimum volume vertical furnace (ASTM D3175) or a TGA system. This article describes experiments designed to help explain the differences in volatile matter yields from coals with the major focus being the moisture content in the samples analyzed. Parameters studied include predrying coal samples, using different heating rates, and using different intermediate temperatures in two-step procedures for the measurements. Factors including the moisture content and plastic behavior of coals, both of which contribute to the differences between the volatile matter values determined by different methods, will be discussed.

Fibre-volume-fraction measurement of carbon fibre reinforced thermoplastic composites using thermogravimetric analysis

The fibre-volume-fraction (FVF) measurement of fibre-reinforced polymers (FRPs) is crucial in understanding and characterising their mechanical performance. To date, there has not been a standardised, labour-efficient method in determining the FVF of a non-crimp fabric (NCF) carbon reinforced thermoplastic composites (CFRTPs). An alternative method such as thermogravimetric analysis (TGA) has merely been commonly used for carbon-fibre reinforced thermosets (CFRTSs) and glass-fibre reinforced thermosets (GFRTSs). Therefore, this paper reports a range of macro TGA measurements of the constituent materials of two NCF CFRTPs; (i) T700 carbon/polyamide6.6 (PA6.6) and (ii) T700 carbon/polyphenylene sulphide (PPS). The TGA measurements were performed using two different purge gases (air and nitrogen) and the mass degradation with respect to time, temperature and atmospheres were recorded and discussed. Additionally, fractographic analysis on the fibres was carried out to scrutinise and further discuss the findings following the TGA. It was concluded that TGA provided a suitable and reliable alternative method to measure the FVF of CFRTPs.

Macro-TGA steam-assisted gasification of lignocellulosic wastes

The kinetics of the steam-assisted gasification for three different agro-industrial solid wastes (sawdust, olive and plum pits) was studied by macro thermo-gravimetric analysis (macro-TGA) at different heating rates (5, 10 and 15 K/min). The progressive CO release was moreover monitored to fully identify each step of the global gasification process. A single-step kinetics modelling was applied by using the Coats-Redfern method, with both a first order model for pyrolysis and a Ginstling - Brounstein 3D-diffusion model for the gasification stages, respectively. A comparison between macro-TGA and previous TGA results for the same bio-wastes was performed. Results indicated that the reaction proceeds in three well-defined and subsequent stages, involving water evaporation [298–473 K], biomass de-volatilization [473–648 K] with the highest production of CO, and char gasification as final step. Reaction rate parameters of the Arrhenius equation were determined for both the pyrolysis and gasification steps.

Isothermal combustion characteristics of anthracite and spent coffee grounds briquettes

The isothermal combustion characteristics of anthracite and spent coffee grounds briquettes in a bench-scale fixed-bed furnace were examined by using a macro-thermogravimetric analysis approach between 873 and 1173 K. The combustion performances in terms of the conversion rates, flame evolution, pollutant emissions, ash compositions and ash fusion temperatures of two anthracite/spent coffee grounds blend briquettes with blending ratios of 40% and 60% were also compared with those of their individuals. There was only an obvious peak in DTG profile for every sample at each temperature. At 973 K, the average burning rate of the spent coffee grounds was about 8 times higher than that of the anthracite. The average burning rate of 60% anthracite/40% spent coffee grounds blend at 1173 K increased by about 3 times in comparison with that at 873 K. NO2 emissions for the four samples were much less than other gaseous emissions. The four ash fusion temperatures for the anthracite were higher than 1791 K. The deformation temperature, softening temperature, hemispherical temperature and flow temperature for the spent coffee grounds were 1526, 1626, 1687 and 1791 K. The ash fusion characteristics of the spent coffee grounds were improved by blending the anthracite.

Pyrolysis behavior and kinetics of corn residue pellets and eucalyptus wood chips in a macro thermogravimetric analyzer

Pyrolysis of corn residue in pellet form and eucalyptus wood in chip form was conducted on a continuously weighing fixed bed reactor acting as a macro thermogravimetric (TG) analyzer with 40 ± 1.0 g of sample loading under high purity nitrogen environment. Effect of heating rate (5, 10, and 15 °C/min) was investigated and pyrolysis behaviors of the pellets and wood chips were also compared with those performed on a typical TG analyzer. Experimental results showed that bigger particle size and higher heating rate significantly delayed the pyrolysis reaction, meanwhile the heating rate affected the characteristic temperatures of the pellets and wood chips more than the smaller size. By differential derivative TG technique, the pyrolysis behaviors could be divided into three stages. Within the main stage of pyrolysis process, only a peak could be differentiated clearly in the derivative TG curve, accounted for approximately 67–81% of weight loss. Flynn-Wall-Ozawa method was used to calculate the activation energy against conversion of reaction on the whole temperature domain. It was found that the activation energy values from the macro TG analyzer, which were 60–70 and 59–71 kJ/mol with average values of 64 and 62 kJ/mol for the pellets and wood chips, respectively, were about four times lower than that obtained from the typical TG analyzer.

Design, calibration and testing of a new macro-thermogravimetric analyzer

The design and development of a macro-thermogravimetric (TG) analyzer are presented. Two sources of measurement bias are studied: balance heating and the effect of viscous forces. Temperature regulation and measurement are discussed. In a second part of the study, results obtained with the newly developed macro-TG system for the dehydration of CuSO4·5H2O are compared with data obtained with a commercial thermobalance. The effects of mass and of the heating rate on TG and differential TG curves are discussed. Finally, the effect of the initial mass of a polyethylene sample on its combustion is studied as an example application of the macro-TG device.