Devolatilization Stage Research Articles

Enhancement and inhibition of the oxidation rates of pyrolytic chars from wood loaded with potassium compounds

The oxidation is studied of chars produced from the highly exothermic packed-bed pyrolysis, carried out at moderate temperatures, of potassium-loaded beech wood (additives KOH, K2CO3, KC2H3O2 and KCl, for potassium contents in char up to about 5 wt%). In all cases, for temperatures up to 750 K, chars undergo the kinetically controlled stages of oxidative devolatilization and oxidation. For the latter, as the potassium content increases, the process dynamics shift from a single to two conversion zones, corresponding to thermal and mixed catalytic-thermal activation, respectively. The ignition and burnout temperatures initially decrease, testifying an enhancement of carbon conversion, the more the basicity of the additive is high. However, for potassium contents above certain threshold limits, effects appear first of saturation and then of inhibition. Moreover, small amounts of char are always oxidized during ash cooking, at high temperatures. Potassium enhances the char oxidation rates up to maximum contents around 1–1.5 wt% (KOH, K2CO3, KC2H3O2) and 2 wt% (KCl), resulting from alkaline catalysis and modifications in the char structure, caused by interactions between additives and wood during both aqueous impregnation and pyrolysis.

Insight into KOH and KCl release behavior of burning wood and straw pellets using quantitative in situ optical measurements

Two-dimensional laser-induced photofragmentation fluorescence (LIPF) was employed to quantitatively visualize the potassium hydroxide (KOH) and potassium chloride (KCl) vapor in the plume above burning wood and straw pellets. In the LIPF measurement, two excitation lasers at 266 and 193 nm were adopted to discriminate KOH and KCl. Meanwhile, tunable diode laser absorption spectroscopy (TDLAS), laser-induced breakdown spectroscopy (LIBS) and two-color pyrometry were used to measure the atomic potassium concentration, total elemental potassium concentration and surface temperature of the burning pellets, respectively. The combustion environment had a temperature of 1550 K and an oxygen concentration of 4.6 vol.%. Two peaks were observed from the temporal potassium release profile of the burning wood, corresponding to the devolatilization and char oxidation stage, while only a single release peak was observed from the burning straw attributed to its high ash content. During the char oxidation and ash cooking stages, KOH was observed to be the dominant potassium species released from the wood, while only KCl was observed for the straw which had a high content of chlorine. About 45% of the total potassium in the wood samples and about 10% in the straw samples were measured to be released during the combustion process. The high content of silicon in the straw retained a considerable amount of potassium in the ash. The wood had the potassium release mainly in the char oxidation stage (∼53% of the total release), while the straw had the main release during the ash cooking stage (∼49% of the total release). During the char oxidation and ash cooking stages, about 32% of Cl was released from the straw pellets in KCl, while the other part of Cl was considered to be released during the devolatilization stage in other Cl species form, such as HCl.

Thermal behavior, synergistic effect and thermodynamic parameter evaluations of biomass/plastics co–pyrolysis in a concentrating photothermal TGA

The heating rate would significantly impact the pyrolysis process, especially for the reactions containing synergistic effects between two different feedstocks. Co-pyrolysis of two widely available biomass (CC–corncob and PS–peanut shell) with plastic (PET–polyethylene terephthalate and PVC–polyvinyl chloride) was studied in a concentrating photothermal thermogravimetric analysis (CP-TGA) system at three heating rates (100, 500, 1000℃/min). The TG and DTG curves of CC and PS differ due to their polymeric components (holocellulose and lignin); two pronounced levels at 100 and 500 ℃/min heating rates were present in PVC. With increasing heating rate, the lateral shift towards higher temperature regions in the TG and DTG curves exceeded 100 °C. The synergistic effects on the blend samples were concentrated in the main decomposition region (250–580℃) due to rapid volatiles release, and the discrepancy values further stabilized at the final decomposition stages. The activation energy (Ea) was assessed using a comparative study of isoconversional methods, namely Kissinger–Akahira–Sunose (KAS), Flynn–Wall–Ozawa (FWO), and Starink. The isoconversional methods demonstrated that the co-pyrolysis process required about 30 % less activation energy than the pyrolysis of plastic (PET/PVC) alone. Coats-Redfern's (CR) model-fitting approach was used to identify the kinetic triplet of the devolatilization stage. The CR models revealed that biomass–PET blends belong to two to four-dimensional diffusion models, whereas biomass–PVC blends are dominated by chemical reactions of 1.5 and 2 orders. The energy barrier between activation energy (Ea) and change in enthalpy (ΔH) for all the blend samples was lower (∼5–6 kJmol−1), which slightly increased at higher heating rate.

Release characteristics of potassium and sodium during pellet combustion of typical MSW fractions using the FES method

The temporal release characteristics of sodium and potassium (Na and K) during the pellet combustion of municipal solid waste (MSW) were comparatively studied using calibrated flame emission spectroscopy (FES). A lab-scale setup with a Hencken burner was used to create a stable high-temperature environment for pellet ignition and combustion. The results revealed a three-stage combustion process (devolatilization, char, and ash stages) for most waste fractions, whereas a one-peak release distribution was observed for plastics. In contrast, biomass-based products and kitchen waste were characterized by dual-maxima release shapes. In general, the release concentrations of both Na and K were the highest in the char and ash stages because of the higher pellet surface temperature than that in the devolatilization stage. Although the variation in pellet mass changed significantly during devolatilization, less than 10% of alkali contents were released. Compared to the combustion characteristics, the waste compositions were considered a critical factor. The peak release concentrations increased almost linearly with the initial alkali concentrations during char oxidation. In addition, paper and wood waste were found to be the potential sources for the release of Na and K, respectively, second only to kitchen waste. Finally, the possible transformation processes of alkalis during waste combustion were discussed.

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.

Performance and mechanism of bamboo residues pyrolysis: Gas emissions, by-products, and reaction kinetics

The performances and reaction kinetics of the bamboo shoot leaves (BSL) pyrolysis were characterized integrating thermogravimetry, Fourier transform infrared spectroscopy, and pyrolysis-gas chromatography/mass spectrometry analyses. The high volatiles and low ash, N, and S contents of BSL rendered its pyrolysis suitable for bio-oil generation. The main mass loss of BSL pyrolysis occurred in the devolatilization stage between 200 and 550 °C. The peak temperatures of pseudo-hemicellulose, cellulose and lignin pyrolysis in BSL were 248.04, 322.65 and 383.51 °C, respectively, while their average activation energies estimated by Starink method were 144.29, 175.79 and 243.02 kJ/mol, respectively. The one-dimensional diffusion mechanism (f (α) = 1/(2α)) best elucidated the hemicellulose reaction. The cellulose (f (α) = 0.74 (1 − α)[−ln (1 − α)]−13/37) and lignin (f (α) = 0.35 (1 − α)[−ln (1 − α)]−13/7) reactions were best described by the nucleation mechanisms. The estimated kinetic triplets accurately predicted the pyrolysis process. 619.3 °C and 5 °C/min were determined as the optimal pyrolytic temperature and heating rate. The C-containing gases were dominant among the non-condensable gases evolved from the pyrolysis. The NOx precursors (NH3 and HCN) were found more important than NO emission in pollution control. 2,3-dihydrobenzofuran, (1-methylcyclopropyl) methanol, heptanal, acetic acid, and furfurals were the main pyrolytic by-products. BSL-derived biochar is a relatively pure carbon-rich material with extremely low N and S content. The BSL pyrolysis yielded a promising performance, as well as value-added by-products to be utilized in the fields of bioenergy, fragrance, and pharmaceuticals.

Pyrolysis kinetics of new bioenergy feedstock from anaerobic digestate of agro-waste by thermogravimetric analysis

In this study, thermogravimetric and kinetic analysis of digestate from anaerobic co-digestion of dairy manure and dry biomass of Amaranthus retroflexus L. is presented. Thermal decomposition of digestate was studied in the temperature range 40–1000 °C in an inert atmosphere using thermogravimetric and differential scanning calorimetry (TG-DSC) at the heating rates of 5, 10, 15 and 20 °C/min. According to the results of TG/DTG analysis, the thermal decomposition of digestate occurs in three stages: dehydration, devolatilization and decomposition of carbonaceous residue. The devolatilization stage in pyrolysis is a key stage; therefore, it was divided into two steps: I-st step and II-nd step and analyzed in detail. The kinetic parameters were estimated by isoconversion Friedman, OFW (Ozawa-Flynn-Wall) and KAS (Kissinger-Akahira-Sunose) methods and using model-based methods, such as CnB (reaction of n-th order with autocatalysis by product), Bna (expanded Prout-Tompkins equation) and Fn (the reaction of n-th order). For the model-free methods, the average Eα values for the I-st step were 136.3 kJ/mol and for the II-nd step 143.1 kJ/mol. The average Eα values obtained using the CnB, Bna, and Fn models were 105.8 kJ/mol for the I-st step and 145.6 kJ/mol for the II-nd step, i.e. Eα increased by 37.6%. The results of the evaluation of the thermal behavior of digestate from agro-waste indicate a good prospect for the use of biomass as a new bioenergy feedstock. The obtained kinetic parameters are of great importance for the design of pyrolysis reactors.

Numerical investigation on H2S formation characteristics in air-staging combustion of a tangentially coal-fired boiler

ABSTRACT Existing H2S generation models are mainly applied in laboratory-scale models and thoughtless about the fuel sulfur release characteristics in fuel-rich zone. So, a novel H2S generation model is proposed for describing the H2S formation characteristics of real-scale boilers in this work. It consists of two parts: fuel sulfur release and chemical reactions. The ratio of the gasification rate to the consumption rate for each char particle is calculated in coal combustion model through the user-defined function (UDF) approach, which is delivered to the H2S generation model for determining the proportions of char sulfur converted to COS and SO2. The numerical results show that the proportions of char sulfur converted to H2S are about 0.545 over the excess air coefficient range from 0.6 to 1.2. The strongly reducing atmosphere could just accelerate the H2S formation to a certain extent in the devolatilization stage. For a 600 MW tangentially coal-fired boiler, the H2S concentration over 400 mg∙kg−1 appears mainly in the zone below burner A and the zone between burner E and the separated over-fire air nozzle. This study is intended to guide for predicting possible corrosion zone and delivering targeted solutions for inhibiting metal corrosion.

Effects of inherent minerals on oily sludge pyrolysis: Kinetics, products, and secondary pollutants

Considerable inherent minerals in oily sludge (OS) caused intricate effects on OS pyrolysis behaviors. This work investigated the effects of individual mineral on pyrolytic products and secondary pollutants by pyrolysis of artificial OS, which was prepared by assembling pure mineral chemicals (SiO2, CaO, MgO, Fe2O3, and Al2O3) with petroleum oil. Results showed that the effects of inherent minerals on OS pyrolysis tightly depended on pyrolysis temperature, where the thermal cracking and secondary reactions of heavy hydrocarbons were promoted at high temperature. Their effects also varied with inherent mineral species. The existence of SiO2 in OS had negligible influences on OS pyrolysis. CaO and MgO were favored for almost invariant quality of liquid product and the lowest total petroleum hydrocarbons (TPHs) content in solid residues. Because CaO and MgO weakened the stabilities of hydrogen bonds and hydroxyls groups and thus accelerating devolatilization of TPHs from OS. Fe2O3 and Al2O3 helped in the lower TPHs content in solid residues as well. Moreover, they were favored for more pyrolytic gases and long chain liquid product though the yield of liquid product decreased. It may attribute to the enhanced deoxidation and polymerization of Fe2O3 and Al2O3. Along with OS pyrolysis, inherent minerals tended to inhibit N/S/Cl-containing pollutants at the stage of dehydration and devolatilization (<358 °C), but promote their releasing at the stage of thermal cracking and secondary reactions (>358 °C). This work might provide inspiration for getting insight into the OS pyrolysis behaviors and proposing clean fuel production strategies.

Evolution of carbon and nitrogen during chemical looping gasification of rapeseed cake with Ca-Fe oxygen carrier

• Higher OC/RC ratio is beneficial to the transformation of carbon. • NH 3 and HCN are the major N species in CLG of rapeseed cake. • Fe and Ca in CaFe 2 O 5 can increase the yields of NH 3 and HCN. • The reaction pathways of nitrogen in CLG are summarized. • CLG is promising process for the sustainable production of NH 3 . Rapeseed cake (RC) is an attractive fuel for its high caloricity, but the high-nitrogen content seriously hinders its utilization. Meanwhile, chemical looping gasification (CLG) is a promising technology for the production of N 2 free high-quality syngas. Inspired by using RC as a source of C for syngas production, it also can be a possible source of N and H for the sustainable production of NH 3 . Hence, recycling N and H from RC via CLG was proposed for NH 3 production. This paper evaluates the effects of oxygen carrier (CaFe 2 O 5 (CaFe) and 60% Fe 2 O 3 /Al 2 O 3 (FeAl)) on kinetic parameters, as well as the evolutions of carbon and nitrogen during CLG of rapeseed cake using TG-FTIR. Results show that the gasification behavior is remarkably influenced by oxygen carrier at both devolatilization and char reaction stages. CaFe shows a remarkably higher reduction activity compared to FeAl, especially at char reaction stage. The superior activity of CaFe can be also reflected in the lower activation energy compared to FeAl. As regards to nitrogen emission, NH 3 and HCN are the dominant nitrogen species, whereas HNCO is minor. Meanwhile, the migration of nitrogen includes catalytic pyrolysis and oxidation by lattice oxygen (O*). It is feasible to control the migration path of nitrogen by adjusting the operating conditions. Thus, CLG is an attractive pathway for efficiently utilizing rapeseed cake, which can not only produce tunable syngas, but also possibly make the most use of nitrogen as valuable chemicals.

Characteristics and formation of nitrogen-containing products from the pyrolysis of maple wood and maize straw

Biomass is widely used in residential and industrial sectors as a renewable and carbon-neutral energy source, however, NOx emissions caused by the heat treatment of biomass are of concern. The nitrogen element in biomass plays an important role in N-containing products generated from pyrolysis, while the migration behaviors of fuel-N are still unknown. Slow pyrolysis experiments of maple wood and maize straw were conducted at 350–650 °C in this study. The TG, XPS and GC/MS technologies were performed to investigate the nitrogen migration pathways during prolysis. Results demonstrated that the fuel-N in the two species mainly exists as protein-N, amide-N and inorganic-N functional groups. Char-N occupied the most of total fuel-N from 350 °C to 450 °C, while the yields of tar-N and NOx precursors-N (NH3-N and HCN-N) increased gradually with the rising temperatures. NH3 was found to be the main NOx precursor for the both species, accounting for 15.01–20.19 wt% and 3.18–5.91 wt% of fuel-N in maple wood and maize straw, respectively. More than 85% of NH3-N was produced between 350 °C and 450 °C, attributing to the conversion of fuel-N and tar-N in the devolatilization stage. Differently, around 50% of HCN-N yields were produced by the secondary decomposition of tar-N and char-N at higher temperatures (≥550 °C). Particularly, char-N showed a greater thermal stability in maize straw, while a much higher conversion ratio of NOx precursors-N was observed from maple wood pyrolysis than that of maize straw. These results could provide some guidances on the control of NOx emissions from biomass energy utilization.

CO2 pyrolysis kinetics and characteristics of lignin-rich hydrolysis residue produced from a tandem process of steam-stripping and acid hydrolysis

High-value utilization of lignin-rich hydrolysis residue (LIHS) from sustainable aviation fuel pilot system by pyrolysis under CO2 atmosphere was proposed to co-produce the carbon-based products in order to improve the techno-economic level and low carbon dioxide emission. Thermal decomposition characteristics and kinetics of the LIHS under CO2 atmosphere was for the first time investigated by using the distributed activation energy models with distributed-free and distributed-fitting methods. The thermal decomposition process of lignin-rich hydrolysis residue in CO2 atmosphere can be divided into drying, devolatilization, carbonization and carbon-loss stages. A middle difference method with variable step was developed for the approximation of the differential term in the Friedman method. The values of activation energy and pre-exponential factor at selected conversion degrees were obtained. The kinetic compensation effect between activation energy and pre-exponential factor was found. The mean activation energy was estimated based on the Maximum Likelihood Estimation. The effective values of the standard deviation and pre-exponential factor were determined by inverse problem method that combines Gauss–Hermite quadrature numerical method and Pattern Search Method (PSM) optimization algorithm. The results showed that the mean activation energy, the standard deviation and pre-exponential factors for the integral method are 261.26 kJ mol−1, 28.760 kJ mol−1 and 1017.658 s−1, those for differential method are 271.36 kJ mol−1, 29.910 kJ mol−1 and 1018.418 s−1. The unavailability of activation energy distributed function for distributed-free method may lose its prediction ability. Finally, the developed distributed activation energy model with distributed-fitting method not only could obtain the real kinetic parameters of the LIHS pyrolysis process, and have a good ability on predicting the reaction process. This work may provide an alternative technical scheme for the non-thermal valorization of the LIHS, and a comprehensive and systematic kinetic analysis of the thermal decomposition of the LIHS for process design.

Experimental Study to Replicate Wood Fuel Conversion in a Downdraft Gasifier: Features and Mechanism of Single Particle Combustion in an Inert Channel

Downdraft gasification is a promising process of energy conversion of wood biomass. There are such fuel conversion conditions that differ favorably from conventional conditions. In such conditions, there is no pyrolysis zone in the fuel bed, which precedes the oxidation zone. Fuel is supplied into the oxidizing zone without charring, where it reacts with the intensive cold air flow from tuyeres. The study aims to replicate the conversion of particles in a gasifier close to tuyeres. For this purpose, the individual particles are burned in the muffle furnace space and the quartz channel replicating presence of other bed particles at a first approximation. In the experiment, the furnace temperature was varied, as well as the velocity of air supplied to the particle. Two-stage and single-stage mechanisms of particle combustion were identified. A two-stage process is observed in the range of tuyere velocities below 20 m s−1. The two-stage mechanism is characterized by a stage of devolatilization and volatiles combustion, followed by a stage of char residue combustion. The stages are predominantly separate from each other, and their degree of overlapping is low, amounting to 24%. At the tuyere velocities above 125 m s−1 combustion of particles is realized primarily as a single-stage process. The intensive air flow reaches the fuel particle surface and initiates combustion of the surface char layer. In this case, the stages of devolatilization and char residue combustion run concurrently for the most part. In the single-stage mechanism, the degree of stage overlapping is significantly higher and amounts to 60–95%. For the two-stage combustion mechanism, the effect of cyclic movement of the flame across the particle surface is evident. The number of cycles can reach eight. This effect is due to the change of conversion stages. At air velocity above 95 m s−1, fragmentation of fuel particles commences. A layer of char formed at an initial stage of burning heats up in the intensive air flow and is separated from the particle surface. The heated walls of the quartz channel contribute to the intensification of particle combustion. This effect is probably due to the swirling of the flame between the wall and the particle surface.

Thermodynamics Simulation Performance of Rice Husk Combustion with a Realistic Decomposition Approach on the Devolatilization Stage

The high calorific value of rice husk and rich silica content in rice husk ash make its valorization becomes attractive. This study presents the thermodynamics simulation performance of rice husk combustion using a realistic decomposition approach. A non-ideal gas approach and fugacity coefficient were also considered in the calculation. In this study, devolatilization of rice husk is simulated to form gas (64.78%), liquid/tar (7.28%), solid/char (27.94%), and all of these are then oxidized with 100% excess air to form flue gas. From the calculation, about 2.6 MJ/kg of specific combustion energy is produced. The maximum combustion temperature in the furnace is up to 1457 °C for perfect insulation and up to 1400 °C if there is a 5% heat loss due to radiation. Furthermore, the thermodynamics simulation expressed that NOX emission amount from rice husk combustion is negligible and there is still a probability for CO and H2 to be produced at above 500 °C due to Boudouard reaction and homogeneous water gas shift reaction (WGSR). It is found that combustion equipped with larger excess air could quench the heat produced and reduce the combustion efficiency but could maintain the temperature at 700 °C. Supplying excess air of about 180–200% is advantageous to keep the combustion temperature at 700 °C to avoid silica crystalline formation which harms human health, as well as suppressing NOX emission and reducing CO emission from the simultaneous reaction of Boudouard-WGSR. Finally, the study concluded that a realistic decomposition approach could predict the rice husk combustion performance with reasonable and logical results.Graphical Abstract

Chemical Composition and Thermogravimetric Behaviors of Glanded and Glandless Cottonseed Kernels.

Common “glanded” (Gd) cottonseeds contain the toxic compound gossypol that restricts human consumption of the derived products. The “glandless” (Gl) cottonseeds of a new cotton variety, in contrast, show a trace gossypol content, indicating the great potential of cottonseed for agro-food applications. This work comparatively evaluated the chemical composition and thermogravimetric behaviors of the two types of cottonseed kernels. In contrast to the high gossypol content (3.75 g kg−1) observed in Gd kernels, the gossypol level detected in Gl kernels was only 0.06 g kg−1, meeting the FDA’s criteria as human food. While the gossypol gland dots in Gd kernels were visually observed, scanning electron microcopy was not able to distinguish the microstructural difference between ground Gd and Gl samples. Chemical analysis and Fourier transform infrared (FTIR) spectroscopy showed that Gl kernels and Gd kernels had similar chemical components and mineral contents, but the former was slightly higher in protein, starch, and phosphorus contents. Thermogravimetric (TG) processes of both kernels and their residues after hexane and ethanol extraction were based on three stages of drying, de-volatilization, and char formation. TG-FTIR analysis revealed apparent spectral differences between Gd and Gl samples, as well as between raw and extracted cottonseed kernel samples, indicating that some components in Gd kernels were more susceptible to thermal decomposition than Gl kernels. The TG and TG-FTIR observations suggested that the Gl kernels could be heat treated (e.g., frying and roasting) at an optimal temperature of 140–150 °C for food applications. On the other hand, optimal pyrolysis temperatures would be much higher (350–500 °C) for Gd cottonseed and its defatted residues for non-food bio-oil and biochar production. The findings from this research enhance the potential utilization of Gd and Gl cottonseed kernels for food applications.

Pyrolytic characteristics of fine materials from municipal solid waste using TG-FTIR, Py-GC/MS, and deep learning approach: Kinetics, thermodynamics, and gaseous products distribution

Fine materials (FM) from municipal solid waste (MSW) classification require disposal, and pyrolysis is a feasible method for the treatments. Hence, the behavior, kinetics, and products of FM pyrolysis were investigated in this study. A deep learning algorithm was firstly employed to predict and verify the TG data during the process of FM pyrolysis. The results showed that FM pyrolysis could be divided into drying (<138 °C), de-volatilization (138–570 °C), and decomposition stage (≥570 °C above). The de-volatilization can further be divided into stage 2 and stage 3, with values of activation energy estimated by Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose methods as 123.35 and 172.95 kJ/mol, respectively. The gas products like H2O, CO2, CH4, and CO, as well as functional groups like phenols and carbonyl (CO), were all detected during the process of FM pyrolysis by thermogravimetric-fourier transform infrared spectrometry at a heating rate of 10 °C/min. The main species detected by pyrolysis-gas chromatography-mass spectrometry analyzer included acid (41.98%) and aliphatic hydrocarbon (22.44%). Finally, the 1D–CNN–LSTM algorithm demonstrated an outstanding generalization capability to predict the relationship between FM composition and temperature, with R2 reaching 93.91%. In sum, this study provided a reference for the treatment of FM from MSW classification as well as the feasibility and practicability of deep learning applied in pyrolysis.

Construction and Demolition Waste-Derived Feedstock: Fuel Characterization of a Potential Resource for Sustainable Aviation Fuels Production

Detailed characterization of physical and fuel properties of construction and demolition waste (CDW) can support research and commercial efforts to develop sustainable aviation fuels. The current study reports time-series data for bulk density, mineral composition, reactivity, and fuel properties (proximate analysis, ultimate analysis, heating value and ash fusibility) of the combustible material fraction of samples mined from an active CDW landfill on the island of Oʻahu, Hawaiʻi. The fuel properties are in ranges comparable to other reference solid wastes such as demolition wood, municipal solid wastes, and landfilled materials. Ash fusion temperatures (from initial deformation to fluid deformation) among the samples were found to lie in a narrow range from 1,117 to 1,247°C. Despite higher ash contents, the CDW derived feedstock samples had comparable heating values to reference biomass and construction wood samples, indicating the presence of higher energy content materials (e.g., plastics, roofing material, etc.) in addition to wood. The waste samples show lower reactivity peaks in the devolatilization stage, but higher reactivity peaks (located at lower temperatures) in the gasification and combustion stage, compared with those of reference biomass and construction woods. Mineral elemental analysis revealed that materials from various sources (gypsum, plastic, rust, paint, paint additives, and soils) were present in the samples. Soil recovered from the landfill contained higher Ca, Cu, Fe, K, Mn, Pb, and Zn levels than soil samples from elsewhere on the island. Results from this study can provide insight on variations in the physical and fuel properties of the CDW derived feedstocks, and support the design of conversion systems.

Thermogravimetric pyrolysis of onion skins: Determination of kinetic and thermodynamic parameters for devolatilization stages using the combinations of isoconversional and master plot methods

Thermogravimetric pyrolysis of onions skins was studied thoroughly for the first time. Kinetic calculations of devolatilization stages were performed applying direct Arrhenius plot (DAP) method and combinations of isoconversional and Criado’s Z(α) master plot (CZMP) methods. The kinetic parameters calculated using combined methods were utilized successfully to reproduce the experimental kinetic curves whereas those calculated using DAP method failed in this sense. The average Ea values of isoconversional methods were between 164.0 and 172.0 kJ/mol. The CZMP method yielded multiple F-type reaction mechanisms. The simplified kinetic models of combined methods were also developed by using single reaction mechanisms deduced from multiple reaction mechanisms. The Friedman-CZMP combination was the best option for developing simplified/unsimplified kinetic models. Determination of reaction mechanism using DAP method by searching for the highest R2 value of regression equation among several candidates was found unreliable. ΔH, ΔG and ΔS values were calculated for 10 °C/min heating rate.

Thermogravimetric and kinetic analyses of the Skeletonema costatum microalgae combustion using the fitting method

This work was intended to understand the potential of Skeletonema costatum (S. costatum) microalgae being the solid biofuel feedstock by studying its combustion behavior under a thermogravimetric analyzer (TGA). The following parameters were used during the experiment: about 5 mg of weighed sample was put into a ceramic crucible; the atmospheric air of 100 ml/min was flowed to the chamber to ensure sufficient combustion air; heating was escalated with a rate of 10 °C/min, and combustion was performed at a temperature range from 30 °C to 1200 °C. The results showed that the combustion process of S. costatum microalgae could be divided into four stages of decomposition, including the evaporation stage of moisture content from a temperature of 31.68 °C to 150.93 °C, the devolatilization stage from a 150.93 °C to 505.053 °C, the stage of char combustion from a 505.053 °C to 1018.15 °C and the final stage of ash decomposition from 1018.15 °C to 1200 °C. The kinetic parameters were calculated in the 1st, 2nd, and 3rd stages based on the fitting model of the Coats-Redfern method by selecting reaction mechanisms. The activation energy values for 1st, 2nd, and 3rd stages were 71.18; 39.49, and 56.92 kJ/mol, respectively, and correlation coefficients (R2) of 0.959; 0.988, and 0.978, respectively in the Chemical Reaction Order models.

Detailed kinetic mechanism of devolatilization stage and CFD modeling of downdraft gasifiers using pelletized palm oil empty fruit bunches

Oil palm residues, such as palm oil empty fruit bunches (PEFBs), are typically abandoned due to high moisture and bulky. Pelletization and downdraft gasification constitute a promising solution for small-scale power and heat production. In this study, the two-dimensional, steady-state computational fluid dynamics (CFD) model of a modified Imbert downdraft gasifier consuming pelletized PEFBs is developed. The detailed kinetic mechanism of biomass devolatilization coupled with particle-scale transport equations is incorporated to enable accurate prediction of the pyrolysis zone in the gasifier. Pelletized-biomass-particles packed bed is simulated by using a porous media model with volumetric species-transport CFD model, which is validated by comparing the prediction of the species volume fractions at the gas outlet with published experimental data. Velocity and temperature profiles of the downdraft gasifier are revealed, along with tar evolution pathline. The effect of the equivalence ratio on the producer gas composition, tar concentration, and cold gas efficiency is investigated. The optimum equivalence ratio is found at 0.30 based on the tar concentration of 5 mg Nm−3 and the cold gas efficiency of 62%.