Mild Pyrolysis Research Articles

Pre-combustion mercury removal potential of rapid pyrolysis in high ash coal and mode of occurrence

Mercury is a widely known pollutant, and coal combustion is one of the largest sources of anthropogenic Hg emission. Mercury reduction technologies globally rely on flue gas treatment. However, pre-combustion techniques show immense potential. Mild pyrolysis of coal offers a promising approach for mitigating mercury emissions. This study investigated the mercury distribution and its mode of occurrence in six high ash coal samples from the Jagannath area of eastern India. The findings revealed that Hg content in coal samples ranged from 0.154-0.308 mg/kg. Majority of the mercury was bound to pyrites (60–90 %) and organic matter (5–15 %). Rapid pyrolysis at temperatures ranging from 200 to 700 °C demonstrated significant mercury removal efficiency (up to 95 %). In particular, at 400 °C with minimal loss in calorific value and mass. Though the high-temperature pyrolysis (600 °C) resulted in maximum mercury removal, but with a notable loss in calorific value and product yield. The Hg content in raw coal, initially ranging from 9 to 20 μg Hg/MJ, was reduced to 3 to 11 μg Hg/MJ in char produced at 400 °C. Further reduction was observed in char produced at 600 °C, where the Hg content decreased to between 2–3 μg Hg/MJ. This research emphasizes the effectiveness of mild pyrolysis in reducing mercury content of high ash coal, thereby facilitating the generation of cleaner energy.

Study of products derived from the microwave-assisted thermal degradation of high-moor peat

Peat reserves are of great interest for various industries (energy, fuel, chemical, etc.). It is common practice to use pyrolysis to process such solid carbon-containing resources with the subsequent yield of fuel and valuable products. One of the environmentally and energetically favorable ways to degrade carbon-containing feedstock that is currently under development is microwave-assisted pyrolysis. Microwave radiation provides volumetric heating of the material, which significantly increases heating uniformity across the volume of the irradiated sample, providing greater efficiency of heat transfer and avoiding local overheating on the reactor surface. In the conducted study, a system was designed for the microwave processing of organic materials. The structural elements of the system are described, and a schematic showing pyrolysis product separation is presented. A prototype of the developed reactor was used to conduct experiments on degrading high-moor sphagnum peat of the Greko-Ushakovskoe deposit under mild pyrolysis conditions induced by microwave radiation. The component composition of reaction products was analyzed via chromatography-mass spectrometry and compared with the results of previous experiments using conventional thermal pyrolysis. More advanced processing of peat is performed under the conditions of microwave-assisted mild pyrolysis with a high yield of valuable products due to a more efficient heat transfer, uniform heating of the material, and the optimal reaction rate. The developed technology is shown to produce raw materials for a wide range of high-tech industrial productions. The prospects for the industrial use of the proposed microwave-assisted peat processing technology are discussed, specifically for the production of efficient hydrophobic sorbent.

UV photodegradation of methylene blue using microstructural carbon materials derived from citrullus colocynthis

A low temperature aqueous growth followed by mild pyrolysis was used in this study to synthesize high-quality carbonized materials from the deserted plant Citrullus Colocynthis. It was found that the carbon material prepared for this study contained an abundance of functional groups and surface active sites. A few microns were evidently the size of the carbon material. This study investigated a variety of photocatalytic performance evaluation parameters, including initial dye concentration of methylene blue, pH effect on dye solution, scavenger stability, and recycle stability via irradiating UV light. Methylene blue degradation was found to be significantly affected by pH and concentration of the dye solution. It has been found that pH five is the most effective pH for the removal of dyes. As a result of the study, we found that methylene blue decays according to pseudo first order kinetics and is estimated to remove dye at an almost 100% rate.

Characteristics of carbon black recycled from lightly pyrolyzed tire rubber and its impact on the high-temperature performance of asphalt

Waste cooking oil (WCO) is commonly used as an excellent reaction medium for the mild pyrolysis of ground tire rubber (GTR). Carbon black is a byproduct of rubber pyrolysis with varying properties depending on the pyrolysis process. To promote the utilization of pyrolytic carbon black (CBp) in asphalt modification, this study aims to characterize the low-temperature pyrolysis carbon black (LTCB) produced through the co-pyrolysis of GTR and WCO, and assess its impact on the high-temperature performance of asphalt. LTCB260 was separated by toluene extraction from the waste rubber-oil mixtures (WRO) containing the highest concentration of soluble substances. The identification of LTCB260 was conducted by thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The results indicated that the pure carbon black content in LTCB260 is 57.35 %, which is lower than CBp and N330. Bound rubber and inorganic salt crystals were observed to be randomly distributed on the surface of LTCB260. High-temperature performance tests conducted on asphalt indicated that the high-temperature deformation resistance of the LTCB260-modified asphalt was comparable to that of the other two carbon black-modified asphalts when using the same mass of carbon black. This suggests that despite being coated with impurities on its surface, the carbon black released from lightly pyrolyzed ground tire rubber still positively influences the high-temperature rheological properties of asphalt. However, when the carbon black content in WRO is significantly lower than that of the light component, the beneficial effect of carbon black on the high-temperature performance of asphalt may not be evident.

Augmenting Neutrophil Extracellular Traps with Carbonized Polymer Dots: A Potential Treatment for Bacterial Sepsis.

Sepsis is a life-threatening condition that can progress to septic shock as the body's extreme response to pathogenesis damages its own vital organs. Staphylococcus aureus (S. aureus) accounts for 50% of nosocomial infections, which are clinically treated with antibiotics. However, methicillin-resistant strains (MRSA) have emerged and can withstand harsh antibiotic treatment. To address this problem, curcumin (CCM) is employed to prepare carbonized polymer dots (CPDs) through mild pyrolysis. Contrary to curcumin, the as-formed CCM-CPDs are highly biocompatible and soluble in aqueous solution. Most importantly, the CCM-CPDs induce the release of neutrophil extracellular traps (NETs) from the neutrophils, which entrap and eliminate microbes. In an MRSA-induced septic mouse model, it is observed that CCM-CPDs efficiently suppress bacterial colonization. Moreover, the intrinsic antioxidative, anti-inflammatory, and anticoagulation activities resulting from the preserved functional groups of the precursor molecule on the CCM-CPDs prevent progression to severe sepsis. As a result, infected mice treated with CCM-CPDs show a significant decrease in mortality even through oral administration. Histological staining indicates negligible organ damage in the MRSA-infected mice treated with CCM-CPDs. It is believed that the in vivo studies presented herein demonstrate that multifunctional therapeutic CPDs hold great potential against life-threatening infectious diseases.

Iron oxyhydroxide catalyzes production of artificial humic substances from waste biomass

Production of artificial humic substances (AHS) from waste biomass will contribute to environmental protection and agricultural productivity. However, there is still a lack of a faster, more efficient and eco-friendly way for sustainable production. In this study, we proposed a method to accelerate the production of AHS from cotton stalks by mild pyrolysis and H2O2 oxidation in only 4 hours, and investigated the formation of AHS during biomass transformation. We found that the process increased the aromatic matrix and facilitated biomass transformation by enhancing the depolymerization of lignin into micromolecular phenolics (e.g., guaiacol, p-ethyl guaiacol, etc.). The optimum conditions of pyrolysis at 250 °C and oxidation with 6 mL H2O2 (5 wt%) yielded up to 19.28 ± 1.30 wt% artificial humic acid (AHA) from cotton stalks. In addition, we used iron oxyhydroxide (FeOOH) to catalyze biomass transformation and investigated the effect of FeOOH on the composition and properties of AHS. 1.5 wt% FeOOH promoted the increased content of artificial fulvic acid (AFA) in AHS from 10.1% to 26.5%, eventually improving the activity of AHS. FeOOH raised the content of oxygen-containing groups, such as carboxylic acids and aldehyde, and significantly increased polysaccharide (10.94%–18.95%) and protein (1.95%–2.18%) derivatives. Polymerization of amino acid analogs and many small-molecule carbohydrates (e.g., furans, aldehydes, ketones, and their derivatives) promoted AFA formation. Finally, carbon flow analysis and maize incubation tests confirmed that AHS were expected to achieve carbon emission reductions and reduce environmental pollution from fertilizers. This study provides a sustainable strategy for the accelerated production of AHS, which has important application value for waste biomass resource utilization.

Catalytic effect of metal salts on deoxygenation and aromatization reaction during pressurized pyrolysis of corncob waste at mild temperatures

Converting biomass to high quality bio-char with high carbon solidification at low energy consumption can greatly promote the application of biomass to alternative coal. Metal salts have been confirmed to enhance carbonization and dehydration during traditional pyrolysis and hydrothermal conversion, whereas the catalytic deoxygenation and aromatization mechanisms during dry mild pyrolysis in the presence of pressure are currently unclear. A mild gas-pressurized pyrolysis assisted by metal salts catalysts at 200–300 °C was proposed in this work. The effects of catalysts on three-phase products as well as synergistic catalytic reaction mechanism were studied. Results indicated that CaCl2, ZnCl2 promoted carbon fixation rates by 19.77 % and 26.89 %, and ZnCl2, KCl could remove oxygen content by 11.45 % and 6.56 % (wt.%, dry ash free basis). ZnCl2 exhibited the best deoxygenation and aromatization effect. With ZnCl2 catalysis at 280 °C, the volatile content reduced to 37.25 %, and O/C, H/C values decreased by 19.05 % and 11.25 %, achieving coking coal-like quality. FTIR and NMR results implied that oxygen-containing functional groups were removed even more rapidly under the catalysis of ZnCl2, facilitating the rearrangement of O-alkyl C and aliphatic C into aromatic C, exhibiting a higher aromatization degree in semi-char. Moreover, CH4 and H2 increased in gas products catalyzed by ZnCl2, while C2H4 and C2H6 decreased. Pressure inhibited the escape of small molecule gas volatiles, making them easily adsorbed on surfaces of molecular structures for secondary reactions. Under the action of the [ZnOZn]2+ acid sites, alkanes underwent dehydrogenation activation to yield H2, and demethylation activation to generate CH4, followed by cyclization reaction. The upgrading promotions of biomass were caused by the synergistic effect of pressure and ZnCl2 catalysis.

Impact of pelletisation on torrefied oil palm empty fruit bunch biochar

This study investigates the impact of pelletisation on the properties and performance of torrefied oil palm empty fruit bunch (EFB) biochar. Torrefaction, a mild pyrolysis process, enhances the energy density and durability of biomass, creating a more stable biochar product. Pelletisation, involving the compression of biochar into pellets, aims to improve its handling, transportation, and application efficiencies. This study examines key parameters such as the effects of pelletisation pressure, temperature, and the use of binders on the physical and chemical properties of torrefied EFB biochar. Evaluations include changes in density, bonding properties, and calorific value. Additionally, the study explores how pelletisation influences the biochar’s porosity, surface area, and elemental composition. Results indicate that pelletisation significantly affects the structural integrity and functional properties of torrefied EFB biochar. Pellets exhibit enhanced bulk density and durability, which are beneficial for storage and transport. However, some reduction in surface area and porosity is observed, potentially impacting the biochar’s effectiveness in applications such as soil amendment and carbon sequestration. Findings suggest that while pelletisation offers practical advantages, optimizing the process parameters is crucial to maintain the beneficial properties of torrefied EFB biochar. Overall, this study provides comprehensive insights into the trade- offs associated with pelletising torrefied EFB biochar, highlighting the potential for improved usability in sustainable agriculture and environmental management practices. Future work should focus on refining pelletisation techniques to balance mechanical benefits with the preservation of biochar’s functional attributes.

Optimized Synthesis of FeNi/TiO2 Green Nanocatalyst for High-Quality Liquid Fuel Production via Mild Pyrolysis

In sustainable energy improvement, the strategic design of economical nanocatalysts has emerged as a pivotal pathway, notably within intricate processes such as asphalt pyrolysis. This study presents a new endeavor, conceptualizing a non-precious metal nanocatalyst FeNi deposited on TiO2, synthesized through an environmentally conscious green synthesis methodology employing mangosteen peel extract as a sustainable reductant. Asphalt, the most complex compound, is used as the pyrolyzed material to measure the activity of nanocatalysts in mild pyrolysis. In this study, the synthesis of the nanocatalyst and pyrolisis are optimized. The research outcomes reflect a notable work towards efficiency enhancement. Initial investigations showcased the highest values before optimization for nanocatalyst synthesis, oil yield, and calorific value, which are 63.23%, 50.78%, and 10684 cal/g, respectively. However, these values increase significantly after optimization to 68.44%, 53.72%, and 10775 cal/g, respectively. Careful validation endeavors have underscored the closeness, manifesting slight errors of 2.52%, 1.86%, and 0.36% for catalyst yield, oil yield, and calorific value, respectively. This validation features the reliability of the research findings. Intriguingly, the GC-MS analysis establishes compelling parallels in composition between the derived product and conventional diesel fuel. The minimal errors and the analogous composition to diesel fuel present a promising trajectory. The results obtained from this study contribute to the development of greener and more efficient energy production technologies, paving the way for a sustainable and eco-friendly approach to utilizing energy resources.

Encapsulation of carbon-nanodots into metal-organic frameworks for boosting photocatalytic upcycling of polyvinyl chloride plastic

Although polyvinyl chloride (PVC) ranks as the third most mass-produced synthetic plastic, the chemical upcycling of non-biodegradable PVC waste remains a significant challenge. Herein, carbon nanodots combined with the metal-organic framework (CDs/Zr-MOF) are fabricated for photocatalytic upcycling of PVC. Specifically, the ultra-small-sized CDs (∼2.0 nm) are encapsulated into Zr-MOF pores via a mild pyrolysis strategy. The maintained MOF structure facilitates charge/mass transfer and improves the surface-to-volume ratio of active sites of CDs. The CDs/Zr-MOF exhibits high activity for PVC conversion of ∼76.5% towards acetic acid with a yield of ∼14%. The mechanism investigation indicates the generated •OH radicals can efficiently trigger cleavage of C-Cl/C-C bonds of PVC. Moreover, the reduction of the energy barrier for the hydroxylation reaction as a rate-limiting step contributed to improved PVC conversion performance. This work offers a feasible method for fabricating nanoparticle-embedded MOF-based photocatalysts and provides new insights into the chemical upcycling of plastics.

Mild pyrolysis of cotton coated with graphene-like materials as a method to produce superhydrophobic and highly absorptive oil sorbents

In recent years, hydrophobized cellulose-based materials have been proposed as oil spill sorbents. We investigate the possibility of using cheap, industrialgrade, graphene-like materials (GM), such as graphite flakes (GrF), exfoliated graphene nanoplatelets (xGNP) and microwave-plasma turbostratic graphene nanoplatelets (mGNP) as hydrophobic agents for naturally hydrophilic cotton. From among investigated GM, mGNP showed the highest ability to form superhydrophobic coating due to small flake size and small amount of impurities. Furthermore, we showed that mild pyrolysis not only makes cotton more hydrophobic, but also increases its sorption capacity towards organic solvents and oils. Pyrolyzed and coated with mGNP and xGNP cotton showed exceptional superhydrophobic properties and water contact angle equal 148° and 142°, respectively, besides the sorption capacity towards motor oil of 46 g/g and 51 g/g, respectively. What is more important, the price of graphene oxide used in previous research is still very high (approx. 100 $/g), while the price of xGNP and mGNP is 0.45 $/g, 7.3 $/g, respectively. This difference may be crucial for the implementation of graphene-based sorbents in the remediation of massive oil spill remediation.

In Situ Hybridization of Polymeric Curcumin to Arginine-Derived Carbon Quantum Dots for Synergistic Treatment of Bacterial Infections.

Effective infectious keratitis treatment must eliminate the pathogen, reduce the inflammatory response, and prevent persistent damage to the cornea. Infectious keratitis is generally treated with broad-spectrum antibiotics; however, they have the risk of causing corneal epithelial cell damage and drug resistance. In this study, we prepared a nanocomposite (Arg-CQDs/pCur) from arginine (Arg)-derived carbon quantum dots (Arg-CQDs) and polymeric curcumin (pCur). Partial carbonization of arginine hydrochloride in the solid state by mild pyrolysis resulted in the formation of CQDs, which exhibited enhanced antibacterial activity. pCur was formed by the polymerization of curcumin, and further crosslinking reduced its cytotoxicity and improved antioxidative, anti-inflammatory, and pro-proliferative activities. The pCur in situ conjugated with Arg-CQDs to form the Arg-CQDs/pCur nanocomposite, which showed a minimum inhibitory concentration of ca. 10 μg mL-1, which was >100-fold and >15-fold lower than that of the precursor arginine and curcumin, respectively, against Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. The Arg-CQDs/pCur nanocomposite with combined antibacterial, antioxidative, anti-inflammatory, pro-proliferative properties, and long-term retention on cornea enabled synergistic treatment of bacterial keratitis. In a rat model, it can effectively treat P. aeruginosa-induced bacterial keratitis at a concentration 4000-fold lower than the commercially used drug, Sulmezole eye drops. Arg-CQDs/pCur nanocomposites have great potential for application in antibacterial and anti-inflammatory nanoformulations for clinical use to treat infectious diseases.

Tannic Acid-Derived Carbon Coating on LiFePO4 Nanocrystals Enables High-Rate Cathode Materials for Lithium-Ion Batteries

Tannic acid (TA) is a plant polyphenol capable of coating hydrothermally grown LiFePO4 nanocrystals by simple wet impregnation and drying. Mild pyrolysis in an inert atmosphere transforms the TA coating on LiFePO4 nanocrystals into homogeneous and compact carbon films. Introducing conductive carbon films on LiFePO4 nanocrystals increases the electrical conductivity of the LiFePO4/C composite. However, reaction kinetics revealed that excessively thick carbon films limit the Li+ diffusivity of the LiFePO4/C composite during delithiation/lithiation. Therefore, the electrical conductivity and Li+ diffusivity must be balanced to achieve the required electrochemical properties.

Torrefaction of Pine Using a Pilot-Scale Rotary Reactor: Experimentation, Kinetics, and Process Simulation Using Aspen Plus™

Biomass is an excellent sustainable carbon neutral energy source, however its use as a coal/petroleum coke substitute in thermal applications poses several challenges. Several inherent properties of biomass including higher heating value (HHV), bulk density, and its hydrophilic and fibrous nature, all contribute to challenges for it to be used as a solid fuel. Torrefaction or mild pyrolysis is a well-accepted thermal pretreatment technology that solves most of the above-mentioned challenges and results in a product with superior coal-like properties. Torrefaction involves the heating of biomass to moderate temperatures typically between 200 °C and 300 °C in a non-oxidizing atmosphere. This study focused on evaluating the influence of torrefaction operating temperature (204–304 °C) and residence time (10–40 min) on properties of pine. Tests were performed on a continuous 0.3 ton/day indirectly heated rotary reactor. The influence of torrefaction operational conditions on pine was evaluated in terms of the composition of torrefied solids, mass yield, energy yield, and HHV using a simulated model developed in Aspen Plus™ software. A kinetic model was established based on the experimental data generated. An increase in torrefaction severity (increasing temperature and residence time) resulted in an increase in carbon content, accompanied with a decrease in oxygen and hydrogen. Results from the simulated model suggest that the solid and energy yields decreased with an increase in temperature and residence time. Solid yield varied from 80% at 204 °C to 68% at 304 °C, and energy yield varied from 99% at 204 °C to 70% at 304 °C, respectively. On the other hand, HHV improved from 22.8 to 25.1 MJ/kg with an increase in temperature at 20 min residence time. Over the range of 10 to 40 min residence time at 260 °C, solid and energy yields varied from 77% to 59% and 79% to 63%, respectively; however the HHV increased by only 3%. Solid yield, energy yield, and HHV simulated data were within the 5% error margin when compared to the experimental data. Validation of the simulation parameters was achieved by the conformance of the experimental and simulation data obtained under the same testing conditions. These simulated parameters can be utilized to study other operating conditions fundamental for the commercialization of these processes. Desirable torrefaction temperature to achieve the highest solid fuel yield can be determined using the energy yield and mass loss data.

Production of Low-Mercury Solid Fuel by Mild Pyrolysis Process

Mercury is considered one of the most harmful ecotoxic elements. A main source of its anthropogenic emissions is fuel combustion. For fuels with a high mercury content, costly methods are required to remove mercury from the flue gases. The solution to this problem is to remove mercury from the fuel before combustion. This can be achieved by a mild pyrolysis process. Solid fuel samples with relatively high mercury content were examined. These included waste (refuse-derived fuel, paper, sewage sludge, and rubber), waste wood biomass (hornbeam leaves, pine and spruce bark), and six coal. The mild pyrolysis process was performed at 300 °C in an argon flow of 500 cm3/min. The residence time was 30 min. Proximate and ultimate analysis (including mercury content) was conducted for raw fuels and chars. The process allowed a significant reduction in mercury content from 36 to 97%. Mercury was most easily removed from biomass and waste with the most difficult being from coal. The effectiveness of mercury removal was determined by the type of fuel and its mercury content. The mercury content in the obtained chars was 0.05–3.4 µg Hg/MJ. The use of such chars will meet current EU emission standards and those to be introduced in the future.

Evaluation of oil palm waste mild pyrolysis kinetic parameters

With the goal of contrasting model-fitting and model-free methods for the kinetics of mild pyrolysis for empty fruit bunches (EFB), EFB were thermal decomposed and the profile was analysed using thermalgravimetric analysis (TGA). Coats-Redfern (CR) and Kissinger-Akahira-Sunose (KAS) methods were selected to represent model-fitting and model-free methods respectively. The activation energies (Ea) calculated for CR ranged between 22.45 and 26.31 kJ mol−1 (regression coefficient, R2 of 0.93 to 0.95) while the average Ea for KAS was 3.98 kJ mol−1. Compared with other typical model fuels, the mild pyrolysis of EFB from this work shows higher thermal instability, hence more reactive compared to previous works. Furthermore, the KAS method is more reliable in representing the mild pyrolysis process due to its higher overall regression coefficients showing that the assumptions of the KAS method are more accurate.

Processing and characterization of ultra-high temperature ceramic matrix composites via water based slurry impregnation and polymer infiltration and pyrolysis

Uncoated PAN-based carbon fibre-reinforced ultra-high temperature ceramic matrix composites via aqueous ZrB 2 powder-based slurry impregnation coupled with mild polymer infiltration and pyrolysis, using allylhydrido polycarbosilane as source of amorphous SiC(O), were manufactured. To demonstrate the versatility of the process to realize tailored materials, unidirectional (UD), two dimensional (2D) and needle-punched (2.5D) cloths were impregnated. Microstructure and mechanical properties were investigated and correlated with fibre properties and architecture. The flexural strength was found over 250 MPa for unidirectional reinforced material, while the modulus exceeded 250 GPa for needle-punched one. The homogeneous distribution of UHTC phase around each single fibre and the weak fibre/matrix interface, due to the mild pyrolysis conditions, are the hallmark of this process and the key to improve durability and performance of materials for extreme environments without the application of expensive coating on fibres.

Green synthesis of gardenia seeds-based carbon dots for bacterial imaging and antioxidant activity in aqueous and oil samples.

In this work, luminescent carbon dots with gardenia seeds as carbon precursors (GCDs) were synthesized using a one-step mild pyrolysis process and were then used as probes for imaging of bacterial (Escherichia coli). The GCDs showed a strong emission at 430 nm when excited at 370 nm. The relative fluorescence quantum yield of GCDs was found to be 1.13% in an aqueous medium. Rapid internalization of the GCDs by bacteria was confirmed by three colors (blue, green, and yellow) images that were obtained using confocal fluorescence microscopy. In addition, GCDs were noted to exhibit potent scavenging activities against DPPH˙, ˙OH, and ˙O2- free radicals. GCDs were also assayed as antioxidants in an oil sample by volumetric determination of the peroxide value. Thus, GCDs exhibited good antioxidant properties both in aqueous and oil media. In addition, a free fatty acid quantification kit in the presence of GCDs showed enhanced fluorescence detection of palmitic acid with a remarkably good limit of detection of 0.08 μM, which is lower than that in the absence of GCDs (0.76 μM). The proposed fluorescence method was then successfully used to determine the concentration of palmitic acid spiked in milk powder samples, with spiked recoveries of 82.6-109.6% and relative standard deviations of 0.9-4.6%.

Combustion and Explosion Characteristics of Pulverised Wood, Valorized with Mild Pyrolysis in Pilot Scale Installation, Using the Modified ISO 1 m3 Dust Explosion Vessel

Biomass is a renewable energy source with great potential worldwide and in the European Union. However, valorization is necessary to turn many types of waste biomass into a tradable commodity that has the potential to replace coal in power plants without significant modifications to firing systems. Mild pyrolysis, also known as torrefaction, is a thermal valorization process of low-quality biomass that could be suitable for such a purpose. In this work, typical Spruce-Pine-Fir residues from a sawmill were tested in terms of the explosion and flame propagation properties. The ISO 1 m3 dust explosion vessel was used, with a modified and calibrated dust dispersion system that could cope with very coarse particles. The deflagration index, Kst, was higher for the torrefied sample, with a peak at 36 bar m/s compared with 27 for the raw biomass. The peak flame speeds were similar for both samples, reaching 1 m/s. The peak Pmax/Pi was between 7.3 and 7.4 bar for both untreated and torrefied biomass. The mechanism for coarse particle combustion is considered to be influenced by the explosion-induced wind blowing the finer fractions ahead of the flame, which burns first, subsequently devolatilizing the coarser fractions.

Probabilistic multi-objective optimization of wood torrefaction conditions using a validated mechanistic model

This paper uses a comprehensive computational model to propose optimal wood torrefaction conditions by probabilistic optimization. Its main outcome is to propose tailor-made heat treatment conditions (temperature levels-duration of mild pyrolysis at temperature levels ranging from 200 to 300 °C) to meet users’ expectations in terms of overall mass loss, duration and homogeneity of treatment. To this purpose, beech wood boards were torrefied with a usual 3-steps treatment schedule (drying, heating and cooling) under contrasting configurations in a well-instrumented device. The heterogeneity of the treatment within the wood sample was assessed through X-ray attenuation profile and water vapour sorption isotherm. These results allowed the model to be validated. In particular, it predicts the evolution of the mass loss and internal temperatures with good accuracy, including the temperature overshot. The results highlight the need to adjust the heat treatment schedule to each input parameter such as the wood piece dimensions and its initial moisture content or density, in order to limit the effect of exothermic reactions. The torrefaction model was then embedded in a probabilistic optimization process. A case study demonstrates the ability of the model to propose an alternative 3-steps treatment schedule able to reach the target mass loss while controlling the temperature overshot within the wood piece.