Dry Torrefaction Research Articles

Effect of temperature on sawdust and sawdust pellets during dry and wet torrefaction

Dry torrefaction (DT) and wet torrefaction (WT) as pretreatment methods to prepare sawdust pellets show great potential for enhancing the quality of biomass pellets. However, few studies have focused on the comprehensive comparison and evaluation of DT and WT. Herein, the effects of DT (200°C–280°C) and WT (180°C–240°C) on the physicochemical properties of sawdust and sawdust pellets were investigated. The results showed that both pretreatment methods reduced the mass yield (92.67–84.33% for DT, 93.42–90.39% for WT) and energy yield (94.78–90.78% for DT, 93.42–92.20% for WT) of sawdust while increasing the higher heating value (17.79–18.73 MJ/kg for DT, 17.44–17.79 MJ/kg for WT). Fourier-transform infrared spectroscopy indicated that WT had a significant effect on the degradation of cellulose and hemicellulose compared with DT samples. Thermogravimetric analysis revealed that DT and WT efficiently reduced the residue (9.16–13.63% for DT, 10.22–10.91% for WT) and improved the stability of sawdust compared with untreated sawdust (13.70%). Sawdust pellets prepared by WT-180 and WT-200 exhibited enhanced hydrophobicity and pressure resistance. The WT-200 had the superior effect on the performance improvement of sawdust and sawdust pellets. This work offers insights into selecting appropriate pretreatment techniques to enhance the quality of biomass pellets and tackle logistics and transport challenges.

Machine learning models for predicting biochar properties from lignocellulosic biomass torrefaction

This study developed six machine learning models to predict the biochar properties from the dry torrefaction of lignocellulosic biomass by using biomass characteristics and torrefaction conditions as input variables. After optimization, gradient boosting machines were the optimal model, with the highest coefficient of determination ranging from 0.89 to 0.94. Torrefaction conditions exhibited a higher relative contribution to the yield and higher heating value (HHV) of biochar than biomass characteristics. Temperature was the dominant contributor to the elemental and proximate composition and the yield and HHV of biochar. Feature importance and SHapley Additive exPlanations revealed the effect of each influential factor on the target variables and the interactions between these factors in torrefaction. Software that can accurately predict the element, yield, and HHV of biochar was developed. These findings provide a comprehensive understanding of the key factors and their interactions influencing the torrefaction process and biochar properties.

Characterization and evaluation of torrefied sugarcane bagasse to improve the fuel properties

Torrefaction is a promising method of treatment with a prospect toward Physco-chemical improvement and thermal upgrading of biomass. In the present study, the torrefaction of sugarcane bagasse in both dry and chemical treatment in comparison with the physical, chemical, and thermal properties of raw bagasse was investigated. Thermochemical torrefaction was carried out by pretreatment of raw bagasse with dilute sulfuric acid. The torrefaction temperature was carried out at a carried temperature (220–280 °C) and a torrefaction period (30–120 min) in a packed bed reactor under an inert environment, whereas dry torrefaction was performed using the same treatment without the addition of a chemical to the raw bagasse. Chars produced by chemical torrefaction were found with improved properties of heating value, energy, and bulk density at 280 °C and 120 min. Increasing temperature resulting in high fixed carbon content apparently decreases moisture content and volatile matter. The mass yield and energy yield were found to be decreased with temperature and time. The carbon content of torrefied bagasse was increased with temperature and time, whereas, hydrogen and oxygen content decreased due to the devolatilization reactions. It was able to upgrade HHV from 16.05 to 20.34 MJ/Kg in dry and 22.29 MJ/Kg in chemical torrefaction.

Exploring the Properties of the Torrefaction Process and Its Prospective in Treating Lignocellulosic Material

The main objective of this review is to present the latest research results regarding the importance of the torrefaction process for different biomass materials in the last 12-year period. Despite the fact that the potential of renewable energy sources has been analyzed, research regarding that of energy derived from waste biomass still remains in the infancy state. Torrefaction is known to be one of the most effective methods for enhancing the energy efficiency of biomass. Among different types of torrefactions, the focus in this study is mostly on dry torrefaction. The influential factors, like temperature and residence time, and physico-chemical properties of torrefied products, and the prospective of torrefaction due to its reduced impact on environment, are discussed in-depth. This review provides valuable insights into the torrefaction process, which is conducive to upgrading biomass for achieving net zero carbon emissions, as it has been stated in several works that torrefied biomass can be used instead of coal.

Effects of potassium on hydrothermal carbonization of sorghum bagasse

Hydrothermal carbonization (HTC) reacts with biomass in water at a high temperature and pressure to produce hydrochar with a higher heating value (HHV) and lower ash content than dry torrefaction. The high potassium content in biomass can promote thermochemical conversion; however, it lowers the melting temperature of the ash, causing slugging and fouling. Therefore, this study, investigated the effect of potassium on the HTC of sorghum bagasse by comparing the removal of potassium by washing with the addition of K2CO3. Consequently, the ash content was the highest in the potassium-added hydrochar and was 3.81% at a reaction time of 2 h. Elemental analysis showed that the lower the potassium content, the higher the carbon content, and the hydrochar with potassium removed by water washing at a reaction time of 3 h had the highest carbon content at 68.3%. Fourier transform infrared spectrometer showed dehydration and decarboxylation reactions due to HTC, but no significant differences were observed between the potassium concentrations. The mass yield decreased with increasing potassium content, and was 27.2% for the potassium-added hydrochar after 3 h. This trend was more pronounced with increasing reaction temperature. On the other hand, HHV was not affected by the potassium content. Therefore, the energy yield was similar to the weight yield. Thermal gravimetry and derivative thermal gravimetry (TG-DTG) analysis showed that higher potassium tended to accelerate the decomposition of lignin and decrease the oxidation temperature.Graphical

Torrefaction of olive pomace with low-density polyethylene (LDPE) plastic and its interactive effects

Olive Pomace (OP) biomass has a high potential for biofuel production. Dry torrefaction of OP was carried out at 200–290 °C in an inert environment in a tubular reactor. Low-Density Polyethylene (LDPE) is the most common plastic seen in landfills. Therefore, the blends of Olive Pomace with LDPE were torrefied at different ratios. The product yield and characteristics of torrefied OP were studied. As the temperature increased, the torrefied OP's mass yield decreased while the HHV increased. In the case of OP-LDPE blends, mass yield and HHV increased with the increase in LDPE content. Results showed that mass yield ranged between 59.2–82.6% for torrefied olive pomace depending on torrefaction temperature. 12% increase in mass yield was noticed when 30 wt% LDPE was blended with OP as compared to the OP at 240 °C. As for fuel properties, torrefaction enhanced HHV from 19.8 to 24.2 and 25.5 MJ/kg for OP at 290 °C and OP-LDPE blend of 30% plastic at 240 °C, respectively. Additionally, the fuel ratio rose to 0.4; the combustibility index reduced to 63.5 MJ/kg for torrefied biomass at 240 °C. The fuel ratio drastically dropped when LDPE was blended with olive pomace, reaching 0.09 with a combustibility index of 284.55 MJ/kg. Thermogravimetric analysis (TGA) revealed that hemicellulose decomposed at the specified temperature range (>200 °C), while cellulose and lignin partially decomposed. TGA showed that plastic breaks down at one stage at temperatures greater than 400 °C. According to Fourier Transform Infrared Spectroscopy (FTIR), adding LDPE replaced alkenyl groups with ketones and aldehydes. FESEM analysis showed that adding plastic clogged biomass pores resulted in higher mass yield.

INFLUENCE OF BIOMASS PRETREATMENT ON SUBSEQUENT PYROLYSIS AND HYDRODEOXYGENATION IN BIO-BASED TRANSPORT FUELS AND CHEMICALS PRODUCTION: A CRITICAL REVIEW

The present article aims to review the influence of various biomass pretreatments on the production of bio-based transportation fuel and chemicals via pyrolysis and hydrodeoxygenation (HDO). The article includes the influence of different thermochemical pretreatments such as dry torrefaction (DT), wet torrefaction (WT), steam explosion treatment (SET), hot water extraction (HWE), acid treatment (ACT), and alkali treatment (AKT) on bio-oil yield and bio-oil properties. HDO primarily includes dehydration, hydrogenolysis, decarbonylation, and hydrogenation. HDO can be classified based on stages (single and two-stage HDO), reaction pressure (high and low), and hydrogen presence (ex situ and in situ). The recent developments, advantages, and drawbacks associated with different types of HDO processes have been included. The article includes recent studies on designing various catalysts based on HDO conversion of different bio-oil compositions or selective model compounds to targeted bio-based products. The various biomass pretreatments impact the concentration of certain families of organic compounds present in bio-oil. Hence, the present review article also includes recommendations of specific biomass pretreatments for various HDO catalysts designed for selective model compounds or different bio-oil compositions. Few praiseworthy techno-economic analysis (TEA) studies on the influence of different biomass pretreatments on the minimum selling price (MSP) of bio-based products obtained at various production stages have been discussed.

Co-torrefaction of corncob and waste cooking oil coupled with fast co-pyrolysis for bio-oil production

Lignocellulosic biomass is a rich source of fixed renewable carbon and a promising alternative to fossil sources. However, low effective hydrogen to carbon ratio limits its applications. This work studied the influence of oil-bath co-torrefaction of corncob and waste cooking oil for co-pyrolysis. It was compared with dry torrefaction and hydrothermal wet torrefaction firstly. Residual of oil-bath co-torrefaction were the highest of 97.01 %. Oil-bath co-torrefaction could maximize hydrogen atoms retention in corncob, which has a positive significance for deoxygenation during pyrolysis. Oil-bath co-torrefaction could also reduce the average activation energy required for corncob decomposition, while it was increased with dry torrefaction. Oil-bath co-torrefaction coupled with co-pyrolysis was more suitable for hydrocarbon-rich bio-oil production. Oil-bath co-torrefaction temperature had the greatest influence on bio-oil composition. High pressure promoted formation of the CC double bond and degradation of lignin, which further promoted the formation of monocyclic aromatics in bio-oil.

Simulation and Optimization of Lignocellulosic Biomass Wet- and Dry-Torrefaction Process for Energy, Fuels and Materials Production: A Review

This review deals with the simulation and optimization of the dry- and wet-torrefaction processes of lignocellulosic biomass. The torrefaction pretreatment regards the production of enhanced biofuels and other materials. Dry torrefaction is a mild pyrolytic treatment method under an oxidative or non-oxidative atmosphere and can improve lignocellulosic biomass solid residue heating properties by reducing its oxygen content. Wet torrefaction usually uses pure water in an autoclave and is also known as hydrothermal carbonization, hydrothermal torrefaction, hot water extraction, autohydrolysis, hydrothermolysis, hot compressed water treatment, water hydrolysis, aqueous fractionation, aqueous liquefaction or solvolysis/aquasolv, or pressure cooking. In the case of treatment with acid aquatic solutions, wet torrefaction is called acid-catalyzed wet torrefaction. Wet torrefaction produces fermentable monosaccharides and oligosaccharides as well as solid residue with enhanced higher heating value. The simulation and optimization of dry- and wet-torrefaction processes are usually achieved using kinetic/thermodynamic/thermochemical models, severity factors, response surface methodology models, artificial neural networks, multilayer perceptron neural networks, multivariate adaptive regression splines, mixed integer linear programming, Taguchi experimental design, particle swarm optimization, a model-free isoconversional approach, dynamic simulation modeling, and commercial simulation software. Simulation of the torrefaction process facilitates the optimization of the pretreatment conditions.

Effect of dry torrefaction pretreatment of the microwave-assisted catalytic pyrolysis of biomass using the machine learning approach

This study employs the Leave-One-Out cross-validation approach to build a machine-learning model using polynomial regression to predict pyro product yield through microwave-assisted pyrolysis of sawdust over KOH catalyst and graphite powder a susceptor. The determination of coefficient (R2) validates the developed models. All the developed models achieved a high prediction accuracy with R2 > 0.93, which signifies that the experimental values are in good agreement with the predicted one. The dependence of the catalyst loading and pretreatment temperature on dominating process parameters such as heating rate, pyrolysis temperature, susceptor thermal energy, and pyro products, namely bio-oil, biochar, and biogas, are explored. The yield of biochar is reduced; however, bio-oil and biogas are enhanced as the catalyst loading increased. On the other hand, increasing the temperature of pretreated sawdust decreased bio-oil and biogas yields while increasing biochar yields. Further, microwave conversion efficiency, and susceptor thermal energy increased with increased catalyst quantity and pretreatment temperatures of sawdust. It was observed that the average heating rate was increased by increasing the catalyst quantity while maintaining the same pyrolysis time until pretreatment temperatures of 150 °C were reached, after which the heating rate dropped due to the continuous microwave energy input to the system.

Comparative study of solid biofuels derived from sugarcane leaves with two different thermochemical conversion methods: wet and dry torrefaction

Comparative study of solid biofuels derived from sugarcane leaves with two different thermochemical conversion methods: wet and dry torrefaction

Optimum Torrefaction Range for Macaw Husks Aiming Its Use as a Solid Biofuel

Abstract Biomass feedstock is broadly available in many countries, and a significant amount of residual biomass comes from agriculture and forest crops. This study aims to identify a consistent criteria for optimize Macaw husks torrefaction process maximizing the energy content and minimizing the mass loss. The optimization criteria is based on the severity factor (SF), HHVTorrefied, and ηSolid-Yield. The energy density (ρEnergy) does not provide consistent and indisputable evidence as an optimization criteria; the same applies to energy-mass co-benefit index (EMCI) and ηEnergy-Yield. This investigation combined few temperatures (180 °C, 220 °C, and 260 °C) with different residence times (20, 40, and 60 min) and found that the optimum torrefaction range for Macaw husk is 220 < T (°C) < 240 and 10 < t (min) < 40. The best experimental result was 220-40 (dry torrefaction at T = 220 °C and t = 40 min) corresponding to SF ∼ 5.14 and HHVTorrefied ∼ 21.71 MJ/kg (ηSolid-Yield ∼ 0.86 and HHVRatio ∼ 1.14). As the raw material has small ρBulk or ρEnergy, the authors suggest the use of a densification process previously to torrefaction. The obtained solid final product had high-quality biofuel following properties: FCdb, H/C, and O/C ratios, high heating value (HHV). The gain and loss optimization method seems promising to identify the optimum torrefaction parameters for any biomass species and the obtained optimum temperature is not far from the ones available as waste heat in industrial processes.

Valorization of Prosopis juliflora Woody Biomass in Northeast Brazilian through Dry Torrefaction

Torrefaction has been investigated to improve the desirable properties of biomass as solid biofuel, usually used in natura as firewood in several countries. This paper has the main objective to present a broad characterization of the biomass Prosopis juliflora (P. juliflora), investigating its potential as a solid biofuel after its torrefaction process. The methodology was based on different procedures. The experimental runs were carried out at 230, 270, and 310 °C for 30 min, using a bench-scale torrefaction apparatus, with an inert atmosphere. In order to investigate the effect of temperature in constant time, torrefaction parameters were calculated, such as mass yield, energy yield, calorific value, base-to-acid ratio (B/A), and the alkaline index (AI). The physicochemical properties of the torrefied samples were determined and thermogravimetric analysis was used to determine the kinetic parameters at four different heating rates of 5, 10, 20, and 30 °C/min. Pyrolysis kinetics was investigated using the Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) isoconversional methods. Highly thermally stable biofuels were obtained due to the great degradation of hemicellulose and cellulose during torrefaction at higher temperatures. The highest heating value (HHV) of the samples varied between 18.3 and 23.1 MJ/kg, and the energy yield between 81.1 and 96.2%. The results indicate that P. juliflora torrefied becomes a more attractive and competitive solid biofuel alternative in the generation of heat and energy in northeast Brazil.

Valorization of sorghum distillery residue to produce bioethanol for pollution mitigation and circular economy

This research aims to study the wet torrefaction (WT) and saccharification of sorghum distillery residue (SDR) towards hydrochar and bioethanol production. The experiments are designed by Box-Behnken design from response surface methodology where the operating conditions include sulfuric acid concentration (0, 0.01, and 0.02 M), amyloglucosidase concentration (36, 51, and 66 IU), and saccharification time (120, 180, and 240 min). Compared to conventional dry torrefaction, the hydrochar yield is between 13.24 and 14.73%, which is much lower than dry torrefaction biochar (yield >50%). The calorific value of the raw SDR is 17.15 MJ/kg, which is significantly enhanced to 22.36–23.37 MJ/kg after WT. When the sulfuric acid concentration increases from 0 to 0.02 M, the glucose concentration in the product increases from 5.59 g/L to 13.05 g/L. The prediction of analysis of variance suggests that the best combination to maximum glucose production is 0.02 M H2SO4, 66 IU enzyme concentration, and 120 min saccharification time, and the glucose concentration is 30.85 g/L. The maximum bioethanol concentration of 19.21 g/L is obtained, which is higher than those from wheat straw (18.1 g/L) and sweet sorghum residue (16.2 g/L). A large amount of SDR is generated in the kaoliang liquor production process, which may cause environmental problems if it is not appropriately treated. This study fulfills SDR valorization for hydrochar and bioenergy to lower environmental pollution and even achieve a circular economy.

Comparative life cycle energy and greenhouse gas footprints of dry and wet torrefaction processes of various biomass feedstocks

This study compares the life cycle energy consumption and greenhouse gas (GHG) emissions of electricity generation from bio-coals produced from various biomass feedstocks via dry torrefaction (DT) and wet torrefaction (WT) processes. Wheat straw, pine woodchips, grape pomace, manure and algae are the main feedstocks evaluated. The energy consumption and the associated GHG emissions at each life cycle stage were calculated. The main stages included are in-field preparation, feedstocks transportation to torrefaction plant, torrefaction process, bio-coal transportation to power plant, and power plant operations. The results show that all pathways are competitive with coal-based electricity in terms of GHG emissions except pathways with algae as feedstock and manure biochar-based electricity generation. Among the pathways, electricity generation from pine woodchips biochar appears to be the best option, with an 82% GHG emissions reduction compared to coal-derived electricity, followed by wheat starw biochar and grape pomace hydrochar with 80% and 75% emission reductions, respectively. Electricity generation from wheat straw biochar, pine woodchips biochar, and grape pomace hydrochar lead to the highest net energy ratios (NERs) of 4.19, 3.58, and 2.59, respectively. The results also show that the combustion of the biomass for supplying electricity used in the plant decreases GHG emissions in all pathways particularly in WT ones. Sensitivity analysis of using different emissions allocation methods, transportation distances to torrefaction plant and to power plant, emission factor of electricity consumed, and quantity of natural gas consumed were aslo conducted. The developed information is novel and can be used for investment decisions and policy formulation around the world.

Effect of different pre-treatment methods on gasification properties of grass biomass

The effect of different pre-treatments method on the gasification efficiency of grass biomass have not previously been evaluated. In this study, the effect of three different pre-treatment methods on gasification properties of grass biomass was investigated under CO2 conditions. The pre-treatment methods were dry torrefaction, wet torrefaction, and leaching (chemical). The results obtained showed that the heating values increased by 2,77% in the leached grass, 8,3% in the dry torrefied grass and 13,5% in the wet torrefied grass. However, the wet torrefaction had the highest reactivity index of 0,25 followed by dry torrefaction 0,182, then leaching 0,156. The effect of the different pre-treatment on activation energy showed that the activation energy of raw grass biomass was reduced from 161,7 kJ/mol to 141.5 kJ/mol for leached grass, 124.3 kJ/mol for dry torrefied and 86.97 kJ/mol for wet torrefied grass. These results show that wet torrefaction can improve gasification properties significantly when compared to dry torrefaction and leaching. The pore structure and pore volume effect of treated biomass was likely the predominant reason for the better char reactivity and conversion during gasification of wet torrefied sample. The research supplied an insight into the effect of different pre-treatment methods on grass biomass gasification.

Enhancement of fuel properties of yard waste through dry torrefaction

Yard waste or green waste is an abundant yet underutilized source of biomass around the world. Yard waste is rich in complex organic compounds, which is beneficial when used as feedstock for chemicals production, but undesirable components within the biomass are detrimental to the quality of the products. In this work, the prospect of yard waste upgrading as a solid fuel source by dry torrefaction (DT) was studied. Dry torrefaction of yard waste was conducted at 170 °C, 200 °C, 250 °C, and 300 °C under N2, CO2, and flue gas (25:75 vol% mixture of CO2:N2) atmosphere in a tubular reactor. As temperature was increased, the mass yield of the torrefied yard waste decreased while the HHV increased. The mass yields obtained were in the order of nitrogen < carbon dioxide < flue gas. HHV was in the order of flue gas < nitrogen < carbon dioxide. Overall, carbon dioxide was shown to be the best carrier gas for energy intensification, where HHV was enhanced from 15.6 to 22.2 MJ/kg at 300 °C, with an energy yield of 98.1%. Flue gas showed no visible improvement in properties up to temperatures of 250 °C. Thermogravimetric analysis (TGA) highlighted that within the given temperature range, hemicellulose was completely degraded as temperature approach 300 °C, while cellulose was partially degraded. Fourier transform infrared spectroscopy (FTIR) emphasised that flue gas was unable to degrade various functional groups to the same degree as the other gases. Field Emission scanning electron microscopy with Energy Dispersive X-ray analysis (FESEM-EDX) revealed that flue gas was unable to degrade the biomass as much as nitrogen or carbon dioxide.

Influence of Molten Salt Torrefaction Pretreatment on Upgrading of Bio-Oil from Camellia Oleifera Shell

As an excellent reaction medium, molten salt had large heat capacity, high thermal conductivity and stable chemical properties. Therefore, a new pretreatment method, molten salt pyrolysis (MT) pretreatment, was studied to pretreat Camellia oleifera shell (COS). The effect of temperature (160~280°C) on MT was mainly studied and compared with conventional dry and hydrothermal torrefaction. Furthermore, the physicochemical and pyrolysis characteristics of COS and torrefied biochar were also studied. The analysis of pyrolysis characteristics indicated that the energy of activation of biochar was reduced after MT, which was conducive to the occurrence of pyrolysis reaction. The content of phenols compounds rose considerably with MT pretreatment. The relative content of phenols at MT-240°C was 74.11%, which was higher than that of hydrothermal and dry torrefaction. In this study, an innovative and successful pretreatment process for converting COS into high-value phenols was proposed.

Preparation of biochar via dry torrefaction of wood meal in a batch reactor under pressure and its co-combustion behavior with anthracite coal

Biochar was prepared by dry torrefaction of wood meal in a batch reactor under pressurized conditions. The biochar prepared at 340 °C (WMB-340) showed a higher heating value (HHV) of 30.5 MJ/kg, and it was employed to co-combust with anthracite coal (AC) with the HHV of 28 MJ/kg. The WMB-340 underwent two combustion stages, while the AC only showed one combustion stage. The combustion of AC was promoted by WMB-340 at temperatures higher than 490 °C, indicating the existence of a synergetic effect during co-combustion. Blending AC with 10% WMB-340 had no obvious effect on the combustion stage of AC. However, three combustion stages existed when blending more than 10% WMB-340 with AC. The activation energy of AC blended with 10% WMB-340 was 84.5 kJ mol-1, much lower than that of AC (179.3 kJ mol-1), indicating a lower energy for initialization of the blend. Therefore, AC blended with 10% WMB-340 was the optimal ratio for co-combustion in this study.

The enhanced rich H2 from co-gasification of torrefied biomass and low rank coal: The comparison of dry/wet torrefaction, synergetic effect and prediction

In this study, the enhanced rich H2 gas was produced via the co-gasification of torrefied biomass and low-rank coal in the fixed bed reactor. The properties of wet/dry torrefied char was compared, and then the synergetic effect between dry/wet torrefied char and the low rank coal during the gasification were analyzed to study the enhancing effect of torrefaction on the H2 yield. Moreover, the co-pyrolysis reactivity and kinetic analysis were investigated to further determine the synergetic mechanism. The results showed that the change of fundamental compositions in biomass after torrefaction, especially, the removal of cellulose played an important role in the enhancement of H2. Thus, dry torrefaction was more beneficial for improving H2 yield than the wet one. Besides, an obviously synergetic effect was observed from coal and dry torrefied biomass in their ratio 1:1 and 3:1, which was mainly due to the catalytic role of alkali and alkaline earth metallic species, and the transfer of active OH and H radicals from the torrefied biomass to the coal. The co-pyrolysis reactivity and kinetic analysis further proved the synergetic effect on reducing activation energy.