Torrefaction Conditions Research Articles

Prediction of Fuel Properties of Torrefied Biomass Based on Back Propagation Neural Network Hybridized with Genetic Algorithm Optimization

Torrefaction is an effective technology to overcome the defects of biomass which are adverse to its utilization as solid fuels. For assessing the torrefaction process, it is essential to characterize the properties of torrefied biomass. However, the preparation and characterization of torrefied biomass often consume a lot of time, costs, and manpower. Developing a reliable method to predict the fuel properties of torrefied biomass while avoiding various experiments and tests is of great value. In this study, a machine learning (ML) model of back propagation neural network (BPNN) hybridized with genetic algorithm (GA) optimization was developed to predict the important properties of torrefied biomass for the fuel purpose involving fuel ratio (FR), H/C and O/C ratios, high heating value (HHV) and the mass and energy yields (MY and EY) based on the proximate analysis results of raw biomass and torrefaction conditions. R2 and RMSE were examined to evaluate the prediction precision of the model. The results showed that the GA-BPNN model exhibited excellent accuracy in predicting all properties with the values of R2 higher than 0.91 and RMSE less than 1.1879. Notably, the GA-BPNN model is applicable to any type of biomass feedstock, whether it was dried or not before torrefaction. This study filled the gap of ML application in predicting the multiple fuel properties of torrefied biomass. The results could provide reference to torrefaction technology as well as the design of torrefaction facilities.

Torrefaction of corncob and khat stem biomass to enhance the energy content of the solid biomass and parametric optimization

Agricultural biomass, as a renewable energy source, is critical in reducing the negative effects on the environment and the depletion of fossil fuels. Corncob and khat stem agricultural residues were investigated as a source of energy in the current study after their energy value was increased through torrefaction. The response surface methodology was used in the investigation of torrefaction parameter optimization. Torrefaction temperature and residence time were investigated as independent variables on energy yield. The energy yield obtained at optimum torrefaction conditions (300 °C, 30 min) was 98.5 % in corncob and 94.9 % in khat stem (300 °C, 45 min). Torrefaction bio-residues significantly affected all of the investigated attributes, according to the findings. Torrefied corncob and khat stem produced demonstrated good mass yield and energy yield characteristics, as well as a corresponding heating value. Torrefied biomasses are used as energy sources for industrial applications, according to the results of the torrefaction process.

Effect of Alkaline Pretreatment on the Fuel Properties of Torrefied Biomass from Rice Husk

Lignocellulosic biomass from rice husk (RH) is a renewable resource for fuel production, but it could pose ash-related challenges. This work focused on investigating the effects of pretreatment at different sodium hydroxide (NaOH) concentrations (i.e., 0.0, 0.25, 0.50, 0.75 and 1.00 M) on the calorific values and ash contents of treated RH products, and also finding the optimal torrefaction conditions. The results showed that alkaline pretreatment by sodium hydroxide (NaOH) reduced the ash content in the RH samples by over 85 wt%. Due to its relatively excellent calorific values and low ash content, the RH sample with 0.25 M NaOH pretreatment (i.e., RH-25) was chosen as a starting feedstock in the subsequent torrefaction experiments as a function of 240–360 °C for holding time of 0–90 min. In addition, the surface properties by scanning electron microscopy—energy dispersive X-ray spectroscopy (SEM-EDS) and Fourier-transform infrared spectroscopy (FTIR) were also used to observe the elemental compositions preliminarily. Based on the fuel properties of the torrefied RH products, the optimal torrefaction conditions can be found at around 280 °C for holding 30 min. As compared to the calorific value of the RH-25 (i.e., 18.74 MJ/kg) and its mass yield (i.e., 0.588), the calorific value, enhancement factor and energy yield of the optimal product were 28.97 MJ/kg, 1.55 and 0.91, respectively. Although the resulting product has a high calorific value like coal, it could have slight potential for slagging and fouling tendency and particulate matter emissions due to the relatively high contents of silicon (Si) and sodium (Na), based on the results of EDS and FTIR.

Predicting the high heating value and nitrogen content of torrefied biomass using a support vector machine optimized by a sparrow search algorithm.

A support vector machine (SVM) model with RBF kernel function combined with sparrow search algorithm (SSA) optimization was developed to predict the HHV and nitrogen content (No) values of torrefied biomass based on the feedstock properties and torrefaction conditions. Results showed that SSA optimization significantly improved the prediction performance of the SVM model for both HHV and No. A coefficient of determination (R 2) larger than 0.91 was achieved when the SSA-SVM model was implemented, and the values of RMSE were also fairly acceptable. The agreement between experimental data and SSA-SVM predicted values demonstrated the high predictive precision of the model. This study provides a reference for the utilization of torrefied biomass in solid fuels and the design of torrefaction facilities.

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.

Application of Random Forest Model Integrated with Feature Reduction for Biomass Torrefaction

A random forest (RF) model integrated with feature reduction was implemented to predict the properties of torrefied biomass based on feedstock and torrefaction conditions. Four features were selected for the prediction of fuel ratio (FR) and nitrogen content (Nt), and five features were selected for O/C and H/C ratios and HHV values. The results showed that the feature-reduced model had excellent prediction performance with the values of R2 higher than 0.93 and RMSE less than 0.58 for all targets. Moreover, partial dependence analysis (PDA) was performed to quantify the impacts of selected features and torrefaction conditions on the targets. Temperature was the dominant factor for FR, O/C and H/C ratios, and HHV values, whereas Nt was determined most on the nitrogen content in the feedstock (Ni). This study provided comprehensive information for understanding biomass torrefaction.

Improving Lignocellulosic and Non-Lignocellulosic Biomass Characteristics through Torrefaction Process

In this study, three locally available biomasses, namely miscanthus, hops, sewage sludge, and additionally, their mixtures, were subjected to the torrefaction process to improve their fuel properties. The torrefaction process was conducted at 250–350 °C and 10–60 min in a nitrogen (N2) environment. The torrefaction temperature and time were studied to evaluate the selected biomass materials; furthermore, heating values, mass and energy yields, enhancement factors, torrefaction severity indexes (TSI), and energy-mass co-benefit indexes (EMCI) were calculated. In addition, thermogravimetric (TGA) and Fourier transform infrared analyses (FTIR) were performed to characterize raw and torrefied biomass under the most stringent conditions (350 °C and 60 min). The results showed that with increasing torrefaction temperature and duration, mass and energy yields decreased, and heating values (HHVs) increased for all studied biomasses. The results of the TSI and EMCI indexes showed that the optimum torrefaction conditions were as follows: 260 °C and 10 min for pure miscanthus and hops, whilst this could not be confirmed for the sewage sludge. Furthermore, the combination of sewage sludge and the above-mentioned types of lignocellulosic biomass exhibited better fuel properties than sewage sludge alone.

Entrained flow Co-gasification of torrefied biomass and coal

In this study, the effect of blending selected torrefied biomass and lower-rank coal samples on entrained flow co-gasification is experimentally investigated, and the results are compared with entrained flow gasification of coal samples. Three biomass samples were torrefied in a lab-scale torrefaction system to obtain a coal-like structure, coherent with the selected coal samples. 275 °C and 40 min were selected as the best-suited torrefaction condition for blending with the coal samples. Four 1:1 coal-torrefied biomass blends were prepared considering the ash and grindability properties for entrained flow co-gasification. The gasification simulations were carried out with Aspen HYSYS to assess the effect of the process conditions. The entrained flow gasifier with 15 kW capacity was built and operated between 1500 °C and 1200 °C with three coals and their four blends. The experimental results show methane (>1300 °C gasification temperature) and tar-free syngas composition. The results of entrained flow co-gasification experiments indicate higher cold gas efficiencies, better syngas quality, and carbon conversion with torrefied biomass blending compared to entrained flow gasification of coal samples. Co-utilization of coal and biomass can be part of a short to medium-term contribution to energy, waste, and global climate change problems.

Comparison and characterization of torrefaction performance and pyrolysis behaviour of softwood and hardwood

ABSTRACT In this study, the torrefaction and pyrolysis behaviors of softwood (pinewood) and hardwood (teakwood) were experimentally explored. Three different torrefaction temperatures (i.e. 210, 240, and 270°C) and two different residence times (20 and 40 min) were adopted. Various property indicators, for example, solid and energy yields, enhancement factor of higher heating value (HHV), and torrefaction severity index, were used to characterize the torrefaction performance. The principal component analysis (PCA) demonstrated the correlation among different torrefied samples with the help of chemical composition, solid yield, and HHV. Moreover, slow pyrolysis experiments were conducted at three different heating rates (i.e. 15, 30, and 40°C/min) to investigate the thermal degradation behavior of the torrefied biomass samples. Both thermogravimetric and differential thermogravimetric curves shifted to a higher temperature as the pyrolysis heating rate increased. The activation energies E a were estimated by using three isoconversional methods, that is, Kissinger-Akahira-Sunose (KAS), Starink and Flynn-Wall-Ozawa (FWO) methods. The E a broadly increased with torrefaction severity. When using the FWO method, the average E a values ranged from 97.51 to 168.68 kJ/mol and 120.73 to 180.25 kJ/mol for torrefied pinewood and teakwood samples, respectively. Scanning electron microscopy (SEM) images revealed that at higher torrefaction conditions, the samples experienced severe structural damages, leading to crack formation and augmentation. All these observations not only reveal that torrefaction can turn raw biomass into fuel with improved properties but also help to clarify the differences between soft and hardwood for energy utilization purpose.

Effects of oxidative torrefaction conditions on the biomass liquid chemical looping reaction from the perspective of thermal behavior and kinetic analysis

Biomass liquid chemical looping conversion process (BLCLP) can produce a high-temperature oxygen-depleted stream. Utilizing the oxygen-depleted air as a torrefaction medium can enhance biomass reactivity and achieve higher energy efficiency. This study aimed to investigate the effect of torrefaction conditions on biomass reactivity in the BLCLP. The torrefaction under proper working conditions effectively enhanced the release of biomass volatiles. The increase in the activation energy of biomass pyrolysis after oxidative torrefaction indicated the need for proper control of the torrefaction condition. More importantly, oxidative torrefaction promoted the reactivity between biochar and liquid oxygen carrier, which was crucial for the BLCLP. The activation energy of the reaction between biochar and Sb2O3 liquid oxygen carrier calculated by the DAEM method was 289.75–296.79 kJ·mol−1, guiding the subsequent reactor design. Ultimately, the optimal torrefaction conditions for the BLCLP were determined as 270 °C and 3 vol% oxygen content.

Transformations of the Structural Components of Sawdust and Peat under Conditions of Hydrothermal Carbonization and Torrefaction

Transformations of the Structural Components of Sawdust and Peat under Conditions of Hydrothermal Carbonization and Torrefaction

A comparison of conventional and oxidative torrefaction of microalga Nannochloropsis Oceanica through energy efficiency analysis and life cycle assessment

Torrefaction is a promising method for producing microalgal solid biofuel. This study compared conventional torrefaction and oxidative torrefaction for microalgal solid biofuel production. Particular attention was paid to evaluating energy efficiency analysis and life cycle assessment, and several parameters and indexes were adopted and calculated. The results showed that mild oxidative torrefaction was the most energy-efficient operation, with the maximum value of relative upgrading energy index and relative energy return on investment. The life cycle assessment indicates that oxidative torrefaction had a lower environmental impact than conventional torrefaction, mainly due to its lower carrier gas consumption and electricity input. The environmental impact positively correlated with the torrefaction severity. The obtained results in this study can provide new insights on improving the cognition of energy efficiency evaluation and environmental impact assessment of the torrefaction process, which helps select optimal torrefaction conditions.

A comparative analysis of biomass torrefaction severity index prediction from machine learning

Machine learning (ML) is one type of artificial intelligence (AI) commonly used for computer programming. Multivariate adaptive regression splines (MARS) and artificial neural networks (ANN) are two common and popular tools in AI that allow the user to analyze the pattern of complex data. The torrefaction severity index (TSI) is an index to define torrefied biomass quality at different torrefaction conditions. In this study, MARS and ANN models are applied to predict TSI. The considered input parameters in predictions using MARS and ANN approaches comprise feedstock type, temperature, and duration. The MARS model indicates that temperature is the most influential factor on TSI, followed by duration and feedstock type. In contrast, the ANN model reveals that the feedstock type is a dominant factor, and temperature and duration are not important. The performance of the ANN model is evaluated in three different combinations of numbers of hidden layers and neurons. It shows 2 hidden layers along with 85 neurons giving the best performance. The highest R2 values in MARS and ANN are 0.9851 and 0.9784, respectively. The relative root means square error analysis shows that both MARS and ANN have good fit quality with the relative errors of 1.49% and 2.16%, respectively. Overall, the comparison reflects that MARS is a more suitable model for predicting solid biofuel’s TSI. The general observation suggests that the ANN lacks sensitivity to the input parameter. Nevertheless, ANN performance may be improved by adjusting the number of hidden layers and neurons.

Effects of oxygen deficient and flue gas torrefaction on the surface property and structural feature of typical agriculture waste: Rice husk

Effects of torrefaction condition on fuel qualities and combustion characteristics of rice husk were studied. The distribution of typical elements and components exhibited that rising torrefaction severity initially decreased and subsequently increased the values of H/C and O/C. The effects of torrefaction condition on lignin content and heating value for torrefied samples expressed identical law. Increasing torrefaction severity decreased the solid yield monotonically, while the corresponding energy yield expressed first upward and then downward trend. The participation of H2O in the torrefaction process was beneficial to the generation of edge nitrogen and the enrichment of reactive functionalities at the expense of hydrophilic groups. The addition of multiple oxidants was conducive to enlarging specific surface area and optimizing fuel combustion behavior at mild temperatures. According to the results obtained from this research, the upgraded sample derived from torrefaction occurred in wet flue gas at 543 K expressed the best fuel quality.

Torrefaction of low-value agro-industrial wastes using macro-TGA with GC-TCD/FID analysis: Physicochemical characterization, kinetic investigation, and evolution of non-condensable gases

Two low-value agro-industrial residues, passion fruit peel waste (PF) and pineapple peel waste (PA), were considered in this study as feedstocks to produce solid biofuels by torrefaction. The experiments were conducted in a macro-TGA with GC-TCD/FID analysis to investigate their torrefaction characteristics. The GC-TCD/FID analysis allowed quantifying the non-condensable gases, including CO, CO2, CH4 and H2. The impacts of pretreatment with torrefaction on the physicochemical properties were investigated by using proximate analysis, ultimate analysis, and calorific values. The torrefaction of PF and PA was investigated at three different temperatures (200, 250, and 300 °C) and two residence times (15 and 60 min). The torrefaction pre-treatment led to higher levels of elemental carbon, fixed carbon, HHV and energy density than in the raw biomass. Experimental results showed that the most favorable torrefaction condition for producing a solid biofuel with a high energy density is a moderate temperature of 250 °C and 15 min of residence time. Two models were applied to the torrefaction kinetics of the two agro-industrial wastes: one with the one-step method and the other with the two-step method. The two-step reaction method was the most appropriate for describing the torrefaction behavior of the two agro-industrial wastes in all conditions studied. As determined by the two-step reaction method, the torrefaction activation energies ranged from 17.9 to 199.9 kJ mol−1 for PF and 5.3–84.0 kJ mol−1 for PA. Findings from this study are potentially valuable for the design of large-scale equipment for the torrefaction of PF and PA residues.

Catalytic pyrolysis of torrefied olive stone for production of potential petrochemical alternatives

AbstractBench‐scale fluidized bed fast pyrolysis of as‐received and torrefied residual olive stone (OS) was carried out at 500 °C in the presence or absence of a solid acid catalytic bed. Light to mild torrefaction conditions were investigated, with temperatures of 200, 225, and 250 °C, set in a bench‐scale fluidized bed torrefier. Light torrefaction temperatures (200 and 225 °C) did not yield appreciable differences in the thermogravimetric pyrolysis studies, despite notable changes in mass and energy yield resulting from the influence of temperature difference. The mass and energy yields decreased from 91.1 to 74.0% and from 92.0 to 80.9%, respectively, moving from light to mild torrefaction. The higher heating value (HHV) increased linearly with an increase in torrefaction temperature, reaching a maximum of 22.1 MJ/kg at 250 °C, which was 9.7% greater than the as‐received OS sample. A comparison was made between the influence of light and mild torrefaction on subsequent bench‐scale pyrolysis experiments. In particular, the quality of bio‐liquids for torrefaction coupled to fast pyrolysis shifted signifcantly towards the production of higher phenolic and aromatic derivatives that may find applications as potentaila drop‐in alternative hydrocarbons. © 2022 The Authors. Biofuels, Bioproducts and Biorefining published by Society of Industrial Chemistry and John Wiley & Sons Ltd.

Torrefaction severity and performance of Rubberwood and Gliricidia

Lab-scale torrefaction experiments of Rubberwood and Gliricidia were conducted at 250-300 oC and 30–60 min in a nitrogen environment to understand the torrefaction behavior. TGA and FTIR were used to characterize raw and torrefied biomass. In the lab-scale experiments, Rubberwood showed 16% mass loss, whereas Gliricidia showed 25% mass loss under the most severe conditions, resulting in 9% and 22% volatile drop, respectively. The higher heating value of the torrefied product increased from 18.9 MJ/kg to 21.39 MJ/kg for Rubberwood and from 19.46 MJ/kg to 22.44 MJ/kg for Gliricidia under the most severe conditions. The calculated Energy Mass Co-benefit Index (EMCI) of Rubberwood at 275 °C and 60 min or 300 °C and 45–60 min and Gliricidia at 300 °C and 60 min indicated favorable torrefaction conditions. Comparatively, Gliricidia was performing well in torrefaction. The severity factor was modified by finding the optimum fitted parameter ω, which establishes a feedstock-specific relationship between torrefaction severity and operating conditions. The normalized severity factor shows a linear correlation with the properties of torrefied biomass, which could facilitate torrefaction modeling.

Investigation of the thermal behavior of Pinus wood pellets during torrefaction for application in metallurgical processes

The aim of this study is to investigate the thermal behavior of Pinus wood pellets during torrefaction under different operational conditions, as well as to evaluate the potential application of the torrefied product in metallurgical processes. Torrefaction tests were carried out in an oxidizing atmosphere (245 °C) and in an inert atmosphere (270 and 290 °C) at residence times of 15 and 60 min. The results of torrefaction in inert atmosphere were also statistically evaluated. To evaluate the potential application of torrefied biomass in metallurgical processes, reactivity tests with CO2 were performed in the temperature range of 200–1000 °C. The results showed that high torrefaction temperature and residence time decreased the mass yield. Statistical analysis showed the possibility of combining high temperatures with low residence times, or vice versa, to obtain satisfactory mass yields. The experimental results showed the highest reactivity for the torrefied biomass obtained in an inert atmosphere, at 290 °C and 60 min. However, considering the mass yield and reactivity with CO2, the best torrefaction conditions for biomass with potential application in metallurgical processes were in an inert atmosphere, at 290 °C and a residence time of 15 min.

Investigation on the fuel quality and hydrophobicity of upgraded rice husk derived from various inert and oxidative torrefaction conditions

Torrefaction is a promising approach which could optimize the behavior of biomass effectively. In this research, a typical and abundant agricultural by-product rice husk was employed for clarifying the correlation between upgradation condition and the fuel quality of upgraded sample. Rice husk were torrefied in inert and oxidative atmospheres (O2: 0, 6, 10 and 21 vol%) at three temperatures (493, 543 and 573 K). After undergoing various torrefaction processes, the torrefied samples were analyzed by elemental analysis, componential determination, fiber component identification, Fourier Transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), pore structure identification, contact angle characterization and moisture re-absorption test. The results illustrated that the additional oxidizing atoms could participate in the optimization of surface physiochemical property of rice husk particles during torrefaction process. Oxygen deficient torrefaction expressed a tendency to increase the heating value and the fixed carbon content in torrefied samples significantly. The minimum hydrophilic groups remained on the surface of rice husk sample pretreated in 6 vol% O2, and the specific surface area of upgraded sample torrefied in 6 vol% O2 at 573 K was the maximum. The contact angle results were consistent with that of moisture re-absorption tests, implying that increasing torrefaction severity appropriately was beneficial to optimizing the surface behavior and hydrophobicity of upgraded rice husk. Torrefaction of rice husk performed in 6 vol% O2 at 573 K was the optimum condition in this study.

Comparison of Characteristics of Poultry Litter Pellets Obtained by the Processes of Dry and Wet Torrefaction

Torrefaction is a technology for the preliminary thermochemical treatment of biomass in order to improve its fuel characteristics. The aim of this work is to conduct comparative studies and select the optimal operating conditions of fluidized bed torrefaction for the processing of poultry litter (PL) into an environmentally friendly fuel. PL torrefaction was evaluated according to three different process configurations: (1) torrefaction of PL pellets in a fixed bed in a nitrogen medium at temperatures of 250 °C, 300 °C and 350 °C (NT1, NT2 and NT3); (2) torrefaction of PL pellets in a fluidized bed of quartz sand in a nitrogen medium at temperatures of 250 °C, 300 °C and 350 °C (NT4, NT5 and NT6); and (3) torrefaction of PL pellets in a fluidized bed of quartz sand in an environment of superheated steam at temperatures of 250 °C, 300 °C and 350 °C (ST1, ST2 and ST3). The duration of the torrefaction process in all experiments was determined by the time required for completion of CO2, CO, H2, and CH4 release from the treated biomass samples. The gas analyzer (Vario Plus Syngaz) was used to measure the concentration of these gases. The torrefaction process began from the moment of loading the PL sample into the reactor, which was heated to the required temperature. After the start of the torrefaction process, the concentration of CO2, CO, H2, and CH4 in the gases leaving the reactor initially increased and, subsequently, dropped sharply, indicating the completion of the torrefaction process. The chemical composition of the obtained biochar was studied, and it was found that the biochar contained approximately equal amounts of oxygen, carbon, nitrogen, hydrogen and ash, regardless of the torrefaction method. Furthermore, the biogas yield of the liquid condensate, obtained from the cooling of superheated steam used in the torrefaction process, was evaluated. The results highlight the efficiency of fluidized bed torrefaction, as well as the performance of superheated steam as a fluidization medium.