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Thermogravimetric analysis (TGA) was performed on six samples of pine wood, poplar sawdust and olive residue, and the kinetic parameters were evaluated by using isoconversional models. The hemicellulose, cellulose and lignin contents were also estimated using the Fraser–Suzuki deconvolution method. In addition, a range of thermodynamic parameters and combustion indices was calculated. Significant correlations were found between the kinetic, thermodynamic and combustion parameters. The ignition index showed an inverse relationship with the activation energy, whereas the burnout index correlated with enthalpy values for most samples. Higher heating rates during TGA increased ignition and combustion efficiencies but decreased combustion stability. Differences in behaviour were detected between the olive residues, which had a much higher lignin content (51.2–56.9%), and the woody biomass samples (24.2–29.2%). Moreover, the sample with the highest ash content also exhibited some distinctive characteristics, including the lowest high heating value and ignition index, coupled with the highest activation energy, indicating a less favourable combustion behaviour than the other samples. The particle size of the samples was also found to be critical for both combustion efficiency and safety. [ABSTRACT FROM AUTHOR]

In Germany, wood pellets must fulfill high quality standards to be utilized in small-scale furnaces. According to current legislation, i.e., the 1st BImSchV, only ENplus A1–certified pellets may be used. Despite these strict requirements, physical fuel parameters can vary within the permissible range and variation usually increases due to fuel transport and storage. Fluctuations in physical fuel parameters may have a strong influence on combustion, especially in pellet stoves with a low degree of automation regarding fuel control and air supply. During this study, pellet length, moisture content, and the content of fines of spruce wood pellets were varied artificially at three levels for each parameter. All pellets were analyzed according to international standards for solid biofuels. Fuels were combusted in a 6 kW pellet stove and selected assortments in a 15 kW pellet boiler. For the pellet stove, pellet length had a significant influence on gaseous but not on total particulate matter (TPM) emissions. Both, rather short (10.3 mm) and long (17 mm) pellets caused an increase in emissions. In contrast, for the boiler, no significant effect of pellet length on gaseous and TPM emissions was observed. A low moisture content (3 w-%) led to increased CO, organic gaseous carbon (OGC), and TPM emissions in the pellet stove. This could be especially relevant for furnaces with very simple or no heat output control as it is common in most pellet stoves. High content of fines (3 to 10 w-%) led to a significant increase in gaseous emissions (CO up to fivefold, OGC up to tenfold) and TPM emissions (up to 1.4-fold) in the pellet stove most likely due to elevated particle entrainment. Overall, the state-of-the-art pellet stove showed larger sensitivity towards variable pellet qualities compared to the automatically stoked pellet boiler; thus, improvements in fuel design and stove technology are recommended. Overall, this study has provided important insights into the influence of pellet length, fines content, and moisture content on emissions from pellet stoves and pellet boilers, which can help drive future technical development in the areas of fuel flexibility and emission reduction. [ABSTRACT FROM AUTHOR]

Wood pellets on the German pellet market mainly consist of spruce wood, but other wood species are increasingly used during pellet production. Moreover, additives such as starch or kaolin can be added to improve fuel quality and combustion behavior. Consequently, wood pellets vary in their physical and chemical properties and this variation might affect combustion behavior in stoves and boilers. In this study, eight different wood species were used for pellet production at the Technology and Support Centre (TFZ). Three types of starch and one type of kaolin were added to spruce wood without bark, using two additivation levels (starch: 0.5 w-% and 1.8 w-%, kaolin: 0.17 and 0.34 w-%). All pellet assortments were analyzed according to international standards for solid biofuels and additional methods. Fuels were combusted in a 6-kW pellet stove and a 15-kW pellet boiler. Selection of wood species had a significant impact on CO emissions for the pellet stove ranging between 85 and 4189 mg/m3 and on TPM emissions ranging between 23 and 263 mg/m3. Similar combustion behavior was observed for the pellet boiler but on a lower emission level. Kaolin reduced CO and TPM emissions as well as slag formation when the additivation level was set according to stoichiometric calculations. When kaolin was overdosed, it had a negative impact on TPM emissions mainly in the pellet boiler, probably due to entrainment. Regarding particles from incomplete combustion, a negative impact of overdosed kaolin was observed. Overall, at the current state of the art, the pellet stove showed larger sensitivity towards variable pellet qualities compared to the automatic pellet boiler. This calls for further improvements in fuel design and stove technology. [ABSTRACT FROM AUTHOR]

From the uncontrolled proliferation of invasive plants, several challenges for the environment arise. Invasive wetland grasses biomass can be collected for biofuel production, thus offering a sustainable solution for invasive plants' management and contributing to the renewable energy sector. The straw-like shoot biomass of common reed (Phragmites australis), widespread across temperate and tropical zones, has been examined to assess its potential use for energy purposes. We seek to determine the fuel-energy characteristics of common reed biomass, which are necessary for converting it into energy through combustion. A comprehensive analysis was conducted to determine the physical and chemical properties of biomass according to the ISO standards for solid biofuels. These properties included calorific values, moisture, ash and volatile matter contents, and contents of C, H, N, and major and minor elements, as well as ash melting behaviour. The measured values were also compared to standard limits for different classes of densified biofuels. Based on the results, the net calorific value (15.33 MJ/kg ar) and other parameters met the requirements for the class A quality of non-woody briquettes and pellets. The only parameters which exceeded the class A limits were ash content (7.1% d.b.) and Cl content (0.16% d.b.). The findings of this study are important for the potential utilisation of common reed biomass for bioenergy as a step towards contribution to the Sustainable Development Goals. [ABSTRACT FROM AUTHOR]

Biomass continues to play a key role as an alternative to fossil fuels. Woody biomass produces lower greenhouse gas emissions than fossil fuels. However, in order to consider biomass as 'green energy', a number of factors should be taken into account, including the characterization of the quality of the resource. Therefore, monitoring quality parameters, such as moisture, ash, N content, is essential to assess the sustainability of biomass for energy production. This paper presents the results of laboratory analyses performed on wood chip samples from four Italian regions over a five-year period (2019–2023). In particular, all quality parameters defined by ISO 17225-9 for industrial wood chips were assessed. Data were analyzed using descriptive, parametric, non-parametric statistics, and multivariate analysis. An interest in quality monitoring has been observed, indicated by an increase in the number of samples received from suppliers and an enhancement in the average values of quality parameters. Moreover, an overall decrease in moisture and N content has been observed, while ash content and heating value have undergone non-linear variations. Statistically significant quality differences between samples from different regions may be the result of different practices, such as outdoor or indoor storage, climate differences, different biomass growth conditions. [ABSTRACT FROM AUTHOR]

The water content is an essential parameter for assessing the quality of solid biofuels. In terms of economic, technical and environmental aspects a continuous determination of the solid fuel water content is sought. This article investigates the use of microwave technology for the continuous measurement of fuel water content. For this purpose, a microwave sensor was evaluated with five different types of wood chips (forest residues, beech, pine, and ash). The results of the online measurements showed a strong correlation with the reference method r < 0.9 for most materials. This means that continuous water content determination of wood fuels using microwave technology is fundamentally possible. [ABSTRACT FROM AUTHOR]

One of the prominent technologies in biomass energy applications is commercial biomass combustion systems. While burning forest-derived biomass is a well-established and proven technology, the combustion of agricultural residues poses more challenges compared to forest-derived fuels. These challenges vary depending on factors such as the design of the combustion system, operational conditions, and the type, physical, and chemical properties of the biomass to be burned. Sintering, agglomeration, slagging, and corrosion are among the major issues that affect the regular and continuous operation of the combustion system, leading to unplanned shutdowns. This study investigates the applicability of common coal ash indices, widely used in the literature to predict these problems, to biomass ash for pre-analysis. Five different biomass feedstocks (reed canary grass, corn stalk, pine, poplar, and tree root) stored in open silos were sampled at two different time periods. Analyses of ash mineral content, chlorine content, sulfur content, and ash fusion temperatures were conducted, and various indices were calculated. Thus, changes in the problems related to biomass fuels depending on storage conditions will also be examined. As a result of the analyses and calculations, no significant relationship or prediction could be demonstrated among the existing indices due to the considerable differences between biomass ash and coal ash, as well as the heterogeneous nature of biomass feedstocks. The contradictory results highlight the necessity for further research and experimental tests under real conditions to establish or verify these indices. It is concluded that a more comprehensive evaluation, taking into account the heterogeneous structure and physicochemical characterization of solid biomass fuels, will be required based on actual combustion experiences. [ABSTRACT FROM AUTHOR]

Thermogravimetric analysis (TGA) was performed on six samples of pine wood, poplar sawdust and olive residue, and the kinetic parameters were evaluated by using isoconversional models. The hemicellulose, cellulose and lignin contents were also estimated using the Fraser–Suzuki deconvolution method. In addition, a range of thermodynamic parameters and combustion indices was calculated. Significant correlations were found between the kinetic, thermodynamic and combustion parameters. The ignition index showed an inverse relationship with the activation energy, whereas the burnout index correlated with enthalpy values for most samples. Higher heating rates during TGA increased ignition and combustion efficiencies but decreased combustion stability. Differences in behaviour were detected between the olive residues, which had a much higher lignin content (51.2–56.9%), and the woody biomass samples (24.2–29.2%). Moreover, the sample with the highest ash content also exhibited some distinctive characteristics, including the lowest high heating value and ignition index, coupled with the highest activation energy, indicating a less favourable combustion behaviour than the other samples. The particle size of the samples was also found to be critical for both combustion efficiency and safety.

Biomass continues to play a key role as an alternative to fossil fuels. Woody biomass produces lower greenhouse gas emissions than fossil fuels. However, in order to consider biomass as ‘green energy’, a number of factors should be taken into account, including the characterization of the quality of the resource. Therefore, monitoring quality parameters, such as moisture, ash, N content, is essential to assess the sustainability of biomass for energy production. This paper presents the results of laboratory analyses performed on wood chip samples from four Italian regions over a five-year period (2019–2023). In particular, all quality parameters defined by ISO 17225-9 for industrial wood chips were assessed. Data were analyzed using descriptive, parametric, non-parametric statistics, and multivariate analysis. An interest in quality monitoring has been observed, indicated by an increase in the number of samples received from suppliers and an enhancement in the average values of quality parameters. Moreover, an overall decrease in moisture and N content has been observed, while ash content and heating value have undergone non-linear variations. Statistically significant quality differences between samples from different regions may be the result of different practices, such as outdoor or indoor storage, climate differences, different biomass growth conditions.

One effective measure to achieve carbon neutrality is to shift away from coal. Wet torrefied biomass (WTB) can be the promising solid biofuels to replace coal, when high moisture content biomass is used as feedstock. To utilize WTB for industrial use, WTB with predetermined energy properties such as higher heating value (HHV) and solid mass yield (SMY) has to be produced to meet the requirement in coal-fired power plants and industrial boilers. In this study, the analytical approach to estimate SMY and HHV of WTB for given wet torrefaction (WT) process parameters, temperature and residence time is investigated for Japanese cedar and rice straw. The Van Krevelen diagram shows that dehydration is considered as a main reaction of WTB, which is the same result as the previous studies on dry torrefied biomass (DTB). HHVs of WTB as well as DTB are well correlated with its SMY, and the experimental correlations of HHV are proposed as a function of SMY. The difference in HHV of rice straw between WTB and DTB and the difference in HHV between Japanese cedar and rice straw are closely related to the difference in ash content and the ash removal effect in WT process. The WT reaction based on volatile release is modeled as the single reaction with only one reaction rate constant of volatiles evolved. It is found that the solid-state reaction function codes F12 and D1 are the most suitable for Japanese cedar and rice straw, and kinetic parameters in WT process are determined. The estimation method of SMY and HHV is proposed based on the WT kinetic model and the HHV experimental correlation. It is found that the WT temperature and residence time to produce WTB with predetermined SMY and HHV can be provided by the proposed estimation method within an accuracy of about 10%.

Forest dendromass is still the major raw material in the production of solid biofuels, which are still the most important feedstock in the structure of primary energy production from renewable energy sources. Because of the high species and type diversity of production residues generated at wood processing sites, as well as at logging sites, the quality of commercial solid biomass produced there has to be evaluated. The aim of this study was to assess the thermophysical characteristics and the elemental composition of ten types of commercial solid biofuels (pinewood sawdust; energy chips I, II, and III; veneer sheets; shavings; birch bark; pine bark; pulp chips; and veneer chips), depending on their acquisition time (August, October, December, February, April, and June). Pulp chips had the significantly lowest moisture content (mean 26.92%), ash content (mean 0.39% DM—dry matter), nitrogen (N) content (mean 0.11% DM), and sulfur (S) content (mean 0.011% DM) and the highest carbon (C) content (mean 56.09% DM), hydrogen (H) content (6.40% DM), and lower heating value (LHV) (mean 13.61 GJ Mg−1). The three types of energy chips (I, II, and III) had good energy parameters, especially regarding their satisfactory LHV and ash, S, and N content. On the other hand, pine and birch bark had the worst ash, S, and N contents, although they had beneficial higher heating values (HHVs) and C contents. Solid biofuels acquired in summer (June) had the lowest levels of moisture and ash and the highest LHV. The highest moisture content and the lowest LHV were found in winter (December). [ABSTRACT FROM AUTHOR]

Due to ongoing changes in the European energy market, there is currently a need to find new and additional uses for waste materials. Horticultural waste, which has not yet been fully recognized, offers a relatively wide potential in this area. Although the properties of these wastes are not ideal for combustion, they can be used as a solid biofuel. The pellets that are produced, however, may have useful properties, either energetic or environmental, and are valuable when utilized in boilers. In this study, six examples of typical input raw materials were selected, analysed, and subsequently pelletized. The experimental results provided an overview of the physio-chemical properties of the evaluated samples. Specifically, the moisture content (9.2–27.8%), bulk density (131.4–242.8 kg·m−3 wt), ash content (3.0–28.0%), lower calorific value (11.3–16.2 MJ·kg−1), and major and minor elements, were evaluated. The pelletization process and resultant pellet characteristics, such as durability (96.3–98.8%), moisture content (7.5–11.5%), and dimensions, were also evaluated. In the statistical evaluation, significant differences were found between individual samples. In particular, both the branches and the mixture of perennial plants met the industry standard limits, showing that they are of sufficient quality. On the contrary, the sample of fallen leaves was particularly problematic with regard to a number of parameters (moisture, ash content, and calorific value). The overview of the analyses performed expands the current state of knowledge on the potential to use selected types of horticultural waste in the field of energy and for the production of shaped biofuels. [ABSTRACT FROM AUTHOR]

Fuel properties of solid biofuels are essential aspects for the energy‐efficient and low‐emission operation of biomass heat and power plants. Hence, fuel quality parameters are often defined and used for pricing in supply contracts. To simplify and accelerate analytical approaches, rapid analysis devices are required to determine fuel properties such as water‐ and ash content, calorific value, and chemical composition on‐site. This article gives an overview about available technologies and, if applicable, their current state of use as rapid analysis devices for solid biofuels. [ABSTRACT FROM AUTHOR]

This study determines the cost of producing different biofuels such as wood chips and pellets. It evaluates the factors that determine the cost of solid biofuels (SBFs), such as raw material, location, and transportation cost. The analysis is carried out with two different raw materials, sawdust, forest residue and pruning, and takes into account three different locations: Durango, State of Mexico, and Jalisco. The production cost in USD per GJ is determined. This cost is compared with the cost of generating the same amount of energy using fuel oil to evaluate the circumstances under which the application of solid biofuel would be feasible. An elementary CO2 emissions analysis of transportation has also been developed to compare these emissions with those of the fuel oil currently used to evaluate the feasibility from an environmental point of view. Transportation largely determines the cost of production and the feasibility of applying solid biofuel. Some indications about the maximum distances that the SBF can be transported to its final use are provided. © 2023 Society of Industrial Chemistry and John Wiley & Sons Ltd. [ABSTRACT FROM AUTHOR]

The transition from original feedstock to torrefied and pyrolyzed biofuels was investigated on a small-scale automatic pellet boiler. Thermal treatment significantly improves fuel quality; however, several technological difficulties were encountered. The entrainment of unburnt fuel particles led to severe CO, TOC and PM emissions as well as a drop in power output. All these issues were exacerbated when firing herbaceous biomass. It was found that most of the emitted particles are smaller than 1 μm in aerodynamic diameter, which necessitates additional flue gas filtering. Furthermore, 16 selected PAHs were individually monitored to evaluate the effect of thermal treatment on PAHs emissions and composition. On average, the most abundant PAH was naphthalene (4135 μg·kg fuel −1), followed by phenanthrene (246 μg·kg fuel −1), acenaphthylene (145 μg·kg fuel −1), fluoranthene (97 μg·kg fuel −1) and pyrene (95 μg·kg fuel −1). Benzo(a)pyrene contributed minimally to the total PAHs emissions (on average 16.6 μg·kg fuel −1). The 16 selected PAHs constitute only about 0.1–1.1 % of the total organic carbon emitted from solid biofuel combustion. [ABSTRACT FROM AUTHOR]

This study reviews the state-of-the-art (2014–2020) of biofuels from all generation categories, collecting information from 150 case studies to address concerns about the environmental sustainability and the potential of biofuels to contribute to the energy system without compromising its viability. Levels of Energy Return on Investment for refined products (EROI final) are used as reference: <3:1 (net sink for society) and >8:1 (better performance than global-average oil products). First-generation biofuels (from edible crops): none of the reviewed studies reported EROI final >8:1; most of the reviewed studies reported EROI final <3:1. Second-generation biofuels (from non-edible crops & residues): The EROI final can be higher compared to first-generation biofuels, although with large uncertainties/range. EROI final >3:1 in the case of herbaceous crops (∼4:1), and for crop and forest residues for certain feedstocks or under certain conditions; EROI final >8:1 in the case of agricultural residues under certain conditions. Third-generation biofuels (from algae): the technological advancements are slow; several challenges need to be overcome to reach large-scale production; reported EROI final close to 1:1. The collected data on environmental aspects for all generation types are fragmentary and insufficient to reach robust conclusions. Only 5 % of the reviewed case studies are based on pilot/demonstration scale plants, raising the question of potential discrepancies between theoretical and actual values. System boundaries and assumptions have a key role in the obtained results; therefore, the utilisation of standard protocols in the calculation of EROI across studies is essential. Studies should consider additional environmental metrics to address all sustainability concerns related to biofuel production. [Display omitted] • Only 5 % of the 150 reviewed case studies are based on pilot/demonstration plants. • EROI final : <3:1 net sink for society; >8:1 better performance than oil products. • 1st generation (edible crops): none of the reviewed studies reports EROI final >8:1. • 2nd generation: EROI final >8:1 for crop residues under certain conditions. • 3rd generation (algae): EROI final close to 1:1. [ABSTRACT FROM AUTHOR]

Forest dendromass is still the major raw material in the production of solid biofuels, which are still the most important feedstock in the structure of primary energy production from renewable energy sources. Because of the high species and type diversity of production residues generated at wood processing sites, as well as at logging sites, the quality of commercial solid biomass produced there has to be evaluated. The aim of this study was to assess the thermophysical characteristics and the elemental composition of ten types of commercial solid biofuels (pinewood sawdust; energy chips I, II, and III; veneer sheets; shavings; birch bark; pine bark; pulp chips; and veneer chips), depending on their acquisition time (August, October, December, February, April, and June). Pulp chips had the significantly lowest moisture content (mean 26.92%), ash content (mean 0.39% DM—dry matter), nitrogen (N) content (mean 0.11% DM), and sulfur (S) content (mean 0.011% DM) and the highest carbon (C) content (mean 56.09% DM), hydrogen (H) content (6.40% DM), and lower heating value (LHV) (mean 13.61 GJ Mg−1). The three types of energy chips (I, II, and III) had good energy parameters, especially regarding their satisfactory LHV and ash, S, and N content. On the other hand, pine and birch bark had the worst ash, S, and N contents, although they had beneficial higher heating values (HHVs) and C contents. Solid biofuels acquired in summer (June) had the lowest levels of moisture and ash and the highest LHV. The highest moisture content and the lowest LHV were found in winter (December).

Biomass represents 10% of the total energy use and 55% of all renewable energy in Mexico. It is a key energy source to help Mexico achieve a low-carbon development path to comply with the strict climate mitigation targets needed to avoid catastrophic consequences. However, a major limitation in the construction of reliable future mitigation scenarios is the lack of information regarding in-country greenhouse emission factors associated to both traditional and modern bioenergy devices. This paper aims to close this gap, providing detailed estimates of energy and emission factors from bioenergy devices in the Mexican residential and industrial sectors. In particular, four energy tasks, comprising 67% of current bioenergy use in the country, were selected (charcoal production, biomass drying, space heating, and cooking) with a total of nine bioenergy devices: traditional earth mound charcoal kiln, flash dryer, heater, five types of cookstoves, and an open fire. The thermal efficiency ranged from 10 ± 1 to 26 ± 5% for the cooking devices, 95 ± 1 to 96 ± 1% for the space heater, 34 ± 8% for the charcoal kiln, and 10 ± 2% for the biomass dryer. The modified combustion efficiency was calculated to be 88 ± 1% for the earth mound charcoal kiln, 96–98% for the cookstove, and 93–98% for the space heater. The products of incomplete combustion ranged from 21 ± 6 to 48 ± 12 g for the cooking devices and 58 ± 18 to 340 ± 107 g for the space heaters. CO2 emission factors ranged from 102 ± 2 to 119 ± 2 g/MJ for the local biomass stoves. Relative to other pollutants, the CO emissions per energy unit were the highest, ranging from 1193 ± 184 mg/MJ for the space heater to 18,121 ± 1232 mg/MJ for the earth mound charcoal kiln. The total global warming potential was estimated to be 35 ± 2 gCO2e/MJ for the ONIL stove (modified) and 158 ± 4 gCO2e/MJ for the earth mound charcoal kiln. The estimates presented in this study represent an important contribution to Mexico's inventories in terms of energy performance and emissions parameters of four energy tasks in the industrial and residential sectors. This information will be a baseline to estimate carbon footprint, life cycle assessments, GHG emissions scenarios, and mitigation strategies for local and regional Mexican conditions. [ABSTRACT FROM AUTHOR]

Detailed studies about energy content and chemical characterization of biomass alternatives are necessary to determine their main features as solid fuels. The aim of this study was to analyze and compare the properties of five types of residual biomass pellets produced throughout Mexico: sawmill pine waste (SPW), spent ground coffee (SGC), pecan nutshell (PN), oil palm waste (OPW), and mango waste (MW). Conventional characterization analyses revealed significant differences in HHV (21.44–17.37 MJ/kg), elemental composition showed a lower carbon content in SPW and MW (around 46%), OPW (close to 47%), and higher carbon content in PN and SGC (around 51%). The concentration of the main structural polymers showed notable significant differences (p < 0.05) too: 49–17% for cellulose, for hemicellulose 21–5% and for lignin 26–4%. High-throughput instrumental techniques were also used: FTIR provided additional information on chemical composition in pellets on which lignocellulosic biomass was not predominant, presence of pectins and starch in MW, and high content of fatty acids in SGC and OPW; TGA showed different thermal stability of pellets in the combustion process, where OPW and SPW presented the lowest and highest thermal stability, respectively, while XPS showed different types of bonds between C and O in the surface of materials with a relevant presence of bonds associated to lignin covering PN and SPW. Based on results of this investigation, a possible rank for the energy use of these five biomasses is suggested: PN, SPW, SGC, OPW, and MW, but future deep research is necessary that incorporate other relevant attributes, mechanical properties, emission profiles, corrosion, and slagging effects. [ABSTRACT FROM AUTHOR]

This study applies environmental life cycle assessment to quantify and compare the environmental profile of the production and use of wood pellets for residential heating (baseline) and compares the pellet system with two different alternative systems for residential heating in Mexico: (1) the use of LPG heater and (2) one electricity heater powered by three different sources of electricity. The baseline system boundaries include the stages of forest management, transportation, industrial, distribution, wood pellet energy conversion, and ash management. First-hand data and measurements of the emission profiles in the field and laboratory were developed. The functional unit was 1 MJ of thermal energy for residential heating. Environmental impacts were calculated for six impact categories from the ReCiPe midpoint method. Furthermore, a sensitivity analysis was performed to evaluate the influence of the allocation criteria (mass and economic) as well as adopting different values for the electricity sources (system's hotspots). The results obtained for each impact category show a relatively wide range of variation when the five scenarios of the heating systems are compared and analyzed. Electricity heater powered with photovoltaic electricity is better for all the impact categories analyzed. The performance of pellets and LPG is very close, but the pellets have lower impacts on global warming (three times), fossil resource scarcity (four times), and acidification. Therefore, the use of pellets in an efficient boiler is a promising option for residential heating. [ABSTRACT FROM AUTHOR]

Summary: Various organic waste streams are generated daily by human activities such as municipal, agricultural and industrial. The sustainable disposal of these organic wastes is a serious societal challenge. When the disposal process is not efficient, this type of wastes creates important pollution risks for air, soil, underground water and sea. Especially, wastes that have high moisture content cannot be eliminated cost effectively via thermo‐chemical conversion by conventional processes such as pyrolysis, gasification and combustion. These processes necessitate the pre‐drying of wet wastes which require additional energy input and increase the operational costs. One promising approach for the management and valorization of highly wet waste streams is the use of hydrothermal technologies. Hydrothermal carbonization is a very appropriate approach for valorizing wet organic wastes using water as a medium at high temperature and pressure under subcritical conditions. The generated "hydrochar" is a solid lignite like material that can be used for energy generation (by gasification or combustion) but also for environmental practices such as soil remediation and carbon fixation. This review focuses on the feedstock potential of wet organic wastes of sewage sludge, food wastes, various animal manure and macroalgae, and their valorization by hydrothermal carbonization. Structural, physical and energy conversion characteristics of hydrochars produced from various wet organic wastes are compared and discussed. Usage areas of hydrochars are also assessed. [ABSTRACT FROM AUTHOR]

The torrefied solid biofuels have come to attract attention as promising alternative fuels to coal in coal-fired power plants and industrial boilers. The torrefaction is a thermal treatment performed at mild pyrolysis temperatures to reform biomass and includes two distinct technologies, dry torrefaction (DT) and wet torrefaction (WT). The DT is the conventional thermal treatment conducted in the absence of oxygen under atmospheric pressure in a temperature range of 200-300 ℃, while the WT is a thermal treatment in hydrothermal media or hot compressed water in a temperature range of 180-260 ℃. Both torrefaction treatments can produce energy dense solid biofuels with better chemical, physical properties than original biomass feedstock, but the external energy input is required for the torrefaction treatment. Especially, when producing the torrefied solid biofuels from biomass feedstock with high moisture content, the energy consumption for drying process may have a negative impact on the sustainability of the torrefied biofuel. In this article, properties of thermally treated biomass by DT and WT are summarized, and then the net energy content of torrefied biofuels is presented to evaluate the sustainability. The net energy content is expressed as a function of mass yield, and the optimum torrefaction condition with high net energy content can be evaluated by the relation for the net energy content. [ABSTRACT FROM AUTHOR]

Leveraging biofuel derived from biomass stands as a pivotal strategy in reducing CO 2 emissions and mitigating the greenhouse effect. Biomass serves as a clean, renewable energy source, offering inherent benefits. However, despite its advantages, biomass encounters obstacles hindering its widespread industrial applications, including its relatively low calorific value, limited grindability, high water content, and susceptibility to corrosion. The torrefaction process has garnered significant attention as an effective method for enhancing the quality of raw biomass for energy production. In this review, we briefly discussed the mechanism of bio-coal preparation using biomass, physico-chemical characterization of different torrefied feedstocks, and the effect of torrefaction parameters, along with the effect of the different types of reactors on biomass torrefaction. Furthermore, bio-coal's emission characteristics and fuel quality throughout the thermal treatment have been covered. Thus, bio-coal finds a wide range of applications in sustainable energy generation, environmental remediation, agri-food development, polymer composites, and others., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Rising environmental concerns associated with the domestic use of solid biofuels have driven the search for clean energy alternatives. This study investigated the in vitro toxicological characteristics of PM 2.5 emissions from residential biomass pellet burning using the A549 epithelial cell line. The potential of modern pellet applications to reduce PM 2.5 emissions was evaluated by considering both mass reduction and toxicity modification. PM 2.5 emissions from raw and pelletized biomass combustion reduced cell viability, indicative of acute toxicity, and also protein expression associated with epithelial barrier integrity, implying further systemic toxicity, potentially via an oxidative stress mechanism. Toxicity varied between PM 2.5 emissions from raw biomass and pellets, with pelletized straw and wood inducing cytotoxicity by factors of 0.54 and 1.30, and causing epithelial barrier damage by factors of 1.76 and 2.08, respectively, compared to their raw counterparts. Factoring in both mass reduction and toxicity modifications, PM 2.5 emissions from pelletized straw and wood dropped to 1.83 and 5.07 g/kg, respectively, from 30.1 to 9.32 g/kg for raw biomass combustion. This study underscores the effectiveness of pelletized biomass, particularly straw pellets, as a sustainable alternative to traditional biofuels and highlights the necessity of considering changes in toxicity when assessing the potential of clean fuels to mitigate emissions of the PM 2.5 complex.

Hardwood sawdust derived from primary wood processing was used to make adhesive-free briquettes in a hydraulic piston laboratory machine. For this purpose, 40 g of sawdust was used, and the conditions of the briquetting process were 5 min of pressing at 20 MPa and 50 °C. The results varied as follows: moisture (5.1 to 8.8%), density (1056.2 to 1208.8 kg m−3), volumetric expansion (3.3 to 38.9%), compressive strength (10.3 to 98.6 N mm−1), impact resistance index (46.6 to 200%), ash (1.2 to 3.9%), volatile matter (79.6 to 90.9%), fixed carbon (7.8 to 16.6%), and calorific value (19.2 to 21.2 MJ kg−1). In general, significant differences (p < 0.05) were found in the results obtained. The density of the briquettes produced was greater than 1000 kg m−3. It was observed that the higher the density of the briquettes and the lower their volumetric expansión were, the higher the breaking force and the higher the impact resistance index were. Ash values were relatively high, and the briquettes did not meet international quality standards but they could be used locally as a source of heat energy. Finally, the physical, mechanical, and energetic evaluation of the briquettes made at the laboratory level indicates that this lignocellulosic residue can be used for densification at an industrial level. [ABSTRACT FROM AUTHOR]

The use of inert gases such as nitrogen continuously during torrefaction causes a burden in terms of operational cost. Therefore, a novel concept of mild pressurization has been introduced to eliminate the dependence on the inlet gas completely. In the present study, the torrefaction of fibrous empty fruit bunch (EFB) was performed for various temperatures of 250 °C–300 °C and residence times of 30–90 min. The pressure exerted by the load during torrefaction was 0.0230 MPa. The results show that torrefaction temperature is a dominant parameter in affecting physical and physicochemical properties as well as thermal stability of the torrefied EFB rather than residence time. An increase in temperature causes an improvement in gross calorific value, hydrophobicity, atomic H/C and O/C ratios as well as thermal stability. Besides, it was found that the EFB experiences a significant change after torrefaction at temperature of 300 °C in terms of surface, microstructure, crystallographic structure and functional groups. This is mainly due to the significant decomposition of the main biomass constituents especially hemicellulose and cellulose. Overall, it can be concluded that the best performance was obtained at torrefaction temperature of 300 °C and residence time of 90 min. [Display omitted] [ABSTRACT FROM AUTHOR]

In 2021, more than 40 countries have agreed with "de-coal" statement at the COP26. The torrefied solid biofuels have come to attract attention as promising alternative fuels to coal in coal-fired power plants and industrial boilers. However, the energy property such as higher heating value (HHV) and energy yield of torrefied biomass, which is one of the most important fuel properties, has been evaluated by means of experiments for various biomass species so far. That is, the torrefaction conditions to produce torrefied solid biofuel with predetermined HHV have been provided only empirically. In this study, a generalized HHV estimation method applicable to any torrefied woody biomass is investigated based on pyrolysis kinetics of primary constituent polymers of woody biomass, cellulose, lignin and xylan. Analyses of pyrolysis kinetics of constituent polymers are conducted by assuming that the process in non-isothermal pyrolysis experiments is modeled as the single reaction. The HHVs of torrefied constituent polymers are obtained by isothermal torrefaction experiments, and the experimental correlations of HHV of torrefied constituent polymers are proposed as a function of solid mass yield. For a given woody biomass whose mass fractions of three constituent polymers are known, HHV of torrefied woody biomass produced with any torrefaction condition can be estimated by applying pyrolysis kinetic models and experimental correlations of HHV for three constituent polymers to the torrefaction process of woody biomass. From the comparison between estimated HHV of torrefied woody biomass and experimental data, it is concluded that the generalized HHV estimation method can be useful for evaluating HHV of torrefied woody biomass with about 10% accuracy, although the HHV is somewhat underestimated.

Lignin pellets were produced using a single pellet system as well as a laboratory-scale pellet mill. The feedstock used in this work was lignin isolated from poplar wood (Populus tremuloides) using a direct saccharification process. An investigation was performed on the influence of the initial moisture content on the dimensions, impact and water resistance, fines content, mechanical durability, calorific value, and ash content, and, finally, the ultimate analysis was performed. These properties were then compared to pellets made from softwood bark using the same pelletization unit. Lignin pellets were then manufactured using four different types of additives (corn oil, citric acid, glycerol, and d-xylose) and ultimately, they were stored in two different conditions prior being tested. In general, manufacturing pellets that were entirely made of lignin generated samples with an overall higher hydrophobicity and higher calorific value. However, the ash and sulfur content of the lignin pellets (1.58% and 0.32% in scenario 2, respectively) were slightly higher than the expected CANplus certification values for Grade A pellets of ≤0.7%, and ≤0.04%, respectively. This study intends to show that lignin could be used to produce this new kind of pellets, pending that the initial material has a low ash and moisture content. [ABSTRACT FROM AUTHOR]

Fuel wood pellets have the tendency of undergoing self-heating and off-gassing during storage and transportation. Self-heating can lead to spontaneous combustion and cause fires while toxic gasses such as carbon monoxide and some volatile organic compounds released due to off-gassing are a human health and environmental hazard. Previous research suggests that the self-heating and off-gassing of wood pellets are as a result of the oxidation of wood extractives. The aim of this study was to identify the extractives, i.e., fatty and resin acids that are responsible for the emissions of carbon monoxide, carbon dioxide and methane from wood pellets by testing the off-gassing tendencies of pellets produced from synthetic microcrystalline cellulose and different additive oils. The additive oils were intentionally selected to represent different types of wood extractives (mainly fatty and resin acids) and they included: tall oil, pine rosin, linseed oil and coconut oil. The highest mean concentrations of carbon monoxide, carbon dioxide and methane were recorded from cellulose pellets with added linseed oil. The concentrations of carbon monoxide and methane for the other four pellet types were negligible and there was no carbon dioxide emission. Pellets with added linseed oil had high off-gas emissions due to the high content of unsaturated fatty acids compared to other pellet types. [ABSTRACT FROM AUTHOR]

Agro-industries, leveraged by the high demand of acai products, promote environmental impact through the generation of wastes in several locals in Amazon. The use with bioenergetic purposes has capacity to mitigate these scenario. Thus, the aim of the study was to characterize the biomass of acai seeds and establish the technical parameters of temperature and pressure of work to the production of briquettes of physical, mechanical and thermal quality. Temperatures of 120, 140 and 160 °C; and pressures of 15, 20 and 25 MPa were studied. We analyzed the briquettes mechanical compressive strength, rate of water absorption, rate of volumetric expansion and energy and apparent density. To the characterization of in natura seeds, the proximate analysis, chemical composition (extractives, holocellulose and lignin contents), higher, lower and useful heating value were determined. The proximate analysis indicated biomass thermal resistance, potential to direct burning and conversion by thermochemical processes. The lignin content may increase briquettes compressive strength produced in high temperatures. It was observed that the temperature had more influence in the evaluated briquettes characteristics than the pressure. The compressive strength was greater in 160 °C and 15 MPa briquettes, indicating that the lignin works as binder in this temperature, however, with pressure improvement the resistance is not favored due to the limit of resistance to compaction. The rate of water absorption decreased with the pressure increase and the temperature statistically affected in 140 °C briquettes. We observed volumetric expansion values in consonance to other found in dense biofuels of the literature. Further, the apparent density and energy density were favored by pressure improvement and the temperature helped in the increase of the apparent density. Moreover, the produced briquettes presented gain in the apparent density regarding the in natura biomass and had energy density comparable to coal and adequate to co-firing in boilers. [ABSTRACT FROM AUTHOR]

Renewable energy technologies have the great advantage of using inexhaustible, low-polluting resources with an insignificant contribution to climate change. In addition, their use reduces dependence on conventional resources that will be depleted in the not-too-distant future. Solid biofuels are produced from biomass materials, especially wood, and are new fuels that meet the new requirements of using "clean" and regenerative energy. The paper presents a series of experimental research for obtaining biomass tablets using specially designed equipment, which are a viable solution for the recovery of lignocellulosic waste from vineyards and orchards and beyond. [ABSTRACT FROM AUTHOR]

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The article is aimed at substantiating the basic technical-economic characteristics of energy plantations of miscanthus and production of solid fuels from the obtained biomass on the example of a particular project. As a result of the study: the analysis of the production volume of solid biofuels on the basis of quantities from a given area of plantation was carried out; net income of the complex was determined, which was calculated on the basis of accepted production volumes and «reasonable» wholesale prices, which were determined in a costly manner and provided for the provision of a sufficient level of profitability of economic activity; the current (operational) costs of economic activity of the complex were determined, calculated according to the standards established by analogues of industrial production of biomass from energy crops and its processing into solid biofuels. Also the economic feasibility of implementing an investment project on laying the plantation of miscanthus and production of solid biofuels from the resulting biomass was assessed. In general, in the presence of adequate State-based stimulation of solid biofuel production from miscanthus biomass, the economic efficiency of the project will be high, and the project itself is commercially feasible. Prospects for further research in this direction are substantiation of the main technical-economic characteristics together with feasibility of creating complexes for the transformation of solid biofuels into commodity energy – both electric and thermal.

The study investigates the impact of decomposition processes of beech and pine wood on the fuel quality and the combustion chemistry in a wood‐burning stove. Especially, when considering the volume of wood fed, the burning time and energy output decrease with the stage of decomposition. The gaseous emissions as well as the total dust emissions do not change, depending on the decomposition processes. However, at the experiments carried out here, the combustion of softwood generally showed lower gaseous emissions than hardwood. [ABSTRACT FROM AUTHOR]