Solid Biofuel Production Research Articles

Carnauba Straw as Feedstock for Solid Biofuel Production

Carnauba straw (<em>Copernicia prunifera</em>), residual biomass derived from wax extraction, was evaluated as a potential feedstock for bioenergy production. The characterization was carried out using elemental analysis, proximate analysis, Higher Heating Value (HHV), FTIR spectroscopy, SEM, and FRX. The carbonization, using a Muffle Furnace, was applied as a thermal conversion technique to improve the fixed carbon content, and preliminary densification was done to assess the potential for future production of briquettes. The C, H, N, O, and S percentages were 44.43%, 5.34%, 2.25%, 46.17%, and 1.81%, respectively. The percentage of fixed carbon (14.17%) increased to 31.10% (250°C) and 35.68% (300°C) after carbonization. At 400°C, the HHV presented a decrease of 9.62%, and ash content increased by 177.66%. FTIR spectra showed bands characteristic of hemicellulose, cellulose, and lignin at 3414 - 3393 cm<sup>-1</sup> (O-H) and decrease of absorbance of 74.01% to 81.37% after carbonization; 1738 – 1603 cm<sup>-1</sup> (C=O), with reduction in the order of 73.94% to 78.31%, and 48.97% to 73.76%, when compared to the absorbances of the biomass in nature. The SEM of the carnauba straw in nature presented the main structural components (cellulose, lignin, and hemicellulose). After carbonization, evidence of degradation and coal formation was observed, which corroborates with the decrease in the HHV and increase of ash. The FRX was inserted in the SEM images, and the elements detected were Ca, K, and S. The quantities and order of abundance in biomass natural and carbonized were compatible with other biomasses used as biofuel. The carnauba straw in natural and carbonized was densified to understand the characteristics of the compacted material. The sample carbonized at 300°C presented a solid with the potential for future production of briquettes. All results follow other reported biomasses and could lead to further investigation of the carnauba straw as feedstock for solid fuel production without or in a mixture with other agricultural residues.

Comparative advantages analysis of oxidative torrefaction for solid biofuel production and property upgrading

This study performs the comparative advantage analysis of oxidative torrefaction of corn stalks to investigate the advantages of oxidative torrefaction for biochar fuel property upgrading. The obtained results indicate that oxidative torrefaction is more efficient in realizing mass loss and energy density improvement, as well as elemental carbon accumulation and surface functional groups removal, and thus leads to a better fuel property. The maximum values of relative mass loss, higher heating value, enhancement factor, and energy yield are 3.00, 1.10, 1.03, and 0.87, respectively. The relative elemental carbon, hydrogen, and oxygen content ranges are 1.30–3.10, 1.50–3.30, and 2.00–6.80, respectively. In addition, an excellent linear distribution is obtained between the comprehensive pyrolysis index and torrefaction severity index, with elemental carbon and oxygen component variation stemming from pyrolysis performance correlating to the elemental component and valance.

Investigation of the Effects of Cohydrothermal Carbonization on the Physicochemical Characteristics and Combustion Behavior of Straw Hydrochars

The use of straw biomass for energy can reduce the use of fossil energy and alleviate air pollution. Herein, the cohydrothermal carbonization (Co‐HTC) of rice straw and wheat straw with corn straw is investigated, and synergistic effects of multistraw biomass are observed in the Co‐HTC process. When the corn straw ratio is 75%, the energetic recovery efficiency, C content, and heating value increase compared to the calculated values of the Co‐HTC products. At 260 °C, the energetic recovery efficiency increases by 8.96% and the heating value increases by 2.28 MJ kg−1, which is beneficial for its application. The positive synergistic effect is probably caused by the enhanced dehydration and decarboxylation reactions. For the combustion behavior analysis, the entire combustion process is divided into two stages. When the corn straw ratio is greater than 50%, compared to the calculated values of the Co‐HTC products, the comprehensive combustibility index and activation energy of stage I increase and the activation energy of stage II decreases at 180 °C, while the activation energy of stage I decreases and the activation energy of stage II increases at 260 °C. These findings demonstrate that the Co‐HTC of multistraw biomass is suitable for solid biofuel production.

Use of Artificial Neural Networks to Model Biomass Properties of Miscanthus (Miscanthus × giganteus) and Virginia Mallow (Sida hermaphrodita L.) in View of Harvest Season

Miscanthus and Virginia Mallow are energy crops characterized by high yields, perenniality, and low agrotechnical requirements and have great potential for solid and liquid biofuel production. Later harvest dates result in lower yields but better-quality mass for combustion, while on the other hand, when biomass is used for biogas production, harvesting in the autumn gives better results due to lower lignin content and higher moisture content. The aim of this work was to determine not only the influence of the harvest date on the energetic properties but also how accurately artificial neural networks can predict the given parameters. The yield of dry matter in the first year of experimentation for this research was on average twice as high in spring compared to autumn for Miscanthus (40 t/ha to 20 t/ha) and for Virginia Mallow (11 t/ha to 8 t/ha). Miscanthus contained 52.62% carbon in the spring, which is also the highest percentage determined in this study, while Virginia Mallow contained 51.51% carbon. For both crops studied, delaying the harvest date had a positive effect on ash content, such that the ash content of Miscanthus in the spring was about 1.5%, while in the autumn it was 2.2%. Harvest date had a significant effect on the increase of lignin in both plants, while Miscanthus also showed an increase in cellulose from 47.42% in autumn to 53.5% in spring. Artificial neural networks used to predict higher and lower heating values showed good results with lower errors when values obtained from biomass elemental composition were used as input parameters than those obtained from proximity analysis.

Systematic homogenization of heterogenous biomass batches – Industrial-scale production of solid biofuels in two case studies

Biomass is a heterogeneous material with respect to its chemical composition due to different plant species and components as well as the potential content of impurities. Especially in the production of large fuel batches heterogeneous chemical compositions are a challenge with respect to the required compliance with fuel standards and emission thresholds during utilization. This can be avoided by fuel pre-treatment and systematic homogenization during fuel production. For this reason, the study analyses the effects of biomass leaching in combination with homogenization of biomass batches on industrial-scale. Within two case studies, low-quality herbaceous biomasses, i.e. foliage and wheat straw were pretreated and homogenized in quantities ranging from 8 to 51 tons. In the first case study, foliage was first leached, then mixed with sawdust and homogenized by separating batch parts with high ash content, followed by systematic recombination of the batches. In the second case study, homogenization of straw pellets (untreated and leached) was attempted by a layering approach during bagging. Both case studies (i) confirm earlier findings that critical fuel components can be substantially reduced by leaching (i.e. reduction of ash content MV by 45 w-%) but indicate that material agitation during leaching is necessary; (ii) underscore that systematic homogenization is necessary for fuel batches consisting of materials from different origins and reduce i.e.-the ash content RSD by 48%, and (iii) demonstrate that even low-quality fuels from herbaceous biomass assortments can comply with the requirements of fuel standards if dedicated fuel pretreatment is employed.

Evaluation of Babassu Cake Generated in the Extraction of the Oil as Feedstock for Biofuel Production

The growing demand for energy and the concern about environmental impacts reinforce the necessity for renewable energy sources such as biofuels. In this study, cake generated in the babassu oil extraction was evaluated as a potential feedstock for solid biofuel production, and it contains a blend of cashew nutshell, sugarcane bagasse, carnauba straw, and carnauba stalk. All samples were characterized by proximate analysis and Higher Heating Value. Carbonization was used to improve energy performance and compaction to understand the mechanism and the characteristics of the biomasses compacted. In the extraction of babassu oil, fresh and aged (90 days) kernel samples were used. The fresh samples reached a yield of 59.8%, and the aged samples reached a yield of 70.66%. The carbonization of babassu cake was carried out in a Muffle furnace at temperatures of 250, 300, 350, and 400 °C. The fresh babassu cake showed an HHV of 23.06 MJ kg−1 and after carbonization of 28.07 (250 °C), 30.69 (300 °C), 28.24 (350 °C), and 18.27 MJ kg−1 (400 °C). At 400 °C, a decrease in HHV of 20.8% occurred, and an increase in Ash (%) of 195% occurred. Proximate analysis showed that biomasses are compatible, with some having a higher compatibility than other biological materials already used as fuels in the industry.

Evaluation of the Processing of Multi-Crop Plants into Pelletized Biofuel and Its Use for Energy Conversion

Multi-crop plants (fibrous hemp, maize, and faba bean) can potentially be an alternative to wood biomass pellets, but there is no detailed knowledge to support the suitability of this biomass for solid biofuel production. The aim of this study is to analyze and justify the suitability of multi-crop plant biomass for the production of biofuel pellets and to assess the environmental impact of burning them. This paper presents studies of physical-mechanical, thermal, and chemical characteristics of biofuel pellets from multi-crop plants and emissions during their combustion under laboratory conditions. The main parameters of the produced pellets were determined according to international standards, which are detailed in the methodology part. The length of the produced pellets ranged from 17.6 to 26.6 mm, and the diameter was about 6 mm. The density of wet pellets varied from 1077.67 to 1249.78 kg m−3. The amount of ash in the pellets varied from 5.75% to 8.02%. Determined lower calorific value of all pellets was close to 17.1 MJ kg−1. The lowest CO and CxHy emissions were determined when burning MIX2-1 pellets (biomass of the binary crop); their values were 572 and 29 ppm, respectively. The lowest content of CO2 was determined when burning S-Mz pellets (mono crop biomass), and it was 3.5%. The lowest NOx emissions were also determined when burning the pellets of this sample, with a value of 124 ppm. Research results show that multi-crop plants are a suitable raw material for the production of solid biofuel, the burning of which does not cause negative consequences for the environment.

Sustainable valorization of water hyacinth waste pollutant via pyrolysis for advance microbial fuel investigation

Present study has been focused on the bio-energy potential of waste biomass (water hyacinth leaves and its stem). Pyrolysis of both biomasses were investigated at five different heating rates (5–25 °C/min) using thermogravimetric analyzer. For both biomasses, maximum thermal degradation occurred within the temperature range of 200–400 °C, which is the active pyrolytic zone. Three non-iso-conversional (degradation models) including the Kissinger-Akahira-Sunose, Flynn-Wall-Ozawa, and Starink were used to calculate the activation energy of both biomasses. The activation energy was around 92–98 kJ/mol for water hyacinth leaves and 151–153 kJ/mol for water hyacinth stems. The results suggest that these low-cost abundantly available biomasses have a good potential for the production of solid bio-fuel.

Chemical Composition and Energy Evaluation of Abies spp. and Pinus spp. Sawdust Collected as a Byproduct of the Primary Wood Sawing

The aim of this paper is to chemically evaluate the byproducts of the primary processing of genera Abies and Pinus, to determine the possibility of using them as solid biofuel. Ash percentage, volatile matter and fixed carbon values were determined by proximate analysis. The basic chemical composition includes the determination of extractives content, lignin and holocellulose. Ash microanalysis was performed with an X-ray spectrometer and the calorific value of the samples was determined by using an AC600 calorimeter. The results of this research varied as follows: the content of inorganic substances (0.33% to 0.41%), volatile matter (88.54% to 82.57%), fixed carbon (11.13% to 17.06%), extractives content (5.37% to 17.82%), Runkel lignin (27.33% to 30.97%), holocellulose content (58.53% to 69.56%) and calorific value (19.09 MJ·kg-1 to 20.42 MJ·kg-1). According to the X-ray analysis, the most abundant elements were potassium, calcium and magnesium; whereas no heavy metals were found. The results of this research show that the two genera studied here are suitable for solid biofuel production.

Economic feasibility analysis and environmental impact assessment for the comparison of conventional and microwave torrefaction of spent coffee grounds

Biomass torrefaction is a promising method for carbon-neutral solid biofuel production. The economic feasibility and environmental pollution potential of the torrefaction operation are of great concern to developing a sustainable energy system. In this study, spent coffee grounds are selected as the feedstocks for comparing the economic feasibility of different torrefaction methods and evaluating the environmental pollution potential of conventional torrefaction and microwave torrefaction. The result shows that microwave torrefaction possesses a more economically efficient approach for biomass upgrading, as a result of lower energy input and carrier gas consumption. For environmental impact assessment, several different indicators are adopted for evaluating the torrefaction process, which is based on openLCA software of CML 2001 method. The life cycle assessment results indicate that the environmental impact of microwave torrefaction is lower than conventional torrefaction, especially when torrefied at light conditions. Thus, microwave light torrefaction is the optimal condition for spent coffee grounds upgrading. However, the growth rate of the environmental impact of microwave torrefaction is greater than conventional torrefaction, including resource depletion and terrestrial ecotoxicity. Moreover, the environmental impact of the torrefaction process is strongly correlated to the torrefaction severity.

The influence of the Miscanthus giganteus pyrolysis temperature on the application of obtained biochars as solid biofuels and precursors of high surface area activated carbons

Two different pathways for utilizing Miscanthus giganteus biochar were evaluated, namely, for the production of sustainable solid biofuels and as a precursor of high surface area activated carbons. Biochars were produced through a simple thermochemical conversion method via pyrolysis at 400, 500, 600, and 800 °C. The obtained biochars and raw biomass were characterized in detailed by proximate and ultimate analyses. The thermal behaviour and structural and strength properties were evaluated. The chemical composition (cellulose, hemicellulose, and lignin content) of raw Miscanthus giganteus was investigated. The biochars afforded a sufficient higher heating value (HHV) of up to 32 MJ kg−1. Activated carbon was obtained via chemical activation with KOH at 800 °C. The effect of the pyrolysis temperature on the surface properties of the activated carbons was investigated over a wide temperature range. The resulting activated carbons were characterised by N2 adsorption–desorption at −196 °C and by determining the pH of aqueous extracts. As a potential application, the obtained activated carbon series was used for the adsorptive removal of isoproturon from aqueous media. The adsorption capacity was as high as 384 mg g−1 and depended on the pore size distribution of the activated carbons. The conducted study follows the current trend of search for novel energy sources and water purification.

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.

Evaluation of harvest time effects on the combustion quality of warm- and cool-season perennial grasses in two contrasting semi-arid environments

In order to achieve economically viable and sustainable solid biofuel production from perennial grasses, high biomass productivity must be complemented by good combustion quality. The aim of this research was to compare the combustion quality of 7 cool-season perennial grasses, comprising bulbous canary grass, reed canary grass, smooth brome grass, orchard grass, tall wheatgrass, tall fescue, and perennial ryegrass, and 3 warm-season perennial grasses, comprising switchgrass, miscanthus, and giant reed, over 2 harvest times (autumn, winter/early spring) in 2 contrasting semi-arid environments (Adana, and Cankiri, Turkey). Delaying the harvest from the autumn to the winter or the spring significantly increased the lignin contents of each of the 3 warm-season grasses and generally decreased the contents of all of the minerals, except for Al and Fe, in miscanthus and switchgrass, and K and Na in giant reed, at both locations. Similar trends were also generally observed for all of the cool-season grasses, except for the orchard grass that was grown in Cankiri. Additionally, delayed harvest resulted in lower slagging tendency and sintering risk in all of the perennial grass species, except for giant reed in Cankiri. However, the autumn harvest caused significantly higher lignin, but generally lower N, P, K, Ca, S, Si, Al, and Fe contents, slagging tendency, and sintering risk in most of the cool-season grasses that were grown in Adana. On the other hand, despite the autumn harvest in Adana, and the spring harvest in Cankiri provided a substantial improvement in combustion quality of the cool-season grasses, mainly due to the reduced mineral and increased lignin contents, they still exhibited relatively lower combustion quality than miscanthus and switchgrass, especially in Adana. These results showed that further effort is needed to improve the combustion quality of cool-season grasses in order for them to be primary biomass feedstock alternatives for dry marginal lands of semi-arid environments.

One-step torrefaction and densification of woody and herbaceous biomass feedstocks

The investigation evaluates the potential of one-step torrefaction and pelleting of various woody and herbaceous feedstocks for the production of high-quality solid biofuels. The feedstocks were first subjected to a comprehensive analysis of chemical, thermal, physical and fuel properties. The samples were size reduced and densified at different temperatures (20–250 °C) and pressure (31–184 MPa). The resulting pellets were characterized for durability, real and bulk density, and lower heating value (LHV) and the results were then compared against quality standards for woody and non-woody pellets according to ISO 17225. The results showed clear responses to temperature and pressure in the ranges 20–80 °C and 31–92 MPa. Some of the feedstock (Jerusalem artichoke stalks, rock rose, scotch broom and vine sprouts) produced pellets of physical properties comparable or superior to pine wood, a feedstock that was used as a reference due to its potential to produce high quality densified fuels. Others (triticale and cynara) produced less satisfactory results and/or required very severe conditions to produce pellets of characteristics comparable to pine wood. However, the presence of specific components in the alternative feedstocks (mainly ash, Cl, K, N) resulted in pellets not complying with ISO quality standards.

PERSPECTIVES FOR THE USE OF BIOMASS GENERATED BY SOME MISCANTHUS GENOTYPES IN THE PRODUCTION OF DENSIFIED SOLID BIOFUELS

Miscanthus is a Poaceae family perennial crop of C4 bioenergy characterized by the multilateral use potential, including the production of biofuels. The paper aimed to study the opportunity to use the biomass generated by two Miscanthus genotypes: Miscanthus × giganteus and Miscanthus sinensis in the production of densified solid biofuels. We quantified the biomass generated by crops that were 5 years old, harvested from both genotypes after the vegetation period, the year 2020. Samples were taken from the experimental lots of the Alexandru Ciubotaru National Botanical Garden (Institute) from the Republic of Moldova in autumn, immediately after the initial onset of senescence and in spring of the following year, before the start of the growing season. The results showed that the above-ground biomass generated by both Miscanthus genotypes harvested in spring had had significantly higher quality characteristics compared to the biomass harvested in autumn. Virtually all qualitative indices of the Miscanthus × giganteus biomass harvested in spring comply with the requirements of the ENPlus international standards for densified solid biofuels. The Miscanthus sinensis biomass, both, had lower indices than the Miscanthus × giganteus biomass from both qualitative and quantitative points of view and the former can be used as a filler in various mixtures of raw material for the production of solid biofuels.

About potential opportunities for the development of solid biofuel production in Russia

The article considers the possibilities of expanding existing woodworking enterprises due to state subsidies for the development of renewable energy. It is proposed to use wood waste and lignified agricultural waste (straw) together as raw materials for the production of solid biofuels. An assessment of the reduction of CO2 emissions at a woodworking enterprise when replacing traditional fuels with solid biofuels is given.

Oxidative torrefaction of microalga Nannochloropsis Oceanica activated by potassium carbonate for solid biofuel production

Oxidative torrefaction is a promising way for biomass upgrading and solid biofuel production. Alkali metals are considered to be efficient activators for enhancing biofuel upgrading during the thermal reaction process. Herein, the microalga Nannochloropsis Oceanica is selected as the feedstock for assessing potassium carbonate activated effect on solid biofuel production through oxidative torrefaction. The potential of potassium carbonate on microalgal biofuel properties upgrading is deeply explored. SEM observation and BET analysis show that torrefied microalgae can be transformed from a spherical structure with wrinkles to smaller particles with larger surface areas and higher total pore volumes, implying that potassium carbonate is a promising porogen. Moreover, potassium carbonate can significantly change the DTG curve at the temperatures of 250 °C and 300 °C from one peak to two peaks, inferring that the activated effect of potassium carbonate occurs on the torrefied microalgae. 13C NMR analysis reveals that the microalgal components significantly change as the torrefaction severity increases, with the decomposition of carbohydrate and protein components. When the potassium carbonate ratio increases from 0:1 to 1:1, the graphitization degree increase from 3.065 to 1.262, along with the increase in the HHV of solid biofuel from 25.024 MJ kg−1 to 31.890 MJ kg−1. In total, this study has comprehensively revealed the activated effect of potassium carbonate on improving the properties of microalgal solid biofuel.

Hydrothermal carbonization of waste ginkgo leaf residues for solid biofuel production: Hydrochar characterization and its pelletization

This study explored the potential of hydrothermal carbonization (HTC) for the production of a carbon-rich solid fuel from Ginkgo leaf residues (GLRs). Density, durability, hardness, hydrophobicity, and energy input estimates for HTC treated and untreated GLRs pellets were determined. Results showed that hydrothermal treatment significantly improved the physical properties of pellets made from GLRs, especially, at the temperature treatment of 220 °C. Pellet durability and hardness from samples treated at 220 °C (HT220) increased from 70.1% and 0.8 N/mm2 to 96.8% and 2.1 N/mm2 when compared to those made from untreated GLR (control). Hydrochar pellets had higher fixed carbon contents, elevated heating values, and enhanced energy densification ratio in comparison to the control pellets. The equilibrium moisture content decreased from 13.9% to 4.8% for HT220 pellets. The activation energy of HT220 pellets decreased from 44.6 to 26.8 kJ/mol in the first order reaction model and from 93.9 to 61.2 kJ/mol in the 3D diffusion model compared to the control pellets. The comprehensive combustibility index S was enhanced twice for HT220 pellets. The high durability, low moisture uptake, and improved pyrolysis property indicated that combining hydrothermal carbonization with pelletization is an efficient way for GLRs utilization as solid biofuel.

Effects of harvest time on bioethanol production and bagasse characteristics for combustion and forage in sweet sorghum

Determining the optimal harvest time is very crucial to achieve sustainable production of first-generation bioethanol as well as efficient use of its bagasse for combustion or feed in sweet sorghum. The aim of the current research was to understand the effects of different harvest times, which comprised flowering (FLW), soft dough (SD), hard dough (HD), and physiological maturity (PM) on the bioethanol production and the combustion and forage characteristics of its bagasse in sweet sorghum. In one study, averaged over a period of 2 years, the mean theoretical total ethanol yield (TEY) was between 4802 and 5316 L ha–1. The PM harvest produced the highest TEY, which was followed by the HD and SD harvests, with sligh differences. These results suggested that sweet sorghum should be harvested at any phenological stage after FLW to achieve sustainable total (juice + lignocellulosic) bioethanol production in a semi-arid Mediterranean environment. Averaged over a period of 2 years, the mean dry bagasse yield (DBY) achieved from the harvest times herein ranged between 12.0 and 14.1 t ha–1. As with TEY, the PM harvest exhibited the highest DBY and desirable bagasse combustion caharacteristics due to exhibiting the lowest moisture and ash contents, which indicated that it seemed be the most suitable harvest time if obtaining solid biofuel production from the bagasse is the main target after the production of juice ethanol. On the other hand, the HD harvest provided the highest bagasse forage quality among the harvest times due to exhibiting the significantly lowest neutral detergent fiber and acid detergent fiber contents, but the significantly highest relative feed value. These results suggested that the HD harvest time was the most suitable for sweet sorghum cultivation when producing juice ethanol that is complemented by the production of forage utilizing the bagasse.

Viability of some African agricultural by-products as a feedstock for solid biofuel production

As a source of renewable energy, agricultural by-products after pre-processing and cleaning in post-harvest lines can be used as a feedstock for the production of pellets or briquettes. This can be achieved by determining the physicochemical properties of the by-products. Groundnut pods, maize cobs and the husks of rice, millet and sorghum were considered, and their properties were determined, which were then compared with the standard properties of pellets and briquettes to ascertain their viability as a feedstock for the pellet or briquette production. The by-products were transported from Nigeria to the Czech Republic and the research was carried out at the Department of Technological Equipment of Buildings, the Faculty of Engineering, Czech University of Life Sciences Prague. The moisture content, ash content, calorific value, nitrogen content and sulfur content were the properties considered of the by-products. Groundnut pods and maize cobs with a calorific value of 17.48 MJ·kg–1 and 16.25 MJ·kg–1, an ash content of 3.46% weight and 1.79% weight, a nitrogen content of 1.24% weight and 0.44% weight and a moisture content of 7.92 weight and 7.56% weight, respectively, were discovered to fulfill all the requirements for graded non-woody pellets A. With the exception of rice husks and millet husks, which were discovered to have high ash contents and low calorific values, all the by-products fulfilled the standard requirements for one or more grade of pellet/briquette. They can, therefore, be used as a good feedstock for pellet or briquette production.