Special Issue "Biomass Pretreatment and Optimisation of Biofuel Production Processes"

A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "Sustainable Energy".

Deadline for manuscript submissions: 30 November 2021.

Special Issue Editors

Dr. Marek Wróbel
E-Mail Website
Guest Editor
Department of Mechanical Engineering and Agrophysics, University of Agriculture in Krakow, 30-149 Kraków, Poland
Laboratory of Production Technology and Quality Assessment of Biofuels – Accredited by Polish Centre for Accreditation nr AB 1585
Interests: biomass;biofuels;torrefaction;quality of biofuels;pressure agglomeration
Special Issues and Collections in MDPI journals
Dr. Marcin Jewiarz
E-Mail Website
Guest Editor
Department of Mechanical Engineering and Agrophysics, University of Agriculture in Krakow, 30-149 Krakow, Poland
Interests: biomass; torrefaction; pellets; agriculture biowaste
Special Issues and Collections in MDPI journals

Special Issue Information

Dear Colleagues,

Recently, research on biofuel production processes from biomass raw materials has become very popular in many scientific centres. As a results of the conducted research, the parameters of a wide range of raw materials and the influence of biomass parameters and process conditions on the final product properties are known, and new technologies are being developed. However, many questions and uncertainties remain. This is due to the diversity of raw material origin, the variety of final products (solid, liquid, and gaseous biofuels), and the multitude of technologies used. Once a greater understanding is obtained in these areas, it will be possible to fully utilize the biomass potential and effectively conduct production processes to obtain high-quality biofuels with minimal effort.

This Special Issue will focus on: biomass pretreatment as well as biofuels process production and optimization with respect to process costs while maintaining high product quality. We therefore invite papers on biomass pretreatment technology, innovative biofuels production technology, modelling and optimization studies, reviews, and case studies. Topics of interest for publication include, but are not limited to, the following:

  • Technical, economic, and environmental aspects of solid, liquid, and gaseous biofuels production;
  • Optimization of biofuels production processes;
  • Impact of raw material processing on product parameters;
  • Ensuring high-quality biofuels;
  • Technology assessment;
  • Processes modelling, forecasting, and optimization techniques. 

Dr. Marcin Jewiarz
Dr. Marek Wróbel
Guest Editors

Manuscript Submission Information

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2000 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Process modelling
  • Innovative technologies
  • Solid, liquid, and gaseous biofuels
  • Biomass pretreatment processes
  • Processes optimization
  • Quality assurance

Published Papers (9 papers)

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Research

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Article
Energy Parameters of Miscanthus Biomass Pellets Supplemented with Copra Meal in Terms of Energy Consumption during the Pressure Agglomeration Process
Energies 2021, 14(14), 4167; https://doi.org/10.3390/en14144167 - 10 Jul 2021
Viewed by 259
Abstract
The process of pelleting miscanthus biomass often encounters issues related to the low durability of the obtained pellets and high energy inputs. To solve these issues, the use of copra meal as a supplement is proposed. This paper presents the results of research [...] Read more.
The process of pelleting miscanthus biomass often encounters issues related to the low durability of the obtained pellets and high energy inputs. To solve these issues, the use of copra meal as a supplement is proposed. This paper presents the results of research on energy parameters of miscanthus biomass pellets supplemented with copra meal in terms of energy consumption in the pressure agglomeration process. As part of this research, the energy parameters of miscanthus biomass, copra meal biomass, and their blends were characterized. Next, the raw materials were used for the production of pellets in the pressure agglomeration process. The investigations included proximate and ultimate analysis and estimation of heating values. Moreover, the total fat content, mechanical durability, kinetic strength, and bulk density were determined, and the energy consumption in the pelleting process was assessed. The results indicate that the energy consumption in the miscanthus biomass pelleting process can be substantially reduced by adding copra meal as a biocomponent. When the copra meal addition did not exceed 30%, the pellets exhibited over 95% durability, over 1200 kg∙m−3 density, and over 417 kg∙m−3 bulk density. Given the 44% reduction in energy consumption in the pellet production process and the energy efficiency of 4815 Wh·kg−1 determined in this study, copra meal may be an interesting material for use as an additive in the production of miscanthus biomass pellets. Full article
(This article belongs to the Special Issue Biomass Pretreatment and Optimisation of Biofuel Production Processes)
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Article
Valorization of Prosopis juliflora Woody Biomass in Northeast Brazilian through Dry Torrefaction
Energies 2021, 14(12), 3465; https://doi.org/10.3390/en14123465 - 11 Jun 2021
Viewed by 296
Abstract
Torrefaction has been investigated to improve the desirable properties of biomass as solid biofuel, usually used in natura as firewood in several countries. This paper has the main objective to present a broad characterization of the biomass Prosopis juliflora (P. juliflora), [...] Read more.
Torrefaction has been investigated to improve the desirable properties of biomass as solid biofuel, usually used in natura as firewood in several countries. This paper has the main objective to present a broad characterization of the biomass Prosopis juliflora (P. juliflora), investigating its potential as a solid biofuel after its torrefaction process. The methodology was based on different procedures. The experimental runs were carried out at 230, 270, and 310 °C for 30 min, using a bench-scale torrefaction apparatus, with an inert atmosphere. In order to investigate the effect of temperature in constant time, torrefaction parameters were calculated, such as mass yield, energy yield, calorific value, base-to-acid ratio (B/A), and the alkaline index (AI). The physicochemical properties of the torrefied samples were determined and thermogravimetric analysis was used to determine the kinetic parameters at four different heating rates of 5, 10, 20, and 30 °C/min. Pyrolysis kinetics was investigated using the Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) isoconversional methods. Highly thermally stable biofuels were obtained due to the great degradation of hemicellulose and cellulose during torrefaction at higher temperatures. The highest heating value (HHV) of the samples varied between 18.3 and 23.1 MJ/kg, and the energy yield between 81.1 and 96.2%. The results indicate that P. juliflora torrefied becomes a more attractive and competitive solid biofuel alternative in the generation of heat and energy in northeast Brazil. Full article
(This article belongs to the Special Issue Biomass Pretreatment and Optimisation of Biofuel Production Processes)
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Article
Productivity and Biomass Properties of Poplar Clones Managed in Short-Rotation Culture as a Potential Fuelwood Source in Georgia
Energies 2021, 14(11), 3016; https://doi.org/10.3390/en14113016 - 23 May 2021
Viewed by 454
Abstract
Georgian forests are very valuable natural resources, but due to the lack of affordable alternatives to firewood, people are forced to use forest resources illegally and unsustainably. The aim of this study was to determine the productivity and biomass properties of four poplar [...] Read more.
Georgian forests are very valuable natural resources, but due to the lack of affordable alternatives to firewood, people are forced to use forest resources illegally and unsustainably. The aim of this study was to determine the productivity and biomass properties of four poplar clones from Aigeiros and Tacamahaca and one control clone, considering their wood and bark characteristics and their proportion in the stems. Short-rotation woody crops with these clones represent a potential source of commercial fuelwood production in Georgia as an alternative to natural forests. These tree characteristics were evaluated after three years of growth. The survival of the clones was generally high. No significant differences in biomass production (dry matter, DM) were found among the four clones tested (DM of approximately 4 Mg ha−1 yr−1), while the control clone achieved significantly lower values for DM. The biomass specific density was exceptionally high, at 481–588 kg m−3, which was a result of the high proportion of bark mass in the stem (23.3–37.7%), with a density almost twice that of wood. On the other hand, the tested clones had a very high ash content in the biomass (2.6–4.5%), which negatively affected their energy potential expressed as a lower heating value (17,642–17,849 J g−1). Our preliminary results indicated that both the quantity and quality of biomass are important factors to justify the investment in an intensive poplar culture. The four clones should be further considered for commercial biomass production and tested at different sites in Georgia to evaluate the genotype-by-environment interactions and identify the site conditions required to justify such an investment. Full article
(This article belongs to the Special Issue Biomass Pretreatment and Optimisation of Biofuel Production Processes)
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Article
Research on Determination of Water Diffusion Coefficient in Single Particles of Wood Biomass Dried Using Convective Drying Method
Energies 2021, 14(4), 927; https://doi.org/10.3390/en14040927 - 10 Feb 2021
Viewed by 424
Abstract
Determination of the mass diffusion coefficient for dried, inhomogeneous material is difficult as it depends on the drying agent temperature and the moisture content and physical structure of the material. The paper presents a method for efficient determination of the water diffusion coefficient [...] Read more.
Determination of the mass diffusion coefficient for dried, inhomogeneous material is difficult as it depends on the drying agent temperature and the moisture content and physical structure of the material. The paper presents a method for efficient determination of the water diffusion coefficient for wood solid cuboids dried using convective drying methods. In this work, the authors define a theoretical dependence of the Fourier number on reduced water content in a convectively dried cuboidal solid, based on a simplified theoretical solution of the diffusion equation for such a body. The material for drying included shoots of common osier, robinia (false acacia), multiflora rose, and energy poplar, dried at temperatures of 40, 50, 60, 70, and 80 °C, in free convection. The obtained results differ from the theoretically anticipated changes of the coefficient. Full article
(This article belongs to the Special Issue Biomass Pretreatment and Optimisation of Biofuel Production Processes)
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Article
Evaluation of Urban Tree Leaf Biomass-Potential, Physico-Mechanical and Chemical Parameters of Raw Material and Solid Biofuel
Energies 2021, 14(4), 818; https://doi.org/10.3390/en14040818 - 04 Feb 2021
Cited by 4 | Viewed by 565
Abstract
The paper presents the results of research aimed at evaluating the possibility of using selected tree leaf species to produce solid biofuels. The possibility of production of qualitative solid biofuels from urban tree leaves meets the expectations of the municipal sector. Collection of [...] Read more.
The paper presents the results of research aimed at evaluating the possibility of using selected tree leaf species to produce solid biofuels. The possibility of production of qualitative solid biofuels from urban tree leaves meets the expectations of the municipal sector. Collection of tree leaves in urban areas is very often necessary for road safety reasons, the need to collect biomass rich in dust and pollution as well as biomass infested with pests. The production of solid biofuels from tree leaves allows for effective management of this raw material with energy recovery. The performed research indicates such a possibility, and the obtained ash is used as a soil improver. The conducted research showed that the biomass of leaves of five tree species used in the experiment can be a source of raw materials for production of qualitative biofuels. The obtained pellets were characterized by properties comparable to those of classical wood pellets. The lower heating value of the obtained pellets ranged from 14.5 to 15.5 MJ∙kg−1. Physical properties of the obtained pellets described by bulk density (BD 600–660 kg∙m−3), mechanical durability (DU 90–96%), moisture (Mar 10–12.5%) indicate that these products can be used in existing combustion equipment. Preliminary analysis of the obtained ashes (determination of ash melting point, bulk density) indicates that they should not cause difficulties in ash removal systems from the combustion chamber. Full article
(This article belongs to the Special Issue Biomass Pretreatment and Optimisation of Biofuel Production Processes)
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Article
Some Aspects of the Modelling of Thin-Layer Drying of Sawdust
Energies 2021, 14(3), 726; https://doi.org/10.3390/en14030726 - 30 Jan 2021
Viewed by 475
Abstract
Drying of spruce, beech, willow, and alder sawdust was examined in a laboratory type dryer. The effect of drying air temperature T (25, 60, and 80 °C) and airflow velocity v (0.01, 0.15, and 1.5 m/s) was investigated. The obtained results demonstrated that [...] Read more.
Drying of spruce, beech, willow, and alder sawdust was examined in a laboratory type dryer. The effect of drying air temperature T (25, 60, and 80 °C) and airflow velocity v (0.01, 0.15, and 1.5 m/s) was investigated. The obtained results demonstrated that drying air temperature and airflow velocity have impacts on the drying of sawdust. The experimental dehydration data of sawdust obtained were fitted to theoretical, semi-theoretical, and empirical thin-layer models. The accuracies of the models were estimated using the correlation coefficient (R), root mean square error (RMSE), and reduced chi-square (χ2). All models except the theoretical model of a sphere described the drying characteristics of sawdust satisfactorily. The effect of T and v on the parameters (constants and coefficients) of the drying models were determined. The effect, by the proposed equations, was also described. This work combines aspects of mechanical engineering and modelling of the drying process. Full article
(This article belongs to the Special Issue Biomass Pretreatment and Optimisation of Biofuel Production Processes)
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Article
Kinetic Parameters of Nut Shells Pyrolysis
Energies 2021, 14(3), 682; https://doi.org/10.3390/en14030682 - 28 Jan 2021
Viewed by 699
Abstract
The European Union created a European Green Deal Program (EGDP). This program aims at a sustainable economy through the transformation of the challenges related to climate and the environment. The main goal of EGDP is climate neutrality by 2050. The increase of alternative [...] Read more.
The European Union created a European Green Deal Program (EGDP). This program aims at a sustainable economy through the transformation of the challenges related to climate and the environment. The main goal of EGDP is climate neutrality by 2050. The increase of alternative biomass residues utilization from various food processing industries and cooperation in the energy and waste management sector is required to meet these expectations. Nut shells are one of the lesser-known, yet promising, materials that can be used as an alternative fuel or a pre-treated product to further applications. However, from a thermal conversion point of view, it is important to know the energy properties and kinetic parameters of the considered biowaste. In this study, the energy and kinetic parameters of walnut, hazelnut, peanut, and pistachio shells were investigated. The results showed that raw nut shells are characterized by useful properties such as higher heating value (HHV) at 17.8–19.7 MJ∙kg−1 and moisture content of 4.32–9.56%. After the thermal treatment of nut shells (torrefaction, pyrolysis), the HHV significantly increased up to ca. 30 MJ∙kg−1. The thermogravimetric analysis (TGA) applying three different heating rates (β; 5, 10, and 20 °C∙min−1) was performed. The kinetic parameters were determined using the isothermal model-fitting method developed by Coats–Redfern. The activation energy (Ea) estimated for β = 5 °C∙min−1, was, e.g., 60.3 kJ∙mol−1∙K−1 for walnut, 59.3 kJ∙mol−1∙K−1 for hazelnut, 53.4 kJ∙mol−1∙K−1 for peanut, and 103.8 kJ∙mol−1∙K−1 for pistachio, respectively. Moreover, the increase in the Ea of nut shells was observed with increasing the β. In addition, significant differences in the kinetic parameters of the biomass residues from the same waste group were observed. Thus, characterization of specific nut shell residues is recommended for improved modeling of thermal processes and designing of bioreactors for thermal waste treatment. Full article
(This article belongs to the Special Issue Biomass Pretreatment and Optimisation of Biofuel Production Processes)
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Article
Physicochemical Properties and Lignin Degradation of Thermal-Pretreated Oil Palm Empty Fruit Bunch
Energies 2020, 13(22), 5966; https://doi.org/10.3390/en13225966 - 16 Nov 2020
Cited by 2 | Viewed by 469
Abstract
Oil palm empty fruit bunches (EFB) are recoverable lignocellulosic biomass serving as feedstock for biofuel production. The major hurdle in producing biofuel from biomass is the abundance of embedded recalcitrant lignin. Pretreatment is a key step to increase the accessibility of enzymes to [...] Read more.
Oil palm empty fruit bunches (EFB) are recoverable lignocellulosic biomass serving as feedstock for biofuel production. The major hurdle in producing biofuel from biomass is the abundance of embedded recalcitrant lignin. Pretreatment is a key step to increase the accessibility of enzymes to fermentable sugars. In this study, thermal pretreatments at moderate temperatures ranging from 150 °C to 210 °C, at different durations (30–120 min) and EFB particle sizes (1–10 mm), were employed to maximize lignin degradation. Observation through a scanning electron microscope (SEM) revealed disruptions in EFB structure and the removal of silica bodies and other impurities upon thermal pretreatment. Remarkable changes on the elemental contents and functional groups occurred, as was evident from the energy dispersive X-ray (EDX) and Fourier transform infrared (FTIR) analyses. The smallest EFB size yielded higher lignin degradation—about 2.3-fold and 1.2-fold higher—than the biggest and moderate tested EFB sizes, indicating a smaller particle size provides a higher surface area for bioreaction. Furthermore, applying a longer duration of treatment and a higher temperature enhanced lignin degradation by up to 58%. This study suggests that moderate thermal treatment could enhance lignin degradation by altering the physicochemical structure of EFB, which is beneficial in improving biofuel production. Full article
(This article belongs to the Special Issue Biomass Pretreatment and Optimisation of Biofuel Production Processes)
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Review

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Review
Thermal Treatment of Biomass: A Bibliometric Analysis—The Torrefaction Case
Energies 2021, 14(1), 162; https://doi.org/10.3390/en14010162 - 30 Dec 2020
Cited by 1 | Viewed by 824
Abstract
The aim of the paper was to summarize and discuss current research trends in biomass thermal treatment (torrefaction process). Quantitative analyses were carried out, in which the main countries, research units and scientists were indicated. The analysis showed a clear upward trend in [...] Read more.
The aim of the paper was to summarize and discuss current research trends in biomass thermal treatment (torrefaction process). Quantitative analyses were carried out, in which the main countries, research units and scientists were indicated. The analysis showed a clear upward trend in number of publications after 2010. Most scientists on selected topics come from China, USA, Canada, South Korea, Republic of China, Poland (Web od Science—Core Collection (WoS-CC) and Scopus databases). Quantitative analysis also showed that the most relevant WoS-CC categories in the summary are: Energy Fuels, Engineering Chemical, Agricultural Engineering, Biotechnology Applied Microbiology and Thermodynamics and Scopus Subject area: Energy, Chemical Engineering, Environmental Science, Engineering and Chemistry. Thematic analysis included research topics, process parameters and raw materials used. Thematic groups were separated: torrefaction process (temp.: 150–400 °C), hydrothermal carbonization process (HTC) (temp: 120–500 °C), pyrolysis process (temp.: 200–650 °C) and gasification and co-combustion process (temp.: 350–1600 °C). In the years 2015–2019, current research topics were: new torrefaction technologies (e.g., HTC), improvement of the physico-mechanical, chemical and energetic properties of produced fuel as well as the use of torrefied biomass in the process of pyrolysis, gasification and co-combustion. The raw materials used in all types of biomass thermal treatment were: energy crops, wood from fast-growing and exotic trees, waste from the agri-food industry, sewage sludge and microalgae. Full article
(This article belongs to the Special Issue Biomass Pretreatment and Optimisation of Biofuel Production Processes)
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Title: Some Aspects of the Modelling of Thin-Layer Drying of Sawdust

Authors: Andrzej Bryś1, Agnieszka Kaleta1, Krzysztof Górnicki1, Szymon Głowacki1,*, Weronika Tulej1,* and Joanna Bryś2

Affiliation: 1. Institute of Mechanical Engineering, Warsaw University of Life Sciences, ul. Nowoursynowska 164, 02–787 Warszawa, Poland

2. Institute of Food Science, Warsaw University of Life Sciences, ul. Nowoursynowska 159c, 02–787 Warszawa, Poland

Abstract: Drying of spruce, beech, willow, and alder sawdust was investigated in a laboratory type dryer. The effect of drying air temperature (25, 60, and 80 °C) and airflow velocity (0.01, 0.15, and 1.5 m/s) was investigated. The results have shown, that drying air temperature and airflow velocity influence on the drying behaviour of sawdust. The experimental dehydration data of sawdust obtained were fitted to the theoretical, semi–theoretical, and empirical thin-layer models. The accuracies of the models were estimated using the correlation coefficient (R), root mean square error (RMSE), and reduced chi–square (χ2). All models except theoretical model of a sphere described the drying characteristics of sawdust satisfactorily. The effect of drying air temperature and airflow velocity on the drying models parameters were also determined.

Title: Research on Determination of Water Diffusion Coefficient in Single Particles of Wood Biomass Dried Using Convective Drying Method
Authors: Szymon Głowacki 1,*; Weronika Tulej 1,*; Andrzej Bryś 1; Piotr Wichowski 2; Mariusz Sojak 1; Krzysztof Górnicki 1
Affiliation: 1 Institute of Mechanical Engineering, Warsaw University of Life Sciences, ul. Nowoursynowska 164, 02–787 Warszawa, Poland. 2 Institute of Environmental Engineering, Warsaw University of Life Sciences—SGGW, Nowoursynowska 159, Warsaw 02-776, Poland
Abstract: Determination of mass diffusion coefficient for dried, inhomogeneous material is difficult as it depends on drying agent temperature, moisture content and physical structure of the material. The paper presents the method for efficient determination of water diffusion coefficient for solid cuboids, dried using convective drying method. The material for drying included shoots of common osier, robinia (false acacia), multiflora rose, energy poplar, dried in the temperatures of 40, 50, 60, 70 and 80 °C, in the free convection. The obtained results differ from the theoretically anticipated changes of the coefficient.

Title: Productivity and Energy Potential of Hybrid Poplar Clones in Georgia, preliminary results
Authors: Marzena Niemczyk1; Margalita Bachilava2; Marek Wróbel3; Marcin Jewiarz3; Giorgi Kavtaradze4; Nani Goginashvili5
Affiliation: 1. Department of Silviculture and Forest Tree Genetics, Forest Research Institute, Braci Leśnej 3, Sękocin Stary, 05-090 Raszyn, Poland; 2. Agricultural University of Georgia, Vasil Gulisashvili Forest Institute Kakha Bendukidze Campus, 240 David Aghmashenebeli Alley, Tbilisi, 0131, Georgia; 3. Department of Mechanical Engineering and Agrophysics, University of Agriculture in Krakow, Balicka 120, 30-149 Kraków, Poland; 4. Agricultural University of Georgia; Vasil Gulisashvili Forest Institute Kakha Bendukidze Campus, 240 David Aghmashenebeli Alley, Tbilisi, 0131, Georgia; 5. Scientific-Research Center of Agriculture, 6,Marshal Gelovani ave, Tbilisi 0159; Georgia;
Abstract: Georgian forests are exceptionally valuable natural resources, both on a regional and global scale. However, the high level of poverty in rural areas and the lack of affordable alternatives to firewood force people to use forest resources illegally and unsustainably. In this context, short rotation plantations with poplars seems to be a good alternative to obtain additional biomass for fuelwood for the country. Therefore, the objective of the study was to determine the productivity and energy value of five poplar clones as a potential source of commercial fuelwood for the country. The genetic material consisted of five clones. Three clones 89.M.061, 89.M.004 and Kocabey (TR - 77/10) were obtained from Turkey; the fourth clone - AF8 was produced by Alasia Franco Vivai in Italy, while Populus pyramidalis was used as a control. The productivity and wood properties of the clones were tested after three years of growth. The survival rate of the clones was generally high. No significant differences in biomass production (dry matter, DM) were found between the four tested clones (DM approximately 4 Mg ha-1 yr-1), while the control clone reached significantly lower DM values than all other clones. In conclusion, the four clones should be further considered for commercial biomass production and tested at different test sites in Georgia to evaluate the interaction between genotype and environment and to identify suitable site conditions required to justify an investment in intensive culture.

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