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Selected paper from 6th International Conference on Renewable Energy Sources (ICoRES 2019)

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

Deadline for manuscript submissions: closed (31 January 2020) | Viewed by 46678

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Dr. Marcin Jewiarz

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Department of Mechanical Engineering and Agrophysics, University of Agriculture in Krakow, 33-332 Krakow, Poland
Interests: biomass; torrefaction; pellets; agriculture biowaste
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The 6^th edition of the Renewable Energy Sources International Conference (ICORES2019) will be one of the most recognisable scientific meetings connected to RES in Poland. From the very beginning, this conference has been a unique occasion for gathering Polish and international researchers’ perspectives on renewable energy sources and balancing them against governmental policy considerations. Accordingly, the conference has also offered panels to discuss best practices and solutions with local entrepreneurs and federal government bodies. The meeting attracts not only scientists but also industry representatives, as well as local and federal government personnel. We are open to new and fresh ideas concerning renewable energy, which is why so many scientists from Central and Eastern Europe visit Krynica to discuss the “Green Future” of this region.

In 2019, the conference is organized by the University of Agriculture in Krakow, in cooperation with the AGH University of Science and Technology (Krakow), State Agrarian and Engineering University in Podilya, University of Žilina, International Commission of Agricultural and Biosystems Engineering (CIGR) and Polish Society of Agricultural Engineering. Honorary auspices were made by the Ministry of Science and Higher Education Republic of Poland, the rector of the University of Agriculture in Krakow, the rector of the AGH University of Science and Technology and the rector of the State Agrarian and Engineering University in Podilya.

Dr. Marcin Jewiarz
Guest Editor

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Keywords

Solar energy
Geothermal energy
Biomass and biomass fuels
Combustion, co-combustion, and CHP in RES systems
Heat pumps
Wind energy
Fuel cell
Waste and heat
Modelling, simulation and optimization of renewable energy systems
Advanced energy storage technologies
Politics and economics of renewable energy sources

Related Special Issue

Selected paper from 7th International Conference on Renewable Energy Sources (ICoRES 2021)- Energy, Enviroment and Economy in RES in Energies (4 articles)

Published Papers (14 papers)

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Research

14 pages, 926 KiB

Open AccessArticle

The Impact of a Controlled-Release Fertilizer on Greenhouse Gas Emissions and the Efficiency of the Production of Chinese Cabbage

by Jakub Sikora, Marcin Niemiec, Anna Szeląg-Sikora, Zofia Gródek-Szostak, Maciej Kuboń and Monika Komorowska

Energies 2020, 13(8), 2063; https://0-doi-org.brum.beds.ac.uk/10.3390/en13082063 - 21 Apr 2020

Cited by 37 | Viewed by 4836

Abstract

Optimization of plant fertilization is an important element of all quality systems in primary production, such as Integrated Production, GLOBAL G.A.P. (Good Agriculture Practice) or SAI (Sustainable Agriculture Initiative). Fertilization is the most important element of agricultural treatments, affecting the quantity and quality of crops. The aim of the study was to assess greenhouse gas (GHG) emissions in the cultivation of Chinese cabbage, depending on the technological variant. The factor modifying the production technology was the use of fertilizers with a slow release of nutrients. One tonne of marketable Chinese cabbage crop was selected as the functional unit. To achieve the research goal, a strict field experiment was carried out. Calculation of the total amount of GHG emitted from the crop was made in accordance with ISO 14040 and ISO 14044. The system boundaries included the production and use of fertilizers and pesticides, energy consumption for agricultural practices and the emission of gases from soil resources and harvesting residue. The use of slow-release fertilizers resulted in a greater marketable yield of cabbage compared to conventional fertilizers. The results of the research indicate a significant potential for the use of slow-release fertilizers in reducing agricultural emissions. From the environmental and production point of view, the most favourable variant is the one with 108 kg N·ha⁻¹ slow-release fertilizers. At a higher dose of this element, no increase in crop yield was observed. At this nitrogen dose, a 30% reduction in total GHG emissions and a 50% reduction in fertilizer emissions from the use of per product functional unit were observed. The reference object was fertilization in accordance with production practice in the test area. Full article

(This article belongs to the Special Issue Selected paper from 6th International Conference on Renewable Energy Sources (ICoRES 2019))

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20 pages, 3541 KiB

Open AccessArticle

Effect of Compaction Pressure and Moisture Content on Quality Parameters of Perennial Biomass Pellets

by Jakub Styks, Marek Wróbel, Jarosław Frączek and Adrian Knapczyk

Energies 2020, 13(8), 1859; https://0-doi-org.brum.beds.ac.uk/10.3390/en13081859 - 11 Apr 2020

Cited by 37 | Viewed by 3425

Abstract

In Poland the use of solid biomass obtained from intentional plantations of energy plants is increasing. This biomass is most often processed into solid fuels. There are growing indications that renewable energy sources, in particular biomass production, will continue to develop, so the better we know the raw material, the more effectively we will be able to use it. The results of tests that determine the impact of compaction pressure on selected quality parameters of pellets made from selected biomass types are presented. Material from plants such as Giant miscanthus (Miscanthus × giganteus Greef et Deu), Cup plant (Silphium perfoliatum L.), Virginia mallow (Sida hermaphrodita (L.) Rusby) was studied. The compaction process was carried out using the SIRIO P400 hydraulic press with a closed chamber with a diameter of 12 mm. Samples were made in four pressures: 131; 196; 262; 327 MPa and three moisture levels: 8%, 11%, 14%. It was found that with increasing compaction pressure and moisture content up to a certain point, the density and durability of the pellets also increased. Each of the materials is characterized by a specific course of changes in the parameters tested. Full article

(This article belongs to the Special Issue Selected paper from 6th International Conference on Renewable Energy Sources (ICoRES 2019))

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12 pages, 2113 KiB

Open AccessArticle

The Effect of the Addition of a Fat Emulsifier on the Amount and Quality of the Obtained Biogas

by Jakub Sikora, Marcin Niemiec, Anna Szeląg-Sikora, Zofia Gródek-Szostak, Maciej Kuboń and Monika Komorowska

Energies 2020, 13(7), 1825; https://0-doi-org.brum.beds.ac.uk/10.3390/en13071825 - 09 Apr 2020

Cited by 15 | Viewed by 2047

Abstract

Slaughterhouse waste management is an important technological, economic, and environmental challenge. Recently, more and more attention has been paid to the possibility of obtaining biogas from waste generated by slaughterhouses. The aim of the paper was to examine the effect of an emulsifier addition in the form of a carboxymethyl cellulose solution to create animal waste fermentation media based on the quantity and quality of the generated biogas. The adopted research goal was achieved based on a laboratory experiment of methane fermenting poultry processing waste. The waste was divided into two fractions: soft (tissue) and hard (bone). A fat emulsifier in a concentration of 1%, 2.5%, 5%, and 10% of fresh weight of the substrate was added to each substrate sample made from the above fractions. The emulsifier used was a 55% carboxymethyl cellulose solution, since this emulsifier is most commonly used in food production. The experiment was conducted in order to determine how the addition of an emulsifier (55% carboxymethylcellulose solution) affects the hydration of fats during methane fermentation, as demonstrated on poultry slaughterhouse waste. The samples were subjected to static methane fermentation, according to the methodology of DIM DIN 38414(DIN Deutches Institut für Normung). The experiment lasted 30 days. The total amount of biogas obtained after fermentation was 398 mL·g⁻¹ for the soft fraction and 402 mL·g⁻¹ for the hard fraction. In the case of the soft waste fraction, the addition of carboxymethylcellulose at 1% of the mass to the biogas process increased the amount of obtained biogas by 16%. In the case of the hard fraction, no effect of the addition of emulsifier on the total amount of biogas obtained was identified. In each case, the biogas from substrates with added emulsifier contained less methane and slightly more carbon. The emulsifier added to the soft fraction of slaughterhouse waste from poultry processing allowed cutting the process of methanogenesis by over 50% while maintaining the efficiency of biogas production. In the case of biogasification of bone tissue, no unambiguous effect of the addition of emulsifier on the improvement of process efficiency was identified. Full article

(This article belongs to the Special Issue Selected paper from 6th International Conference on Renewable Energy Sources (ICoRES 2019))

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17 pages, 4032 KiB

Open AccessArticle

Influence of Raw Material Drying Temperature on the Scots Pine (Pinus sylvestris L.) Biomass Agglomeration Process—A Preliminary Study

by Marek Wróbel, Marcin Jewiarz, Krzysztof Mudryk and Adrian Knapczyk

Energies 2020, 13(7), 1809; https://0-doi-org.brum.beds.ac.uk/10.3390/en13071809 - 09 Apr 2020

Cited by 18 | Viewed by 2477

Abstract

For biomass compaction, it is important to determine all aspects of the process that will affect the quality of pellets and briquettes. The low bulk density of biomass leads to many problems in transportation and storage, necessitating the use of a compaction process to ensure a solid density of at least 1000 kg·m⁻³ and bulk density of at least 600 kg·m⁻³. These parameters should be achieved at a relatively low compaction pressure that can be achieved through the proper preparation of the raw material. As the compaction process includes a drying stage, the aim of this work is to determine the influence of the drying temperature of pine biomass in the range of 60–140 °C on the compaction process. To determine whether this effect is compensated by the moisture, compaction was carried out on the material in a dry state and on the materials with moisture contents of 5% and 10% and for compacting pressures in the 130.8–457.8 MPa range. It was shown that drying temperature affects the specific density and mechanical durability of the pellets obtained from the raw material in the dry state, while an increase in the moisture content of the raw material neutralizes this effect. Full article

(This article belongs to the Special Issue Selected paper from 6th International Conference on Renewable Energy Sources (ICoRES 2019))

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24 pages, 3739 KiB

Open AccessArticle

Decision Support System for the Production of Miscanthus and Willow Briquettes

by Sławomir Francik, Adrian Knapczyk, Artur Knapczyk and Renata Francik

Energies 2020, 13(6), 1364; https://0-doi-org.brum.beds.ac.uk/10.3390/en13061364 - 15 Mar 2020

Cited by 17 | Viewed by 3051

Abstract

The biomass is regarded as a part of renewable energy sources (RES), which can satisfy energy demands. Biomass obtained from plantations is characterized by low bulk density, which increases transport and storage costs. Briquetting is a technology that relies on pressing biomass with the aim of obtaining a denser product (briquettes). In the production of solid biofuels, the technological as well as material variables significantly influence the densification process, and as a result influence the end quality of briquette. This process progresses differently for different materials. Therefore, the optimal selection of process’ parameters is very difficult. It is necessary to use a decision support tool—decision support system (DSS). The purpose of the work was to develop a decision support system that would indicate the optimal parameters for conducting the process of producing Miscanthus and willow briquettes (pre-comminution, milling and briquetting), briquette parameters (durability and specific density) and total energy consumption based on process simulation. Artificial neural networks (ANNs) were used to describe the relationship between individual parameters of the briquette production process. DSS has the form of a web application and is opened from a web browser (it is possible to open it on various types of devices). The modular design allows the modification and expansion the application in the future. Full article

(This article belongs to the Special Issue Selected paper from 6th International Conference on Renewable Energy Sources (ICoRES 2019))

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18 pages, 9289 KiB

Open AccessArticle

Finite Element Modeling of Geothermal Source of Heat Pump in Long-Term Operation

by Elżbieta Hałaj, Leszek Pająk and Bartosz Papiernik

Energies 2020, 13(6), 1341; https://0-doi-org.brum.beds.ac.uk/10.3390/en13061341 - 13 Mar 2020

Cited by 9 | Viewed by 2929

Abstract

Model simulation allows to present the time-varying temperature distribution of the ground source for heat pumps. A system of 25 double U-shape borehole heat exchangers (BHEs) in long-term operation and three scenarios were created. In these scenarios, the difference between balanced and non-balanced energy load was considered as well as the influence of the hydrogeological factors on the temperature of the ground source. The aim of the study was to compare different thermal regimes of BHEs operation and examine the influence of small-scale and short-time thermal energy storage on ground source thermal balance. To present the performance of the system according to geological and hydrogeological factors, a Feflow^® software (MIKE Powered by DHI Software) was used. The temperature for the scenarios was visualized after 10 and 30 years of the system’s operation. In this paper, a case is presented in which waste thermal energy from space cooling applications during summer months was used to upgrade thermal performance of the ground (geothermal) source of a heat pump. The study shows differences in the temperature in the ground around different Borehole Heat Exchangers. The cold plume from the not-balanced energy scenario is the most developed and might influence the future installations in the vicinity. Moreover, seasonal storage can partially overcome the negative influence of the travel of a cold plume. The most exposed to freezing were BHEs located in the core of the cold plumes. Moreover, the influence of the groundwater flow on the thermal recovery of the several BHEs is visible. The proper energy load of the geothermal source heat pump installation is crucial and it can benefit from small-scale storage. After 30 years of operation, the minimum average temperature at 50 m depth in the system with waste heat from space cooling was 2.1 °C higher than in the system without storage and 1.6 °C higher than in the layered model in which storage was not applied. Full article

(This article belongs to the Special Issue Selected paper from 6th International Conference on Renewable Energy Sources (ICoRES 2019))

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13 pages, 1994 KiB

Open AccessArticle

The Efficiency of Industrial and Laboratory Anaerobic Digesters of Organic Substrates: The Use of the Biochemical Methane Potential Correction Coefficient

by Krzysztof Pilarski, Agnieszka A. Pilarska, Piotr Boniecki, Gniewko Niedbała, Karol Durczak, Kamil Witaszek, Natalia Mioduszewska and Ireneusz Kowalik

Energies 2020, 13(5), 1280; https://0-doi-org.brum.beds.ac.uk/10.3390/en13051280 - 10 Mar 2020

Cited by 22 | Viewed by 2630

Abstract

This study is an elaboration on the conference article written by the same authors, which presented the results of laboratory tests on the biogas efficiency of the following substrates: maize silage (MS), pig manure (PM), potato waste (PW), and sugar beet pulp (SB). This article presents methane yields from the same substrates, but also on a technical scale. Apart from that, it presents an original methodology of defining the Biochemical Methane Potential Correction Coefficient (BMPCC) based on the calculation of biomass conversion on an industrial scale and on a laboratory scale. The BMPCC was introduced as a tool to enable uncomplicated verification of the operation of a biogas plant to increase its efficiency and prevent undesirable losses. The estimated BMPCC values showed that the volume of methane produced in the laboratory was overestimated in comparison to the amount of methane obtained under technical conditions. There were differences observed for each substrate. They ranged from 4.7% to 17.19% for MS, from 1.14% to 23.58% for PM, from 9.5% to 13.69% for PW, and from 9.06% to 14.31% for SB. The BMPCC enables estimation of biomass under fermentation on an industrial scale, as compared with laboratory conditions. Full article

(This article belongs to the Special Issue Selected paper from 6th International Conference on Renewable Energy Sources (ICoRES 2019))

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8 pages, 1286 KiB

Open AccessArticle

Energy Utilization of Spent Coffee Grounds in the Form of Pellets

by Radovan Nosek, Maw Maw Tun and Dagmar Juchelkova

Energies 2020, 13(5), 1235; https://0-doi-org.brum.beds.ac.uk/10.3390/en13051235 - 06 Mar 2020

Cited by 29 | Viewed by 5769

Abstract

Nowadays it is important to limit the use and combustion of fossil fuels such as oil and coal. There is a need to create environmentally acceptable projects that can reduce or even stop greenhouse gas emissions. In this article, we dealt with the objectives of energy policy with regard to environmental protection, waste utilization, and conservation of natural resources. The main objective of the research was to assess the possibility of the use of spent coffee grounds (SCG) as fuel. As a part of the solution, the processing of coffee waste in the form of pellets, analysis of calorific value and combustion in the boiler were proposed. The experiments were done with four samples of pellets. These samples were made from a mixture of wood sawdust and spent coffee grounds with ratio 30:70 (wood sawdust: spent coffee grounds), 40:60, 50:50 and 100% of spent coffee grounds. The calorific values were compared with wood sawdust pellets (17.15 MJ.kg⁻¹) and the best lower calorific value of 21.08 MJ.kg⁻¹ was measured for 100% of spent coffee grounds. This sample did not achieve the desired performance during the combustion in the boiler due to the low strength of the sample. Full article

(This article belongs to the Special Issue Selected paper from 6th International Conference on Renewable Energy Sources (ICoRES 2019))

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19 pages, 1112 KiB

Open AccessArticle

Assessment of Reducing Pollutant Emissions in Selected Heating and Ventilation Systems in Single-Family Houses

by Joanna Hałacz, Aldona Skotnicka-Siepsiak and Maciej Neugebauer

Energies 2020, 13(5), 1224; https://0-doi-org.brum.beds.ac.uk/10.3390/en13051224 - 06 Mar 2020

Cited by 10 | Viewed by 1927

Abstract

The article presents the results of a study aiming to select the optimal source of heat for a newly designed single-family home. Commercial software was used to compare heating and ventilation systems involving a bituminous coal boiler, a condensing gas boiler, a biomass boiler, a heat pump with water and glycol as heat transfer media. The effectiveness of natural ventilation, mechanical ventilation with a ground-coupled heat exchanger, and solar heater panels for water heating were evaluated. The analysis was based on the annual demand for useful energy, final energy, and non-renewable primary energy in view of the pollution output of the evaluated heating systems. The analysis revealed that the heat pump with water and glycol was the optimal solution. However, the performance of the heat pump in real-life conditions was below its maximum theoretical efficiency. The biomass boiler contributed to the highest reduction in pollutant emissions (according to Intergovernmental Panel on Climate Change Change guidelines, carbon dioxide emissions have zero value), but it was characterized by the highest demand for final energy. Mechanical ventilation with heat recovery was required in all analyzed systems to achieve optimal results. The introduction of mechanical ventilation decreased the demand for final energy by 10% to around 40% relative to the corresponding heating systems with natural ventilation. Full article

(This article belongs to the Special Issue Selected paper from 6th International Conference on Renewable Energy Sources (ICoRES 2019))

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16 pages, 10266 KiB

Open AccessArticle

A New Concept and a Test of a Bubble Pump System for Passive Heat Transport from Solar Collectors

by Daniel Chludziński and Michał Duda

Energies 2020, 13(5), 1185; https://0-doi-org.brum.beds.ac.uk/10.3390/en13051185 - 05 Mar 2020

Viewed by 3158

Abstract

Heat is usually transported by hydraulic circuits where the working medium is circulated by an electric pump. Heat can also be transferred by natural convection in passive systems. Passive systems where heat is transported downward have also been described and studied in the literature. These types of devices are referred to as reverse thermosiphons. However, systems of the type are not widely applied in practice due to the problems associated with the selection of the optimal working medium. In water-based thermosiphons, negative pressure is produced when water temperature falls below 100 °C, and non-condensable gas can enter the system. These problems are not encountered in systems where the working medium has a low boiling point. However, liquids with a low boiling point can be explosive, expensive, and harmful to the environment. The solution proposed in this paper combines the advantages of water and a liquid with a low boiling point. The described system relies on water as the heat transfer medium and small amounts of a substance with a low boiling point. The developed model was tested under laboratory conditions to validate the effectiveness of a passive system where heat is transported downward with the involvement of two working media. The system’s operating parameters are also described. Full article

(This article belongs to the Special Issue Selected paper from 6th International Conference on Renewable Energy Sources (ICoRES 2019))

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9 pages, 1068 KiB

Open AccessArticle

The Follow-up Photobioreactor Illumination System for the Cultivation of Photosynthetic Microorganisms

by Beata Brzychczyk, Tomasz Hebda, Jakub Fitas and Jan Giełżecki

Energies 2020, 13(5), 1143; https://0-doi-org.brum.beds.ac.uk/10.3390/en13051143 - 03 Mar 2020

Cited by 8 | Viewed by 2937

Abstract

The article presents the basic conceptual assumptions of a photobioreactor with a complementary lighting system. The cylindrical bioreactor has three independent, interconnected, and fully controlled lighting systems. A characteristic feature is the combination of the lighting system with the measurement of photosynthetically active PAR (photosynthetically active radiation) and the optical density of the culture medium. The entire lighting system is based on RGBW (“red, green, blue, white”) LED and RBG (“red, green, blue”) LEDs. The pilot study was conducted on a simplified prototype of a photobioreactor designed for the distribution and optimization of light in algae cultures designed for energy purposes. The study was carried out on microalgae Chlorella Vulgaris BA0002a from the collection of marine algae cultures. Full article

(This article belongs to the Special Issue Selected paper from 6th International Conference on Renewable Energy Sources (ICoRES 2019))

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11 pages, 11020 KiB

Open AccessArticle

A New Design for Wood Stoves Based on Numerical Analysis and Experimental Research

by Przemysław Motyl, Marcin Wikło, Julita Bukalska, Bartosz Piechnik and Rafał Kalbarczyk

Energies 2020, 13(5), 1028; https://0-doi-org.brum.beds.ac.uk/10.3390/en13051028 - 25 Feb 2020

Cited by 3 | Viewed by 2856

Abstract

This work proposes a comprehensive approach to modifying the design of wood stoves with a heating power up to 20 kW, including design works, simulations, and experimental research. The work is carried out in two stages. In the first part, a numerical model is proposed of the fireplace insert including fluid flow, the chemical combustion reaction, and heat exchange (FLUENT software is applied to solve the problem). The results of the simulation were compared with the experiment carried out on the test bench. A comparison of the experimental and numerical results was made for the temperature distribution along with the concentration of CO, CO₂, and O₂. Construction changes were proposed in the second stage, together with numerical simulations whose goal was an increase in the efficiency of the heating devices. The results obtained show that the average temperature in the chimney flue, which has a low value that is a determinant of the higher efficiency of the heating devices, was reduced relative to the initial design of the fireplace intake by 11%–16% in all cases. The retrofit enhanced stable heat release from the wood stove, which increased the efficiency and reduced the harmful components of combustion. Full article

(This article belongs to the Special Issue Selected paper from 6th International Conference on Renewable Energy Sources (ICoRES 2019))

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17 pages, 8038 KiB

Open AccessArticle

Parameters Affecting RDF-Based Pellet Quality

by Marcin Jewiarz, Krzysztof Mudryk, Marek Wróbel, Jarosław Frączek and Krzysztof Dziedzic

Energies 2020, 13(4), 910; https://0-doi-org.brum.beds.ac.uk/10.3390/en13040910 - 18 Feb 2020

Cited by 30 | Viewed by 5261

Abstract

Increasing production of waste has compelled the development of modern technologies for waste management. Certain fractions of municipal solid wastes are not suitable for recycling and must be utilised in other ways. Materials such as refuse-derived fuel (RDF) fractions are used as fuel in cement or CHP (combined heat and power) plants. The low bulk density leads to many problems pertaining to transportation and storage. In the case of biomass, these problems cause reduction in pelletisation. This paper therefore presents a comprehensive study on RDF pellet production, which is divided into three major areas. The first describes laboratory-scale tests and provides information on key factors that affect pellet quality (e.g., density and durability). Based on this, the second part presents a design of modified RDF dies to form RDF pellets, which are then tested via a semi-professional line test. The results show that RDF fraction can be compacted to form pellets using conventional devices. Given that temperature plays a key role, a special die must be used, and this ensures that the produced pellets exhibit high durability and bulk density, similar to biomass pellets. Full article

(This article belongs to the Special Issue Selected paper from 6th International Conference on Renewable Energy Sources (ICoRES 2019))

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21 pages, 3191 KiB

Open AccessArticle

A New Model for Environmental Assessment of the Comminution Process in the Chain of Biomass Energy Processing ^†

by Weronika Kruszelnicka

Energies 2020, 13(2), 330; https://0-doi-org.brum.beds.ac.uk/10.3390/en13020330 - 09 Jan 2020

Cited by 17 | Viewed by 2485

Abstract

Acquiring energy contained in biomass requires its prior appropriate preparation. These treatments require some energy inputs, which significantly affect the reduction of the energy and the environmental balance in the entire life cycle of the biomass energy processing chain. In connection with the above, the aim of this work is to develop a methodology for the environmental assessment of biomass grinding in the processing chain for energy purposes. The research problem is formulated as follows: Is it possible to provide an assessment model that takes into account the environmental inputs and benefits of the grinding process of biomass intended for further energy use (for example, combustion)? How do the control variables of the grinding machine affect the environmental process evaluation? In response to these research problems, an original, carbon dioxide emission assessment index of the biomass grinding process was developed. The model was verified by assessing the process of rice and maize grinding on a real object—a five-disc mill—with various speed settings of the grinding disc. It was found that the carbon dioxide emission assessment model developed provides the possibility of comparing grinding processes and identifying the grinding process with a better CO₂ emission balance, where its values depend on the control parameters of the mill. Full article

(This article belongs to the Special Issue Selected paper from 6th International Conference on Renewable Energy Sources (ICoRES 2019))

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