| 1. |
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| 2. |
- Ottosson, Anders, 1978-, et al.
(författare)
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A mathematical model of heat and mass transfer in Yankee drying of tissue
- 2017
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Ingår i: Drying Technology. - : Taylor & Francis. - 0737-3937 .- 1532-2300. ; 35:3, s. 323-334
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Tidskriftsartikel (refereegranskat)abstract
- Final dewatering in the production of dry creped tissue is performed by Yankee drying, which includes hot pressing followed by simultaneous contact and impingement drying. The present study models Yankee drying and compares simulation results to the data obtained from trials on a pilot tissue machine. It advances models published previously by the representations developed for the transport of heat in the pressing stage and for the heat transfer involved in the dehydration of the cylinder coating spray. The model predicts an average specific drying rate within 4% in the range of the experimental data used.
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| 3. |
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| 4. |
- Rezk, Kamal, 1983-, et al.
(författare)
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Characterizing flow resistance in 3-dimensional disordered fibrous structures based on Forchheimer coefficients for a wide range of Reynolds numbers
- 2016
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Ingår i: Applied Mathematical Modelling. - : Elsevier. - 0307-904X .- 1872-8480. ; 40:21-22, s. 8898-8911
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Tidskriftsartikel (refereegranskat)abstract
- The flow resistance in 3-dimensional fibrous structures are investigated in particle Reynolds number representing flow characteristics with strong inertia. The resistance coefficients are established based on steady state simulations of single-phase processes of water numerically. An automatized simulation process in COMSOL is developed with a MATLAB algorithm in which production runs could be carried for various 3-dimensional fibrous structures. Simulation of flow processes ranging from Reynolds numbers at creeping flow levels to high Reynolds number at approximately 1000 are calculated and a numerical data set is established in order to estimate Forchheimer coefficients which are used to correlate a dimensionless friction factor to a modified Reynolds expression for porous media.The friction factor and dimensionless permeability are calculated for fibrous structures with (i) disordered unidirectional fibers (ii) an isotropic fiber orientation in-plane perpendicular to the flow, and (iii) an isotropic fiber structure in a the 3-dimensional space. Empirical correlations of the friction factor and Reynolds number are used to compare our simulation data in order to assess the validity of our models and flow resistance estimations. The dimensionless permeability is moreover compared to other numerical simulations of flow through fibrous structures in order to assess flow resistance at low Reynolds number.It is concluded that flow resistance in the isotropic fiber arrangement in space is lower than the in-plane isotropic orientation and disordered unidirectional fiber arrangements at creeping flow conditions, however, all friction actors converges towards the same value at higher Reynolds numbers indicating that fiber orientation is independent at high inertia flow regimes. Overall, our numerical simulations agree well to classical empirical formulations for a wide range of Reynolds number. However, the comparison differs considerably depending on the porosity level.
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| 5. |
- Rezk, Kamal, 1983-, et al.
(författare)
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Modelling of water removal during a paper vacuum dewatering process using a Level-Set method
- 2013
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Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509 .- 1873-4405. ; 101, s. 543-553
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Tidskriftsartikel (refereegranskat)abstract
- Water removal in paper manufacturing is an energy-intensive process. The dewatering process generally consists of four stages of which the first three stages include mechanical water removal through gravity filtration, vacuum dewatering and wet pressing. In the fourth stage, water is removed thermally, which is the most expensive stage in terms of energy use.In order to analyse water removal during a vacuum dewatering process, a numerical model was created by using a Level-Set method. Various different 2D structures of the paper model were created in MATLAB code with randomly positioned circular fibres with identical orientation. The model considers the influence of the forming fabric which supports the paper sheet during the dewatering process, by using volume forces to represent flow resistance in the momentum equation.The models were used to estimate the dry content of the porous structure for various dwell times. The relation between dry content and dwell time was compared to laboratory data for paper sheets with basis weights of 20 and 50 g/m2 exposed to vacuum levels between 20 kPa and 60 kPa. The comparison showed reasonable results for dewatering and air flow rates. The random positioning of the fibres influences the dewatering rate slightly. In order to achieve more accurate comparisons, the random orientation of the fibres needs to be considered, as well as the deformation and displacement of the fibres during the dewatering process.
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| 6. |
- Rezk, Kamal, 1983-, et al.
(författare)
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Simulation of water removal in paper based on a 2D Level-Set model coupled with volume forces representing fluid resistance in 3D fiber distribution
- 2015
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Ingår i: Drying Technology. - : Taylor & Francis. - 0737-3937 .- 1532-2300. ; 33:5, s. 605-615
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Tidskriftsartikel (refereegranskat)abstract
- A numerical model of a vacuum dewatering process was established with a Level-Set method to simulate two-phase flow in a 2-dimensional paper sheet model with constructed volume forces representing flow resistance in a 3-dimensional environment. Nine cases of various volume force representations were compared to numerical and experimental data. Based on the dry content and dwell time relation, the case with the influence of the paper/wire interface showed the most pleasing result compared to experimental data. Compared to the other numerical cases, considering the blockage of the pore space at the top layer of the forming fabric plays an essential role in determining the flow resistance during the vacuum process. Also, the dynamics of the dewatering rate is captured well with the influence of the blockage of fibers on the top layer of the forming fabric. The peak of the dewatering rate could be investigated further with a higher frequency of sample points on new experimental data.The computational time for the two-phase flow models in this study is extensively reduced due to the removal of the internal structure. This distinction enables time efficient simulations of vacuum dewatering process in which several dewatering parameters such as level of vacuum, influence of moving vacuum pulse and higher basis weights could be investigated.
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| 7. |
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| 8. |
- Anukam, Anthony, et al.
(författare)
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A comparative analysis of the gasification performances of torrefied and untorrefied bagasse : Influence of feed size, gasifier design and operating variables on gasification efficiency
- 2018
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Ingår i: International Journal of Engineering & Technology. - : Science Publishing Corporation. - 2227-524X. ; 7:2, s. 859-867
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Tidskriftsartikel (refereegranskat)abstract
- This study conducted a comparative assessment of the gasification performances of torrefied and untorrefied bagasse with emphasis on feed size, gasifier design and operating conditions that would influence gasification efficiency. Torrefaction greatly improved the characteristics of bagasse and had significant impact on its gasification performance. The gasifier design parameters studied were throat angle and throat diameter. Temperature of input air and feed input were the gasifier operating conditions examined in the course of the gasification processes of both torrefied and untorrefied bagasse. These parameters were considered the most critical operating parameters that affect gasifier performance and, correlation between the parameters was established in the course of gasification. The results obtained showed higher gasification efficiency for torrefied bagasse in comparison to untorrefied bagasse under varied conditions of gasification, which was attributed mainly to changes in the characteristics of the torrefied material.
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| 9. |
- Anukam, Anthony, et al.
(författare)
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A review of the mechanism of bonding in densified biomass pellets
- 2021
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Ingår i: Renewable & sustainable energy reviews. - : Elsevier. - 1364-0321 .- 1879-0690. ; 148
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Tidskriftsartikel (refereegranskat)abstract
- The production of durable biomass pellets have always been challenged by several factors including the lack of understanding of the mechanism involved in how particles combine to form pellets under standard conditions of the pellet press. This is because contributing factors span several molecular, microscopic, and even nanoscopic levels as biomass undergoes pelleting. The characteristics of the bonds formed between the combining particles and their relevance to the quality of pellets remains vague, no matter how quality is defined. However, even though few researchers have attempted to explain the mechanism of bonding in densified biomass pellets using different theories, none of their hypotheses supports particle bonding from a structural chemistry perspective. There are still no clear explanations which consider the role of molecular structure and the interactions of substances as milled biomass undergo pelleting. In view of these arguments therefore, this review presents an in-depth analysis of a structural chemistry perspective of the mechanism of bonding and the use of additives in densified biomass pellets and helps identify research areas needed to facilitate better understanding of bonding in densified biomass pellets. The status of current research in biomass pelleting, types of materials suitable as additives and their structural characteristics, as well as the current technical specifications of using additives are also discussed.
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| 10. |
- Anukam, Anthony Ike, et al.
(författare)
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Characterization of pure and blended pellets made from Norway spruce and pea starch : A comparative study of bonding mechanism relevant to quality
- 2019
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Ingår i: Energies. - : MDPI. - 1996-1073. ; 12:23, s. 1-22
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Tidskriftsartikel (refereegranskat)abstract
- The mechanism of bonding in biomass pellets is such a complex event to comprehend, as the nature of the bonds formed between combining particles and their relevance to pellet quality are not completely understood. In this study, pure and blended biomass pellets made from Norway spruce and pea starch were characterized using advanced analytical instruments able to provide information beyond what is visible to the human eye, with intent to investigate differences in bonding mechanism relevant to quality. The results, which were comprehensively interpreted from a structural chemistry perspective, indicated that, at a molecular level, the major disparity in bonding mechanism between particles of the pellets and the quality of the pellets, defined in terms of strength and burning efficiency, were determined by variation in the concentration of polar functional groups emanating from the major organic and elemental components of the pellets, as well as the strength of the bonds between atoms of these groups. Microscopic-level analysis, which did not provide any clear morphological features that could be linked to incongruity in quality, showed fracture surfaces of the pellets and patterns of surface roughness, as well as the mode of interconnectivity of particles, which were evidence of the production of pellets with dissimilarities in particle bonding mechanism and visual appearance.
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| 11. |
- Anukam, Anthony, et al.
(författare)
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Improving the understanding of the bonding mechanism of primary components of biomass pellets through the use of advanced analytical instruments
- 2020
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Ingår i: Journal of wood chemistry and technology. - : Taylor & Francis Group. - 0277-3813 .- 1532-2319. ; 40:1, s. 15-32
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Tidskriftsartikel (refereegranskat)abstract
- Previous studies have attempted to explain forces holding particles together in densified biomass pellets using theories of forces of attraction between solid particles, forces of adhesion and cohesion, solid bridges and mechanical interlocking bonds including interfacial forces and capillary pressure. This study investigated the bonding mechanism of primary biomass components in densified pellets through the use of advanced analytical instruments able to go beyond what is visible to the naked eye. Data obtained were used to predict how primary biomass components combine to form pellets based on the theory of functional groups and the understanding of structural chemistry. Results showed that hydroxyl and carbonyl functional groups played key roles in helping to identify the type of forces acting between individual particles, at a molecular level. At a microscopic level, morphological examination of the pellet clearly showed solid bridges caused by intermolecular bonding from highly electronegative polar functional groups linked to cellulose and hemicellulose.
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| 12. |
- Bengtsson, Peder, 1968-, et al.
(författare)
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A household dishwasher heated by a heat pump system using an energy storage unit with water as the heat source
- 2015
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Ingår i: International journal of refrigeration. - : Elsevier. - 0140-7007 .- 1879-2081. ; 49, s. 19-27
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Tidskriftsartikel (refereegranskat)abstract
- Electricity usage by a household dishwasher can be reduced by using a heat pump system to heat the dishwasher cabinet, dishware and washing water. The evaporator obtains the energy from an energy storage unit which consists of a container filled with water which freezes to ice. The majority of the heat transfer from the energy storage to the evaporator occurs when ice is created in the energy storage unit. A transient simulation model of a dishwasher with a heat pump system was developed and compared to an experimental setup with good agreement. A simulation study of the compressor cylinder volume and the compressor operating time was performed. The results showed a 24% reduction in total electricity use compared to a dishwasher cycle using a traditional electric element.
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| 13. |
- Bengtsson, Peder, 1968-, et al.
(författare)
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Concept Study of a New Method for Drying Dishware in a Heat Pump Dishwater
- 2017
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Ingår i: Energy Efficiency. - : Springer Nature. - 1570-646X .- 1570-6478. ; 10:6, s. 1529-1538
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Tidskriftsartikel (refereegranskat)abstract
- In a heat pump dishwasher, the whole dishwasher with the cabinet, dishware and process water is the heat sink, while a water tank, whose contents will freeze, is the heat source. The aim of the experimental concept study presented here was to evaluate a new drying method for a heat pump dishwasher. In this method, the drying of the dishware occurs as a fan circulates humid air in a closed system in which the water on the dishware evaporates inside the warm dishwasher cabinet and then condenses on a cold surface of the frozen water tank. The evaluation of drying performance was based on the European standard EN50242, which considers visible water drops left on the dishware after a completed dishwashing cycle. The results showed that this new closed drying method was more energy efficient compared to an existing open drying method, and that the drying start temperature and the drying time had a significant effect on the drying performance. Its lower electricity consumption and the fact that it does not vent humid air into the kitchen gives this heat pump dishwasher a competitive advantage over dishwashers using an open drying method.
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| 14. |
- Bengtsson, Peder, et al.
(författare)
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Performance Study of a Closed-Type Heat Pump Tumble Dryer Using A Simulation Model and an Experimental Set-Up
- 2014
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Ingår i: Drying Technology. - : Taylor & Francis Group. - 0737-3937 .- 1532-2300. ; 32:8, s. 891-901
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Tidskriftsartikel (refereegranskat)abstract
- In the interests of competitiveness, manufactures of tumble dryers are seeking to reduce both their electricity use and the drying time. This study examines how the cylinder volume of the compressor and the total heat transfer of the condenser influence the drying time and electricity use in a heat pump tumble dryer. A transient simulation model was developed and compared to an experimental set-up with good similarity. The simulations show that increasing the cylinder volume of the compressor by 50% decreases the drying time by 14% without using more electricity.
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| 15. |
- Berghel, Jonas, 1966-, et al.
(författare)
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A comparison of relevant data and results from single pellet press research is Mission Impossible : A review
- 2022
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Ingår i: Bioresource Technology Reports. - : Elsevier. - 2589-014X. ; 18
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Tidskriftsartikel (refereegranskat)abstract
- A global increase in the wood fuel pellet market requires knowledge of new biomasses pelleting abilities. As large-scale industrial tests of new materials are costly, tests in e.g., a single pellet press (SPP) are desirable. SPPs have many different configurations and it typically produces one pellet at a time and can give results of its pelletability. This review has surveyed the research that has been carried out of SPPs to ascertain the feasibility of comparing their obtained data and the results. The results show that it is almost impossible to compare the data and results of the various different SPP studies, e.g., some information from the data used was missing, resulting in that only 27 out of 70 papers were comparable. One solution could be the introduction of a common SPP testing method using a determined set of data that enables a reference pellet to be produced in every study.
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| 16. |
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| 17. |
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| 18. |
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| 19. |
- Berghel, Jonas, 1966-, et al.
(författare)
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From sawdust to pellets. Still a challenge...
- 2012
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Ingår i: Public Service Review European Union. - : European union. ; :33, s. 398-399
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 20. |
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| 21. |
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| 22. |
- Berghel, Jonas, 1966-, et al.
(författare)
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Lösningarna finns! Är pelletsproducenterna medvetna om problemen?
- 2011
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Ingår i: Bioenergi. - Gävle : Region Gävleborg. - 9789163391262 ; , s. 25-29
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Sverige är inte längre världsledande som pelletsproducent. USA producerar allra mest pellets i världen. Kanada och Ryssland producerar också allt mer pellets. Ingen av dessa länder har någon omfattande inhemsk konsumtion. I stort sett all pellets exporteras och det sker huvudsakligen till Europa. Sannolikt kommer det att leda till att priset på pellets i Europa sjunker, med följd att lönsamheten för svenska pelletsproducenter minskar.
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| 23. |
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| 24. |
- Berghel, Jonas, 1966-, et al.
(författare)
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The effects of kraft lignin additives on wood fuel pellet quality, energy use and shelf life
- 2013
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Ingår i: Fuel processing technology. - : Elsevier BV. - 0378-3820 .- 1873-7188. ; 112:0, s. 64-69
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Tidskriftsartikel (refereegranskat)abstract
- In 2011, the total consumption of pellets in Sweden amounted to 1.9 million tons, which represents an energy value of 9 TWh. The pellets are used in large-scale as well as in small-scale applications, and increased demands on pellet quality are likely to force pellet producers to improve on the pellet properties. One way of increasing pellet quality is by using additives. The purpose of this article, therefore, is to examine kraft lignin as an additive. Pelletswere produced in a small industrial pellet press located at KarlstadUniversity, Karlstad, Sweden, and 1–4% of kraft lignin was added to the pellets. The results indicate that the addition of an increased amount of kraft lignin to the pellets increases their mechanical durability and their lengths. The results also indicate that dry kraft lignin yields pellets with higher durability as compared to wet kraft lignin. The energy demand was unaffected by the increased use of kraft lignin. The general results presented in this paper are useful for producers of lignin, pellet producers and end-users of pellets, who are interested in developing their products and/or improving the production processes.
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| 25. |
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| 26. |
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| 27. |
- Frodeson, Stefan, Universitetsadjunkt, 1968-, et al.
(författare)
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Compression of Biomass Substances-A Study on Springback Effects and Color Formation in Pellet Manufacture
- 2019
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Ingår i: Applied Sciences. - : MDPI. - 2076-3417. ; 9:20
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Tidskriftsartikel (refereegranskat)abstract
- In order to increase the use of a variated raw material base for pellet production with a maintained density level, knowledge of the biomaterials' ability to counteract any springback effects is essential. In this study, the springback effects were investigated for single press produced pellets from cellulose, hemicelluloses, pectin, and two woods at different moisture contents. The change in pellet coloring was also tested through a spectrophotometer for both xylan and carboxymethyl cellulose (CMC) pellets. The results show that the density of xylan pellets is much higher than glucomannan, for both green and cured pellets, and that the length of the pellets, as well as springback contribution, differ between the hemicelluloses. The study also presents results showing that both xylan and CMC pellets have a mutually identical spectrum and that the changes in the structure of xylan are not only related to moisture content, but are also pressure-related. The study also postulates that the color difference of the xylan pellets is a result of physical changes in the structure, as opposed to being of a chemical nature.
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| 28. |
- Frodeson, Stefan, Universitetsadjunkt, 1968-, et al.
(författare)
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Densification of Wood-Influence on Mechanical and Chemical Properties when 11 Naturally Occurring Substances in Wood Are Mixed with Beech and Pine
- 2021
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 14:18
-
Tidskriftsartikel (refereegranskat)abstract
- The need to increase the use of renewable biomasses for energy supply, such as fuel pellets is significant. However, different types of biomasses have different mechanical properties to be pelletized, which entails a limitation in available raw materials for pellet producers. Within this study eleven different pure substances from biomasses were separately mixed with European beech and Scots pine, to identify its impact on the densification process. Beech and pine pellets were used as control materials against their corresponding pellets mixed with substances representing: cellulose, hemicelluloses, other polysaccharides, lignin, protein, and extractives. The mechanical properties were investigated as well as FT-IR and SEM analyses on the pellets. The results showed that the addition of the substances xylan and galactan created the hardest pellets for both pine and beech and that adding extractives to wood affects pine more than beech in relation to hardness. The FT-IR data could not provide clear explanations as to the variation in hardness and springback behavior through the identification of major functional groups in each pellet. It can be concluded that biomass residues rich in xylan and galactan increase pellet quality in terms of strength and durability without affecting the production process.
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| 29. |
- Frodeson, Stefan, Universitetsadjunkt, 1968-, et al.
(författare)
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Effects of moisture content during densification of biomass pellets, focusing on polysaccharide substances
- 2019
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Ingår i: Biomass and Bioenergy. - : Elsevier. - 0961-9534 .- 1873-2909. ; 122, s. 322-330
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we pelletized four different pure polysaccharides represented cellulose - Avicel, hemicelluloses - locus bean gum mannan and beech xylan and other polysaccharides - apple pectin, and three woods - pine, spruce and beech. All were pelletized at 100° in a single pellet press unit with different level of moisture content from 0 to 15%. The maximal friction force and work required for compression and friction was analyzed together with the pellet density and hardness. The results showed that xylan pellets completely changed in color at 10% moisture content, and this also occurred to some extent with pectin pellets. The color of both Avicel and locus bean gum pellets were not affected at all. During compression, the results showed that water does not affect compression up to 5 kN, while above 5 kN water decreases the energy need for densification of Avicel, locus bean gum and woods. Above 5 kN the energy needs for compressing xylan and pectin increases with increased moisture content. The hardest pellets were produced from Avicel, while locus bean gum produced the weakest pellets. The study concludes that there is a significant difference in how water affects the two hemicelluloses, glucomannan and xylan, during densification.
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| 30. |
- Frodeson, Stefan, Universitetsadjunkt, 1968-, et al.
(författare)
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Pelletizing pure biomass substances to investigate the mechanical properties and bonding mechanisms
- 2018
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Ingår i: BioResources. - : North Carolina State University. - 1930-2126. ; 13:1, s. 1202-1222
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Tidskriftsartikel (refereegranskat)abstract
- Solid fuel for heating is an important product, and for sustainability reasons, it is important to replace nonrenewable fuels with renewable resources. This entails that the raw material base for pellet production has to increase. A broader spectrum of materials for pelleting involves variation in biomass substances. This variation, due to lack of knowledge, limits the possibilities to increase the pellet production using new raw materials. In this study, pellets were produced with a single pellet press from 16 different pure biomass substances representing cellulose, hemicellulose, other polysaccharides, protein, lignin, and extractives, and five different wood species, representing softwoods and hardwoods. All pellets were analyzed for the work required for compression and friction, maximum force needed to overcome the backpressure, pellet hardness, solid density, and moisture uptake. The results showed that the hardest pellets were produced from the group of celluloses, followed by rice xylan and larch arbinogalactan. The weakest pellets were from the group of mannans. Conclusions are that the flexible polysaccharides have a greater impact on the pelletizing process than previously known, and that the differences between xylan and glucomannan may explain the difference in the behavior of pelletizing softwoods and hardwoods.
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| 31. |
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| 32. |
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| 33. |
- Frodeson, Stefan, Universitetsadjunkt, 1968-, et al.
(författare)
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The Potential for a Pellet Plant to Become a Biorefinery
- 2019
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Ingår i: Processes. - Basel : MDPI. - 2227-9717. ; 7:4, s. 1-11
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Tidskriftsartikel (refereegranskat)abstract
- The use of bioenergy has increased globally in recent years, as has the utilization of biomaterials for various new product solutions through various biorefinery concepts. In this study, we introduce the concept of using a mechanical dewatering press in combination with thermal drying in a pellet plant. The purpose of the study is to increase the understanding of the effects a mechanical dewatering press has in a pellet production chain and investigate whether a pellet plant could thus become a biorefinery. The evaluations in this study are based on industrial data and initial tests at the university. The results show that the concept of using the mechanical dewatering press together with a packed moving bed dryer reduces energy use by 50%, compared to using only a packed moving bed dryer. The press water could be used as a raw material for biogas, bioplastics, and biohydrogen. Hence, this study points out the possibilities of a pellet plant increasing the efficiency of the drying step, while moving towards becoming a biorefinery.
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| 34. |
- Frodeson, Stefan, 1968-, et al.
(författare)
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The Potential of Using Two-Step Drying Techniques for Improving Energy Efficiency and Increasing Drying Capacity in Fuel Pellet Industries
- 2013
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Ingår i: Drying Technology. - : Taylor & Francis. - 0737-3937 .- 1532-2300. ; 31:15, s. 1863-1870
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Tidskriftsartikel (refereegranskat)abstract
- The use of wood fuel pellets has increased worldwide in recent years, and pellet producers conclude that the lack of drying capacity is a barrier to increased production. In this study, we develop a concept of two different dryers called the two-step drying technique. The aim is to show the potential for increasing the drying capacity and improving energy efficiency when introducing a second dryer into the pellet plant. The study is theoretical and based on an industrial packed moving bed dryer. It shows that the drying capacity increased by 22% when a pneumatic second dryer was used.
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| 35. |
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| 36. |
- Henriksson, Lisa, et al.
(författare)
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Bioresources for Sustainable Pellet Production in Zambia : Twelve Biomasses Pelletized at Different Moisture Content
- 2019
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Ingår i: BioResources. - North Carolina : North Carolina State University. - 1930-2126. ; 14:2, s. 2550-2575
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Tidskriftsartikel (refereegranskat)abstract
- The use of charcoal and firewood for cooking is common in Zambia,and its utilization is suchthat the deforestation rate is high, energy utilization is low, and unfavorable cooking methods lead to high death rates due to indoor air pollution mainly from particulate matter and carbon monoxide.Byusing an alternative cooking method, such as pellet stoves, it is possible to offer a sustainable solution, provided that sustainable pelletproduction can be achieved. In this study, 12different available biomaterials were pelletizedina single pellet unitto investigate their availability as raw materials for pellet production in Zambia. The study showedthat sicklebush and pigeon pea generatedthe same pelleting properties correlated withcompression and frictionand that both materials showedlow moisture uptake. The study also identifiedtwo groups of materials that broadenedthe raw material base and helpedto achieve sustainable pellet production.Group 1consisted of materials with equal pelletingabilities (miombo, peanut shell, pigeon pea,and sicklebush) andGroup 2 consistedof materialsthat showed low impact of varying moisture content(eucalyptus, miombo, peanut shell, pigeon pea, and sicklebush). The hardest pellet was made from Tephrosia, which wasfollowed by Gliricidia.
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| 37. |
- Mattsson, Lisa, et al.
(författare)
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Waste of fresh fruit and vegetables at retailers in Sweden : Measuring and calculation of mass, economic cost and climate impact
- 2018
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Ingår i: Resources, Conservation and Recycling. - : Elsevier BV. - 0921-3449 .- 1879-0658. ; 130, s. 118-126
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Tidskriftsartikel (refereegranskat)abstract
- Food waste is a significant problem for environmental, economic and food security reasons. The retailer, food service and consumers have been recognised as the parts of the food supply chain where the possibility of reducing food waste is greatest in industrialised countries. In this study, primary data on fresh fruit and vegetables (FFV) waste collected through direct measurements in three large retail stores in Sweden were analysed from the perspectives of wasted mass, economic cost and climate impact. A method of measuring and calculating the economic cost of FFV waste was developed and includes the cost of wasted produce, the cost of personnel time for waste management and the cost of waste collection and disposal. The results show that seven FFV categories, which have been termed "hotspot categories", contributed to the majority of the waste, both in terms of wasted mass, economic cost and climate impact. The "hotspot categories" are apple, banana, grape, lettuce, pear, sweet pepper, and tomato. The cost benefit analysis conducted showed that it is economically wise to invest in more working time for employees in waste management to accomplish a reduction of wasted mass and climate impact without an economic loss for the store. These results are relevant for supporting the implementation of policies and initiatives aimed at food waste reduction at retail level.
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| 38. |
- Persson, Tomas, et al.
(författare)
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Deposit formation in a small-scale wood pellet boiler using pellet with additives
- 2013
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Ingår i: Journal of Fuel Chemistry and Technology. - 1872-5813. ; 41:5, s. 530-539
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Tidskriftsartikel (refereegranskat)abstract
- This work studies the amount of gaseous and particle emissions and deposits on heat exchanger surfaces in a boiler fired with commercially available pellets and with pellets primed with magnesium oxide and magnesium hydroxide. The combustion experiments were performed on a residential boiler of 20 kW. Substrates placed in the heat exchanger was analysed with SEM-EDX-mapping to evaluate the chemical composition of the deposits. The results show that particle emissions (PM 2.5) using the additives increased by about 50% and the mass of the deposits in the flue gas heat exchanger (excluding loose fly ash) increased by about 25% compared to the combustion of pellets without additives. The amount of additives was found to be eight times higher than the amount of the main alkali metals potassium (K) and sodium (Na) which leads to the assumption that the additives were overdosed and therefore caused the problems reported. The SEM analysis of the substrates placed in the flue gas heat exchanger indicate that the deposits of sodium (Na), potassium (K), chlorine (Cl) and sulphur (S) decrease using the additives. If this was due to the expected chemical reactions or due to the loose fly ash covering the substrates after the test, could not be determined in this study.
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| 39. |
- Persson, Tomas, 1972-, et al.
(författare)
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Emissions and deposit properties from combustion of wood pellet with magnesium additives
- 2013
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Ingår i: Journal of Fuel Chemistry and Technology. - : Elsevier. - 1872-5813. ; 41:5, s. 530-539
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Tidskriftsartikel (refereegranskat)abstract
- This work studies the amount of gaseous and particle emissions and deposits on heat exchanger surfaces in a boiler fired with commercially available pellets and with pellets primed with magnesium oxide and magnesium hydroxide. The combustion experiments were performed on a residential boiler of 20 kW. Substrates placed in the heat exchanger was analysed with SEM-EDX-mapping to evaluate the chemical composition of the deposits. The results show that particle emissions (PM 2.5) using the additives increased by about 50% and the mass of the deposits in the flue gas heat exchanger (excluding loose fly ash) increased by about 25% compared to the combustion of pellets without additives. The amount of additives was found to be eight times higher than the amount of the main alkali metals potassium (K) and sodium (Na) which leads to the assumption that the additives were overdosed and therefore caused the problems reported. The SEM analysis of the substrates placed in the flue gas heat exchanger indicate that the deposits of sodium (Na), potassium (K), chlorine (Cl) and sulphur (S) decrease using the additives. If this was due to the expected chemical reactions or due to the loose fly ash covering the substrates after the test, could not be determined in this study.
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| 44. |
- Siwale, Workson, et al.
(författare)
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Fuel Wood Pellets Produced from Sawdust of Scots Pine Mature and Juvenile Wood : Self-Heating and Off-Gassing Tests at Industrial Scale
- 2024
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Ingår i: Bioenergy Research. - : Springer. - 1939-1234 .- 1939-1242.
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Tidskriftsartikel (refereegranskat)abstract
- This study investigated self-heating and off-gassing of Scots pine (Pinus sylvestris) wood pellets made from sawdust generated from separated mature and juvenile wood. The pellets were produced at an industrial scale and stored in large piles of about 7.2 tonnes. The production process involved drying the sawdust using three different methods and to varying moisture contents. The results indicated significant influences of both raw material type (F(6) = 61.97, p < 0.05) and drying method (F(2) = 65.38, p < 0.05) on the self-heating of the pellets. The results from the multiple regression analysis further showed that both the raw material type and pellet moisture content significantly influenced the temperature increase, with strong correlations observed for pellets produced using low-temperature drying (F(3, 14) = 83.52, multiple R2 = 0.95, p < 0.05), and medium temperature drying (F(3, 13) = 62.05, multiple R2 = 0.93, p < 0.05). The pellets produced from fresh mature wood sawdust were found to be more prone to self-heating and off-gassing while steam drying the sawdust at high temperature and pressure led to a significant reduction in heat and gas generation across all materials. The heightened self-heating and off-gassing in mature wood pellet can be attributed to a higher proportion of sapwood in the raw material. The probable explanations to the observed differences are in line with biological mechanisms for self-heating and off-gassing, as well as the chemical oxidation of fatty and resin acids.
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| 45. |
- Siwale, Workson, et al.
(författare)
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Influence of Sapwood/Heartwood and Drying Temperature on Off-Gassing of Scots Pine Wood Pellets
- 2024
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Ingår i: Bioenergy Research. - : Springer. - 1939-1234 .- 1939-1242. ; 17:1, s. 479-490
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Tidskriftsartikel (refereegranskat)abstract
- Wood pellets produced from fresh sawdust can form and release uncontrolled gases during bulk storage, a tendency referred to as off-gassing. This study investigated the off-gassing tendencies of Scots pine wood pellets made from separated sapwood and heartwood sawdust. The effects of drying temperature, raw material storage, as well as varying proportions of sapwood and heartwood were also investigated. There was a strong linear correlation between off-gassing and sapwood content, with correlation coefficient (R) values greater than 0.9 at p < 0.001 for all the off-gases. An increase in sapwood content of the feedstock led to a significant increase in off-gassing of CO2, CO, and CH4, and O2 consumption. The drying temperature of the raw material had a significant effect on off-gassing of both sapwood (F (8, 26) = 51.32, p < 0.05) and heartwood (F (8, 26) = 334.1, p < 0.05) pellets. Increasing the drying temperature for heartwood resulted in increased off-gassing, while for sapwood, the off-gassing reduced. Storage of sapwood raw material before pelletization reduced the off-gassing of wood pellets, whereas for heartwood, it had no significant impact. Based on the results, it is suggested that a biological process, in combination with the chemical oxidation of fatty acids, lay behind the off-gassing of wood pellets.
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| 46. |
- Siwale, Workson, et al.
(författare)
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Influence on off-gassing during storage of Scots pine wood pellets produced from sawdust with different extractive contents
- 2022
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Ingår i: Biomass and Bioenergy. - : Elsevier. - 0961-9534 .- 1873-2909. ; 156
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Tidskriftsartikel (refereegranskat)abstract
- Off-gassing and self-heating are the major challenges when it comes to transportation and storage of wood pellets. The heat generated due to self-heating poses a fire risk while off-gassing of toxic gasses such as carbon monoxide (CO) and some volatile organic compounds (VOCs) is an environmental and human health risk. With the increase in production volumes of wood pellets which has subsequently increased the amounts of wood pellets in transportation and storage, there is need to find lasting solutions to off-gassing and self-heating of wood pellets. The objective of this study was to test the off-gassing abilities of Scots pine wood pellets produced from sawdust with varying amounts of extractives. The aim is to come up with raw material pre-treatment measures so as to produce wood pellets that are not liable to off-gassing. Six (6) types of sawdust raw materials namely; fresh pine sawdust (FPS), stored pine sawdust (SPS), sawdust plus pine rosin (PRS), sawdust plus linseed oil (LOS), sawdust plus tall oil (TOS) and acetone extracted sawdust (AES) were used to produce the pellets. The produced pellets were then subjected to off-gassing tests under controlled conditions using the ECOM J2KN analyser. The concentrations of carbon monoxide, carbon dioxide and methane increased with storage time but slowed down towards the end of the nine days test period. The formation of these gasses were largely dependent on the type of extractives present in the raw material and not the total extractive content. The formation of methane started later than the other gases and coincided with the time when residual oxygen was depleted.
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| 47. |
- Siwale, Workson
(författare)
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Mitigating Off-Gassing and Self-Heating in Fuel Wood Pellets Storage : A Raw Materials Selection and Pre-Treatment Centred Approach
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wood pellets have become a preferred solid biomass fuel for heat and power generation due to their standardized nature, known properties, and consistent quality. However, pellets produced from fresh sawdust sometimes undergo self-heating and off-gassing during storage. This poses a challenge for their transportation and storage. The aim of this thesis was to increase the body of knowledge towards understanding the mechanisms underlying the self-heating and off-gassing of wood pellets, and offer solutions for producing wood pellets from freshly generated sawdust, with reduced self-heating and off-gassing tendencies.The effects of total wood extractive content and types of extractives in the raw material on off-gassing of wood pellets were investigated through two separate studies (papers I and II). The results from paper I showed that the total amount of extractives in the raw material has little effect on off-gassing. While gas emissions were reduced for pellets produced from Scots pine sawdust that had low amounts of extractives (stored and acetone extracted), the coefficients of determination (R2) from the linear correlation analysis between off-gassing and the total extractive content of the raw materials were below 0.5 for all the three off-gasses indicating low or no correlation. The results of cellulose pellets with added additive oils (paper II) showed that the off-gassing is highly dependent on the type of extractives in the raw material. The highest mean concentrations of the carbon oxides and methane were recorded from cellulose pellets with added linseed oil. Pellets with added linseed oil had higher off-gas emissions due to the high content of unsaturated fatty acids of 73.9% linolenic and 7.6% linoleic.The effects of raw material type and pre-treatments on self-heating and off-gassing of wood pellets were also investigated through two separate studies (papers III and IV). The results from both studies indicated significant influences of both raw material type and drying temperature. There was a strong linear correlation between off-gassing and sapwood content, with correlation coefficient (R) values greater than 0.9 at p < 0.001 for all the off-gases (paper III). An increase in sapwood content of the raw material (fresh Scots pine sawdust) led to a significant increase in off-gassing of CO2, CO and CH4, and O2 consumption. Storing of sawdust for over six months prior to pellet production, and increasing the temperature of drying the sawdust led to significant reduction of off-gassing for sapwood pellets. For heartwood pellets, increasing the drying temperature resulted in increased off-gassing and raw material storage had no effect. In the other study (paper IV), the pellets produced from Scots pine mature wood sawdust were more prone to self-heating and off-gassing compared to those produced from juvenile wood sawdust. Steam drying the sawdust at high temperature and pressure led to a significant reduction in heat and gas generation for both materials. Furthermore, the study established a notable connection between self-heating and off-gassing, the storage piles with high temperature increase also exhibited high concentrations of off-gases.The overall results indicated that a biological process, in combination with the chemical oxidation of unsaturated fatty acids lay behind the self-heating and off-gassing of wood pellets. The other notable effect was that methane formation is dependent on anaerobic conditions, whereas formation of carbon oxides can occur both under aerobic and anaerobic conditions. While storing fresh sawdust for a period of time prior to pellet production remains the most effective method for mitigating self-heating and off-gassing during pellet storage, sorting and separating the raw materials at source can facilitate the development of storage schedules tailored to specific raw materials, thereby reducing on the raw material storage time.
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| 48. |
- Siwale, Workson, et al.
(författare)
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Understanding Off-Gassing of Biofuel Wood Pellets Using Pellets Produced from Pure Microcrystalline Cellulose with Different Additive Oils
- 2022
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Ingår i: Energies. - : MDPI. - 1996-1073. ; 15:6
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 49. |
- Siwale, Workson
(författare)
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Understanding the Influence of Wood Extractives on Off-Gassing during Storage of Wood Pellets
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wood pellets have become a solid biomass fuel of choice because they are a standardized product with known quality properties. However, the self-heating and off-gassing tendencies during storage of wood pellets threatens the consistency of the pellets’ quality properties. The aim of this thesis was to increase the body of knowledge towards understanding of the off-gassing of wood pellets. The effects of total wood extractive content and types of extractives in the raw material on off-gassing of wood pellets were investigated through two separate studies. In the first study, the pellets were produced from fresh and pre-treated Scots pine sawdust. The pre-treatments involved storing, extraction and adding additive oils. The second study used synthetic pure cellulose that was pre-treated by adding different additive oils. The pellets were subjected to off-gassing tests under controlled conditions.The results from the first study showed that the total amount of extractives in the raw material has little effect on off-gassing. While gas emissions were reduced for stored and acetone extracted pine pellets, the coefficients of determination (R2) from the linear correlation analysis between off-gassing and the total extractive content of the raw materials were below 0.5 for all the three off-gasses indicating no correlation. The results of cellulose pellets with added additive oils in the second study showed that the off-gassing is highly dependent on the type of extractives in the raw material. The highest mean concentrations of the carbon oxides and methane were recorded from cellulose pellets with added linseed oil. Pellets with added linseed oil had higher off-gas emissions due to the high content of unsaturated fatty acids of 73.9% linolenic and 7.6% linoleic. Based on these results, it was concluded that one of the main causes of off-gassing during storage of wood pellets is the α-oxidation of unsaturated fatty acids. The other notable effect was that methane formation is dependent on anaerobic conditions, whereas formation of carbon oxides can occur both under aerobic and anaerobic conditions.
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