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Towards Understanding the Pelletizing Process of Biomass: Perspectives on Energy Efficiency and Pelletability of Pure Substances
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013). Environmental and Energy Systems. (Pro2Be)ORCID iD: 0000-0003-0446-4251
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The use of fossil resources has to decrease and the use of renewable resources has to increase significantly to mitigate the climate change. In this change towards more renewable resources, biomasses will play an important role, both for energy use and for products. Thus, the utilization of biomasses must be optimized, both linked to which biomass species that are used, as well as the actual production processes. This thesis relates to the production of lignocellulosic biomass pellets, with the purpose to increase the understanding of how a pellet process can be improved. 

There are many benefits to pelletize the biomass, such as increased density, more economical transports solutions and increased doseability. However, there is a lack of knowledge on how different biomass species affect the actual pelletizing. This causes pellet producers to strive for a feedstock with a chemical composition that is as uniform as possible, which reduces the possibility of increasing intake of, for example, seasonal or residual products of other kinds.

If pellet producers can handle, predict and combine different biomaterials over time without stopping the production, new ways of acquiring raw materials for production would be possible. This will be important for future pellet producers, as the general use of biomasses will increase, so will the competition of the raw material. It will also be of importance in developing countries, which have a greater variation in wood species than today's large pellets producing countries. 

This work has been focused on understanding biomasses pelletability, and the method has been to start with components such as, cellulose, hemicellulose, lignin etc. Results shows that there is a significant difference between the hemicelluloses, xylan and glucomannan, in terms of pelletability. During pelletizing, xylan changes its form, generates hard pellets and, correlated to pelletability, xylan are affected by actual moisture content or added water to the process. Glucomannan, however, shows the opposite, a low impact on pelletability and a minimal impact from water during the pelletizing process. A difference that can explain the difference in pelletability, between hardwood and softwood. 

Solutions to improve the pelletizing process have also been studied. One result is that adding oxidized starch additive, reduces the energy consumption in the pelletizer and increasing the durability of the pellets, more than native starches. Another result is that a two-stage drying technique, reduces the heat power consumption per tonne of dried materialand at the same time increases the drying capacity. Also, the possibilities for a pellet producer to handle, predict and combine different biomaterials has been studied. Presented results show howbiomasses from Zambia can be used as an single resource or in different resources combinations in a pellet production. 

Finally, a recommendation to pellet researchers to include the cellulose material, Avicel, in single pellet studies. By using the same reference material, the methods can be normalized and the pelletability of biomaterials can be validated in a new way. This step would develop the research in the field, and the possibility of increased use of biomass towards the use of more renewable resources in pellet production.

Abstract [sv]

För att begränsa klimatpåverkan måste användandet av fossila resurser minska till förmån för förnyelsebara. In denna omställning är och kommer biomassa att bli en mycket viktigresurs att använda tillenergi samt olika produkter. Detta innebär att det är viktigt att både användningen och hanteringen sker resurs- och energieffektivt. Den här avhandlingen handlar om att pelletera lignocellulosisk biomassa med motivet att energieffektivisera pelletsprocessen, samt öka kunskapen om olika biomassors pelleterbarhet. 

Det finns många fördelar med att pelletera biomassa, såsom att produkten blir doserbar, lättare att lagra samt att den blir billigare att transporteratack vare högre densitet. Men olika biomassor har olika egenskaper beroende på deras kemiska uppbyggnad, och idag är kunskapen begränsad kring vad som påverkar pelleterbarheten i olika biomassor. Dettamedför att pelletsproduktionen eftersträvarsmå variationer i inkommande råmaterial såsom att bara använda färsk gran, bara lövträd eller en specifik mix. Att förstå och kunna hantera olika biomassors pelleterbarhet skulle innebära att pelletsproducenter kan nyttja ett varierat inflöde, utan att stoppa produktionen. Vilket kommer bli viktigt när omställningen mot mer förnyelsebart ökar konkurrensen om råvaran. En annan aspekt är ett ökat användande av pellets i utvecklingsländer, vilka många har en mycket större variation i träslag än dagens stora pelletsproducerande länder. 

Arbetet har inriktats på att förstå hur olika biomaterial påverkar pelleterbarheten. Metoden för detta har varit att utgå från komponenter i biomassan tex. cellulosa, hemicellulosa, lignin m.m. och bygga kunskap därifrån. Resultatet visar att hemicellulosans (i huvudsak xylan och glucomannan) påverkan på pelleterbarhet är större än vad som tidigare varit känt. Xylan under kompression påverkas genom att ändra form vilket resulterar i hårda pellets och starka bindningar, samt att dess påverkan av tillsatt vatten i processen är stor. Glucomannan visar på motsatsen, låg påverkan på pelleterbarhet samt att dess inverkan av tillsatt vatten är liten. Denna skillnad kan förklara olikheterna i att pelletera löv- och barrträd, eftersom xylan är huvudsakliga hemicellulosan i lövträd medan glucomannan är det i barrträd. 

Avhandlingen tar även upp hur pelletsprocessens kan effektiviseras. Ett resultat är att oxiderad stärkelse som additiv reducerar energiåtgången i pelletspressen mer än icke oxiderad stärkelse, samtidigt som pelletens hållfasthet förbättras. Ett annat resultat är en tvåstegs-torkteknik som energieffektiviserar torkprocessen samtidigt som torkkapaciteten ökar. Även att kunna hantera olika biomassors pelleterbarhet presenteras, inriktat på hur olika biomassor från Zambia, kan användas för pelletsproduktion.

Slutligen finns en rekommendation till pelletsforskare om att inkludera cellulosamaterialet Avicel, i singelpellets-studier. Om alla använder samma referensmaterial, kan metoderna normaliseras och biomassors pelleterbarhet valideras på ett nytt och bättre sätt. Något som utvecklar både forskningen och omställning mot ett ökat nyttjande av förnyelsebara resurser. 

Abstract [en]

The use of fossil resources has to decrease and the use of renewable resources has to increase significantly to mitigate the climate change. In this transformation, biomasses will play an important role, and the utilization of biomasses must be optimized. 

As a pelletized product the biomass gets increased density, are more economical to transport and the doseability of the product are increased. Thus, as pellets the possibilities to add biomasses in variated application will be both more energy efficient and can be optimized in a better way. Today, there is a lack of knowledge how different biomass species affect the actual pelletizing, and this causes pellet producers to strive for a feedstock with a chemical composition that is as uniform as possible. 

In this thesis, it is shown how the pelletizing process can be improved and how a wider utilization of biomasses can be used by an increased understanding about the pelletability when pelletizing pure substances. Results shows that there is a significant difference between the substances within the hemicelluloses. A difference that can explain the difference in pelletability, between hardwood and softwood.

Abstract [en]

The use of fossil resources has to decrease and the use of renewable resources has to increase significantly to mitigate the climate change. In this transformation, biomasses will play an important role, and the utilization of biomasses must be optimized. 

As a pelletized product the biomass gets increased density, are more economical to transport and the doseability of the product are increased. Thus, as pellets the possibilities to add biomasses in variated application will be both more energy efficient and can be optimized in a better way. Today, there is a lack of knowledge how different biomass species affect the actual pelletizing. This causes pellet producers to strive for a feedstock with a chemical composition that is as uniform as possible. 

This thesis has been focused on understanding biomasses pelletability, and the method has been to start with pure substance such as, cellulose, hemicellulose, lignin etc. In total, thirty-eight different material are included, divided into seventeen biomasses and twenty-one pure substances. Results shows that there is a significant difference between the components within the hemicelluloses, xylan and glucomannan. A difference that can explain the difference in pelletability, between hardwood and softwood.

Also, how the pelletizing process can be more energy efficient, with increased drying capacity and increased pellet durability are presented. As well as there are solutions to combined and used a biomass flow as single resources or in combinations without stopping the production line. 

Place, publisher, year, edition, pages
Karlstad: Karlstads universitet, 2019. , p. 70
Series
Karlstad University Studies, ISSN 1403-8099 ; 2019:32
Keywords [en]
Pelletability, wood pellets, densification, chemical composition
National Category
Energy Engineering
Research subject
Environmental and Energy Systems
Identifiers
URN: urn:nbn:se:kau:diva-75440ISBN: 978-91-7867-057-4 (print)ISBN: 978-91-7867-067-3 (electronic)OAI: oai:DiVA.org:kau-75440DiVA, id: diva2:1366777
Public defence
2019-12-05, 9C 203, Universitetsgatan 2, Karlstad, 09:00 (Swedish)
Opponent
Supervisors
Available from: 2019-11-15 Created: 2019-10-30 Last updated: 2019-11-15Bibliographically approved
List of papers
1. Effects on Pellet Properties and Energy Use When Starch Is Added in the Wood-Fuel Pelletizing Process
Open this publication in new window or tab >>Effects on Pellet Properties and Energy Use When Starch Is Added in the Wood-Fuel Pelletizing Process
Show others...
2012 (English)In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 26, no 3, p. 1937-1945Article in journal (Refereed) Published
Abstract [en]

The production and use of wood-fuel pellets have increased significantly worldwide in recent years. The increased use of biomaterials has resulted in higher raw material prices, and there are no signs that indicate a decrease in raw material competition. Additives can be used for different purposes. Partly, they are used to facilitate the use of new raw materials to increase the raw material base, and partly, they are used to decrease the energy use in the pelletizing process. They are also used to increase durability or shelf life. Consequently, it is necessary to do research that systematically investigates the consequences of using additives. In this work, it is investigated how various percentages of different kinds of starch influence pellet properties, including shelf life and energy use in the pelletizing process. Four different starch grades were used: native wheat starch, oxidized corn starch, native potato starch, and oxidized potato starch. The pellets were produced in a small industrial pellet press located at Karlstad University, Karlstad, Sweden. The result shows that starch increases the durability of the pellets. Oxidized starches increase the durability more than native starches, and the best results were obtained by adding oxidized corn starch. The durability did not decrease with storage time when the pellets were stored indoors during 7 months. The oxidation process was not consistently altered by the addition of starch. The energy consumption of the pellet press decreases when starch is added. Again, the oxidized corn starch showed the best result; when 2.8% of corn starch was added, the average energy consumption was reduced by 14%

Place, publisher, year, edition, pages
Washington DC, Oxford UK: American Chemical Society (ACS), 2012
National Category
Energy Engineering Energy Systems
Research subject
Environmental and Energy Systems
Identifiers
urn:nbn:se:kau:diva-12282 (URN)10.1021/ef201968r (DOI)000301509300046 ()
Available from: 2012-03-15 Created: 2012-03-15 Last updated: 2019-10-30Bibliographically approved
2. The Potential of Using Two-Step Drying Techniques for Improving Energy Efficiency and Increasing Drying Capacity in Fuel Pellet Industries
Open this publication in new window or tab >>The Potential of Using Two-Step Drying Techniques for Improving Energy Efficiency and Increasing Drying Capacity in Fuel Pellet Industries
2013 (English)In: Drying Technology, ISSN 0737-3937, E-ISSN 1532-2300, Vol. 31, no 15, p. 1863-1870Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Taylor & Francis, 2013
Keywords
Drying capacity, Energy efficiency, Packed moving bed, Pneumatic dryer, Wood fuel pellet
National Category
Energy Engineering
Research subject
Environmental and Energy Systems; Energy Technology
Identifiers
urn:nbn:se:kau:diva-29958 (URN)10.1080/07373937.2013.833520 (DOI)000335776300015 ()
Available from: 2013-11-01 Created: 2013-11-01 Last updated: 2019-10-30Bibliographically approved
3. Pelletizing pure biomass substances to investigate the mechanical properties and bonding mechanisms
Open this publication in new window or tab >>Pelletizing pure biomass substances to investigate the mechanical properties and bonding mechanisms
2018 (English)In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 13, no 1, p. 1202-1222Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
North Carolina State University, 2018
Keywords
Biomass pellets, Renewable energy, Single pellet press, Wood pellets, Biomass, Cellulose, Fuels, Hardwoods, Polysaccharides, Presses (machine tools), Softwoods, Wood, Bonding mechanism, Non-renewable fuels, Pellet hardness, Pellet production, Renewable energies, Renewable resource, Wood pellet, Pelletizing
National Category
Energy Systems Paper, Pulp and Fiber Technology
Research subject
Environmental and Energy Systems; Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-66400 (URN)10.15376/biores.13.1.1202-1222 (DOI)000427790000089 ()2-s2.0-85041345528 (Scopus ID)
Available from: 2018-02-16 Created: 2018-02-16 Last updated: 2019-11-08
4. Effects of moisture content during densification of biomass pellets, focusing on polysaccharide substances
Open this publication in new window or tab >>Effects of moisture content during densification of biomass pellets, focusing on polysaccharide substances
2019 (English)In: Biomass and Bioenergy, ISSN 0961-9534, E-ISSN 1873-2909, Vol. 122, p. 322-330Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Wood pellets, densification, cellulose, hemicellulose, xylan, glucomannan
National Category
Paper, Pulp and Fiber Technology Bioenergy Energy Systems
Research subject
Environmental and Energy Systems; Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-71411 (URN)10.1016/j.biombioe.2019.01.048 (DOI)000459461800034 ()
Note

APC betald 2019.

Available from: 2019-03-02 Created: 2019-03-02 Last updated: 2019-10-30Bibliographically approved
5. Compression of Biomass Substances—A Study on Springback Effects and Color Formation in Pellet Manufacture
Open this publication in new window or tab >>Compression of Biomass Substances—A Study on Springback Effects and Color Formation in Pellet Manufacture
2019 (English)In: Applied Science, E-ISSN 2076-3417, Vol. 9, no 20, article id 4302Article in journal, Editorial material (Refereed) Published
Abstract [en]

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.

Keywords
biomass pellets; densification; glucomannan; xylan; hemicelluloses
National Category
Energy Engineering Chemical Engineering
Research subject
Environmental and Energy Systems; Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-75452 (URN)10.3390/app9204302 (DOI)
Funder
Swedish Agency for Economic and Regional Growth, 202001239
Available from: 2019-10-26 Created: 2019-10-26 Last updated: 2019-10-30
6. Bioresources for Sustainable Pellet Production in Zambia: Twelve Biomasses Pelletized at Different Moisture Content
Open this publication in new window or tab >>Bioresources for Sustainable Pellet Production in Zambia: Twelve Biomasses Pelletized at Different Moisture Content
Show others...
2019 (English)In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 14, no 2, p. 2550-2575Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
North Carolina: North Carolina State University, 2019
Keywords
Biomass pellets, Single pellet press, Densification, Backpressure, Chemical composition
National Category
Paper, Pulp and Fiber Technology Energy Systems Other Environmental Engineering
Research subject
Environmental and Energy Systems
Identifiers
urn:nbn:se:kau:diva-71412 (URN)10.15376/biores.14.2.2550-2575 (DOI)000466449000010 ()
Available from: 2019-03-02 Created: 2019-03-02 Last updated: 2019-10-30Bibliographically approved

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