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Pelletizing pure biomass substances to investigate the mechanical properties and bonding mechanisms
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).ORCID iD: 0000-0003-0446-4251
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013). (Kemiteknik)ORCID iD: 0000-0001-8817-2031
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013). (Miljö- och energisystem)ORCID iD: 0000-0002-9707-8896
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. Vol. 13, no 1, p. 1202-1222
Keywords [en]
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: urn:nbn:se:kau:diva-66400DOI: 10.15376/biores.13.1.1202-1222ISI: 000427790000089Scopus ID: 2-s2.0-85041345528OAI: oai:DiVA.org:kau-66400DiVA, id: diva2:1183404
Available from: 2018-02-16 Created: 2018-02-16 Last updated: 2019-11-08
In thesis
1. Towards Understanding the Pelletizing Process of Biomass: Perspectives on Energy Efficiency and Pelletability of Pure Substances
Open this publication in new window or tab >>Towards Understanding the Pelletizing Process of Biomass: Perspectives on Energy Efficiency and Pelletability of Pure Substances
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
Pelletability, wood pellets, densification, chemical composition
National Category
Energy Engineering
Research subject
Environmental and Energy Systems
Identifiers
urn:nbn:se:kau:diva-75440 (URN)978-91-7867-057-4 (ISBN)978-91-7867-067-3 (ISBN)
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

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Frodeson, StefanHenriksson, GunnarBerghel, Jonas

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