Undersøkelse av torrifisering (forkulling) og alternative råvaretillegg i biomasse pelletering

The interest in renewable energy sources is growing continuously owing to climate change and the limited amount of fossil fuels. Biomass is the most popular renewable energy source, and it will continue to play a key role in further reduction of the consumption of fossil fuels. Extensive usage of wood worldwide for generating energy is making this resource scarcer. From the perspective of ensuring sufficient supply of biomass for future needs, the application of inexpensive alternative raw materials, such as agricultural and industrial residues, has gained great interest. The typically poor fuel properties of alternative biomasses can be upgraded through different technologies such as pelleting and torrefaction. The main objective of the present PhD thesis is to develop pelletized solid biofuels by adding alternative raw materials and applying the torrefaction process. Additionally, the thesis also contributes to the development and application of novel, non-conventional methods for testing pellet quality. The thesis is based on four scientific papers that investigated different aspects of biomass pelleting, the application of new raw materials, a thermal pretreatment process, and the development of novel methodologies for pellets analysis. The initial activity in the present PhD project involved screening and selecting the alternative raw materials that could be used for pellet production. Through the rheological examination of five liquid and semi-solid materials, an attempt was made to anticipate their behavior during different stages of biofuel production, when they were added to powder biomass for densification (Paper I). Based on the rheological properties, availability, and price, waste vegetable oil and molasses were selected for further examination of their effects on biomass pelletability and physical pellet quality. Waste vegetable oil exhibits Newtonian behavior; its viscosity decreased sharply when heated in the temperature range that occurs during pellet production, and this allowed easy application of the oil in the production process. Molasses was chosen because of its ability to harden and form solid bridges between particles. This indicated that molasses could be a good binder in the pelleting process. The second approach to upgrade biomass fuel properties was biomass torrefaction. The effects of torrefaction on Norwegian spruce and birch branches are examined in Paper II. Torrefaction improved the properties of wood by realizing higher energy density, better grindability, and hydrophobicity. It was demonstrated that the effects of torrefaction depend on the tree species. Torrefaction had a positive impact on the strength of birch pellets, while the strength of spruce pellets was reduced. However, results indicated that the densification of torrefied biomass requires more energy than the densification of raw wood. In Paper III, the pelleting of spruce sawdust with added waste vegetable oil is described. This work presented a novel method for testing the surface hydration properties of pellets; this method is based on measurements of the contact angle of a water drop on the pellet surface. Surface hydration properties were assessed on the basis of the initial contact angle and apparent water absorption rate. Addition of waste vegetable oil reduced inter-particle binding, resulting in poor pellet physical quality in terms of pellet density, strength, and surface hydration properties. Addition of oil was beneficial because it increased the energy content of pellets and lowered the energy requirement for pellets production. Molasses, as a potential binder, was added to wheat straw before pelleting (Paper IV). Pellets were produced in a single pellet press and in a roller-die pellet press. Molasses made the pellets stronger, and this effect was particularly pronounced at low pelleting temperatures (60°C). Comparison of the two pelleting methods showed that the single pellet press is a useful tool for examining pelletability and material-compacting properties. The information obtained by this method can serve as a basis for material and process modification before large-scale production.Interessen for fornybare energikilder er stadig økende på grunn av klimaendringer og begrensede mengder av fossilt brensel. Biomasse er en av de mest populære fornybare energikildene. Biomasse vil fortsette å spille en sentral rolle i ytterligere reduksjon av fossilt brenselforbruk. Omfattende bruk av trevirke til energiproduksjon gjør det enda knappere på et globalt nivå. For å kunne forsyne nok biomasse slik at det møter fremtidige behov, har det derfor blitt en økende interesse for anvendelse av billige, alternative råmaterialer samt landbruks- og industriavfall. Vanligvis kan dårlige egenskaper av alternative biomasser bli oppgradert med ulik teknologi slik som pelletering og torrifisering (forkulling). Det viktigste målet for den presenterte doktorgradsavhandlingen er å utvikle pelleterisert biodrivstoff ved inkludering av nye råvarer og anvendelse av torrifiseringsprosessen. Et viktig bidrag for denne doktorgradsavhandlingen er å utvikle og anvende nye og ukonvensjonelle metoder for kvalitetstesting av pellets. Doktorgradsavhandlingen er basert på fire vitenskapelige artikler som undersøker ulike aspekter av pelletering av biomasse, bruk av nye råvarer, prosess av termisk forbehandling og etablering av nye metoder for analysering av pellets. Den innledende aktiviteten i dette doktorgradsprosjektet var søking og valg av alternative råvarer som kan brukes til produksjon av pellets. Reologisk undersøkelse av fem væske- og halvfaste (myke) råvarer ble utført med formål å forutse deres oppførsel under ulike stadier av biodrivstoffproduksjon, særlig når de er tilsatt biomasse i pulverform for å øke tettheten (artikkel I). Basert på reologiske egenskaper, tilgjengelighet og pris, ble vegetabilske oljerester og melasse valgt for videre undersøkelse av deres effekter på pelletabilitet av biomasse og fysisk kvalitet av pellets. Vegetabilske oljerester hadde Newtonsk-atferd. Viskositeten av vegetabilske oljerester var redusert etter oppvarming i et temperaturområde som er standard under produksjon av pellets. Dette tillot lett tilsetting av olje i produksjonsprosessen. Melasse ble valgt ettersom den kunne stivne raskt og danne faste broer mellom partiklene. Dette indikerte at melasse kunne være et godt bindemiddel i pelleteringsprosessen. En annen tilnærming for oppgradering av egenskaper av biobrensel var torrifisering av biomasse. Effektene av torrifisering av norske gran og bjørk ble undersøkt i artikkel II. Torrifisering oppgraderte egenskaper til tre-biomasse ved høy energitetthet, bedre formalingsmuligheter og hydrofobisitet. Det ble demonstrert at effekt av torrifisening avhenger av arten av biomasse. Torrifisering hadde positiv innvirkning i forbindelse med styrken av bjørkepellets. Styrken av gran pellets ble på den annen side redusert. Resultatene indikerte at fortetting av torrefiserte biomasse er mer energikrevende enn ubehandlet trevirke. I artikkel III, ble pelletering av sagflis fra gran med tilsetning av vegetabilsk oljerester beskrevet. Innenfor denne studien ble det utviklet en ny metode for testing av hydrering av overflatevæskeegenskaper av pellets. Metoden er basert på kontaktvinkelmåling av en vanndråpe på overflaten av trepellets. Til slutt ble materialet vurdert ved første kontaktvinkel og tilsynelatende absorberingsgrad av vann. Tilsetting av vegetabilske oljerester reduserte binding av inter-partikkeler, og som endelig resultat ble derfor fysisk kvalitet (hardhet) av pellets lav; samtidig ble egenskaper for hydrering av pelletsoverflaten dårlige. Tilsetting av olje viste seg derfor å være gunstig ettersom det førte til lavere energikrav for pelletsproduksjon samtidig som det økte innholdet i pellets. Melasse som er et potensielt bindemiddel, ble tilsatt til hvetehalm før pelletering (artikkel IV). Pellets ble produsert med en enkeltmatrise pelletpresse og i en flat-matrise pelletpresse. Melasse førte til sterkere og mer faste pellets, denne effekten var spesielt tydelig ved lave pelleteringstemperaturer (60 °C). Sammenligning av metoder viste derfor at laboratorieutstyr kan være et nyttig verktøy for analysering av pelletering og komprimeringsegenskaper av forskjellige materialer. Opplysninger innhentet med disse metodene kan brukes som grunnlag for modifisering av materialer og prosesser før kommersiell produksjon

Uncertainty Analysis of the Life-Cycle Greenhouse Gas Emissions and Energy Renewability of Biofuels

Biofuels can contribute substantially to energy security and socio-economic development. However, significant disagreement and controversies exist regarding the actual energy and greenhouse gas (GHG) savings of biofuels displacing fossil fuels. A large number of publications that analyze the life-cycle of biofuel systems present varying and sometimes contradictory conclusions, even for the same biofuel type (Farrell et al., 2006; Malca and Freire, 2004, 2006, 2011; Gnansounou et al., 2009; van der Voet et al., 2010; Borjesson and Tufvesson, 2011). Several aspects have been found to affect the calculation of energy and GHG savings, namely land use change issues and modeling assumptions (Gnansounou et al., 2009; Malca and Freire, 2011). Growing concerns in recent years that the production of biofuels might not respect minimum sustainability requirements led to the publication of Directive 2009/28/EC in the European Union (EPC 2009) and the National Renewable Fuel Standard Program in the USA (EPA 2010), imposing for example the attainment of minimum GHG savings compared to fossil fuels displaced. The calculation of life cycle GHG emission savings is subject to significant uncertainty, but current biofuel life-cycle studies do not usually consider uncertainty. Most often, life-cycle assessment (LCA) practitioners build deterministic models to approximate real systems and thus fail to capture the uncertainty inherent in LCA (Lloyd and Ries, 2007). This type of approach results in outcomes that may be erroneously interpreted, or worse, may promote decisions in the wrong direction (Lloyd and Ries, 2007; Plevin, 2010). It is, therefore, important for sound decision support that uncertainty is taken into account in the life-cycle modeling of biofuels. Under this context, this chapter has two main goals: i) to present a robust framework to incorporate uncertainty in the life-cycle modeling of biofuel systems; and ii) to describe the application of this framework to vegetable oil fuel in Europe. In addition, results are compared with conventional (fossil) fuels to evaluate potential savings achieved through displacement. Following this approach, both the overall uncertainty and the relative importance of the different types of uncertainty can be assessed. Moreover, the relevance of addressing uncertainty issues in biofuels life-cycle studies instead of using average deterministic approaches can be evaluated, namely through identification of important aspects that deserve further study to reduce the overall uncertainty of the system

CHARACTERISTICS OF VEGETABLE OILS FOR USE AS FUEL IN STATIONARY DIESEL ENGINES - TOWARDS SPECIFICATIONS FOR A STANDARD IN WEST AFRICA

International audienceWest African countries are increasingly interested in producing straight vegetable oil (SVO) for direct use as fuel in diesel engines for stationary applications in the fields of agriculture, power generation and industry. Straight vegetable oil fuel quality, i.e impurities content and physico-chemical properties, is a recurring issue that seriously impedes the development of the sector. However, there is still no standard defining the quality characteristics of vegetable oils for fuel purposes in stationary engines. The aim of this study was to propose a quality standard with a set of specifications (parameters, test method, limit value), which SVOs must comply with in order to be used as fuel in stationary diesel engines without causing breakdowns or serious lifetime reductions. After a brief review of SVO production and use techniques, we present a critical review of existing fuel standards (fossil fuels, biodiesel and European SVO) that must be adapted to the use of SVO for stationary engines, with regard to the requirements of engine manufacturers. Based on this critical analysis and current knowledge of vegetable oil characterization, we propose a simplified, inexpensive and efficient basic standard of seven specifications. This standard enables easy assessment of SVO quality for fuelling a stationary diesel engine

A contribution to the risk assessment in relation to the formation of toxic aldehydes in foods as a result of lipid oxidation

Lipid containing foods are known to be sensitive to lipid oxidation which is responsible for quality deterioration. Lipid oxidation leads to the formation of hydroperoxides and secondary products such as aldehydes and ketones. Malondialdehyde, 4-hydroxy-nonenal , 4-hydroxy-hexenal and 2-butenal are typical examples of aldehydes generated during the oxidation of polyunsaturated fatty acids and are considered as toxic. Increased consumption of ready-to-eat meals, along with a large demand on ω-3 fatty acid enriched products the last years, has emerged the importance of monitoring and controlling the occurrence of these compounds in foods. This study included development, implementation and validation of reliable analytical methods which allow the determination of secondary oxidation products in various food systems. Once developed, these analytical methods were applied for investigation of the formation of secondary lipid oxidation products in model systems as well as foods available in the Belgian market. Based on the obtained results, an exposure assessment to the target components was carried out taking into account the consumption data of the Belgian population and the potential risk was evaluated

Bioliquids and their use in power generation - a technology review

The first EU Renewable Energy Directive (RED) served as an effective push for world-wide research efforts on biofuels and bioliquids, i.e. liquid fuels for energy purposes other than for transport, including electricity, heating, and cooling, which are produced from biomass. In December 2018 the new RED II was published in the Official Journal of the European Union. Therefore, it is now the right time to provide a comprehensive overview of achievements and practices that were developed within the current perspective. To comply with this objective, the present study focuses on a comprehensive and systematic technical evaluation of all key aspects of the different distributed energy generation pathways using bioliquids in reciprocating engines and micro gas turbines that were overseen by these EU actions. Methodologically, the study originates from the analyses of feedstock and fuel processing technologies, which decisively influence fuel properties. The study systematically and holistically highlights the utilisation of these bioliquids in terms of fuel property specific challenges, required engine adaptations, and equipment durability, culminating in analyses of engine performance and emissions. In addition, innovative proposals and future opportunities for further technical improvements in the whole production-consumption cycle are presented, thus serving as a guideline for upcoming research and development activities in the fast-growing area of bioliquids. Additionally, the paper systematically addresses opportunities for the utilisation of waste streams, emerging from the ever increasing circular use of materials and resources. With this, the present review provides the sorely needed link between past efforts, oriented towards the exploitation of bio-based resources for power generation, and the very recent zero-waste oriented society that will require a realistic exploitation plan for residuals originating from intensive material looping

Polymer damage mitigation--predictive lifetime models of polymer insulation degradation and biorenewable thermosets through cationic polymerization for self-healing applications

Over the past 50 years, the industrial development and applications for polymers and polymer composites has become expansive. However, as with any young technology, the techniques for predicting material damage and resolving material failure are in need of continued development and refinement. This thesis work takes two approaches to polymer damage mitigation--material lifetime prediction and spontaneous damage repair through self-healing while incorporating bio-renewable feedstock. First, material lifetime prediction offers the benefit of identifying and isolating material failures before the effects of damage results in catastrophic failure. Second, self-healing provides a systematic approach to repairing damaged polymer composites, specifically in applications where a hands-on approach or removing the part from service are not feasible. With regard to lifetime prediction, we investigated three specific polymeric materials--polytetrafluoroethylene (PTFE), poly(ethylene-alt-tetrafluoroethylene) (ETFE), and Kapton. All three have been utilized extensively in the aerospace field as a wire insulation coating. Because of the vast amount of electrical wiring used in aerospace constructions and the potential for electrical and thermal failure, this work develops mathematical models for both the thermal degradation kinetics as well as a lifetime prediction model for electrothermal breakdown. Isoconversional kinetic methods, which plot activation energy as a function of the extent of degradation, present insight into the development each kinetic model. The models for PTFE, ETFE, and Kapton are one step, consecutive three-step, and competitive and consecutive five-step respectively. Statistical analysis shows that an nth order autocatalytic reaction best defined the reaction kinetics for each polymer\u27s degradation. Self-healing polymers arrest crack propagation through the use of an imbedded adhesive that reacts when cracks form. This form of damage mitigation focuses on repairing damage before the damage causes a failure in the polymer\u27s function. In this work, the healing agent (adhesive) is developed using bio-renewable oils instead of solely relying on petroleum based feedstocks. Several bio-renewable thermosetting polymers were successfully prepared from tung oil through cationic polymerization for the use as the healing agent in self-healing microencapsulated applications. Modifications to both the monomers in the resin and the catalyst for polymerization were made and the subsequent changes to mechanical, thermal, and structural properties were identified. Furthermore, compressive lap shear testing was used to confirm that the adhesive properties would be beneficial for self-healing applications. Finally, scanning electron microscopy of the crack plane was used to study the fracture mechanism of the crack

Trends in technology, trade and consumption likely to impact on microbial food safety

Current and potential future trends in technology, consumption and trade of food that may impact on food-borne disease are analysed and the key driving factors identified focusing on the European Union and, to a lesser extent, accounting for the United States and global issues. Understanding of factors is developed using system-based methods and their impact is discussed in relation to current events and predictions of future trends. These factors come from a wide range of spheres relevant to food and include political, economic, social, technological, regulatory and environmental drivers. The degree of certainty in assessing the impact of important driving factors is considered in relation to food-borne disease. The most important factors driving an increase in the burden of food-borne disease in the next few decades were found to be the anticipated doubling of the global demand for food and of the international trade in food next to a significantly increased consumption of certain high-value food commodities such as meat and poultry and fresh produce. A less important factor potentially increasing the food-borne disease burden would be the increased demand for convenience foods. Factors that may contribute to a reduction in the food-borne disease burden were identified as the ability of governments around the world to take effective regulatory measures as well as the development and use of new food safety technologies and detection methods. The most important factor in reducing the burden of food-borne disease was identified as our ability to first detect and investigate a food safety issue and then to develop effective control measures. Given the global scale of impact on food safety that current and potentially future trends have, either by potentially increasing or decreasing the food-borne disease burden, it is concluded that a key role is fulfilled by intergovernmental organisations and by international standard setting bodies in coordinating the establishment and rolling-out of effective measures that, on balance, help ensure long-term consumer protection and fair international trade. Keywords: Microbial food safety; Food technology; Globalizatio