| 1. |
- Lindström, Erica, et al.
(author)
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Slagging characteristics during combustion of woody biomass pellets made from a range of different forestry assortments
- 2010
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In: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 24:6, s. 3456-3461
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Journal article (peer-reviewed)abstract
- In this study, multivariate methods were used to select representative raw materials of the pellet assortments prior to combustion. The fuels were selected to form a range of expected slagging tendencies. During combustion, temperatures and O2, CO, NO, and SO2 were measured continuously. The deposits (i.e., slag and bottom ash) were quantified after every experiment and collected for analysis to identify the crystalline phases and to study the morphology and elemental composition respectively. As expected, the slagging was most severe for the whole-tree assortments because of their content of branches, foliage, and twigs. In the most severe case over three-quarters of the total amount of ash melted to form slag. This study indicates that certain concentrations of silicon, inherent in the fuel but also as silicates from contamination, together with alkali metals, mainly potassium, are prerequisites for the initiation of and progress of slag formation. Generally the concentrations of silicon and potassium are low in stemwood but higher in bark, foliage, and living tissues of the tree. Also, the contamination from sand and/or soil is present in the bark and foliage.
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| 2. |
- Örberg, Håkan, et al.
(author)
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Teknikutveckling för ökad etablering och nyttjande av rörflen : demonstrationsförsök i fullskala
- 2010
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Reports (other academic/artistic)abstract
- Resultaten visar att energigräset rörflen kan utgöra ett kompletterande bränsle till det skogsbränsle och den torv som idag används i svenska värme- och kraftvärmeanläggningar. En inblandning av rörflen med ca 10 % på energibasis i en bränslemix som för övrigt består av 10-20 % carextorv och 70-80 % träbränsle har i demonstrationsförsök visat goda resultat. Denna bränslemix har vid fullskaliga förbränningsförsök i fluidiserande bädd (Hedensbyn,CFB 98 MW) under sammanlagt 4 dygn inte gett upphov till störningar eller negativa effekter på utrustning eller ökade utsläpp i rökgaserna i form av partiklar eller gasformiga emissioner. Vid simulerade påverkan på överhettare i form av kylda sonder har även konstaterats att beläggningstillväxten varit oförändrad och ej givit upphov till ökad korrosion. Inblandning i bränslemixen har skett med hackad rörflen (40-50 mm) i torvdelen för att en jämn inblandning kunde åstadkommas. Rörflensmaterialet har levererats i samband med skörden så att det hackats direkt på fältet med exakthack kopplad till vagn eller med containerhantering. Vid leverans under vår och försommar har rörflenen hållit mycket låg fukthalt med ett medel på 11,3 % fukt. Jämförande studier har gjorts med system där rörflen vid skörden under vår pressats till storbalar för vidare transport till terminal eller gårdscentrum. Detta system har visat sig mindre effektivt jämfört med direkthackning på fältet och transport av hackat material till värmeverk. En fördel med storbalssystemet är dock att det möjliggör mer kostnadseffektiv lagring utan att t.ex. fukthalten höjs under lagringstiden. Även vägtransport från terminal eller gårdscentrum till värmeverk har visat sig mer effektivt med storbalar jämfört med hackat material. Vid lastning av stora fyrkantsbalar (90x120x220 cm) på lastbil med släp uppnåddes i stort sett dubbla lastvikten jämfört med hackad rörflen (20,9 ton jmf. m. 11,0 ton). För de något mindre anläggningarna av typen rosterpannor som provats (0,6 och 4 MW) har den briketterade formen av rörflen använts för att uppnå en jämn och koncentrerad bränslematning. Även här har en blandning av rörflen och torv visat sig användbar och speciellt för rörflen med låg askhalt har torvinblandning på 15 vikts-% av gett minskad tendens till sintring av askan. Rörflen med hög askhalt (utan torvinblandning) har kunnat sameldas med träbränsle utan risk för sintrad aska i dessa anläggningar. Tillverkningen av briketter för försöken, sammanlagt ca 35 ton, varav hälften med inblandning av torv har genomförts utan störningar och med bra kvalité på briketterna.
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| 3. |
- Diaz-Ramirez, Maryori, et al.
(author)
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Ash Characterization and Transformation Behavior of the Fixed-Bed Combustion of Novel Crops : Poplar, Brassica, and Cassava Fuels
- 2012
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In: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 26:6, s. 3218-3229
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Journal article (peer-reviewed)abstract
- New biofuel raw materials for energy pellet production are now being studied as potential energy sources for the heating market. Because of the complexity of the chemical and physical properties of novel fuels, such as some agricultural residues and energy crops, the study of their ash-related aspects is crucial for the sustainable development of this potential energy sector. Ash fractions formed during fixed-bed combustion of different pelletized novel crops; i.e., two Mediterranean crops (one herbaceous, brassica, and one woody species, poplar) and three Chinese cassava stems (cassava species from three different Chinese regions), and three Chinese cassava stems (cassava species from three different Chinese regions), were characterized, and their formation paths assessed in this study. Special emphasis was placed on elucidating the role of major ash-forming elements in the fractionation and transformation behavior, leading to the formation of bottom ash, deposits, and particulate emissions (fine and coarse ash particle fractions) on the basis of experimental data. In the Mediterranean fuels, the predominant ash fraction obtained was bottom ash, mainly characterized by silicates. Phosphates were found to be the main crystalline phases in the Chinese fuels. The slagging tendency was low for all of the fuels, although more significant for the cassava species under the studied conditions. Further, combustion of the studied Chinese energy crops resulted in a considerably finer particle fraction compared to the Mediterranean fuels. Deposits and particulate matter were dominated by K-sulfates as well as K-chloride in all fuels (except poplar), with the occurrence of K-phosphates for cassava pellets. Overall, this study showed fundamental differences in ash transformation behavior during combustion of P-rich fuels (i.e., cassava mixtures) compared to Si-rich fuels (i.e., poplar and brassica mixtures). Of major importance is the experimental verification of the higher thermodynamic stability of phosphates in relation to silicates. Furthermore, in P-rich fuels at high (K + Na)/(Ca + Mg) ratios, a significant degree of alkali metal volatilization occurs, which forms larger amounts of particulate matter, whereas this ratio has no/low effect in Si-rich fuels at high alkali metal ratios.
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| 4. |
- Díaz-Ramírez, Maryori, et al.
(author)
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Environmental performance of three novel opportunity biofuels : poplar, brassica and cassava during fixed bed combustion
- 2013
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In: Herbaceous plants. - : Nova Science Publishers, Inc.. - 9781626187290 - 9781626187306 ; , s. 133-147
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Book chapter (peer-reviewed)abstract
- In the last few decades several types of solid biofuels have been proposed as possible sources for heat generation because of growing concerns about environmental pollution, and future fossil fuel supply uncertainties. Among other biomass assortments, short rotation coppice and herbaceous species have been considered. An important aspect to be evaluated to enable a sustainable introduction of such novel fuels is related to their environmental performance during combustion. In this work, three fuel types; one herbaceous energy crop and one short rotation coppice (both cultivated and pelletized in Spain), together with one agricultural residue (cultivated in China) have been assessed in terms of their emission levels of gases (CO and NOX) and particulate matter. The experiments showed that combustion of the fuels was attained under an acceptable level of CO emissions. However, concentration of NOX was rather high, but perhaps more important, a considerably high formation of fine particle emissions was observed. Consequently, the incorporation of primary or secondary particle precipitating reduction measures might be needed. In addition, the high ash content in these fuels can severely deteriorate the combustion performance and reliability. Thus, specially designed burners/grate units are therefore needed if a utilization of these fuels in small and medium scale combustion systems seeks to be feasible. Although the applicability of introducing this kind of biofuels to the residential heating sector perhaps seems to be rather limited, it should not always be rejected. Nevertheless, technology improvements would have to be considered to manage the current limitations.
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| 5. |
- Wei, Maogui, et al.
(author)
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Properties of Cassava Stem Starch Being a New Starch Resource
- 2018
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In: Starke (Weinheim). - : John Wiley & Sons. - 0038-9056 .- 1521-379X. ; 70:5–6
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Journal article (peer-reviewed)abstract
- This study aims to understand the starch properties of cassava stems, currently a discarded crop residue, which contain up to 40% starch by dry mass. Granule sizes and size distribution of cassava stem starch, and their variations with genotype, growing location, and position along the stem are investigated using scanning electron microscopy (SEM) images. Amylose contents, crystallinity, and pasting characteristics of stem and root starch are also compared. The mean of granule sizes range from 5.65 to 7.64 µm, depending on the environment and position along stems, but not on genotype. Stem starch has a similar granule shape, X-ray diffraction pattern, and amylose content (20.8% of starch basis) to root starch, but a significantly smaller granule size with narrower distribution range and higher pasting temperature (72.1 degrees C). Cassava stem has a woody nature; a development of an efficient starch isolation method shall be included in future studies.
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| 6. |
- Zhu, Youjian, et al.
(author)
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Cogasification of Australian Brown Coal with Algae in a Fluidized Bed Reactor
- 2015
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In: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 29:3, s. 1686-1700
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Journal article (peer-reviewed)abstract
- Recently, the use of algae for CO2 abatement, wastewater treatment, and energy production has increasingly gained attention worldwide. In order to explore the potential of using algae as an alternative fuel as well as the possible challenges related to the algae gasification process, two species of macroalgae, Derbesia tenuissima and Oedogonium sp., and one type of microalgae, Scenedesmus sp. were studied in this research. In this work, Oedogonium sp. was cultivated with two protocols: producing biomass with both high and low levels of nitrogen content. Cogasification of 10 wt % algae with an Australian brown coal was performed in a fluidized bed reactor, and the effects of algae addition on syngas yield, ash composition, and bed agglomeration were investigated. It was found that CO and H-2 yield increased and CO2 yield decreased after adding three types of macroalgae in the coal, with a slight increase of carbon conversion rate, compared to the coal alone experiment. In the case of coal/Scenedesmus sp, the carbon conversion rate decreased with lower CO/CO2/H-2 yield as compared to coal alone. Samples of fly ash, bed ash, and bed material agglomerates were analyzed using scanning electron microscopy combined with an energy dispersive X-ray detector (SEM-EDX) and X-ray diffraction (XRD). It was observed that both the fly ash and bed ash samples from all coal/macroalgae tests contained more Na and K as compared to the coal test. High Ca and Fe contents were also found in the fly ash and bed ash from the coal/Scenedesmus sp. test. Significant differences in the characteristics and compositions of the ash layer on the bed particles were observed from the different tests. Agglomerates were found in the bed material samples after the cogasification tests of coal/Oedogonium N+ and coal/Oedogonium N. The formation of liquid alkalisilicates on the sand particles was considered to be the main reason for agglomeration for the coal/Oedogonium N+ and coal/Oedogonium N tests. Agglomerates of fused ash and tiny silica sand particles were also found in the coal/Scenedesmus sp. test. In this case, however, the formation of a Fe-Al silicate eutectic mixture was proposed to be the main reason for agglomeration. Debersia was suggested to be a potential alternative fuel, which can be cogasified with brown coal without any significant operating problems under the current experimental conditions. However, for the other algae types, appropriate countermeasures are needed to avoid agglomeration and defluidization in the cogasification process.
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| 7. |
- Zhu, Youjian, et al.
(author)
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Fluidized bed co-gasification of algae and wood pellets : gas yields and bed agglomeration analysis
- 2016
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In: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 30:3, s. 1800-1809
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Journal article (peer-reviewed)abstract
- Algae utilization in energy production has gained increasing attention as a result of its characteristics, such as high productivity, rapid growth rate, and flexible cultivation environment. In this paper, three species of algae, including a fresh water macroalgae, Oedogonium sp., a saltwater macroalgae, Derbersia tenuissima, and a microalgae species, Scenedesmus sp., were studied to explore the potential of using smaller amounts of algae fuels in blends with traditional woody biomasses in the gasification processes. Co-gasification of 10 wt % algae and 90 wt % Swedish wood pellets was performed in a fluidized bed reactor. The effects of algae addition on the syngas yield and carbon conversion rate were investigated. The addition of 10 wt % algae in wood increased the CO, H2, and CH4 yields by 3–20, 6–31, and 9–20%, respectively. At the same time, it decreased the CO2 yield by 3–18%. The carbon conversion rates were slightly increased with the addition of 10 wt % macroalgae in wood, but the microalgae addition resulted in a decrease of the carbon conversion rate by 8%. Meanwhile, the collected fly ash and bed material samples were analyzed using scanning electron microscopy combined with an energy-dispersive X-ray detector (SEM–EDX) and X-ray diffraction (XRD) technique. The fly ashes of wood/marcoalgae tests showed a higher Na content with lower Si and Ca contents compared to the wood test. The gasification tests were scheduled to last 4 h; however, only wood and wood/Derbersia gasification experiments were carried out without significant operational problems. The gasification of 10 wt % Oedogonium N+ and Oedogonium N– led to defluidization of the bed in less than 1 h, and the wood/Scenedesmus (WD/SA) test was stopped after 1.8 h as a result of severe agglomeration. It was found that the algae addition had a remarkable influence on the characteristics and compositions of the coating layer. The coating layer formation and bed agglomeration mechanism of wood/macroalgae was initiated by the reaction of alkali compounds with the bed particles to form low-temperature melting silicates (inner layer). For the WD/SA test, the agglomeration was influenced by both the composition of the original algae fuel as well as the external mineral contaminations. In summary, the operational problems experienced during the co-gasification tests of different algae–wood mixtures were assigned to the specific ash compositions of the different fuel mixtures. This showed the need for countermeasures, specifically to balance the high alkali content, to reach stable operation in a fluidized bed gasifier.
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