| 1. |
- Chambi, Diego, et al.
(författare)
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Production of Exopolysaccharides by Cultivation of Halotolerant Bacillus atrophaeus BU4 in Glucose- and Xylose-Based Synthetic Media and in Hydrolysates of Quinoa Stalks
- 2022
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Ingår i: Fermentation. - : MDPI AG. - 2311-5637. ; 8:2
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Tidskriftsartikel (refereegranskat)abstract
- A halotolerant, exopolysaccharide-producing bacterium isolated from the Salar de Uyuni salt flat in Bolivia was identified as Bacillus atrophaeus using next-generation sequencing. Comparisons indicate that the genome most likely (p-value: 0.0024) belongs to a subspecies previously not represented in the database. The growth of the bacterial strain and its ability to produce exopolysaccharides (EPS) in synthetic media with glucose or xylose as carbon sources, and in hydrolysates of quinoa stalks, was investigated. The strain grew well in all synthetic media, but the growth in glucose was better than that in xylose. Sugar consumption was better when initial concentrations were low. The growth was good in enzymatically produced cellulosic hydrolysates but was inhibited in hemicellulosic hydrolysates produced using hydrothermal pretreatment. The EPS yields were up to 0.064 g/g on initial glucose and 0.047 g/g on initial xylose, and was higher in media with relatively low sugar concentrations. The EPS was isolated and purified by a sequential procedure including centrifugation, cold ethanol precipitation, trichloroacetic acid treatment, dialysis, and freeze-drying. Glucose and mannose were the main sugars identified in hydrolyzed EPS. The EPS was characterized by size-exclusion chromatography, Fourier-transform infrared (FTIR) spectroscopy, heteronuclear single-quantum coherence nuclear magnetic resonance (HSQC NMR) spectroscopy, scanning electron microscopy, X-ray diffraction, and thermogravimetric analysis. No major differences were elucidated between EPS resulting from cultivations in glucose- or-xylose-based synthetic media, while some divergences with regard to molecular-weight averages and FTIR and HSQC NMR spectra were detected for EPS from hydrolysate-based media.
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| 2. |
- Eriksson, Matias, et al.
(författare)
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Characterization of ring deposits inside a quicklime producing long rotary kiln
- 2019
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 33:11, s. 11731-11740
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Tidskriftsartikel (refereegranskat)abstract
- Ring deposits are common problems in rotary kiln operations. The ring is constantly subjected to thermal and mechanical wear counteracting the growth of the ring. If the ring hardens or if the growth of the ring is too rapid the kiln needs to be shut down and the ring removed, reducing the operational time and profitability of the process. In the present study, ring deposits from a limestone fed long rotary kiln producing quicklime was sampled and characterized in detail by SEM-EDS, dynamic rate TG and XRD. This work identifies three hardening mechanisms active in the kiln, an increased densification of the ring deposits near the refractory surface, the formation of calcite and spurrite through carbonation of the ring deposits, and the intrusion of molten fuel ash and product into the refractory, resulting in a strong attachment of the deposit to the refractory surface. The work also concludes that a significant part of the ring deposit has its origin in the fuel ash, contributing to deposit mass and increasing ring growth rate.
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| 3. |
- Eriksson, Matias, et al.
(författare)
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Impact of limestone surface impurities on quicklime product quality
- 2024
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Ingår i: Minerals. - : MDPI. - 2075-163X. ; 14:3
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Tidskriftsartikel (refereegranskat)abstract
- Quicklime is produced through the thermal processing of limestone in industrial kilns. During quarry operations, fine particulate quarry dust adheres to limestone lump surfaces, increasing the bulk concentration of impurities in limestone products. During thermal processing in a kiln, impurities such as Si, Mg, Al, Fe, and Mn react with Ca, reducing quicklime product quality. Which reactant phases are formed, and the extent to which these result in a reduction in quality, has not been extensively investigated. The present study investigated as-received and manually washed limestone product samples from two operational quarries using elemental compositions and a developed predictive multi-component chemical equilibrium model to obtain global phase diagrams for 1000–1500 °C, corresponding to the high-temperature zone of a lime kiln, identifying phases expected to be formed in quicklime during thermal processing. The results suggest that impurities found on the surface of the lime kiln limestone feed reduce the main quality parameter of the quicklime products, i.e., calcium oxide, CaO (s), content by 0.8–1.5 wt.% for the investigated materials. The results also show that, in addition to the effect of impurities, the quantity of CaO (s) varies greatly with temperature. More impurities result in more variation and a greater need for accurate temperature control of the kiln, where keeping the temperature below approximately 1300 °C, that of Hatrurite formation, is necessary for a product with higher CaO (s).
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| 4. |
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| 5. |
- Kumar Wagri, Naresh, 1988-
(författare)
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Assessment of bio-based fuel ash effects on magnesia refractory materials in quicklime production kilns
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Limestone is calcined into quicklime in lime kilns at temperatures above 1000°C. Heat is supplied through combustion inside the kilns, which are insulated with a lining of refractory bricks to mitigate heat loss and to protect the kiln from the hot, chemically aggressive, and mechanically abrasive environment. While magnesia bricks have proven to be effective lining materials, they are still susceptible to extensive wear in lime kilns, especially in the burn zone. Refractory corrosion, in particular, can occur when melted fuel ash infiltrates the refractory materials through pores and small cracks. This resultant wear can lead to high maintenance and operational costs, often due to unplanned kiln shutdowns.To reduce the release of fossil-based carbon dioxide into the atmosphere from lime production kilns, there is a growing interest in introducing bio-based fuels with only relatively minor modifications to the process. Biomass fuels can be sourced from bio-based waste streams from industries or be specifically cultivated for combustion. However, the ash content and properties of bio-based fuels tend to be problematic from an ash chemistry perspective. Therefore, before introducing a new fuel source, it is essential to investigate its potential effects on the kiln lining material. In this thesis work, the interactions between melted olive pomace ash and coal ash with commercially available magnesia refractory materials, primarily composed of periclase (MgO) with minor amounts of spinel (MgAl2O4), were studied. A procedure for quantifying the intrusion depths was described. Refractory samples were exposed to the fuel ashes under a simulated lime kiln atmosphere with high CO2 levels at 1200 and 1400°C for 15 and 60 minutes. Cold crushing strength tests were conducted on refractory samples exposed to coal and olive pomace ash, along with CaO powder, at 1400°C for 96 hours. Additionally, postmortem analyses of spent MgO-based refractory bricks were carried out to investigate their chemical characterization and resistance to slag attack after serving as part of the lining in a quick lime rotary kiln for six months.The morphology and elemental compositions of the exposed samples were examined using scanning electron microscopy and energy-dispersive X-ray spectroscopy. Crystalline phases were investigated with powder X-ray diffraction. Thermodynamic equilibrium calculations were performed to further investigate the ash’s melting behavior in contact with the refractories.The results indicated that the potassium-rich olive pomace ash exhibited a greater tendency to infiltrate compared to the silicon-rich coal ash, while the latter formed a glassy melt layer on top of the refractory samples. The ash slags primarily infiltrated through the porous matrix and grain boundaries of the refractory materials. Also, refractory phases were observed in both types of ashes, indicating migration of refractory constituents. K2MgSiO4 phase was found in the olive pomace ash residues on top of the samples, both for the 1200°C and 1400°C exposures. Similarly, Al6Si2O13 phase was dominant in the residual coal ash, in both the 1200°C and 1400°C exposed samples. None of these phases were present in the original ashes.The results of the postmortem analysis revealed that there was no potassium (K) from the fuel ash present on the hot side of the refractory bricks. However, some K was detected in the middle and back parts of the bricks. On the other hand, some phases, possibly connected to degradation, could be found on the hot side of the bricks, where most of the wear was observed.The crushing strengths increased after exposure for all samples, except for those exposed exclusively to coal ash. One possible explanation for this is that the refractory materials exhibited a sintered structure, as a result of their interaction with the ashes and CaO. However, in the samples exposed to coal ash, forsterite (Mg2SiO4) was identified, which can be considered a corrosion product.
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| 6. |
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| 7. |
- Kumar Wagri, Naresh, et al.
(författare)
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High temperature interactions between coal ash and MgO-based refractories in lime kiln conditions
- 2023
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Ingår i: Fuel. - : Elsevier. - 0016-2361 .- 1873-7153. ; 342
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Tidskriftsartikel (refereegranskat)abstract
- Magnesium oxide (MgO)-based refractories are commonly used in quicklime and cement rotary kilns. At the high temperatures in the kiln burn zone, the infiltration of molten fuel ash into the refractory can occur. Subsequent chemical interactions can cause refractory wear that inflicts high maintenance costs and loss of production. To improve refractory reliability, it is necessary to increase the understanding of the interactions between fuel ash slag and refractory liner materials. Three commercially available MgO-based refractory materials were exposed to coal ash at 1200 °C and 1400 °C for between 15 and 60 min under a CO2-rich gaseous environment. Hot slag from the coal ash infiltrated the refractories and the infiltration depths were estimated with scanning electron microscope with energy dispersive X-ray spectroscopy. Based on detailed elemental and microstructure analyses, the interactions between ash and refractory were examined. Molten silicates infiltrated the refractory through grain boundaries and pores into depths of up to 2.8 mm. Powder X-ray diffraction of the exposed refractory samples indicated that MgO grains reacted with SiO2-containing phases to form Mg2SiO4. This was identified as a corrosion product whose formation was supported by thermochemical equilibrium calculations. Elevated Mg content was found in the ash residue on top of the samples, indicating the dissolution or dislocation of refractory components. In addition, phases such as MgO were identified in the ash residue.
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| 8. |
- Kumar Wagri, Naresh, et al.
(författare)
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High temperature interactions between K-rich biomass ash and MgO-based refractories
- 2023
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Ingår i: Journal of the European Ceramic Society. - : Elsevier. - 0955-2219 .- 1873-619X. ; 43:8, s. 3770-3777
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Tidskriftsartikel (refereegranskat)abstract
- MgO-based refractories are used in lime kilns to withstand the high temperature and chemical environment. Efforts to reduce CO2 emissions have led to an increased interest to use bio-based fuels as alternatives to traditional fossil sources. The potential for refractory corrosion from a potassium-rich biomass ash was investigated by studying the infiltration of olive pomace ash into magnesia/spinel refractories. Refractory samples were exposed to the ash at up to 1400 °C for 15–60 min in a CO2–rich atmosphere. Molten ash infiltrated the refractories through pores and grain boundaries to a depth of up to 9.6 mm, which was quantified with a new systematic procedure. The phase KAlO2 was identified inside the refractories after exposure, indicating an attack of spinel components by potassium. Phases found in the ash residues also indicated the migration of refractory constituents. Thermochemical equilibrium calculations were also used to investigate the ash/refractory chemistry.
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| 9. |
- Kumar Wagri, Naresh, et al.
(författare)
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Interaction of olive pomace ash and coal ash with magnesium oxide based refractories
- 2022
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Ingår i: Proceedings of the 28th International Conference on the Impact of Fuel Quality on Power Production and the Environment. - : Department of Applied Physics and Electronics, Umeå University.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In quicklime production, limestone is calcined at temperatures above 1000°C, depending on the desired product quality. Heat is supplied to the process from combustion inside the kilns that are insulated to reduce heat loss. The kilns are lined with insulating refractory bricks to withstand the hot, chemically aggressive, and mechanically abrasive environment. Magnesia bricks have emerged as well-performinglining materials, but they are still prone to extensive wear in kilns that are operated at higher temperatures. In particular, refractory corrosion can be caused by fuel ash infiltration that results inmaterial wear, which can incur high maintenance and operational costs through unplanned shutdowns of the kilns. At the same time, to reduce the release of fossil-based carbon to the atmosphere, it is of interest to introduce bio-based fuels into the kilns with only relatively small modifications to the process. Biobased waste streams from existing industries are preferable rather than biomass grown with the sole purpose of combustion. The ash content and properties of these types of waste residues do, however, tend to be problematic from a fuel ash chemistry point of view. Therefore, before introducing a new fuel, their potential effects on kiln lining material should be investigated. In this study, the infiltration of olivepomace ash and coal ash into commercially available refractory materials composed of mainly periclase(MgO) with minor amounts of spinel (MgAl2O4) were compared. They were exposed to the fuel ashes under a simulated lime kiln high CO2 atmosphere at 1200 and 1400°C for 15 and 60 minutes. The morphology and elemental composition of the exposed samples were investigated with scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy. Ash-forming elements infiltrated the porous parts of the materials. The analytical results are complemented with thermodynamic equilibrium calculations to investigate the ash melting behavior. Crystalline phases in the residual ashes were investigated with X-ray diffraction. Refractory phases could be found in both ashes, indicating migration of refractory constituents. Olive pomace ash formed new crystalline compounds together with the refractory components whereas this was not observed for the coal ash, indicating that the former is more of a risk for material failure.
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| 10. |
- Ma, Charlie, et al.
(författare)
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Structures and diffusion motions of K and Ca in biomass ash slags from molecular dynamics simulations
- 2021
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Ingår i: Fuel. - : Elsevier. - 0016-2361 .- 1873-7153. ; 302
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Tidskriftsartikel (refereegranskat)abstract
- The ash slag formations that can occur in combustion and gasification of solid fuels often consist of silicate melts that can cause operational problems, e.g., bed agglomeration or slag build-up. This study aims to better understand the underlying molecular structures and motions that bring about viscosity variations in biomass ash slags that are rich in Ca and K. Aspects of slag structure, diffusivity, and cation motion in the molten CaO–K2O–SiO2 system were acquired from molecular dynamics simulations. These results are discussed in relation to viscosity values found in literature. Among the structural characteristics of the silicate network, the simulations showed that the local structures of both Ca and K were affected by composition, with stronger integration of Ca within the silicate network than K. The formation of larger ring structures due to network depolymerisation occurred with increasing diffusivity and lower viscosity, but small rings prevailed due to clusters of Si and O atoms that formed cohesive structures. Both Ca and K showed hopping motions as they diffused through the network, especially in high viscosity compositions. These cations exhibited preferential migration to positions previously occupied by the same species, as a means of moving around the network-forming Si and O atoms that diffused slower. The diffusivity of K ions was facilitated by transport in percolation channels. The presence of slower-diffusing Ca ions occupied positions that could otherwise have contributed to K diffusivity. This work contributes towards understanding of ash slags in thermochemical processes by exploring network modifier mobility in silicate slags.
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| 11. |
- Ma, Charlie, et al.
(författare)
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Viscosity of molten CaO-K2O-SiO2 woody biomass ash slags in relation to structural characteristics from molecular dynamics simulation
- 2020
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Ingår i: Chemical Engineering Science. - : Elsevier. - 0009-2509 .- 1873-4405. ; 215
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Tidskriftsartikel (refereegranskat)abstract
- Molten compositions in the CaO-K2O-SiO2 system relevant to woody biomass ash slags were simulated with molecular dynamics to extract structural characteristics. Multivariate analysis elucidated correlations of these structural characteristics with viscosity measurements. The simulations show SiO4/silicate tetrahedral units (STUB) diffusing slowly and forming flexible networks via oxygen bridges. The degree of STU polymerization varies linearly with the (K2O + CaO)/SiO2 ratio. Ca depolymerises stronger than K, but K diffuses quicker. Depolymerization and diffusion cause network disruptions and agitations that promote collective atomic mobility of the system. This imposes structural characteristics in the slag that correlate with viscosity. The inter-STU Si-O-Si angle narrows with decreasing viscosity, while the Si-O bond length of these bridges increases. Attributes related to atomic mobility, such as the variations in the Si-O-Si angle and the distance of nearest Si-Si pairs, also correlate with viscosity. The discussion provides insight into the connection between structural characteristics and viscosity.
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| 12. |
- Miranda, Diego A., et al.
(författare)
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Production and characterization of poly(3-hydroxybutyrate) from Halomonas boliviensis LC1 cultivated in hydrolysates of quinoa stalks
- 2023
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Ingår i: Fermentation. - : MDPI. - 2311-5637. ; 9:6
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Tidskriftsartikel (refereegranskat)abstract
- The global production of fossil-based plastics has reached critical levels, and their substitution with bio-based polymers is an urgent requirement. Poly(3-hydroxybutyrate) (PHB) is a biopolymer that can be produced via microbial cultivation, but efficient microorganisms and low-cost substrates are required. Halomonas boliviensis LC1, a moderately halophilic bacterium, is an effective PHB producer, and hydrolysates of the residual stalks of quinoa (Chenopodium quinoa Willd.) can be considered a cheap source of sugars for microbial fermentation processes in quinoa-producing countries. In this study, H. boliviensis LC1 was adapted to a cellulosic hydrolysate of quinoa stalks obtained via acid-catalyzed hydrothermal pretreatment and enzymatic saccharification. The adapted strain was cultivated in hydrolysates and synthetic media, each of them with two different initial concentrations of glucose. Cell growth, glucose consumption, and PHB formation during cultivation were assessed. The cultivation results showed an initial lag in microbial growth and glucose consumption in the quinoa hydrolysates compared to cultivation in synthetic medium, but after 33 h, the values were comparable for all media. Cultivation in hydrolysates with an initial glucose concentration of 15 g/L resulted in a higher glucose consumption rate (0.15 g/(L h) vs. 0.14 g/(L h)) and volumetric productivity of PHB (14.02 mg/(L h) vs. 10.89 mg/(L h)) than cultivation in hydrolysates with 20 g/L as the initial glucose concentration. During most of the cultivation time, the PHB yield on initial glucose was higher for cultivation in synthetic medium than in hydrolysates. The produced PHBs were characterized using advanced analytical techniques, such as high-performance size-exclusion chromatography (HPSEC), Fourier transform infrared (FTIR) spectroscopy, 1H nuclear magnetic resonance (NMR) spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). HPSEC revealed that the molecular weight of PHB produced in the cellulosic hydrolysate was lower than that of PHB produced in synthetic medium. TGA showed higher thermal stability for PHB produced in synthetic medium than for that produced in the hydrolysate. The results of the other characterization techniques displayed comparable features for both PHB samples. The presented results show the feasibility of producing PHB from quinoa stalks with H. boliviensis.
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| 13. |
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| 14. |
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| 15. |
- Sepman, Alexey, et al.
(författare)
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Laser-based detection of methane and soot during entrained-flow biomass gasification
- 2022
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Ingår i: Combustion and Flame. - : Elsevier Inc.. - 0010-2180 .- 1556-2921. ; 237
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Tidskriftsartikel (refereegranskat)abstract
- Methane is one of the main gas species produced during biomass gasification and may be a desired or undesired product. Syngas CH4 concentrations are typically >5 vol-% (when desired) and 1–3 vol-% even when efforts are made to minimize it, while thermochemical equilibrium calculations (TEC) predict complete CH4 decomposition. How CH4 is generated and sustained in the reactor core is not well understood. To investigate this, accurate quantification of the CH4 concentration during the process is a necessary first step. We present results from rapid in situ measurements of CH4, soot volume fraction, H2O and gas temperature in the reactor core of an atmospheric entrained-flow biomass gasifier, obtained using tunable diode laser absorption spectroscopy (TDLAS) in the near-infrared (1.4 µm) and mid-infrared (3.1 µm) region. An 80/20 wt% mixture of forest residues and wheat straw was converted using oxygen-enriched air (O2>21 vol%) as oxidizer, while the global air-fuel equivalence ratio (AFR) was set to values between 0.3 and 0.7. Combustion at AFR 1.3 was performed as a reference. The results show that the CH4 concentration increased from 1 to 3 vol-% with decreasing AFR, and strongly correlated with soot production. In general, the TDLAS measurements are in good agreement with extractive diagnostics at the reactor outlet and TEC under fuel-lean conditions, but deviate significantly for lower AFR. Detailed 0D chemical reaction kinetics simulations suggest that the CH4 produced in the upper part of the reactor at temperatures >1700 K was fully decomposed, while the CH4 in the final syngas originated from the pyrolysis of fuel particles at temperatures below 1400 K in the lower section of the reactor core. It is shown that the process efficiency was significantly reduced due to the C and H atoms bound in methane and soot. © 2021 The Authors
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| 16. |
- Strandberg, Anna, Dr, 1984-, et al.
(författare)
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Ash Transformation During Single-Pellet Combustion of a Silicon-Poor Woody Biomass
- 2019
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 33:8, s. 7770-7777
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Tidskriftsartikel (refereegranskat)abstract
- Biomass fuels with calcium and potassium as the main ash-forming elements are expected to form ash consisting mainly of carbonates and oxides. These carbonates are stable in a rather narrow temperature range, which in turn depends on the Ca/K ratio, as well as on the surrounding atmosphere. The objective of the present study was to perform a detailed characterization of ash formation and transformation at a single-pellet level during combustion of silicon-poor woody biomass fuel. Combustion tests were performed with poplar in a single-pellet isothermal thermogravimetric analyzer operated at different temperatures and atmospheres and quenched at different stages of fuel conversion. The char and residual ashes were characterized for morphology and chemical composition. The focus of the experimental work in this study was on the time (conversion) resolved ash formation and transformations at the late part of the char combustion phase. Thermodynamic equilibrium calculations were used both to design the experiments and to support the interpretation of experimental results. It was concluded that carbonates were, in general, stable at low temperatures (here, 600–800 °C), identified as CaCO3, K2Ca2(CO3)3, and K2Ca(CO3)2, and decomposed at higher temperatures. In addition, a combined carbonate and phosphate phase in the form of carbonate apatite, Ca9.9(PO4)6(CO3)0.9, was also found, mainly at lower temperatures. However, for char/ash samples quenched before full conversion, CaCO3 was still found at temperatures higher than expected, possibly explained by the stabilizing effect of locally higher CO2 partial pressure within the burning fuel particles. Thus, the results of the present study provide new insights into conversion-based ash formation and transformation in a burning fuel particle with relevance for combustion of Si-poor woody biomass fuels.
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| 17. |
- Thorin, Emil, et al.
(författare)
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Quantitative real-time in situ measurement of gaseous K, KOH and KCl in a 140 kW entrained-flow biomass gasifier
- 2023
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier Ltd. - 1540-7489 .- 1873-2704. ; 39:1, s. 1337-1345
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Tidskriftsartikel (refereegranskat)abstract
- Photofragmentation tunable diode laser absorption spectroscopy (PF-TDLAS) was used to simultaneously measure the concentrations of gas phase atomic potassium (K), potassium hydroxide (KOH) and potassium chloride (KCl) in the reactor core of a 140 kWth atmospheric entrained-flow gasifier (EFG). In two gasification experiments at air-to-fuel equivalence ratio of 0.5, the EFG was first run on forest residues (FR) and then on an 80/20 mixture of FR and wheat straw (FR/WS). Combustion at air-to-fuel equivalence ratio of 1.3 was investigated for comparison. A high K(g) absorbance was observed in gasification, requiring the photofragmentation signals from KOH(g) and KCl(g) to be recorded at a fixed detuning of 7.3 cm-1 from the center of the K(g) absorption profile. In combustion, the fragments recombined instantly after the UV pulse within around 10 μs, whereas in gasification, the K(g) fragment concentration first increased further for 30 μs after the UV pulse, before slowly decaying for up to hundreds of μs. According to 0D reaction kinetics simulations, this could be explained by a difference in recombination kinetics, which is dominated by oxygen reactions in combustion and by hydrogen reactions in gasification. The K species concentrations in the EFG were stable on average, but periodic short-term variations due to fuel feeding were observed, as well as a gradual increase in KOH(g) over the day as the reactor approached global equilibrium. A comparison of the average K species concentrations towards the end of each experiment showed a higher total K in the gas phase for FR/WS, with higher K(g) and KCl(g), but lower KOH(g), compared to the FR fuel. The measured values were in reasonable agreement with predictions by thermodynamic equilibrium calculations. © 2022 The Author(s).
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| 18. |
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| 19. |
- Borén, Eleonora, et al.
(författare)
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Kaolin as fuel additive in grate combustion of biomass to mitigate ash related problems and particle emissions
- 2022
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Ingår i: Proceedings of the 28th International Conference on the Impact of Fuel Quality on Power Production and the Environment. - : Department of Applied Physics and Electronics, Umeå University.
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Konferensbidrag (refereegranskat)abstract
- Bioenergy is a fundamental part in sustainable development but use of novel fuel feedstocks potentiallymore sustainable may also bring associated ash-related challenges in practical operation that could bemitigated by co-conversion or additives. Kaolin, a clay mineral, is an additive known to be beneficialfor reduction of slagging tendencies and particulate matter formation in combustion of traditionalwoody-type biomass but its impact on thermal conversion of other biomasses still warrantsinvestigation. The aim of the present work is therefore to investigate how thermal conversion of atypical K-Ca-rich woody-type biomass, poplar, and a K-Si-rich annual crop, grass, is affected by kaolinaddition in fixed bed combustion. Additivation levels were calculated according to amount of alkaliintroduced with the two feedstocks, and incorporated by co-pelletization, in the case of poplar, anadditional blending d method was tested, by powder coating of pellets The results show that kaolinaddition improved the bottom ash characteristics, especially for grass, but the main differencesbetween feedstocks were found in particulate matter and flue gas composition. The particulate matterconcentrations were reduced with kaolin addition due to removal of gaseous K compounds which inturn caused higher SOx and HCl concentrations due to the lower amount of gaseous alkali for reaction.Further, initially high CO levels observed for both fuel feedstocks were reduced with the addition ofkaolin where co-pelletization with poplar proved more effective than powder coating the fuel particlesurfaces. This suggests that high concentrations of gaseous K-compounds may impact conversion ofthe carbonaceous matrix negatively.
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| 20. |
- Carlborg, Markus, 1986-
(författare)
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Refractory corrosion in biomass gasification
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- To stop the net emission of CO2 to the atmosphere, we need to reduce our dependency of fossil fuels. Although a switch to a bio-based feedstock hardly can replace the total amount of fossils used today, utilization of biomass does still have a role in a future in combination with other techniques. Valuable chemicals today derived from fossils can also be produced from biomass with similar or new technology. One such technique is the entrained flow gasification where biomass is converted into synthesis gas. This gas can then be used as a building stone to produce a wide range of chemicals.Slagging and corrosion problems are challenges presented by the ash forming elements in biomass during thermochemical energy conversion. The high temperature in the entrained flow process together with ash forming elements is creating a harsh environment for construction materials in the reactor. Severe corrosion and high wear rates of the lining material is a hurdle that has to be overcome to make the process more efficient.The objective of this work is to investigate the nature of the destructive interaction between ash forming elements and refractory materials to provide new knowledge necessary for optimal refractory choice in entrained flow gasification of woody biomass. This has been done by studying materials exposed to slags in both controlled laboratory environments and pilot scale trials. Morphology, elemental composition and distribution of refractories and slag were investigated with scanning electron microscopy and energy dispersive X-ray spectroscopy. Crystalline phases were investigated with X-ray diffraction, and thermodynamic equilibrium calculations were done in efforts to explain and make predictions of the interaction between slag and refractory.Observations of slag infiltration and formation of new phases in porous materials indicate severe deterioration. The presence of Si in the materials is limiting intrusion by increasing the viscosity of infiltrated slag. This is however only a temporary delay of severe wear considering the large amount of slag that is expected to pass the refractory surface. Zircon (or zirconium) (element or mineral?) based material show promising properties when modeled with thermodynamic equilibrium, but disassembling of sintered material and dissociation of individual grains was seen after exposure to a Si- and Ca-rich slag. Fused cast materials have a minimal slag contact where the only interaction is on the immediate hot face. Dissolution was however observed when exposed to a silicate-based slag, as was the formation of NaAlO2 after contact with black liquor.
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| 21. |
- Kou, Wen, 1979-, et al.
(författare)
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The effect of artificial aging on high translucent zirconia
- 2019
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Ingår i: Biomaterial Investigations in Dentistry. - : Informa UK Limited. - 2641-5275. ; 6:1, s. 54-60
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Tidskriftsartikel (refereegranskat)abstract
- Zirconia is known for its high strength but lacking translucency. Recently, a new type of high translucent zirconia, 5 mol% yttria partially stabilized zirconia (5Y-PSZ), with a larger fraction of cubic zirconia phase has become commercially available. However, the resistance to aging of these commercially available zirconia materials is not yet fully established.Purpose: The aim of the present study was to analyze the effects of artificial aging on surface roughness, transparency, phase transformation and biaxial flexural strength of two 5Y-PSZ products, DD cubeX2 and Prettau Anterior.Materials and methods: The artificial aging was performed in an autoclave under 2 bars of pressure at 134 °C for 10 hours, which is estimated to correspond to 30–40 years in vivo. Artificial aging for 10 hours had no significant effect on surface roughness, transparency, or phase transformation for either of the tested materials.Results: DD cubeX2 had higher mean flexural strength than Prettau Anterior both before and after artificial aging for 10 hours (p < .05). DD cubeX2 showed, however, a significant reduction in flexural strength after artificial aging (p < .05), whereas Prettau Anterior showed a slight increase in flexural strength after artificial aging but not at a significant level.Conclusion: Within the limitation of the present study, both DD cubeX2 and Prettau Anterior seems to be relatively resistant to aging. However, a wider range of measured flexural strength indicated that Prettau Anterior probably is a less stable material than DD cubeX2, which also means that the flexural strength of DD cubeX2 could be more predictable.
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| 22. |
- Latham, Kenneth G., et al.
(författare)
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Self-generation of low ash carbon microspheres from the hydrothermal supernatant of anaerobic digestate : Formation insights and supercapacitor performance
- 2021
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Ingår i: Chemical Engineering Journal Advances. - : Elsevier. - 2666-8211. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- This work provides the first observations of and insights into the self-generation of carbon microspheres from the supernatant after hydrothermal carbonization of anaerobic digestate has been completed and the hydrochar removed. Solid State NMR and XPS revealed that the carbon microspheres were comprised of decomposed fragments of proteins, carbohydrates and lignin. The carbon microspheres were significantly lower in ash content (3.1%), compared to the hydrothermal solid (41.2%) and precursor (25.2%) and their formation reduced the total organic carbon load of the supernatant. The low ash content allowed them to be easily activated, achieving a surface area of 1711.0 m2 g−1, compared to 51.4 m2 g−1 for the activated hydrothermal solid and 12.8 m2 g−1 for the activated precursor. The microcarbon spheres achieved a specific capacitance from cyclic voltammetry of 86 F g−1 at 100 mV s−1 to 176 F g−1 at 1 mV s−1, while the gravimetric capacitance was 42 F g−1 at 25 A g−1 and 140 F g−1 at 0.5 A g−1 in 0.5 M Li2SO4 and a 1.8V potential window. Overall, this study highlights the importance of exploring this new product and its valorisation potential for the hydrothermal carbonization of ash-rich precursors.
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| 23. |
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| 24. |
- Rebbling, Anders, 1980-, et al.
(författare)
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Demonstrating Fuel Design To Reduce Particulate Emissions and Control Slagging in Industrial-Scale Grate Combustion of Woody Biomass
- 2020
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Ingår i: Energy & Fuels. - : AMER CHEMICAL SOC. - 0887-0624 .- 1520-5029. ; 34:2, s. 2574-2583
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Tidskriftsartikel (refereegranskat)abstract
- The demand for increased overall efficiency, improved fuel flexibility, and more stringent environmental legislations promotes the development of new fuel- and technology-related concepts for the bioenergy sector. Previous research has shown that careful consideration of the fuel ash composition and the adjustment of the same via various routes, i.e., fuel design, have the potential to alter the ash transformation reactions, leading to, e.g., a reduction of the formation of slag or entrained inorganic ash particles. The objective of the present work was, therefore, to demonstrate the use of fuel design as a primary measure to reduce the emission of PM1 during combustion of woody biomass in medium-scale grate-fired boilers while keeping the slag formation at a manageable level. This was achieved by designing fuel blends of woody biomass with carefully selected Scandinavian peats rich in Si, Ca, and S. The work includes results from three experimental campaigns, performed in three separate grate-fired boilers of different sizes, specifically 0.2 MWth, 2 MWth, and 4 MWth. In one of the campaigns, softwood-based stemwood pellets were copelletized with different additions of peat (5 and 15 wt %) before combustion. In the other campaigns, peat was added in a separate fuel feed to Salix chips (15 wt % peat) and softwood-based stemwood pellets (10 and 20 wt % peat). Particulate matter and bottom ashes were characterized by scanning electron microscopy-energy-dispersive X-ray spectroscopy for morphology and elemental composition as well as by powder X-ray diffraction for crystalline phase composition. The results show that the fuel design approach provided PM1 reduction for all fuel blends between 30 and 50%. The PM1 reduction could be achieved without causing operational problems due to slagging for any of the three commercial boilers used, although an expected increased slagging tendency was observed. Overall, this paper illustrates that fuel design can be implemented on an industrial scale by achieving the desired ash transformation reactions, in this case, leading to a reduction of fine particulate emissions by up to 50% without any operational disturbances due to slag formation on the grate.
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| 25. |
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| 26. |
- Rebbling, Anders, 1980-, et al.
(författare)
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Reduction of Alkali Release by Two Fuel Additives at Different Bed Temperatures during Grate Combustion of Woody Biomass
- 2019
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 33:11, s. 11041-11048
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Tidskriftsartikel (refereegranskat)abstract
- The use of small- and medium-scale combustion of biomass for energy utilization is expected to grow in the coming decades. To meet standards and legislation regarding particle emissions and to reduce corrosion and deposit formation, it is crucial to reduce the release of alkali species from the fuel. This can be achieved by capturing the volatile alkali in the residual bottom ash as more thermally stable compounds. In this work, we investigate the combination of primary measures, i.e., process parameters and fuel additives, for reduction of the release of K and Na from the fuel bed during fixed bed combustion. In addition, the influence of these combined measures on fine particle emissions was explored. The results showed a clear influence of the process parameters, herein bed temperature, and that a significant reduction of the alkali release and PM1 emissions can be achieved by correct settings. Furthermore, the application of additives (kaolin and diammonium sulfate) reduced both K and Na release even further. The observed effects on the release behavior was mainly explained by the formation of KAlSiO4 and K2SO4 during addition of kaolin and diammonium sulfate, respectively. This work therefore emphasizes the importance of good control over the fuel bed conditions, especially temperature, when these additives are applied. To reduce the potential deactivation (for kaolinite) and melting (for K2SO4), the control of bed temperature is vital. Thus, it was concluded that the release of volatile alkali species and related fine particle emissions in small- and medium-scale biomass heat and power plants using wood fuels could be significantly reduced by a correct combination of controlling the combustion parameters and the use of fuel additives.
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