7 results on '"Öhman, Marcus"'
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2. Role of surface morphology in bed particle layer formation on quartz bed particles in fluidized bed combustion of woody biomass.
- Author
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Valizadeh, Ali, Skoglund, Nils, Forsberg, Fredrik, Lycksam, Henrik, and Öhman, Marcus
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FLUIDIZED-bed combustion , *BIOMASS burning , *SURFACE morphology , *CONCAVE surfaces , *X-ray computed microtomography , *QUARTZ - Abstract
• Bed particle layer growth on quartz is faster at convex regions of the particle. • Convexes show thick inner and outer layer, concaves mainly show a thin inner layer. • Smooth areas of bed particles have the thickest Ca-rich inner and outer layers. • Crack layers form in concaves with cracks in the inner and a missing outer layer. • Ca-rich protective layers on smooth particles may reduce operational problems. The influence of quartz bed particle surface morphology on the bed particle layer and crack layer formation process in fluidized bed combustion of woody biomass was investigated in this work. Bed material samples were collected at different sampling times from the startup with a fresh bed in industrial scale bubbling fluidized bed (BFB) and circulating fluidized bed (CFB) boilers, both utilizing woody biomass. X-ray microtomography (XMT) and scanning electron microscopy coupled with energy dispersive spectroscopy (SEM/EDS) were employed to characterize bed particle layers and crack layers in the samples. Results showed that there is a noticeable difference between the bed layer characteristics over the so-called "concave" and "convex"-shaped morphologies on the bed particle surface with respect to layer formation. The concave areas are mainly covered with a thin inner layer, whilst the convex display a comparably thick inner layer and an outer layer. In addition, 3D images of the particles revealed that the crack layers mainly originate from concave areas where the particle is less protected by an outer bed particle layer in conjunction with cracks in the inner layer. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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3. A comparative study in 3D of bed particle layer characteristics in quartz and K-feldspar from fluidized bed combustion of woody biomass using X-ray microtomography.
- Author
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Valizadeh, Ali, Skoglund, Nils, Forsberg, Fredrik, Lycksam, Henrik, and Öhman, Marcus
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FLUIDIZED-bed combustion , *X-ray computed microtomography , *BIOMASS burning , *ORTHOCLASE , *QUARTZ - Abstract
• X-ray microtomography is demonstrated as a key technique in bed material studies. • Interaction of ash and bed particles in combustion of woody fuels was investigated. • Bed particle layers were thicker on quartz than K-feldspar after 5 days of interaction. • Internal crack layers comprised 32 vol% of quartz, but K-feldspar had almost none. • Total interaction volume was larger for quartz than K-feldspar due to crack layers. Bed particle layer and crack layer characteristics at different ages were studied for quartz and K-feldspar bed particles from a 30 MW th bubbling fluidized bed and a 90 MW th circulating fluidized bed, both using woody biomass as fuel. X-ray microtomography (XMT) was utilized to determine the bed particle layer distribution on the bed particles' surface. For each bed particle type, the average bed particle layer thickness as well as average volume fractions of the bed particle layer and crack layers to the entire bed particle volume were determined at three different bed particle ages by utilizing XMT analysis. Comparison of the two different bed particle types showed that K-feldspar retains a thinner bed particle layer in both conversion processes compared to quartz. Crack layers were observed extensively in quartz bed particles to the extent of 19.3 vol% and 32.1 vol% after 13 days in the BFB and the CFB, respectively, which could cause deposition of the bed particle fragments. On the contrary, K-feldspar has almost no tendency toward forming crack layers. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
4. Calcium oxide as an additive for both conservation and improvement of the combustion properties of energy grass: A preliminary study.
- Author
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Xiong, Shaojun, Bozaghian, Marjan, Lestander, Torbjörn A., Samuelsson, Robert, Hellqvist, Sven, and Öhman, Marcus
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BIOMASS burning , *LIME (Minerals) , *REED canary grass , *SORBENTS , *FEEDSTOCK - Abstract
Degradation of biomass is one of the major reasons for high costs of feedstock collection, transport, and storage, which is largely associated with biomass moisture and microbial activities. Our concept is to add calcium oxide (CaO) to the biomass already when it is collected and in its natural (wet) condition. When a suitable quantity of CaO is added to moistened biomass, an alkali microenvironment will be formed with a pH exceeding 9, based on the reaction CaO + H 2 O ↔ Ca(OH) 2 . As a consequence, microbial activities are largely inhibited. The Ca(OH) 2 will then successively react with CO 2 , following the reaction Ca(OH) 2 + CO 2 ↔ CaCO 3 + H 2 O. The CaCO 3 will reside in the feedstock throughout the entire production chain and end up as an additive/sorbent to improve combustion by decreasing slagging. Two experiments were conducted and proved the concept works for at least reed canary grass, but, as expected, the strength of the effect was dependent on the CaO dosage and initial biomass moisture. [ABSTRACT FROM AUTHOR]
- Published
- 2017
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5. Ash transformations in pulverised fuel co-combustion of straw and woody biomass
- Author
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Nordgren, Daniel, Hedman, Henry, Padban, Nader, Boström, Dan, and Öhman, Marcus
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FLY ash , *CO-combustion , *STRAW as fuel , *FUELWOOD , *BIOMASS burning , *THERMODYNAMIC equilibrium , *WHEAT straw - Abstract
Abstract: Ash transformation processes have been studied during co-firing of wheat straw and pine stem wood and softwood bark. Pilot-scale trials in a 150kW pulverised-fuel-fired burner were performed. Thermodynamic equilibrium calculations were made to support the interpretation of the results. The results show that reactions involving condensed phases are kinetically limited compared to reactions between gaseous ash compounds. Accordingly, the conditions promote gas phase reactions resulting in the formation of chlorides, sulphates and carbonates whereas reactions involving condensed reactants are suppressed. Both the slagging and fouling propensities of all co-firing mixes were reduced compared to that for pure straw. For the wood/straw mixes this was mainly due to a dilution of the ash forming elements of straw whereas for straw/bark, an additional effect from interaction between the fuel ash components was observed to reduce slagging. In general it can be concluded that under powder combustion conditions equilibrium is approached selectively and that the ash matter is strongly fractionated. The general results in this paper are useful for straw-fired power stations looking for alternative co-firing fuels. [Copyright &y& Elsevier]
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- 2013
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6. Combustion and fuel characterisation of wheat distillers dried grain with solubles (DDGS) and possible combustion applications
- Author
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Eriksson, Gunnar, Grimm, Alejandro, Skoglund, Nils, Boström, Dan, and Öhman, Marcus
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RENEWABLE energy sources , *BIOMASS burning , *ELECTRIC power production , *PHASE transitions , *AGRICULTURAL wastes as fuel , *TEMPERATURE effect - Abstract
Abstract: The present transition to a sustainable global energy system requires that biomass is increasingly combusted for heat and power production. Agricultural fuels considered include alkali-rich fuels with high phosphorus content. One such fuel is wheat distiller’s dried grain with solubles (wheat DDGS) from wheat-based ethanol production. Further increases in ethanol production may saturate the current market for wheat DDGS as livestock feed, and fuel uses are therefore considered. Fuel properties of wheat DDGS have been determined. The ash content (5.4±1.6%wtd.s.) is similar to many agricultural fuels. In comparison to most other biomass fuels the sulphur content is high (0.538±0.232%wtd.s.), and so are the contents of nitrogen (5.1±0.6%wtd.s.), phosphorus (0.960. ±0.073%wtd.s.) and potassium (1.30±0.35%wtd.s.). To determine fuel-specific combustion properties, wheat DDGS and mixes between wheat DDGS and logging residues (LR 60%wtd.s. and DDGS 40%wtd.s.), and wheat straw (wheat straw 50%wtd.s., DDGS 50%wtd.s.) were pelletized and combusted in a bubbling fluidised bed combustor (5kW) and in a pellets burner combustor (20kW). Pure wheat DDGS powder was also combusted in a powder burner (150kW). Wheat DDGS had a high bed agglomeration and slagging tendency compared to other biomass fuels, although these tendencies were significantly lower for the mixture with the Ca-rich LR, probably reflecting the higher first melting temperatures of K–Ca/Mg-phosphates compared to K-phosphates. Combustion and co-combustion of wheat DDGS resulted in relatively large emissions of fine particles (<1μm) for all combustion appliances. For powder combustion PMtot was sixteen times higher than from softwood stem wood. While the Cl concentrations of the fine particles from the the mixture of LR and wheat DDGS in fluidised bed combustion were lower than from combustion of pure LR, the Cl- and P-concentrations were considerably higher from the wheat DDGS mixtures combusted in the other appliances at higher fuel particle temperature. The particles from powder combustion of wheat DDGS contained mainly K, P, Cl, Na and S, and as KPO3 (i.e. the main phase identified with XRD) is known to have a low melting temperature, this suggests that powder combustion of wheat DDGS should be used with caution. The high slagging and bed agglomeration tendency of wheat DDGS, and the high emissions of fine particles rich in K, P and Cl from combustion at high temperature, mean that it is best used mixed with other fuels, preferably with high Ca and Mg contents, and in equipment where fuel particle temperatures during combustion are moderate, i.e. fluidised beds and possibly grate combustors rather than powder combustors. [Copyright &y& Elsevier]
- Published
- 2012
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7. Prediction of slag related problems during fixed bed combustion of biomass by application of a multivariate statistical approach on fuel properties and burner technology.
- Author
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Rebbling, Anders, Näzelius, Ida-Linn, Schwabl, Manuel, Feldmeier, Sabine, Schön, Claudia, Dahl, Jonas, Haslinger, Walter, Boström, Dan, Öhman, Marcus, and Boman, Christoffer
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BIOMASS burning , *BURNERS (Technology) , *FLUIDIZED-bed combustion , *SLAG , *FORECASTING , *FUEL , *PULVERIZED coal - Abstract
Slag is related to the melting properties of ash and is affected by both the chemical composition of the fuel ash and the combustion parameters. Chemical analysis of slag from fixed bed combustion of phosphorus-poor biomass show that the main constituents are Si, Ca, K, O (and some Mg, Al, and Na), which indicates that the slag consists of different silicates. Earlier research also points out viscosity and fraction of the ash that melts, as crucial parameters for slag formation. To the authors' knowledge, very few of the papers published to this day discuss slagging problems of different pelletized fuels combusted in multiple combustion appliances. Furthermore, no comprehensive classification of both burner technology and fuel ash parameters has been presented in the literature so far. The objective of the present paper was therefore to give a first description of a qualitative model where ash content, concentrations of main ash forming elements in the fuel and type of combustion appliance are related to slagging behaviour and potential operational problems of a biomass fuel in different small- and medium scale fixed bed appliances. Based on the results from the combustion of a wide range of pelletized biomass fuels in nine different burners, a model is presented for amount of slag formed and expected severity of operational problems. The model was validated by data collected from extensive combustion experiments and it can be concluded that the model predicts qualitative results. • The paper presents a validated qualitative statistical model for prediction of slagging and operational problems. • The model considers combined effects of ash content, ash composition, and combustion appliance. • The fuel parameters K-, Ca-, Si, and ash content impact the slag formation. • Combustion technologies having continuous ash discharge systems is advantageous, especially for Si-rich straw-/grass fuels. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
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