| 1. |
- Jerndal, Erik, 1980, et al.
(författare)
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Using Low-Cost Iron-Based Materials as Oxygen Carriers for Chemical Looping Combustion
- 2011
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Ingår i: Oil and Gas Science and Technology. - : EDP Sciences. - 1294-4475 .- 1953-8189. ; 66:2, s. 235-248
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Tidskriftsartikel (refereegranskat)abstract
- In chemical looping combustion with solid fuels, the oxygen-carrier lifetime is expectedto be shorter than with gaseous fuels. Therefore, it is particularly important to use low-cost oxygencarriers in solid fuel applications. Apart from being cheap, these oxygen carriers should be able toconvert the CO and H2 produced from the solid fuel gasification and be sufficiently hard to withstandfragmentation. Several low-cost iron-based materials displayed high conversion of syngas and highmechanical strength and can be used for further development of the technology. These materials includeoxide scales from Sandvik and Scana and an iron ore from LKAB. All tested oxygen carriers showedhigher gas conversion than a reference sample, the mineral ilmenite. Generally, softer oxygen carrierswere more porous and appeared to have a higher reactivity towards syngas. When compared withilmenite, the conversion of CO was higher for all oxygen carriers and the conversion of H2 was higherwhen tested for longer reduction times. The oxygen carrier Sandvik 2 displayed the highest conversion ofsyngas and was therefore selected for solid fuel experiments. The conversion rate of solid fuels washigher with Sandvik 2 than with the reference sample, ilmenite.
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| 2. |
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| 3. |
- Lundberg, Louise, 1987, et al.
(författare)
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A 1-dimensional model of indirect biomass gasification in a dual fluidised bed system
- 2014
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Ingår i: 11th International Conference on Fluidized Bed Technology, CFB 2014; Beijing; China; 14 May 2014 through 17 May 2014. ; , s. 607-612
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Konferensbidrag (refereegranskat)abstract
- A 1-dimensional model is used to analyse how solids material circulation, biomass reactivity and gas mixing affect the char conversion in the Chalmers 2-4 MW indirect biomass gasifier. For the geometry and operational conditions particular to this unit, the model predicts a peak in char conversion for a solids circulation rate of around 3 kg/s. Char conversion is found to increase substantially with biomass reactivity and the level of gas mixing. At the experimental rate of solids circulation (6 kg/s), modelled char conversion values lie between 9% and 39% and are thus quite far from the experimental value of 2% (although potentially ranging between 0 and 10% due to experimental uncertainty). An explanation of the higher char conversion provided by the model could be the uncertainty in the reactivity of the biomass used. A further possible explanation, which has been studied by means of modelling in this work, is the gas mixing. The model uses expressions for the gas mixing which have been derived from measurements in smaller lab units with a high-pressure drop gas distributor, i.e. which induce a better gas mixing than the limited one existing in the large-scale unit studied here, caused by the presence of large bubbles and regions with weak fluidisation.
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| 4. |
- Lundberg, Louise, 1987, et al.
(författare)
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A conversion-class model for describing fuel conversion in large-scale fluidized bed units
- 2017
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 197, s. 42-50
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Tidskriftsartikel (refereegranskat)abstract
- Solid fuel conversion in fluidized beds is often modelled with the use of population balances, where the fuel conversion process is divided into a number of classes based on for example fuel particle size. The present work investigates and evaluates different methods for the discretisation of the fuel conversion process into classes, as well as the number of classes necessary to yield a satisfactory accuracy. A discretisation method, which defines classes based on the conversion degree (rather than size or density) and that is valid for all conversion regimes, is proposed. The results show that application of the proposed class division method for modelling biomass gasification in a fluidized bed gives an accuracy that is up to ten times higher than that given by a distribution with equally large classes. For all three conversion processes of biomass gasification (drying, pyrolysis, and char gasification), discretisation into 6 classes is sufficient to yield errors of around 1%, when compared to the continuous conversion curves given as input to the conversion class discretisation model (generated by a particle model in the present work). In line with this, when the conversion class model is used in a semi-empirical 1D model of indirect biomass gasification, the resulting char conversion in the gasifier does not change significantly when more than 3–6 char conversion classes are used.
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| 5. |
- Lundberg, Louise, 1987, et al.
(författare)
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Determination of Kinetic Parameters for the Gasification of Biomass Char Using a Bubbling Fluidised Bed Reactor
- 2015
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Ingår i: Proceedings of the 22nd International Conference on Fluidized Bed Conversion. ; , s. 456-464
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Konferensbidrag (refereegranskat)abstract
- A laboratory scale bubbling fluidised bed is used to investigate the gasification kinetics of char from wood pellets. As expected, the experiments show that the char gasification rate increases with temperature, but also that it does not significantly depend on the steam concentration for the conditions investigated. The kinetic parameters are determined and three models accounting for changes in the char structure during char conversion are tested: the grain model, the random pore model and an empirical model. The empirical model is the only one which gives a satisfactory agreement with the experimental data obtained in the lab unit.
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| 6. |
- Lundberg, Louise, 1987, et al.
(författare)
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Impacts of Bed Material Activation and Fuel Moisture Content on the Gasification Rate of Biomass Char in a Fluidized Bed
- 2019
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society. - 0888-5885 .- 1520-5045. ; 58:12, s. 4802-4809
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Tidskriftsartikel (refereegranskat)abstract
- The use of certain bed materials has been found to increase the steam gasification rate of biomass char. The present work investigates how this phenomenon is influenced by different parameters (e.g., temperature, fuel type, and fuel moisture content), using a laboratory-scale bubbling fluidized bed gasifier. Silica sand, fresh olivine, and activated olivine were employed as bed materials, and three biomass fuels (wood chips, wood pellets, and forest residue pellets) were considered. Switching the bed material from silica sand to activated olivine resulted in a significant increase in the char gasification rate for all three fuels, with further increases noted as the fuel particle size was decreased. The observed effect was strongest (up to 4-fold) during the initial conversion phase (char gasification degrees < 20%) when the temperature was relatively low (≤ 800 °C). The moisture content of the wood chips (0-40%) had no significant effect on the char gasification rate.
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| 7. |
- Lundberg, Louise, 1987, et al.
(författare)
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Influence of surrounding conditions and fuel size on the gasification rate of biomass char in a fluidized bed
- 2016
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Ingår i: Fuel processing technology. - : Elsevier. - 0378-3820 .- 1873-7188. ; 144, s. 323-333
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Tidskriftsartikel (refereegranskat)abstract
- While the operational conditions of a fluidized bed are known to influence the fuel axial mixing, the effect of the resulting axial location of the fuel particles on the char gasification rate remains unexplored. In this work, a laboratory-scale bubbling fluidized bed was used to investigate how the gasification rate of biomass char was influenced by the fuel axial location (during pyrolysis and char gasification), the pyrolysis atmosphere, the fuel size, and the fuel concentration. When pyrolysis at the bed surface was followed by char gasification inside the dense bed the char gasification rate was up to 2-fold lower than the other combinations of the fuel axial location, which held similar rates. Cooling the char after pyrolysis decreased the char gasification rate in all cases studied. The gasification rate increased when the fuel particle size was decreased, and its dependence on the degree of char conversion was also affected. Thus, the operational conditions of a fluidized bed reactor, through modified fuel axial mixing, can influence the char gasification rate. Furthermore, experimental determination of reactivity data in laboratory-scale systems must account for the axial location of the fuel at the desired end-scale, using similar fuel particle sizes.
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| 8. |
- Lundberg, Louise, 1987
(författare)
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Investigation of Solid Fuel Conversion in a Fluidised Bed Gasifier – Modelling and Experiments
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A substantial proportion of Sweden’s greenhouse gas emissions originates from the transportation sector, and the Swedish government has set the goal that the entire Swedish vehicle fleet will be independent from fossil fuels by 2030. One of the strategies investigated to achieve this goal is biomass gasification, which is a technology that can be used to transform lignocellulosic materials into a raw gas. This gas can be further upgraded into a transportation fuel, such as substitute natural gas (SNG), Fischer-Tropsch diesel, dimethyl ether, or methanol. Three major techniques can be used for biomass gasification: entrained-flow gasification; single fluidised bed gasification; and dual fluidised bed gasification (DFBG). This thesis focuses on DFBG with SNG as the end-product. For this process, there is an optimal overall efficiency of SNG production for a certain degree of char conversion in the gasification chamber. The aim of the work of this thesis is to elucidate how the degree of fuel conversion in the gasifier of a DFBG unit is influenced by different parameters. This knowledge is valuable for the design, upscaling, and optimisation of such units.For this purpose, semi-empirical modelling is combined with experimental work. The model is used to identify the key parameters that affect char gasification in a DFBG unit and to provide the corresponding sensitivity analyses. Furthermore, a general approach for optimising the definition of the conversion classes used in modelling the fuel population balance is proposed and evaluated. Experiments conducted at the laboratory scale examine how the conversion conditions of a fuel particle (fuel vertical mixing, fuel concentration, fuel size, pyrolysis atmosphere, and cooling of the char after pyrolysis) affect the char gasification rate. Experiments are also used to determine the particular kinetic and structural parameters of the biomass fuel used in the Chalmers DFBG unit. The 1D model, combined with the developed discretisation method for the fuel conversion classes and the experimentally determined kinetic and structural parameters, gave results that were in good agreement with the experimental data for the char conversion degree in the gasification chamber of the Chalmers DFBG unit. Furthermore, the experiments showed that the position of the fuel during pyrolysis and char gasification had a significant effect on the char gasification rate, for conditions relevant for DFBG. Particle size was also identified as an important parameter. Thus, when carrying out laboratory-scale tests to generate fuel reactivity data to be used for modelling large-scale units, it is important to replicate the conditions experienced by the fuel particles in the large-scale unit and to use similar fuel sizes.
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| 9. |
- Lundberg, Louise, 1987
(författare)
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Solid Fuel Conversion in Dual Fluidized Bed Gasification - Modelling and Experiments
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Dual fluidized bed gasification (DFBG) is the initial step towards the transformation of ligno-cellulosic materials into a raw gas, which can be further upgraded into transportation fuels, such as substitute natural gas, Fischer-Tropsch diesel, dimethyl ether, and methanol. DFBG units can be operated in two distinctly different ways, depending on whether the main product is a gas (to be refined into a transportation fuel) or heat and power (with gas as a by-product). For efficient operation in either mode, the degree of char conversion in the gasification chamber needs to be controlled and optimised. For this purpose, extensive knowledge is required regarding how the degree of char gasification is affected by different parameters. The aim of this thesis is to identify and fill key knowledge gaps regarding how different parameters influence solid fuel conversion in the gasification chamber of a DFBG unit, using a combination of laboratory-scale experiments and semi-empirical modelling. In addition, the possibility of ensuring adequate fuel conversion for either of the target modes described above is investigated. The results of the experiments presented in this thesis confirm that the laboratory-scale conditions applied in the experimental determination of reactivity data aimed at modelling fluidized bed gasification should, as much as possible, mimic the conditions of the end-scale reactor to be modelled. In particular, the effects of fuel axial mixing and of catalytic bed materials on char gasification were found to be significant. A validated semi-empirical 1D model of the gasification chamber of a DFBG unit has been formulated that: 1) accounts for the effect of fuel axial mixing on the char gasification rate; and 2) introduces a computationally efficient method for describing fuel conversion in fluidized beds. The modelling results show that the dominance of fuel convection over fuel dispersion increases with scale. Satisfactory fuel conversion is easily achieved when heat and power are the main products, with gas as a by-product. However, when the main goal is to improve the efficiency of gas production, a combination of baffles, properly chosen operational conditions, and/or the use of an active bed material is likely necessary to achieve sufficient fuel conversion.
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| 10. |
- Lundberg, Louise, 1987, et al.
(författare)
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The role of fuel mixing on char conversion in a fluidized bed
- 2016
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Ingår i: Fluidization XV.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Operational conditions, such as the fluidization velocity and the solids cross-flow, affect the degree of char conversion in a fluidized bed by influencing the different mechanisms related to the fuel mixing. Char conversion is influenced by fuel mixing in both the lateral direction (affecting the fuel residence time) and the axial direction (affecting the char gasification rate). In the present work, this effect is investigated through a combination of dedicated experiments in a cold unit, in which the effect of the excess velocity on the char segregation is quantified, and validated mathematical modelling. The case of indirect gasification of wood pellets in the Chalmers 2–4-MW indirect gasifier is used to exemplify the findings. The experimental investigation shows that char segregation strongly decreases as the excess velocity is increased over a certain threshold. The larger the char particle, the higher is the threshold fluidization velocity above which the char particle becomes immersed in the dense bed. The model shows that the degree of char conversion in the gasification chamber of an indirect gasifier decreases strongly as the fluidization velocity is increased, due to the decrease in the fuel residence time caused by enhanced lateral mixing. Neglecting the effect of fuel axial mixing on the gasification rate results in modelled char conversion degrees up to 1.3 times higher than when axial mixing is accounted for. This impact of fuel axial mixing increases with the solids cross-flow. While both axial and lateral mixing affect the degree of char conversion in the indirect gasification chamber studied, the effect of fuel lateral mixing is much stronger than that of fuel axial mixing, for the conditions investigated in the present work.
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