| 1. |
- Berdugo Vilches, Teresa, 1985, et al.
(författare)
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Behaviour of biomass particles in a large scale (2-4MWth) bubbling bed reactor
- 2015
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Ingår i: WIT Transactions on Engineering Sciences- Computational methods in multiphase flow VIII. - 9781845649463 ; 89, s. 151-160
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Biomass is regarded as an interesting fuel for energy-related processes owing to its renewable nature. However, the high volatile content of biomass adds a number of difficulties to the fuel conversion and process operation. In the context of fluidized bed reactors, several authors have observed that devolatilizing fuel particles tend to float on the surface of a gas-fluidized bed of finer solids. This behaviour, known as segregation, leads to undesired effects such as poor contact between volatiles and bed material. Previous investigations on segregation of gas-emitting particles in fluidized beds are conducted in small units and they are often operated at rather low gas velocities, typically between the minimum fluidization velocity (umf) and 2·umf. Therefore, it is not known to what extent such results are of relevance for industrial scale units and for higher fluidization velocities that are commonly used in large bubbling beds. In this work the behaviour of biomass particles in a large scale bubbling bed reactor is investigated. Tests were conducted at a wide range of fluidization velocities with three different bed materials of varying particle size and density. The fuel was wood pellets and the fluidization medium was steam, which makes the findings relevant for indirect gasification, chemical looping combustion (CLC) and bubbling bed combustion applications. The experiments were recorded by means of a digital video camera and the digital images were subsequently analysed qualitatively. The results show high level of segregation at fluidization velocity up to 3.5umf. Beyond this point fuel mixing was significantly enhanced by increasing fluidization velocities. At the highest fluidization velocity tested (i.e. >8umf), a maximum degree of mixing was achieved.
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| 2. |
- Olsson, Jens, et al.
(författare)
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Experimental evaluation of the lateral mixing of fuel in a fluidized bed with cross-flow of solids - influence of tube banks
- 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. 119-124
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Konferensbidrag (refereegranskat)abstract
- This work investigates the lateral fuel mixing in fluidized beds with a crossflow of solids by means of experiments in a fluid-dynamically downscaled unit of the Chalmers indirect biomass gasifier. Fuel lateral mixing is expressed as the combined effect of fuel dispersion and drag from the solids cross flow, and the work evaluates quantitatively these two effects at two different fluidization velocities. In addition, the work investigates the influence of a bank of horizontal tubes. It is found that there is a significant increase in both lateral fuel dispersion and drag of the fuel particles with fluidization velocity. Furthermore, the two mechanisms for lateral fuel mixing are drastically lowered by the insertion of the tube bank.
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| 3. |
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| 4. |
- Sette, Erik, 1984, et al.
(författare)
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3-dimensional particle tracking in a fluid-dynamically downscaled fluidized bed using magneto resistive sensors
- 2015
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Ingår i: The 8th International Symposium on Coal Combustion.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents a measurement technique for continuous tracking of particles in 3-dimensional bubbling fluidized beds operated according to scaling laws. By applying Glicksman’s full set of scaling laws to both bulk solids and tracer particle the bed is assumed to be fluid-dynamically similar to a combustor operated at 900 °C with the tracer particle corresponding to a fuel particle with properties similar to anthracite coal. Two different gas distributors with varying pressure drop are used to investigate the influence of bed design on fuel mixing.Flow structures formed around rising gas bubbles, so called bubble paths, are identified and the tracer particle traverses the entire bed for a gas distributor yielding a high pressure drop. For a gas distributor yielding a low pressure drop flow structures are less pronounced and the tracer particle is not circulating the entire bed.
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| 5. |
- Sette, Erik, 1984, et al.
(författare)
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3-Dimensional Particle Tracking in a Fluid Dynamically Downscaled Fluidized Bed Using Magnetoresistive Sensors
- 2016
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Ingår i: Clean Coal Technology and Sustainable Development. Proceedings of the 8th International Symposium on Coal Combustion (ISCC). Tsinghua Univ, Beijing, Peoples rep of China, 19-22 July, 2015. - Singapore : Springer Singapore. - 9789811020223 ; 0, s. 317-322
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Konferensbidrag (refereegranskat)abstract
- This paper presents a measurement technique for continuous tracking of particles in 3-dimensional bubbling fluidized beds operated according to scaling laws. By applying Glicksman's full set of scaling laws to both bulk solids and tracer particle, the bed is assumed to be fluid dynamically similar to a combustor operated at 900 C-circle with the tracer particle corresponding to a fuel particle with properties similar to anthracite coal. Two different gas distributors with varying pressure drop are used to investigate the influence of bed design on fuel mixing. Flow structures formed around rising gas bubbles, the so-called bubble paths, are identified, and the tracer particle traverses the entire bed for a gas distributor yielding a high pressure drop. For a gas distributor yielding a low pressure drop, flow structures are less pronounced, and the tracer particle is not circulating the entire bed.
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| 6. |
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| 7. |
- Sette, Erik, 1984, et al.
(författare)
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ANALYSIS OF LATERAL FUEL MIXING IN A FLUIDDYNAMICALLY DOWN-SCALED BUBBLING FLUIDIZED BED
- 2013
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Ingår i: Fluidization XIV Conference.
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Konferensbidrag (refereegranskat)abstract
- A method to evaluate the lateral mixing process of fuel particles in bubbling fluidized beds is proposed. The method determines the lateral dispersion coefficient of the fuel particles by means of digital image analysis to video recordings of tracer particle measurements in a fluid-dynamically downscaled 3-dimensional cold-flow model. The work applies direct measurements of tracer particles coated with fluorescent paint, which are irradiated with an ultraviolet light emitting lamp, mounted above the bed. The cold-flow model has cross-sectional dimensions of 0.3 m x 0.3 m and can be operatedwith bed heights up to 0.16 m. According to the scaling laws this setup is assumed to fluid-dynamically resemble a bubbling fluidized bed operated at 900°C with crosssectional dimensions of 1.5 m x 1.5 m and bed heights up to 0.8 m. The measurements were made for fluidization velocities ranging from 0.17 to 0.83 m/s (up-scaled). The lateral fuel dispersion coefficient is found to increase with superficial velocity over the entire range of velocities investigated. The results show up-scaled (i.e. at hot conditions) dispersion coefficients ranging from 10-2 to 10-1 m2/s, which is similar to values obtained previously in large-scale bubbling beds under hot conditions.
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| 8. |
- Sette, Erik, 1984, et al.
(författare)
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Camera-probe fuel tracking under industrial fluidized-bed conditions
- 2015
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Ingår i: 22nd International Conference on Fluidized Bed Conversion. ; 2, s. 708-715
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Konferensbidrag (refereegranskat)abstract
- This work presents direct fuel tracking measurements with a camera probe in an indirect fluidized-bed gasifier with a cross-flow of solids operating at 800°C. From the measurements a lateral dispersion coefficient for fuel is determined to be in the order of 10-2 m2/s at the conditions applied (0.2 m/s), which is consistent with the few previous literature data from industrial units. The camera probe used in this work is cooled by several cooling circuits and the temperature was maintained at a level so that condensation on the front lens was avoided. The direct tracking method yields dynamic data on the location of individual fuel particles but the method is obviously limited by the fact that fuel particles can only be tracked when they are at the bed surface. The effect of devolatilizing particles releasing gases which cause them to float at the dense bed surface previously reported in literature is only observed at the lowest fluidization velocity (0.1 m/s) investigated, but is not evident at the higher velocity (0.2 m/s).
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| 9. |
- Sette, Erik, 1984, et al.
(författare)
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Experimental evaluation of lateral mixing of bulk solids in a fluid-dynamically down-scaled bubbling fluidized bed
- 2014
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Ingår i: Powder Technology. - : Elsevier BV. - 1873-328X .- 0032-5910. ; 263, s. 74-80
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Tidskriftsartikel (refereegranskat)abstract
- An indirect tracking method for bed material using magnetic separation was applied to a fluid-dynamically down-scaled fluidized bed, to evaluate the influences of different parameters on the lateral dispersion coefficients of the bed material. Solutions to the transient diffusion equation were fitted to the experimental data and showed that the dispersion approach could be used to describe the lateral mixing of solids at the macroscopic level. The values obtained for the dispersion coefficient were scaled-up to be relevant to large-scale boilers operated under high-temperature conditions. The scaled-up lateral solid dispersion coefficients were in the order of 10(-2) m(2)/s, i.e., two orders of magnitude greater than those reported in the literature for smaller sized fluidized and/or fluidized beds operated under ambient-temperature conditions. This paper also considers the mixing phenomena at the mesoscopic level, applying the so-called "mixing cell" concept to elucidate how the mixing of solids is dependent upon the flow characteristics around the main bubble paths.
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| 10. |
- Sette, Erik, 1984, et al.
(författare)
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Experimental quantification of lateral mixing of fuels in fluid-dynamically down-scaled bubbling fluidized beds
- 2014
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Ingår i: Applied Energy. - : Elsevier BV. - 1872-9118 .- 0306-2619. ; 136, s. 671-681
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Tidskriftsartikel (refereegranskat)abstract
- This work presents two methods for evaluating the lateral dispersion coefficient in a fluidized bed for three different fuel types, namely wood chips, pellets and char of pellets. Mixing of the different fuels is also related to the mixing of bed material to evaluate to what extent they are correlated. The experimental work is conducted in fluid-dynamically downscaled fluidized beds and the validity of this approach is shown by replicating an experiment presented in literature which was conducted in a large scale boiler.The two methods, a direct one and an indirect one, are shown to yield similar results which suggest that both of them are robust.The wood chips and pellets are found to behave similarly and to follow the flow of bed material well. On the other hand char particles are found to be less influenced by the flow of bed material and char particles are also more sensitive to changes in the pressure drop over the gas distributor compared to wood chips and pellets.
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