| 1. |
- Benavides, Aldo, 1978, et al.
(författare)
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Comparison of experimental and simulation results for turbulent gas-solid riser flow
- 2008
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Ingår i: Circulating Fluidized Bed Technology IX. Proceedings of the 9th International Conference on Circulating Fluidized Beds, CFB-9. May 13-16, 2008. Hamburg, Germany..
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Konferensbidrag (refereegranskat)abstract
- This paper compares measurements of the radial solids concentration in a riser with CFD simulations. An Eulerian model based upon the kinetic theory for granular flow, extended with models describing turbulence modulation and dispersion, is used to treat the particulate phase. Coupling between momentum equations of the gas and particulate phases is taken into account via a mean drag force formulation. Solids distribution profiles over three horizontal planes are measured by the use of optical probes. The pressure drop is used to estimate an average solids concentration profile along the riser. The comparison is reported for a single superficial gas velocity and solids mass flux.
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| 2. |
- Derda, Patrycja, et al.
(författare)
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Fate of Alkali Metals during Co-Combustion of Biodiesel Residues with Coal in a Semi-Industrial CFB Boiler
- 2008
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Ingår i: 9th International Conference on Circulating Fluidized Beds, CFB 2008, in Conjunction with the 4th International VGB Workshop on Operating Experience with Fluidized Bed Firing Systems; Hamburg; Germany; 13 May 2008 through 16 May 2008. - 9783930400577
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Konferensbidrag (refereegranskat)abstract
- The use of biodiesel, especially of Rapeseed Methyl Ester (RME), has recently increased inthe European countries. This gives rise to an increasing amount of after production residues. Rapeseedcake is the main residue of the RME production process, and may become available in large amounts forenergy recovery. Since rapeseed cake contains high levels of alkali metals, it may cause bedagglomeration, deposit formation and corrosion upon combustion in fluidized beds.This paper presents the fate of alkali metals formed during co-combustion of coal and up to 25% ofrapeseed cake pellets in a 12 MW Circulating Fluidized Bed Boiler at Chalmers University ofTechnology (Sweden). Standard fuel analyses combined with sequential leaching and SEM/EDX, showedthe alkali entering the boiler. Gaseous emissions, bed samples, fly ash and deposits were analyzed inorder to monitor the alkali metals distribution. Gaseous alkali chlorides were measured upstream from theconvective pass at a flue gas temperature of 800 oC using an In-situ Alkali Chloride Monitor (IACM). Inthe same location, deposits were collected on a deposit probe fitted with rings for SEM/EDX analysis.Re-circulated bed material was analyzed as well.Two-day tests showed successful co-firing of up to 25% rapeseed cake on energy basis in the semiindustrialfluidized-bed boiler. Alkali metals were enriched in fly ash. No significant difference could benoticed in the distribution of alkali metals when increasing the share of rapeseed cake from 15% to 25%on energy basis. In the near future, further studies will be carried out to determine the influence oflimestone on the performed tests.
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| 3. |
- Gómez Barea, Alberto, et al.
(författare)
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Conversion of char in CFB gasifiers
- 2008
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Ingår i: Circulating Fluidized Bed Technology IX. - 9783930400577 ; 9, s. 727-732
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Konferensbidrag (refereegranskat)
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| 4. |
- Kassman, Håkan, et al.
(författare)
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Nitrogen containing additives for simultaneous reduction of KCL and NOx during biomass combustion in a CFB boiler
- 2008
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Ingår i: 9th International Conference on Circulating Fluidized Beds, CFB 2008, in Conjunction with the 4th International VGB Workshop on Operating Experience with Fluidized Bed Firing Systems; Hamburg; Germany; 13 May 2008 through 16 May 2008. - 9783930400577 ; , s. Paper 14_13-
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Konferensbidrag (refereegranskat)abstract
- High levels of alkali chlorides in the flue gas can cause enhanced deposit formation and superheater corrosion during combustion of biofuels. These alkali chlorides mainlyoriginate from potassium chloride (KCl). A challenge during combustion of biofuels is to simultaneously reduce NOx and KCl. The ChlorOut concept has been developed by Vattenfallto minimise deposit formation and corrosion. It consists of IACM, an instrument for on-line measurements of gaseous alkali chlorides, and a sulphate-containing additive that converts alkali chlorides to less corrosive alkali sulphates. The sulphate-containing additive is oftenammonium sulphate, (NH4)2SO4, and, therefore, a significant NOx reduction is also achieved.This paper presents the results from a comparison of the conventional SNCR additives (ammonia or urea) and (NH4)2SO4 for reduction of NOx and/or KCl during combustion in a CFB boiler. The fuel consisted of either a mixture of wood chips and wood pellets with added PVC or with straw pellets. Of special interest was the influence of sulphation of KCl in parallel to the reduction of NO and if these processes interact. The results show that there are rather small differences in performance concerning NOx reduction between the additives.
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| 5. |
- Leckner, Bo G, 1936
(författare)
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The role of CFB in co-combustion
- 2008
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Ingår i: Circulating Fluidized Bed Technology IX. - 9783930400577 ; 9, s. 827-832
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Konferensbidrag (refereegranskat)abstract
- Co-combustion is an advantageous way to use biofuels and wastes for energy purposes and CFB is a suitable combustion device for this purpose because of its fuel flexibility and its capacity in receiving various fuels with less preparatory treatment than other devices. An overview over methods of CFB co-combustion is made. The impact of the heat balance, ash properties and other influencing factors is discussed.
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| 6. |
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| 7. |
- Pallarès, David, 1975, et al.
(författare)
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A comprehensive model of CFB combustion
- 2008
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Ingår i: 9th International Conference on Circulating Fluidized Beds, CFB 2008, in Conjunction with the 4th International VGB Workshop on Operating Experience with Fluidized Bed Firing Systems; Hamburg; Germany; 13 May 2008 through 16 May 2008. - 9783930400577
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Konferensbidrag (refereegranskat)abstract
- This paper presents a new comprehensive model for circulating fluidized bed boilers to be used to support design and scale up as well as a learning tool of the process. The model covers the entire circulating loop and provides a 3-dimensional description of the in-furnace processes in mixing, combustion and heat transfer. The model is unique in that the input data are limited to operational data and that a large number of experimental boiler data has been used to verify the different submodels as well as the overall model.The model is built up by combination of several submodels, each covering main phenomena in the three key fields of CFB boiler modeling: fluiddynamics including gas and solids mixing, char and gas combustion and heat transfer. The modeling of the gas mixing (which governs the gas combustion, assumed to be transport controlled) has a dynamical basis in the modeled fluctuations in velocity and concentration values of the gas phase originating from the dense bottom bed dynamics. This unique feature enables verification of the model by means of time-averaged gas concentration measurements also in the lower region of the furnace. Such measurements sense fluctuations between high-velocity oxidizing gas phase and low velocity oxygen lean phase, yielding results biased towards low oxygen concentrations. The model includes phenomena such as solids backflow effect at the riser exit and corner effects in wall layers and can handle input data on fuel fragmentation. Model main output data consists of spatial distributions of the following parameters: pressure, temperature, heat flux, concentration and flow of main gas species and solid fractions (i.e. inert solids and fuel particles) and particle size distribution of solid fractions. The model gives generally good agreement with experiments from large CFB units for which required input data is available.
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