| 1. |
- Ahlström, Johan, 1990, et al.
(författare)
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Bark as feedstock for dual fluidized bed gasifiers. Operability, efficiency, and economics
- 2019
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Ingår i: International Journal of Energy Research. - : Hindawi Limited. - 1099-114X .- 0363-907X. ; 43:3, s. 1171-1190
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Tidskriftsartikel (refereegranskat)abstract
- The demand for biofuels and biochemicals is expected to increase in the future, which will in turn increase the demand for biomass feedstock. Large gasification plants fueled with biomass feedstock are likely to be a key enabling technology in a resource-efficient, bio-based economy. Furthermore, the costs for producing biofuels and biochemicals in such plants could potentially be decreased by utilizing inexpensive low-grade residual biomass as feedstock. This study investigates the usage of shredded tree bark as a feedstock for the production of biomethane in the GoBiGas demonstration plant in Gothenburg, Sweden, based on a 32 MWth industrial dual fluidized bed gasification unit. The plant was operated with bark feedstock for 12 000 hours during the period 2014 to 2018. Data from the measurement campaign were processed using a stochastic approach to establish the plant's mass and energy balances, which were then compared with operation of the plant with wood pellets. For this comparison, an extrapolation algorithm was developed to predict plant performance using bark dried to the same moisture content as wood pellets, ie, 8%w.b. Plant operation with bark feedstock was evaluated for operability, efficiency, and feedstock-related cost. The gas quality achieved during the test period was similar to that obtained for operation with wood pellets. Furthermore, no significant ash sintering or agglomeration problems were observed more than 750 hours of operation. The calculated biomass-to-biomethane efficiency is 43% to 47% (lower heating value basis) for operation with wet bark. However, the predicted biomass-to-biomethane efficiency can be increased to 55%–65% for operation with bark feedstock dried to 8% moisture content, with corresponding feedstock costs in the range of 24.2 to 32.7 EUR/MWh; ie, a cost reduction of about 40% compared with wood pellets.
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| 2. |
- Alamia, Alberto, 1984, et al.
(författare)
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Performance of large-scale biomass gasifiers in a biorefinery, a state-of-the-art reference
- 2017
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Ingår i: International Journal of Energy Research. - : Hindawi Limited. - 1099-114X .- 0363-907X. ; 41:14, s. 2001-2019
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Tidskriftsartikel (refereegranskat)abstract
- The Gothenburg Biomass Gasification plant (2015) is currently the largest plant in the world producing biomethane (20 MWbiomethane) from woody biomass. We present the experimental data from the first measurement campaign and evaluate the mass and energy balances of the gasification sections at the plant. Measures improving the efficiency including the use of additives (potassium and sulfur), high-temperature pre-heating of the inlet streams, improved insulation of the reactors, drying of the biomass and introduction of electricity as a heat source (power-to-gas) are investigated with simulations. The cold gas efficiency was calculated in 71.7%LHVdaf using dried biomass (8% moist). The gasifier reaches high fuel conversion, with char gasification of 54%, and the fraction of the volatiles is converted to methane of 34%mass. Because of the design, the heat losses are significant (5.2%LHVdaf), which affect the efficiency. The combination of potential improvements can increase the cold gas efficiency to 83.5%LHVdaf, which is technically feasible in a commercial plant. The experience gained from the Gothenburg Biomass Gasification plant reveals the strong potential biomass gasification at large scale.
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| 3. |
- Baskakov, A.P., et al.
(författare)
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Complex Heat Transfer in Furnaces with a Circulating Fluidized Bed
- 2001
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Ingår i: Heat Transfer Research. - 1064-2285. ; 37:7-8, s. 343-348
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Tidskriftsartikel (refereegranskat)abstract
- Intensity of heat transfer to screen surfaces in the furnaces with a circulating fluidized bed (CFB) is determined by both radiation and convection of particles. Due to the formation of a thermal boundary layer near the screens the role of radiation decreases and that of convection increases with an increase in concentration of particles in the furnace. Generalization of the data obtained in pilot-full-scale and industrial furnaces with a CFB allowed one to obtain a simple empirical dependence of the furnace-mean coefficient of heat transfer α (W/(m2·K) on the volumetric-mean concentration of particles c (kg/m3): α = 85·c0.3.
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| 4. |
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| 5. |
- Breitholtz, Claes, 1967, et al.
(författare)
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Heat balance over the fluid-dynamic boundary layer of a circulating fluidized bed furnace
- 1998
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Ingår i: International Journal of Heat and Mass Transfer. - 0017-9310. ; 41:8-9, s. 1013-1024
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Tidskriftsartikel (refereegranskat)abstract
- A heat balance over the fluid-dynamic boundary layer of a circulating fluidized bed furnace hasbeen formullated in order to calculate the heat transfer to the walls. The convective heat transfer is relatedto a horizontal particle flow from the core to the wall region, and an additive radiative heat transferconstituent is calculated for the particulate medium. An empirical description of the vertical distributionof solids and the transversal temperature profile are needed for the evaluation. The calculated heat transfercoefficients were compared with measurements in three commercial boilers and the deviation was less than40%, which is in the same order as the uncertainty of the experimental data.
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| 6. |
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| 7. |
- Breitholtz, Claes, 1967
(författare)
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Heat Transfer in Circulating Fluidized Bed Boilers
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Heat transfer to single particles in the transport zone of circulating fluidized beds and heat transfer to membrane tube walls have been investigated. The heat transfer coefficient to spheres in the transport zone of a circulating fluidized bed boiler has been measured with dark and light calorimeters. A model was developed for the heat transfer mechanisms involved: radiation, gas and particle convection. The model predicts the measured data within 30 %. The gas convective constituent is 50% larger than in a single-phase non turbulent flow, which is explained by turbulence induced by bubbles in the bottom bed. The heat transfer model and a correlation for mass transfer were used to calculate the temperature of burning char particles. The calculation confirmed previous measurements, showing particle temperatures of several hundred degrees above the average bed temperature. Heat transfer from the core to the wall-layer was investigated by a heat balance of the wall-layer. It was found that the computation underestimates the measurements with in average 25%. This is explained by a horizontal in-flow and out-flow of particles, instead of the net-flow used in the model. Heat transfer and suspension density data from circulating fluidized bed boilers were averaged over the entire heat transfer surface of the furnace. The averaged data forms the basis for a correlation, which estimates the heat transfer coefficient with a standard deviation of 15 %. An attempt to separate radiation from convection was made, but it did not improve the accuracy of the correlation. Heat transfer experiments in a laboratory unit under thermally scaled conditions has been investigated theoretically and experimentally. Criteria for thermal similarity were derived from the energy equations of gas and particles. It was found that the ratio of the heat capacity of the particles and the gas should be constant in addition to the fluid-dynamic scaling. Measurements in a boiler and a scaled laboratory rig showed that the Nusselt number was not the same in the two units. However, the heat transfer coefficients from the two units coincided if they were compensated for the difference in thermal conductivity of the gas.
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| 8. |
- Breitholtz, Claes, 1967, et al.
(författare)
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Heat transfer in circulating fluidized bed boilers - do we know sufficiently?
- 1997
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Ingår i: Trends in heat mass and momentum transfer. - 0973-2446. ; 3, s. 85-104
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Tidskriftsartikel (refereegranskat)abstract
- A considerable amount of work, mostly measurements, has been dedicated to heat transfer in circulating fluidized bed combustors. The results show that the radiative constituent of heat transfer varies between limits depending on the optical thickness of a particle boundary layer, and that the convective constituent can be related to the average cross-sectional suspension density. Based on this information reasonable estimates of heat transfer coefficients can be made. Experimental data from boiler conditions and ambient conditions are compared introducing a compensation for thermal radiation and changes in the properties of the gas with temperature. A good agreement is achieved between the two sets of data, except for cross-sectional average suspension densities below about 5 kg/m3. Locally there is a variation in heat transfer across the membrane-tube wall, and the heat transfer to the tube crest can be twice that to the adjacent fin. Heat transfer models are reviewed and applied to a hot (boiler) case and a cold (laboratory) case. The deviation of computed heat transfer coefficients from the measured ones was larger than the scatter in the measured data. The differences in the results from the models are primarily explained by uncertainties in the fluid-dynamic model parameters. For refined estimates and optimisation, knowledge of the detailed behaviour of the fluid-dynamics of the combustor is necessary. In this field the thickness of the a gas-gap between wall and particle suspension, the cover factor of the time-resolved fluctuating particle concentration, and the in-flow of particles towards the wall are insufficiently known and further work is necessary. In addition, further work is needed concerning the local heat transfer to membrane-tube walls
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| 9. |
- Breitholtz, Claes, 1967, et al.
(författare)
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Translation of Heat Transfer Measurements from Laboratory CFBs to the Conditions of CFB-Boilers
- 2003
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Ingår i: Heat Transfer Research. - 1064-2285. ; 34:3-4, s. 252-269
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this work is to find a method for translation of heat transfer data from cold laboratory units to boiler conditions. From a compilation of existing data on heat transfer to walls in hot and cold circulating fluidized beds it is concluded that the results can be translated approximately by compensating for changes in the thermal conductivity of the gas and thermal radiation. A more general methodology is developed by deriving the criteria for thermal similarity. The only criterion that was added to those for fluid-dynamic similarity was the ratio of heat capacity of gas and particles. The thermal scaling is tested by comparing heat transfer measurements in a boiler with measurements in a scaled laboratory model. The results show that the Nusselt numbers were not the same in the boiler and the scaled model, which can be a result of the characteristic length-scale chosen, a too low heat capacity of the scaled particles or a failure to scale the local fluid-dynamics at the wall.
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| 10. |
- Breitholtz, Claes, 1967, et al.
(författare)
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Translation of heat transfer measurements from laboratory CFBs to the conditions of CFB-boilers
- 2000
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Ingår i: IV Minsk Int Heat and Mass Transfer Forum,. / V.A. Borodulya, Teplitsky, J.C., Vinogradov, L.M., Palchonok, G.I.. - 9856456126 ; 6, s. 12-23
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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