| 1. |
- Farha, Munavara, 1995, et al.
(författare)
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Characterization of the solids crossflow in a bubbling fluidized bed
- 2024
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Ingår i: Powder Technology. - 1873-328X .- 0032-5910. ; 443
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Tidskriftsartikel (refereegranskat)abstract
- The horizontal transport of solids in bubbling fluidized beds that have a solids crossflow is characterized by applying magnetic tracer measurements and modeling techniques to determine: the contributions of convective and dispersive forms of transport of solids; the residence time distributions of the solids; the feasibility of achieving a plug-flow or well-stirred tank behavior of the solids flow; and the overall fluidization quality. The latter is quantified by determining the extent of de-fluidized zones under varying operational conditions. The experiments are conducted in a bubbling fluidized bed with different rates of forced horizontal flow of solids, applying different bed heights and fluidization velocities. The setup is designed and operated in accordance with Glicksman's full set of scaling laws for fluidized beds, allowing scaling-up of the results to hot, large-scale conditions that resembling, for example, indirect gasification. The assessment of horizontal solids flow involves the sampling of a ferromagnetic tracer using impedance measurements at distinct locations within the bed to: i) fit the convection-dispersion transport equation and, thereby, determine the horizontal dispersion coefficient and velocity of the solids; and ii) feed a deconvolution routine for studying reduced-order (simplified) representations of the solids flow through compartment models. The results from the fitting to the convection-dispersion equation show a strong and close-to-linear correlation between the horizontal solids dispersion coefficient and the forced horizontal solids velocity. This strong interdependency may be attributable to increased shear-related mixing at higher bed-wall shear rates, and it implies a greater challenge linked to attaining a convection-controlled (plug flow) pattern for the solids crossflow. The residence time distributions obtained reveal the limitations of the convection-dispersion equation in providing a general description of the solids flow. Compartment model fitting, when applied to the observed residence time distributions, reveals that an increase in solids crossflow or, to a lesser extent, increased bed height leads to improved fluidization quality.
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| 2. |
- Karlsson, Sebastian, 1994, et al.
(författare)
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Cost-optimal CO 2 capture and transport infrastructure—A case study of Sweden
- 2024
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Ingår i: International Journal of Greenhouse Gas Control. - 1750-5836. ; 132
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Tidskriftsartikel (refereegranskat)abstract
- This work applies a mixed integer cost-minimisation model to identify cost-optimal carbon capture and storage (CCS) infrastructure systems. The modelling applies two types of incentives for CCS implementation: carbon pricing, and binding emissions budgets. Both incentive schemes are applied with and without accounting for CO2 capture from biogenic emissions sources. In the case of CO2 pricing, biogenic CO2 capture is implemented by letting each ton of biogenic CO2 captured generate value for the model equivalent to the cost of emitting one ton of fossil CO2. In the case of emissions budgets, biogenic CO2 capture is included by allowing the model to use both biogenic and fossil CO2 capture to stay within the budget. The main fossil and biogenic emissions sources in Swedish industry are used as a case study. The results show that incentivising carbon removal has a significant impact on the design and development of the cost optimal system for CCS if there are suitable biogenic emission sources available for implementing biogenic CO2 capture. The timing for investments in carbon capture is highly dependent on the discount rate - increasing the discount rate in the modelling from 5 % to 15 % delays the first investments in CO2 capture by three years. To facilitate technology development and timely implementation of CCS on biogenic and fossil sources, it is important to consider that inclusion of carbon dioxide removal into the policy regime controlling fossil fuel emissions, might result in that the cost optimal strategy will be a delay in fossil fuel mitigation.
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| 3. |
- Ullmark, Jonathan, 1993, et al.
(författare)
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Potential Revenue from Reserve Market Participation in Wind Power- and Solar Power-Dominated Electricity Grids: The Near-Term, Mid-Term, and Long-Term
- 2024
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Ingår i: International Journal of Energy Research. - 1099-114X .- 0363-907X. ; 2024
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Tidskriftsartikel (refereegranskat)abstract
- As electricity systems become increasingly dominated by variable inverter-based generation (such as wind and solar photovoltaics (PV)), additional sources of variability appear, while the share of dispatchable thermal power plants decreases. Maintaining a stable grid frequency requires new sources of inertia to slow the frequency changes, as well as new sources of reserve power to counter the imbalances. This work uses a linear optimization modeling approach to analyze the reserve market of the electricity system during the transition to a carbon-free system with high shares of variable electricity generation. The modeling is performed for three regional contexts and with varying degrees of available flexibility technologies. As for the reserve supply, batteries, electrolyzers, electric boilers and heat pumps for district heating, curtailed wind and solar power, and hydropower and thermal power plants are all included. The results indicate that of these suppliers of reserves, the introduction of grid-scale batteries into the system drastically reduces the reserve market size. Only early in the transition is revenue from the reserve market greater than 5% of the total revenue for any technology. While the demand for reserves increases as the share of solar PV and wind power increases, the modeling reveals that access to flexible loads, storage units, and emulated inertia from wind power also increases. Depending on the choice of flexibility measures available, demand-side participation could play a major role in minimizing the cost of grid stability in the future.
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| 4. |
- Wu, Wanqiang, 1992, et al.
(författare)
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Radar-based measurement of solids back-mixing in the freeboard of a circulating fluidized bed
- 2024
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Ingår i: Chemical Engineering Journal. - 1385-8947. ; 488
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Tidskriftsartikel (refereegranskat)abstract
- This work investigates solids back-mixing in the freeboard of a circulating fluidized bed based on THz-radar measurements of the concentrations and velocity distributions of the solid particles along the height of the riser. These data allow height-resolved closure of the solids mass balance and, thereby, quantification and further insight of the two main mechanisms for the back-mixing of the solids entrained from the bottom region of the fluidized bed: (i) solids disengagement and backmixing within the core region of the riser cross-section,; and (ii) solids lateral transfer of from the core region to the wall layers. The experiments were carried out in a circulating fluidized bed riser (3.1 m in height and 0.45 m2 in cross-section), which was operated with Geldart B solids fluidized with air at room temperature and for different gas velocities. The experimentally-derived data are expressed in terms of the disengagement rate and a lateral core-to-wall layer mass transfer coefficient. From the results, it is estimated that the presence of disengagement-based solids back-mixing is significant all along the 3-m riser. The disengagement rate shows a non-linear dependency on the solids concentration, with the lateral solids transfer to the walls (which follows a linear dependency on the solids concentration) eventually becoming the dominant form of back-mixing at upper heights.
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| 5. |
- Yu, Hyunkyo, 1991, et al.
(författare)
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Combining techno-economic modeling and spatial analysis for heat planning in rural regions: A case study of the Holbæk municipality in Denmark
- 2024
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Ingår i: Smart Energy. - 2666-9552. ; 14
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Tidskriftsartikel (refereegranskat)abstract
- This study examines the opportunities and challenges related to heat decarbonization in rural municipalities by applying a spatial analysis in combination with techno-economic modeling using TIMES. While the transition to low-carbon heating technologies is progressing in urban areas, this shift is happening more slowly in rural areas, reflecting a difference in decarbonization rate between urban and rural contexts. This study takes the Holbæk Municipality in Denmark as a case to investigate the potential for rural heating systems considering local fuels, excess heat, and investments in different energy infrastructures. The technology options investigated include both individual heating technologies, such as domestic boilers and heat pumps, and district heating. The modeling results demonstrate that use of excess heat from the municipal wastewater treatment plant and the neighboring industrial site for district heating competes with individual heating systems that have heat pumps and biogas-fueled boilers, where the mix depends on the conditions assumed for each technology and the heat demand density. The extent of district heating expansion differs between districts in the municipality, ranging from 14% to 100% depending on the heat demand density and proximity to the current district heating network. The different possibilities for the transition of the heating sector revealed in this work indicate that a successful transition will require both a clear policy for the heating sector and an explicit decarbonization strategy for the industries that can provide excess heat for district heating.
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