| 1. |
- Bonmann, Marlene, 1988, et al.
(författare)
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Sub-millimetre wave range-Doppler radar as a diagnostic tool for gas-solids systems - solids concentration measurements
- 2023
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Ingår i: Advanced Powder Technology. - : Elsevier BV. - 0921-8831 .- 1568-5527. ; 34:1
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Tidskriftsartikel (refereegranskat)abstract
- Current non-intrusive measurement techniques for characterising the solids flow in gas-solids suspensions are limited by the low temporal or low spatial resolution of the sample volume, or in the case of optical methods, by a short range of sight. In this work, a sub-millimetre wave range-Doppler radar is developed and validated for non-intrusive sensing of solids concentrations in a gas-solids particle system with known characteristics. The radar system combines favourable features, such as the ability to see through at optical frequencies opaque materials, to measure the local solids velocity and the reflected radar power with a spatial resolution of a few cubic centimetres over distances of a few metres. In addition, the radar hardware offers flexibility in terms of installation. After signal processing, the output of the radar is range-velocity images of the solids flowing along the radar’s line-of-sight. The image frame rate can be close to real-time, allowing the solids flow dynamics to be observed. While the well-established Doppler principle is used to measure the solids velocity, this paper introduces a method to relate the received radar signal power to the solids volumetric concentrations (cv) of different particulate materials. The experimental set-up provides a steady stream of free-falling solids that consist of glass spheres, bronze spheres or natural sand grains with known particle size distributions and with particle diameters in the range of 50–300 µm. Thus, the values of cv found using the radar measurements are validated using the values of cv retrieved from closure of the mass balance derived from the measured mass flow rate of the solids stream and the solids velocity. The results show that the radar system provides reliable measurements of cv, with a mean relative error of approximately 25 % for all the tested materials, particle sizes and mass flow rates, yielding values of cv ranging from 0.2 × 10-4 m3/m3 up to 40 × 10-4 m3/m3 and solids velocities within the range of 0–4.5 m/s. This demonstrates the ability of the radar technology to diagnose the solids flow in gas-solids suspensions using a unique combination of penetration length, accuracy, and spatial and time resolution. In future work, the radar technique will be applied to study non-controlled solids flow at a larger scale, and to understand flow conditions relevant to industrial reactor applications, e.g., fluidised bed, entrained flow, and cyclone units.
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| 2. |
- Farha, Munavara, 1995, et al.
(författare)
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Assessment of experimental methods for measurements of the horizontal flow of fluidized solids under bubbling conditions
- 2023
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Ingår i: Fuel. - 0016-2361. ; 348
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Tidskriftsartikel (refereegranskat)abstract
- Dual fluidized bed systems are indispensable for future energy systems that require solids cycling between different atmospheres. However, controlling the residence time of solids in the reactor, which is crucial for controlling the heat and mass transfer of the fuel, is a significant challenge. This study investigates four experimental techniques to quantify the horizontal flow of solids fluidized under bubbling conditions: integral mass accumulation; differential mass accumulation; thermal tracing; and magnetic solids tracing. Integral mass accumulation entails collecting bed material using a defluidized box within a given time period. Differential mass accumulation measures the material accumulation rate in a section of the bed that is monitored using pressure measurements. Thermal tracing calculates the solids flow rate by solving the heat balance to match the temperature field captured by a thermographic camera. Magnetic solids tracing involves injecting a batch of magnetic tracer solids into the reactor and then measuring the residence time distribution using impedance coils. The experiments were conducted under down-scaled conditions that resemble large-scale operations with a length scaling factor of 0.12. For this study, three operational parameters were varied: the fixed bed height; the volumetric flow rate of the conveying air; and the fluidization velocity in the bed. The horizontal solids circulation rates achieved ranged from 1.7×10−4 to 10 kg/m·s, corresponding to 1.2×10−3 to 70 kg/m·s on a hot up-scaled basis, which is a relevant range to indirect biomass gasification in an industrial setting. The three selected operational parameters led to increases in the horizontal solids flow. While all four methods replicated the trends, quantitative variations in the measured circulation rates occurred due to the inherent characteristics of the methods. High circulation rates resulted in a continuous decrease in the solids inventory, leading to an underestimation of the circulation rate when using the integral mass accumulation method. The accuracy of the differential mass accumulation method relied on transient pressure measurements, which were less-effective at low solids flow rates. Conversely, the accumulation time required for pressure measurements was reduced at high circulation rates, resulting in uncertainties in the analysis. The accuracy of the thermal tracing method decreased drastically with higher solids circulation, resulting in an overestimation of the circulation rate. Moreover, low circulation rates adversely affected the accuracy of the magnetic solids tracing by producing barely discernible tracer concentration gradients.
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| 3. |
- Guío-Pérez, Diana Carolina, 1985, et al.
(författare)
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Effective drag on spheres immersed in a fluidized bed at minimum fluidization—Influence of bulk solids properties
- 2023
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Ingår i: Canadian Journal of Chemical Engineering. - : Wiley. - 1939-019X .- 0008-4034. ; 101:1, s. 210-226
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Tidskriftsartikel (refereegranskat)abstract
- The aims of this work are to elucidate the effects that bulk solids properties have on the effective drag experienced by large spheres immersed in an emulsion of group-B solids under minimum fluidization conditions and to analyze the ways in which the different suspensions react towards different applied shear rates. To investigate this, magnetic particle tracking was applied to resolve the trajectory of falling-sphere measurements in which the size, density, and sphericity of the bulk solids were varied as well as the size and density of the spherical tracers. The resulting experimental scope included both rising and sinking tracers as well as full segregation and in-bed stagnation of the tracers. The set-up provided highly resolved tracer trajectories, from which the drag experienced by the sphere can be calculated. For sinking tracers, the results showed that an increase in bulk solids size, angularity, and density reduced the terminal velocity of the sphere. This effect correlated well with the bed expansion and Hausner ratio, indicating that a reduced void space among the bulk solids is the main reason for the increase in motion resistance. At lower shear rates, namely, during the de-acceleration towards the stagnant state, beds of larger, more angular, or denser bulk solids yield lower levels of shear stress. The angle of repose of the bulk solids correlated with the rate at which the emulsion thins with increasing shear rate. For rising tracers, shear stress did not show any significant dependency on the properties of the bulk solids.
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| 4. |
- Guio Perez, Diana Carolina, 1985, et al.
(författare)
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Experimental investigation of the lateral mixing of large and light particles immersed in a fluidized bed
- 2023
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Ingår i: Fuel. - 0016-2361. ; 346
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Tidskriftsartikel (refereegranskat)abstract
- Fluidized bed reactors for solid fuel conversion are characterized by the presence of a small fraction of fuel particles that are significantly larger (usually 1–2 orders of magnitude larger) and lighter (2–20-fold less dense) compared to the bulk solids. This difference in physical properties strongly influences the mixing of the fuel particles and therefore affects the mass, momentum and heat transfers between the fuel particles and the surrounding bed. This work uses Magnetic Particle Tracking (MPT) to acquire highly resolved trajectories for single tracer particles immersed in a bubbling fluidized bed operated under ambient conditions and with a cross-sectional area of 0.45 m2. This bed size is sufficiently large to abrogate the influence of the reactor walls, allowing data post-processing to study the free movement of the tracer particle, which has not been available to date. This required the enhancement of the MPT system from that in previous works: 12 sensors and a communication protocol in series are here applied, which showed good performance in both spatial accuracy (1 mm) and time resolution (100 Hz). The bed material used in the experiments was glass beads (mean particle size of 106 µm, particle density of 2,486 kg/m3). Two different tracer particles, with diameters of 18 mm but with different densities (572 kg/m3 and 1,015 kg/m3) were used to mimic the sizes and densities of the solid fuel particles. Fluidization velocity was varied within 0.2–0.7 m/s and two fixed bed heights (50 mm and 130 mm) were tested. Based on the trajectories, dispersion coefficients were calculated for quantitative evaluation of the solids mixing. The results reveal that increased bed height yields higher dispersion coefficients with a higher sensitivity for fluidization velocity. The properties of the tracer particles appear, within the tested range, to exert little impact on its lateral dispersion. From the velocity maps generated, a swirling pattern was observed in the vicinity of the walls, while zones of preferential ascendent or descendant movement were observed in the cross-section centre, although clearly defined mixing cells were not exhibited.
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| 5. |
- Guio Perez, Diana Carolina, 1985, et al.
(författare)
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Radar-based measurements of the solids flow in a circulating fluidized bed
- 2023
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Ingår i: Fuel. - 0016-2361. ; 345
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this work is to demonstrate the value of radar technology for studying experimentally the solids flows in gas-solids fluidized beds. The work presents original results regarding the solids concentration and velocity acquired in a non-intrusive manner from a cold flow model. The tailored radar setup operates at submillimeter wave frequencies (0.34 THz) and can measure the location of solids with a spatial resolution of 1/8 mm−1 in the direction of the radar beam, and of 40–60 mm across the radar beam. The solids velocity in the direction of the beam propagation is determined through measurement of the Doppler shift caused by the reflection of the transmitted radar signal by solids moving in relation to the antenna. The measurements were performed in both the horizontal and vertical directions in the riser of a circulating fluidized bed (cross-sectional area of 0.45 m2 and height of 3.1 m) operated with glass beads (mean particle size of 106 µm, and particle density of 2,486 kg/m3) and using air at ambient temperature as the fluidization agent, with superficial velocities in the range of 0.3–1.3 m/s. The measurements are used to assess the validity of the technique and are not intended to characterize the unit fluid dynamically. The solids concentrations derived from the radar measurements follow the qualitative trends derived from pressure-drop measurements, resembling the expected changes that occur in the concentration profiles as the fluidization velocity increases. Concentrations in the range from 10-6 m3/m3 to 10-1 m3/m3 are measurable. In quantitative terms, for low concentrations of solids (<5·10-3 m3/m3, approximately) the radar measurements exhibited the ability to provide more consistent measurements of the solids concentration than those obtained from pressure transducers, for which the small pressure differences lead to unstable and even negative values for solids concentrations. The two measurement methods were in quantitative agreement for solids volume fractions higher than the threshold. Concentrations ≥ 1·10-1 m3/m3, though measurable, strongly attenuate the radar signal, thereby reducing the beam penetration to a depth of centimeters. For each position along the radar beam, the distribution of solids velocity measured from the Doppler effect was found to be within the expected ranges and allowed observations of solids back-mixing. The radar technique applied in this work is a promising technique for detailed characterization of the solids flow in fluidized beds, offering high spatial and temporal resolutions, allowing the determination of both solids velocity and concentration, and having a reasonably high penetration depth.
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| 6. |
- Guio Perez, Diana Carolina, 1985, et al.
(författare)
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Thermochemical Energy Storage with Integrated District Heat Production—A Case Study of Swede
- 2023
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Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 16:3
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Tidskriftsartikel (refereegranskat)abstract
- The implementation of electricity-charged thermochemical energy storage (TCES) using high-temperature solid cycles would benefit the energy system by enabling the absorption of variable renewable energy (VRE) and its conversion into dispatchable heat and power. Using a Swedish case study, this paper presents a process for TCES-integrated district heating (DH) production, assesses its technical suitability, and discusses some practical implications and additional implementation options. The mass and energy flows of a biomass plant retrofitted with an iron-based redox loop are calculated for nine specific scenarios that exemplify its operation under electricity generation mixes that differ with respect to variability and price. In addition, the use of two types of electrolyzers (low-temperature and high-temperature versions) is investigated. The results show that for the Swedish case, the proposed scheme is technically feasible and capable of covering the national DH demand by making use of the existing DH plants, with an estimated process energy efficiency (electricity to heat) of 90%. The results also show that for a retrofit of the entire Swedish DH fleet, the required inventories of iron are approximately 2.8 Mt for the intermediate scenario, which represents 0.3% and 11.0% of the national reserves and annual metallurgical production rates of the national industry, respectively. In addition to the dispatchable heat, the process generates a significant amount of nondispatchable heat, especially for the case that employs low-temperature electrolyzers. This added generation capacity allows the process to cover the heat demand while decreasing the maximum capacity of the charging side computed herein.
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| 7. |
- Martinez Castilla, Guillermo, 1993, et al.
(författare)
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Calcium looping for combined CO 2 capture and thermochemical energy storage
- 2023
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Ingår i: Circular Economy Processes for CO2 Capture and Utilization: Strategies and Case Studies. - 9780323956680 ; , s. 119-162
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The carbonation of calcium oxide (CaO) has been extensively investigated concerning the separation of CO2 from gaseous streams. The carbonation reaction is of special interest in postcombustion processes for the capture of CO2 since the produced calcium carbonate (CaCO3) can be calcined in a separate reactor to generate a stream of pure CO2 for sequestration and storage. The cycle, which consists of carbonation and calcination reactions, involves considerable heat of reaction, rendering the process relevant not only for CO2 capture but also for energy storage purposes in the form of thermochemical energy storage (TCES). Energy storage is envisioned as an important flexibility measure to increase the penetration of variable renewable electricity (VRE), thereby increasing the value of VRE due to the reduced share of generation that needs to be curtailed. In this chapter, the general characteristics of the calcium looping process for both CO2 capture and energy storage are presented. Thereafter, the process that combines these two features is described, focusing on its layout specifications, associated opportunities and challenges, and the most recent advances toward its development.
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| 8. |
- Martinez Castilla, Guillermo, 1993, et al.
(författare)
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Techno-Economic Assessment of Calcium Looping for Thermochemical Energy Storage with CO2 Capture
- 2021
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Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 14:11
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Tidskriftsartikel (refereegranskat)abstract
- The cyclic carbonation-calcination of CaCO3 in fluidized bed reactors not only offers a possibility for CO2 capture but can at the same time be implemented for thermochemical energy storage (TCES), a feature which will play an important role in a future that has an increasing share of non-dispatchable variable electricity generation (e.g., from wind and solar power). This paper provides a techno-economic assessment of an industrial-scale calcium looping (CaL) process with simultaneous TCES and CO2 capture. The process is assumed to make profit by selling dispatchable electricity and by providing CO2 capture services to a certain nearby emitter (i.e., transport and storage of CO2 are not accounted). Thus, the process is connected to two other facilities located nearby: a renewable non-dispatchable energy source that charges the storage and a plant from which the CO2 in its flue gas flow is captured while discharging the storage and producing dispatchable electricity. The process, which offers the possibility of long-term storage at ambient temperature without any significant energy loss, is herein sized for a given daily energy input under certain boundary conditions, which mandate that the charging section runs steadily for one 12-h period per day and that the discharging section can provide a steady output during 24 h per day. Intercoupled mass and energy balances of the process are computed for the different process elements, followed by the sizing of the main process equipment, after which the economics of the process are computed through cost functions widely used and validated in literature. The economic viability of the process is assessed through the breakeven electricity price (BESP), payback period (PBP), and as cost per ton of CO2 captured. The cost of the renewable energy is excluded from the study, although its potential impact on the process costs if included in the system is assessed. The sensitivities of the computed costs to the main process and economic parameters are also assessed. The results show that for the most realistic economic projections, the BESP ranges from 141 to −20 $/MWh for different plant sizes and a lifetime of 20 years. When the same process is assessed as a carbon capture facility, it yields a cost that ranges from 45 to −27 $/tCO2-captured. The cost of investment in the fluidized bed reactors accounts for most of the computed capital expenses, while an increase in the degree of conversion in the carbonator is identified as a technical goal of major importance for reducing the global cost.
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| 9. |
- Martinez Castilla, Guillermo, 1993, et al.
(författare)
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Techno-economic assessment of fluidized bed calcium looping for thermochemical energy storage with CO2 capture
- 2021
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Ingår i: Short papers from the 11th International Trondheim CCS Conference. - 2387-4295. - 9788253617145 ; , s. 390-397
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Konferensbidrag (refereegranskat)abstract
- The multicyclic carbonation-calcination of CaCO3 in fluidized bed reactors is a promising process for both thermochemical energy storage (TCES) and CO2 capture. In this paper, a techno-economic assessment of the calcium loop (CaL) process with simultaneous TCES and CO2 capture from an existing CO2-emitting facility is carried out. Inputs to the process are non-dispatchable high temperature heat and a stream of flue gas, while the process outputs are electricity (both dispatchable and non-dispatchable) and CO2 for compression and storage. The process is sized so the charging section can run steadily during 12h per day and the discharging section to operate steadily 24h per day. The study assesses the economic performance of the process through the breakeven electricity price (BESP) and cost per CO2 captured. The study excludes the costs of the renewable energy plant and the CO2 transport and storage. The sensitivity of the results to the main process and economic parameters is also assessed. Results show that the BESP of the case with the most realistic set of economic predictions ranges between 141 and-20 $/MWh for varying plant size. When assessed as a carbon capture facility with a revenue made from both the electricity sale and the carbon capture services, the cost ranges between 178 and 4 $/tCO2-captured. The investment cost of the reactors is found to be the largest fraction of the computed costs, while the sensitivity analysis points at the degree of conversion in the carbonator as the most crucial parameter, with large cost reductions for increased conversion.
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| 10. |
- 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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