| 1. |
- Seddighi, Sadegh, 1977, et al.
(författare)
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Assessment of Oxyfuel Circulating Fluidized Bed Boilers – Modeling and Experiments in a 5 MW Pilot Plant
- 2011
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Ingår i: 2nd International Oxyfuel Combustion Conference, International Energy Agency Greenhouse Gas R&D Programme.
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Konferensbidrag (refereegranskat)abstract
- As in air-firing, oxy-fired combustion using the Circulating Fluidized Bed (CFB) technology may offer advantages in that the CFB technology provides high fuel flexibility, in-furnace reduction of SOx emissions and a relatively smooth distribution of the extracted heat flux. Furthermore, the thermal flywheel induced by the solids flow and the possibility of heat extraction in the solids recirculation system (i.e. outside the furnace) represent a potential to achieve high oxygen concentrations while limiting the temperature level. Allowing such higher oxygen concentrations would imply significantly more compact (and thus less costly) furnaces than those used in air combustion.The present work summarizes the current status of an ongoing project which has the aim to assess the oxyfuel CFB technology by means of pilot testing and modeling. The pilot testing is carried out in a 5 MW oxyfuel CFB pilot plant (representing the largest oxy-fired CFB unit running at present date). The model is an extended version of a model for air-fired CFB combustion developed over the last six years by the authors and validated for utility-scale units.Considering that the model has previously undergone an extensive validation against data from air-fired large-scale boilers, the model is expected to represent a useful tool for the assessment, design and scale-up of oxyfuel boilers once validated with measurements from the 5 MW oxyfuel unit,. An obvious application of the model is in the dimensioning and designing heat extraction surfaces. High oxygen concentrations require more heat extraction in the solids recirculation system, which is allowed by means of increased external circulation of solids. Such increased solids circulation can be established with modifications to the furnace design and a change in operating conditions and/or solids properties.
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| 2. |
- Seddighi, Sadegh, 1977, et al.
(författare)
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Carbon Monoxide Formation during Oxy-fuel-Fired Fluidized-Bed Combustion
- 2013
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 27:4, s. 2275−2282-2282
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Tidskriftsartikel (refereegranskat)abstract
- This paper investigates the heterogeneous and homogeneous reactions involved in the formation and reduction of carbon monoxide (CO) in a 100 kW oxy-fuel-fired circulating fluidized-bed furnace, using CO as an indicator of the progress of combustion. A mathematical combustion model, which takes into account both the mixing and kinetics, is developed for simulating char and gas combustion under air- and oxy-fuel-fired conditions. The experimental results demonstrate that, for similar fluid dynamic and thermal conditions, oxy-fuel conditions typically yield a vertical CO profile with higher peak concentrations than are obtained with air-firing, mainly because of the higher inlet concentrations of O2, whereby CO released from the increased fuel feeding is diluted in the same total volumetric flow of gas. On the basis of a comparison of the modeling results and the experimental results, it is proposed that the effects of CO2 should be considered in determining the rate of CO oxidation that is valid for both air- and oxy-fuel-fired conditions. The vertical in-furnace profiles of CO from the combustion model were compared to the corresponding experimental results from five test runs under air- and oxy-fuel-fired conditions. The results show good agreement, with the agreement for oxy-fuel-fired conditions made possible by adding a CO2-dependent term to the expression for the CO oxidation rate.
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| 3. |
- Seddighi, Sadegh, 1977, et al.
(författare)
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Heat extraction from a utility-scale oxy-fuel-fired CFB boiler
- 2015
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Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509. ; 130, s. 144-150
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Tidskriftsartikel (refereegranskat)abstract
- The temperature and heal extraction parameters of a utility-scale, oxy-fuel-fired boiler are investigated using a mathematical model that was originally developed and validated with data from 100-kW(th) to 4-MWth, oxy-fuel-fired circulating fluidized bed units. This work involves an existing furnace, which was developed for air bring, and evaluates its operational potentials under oxy-fuel conditions, allowing additional heat extraction through an external heat exchanger (EHE). The modeling shows that even though the heat extraction levels from the entire furnace, flue gas pass, and EHE increase with increases in the inlet 02 concentration, the heat extraction from the EHE dominates the heat extraction for high inlet 02 concentrations and, consequently, requires an increase in the circulating solids flow, which transfers heat from the furnace to the seal. While maintaining the same dense bed temperature as in the air Fired case, an increased inlet 02 concentration in the oxy-fired case leads to dramatic increases in the maximum in furnace temperature and maximum heat extraction flux rate. Thus, to control the maximum furnace temperature, the circulating solids flux must be increased beyond what is required to close the heat balance across the CFB loop. For the conditions investigated, limitation of the maximum furnace temperature to 1273 K yields that 48%, 56%, and 70% are the highest possible inlet oxygen concentrations if the external circulation flux rate is limited to 10, 20, and 30 kg/m(2)/s, respectively.
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| 4. |
- Seddighi, Sadegh, 1977, et al.
(författare)
-
Heat transfer in a 4 MWth circulating fluidized bed furnace operated under oxy-fired and air-fired conditions: modeling and measurements
- 2015
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Ingår i: International Journal of Greenhouse Gas Control. - : Elsevier BV. - 1750-5836. ; 37, s. 267-273
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Tidskriftsartikel (refereegranskat)abstract
- Heat transfer to wall panels in the furnace of a circulating fluidized bed (CFB) is investigated by means of a 1.5-dimensional mathematical model together with measurements from a 4-MWth CFB unit under air and oxy-fuel conditions. The conditions at the wall panels correspond to solids concentration between 0.35 and 18 kg/m3 and temperatures between 1054 and 1168 K. The heat transfer coefficient to the wall panels is similar in oxy-fuel and air-firing due to that the solids flow, which plays the main role in CFB furnace heat transfer, was kept similar in air and oxyfuel conditions. The modeled furnace heat extraction and in-furnace vertical profiles of temperature and solids concentration show generally good agreement with the corresponding measured values. Modeling results show that for all cases studied, the share of radiation in the total furnace heat extraction exceeds 70% and increases with the increase in furnace temperature. Modeling results also show that gas radiation has a small influence on furnace heat extraction.
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| 5. |
- Seddighi, Sadegh, 1977, et al.
(författare)
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One-dimensional modeling of oxy-fuel fluidized bed combustion for CO2 capture
- 2010
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Ingår i: 13th Int. Conf. on Fluidization.
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Konferensbidrag (refereegranskat)abstract
- A one-dimensional model has been developed with the aim of investigating oxyfuel circulating fluidized bed (CFB) combustion for CO2 capture with the main focus of assessing the heat balance of the CFB loop. For different oxygen concentrations in the gas flow fed to the furnace, the model calculates the external solids recirculation and the heat load in the furnace and in external particle coolers.
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| 6. |
- Seddighi, Sadegh, 1977, et al.
(författare)
-
Progress of Combustion in an Oxy-fuel Circulating Fluidized-Bed Furnace: Measurements and Modeling in a 4 MWth Boiler
- 2013
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 27:10, s. 6222-6230
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Tidskriftsartikel (refereegranskat)abstract
- Oxy-fuel combustion, which is a promising technology for the abatement of carbon dioxide emissions, can be applied in circulating fluidized-bed (CFB) power plants. In this study, the effects of operational conditions on the progress of oxy-fuel CFB combustion were investigated by means of a mathematical model for CFB oxy-fuel combustion together with experimental data from a 4 MWth oxy-fuel CFB, currently representing the largest oxy-fuel CFB combustion experiments in the literature. Modeled in-furnace profiles for carbon monoxide (CO) and oxygen (O2) were compared to the corresponding measurements, yielding a general good agreement for both air- and oxy-fuel-fired conditions. The developed model was also used to investigate the effects of varying the inlet O2 concentration over a wider range than that applied in the experiments. The experimental results show that, for an equivalent inlet O2 concentration, the peak CO concentration is higher under oxy-fuel-fired conditions than under air-fired conditions. The model result shows that a higher inlet O2 concentration generates combustion of greater intensity up through the furnace with a lower level of CO at the furnace exit.
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| 7. |
- Seddighi, Sadegh, 1977, et al.
(författare)
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The interplay between energy technologies and human health: Implications for energy transition
- 2023
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Ingår i: Energy Reports. - 2352-4847. ; 9, s. 5592-5611
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Forskningsöversikt (refereegranskat)abstract
- This paper explores the relationship between human health and energy technologies, with a focus on how energy technology needs to adapt to new health challenges. The authors examine how a clean, affordable, and reliable energy infrastructure is critical for mitigating the impact of future pandemics. They also look at how increasing the proportion of solar and wind energy can create a near-zero emission energy system that is independent of fuel supply and its associated environmental problems. However, to ensure system resilience, significant investments in energy storage and smart control systems are necessary. For instance, the pandemic led to around 5% increase in US residential sector electricity consumption share in 2020 compared to 2019 due to stay-at-home orders, which could impact grid reliability and resiliency. This work also highlights the importance of designing energy-efficient and low-cost cooling and heating technologies for residential buildings to protect vulnerable populations from the health consequences of rising temperatures due to climate change. Additionally, the growing number of refugees worldwide and the need for efficient portable power sources in refugee camps are also addressed. The authors demonstrate how pandemics like COVID-19 can have far-reaching effects on energy technologies, from household energy use to large energy companies, and result in energy insecurity and decreased quality of life for many.
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