| 201. |
- Markström, Pontus, 1980, et al.
(författare)
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Analytical model of gas conversion in a 100 kW chemical-looping combustor for solid fuels—Comparison with operational results
- 2013
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Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509. ; 96, s. 131-141
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Forskningsöversikt (refereegranskat)abstract
- This study analyses results from a 100 kWth chemical-looping combustor, consisting of two interconnected circulating fluidised-bed reactors, for use with solid fuels. The fuel reactor has an internal circulation loop, whereas the circulation loop of the air reactor leads to the fuel reactor. Operation of the unit is flexible, as it is possible to vary key operational parameters in a wide range to investigate the response in system behaviour and performance. Results from a previous study have shown that by varying the fluidisation velocity in three different sections of the unit, a phenomenological relation between gas conversion, fuel reactor bed inventory and global solids circulation can be found. This relation is here studied in more depth, clearly indicating that high gas conversion can only be reached if the fuel reactor bed inventory is large. Furthermore, an analytical model describing gas conversion is applied to the fuel reactor. It is shown that the model predicts the effect of variations in solids inventory well. Corrections to the model based on circulation, temperature and time of operation were assessed, but the effect was small under the present conditions. Data for the analysis are compiled from four operational periods, ranging from 2.4 h to 5.9 h of continuous fuel feeding. The oxygen carrier used was ilmenite, and the fuel a bituminous coal from Colombia.
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| 202. |
- Markström, Pontus, 1980, et al.
(författare)
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Chemical-Looping Combustion in a 100 kW Unit for Solid Fuels
- 2012
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Ingår i: The 21st International Conference on FBC. ; 1, s. 285-292
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Konferensbidrag (refereegranskat)abstract
- Chemical-looping combustion is a novel technology for combustion of fossil fuels. By using a circulating bed material to transfer oxygen to the fuel, a pure stream of CO2 can be obtained from the flue gas, undiluted by N2 from the air. The main advantage of this capture technology is that there is no direct efficiency loss in obtaining the CO2 in a separate stream. This study describes results from operation in a 100 kWth chemical-looping combustor for solid fuels. The oxygen carrier used was ilmenite, an iron-titanium oxide. Coal is fed directly into a loop seal, leading to the fuel reactor, through a set of screws. All parts of the unit are fluidized with steam, except for the air reactor, which is fluidized with air, and the loop seal with the fuel insertion, which is fluidized with nitrogen. All-in-all, the unit has eleven windboxes, of which four are loop seals. Three experiments have been conducted using a Colombian coal as fuel. Operation was stable and loss of char to the air reactor was small, meaning that the CO2 capture efficiency was high (>90%). Gas concentration measurements showed the presence of unconverted CO, H2 and CH4 corresponding to an oxygen demand of 18.5% at 950°C.
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| 203. |
- Markström, Pontus, 1980, et al.
(författare)
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Chemical-looping combustion of solid fuels – Design and operation of a 100 kW unit with bituminous coal
- 2013
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Ingår i: International Journal of Greenhouse Gas Control. - : Elsevier BV. - 1750-5836. ; 15, s. 150-162
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Forskningsöversikt (refereegranskat)abstract
- Chemical-looping combustion is a novel technology with inherent capture of CO2 when burning gaseous, liquid or solid fuels. By using two interconnected fluidised beds with a bed material capable of transferring oxygen from air to the fuel, a nitrogen-free stream of CO2 can be obtained with no direct efficiency loss. Here, approximately 20 h of experimental results from a 100 kW unit for solid fuels are presented. Using ilmenite oxygen carrier and a Colombian bituminous coal (Cerrejón coal), five periods of operation were conducted at 940-980°C in the fuel reactor for 1.5-6 h. The unit worked well and stable operation was easily reached. The investigation involves variations of operational parameters to see the effect on performance. It was shown that an oxygen demand below 16% and a CO2 capture above 99% can be reached during extended periods at close to optimal conditions. By replacing the steam fluidisation with inert nitrogen, the influence of the carbon stripper with respect to the steam gasification was tested. It was shown that CO2 capture decreased from 98.5% to 95.5% without the gas conversion provided by the carbon stripper. Finally, pressure profiles from two experiments are presented and compared to a pressure profile predicted from cold-flow model experiments. The work shows the first extended operation of chemical-looping combustion with solid fuels in the 100 kW scale and the operational experience gives strong indication that the process is viable.
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| 204. |
- Markström, Pontus, 1980, et al.
(författare)
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Designing and operating a cold-flow model of a 100 kW chemical-looping combustor
- 2012
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Ingår i: Journal of Logic and Computation. - : Elsevier BV. - 0955-792X .- 1465-363X. ; 222, s. 182-192
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Forskningsöversikt (refereegranskat)abstract
- This work presents the design and experimental evaluation of a cold-flow model system, built to simulate a 100 kW chemical-looping combustor for solid fuel. A theoretical background is provided, as well as some initial results using air as fluidization medium. The system has been operated for about 10 hours and shows no indication of imbalances in the bed inventories. In the fuel and air reactors, the mass fluxes were found to be linear in the riser pressure drop and the corresponding measured mass flows were approximately proportional to the mass flows calculated from the riser pressure drop. From the study of mass flows, residence times in both the fuel and air reactor were obtained. From pressure profile investigations, it was found that the system remained stable to changes in the fluidization velocity. Thus, both the internal circulation in the fuel reactor, and the circulation between air and fuel reactor, could be varied in a large range with only minor impact on the solids inventories of the air and fuel reactors.
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| 205. |
- Markström, Pontus, 1980, et al.
(författare)
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Operation of a 100 kW chemical-looping combustor with Mexican petroleum coke and Cerrejón coal
- 2014
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Ingår i: Applied Energy. - : Elsevier BV. - 1872-9118 .- 0306-2619. ; 113, s. 1830-1835
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Tidskriftsartikel (refereegranskat)abstract
- This study describes the design and operation of a 100 kW chemicallooping combustor for solid fuels. Six experiments of continuous operation, varying between 8 and 32 minutes in length, have been conducted. The fuels investigated were a Mexican petroleum coke and a bituminous coal from Cerrejón in Colombia. Overall, it was found that operation was stable and loss of char to the air reactor was small, meaning that the CO2 capture efficiency was high (up to 90% at temperatures close to 950°C in the fuel reactor). Gas concentration measurements showed the presence of unconverted CO, H2 and CH4 corresponding to an oxygen demand of around 20%, depending on the fuel reactor temperature. In addition, a residence-time analysis was conducted from a batch experiment, enabling an estimation of the mass flow of oxygen carriers through the system using the riser pressure drop in the air reactor.
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| 206. |
- Markström, Pontus, 1980, et al.
(författare)
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The Application of a Multistage-Bed Model for Residence-Time Analysis in Chemical-Looping Combustion of Solid Fuel
- 2010
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Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509. ; 65:18, s. 5055-5066
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Tidskriftsartikel (refereegranskat)abstract
- The behavior of a 10 kW chemical-looping combustor for solid fuels, normally operated in continuous mode, has been studied by addition of fuel batches. From analysis of gas leaving the air reactor, it was possible to determine the residence time and residence-time distribution of particles in the fuel reactor. Knowing the solids inventory in the fuel reactor, the circulation mass flow could be directly correlated to measured operational data, i.e. pressure drop, temperature and gas flow in air reactor riser. Using results for carbon-capture efficiency and residence-time distribution, a model was developed which could determine a mass-based reaction-rate constant for char conversion. The reaction-rate constant of a Mexican petroleum coke at both 950°C and 970°C was calculated to 8.2 wt%/min and 28.8 wt%/min, respectively. The reaction-rate constant of a South African coal at 950°C was calculated to 26.1 wt%/min. This reaction-rate constant could also be determined independently from the conversion rates of char during the batch tests. The results showed a good agreement between the two approaches, indicating that the model well describes the behavior of the unit. From the determination of the circulation mass flow, and comparison with previous testing with different circulation, it was also possible to estimate the limit for which the ilmenite was unable to supply sufficient oxygen to achieve good conversion. This limit was compared to theoretical limits for ilmenite as well as the limit set by a heat balance. It was concluded that the latter will be the one setting the limit.
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| 207. |
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| 208. |
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| 209. |
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| 210. |
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