| 1. |
- Gogolev, Ivan, 1984, et al.
(författare)
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Commissioning, performance benchmarking, and investigation of alkali emissions in a 10 kWth solid fuel chemical looping combustion pilot
- 2021
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361 .- 1873-7153. ; 287
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Tidskriftsartikel (refereegranskat)abstract
- Chemical looping combustion of biomass-sourced fuels (bio-CLC) is a novel bio-energy with carbon capture and storage (BECCS) technology for power and heat generation with net negative CO2 emissions. In this study, a new 10 kWth CLC pilot designed for high-volatiles biomass fuels was commissioned with ilmenite oxygen carrier and five different biomass fuels of varying volatile and alkali content fractions. The system was tested for its ability to convert high and low volatile content biomass, while achieving high carbon capture efficiency. The new pilot achieved carbon capture close to 100% for high-volatiles biomass, and >94% for low-volatiles biomass char fuels. Furthermore, due to the implementation of a volatiles distributor, the new pilot demonstrated an improvement of up to 10 percentage points of gas conversion efficiency for high-volatiles biomass vs. the previous generation reactor. Gaseous alkali emissions were measured with a surface ionization detection system. Flue gas alkali release levels were found to rise with higher fuel alkali content. Alkali emissions were found to be approximately similar in the AR and the FR for all but the straw pellet mixture fuel (highest alkali content fuel). For the straw pellet mixture, gaseous alkali release levels in the AR were up to seven times higher than those of the FR. In all cases, over 96% of the fuel's alkalis were absorbed by the ilmenite bed material. Ilmenite's strong alkali absorption characteristics were concluded to be the key determinant of gas-phase release of biomass alkali in the conducted experiments.
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| 2. |
- Linderholm, Carl Johan, 1976, et al.
(författare)
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Chemical-looping combustion of solid fuels – Operation in a 10 kW unit with two fuels, above-bed and in-bed fuel feed and two oxygen carriers, manganese ore and ilmenite
- 2012
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 102, s. 808-822
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Tidskriftsartikel (refereegranskat)abstract
- Chemical-looping combustion (CLC) is a combustion concept with inherent separation of CO2. The processuses a solid oxygen carrier, which consists of metal oxide, to transfer the oxygen from air to fuel.The chemical-looping combustor used in the present experiments features two interconnected fluidizedbeds; a fuel reactor (FR) and an air reactor (AR). In the FR, fuel is gasified with steam whereupon gasificationproducts react with the oxygen carrier to form, ideally, CO2 and H2O. This study concerns CLC ofsolid fuels in a continuously operating 10 kW unit using two natural ores as oxygen carrier: (a) ilmenite,an iron–titanium mineral and (b) a manganese ore containing smaller amounts of Fe, Al and Si. The fuelfeed was re-designed in order to increase contact between oxygen carrier and fuel. The new in-bed fuelfeed was found to significantly improve gas conversion, mainly caused by increased contact between theoxygen carrier and volatile gases released in the fuel chute. Two fuels were used to evaluate the effect offuel feed; a bituminous coal and a pet coke. The in-bed fuel feed was used when ilmenite and manganeseore were compared. The use of a manganese ore as oxygen carrier was shown to significantly enhance therate of char gasification and also improve gas conversion. A concern with the manganese ore is the largeproduction of fines.
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| 3. |
- Lyngfelt, Anders, 1955
(författare)
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Chemical looping combustion
- 2013
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Ingår i: Chapter 20 , Fluidized-bed technologies for near-zero emission combustion and gasification, Ed. Scala, F., Woodhead Publishing.
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 4. |
- Lyngfelt, Anders, 1955, et al.
(författare)
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Dependence of Sulphur Capture Performance on Air Staging in a 12 MW Circulating Fluidised Bed Boiler
- 1993
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Ingår i: Gas Cleaning at High Temperatures, Eds. R. Clift and J.P.K. Seville, Blackie Academic & Professional, Glasgow, ISBN 0 7514 0178 1.. - 0751401781 ; , s. 470-491
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Three cases of air staging were examined in a 12 MW circulating fluidised bed boiler: i) no staging, ii} normal staging and iii) intensified staging. The conditions inside the combustion chamber were investigated by zirconia cell measurements of the oxygen partial pressure, 0.35, 0.65 and 8 m above the bottom air distributor plate. A significant effect of the degree of staging was seen in the two lower locations: At 0.65 m height the fraction of time under substoichiometric conditions was low in the no-staging case (2-35%), at normal staging it was 70-90%, whereas at intensified staging it was 100Y.. At 0.35 m height, i.e. in the dense bed, a similar effect was seen, although the fraction of time under reducing conditions was lower. The fraction of time under reducing conditions was low in the top of the combustion chamber in all three cases . The increase in the fraction of time under reducing conditions with a higher degree of staging is associated with a decrease in sulphur capture. It is assumed that a release of SO2 from CaSO4 takes place during the transitions between oxidising and reducing conditions. Thus, the rapid alternations between oxidising and reducing conditions, as seen with the zirconia cell, offer an explanation of the reductive decomposition and, accordingly, of the dependence of sulphur capture on temperature and on the extent of staging.
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| 5. |
- Lyngfelt, Anders, 1955, et al.
(författare)
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Materials for chemical-looping combustion
- 2011
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Ingår i: Efficient Carbon Capture for Coal Power Plants, Ed. Stolten, D., and Scherer, V., WILEY-VCH Verlag GmbH & Co.. KGaA, Weinheim. ; :Chapter 17, s. 475-504
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Chemical-looping combustion (CLC) is a combustion technology with inherent separation of the greenhouse gas CO2. Two inter-connected fluidized beds, a fuel reactor and an air reactor, are used. The fuel is oxidized by the metal oxide in the fuel reactor, and the metal oxide is regenerated in the air reactor. The outlet gas from the fuel reactor consists of CO2 and H2O, easily separated by condensation. Oxides of Ni, Co, Fe, Cu and Mn are used as oxygen-carrier materials. More than 900 materials have been investigated and some have been used in actual operation in chemical-looping combustors in the size range 0.3 – 140 kW. The total time of operational experience is more than 4000 hours. The work indicates that almost complete conversion of the fuel can be obtained and 100% CO2 capture is possible. Most work so far has been focused on gaseous fuels, but the direct application to solid fuels is also rapidly advancing. Moreover, chemical-looping technologies to produce hydrogen with inherent CO2 capture are being developed. This paper presents an overview of the current status of the technology with focus on materials.
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| 6. |
- Mei, Daofeng, 1986, et al.
(författare)
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Modelling of gas conversion with an analytical reactor model for biomass chemical looping combustion (bio-CLC) of solid fuels
- 2022
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Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947 .- 1873-3212. ; 433
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Tidskriftsartikel (refereegranskat)abstract
- Manganese ores are promising oxygen carriers for chemical looping combustion (CLC), due to their high reactivity with combustible gases. In this work, a manganese ore called EB (Elwaleed B, originating from Egypt) is studied for its reaction rate with CH4, CO and H2 and the data are used in an analytically solved reactor model. The reactivity of fresh and three used EB samples from previous operation in a 10 kWth pilot was examined in a batch fluidized bed reactor with CH4 and syngas (50%CO + 50%H2). In comparison with other manganese ores, the EB ore has a lower rate of reaction with CH4, while showing a significantly higher reactivity with syngas. Nevertheless, this manganese ore always presents a better conversion of CH4 and syngas than the benchmark ilmenite. Mass-based reaction rate constants were obtained using a pseudo first-order reaction mechanism: 1.1·10-4 m3/(kg·s) for CH4, 6.6·10-3 m3/(kg·s) for CO and 7.5·10-3 m3/(kg·s) for H2. These rate constants were used in an analytical reactor model to further investigate results from previous operation in the 10 kWth unit. According to the analytical model, in the 10 kWth operation, 98% of the char in the biomass fuels was gasified before leaving the fuel reactor, while the char gasification products (CO and H2) have a 90% contact efficiency with the bed material. On the contrary, the volatiles have a much lower contact efficiency with the oxygen carrier bed, i.e. 20%, leading to low conversion of volatiles released. Thus, the results emphasize the importance of improving the contact between volatiles and bed material in order to promote combustion performance in the CLC process.
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| 7. |
- Aronsson, Jesper, 1985, et al.
(författare)
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Effects of the Choice of Gas on the Hydrodynamics of Fluidized Beds
- 2019
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 58:20, s. 8847-8855
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Tidskriftsartikel (refereegranskat)abstract
- Using a cold-flow model, this work examines how the hydrodynamics in the dense region of a fluidized bed are affected when the gas acting as the fluidizing agent is changed. While the focus here is on the use of a gas other than that suggested by scaling laws in cold-flow models, the study also has relevance for fluidized bed processes in which different fluidization agents can be used, such as drying or coating. For cold-flow models, the scaling criteria for the hydrodynamics of the fluidized bed prescribe certain properties of the gas to be used as the fluidizing agent. In certain scenarios, air does not match the suggested properties, and other gases must be used, which increases the complexity and cost. In the worst-case scenario, no gas will fulfill the prescribed properties, and experimentation under strictly scaled conditions will be impossible. Assessing the impact of not using the correct gas allows researchers to evaluate the reliability of their findings when there is no compliance with the scaling laws. In this work, experiments were carried out in a hydrodynamically down-scaled model of a 100 kW chemical looping combustion (CLC) unit, which under hot conditions contains metal oxide particles fluidized with steam. If the hydrodynamic properties are to be resembled at ambient temperature with the same solids, a gas lighter than air, e.g., helium, must be used according to the scaling laws. This entails an experimental setup with gas recycling, adding cost and complexity to the system in comparison to using air. This work investigates how fluidization with air, instead of helium, affects the hydrodynamics of the cold-flow model based on two different approaches: (i) maintained superficial gas velocity and (ii) maintained decay constant in the splash zone. The results show that air does not adequately substitute for helium in a bubbling bed with respect to the following key hydrodynamic properties: pressure fluctuations were 30% lower; the bubble fraction was up to 36% smaller; bubble frequency was up to 17% lower; and the solids concentration was up to 10% higher. It was also found that the use of air yields a poorer horizontal distribution of the gas injected from the reactor side-walls, which affected the cross-sectional distributions of the solids concentration, bubble fraction, and bubble frequency.
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| 8. |
- Li, Xiaoyun, 1990, et al.
(författare)
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An experimental study of a volatiles distributor for solid fuels chemical-looping combustion process
- 2021
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Ingår i: Fuel Processing Technology. - : Elsevier BV. - 0378-3820. ; 220
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Tidskriftsartikel (refereegranskat)abstract
- A novel concept called volatiles distributor (VD), with the purpose to achieve an even distribution of volatiles over the cross-section of a fluidized-bed and better contact between volatiles and bed materials, has been investigated. The concept could be useful for chemical- looping combustion, as well as other solid fuel conversion processes in fluidized-beds. An experimental study of the VD in a circulating fluidized-bed (CFB) cold-flow model was conducted under different fluidization velocities and flows of simulated volatiles. In the reference case without VD, a local plume of volatiles is formed and the maldistribution becomes more pronounced at higher fluidization velocity in the range from 1 m/s to 4 m/s. Conversely, higher fluidization velocity gives a more even volatiles distribution in the presence of VD. The relative standard deviation of volatiles horizontal distribution decreases from 131% in absence of VD to 22% in presence of VD at the fluidization velocity of 4 m/s. There is no significant effect of volatiles flow rate on VD performance at a fluidization velocity 1 m/s. As the fluidization velocity and volatiles flow rate increase, the bed level inside VD is lowered and the volatiles inside the VD become less diluted, because less air from the main fluidization passes through the VD.
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| 9. |
- Li, Xiaoyun, 1990, et al.
(författare)
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CFD modeling of a fluidized bed with volatiles distributor for biomass chemical looping combustion combustion
- 2024
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Ingår i: Chemical Engineering Science. - 0009-2509. ; 295
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Tidskriftsartikel (refereegranskat)abstract
- Achieving high volatiles conversion is crucial to biomass chemical looping combustion. Challenges arise from rapid devolatilization of biomass and limited biomass injection ports, resulting in volatiles with insufficient contact with oxygen carriers in fluidized beds. A concept called volatiles distributor (VD) has recently been proposed and investigated in a cold-flow fluidized bed, which shows excellent performance in achieving an even distribution of volatiles over the cross section. To deeply understand VD's impact on hydrodynamics behaviors, pioneering three-dimensional full-loop cold-flow CFD simulations were conducted using an Eulerian multiphase granular model. Three drag models, i.e., Gidaspow, Filtered, and two-step EMMS/bubbling, were evaluated against experimental data. While all models perform well in bubbling fluidization, the two-step EMMS/bubbling model excels in turbulent fluidization. Additionally, CFD simulations reveal improved mixing between volatiles and bed materials with VD, highlighting its efficiency in addressing incomplete conversion of high-volatile fuels like biomass in fluidized bed systems.
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| 10. |
- Li, Xiaoyun, 1990, et al.
(författare)
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Investigation on the Performance of Volatile Distributors with Different Configurations under Different Fluidization Regimes
- 2022
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 36:17, s. 9571-9587
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Tidskriftsartikel (refereegranskat)abstract
- The uniform horizontal distribution of volatiles over the cross section of a fluidized bed with the purpose to obtain good contact between volatiles and bed materials is a key issue to improve the gas conversion in the fuel reactor of chemical looping combustion of solid fuels. The effectiveness of the volatile distributor (VD) concept on the lateral distribution of volatiles in a fluidized bed has been investigated under different operational conditions using a cold-flow model. Furthermore, the performance of the VD has been examined using different configurations of the holes used to distribute the volatiles. The fluidization regimes, i.e., single bubble regime, with only one large bubble formed at a time at the bottom bed, exploding bubble regime, with irregular bubbles containing more particles, and multiple bubble regime, with many small bubbles formed and distributed in the bed, are determined by visual observation of the bottom riser and analysis of the pressure fluctuations, including frequency analysis. The VDs with uneven hole arrangements, which have less distribution holes at the simulated volatile inlet side and a larger open area far from the inlet, provide a more even horizontal distribution of volatiles compared to the VD with equally distributed holes. A larger simulated volatile flow and less open area of the VD increase the pressure drop over the distribution holes and improve the horizontal distribution. In general, the VD gives a more uniform distribution of the volatiles under the exploding bubble regime and better distribution in the single bubble regime compared to the multiple bubble regime. However, the bottom leakage, i.e., the volatile leakage from the bottom of the VD, should be considered, especially in the single bubble regime.
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