Sulfur capture and release by ilmenite used as oxygen carrier in biomass combustor

Vigoureux, Mariane; Leffler, Tomas; Knutsson, Pavleta; Lind, Fredrik

doi:10.1016/j.fuel.2021.121978

Cited by 7 publications

(7 citation statements)

References 24 publications

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“…Ilmenite as the oxygen carrier used in this study was produced by Titania A/S in Norway. Ilmenite has been used in pilot-scale CLC reactors at different scales and even a commercial fluidized bed boiler with an oxygen carrier combustion process; thus, the material is deemed as the benchmark oxygen carrier. − Vigoureux et al presented the composition of ilmenite used in this study, which mainly comprises of 34.2% Fe and 27.9% Ti. Ilmenite was primarily calcined at 950 °C for 12 h in a high-temperature oven to obtain the oxygen carrier at a fully oxidized state and improve its reactivity to some extent .…”

Section: Methodsmentioning

confidence: 99%

Effect of the Mass Conversion Degree of an Oxygen Carrier on Char Conversion and Its Implication for Chemical Looping Gasification

et al. 2022

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Chemical looping gasification (CLG) is an emerging process that aims to produce valuable chemical feedstocks. The key operational requirement of CLG is to limit the oxygen transfer from the air reactor (AR) to the fuel reactor (FR). This can be accomplished by partially oxidizing the oxygen carrier in the AR, which may lead to a higher reduction degree of the oxygen carrier under the fuel conversion. A highly reduced oxygen carrier may experience multiple issues, such as agglomeration and defluidization. Given such an interest, this study examined how the variation of the mass conversion degree of ilmenite may affect the conversion of pine forest residue char in a fluidized bed batch reactor. Ilmenite was pre-reduced using diluted CO and then underwent the char conversion at 850, 900, 950, and 975 °C. Our investigations showed that the activation energy of the char conversion was between 194 and 256 kJ/mol, depending upon the mass conversion degree of ilmenite. Furthermore, the hydrogen partial pressure in the particle bed increased as the oxygen carrier mass conversion degree decreased, which was accompanied by a lower reaction rate and a higher reduction potential. Such a hydrogen inhibition effect was confirmed in the experiments; therefore, the change in the mass conversion degree indirectly affected the char conversion. Langmuir–Hinshelwood mechanism models used to evaluate the char conversion were validated. On the basis of the physical observation and characterizations, the use of ilmenite in CLG with biomass char as fuel will likely not suffer from major agglomeration or fluidization issues.

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Section: Methodsmentioning

confidence: 99%

Effect of the Mass Conversion Degree of an Oxygen Carrier on Char Conversion and Its Implication for Chemical Looping Gasification

et al. 2022

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“…If the approximate speciation of gas-phase K is known, the factors from Table can be used to estimate a range of K that is detected in the flue gases by the SID. In current experiments, the amount of K associated as K 2 SO 4 in the flue gas is expected to be insignificant, because K 2 SO 4 is unlikely to form in reducing conditions . The majority of the gas-phase alkalis are expected to occur as KCl, as far as Cl availability allows, with the remainder of K likely to exist as KOH(g) in the flue gas and as K 2 CO 3 as the sample flow is cooled in the presence of CO 2 within the SID sampling system.…”

Section: Resultsmentioning

confidence: 89%

“…In current experiments, the amount of K associated as K 2 SO 4 in the flue gas is expected to be insignificant, because K 2 SO 4 is unlikely to form in reducing conditions. 41 The majority of the gas-phase alkalis are expected to occur as KCl, as far as Cl availability allows, with the remainder of K likely to exist as KOH(g) in the flue gas and as K 2 CO 3 as the sample flow is cooled in the presence of CO 2 within the SID sampling system. Thus, the amount of gas-phase K contained in the flue gas can be better estimated as a range using the response factors for KCl and KOH/K 2 CO 3 .…”

Section: Resultsmentioning

confidence: 99%

Effects of Temperature, Operation Mode, and Steam Concentration on Alkali Release in Chemical Looping Conversion of Biomass─Experimental Investigation in a 10 kW_th Pilot

et al. 2022

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Alkali release was studied in a 10 kW th chemical looping pilot operated with a Linz–Donawitz (LD) slag oxygen carrier (OC) and three biomass fuels. Experiments were performed at three temperatures and in three operation modes: chemical looping combustion (CLC), chemical looping gasification (CLG), and oxygen-carrier-aided combustion (OCAC). Gas-phase alkali release was measured with a surface ionization detector (SID). Fuel reactor (FR) gas-phase alkali emissions increased with the temperature. This occurred as a result of increased evaporation of KCl and enhanced decomposition of alkali salts during char conversion. Air reactor (AR) alkali emissions were lower than in the FR and independent of the operating temperature. In comparison of operating modes, CLC and CLG modes resulted in similar gas-phase alkali emissions due to the similar extent of char conversion. In contrast, operation of the reactor system in OCAC mode resulted in significantly lower levels of gas-phase alkalis. The difference in alkali emission was attributed to the steam-rich atmosphere of CLC. The effect of steam was further investigated in CLC and OCAC tests. Lowering steam concentrations in CLC operation resulted in lower gas-phase alkali emissions, while introducing steam to the FR during OCAC operation resulted in higher alkali emissions. It was concluded that steam likely enhances gas-phase K release through a reaction of K 2 CO 3 within the fuel char with steam to produce KOH(g). Solid sampling and analysis for K content was used along with SID measurements to develop a K mass balance for the reactor system. Mass balance results for the straw pellet fuel tests showed that LD slag OC absorbs approximately 15–51% of fuel K, 2.2% of fuel K is released to the gas phase, and up to 3.4% of fuel K is captured in the AR fly ash. The residual 40–80% of fuel K was determined to leave the FR as K-rich fly ash.

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“…Table 1 presents the used oxygen carriers along with their chemical contents. Ilmenite, a benchmark chemical‐looping oxygen carrier, is an iron‐titanium ore, which was provided by Titania A/S 17 . Iron sand, also known as copper slag, is a by‐product from a copper smelting plant run by Boliden AB and contains mainly iron and silicon 7 .…”

Section: Methodsmentioning

confidence: 99%

“…Ilmenite, a benchmark chemical-looping oxygen carrier, is an iron-titanium ore, which was provided by Titania A/S. 17 Iron sand, also known as copper slag, is a by-product from a copper smelting plant run by Boliden AB and contains mainly iron and silicon. 7 Linz-Donawitz (LD) slag is a by-product from steel manufacturing process, which was obtained from the Swedish steel production company SSAB, and is notable for its calcium content, about 32 wt.%.…”

Section: Iron-based Oxygen Carriers and Potassium Saltsmentioning

confidence: 99%

Interactions between potassium ashes and oxygen carriers based on natural and waste materials at different initial oxidation states

et al. 2023

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One of the most essential features of an oxygen carrier is its ability to be oxidized and reduced in order to transfer oxygen in a chemical looping system. A highly reduced oxygen carrier can experience multiple performance issues, such as decreased reactivity, agglomeration, and defluidization. This is crucial for processes that require limited oxygen transfer from the air reactor to the fuel reactor. Meanwhile, biomasses as environmentally friendly fuel options contain ashes, which would inevitably react with oxygen carriers and exacerbate the performance issues. To mimic the interactions between a highly reduced oxygen carrier and biomass ash compounds, four iron-based oxygen carriers, based on natural ores and waste materials, and three potassium salts, K 2 CO 3 , KH 2 PO 4 , and K 2 SO 4 , were investigated in a tubular reactor under an atmosphere consisting of 2.5% H 2 and 10% steam in Ar and N 2 at 900°C for 3 h. The results from the X-ray diffraction (XRD) material analysis showed that both initially fully oxidized and highly reduced materials reach the same oxidation state after the experiment. Based on the scanning electron microscopy coupled with energy dispersive X-ray spectroscopy results, K from K 2 CO 3 and K 2 SO 4 diffuses in the oxygen carrier particles, while K from KH 2 PO 4 always forms a distinct layer around the particles. The initial oxidation state of an oxygen carrier surface affects the interactions with the potassium salt only to minor extents. Thus, the final state of the material and its performance in a large-scale process are only occasionally and mildly affected by its initial oxidation state.

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Sulfur capture and release by ilmenite used as oxygen carrier in biomass combustor

Cited by 7 publications

References 24 publications

Effect of the Mass Conversion Degree of an Oxygen Carrier on Char Conversion and Its Implication for Chemical Looping Gasification

Effect of the Mass Conversion Degree of an Oxygen Carrier on Char Conversion and Its Implication for Chemical Looping Gasification

Effects of Temperature, Operation Mode, and Steam Concentration on Alkali Release in Chemical Looping Conversion of Biomass─Experimental Investigation in a 10 kW_th Pilot

Interactions between potassium ashes and oxygen carriers based on natural and waste materials at different initial oxidation states

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Sulfur capture and release by ilmenite used as oxygen carrier in biomass combustor

Cited by 7 publications

References 24 publications

Effect of the Mass Conversion Degree of an Oxygen Carrier on Char Conversion and Its Implication for Chemical Looping Gasification

Effect of the Mass Conversion Degree of an Oxygen Carrier on Char Conversion and Its Implication for Chemical Looping Gasification

Effects of Temperature, Operation Mode, and Steam Concentration on Alkali Release in Chemical Looping Conversion of Biomass─Experimental Investigation in a 10 kWth Pilot

Interactions between potassium ashes and oxygen carriers based on natural and waste materials at different initial oxidation states

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Effects of Temperature, Operation Mode, and Steam Concentration on Alkali Release in Chemical Looping Conversion of Biomass─Experimental Investigation in a 10 kW_th Pilot