An improved method for feeding ash model compounds to a bubbling fluidized bed – CLC experiments with ilmenite, methane, and K₂CO₃

Abstract

Biomass conversion with carbon capture and storage (Bio‐Energy CCS; BECCS) is one of the options considered for mitigating climate change. In this paper, the carbon capture technology chemical‐looping combustion (CLC) is examined in which the CO2 is produced in a stream separate from the combustion air. A central research topic for CLC is oxygen carriers; solid metal oxides that provide oxygen for the conversion process. Biomass and waste‐derived fuels contain reactive ash compounds, such as potassium, and interactions between the oxygen carrier and the ash species are critical for the lifetime and performance of the oxygen carrier. This work develops and demonstrates an improved method for studying the interactions between ash species and oxygen carriers. The method uses a lab‐scale reactor operating under fluidized conditions, simulating CLC batch‐wise by switching between feed gas. The novelty of the setup is the integrated system for feeding solid particles of ash model compounds, enabling the simulation of ash species accumulating in the bed. Ilmenite is a benchmark oxygen carrier for solid fuel conversion and was used in this study to evaluate the method using K2CO3 as a model ash compound. Experiments were done at 850 and 950°C. Methane conversion in CLC cycles and fluidization was evaluated with gas analysis and pressure drop measurements. Scanning electron microscopy and energy dispersive X‐ray spectroscopy (SEM‐EDS) and X‐ray diffraction (XRD) analysis of bed particles were done after the experiments to establish changes in the morphology and composition of the ilmenite. The method for feeding the ash model compound was concluded to be satisfactory. At 950°C, K accumulated in the particles forming K‐titanates and agglomeration was enhanced with K2CO3 addition. The agglomeration mechanism was solid‐state sintering between the Fe‐oxides forming on the particle surfaces. The bed defluidized at 950°C, but no such effect was seen at 850°C. The method is suitable for studying the Fe‐Ti‐K system with ilmenite and potassium without the influence of other ash species. © 2023 The Authors. Greenhouse Gases: Science and Technology published by Society of Chemical Industry and John Wiley & Sons Ltd.

Enhanced solar‐light driven CO2 conversion using Pt‐doped graphitic carbon nitride photocatalyst

“…Such a slight decrease over consecutive runs—translating to a persistence of 87.1% of the initial performance by the fifth cycle—attests to the resilience and robust nature of the Pt/g‐C 3 N 4 photocatalyst. These findings emphasize the catalyst's potential for sustained CO 2 reduction operations, making it a promising candidate for extended applications in mitigating CO 2 emissions 30,31,36–39 …”

“…S2, the photoluminescence (PL) emission of g‐C 3 N 4 shows a pronounced and extensive peak, suggesting inefficient separation of charge carrier or electron‐hole pairs. Conversely, the doped Pt/g‐C 3 N 4 displays a less pronounced PL emission, which implies a more extended electron‐hole recombination lifetime 31,33 . An enhanced separation efficiency of these charge carriers often leads to more efficient chemical reactions during CO 2 photocatalysis, enhancing overall photocatalytic activities 33 …”

“…It exhibits a layered structure with a smooth and thin surface, characterized by individual sheets stacked together. When doped with Pt, the catalyst's surface morphology displays a layered structure with a more textured surface marked by small spherical particles 31,33 . These particles can be attributed to the Pt nanoparticles introduced during the g‐C 3 N 4 modification process.…”

“…Solar light‐driven photocatalytic CO 2 reduction presents a sustainable alternative to address the ever‐increasing CO 2 concentrations 20–22,24–29 . A range of photocatalysts, including CuO/SnO 2 , N‐doped carbon nanotubes/Ni/g‐C 3 N 4 , WP/g‐C 3 N 4 , Ag/AgCl/ZnTiO 3 , ZnAl/g‐C 3 N 4 , and α‐Fe 2 O 3 /g‐C 3 N 4 have been investigated for their potential in conversion of CO 2 into other chemicals 15,30–32 . Notably, g‐C 3 N 4 stands out due to its unique attributes and effective performance under solar light.…”

Thermodynamic Modeling and Experimental Investigation of the System Fe–Ti–O-K for Ilmenite Used as Fluidized Bed Oxygen Carrier

“…In the published investigations the uptake of potassium has been measured and the obtained values vary from 2–4 wt % ,, and up to 10 wt % . From thermodynamic calculations conducted for the interactions of K 2 O with ilmenite, K 2 Ti 6 O 13 is commonly found as the most stable product, ,, while studies using phase analysis with X-ray diffraction (XRD) usually find the formation of priderite. ,,− Even though the existing studies provide a certain understanding of the mechanism of potassium diffusion, they do not provide the mechanism behind the formation of different titanates which could explain the different observed uptake mechanisms of potassium by ilmenite. Understanding potassium diffusion and interactions, as well as predicting maximum potassium uptake is crucial to decide the residence time of the material in the plant and to plan for optimal operational conditions and rate of replacement of bed material.…”