Gasification kinetics of lignite char in a fluidized bed of reactive oxygen carrier particles

Haus, Johannes; Goltzsche, Matthis; Hartge, Ernst‐Ulrich; Heinrich, Stefan; Werther, Joachim

doi:10.1016/j.fuel.2018.08.151

Cited by 13 publications

(9 citation statements)

References 23 publications

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“…C i ,b (mol m –3 ) is the concentration of the gas component in the bulk, and C i ,s (mol m –3 ) is the concentration of the gas component on the particle surface. When the gasification agent consists of CO 2 and H 2 O, the gasification characteristics are basically the same as when coal is gasified alone with H 2 O . When CO and H 2 exist together, CO does not show a significant inhibitory effect .…”

Section: Kinetic Modelmentioning

confidence: 93%

“…In a tubular furnace, the temperature was raised to 1223 K at a rate of 20 K min –1 , and then, coal char was generated at the stabilized temperature for 30 min. After crushing and screening of the coal char samples, particles in the size range of 25–58 μm were selected for experiments to avoid the effect of internal diffusion . The proximate and ultimate analysis results of coal chars are shown in Table .…”

Section: Methodsmentioning

confidence: 99%

“…After crushing and screening of the coal char samples, particles in the size range of 25−58 μm were selected for experiments to avoid the effect of internal diffusion. 34 The proximate and ultimate analysis results of coal chars are shown in Table 1.…”

Section: Methodsmentioning

confidence: 99%

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Kinetics of Coal Char Gasification with Fe-Based Oxygen Carriers under Pressured Conditions

et al. 2020

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Under high-pressure conditions, coal chemical looping gasification (CLG) is a potential technology for industrial applications based on its ability to provide clean and efficient conversion of coal to produce syngas. Within the range of 0.1–1.2 MPa, simulations and experiments were carried out as a validation methodology to study the gasification of coal chars with H2O in the presence of Fe2O3/Al2O3 as the oxygen carrier (OC) in a fixed-bed reactor. The characteristics of pressurized CLG and the crystalline phase of the reduced OC were investigated by combining the mass transfer model with intrinsic kinetic experiments. The results showed that H2O replenishment and H2 removal on the particle surface of coal char by causing the Fe-based OC to undergo reduction, within the mass transfer coefficient K m a m of 0.0015–0.0035 m3 mol–1 min–1, minimized the concentration gradient between the particle surface and the bulk caused by external diffusion as well as the H2 inhibition effect on the surface of coal char particles. The maximum gasification rate of CLG was 2.14 times greater than the gasification rate without OC, and the influence of the coal type on the gasification rate decreased with increasing pressure. The reduced state of the Fe-based OC was Fe3O4 at atmospheric pressure, but FeAl2O4 appeared when the total pressure was greater than 0.3 MPa, while the average rate of oxygen release slowed significantly, and the maximum oxygen release increased. The deep reduction process of Fe2O3/Al2O3 to Fe–Al spinel could significantly enhance the gasification rate of coal char. In addition, an overall kinetic model was established that could describe the variations in the gasification rate with the temperature, pressure, carbon conversion, and lattice oxygen release, including the influence of external diffusion. The simulations reveal the pressured reaction mechanisms of the enhancement of char gasification during CLG with the kinetic model.

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Section: Kinetic Modelmentioning

confidence: 93%

Section: Methodsmentioning

confidence: 99%

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Kinetics of Coal Char Gasification with Fe-Based Oxygen Carriers under Pressured Conditions

et al. 2020

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“…More details about the reactor can be found in [8]. The biomass pellets are fed through a small pipe ending shortly before the distributor plate.…”

Section: Fbr-fluidized Bed Reactor For Type a And Type B Pelletsmentioning

confidence: 99%

Characterizing devolatilized wood pellets for fluidized bed applications

Jarolin

Wang

Dymala

et al. 2021

Biomass Conv. Bioref.

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We investigated devolatilized wood pellets to characterize their mechanical behavior and their microstructure. The work’s aim is to increase the understanding and modeling capabilities for the application in fluidized bed gasification as a sustainable alternative to generate synthesis gas. Our experiments showed that devolatilized wood pellets are a stable but highly porous and fragile structure. Computed tomographic images of the same pellets before and after devolatilization showed that the existing pore network in raw conditions characterizes the final structure. Along with the pores, the reaction rate likely increases and the pores massively enlarge, and internal cavities are formed. The resulting pore network dominates the mechanical behavior and leads to micro fragmentations already at low static loads or slow dynamic impacts. This results in the creation of fines or breakage already at low impact velocities. For fluidized bed devolatilization, the large-scale open pore network of the biochar pellets allows the penetration of bed material into the pellet leading to an estimated increase in the pellet’s mass of up to 45%. However, an increase in pore size caused by the penetration was not apparent. Due to the pellet’s porous structure, breakage and attrition induced by mechanical stresses are likely to be as or even more important than primary fragmentation caused by the devolatilization process itself in a reactor.

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“…There are about four rate-controlling steps for heterogeneous reactions kinetics, including (i) external diffusion of gas from the gas phase to the particle surface, (ii) intraparticle diffusion of gas molecule inside the pore, (iii) adsorption at the surface active sites and surface reaction, and (iv) the change of solid structure due to the chemical reaction. To describe the above kinetic steps of heterogeneous redox reactions of fluidizing oxygen carrier particles, different models have been developed, such as semiempirical models, , the pore diffusion model, , the shrinking core model, , and the particle-scale kinetic model. , Regardless of the type of model used to describe the above heterogeneous kinetics, the model must be validated, and the model parameters must be obtained based on a reliable experimental method and reliable measurement data.…”

Section: Introductionmentioning

confidence: 99%

Microfluidized Bed Thermogravimetry Combined with Mass Spectrometry (MFB-TG-MS) for Redox Kinetic Study of Oxygen Carrier

Cai

2020

Energy Fuels

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Heterogeneous reduction/oxidation reactions in fluidization state play vital roles in chemical looping combustion (CLC) processes. A key task in studying heterogeneous reduction/oxidation reactions and developing CLC technology is to measure the heterogeneous redox kinetics of oxygen carrier particles in fluidizing state. Here we compared two methods to measure heterogeneous redox kinetics of fluidizing oxygen carrier particles by both the solid mass signal measured from the weight balance and the gas evolution signal measured by mass spectroscopy. Microfluidized bed thermogravimetry combined with the mass spectrometry method (MFB-TG-MS) was used here to measure the tail gas signal, and heterogeneous redox kinetics was obtained from the analysis of the tail gas signal. The oxidation by air and reduction by H2 of a manganese oxide were chosen to be the target reactions. The heterogeneous redox kinetics of manganese oxide obtained from the analysis of the tail gas signal measured by mass spectroscopy was compared with the previously developed MFB-TGA method in which the real-time solid mass signal of fluidizing oxygen carrier was measured by weight balance. A K–L two-phase fluidized bed model, developed by Kunni and Levenspiel to describe the mass transfer and reaction behavior in a bubbling fluidized bed, was used to analyze the experimental data from MFB-TG-MS. It was found that there is no big difference for the reduction kinetics of manganese oxide measured by the two signals. Mass balance was achieved for the gas signal method, and the outlet mole fraction of H2 is consistent with the model result, while for the fast heterogeneous oxidation reaction, the deconvolution of the gas signal is needed. It was found that the oxidation conversion calculated by the deconvoluted gas signal was close to the previous results measured by the weight balance method, while the estimation of the initial oxidation rate from the gas signal was not so accurate. For studying many redox cycles of oxygen carrier, it is more suitable to obtain the heterogeneous kinetics from the solid mass signal measured by the weight balance method. We anticipate that this new MFB-TG-MS method can be readily applied to measure fast heterogeneous redox kinetics of fluidizing oxygen carrier and provide a more comprehensive understanding for heterogeneous reactions occurring inside the fluidized bed reactor.

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Gasification kinetics of lignite char in a fluidized bed of reactive oxygen carrier particles

Cited by 13 publications

References 23 publications

Kinetics of Coal Char Gasification with Fe-Based Oxygen Carriers under Pressured Conditions

Kinetics of Coal Char Gasification with Fe-Based Oxygen Carriers under Pressured Conditions

Characterizing devolatilized wood pellets for fluidized bed applications

Microfluidized Bed Thermogravimetry Combined with Mass Spectrometry (MFB-TG-MS) for Redox Kinetic Study of Oxygen Carrier

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