Multi-scale analysis and optimization of chemical looping gasification of biomass
Final Report Abstract
Chemical looping gasification (CLG) of biomass might be one possible approach, to generate synthesis gas from biomass and allow, for example, the production of hydrogen or biofuel from agricultural residuals. For better fuel properties biomass is often pelletized, which increases the heating value and simplifies storage and transport. By applying the chemical looping concept to the gasification of biomass pellets, dilution of the generated syngas can be prevented without the need of using expensive pure oxygen or high amounts of gasification agent gases. However, the technology is still not matured enough for a commercially viable operation and further optimizations are needed. The goal of the here investigated dual-stage reactor design is to reduce the final tar content while maintaining high hydrogen contents and high efficiency. For investigating the design, a multi-scale analysis and optimization were performed studying the single pellet’s behavior and the reactor dynamics experimentally as well as simulative. The microscale analysis of a single pellets’ behavior revealed that the pellets’ structure mostly withstands the rapid devolatilization. However, the formation of a large internal pore network has significant implications on the gasification. Firstly, mechanical testing and simulations with newly developed methods have shown that the pore network dominates the mechanical behavior of the pellets. Secondly, micro-computed tomography revealed that bed material can penetrate the pellet. This phenomenon could be exploited to promote the internal conversion by the choice of the oxygen carrier size. To translate the experimental and micro-scale simulation results into an adapted reactor design, the multiphase particle-in-cell (MP-PIC) method in the framework of Barracuda VR® 21.0 has been applied. Since predicting the mixing accurately is crucial for assessing the reactor, a more accurate drag model based on the energy minimization multi-scale had to be developed and tested. While the chosen MP-PIC framework enabled studying a reactor at a megawattscale, it prevented a detailed consideration of the microscale analysis results due to the limited customizability. For example, biomass particle breakage, particle shrinkage, or temperature gradients inside the thermally-thick pellets could not be considered. For a more in-depth simulation model, a direct coupling of the micro-scale simulation results with the macro-scale simulation would be beneficial but requires a more academically focused software package. Based on the results of the micro-scale and macro-scale simulation and experiments we propose a two-stage design where the biomass pellets are injected in the freeboard of the lower stage. This will allow tars and volatiles to rapidly move to the second stage for further decomposition and prevents a high conversion of the valuable syngas species. A high fluidization velocity in the lower bubbling bed is proposed to promote char gasification. The increased mixing improves the conversion rate but will also result in a higher breakage and attrition of the char pellets. The two-stage design should counteract an increase in fine elutriation since the fines need to travel to and pass the second stage. In the second stage, a lower fluidization velocity can be used for more homogenous gas distribution and a better tar conversion. The availability of oxygen needs to be adjusted to reduce the oxidation of the volatiles in the second stage. However, the influences on tar cracking could not be investigated within this work due to the imitated availability of measured data and models.
Publications
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Modelling of Mechanical Behavior of Biopolymer Alginate Aerogels Using the Bonded-Particle Model, Molecules 2019, 24(14), 2543, pp. 1-15
Dosta, M.; Jarolin, K.; Gurikov, P.
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Syngas, tar and char behavior in chemical looping gasification of sawdust pellet in fluidized bed, Fuel, 270 (2020), 117464, pp. 1-11
Wang, S.; Song, T.; Yin, S.; Hartge, E.-U.; Dymala, T.; Shen, L.; Heinrich, S.; Werther, J.
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Characterizing devolatilized wood pellets for fluidized bed applications, Biomass Conversion and Biorefinery, 2021
Jarolin, K.; Wang, S.; Dymala, T.; Song, T.; Heinrich, S.; Shen, L.; Dosta, M.
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Linearization-based methods for the calibration of bonded-particle models, Comp. Part. Mech. 8, 2021, pp. 511-523
Jarolin, K.; Dosta, M.
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Mechanical strength evolution of biomass pellet during chemical looping gasification in fluidized bed, Fuel Processing Technology, 2021, Volume 221, 106951, pp. 1-13
Wang, S.; Yin, X.; Jarolin, K.; Dymala, T.; Xu, J.; Yin, S.; Dosta, M.; Song, T.; Heinrich, S.; Shen, S.
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MP-PIC simulation of circulating fluidized beds using an EMMS based drag model for Geldart B particles, Particuology, 59 (2021), pp. 76-90
Dymala, T.; Wytrwat, T.; Heinrich, S.
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The MP-PIC method for CFD- simulation of biomass gasification in a lab-scale fluidized bed, CFB 2021 – Proceedings of the 13th International Conference on Fluidized Bed Technology, pp. 208-213
Dymala, T.; Hartge, E.-U.; Song, T.; Shen, L.; Heinrich, S.
