Publication type: Conference other
Type of review: Peer review (abstract)
Title: Conference talk on investigating tar formation at low pressures in wood gasification systems, applying a novel thermo-chemical simulation model
Authors: Boiger, Gernot Kurt
Buff, Vincent
Zubiaga, Asier
Caels, Pedro
et. al: No
Proceedings: Proceedings of the ICPS19 : 5th international conference on polygeneration strategies
Volume(Issue): 5
Conference details: ICPS19 - 5th International Conference on Polygeneration Strategies, Vienna, 18-20 November 2019
Issue Date: 18-Nov-2019
ISBN: 978-3-9503671-1-9
Language: English
Subjects: Wood gas; Simulation; Thermodynamics; Tar
Subject (DDC): 540: Chemistry
Abstract: Introduction and Short Description: The method of gasifying wood via pyrolysis, gas purification, feeding a gas motor and producing electricity via a generator, has been applied for decades. Even-though wood gasification remains a promising technology regarding de-centralized sustainable energy supply, its main limitations, namely the issues of unsteady operation, excessive tar-formation and consequential high maintenance requirements, have never been fully overcome. In order to tackle these deficiencies and to increase the understanding of thermo-chemical wood-gas phase reaction dynamics, a numerical model has been created. After validating the simulator against comparable software, it has been applied to predict and thus understand tar-formation phenomena within a small experimental co-current gasification system. A particular focus within this work is laid on the investigation and minimization of tar-formation phenomena within low-pressure zones (e.g. downstream of valves) at temperatures T≤500K. Model-based analysis has led to a range of recommended process modifications to reduce the occurrence of tars. Methodology, Results and Discussion: The novel thermo-chemical wood-gas model is inspired by a unifying perspective on physical phenomena, based on Gibbs fundamental equation. The tool considers coal C(s), water H2O(v), methane CH4, carbon-dioxide CO2, carbon-monoxide CO, hydrogen H2 and tar represented by naphthalene C10H8 as interacting chemical species i. Within the applied simulation concept, any chemical reaction k such as, but not exclusively the hetero-/homogeneous Boudouard-, Methanation- or Water-Gas-Shift reaction is driven by non-zero molar Gibbs free energies of reaction ΔGR,k. The solver has been validated by comparison to a well-known approach based on minimizing global Gibbs free energy within a LaGrange function. Graphs compare respective results of calculated wood-gas equilibria compositions over a process-relevant temperature range, and clearly shows 1:1 correspondences between the solvers. Applying the solver and accounting for decreasing temperature and pressure along the wood-gas flow path, shifts in species concentrations can be qualitatively predicted. On this basis the following measures can be recommended to minimize tar occurrence in low-pressure zones: i) Decrease gas residence time and ii) increase temperatures. iii) Increase hydrogen to carbon ratio RH/C as well as iv) oxygen to carbon ratio RO/C in the wood gas, either by v) removing coal from the reaction zone or by adding either vi) water or vii) process air. Graphs show the comparison of three simulation runs where wood-gas with varying RH/C ratios is exposed to temperature and pressure drop. According to this prediction the amount of naphthalene decreases strongly at increasing RH/C. Conclusion and Outlook: The full paper will contain more detailed insights into the physical and methodical principles behind the dynamic wood-gasification solver and will provide more detailed insights into predicted gas compositions as well as investigations leading to the “recommendations for minimizing tar formation under low-pressure conditions” formulated in 2.
URI: https://digitalcollection.zhaw.ch/handle/11475/19478
Fulltext version: Published version
License (according to publishing contract): Not specified
Departement: School of Engineering
Organisational Unit: Institute of Computational Physics (ICP)
Appears in collections:Publikationen School of Engineering

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