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CFD modeling of presurized entrained flow biomass gasification (PEBG): design simulation of the oxygen register in a pilot reactor
2010 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Biomass is considered to be one of the most promising renewable energy sources in the future. Due to stringent policy on emission reduction, biomass has become a centre of attention worldwide as a source of green energy, e.g. motor fuel. This thesis work has been carried out in order to perform computer simulation of the Pressurized Entrained flow Biomass Gasification (PEBG) process developed at Energy Technology Centre (ETC) in Piteå, Sweden. For an efficient and economically feasible conversion of biomass particles to a high quality synthesis gas, the thermo-chemical conversion process based on entrained flow gasification has to be investigated and evaluated thoroughly. Computational fluid dynamics (CFD) has become a well known aiding tool in these regards as to characterize the conversion process, optimize the design, visualize the flow fields in the reacting flow environment, and to improve the operating efficiency as a whole. With this background, the commercial code Ansys-CFX has been used to perform CFD simulations of the PEBG reactor being developed at ETC and evaluate different designs of the oxygen register in the burner. In this thesis work, 2D calculations of the reacting multiphase-flow (Euler- Lagrangian approach) have been performed in an axi-symmetric PEBG reactor using boundary condition with rotational periodicity. The gas phase reactions in this work have been modelled by the combined EDM/FRC combustion model. And the most important multiphase reactions, such as devolatilization and char gasification with carbon dioxide and steam, have been implemented. Inert gas flow simulations have been performed for the purpose of grid convergence study. However, the outcome of this part of the work has not been satisfying. Due to difficulties with controlling the unstructured mesh refinements for the different length scales in the reactor geometry with very small oxygen inlets in the burner, no formal error estimation was conducted. However, a number of simulations have been performed with the implemented reacting flow model for different burner designs, considering degree of swirl and amount of radial directed flow. The responses of the different burner designs on the general flow field and conversion characteristics are evaluated and compared between the considered cases. Considering all the simulations that were performed within this thesis work, the results obtained for designs with large value of radial attack angles (up to 30°) and low degree of swirl (1-2°) have shown favorable results. The results are favorable regarding the flame shape and its location, re-circulating flow pattern, carbon conversion, and low thermal load on the rector lining. Within the given time frame for the current applied research project, maximum efforts have been exerted in order to fulfil the objectives of the work. The results obtained from the comprehensive simulations within this work are to be considered as reliable with respect to how the model was formulated, implemented and finally used. However, the simulation results should be compared with experimentally obtained data from the PEBG pilot plant (when available) before any final conclusions about the validity of results can be made and for any further predictions of the performance of PEBG reactor.

Place, publisher, year, edition, pages
Keyword [en]
Technology, CFD modeling, Biomass gasification, Oxygen register, Oxygen, attack angle, swirl angle
Keyword [sv]
URN: urn:nbn:se:ltu:diva-59358ISRN: LTU-PB-EX--10/055--SELocal ID: fe5454c0-5c29-4ada-8e54-636af56ad2a5OAI: diva2:1032745
Subject / course
Student thesis, at least 30 credits
Educational program
Energy Engineering, master's level
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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