- Title
- A fundamental study on the gasification kinetics of biomass chars
- Creator
- Cetin, Emre
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2004
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Biomass (i.e. organic matter derived from living organisms) is currently the world's most underutilised fuel source and does not contribute to the global warming when combusted. Fossil fuel-fired power plants are Australia's major contributors to its total greenhouse gas emissions. The usage of the fossil fuels needs to be decreased in our world as its negative impact, global warming, is becoming more evident. Therefore, research efforts need to be direct to the development of advanced biomass-fired systems, such as Integrated Gasification Combined Cycle. While these high efficiency energy production methods are being implemented, Australia will be able to achieve its Mandatory Renewable Energy Target (MRET) and moreover will be able to meet the responsibilities to the generations to come. Pressurised biomass gasification is a key area in the successful development of these new concepts. Unfortunately, there has been very little information on biomass gasification at high pressure and/or high heating rate conditions in the literature. Therefore, the aim of this project was to gain a fundamental understanding about the gasification characteristics of chars that are generated from three different biomass species, namely, radiata pine, spotted gum and sugarcane bagasse. The research, in particular, focused on: (i) determining the gasification reactivities. ; (ii) investigating the structural and compositional transformations during pyrolysis. ; (iii) their influence on the gasification reactivity. The physical and chemical structures as well as gasification reactivities of chars were studied to gain insight into the role of heating rate and pressure on the gasification characteristics of biomass chars. Char samples were generated in a wire mesh reactor (WMR) and a tubular reactor. Scanning electron microscopy (SEM) analysis, X-Ray diffractometry (XRD), digital cinematography and surface area analysis were employed to determine the impact of operating conditions on the char structure. Char reactivities were found to increase with increasing pyrolysis heating rates the char particles underwent plastic deformation (i.e. melted), developing a structure different to that of the virgin biomass. Pressure was also found to influence the physical and chemical structures of char particles. The difference in the gasification reactivities of biomass chars at pressure was found to correlate well with the effect of pyrolysis pressure on the graphitisation process in the biomass char structure. The gasification kinetics of biomass chars have been investigated within the temperature range of 800-950°C, CO₂ concentrations of 10% to 100% v/v, pressures between 1-20 bar using the thermogravimetric analysis (TGA) technique. For the range of biomass species studied the activation energies of atmospheric CO₂ gasification were within 200-240 kJ/mol, and the reaction orders between 0.4-1. These results are in good agreement with kinetic data reported in the literature. The Quartz Wool Matrix (QWM) method was used to simulate circulating fluidised bed conditions and reactivity results were compared with the TGA data. Kinetic data from TGA analyses was found to be suitable for predicting CFB gasification reactivity. Total pressure variations have been found to have no effect on reactivity during char conversion. The Langmuir-Hinselwood rate equation represents the pressurised biomass char gasification kinetics well. The Langmuir-Hinshelwood expression for radiata pine char at studies conditions can be described as the following: [formula could not be replicated]. The number of experiments and the biomass samples used in this study could of course be increased. However, in its current order, it is filling a very substantial gap in the current literature, especially in the pressurised pyrolysis and gasification studies. Furthermore, it is going to produce immediate solutions in a wide range of practical applications in power generation industry.
- Subject
- biomass chars; fuel source; fossil fuels; kinetics; biomass-fired systems; gasification
- Identifier
- http://hdl.handle.net/1959.13/1312434
- Identifier
- uon:22389
- Rights
- Copyright 2004 Emre Cetin
- Language
- eng
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