CO₂ gasification of bio-char derived from conventional and microwave pyrolysis

Thermal-chemical processing of biomass is expected to provide renewable and clean energy and fuels in the future. Due to the nature of endothermic reactions, microwave and conventional heating have been applied to this technology. However, more studies need to be carried out to clarify the difference between these two heating technologies. In this work, we investigated two bio-char samples produced from conventional pyrolysis of wood biomass (yield of bio-char: 38.48 and 59.70 wt.%, respectively) and one bio-char produced from microwave pyrolysis with a yield of 45.16 wt.% from the same biomass sample at different process conditions. Various methodologies have been used to characterise the bio-chars. CO₂ gasification of bio-char has also been studied using a thermogravimetric analyser (TGA) and a fixed-bed reaction system. The results show that volatile and carbon contents of the bio-char derived from microwave pyrolysis were between the two conventional bio-chars. However, the microwave bio-char is more reactive for CO₂ gasification, as more CO was released during TGA experiments, and the CO release peak was narrower compared with the CO₂ gasification of the conventional bio-chars. It is suggested that the conventional bio-char is less reactive due to the presence of more secondary chars which are produced from secondary reactions of volatiles during the conventional biomass pyrolysis. While the microwave pyrolysis generates more uniform bio-chars with less secondary char, and therefore, has advantages of producing bio-char for downstream char gasification

A study of the importance of secondary reactions in char formation and pyrolysis : a dissertation presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Process Engineering at Massey University, Manawatū, New Zealand

Anthropogenic climate change, caused primarily by excessive emissions of carbon dioxide, has led to a renewed interest in char, the solid product of pyrolysis. When applied to soil as biochar it can both sequester carbon and improve soil function. To make its manufacture environmentally friendly and economically viable it is important to maximise char yield, which can be done by promoting secondary reactions. This research shows that secondary reactions, which are enhanced by prolonged vapour-phase residence time and concentration, not only increase the char yield but are the source of the majority of the char formed. All four biomass constituents (extractives, cellulose, hemicellulose and lignin) undergo secondary reactions concurrent with primary reactions over the entire pyrolysis range ≈ 140 to 500 °C, which makes it practically impossible to separate them. Secondary char formation was confirmed to be exothermic which affects the overall heat of pyrolysis. Impregnating the feedstock with the elements K, Mg and P, which are plant macro-nutrients naturally present in biomass, resulted in the catalysis of secondary char formation. The results reveal that a first order reaction model does not describe pyrolysis accurately when char formation is enhanced by catalysis and secondary reactions. Secondary char can be enhanced by increasing the particle size but there is a limit due to increased cracking and fracturing of the pyrolysing solid. This limitation is overcome by pyrolysis in an enclosed vessel, termed autogenous pressure pyrolysis, which was discovered to cause significant changes in the volatile pyrolysis products; indicating the co-production of a high quality liquid. This process, however, negatively affects the char properties relevant for biochar like the surface area, similar to self-charring and co-carbonisation of condensed volatile pyrolysis products. To increase research capabilities a unique high temperature/ high pressure reactor (600 °C at 20 MPa) was designed to allow the detailed characterisation of all three pyrolysis product classes under extreme pyrolysis conditions. This was demonstrated to be invaluable for understanding the underlying pyrolysis mechanism and physical processes at play

Mathieu subspaces of codimension less than n of Mat_n(K)

We classify all Mathieu subspaces of ${\rm Mat}_n(K)$ of codimension less than $n$, under the assumption that ${\rm char\,} K = 0$ or ${\rm char\,} K \ge n$. More precisely, we show that any proper Mathieu subspace of ${\rm Mat}_n(K)$ of codimension less than $n$ is a subspace of $\{M \in {\rm Mat}_n(K) \mid {\rm tr\,} M = 0\}$ if ${\rm char\,} K = 0$ or ${\rm char\,} K \ge n$. On the other hand, we show that every subspace of $\{M \in {\rm Mat}_n(K) \mid {\rm tr\,} M = 0\}$ of codimension less than $n$ in ${\rm Mat}_n(K)$ is a Mathieu subspace of ${\rm Mat}_n(K)$ if ${\rm char\,} K = 0$ or ${\rm char\,} K \ge n+1$.Comment: 20 page

XLOOPS -- A Program Package calculating One- and Two-Loop Feynman Diagrams

The aim of XLOOPS is to calculate one-particle irreducible Feynman diagrams with one or two closed loops for arbitrary processes in the Standard model of particles and related theories. Up to now this aim is realized for all one-loop diagrams with at most three external lines and for two-loop diagrams with two external lines.Comment: 84 pages, Postscript, program package and this manual also available at http://wwwthep.physik.uni-mainz.de/~xloops/, minor changes and bug fixes are included no

Potentials for Generating Alternative Fuels from Empty Palm Fruit Bunches by Pyrolysis

The threat that the disposal of empty palm fruit bunches constitute to communities in oil palm processing areas in Nigeria coupled with the current global focus on alternative energy is the trigger for this work. An existing pyrolytic reactor consisting of a reactor unit, condensate receiver, copper pipe connectors and gas receiver was modified and adapted for converting empty palm fruit bunches to alternative fuels. The average char yield was 44.9%, and the percentage of feedstock converted into pyrogas and tar oil was 55.1%. The char yield decreased gradually as temperature was increased from 300-700°C. Char yield was highest (39.78%) when the temperature was 300°C and the lowest char yield was 25.05% at 700°C The calorific values of char ranged between 21.12 and 23.76 MJ/kg. Apart from the potential of generating energy from pyrolysed EFB, it abates the disposal problem that EFB constitutes in the oil palm industry

Glass fiber addition strengthens low-density ablative compositions

Approximately 15% of E-glass fibers was added to compositions under test and greatly improved char stability. Use of these fibers also reduced thermal strains which, in turn, minimized char shrinkage and associated cracks, subsurface voids, and disbonds. Increased strength allows honeycomb core reinforcement to be replaced by equivalent amount of glass fibers

Evaluation of the energy transfer in the char zone during ablation. Part 2: In-depth response of ablative composites, volume 1

The decomposition of ablative composites is described along with the transport phenomena of pyrolysis gases which result from the decomposition of these plastics as they flow through the porous char of char-forming ablators. The pyrolysis products are those formed by the thermal degradation of nylon-phenolic resin and silicone elastomer composites. Emphasis is placed on the nature and extent of chemical reactions of the pyrolysis products and the char, along with the energy absorbed by the combined pyrolysis and char zone. Chemical reactions with thermodynamically consistent kinetic data are determined in order to develop a realistic analysis for predicting the thermal performance of ablative heat shields

Steam gasification of bagasse: Effect of heating rate

Bagasse residue is a potential feedstock for steam gasification, but knowledge of this technology is still small and fragmented. Heating rate is of the most important factors influencing the gasification process. However, this parameter has not yet been fully investigated. In this study, the characteristics of bagasse and its chars were identified, and the effect of heating rate on steam gasification kinetics was studied. Bagasse contained little ash content, comparable to woody biomass, which is beneficial for thermochemical conversion processes. The bagasse char had a high heating value, comparable to coal. Effect of a small change in heating rate from 5 to 15 °Cmin-1 was not observed, while a significant increase from 15 to 1800 °Cmin-1 had a considerable effect on steam gasification kinetics. A char produced at a high heating rate increased gasification kinetics by 1.35 times compared to a char produced at a low heating rate. Results and data produced could be useful for the conception of new gasifiers using bagasse, such as staged-gasifiers in which the char production zone is separated from the gasification zone