Manovic, VasilijeMock, Chinsung2022-06-012022-06-012017-01http://dspace.lib.cranfield.ac.uk/handle/1826/17980Based on direct observation, this thesis describes the combustion behaviour of solid particles. In particular, biomass and co-firing particles reduce carbon dioxide emissions because the biomass is a carbon-neutral resource. Here, the particles are used in pulverised-combustion applications, but their combustion qualities are not identical. Therefore, single particle combustion plays an important role in demonstrating their combustion quality. Biomass is a renewable energy source and is used in pulverised-combustion applications such as the combustion of low-emission-energy solid fuel. Compared with coal, such solid fuel has a relatively low particle density, more volatiles and less fixed carbon, which results in different combustion characteristics in practical furnaces. The experimental investigation reported herein involves a quantitative analysis of biomass ignition and its volatile flames. The biomass was combusted in a laboratory-scale entrained flow reactor under various oxygen concentrations, with particle size serving as an experimental parameter. The cross-jet configuration, in which the jet injection flow are perpendicular to the main vertical flow on the test rig, leads to the optimal trajectory of entrained single particles and sequential combustion. The combustion process involves heat-up, ignition, devolatilisation and char combustion. Overall, the experiments investigated (a) general biomass samples, (b) torrefied sludge and (c) single particles of coal and wood mixtures. For small-particle combustion and quantitative analysis, all samples were sieved to obtain particle sizes of a few hundred microns, following which they were separated by using an inclined-slope particle-shape separator to isolate the spherical-like particles. Next, the spherical-like particles from the three particle groups were entrained into a hot gas stream to study their burning characteristics using a high-speed optical camera (7000 frames per second) and optical microscopy with LED backlighting to observe morphological combustion events such as overlapping combustion,volatile ignition and flame modes. The biomass samples comprised torrefied wood, coffee waste and sewage sludge with sizes ranging from 150–215 to 425–500 μm. In addition, for a comparative study, subbituminous coal was prepared. The experiment reported herein focused on the flame structure of four solid-fuel particles as a function of time and particle displacement; specifically, we look at (a) the effective radii of volatile flame and (b) the volatile-flame intensity. The results illustrate how, in the cross-jet configuration, realistic trajectories of biomass particles lead to burning that depends on particle size. In addition, an optimum range of particle size is suggested for complete burning. Torrefied sewage sludge particles were prepared under various torrefaction temperatures (473 or 573 K) and residence times (10 or 30 min) and the particles ere sieved to obtain particles sizes in the ranges 150–215 and 255–300 μm. To understand the flame structure, the morphology of carbonaceous species in a flame was observed at three points: (a) the centre of pyrolysis, (b) just inside pyrolysis and (c) just outside pyrolysis. Ignition delay and apparent flame are discussed as a function of degree of torrefaction. The special single particles for co-firing were milled from two types of coal- biomass pellets: (a) 50:50 and (b) 20:80 (coal: biomass by volume). Raw wood and subbituminous coal were also prepared to study their intrinsic characteristics and to make a comparative analysis. Four particles were burned to study their flame characteristics in the range of 10%–40% O₂, and the impact of fuel mixtures are discussed based on quantitative measurements. Furthermore, the sequential combustion processes under slow heating are compared with those under the current rapid heating rate to compare thermal decomposition.en© Cranfield University, 2015. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright holder.Single particlebiomasstorrefactionco-firingcross-jet injectiondirect observationThesis