Browsing by Author "Mock, Chinsung"

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    Burning characteristics of single particles of coal and wood mixtures for co-firing in an upward-flowing hot gas stream
    (Elsevier, 2017-04-14) Mock, Chinsung; Lee, Hookyung; Choi, Sangmin; Yang, Won; Manovic, Vasilije
    This study presents the comparative burning behaviours of single solid particles of coal and biomass mixtures for co-firing. In this experimental investigation, a direct observation approach was used to investigate the ignition, flame characteristics and combustion times by means of high-speed photography at 7000 frames per second. Single particles were entrained into a hot gas stream at 1340 K and a rapid heating rate of 104–105 K/s. The apparent volatile flames from the prepared particle size groups were observed within 20–50 ms. To assess the effect of oxygen concentration, particles were burned for their flame characteristics in a range of 10%–40% O2. The test particles were sieved into three size groups (215–255 μm, 255–300 μm and 300–350 μm) to assess the effect of particle size. Special particles for the co-firing effect were collected individually from two types of mixed pellet: 20:80 and 50:50 coal/wood. Pure sub-bituminous coal and wood particles were also prepared in order to compare their combustion behaviours. In the experimental setup with a cross-injection configuration, sequential combustion processes were effectively and clearly described in terms of particle displacement with time. The experimental results showed distinguishable flame characteristics from single particles of coal, 50:50 coal/wood, 20:80 coal/wood and wood, including soot flame size and intensity. The impact of high coal-blending ratio caused an increase in the flame size and intensity and the ignition time was close to that of pure coal particles. Quantitative measurements of combustion events on co-firing particles were also discussed in relation to significant impacts of the particle size and the oxygen concentration.
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    Combustion behaviour of relatively large pulverised biomass particles at rapid heating rates
    (American Chemical Society, 2016-10-28) Mock, Chinsung; Lee, Hookyung; Choi, Sangmin; Manovic, Vasilije
    A pulverized solid fuel particle in a hot gas stream appears to have different characteristic behaviors at several stages, including heat-up, release of volatile matter, gas phase, and solid combustion. The characteristics of these stages may vary distinctly depending on devolatilization rate, the particle temperature history, and its chemical and physical properties. Biomass particles manifest different combustion behavior from that of burning coal particles under the same combustion conditions because they contain more volatiles (less fixed carbon), and they have a relatively lower particle density due to their fibrous structure. This paper presents an experimental study of burning behavior of different types of biomass particles (torrefied wood, coffee waste, and sewage sludge). The main experimental parameters—gas temperatures of 1090 and 1340 K, and O2 concentrations ranging from 10% to 40%—were employed to investigate the burning of biomass through a direct-observation approach using a high-speed photography technique at 7000 frames/s. In the case of firing/cofiring, biomass particles must be larger than the coal particles in order to achieve an equivalent thermal balance due to the higher energy density of coal. Therefore, the selected biomass samples were in the size range from 150–215 μm to 425–500 μm. The experimental setup has a cross-flow configuration for particle injection in order to enhance interaction between the particle and the two different streams—a cold carrier gas at 298 K, and upward-flowing postcombustion gases. It is believed that the employed experimental conditions are similar to those in a realistic furnace with a rapid heating rate of 105 K/s. The experimentally significant results, including the effective radii of the volatile flames, degrees of flame intensity, and the maximum size of a particle, are important for validation of models of single biomass particle combustion.
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    Combustion behaviour of single pellets of coal–wood mixtures in a hot gas flow field
    (2018-09-21) Mock, Chinsung; Lee, Hookyung; Choi, Seuk-Cheun; Yang, Won; Choi, Sangmin; Manovic, Vasilije
    This experimental study explores the burning characteristics of single pellets made of wood and coal mixtures for co-firing. Three types of pellets were prepared with different wood–coal ratios (100:0, 80:20, and 50:50). Experiments were carried out in a laboratory reactor at rapid heating rates and under oxygen concentrations between 10 and 40%. To investigate their combustion behavior, single pellets were suspended on a wire injected into a hot gas stream at 1340 K and flame and char combustion were recorded through an observation window by means of a high-resolution (4K) camera. The sequential combustion time, volatile flame characteristics, and mass reduction rate were obtained over a time profile by carefully controlled particle injection. The results demonstrated that the char combustion time increased significantly in comparison to the volatile combustion time, which only varied a little, when the pellets contained coal in the mixture. Partially detached flames were also predominantly observed on pure biomass pellets at oxygen concentrations between 21 and 40%. During the homogeneous combustion period, the cross-sectional area of a pellet shrunk by 26.3–37.5% depending upon the type of pellet.
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    An experimental investigation of single biomass particle combustion in hot gas flow.
    (2017-01) Mock, Chinsung; Manovic, Vasilije
    Based 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.
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    Flame structures and ignition characteristics of torrefied and raw sewage sludge particles at rapid heating rates
    (Elsevier, 2017-04-07) Mock, Chinsung; Lee, Hookyung; Choi, Sangmin; Manovic, Vasilije
    Torrefaction is a promising method for improving the quality of pulverised solid fuel, as it increases the flame stability, radiative heat transfer and energy density of the fuel. Raw sewage sludge contains less fixed carbon and more ash compounds than other biomasses; consequently, it has poor energy quality with a long ignition delay and forms a relatively low, sooty flame. In this study, we directly investigate the combustion behaviours of particles with varying degrees of torrefaction by burning them at 1340 K. The torrefied particles were prepared at different temperatures (473 K or 573 K) for different residence times (10 min or 30 min). The experimental parameters examined were the size range of the particles (150–215 μm and 255–300 μm) and the O2 percentage (10–40%). The particles were entrained from a cold carrier gas into a hot gas stream, igniting a volatile flame that was extinguished a few milliseconds later. These temporal variations in the burning particles were detected by in-situ high-speed photography (7000 frames/s). The torrefaction degree affected the flame structure and varied the ignition delay, due to the mismatched reactivity and soot formation at rapid heating rates. The most torrefied sludge particles exhibited a relatively luminous volatile cloud and a large flame, while preserving the duration of volatile combustion. These observations confirm the improved pulverised combustion of the torrefied sludge particles. We also obtained valuable flame parameters (radius, intensity and combustion time) of the differently torrefied sludge particles.