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Suspension Burning
Published in Kenneth M. Bryden, Kenneth W. Ragland, Song-Charng Kong, Combustion Engineering, 2022
Kenneth M. Bryden, Kenneth W. Ragland, Song-Charng Kong
Between 0.01 s and 1 s, char burn continues, and the particle surface temperature is several hundred degree Celsius hotter than the gas temperature due to the surface reaction with oxygen. After 0.5 s, half of the char is consumed. Fissures are formed in the char particle, the porosity of the particle has increased, and the particle has begun to shrink in size. The mineral matter (which is dispersed throughout the char in nodules mostly less than 2 μm in size) becomes molten, and the trace metals in the mineral matter volatilize. The many molten mineral matter nodules agglomerate into a few nodules, and toward the latter stages of char burnout the char may fragment into several pieces. The mineral matter nodules meanwhile have grown large enough through agglomeration for vapor pressure to overcome surface tension effects. Consequently, they puff up into tiny hollow glass-like spheres called cenospheres. These cenospheres are like miniature Christmas tree ornaments that vary in size from 0.1 to 50 μm and are spherical. After approximately l s, char combustion and cenosphere formation are complete, and the combustion products begin to cool as they flow past the convective tubes. In the ambient air, fly ash from pulverized coal-fired boilers (and also residual fuel oil–fired boilers) can be identified by its characteristic cenospheres, as opposed to soil dust for example, which is irregular in shape.
Cement
Published in A. Bahurudeen, P.V.P. Moorthi, Testing of Construction Materials, 2020
The microstructure of fly ash shows that fly ash is a solid spherical particle. A set of hollow spherical fly ash particles with entrapped gas in it is called cenospheres. Another set of hollow spherical fly ash particles with solid particles inside them are called plerospheres.
Ocean Disposal
Published in Stephen M. Testa, Geological Aspects of Hazardous Waste Management, 2020
Fly ash is denser than water and characterized as a solid produced in large quantities from the combustion of coal; it consists mostly of small, solid spheres with diameters ranging from 0.5 to approximately 200 μm. The settling behavior of fly ash is complex. Obviously, smaller sized particles (i.e., <10 μm) will have very low settling rates (on the order of 10−3 cm/s−1) relative to larger particles. Some of the fly ash will float, that being the cenospheres. Cenospheres are glassy spheres ranging in diameter from 20 to 200 μm that are filled with nitrogen and carbon dioxide gases, comprising up to 20% in total volume of fly ash. The variability in fly ash composition and physical properties reflect the origin of the coal, degree of pulverization before the coal is burned, and the type of boiler unit utilized. Scrubber sludge is principally gypsum and calcium sulfite hemihydrate. Solids density for fly ash ranges from 1.5 to 1.7 g cm−3.
Incorporation of a high volume of cenosphere particles in low water-to-cement matrix for developing high strength and lightweight cementitious composites
Published in Journal of Sustainable Cement-Based Materials, 2023
Jyoti Mahato, Jingwei Yang, Nankyoung Lee, Hyunuk Kang, Juhyuk Moon
The raw materials used in the present study were ordinary Portland cement (OPC; Union Corp., Korea), undensified silica fume (SF; Grade 940-U, Elkem Microsilica, Oslo, Norway), quartz powder (QP; 10 microsilica, SAC Corporation, Ulsan, South Korea), polycarboxylate-based high-range water-reducing superplasticizer (SP; Flowmix 3000 U, Dongnam Co. Ltd., Chungnam, South Korea), and cenospheres (CS; SphereTek Ltd., Hebei, China). The particle size distributions of the OPC, QP, SF, and cenospheres were obtained with a laser diffraction analyzer (HORIBA SZ-100Z, Horiba Ltd., Kyoto, Japan), and the results are illustrated in Figure 1. The chemical composition of the raw materials was found via X-ray fluorescence (XRF) spectroscopy (S4 Pioneer, Bruker AXS GmbH, Karlruhe, Germany) and is listed in Table 2. Based on the measured XRD (Figure 2), the mineralogical compositions of the raw materials can be quantitatively analyzed. In the OPC, the constituents were alite (51.6%), belite (0.5%), dolomite (18.1%), and limestone (29.7%). The large amount of limestone powder was included in the OPC, which was verified in previous studies of ultra-high-performance concrete [31–33]. The 97 wt% amorphous silica and the 98 wt% crystalline quartz were found in the SF and QP, respectively [32, 34]. The size of the cenospheres ranged from 10 to 100 µm, with an average particle size of 52 µm. The density of the cenospheres was 0.75 g/cm3, according to the manufacturer. The XRD pattern shows that the cenospheres were mainly amorphous phase, with small amounts of quartz and mullite crystals (Figure 2(d)).
High temperature resistant restoration mortar with fly ash and GGBFS
Published in Journal of Sustainable Cement-Based Materials, 2022
Rüya Kılıç Demircan, Gökhan Kaplan, Damla Nur Çelik
Cenospheres are hollow spheres within the spherical size FA particles that are produced in thermal power plants. Cenospheres have a low density of 400–900 kg/m3 and a particle size distribution in the range of 10–300 µm [99, 100]. Cenosphere content of fly ash particles varied between 0.1 and 3.8% by weight depending on the type of coal [101]. Haustein and Cudowska have determined that as the cenosphere content increased, the apparent porosity values of concrete increased [102]. Kim and Lee observed that the water absorption coefficient increased with FA content, while it decreased with GBFS content [103]. Shaikh and Supit conducted that the depth of water penetration has increased when FA is used at 60% instead of 40% [104]. Chinchillas-Chinchillas et al. [88] were determined that with the use of microfibers, the water penetration depth of the mortars was reduced. Similar results were observed in the study by Rashid [105].
Life cycle assessment of lightweight concrete containing recycled plastics and fly ash
Published in European Journal of Environmental and Civil Engineering, 2022
Yusuf Cagatay Ersan, Sedat Gulcimen, Tuba Nur Imis, Osman Saygin, Nigmet Uzal
Currently, FA is known as the world’s fifth largest raw material source (Mukherjee et al., 2008). Global FA market size is valued about 4.1 Billion USD and recent reports revealed that it is growing with a 6.5% compound annual growth rate (Reports and Data, 2019). Utilization of FA in concrete dramatically increased in the last 50 years (Yahia et al., 2017). In addition to FA, fly ash cenospheres (FACs), which are hollow spherical particles constituting 1–2% of the FA (Siddique, 2010), has been utilized as a lightweight filler material for about the last 35 years (Hanif, Lu, et al., 2017). Although, spherical particles of FACs are comparatively larger in size (10–1000 μm) than FA, they both have similar chemical compositions (Żyrkowski et al., 2016). Low density, good dispersibility, good workability, high strength and thermal resistance can be listed among the superior properties of cenospheres (Ranjbar & Kuenzel, 2017). Zhou and Brooks (2019) reported that including micro-size FAC into the cementitious matrix can decrease density and thermal conductivity of lightweight concrete (LWC). Furthermore, FAC can provide barriers to hinder crack propagation due to their strong shell and small particle size (Zhou & Brooks, 2019).