Ash Cenosphere from Solid Fuels Combustion. Part 1: An Investigation into Its Formation Mechanism Using Pyrite as a Model Fuel

Abstract

This paper reports a systematic investigation into the fundamental formation mechanism of ash cenosphere during solid fuels combustion using pyrite as a model fuel. The combustion of pulverized pyrite particles (38–45 μm) was carried out in a laboratory-scale drop-tube furnace at furnace temperatures of 530–1100 °C. The formation of ash cenosphere commences at 580 °C. At temperatures ≥600 °C, the ash products of pyrite combustion consist of dominantly large ash cenospheres (up to 130 μm in diameter) with thin shells (1–3 μm) and ash cenosphere fragments of various sizes. An increase in the temperature results in enhanced ash cenosphere fragmentation. The formation of molten Fe–S–O droplets during pyrite combustion is essential to ash cenosphere formation. The Fe–S–O melts inflate and expand into cenospheric forms (that may also burst into smaller fragments) via sulfur oxide gas generation inside the molten droplets as oxidation reactions progress. Further oxidation and resolidification transforms these cenospheric precursors into final ash cenospheres that also experience fragmentation and contain dominantly iron oxides.

Composition, Structure, and Formation Routes of Blocklike Ferrospheres Separated from Coal and Lignite Fly Ashes

“…The carbon matrix prevents successive conversion of iron-oxysulfide melt droplets into hollow globules, which can occur during direct oxidation of pyrite particles. In particular, it was shown by Li and Wu that conversion of 38–45 μm pulverized pyrite particles in an oxidizing atmosphere at 530–1100 °C results in the formation of 130 μm iron oxide cenospheres with a shell thickness of 13 μm, instead of monoblock globules . The fragmentation of hollow globules at 600 °C produces PM 10 particles with an aerodynamic diameter of less than 10 μm …”

“…In particular, it was shown by Li and Wu that conversion of 38−45 μm pulverized pyrite particles in an oxidizing atmosphere at 530−1100 °C results in the formation of 130 μm iron oxide cenospheres with a shell thickness of 13 μm, instead of monoblock globules. 49 The fragmentation of hollow globules at 600 °C produces PM 10 particles with an aerodynamic diameter of less than 10 μm. 50 Compared to monoblock FSs of series S, globules of series B contain a lower FeO concentration of 83−93.7 wt % and significantly higher concentrations of spinel-forming MgO and MnO oxides, which reach 7 and 3 wt %, respectively (Table 2, Figure 4).…”

Understanding mineral behaviors during anthracite fluidized-bed gasification based on slag characteristics

“…Pyrite decomposes to pyrrhotite and oxidizes from the surface inward to produce molten FeO-FeS [51]. Generation of sulfur dioxide in the FeO-FeS molten droplets leads to rupture of the ash particles [52], which might increase the amount of lowmelting-point eutectics of hercynite and anorthite. Moreover, the fine SiO 2 , Al 2 O 3 , and CaO particles with high reactivity (less than 1 lm, and larger surface specific area) interact each other, and form low-melting-point, spherical gehlenite (Ca 2 Al 2 SiO 7 ) grains.…”

Separation Process and Microstructure-Chemical Composition Relationship of Cenospheres from Lignite Fly Ash Produced from Coal-Fired Power Plant in Thailand

“…To this point of view, it is interesting to note herein that there is a riation in chemical composition and cenospheres yield across the power stations and s. The chemistry in cenospheres is strongly governed by the process of ash cenospheres the furnace. The chemical composition of the molten droplets associated with the in the furnace considerably determined the particle size of cenospheres [16,69]. The large particle size was attributed to a result of an increased Al content that increases e molten droplets, in turn stabilizing them during the expansion, rather than exploding gments [18].…”

“…Besides, a noticeable difference observed is magnetite; the magnetite structure of the bulk cenospheres collected in this study is orthorhombic (a = 5.9340 Å, b = 5.9250 Å, and c = 16.7520 Å), whereas that of fly ash is cubic (a = 8.3778 Å). The formation of the ash cenospheres involves fundamentally the chemical oxidation reactions, the resulting gas generation, and particle expansion [69]. Within the Fe-S-O molten droplet precursor, the reactions consume sulfur dioxide gas while solidifying and forming the ash cenospheres.…”