In this paper, an intensive characterization of ash deposits collected from different positions of a pulverized-coal (PC) boiler has been conducted to diagnose the ash slagging and fouling issues within this boiler and to clarify the mass balance/ flow of individual major elements and their role on ash slagging and fouling. A lab-scale drop-tube furnace has also been employed to elucidate the partitioning of the major metals during coal pyrolysis and char oxidation, to interpret the PC boiler results. The lignite tested is rich in Na and Ca, which are mostly present as organically bound cations and superfine mineral grains. In the air-fired boiler, the refractory minerals of silicates, aluminates, or aluminosilicates preferentially remained in fireside slag and bottom ash, forming low-temperature eutectics via the interaction with CaO and Fe 2 O 3 on the receding char surface. The complex eutectic Ca−Al−Si consists of the liquidus matrix of the dense layer of fireside slag, in which Fe 2+ -bearing oxide was highly crystallized into a diamond-shape crystal on the water-tube surface. The ash fouling on Feston and superheater tubes was formed with a thinner Fe-rich layer that is followed by the deposition of Na 2 SO 4 liquids. The abundance of Fe 2 O 3 and CaO in the char matrix is crucial, which triggered the formation of around 80% liquids in the fireside slag with a viscosity of approximating 100 poise at 1200 °C. On the reheat tube surface, about 60% of the fully oxidized hematite was even reduced by the metallic iron into magnetite. Na 2 O and MgO in the char matrix preferentially escaped into flue gas as vaporized metallic vapor and fine oxide particles, respectively. The sulfation of Na-bearing vapor and CaO particle in flue gas was controlled by the partial pressure of Na 2 SO 4 vapor and reaction rate, respectively.
The photocatalytic decolorisation of CI Reactive Black 5 using titanium dioxide nanopowder as a catalyst was studied and the results obtained are discussed in terms of its decolorisation efficiency. All experiments were performed using a double‐walled quartz immersion well batch reactor in which the slurry form of the reactants was at its natural pH of 5.1. The performance of titanium dioxide nanopowder (size <25 nm; surface area 200–220 m2/g) was compared with that of reference titanium dioxide powder (size ca. 230 nm; surface area 11 m2/g); in both cases, the titanium dioxide samples were anatase. It was found that the photocatalytic decolorisation efficiencies obtained using titanium dioxide nanopowder were higher than those of the reference titanium dioxide powder, with the latter taking approximately 8 min longer to achieve almost complete decolorisation of 10 mg/l CI Reactive Black 5. The photocatalytic decolorisation rate of CI Reactive Black 5 using both titanium dioxide photocatalysts typically followed a first‐order reaction and the decolorisation kinetics were successfully fitted to a simplified Langmuir–Hinshelwood kinetic model. In addition, the effects of light type and intensity, catalyst loading and initial CI Reactive Black 5 concentration were investigated using titanium dioxide nanopowder as the photocatalyst in the decolorisation of the dye. This study shows that the recommended parameters for treating 10 mg/l CI Reactive Black 5 based on the experimental set‐up and operating conditions are an ultraviolet light power of 125 W (39.3 mW/cm2) and a 0.3‐g/l catalyst loading.
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