“…However, because Miccio et al assumed that the ash surface tension is constant (equal to 0.1 N/m), because the ash surface tension is not sensitive to temperature, compared with the ash viscosity, we use the same value in this study. It is assumed that ash melts when the ash viscosity is lower than the critical viscosity of μ ash = 10 5 Pa s, as reported in previous papers. − 4 Schematic of the drop tube furnace facility (DTF).…”
The percolation model, which can account for swelling due to devolatilization and ash
agglomeration, is applied to the ash formation process in coal combustion, and its validity is
examined by comparison with the experimental results obtained using the drop tube furnace
facility (DTF). The characteristics of a burning coal particle, such as particle diameter and specific
surface area, are investigated in detail. Newlands and Plateau coals with different fuel ratios
and ash contents are tested. The ambient temperature is set at 850 or 1400 °C, at which
temperature fluidized-bed or pulverized coal combustion occurs. The relationship between particle
temperature and conversion of coal required in the percolation model is obtained by performing
a numerical simulation of a combustion field in the DTF. The results show that the characteristics
of the burning coal particle obtained through the computations of the percolation model are
generally in agreement with the experimental data. The particle diameter of Newlands coal with
a higher fuel ratio and ash content is larger than that of Plateau coal in the char-combustion-dominant process. For both Newlands and Plateau coals, compared to the particle diameter of
the lower ambient temperature case of 850 °C, that of the higher ambient temperature case of
1400 °C becomes small in the early stage of the char-combustion-dominant process, but becomes
large afterward. These behaviors can be explained in terms of swelling due to devolatilization
and ash agglomeration.
“…However, because Miccio et al assumed that the ash surface tension is constant (equal to 0.1 N/m), because the ash surface tension is not sensitive to temperature, compared with the ash viscosity, we use the same value in this study. It is assumed that ash melts when the ash viscosity is lower than the critical viscosity of μ ash = 10 5 Pa s, as reported in previous papers. − 4 Schematic of the drop tube furnace facility (DTF).…”
The percolation model, which can account for swelling due to devolatilization and ash
agglomeration, is applied to the ash formation process in coal combustion, and its validity is
examined by comparison with the experimental results obtained using the drop tube furnace
facility (DTF). The characteristics of a burning coal particle, such as particle diameter and specific
surface area, are investigated in detail. Newlands and Plateau coals with different fuel ratios
and ash contents are tested. The ambient temperature is set at 850 or 1400 °C, at which
temperature fluidized-bed or pulverized coal combustion occurs. The relationship between particle
temperature and conversion of coal required in the percolation model is obtained by performing
a numerical simulation of a combustion field in the DTF. The results show that the characteristics
of the burning coal particle obtained through the computations of the percolation model are
generally in agreement with the experimental data. The particle diameter of Newlands coal with
a higher fuel ratio and ash content is larger than that of Plateau coal in the char-combustion-dominant process. For both Newlands and Plateau coals, compared to the particle diameter of
the lower ambient temperature case of 850 °C, that of the higher ambient temperature case of
1400 °C becomes small in the early stage of the char-combustion-dominant process, but becomes
large afterward. These behaviors can be explained in terms of swelling due to devolatilization
and ash agglomeration.
“…Huang et al [14] employed a value of 10 4 Pa.s in their study. Fan et al [7], Fang et al [12], Lee and Lockwood [15], Richards et al [6], Costen et al [16], and Erickson et al [11] utilized 10 5 Pa.s in their simulations. Rushdi et al [8] and Degereji et al [10] adopted a critical viscosity of 10 8 Pa.s while Yilmaz and Cliffe [9] reported~10 9 Pa.s.…”
“…Recently, considerable advances have been made in developing models to predict ash deposition behavior. − Wang 1 had conducted the modeling of ash deposition in large-scale coal combustion facilities. Detailed analyses of coal ash deposits were performed with the use of scanning electron microscopy (SEM), X-ray, and image analysis to characterize local deposit properties as a function of the position.…”
Fluid flow, heat transfer, coal combustion, and slagging processes had been numerically simulated near a swirl burner throat. The effect of the ratio distribution of each burner air, their swirling numbers, and the coal character on the slagging process had been analyzed. The computation results indicate that the maximal stickingparticle numbers occur at the uppermost waterwall, while the sticking-particle number at neither waterwall near the swirl burner outlet is very small. The swirling number has a significant effect on the number of the sticking particle. The sticking-particle number increases rapidly with the increment of the outer secondary air and the primary air-swirling numbers, respectively, because it can strengthen the flow entrainment ability to carry more particles to the waterwall. The inner secondary air has a complicated influence on the slagging process. When the inner secondary air-swirling number is about middle intensive degree (about 0.9), the stickingparticle number reaches maximum. If the inner secondary air-swirling number continues increasing, then the coal particles will combust completely and reduce the particle concentration, thus decrease the sticking-particle number. The ratio of each air has a slight influence on the sticking-particle number relative to the swirling number. The coal particles with small mean diameter combust completely, which can reduce the stickingparticle number.
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