Combustion characteristics of high ash anthracite coals in fluidized beds = 저열량 무연탄의 유동층 연소특성

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Combustion and hydrodynamic characteristics of high ash contents anthracite coal in a cold model fluidized bed (0.38 m-ID $\times$ 9.6 m-high) and two fluidized bed comustors ($0.3 \times 0.3 m \times 4.7 \mbox{m-high},\; 1.01 \times 0.83 \times 4.2 \mbox{m-high}$) have been studied. The effects of fluidizing gas velocity, bed temperature, static bed height, air-fuel ratio, and solids recycle rate on the combustion characteristics such as the axial temperature profile, carbon conversion in each particle size, overall carbon combustion efficiency, and particle entrainment rate have been determined in two combustors. A theoretical model for a mean bubble size and its frequency based on the collision theory with the random spatial bubble distribution in freely bubbling gas-fluidized beds has been developed. A hemispherical bubble velocity diagram about the time-averaged instantaneous bubble motion is constructed in a fluidized bed to determine the average bubble collision frequency. The proposed theoretical model equation for predicting bubble size is $$(U-U_{mf}) (D_b-D_{bo}) + 0.474 g^{1/2} (D_b^{3/2}-D_{bo}^{3/2}) = 1.132 (U-U_{mf})h$$ As can be seen in the above model equation, the gradient of bubble size increases linearly with bubble voidage. Also, the bubble Froude number increases along the bed height with bubble voidage. The bubble Froude number represents approximately a linear relationship with the average fractional change of square root of the static energy of bubble rise along the bed height. The present model of bubble size is found to represent well the data in literature. The overal particle entrainment was measured by collecting the entrained particles in dust collectors and it is analyzed by the one-dimensional particle motion in the freeboard, the entrainment rate at the bed surface, the distribution of particle rising velocity from the bed surface, and the particle attrition in the bed. The overall entrainment rate of particles at the bed surf...
Kim, Sang-DoneresearcherSon, Jae-Ekresearcher김상돈researcher손재익researcher
한국과학기술원 : 화학공학과,
Issue Date
61335/325007 / 000795273

학위논문(박사) - 한국과학기술원 : 화학공학과, 1989.8, [ xviii, 338 p. ]

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