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COAL COMBUSTION CHARACTERISTICS IN A FLUIDIZED BED COMBUSTOR WITH A DRAFT TUBE
Kim, Sang Done,Lee, Woon Jae,Cho, Yong Jun,Kim, Jung Rae 한국화학공학회 1992 Korean Journal of Chemical Engineering Vol.9 No.4
The effects of gas velocity to draft tube (3-6 U_mf), bed temperature (800-900℃) and excess air ratio (0-30%) on the total entrainment rate, overall combustion efficiency and heat transfer coefficient have been determined in an internally circulating fluidized bed combustor with a draft tube. The total entrainment rate increases with an increase in gas velocity to draft tube, but decreases with increasing bed temperature and excess air ratio. The overall combustion efficiency increases with increasing excess air ratio, but decreases with increasing gas velocity to draft tube. The overall combustion efficiency obtained in internally circulating fluidized beds was found to be somewhat higher than that in a bubbling fluidized bed combustor.
Axial Dispersion Characteristics in Three Phase Fluidized Beds
Kim, Sang Done,Kwon, Hyeuk Woong 한국화학공학회 1990 NICE Vol.8 No.4
Axial dispersion coefficients in three-phase fluidized beds have been measured in a 0.152 m-IDX L8 m high column by the two points measuring technique with the axially dispersed plug flaw model. The effects of liquid velocity (0.05-0.13 m/s), gas velocity (0.02-0.16 m/s) and particle size (3-8 mm) on the axial dispersion coefficient at the different axial positions (0.06-0.46 m) in the bea have determined. The axial dispersion coefficient increases with increasing gas velocity but it decreases with an increase in particle size and exhibits a maximum value with an increase in the axial position from the distributor. The axial dispersion coefficients in terms of the Peclet number have been correlated in terms of the ratio of fluid velocities, the ratio of the particle size to column diameter, and the dimensionless axial position in the bed based on the isotropic theory.
On the Heat Transfer Mechanism in Three Phase Fluidized Beds
Kim, Sang Done,Kang, Yong 한국화학공학회 1988 NICE Vol.6 No.4
A two resistance model is proposed for the heat transfer between a coaxially mounted heater and a three phase fluidized bed. Effects of gas and liquid velocity and particle size on individual heat transfer resistances in the heater and in the fluidized bulk zones have been determined. The optimum bed porosity at which the maximum heat transfer coefficient occurred coincided with the bed porosity at which the boundary layer thickness around the heater attained a minimum value. The fluidized bed resistance attained its minimum value when the maximum heat transfer coefficient is achieved in two and three phase fluidized beds. The heat transfer in the zone adjacent to the heater is found to be the rate controlling step since the contribution of fluidized bed resistance was found to be less than 10%a of the heater zone resistance in two and three phase fluidized beds. The heat transfer resistances in liquid and three-phase fluidized beds have been represented by a modified Stanton and Peclet numbers based on the heat transfer resistances in the heater zone and in the fluidized bulk zone in series.
Slug Characteristics of Polymer Particles in a Fluidized Bed with Different Distributors
Kim, Sang Done,Lee, Dong Hyun,Lee, See Hoon 한국화학공학회 2001 Korean Journal of Chemical Engineering Vol.18 No.3
Pressure fluctuations in a fluidized bed (0.38 m-LD.×4.4 m-high) of 1.23-mm polymer particles (LLDPE) were measured with different distributors. Slug characteristics (slug frequency and slug rising velocity) were determined by analyzing pressure fluctuations in the bed. The effects of gas velocity (0.6-1.2 m/s) and distributor geometry (opening area ratio, number of orifices and distributor types) on the slug characteristics were determined. The slug frequency decreases slightly with increasing gas velocity. However, slug rising velocity increases linearly with increasing excess fluidization velocity regardless of the distributors used.
Kim, Sang Done,Ahn, Hong Sik,Lee, Woon Jae,Song, Byung Ho 한국화학공학회 1999 Korean Journal of Chemical Engineering Vol.16 No.5
The effects of orifice diameter in the draft tube, particle size, gas velocities and bed height on the circulation rate of solids and gas bypassing between the draft tube and annulus have been determined in an internally circulating fluidized bed (i.d., 0.3m ; height, 2.5m) with an orifice-type draft tube. A conical shape gas separator has been employed above the draft tube to facilitate the separation of gases from the two beds. The circulation rate of solids and the quantity of gas bypass from the annulus to draft tube show their minimums when the static bed height is around the bottom of the separator. The circulation rate of solids increases with an increase in orifice diameter in the draft tube. At fixed aeration to the annulus, gas bypassing from the draft tube to annulus sections decreases, whereas reverse gas bypassing from the annulus to the draft tube increases with increasing the inlet gas velocity to the draft tube. The obtained solids circulation rate has been correlated by a relationship developed for the cocurrent flow of gas and solid through the orifice.
Mass Transfer in Two - and Three - Phase Fluidized Beds
Kim, Sang Done,Kim, Ihl Yong 한국화학공학회 1990 NICE Vol.8 No.2
The effects of liquid (0.03-0.12 m/s) and gas (0.04-0.20 m/s) velocities, and partile size (0-8.0 mm) on the volumetric mass transfer coefficients at the grid zone have been determined in a 0.152 m-I.D. x 1.8 m high Plexiglas column. The volumetric mass transfer coefficient in the grid zone increases with increasing gas velocity and particle size. However, the coefficient exhibits a maximum value at an optimum bed porosity condition. The volumetric mass transfer coefficients in terms of the Sherwood number in three-phase fluidized beds have been correlated with the Schmidt number and particle Reynolds number which is related to the energy dissipation rate in the beds based on the local isotropic turbulence theory. Also, the coefficient has been correlated with the experimental variables.
Functionalization of HDPE Powder by CF4 Plasma Surface Treatment in a Fluidized Bed Reactor
Kim, Sang Done,Park, Soung Hee 한국화학공학회 1999 Korean Journal of Chemical Engineering Vol.16 No.6
The surface of HDPE polymer powder was fluorinated by CF₄ plasma in a fluidized bed reactor. Plasma is generated by an inductively coupled electrode at 13.56 MHz (rf) frequency, connected to an auto matching network and an rf power generator. In plasma surface fluorination, the CF_4 gas is diluted with He gas. The experimental variables are treatment time and rf power. The chemical property of the modified powder has been determined by using ESCA and FTIR. Plasma surface fluorination with the powder in a fluidized bed reactor results from the formation of CHF-CH₂, CHF-CHF and CF₂ groups. These fluorine functionalities and the fluorine atomic ratio on the surface increase with the treatment time and rf power. It has been found that the composite parameter is a good measure for determining the effect of total energy input on the plasma surface treatment of polymer powder in a fluidized bed reactor.
BUBBLE PROPERTIES AND PRESSURE FLUCTUATIONS IN BUBBLE COLUMNS
Kim, Sang Done,Han, Joo Hee,Kown, Hyeuk Woong,Kang, Yong 한국화학공학회 1994 Korean Journal of Chemical Engineering Vol.11 No.3
The effects of gas (0.02-0.1 ㎧) and liquid velocities (0.0-0.10 ㎧) on the bubble properties and pressure fluctuations have been determined in a 0.376 m-ID × 2.1 m-high bubble column. The pressure fluctuations have been analyzed by resorting to the Fractal analysis; the time series of pressure fluctuation signals have been analyzed by means of the Resealed range analysis and the Hurst exponent has been obtained. The bubble chord length and its rising velocity increase but the Hurst exponent decreases with increasing gas velocity. Whereas, the bubble chord length decreases, but the Hurst exponent increases with an increase in liquid velocity in the continuous bubble column (U_L$gt;0.02 ㎧). The Hurst exponent has been found to have a definite relationship with the bubble chord length and its standard deviation.