Sang Done Kim

Co-pyrolysis characteristics of sawdust and coal blend in TGA and a fixed bed reactor

Co-pyrolysis characteristics of sawdust and coal blend were determined in TGA and a fixed bed reactor. The yield and conversion of co-pyrolysis of sawdust and coal blend based on volatile matters are higher than those of the sum of sawdust and coal individually. Form TGA experiments, weight loss rate of sawdust and coal blend increases above 400 degrees C and additional weight loss was observed at 700 degrees C. In a fixed bed at isothermal condition, the synergy to produce more volatiles is appeared at 500-700 degrees C, and the maximum synergy exhibits with a sawdust blending ratio of 0.6 at 600 degrees C. The gas product yields remarkably increase at lower temperature range by reducing tar yield. The CO yield increases up to 26% at 400 degrees C and CH(4) yield increases up to 62% at 600 degrees C compared with the calculated value from the additive model.

Heat and mass transfer in three-phase fluidized-bed reactors—an overview

Abstract This overview examines the heat and mass transfer characteristics in three-phase (gas-liquid-solid and liquid-liquid-solid) fluidized beds to provide prerequisite knowledge for reactor design. The effects of gas and liquid velocities, solid and liquid properties on the heat and mass transfer coefficients in three-phase fluidized beds have been determined. The various correlations and models to predict the heat and mass transfer coefficients in the literature have been examined and the unified correlations based on the concepts of surface renewal theory and energy dissipation rate in the beds have been proposed. The analogy between the heat and the mass transfer in three-phase fluidized beds have been discussed. The areas wherein future research should be undertaken to improve the state of the present knowledge are defined with recommendations.

Heat transfer and bubble characteristics in a fluidized bed with immersed horizontal tube bundle

The effect of gas velocity on the average and local heat transfer coefficients between a submerged horizontal tube (25.4 mm-OD) and a fluidized bed has been determined in a fluidized-bed-heat-exchanger (0.34×0.50×0.6 m-high) of silica sand particles. The heat transfer coefficients and the properties of bubble and emulsion phases were simultaneously measured at the same location around the tube circumference by thermocouples and an optical probe. The average heat transfer coefficient (havg) exhibits a maximum value with variation of gas velocity (Ug). The local heat transfer coefficient (hi) exhibits maximum values at the side of the tube (0°). Bubble frequency (fb) increases and the emulsion contacting time (te) decreases with increasing Ug. The hi increases with increasing fb and decreasing te. The fb exhibits higher values and te is shorter at the bottom (under each side) than those at the top section of the tube. The te and bubble fraction (δb) have been correlated with Froude number. The predicted havg values of small particles based on the packet renewal model and the emulsion contacting characteristics around the tube well accord to the experimental data.

Heat-transfer characteristics of a latent heat storage system using MgCl2.6H2O

Heat-transfer characteristics have been determined for the circular finned and unfinned-tube units during the freezing of magnesium chloride hexahydrate (MgCl2 · 6H2O) used as a phase-change material (PCM) with a melting temperature of 116.7 °C. The effects on the heat-transfer characteristics have been determined of the inlet temperature and the flow rate of air used as the heat-transfer fluid (HTF). With the unfinned-tube unit, the heat-transfer coefficients obtained between the PCM and the tube are larger than the calculated values based on the theory of steady-state heat conduction due to the dendritical crystal growth of PCM. The ratio of the heat-transfer coefficient of the finned-to the unfinned-tube systems is about 3.5 within the finned section and decreases gradually far from the finned section with an increase in crystal volume. The total amounts of heat recovered have been correlated in terms of the Fourier, Stefan, and Reynolds numbers to provide basic design data for circular finned- and unfinned-tube heat-storage units.

Coal-gasification kinetics derived from pyrolysis in a fluidized-bed reactor

Coal pyrolysis and gasification reactions were carried out in a fluidized-bed reactor (0.1m i.d. by 1.6m height) over a temperature range from 1023 to 1173K at atmospheric pressure. The overall gasification kinetics for the steam–char and oxygen–char reactions were determined in a thermobalance reactor. The compositions of the product gases from the coal-gasification reactions are 30–40% H2, 23–28% CO, 27–35% CO2 and 6–9% CH4 with heating values of 2000–3750kJm−3. The heating value increases with increasing temperature and steam/coal ratio but decreases with increasing air/coal ratio. Our kinetic data derived from the two-phase theory on coal gasification in a thermobalance reactor and coal pyrolysis in a fluidized bed may be used to predict the product-gas compositions.

Coal gasification characteristics in an internally circulating fluidized bed with draught tube

Abstract Australian coal was gasified at atmospheric pressure in an internally circulating fluidized bed (0.3 m i.d. × 2.7 m high) with a draught tube (0.1 m i.d. × 0.9 m high) and a gas separator over the draught tube. The effects of reaction temperature (780–900°C), oxygen/coal mass ratio (0.30–0.53), coal feed rate (5.3–12.1 kg h −1 ) and steam/coal mass ratio (0.30–0.81) on composition of product gas, carbon conversion, cold gas efficiency and gas yield and calorific value were determined. Low-CV gas in the draught tube region and medium-CV gas in the annulus region can be obtained. In the annulus region, the composition of the product gas (vol.%) is H 2 31.8–46.2, CO 18.8–25.6, CO 2 13.2–20.4 and CH 4 5.3–10.4, with a CV of 8.6–13.2 MJ m −3 . In the draught tube region, the composition is H 2 8.3–19.7, CO 6.7–13.1, CO 2 18.9–35.3 and CH 4 1.9–4.4, with a CV of 3.3–5.9 MJ m −3 .

Trichloroethylene degradation by photocatalysis in annular flow and annulus fluidized bed photoreactors

The effects of trichloroethylene (TCE) gas flow rate, relative humidity, TiO(2) film thickness, and UV light intensity on photodegradation of TCE have been determined in an annular flow type photoreactor. Phosgene and dichloroacetyl chloride formation could be controlled as a function of TCE gas flow rate and photodegradation of TCE decreased with increasing relative humidity. The optimum thickness of TiO(2) film was found to be approximately 5 mum and the photocatalytic reaction rate of TCE increased with square root of UV light intensity. In addition, the effects of the initial TCE concentration, phase holdup ratio of gas and solid phases (epsilon(g)/epsilon(s)), CuO loading on the photodegradation of TCE have been determined in an annulus fluidized bed photoreactor. The TCE photodegradation decreased with increasing the initial TCE concentration. The optimum conditions of the phase holdup ratio (epsilon(g)/epsilon(s)) and CuO wt.% for the maximum photodegradation of TCE was found to be 2.1 and 1.1 wt.%, respectively. Therefore, an annulus fluidized bed photoreactor is an effective tool for TCE degradation over TiO(2)/silica gel with efficient utilization of photon energy.

Effects of particle properties on solids recycle in loop-seal of a circulating fluidized bed

The effects of particle size (dp) and density on solids recycle characteristics of loop-seal (0.08 m i.d.) have been determined in a circulating fluidized bed (CFB; 0.1 m i.d.×5.3 m high). Five different particles (silica sands and FCC) were used to determine the effects of particle properties on solids recycle characteristics. As the particle size is increased, aeration requirement in the loop-seal increases to attain the same mass flux (Gs) of silica sands with different size. The effects of aeration rate, particle size, and density on pressure balance around the CFB have been determined. As particle size is increased, solid holdup in the riser decreases at a given Gs and gas velocity. Pressure drops in the weir section of loop-seal increase with larger and denser particles. In the vertical aeration section, pressure drop increases with decreasing particle size and increasing particle density. Split of vertical aeration to the downward direction increases with increasing Gs. The pressure drops across the loop-seal have been correlated with the modified Froude, Reynolds numbers, and the density ratio of gas and solid.

Characteristics of entrained flow coal gasification in a drop tube reactor

Abstract The effects of reaction temperature, oxygen/coal and steam/coal ratios and residence time on coal gasification performance in entrained flow were determined by means of a drop tube reactor (0.05 m.i.d. × 1.0 m high). The H 2 CO molar ratio decreases with increasing reaction temperature and the H2 + CO content of the product gas exhibit a maximum around the ash fusion temperature. With increasing O2 content, carbon conversion increases and the rate of production of H2 and CO increases initially to a maximum value. The optimum O 2 coal ratio is in the range 0.6-0.9 for different coals.

Modeling of coal gasification in an internally circulating fluidized bed reactor with draught tube

A predictive mathematical model is proposed based on the bed hydrodynamics, reaction kinetics and the empirical correlation of pyrolysis yields to predict gasification characteristics in an internally circulating fluidized bed gasifier with a draught tube. With the justifiable assumptions, steady state mathematical equations are derived and solved numerically. The simulated results of product gas composition, gas yield, carbon conversion, cold gas efficiency and calorific value of the product gas in each reaction region are compared with the obtained experimental data. The proposed model can explain the reaction behavior in the present reactor system within the range of variables studied.