Jea-Keun Lee

Prediction of Gaseous Pollutants and Heavy Metals during Fluidized Bed Incineration of Dye Sludge

This research provides an equilibrium model for predicting both the emission of gaseous pollutants and the fate of heavy metals during incineration of biologically treated dye sludge in a bench-scale fluidized bed incinerator. Major gaseous pollutants and hazardous trace heavy metals have been also measured under various operating conditions. The predicted values, which were derived by using a thermodynamic equilibrium model, can be used to determine the optimum operating parameters and the risk associated with hazardous waste incineration by means of verifying experimental data. However, prediction of NOx emission using a thermodynamic equilibrium model during incineration of waste was not simple. The reason is that the variation of NOx emission during incineration of waste was affected by the various operating parameters, such as air-fuel ratio(λT), primary air factor(λ1/λT), combustor geometry, method of heat release, and preheating of combustion air. According to the distributions of Cr and Pb simulated by the equilibrium model, all of the Cr in the feed was retained in the ash as the solid phase of Cr2CO3. However, most Pb was retained in the ash during incineration as the solid phase of PbSO4, or heterogeneously deposited onto the fly ash as PbO(g) when the combustion gas becomes cool.

Reduction of carbon dioxide in 3-dimensional gas diffusion electrodes

Experiments on the electrochemical reduction of CO2 were carried out by using a Cu/PTFE-bonded gas diffusion electrode (GDE) to investigate the effect of solvents, Cu/C ratio and electrolyte concentration on the characteristics of reduction products The experimental conditions were a voltage range from -2 0 to -3 5 V vs saturated calomel electrode (SCE) and electrolyte concentration from 0 1 M to 0 5 M Significant performance differences were found between water and organic solvent (isobutanol + EtOH) The GDE was more active with water than that with organic solvent And then, in the case of the Cu/PTFE-bonded gas diffusion electrode using organic solvent, the maximum faradaic efficiencies of reduction products were achieved in a Cu/C ratio of 0 5 The faradaic efficiency of C2H4 among the reduction products decreased as the Cu/C ratio increased, whereas, those of CO and alcohol increased Since the difference in pH at the electrode influences the variation of product selectivity, the faradaic efficiency of C2H4 might increase due to the pH increase caused by electrolyte concentration difference

Reaction Pathways and Kinetic Modeling for Sonochemical Decomposition of Benzothiophene

Benzothiophene (BT) decomposed rapidly following pseudo-first-order kinetics by ultrasonic irradiation in aqueous solution. The rate constant increased with increasing ultrasonic energy intensity. Hydroxybenzothiophenes, dihydroxy-benzothiophenes, and benzothiophene-dione were identified as reaction intermediates. It was proposed that benzothiophene was oxidized by OH radical to sequentially form hydroxybenzothiophenes, dihydroxybenzothiophenes, and benzothiophene-dione. Evolution of carbon dioxide and sulfite was also observed during ultrasonic reaction. Kinetic analysis suggested that approximately 77% of the benzothiophene decomposition occurred via OH radical addition. Pathways and a kinetic model for ultrasonic decomposition of benzothiophene in aqueous solution were proposed.

A simulation of electrochemical kinetics for gas-liquid-solid phase of MCFC anode

A porous Ni-Al alloy anode for the molten carbonate fuel cell has been developed to enhance the creep resistance of the anode as well as to minimize the electrolyte loss A dual-porosity filmed agglomerate model for the Ni-Al alloy anode has been investigated to predict the cell performance The major physicochemical phenomena being modeled include mass transfer ohmic losses and reaction kinetics at the electrode-electrolyte interface The predicted polarization curves are compared with the experimental results obtained from a half cell test The model predicted very well the steady-state cell performance at the given conditions that characterize the state of the electrode

Degradation of chlorophenol by photocatalysts with various transition metals

In this research, the photocatalytic degradation of 4-chlorophenol (4-CP) in TiO2 aqueous suspension was studied. TiO2 photocatalysts were prepared by sol-gel method. The dominant anatase-structure on TiO2 particles was observed after calcining the TiO2 gel at 500 °C for 1 hr. Photocatalysts with various transition metals (Fe, Cu, Nd, Pd and Pt) loading were tested to evaluate the effect of transition metal impurities on photodegradation. The photocatalytic degradation in most cases follows first-order kinetics. The maximum photodegradation efficiency was obtained with TiO2 dosage of 0.4 g/L, retention time of 1 min and air flow rate of 2,500 cc/min. The photodegradation efficiency with Pt-TiO2 or Pd-TiO2 is higher than pure TiO2 powder. The optimal content value of Pt and Pd is 2 wt%. However, the photodegradation efficiency with Fe(1.0 wt%)-TiO2 and Cu(1.0 wt%)-TiO2 is lower than pure TiO2 powder.

Effect of ash compositions on air pollutant emissions during fluidized bed sludge incineration

A simulation using a thermodynamic equilibrium model was performed to predict the effect of ash compositions on the behavior of air pollutants during fluidized bed sludge incineration. To investigate emission characteristics, the incineration temperature, air-fuel ratio (λT) and contents of calcium and chlorine were chosen as major operating parameters. For the analyses of the desulfurization of SOx and the pollutant emissions by the limestone addition, the Ca/S molar ratio was changed from 0.5 up to 7.0. According to the simulation, NOx was not influenced markedly by the air-fuel ratio, though greatly influenced by operating temperature. The effect of desulfurization with limestone addition was greatly influenced by ash composition, and desulfurization occurred over the Ca/S molar ratio of 5.5. This was attributed to the fact that the reactivity of the P component in ash to the added CaO was higher than that of sulfur in fuel.

The characteristics of coincineration of dewatered sludge, waste oil and waste solvent in commercial-scale fluidized bed incinerator

A commercial-scale Fluidized Bed Incinerator (FBI), which has a capacity of 60 tons per day to treat dewatered sludge and waste oil or solvent, was developed as one of the governmental R&D projects from 1990 to 1997. From the design, construction and operation of the plant, the characteristics of co-combustion and appropriate operating conditions with successful fly ash recirculation and with effluent controls have been investigated. Without adding any bed materials, sand, the co-incineration of sludge and spent-solvent can be achieved. The sludge combustion steps could be observed and confirmed, which consist of evaporation, agglomeration, devolatilization, combustion and attrition. The plant can also incinerate various types of sludge from wastewater treatment facilities with waste oil or solvent.

CO2 absorption characteristics of a jet loop reactor with a two-fluid swirl nozzle in an alkaline solution

To investigate the performance of a jet loop reactor with the two-fluid swirl nozzle (TSN), CO2 absorption experiments in an alkaline solution were performed. The experimental results obtained in the reactor were compared with those in a jet loop reactor with the two-fluid conventional nozzle (TCN). The neutralization time of alkaline solution and the CO2 removal efficiency were used as the indices for a comparison of the reactor performance. Due to the swirling flow, the neutralization times of alkaline solutions by CO2 in the reactor with the TSN were shortened compared with those in the reactor with the TCN. Also, the instantaneous and/or overall CO2 removal efficiencies in the reactor with the TSN were higher than those in the reactor with the TCN at the same liquid circulation flow rate.

Cultivation of Chlorella Sp. Using Light Emitting Diode

The purpose of this study was to determine optimum conditions for the cultivation of Chlorella sp. FC-21 using light emitting diodes (LEDs). Specific growth rate and cell concentration were measured for the reactors at the illuminations of different wavelengths of LEDs. Among various types of LEDs, red LEDs were the most effective light source, and also greatest increases of specific growth rate and cell concentrations were obtained when light intensity of red LEDs increased. The specific growth rate decreased when initial cell concentration increased due to the shading effect of each cell in the reactor. To determine beneficial effect of aeration to cell cultivation, micro-air bubbles were aerated at 0.35 vvm in the reactor at the illumination of red LEDs. Two and ten times greater specific growth rate and cell concentration were obtained when aeration was applied. From this study, we found that red LEDs with aeration were the most appropriate light source for the cultivation of Chlorella sp. FC-21.

Photochemical heterogeneous catalytic reaction at recirculated reactor system

A study was undertaken to examine the possibility of combining a batch-recirculated photoreactor with a ceramic membrane filter for heterogeneous photocatalysis applications. D-cargo red GS (GS) was used as the test substrate and titanium dioxide was used as photocatalyst for this study. The dark adsorption of GS on the TiO2 particle surface was also analyzed. The adsorption trends of GS at various initial concentrations followed the Langmuir isotherm trend. The GS were decolorized from 20% to 70% by the dark adsorption with various concentrations. The photodegradation of GS after the dark adsorption showed the behavior of Langmuir-Hinshelwood model. The variation of recirculation flow rate did not much influence photocatalysis. Variation tendencies of GS concentration were almost similar after about 90 minutes illumination in spite of the flow rate change. The values ofk (apparent first order rate constant) also varied with increase of the recirculation flow rate, but there were no observable significant differences between them.