Young Min Jo

Development of a post cyclone to improve the efficiency of reverse flow cyclones

Abstract An auxiliary device named “Post Cyclone” (PoC) was developed to reduce the emission of fines from the exhaust of reverse flow cyclones. The PoC makes use of the strong swirl of the gas as it exits through the vortex finder of a cyclone to capture certain fraction of the escaping particles. In its basic configuration, PoC consists of two annular shells placed vertically on the exit of a conventional cyclone. The separation of dust in PoC occurs primarily due to the centrifuging out of the particles in tangential velocity field. In addition to centrifugation, other mechanisms such as flocculation or agglomeration, turbulent dispersion, and particle bouncing may influence the actual collection of the particles in PoC. The relative importance of these mechanisms will depend on PoC geometry, inlet velocity and inlet dust concentration. In order to achieve an optimum design of the PoC for an existing cyclone, the effects of process variables need to be investigated in great detail. This work presents some of the results of the experiments conducted with two different combinations of cyclone and PoC under a range of process variables. In addition, results of modeling of the PoC using computational fluid dynamics (CFD) are also presented.

Evaluation of moisture effect on low-level CO2 adsorption by ion-exchanged zeolite

To enhance the capture of low-level indoor CO2, a commercial zeolite (13X) was modified with alkali and alkaline earth metals using an ion-exchange method. Although the calcium-impregnated sorbent (zeo-Ca) showed the largest adsorption capacity, with a strong binding force for carbon dioxide, its regeneration by heat treatment was very difficult. Moisture in the gas flow caused significant decreases in CO2 adsorption capability as well as in the lifetime of the adsorbents. As for the regeneration gas, the test showed that nitrogen would hinder the CO2 adsorption more significantly than helium gas. Water vapour and nitrogen gas molecules are apt to competitively occupy the available sites of the adsorbent over the CO2 molecules.

Dust Collection by a Fiber Bundle Electret Filter in an MVAC System

Electret filters are composed of thin, electrically charged fibers that are often utilized in industrial fields that require high collection efficiency with low flow resistance. A bundle-type electret filter in the Mechanical Ventilation and Air-Conditioning (MVAC) system of a Metro-subway was characterized in this study. The particle penetration and pressure drop parameters were examined under a filtration velocity ranging from 0.5 to 2.5 m/s. Particle penetration increased significantly in the early stages of filtration, but then became steady. The filter quality, which is a useful index of the filtration performance incorporating pressure drop and filtration efficiency, was evaluated for the test filters. The fiber bundle filter demonstrated a higher filter quality than the mechanical filter or the general panel-type electret filter with a small drop in pressure even at a high filtration velocity. In addition, the three dimensional structure and high electrostatic charge of the fiber bundle filter would enable a long retention time and constant level of pressure drop throughout the filtration.

Influence of pleat geometry on filter cleaning in PTFE/glass composite filter

A pleated filter bag is often used to treat exhaust gas in many industrial applications, due to its fairly high dust collection efficiency and relatively low pressure drop. This work deals with the optimum pleating geometries of a pleated filter made with a newly developed PTFE/glass composite filter. It was found that pleating geometries, including pleat height and pleat pitch, directly affect the cleaning efficiency. The design index, α, which stands for the ratio of pleat height to pleat pitch, is 1.48 for optimum operation. When the α value was higher than 1.48, the pressure drop across the pleated filter medium increased, resulting in a decreased cleaning interval due to the difficulty of filter cleaning. Therefore, it is necessary that the optimum pleating geometry should be determined by employing the dimensionless parameter, α, in the design of cartridge filters. Implications: A pleated filter bag is often used to treat exhaust gas in many industrial applications due to its fairly high dust collection efficiency and relatively low pressure drop. The present paper introduces an optimum design configuration to make a pleated filter with newly developed PTFE/glass composite filter media. A dimensionless parameter that is the ratio of pleat height to pleat pitch should be considered to make the best quality pleated filter.

Preparation and Characterization of Porous Composite Filter Medium by Polytetrafluoroethylene Foam Coating

Abstract The high costs of ceramic and Teflon filter media for hot gas cleaning has limited their industrial applications. This paper presents a foam coating technology that can be used to produce an inexpensive and highly efficient filter for industrial applications. A new apparatus was designed and built that coats porous glass mats with liquid-phase polytetrafluoroethylene (PTFE). The machine generates bubbles, enables the formation of uniform micropores less than 45 μm in diameter, and produces a product with air permeability greater than 5.5 cm3/cm2/sec. The resulting filter was found to be thermally stable up to 270 °C without any visible distortion and was comparable in dust collection efficiency to other commercial filter media. In addition, its de-dusting efficiency was greater than 85%, which is similar to that of other test filter media.

Ambient Adsorption of Low-level Carbon Dioxide by Metal Treated Activated Carbon

Carbon based sorbents for adsorption were prepared by impregnation with alkali metals (, ) and alkaline earth metals (, ). BET surface area of test sorbents was lower than the intrinsic activated carbon. In particular, impregnation of or resulted in lower surface area of specific adsorption sites than that of or . While the adsorption capacity for was high in the sorbents containing and , strong interaction with would cause to drop the capacity after regeneration. The adsorption was found high relatively in the flow with a high concentration of and in a low flow rate. The adsorption isotherm for the present modified AC sorbents fits well with the Freundlich model.

Utilization of Coal Fly Ash as a Slow-Release Granular Medium for Soil Improvement

Abstract This work proposes a new potential application of waste coal fly ash as a K fertilizer support. Fly ash was reacted with KOH to facilitate the impregnation of K as well as to enhance the bonding force. In particular, the applied process resulted in a significant slow-releasing characteristic of fertilizer elements. To examine the effect of K impregnation, a few detailed leaching tests were carried out in terms of process variables such as reaction time and temperature, sintering time and temperature, and KOH concentration. The current experiment presented an optimum preparation condition that is competitive with conventional commercial fertilizers. The manufactured ash fertilizers inhibited release of the K elements. It was also found through the continuous leaching test with pure water that the ash fertilizer had excellent moisture absorbability. However, the effects of some trace elements in fly ash on soil health and crop productivity as well as environmental considerations need to be established with long-term studies.

Structural Effect of Potassium Sulfamate on Synthesis of Ammonium Dinitramide

Abstract Potassium sulfamate (PS) is an efficient starting material for the nitration reaction used in the synthesis of ammonium dinitramide (ADN), which is an environmentally friendly high-energy oxidizer for propellants that does not release chlorine-based compounds. PS is a core structure to form dinitramide, -N(NO2)2, by taking NO2− from nitric acid. In this work, five test batches of PS were prepared using a few solvents including ethanol, methanol, acetone, isopropanol, and their mixtures. The lab-made PSs matched well with the commercial PS in terms of the chemical structure. The use of acetone led to a high recovery of PS up to 97 w/w% and ultimately contributed to the formation of high-purity and (99.2%) and a high yield (57.3%) that are greater than those for commercial PS (87.3% purity and 31.3% yield). Therefore, we proved that the crystallinity and homogeneity of PS influenced the properties of ADN and the synthesis efficiency.

Comparative evaluation of purity of green energetic material (ammonium dinitramide) depending on refining method

Although the solid propellant, ammonium dinitramide (ADN, NH4N(NO2)2) is safe and thermally stable, it requires high purity for practical commercial applications. Even a small amount of impurities in ADN can create negative effects, including catalyst poisoning and thruster nozzle cloggings when it is used as a liquid propellant. Thus, we explored several purification processes for the precipitated ADN particles, such as repetition extraction, adsorption by activated carbons, and low-temperature extraction. These purifying methods help to improve the chemical purity as evaluated by FTIR, UV-vis, DSC, and IC analyses. Among the purification processes, adsorption was found to be the best method, showing a final purity of 99.768% based on relative quantification by ion chromatography.

CO2 decomposition using metal ferrites prepared by co-precipitation method

To catalytically decompose the greenhouse gas, CO2, spinel structure M-ferrites (M=Co, Ni, Cu, Zn) were synthesized by chemical co-precipitation using metal salts and sodium hydroxide as starting materials. The crystallite size of the newly-prepared M-ferrites increased and the BET surface area decreased with increasing calcination temperature. A thermal analysis of the reduction and reoxidation of M-ferrites indicated that substitution of divalent transition metals (i.e., Cu, Ni and Co) into Fe3O4 improved the reduction kinetics in the order of Cu>Ni>Co. ZnFe2O4 was the most difficult compound to completely reduce due to its stable structure. Commercial samples of the reduced Fe3O4, CoFe2O4 and ZnFe2O4 showed an increase in mass through the reoxidation process, but it was much more difficult for oxygen atoms to enter the structure of the reduced samples of NiFe2O4 and CuFe2O4. The M-ferrites in a batch type reactor showed better efficiency than the commercial Fe3O4. Also found was that CoFe2O4 showed a high regeneration potential, although it required a higher critical reaction temperature. NiFe2O4 and CuFe2O4 were excellent candidate materials for CO2 decomposition at lower temperatures.