• Journal of Soil and Groundwater Environment
• /
• v.14 no.5
• /
• pp.62-70
• /
• 2009

A field soil highly contaminated with petroleum hydrocarbons (JP-8 and diesel fuels) was employed for its remediation by a lab-scale thermal desorption process. The soil was collected in the vicinity of an underground storage tank in a closed military base and its contamination level was as high as 4,476 ppm as total petroleum hydrocarbon (TPH). A lab scale directly-heated low temperature thermal desorption (LTTD) system of 10-L capacity was developed and operated for the thermal treatment of TPH contaminated soils in this study. The desired operation temperature was found to be approximately $200-300^{\circ}C$ from the thermal gravimetric analysis of the contaminated field soils. The removal efficiencies higher than 90% were achieved by the LTTD treatment at $200^{\circ}C$ for 10 min as well as at $300^{\circ}C$ for 5 min. As the water content in the soils increased and therefore they were likely to be present as lumps, the removal efficiency noticeably decreased, indicating that a pre-treatment such as field drying should be required. The analysis of physical and chemical properties of soils before and after the LTTD treatment demonstrated that no significant changes occurred during the thermal treatment, supporting no needs for additional post-treatments for the soils treated by LTTD. The results presented in this study are expected to provide useful information for the field application and verification of LTTD for the highly contaminated geo-environment.

• Transactions of the Korean hydrogen and new energy society
• /
• v.22 no.3
• /
• pp.363-371
• /
• 2011

In this paper, a three-dimensional hydrogen desorption model is developed to precisely study the hydrogen desorption kinetics and resultant heat and mass transport phenomena in metal hydride hydrogen storage vessels. The metal hydride hydrogen desorption model, i.e. governed by the conservation of mass, momentum, and thermal energy is first experimentally validated against the temperature evolution data measured on a cylindrical $LaNi_5$ metal hydride vessel. The equilibrium pressure used for hydrogen desorption simulations is derived as a function of H/M atomic ratio and temperature based on the experimental data in the literature. The numerical simulation results agree well with experimental data and the 3D desorption model successfully captures key experimental trends during hydrogen desorption process. Both the simulation and experiment display an initial sharp decrease in the temperature mainly caused by relatively slow heat supply rate from the vessel external wall. On the other hand, the effect of heat supply becomes influential at the latter stages, leading to smooth increase in the vessel temperature in both simulation and experiment. This numerical study provides the fundamental understanding of detailed heat and mass transfer phenomena during hydrogen desorption process and further indicates that efficient design of storage vessel and heating system is critical to achieve fast hydrogen discharging performance.

• Journal of Korean Society for Atmospheric Environment
• /
• v.27 no.2
• /
• pp.191-200
• /
• 2011

A way to adsorptively remove indoor carbon dioxide at relatively lower concentration under ambient temperature was studied. A small lab-scale carbon dioxide adsorption and desorption reactors were prepared, and 5A and 13X zeolites were packed in this reactors to investigate their adsorption and desorption characteristics. The inflow carbon dioxide concentration was controlled to 5,000 ppm, relatively higher concentration found in indoor spaces with air quality problems, by diluting carbon dioxide with nitrogen gas. The flow rate was varied as 1~5 L/min, and the carbon dioxide concentration after this reactor was constantly monitored to examine the adsorption characteristics. It was found that 5A adsorbed more carbon dioxide than 13X. A lab-scale carbon dioxide desorption reactor was also prepared to investigate the desorption characteristics of zeolites, which is essential for the regeneration of used zeolites. The desorption temperature was varied as $25{\sim}200^{\circ}C$, and the desorption pressure was varied as 0.1~1.0 bar. Carbon dioxide desorbed better at higher temperature, and lower pressure. 5A could be regenerated more than three times by thermal desorption at $180^{\circ}C$. It is required to modify zeolites for higher adsorption and better regeneration performances.

• Proceedings of the Korean Vacuum Society Conference
• /
• 1997.07a
• /
• pp.94-94
• /
• 1997

• Transactions of the Korean hydrogen and new energy society
• /
• v.9 no.3
• /
• pp.111-118
• /
• 1998

The intrinsic degradation behavior of $(V_{0.53}Ti_{0.47})_{0.925}Fe_{0.075}$ alloy with BCC structure and the two plateau regions (the low and high plateau region) has been investigate during the temperature-induced hydrogen absorption-desorption cycling (thermal cycling). After 400 thermal cycles between room temperature and $600^{\circ}C$ under 10atm $H_2$, the total reversible hydrogen absorption capacity decreased by about 40%. From thermal desorption analysis it was found that the degradation behavior at each plateau region was different. In addition, XRD analysis showed that the crystal structure of the sample in de-hydrided state was changed from BCC to BCT after degradation, and that of the sample in hydrided state it was maintained as FCC although peaks were broadened after degradation. From the result of static isothermal hydrogenation treatment it were found that crystal structure change from BCC to BCT was caused by the thermal energy. TEM analysis showed that the peak broadening was due to the formation of an amorphous phase in FCC matrix.

• Journal of Soil and Groundwater Environment
• /
• v.18 no.3
• /
• pp.73-81
• /
• 2013

Various remediation methods have been applied to clean soils contaminated with pollutants. They remove contaminants from the soils by utilizing physicochemical, biological, and thermal processes and can satisfy soil remediation standards within a limited time; however, they also have an effect on the biological functions of soils by changing soil properties. In this study, changes of the biological properties of soils before and after treatment with three frequently used remediation methods-soil washing, land farming, and thermal desorption-were monitored to investigate the effects of remediation methods on soil biological functions. Total microbial number and soil enzyme activities, germination rate and growth of Brassica juncea, biomass change of Eisenia andrei were examined the effects on soil microorganisms, plant, and soil organisms, respectively. After soil washing, the germination rate of Brassica juncea increased but the above-ground growth and total microbial number decreased. Dehydrogenase activity, germination rate and above-ground growth increased in both land farming and thermal desorption treated soil. Although the growth of Eisenia andrei in thermal desorption treated soil was higher than any other treatment, it was still lower than that in non-contaminated soil. These results show that the remediation processes used to clean contaminated soil also affect soil biological functions. To utilize the cleaned soil for healthy and more value-added purposes, soil improvement and process development are needed.

• Analytical Science and Technology
• /
• v.19 no.6
• /
• pp.553-558
• /
• 2006

In this study, an attempt was made to measure uncertainties involved in the VOC analysis for the VOC working standards prepared by a dilution technique using Tedlar bags. For this purpose, VOC standard gases of benzene, toluene, xylene, and styrene were prepared at four different concentrations (4, 8, 20, and 40 ppb). These standard samples were then loaded on to the GC system equipped with air server/thermal desorption (AS/TD) system. Each of these four standard concentrations was analyzed individually to derive their respective calibration results. These calibration data sets were then compared across four different compounds. According to this comparison, differences in calibration patterns were moderately insignificant within the selected concentration range of 4~40 ppb. It was also observed that the loss of styrene standard was fairly high compared to other VOCs investigated simultaneously. The results of our study suggest that the analytical uncertainty associated with the preparation of VOC starndard gas using a dilution technique can be assessed in a fairly reasonable manner for samples with a narrow concentration range.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2000.02a
• /
• pp.146-146
• /
• 2000

We have studied the etching of Si(100)-2xl by Cl and Br, using scanning tunneling microscopy to obtain morphological information that can be related to reaction and desorption pathways. Clean surfaces were exposed to molecular halogens at room temperature to produce well-defined chemisorption structures for coverages in the range 0.2-1.0 ML. Heating to 750-750 K induced etching by thermal desorpton. Analysis of the halogen concentration before and after heating indicated that the rates of desorption for SICl2 or SiBr2 were greatest for intermediate coverages and that etching was suppressed as saturation was reached. Hence, desorption is not simply proportional to the concentration of species that can form adsorbed precursors SiX2(a). Instead, it is directly coupled to the creation of monomer vacancies adjacent to the SiX2 (a) unit because this increases the lifetime of the excited state and increases the likelihood of its desorption. Increasing the surface concentration of halogens reduces the rate of vacancy formation. We show that these rates are also affected by a re-dimerization process in the high temperature Br-stabilized Si(100)-3xl reconstruction that increases the likelihood of siBr2(a) formation and enhances its desorption. I will also discuss recent result for F etching on Si(100)-2xl.

• Journal of the Korean Vacuum Society
• /
• v.15 no.1
• /
• pp.73-80
• /
• 2006

Thermally-driven effusion of inert gases out from Si(100), into which energetic $\~l keV\;He^+,\;Ne^+,\;A^r+,\;and\;Kr^+ ions$ had been implanted at a moderate substrate temperatures of $\~400 K$, was investigated by means of temperature-programmed desorption (TPD) mass spectrometry. While He effused out broadly over $500\~1,100 K$, Ne, Ar, and Kr effusion occurred sharply at 810, 860, and 875 K, respectively. Hydrogen adsorption/desorption analysis for the ion-treated Si(100) surfaces indicated minimal to severe damage by ions with increasing mass from He to Kr. Implications of these results in light of literature reports are discussed.

• Nuclear Engineering and Technology
• /
• v.49 no.4
• /
• pp.873-880
• /
• 2017

To identify the feasibility of disposing of spent activated carbon as a clearance level waste, we performed characterization of radioactive pollution for spent activated carbon through radioisotope analysis; results showed that the C-14 concentrations of about half of the spent activated carbon samples taken from Korean NPPs exceeded the clearance level limit. In this situation, we selected thermal treatment technology to remove C-14 and analyzed the moisture content and thermal characteristics. The results of the moisture content analysis showed that the moisture content of the spent activated carbon is in the range of 1.2-23.9 wt% depending on the operation and storage conditions. The results of TGA indicated that most of the spent activated carbon lost weight in 3 temperature ranges. Through py-GC/MS analysis based on the result of TGA, we found that activated carbon loses weight rapidly with moisture desorption reaching to $100^{\circ}C$ and desorbs various organic and inorganic carbon compounds reaching to $200^{\circ}C$. The result of pyrolysis analysis showed that the experiment of C-14 desorption using thermal treatment technology requires at least 3 steps of heat treatment, including a heat treatment at high temperature over $850^{\circ}C$, in order to reduce the C-14 concentration below the clearance level.