• Environmental Engineering Research
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• v.20 no.2
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• pp.191-197
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• 2015

The first objective of this study was to discuss the applicability of the $CO_2/CH_4$ ratio method in order to assess $CH_4$ oxidation efficiency. To achieve this objective, a comparison between $CO_2/CH_4$ ratios and the mass balance method was conducted. The second objective of this study was to estimate the $CH_4$ oxidation efficiency in an interim landfill soil cover and assess how a $CH_4$ influx influences the $CH_4$ oxidation efficiency. The results showed that despite the $CO_2$ problems brought by respiration, the $CH_4$ oxidation efficiencies obtained by the $CO_2/CH_4$ ratio method led to similar results compared to the mass balance method. In this respect, the $CO_2/CH_4$ ratio method can be an indicator of the $CH_4$ oxidation efficiencies for landfill cover soils. The $CH_4$ oxidation efficiencies derived in this study through the $CO_2/CH_4$ ratio method ranged between 46% and 64%, and between 41% and 62% through the mass balance method. The results imply that the Intergovernmental Panel on Climate Change's (IPCC) default value of 10% for the $CH_4$ oxidation efficiency is an underestimation for landfill cover soils. $CH_4$ oxidation efficiency tends to be negatively correlated with $CH_4$ influx. Therefore, $CH_4$ influx reaching a landfill cover should be limited in order to increase the $CH_4$ oxidation efficiency.

• Applied Chemistry for Engineering
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• v.29 no.4
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• pp.382-387
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• 2018

In this study, the reaction characteristics of combined steam and carbon dioxide reforming of methane (CSCRM) reaction using Pd-Ni-YSZ catalyst were investigated according to types of catalysts and gas compositions. Catalysts were prepared in the form of powder and porous disk. The injected gases were supplied at different ratios of $CH_4/CO_2/H_2O$. As a result, the conversion of $CH_4$ and $CO_2$ was improved as a result of using the porous disc type catalyst as compared with that of the powder type catalyst. When the $CH_4/CO_2/H_2O$ ratio of the feed gas was 1 : 0.5 : 0.5, the $H_2/CO$ ratio was adjusted close to 2. However, after 6 hours of the reaction, $CH_4$ conversion was partially reduced by the carbon deposition and the pressure drop increased from 0.1 to 0.8. This issue was then solved by optimizing the water content. As a result, it was confirmed that the durability was secured by preventing the carbon deposition when the gas was supplied at a $CH_4/CO_2/H_2O$ ratio of 1 : 0.5 : 1, and the conversion rate was maintained at a relatively high level.

• Applied Chemistry for Engineering
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• v.22 no.6
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• pp.653-657
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• 2011

Conversion characteristics of $CH_4$ and $CO_2$ was studied using an atmospheric pressure plasma for the preparation of synthesis gas composed of $H_2$ and CO. The effects of delivered power, total gas flow rate, and gas residence time in the reactor on the conversion of $CH_4$ and $CO_2$ were evaluated in a plasma reactor with the type of dielectric barrier discharge. The increase of reactor temperature did not affect on the increase of conversion if the temperature does not reach to the appropriate level. The conversion of $CH_4$ and $CO_2$ largely increased with increasing the delivered power. As the $CH_4/CO_2$ ratio increased, the $CH_4$ conversion decreased, whereas the $CO_2$ conversion increased. Generally, the $CH_4$ convesion was higher than the $CO_2$ conversion through the variation of the process parameters.

• Korean Chemical Engineering Research
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• v.50 no.5
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• pp.802-807
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• 2012

The autothermal reforming of methane to syngas has been carried out in a reactor charged with both a Ni (15 wt%)-Ru (1 wt%)/$Al_2O_3$-MgO metallic monolith catalyst and an electrically-heated convertor (EHC). The standalone type reactor has a start-up time of less than 2 min with the reactant gas of $700^{\circ}C$ fed to the autothermal reactor. The $O_2/CH_4$ and $H_2O/CH_4$ ratio governed the methane conversion and temperature profile of reactor. The reactor temperature increased as the reaction shifted from endothermic to exothermic reaction with decreasing $H_2O/CH_4$ ratio. Also the amount of $CO_2$ in the products increases with increasing $H_2O/CH_4$ ratio due to water gas shift reaction. The 97% of $CH_4$ conversion was obtained and the reactor temperature was maintained $600^{\circ}C$ at the condition of $GHSV=10,000\;h^{-1}$ and feed ratio ($H_2O/CH_4=0.6$ and $O_2/CH_4=0.5$). In this condition, the maximum flow rate of the syngas generated from the reactor charged with 170 cc of the metallic monolith catalyst is $0.94\;Nm^3/h$.

• Korean Chemical Engineering Research
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• v.47 no.6
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• pp.700-704
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• 2009

A simulation study on SCR(steam carbon dioxide reforming) in gas-to-liquid(natural gas to Fischer-Tropsch synthetic fuel) process was carried out in order to find optimum reaction conditions for SCR experiment. Optimum operating conditions for SCR process were determined by changing reaction variables such as temperature and $CH_4/steam/CO_2$ feed ratio. Simulation was carried out by Aspen Plus. During the simulation, overall process was assumed to proceed under steady-state conditions. It was also assumed that physical properties of reaction medium were governed by RKS(Redlich-Kwong-Soave) equation. Optimum simulation variables such as temperature and feed ratio were determined by considering $H_2/CO$ ratio for FTS(Fischer-Tropsch synthesis), $CH_4$ conversion, and $CO_2$ conversion. Simulation results showed that optimum reaction temperature and $CH_4/steam/CO_2$ feed ratio in SCR process were $850^{\circ}C$ and 1.0/1.6/0.7, respectively. Under optimum temperature of $850^{\circ}C$, $CH_4$ conversion and $CO_2$ conversion were found to be 99% and 49%, respectively.

• Journal of the Korean Society of Combustion
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• v.13 no.4
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• pp.47-53
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• 2008

The reaction mechanism of methane dry reforming has been investigated using an arc-jet reactor. The effects of input power, $CO_2/CH_4$ and added $O_2$ were investigated by product analysis, including CO, $H_2$, $C_{2}H_{Y}$ and $C_{3}H_{Y}$ as well as $CH_4$ and $CO_2$. In the process, input electrical power activated the reactions between $CH_4$ and $CO_2$ significantly. The increased feed ratio of the $CO_2$ to $CH_4$ in the dry reforming does not affect to the $CH_4$ conversion. but we could observe increase in CO selectivity together with decreasing $H_2$ generation. Added oxygen can also increase not only CO selectivity but also $CH_4$ conversion. However, hydrogen selectivity was decreased significantly due to a increased $H_{2}O$ formation.

• Korean Journal of Environmental Agriculture
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• v.26 no.1
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• pp.1-6
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• 2007

In view of energy supply, biogas can be seen as alternative fuel by substituting considerable amount of fossil fuel and may be utilized for heat and power production or for transport fuel production ($CH_4-enriched$ biogas). The aim of this research is to analyse the emission of $NO_x$ and CO from biogas fired combustion engine for electric power production. The result indicate a significant effect of biogas composition ($CH_4-CO_2$ ratio) and biogas flow rate on the air pollutants emission. The emission factors from this study were compared with those of U.S. EPA. Low $CH_4-CO_2$ ratio condition typically shows the lower $NO_x$ and CO emission than higher $CH_4-CO_2$ ratio condition. At normal $CH_4-CO_2$ ratio (7:3) emission factors of $NO_x$ and CO were 1.29 and 30.43 g/MMBtu, respectively. At low $CH_4-CO_2$, ratio (6:4) emission factors of $NO_x$ and CO were 0.646 and 60.86 g/MMBtu, respectively, It should be emphasized that the actual emission may vary considerably from these results due to operating conditions including torque load and engine speed.

• Korean Chemical Engineering Research
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• v.46 no.5
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• pp.1002-1007
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• 2008

The purpose of this paper studied the optimal hydrogen production condition of plasma reforming system to operate the PEMFC. Plasma reforming reactor used with Ni catalyst reactor at the same time, So $H_2$ concentration increased. Also the WGS and PrOx reactor were designed to remove CO concentration under 10 ppm, because CO has effect on catalyst poisoning of PEMFC. The maximum $H_2$ production condition in plasma reforming system was S/C ratio 3.2, $CH_4$ flow rate 2.0 L/min, catalytic reactor temperature $700{\pm}5^{\circ}C$ and input power 900 W. At this time, the concentration of produced syngas was $H_2$ 70.2%, CO 7.5%, $CO_2$ 16.2%,$CH_4$ 1.8%. The hydrogen yield, hydrogen selectivity and $CH_4$ conversion rate were 56.8%, 38.1% and 92.2% respectively. The energy efficiency and specific energy requirement were 37.0%, 183.6 kJ/mol. In additional, The experiment of $CO_2/CH_4$ ratio proceeded. Also WGS reactor experiment was proceeding on optimum condition of plasma reactor and the exit concentration were $H_2$ 68%, CO 337 ppm, $CO_2$ 24.0%, $CH_4$ 2.2%, $C_2H_4$ 0.4%, $C_2H_6$ 4.1%. At this time, experiment result of PrOx reactor were $H_2$ 51.9%, CO 0%, $CO_2$ 17.3%.

• Journal of Animal Environmental Science
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• v.18 no.3
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• pp.145-150
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• 2012

This study was conducted to measure methane ($CH_4$) and nitrous oxide ($N_2O$) emissions from the 6 month old litter stockpile used for korean native cattle (Hanwoo) from August 3, 2007 to October 4, 2007. Daily mean $CH_4$ emissions was peaked to 273.013 ${\mu}g\;m^{-2}\;s^{-1}$ (SE : ${\pm}1.047{\mu}g\;m^{-2}\;s^{-1}$) on first day and then gradually decreased to 2.309 ${\mu}g\;m^{-2}\;s^{-1}$ (SE : ${\pm}0.061{\mu}g\;m^{-2}\;s^{-1}$) at the end of this experiment. Daily mean $N_2O$ emissions was as little as 0.269 ${\mu}g\;m^{-2}\;s^{-1}$ (SE : ${\pm}0.018{\mu}g\;m^{-2}\;s^{-1}$) on first day, but exponentially increased up to 3.569 ${\mu}g\;m^{-2}\;s^{-1}$ (SE : ${\pm}0.454{\mu}g\;m^{-2}\;s^{-1}$) on 43rd day and then slowly decreased to 1.888 ${\mu}g\;m^{-2}\;s^{-1}$ (SE : ${\pm}0.012{\mu}g\;m^{-2}\;s^{-1}$) at the end of this experiment. Carbon dioxide equivalent ($CO_2$-eq), calculated by global warming potentials of $CH_4$ or $N_2O$, of $CH_4$ on first day occupied approximately 99% of sum of $CO_2$-eq of $CH_4$ and $N_2O$. Methane emissions decreased and $N_2O$ emissions increased so that $CO_2$-eq ratio of $CH_4$ to $N_2O$ was 50:50 on 34th day. The effect of $N_2O$ on the ratio was increase thereafter. The ratio of daily mean $CH_4$ and $N_2O$ emissions to daily error of the mean was calculated to find daily fluctuation of $CH_4$ and $N_2O$ emissions. The ratio of $CH_4$ was less than 1.0% till 11th day but increased to 10.9% on 57th day. The ratio of $N_2O$ (0.4%~51.0%) was higher than that of $CH_4$, showing high in early stage and then gradually decrease, which was different from the pattern of $CH_4$. The ratio of daily mean emissions to daily error of the mean was little in case of active $CH_4$ or $N_2O$ generation period, which would be caused by the temporal and spatial heterogeneity of composting process. Hence more air supply on early stage to decrease $CH_4$ generation and proper turning to reduce spatial heterogeneity are needed to mitigate greenhouse gas emissions.

• Journal of the Korean Institute of Gas
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• v.27 no.2
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• pp.25-31
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• 2023

The purpose of this study is to increase the thermal efficiency of a landfill gas (LFG) power generation engine by capturing carbon dioxide (CO₂) from landfill gas (LFG) using monoethanolamine (MEA), which is widely used in the chemical CO₂ absorption process. Since the use of LFG as an energy source can be a means of reducing greenhouse gas emissions, MEA can be used to reduce CO₂ in LFG and increase the concentration of CH₄ to improve the efficiency of power generation. In this study, experiments were conducted to measure the solubility of CO₂ and CH₄ in MEA solution, increase the solubility under different conditions, and analyse the dissolution characteristics. It was found that the CO₂ absorption rate increased as the ratio of MEA to reaction gas increased. There is an optimum MEA concentration to maximise CO₂ solubility, and even if the concentration is increased above this concentration, the solubility does not improve significantly. This study provided fundamental work to develop a more practical fuel by capturing CO₂ from LFG and increasing the concentration of CH₄ while reducing greenhouse gas emissions.