• Journal of the Korean Ceramic Society
• /
• v.33 no.9
• /
• pp.1031-1037
• /
• 1996

• Korean Journal of Soil Science and Fertilizer
• /
• v.22 no.4
• /
• pp.323-328
• /
• 1989

This study was conducted to find out the behavior of anaerobic microorganisms and anaerobic decomposition products of rice straw in the strict anaerobic condition. The number of methanogenic bacteria were more isolated than cellulolytic bacteria from the digester decaying rice straw during the entire incubation time. The activity of anaerobic microorganisms, such as methanogens and cellulolytics, were high the early incubation time in the treatment of rice straw with urea, but without urea was low at that time and increased moderately after 10 days incubation. Volatile fatty acid as intermediate anaerobic decomposition products had a longer retention time and higher accumulation rate in the treatment of rice straw without urea than with urea, and predominant fatty acid was propionic acid. Gas generation rate as final products were very intimate relationship with the activity of methanogenic bacteria. Average Eh value was -250mV during the incubation time and $CH_4$ : $CO_2$ percent ratio was about 60~65 : 35~40 in this Eh value. Decomposition rate of rice straw calculated from $CH_4$ and $CO_2$ gas wars 45.6% for 50 days in the treatment of rice straw with urea, and 36.8% without urea.

• Journal of the Korean Applied Science and Technology
• /
• v.22 no.2
• /
• pp.168-174
• /
• 2005

Aluminum tri-butoxide was mixed with the water/ethanol solution and then chloroplatinic acid was added to the solution. The solution was dried at $100^{\circ}C$ for 15hrs to remove the solvent and water then it was calcined at $500^{\circ}C$. The catalyst was activated with a gas mixture. During the activation, the temperature was increased from $150^{\circ}C$ to $500^{\circ}C$. The necessary amount of urea was dissolved in 50mL water and injected. Aqueous urea solution was then mixed with the feed gas stream. At low temperatures, nitrogen containing compounds of urea decomposition are used as reductants in the reducton of $NO_X$. However at high temperatures the nitrogen containing compounds are oxidized to NO and $NO_2$ by oxygen instead of being used in the reduction. The activity of the catalyst was dependent on urea concentration in the feed stream when there was not adequate water vapor in the feed. The maximum conversion was shifted from $250^{\circ}C$ to $150^{\circ}C$ when water concentration was increased from 2 to 17%. It seems that the maximum temperature shifts to lower temperatures because the hydrolysis rate of HNCO increases with water, resulting in higher amounts of $NH_3$.

• Journal of Korean Society of Environmental Engineers
• /
• v.31 no.7
• /
• pp.531-540
• /
• 2009

In this study, thermo-gravimetric analysis(TGA) was used to investigate the effect of urea concentration and heating rate on the ammonia($NH_3$) formation process from urea solution. A newly designed pipe nozzle was inserted through a 1,000 N${\ss}$(C)/h oil firing boiler to compare the DeNOx efficiencies between the upward and downward nozzle. This experiment reveals the effect of path which an urea droplet goes through. Urea solution showed the same TGA graph without regard to the presence of oxygen. Heating rate had a great influence on the weight loss trend. But the concentration of urea solution between 10% and 40% did not affect so much the thermal decomposition temperature. Therefore, heating rate is more important factor on the thermal decomposition of urea than the concentration of urea solution. Three nozzles located at different positions showed similar DeNOx efficiencies such as 68.1%, 71.8%, 70.8% at the same temperature. Even though urea solution was injected for the same zone, the injection direction made much difference in DeNOx efficiency. A upward nozzle showed 68.1% and downward nozzle 9.5%. This results illustrate the importance of heating rate.

• KOREAN JOURNAL OF CROP SCIENCE
• /
• v.47 no.2
• /
• pp.137-141
• /
• 2002

Decomposition of green manure is necessary for the nutrient supply in farm soil. Hairy vetch as a green manure is superior to other winter legumes in terms of wintering ability and N accumulation. This experiment was carried out to investigate the decomposition and N release of hairy vetch and its effect on rice production as the following crop in paddy field. Decomposition of hairy vetch placed by soil depth of 0, 10 and 20cm at transplanting time was investigated by mesh bag method, which was enclosed chopped residue in mesh bags. The fate of $^{15}$ N derived from $^{15}$ N-labeled hairy vetch was investigated at harvest in three levels of N fertilization. Grain yield of the transplanted paddy rice cultured with hairy vetch as starter N were compared with that of applying urea as starter N in the field. Hairy vetch residue decomposed very rapidly both in transplanted and dry-seeded paddy field. In transplanted paddy field, hairy vetch residue lost 72-81 % and 86-90% of its weight after one and five month, respectively, as affected by incorporation depth. The C/N ratio of the decomposing vetch residue increased sharply during the early stages and after then, decreased slowly. The amounts of N and P released from the vetch were about 90% and 97% of initial content after one month, respectively. Recoveries of hairy vetch-$^{15}$ N by rice plant were 30.6, 34.6 and 35.7% in 0, 6 and 12 kg urea-N 10 $a^{-l}$ application, respectively, indicating that N fertilization increased the recovery of hairy vetch. $^{15}$ N. Hairy vetch residue incorporated as starter maintained significant N $H_4$$^{+}$-N concentration in soil water of plow layer until effective tillering stage. Grain yield in the plot applied with hairy vetch was not significantly different from that in the plot with urea. We concluded that hairy vetch incorporation could substitute starter N fertilization and showed possibility to reduce N amount of top-dressing.g.g.

• Journal of ILASS-Korea
• /
• v.20 no.1
• /
• pp.20-27
• /
• 2015

Urea-SCR which is one of the aftertreatment technologies for reducing the NOx emission is widely used. An experimental study was performed to investigate urea decomposition under various thermo-fluid conditions, with different temperatures and velocities of inflow gas, and urea solution quantities. 40 wt. % aqueous urea solutions were used in this study. The inflow gas conditions were similar to the exhaust conditions of a large marine engine. The spray performance of urea solution injector was identical under all experimental conditions. The conversion efficiency of $NH_3$ was larger than that of HNCO under all experimental conditions, unlike for the theoretical thermolysis reaction.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.39 no.2
• /
• pp.177-182
• /
• 2015

The NOx emissions from diesel engines and industrial boilers are a major cause of environmental pollution. The selective catalytic reduction of urea is an aftertreatment technology that is widely used for the reduction of NOx emissions. The objective of this study was to investigate the characteristics of the thermal decomposition of a urea aqueous solution using laboratory-scale experimental equipment under conditions similar to those of marine diesel engines. A 40 wt. urea aqueous solution was used in this study. It was found that the total conversion rate varied with the inflow gas conditions and flow rates of the urea aqueous solution. In addition, there were conversion rate differences between NH3 and HNCO. At inflow gas temperature conditions of $210^{\circ}C$ and $250^{\circ}C$, the $NH_3$ conversion rate was found to be higher than that of the HNCO, depending on the residence time.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.16 no.4
• /
• pp.165-172
• /
• 2008

Urea-SCR, the selective catalytic reduction using urea as reducing agent, has been investigated for about 10 years in detail and today is a well established technique for deNOx of stationary diesel engines. In the case of the SCR-catalyst a non-uniform velocity and $NH_3$ profile will cause an inhomogeneous conversion of the reducing agent $NH_3$, resulting in a local breakthrough of $NH_3$ or increasing NOx emissions. Therefore, this work investigates the effect of flow and $NH_3$ non-uniformities on the deNOx performance and $NH_3$ slip in a Urea-SCR exhaust system. From the results of this study, it is found that flow and $NH_3$ distribution within SCR monolith is strongly related with deNOx performance of SCR catalyst. It is also found that multi-hole injector shows better $NH_3$ uniformity at the face of SCR monolith face than one hole injector.

• KOREAN JOURNAL OF CROP SCIENCE
• /
• v.20
• /
• pp.122-133
• /
• 1975

In recent years, farmers have substituted urea for ammonium sulfate as nitrogen fertilizer in their crop production. Since crops can not take urea itself directly as it is, we attempted to determine the amount of decomposition of urea in soil. It was observed that 25 percent of urea which had initially mixed with soil was decomposed in 10 days at 15$^{\circ}C$ and 80 percent in 2 days at $25^{\circ}C$. Therefore, it was considered that large amount of urea could be lost in cool season and cool areas. In the other experiment, ammonium sulfate, as a source of sulfur, was so mixed with urea that the ratio of sulfur to nitrogen would be 15 percent. Small amount of dolomite was also added to this mixture and the resulting fertilizer was applied on the rice plants. Eight percent of yield increase was obtained together with the increased protein content in brown rice.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.15 no.6
• /
• pp.128-136
• /
• 2007

It is well known that two representative methods satisfy EURO-IV regulation from EURO-III. The first method is to achieve the regulation through the reduction of NOx in an engine by utilizing relatively high EGR rate and the elimination of subsequently increased PM by DPF. However, it results in the deterioration of fuel economy due to relatively high EGR rate. The second is to use the high combustion strategy to reduce PM emission by high oxidation rate and trap the high NOx emissions with DeNOx catalysts such as Urea-SCR. While it has good fuel economy relative to the first method mentioned above, its infrastructure is demanded. In this paper, the number distribution of nano PM has been evaluated by Electrical Low Pressure Impactor(ELPI) and CPC in case of Urea-SCR system in second method. From the results, the particle number was increased slightly in proportion to the amount of urea injection on Fine Particle Region, whether AOC is used or not. Especially, in case of different urea injection pressure, the trends of increasing was distinguished from low and high injection pressure. As low injection pressure, the particle number was increased largely in accordance with the amount of injected urea solution on Fine Particle Region. But Nano Particle Region was not. The other side, in case of high pressure, increasing rate of particle number was larger than low pressure injection on Nano Particle Region. From the results, the reason of particle number increase due to urea injection is supposed that new products are composited from HCNO, sulfate, NH3 on urea decomposition process.