• 한국결정성장학회지
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• 제5권3호
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• pp.223-232
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• 1995

Urea($(NH_2)_2CO$) 및 THAMP(Tris(hydroxymethyl)aminomethane phosphate) 유기 단결정은 레이저의 파장변환소자등의 응용에 유용한 새로운 유기 비선형 광학재료(NLO)이다. 온도하강법과 온도차법을 이용하여 urea와 THAMP 유기 단결정의 육성을 시도하였으며 이들 방법에 따른 육성조건을 확립하였다. Urea의 용매로는 용해도의 측정을 통하여 메탄올이 가장 적합하였으며, 용해도에 대한 온도계수는 posotive였으며, 용해열은 - 2.58 kcal/mol이었다. 육성된 urea 결정은 z축의 성장이 지배적이었고, z축의 성장제어와 x, y축의 성장을 위하여 $NH_4_H_2PO_4$, KCL, $H_3PO_4$, $CaCl_2{\cdot}2H_2O$, $C_2H_5OH$의 첨가제를 사용하여 z축의 성장제어와 x, y축의 성장을 증진시켰다. THAM과 $H_3PO_4$의 화학 양론적 혼합비 1 : 1의 몰비로부터 양질의 THAMP 유기 단결정을 육성하였고 용해도에 대한 온도계수는 positive였으며, 용해열은 - 1.70 kcal/mol이었다.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2014년도 제49회 KOSCO SYMPOSIUM 초록집
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• pp.235-236
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• 2014

An experimental study has been carried out to investigate a thermal decomposition of urea solution at relative low temperature with a lab-scaled exhaust pipe. The conversion efficiency of reductant considered with both ammonia and HNCO related with the urea injection quantity, inflow gas velocity and temperature. The conversion efficiency of ammonia was larger than that of HNCO under all experimental conditions unlike the theoretical thermolysis reaction.

• 대한기계학회논문집B
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• 제39권2호
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• pp.177-182
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• 2015

디젤 엔진과 산업용 보일러에서의 질소산화물(NOX) 배출은 환경오염을 유발시키는 주요물질 중의 하나이다. 이러한 질소산화물 발생을 저감시키기 위한 방법으로 후처리 기술 중의 하나인 우레아 선택적 촉매 환원(Urea-SCR)기술이 널리 사용되고 있다. 본 연구에서는 선박용 디젤엔진의 배기가스 조건을 모사한 실험실 스케일의 실험장치를 통해 우레아 수용액의 열분해 특성에 대해 고찰하였다. 40 wt. %의 우레아 농도를 가진 우레아 수용액을 사용하였고, 모사가스의 온도와 유속변화, 우레아 수용액의 유량에 따른 총 전환율 뿐만 아니라 암모니아($NH_3$)와 이소시안산(HNCO)의 전환율 차이를 알아보았다. $210^{\circ}C$와 $250^{\circ}C$ 모사가스 온도에서 체류시간에 따라 암모니아의 전환율이 이소시안산의 전환율보다 높게 나타남을 확인하였다.

• 대한화학회지
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• 제24권3호
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• pp.209-217
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• 1980

요소 1,3-디메틸요소(DMU), 아세트아미드, 프로피온아미드의 상대점도와 삼투계수를 dimethylsulfoxide(DMSO), 메탄올, 에탄올 및 물용액에서 $25^{\circ}$C와 $45^{\circ}$C에서 각각 측정하였다. 수용액에서 각 용질의 점도증가량은 분몰랄부피가 증가하면서 증가하였으나 물아니 용액에서는 오히려 감소하였다. 또한 요소의 점도 증가량은 수용액에서는 DMU보다 작았으나, 물아닌 용액에서는 DMU보다 컸다. 그러나 아미드류는 어느 용매에서나 거의 같은 점도증가량을 나타내었다. 요소수용액에서 삼투계수는 DMU 수용액보다 컸으며, 물아닌 용액에서 요소용액은 DMU보다 Raoult의 법칙에서 크게 벗어났다. 이러한 사실로부터 요소는 DMSO 용액에서 자체회합을 크게 일으키고 있으며 알코올용액에서는 DMU보다는 큰 정도의 용매-용질상호작용, 수용액에서는 용매구조를 파괴하고 있음을 알았다. 아세트아미드나 프로피온아미드는 수용액이나 DMSO 용액에서보다 알코올용액에서 더 크게 용매구조를 파괴하고 있음을 알았다.

• Journal of Plant Biology
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• 제5권2호
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• pp.6-12
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• 1962

For the comparison with the previous paper (4) the present report deals with the absorption and metabolism of urea and other nitrogen ions in barley seedling absorbed through root. 1. The amount of nitrate in barley treated with urea reach it peak on the 8th day. NO3 on the 4th, NH4 on the 6th or 8th, respectively. 2. The ammonia content in urea group reaches its peak on the 6th day but other groups on the 4th day. The present data in the urea group show to shorten 4 days compared with that of the previous paper(4). 3. the content of total amide from the present data aare gradully increased on all of the groups during this experiment. These are agreement with the result of the previous paper (4). 4. the alcohol solution nitrogen in the urea gorup shows the similar tendency to the NaNO3 group but reaches it peak 2 days later than in the (NH4)2SO4 group. 5. The content of total nitrogen in the urea series has the lowest amount at the beginning while the richest from the 4th day after. These would be explained on that the absorption of urea is delayed and the PH in the urea solution does not change, so called "physiological neutrality". The author should like express his sincere thanks to Prof. M.J.Lee of Seoul National University for his valuable advices.e advices.

• 대한환경공학회지
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• 제31권7호
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• pp.531-540
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• 2009

본 연구에서는 열중량분석법(Thermo-Gravimetric Analysis, TGA)을 이용하여 우레아 수용액의 농도와 열전달 속도가 우레아 수용액으로부터 암모니아가 생성되는 과정에 미치는 영향을 관찰하였다. 또한 1,000 $Nm^3$/h 규모의 유류 연소 보일러에 도입된 관통형 노즐을 사용하여 우레아의 분사방향을 상방과 하방으로 하였을 때를 비교함으로써 분사된 우레아가 지나는 경로에서 주위온도가 미치는 영향을 검토하였다. 질소 또는 공기 분위기에서 수행된 열중량분석 실험에서, 우레아는 산소의 존재유무에 관계없이 동일한 열분해 과정을 거쳤으며, 우레아 수용액은 가열속도에 따라 매우 다른 무게 감량 경향을 보여 가열속도가 우레아의 분해에 중요한 인자임을 나타내었다. 농도가 10%~40%인 우레아 수용액에서 우레아 열분해 시작 온도는 큰 차이를 보이지 않으므로, 농도의 영향은 그리 크지 않았다. 위치가 다른 세 곳에서 온도를 동일하게 유지하였을 때 상부 분사인 경우 탈질 효율은 각각 68.1%, 71.8%, 70.8%로 나타나 크게 차이가 나지 않았다. 동일 지역을 향하여 하부에서 분사한 경우와 상부에서 분사한 경우의 탈질 효율을 비교하면 각각 68.1%와 9.5%를 보여 동일한 지역에 분사된 우레아일지라도 분사방향에 따라 탈질 효율에는 큰 차이를 보였다.

• 한국대기환경학회지
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• 제32권5호
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• pp.526-535
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• 2016

Recently, fine dust in atmosphere have been considerably issued as a harmful element for human. Nitrogen oxide ($NO_x$) exhausted from diesel engines and power plants has been disclosed as a main source of secondary production of fine dust. In order to prevent exhausting these nitrogenous compounds into atmosphere, a treatment system with selective catalytic reduction (SCR) catalyst with ammonia as a reductant has been used in various industries. Urea solution has been widely studied to supply ammonia into a SCR catalytic reactor, safely. However, the conversion of urea solution to ammonia has several challenges, especially on a slow conversion velocity. In the present study, a fast urea conversion system including a plasma burner was suggested and designed to evaluate the performances of urea conversion and initial operation time. A designed lab-scale facility has a plasma burner, urea nozzle, mixer, and SCR catalyst which is for hydrolysis of isocyane. Flow rate of methane that is a fuel of the plasma burner was varied to control temperatures in the urea conversion facility. From experimental results, it is found that urea can be converted into ammonia using high temperature condition of above $400^{\circ}C$. In the designed test facility, it is found that ammonia can be produced within 1 min from urea injection and the result shows prospect commercialization of proposed technology in the SCR facilities.

• Asian-Australasian Journal of Animal Sciences
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• 제4권1호
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• pp.91-97
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• 1991

Twenty five 75% Holstein Friesian cross bred bullocks fed rice straw (Oryza sativa) of long form, were fed with the following five treatments. 1. Rice straw, untreated (RS) 2. RS + water (1:1), stored for 24 hours (WRS) 3. RS (100 kg) + urea solution (4 kg urea/100 litre water) and dried (USRS) 4. RS (100 kg) + urea solution (as in 3) stored in wet condition for 24 hours (UWRS) 5. RS (100 kg) + urea solution (as in 3) stored in pit for 21 days (UTRS). Potential digestibility of treatments of RS was evaluated by monitoring (in vitro) Simulating Rumen like Fermentation (SRLF). The results indicated that Dry Matter Intake (DMI), digestibility of nutrients, N utilization were of the order UTRS > UWRS > USRS > WRS and RS (p < 0.05 to p < 0.01). SRLF index was high (255.84) for UTRS and least (145.58) for USRS. It was intermediary (199.66) for UWRS. The acetyl content (AC) of UTRS with higher hemicellulose (HCE) digestibility (80.8%) was low compared to UWRS, USRS, RS and WRS. The acetate content was of the order UTRS < UWRS < USRS < WRS and RS thereby indicating that reduction in acetyl content was an index of positive response of urea-treatment of RS. In addition, the ratio of HCE/AC in faeces of UTRS was 0.87 as against the ratios (2.26-2.48) observed in other treatments recording reduction in AC due to urea-treatment. Among the treatments, USRS only supplemented N while UTRS in addition to utilization N, increased the digestibility of structural carbohydrates. Reduction in treatment time from 21 days to 1 day (UWRS) resulted in improvements similar to those of UTRS.

• 한국응용과학기술학회지
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• 제22권2호
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• pp.168-174
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• 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 Advanced Marine Engineering and Technology
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• 제28권5호
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• pp.818-826
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• 2004

The spray-induced mixing characteristics and thermal decomposition of aqueous urea solution into ammonia have been studied to design optimum sizes and geometries of the mixing chamber in SCR(Selective Catalytic Reduction) system. The cold flow tests about the urea-injection nozzle were performed to clarify the parameters of spray mixing characteristics such as mean diameter and velocity of drops and spray width determined from the interactions between incoming air and injected drops. Discrete particle model in Fluent code was adopted to simulate spray-induced mixing process and the experimental results on the spray characteristics were used as input data of numerical calculations. The simulation results on the spray-induced mixing were verified by comparing the spray width extracted from the digital images with the simulated Particle tracks of injected drops. The single kinetic model was adopted to predict thermal decomposition of urea solution into ammonia and solved simultaneously along with the verified spray model. The hot air generator was designed to match the flow rate and temperature of the exhaust gas of the real engines The measured ammonia productions in the hot air generator were compared with the numerical predictions and the comparison results showed good agreements. Finally, we concluded that the design capabilities for sizing optimum mixing chamber were established.