• 설비공학논문집
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• 제16권8호
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• pp.770-777
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• 2004

Fouling and cleaning tests are performed for a uniquely designed 7,000 ㎉/hr fluidized bed heat exchanger for exhaust gas heat recovery. Fuel rich condition is maintained in the combustor for a limited time period to generate soot that is to be deposited on the heat transfer surfaces (fouling) and 600 Um glass beads are circulated inside the heat exchanger system for cleaning and enhancing the heat transfer performance. According to the present experimental study, performance degradation mode could be monitored and the effect of particle circulation on the heat transfer improvement could be identified. Through the present study, it is demonstrated that circulating particles contribute not only to the fouling reduction in gas side, but also to the heat transfer enhancement of the unit, while other possible aging factors including water side corrosion seemed to contribute to the accumulated performance deterioration.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2005년도 제31회 KOSCO SYMPOSIUM 논문집
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• pp.231-237
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• 2005

Interruption of good fluidization in a fluidized bed ash cooler(FBAC) for discharging bed materials such as sand or coal ash particles from the CFB combustor is frequently happened because of agglomeration of the particles in the bed. This unstable operation may, in the worst case, result in an unscheduled boiler shut down. In this study, we examined the operation problems of the FBAC of Tonghae CFB boiler and studied and introduced the simple detection and solution techniques with analyzing the mixing property and the occurrence of defluidization in a simulated fluidized bed ash cooler system (0.5m-H x 0.5m-W x 1.0m-L). The bridge of the large particles at the bed surface could be observed, and this caused to form the defluidization area at the entrance of the FBAC. The defluidization was affected not only by airflow rates but also by the particles discharging rates as well as particle size distribution in the FBAC. The local defluidization could be detected by analysis of the accumulated standard deviation error at a given period of time. Also, the regulation of the overall or local airflow rate made clearing up the local defluidization possible.

• 한국연소학회지
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• 제1권1호
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• pp.19-29
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• 1996

This study is to investigate the characteristics of heat transfer of a horizontal tube, with radial fins of various configuration, immersed in a high temperature fluidized bed. The experimental heat transfer variation is compared with that of a smooth tube. The finned tubes and smooth tube, with outside and inside diameter of 48.6mm and 30.6mm, are made of steel tubes. The depth of the fin is 5mm, the rake angles of fin are $25^{\circ},\;35^{\circ},\;45^{\circ}$ and the widthes of fin for each rake angle are 0mm, 1mm, 2mm and 3mm. A bed temperature is fixed at $880\;{\pm}\;10^{\circ}C$. A granular refractory(silica sand) is used as a bed material with mean particle diameters of 1.22mm and 1.54mm. The maximum heat transfer coefficient is achieved with the rake angle of $25^{\circ}$ and the width of 0mm for the mean particle size 1.22mm. The coefficient is 2.14 times larger than that for a smooth tube. The rake angle for the maximum heat transfer coefficient depends on the particle size of bed material. Also the transfer coefficient decreases as the width of fin increases.

• 공업화학
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• 제17권5호
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• pp.547-551
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• 2006

ASTM D5757-95에 따른 입자 마모 측정기와 lab-scale 유동층 연소로에서 국내 무연탄 회재와 모래의 입자 마모 특성을 실험하였다. 기체유속에 따른 마모 특성으로 비산 회재의 입도 분포, 마모 속도, 마모율 등을 측정하였다. 일반적으로 유동층 층물질로 사용되는 모래보다 회재가 마모에 취약해 비산 회재의 발생이 높았으며 마모지수의 경우 5배 정도 높게 나타났다. 기체 유속 변화에 따라 입자의 마모에 의해 미세 입자의 생성이 지속적으로 발생하였으며 다음과 같은 식을 따른다. $$\frac{dW}{dt}=-3.18{\times}10^{-7}(U-U_{mf})W$$.

• 한국수소및신에너지학회논문집
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• 제28권1호
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• pp.85-91
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• 2017

To develop a pressurized chemical looping combustor, effect of pressure on minimum fluidization velocity and transition velocity to fast fluidization was investigated in a two-interconnected pressurized fluidized bed system using oxygen carrier particle. The minimum fluidization velocity was measured by bed pressure drop measurement with variation of gas velocity. The measured minimum fluidization velocity decreased as the pressure increased. The transition velocity to fast fluidization was measured by emptying time method and decreased as the pressure increased. Gas velocity in the fuel reactor should be greater than the minimum fluidization velocity and gas velocity in the air reactor should be greater than the transition velocity to fast fluidization to ensure proper operation of two interconnected fluidized bed system.

• 한국대기환경학회지
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• 제20권4호
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• pp.429-436
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• 2004

Circulating fluidized bed combustion (hereafter CFBC) technology enables an efficient combustion for the materials with low heating values such as high ash coal and sludges. It also has desulfation function by adding limestone directly to combustor. The CFBC has been considered as one of the best processes for low grade coal containing with large contents of ash and sulfur. In this paper, in order to various tests were performed to find the optimum desulfation condition for CFBC using Korean Anthracite. We surveyed possible parameters and conducted desulfation efficiency test in D Thermal Power Plant. In addition, the result of some fundamental theoretical consideration was discussed with CFBC. Optimum limestone size could be considered to be 0.1-0.3mm irrespective of combustion temperature and Ca/S molar ratio variation. Desulfation efficiency increased as the molar ratio increased. Because desulfation process occurs at the surface at higher temperature, inner side of limestone can＇t be utilized. When surface area is not appropriate, some SO$_2$ emit without reaction. Optimum molar ratio should be decided after considering chemical and physical properties of limestone and coal thoroughly such as particle size, pore size and HGI. Commercial CFBC is operated at Ca/S 1.6. Combustor temperature 840-87$0^{\circ}C$ shows good desulfation efficiency.

• Korean Chemical Engineering Research
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• 제58권4호
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• pp.642-650
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• 2020

순환유동층 보일러에서 유동 입자들의 순환 경로는 연소로에서 비산된 입자들이 사이클론에서 포집되어 비기계적 밸브인 실포트(Sealpot)를 거쳐 연소로로 재순환하는 일반적인 경로를 갖는다. 그러나, 유동 입자들로부터 열을 추가적으로 흡수하기 위해 유동층 외부열교환기(FBHE; Fluidized Bed Heat Exchanger)가 설치된 경우, 실포트의 일부 입자들은 FBHE를 거쳐 연소로로 재순환하는 경로를 갖게 된다. 이때 기포유동층 영역으로 운전되는 FBHE는 실포트로부터 유입되는 고온(800~950 ℃)의 입자들의 유동 특성에 따라 열교환 튜브의 국부적 가열로 인한 손상 및 hot spot에 의한 입자들의 고온 뭉침(agglomeration)이 발생할 수 있어 순환유동층의 안정적 조업에 영향을 미칠 수 있다. 본 연구에서는 국내 D 순환유동층 보일러의 FBHE에 대한 운전자료 분석 및 바라쿠다를 통한 CPFD(Computational Particle Fluid Dynamics) 해석을 통해 구조적 문제로부터 발생하는 열흐름의 불균일성을 밝혀내었다. 실제 D 순환유동층의 FBHE 열교환 튜브 온도는 실포트의 고체온도 변화와 가장 밀접한 상관관계를 나타내었으며, FBHE 내의 열흐름의 불균일성은 FBHE의 조업 유속의 증가(0.3→0.7 m/s)로는 그 불균일성을 해소하기 어려운 것으로 나타났다. 그러나, FBHE로 유입되는 고온 입자들에 대한 사전 혼합 영역(Premixing Zone)이 설치된 경우와, 연소로로 재순환되는 입자 배출 라인의 대칭화를 통한 구조변경 시, 입자 혼합의 증대와 더불어 열흐름의 불균일성은 상당 부분 감소하는 것으로 고찰되었다. 이에, FBHE의 구조 최적화가 열교환 성능 및 운전 안정성을 확보하는 대안임을 제시하였다.

• 설비공학논문집
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• 제2권2호
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• pp.112-118
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• 1990

Characteristics of heat transfer in a smooth and finned tube located vertically in atmospheric fluidized bed combustor which uses low grade anthracite coals was studied. Experiments to investigate the characteristics of heat transfer between smooth and finned tube are carried out and the results depend on particle size, fluidizing air velocity and bed temperature are summarized. It is found that heat transfer coefficient of the smooth and finned tube increases with decrease in particle diameter and increase in bed temperature. Furthermore, it is noted that heat transfer coefficient increase at the first with increase in the velocity of fluidizing air and tends to decrease at a certain fluidizing air velocity. The increase of heat transfer coefficient for the finned tube is appeared to be increased in 30% compared to that for the smooth tube.

• Korean Chemical Engineering Research
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• 제46권6호
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• pp.1057-1062
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• 2008

기존 2탑 유동층 공정의 단점을 극복하기 위해 두 개의 기포유동층, 고체분사노즐, 상승관 및 고체재순환관으로 구성된 신개념 2탑 유동층 공정을 적용한 3 kW 매체순환식 가스연소기를 개발하였다. 본 연구에서는 3 kW급 매체순환식 가스연소기에서 고체순환속도에 미치는 고체분사노즐 유속, 유동화속도, 고체층 높이, 고체유입구의 단면적, 층 온도 등의 영향을 고찰하였다. 고체순환속도는 고체층 높이가 증가하고 고체유입구의 단면적이 증가할수록 증가하는 경향을 나타내었으며 유동화속도와 온도의 영향은 크지 않았다. 장기연속운전 가능성을 검토하기 위해 50시간까지 고체순환 장기연속운전을 실증하였다. 두 유동층과 고체재순환관의 압력강하 값이 안정적으로 유지되어 고체순환이 원활하고 안정적으로 유지되는 것을 확인하였다.

• 한국환경과학회지
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• 제6권3호
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• pp.267-276
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• 1997

It has been studded that combustion and the production of air pollution of anthracite - bituminous coal blend In a fluidized bed coal combustor, The objects of thIns study were to investigate mixing characteristics of the particles as well as the combustibility of the low grade domestic anthracite coal and Imported h19h calorific bltununous coal in the fluidized bed coal combustor. They were used as coal samples ; the domestic low grade anthracite coal with heating value of 2,010kca1/kg and the Imported high grade bituminous coal with beating value of 6,520kca1/kg. Also, the effects of air flow rate and anthracite fraction on the reaching time of steady state condition have been studied. The experimental results are presented as follows. The time of reaching to steady state was affected by the temperature variation. The steady state time was about 120 minute at 300sc1h which was the fastest. It has been found that $O^2$ and $CO^2$ concentration were reached steady state at about 100 minute. It has been found that $O^2$ concentration decreased and $CO^2$ concentration increased as the height of fluidlzed bed Increased. It was found that splash zone was mainly located from 25cm to 35cm above distributor. Also, as anthracite traction Increased, the mass of elutrlatlon particles Increased, and $CO^2$ concentration decreased. As gk flow rate Increased,$O^2$ concentration decreased and $CO^2$ concentration increased. Regardless of anthracite fraction and flow rate, the uncombustible weight percentage according to average diameter of elutriation particles were approldmately high In the case of One Particles. As anthracite traction and k now rate Increased, elutriation ratio Increased. As anthracite fraction was increased, exit combustible content over feeding combustible content was Increased. Regardless of anthracite fraction, size distribution of Ued material from discharge was almost constant. Over bed temperature 85$0^{\circ}C$ and excess air 20% , the difference of combution efficiencies were little. It is estimate that the combustion condition In anthracite-bituminous coal blend combustion is suitable at the velocity 0.3m/s, bed temperature 85$0^{\circ}C$, the excess air 20%.