Evaluation of ash deposition behavior and fine particle formation from combustion of low-rank coal impregnated with molasses in DTF

Hyung-taek Kim
일반대학원 에너지시스템학과
The Graduate School, Ajou University
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Alternative Abstract
In recent years, many countries have invested enormous efforts to tackle increasingly harsh environmental problems, especially the greenhouse effect. The addition of biomass into coal is regarded as a promising technology to mitigate CO2 emissions. However, the costs related to retrofitting injection systems and unstable combustion inhibit this option. Therefore, this thesis developed a two-in-one fuel that impregnates molasses into the holes of low-rank coal (LRC), which can be directly applied to existing boilers. However, due to the existence of alkali and alkaline earth metals (AAEMs) in molasses, the impregnation of molasses into the coal pores possibly lead to the ash deposited on the surface of the heat exchanger, reducing the heat exchange efficiency. Besides, a part of fine particles will emit into the atmosphere, resulting in a series of air pollutions. Thus, the investigation of ash deposition and fine particle formation is a significant topic to promote heat exchanger efficiency and protect the environment. In this study, five fuels, Berau coal, Berau coal impregnate with 10wt% and 20wt% molasses, Bayan coal and Bayan coal impregnate with 3wt% molasses are selected. In the following sections, these fuels will be denoted as Berau coal, 10% HCK, 20% HCK, Bayan coal and 3% HCK respectively. Experiments are carried out in drop tube furnace (DTF) under the combustion temperature of 1300°C and the ash probe temperature of 800°C with access air. The fuel is fed at a rate of 0.45g/min for 10min. The properties of the ash deposition and fine particles are characterized. It is concluded that 20% HCK showed the most serious deposition tendency, followed by 10% HCK, Berau coal, Bayan coal and 3% HCK. SEM-EDX, XRD and theoretical model analysis indicate that CaO and Fe2O3 are the main factors affecting the deposition propensity. Meanwhile, the difference between the top and bottom layers are also due to CaO and Fe2O3. As far as the fine particle formation is concerned, it was obvious that volatile elements, K, S and Mg, are rich in fine particles (<1μm). Si, Al, Ca and Fe are rich in coarse particles (>1μm), this phenomenon is due to the different formation mechanisms. The boiling point of K, S and Mg is 774°C, 445°C and 1090°C respectively. So, these elements are easy to vaporize and condense to form fine particles (<1μm). The boiling point of Si, Al, Ca and Fe is 2355°C, 2327°C, 1484°C and 2750°C respectively, it is difficult to vaporize under testing temperature, thus, these elements are rich in coarse particles (>1μm).

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Graduate School of Ajou University > Department of Energy Systems > 3. Theses(Master)
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