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Experimental Studies on K2CO3-Catalyzed Gasification Process of Pre-treated Coal Samples (Hybrid Coal, Ash-free Coal and Ionic Liquid-treated Coal) in a Fixed-bed Reactor
- Author(s)
- 윤상필
- Alternative Author(s)
- Sang-phil Yoon
- Advisor
- 김형택
- Department
- 일반대학원 에너지시스템학과
- Publisher
- The Graduate School, Ajou University
- Publication Year
- 2018-02
- Language
- eng
- Alternative Abstract
- Low-rank coal has a high content of moisture and ash, resulting in a low heating value and higher probability of spontaneous combustion. In addition, low-rank coal is coal that emits significant environmental pollutants during combustion. Lignite and sub-bituminous coals are low-rank coals. The demand for low-cost low-rank coal is increasing, both domestically and internationally, due to the recent rise in oil prices and demand for power generation. The use of low-rank coal generates greenhouse gases, such as SOx and NOx, and fine dust. The cost to remove these air pollutants is high. Furthermore, the use of low-rank coal generates more green house gases because of its remarkably low combustion efficiency. Coal upgrading to remove moisture and ash from low-rank coal is therefore required. The objective of the present study is to compare coal gasification characteristics before and after coal upgrading to determine the coal gasification performance after coal upgrading and simultaneously identify technical and environmental characteristics. The coals used in this study are coal-upgraded low-rank coals, which can be classified into three types. The first one is ash-free coal. The ash was extracted from low-rank coal using an organic solvent. The ash content of this coal is less than 200 ppm. The second type of coal is hybrid coal obtained by mixing low-rank coal with biomass after removing the moisture and carbonizing it. Its heating value has been improved by 20% compared with that of raw coal. The third type is ionic liquid-treated coal, which was obtained by mixing low-rank coal and ionic liquid, drying the mixture, and reconfiguring the internal coal structure. It is looser than raw coal and exhibits a porous structure. Catalytic gasification experiments were conducted on three types of upgraded coals using the same conditions. Catalytic gasification is a gasification process in which a catalyst is added during gasification. Catalytic gasification is characterized by a gasification process occurring at a temperature lower than the conventional gasification temperature. In addition, the time spent in the reactor is short and steam is used as oxidant instead of air. Therefore, the reactor size is smaller than that of a traditional gasification reactor. The catalyst was K2CO3, which is has been used in many studies due to its favorable reactivity. The coal and the catalyst were mixed by the impregnation method using a agitator. All coal was first pulverized to a grain size below 75μm and steam was used as oxidant. The experimental variables were temperature (700℃, 800℃, and 900℃) and catalyst content (0%, 5%, 10%, and 15%). After the coal gasification took place with respect to the two variables (temperature and catalyst content), the resulting syngas was collected in real time using a Non-dispersive infrared absorption-type analyzer. In this work, gas production, carbon conversion rate, and cold gas efficiency were computed using the gas collected in real time and the gasification characteristics of the coal before and after coal upgrading were compared. As a result, the total syngas volume and cold gas efficiency of the raw coals HCK for five times and AFC for three times increased respectively, with respect to the temperature rise. Furthermore, the total syngas volume and cold gas efficiency of raw coal increased by a factor of 3 and 2, respectively, as the catalyst content increased. However, the total syngas volume and cold gas efficiency did not increase continuously as the catalyst content of HCK and AFC increased; instead, the reactivity remained constant or decreased after reaching a certain content. In most coals, CH4 was typically produced at low temperatures of 700℃ and 800℃; however, AFC produced about twice as much CH4 at 900℃ than at 700℃. The CO2 emission was reduced in all upgraded coals. The reduction of CO2 in HCK was 65% lower than that of raw coal and the reduction of CO2 in AFC was 50% lower than that of raw coal. Based on the analysis of syngas presented in this work, coal upgrading improved the gasification performance and resulted in lower CO2 emission compared with that of raw coal. Moreover, this study verified the validity of using the syngas produced for gasification applications, such as IGCC, SNG, and DME process, according to experimental conditions.
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- Graduate School of Ajou University > Department of Energy Systems > 4. Theses(Ph.D)
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