生物质两段式气化基础及试验研究
文献类型：学位论文
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| 作者 | 黄艳琴 |
| 学位类别 | 博士 |
| 答辩日期 | 2009-05-27 |
| 授予单位 | 中国科学院广州能源研究所 |
| 授予地点 | 广州能源研究所 |
| 导师 | 吴创之 |
| 关键词 | 两段式气化 生物质半焦 气化反应性 动力学 焦油 |
| 其他题名 | the fundamental and experimental research on biomass two-stage gasification |
| 中文摘要 | Based on the high volatile content characteristic of biomass, two-stage gasification technology which basic principle is to separate pyrolysis zone from reduction zone is proposed, and this allows optimizing the operating parameters in each conversion step. During two-stage gasification, biomass is firstly pyrolyzed in the pyrolysis unit (first stage), and then the gas, tar along with char are fed into reduction unit (second stage). In the second stage, tar formed during pyrolysis zone is decomposed into lightweight gas when passing the high temperature partial oxidation zone. Therefore, two-stage gasification is gaining more and more attention. Based on two-stage gasification principle, the following fundamental and experimental researches were studied. Firstly, the effects of biomass characteristic, pyrolysis conditions and metal-catalysts on biomass char reactivity were investigated. Then, Pore structure characteristics and gasification reactivity of residual char obtained from steam and CO2 gasification were studied. The H2O and CO2 gasification reactivity of corncob char was also studied. Finally, the characteristic of corncob gasification in a lab-scale two-stage gasifier was investigated. The CO2 gasification reactivity of eight char samples generated from forestry and agricultural residuals were studied. Results shown that for char with low SiO2 content, the sequence of char reactivity from high to low coincided with that of (K+Ca) content from high to low，which indicated that (K+Ca) played an key role in char reactivity, and that for char with high SiO2 content, the sequence of char reactivity coincided with that of (Ca) content，which indicated that SiO2 reduced the catalytic effect of K. Finally, the kinetic parameters of CO2 gasification of char samples were calculated mathematically and the reaction index were between 0 and 0.5. The structure and CO2 gasification reactivity of rice straw char were studied to gain insight into effects of both pyrolysis temperature and heating rate on its gasification characteristics. Char samples were prepared at temperatures range from 550 to 950℃, with heating rates from 0.1 to 500 K s-1 in three different pyrolyzing reactors. The char reactivity was determined at 850~950℃ by means of isothermal thermo-gravimetric analysis. X-ray diffractometry (XRD), scanning electron microscopy (SEM) and surface area analyses were employed to investigate the impact of pyrolytic conditions on char structure. Study results showed that the CO2 gasification reactivity of char increased with decreasing pyrolysis temperature and increasing heating rate as well as gasification temperature. And the analysis results also showed that the order degree of carbon structure in char pyrolyzed at 950℃ was greater than that at 550℃, and higher heating rate led to more cavities and larger BET surface area. Finally, a mixed reaction model of kinetics for rice straw char gasification is formulated, and its simulated data can match the experimental results very well. The effects of five metal catalysts (K, Na, Ca, Mg, and Fe) on CO2 gasification reactivity of fir char were studied using thermal gravimetric analysis. The degree of carbonization, crystal structure and morphology of char samples were characterized by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The CO2 gasification reactivity of fir char was improved through the addition of metal catalysts, in the order K>Na >Ca >Fe >Mg. XRD analysis indicated that Na and Ca improved the formation of crystal structure, and that Mg enhanced the degree of carbon structure ordering. SEM analysis showed that spotted activation centers were distributed on the surface of char samples impregnated with catalysts. Moreover, a loose flake structure was observed on the surface of both K-char and Na-char. Finally, the kinetic parameters of CO2 gasification of char samples were calculated mathematically. Residual chars during CO2 and H2O gasification were obtained on fixed-bed apparatus. Pore structure characteristics and CO2 gasification reactivity of residual chars were investigated with isothermal nitrogen adsorption and thermal gravimetric analyzer (TGA), respectively. Pore structure analysis indicated that micropores are mainly developed during whole CO2 gasification process, while micropores are produced at the beginning of H2O gasification and then mesopores are mainly developed. Results of TGA showed that during CO2 gasification reaction rate plot of residual char with different porosity changes differently. Finally, the fractal characteristics of fir char are validated, and the fractal dimension of char during CO2 gasification is 2.67, less than that of char during H2O gasification 2.74. Finally, a modified random pore model was proposed to describe the CO2 gasification of residual char. Gasification reactivity of corncob char was investigated using thermobanlance and the effects of agent, temperature and steam partial pressure on gasification were studied. It was shown that corncob char had good gasification reactivity with both steam and CO2. And at the same experimental condition, the reaction rate of C-H2O is about twice as large as that of C-CO2. At 950℃, the reaction rate was increasing along with steam partial pressure. Finally, a correlation equation for reaction rate to temperature, steam partial pressure and conversion in steam was derived. The activation energy of char during CO2 and H2O gasification was also obtained. The characteristic of corncob gasification in a lab-scale two-stage gasifier was investigated. The variation of gas composition, gas yield, LHV, carbon conversion and gas efficiency along with air ER was obtained. The gasification characteristic during four gasification technology was compared. At different S/B, Gas compositon along with O2 ER was investigated. The tar content produced from two-stage gasification was weighed. |
| 语种 | 中文 |
| 公开日期 | 2011-07-14 ; 2011-07-15 |
| 页码 | 141 |
| 源URL | [http://ir.giec.ac.cn/handle/344007/5836]  |
| 专题 | 中国科学院广州能源研究所 |
| 推荐引用方式 GB/T 7714 | 黄艳琴. 生物质两段式气化基础及试验研究, the fundamental and experimental research on biomass two-stage gasification[D]. 广州能源研究所. 中国科学院广州能源研究所. 2009. |
入库方式： OAI收割
来源：广州能源研究所
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