生物质两段式气化基础及试验研究

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	生物质两段式气化基础及试验研究
其他题名	the fundamental and experimental research on biomass two-stage gasification
	黄艳琴
导师	吴创之
	2009-05-27
学位授予单位	中国科学院广州能源研究所
学位授予地点	广州能源研究所
学位名称	博士
关键词	两段式气化生物质半焦气化反应性动力学焦油
摘要	生物质两段式气化根据物料高挥发份的特性，将气化过程中的热解和氧化还原反应分开在不同反应器内进行，可根据热解和气化反应的特性分别控制反应条件，优化气化过程。在两段式气化工艺中，生物质首先在热解段受热裂解为气体、焦油和固体焦，之后热解产物一起进入气化段发生气化还原反应，气化段内形成的高温氧化区能大大降低产气中焦油的含量；因而也越来越受到研究者的关注。本论文基于两段式气化展开了基础及试验研究，考察了生物质物料特性、热解条件、金属催化剂对热解固体半焦气化反应性的影响；分析了热解半焦在水蒸气和CO2气化过程中孔隙结构及反应性的变化规律；研究了热解半焦在水蒸气和CO2两种气氛下反应特性；设计了一个实验室规模的两段式气化炉，并以玉米芯为原料在试验装置进行了气化特性的研究。利用热重分析仪考察了林业类和农业类剩余物中的8种生物质热解半焦的CO2反应性。结果显示，对于灰分中SiO2含量低的生物质焦，其反应活性从大到小顺序与其中水溶性金属(K、Ca)含量从高到低顺序一致，说明（K+Ca）含量是影响不同种类生物质焦反应性不同的主要原因；对于灰分中SiO2含量比较高的生物质焦，其反应活性从大到小顺序与其中Ca含量从高到低顺序一致，说明SiO2削弱了碱金属K的催化作用，但对Ca的催化效果影响不大；最后得出了8种生物质焦与CO2反应的气化动力学参数，反应级数在0~0.5之间。利用3种热解炉装置，分别在热解终温550-950℃、加热速率0.1-500 K/s下热解制取了稻秆半焦。采用等温热重法，在STA409综合热分析仪考察了热解终温、热解速率及气化温度对稻秆半焦CO2气化反应性的影响。利用XRD、SEM、比表面积分析仪观测了热解条件对半焦结构特性的影响。反应性测试结果显示：在热解终温为550-950℃之间，随着热解温度的提高，其气化反应性呈下降趋势；热解速率越高，其气化反应性越好；在850-950℃之间，提高气化温度能提高稻秆半焦与CO2的反应性。XRD结果显示950℃下的热解半焦的碳有序化程度相对较高；SEM和比表面积分析结果显示，500K/s热解速率下的半焦具有更丰富的孔隙结构和较大的比表面积。采用混合反应模型描述了稻秆半焦与CO2的气化反应过程，求取了反应动力学参数。在热重分析仪上进行了几种金属盐（K、Na、Ca、Mg、Fe）对杉木粉半焦CO2催化气化反应特性的研究；利用XRD和SEM技术对半焦样品的碳化程度、晶相结构及表面形貌进行了表征。研究表明：5种金属盐均提高了半焦样品的反应活性；且反应活性指标显示其催化效果顺序为K>Na>Ca>Fe>Mg。XRD结果显示：Na和Ca在制焦过程中形成了明显的晶相结构；Mg促使了半焦中碳的有序化程度。SEM结果表明：5种金属盐均在半焦表面形成了‘斑点’状的活化中心点；且在碱金属半焦的部分表面观测到疏松片状结构；利用数值计算方法求取了半焦样品的反应动力学参数。利用固定床实验装置，分别对木粉热解焦进行CO2和H2O两种气氛下的气化试验，并分析热解焦在经过部分气化反应后孔隙结构变化特点和气化反应特性。研究结果表明：木粉焦气化过程孔结构的变化规律与气化介质有关：CO2气化过程以产生微孔为主，孔径范围大部分在0.4-0.9 nm之间，而H2O气化在反应初期以产生微孔为主，反应后期以扩孔为主；利用孔结构的分形理论分析发现，杉木粉焦气化过程孔隙结构变化符合分形关系，且CO2气化过程的分形维数2.67，小于H2O气化过程中的分形维数2.74；最后提出了一个修正的随机孔模型，能较好的描述气化残余焦的CO2气化过程。在热天平上考察了不同的化学反应条件，包括温度、压力及气氛等因素对玉米芯焦气化反应的影响。结果显示，在水蒸气和CO2两种气氛下，玉米芯焦均具有较好的气化反应性；相同条件下的C-H2O反应速率是C-CO2反应速率的2倍；气化反应速率随水蒸气分压的增大而增加。最后，利用混合反应模型得到了H2O和CO2两种气氛下气化反应动力学参数，及玉米芯焦在水蒸气气氛下反应速率与温度、水蒸气分压和转化率的关系。在实验室规模的两段式气化炉上对玉米芯的气化特性进行了试验研究，考察了两段式气化工艺下气体组分、热值、产气率、碳转化率、气化效率等随空气当量比ER的变化规律；对比分析了4种气化工艺下的气化效果；以富氧和水蒸气为气化介质，考察了不同水蒸气配比下气体组分随氧气当量比的变化；测量分析两段式气化产气中焦油的含量。
其他摘要	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.
页数	141
语种	中文
文献类型	学位论文
条目标识符	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[D]. 广州能源研究所. 中国科学院广州能源研究所,2009.

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