【作者】 王晶博；

【导师】 肖波；

【作者基本信息】 华中科技大学 ， 环境工程， 2013， 博士

【摘要】 针对目前化石能源短缺以及其利用所带来的严重环境污染问题,人们越来越重视清洁能源—氢能的开发和利用。由于城市生活垃圾产量不断增加,对环境造成的污染日益严重,垃圾的处理问题已经成为目前亟需解决的迫切问题。而城市生活垃圾有机组分中含有大量的碳氢化合物,因而可以看作是一种可再生资源,利用热解气化技术处理城市生活垃圾不仅能对城市生活垃圾进行大量的减量化,而且还能进行能源—氢能的回收。本文采用含水城市生活垃圾作为气化原料,利用其本身所含有的水分在高温热解时挥发成蒸汽,形成一个自发的蒸汽氛围,产生的蒸汽作为后续城市生活垃圾气化时所需的气化剂；并在城市生活垃圾原料中添加一定的CaO对气化过程中产生的CO2进行高温原位吸附以及对焦油进行一定的原位催化裂解,提高氢气产率；针对在该条件下焦油含量较高的问题,研制了一种新型的改性白云石载镍催化剂使得城市生活垃圾原位水蒸气催化气化过程中产生的焦油进一步催化裂解和促进富氢燃气的产生。围绕着该工艺的构建,本文开展以下研究工作：(1)选取城市生活垃圾有机组分(织物、木屑、纸张、塑料)为气化原料,并测定了样品的工业分析、元素分析及其热值。结果表明,城市生活垃圾有机组分的挥发分和固定碳含量较高,而灰分含量低于2%。主要的元素组成为C、H、O三种元素。此外,混合垃圾样品的低位热值达到17.09MJ/kg。(2)通过TG/DTG/DTA方法分别探讨了各单一有机组分的热解特性,分析了各组分间在热解过程中的相互影响规律,对混合垃圾样品的热失重行为和动力学特征进行了研究。结果表明,织物、塑料及木屑的热解过程均只有一个主要的失重阶段,而纸张有两个失重阶段；对城市生活垃圾中各组分之间的共热解特性研究时发现当各组分的组成相似时,混合热解时不受单组分之间的相互影响；当各组分的组成差别较大时,各单独组分热解转化阶段温度分布是否重叠成为混合热解规律的主要影响因素。对混合垃圾进行热重分析时得到在低温区(240-385℃)失重的主要是混合垃圾样品中纤维素和半纤维素的分解以及部分塑料的低温分解,而发生在385～500℃间的第二失重峰主要是塑料和木质素组分的分解。使用等转化率法求解了城市生活垃圾混合组分的热解动力学参数,样品热解的表观活化能E值在170～225kJ/mol范围之间。(3)在小型管式炉固定床反应器上对城市生活垃圾原位水蒸气气化特性进行了系统的研究,考察了加热方式、反应温度、含水率、气化停留时间对城市生活垃圾原位水蒸气气化产物分布、气体成分的影响,并对该气化工艺进行了物料衡算和能量分析,探讨了城市生活垃圾原位水蒸气气化工艺的可行性。实验结果表明,快加热方式有利于提高燃气品质和减低焦油含量；随着反应温度的增加,气体产物含量增加,而焦油含量和半焦含量下降,气体组分中H2和CO含量升高,CIO2、CH4和C2烃类气体含量降低；当城市生活垃圾中的含水率为39.45wt.%时,气体成分中H2的含量达到最高值为25.8vol.%；通过N2流速来间接反映气相停留时间,随着N2流速的降低产生的气体中氢气含量从22.84vol.%升高到28.49Vol.%；在该工艺条件下得到的物料平衡误差为6.80%,通过能量分析得到冷气效率、能源回收率和稳态理论能耗比分别为54.24%、85.56%和2.78。(4)采用TG-MS分析方法研究CaO的添加对城市生活垃圾热解特性和热解产物的影响,同时对以CaO为添加剂的城市生活垃圾原位水蒸气气化制氢进行了试验研究。结果表明,添加CaO有利于城市生活垃圾在低温区域的热解,能减少焦油组分的逸出,并且能减弱CO2的逸出峰强度；随着[Ca]/[C]由0增加到1.5,H2的浓度和产率由25.89vol.%和10.86gH2/kg MSW增加到45.90vol.%和31.56gH2/kg MSW;水蒸气的引入提高CaO的碳酸化反应活性,促进了H2的产生,但是过高的含水率会降低产气品质,最佳的含水率为39.45wt.%；高温强化了城市生活垃圾、焦油的热分解等反应产生更多的H2,但不利于CaO的碳酸化反应,最佳的操作温度为700～750℃。(5)研制了一种以改性白云石为载体,采用沉淀-沉积法负载氧化镍,制备新型的改性白云石载镍催化剂,在自行设计的两段式固定床反应器上对城市生活垃圾原位水蒸气催化气化制氢特性进行研究,评价并比较该催化剂与传统镍基催化剂和煅烧改性白云石催化剂的催化活性,采用GC-MS方法对焦油产物中的主要化学成分在不同催化剂作用下的变化规律进行了分析。结果表明,与Calcined MD催化剂和NiO/O-Al2O3催化剂相比,NiO/MD催化剂具有更好的催化活性和催化稳定性,焦油的去除率能达到90%以上,氢气含量达到了52.79vol.%；随着催化剂依次由Calcined MD、NiO/γ-Al2O3和NiO/MD催化剂的变化,焦油中PAHs的含量持续降低,而单环芳烃的含量则增加；随着催化温度的升高焦油产率降低,气体产物组分中H2和CO的含量提高。更多还原

【Abstract】 With the shortage of fossil fuels and the environmental pollution during its utilization, people are more focusing on the development and utilization of a clean energy-hydrogen. Moreover, the amount of municipal solid waste (MSW) increases dramatically, which leads to serious environmental pollution. Therefore, the treatment of MSW is becoming an urgent problem to be solved. The organic components in MSW with high content of hydrocarbon can be considered as a renewable energy. The application of MSW pyrolysis-gasification technology not only reduces MSW but also recovers hydrogen energy.In this thesis, MSW with a certain content of moisture is used as raw material. The water in MSW turns into steam at high temperature, forming an auto-generated steam atmosphere. The steam produced can be used as gasifying agent during the gasification of MSW. CaO is added into the raw material for hydrogen production with in-situ CO2removal and catalytic cracking of tar at high reaction temperature. Since the tar yield is still high under this condition, the NiO supported on modified dolomite catalyst is developed for further catalytic cracking of tar and hydrogen-rich gas production. According to this process, the following work was carried out in this thesis:(1) The organic components of MSW including fabric, sawdust, paper and plastic were selected as raw material. The proximate analysis shows that the MSW is rich in volatile matter and fixed carbon, but the ash content is lower than2wt%. From the ultimate analysis of MSW, the main elements are C, H and O. The lower heating value of MSW is17.09MJ/kg.(2) Through the TG/DTG/DTA method, the pyrolysis characteristics of each organic component and mutual influence of the various components in the pyrolysis process were discussed respectively, and the thermogravimetric behavior of MSW sample was analyzed and pyrolysis kinetic parameters were calculated too. The results show that there is only one main weight loss stage during the individual pyrolysis of fabric, plastic and wood, while there are two mass loss processes appeared in waste paper pyrolysis. Studying the co-pyrolysis characteristics of the mixed components, it is found that when the composition of each component is similar, the mixing pyrolysis does not subject to the mutual influence between the single-component. If the composition of each component varies greatly, the overlapping of the conversion stage temperature distribution in the individual component pyrolysis process becomes the main influence factor of mixed pyrolysis. Thermogravimetric analysis of MSW sample indicates that the cellulose, hemicelluloses and some plastics are decomposed in low temperature zone (240～385℃). The second weightlessness peak between385～500℃is mainly attributed to the degradation of plastic and lignin components. The pyrolysis kinetic parameters of MSW were calculated by iso-conversional methods. The apparent activation energy of MSW pyrolysis is in the range of170～225kJ/mol.(3) The characteristics of MSW gasification with in-situ steam agent has been systematic studied, which was carried out in a lab-scale fixed bed. The effects of heating rate, temperature, moisture content, and residence time on product distribution and gas composition were investigated. The material balance and energy analysis of this gasification process were also studied to discuss the feasibility of MSW in-situ steam gasification process. The results show that the fast heating method improves the quality of gas and reduces the yield of tar. The gas yield increases with temperature rising, but the yield of tar and char show an opposite trend. Meanwhile, the contents of H2and CO increase, while those of the other gases such as CO2, CH4and C2hydrocarbon gas decrease. When the moisture content of MSW is39.45wt%, the highest value of H2content in gas production is25.8vol%. The flow rate of N2can indirectly reflect the gas residence time, and the H2content increases from22.84vol%to28.49vol%as N2flow rate reduced. The error of material balance is6.8%under this experimental condition. The energy evaluation on the gasification process showed that cold gas efficiency, energy recovery and steady-state theoretical energy consumption ratio are54.24%,85.56%and2.78, respectively.(4) The TG-MS was used to analyze the pyrolysis characteristics of MSW with CaO addition. Meanwhile, hydrogen-rich gas production from in-situ steam gasification of MSW with CaO addition was experimental investigated. The results show that the addition of CaO is favorable to the pyrolysis of MSW in lower temperature. Adding CaO in MSW can reduce the escape of tar components and weaken the escape intensity of CO2. With the [Ca]/[C] ratio increasing from0to1.5, the hydrogen content and hydrogen yield increase from25.89%to45.90%and10.86g H2/kg MSW to31.56g H2/kg MSW, respectively. The introduction of steam can improve the activity of CaO carbonation reaction, which promotes the hydrogen production. However, the higher content of moisture would reduce the quality of gas production, and the optimal moisture content of MSW is found to be39.45wt%. Higher temperature could strengthen the thermal decomposition of MSW, which is greatly benefit for hydrogen production but unfavorable to CaO carbonation reaction. The best operating temperature is in the range of700-750℃.(5) The NiO supported on modified dolomite (NiO/MD) was prepared by deposition-precipitation (DP) method. The effect of catalyst on hydrogen production from catalytic gasification of MSW with in-situ steam agent was investigated in a two-stage fixed bed reactor. The GC-MS was used to analyze the main chemical components of tar product with different catalysts. The results show that the NiO/MD catalyst is better at catalytic activity and stability than that calcined MD and NiO/γ-Al2O3catalyst. With the NiO/MD catalyst, the removal ratio of tar is over90%, and the content of hydrogen in gas production reaches52.79vol%. As the catalyst changed from calcined MD to NiO/γ-Al2O3and NiO/MD, the content of PAHs in tar components continues to decrease, while that of single-ring aromatic increases. The higher catalytic temperature could favor the steam cracking and tar reforming, and promote H2and CO production.更多还原