【作者】 杨国来；

【导师】 陈汉平；

【作者基本信息】 华中科技大学 ， 热能工程， 2007， 博士

【摘要】 生物质能是由植物的光合作用固定于地球上的太阳能,具有二氧化碳“零排放”、存储量大、可再生和利用方式多元化等独特的优点而倍受青睐,生物质气化是生物质能开发利用的主要方式之一,对全球的环境保护和能源利用有着重要意义。但是,生物质气化产品气中的高焦油含量严重制约了产品气的应用。本文以降低气化产品气中的焦油含量、提高气体热值和改善气化指标为目的,研究三种炉内催化剂(白云石、菱镁矿和橄榄石)在不同工况下的催化气化效果。而且,将超声波辐射应用到镍基催化剂的制备过程中,研制了一种可以降低裂解催化剂的积炭量,延长催化剂使用寿命的新型镍基催化剂,为研制新型镍基催化剂做出了积极的尝试并取得了较好的效果。本文首先研究了三种生物质在CO2气氛下的热解失重过程,通过改变升温速率和热解终温,总结出三种生物质在热解过程的四个阶段中的热解规律。生物质在CO2气氛下热解的最佳条件为:生物质的样品量以10 mg为宜,最佳升温速率在10-20℃/min之间,终温为960℃。然后对200-450℃这个主要热解失重区间进行一级热解动力学参数求解,结果表明:在挥发分析出时,花生壳的活化能最低,与木屑和稻草相比,花生壳的热解特性最好。镍基催化剂是裂解反应器中应用得最广泛的催化剂之一,但是,镍基催化剂用于焦油裂解时最常见的问题就是容易失活,降低裂解效果,缩短其使用寿命。本文将超声波应用到镍基催化剂的制备工艺中,首先用正交试验法确定超声波功率、助剂La2O3和CeO2以及煅烧温度等四个因素对Ni/γ-Al2O3催化剂积炭量的影响顺序为:煅烧温度≈超声波功率>CeO2>La2O3。其中煅烧温度和超声波功率的影响高度显著,助剂CeO2的影响显著。然后专题研究超声波辐射对镍基催化剂积炭量的影响。通过BET、XRD和SEM等表征手段分析三种催化剂样品积炭前后的变化,并对积炭后的催化剂进行多次重复的热重试验,最终的研究结果表明:超声辐射可以使载体中的部分微孔转变为中孔,中孔孔径大小与活性组分颗粒大小相当,使活性组分较容易地分散在中孔中;超声辐射能够抑制活性组分与载体发生反应,避免生成无活性的NiAl2O4晶相;超声辐射可明显降低催化剂的积炭量,低功率的超声辐射比高功率的超声辐射对减少催化剂中的积炭量更有效。以三种具有代表性的生物质(木屑、花生壳和稻草)为原料在流化床气化反应器中进行催化气化,改变运行条件(当量比、气化温度),研究各运行工况对生物质气化产品气及焦油组分的影响,利用GC确定产品气组分,GC/MS确定产品气中的焦油含量。结果表明:生物质气化过程按照不同的产气目的可通过改变工况进行优化;气化生物质时,添加价廉易得的炉内催化剂可降低反应器出口处产品气焦油含量一半以上,焦油转化率在48.4-70.5%之间。同时可以调节焦油组分,降低重质焦油含量,有利于下游工序进一步裂解焦油。本文在最后利用大型ASPEN PLUS软件建立流化床气化反应器内的物质平衡、化学平衡和能量平衡模型。通过比较模拟值与试验值,发现模拟值与试验值吻合良好,证明模型是可信的。更多还原

【Abstract】 Biomass energy is derived from solar energy through plant photosynthesis, which has been attracted increasing concern with many advantages: carbon dioxide zero emission, huge amount, renewable and versatile utilization technologies. Biomass gasification is one of the most promising technologies to convert biomass to energy, it is favorable for global environmental protection and energy utilization. However, high content of tar in the production gas limits its application widely. With the focus of decreasing tar amount and upgrade the quality of product gas, the gasification of local biomass samples was performed in Fluid bed gasifier. The influence of catalyst (dolomite, magnesite and olivine) and variant operting condition on tar cracking was studied in detail. A novel nickel-based catalyst was observed with ultrasonic radiation, it is efficient to reduce the coked amount coating on catalyst and prolong the operational life of catalyst. It is important for the utilization of catalyst. It is great for the development of biomass gasification technology.Firstly, the pyrolysis under CO2 condition of three different biomass samples was carried out in TGA with variant heating rates and final temperatures. It was observed that the pyrolysis of biomass was taken place in four stages. The optimum condition for biomass pyrolysis are : 10mg of biomass sample, 10-20℃/min for elevating temperature velocity with the final temperature 960℃. Then, the first-order pyrogenation kinetics parameters was calculated in the main pyrolysis range 200-450℃. It was showed that peanut shell has the lowest activation energy during emission of volatile and the best pyrolysis feature.The nickel based catalyst is one of the most widely used in the cracking reactor. However, the most popular problem is the coke coating on the surface of the nickel based catalyst, hence the catalysis was decreased, catalytic activity was reduced and the operational life was shorten. Here ultrasonic was applied in the preparation process of the nickel based catalyst. the influence of the ultrasonic radiation, additive La2O3, CeO2 and the calcined temperature on the coked amount of Ni/γ-Al2O3 catalyst was analyzed. It was observed that the impact order is: calcined temperature≈the ultrasonic radiation > CeO2 > La2O3. The influence of calcined temperature and ultrasonic radiation was obvious, and the influence of auxiliary CeO2 was also significant. Simultaneously, the influencing factor of ultrasonic radiation was studied in depth. The difference of the coke amount for three catalyst samples were analyzed with characteristic approaches (BET, XRD and SEM, etc), and thermogravimetric experiments. it can be found that ultrasonic radiation can make small pores in the carrier change into the middle ones. The diameter of middle pore is comparative to the size of active component particles, to make the active component dispersed in the middle pore more easily. Ultrasonic radiation can refrain the reaction of the active component and the carrier, and avoid producing NiAl2O4 crystalling phases and loss activity. Ultrasonic radiation can also reduce the coked amount of the catalyst greatly. The ultrasonic radiation in low power is more effective on reducing the coked amount in catalyst than the ultrasonic radiation in high power.Then, the gasification of three local biomass samples (saw-dust, peanut shell and straw) was carried out in fluidized bed gasifier system. the influence of catalyst addition (dolomite, magnesite and olivine), operation conditions (ER, temperature) on the production of biomass gasification and tar component was investigated in detail. The component of the gas products was determined by GC, and the species of collected tar was measured with GC/MS. it can be observed that the process of the biomass gasification can be optimized through changing the operating conditions according to target. Adding cheaper catalyst in the process of biomass gasification can reduce over half of tar amount in the final products, the conversion ratio of tar is 48.4-70.5%. Adjust the componente of tar and reducing the content of heavy tar are favorable for the downstream process.Finally, ASPEN PLUS, a computer program to simulate chemical industry process based on the principle of Gibbs free energy minimization was involved in to approach the behavior of biomass gasification. The model was approached based on mass, energy and chemical element constant. As the equilibrium state is impossible to arrive in the gasifier, a restricted equilibrium of RGIBBS reactor was introduced in according to the experiment result. It was observed that a good agreement was shown between simulation and experiment result. It is great for the understanding and development of biomass gasification.更多还原