【作者】 张川；

【导师】 廖强；

【作者基本信息】 重庆大学 ， 工程热物理， 2010， 博士

【摘要】 当今世界经济的发展强烈依赖于以化石燃料为主的能源供应,然而这些资源并非是取之不竭的。能源持续紧张,国际石油价格大幅振荡,不断攀升,能源短缺问题日益成为困扰社会和经济发展的首要问题,同时化石能源的开采和应用对环境造成了严重破坏,特别是产生的CO2引起的温室效应带来的极端和异常气候变化、氮氧化物和SO2带来的酸雨等问题严重地威胁着地球和人类的可持续发展。我国是一个能源资源相对贫乏的国家,特别是石油、天然气人均资源量仅为世界平均水平的7.7%和7.1%。因此开发可再生的生物能源对于促进可持续社会的发展具有重要意义。氢气在所有已知能源中具有最高的单位质量能量密度,并在通过电化学或者燃烧的能量转化过程中不释放危害环境的产物,因此成为最具潜力的清洁可再生能源。2007年4月国家颁布能源发展“十一五”规划更明确指出将氢能开发作为我国今后重点的前沿发展技术之一。目前广泛采用的传统制氢方法一方面仍消耗化石能源,另一方面对环境造成破坏。太阳辐射能是目前世界储量最大的可再生能源。采用光合细菌的光生物制氢技术反应条件温和,可以把太阳能利用与有机污染物降解耦合起来,完美解决了能源需求和环境保护之间的矛盾。采用细胞固定化技术实现连续化的产氢是光生物制氢付诸实际的基础。生物膜和包埋这两种细胞固定化方法已经应用于生物制氢的研究。采用该技术可提高制氢反应器单位体积内的生物量、反应器内细菌的环境耐受力、以及产氢速率和生物降解速率。然而包埋方法由于传质阻力大、透光性差以及机械强度差的缺点不利于反应器长期运行。本文采用生物膜细胞固定化技术,分别从提高反应器中的生物持有量、强化传质和提高光能转化效率出发,构造了微槽透光板式光生物制氢反应器、环流形光纤生物膜反应器和光纤束生物膜制氢反应器等三个能够高效连续产氢的新型光生物制氢反应器。实验研究了不同操作条件下上述光生物制氢反应器的产氢速率、底物消耗速率、产氢得率和光能转化效率等特性和变化规律。通过微槽透光板式光生物制氢反应器与普通平板生物膜光生物制氢反应器的对比实验发现,由于微槽道结构可以提高反应器的比表面积进而增加了反应器的生物持有量,同时微槽道的起伏结构又可以增加反应器主流区和生物膜区域之间的对流传质系数,底物和产物传输的增强使得生物膜区域可维持较好的微生态环境。另外微槽道还可以增强光照在生物膜区域的散射,从而提高该区域的光照均匀性,使得生物膜区域内的微生物具有更高的光能转化效率。在相同的实验条件下,微槽透光板式光生物制氢反应器的产氢速率、产氢得率系数和光能转化效率分别达到3.816 mmol/m2/h, 0.75 molH2/molglucose和3.8%,比普通平板反应器产氢速率提高约75%。微槽道的结构形式可以为生物膜方法光生物制氢反应器的载体改良提供参考。本文首次将生物膜细胞固定化技术与导光载体相结合构造了环流形光纤生物膜制氢反应器,用于解决目前光生物制氢反应器存在的实现细胞固定化和增强反应器导光性之间的矛盾。通过实验研究发现该反应器在入射光波长为530 nm光纤表面光强度为4.15 W/m2的条件下,反应器的光能转化效率和产氢速率得到显著提高,分别达到47.9 %和0.83 mmol/g cell/h。在实验研究的基础上建立了环流型光纤生物膜制氢反应器中底物传输与消耗的数学模型,分析了外界操作因素对该反应器内质量传递和底物降解的影响规律,理论预测值与实验值基本吻合。在此基础上构造的光纤束生物膜制氢反应器实现了反应器的内容积空间的充分利用并获得了反应器内均匀的光强分布。在模拟自然光照的实验条件下得到了当光照强度为5.1 W/m2时,反应器的产氢速率和光能转化效率分别达到0.6 mmol/L/h和3.64%。固定化技术是当今生物工程领域中的研究热点,但关于固定化细胞光生物制氢反应器中传输特性的研究还极少进行,本文的研究工作将促进对固定化细胞光生物制氢的传递及产氢的强化机理和规律的认识,解决固定化细胞技术中的传输限制性问题和光生物制氢反应器内光能利用率低、产氢率低等问题,为新型高效规模化光生物制氢反应器的开发和应用奠定基础,具有重要的学术价值和工程实际意义。更多还原

【Abstract】 Economic growth in the last few decades was strongly dependant on fossil fuels as sources of energy, while these resources were not unlimited on a long view. Today absence of energy supply in the world remains in strain that lead to the always rising of international price of oil.The primary obstacle affecting the development of society and economy presently is the increasing shortage of energy resources. Meanwhile, the exploitation and application of fossil fuel brought seriously environmental problems, especially the resent worldwide‘greenhouse effect’attributed to an increasing concentration of carbon dioxide in the air due to combustion of fossil fuels, while the acid rain was ascribed to the emitted NOx and SO2. These pollutants disturbed the sustainable development of earth and human being. Compared with other country, there was less energy resources in Chinese. The storage amount per capita of oil and natural gas in our country is only 7.7% and 7.1% of word average level. So our requirement for new technologies to obtain sustainable and environmentally acceptable energy was more urgently.Hydrogen has the highest gravimetric energy density among any known fuel and is compatible with electrochemical and combustion processes for energy conversion without producing emissions that add to environmental pollution. Therefore, offers tremendous potential as clean, renewable energy supplyment. And in the 11th Five-Year Plan of energy resource promulgated the exploitation of hydrogen energy will become one of the important and advanced technologies needed to study. However, hydrogen production by conventional methods needed fossil energy consumption thus destroyed our living environment also. Solar energy is the most abundant one of various renewable energy sources. Its radiation provides the biggest flow of energy on the earth. Hydrogen production via biological process by photosynthetic bacteria can operate in moderate reaction condition that coupled with the organic contamination degradation and solar energy utilization, leading to a solution for the confliction of energy requirements and environment protection perfectly.It should be pointed out that one necessary premise of practical photobiological hydrogen production is to make the process operate continuously. Cell immobilization was the feasible technique to realize the continuous hydrogen production. A few studies on immobilized-cell techniques for biological hydrogen production had been carried out revealed that the reactor using cell immobilization technology ,gel entrapment and biofilm, could effectively increase the biomass amount in the unit bioreactor space, enhance the tolerance ability of the bacteria and increase the hydrogen production rate and bio-degradation rate. For gel entrapment, the main drawbacks were low hydrogen production rate, insufficient light supply, weak mechanical strength and poor stability for long-term operation. Immobilized-cell systems with biofilm formation were considered as suitable means for continuous and efficient hydrogen production. Measures on mass transfer enhancement, biomass immobilization increasing and light conversion efficiency improvement are motivations of present study. Three novel photobiological reactors of groove-type photobioreactor, annular fiber-illuminating biofilm photobioreactor and annular bundle of optical-fiber-illuminating photobioreactor were developed for continuous and efficient hydrogen production by immobilized PSB. The different performances with respect to hydrogen production rate, substrate consumption rate, hydrogen yield and light conversion efficiency of the photobioreactor were investigated and effects of different operation conditions on the performance of photobioreators were obtained also.Results of parallel experiments on groove-type photobioreactor and flat panel photobioreactor indicated that groove structure with large specific surface area was beneficial to cell immobilization and biofilm formation of the photosynthetic bacteria on photobioreactor surface to increase the amount of biomass in the bioreactor. The fluctuant structure could also enhance the convective mass transfer of the substrate from the bulk flow to the biofilm and metabolic production transfer from the biofilm to the bulk flow to attain a better microenvironment in biofilm zone. Moreover, the groove structure with a high surface-to-volume ratio offered a larger illumination area for the photobioreactor and this, in turn, leaded to even distribution of the light and less light attenuation in the biofilm zone, hence improved the light conversion efficiency. The maximum hydrogen production rate, H2 yield and light conversion efficiency in the groove-type photobioreactor were 3.816 mmol/m2/h, 0.75 molH2/molglucose and 3.8%, respectively, which were about 75% higher than those in the flat panel photobioreactor. The groove-type structure offered a reference about the improvement of the carrier within bioreactor for photobiological hydrogen production with biofilm technology.Our newly developed annular fiber-illuminating biofilm photobioreactor firstly solved the confliction of cell immobilization and light transfer enhancement in the study field of photobiological hydrogen production. A comprehensive investigation of operational conditions on the performance of AFIBR was carried out by a series experiments. A novel increasement of light conversion efficiency of 47.9% and hydrogen production rate of 0.83 mmol/g dry cell/h were attained by monochromatic light illumination at 530 nm and even light intensity distribution character of inside light source in AFIBR at 4.15 W/m2. A mathematic model on substrate transfer and degradation of AFIBR was built based on experimental results. It described effects of different operating conditions on characters of the AFIBR, model predictions were accordant with experimental results on the whole. The newly developed annular bundle of optical-fiber-illuminating photobioreactor based on the previous studies attained sufficient utilization of inner space and evenly light intensity distribution in the bioreactor. It achieved excellent hydrogen production rate (0.6 mmol/L/h) and light conversion efficiency (3.64%) under sunlight simulative conditions of 5.1 W/m2. These results have instructional effects on the study of efficient photobiological hydrogen production in large scale.So far, the cell immobilization technology has become positive in biotechnology, but there was few study on the transfer characteristics of immobilized PSB cells in the process of photobiological hydrogen production. Our researches, which would set a primitive effort for application of immobilized cells technology in bioenergy production to solve the problem of mass transfer limitation within immobilized cells, low light conversion efficiency and low hydrogen production rate of the bioprocess. These studies offered valuable referents on the research of efficient photobioreactor for continuous hydrogen production in large-scale, they could give necessary aidances for both therotical and practial studies in the future.更多还原