【作者】 荆艳艳；

【导师】 张全国；

【作者基本信息】 河南农业大学 ， 农业生物环境与能源工程， 2011， 博士

【摘要】 本论文是在国家自然科学基金项目“超微秸秆类生物质光合连续产氢过程及代谢热研究”(项目编号:50976029)的资助下完成的。利用资源量大、廉价的农作物秸秆为原料生产纤维素氢气,研究能够达到工业化生产规模的秸秆类生物质制氢技术,对于补充能源不足,保障国家能源战略安全,减少对化石能源的依赖,降低环境污染以及生物质资源的再生利用等方面具有重要的意义。秸秆类生物质光合产氢料液是由固、液两相构成的多相体系,反应器内流体的流变特性会造成容器内各点温度、流速等的分布不均,影响反应器内光合色素形成、采光面沉积程度及光合细菌与秸秆类物质的接触程度。秸秆生物质制氢的多相反应使固体颗粒对液体原有的流动特性和生化反应历程产生影响,进而影响生物反应器的整体混合行为,速度场、浓度场、温度场的分布规律及各种传质和传热程度,最终影响光合细菌的产氢能力。另外,秸秆类生物质光合产氢反应的多相流动使一些区域形成停滞区,一些区域受冲击较大,造成反应器的磨损,可能减少其使用寿命。本文主要依据光合细菌制氢的特点和多相反应原理,利用课题组筛选的光合细菌,研究了秸秆类生物质光合产氢体系液相流变特性和体系浊度变化规律,以及粘度、浊度和产氢之间的相关关系,分析探讨了折流式秸秆类生物质光合连续产氢反应器内料液速度场、浓度场的分布,初步建立了超微秸秆类生物质光合连续产氢体系多相流流场数学模型,并完成了超微秸秆类生物质光合连续产氢体系多相流数值计算及其实验研究。结果表明:(1)秸秆类生物质超微处理后的粒度和产氢反应工艺条件是影响产氢体系相对粘度的主要因素,在颗粒总质量不变的情况下,颗粒粒径变小,增强了颗粒间的相互作用强度,降低了体系的流动性,使得超微秸秆产氢体系的相对粘度增加最快;通过对温度、接种量、光照度、底物浓度等四因素的正交实验得到各因素对产氢体系粘度的影响次序为:底物浓度>温度>接种量>光照强度。并且料液为非牛顿型流体,其流变学性质随着产氢反应的进行变得较为复杂。(2)超微秸秆产氢料液的固相颗粒浓度、颗粒度、处理方式是影响产氢体系浊度大小的主要因素,固相颗粒浓度越大其体系浊度越大,不同颗粒度,超微处理高粱秸秆产氢体系的浊度一直比较大,各处理方式下其体系浊度总的变化规律不变,都呈现先稍微增大后不断减小的趋势,乙酸、盐酸和碱处理的体系浊度相差不大。(3)比较分析产氢体系粘度、浊度和产氢量的变化规律可知,随菌种浓度增大,颗粒度减小,对秸秆的降解能力增强,生成的胞外多糖增加了体系的相对粘度,造成沉降阻力增大,同时由于光合细菌生长使得体系浊度增加,导致体系浊度整体增加的量在开始阶段大于秸秆沉淀使体系浊度降低的量。菌种进入稳定期和衰亡期,胞外多糖被分解为氢气、挥发性脂肪酸和醇类,液相的相对粘度显著降低,体系粘度降低使得固相的沉降速度增大,加之细菌衰亡,体系浊度进一步降低,产氢量不断增加。(4)折流式秸秆类生物质光合连续产氢反应器内相对粘度差别不大,但由于进水的影响,体系浊度增加,固液接触面积增大,起到一定的搅拌作用。同一隔室,同一对应位置点下流室内的速度大于上流室内的速度,底物浓度较大的体系,流动能力较差,速度相对较小。Matlab软件编程计算得出折流式超微秸秆产氢的最优组合为温度33℃,光照强度3500 Lx ,接种量25%,底物浓度55 g/L。(5)采用CFD技术对超微秸秆光合产氢反应器内的流场进行了数值模拟和分析,基于混合模型得出超微秸秆光合产氢体系速度由较集中的主流区向周围不断发展,逐步达到速度的均匀分布,下流室内的速度大于上流室内的速度,并且反应器底部存在明显的推流运动,使得沉淀的固体颗粒向前运动,大部分集聚在上流室,上流室内固相分布高度和浓度都明显大于下流室;反应器内很大一部分区域都存在涡流,底部区域的涡流强度最大,这保障了光合细菌和超微秸秆颗粒的充分混合、接触,强化了传质,起到很好的自动搅拌作用。利用模型计算的节点理论值与节点实测数据比较接近,建立的模型比较切合实际。更多还原

【Abstract】 ABSTRACT: This paper is supported by the National Natural Science Foundation (No. 50976029).Energy shortage and environment pollution is the most serious problems in 21th century. So it is necessary to search cellulose hydrogen with low-cost crop straw as raw material and develop industrial-scale biomass hydrogen production technology to supply energy inadequate, protect national energy security strategy, reduce dependence on fossil fuel and improve biomass recycling. Biomass straw photosynthetic hydrogen production is multiphase flow system consisting of solid phase and liquid phase. The fluid rheological properties in the reactor can influence temperature and velocity evenly distribution, photosynthetic pigment synthesis, lighting suface sedimentary and contact between photosynthesis bacteria and biomass straw. The change on the original liquid characteristics and biochemical reaction process influence bioreactor overall hybrid behavior, mass and heat transfer, and ultimately affect the ability of photosynthetic bacteria produce hydrogen. In addition, multiphase flow make some area become stagnant area and some area have bigger wallop which would reduce biomass straw photosynthetic hydrogen production reactor service life. So studying flow field mathematical simulation and rheological properties of photosynthetic bacteria hydrogen production system with ultramicro straw is very important.It was mainly based on the principle of multiphase flow and the characteristics of photosynthetic bacteria hydrogen production to research rheological properties and system turbidity. Furthermore, it revealed the influence of rheological properties and turbidity on biomass straw hydrogen production, analyzed velocity field and concentration field distribution, completed flow field mathematical simulation, and established multiphase flow mathematical model. The results showed that:(1)Particle size and process parameters was main influence factors on relative viscosity of hydrogen production system. When the total mass of particles remained unchanged, the smaller particle size enhanced the interaction strength among each other, reduced the liquidity of the system. The relative viscosity of hydrogen production system with ultramicro biomass straw were higher than other granularity. The orthogonal experiment indicated that the infuence of hydrogen production process parameters on relative viscosity was substrate concentration> temperature > inoculation>illumination. The mixtuere of supemicro straw hydrogen production was non-newtonian fluid, and its rheological properties became more complex with hydrogen production process.(2) The turbidity of hydrogen production system mainly influenced by solid phase particle concentration, particle size and pretreatment. The turbidity was the highest for ultramicro sorghum hydrogen production system, and increased with the increase of the solid phase particle concentration, while total variation which slightly increased at first and then decreased during the hydrogen production process unchanged with different pretreatment. Ultramicro deal was conducive to hydrogen production, but the capacity of hydrogen production lagged behind turbidity and viscosity changes.(3) The increased degradation ability of photosynthetic bacteria on biomass straw caused liquid relative viscosity and settlement resistance increase when inoculation increased, and particle size minished. Meanwhile, photosynthetic bacteria growth made system turbidity increase. After photosynthetic bacteria going into stabilization and decay period, exocellular polysaccharide was broken into hydrogen, volatile fatty acids and alcohols which made liquid relative viscosity significantly decrease, solid phase settling velocity increase, system turbidity rapidly reduce and hydrogen production amount increase.(4) Relative viscosity was not very different in the photobioreactor. The wallop of inflow wate make solid particles float, system turbidity increase, and solid-liquid contact area increase. The velocity of upflow chamber were significantly higher than downflow chamber in the same positions. The influence of substrate concentration mainly was that flow ability bacome bad due to the impact of relative viscosity. According to matlab software, 33℃temperature, 3500 Lx illumination, 25% inoculation and 55 g/L substrate were appropriate for the biological hydrogen production of PSB with ultramicro straw.(5)The CFD technology was applied to simulate and analyze the flow field in photosynthetic hydrogen production reactor. Based on mixture model, information about flow field was obtained in detail. The flow velocity of photosynthetic hydrogen production reactor evolved from the mainstream to the surrounding area, and gradually achieved uniform distribution. The bottom of reactor had obvious plug-flow movement which made sedimentation solid particles move forward and assemble in the upflow chamber. The height and the concentrations of solid-phase distribution of upflow chamber were significantly higher than downflow chamber. Most areas of the reactor were eddy current, and the maximum eddy current was at the bottom of the reactor, which was conducive to mix photosynthetic bacteria and straw particles and enhance mass transfer. In addition, the calculated results showed that the simulation results of flow field and notes were in accordance with the experimental results.更多还原