Knowledge Management System Of Institute of process engineering,CAS
|关键词||汽爆预处理 生物质炼制 物料特性 热质传递 提取强化|
生物质炼制是生物质资源大规模利用关注的热点，汽爆技术是生物质炼制的关键技术之一。随着汽爆技术原料范围不断拓宽，认知生物质复杂物料特性与汽爆过程的关系，提出适用于不同种类生物质的汽爆过程理论依据，是实现汽爆作为生物质通用炼制技术的关键。论文基于对生物质汽爆过程热质耦合传递规律的研究，解析生物质主要物料特性（组成结构、水分状态、力学强度、堆积密度）与汽爆过程的关系，在此基础上研究药用植物汽爆炼制过程并发明新型汽爆方法，拓宽汽爆应用领域。 论文取得了如下主要研究结果： （1）基于汽爆过程水分和压力变化，将汽爆过程创新性地划分为气相驱替、气相渗透、气相蒸煮、气相爆破四个阶段，建立了汽爆过程多阶段热质耦合传递模型，为汽爆过程放大和工艺开发奠定理论基础。基于模型，研究汽爆过程热量传递与水分迁移规律，构建汽爆能耗的重要评价指标——单位质量干基耗气量，揭示出气相渗透阶段能耗占汽爆过程总能耗90%以上，并提出若干节能降耗的措施，提高汽爆过程经济性；推出汽爆料含水率表达式，获得汽爆过程各阶段水分变化的定量关系，给出汽爆过程水分迁移的调控策略，为汽爆余汽回收和后续操作参数的选取提供指导。 （2）研究了典型禾本科草本植物和木本植物的化学组分和多孔特性对汽爆物化作用效果的影响。发现草本植物中木质素含量低、半纤维素及其乙酰基含量高，使其在汽爆过程中易于发生热化学反应，从而汽爆后物料半纤维素降解率和可溶性产物生成率高。同时草本植物的结构多孔性导致其渗透率高、力学强度低，易于蒸汽渗入和降低爆破时的物理撕裂阻力，从而提高汽爆后物料孔隙率和孔体积增长率。该结果为认知草本植物和木本植物汽爆条件差异性的本质原因提供理论基础。 （3）认知干秸秆复水过程水分状态的变化规律，考察秸秆内不同水分状态对力学强度和汽爆过程的影响，阐明不同水分状态在汽爆过程发挥的作用。发现秸秆中主要存在束缚水和相对自由水，其纤维饱和点（FSP）约在绝干含水率30%。随复水量和时间增加，FSP前，束缚水含量增加、流动性保持不变；FSP后，束缚水基本不变，相对自由水增多且流动性增强。研究表明秸秆束缚水增加导致其硬度和断裂性分别降低31.43%和26.67%，有利于汽爆物理撕裂作用；自由水增加阻碍汽爆过程热量传递，使汽爆升温时间和能耗分别增加1.29倍和2.18倍，对汽爆热化学反应产生“缓冲效应”。最终优化出干秸秆汽爆的最佳水分状态为FSP，复水平衡时间为6 h~10 h，有利于指导汽爆前纤维质干物料的复水操作以提高汽爆效果。 （4）基于聚合物弹性力学原理，建立汽爆过程植物细胞应力-应变模型，获得爆破压力与细胞壁应力、细胞体积应变之间的关系。揭示出汽爆过程细胞壁应力分布和体积应变的不均一性，其周向应力与纵向应力之比为2:1，导致细胞周向伸长比大于纵向伸长比。推出植物细胞的理论临界爆破压力（Pc）及其影响因素，Pc随细胞壁厚和弹性模量增加而增加、随细胞内径增加而降低，为不同种类生物质汽爆压力的选取提供理论基础。 （5）建立生物质堆积密度与汽爆设备装料系数的关系，系统研究装料参数对汽爆过程热量传递与能耗、质量传递与汽爆物料水分含量、泄压过程与放气速度的影响，并以提高汽爆效果、降低过程能耗为原则，给出装料参数优化策略，以指导实际汽爆过程。研究表明汽爆设备装料系数由生物质堆积密度和装料体积比共同决定，随二者增加而增加。增加装料体积比、提高粉碎后物料颗粒尺寸以适当降低堆积密度，有利于提高汽爆过程经济性。在研究范围内优化出玉米秸秆装料体积比为123.7%、颗粒尺寸为3 cm~5 cm即堆积密度为72.33 kg/m3时，获得汽爆料酶解总糖得率最高且汽爆过程能耗低。 （6）研究药用植物汽爆炼制过程，从多孔介质角度揭示汽爆强化黄芪皂苷提取传质机理，系统表征汽爆黄芪多孔特性并建立其与皂苷提取性能的关系。研究表明汽爆显著改变黄芪多孔结构，具有增孔、扩孔和开孔作用；发现汽爆黄芪平均孔径是影响皂苷提取参数的关键多孔特性；汽爆后黄芪（1.8 MPa、4.5 min）中孔和大孔（100 nm~10000 nm）所占孔面积比例由8.25%增加至91.57%，对强化提取传质过程发挥主要贡献。针对热敏性成分在常规汽爆高温蒸汽下易降解的问题，发明混合介质汽爆新方法，通过引入其他气体介质，有效提高爆破压力、降低维持温度。与常规汽爆相比，混合介质汽爆使蒸汽对杜仲叶热穿透性降低12.66%，杜仲叶中热敏性成分绿原酸提取率增加95.94%。由此将以蒸汽为介质的汽爆技术提升到以混合气体为介质的气相爆破技术，拓宽汽爆原料范围。 （7）基于上述对生物质物料特性和汽爆炼制过程的研究，提出生物质多孔特性是生物质炼制工程的共性关键科学问题，解析生物质本征多孔结构特性与物料特性之间的关系，并探讨生物质多孔特性在汽爆炼制过程中的地位和作用，以期为植物生物质炼制工程提供工程学上的理论基础。
Steam explosion is one of the most leading and promising biorefinery technologies for lignocellulosic biomass. With the expanding scope of its raw materials, cognition on biomass complex properties and their correlation with steam explosion refinery process so as to propose the common theoretical foundation for steam explosion, should be crucial to achieve steam explosion as a common refinery technology for various biomass materials. In this thesis, the heat and mass coupled transfer rule in steam explosion refinery process was firstly revealed, the correlation of major biomass properties and steam explosion was systematically studied, on these bases, novel steam explosion method was invented to broaden its application field. The main research results obtained are as follows: (1) From chemical transfer perspectives, steam explosion process was innovatively divided into four specific stages and the multi-stage heat and mass transfer models of steam explosion process integrating technical features were firstly established, which laid the foundation for the process scaling up and development. From the heat transfer model, the significance of gas penetration stage was revealed for which contributed the most majority of process energy consumption. The amount of steam consumption for unit mass of dry materials was presented to quantitatively evaluate the energy consumption and related operation strategies were proposed to improve energy efficiency. From the mass transfer model, quantitative relationship of water composition in each stage and final water content formula were evaluated, which were efficient to guide the recovery of waste heat and the selection of follow-up procedures’ parameters. (2) The compositional and structural features of typical herbaceous and wood plants and their correlation with physical and chemical effects of steam explosion were studied to reveal the difference of herbaceous and wood plants in steam explosion conditions. It was found that high hemicellulose and acetyl content and low lignin content of herbaceous plants were conducive to hydrothermal effects of steam explosion, leading to the high hemicellulose degradation yield. High porosity of herbaceous structure and its induced high permeability and low mechanical strength were conducive to steam penetration and explosion occurrence, leading to high increasing ratio of plant’s porosity and pore volume. (3) The complexity and roles of water states in steam explosion process of corn straw were identified to enhance the treatment efficiency. Results showed that two main water states with different mobility existed in corn straw and influenced steam explosion treatment. By correlating dynamic water states data to feedstock mechanical properties and treatment process characteristics, the bound water being the excellent plasticizer that reduced the hardness and fracturability of fibers by 31.43% and 26.67% respectively, was conducive to treatment; while, the free water presenting buffering effects in treatment by hindering heat transfer which was reflected by the increment of temperature rising time by 1.29 folds and steam consumption by 2.18 folds, was not conducive. The distinguished point of these two waters was fiber saturated point. By considering treatment efficacy and energy consumption, the significance of fiber saturated point was highlighted as the optimal water states for steam explosion of corn straw. (4) The stress-strain model of plant cell wall during steam explosion process was firstly build based on the polymer elastic mechanics. From the model, the relationship of holding pressure, cell wall stress and cell volumetric strain was obtained, which reflected the nonuniform distribution of cell wall stress during steam explosion process. The ratio of circumferential stress to longitudinal stress of cell wall was 2:1, resulting in the circumferential elongation ratio higher than the longitudinal elongation ratio. Theoretically critical explosion pressure of plant cell was firstly proposed with several impact factors. It was increased with the increment of cell wall thickness and cell elastic modulus while decreased with the increase of cell radius. These provided the theoretical bases for the selection of holding pressure for different kinds of biomass materials. (5) The relation between loading coefficient of steam explosion apparatus and biomass property was revealed, then its effect on steam explosion transfer process and treatment efficacy was assessed by established models and enzymatic hydrolysis tests, in order to propose its optimization strategy for improving the process economy. Results showed that loading coefficient was increased by increasing biomass bulk density and loading volume ratio of material to reactor. The energy efficiency of steam explosion and overall sugar yield of treated materials were both increased by the increment of particle size after comminution and loading volume ratio. In the studied scope, the particle size of 3 cm~5 cm and loading volume ratio of 123.7% were optimized to improve the process economy. (6) The steam explosion refinery process of medicinal plant was studied. In order to reveal the extraction enhancing mechanism of steam explosion, innovatively from the view of plant porous medium, the porous property of steam exploded Radix Astragali was characterized and its correlation with saponins extraction performance was established. The results indicated that average pore diameter was the most relevant to extraction parameters among various porous properties. Area percentage of middle and large pores with diameter of 100 nm~10000 nm of Radix Astragali was increased from 8.25% to 91.57% by steam explosion and the increase of these pores was the major contributor to enhance extraction performance. It was concluded that altered porous properties by steam explosion improved the porous transfer performance during extraction process. In addition, to solve the degradation problem of heat-sensitive ingredients under high-temperature steam of steam explosion process, a novel mixed-gas explosion method was invented by introducing other gas medium to increase explosion pressure and lower holding temperature. Compared with steam explosion, mixed-gas explosion reduced the heat penetrability of Eucommia Ulmoides leaves by 12.66%, and the extraction yield of chlorogenic acid form the leaves was increased by 95.94%. The proposed gas explosion was an upgrade to steam explosion for further widening its application fields. (7) Based on the studied relationship between biomass properties and steam explosion refinery process, the biomass intrinsic porous property was proposed to be the key and common scientific issue for biomass refinery engineering. It correlation with other biomass properties and vital roles played in steam explosion refinery process were preliminarily studied and explored, in order to provide the engineering theoretical foundation for biomass refinery process.
|隋文杰. 生物质物料特性与汽爆炼制过程关系的研究[D]. 北京. 中国科学院研究生院,2016.|