Relationship Between Biomass Properties And Steam Explosion Refinery Process

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.