【作者】 雷廷宙；

【导师】 沈胜强；

【作者基本信息】 大连理工大学 ， 动力机械及工程， 2006， 博士

【摘要】 生物质能源是唯一可储存和运输的可再生能源,也是目前最有可能实现规模化利用的替代能源。生物质能源的应用对于改善我国的能源结构、保障能源安全、降低环境污染具有十分重要的意义。近十年来生物质能源的应用技术研究得到大力发展,但无论是生物质能源的哪种利用方式(气化、液化、固化等),都需要对其进行干燥,使其含湿量降到15%以下才可利用。因此,国家“十五”“863”计划项目“生物质气化发电优化系统及其示范工程”的子课题“农业废弃物流化床气化过程预处理技术研究”把在生物质能源中占主导地位的农作物秸秆的快速、高效干燥作为一个重要内容开展研究。 本文全面系统地进行了秸秆的各种理化特性、热重特性、等温干燥特性和微观结构特性实验,提出了这些特性对秸秆干燥过程的影响。在秸秆等温干燥特性实验中,归纳了四种秸秆在不同工况下的最佳干燥温度;在研究初始含湿量对干燥时间的影响时,提出了适量的秸秆含湿量的增加对干燥时间的影响可以忽略的看法。在秸秆微观结构实验中,’首次提出了秸秆干燥骨架与空隙的分布规律以及水分迁移的路径。 以体积平均理论为指导思想、以热质平衡为基本出发点,进行了描述秸秆干燥过程的气化界面内移的理论分析;以移动气化界面为表征干燥过程的动态效应,重新定义了表征单元体干、湿区的界限;在充分考虑气化界面处壁温T_w对扩散系数D_r的影响后,建立了以壁温T_w为变量的边界条件。在降速干燥阶段,水分的扩散有较大阻力,引入内移系数来表示这种阻力,从而避免了引入复杂公式带来的计算量增加。 通过对比实验值与计算值,得出表征自由水分传导阻力系数H、扩散阻力系数F和内移系数人,采用上述系数对计算值进行修正,最终修正值与实验值吻合良好,验证了理论分析的正确性,最终推导出初含湿量为70%的玉米秸秆在不同干燥温度下恒速干燥阶段干燥速率的表达式和干燥温度为130℃时降速干燥阶段干燥速率的计算公式。 运用秸秆干燥特性实验的基础数据及理论分析的研究成果,优化设计一套板箱式秸秆干燥试验机。巧妙地构思出“射流加热板”,使得干燥介质在不同加热板上有不同的加热方式、提供不同的能量,实现了不同干燥阶段的按需供能。在秸秆干燥试验装置的实验研究中,验证了等温干燥实验时提出的秸秆干燥分为三个阶段的理论,并测算出不同阶段的需能状况,验证了理论分析的正确性。在进一步的实验中得到如下结果:秸秆干燥试验装置产量为208.6kg/h,热能利用率为71.02%,干燥后秸秆含湿不均匀度为2%,达到了设计要求,对优化设计工业化生产规模的秸秆干燥设备具有重要指导意义。更多还原

【Abstract】 Bio-mass energy is the only storable and transportable renewable energy, and for the time being, is the most hopeful substituting energy to realize the utilization at a large scale. The application of the bio-mass energy is very significant to improve the energy structure, guarantee the energy safety and reduce the environmental pollution. In recent ten years, the research on the applicable technologies of bio-mass has been developed vigorously. However, no matter which kind of utilizing method (gasification, liquefaction or solidification etc.) is used, the bio-mass energy requires drying and it can only become useful after the moisture content is reduced to 15% or lower. Therefore, the fast and highly-efficient drying of the crop stalks, which occupy a leading position in the bio-mass energy, was studied as an important part of "Research on Pre-processing Technology during Gasification Process of Fluidized Bed for Agricultural Waste", the sub-subject of "Gasified Bio-bass Power Generation Optimized System and Its Model Project", which is the program project of the tenth five-year plan and "863" program.In the paper various tests were conducted regarding the physical and chemical characteristics, thermogravimetric characteristics, isothermal drying characteristics and microstructure characteristics of stalks and the influence of such characteristics on the drying process is pointed out. In the test of isothermal drying characteristics of stalks, the best drying temperatures of four kinds of stalks under different working conditions were concluded. This paper raises the view that the influence of proper increase of moisture content of the stalk on the drying time can be neglected. By the stalk microstructure test, the distribution rule of the stalk drying framework and void as well as the moisture transferring path are put forward for the first time.Taking the volume averaging theory as the guide and taking the heat/mass balance as the starting point, the theoretical analysis on inward-moving gasification interface during the stalk drying process was set up. By taking the moving gasification interface as the dynamic effects of the manifestative drying process, the boundary of the dry and wet zones of the manifestative unit was redefined. After fully considering the influence of wall temperature zone T_w at the gasification interface on the diffusion coefficient D_T, the boundary conditions with wall temperature T_w as the variable were established. In the drying phase, the resistance of moisture diffusion becomes significant, and thus the inward-moving coefficient isintroduced to indicate such a resistance to avoid the increase of calculations brought by the use of complex formulas.From the comparison of the tested values and computational values, the manifestative free moisture conductivity resistance coefficient H, diffusion resistance coefficient F and inward-moving coefficient A are obtained, and the calculated values are corrected with the above-mentioned coefficients. The final corrected values are consistent with the tested values, thus it has testified the accuracy of the theoretical analysis;finally, it produces the expression of the drying speed during the constant-speed drying phase under different drying temperatures and the calculation formula of drying speed during the speed-reducing drying phase at a drying temperature of 130℃ for the com stalk with an initial moisture content of 70%.A set of crate type stalk drying tester was designed in an optimized way based on the basic data obtained in the stalk drying characteristics test and the returns of the theoretical analysis. The "jet flow heating plate" is suggested dexterously to supply different heating schemes and different energy for the dry medium on different heating plates, which has realized the energy supply depending on the demand in different drying phases. The experimental study was also conducted on the designed stalk drying tester, which has testified that the division of three phases of stalk drying, raised in the isothermal drying test, and the energy demand in different phases are measured to prove the accuracy of the theoretical analysis. In the further experiment, the various technical indexes of the tester is tested, and the results are as follows: output of 208.6kg/h, thermal energy utilization rate of 71.2%, and the dried stalk moisture content unevenness of 2%, which has met the design requirements and is significant for guiding the optimized design of the industrialized production of stalk drying equipment.更多还原