【作者】 李晓兰；

【导师】 叶京生；

【作者基本信息】 天津科技大学 ， 化工过程机械， 2008， 硕士

【摘要】 随着工农业的发展,流态化干燥技术在散粒状物料的干燥方面获得了广泛的应用。但是对于大颗粒(如农作物的种子)以及形状不规则的物料,使用流化床干燥时会出现沟流现象,造成干燥不均匀;同时由于一部分热空气几乎没有与物料发生热量传递便排出,并且大颗粒流化需要较高的气速,因而能量消耗增大。当大颗粒物料在流化床中干燥时,通过加入一定量易流化的小颗粒,可使物料易于流化,从而使被干燥物料在均一的环境中进行热质传递,并在一定程度上减小了最小流化速度;因而干燥产品质量好,能耗低。如果添加的易流化小颗粒具有吸附性,则为流态化吸附干燥。流态化吸附干燥是将流化床中气流的干燥作用和吸附剂的脱水作用相结合,吸附剂不仅起着流化的作用,同时起着传热介质和蒸汽载体的作用,可使物料周围的水蒸气分压很低。流态化吸附干燥利用吸附剂吸收水分后放热的特点,实现生物性物料的低温低湿度干燥。本文以大豆种子为实验物料,硅胶为吸附剂,进行了静态吸附实验研究,通过在流化床中通入一定流量空气进行了动态吸附实验和动静结合吸附干燥实验的研究,并且在此基础上,对吸附干燥系统的性能及其影响因素作了较为全面的实验和理论研究,建立了大豆的吸附干燥模型,详细分析了系统中各操作参数之间的相互关系及其对干燥特性的影响,并对此进行了优化。本文分析了大豆初始湿含量、吸附剂与大豆的混合比、硅胶粒径、床层高度以及风速等因素对干燥过程的影响,同时分析了硅胶的吸水状况;对动态吸附和动静结合吸附干燥进行了对比分析。本文实验结果表明:通过加入硅胶吸附剂,促进了大豆流化,增加了大豆种子的湿分扩散率,提高了干燥速率;但是硅胶粒径的变化对于大豆干燥速率没有显著影响;大豆初始湿含量、混合比及风速对大豆的干燥速率影响较为显著:大豆初始湿含量越高,风速越高,干燥速率越快;混合比在2:1时干燥最快;通过实验还发现,动静结合吸附干燥与动态吸附干燥相比,干燥速率并无明显区别,但干燥产品质量提高,大豆爆裂率减少。更多还原

【Abstract】 With the development of industry and agriculture, fluidized bed drying technology has been widely used in the drying of particulate and powdered materials. But for large articles (such as crop seeds), as well as irregularly shaped materials, fluidized bed drying will ditch reflow phenomenon and cause non-uniform drying, some of hot air is discharged without transferring heat to materials; in addition, the fluidization need higher air velocity and higher energy consumption.This research adopts media-fluidization technology, by adding smaller particles to facilitate fluidization and meanwhile adsorb water from larger particles to be dried in the uniform condition; therefore, the quality of material can be ensured and the minimum fluidization velocity can be reduced to a certain extent. If the small particles are adsorbents, then the technology is called "fluidized adsorption drying". Fluidized adsorption drying is the combination of air fluidized bed drying and the role of the adsorbent with dehydration. Adsorbent is not only to play the role of fluidization, but also is the medium of heat transfer and steam, which can make the vapor partial pressure lower. The technology can achieve low temperature and low humidity drying to biological materials because adsorbents released heat after water absorption.In this paper, experiment is carried out with soybean seeds as materials and silica gel particles as adsorbents to investigate static adsorption drying, dynamic adsorption drying and hybrid of fluidized bed drying and fixed drying. The drying characteristics and influencing factors on adsorption drying system is investigated experimentally. The mathematical model was developed to describe the water transport that occurs in the soybean-silica gel system. The relationship between the operating parameters and their effects on the drying process is analyzed. The effects of initial moisture content, the mixed ratio, silica gel particles, bed height and air velocity on the drying characteristics of soybean is investigated; the differences between dynamic adsorption drying and hybrid drying is compared.The experiment results indicate that the moisture content dispersion rate of soybean seeds increased with addition of silica gel particles. It is inferred that gas-solids contacting is improved with addition of small particles to the bed of large particles. In addition, from the result we can find that changing the size of silica gel particles conspicuously affects drying rate, but it is improved with the increase of gas velocity, with the decrease of initial moisture content, and when mass ratio being 2:1, the drying speed is high. In hybrid drying scheme the drying rate has no significant difference compared with dynamic adsorption drying, but product quality is improved and soybean burst rate is reduced.更多还原