Investigation On The Adsorption Drying Kinetics In Fluidized Bed

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.