Characteristic analysis of heat loss in multistage counter-flow paddy drying process

Abstract

Drying is one of the most important and high-energy consumption unit operations in post-harvest treatment and storage of paddy, and heat loss is a major factor affecting drying efficiency and energy consumption of paddy drying process. To reveal the heat loss characteristics of paddy drying system, a multistage counter-flow drying process of industrial scale dryer was designed based on the conservations of energy and mass, thermodynamics theory and mechanisms of heat and mass transfer. And variation characteristics of heat loss in multistage counter-flow paddy drying process were investigated using psychrometric chart. Meanwhile, parameters of heat and mass transfer were used to analyse the experimental results of heat loss in multistage counter-flow drying. Results indicated that the method of analysing the variation characteristics of heat loss by using psychrometric chart was feasible, and heat losses of drying system were significantly affected by paddy properties, state parameters of drying medium and flow state. Furthermore, the specific heat losses of paddy warming, evaporated water vapour warming, exhaust and other were respectively in ranges of 75.33–238.92 KJ/kg, 2.61–4.67 KJ/kg, 54.34–757.76 KJ/kg and 33.44–236.28 KJ/kg. In high temperature drying segment, the maximum heat losses of the first high temperature drying chamber and other high temperature drying chambers were the heat loss of paddy warming and other heat loss, respectively. The maximum heat loss in all low temperature drying chambers was the heat loss of exhaust, and the heat loss for evaporated water vapour warming was the smallest in any drying chamber. Additionally, energy-saving measures were proposed based on the heat loss characteristics in industrial scale dryer.