Abstract

The impinging stream drying technique has a high capability for removing water in a very short period. Energy consumption is strongly impacted by several of this type of dryer’s operating parameters, i.e., air temperature, air velocity, particle feed rate, and air recycle percentage. A mathematical model would be useful for finding the optimum condition from just a small number of experiments. A mathematical model at a mesoscopic scale that couples heat and mass transfer between gas and solid particles and tracks moisture or temperature distribution inside a single particle was developed in this study; it was used to simulate the effects of air velocity (15–25 m/s), parboiled paddy feed rate (80–250 kg_{dry solid}/h) and exhaust air recycle level (0–80%) on the specific energy consumption (SEC). The developed model was able to predict the average moisture content, average grain temperature, and SEC accurately. The simulated moisture distribution inside a grain kernel showed that this drying technique, which incorporated 4 min tempering between drying cycles, provided a nearly constant rate of drying even though the moisture content decreased to 0.22–0.25 d.b. (dry basis). The use of higher air temperatures noticeably reduced the total specific energy consumption (SEC_total). The air velocity and parboiled paddy feed rate had synergetic effects on the energy consumption. Drying at lower air velocities consumed lower energy when the parboiled paddy feed rate was lower than 170 kg_{dry solid}/h. At higher parboiled paddy feed rates, ranging from 170–250 kg_{dry solid}/h, however, the use of higher air velocities tended to save more total energy. At 80% of recycled exhaust air, the SEC_total was around 4 MJ/kgH₂O, which saved 40–45% of SEC_total compared with the case of without exhaust air recycle.

摘要

冲击流干燥技术在很短的时间内具有很强的除水能力。能源消耗受多种此类干燥机运行参数的强烈影响，即空气温度、空气速度、颗粒进料速率和空气循环百分比。数学模型对于从少量实验中找到最佳条件很有用。本研究开发了一种介观尺度的数学模型，该模型将气体和固体颗粒之间的热量和质量传递耦合并跟踪单个颗粒内部的水分或温度分布；它用于模拟空气速度 (15–25 m/s)、半熟稻谷进料速率 (80–250 kg_干固体/h) 和废气再循环水平 (0–80%) 对特定能耗 (SEC) 的影响。开发的模型能够准确预测平均水分含量、平均谷物温度和 SEC。谷粒内部的模拟水分分布表明，这种干燥技术在干燥周期之间结合了 4 分钟的回火，即使水分含量降低到 0.22-0.25 分贝（干基），也能提供几乎恒定的干燥速率。使用更高的空气温度显着降低了总比能耗（SEC_总计）。空气速度和预煮稻谷的进料速度对能量消耗有协同作用。当预煮稻谷的进料量低于 170 kg_干固体时，在较低风速下干燥消耗的能量较低/H。然而，在更高的预煮稻谷进料速率下，范围为 170-250 kg_干固体/h，然而，使用更高的空气速度往往会节省更多的总能量。在回收废气的 80% 时，SEC_总量约为 4 MJ/kgH ₂ O，与没有废气再循环的情况相比，SEC_总量节省了 40-45% 。