【作者】 王瑾；

【导师】 李树君； 杨延辰； 张清泉；

【作者基本信息】 中国农业机械化科学研究院 ， 机械设计及理论， 2011， 博士

【摘要】 滚筒干燥机因其操作弹性大、适应性广、热效率高、设备成本低而广泛应用于食品工业中。与其他干燥方式相比,滚筒干燥有预糊化作用,可以提高产品的糊化度,改善产品的冲调性,同时,滚筒干燥有利于增大产品的孔隙率,提高产品的复水性。南瓜粉是一种深受消费者喜爱的产品,具有很高的经济价值。目前,南瓜粉的干燥方法主要有喷雾干燥和热风干燥。热风干燥的干燥温度高、加热时间长,生产的南瓜粉不仅感官质量差,营养物质也损失严重,喷雾干燥生产的南瓜粉均匀细腻、速溶性好,但是喷雾干燥能耗高、设备投入成本高。本课题通过对滚筒干燥原理的分析及滚筒干燥机结构的研究,设计制造了一台可以适用于干燥多种物料的单滚筒干燥试验台,在此试验台上,进行开发滚筒干燥生产南瓜粉的试验研究,并以南瓜为原料研究滚筒干燥过程中的干燥动力学及传热传质特性,用数学的方法对滚筒干燥过程进行模拟和分析。主要研究内容和结论如下：1、研制了滚筒干燥试验台,并对试验台进行整机性能检测和新产品开发的试验研究。详细分析了滚筒干燥机的结构和设计原理,研制的滚筒干燥试验台具有广泛的适用性,各项指标和功能既符合了生产实际又满足了试验要求。2、开发了一种滚筒干燥生产南瓜粉的工艺。确定了滚筒干燥生产南瓜粉的工艺步骤,即：选材、切分、热处理、打浆、滚筒干燥和粉碎筛分；通过试验确定热处理方式及热处理工艺参数为南瓜丁在80℃水中漂烫2min,迅速放到自来水中冷却至物料中心温度达到室温,再常压蒸制4min;优化出滚筒干燥生产南瓜粉的最佳干燥工艺参数组合为：进料质量流量40kg/h、滚筒转速1.00r/min、蒸汽压力0.39MPa。3、研究了不同蒸汽压力下南瓜浆滚筒干燥的动力学特性。根据物料在干燥过程中的状态,将滚筒干燥过程分为浆状区和膜状区两个阶段,物料中的大部分水分是在浆状区中蒸发；水分在膜状区的干燥为降速干燥,蒸汽压力越高、物料进入膜状区的初始水分含量越低、初始阶段干燥速率越小,但是蒸汽压力越高,干燥速率降低得越慢,整体干燥时间越短；将试验数据与薄层干燥模型进行拟合,优选出在各个压力下最匹配的南瓜滚筒干燥动力学模型均为Midilli-Kucuk模型。4、分析了膜状区中物料温度和滚筒外表面温度的变化规律。不同蒸汽压力下,物料温度和滚筒外表面温度均沿位移呈现上升趋势,温度的变化与水分干燥速率有关,干燥速率越快,物料表面温度升高越慢,干燥速率降低得越快,滚筒表面温度升高越快。5、建立了膜状区中滚筒干燥传热传质模型,并在稳态循环条件下对模型求解,以南瓜为原料对模型进行了验证,通过模型计算出的物料温度与试验值有较高的匹配程度,真实反映了滚筒干燥过程中物料温度随位移的变化规律。6、比较了不同干燥工艺对南瓜粉感官质量、冲调性、营养性、得率和能耗的影响。滚筒干燥工艺生产的南瓜粉感官质量和冲调性都与喷雾干燥南瓜粉相近,但营养物质的保存率低于喷雾干燥,热风干燥产品的品质最差；滚筒干燥的得率高于喷雾干燥,低于热风干燥,但是滚筒干燥的干燥速率快,单位时间产量高,单位能耗与喷雾干燥相比降低了35.89%。更多还原

【Abstract】 Drum dryer is widely used in food industry because of its easy operation, good adaptability, high thermal efficiency, short drying time and low equipment cost. Compared with the other drying methods, drum drying has the advantage of pregelatinization which can improve the grade of gelatinization of the product and make the product to be instant edible. Moreover, product dried by drum drying has a higher quality of rehydration because of increasing porosity and complete inner structure. Pumpkin powder with high economic value is one of the most popular pumpkin products. Hot wind drying and spray drying are widely used in producing of pumpkin powder at present. However, both of them have some disadvantages such as high temperature, long drying time, low quality, and highly lost of nutrients of hot wind drying method and its production. For spray drying although the production maintains a relatively large amount of the nutrients and is characterized by good solution and satisfactory taste, it still cannot be widely used in the industry owing to its high investment of spray dryer and high energy consumption and operation cost. In order to design and manufacture a test bed of drum drying which can be used to dry many different kinds of materials, the drying theory and the structure of the drum dryers were deeply studied in this paper. By using the drum drying method, a new type of pumpkin powder was developed and the processing was optimized. According to the heat and mass transfer mechanism, the drying kinetic was analyzed and a numerical model was developed in the study. The main research contents and results were summarized as follows:1. A test bed of single drum drying was developed. The configuration and operating principle of the equipment was deeply analyzed. The test bed of drum drying can be used to dry different kinds of materials. The test indicators and functions of the test bed not only are consistent with the actual production but also meet the experimental requirements.2. The product processing of a new kind of pumpkin powder with drum drying was developed. The determined process steps include selection, cutting, cooking, mashing, drum drying and smashing. Through numerous experiments, the best cooking process was determined:small pumpkin pieces should be blanched in 80℃water for 2min, then be put into running water to cool down with its core temperature getting to room temperature, and finally be steamed for 4min. The drying processing was optimized by using the Orthogonal Rotatable Central Composite Design. Considering the higher product quality, the optimum data were developed: flow mass is 40 kg/h, rotary speed is 1.00 r/min, and vapor pressure is 0.39 MPa.3. Drum drying characteristics of pumpkin pulp were investigated. The drum drying process was divided into two phases:pulp phase and flake phase. It was indicated from the results that most of the moisture evaporated during the pulp phase; the higher the steam pressure was the higher the drying rate became. It was also shown that during the flake phase only falling rate period took place. As the steam pressure increased, on the one hand, the initial moisture content of flake phase became less and the drying rate decreased, on the other hand, the decreasing of the drying rate slowed down and the drying time was much shorter. The experimental moisture loss data were fitted with 10 thin-layer drying models. Consequently, of all the drying models, a semi-theoretical Midilli - Kucuk model was fitted best.4. During the flake phase, variation of the temperatures of the product and the outer surface of the drum dryer was analyzed. Results showed that both of the temperatures increased with displacement under different vapor pressures. It can also be indicated that variation of the temperatures were related to variation of the drying rate, the faster the drying rate was the slower the temperature of the product increased, the faster the drying rate decrease the faster the temperature of the outer surface of the drum dryer increased.5. The heat and mass transfer model of the product during flake phase was established and the equations were solved under steady-state condition. The experimental data of the pumpkin pulp dried by drum drying were used to validate the simulation results. The experimental and simulation results had a high correlation value which shows that the model could be used to predict the variation of the product temperature with displacement.6. Comparison analysis on sensory quality, dissolvability, nutritional quality, yield and energy consumption of the pumpkin powder with drum drying, spray drying and hot wind drying was done. Results showed that compared with the spray drying pumpkin powder with drum drying had a similar quality on sensory and dissolvability, higher yield, but lower nutritional preservation rate. The product quality of the hot wind drying was the worst. The energy consumption of drum drying decreased 35.89% per kilogram water compared with spray drying.更多还原