高温除湿与常规蒸汽联合干燥的试验与分析

讨论了高温除湿与常规蒸汽联合干燥过程中干燥室内空气温度、相对湿度及木材含水率的变化趋势，分析了干燥过程中除湿量及能耗的变化规律。实验结果显示，高温除湿与常规蒸汽联合干燥节能效果显著，干燥质量好。高温除湿机可以直接放在木材干燥室内部工作，无需对干燥室窑体进行改装。     

浅析热风干燥技术中的节能途径

阐述了我国碳排放现状及节能减排的紧迫感。以传统的热风炉粮食干燥的和传统的木材蒸汽干燥为例,分析了传统干燥热效率不高的主要因素,指出排气余热回收是传统干燥作业节能减排的主要途径之一,采用普通换热器、热泵及热管换热器回收排气余热,均有明显的节能效果。采用普通换热器平均节能12.4%,采用热泵平均节能40%左右,采用热管换热器居二者之间。介绍了太阳能干燥、太阳能与热泵组合干燥、热风与真空微波组合干燥、超声波与热风干燥组合等各种低碳干燥技术。建议逐渐推广用生物质能源作为干燥的热源,有利于实现低碳干燥。     

蒸汽与热泵联合干燥木材的匹配分析

对单独的常规蒸汽干燥、热泵(除湿)干燥以及二者联合干燥三种工况进行了能耗分析，结果以联合干燥能耗最低，热泵(除湿)干燥次之，常规蒸汽干燥能耗最高。文中还就相应干燥条件下蒸汽-热泵(除湿)联合干燥的匹配条件作了研究。     

太阳能与热泵联合干燥木材特性的实验研究

介绍了国内外利用太阳能干燥木材的概况、太阳能与热泵联合干燥系统的组成与工作原理、太阳能与热泵联合干燥木材的特性和干燥木材的工艺实验。实验结果显示。太阳能与热泵联合供热可以弥补太阳能或热泵单独供热的缺点。太阳能比联合干燥节能3．8％,而联合干燥比热泵干燥节能11．8％;联合干燥比太阳能干燥时间缩短了14．9％。从能耗及生产效率综合考虑。太阳能与热泵联合干燥是值得推荐的一种干燥方法。     

落叶松太阳能热泵干燥特性研究

本文介绍了一种木材太阳能热泵干燥装置及其三种不同的运行方式,并以落叶松为试材,通过两组对比实验,分析干燥介质与干燥箱内的温度变化以及木材含水率变化之间的关系。结果表明太阳能水源热泵联合干燥的优化比传统干燥节能约76．7％,太阳能水源热泵联合干燥比传统干燥节能约66．2％,优化模式比只用太阳能水源热泵联合干燥木材时耗能更低,且干燥质量更好。     

太阳能-热泵联合干燥系统的开发和测试

建设太阳能-热泵联合干燥示范平台,以期更好推广其在干燥行业的应用。使用自动控制系统,实现对干燥过程中恒温操作,并采用智能启停的热回收器回收排放的废热。基于干燥系统平台对新鲜蔬菜进行干燥实验,测试结果表明:新开发的联合干燥系统的能耗比传统干燥方式降低3~4倍,干燥后的菜干品相上乘。实验证明,本次开发的智能控制干燥系统节能减排效果显著,适合在干燥行业推广应用。     

农产品干燥加工节能减排工艺及装备研发

农产品干燥加工占干燥行业能耗的12%左右,是一项高能耗的过程。为促进农产品加工业的健康发展,本文介绍了回热热泵、真空带式干燥、旋流床气流膨化、太阳能和热泵组合干燥等四种节能减排的新工艺新装备,同时还探讨了农产品干燥加工节能减排的发展方向。     

我国太阳能干燥现状及在热利用中应有的地位

阐述了我国太阳能干燥的应用与研究概况,列举了谷物、蔬菜与果品、中草药及木材太阳能干燥的部分实例。干燥作业是耗能大户之一,所用能源占国民经济总能耗的12%左右,我国太阳能干燥在热利用中的地位应该引起重视,但我国对太阳能干燥缺乏资金与政策支持,宣传力度不够,因此目前太阳能干燥在我国的推广应用不太理想。论文分析了影响太阳能干燥推广应用的主要原因,提出了促进太阳能干燥发展的几条建议。     

我国木材干燥技术与研究动态

阐述了我国木材干燥技术应用状况及面临的问题,介绍了我国木材干燥学术活动的情况和理论研究动态。指出以蒸汽为热源的常规干燥仍将占木材干燥的主导地位,约在80％以上;真空干燥、热泵除湿干燥、微波与高频干燥、高温干燥、加压干燥等其它干燥方法都在各自适用的范围内有一定的发展。木材的渗透性、木材干燥过程的水分迁移机理等有关木材干燥的传热传质方面的基础理论研究正在加强;高效节能的木材干燥技术是目前研究的重点课题。我国木材干燥技术正由经验型转向以干燥理论为基础的科学型方向发展。     

新型组合干燥器在镍精矿干燥中的应用

传统的回转窑等干燥设备在镍精矿的干燥上存在污染环境、能耗高及效率低等弊端,急切需要一种节能、环保、高效的干燥设备应用于镍精矿的干燥上。采用双桨叶干燥器和盘式连续干燥器组合干燥器对硫精矿进行干燥,通过25 d的半工业化试验,取得了成功,证明了此新型组合干燥设备在镍精矿干燥上的优越性,特别适合现在节能环保的要求,具有较大的社会推广意义。     

造纸污泥干化热力计算及方案选择

文章利用空心浆叶干燥机作为干化造纸污泥的设备,对采用过热蒸气和饱和蒸气作为热源的两个方案进行了热力计算。比较结果表明:把污泥的含水率从80%干化到40%,利用0.4 MPa,200℃过热蒸汽为热介质来干燥污泥时,耗气量是1712 kg/h;利用0.4 MPa,150℃的饱和蒸气作为热源,耗气量是1800 kg/h。     

Effect of Microwave-Vacuum Drying on the Carotenoids Retention of Carrot Slices and Chlorophyll Retention of Chinese Chive Leaves

Microwave-vacuum drying, and combined microwave-vacuum with air or vacuum drying were investigated as potential methods for drying green and high-carotenoid vegetables of Chinese chive leaves and carrot slices. The samples were dried by microwave-vacuum until the moisture content reached about 20% (wet basis), and then by conventional air drying at the temperature of 45-50°C or conventional vacuum drying at the temperature of 55-60°C or by continued microwave-vacuum drying at lower power level to final moisture content about 6% (wet basis). The carotenoid retention of carrot slices and chlorophyll retention of Chinese chive leaves, dried by these methods, was evaluated and compared with those dried by freeze-drying and conventional hot-air drying. The comparison showed that the carotenoid retention of carrot slices and chlorophyll retention of chive leaves, dried by the current methods, was very close to or even as much as those dried by freeze-drying and much better than those dried by conventional hot-air. Blanching was not necessary when using microwave-vacuum drying or combined microwave-vacuum with conventional hot-air drying or vacuum drying, because the activity of enzymes which were responsible for the degradation of color was greatly reduced with extremely rapid decreasing of moisture, and because oxygen was absent in microwave-vacuum drying.     

Drying Characteristics of Coriander Seed Particles in a Reduced Pressure Superheated Steam Fluidized Bed

Drying characteristics of coriander seed particles were experimentally analyzed in a reduced pressure superheated steam fluidized bed. The typical moisture gain, reported in some other studies during the warm-up period of the process, was reduced in most of the cases by supplying additional heat into the column. The experimental results demonstrated that the drying rate increases and the equilibrium moisture content decreases by increasing the operating temperature. However, variation of the operating pressure (40–67 kPa) and the superficial steam velocity (2.3–4.0 m/s) did not present significant effects on the moisture contents. The degree of superheating was found to be the most important parameter for the process. The experiments also showed that the equilibrium moisture content decreases upon increasing the degree of superheating. Finally, employing a reduced pressure superheated steam fluidized bed appears as an option to carry out drying processes at relatively lower temperatures.     

Drying of soy sauce residue in superheated steam at atmospheric pressure

Soy sauce residue needs drying to avoid fermentation and oxidation during storage and transportation, and its reutilization as a useful resource is expected. Superheated steam drying was applied to investigate the effects of drying conditions on the drying characteristics and the content changes of salt and protein. The results showed that the inversion temperature was about 130°C, beyond which superheated steam drying was faster than hot air-drying. The drying time approaching equilibrium moisture content was reduced with elevated drying temperature as well as higher steam mass flow rate in the present experimental conditions. The effect of bed thickness on drying time was not obvious when drying temperature increased. Interestingly, the salt content of soy sauce residue could be decreased by 34.8% due to condensate water in the initial drying period (wetting), while protein content had no significant loss (p?相似文献   

Drying Kinetics and Quality of Shrimp Undergoing Different Two-Stage Drying Processes

An innovative two-stage drying concept is presented in this article. The work considered drying of shrimp using a superheated steam dryer followed by a heat pump (SSD/HPD) or a hot air dryer (SSD/AD) both from drying kinetics and dried product quality points of view. The experiments were performed using the first-stage superheated steam drying temperature of 140°C while the second-stage heat pump drying (or hot air drying) was performed at 50°C. The moisture content of shrimp at the end of the superheated steam drying stage was varied between 30 and 40% (w.b.). The effect of tempering between SSD/HPD was also investigated. Shrinkage, color, rehydration behavior, texture (toughness and hardness), and microstructure of dried shrimp were measured. The results showed that SSD/HPD dried shrimp had much lower degree of shrinkage, higher degree of rehydration, better color, less tough and softer, and more porous than single-stage SSD dried shrimp. It was also found that SSD/AD gave redder shrimp compared to shrimp dried in a single-stage superheated steam dryer. No improvement in terms of shrinkage and rehydration behavior was observed, however.     

Simulation and Validation of Microwave-Assisted Fluidized Bed Drying of Soybeans

A general mathematical model of heat and mass transfer was developed to simulate the microwave-assisted fluidized bed drying of bulk grain. The model was solved using the well-known Runge-Kutta-Gill method. The model is capable of predicting the moisture content of soybean as well as the drying air parameters (i.e., drying air temperature and moisture content) during drying. The values of mean relative deviation (MRD) were less than 8 and 10% for prediction of grain moisture content and outlet air parameters, respectively, which reflects an acceptable accuracy. In comparison with conventional fluidized bed drying of soybean, microwave-assisted fluidized bed drying led to 83.39–98.07% savings in drying time and 82.07–95.22% savings in specific energy consumption when reducing soybean moisture content from 18.32 to 12% (db).     

Variation in Drying Behavior and Final Moisture Content of Wood during Conventional Low Temperature Drying and Vacuum Drying of Betula pendula Timber

Conventional and vacuum drying experiments were conducted on Betula pendula timber, which was sawn from trees felled during three different seasons. The influence of the wood procurement season on drying behavior differed, on the one hand, between the drying phases above and below 30% moisture content in the conventional drying, and, on the other hand, between the conventional and vacuum drying methods. During the first steps of the conventional drying process, relative humidity in the kiln, as well as drying time and drying rate, varied according to the felling season. Variations in environmental conditions outside the kiln and the seasonal variation in the physical properties of the wood were presumed to be the reasons for differences in drying behavior. The difference in moisture content gradient, i.e., the difference in final moisture content between the inner wood and the surface layer of boards, was greater in conventionally dried timber than in vacuum-dried timber. In conventionally dried timber there was a clear seasonal variation in the gradient of final moisture content, which was greatest for winter-felled wood. The premature drying of the surface layer during the first steps of the conventional drying process of winter-felled wood was the reason for the higher gradient of moisture content. Storage of wood as logs decreased the standard deviation of the final moisture content.     

Efficient Energy Recovery with Wood Drying Heat Pumps

This article presents a 13-m³ wood dryer coupled with a 5.6-kW (compressor power input) heat pump. Drying tests with hardwood species such as yellow birch and hard maple were completed in order to determine the system's energy performance. Supplementary heating to compensate for the dryer heat losses was supplied using electrical coils or steam exchangers. The heat pump running profiles and dehumidification performance in terms of volumes removed and water extraction rates, coefficients of performance, and specific moisture extraction rates were determined for two all-electrical and two hybrid drying tests. The hardwood drying curves, share of the final moisture content, and final quality of the dried wood stacks, as well as total drying energy consumption and costs, were determined for each drying run. Finally, the total energy consumption of the drying cycles using a heat pump was compared with that of a conventional drying cycle using natural gas as a single energy source.     

Freeze Drying of Apple Slices with and without Application of Microwaves

In this study, Fuji apple slices were dehydrated using freeze drying (FD) combined with microwave assisted with vacuum drying (VMD). The optimal parameter for the diversion point of moisture content from FD to VMD process was at the moisture level of 21%, and for VMD the optimal parameter for vacuum pressure was at 9.15 kPa and microwave power density was at a level of 3.18 w/g. The results show that the two-step technique can significantly reduce total FD time required by up to 40%, while the nutritional value of the dried apple chips remained unchanged compared to FD used alone.     

Dehydration of Concentrated Ganoderma lucidum Extraction by Combined Microwave-Vacuum and Conventional Vacuum Drying

Combination of microwave-vacuum drying and conventional vacuum drying was investigated as a potential method for drying concentrated Ganoderma lucidum extraction. The Ganoderma lucidum was extracted by hot water (60-65°C) and then concentrated to moisture of about 70% (wet basis) in a rising-film evaporator. The concentrated sample was dried by microwave-vacuum until the moisture content reached 10% (wet basis), and then by conventional vacuum drying at the temperature of 55-60°C to final moisture content about 6% (wet basis). The retention of polysaccharide and triterpenes of Ganoderma lucidum dried by this method were evaluated and compared with those dried by freeze drying and conventional vacuum drying alone. The comparison showed that the quality of extraction dried by the current method was close to that of freeze-dried extraction and much better than that of conventional vacuum-dried ones.