典型中华菜肴鱼香肉丝的真空冷冻干燥工艺研究

以鱼香肉丝这一典型的中华菜肴为对象，通过正交实验求出了最佳真空冷冻干燥工艺参数，即物料铺放厚度5mm、升华干燥的真空度140Pa、解析干燥的真空度30Pa、解析时加热板温度20℃。试验得出的影响冷冻干燥的主要工艺因素其次序为：加热板温度、物料铺放厚度、升华压力和解析压力。同时还求出了这种菜肴的复水工艺参数，即复水量为干制品含水率的140％～150％，复水温度65～85℃，复水时间20～30min。最后通过本研究建立的数学模型对干燥时间进行了验证。     

真空低温连续干燥工业自动化生产线关键技术研究

通过对真空低温连续干燥生产线工艺性分析和关键技术研究,建立了300t／d高水分玉米真空低温连续干燥工业自动化生产线,并对生产线系统进行了生产性试验和关键技术验证分析。试验验证表明,该真空低温连续干燥新技术具有节能高效、绿色环保、干燥品质好的特点,是我国解决粮食干燥问题的一条新途径,是我国绿色干燥技术的发展方向。     

真空干燥机试用低位水喷射泵

锦纶生产过程中的切片干燥是将萃取后的湿切片(含水率在15％至20％之间)经过真空干燥机干燥除去水份,使切片含水率在0.04％以下。如果干燥后的切片含水较高,则在高温下纺丝容易水解,形成汽泡丝,在牵伸时易断头,影响纤维质量。在切片干燥过程中,必须控制干燥的温度、干燥时间和干燥的真空度,尤其是真空度。抽真空的目的是为了防止切片在空气中氧化,同时在真空条件下,水沸点下降,有利于切片在较低温度下去除水份。因而     

核电站放射性浓缩液干燥处理初步研究

针对核电站放射性浓缩液的特性,以模拟浓缩液为研究对象,利用烘箱开展了干燥技术处理浓缩液的初步研究,对干燥产物性状的变化以及干燥条件对水分蒸发速率和产物含水率的影响进行了测定。浓缩液经干燥处理后质量为原先的20%左右,减容比为4.5左右,含水率小于15%;干燥温度越高,真空度越大,干燥的速率越快,但是温度和真空度的增高会带来干燥产物的膨胀;干燥过程的补料会导致产物下层含水率升高;结果表明,干燥技术处理放射性浓缩液是一种减容处理技术,有必要进行进一步深入研究。     

微波干燥工艺参数对玉米爆腰率的影响

玉米收获后需干燥至安全水分后储藏,干燥方式及合理的工艺过程对干燥品质有很大的影响,玉米干燥后的爆腰率是其品质的重要指标。利用自制的微波干燥试验测试系统对玉米进行干燥试验,得出了玉米微波干燥的特征曲线及干燥温度特性,探讨了三个主要工艺参数单位功率、干燥最高温度、平均失水率对爆腰率的影响。实验结果表明,玉米微波干燥中按失水率的变化可以分为预热、恒速、降速三个阶段,预热段较长,水分主要在恒速段排出;温度经历了上升和趋于稳定的过程;爆腰率随各参数的增大而升高。得到的初步结论是：玉米微波干燥最好在单位干燥功率0.3W／g以下、干燥最高温度不超过70℃、平均失水率不大于0.2％／min的条件下进行。     

甘肃窑街油页岩等温干燥机理分析

采用甘肃窑街油页岩颗粒作为原料,利用电热鼓风箱和电子天平及红外温度测定仪,测定油页岩样品在外界温度恒定条件下的含水率和干燥速率曲线,并讨论各段的干燥机理方程,分析温度、粒径大小对甘肃油页岩干燥效果的影响。结果表明:干燥速率曲线上明显存在拐点,由此可知干燥过程存在不同的干燥机理,当含水率大于拐点含水率时,主要是大孔隙中的自由水和束缚水脱除过程且伴随着体积的缩小,由Keliven公式,这一过程受到毛细管作用影响,蒸发速率逐渐降低;含水率小于拐点含水率阶段对应着油页岩内部更细小孔内水分的受热过程,当水分子动能达到一定值后突然汽化逸出引起含水率下降并引起油页岩干燥后期的热破碎现象。     

微波真空干燥高粘度的灵芝浓缩液

热敏性、高粘度物料的干燥仍是现代干燥技术中的一个难题。灵芝水提后，由薄膜蒸发器浓缩至含水量70％左右，然后采用微波真空干燥（真空度3000Pa）至水分含量10％左右，改用传统的电热真空干燥（55～60℃）至含水量6％～7％。对干燥产品的主要生物活性成分——灵芝多糖和三萜酸进行了分析检测并与其它干燥方法进行了比较。结果表明：利用微波真空干燥的灵芝产品其灵芝多糖和三萜酸的保留率与冷冻干燥产品十分接近。而比传统真空干燥（60—65℃）的产品要高得多，此外采用微波真空干燥的干燥时间要短得多。     

富含果胶和黄酮类化合物的柑橘皮渣干燥工艺研究

为全组分高值化利用柑橘皮渣,研究了富含果胶和黄酮类化合物的柑橘皮渣干燥工艺。依次采用热风干燥和微波真空干燥脱除柑橘皮渣的水分,考察柑橘皮渣铺放厚度、干燥温度、干燥时间对皮渣含水率、果胶和总黄酮含量的影响。结果表明,热风干燥的最佳工艺条件为:皮渣铺放厚度2.0 cm,60℃干燥0.5 h;微波真空干燥的最佳工艺条件为:真空度-0.085 MPa,铺放厚度2.5 cm,50℃干燥2.0 h。在该条件下,柑橘皮渣含水率降至10%以下,果胶含量损失少于20%,总黄酮含量损失少于15%。该干燥工艺简单,可操作性好,能在脱除柑橘皮渣水分的同时最大限度保留了其中的果胶和黄酮类化合物,为全组分高值化利用柑橘皮渣提供有益的参考,为异地提取柑橘皮渣中果胶、黄酮等活性物质提供方便。     

富含果胶和黄酮类化合物的柑橘皮渣干燥工艺研究

为全组分高值化利用柑橘皮渣,研究了富含果胶和黄酮类化合物的柑橘皮渣干燥工艺。依次采用热风干燥和微波真空干燥脱除柑橘皮渣的水分,考察柑橘皮渣铺放厚度、干燥温度、干燥时间对皮渣含水率、果胶和总黄酮含量的影响。结果表明,热风干燥的最佳工艺条件为:皮渣铺放厚度2.0 cm,60℃干燥0.5 h;微波真空干燥的最佳工艺条件为:真空度-0.085 MPa,铺放厚度2.5 cm,50℃干燥2.0 h。在该条件下,柑橘皮渣含水率降至10%以下,果胶含量损失少于20%,总黄酮含量损失少于15%。该干燥工艺简单,可操作性好,能在脱除柑橘皮渣水分的同时最大限度保留了其中的果胶和黄酮类化合物,为全组分高值化利用柑橘皮渣提供有益的参考,为异地提取柑橘皮渣中果胶、黄酮等活性物质提供方便。     

污水污泥动态间壁热干燥特性及工艺

建立了序批式动态污泥间壁热干燥实验平台，并借此研究了干燥温度对干燥效率、干污泥热值、干污泥有机物含量（VS）、干燥冷凝水有机物含量（TOC）的影响;研究了水分蒸发速率与含水率的关系。结果表明：干燥温度低于160℃，水分蒸发速率较慢，干燥效率较低;干燥温度高于180℃，污泥絮体和微生物细胞发生破坏，水分存在形态发生改变，干燥效率提高较大，干污泥热值降低以及干燥冷凝水TOC浓度增加。干燥冷凝水属高浓度有机废水，须处理达标后才能排放。     

利用热泵干燥污泥技术的试验研究

为了对热泵干燥污泥的方法进行研究,采用自行设计的污泥热泵干燥装置对含水率为55%-60%的污泥进行干燥试验研究。分析了风量、空气参数、冷凝温度和蒸发温度等对干燥效果的影响。试验表明,风量、空气参数、冷凝温度和蒸发温度对干燥效果有较大的影响,随着风量的增大,出水量逐渐增多,在风量达到800-1000m3/s,达到一个最佳的干燥效果,此时能耗比为0.73。     

ENERGY CONSUMED IN LOW TEMPERATURE CORN DRYING

Data collected on corn drying bins employing unheated air and bins utilizing electric heat for small air temperature rises indicate better energy efficiency when the energy is used to provide more air as compared to using a portion of the energy to increase the temperature of a smaller quantity of air. Unheated air drying of shelled corn was accomplished with an average of about 6.0 kWh per metric ton per percentage point of moisture removed as compared to an average of about 12.0 kWh/t- % when electric heaters were used to increase the air temperature. Final corn moisture content was approximately the same for both methods since the unheated air drying systems, with more air per unit of grain, completed drying earlier. Early fall weather, as contrasted to late fall, is generally more favorable to drying and the existence of lower average daily relative humidities permit the drying of corn to 15% or less, wet basis, without the addition of heat.     

Conjugate heat and mass transfer model for predicting thin-layer drying uniformity in a compact,crossflow dehydrator

Abstract

A conjugate heat and mass transfer model was implemented into a commercial CFD code to analyze the convective drying of corn. The Navier–Stokes equations for drying air flow were coupled to diffusion equations for heat and moisture transport in a corn kernel during drying. Model formulation and implementation in the commercial software is discussed. Validation simulations were conducted to compare numerical results to experimental, thin-layer drying data. The model was then used to analyze drying performance for a compact, crossflow dehydrator. At low inlet air temperatures, the drying rate in the compact dehydrator matched the thin-layer drying rate. At higher temperatures, heat losses through the external walls resulted in temperature and moisture variations across the dehydrator.     

基于化学改性的脱水污泥低温热风干化特性

我国每年污泥总产量逐渐增加,在其处理过程中普遍对含水率要求较高。采用热泵技术进行污泥低温干化,是一种既节能高效又不受地域限制的方法。但由于污泥的低温热干化特性尚不清楚,本文将通过在恒温恒湿箱中分别控制温度和污泥粒径两个单一变量,探究低温下二者对干化速率的影响,用曲线拟合得到直观的变化规律;并使用自主设计的立式污泥干化台架,对比探究铁-钙-碳基调理污泥在低温干化和传统干化下的水分释放特性。结果表明即使在60～80℃下,干化速率随温度升高仍然明显加快,干化时间缩短量与温度升高量满足递减的2次拟合多项式;而干化时间随污泥颗粒质量的变化满足递增的3次拟合多项式,所得拟合关系式适用于多种污泥;铁-钙-碳基调理剂可以显著提高污泥干化性能,稻壳和CaO会增加污泥孔隙和热导率,且稻壳在低温干化前期效果更明显。     

Efficient drying and oxygen-containing functional groups characteristics of lignite during microwave irradiation process

To remove the high moisture of ZhaoTong lignite, the efficient drying characteristics and oxygen-containing functional groups changes in lignite during microwave irradiation process were highlighted in this study. As the microwave absorbers, lignite char and NaNO₃ were added to microwave drying of ZhaoTong lignite. The minimum chemical oxygen demand of waste water generated from microwave drying process of lignite was 99.89?mg?O₂?L^?1. The effects of microwave power, lignite mass, the weight ratio of lignite char to lignite and NaNO₃ content on the drying rate, and moisture diffusion coefficient of lignite were investigated during lignite microwave irradiation process. It was found that the drying rate and moisture diffusion coefficient of lignite increased with increasing microwave power, the weight ratio of lignite char to lignite and NaNO₃ content, but decreased with increasing lignite mass. Lignite char and NaNO₃ were mixed with lignite that can enhance the instantaneous surface temperature of lignite sample under microwave irradiation. Compared with addition of lignite char to lignite, the addition of NaNO₃ to lignite can decrease the unit electric power consumption of moisture evaporating. And the minimum unit electric power consumption of moisture evaporating was 9.44?Wh?g^?1. The FTIR technology was used to investigate the oxygen-containing functional groups changes in lignite during microwave drying process. The oxygen-containing functional groups of lignite were effectively removed with increasing microwave power.     

Modeling Superheated Steam Vacuum Drying of Wood

A two-dimensional mathematical model developed for vacuum-contact drying of wood was adapted to simulate superheated steam vacuum drying. The moisture and heat equations are based on the water potential concept whereas the pressure equation is formulated considering unsteady-state mass conservation of dry air. A drying test conducted on sugar maple sapwood in a laboratory vacuum kiln was used to infer the convective mass and heat transfer coefficients through a curve fitting technique. The average air velocity was 2.5 m s^-1 and the dry-bulb temperature varied between 60 and 66°C. The ambient pressure varied from 15 to 11 kPa. Simulation results indicate that heat and mass transfer coefficients are moisture content dependent. The simulated drying curve based on transfer coefficients calculated from boundary layer theory poorly fits experimental results. The functional relation for the relative permeability of wood to air is a key parameter in predicting the pressure evolution in wood in the course of drying. In the case of small vacuum kilns, radiant heat can contribute substantially to the total heat transfer to the evaporative surface at the early stages of drying. As for conventional drying, the air velocity could be reduced at the latter stage of drying with little or no change to the drying rate.     

MEASURED GAS VELOCITY AND MOISTURE CONTENT DISTRIBUTION IN A CONVECTIVE VACUUM KILN

Transferring the necessary heat of evaporation to the stack is the bottleneck in convective vacuum drying of wood. Higher gas velocities are applied to compensate for the lower gas density and to obtain similar heat and mass transfer characteristics as under normal pressure. Like in conventional kiln drying the region with the most unfavorable drying conditions determines drying time and product quality. To use the full potential of the meanwhile established superheated steam vacuum drying technology, it is therefore necessary to work on an improved uniformity of process conditions in the kiln.

To evaluate the fluid dynamics and its influence on the final moisture content, experimenls in a laboratory convective vacuum kiln were carried out. For different total pressures the profiles of dynamic pressure in the stack entry section were measured in a dry atmosphere. At normal pressure the profiles were determined between the board layers throughout the whole stack. For the same slack configuration vacuum drying tests were used to assess the impact of the velocity distribution in the slack on the final moisture content distribution-Regions of low gas velocities coincided well with regions of high final moisture content.     

Parametric studies on catalytic pyrolysis of coal-biomass mixture in a circulating fluidized bed

Pyrolysis is an efficient way of thermally converting biomass into fuel gas, liquid product and char. In this research, pyrolysis experiments were carried out in a circulating fluidized bed reactor with a riser diameter of 25 mm and height 1.65 m. The biomass used was corn cobs. The experiments were conducted systematically using two level factorial design with temperature ranging from 650 to 850 degree Celsius, corn cobs and catalyst contents in feed ranging from 0 to 100%, and from 1 to 5 wt%, respectively, and Ni loaded on catalyst ranging from 5 to 9 wt%. The results showed that when temperature and catalyst contents in feed and Ni loaded on catalyst increased, the percent of hydrogen and carbon monoxide increased. The amount of corn cobs was found to have an effect only on the composition of hydrogen. Carbon dioxide was also observed to increase slightly. On the other hand, the percent of methane was considerably decreased. The optimum conditions were 850 degree Celsius, corn cob content in feed of 100%, catalyst content in feed of 5% and Ni loaded on catalyst of 9%. At this condition the percentages of hydrogen and carbon monoxide were 52.0 and 18.0, respectively.     

Numerical Simulation of Vacuum Drying by Luikov's Equations

A two-dimensional mathematical model was developed to simulate coupled heat and mass transfer in apple under vacuum drying. Luikov's equations are the governing equations in analyzing heat and mass diffusion problems for capillary-porous bodies. The model considers temperature- and moisture-dependent material properties. The aim of this study is to analyze the influence of some of the most important operating variables, in particular, pressure and temperature of drying air, on the drying of apple. The resulting system of unsteady-state partial differential equations has been solved by a commercial finite element method (FEM) package called FEMLAB (COMSOL AB, Stockholm, Sweden). Simulations, carried out in different drying conditions, showed that temperature is more effective than air pressure in determining the drying rate. A parametric study was also carried out to determine the effects of heat and mass transfer coefficients on temperature and moisture content distributions inside apple during vacuum drying. A comparison between the theoretical predictions and a set of experimental results reported in the literature showed very good agreement, especially during the first 4,200 s, when experimental data and theoretical predictions overlapped and relative errors never exceeded 2%.