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河北工业大学
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基于图像处理的过热蒸汽与热风干燥污泥收缩特性分析.

Title: 基于图像处理的过热蒸汽与热风干燥污泥收缩特性分析.
Alternate Title: Analysis of shrinkage characteristics of sludge in superheated steam and hot air drying processes based on image processing.
Language: Chinese
Authors: 张绪坤1 xukun008@163.com
王高敏1
温祥东1
邹加富1
姚斌1
吴青荣1
邢普1
Source: Transactions of the Chinese Society of Agricultural Engineering. Oct2016, Vol. 32 Issue 19, p241-248. 8p.
Document Type: Article
Author-Supplied Keywords: drying ; effective diffusion coefficient ; image processing ; models ; shrinkage ; sludge ; 图像处理 ; 干燥 ; 收缩 ; 有效扩散系数 ; 模型 ; 污泥 ; drying ; effective diffusion coefficient ; image processing ; models ; shrinkage ; sludge ; Language of Keywords: English; Chinese
Abstract (English): Large amounts of sewage sludge with high moisture content are generated every year. There are varieties of methods to manage sewage sludge such as land filling, composting, pyrolysis, incineration and thermal drying. Decreasing the moisture content of sludge is a critical step in harmlessness, bulkiness reduction, and resource utilization. Thermal drying has been proven to be an effective approach to reduce solid volumes compared with other ways. Drying is a complex process which may consist of molecular diffusion, capillary flow, Knudsen flow, surface diffusion and so on. Generally, the phenomena of shrinkage crack and skin layer formation can be observed during the drying process and each of them occurs can modify the drying kinetics. Currently, there are many studies on sludge shrinkage in hot air drying but lack of studies in superheated steam drying which has the advantages of energy saving, high efficiency and great heat and mass transfer coefficients. Furthermore, most of moisture diffusion models proposed by researchers are not consider the shrinkage and regard the finite regular geometry as an infinite one when they deal with the drying process, it may result in large error or erroneous results. The purpose of this paper is to investigate the shrinkage characteristics of sludge in superheated steam and hot air drying processes and their influences on the effective diffusion coefficients. The experimental devices for superheated steam drying under atmospheric pressure and hot air drying were built. The drying experiments were carried out with caky sludge samples of 10 mm in thickness and 50 mm in diameter at the temperature of 160 and 200 ℃. During the drying process, the photographs of sludge samples were obtained with digital camera by taking out the sludge samples from the drying chamber every ten minutes. In order to study the shrinkage phenomenon and its characteristic of caky sludge, the image processing technique was used to processing and analyze the photographs. In addition, the moisture diffusion theory model based on Fick's second law, infinite slab model and infinite cylinder model concerning finite round slab was also built, which considered the shrinkage phenomenon, by superimposition technique. Combining the empirical model, the expression of calculating effective diffusion coefficients was elicited. The results showed that the shrinkage phenomena can be observed remarkably during the drying process and the variation law was corresponding with the moisture that decreased sharply in great range at the forepart and reduced slowly in narrow range after that. The volume ratio is about 0.3 and the volume shrinkage coefficient equal to 0.7 at the end of superheated steam and hot air drying at the temperature of 160 and 200℃. The influences on sludge shrinkage were consistent between superheated steam and hot air drying. The change of effective diffusion coefficients was coincident with the moisture ratio. Considering the shrinkage of sludge samples, the average effective diffusion coefficients of superheated steam drying were equal to 1.92×10-8, 3.75×10-8 m2/s at the temperature of 160 and 200℃, respectively. The average effective diffusion coefficients of hot air drying were equal to 0.94×10-8, 1.31×10-8 m2/s in the same conditions, respectively. The average effective diffusion coefficients were half compared with those without shrinkage. A valuable reference for analysis of drying process mechanism, process parameter optimization of sludge drying and design of drying devices can be provided from the experimental results. [ABSTRACT FROM AUTHOR]
Abstract (Chinese): 为了解污泥过热蒸汽与热风干燥过程收缩特性,搭建了常压过热蒸汽和热风干燥试验台,选用直径为50 mm厚度为10 mm的污泥样品在160和200 ℃下进行试验。利用图像处理技术分析干燥过程污泥收缩现象及特性,采用叠加技术,建立了基于无限大平板和无限长圆柱体叠加而成的有限圆平板在考虑收缩情况下的Fick第二定律湿分扩散模型,并结合经验模型推导出计算有效扩散系数的表达式。结果表明:污泥在干燥过程中存在明显的收缩现象,前段干燥收缩幅度大,后段干燥收缩幅度小,收缩变化规律与水分变化规律一致。160、200 ℃污泥过热蒸汽与热风干燥终了时刻体积比约为0.3,体积收缩系数为0.7。过热蒸汽干燥和热风干燥对污泥的收缩影响一致。160、200 ℃污泥过热蒸汽与热风干燥有效扩散系数的变化与水分比的变化相对应。在考虑污泥收缩的条件下,160、200 ℃污泥过热蒸汽干燥平均有效扩散系数分别为1.92×10-8和3.75×10-8 m2/s,热风干燥平均有效扩散系数分别为0.94×10-8和1.31×10-8 m2/s,约为不考虑收缩条件下平均有效扩散系数值的1/2。试验结果为污泥干燥过程机理分析、工艺参数优化和干燥设备开发提供参考。 [ABSTRACT FROM AUTHOR]
(Copyright applies to all Abstracts.)
Author Affiliations: 1南昌航空大学机电设备研究所,南昌 330063
ISSN: 1002-6819 (Sherpa/RoMEO, JCR)
PageCount: 241-249
volume: 32
issue: 19
issn: 10026819
pubdate: 2016
DOI: https://doi.org/10.11975/j.issn.1002-6819.2016.19.033
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