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糖膏流变学特性及其应用的研究
【作者】 陈朝俊；
【导师】 李斌；
【作者基本信息】 昆明理工大学 ， 化工过程机械， 2009， 硕士
【摘要】 制糖工业是我国重要的传统工业,在2006年我国食糖产量就稳居世界第四位。云南作为产糖大省,制糖企业多,从业人员多,制糖产业对当地经济发展起着重要作用。煮糖结晶是制糖生产的重要工序之一,但云南大部分糖厂的煮糖结晶过程还处于凭人工经验操作的状况,云南省元江县金柯集团糖业有限责任公司就是这种状况,严重影响了制糖的质量和效益。因此,实现煮糖结晶过程的自动化是非常有必要的。本文通过分析国内外煮糖研究现状得知：一是糖膏粘度与煮糖过程中的过饱和系数和晶粒含量这两个重要参数都有明显的关系,而通常使用的折光仪和电导仪等只能反映单一参数,所以把糖膏粘度作为煮糖结晶控制参数显示了独特的优越性。第二是目前国内关于糖膏流变学特性研究的报道很少,并且国内粘度在线检测技术相当薄弱,而这两个方面又是进行糖膏粘度控制依赖的基础。为此,本文针对上述问题进行了初步研究。以云南省元江县金柯集团糖业有限责任公司煮制甲糖膏为研究对象,在煮糖结晶过程中取样,用数字粘度测量仪对糖膏样品进行流变学特性的试验研究,并分析了温度、锤度和剪切速率对糖膏流变学特性的影响。在试验条件范围内研究表明：糖膏是拟塑性非牛顿流体,具有触变性。粘度先随着剪切速率的增大而较快的降低,当剪切速率达到10s-1后降低较缓慢。粘度先随温度的升高显著降低,当温度达到55℃后粘度降低很缓慢。当温度一定时,随着锤度的增加,粘度升高,非牛顿性也越显著。当锤度一定时,温度越高,非牛顿性越不显著。在试验温度和糖膏样品锤度范围内,通过对试验数据的回归处理得到：稠度系数K和流变指数n随温度的变化规律是,糖膏锤度低于77.30°BX时适合指数模型,高于这个锤度的糖膏适合多项式模型。流变指数n随锤度的变化规律适合多项式模型,稠度系数k随锤度的变化规律适合几何模型。粘度测量是进行粘度控制的先决条件,本文针对糖膏的流变学特性,并依据剪应力的原理,在理论上设计了一种单圆筒旋转式粘度在线检测传感器。该传感器结构新颖,主要包括5部分：恒速驱动部分的步进电机、力矩部分的套筒和悬臂梁式弹性元件、测矩部分的两个增量式旋转编码器、传感部分的转子和支撑部分的底座和支架,它适合安装在结晶罐上进行在线粘度检测。该糖厂甲糖膏的间歇煮制过程有煮水、整晶、养晶、甲洗和浓缩五个阶段,煮糖过程中对丰富经验师傅的所有关键操作进行糖膏取样,通过试验绘出了煮糖过程中糖膏粘度随煮糖时间变化的曲线,它由每个煮糖阶段不同斜率的曲线段组成,并表明煮糖过程中有明显的粘度变化规律,糖膏粘度作为煮糖过程控制参数是可行的。由此,提出了以粘度和时间参数控制煮糖的控制方案。
【Abstract】 The sugar industry is our tradition industry, and its sugar output has been on the fourth in the world in 2006. Yunnan is a big sugar producing province, there are many sugar factories and workers, which play important roles in the local economy. Sugar boiling is one of the important processes, but sugar boiling process of most factories in Yunnan, such as the JinKe sugar Ltd, co. in Yunjiang, is depending on the experience control, which has seriously affected the quality and efficiency of the sugar boiling.Therefore, it is necessary to realize automation of the sugar boiling process.Two main conclusions have beeen summarized in the analysis of domestic and foreign sugar boiling processes:one is that the sane sugar viscosity has a obvious relationship with supersaturation coefficient and crystal content which are two important parameters in sugar boiling processes, however, the common used refractometer and the electric conductivity meter only reflect one parameter, so taking sane sugar viscosity as control parameter displays a unique superiority. The other is that experimental research about the rheological behavior of sane sugar is seldom found on the domestic study papers, and the technology of viscosity sensor for online examination is weak, but these two aspects are the foundation of viscosity control. Therefore, the questions in view of the above presentation was analyzed in this paper.Using the digital viscometer, the rheological behavior of armor sane sugar was experimentally researched which is taken from the Yunjiang JinKe sugar Ltd, co. in Yunnan, also, the affect of temperature,concentration and shearing rate on the rheological behavior of sane sugar has been discussed.In the scope of test condition, the experimental results showed that sane sugar become pseudo-plasticity fluid and take on thixotropy. Its viscosity reduced quickly with the rise of temperature, however, the viscosity reduced slowly when reached to 55℃. Its viscosity reduced quickly with the rise of shearing rate, however, the viscosity reduced slowly when shearing rate reache to 10 s-1. When temperature is certain, viscosity increased and non-Newton was more remarkable along with concentration being increased. And when concentration is certain, if concentration was much bigger, the rheological behavior was effected by temperature much greater; if temperature was much higher, non-Newton was less significant.Through experimental data’s return process, consistency index K and rheological property index n changes along with the temperature changes, index model was suitable for concentration lower than 77.30°Bx, otherwise suitable for multinomial model. Rheological property index n changes along with the concentration changs, which uses the multinomial model. Consistency index K with the changes of concentration is suitable for the geometric model.Viscosity measurement is a prerequisite for viscosity control, based on the rheological behavior of sane sugar, a single-cylinder rotary viscosity sensor for online examination was designed in this paper. The sensor includes five parts:the constant speed part of stepping motor, the torque part of sleeve and cantilever elastic unit, the torque measurement part of two increase type rotary encoder, the sensing part of rotor and the support part of foundation, and the sensor is fit for on-line measurement installed on the vacuum pan.The armor sugar boiling process includes five stages:boiling water, reorganization crystal, crystal growth, armor washing and concentration. Samples were taken from all key operation points of sugar boiling process that operated by skilled worker, and then a curve that viscosity fluctuated with time in the sugar boiling process was drew, which is composed by different slope of the curve in the each stage, so it prove that taking viscosity as automatic control parameter is feasible. Finally, on the basis of the viscosity and the time parameters, the control method of the sugar boiling process was proposed.