微咸水滴灌系统灌水器化学堵塞机理及控制方法研究

发布时间：2018-11-01 18:38

【摘要】：微咸水用于农业灌溉是缓解全球性水资源紧缺问题的重要途径之一,同时滴灌被认为是利用微咸水灌溉最为有效和可靠的方式。但微咸水中含有大量的盐分离子,易于诱发灌水器化学堵塞,严重制约了微咸水滴灌的大规模发展。本文研究了微咸水滴灌条件下灌水器化学堵塞发生行为及其动态响应机制,综合利用电化学、精细电子显微等现代分析技术定量定性的分析了灌水器流道内堵塞物质组成,建立了灌水器化学堵塞物质生长的水动力学模型。并基于裸地加速抗堵塞试验、大田试验及CFD方法,从运行方式、水质控制与灌水器自身结构多方面提出了面向化学堵塞的控制方法。主要结论如下：(1)对微咸水滴灌系统灌水器化学堵塞特性进行了研究,结果表明随着运行时间的增加,灌水器相对流量Dra和均匀度CU逐渐降低,其中圆柱型灌水器降呈现平缓降低规律,片式灌水器呈先平缓-后剧烈的降低形式,大流量的圆柱式灌水器表现出较强的抗堵塞性能。(2)探寻了微咸水滴灌系统灌水器化学堵塞物质组成及关键因素。堵塞物质单位面积分布密度与灌水器Dra和CU度呈显著线性负相关(R20.81),微咸水滴灌系统灌水器内堵塞物质为钙镁碳酸盐(CaCO3、CaMgCO3和CaMg(CO3)2)、硅酸盐(Mg5Al(Si3Al)O10(OH)8和NaAlSi3O8)、石英(SiO2)、氯化钠(Nacl),其中诱发灌水器化学堵塞的主要物质为钙镁碳酸盐类沉淀,含量在88.31%以上。(3)构建了微咸水滴灌条件下灌水器化学堵塞物质生长动力学模型,发现堵塞物质生长过程为渐进型,包括快速增长-渐进增长两个阶段。基于灌水器堵塞物质沉积与剥蚀过程,以Kern-Seaton污垢预测模型为原型,综合考虑灌水器结构类型、流道几何参数和水源特征等因素,建立的灌水器化学堵塞物质生长动力学模型可以很好的描述灌水器内附生堵塞物质及其特征组分的生长过程。(4)建立了面向灌水器化学堵塞的控制方法。从运行模式来看,采用淡水与微咸水进行交替滴灌可以缓解化学堵塞的发生；对于全咸水灌溉来说,采用1d/次的高频滴灌下灌水器能保持相对较高的流量；从水质控制来看,微咸水电导率与灌水器堵塞参数间存在线性负相关关系,微咸水电导率会在一定程度上影响灌水器化学堵塞的发生过程与堵塞分布特征,建议河套灌区地下微咸水滴灌系统适宜电导率应低于4.0 dS/m；从灌水器自身结构来看,采用CFD数值模拟方法,综合考虑流道内流场分布及其水力性能与抗堵塞性能,建议分形流道灌水器适宜的几何参数为宽度1.0 mm左右,流道长度不宜超过224 mm,并可以借助缩减流道深度来控制灌水器出流量,研究结果可为实际流道设计与开发提供理论参考。
[Abstract]:The application of brackish water to agricultural irrigation is one of the most important ways to alleviate the global shortage of water resources, and drip irrigation is considered to be the most effective and reliable way to use brackish water. However, there are a lot of salt ions in brackish water, which is easy to induce chemical clogging of irrigator, which seriously restricts the large-scale development of drip irrigation of brackish water. In this paper, the chemical clogging behavior and its dynamic response mechanism of the emitter under the condition of brackish drip irrigation were studied. The composition of the plugging material in the irrigation channel was analyzed quantitatively and qualitatively by using modern analytical techniques such as electrochemistry, fine electron microscopy and so on. A hydrodynamic model for the growth of chemically blocked substances in an emitter was established. Based on the accelerated anti-clogging test, field test and CFD method, the chemical clogging control method is put forward from the aspects of operation mode, water quality control and the structure of the emitter itself. The main conclusions are as follows: (1) the characteristics of chemical plugging of the emitters in brackish drip irrigation system are studied. The results show that the relative flow rate Dra and the uniformity CU of the emitters decrease gradually with the increase of the running time. Among them, the drop of cylindrical water emitters shows the rule of gentle decrease, and the slice type emitters show the form of first level-then violent reduction. The cylindrical emitters with large flow rate have strong resistance to blockage. (2) the composition and key factors of chemical blockage in the emitters of brackish water drip irrigation system are explored. There was a significant linear negative correlation between the density of blocking matter per unit area and the degree of Dra and CU of the emitter (R20.81). The plugging material in the emitter of brackish water drip irrigation system was calcium-magnesium carbonate (CaCO3,CaMgCO3 and CaMg (CO3) 2). Silicate (Mg5Al (Si3Al) O10 (OH) 8 and NaAlSi3O8), quartz (SiO2) and sodium chloride (Nacl), are the main substances that induce the chemical clogging of the emitters. (3) the growth kinetics model of chemical clogging substances in the emitters under drip irrigation was established. It was found that the growth process of clogging substances was gradual, including two stages of rapid growth and gradual growth. Based on the process of deposition and denudation of clogged material in the emitter, the Kern-Seaton fouling prediction model is used as the prototype, and the factors such as the type of the emitter structure, the geometric parameters of the runner and the water source characteristics are considered synthetically. The kinetic model of the chemical clogging material growth in the emitter can describe the growth process of the epiphytic plugging material and its characteristic components. (4) the control method for the chemical plugging in the emitter is established. From the view of operation mode, using fresh water and brackish water alternately drip irrigation can alleviate the occurrence of chemical blockage, for all salt water irrigation, the high frequency drip irrigation emitter with 1d/ can keep relatively high flow rate. From the point of view of water quality control, there is a linear negative correlation between the electrical conductivity of brackish water and the plugging parameters of the emitter. To some extent, the electrical conductivity of brackish water will affect the occurrence process and the distribution characteristics of the chemical blockage of the emitter. It is suggested that the suitable electrical conductivity of drip irrigation system for underground brackish water in Hetao irrigation area should be less than 4.0 dS/m;. According to the structure of the emitter itself, the CFD numerical simulation method is used to synthetically consider the flow field distribution in the channel, its hydraulic performance and anti-blocking performance. It is suggested that the suitable geometric parameter of the fractal channel emitter is about 1.0 mm in width. The length of the runner should not exceed 224 mm, and the discharge of the emitter can be controlled by reducing the depth of the channel. The results of the study can provide a theoretical reference for the design and development of the actual runner.
【学位授予单位】：中国农业大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：S275.6

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