高粘度范围内灰的沉积及粘结特性的实验研究

发布时间：2018-01-14 19:35

本文关键词：高粘度范围内灰的沉积及粘结特性的实验研究　出处：《清华大学》2014年博士论文　论文类型：学位论文

【摘要】：灰沉积一直是影响电站锅炉正常运行的难题之一，，严重威胁着锅炉的安全、经济运行。本文以高粘度范围内（灰的温度低于其临界温度时的粘度范围）灰的沉积和粘结特性作为研究对象，采用实验测试与理论分析方法开展了灰的沉积特性及其影响规律、粘结机理与模型的研究，对于深入认识高粘度范围内灰的沉积过程具有重要的理论和实际意义。本文首先从高粘度范围内灰的沉积特性着手，在灰沉积特性测试实验装置上开展了换热面温度、灰颗粒撞击速度、沉积时间、灰的粒径以及灰的化学成分对高粘度范围内灰沉积行为的影响规律研究。实验结果表明，高粘度范围内的灰颗粒具有较强的沉积倾向，其沉积过程可以分为两个阶段：在初始阶段发生的为积灰过程，随着沉积物的生长逐步转变为结渣现象。较低的换热面温度、较大的灰颗粒速度和较大的粒径能够显著抑制灰的沉积过程。碱金属和碱土金属含量较高的灰颗粒在高粘度范围内具有较强的沉积倾向。灰的化学成分及其所处的环境条件是影响高粘度范围内灰沉积行为的两个关键因素。然后，开展了灰的化学成分与烧结特之间关系的规律与模型研究。通过将生物质与兖矿烟煤进行混燃，改变了燃料中灰的化学成分，在沉降炉和烧结温度测量实验装置上开展了灰的成分变化对于烧结特性的影响规律研究。实验结果表明，生物质灰中的碱金属含量较高，导致烧结温度远低于煤灰，且混合燃料灰的烧结温度随着生物质含量的升高而降低。灰的烧结温度随碱酸比的增大而减小，提出了基于灰的化学成分的烧结温度计算模型，计算结果与实验值符合良好。最后，从粘结机理着手，针对固体桥力主导的高粘度范围内灰的粘结过程进行了研究。开发了高温条件下灰的固体桥力及抗拉强度的测量实验系统，获得了温度、接触时间和接触压力对于高粘度范围内灰的脖颈抗拉强度的影响规律，发现了灰的脖颈抗拉强度与温度之间呈现双峰分布曲线的关系，高粘度范围内灰的脖颈抗拉强度远小于同温度下的材料抗拉强度。通过对实验结果进行无量纲化处理，提出了高粘度范围内灰的无量纲脖颈抗拉强度计算公式，并对该公式进行了验证，计算值与实验值符合较好。该计算公式为建立以灰颗粒受力分析为基础的高粘度范围内灰的沉积模型奠定了基础。
[Abstract]:Ash deposition has always been one of the difficult problems affecting the normal operation of power plant boilers, which seriously threatens the safety of boilers. Economic operation. In this paper, the deposition and bonding characteristics of ash in high viscosity range (when the temperature of ash is lower than its critical temperature) are studied. The deposition characteristics of ash and its influence law, bonding mechanism and model were studied by means of experimental test and theoretical analysis. It has important theoretical and practical significance for further understanding the deposition process of ash in high viscosity range. In this paper, the heat transfer surface temperature, ash particle impact velocity and deposition time are carried out on the test device of ash deposition characteristics from the point of view of the ash deposition characteristics in the high viscosity range. The influence of particle size and chemical composition of ash on the ash deposition behavior in high viscosity range is studied. The experimental results show that the ash particles in high viscosity range have a strong deposition tendency. The deposition process can be divided into two stages: in the initial stage, ash deposition process, with the sediment growth gradually changed to slagging phenomenon, lower heat transfer surface temperature. Larger ash particle velocity and larger particle size can significantly inhibit the ash deposition process. The ash particles with higher alkali metal and alkali earth metal content have a strong tendency to deposit in the high viscosity range. The chemical composition of ash and its location. Environmental conditions are two key factors affecting ash deposition behavior in high viscosity range. Then, the relationship between ash chemical composition and sintering characteristics was studied. By mixing biomass with Yankuang bituminous coal, the chemical composition of ash in fuel was changed. The influence of ash composition change on sintering characteristics was studied in the settling furnace and sintering temperature measuring device. The experimental results showed that the alkali metal content in biomass ash was higher than that in biomass ash. The sintering temperature is much lower than coal ash, and the sintering temperature of mixed fuel ash decreases with the increase of biomass content, while the sintering temperature of ash decreases with the increase of alkali-acid ratio. The calculation model of sintering temperature based on the chemical composition of ash is presented. The calculated results are in good agreement with the experimental values. Finally, the bond process of ash in the high viscosity range dominated by solid bridge force is studied from the point of view of bonding mechanism, and an experimental system for measuring the solid bridge force and tensile strength of ash under high temperature is developed. The effects of temperature, contact time and contact pressure on the tensile strength of the neck of ash in the high viscosity range were obtained, and the relationship between the tensile strength of the neck and the temperature was found. The tensile strength of the neck of the ash in the high viscosity range is much lower than that of the material at the same temperature. By dimensionless treatment of the experimental results, a formula for calculating the dimensionless tensile strength of the neck of the ash in the high viscosity range is proposed. The formula is verified, and the calculated value is in good agreement with the experimental value. This formula lays a foundation for the establishment of ash deposition model in high viscosity range based on the analysis of the force of ash particles.
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM621.2

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