【作者】 孔令波；

【导师】 刘焕彬；

【作者基本信息】 华南理工大学 ， 制浆造纸工程， 2013， 博士

【摘要】 本论文以节能减排作为出发点，概述了国内外造纸工业的节能研究现状和相关的节能技术，包括已有商业化节能技术与新兴节能技术；探讨了造纸工业中常用的能效对标与能源审计等节能潜力评估方法，并对其应用做了综述；就此还以某造纸企业为例开展了全面的能源审计，找出了约14%的节能潜力。分析发现纸页干燥是造纸流程中脱水量最少，但能耗与成本却最高，且节能机会最多的单元操作之一，纸页干燥过程性能的优劣对于造纸过程的总能效水平有极大影响，故以纸页干燥过程作为本论文研究的主要落脚点。首先，本论文对纸机干燥部能量系统进行了诊断分析，应用本课题组设计的系统分析方法以及关键状态参数测试方法，以某瓦楞纸机为例，对其干燥部的运行现状进行了综合分析，诊断出了影响干燥能耗的主要问题所在，提出了有效的节能改造建议。另外，还探讨了能量分析与分析相结合的纸机热回收系统分析方法，以某涂布纸机热回收系统为研究对象，基于分析结果提出了余热联合利用的节能措施，预计可使能源利用率提高7.3%。干燥过程节能诊断与热回收系统分析方法以及相应的应用实例对于指导纸机干燥部节能降耗有一定的借鉴意义。其次，基于质量与能量守恒原则，以烘缸组为建模单元，采用序贯模块法构建了符合纸页干燥工艺规程的静态能量模型和模拟系统。该模拟系统共由八个基本功能模块构成，包含了干燥部各子系统之间的相互关系。以某新闻纸机为例，根据其工艺规程搭建了干燥静态能量模型和模拟系统，并在MATLAB上实现了静态模拟，模拟结果显示该模型可以较准确的仿真实际纸页干燥过程。此外，还模拟了进纸温度和干度、送风温度、排风湿度以及环境温湿度对干燥性能的影响，仿真结果与工程经验基本相符。该静态模拟系统不仅可以从宏观上模拟干燥过程的物流和能流信息，还可用来分析某些关键操作参数对纸页干燥性能的影响，有助于加深对纸页干燥全过程的认识和理解，且对于指导实际纸机干燥过程中的节能优化具有一定的参考价值。随后，根据纸页中水分的不同存在形态及其各自的蒸发机制，分别给出了描述自由水和吸着水传质速率的基本方程。选取纸页接触干燥为研究对象，探索了其传热传质解析性数学模型的建立，并采用数值技术开展了干燥动力学模拟，得到了纸页温度与含水率以及蒸发速率随干燥时间的变化规律，模拟结果基本符合文献中对纸页理论干燥过程的定性描述。此外，还数值研究了初始纸页干度、热源温度与空气流速对干燥速率和能耗的影响，结果表明：提高初始纸页干度可降低干燥时间和能耗；提高热源温度不仅会降低干燥时间和能耗，还会改善干燥效率；而空气流速的增加除令干燥时间缩短外，可能会影响干燥效率。该解析数学模型以及所提出的纸页干燥数值研究方法可以作为对现行纸页理论干燥曲线定性描述的补充，且对于进一步开发实际纸机干燥过程的传热传质机理数学模型具有重要的理论指导意义。最后，基于静态能量模型对干燥部的整体性理解以及纸页接触干燥传热传质模型对干燥机理的描述，对纸页在纸机干燥过程的传热传质解析性数学模型进行了探索性研究与初步模拟。对此，分别选取纸页微元体和与其耦合的烘缸微元体作为建模单元，由局部到整体地建立了描述纸页干燥全过程的较为完整的解析数学模型。根据纸页在贴缸干燥区与对流干燥区以及纤维饱和点前后截然不同的传热传质机理对纸页质量和能量方程中的自由项进行了逐一论述，并考虑了不同情况下烘缸能量方程的边界条件。该解析数学模型对纸页干燥过程的描述最终表现为一个常微分方程初值问题与一个偏微分方程边值问题相耦合的问题。对此问题涉及的计算区域，采用数值方法进行了网格划分，并对纸页和烘缸控制方程及其边界条件进行了离散化处理，得到了纸页运行方向上和烘缸弦向与径向上各离散单元的有限差分格式。然后，在利用MATLAB编程对构成所有节点的差分方程组采用迭代法逐一节点进行了数值求解，得到了整个纸页干燥计算域内的数值解。模拟结果显示：计算得到的干燥过程曲线与理论过程和实际经验趋势基本吻合，尤其是在干燥的前端和末端，但还需深入完善该模型及其计算过程，尤其是模型所涉及的各类传热传质系数和过渡区不同形态水分同时蒸发的机理，才能使其更加接近于工程实际，以达到为实际生产提供理论指导的终极目标。更多还原

【Abstract】 With a focus on energy saving and emissions reduction, this study presents an overviewof the current energy related research status for both domestic and international paper industry,outlines commercialized and emerging energy-efficiency technologies. It also discusses thecommonly applied energy-saving potential assessment methods, e.g. energy-efficiencybenchmarking and energy auditing. As an application, a plant-wide energy audit is conductedfor a paper mill, the results identified14%total energy-saving potentials. From above analysis,we found the paper drying process dehydrated the smallest amount of water with the largestamount of energy use and cost. It is also found that paper drying process has the highestenergy-saving opportunities among the papermaking processes. In addition, it has asignificant implication on the overall energy efficiency of the whole papermaking process.Therefore, we finally choose the paper drying process as the main research object for thefollowing studies.Initially, with the purpose of having a full picture about the current operational status andthe drying performance of paper machine, we conducted a diagnostic analysis on the energysystem of a corrugated paper machine dryer section. A completed test and analysis methodsthat focused on the key operation parameters is also presented. The comprehensive analysis isfound to be a useful assistant tool for help understanding the current drying performance. Themain energy-saving opportunities is recommended based on the dominant issues that affectedthe drying energy consumption. As part of the dryer section, the heat recovery system is alsoanalyzed combined energy and exergy analysis methods. Based on the results of a coatedpaper machine, a new waste heat integrated proposal is expected which could increase theenergy utilization by7.3%. The proposed energy diagnosis method of dryer section and thecombined analysis methods of heat recovery systems, as well as the corresponding casestudies, could have a significant meanings for reducing the energy use of paper machine dryersection.Next, a static energy model and related modeling system of the paper drying process isdeveloped using sequential modular approach based on the principle of mass and energy conservation. The developed static model is composed of eight basic functional blocks, whichalso considering the relationship between each subsystems. As the case study, the static modeland system of a newsprint machine is then constructed according to its specific drying processand conditions. The MATLAB simulation result shows that it could be used to simulate theactual newsprint drying process correctly. A series of simulations are also performed toinvestigate the influences of some key operating parameters on the drying performance, e.g.initial paper dryness and its temperature, supply air temperature, exhaust air humidity, andambient conditions. The simulated results indicate that the consistency of the static modelwith experimental results and experience is reasonable. Some commonly important results arepresented in this chapter. Not only could the static model simulate the mass and energy flowinformation of the drying process at a macro level, it could also be used to analyze howoperating parameters affected the drying performance. The static model could also helpdeepen awareness and understanding of the whole paper drying process thoroughly. Inaddition, it could provides some constructive advice to guide energy saving and processoptimization for the practical paper drying process.Subsequently, this study focus on the various water existing status within paper web andrelated evaporation mechanisms. The basic mass transfer equations of free water andhygroscopic water are presented at the beginning. To investigate the performance of contactpaper drying process, we established a mathematical model on the basis of heat and masstransfer theory, then the drying kinetics for this process was studied with numericaltechnology. The simulation result shows that the predicted paper temperature, moisturecontent and evaporation rate, varying with drying time, is basically fit in with the qualitativedescriptions about the theoretical paper drying process cited in the literatures. Additionally,the initial paper dryness, hot wall temperature, and air velocity were quantitatively examinedto study their impacts on drying rate and energy consumption. The results from this studypresented that increasing initial sheet dryness could reduce drying time and energy use.Increasing heat-wall temperature could improve drying efficiency besides reducing dryingtime and energy use. Increasing air velocity could also help to reduce the drying time, butmay influence drying efficiency negatively at some ranges. It was found the contact paperdrying model and the numerical research methods for theoretical paper drying process could be acted as a qualitative supplement to the current available theoretical paper drying curves.This research also has some instructive significance for further developing some moreaccurate paper drying mathematical model for paper machine drying process.Finally, we developed a original and innovative paper drying model based on the heatand mass transfer theories with the intention of conducting some exploratory studies andpreliminary simulations for paper machine dryer section according to its drying state of the art.This model coverers the holistic understanding of the dryer section reflected by the staticenergy model and the quantitative description of the drying mechanism revealed by abovecontact drying model. It was constructed from the viewpoint of heat and mass transferaccording to the relationship of the local and the entire drying process. The basic paperelement and coupled cylinder element were chosen as the basic modeling unit, respectively.Then the governing equations for paper moisture content, paper temperature and cylindertemperature were deduced step by step, including the detailed description of the relatedboundary conditions under different circumstances and the physical properties of materials formodeling the actual paper drying process. The free-term presented in the paper and cylindergoverning equations were paid more attention to describe considering the different heat andmass transfer mechanisms between the contact drying zone and the convective drying zone.Besides, the influence of the fiber saturation point on drying process was also always kept inmind. The paper drying mathematical model was ultimately presented as an ordinarydifferential equations initial value problem coupled with a partial differential equationsboundary value problem. Next, we solving this coupled problem using finite differencemethod based on the distributed computational grids and the differential governing equationsas well as its boundary conditions. After that, all the distributed algebraic equations alone thewhole calculated domains for each node were automatically solved using iterative methodswith MATLAB. The modeling results imply that the predicted drying curves are basically inaccordance with the theoretical drying process and practical engineering experience. However,the developed drying model and the simulation process, particularly the involved heat andmass transfer coefficients and evaporation mechanism in the transition drying zone, still need further study to improve the predicted results in order to make it more closely represent theactual paper drying process.更多还原