【作者】 牛蔚然；

【导师】 田茂诚；

【作者基本信息】 山东大学 ， 热能工程， 2009， 博士

【摘要】 大型煤粉锅炉安全稳定高效清洁燃烧是保障电站锅炉节能环保的关键因素。研究炉内过程的非线性机理,分析可表征炉内过程的非线性特征参数,掌握实际设备运行期间非线性特征参数的变化规律,不仅可为工程实践提供理论依据,还可以提高实际锅炉运行的效能和稳定性,具有深远的社会和经济效益。本文将非线性理论与电站锅炉现场试验研究相结合,共开展了4个方面的研究:1、基于统计理论,开展了对炉内压力纵向及横向数据的统计分析,确认炉内压力可作为炉内过程的参考变量;确认炉内压力序列分布基本不服从正态分布形式;炉膛压力序列存在明显的序列相关性,相关阶数最高约为13阶,大多数样本为非平稳序列,且序列中季节性表现不突出。这是研究炉内压力序列的分形及混沌特性的基础。2、开展了实炉压力序列的分形及多重分形特性研究。确认多变量影响造成的不可预测的间断性跳跃,是炉内压力波动服从分形分布特征的根本性原因;炉内压力样本的方差无统计意义。确认炉内压力序列是一个局部稳定,整体波动的综合过程,属于非随机序列,并具有明确的持续性或反持续性特征,存在显著性变化和显著性持续影响两个标度时间。炉内压力序列的分形维可表征影响炉内运动复杂性的主要因素,Hurst指数可表征炉内运行期间的实际状况。综合利用分形维和Hurst指数,可对实炉运行过程中影响炉内工况变化的各因素加以区分,有利于实炉的故障诊断和运行优化。实际炉内压力序列具有多重分形特征,其局部奇异性的完整描述是对Hurst指数、分形维等整体特征标度指数的有益补充与完善,其由局域标度特征导出整体行为的思想可为描述炉内过程提供了新的方法。3、开展了实炉压力序列的混沌时间序列分析及混沌特性研究。确认炉内压力信号为包含着随机信号的混沌信号,计算获得最优延时为8s、最小嵌入维数为8维,在重构炉内过程相空间基础上,计算得到某300MW机组满负荷正常运行状态下,炉内运动关联维为6.56,存在正的lyapunov指数0.0194,Kolmogorov熵为0.297bits/s。基于反演理论对炉内过程运动方程组进行了重建。反演方程组和实际炉内过程具有相似的非线性特性。分析方程组可知,相对单变量变化而言,不同影响因素间的非线性交互作用是影响炉内过程稳定的主要因素。4、对某600MW超临界直流锅炉实际运行条件下的非线性规律开展研究,通过现场试验及理论计算总结可知:(1)变负荷过程中,锅炉炉内过程非线性特征参数的变化规律为:锅炉冷态通风时炉内压力近似为随机运动。锅炉点火后炉内压力则转变为具有正或反持续性的非随机运动。锅炉升负荷过程中,原始压力序列Hurst指数规律性不明显;差分序列的Hurst指数显示,在较低负荷阶段,随负荷升高,炉内运动的反持续性具有增加趋势;在较高负荷阶段,反持续会保持在较高水平,但随锅炉负荷提高略有降低。锅炉冷态通风的分形维数均高于锅炉点火后各工况而相应差分序列却呈相反规律。升负荷过程中,炉内压力序列的分形维呈上升趋势,但差分序列的分形维变化不大。随锅炉负荷的提高,炉内过程的奇异性具有增加趋势。奇异性指数在冷态及低负荷阶段趋于大值,在高负荷阶段趋于小值。实际炉内过程的奇异性在整体上小值占优,炉内压力序列结构趋于粗糙。升负荷过程各阶段炉内运动混沌特征量的计算表明,冷态K熵均大于点火后各工况,但关联维却最小。随负荷增加,关联维和K熵均具有增长趋势。由关联维可知,描述炉内运动需要的维数约为6维,即决定炉内运动的独立参变量的个数约为6个。(2)炉内过程非线性特征参数与锅炉经济性指标间存在较为密切的关系。由相关性、拟合和预测分析可知,与锅炉效率相关性较高的非线性特征量为H、K和Δf;与飞灰含碳量相关性较高的非线性特征量为K、H、Hd;与炉渣含碳量相关性较高的非线性特征量为K、H、和Δα。利用BP神经网络,可较好的构建起非线性特征指数与锅炉经济性指标间的映射关系。总之,通过本文的工作,可大致了解以炉内压力为参考变量的炉内过程中存在的非线性特性及其运行规律。结合锅炉运行经济性和稳定性研究,非线性理论在电站锅炉运行优化中将具有深广的应用价值。但是本文工作还只是非线性理论在电站锅炉炉内过程研究中的初步应用,本文所得结论的正确性均受限于所取样本的代表性,还需要后期更深入的理论和应用研究加以验证。更多还原

【Abstract】 Keeping combustion in a large-scale pulverized coal boiler safety,stability,high efficient and clean is the key to energy conservation and reducing emissions.So there are very important to study the nonlinear mechanism of the furnace process,analyze non-linear parameters of the furnace process,and get the non-linear characteristic during the boiler running.These researches could provide theoretical bases for engineering practice and increase the boiler performance and stability, have far-reaching social and economic benefits.Combined nonlinear theories and experimental investigation,the paper is proceeded in 4 aspects:1.Based on statistical theories,lots of longitudinal and transverse furnace pressure series are analyzed.As study shows,furnace pressure as a reference variable can be used to study furnace process.The furnace pressure distribution doesn’t obey normal distribution basically.Obvious serial correlations exist in furnace pressure sequences.The largest correlated order in sequences approximately is 13.Most of samples are non-stationary series.Seasonal performance doesn’t highlight in sequences.These analyses are the foundation to investigate the fractal and chaos characteristics of furnace pressure sequences.2.Researches on fractal and multi-fractal characteristics of the furnace pressure sequence are carried.Multi-variable induced unpredictable intermittent jumps are the essential reason why the furnace pressure fluctuation subject to the fractal distribution.Furnace pressure’s variance doesn’t have statistical significance.The furnace pressure sequence is a integrated process with locally stable and overall volatility.It belongs to non-random sequence,has the features of clear continuity or anti-persistent,exists two scale time of significant change and significant continuing impact. The main factors which influence on the complexity of furnace process can be characterized by the fractal dimension.The actual state of the furnace during operation can be characterized by Hurst index.Comprehensive utilization of fractal dimension and Hurst index,various factors which effect furnace operating conditions during actual furnace operation can be distinguished.It is helpful to the furnace fault diagnosis and operation optimization.Furnace pressure series have multi-fractal characteristics.The complete description of local singularity is a useful complement and improvement to Hurst index and fractal dimension.The overall behavior of the furnace can be derived from scale of its local characteristics,which also provide a new approach to describe the furnace process.3.Researches on chaotic time series analysis and chaos characteristics of the furnace pressure sequence are carried.Furnace pressure signal belongs to chaotic signals with random component,and its optimal delay time is 8s,the minimum embedding dimension is 8.Based on reconstructing phase space of furnace process,the parameters when one 300MW unit normal operates at full capacity are got,where,correlation dimension is 6.56;positive Lyapunov index is 0.0194;Kolmogorov entropy is 0.297bits/s.Based on the inversion theory,the motion equations of the furnace process are reconstructed.Rebuild equations has similar non-linear characters with real furnace process.Analysis shows non-linear interactions between different factors is a major factor affected the furnace process’s stability.4.Researches on non-linear characters of a 600MW supercritical concurrent boiler are carried by field test and theoretical calculation.(1) During the boiler load charging,variation law of nonlinear characteristic parameters of the boiler can be concluded as:The furnace pressure of cold air is approximately random motion.After the boiler ignition furnace pressure changes into a positive or anti-persistence non-random movement.During the up-loading,theHurst index of original series don’t have any rule distinctly,but the difference series Hurst index show the anti-persistence character of the furnace process is increasing during low load stage while the up-loading,and it will keep in a high level and lower slightly in high load stage.The fractal dimension of cold air is higher than that after ignition.The difference series fractal dimension has the anti-rule.During the uploading,the fractal dimension has increase trend,but difference series fractal dimension doesn’t change much.With the increase in boiler load,the furnace process singularity increase too. Singularity exponents have a trend to big value in low load and a trend to small value in high load.Overall singularity of furnace process small value is dominant;the structure of furnace pressure series has a trend to coarse. With the increase in boiler load,the furnace process has its chaos character. Entropy K of cold air is bigger than that after ignition,Correlation dimension is smallest contrarily.With uploading,Correlation dimension and entropy K both have an increasing trend.By Correlation dimension,the dimension to describe furnace motion is about 6,in a other word,the independency variable number is 6.(2) Between the non-linear characteristic parameters of the furnace process and the boiler economic indicators exists closely relationship.By relevance, fitting and forecasting analysis,the non-linear characteristics highly associated with boiler efficiency are H,K andΔf;the non-linear characteristics highly associated with fly ash carbon content are K,H andΔα.By BP network, non-linear characteristics and boiler economic indicators could have a nice mapping.In the paper,the non-linear characteristics and its running law is gotten by using the furnace pressure as variable.Combined with boiler economic and stable operation research,non-linear theory has huge applied value in boiler operation optimization.But the work in the paper is a preliminary application;the result in the paper is Iimited by the samples’ representation.The in-depth theoretical and applied researches are needed to validate it.更多还原