Large-scale Pulverized Coal Boiler Furnace Pressure Non-linear Characteristics Research Based On Fractal And Chaos Theory

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.