Characteristic And Modeling Research Of 300MW CFB Boiler's Combustion System

For the unique advantages of direct desulfurization in burning and low quality fuel using, circulating fluidized bed (CFB) boiler has become the focus technology among clean coal combustion development in China. However, the modelling and automatic control of the combustion system are very difficult problems, which have aroused much attention of academic researchers. For the numerical simulation and mechanism modeling of combustion system involve the gas-solid flow principle, existing models are to complex to be suitable for design and optimizing of CFB unit. Understanging the thermal characteristic and establishing suitable models is the first step in order to improve the control strategy of large scale CFB boilers. In this work, the research is launched to 2 directions around thermal characteristic and modeling of the combustion system of the major large-scale CFB units.(1) Rearch on the practical way of industrial process identification based on the history dataToday, modelling theory and system identification technology have formed a completed system, but they are in an awkward position in practical industrial application. In this paper, the inadequacy of Least Square Identification(LSF) is first brought forward from its mathematical reasoning, then the concept is emphasized that the 2n-order persistent excitation condition is only sufficient and necessary in LSF. With describing the Asymtotic Theory(AT) when the transfer function model is used, the effectiveness of intelligent identification base on history operating data is proved. Meanwhile, practical engineering problems are considered, such as the standards of data selection and methods of data pretreatment. Cross-correlation function iterative method is provided to solve the delay-time identification problem. Method of transfer function's high speed simulation is given which avoids the output hook problem offten appeared in neural netword modelling and fuzzy modelling. At last, the identification software is developed.(2) Research on the combustion system's characteristic and modeling of ALSTOM large-scale CFB boilerAlstom 300MW CFB boiler occupies the most important market in China now. The main features of this kind of boiler are pant-legs structure and external heat exchanger design, which are for solving the secondary air weakness problem and strong coupling problem. However, the bed pressure imbalance problem and large inertia of combustion system are also brought out.In this work, the thermal characteristic of combustion sytem and pressure system on bed are firstly theoretically analyzed, then the linear transfer function models are set up based on selecting large amount of unit operating data, by which the quantitative results of delay time of the combustion system are given. At last, this paper has analyzed the bed inventory overturn phenomena. The results can be reference of the design or optimization of large-scale CFB boiler's control system.