Study On Modelling And Intelligent Control System Of Circulating Fluidized Bed Boilers

The Circulating Fluidized Bed Boiler (CFBB), which pollutes the environment less, has been widely applied in power and cogeneration industry due to its advantages such as high combustion efficiency, fuel adaptation. However, the application of CFBB is far from perfect because it is a multivariate coupling with distribution parameters, nonlinear, and time-vary characteristics. The thermo technical control is the main factor that prevents the CFBB from commercial application. Therefore, this thesis is elaborated from the following four aspects.1. Study on control model of CFBB bed temperatureUp till now, a concise system mathematical model has not been set up yet because the circulating fluidized bed boiler is a multivariate coupling featured by distributive parameters, non-linear, and time-variation. Combustion model and steam pressure model are established after analyzing the kinetic hydrodynamic and dominant factors affecting CFBB bed temperature. The stimulation and the field test have showed that the above-mentioned models are able to reflect accurately the bed temperature changes when fuel feed rate disturbance occurs, which provided theoretical basis for the CFBB operation and controller design.2. Study on CFBB load controlObserved from the local operation, the CFBB load will change according to the bed temperature that corresponds to unequal load. Variation of the fuel feed alters the bed temperature at first, and then the boiler load. Conversely, the quantity of fuel feed will reflect the variation at bed temperature. Therefore, cascade control is put forward in the thesis. Together with the application of predictive fuzzy algorithm, the cascade control eliminates the steam pressure fluctuation caused by fuel feed disturbance, thus adding stability of the control system and at the same time reducing system overshot.The controller has been designed based on the comustion model. The simulation and industry application show that satisfactory results have been achieved.3. Study on CFBB sup-heated steam temperatureThe sup-heated steam temperature is a complicated process control system which requires high precision and is also time-delaying, time-variation and inertia as well. Therefore, stronger robusticity and self-adaptation are indispensable to overcome the time-variation and to ensure the control precision. To solve the problem, the thesis presents multi-objective optimal algorithm after perfecting the artificial neuron net PID(NN-PID) controller. Compared with the existing PID, the new algorithm is satisfactory for its shorter transient period, lower over shoot, robustness and adaptive ability. Moreover, the new algorithm has faster responding rate compared with PID algorithm. These satisfactory results have been achieved when it was applied in the industry process and stimulation of the super-heated steam temperature control system.4. Study of CFBB Performance CalculationCFBB is widely used in power industry because of high efficiency and lower environmental pollution. As a new technology the combustion technology has aroused heated discussions about its performance calculation. However, so far no official criterion about the CFBB performance calculation has been established. Based on desulphurizing model, the thesis proposes a method, which takes into account the changes of heat loss calculation owing to limestone injection. The method has been put into practical uses in 13Ot/h CFBB performance calculation and optimization at Susheng cogeneration plant.