Cfbb Unit Advanced Control Methods Applied Research

Circulating Fluidized Bed Boiler(abbr. CFBB or CFB Boiler) is becoming the main coal combustion technique all over the world for its advantages of high combustion efficiecy, efficient sulfur removal, low NO₂ emission, fuel flexibility, good load-following capability and simple fuel making system . The small and medium-sized CFBB had been developed well, because of the fast development of more than ten years. Now the CFBB research is mainly on the large scale problem. Every CFBB manufacturers and research setups pay much emphases on the development of large size CFBB.With the large size CFBB development, there are controlling characteristics and difficulties, especially the safety and economy of the set. The large scale CFBB make the water circulating to be accelerated, and easily to be unstable. The drum water level, the steam temperature and the main steam pressure is the sign of CFBB safe running , and they are difficulties on CFBB control. It is important to have good control on the water system and load system. Because large scale CFBB sets are complex thermal processes which are generally strongly coupled ,nonlinear and time varying systems with large settling times and a lot of uncertainties, it is undependable for the operator to tune the parameter of the controller manually. It is hardly to attain the best control result with the traditional fixed parameter of controller. We must change the model parameter in time to get online system model identification, when there are large varieties on system dynamic characteristic; then tune the parameters of PI or PID controller to control the process well.The simulation results and practical operation of the large scale CFBB set prove that advanced control techniquescan successfully solve the set's automatic control problems. Automatic operation can give greater economic benefit to thermal power enterprises,cut down energy consumption of the process of thermal power production and reduce incidence of equipment and installations failure.After the study of characteristics and difficulties and shortage in large size CFBB control system, a approach of SISO and MIMO system model identification suited applying on engineering is proposed based on step response tests and Fast Fourier Transform Algorithm and refined nonlinear least-squares. The approach has been used in MATLAB software on drum water level system and steam temperature system and load control system. And the simulation results are better than the results of traditional design.Because of the structure limit of PI or PID controller with fixed parameters in the traditional feed-back control of the CFBB set drum water level process , its control performance will be poor based on the process model obtained beforehand when it is used to control such process. A high performance feedback control system design method is proposed for drum water level integrating process, by integrating fuzzy self-tuning with relay feedback auto-tuning technique. This will ensure the process to run well in complex operating conditions. This novel scheme is effective in other process control systems with integrating process.In thermal power plants the CFBB set drum water level process is a typical non-self-regulating (integrating) process with lots of disturbances and other uncertainties. A refined DMC predictive control approach is ' proposed for this non-self-regulating process. The algorithm modifies the shifting matrix of original DMC . A engineering software package is programmed based on the refined DMC approach. The software isembedded in DCS control system. This help to realize the dynamic optimization control in 130t/h CFBB set water drum level process of a thermal power plant,and good engineering results are obtained. It is important for large size CFBB set to run safely, stably and economically.Some problems needed to explor and research further in the future are proposed in the end.