Dynamic Simulation Study On A New Strategy Of Boiler Superheated Steam Temperature Control

The boiler thermodynamic system plays an important part in the thermal generator set.In-depth research on its static and dynamic characteristics was an important study directionall the while in the past decades, which is still active up to the present. It is helpful tounderstand the dynamic performance of the whole unit to research on the dynamiccharacteristics of boiler thermodynamic system. It can provide evidences for performanceanalysis, operation optimization and failure diagnosis. And the mathematic dynamic modelcan also be used in the study of boiler control system. In this paper, the study actuality and development of modeling and simulation ofboiler thermodynamic system is reviewed at first. The basic situation of boiler automaticcontrol is introduced, and so does the application of the new control technology andstrategy in power station. Some basic knowledge of modeling and simulation ofthermodynamic system is introduced too, such as theoretic base of modeling and simulation,basic methods of modeling, distributed parameter model and lumped parameter model,basic procedure of modeling and simulation, and so on. In this paper the complete dynamic mathematic model of boiler superheat system isbuilt up, which includes one-dimensional distributed parameter model and lumpedparameter model of superheaters, mathematic model of spray-type desuperheaters,calculation model of thermodynamic property of water and steam, and calculation model ofthermodynamic and transportation property of flue gas. Using the superheat system of a300MW W-flame boiler as an example, several dynamic processes when the steam pressure,the mass flow of spray or the flue gas temperature changes are simulated. The variations ofsome main parameters are shown in curves. The results are analyzed and they can basicallyreflect the dynamic characteristics of boiler superheat system rightly. The flue gas outlettemperature calculation formula in simulation is given according to simulation experiences. During boiler operation superheated steam temperature must be kept in allowable IIrange and the temperature excursion must be rigidly controlled. Generally the excessivetemperature of flue gas is the main reason of the temperature excursion. Traditional boilersuperheated steam temperature control system regulates the mass flow of spray bydetecting superheated steam temperature and its change trend to control itself. With thedevelopment of control theory, some intelligent control technologies are applied in boilersuperheated steam temperature control. But they do not deal with the problem from thesource of the phenomenon. Whereas this, a new strategy of boiler superheated steam temperature control ispresented, which regulates the mass flow of spray ahead of time by detecting flue gastemperature and its change trend to control superheated steam temperature. The variation ofsuperheated steam temperature when the flue gas temperature and the mass flow of spraychange at the same time is simulated, and the validity of the control strategy is proved.According to the new strategy, a new superheated steam temperature control system isdesigned and its structural sketch map is given too.