The Research Of The Drum Level Dynamic Simulation Modeling Based On Level Sloshing

Drum level sloshing is a negative phenomenon under the operation of Combined Cycle Heat Recovery Steam Generator(HRSG), but, at present there are still no effective means to control or eliminate it. With the increased requirements that the combined cycle has for drum level controlling, how to build the model of drum level sloshing, how to study the rules of drum level sloshing, and how to eliminate the negative effect that the drum level sloshing brings to the control system already become a challenging research object. Under the support of International Co-operation Project[200310] and National Natural Science Foundation[5997022], the mechanism of drum level sloshing was analyzed, according to hydrodynamics and thermodynamics characteristic in drum, corresponding hydrodynamics and thermodynamics models were set up respectively, so the drum level dynamic simulation model based on level sloshing was set up using the knowledge from the two models. Dynamic simulation was done based on the model, the influence rules that some factors bring to the level sloshing were got, simulation research of drum level controlling was carried out based on the model, how to eliminate the negative effect that the drum level sloshing brings to the level control system was discussed. Main research work done in the paper was listed as following:1 Modeling and Dynamic Simulation Research of Hydrodynamics Model of Drum LevelThe method of modular modeling was adopted in this paper, module dividing of drum was done alone drum length direction, and according to the mass and momentum conservation laws, drum sub-modules were built. And hydrodynamics model of drum level was also set up based on the Easy5 software platform, the simulation research was carried out on the model, conclusion and some rules of drum level sloshing were obtained as follows: The drum level and drum length have much influence on the drum level sloshing, liquid density has little effect on the period of drum level sloshing, but the amplitude of drum level sloshing increases as the liquid density decreasing. As the period of level sloshing, non-uniformity division of module has little effect on modeling, and the numbers of sub-modules almost has no effect on modeling within certain range too. The important theoretic base and method in this research were provided for building the drum level dynamic simulation model based on level sloshing.2 Experiment Validation of Hydrodynamics Model of Drum LevelThe experiment rig was designed, and the experiment equipment was also set up. The experiment results show: As the validation of sloshing period under different levels, maximum error between the results of the experiment and the model is within±10%. As the experiment validation of model under in-and-output flux, changing trends of results of the model and the experiment are consistent, though there is some error in sloshing amplitude, the numeric error is within±20%. So hydrodynamic characteristics in drum can be simulated reasonably by the hydrodynamics model.3 Modeling and Dynamic Simulation Research of Thermodynamics Model of Drum LevelBased on Easy 5 simulation software platform, the model of lumped parameter was set up using method of lumped parameter, and this model was taken as the reference model. Module division was deeply done according to the requirements of modeling of thermodynamics model of drum level, and the problem caused by module division was analyzed, and four methods of modeling were proposed to solve the problems. The modules were built for the mixture and the steam respectively, and the mixture sub-module and the steam sub-module were obtained, based on these two kinds of sub-modules, and according to the proposed four proposed methods, corresponding four kinds of models were obtained. In order to ensure the reasonable modeling method for thermodynamics model, by adopting these four kinds of models and the reference model, the typical thermodynamics characteristic in drum-the dynamic process of"false level"were dynamically simulated, the results of simulation indicate: The modeling method of considering the changing rates of pressure and volume simultaneously is more reasonable, it's simulation result can be consistent with the result of the reference model, and the numeric error is within±5%, so, this method can be used to build thermodynamics model of drum level. Work done in this paper established an important foundation for modeling of drum level dynamic simulation model based on sloshing.4 Modeling and Dynamic Simulation Research of Drum Level Dynamic Simulation Model Based on Level SloshingBased on the modeling knowledge from hydrodynamics and thermodynamics models, and module division of drum level dynamic simulation model was considered reasonably according to configuration of field drum, 2-D drum level dynamic simulation model based on level sloshing was set up by adopting mass,momentum and energy conservation laws. Theoretical validations of the model were carried out respectively on thermodynamics and hydrodynamics, the result indicates that the thermodynamics and hydrodynamic characteristics in drum can be reflected well by the model.Based on the drum level dynamic simulation model, the influence rules that some factors bring to the drum level sloshing were studied, the results indicate: With the feed-water flowrate decreasing, and the main-steam flowrate and the heating quantity increasing, the frequency of level sloshing decreases, on the contrary, with the feed-water flowrate increasing, and the main-steam flowrate and the heating quantity decreasing, the frequency of level sloshing increases.5 Dynamic Simulation Research of Drum Level ControllingThe dynamic simulation model of HRSG based on level sloshing was set up, the model includes the Economizer module, superheater module, volume module, evaporator module etc, and the filter of drum level sloshing noise was designed according to the characteristics of drum level sloshing frequency. Based on the model, some simulation research was carried out for the drum level controlling, the results of simulation research indicate: With the noise of drum level sloshing being considered, and the filter of drum level sloshing noise being introduced, drum level sloshing noise is filtered to some degree, and the influence that the sloshing noise brings to the PI controller is eliminated in some extent, the"false level"is controlled effectively, and the frequent action of the control system become moderate, the wave action of whole drum level also get relatively milder.