About Modeling and Simulation of Heat Exchange Convective Surfaces of the Steam Generator
Abstract
Among the priority issues that the modern society has to be solved, include also the energy and environmental issues. The notion of control (process control) has expanded in recent years, encompassing new areas such as automatic control of quality, the data processing with decisional purpose for one strategic leadership, ensuring uninterrupted of the system maintainability and thus, security and viability of the entire ensemble. In this context are part and the simplified simulation methods of the energetic installations from the power plants. The paper expose, in the first part, the importance of the steam generator in the operation of power plants, presents the energy processes complexity, emphasizing the importance of their management and automation to increase energy efficiency of each link in the chain. Then, taking as its starting point the real operational aspects, the mathematical modeling, the simulation and automatic control of steam generator, the paper proposes the development of a mathematical model in absolute units and the simulation the operation of a convective heat exchange surface of the steam generator in steady and dynamic regime.
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Introduction
The paper presents a study for the application about the steam generators in terms of modeling and simulation of their operation in steady and dynamic regime in power plants. Treat modeling itself of steam generator: it is based on physical model of each heat exchange surfaces, simplifying assumptions adopted, equations for conservation of mass, energy and momentum and the heat transfer equations. Also is presented the model in relative units imposed by the literature - highlighting the entire set of mathematical equations the processes occurring in the installation, the coefficients given in the literature, and the disadvantages involved in its use. Then, as an alternative, is proposed the steam generator model in absolute units: processing of the basic equations, are highlighted development its advantages - eliminating the recalculation sequence of parameters at each step, eliminating the linearization around the stabilized operating point, nonlinear characteristics are included in the model, determining the coefficients of thermal heat exchange between agents and the exchange surfaces in real-time, and the disadvantages involved in its use. The theoretical model proposed, in absolute units, implemented in Matlab-Simulink, leads to the simulations of the operating in dynamic regime for all components of steam generator. The model provides information about the influence of each parameter - input and output (pressure, temperature, and flow for water supply, combustion gases) on monitored parameters, namely pressure and temperature live steam. The results from the simulation are compared with values measured for parameters in real operation. The aim was to provide information allowing analysis of the model of each heat exchange surfaces on the one hand and on the other hand time for calculation to be within the real time operation. The steam generator model can be completed with the modules of the turbine-generator group with their installations and internal services and of the electrical part of power plant. All these models of the stationary and dynamic regimes can be implemented in computer systems and leads to the creation of a system for the management and control in electrical and thermal energy supply.
Conclusion
The model in absolute units is the basis for simulating the operation of the dynamic steam generator, [7]. He presents the major advantage of eliminating the sequence of recalculation of parameters at each step - in the models in relative units the whole set of coefficients is determined and entered into the model according to the parameters achieved in a previous reference regime; eliminates linearization around the stabilized operating point, nonlinear features being included in the model; it finds its own non-linear function points and updates parameter values; allows the determination of heat exchange coefficients between thermal agents and real-time exchange surfaces, their values obtained by computing within the limits recommended by the literature; removes the empirically determined coefficients, including the calculated exchange coefficients, from the heat exchanges exchanged between the thermal agents; it is characterized, with all its advantages presented above, as a slower model - relative to the one in relative units - due to the iterative calculation. The model in absolute units can be the basis for an intelligent system for simulation in real time operation of a steam generator. It is recommended to develop on other energy equipment. This supposes mathematical models in absolute units for the turbine and the electric generator, simulations of their static and dynamic regimes operation.