Abstract
The paper discusses optimization issues related to start-ups from intermediate states defined as hot and warm, i.e. start-ups carried out after a few or several hours of downtime. Such start-ups are characterized by a non-uniform field of the initial temperature. For this reason, any simulation of start-up processes should be preceded by simulations of the cooling process to obtain a close-to-real temperature distribution at the moment when the start-up process is to begin. This is of particular importance in the case of elements in contact with the outer environment, such as outer casings and rotors. The simulation results indicate that it is possible to speed up the start-up procedure as recommended by the turbine manufacturer without exceeding allowable stresses in the turbine elements. Naturally, this will have a beneficial impact on the flexibility of the power unit operation. Rotors are characterized by the most difficult operating conditions and it is for them directly that start-ups should be optimized. The maximum start-up rate is determined by the initial temperature field of the turbine element material. For this reason, the paper presents a concept of initial heating of the turbine key elements. Running the process during the boiler heating and start-up might substantially shorten the total time needed to restore the power unit operation. Instead of sequential heating, the boiler heating and the turbine heating processes could be carried out in parallel.
Highlights
The changing structure of power systems and the new role of coal-fired power units which more and more often act as sources balancing the demand for electricity call for a change in the character of their operation [1]
The further part of this paper presents a discussion of problems related to the optimization of warm and hot start-ups, as start-ups from these thermal states will become dominant in the current operating conditions of power plants
The model of the turbine start-up optimization presented above indicates that the process of heating the turbine main elements can be accelerated safely, which means that it is possible to shorten the start-up time
Summary
The changing structure of power systems and the new role of coal-fired power units which more and more often act as sources balancing the demand for electricity call for a change in the character of their operation [1]. This means that coal-fired power units have to be able to respond appropriately to rapid and substantial variations in loads and they must have the capacity for shortening the start-up time, especially after a few or several hours of downtime Considering that these requirements increase the thermal load of individual elements of power units and taking account of the relatively long service life, new and optimal operating conditions have to be determined to ensure adequate safety of the power plant future operation in the new analysis under cold start-up conditions to establish an online damage-monitoring model of a steam turbine rotor. Numerical models of the turbine elements, as well as details of thermal and flow analyses and the selection of boundary conditions, are described e.g. in [12, 13]
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