OPTIMIZATION OF START-UP PROCESSES AT HRSG WITH NATURAL CIRCULATION SYSTEM

摘要

The demand for high flexibility within a stable energy supply is nowadays required. Combined cycle power plants (CCPP) gain therefore more and more importance. Due to their rapid response on demand they are capable to compensate power-grid fluctuations. Within this study some parameters for the limits of start-up as well as load change behavior of heat recovery steam generators with natural circulation system will be discussed. In the first step a simulation model is developed which is compared and validated by measurements at different start-up processes of a HRSG. As one result it may be concluded that a relative simply quasi-steady approximation reveals appropriate results. However, still more exact findings are reached by means of a complete transient simulation. In the second step the optimization of the start-up process will be analyzed with aim to minimize this time period. For limitations as well as economic reasons beside the nature of the start-up process and the applied materials, all thick walled components e.g. steam drum and steam headers have to be considered for maximum allowable gradients. For boilers with requirements for short start-up times it can be helpful to conduct additionally a comprehensive FEM calculation. For a deeper detail discussion of some parts of this study it may be referred to [1] and [7]. Based on the analyses it is possible to specify parameters for a dynamic boiler simulation to estimate the start-up thereof. Ideally, one should in practice install a differential temperature measurement in the drum shell and assign the allowable temperature differences to the actual pressure to comply with the limits. In this way, it would be possible to optimally design the start-up process in relation to the start-up time according to actual values.