scope:

The present guideline deals with the specifications of the guideline VDI/VDE 3508 on the "unit control of thermal power plants" inasmuch as they concern power plants where all, or part, of the thermal energy for steam generation is drawn from the hot flue gases of a gas turbine which, in turn, contributes to power generation by the unit as a whole. The original explanations given in VDI/VDE 3508, Section 5.5 are limited to two types of processes or power plants typical of the technology of large-scale power plants. Upon closer examination, however, the application range of gas turbines in steam power plants proves to be much broader. In the course of time, a multitude of power plant types have been developed which must be treated quite differently as far as their control is concerned. Furthermore, no systematic and agreed terminology has so far been used for the different types. On the contrary, various abbreviations and designations such as CCPP (combined cycle power plant), gassteam power plant or compound power plant are often used, depending on which term was used first (historically), or on special company interests. With a view to desirable harmonisation, it was necessary to give precise terminological specifications; the designations chosen here are largely in line with the recommendations of VDI/VDE 3508, Section 4.4.

The present guideline treats the applications of gas turbines in so far as they contribute to steam generation in thermal power plants. First, the various technical types of power plants are classified systematically, and harmonised and clear designations are introduced for the different types. Then, the process characteristics and unit-control specifics of the principal power plant types are dealt with in greater detail. First of all, however, a list of definitions explains the most important terms which are still often used without a strict definition in general usage but used in an exclusive sense in this guideline.

By thermal power plants, this guideline, in accordance with the guideline VDI/VDE 3508, means steam power plants in the broadest sense, which are used as unit-type power plants. The scope of this guideline is thus technically limited in two different ways. On the one hand, although pure gas-turbine power plants appear to be unit-type power plants outwardly, they lack the water/steam cycle which is the principal subject of this guideline. On the other hand, common-header power plants, where several boilers supply steam to a common header which, in turn, supplies steam to one or several turbines, do not fall within the scope of unit control as specified in VDI/VDE 3508, on account of their conceptual design. These two types of power plants are, therefore, not included in the scope of this guideline.