DYNAMIC ANALYSIS OF THE AIR GAS PATH OF FOSSIL FUEL POWER PLANTS

Abstract

In this work a dynamic analysis for the air-gas path of a balanced draft boiler is presented. As is well known, in this part of the plant large and rapid pressure variations can arise in particular situations (for instance in case of fuel trip) which can cause damage to mechanical structures. To achieve a basis of evaluation of these phenomena, a mathematical model of the air-gas system has been developped; the system has been divided into subsystems (fans, air and gas ducts, furnace, air preheaters, dampers) and for each of them a first principles mathematical model has been written. The submodels have then been coupled together to obtain the description of the whole system. This task has been accomplished automatically by means of a suitable “computer aided modelling” code, described in detail in (Marcocci and Spelta, 1983). Owing to this modular approach, a wide range of possible plant configurations can be represented. This paper first describes the models of the principal subsystems and the criteria which have been followed to represent with acceptable accuracy the main phenomena involved; a practical application to the air gas path of a real power plant in then presented, and the results obtained in the most critical situations are discussed, with particular attention to operating strategies and control system evaluation.