Mathematical Models of Air-Cooled Condensers for Thermoelectric Units

The present paper deals with the use of air cooled condensers in thermoelectric units, such as steam power plants or combined cycle units. The paper describes the main features of air cooled condensers, showing the problems related to their use, such as the presence of non-condensable gases inside the steam flow or the condenser performances variability due to ambient conditions. The present study refers to A-frame air cooled condensers characterized by single-pass and multiple-row arrangement. A phenomenological study has been done in order to calculate the main physical parameters which describe the condenser operating conditions. In particular, three mathematical models have been developed: while both the first and the second model consider a condenser with tubes characterized by the same finned surface, with or without the use of throttling valves upstream of each tube, the third model examines the behaviour of a condenser with different row effectiveness. The three mathematical models permit also to investigate the possible vapour back flow inside each row of tubes, by calculating the axial coordinate value along each tube at which the condensing steam mass flow rate becomes null; the third mathematical model has been implemented in the Matlab/Simulink environment in order to couple the simulator of the condenser with the whole plant simulation model.