Influence of the reheat temperature on the efficiency of the wet-steam turbines of thermal power plants that operate under variable conditions

Abstract

A brief analysis of the existing methods for controlling the operating conditions of the turbine units that operate at variable loads is presented. In practice, the outdated rule of operation is most frequently used that states that the higher the parameters of the live and reheat steam and the lower the condenser pressure are, the higher is the efficiency of the turbine unit. However, in the technical literature, there is sufficiently substantiated evidence that this approach is not always correct, especially under low loads. This applies to both the regulation of the initial and final pressure and reheat temperature tr. In the article, particular stress is laid on the controllable parameter tr, the effect of which in the operational practices, according to the results of the analysis, is underestimated. The causes are considered that constrain more effective use of reheat temperature tr as a process variable. The results of field trials to investigate the influence of tr on the efficiency of turbine units of various capacities, viz., of 210, 250, 300, and 325 MW, during operation at varying loads are presented. It is shown that a decrease in tr to an optimal value of 10–30°C, depending on the load and the condenser pressure, increases the thermal efficiency by 1–2%. The following general pattern has been set: the lower the load, the lower the optimal reheat temperature. The main causes and factors that result in more efficient use of the heat phase transition in the steam path of the low-pressure cylinder and increased efficiency of the unit under rational choice of the reheat temperature are studied.