THERMAL STATE OF THE LOW-PRESSURE CYLINDER WORKING BLADES OF THE COGENERATION TURBINE T-250/300-240

Abstract

The important problem of researching the temperature state of the low-pressure cylinder of a powerful cogeneration turbine, which works, unlike condensing turbines, in conditions of significant changes in electrical and thermal load, is considered. This is since the low-pressure cylinder of the cogeneration turbines in the heating season operates at the low-flow rate modes due to the large selection of steam for heating. Such operating conditions are accompanied by the nucleation of vortex structures in the flow path, which leads to a significant increase in mechanical energy losses and, consequently, to an increase in the temperature of the elements of the flow path. The aim of the study is to determine the thermal state of the steam in a wide range of changes in the operation modes of the cogeneration turbine. The analysis of the results of experimental studies obtained on full-scale low-pressure cylinders of a powerful T-250/300-240 steam turbine by various authors in conditions of wide changes in operating parameters (the pressure in the condenser, the steam consumption in the flow path, the temperature of the lower heating selection) was performed. This made it possible to determine the temperature distribution along the height of the working blade of the last stage, which is of the greatest interest in the conditions of operation at the low-flow rate modes. The location of the minimum temperature is established, and a dependence is proposed for its determination at the exit from the working wheel of the stage, considering that the main generator of heat during steam heating is a rotating vortex in the rim clearance. It is shown that the limiting value of steam consumption through the last stage, which corresponds to the transition of the flow from the area of wet steam to the area of superheated steam, at a given temperature level in the lower heating selection, depends on the pressure in the condenser and can be determined as a function of these parameters. At the same time, with a decrease in the temperature in the lower heating selection and the pressure in the condenser, it will lead to the fact that the transition from the west steam to the superheated steam is observed at lower consumption. The increase of process moisture at the outlet of the working wheel occurs when the steam flow is greater than its limiting value.