Effect of Operating Conditions of a T-250/300-240 Turbine on the Level of Wetness in the Stages of the Low-Pressure Cylinder

Abstract

The operation of the low-pressure turbine part in variable condensing and extraction regimes is analyzed. The effect of steam parameters at the inlet to the low-pressure part (in the lower extraction chamber) and of operation of the regulating stage of the LPP on the level of wetness in the low-pressure stages is determined. It is shown that the moving blades of the last stages of cogeneration turbines operate under heavier erosion conditions than in condensing turbines. This is one of the main causes of their intense erosion wear.Experience of operation of cogeneration turbines has shown that the entrance edges of moving blades of low-pressure stages undergo considerable erosion wear. Blades of the last stages of T-250/300-240-type turbines, the height of which (940 mm) is the greatest of all operating cogeneration turbines, are no exception. Today partial or full replacement of these blades is performed in virtually any overhaul of turbines of the cogeneration plants of the Mosénergo Company. The cost of a new set of blades is quite high. Repair replacement of the blades also costs much. The expensed can be reduced by 30 -40% by facing metal on partially damaged blades. Such technologies have been developed by a joint effort of TsRMZ and VTI and by the "Turboénergoservis-ÉK" Company. However, they have not found wide application yet and require further study and gaining of reconditioning experience.At the same time, for the greater part of year, the turbines of type T-250/300-240 serve in a heating (extraction) mode with partial opening of regulating diaphragms and reduced passage of steam to the low-pressure part (LPP). Under these conditions during the heating season the last stages operate in a ventilating mode and do not produce net power. In the summer months these turbines supply some heat to the hot water supply system and do not serve in a purely condensing mode, though their regulating diaphragms are fully opened. Under these conditions the production of power by the last stages is substantially lower than the rated output due to reduced steam flows and elevated pressure in the condenser as compared to the design values, which are determined by the circulation water temperature.These considerations show that it would be expedient to update the low-pressure part of the T-250/300-240 turbine by mounting shorter blades in the last stages, which should not only lower the intensity of erosion processes but also increase the efficiency of the turbine unit operating in the heating mode. The possibility of operation of such turbines without moving blades of the last stages is also being considered.Enhanced erosion wear of moving blades of cogeneration turbines as compared to condensing turbines is a result of some objective factors, the most important of which will be considered below.Effect of regime factors on development of erosion wear of moving blades of T-250/300-240 turbine. In condensing turbines and in cogeneration turbines operating in a purely condensing mode the maximum moisture content of steam in...

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