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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The results of detailed computations performed for actual electric and heat loads, pressure in the condenser, and other operating parameters are used to consider the changes in the efficiency of operation of a T-250/300-240 turbine after the removal of moving blades of the last stages of the low-pressure cylinder. It is shown that the expediency of running the turbine with removed blades should be determined proceeding from the expected modes of operation of the cogeneration plant in question for the whole year.Experience in the operation of cogeneration turbines has shown that the inlet edges of moving blades of low-pressure stages experience considerable erosion wear. Blades of last stages of T-250/300-240 turbines, which have the greatest height (L = 940 mm) of all operating cogeneration turbines, are no exception [1].In this connection it has been suggested to solve the problem of their reliability "radically" by operating with removed moving blades of the last (31 and 40) stages (the baffles of these stages are preserved in order to prevent damage of the penultimate stages). The topics of economic expediency and efficiency of such operation for the turbosets considered came to the fore.When a low-pressure cylinder (LPC) operates without moving blades of the last stages, the production of internal power can either decrease or grow depending on the steam flow rate in the LPC and on the pressure in the condenser. At the same time, the available heat load of the turboset can be increased because it becomes possible to lower the minimum (ventilation) steam flows into the LPC necessary for maintaining the permissible thermal state of the exhaust part.It is hard to determine the efficiency of the engineering solution in question experimentally and to obtain an accurate enough estimate. Primarily, this is connected with the fact that the capacity of the LPC during testing is determined as the difference between the measured capacity of the whole of the turbine and the capacities of the HPC and both IPC calculated from the measured values of the pressures, temperatures, and steam flow rates. All the errors in the measurement of steam parameters, temperature differences, and efficiencies of the high-pressure and intermediate-pressure cylinders, and steam flows through them are summed and divided by the determined capacity of the low-pressure cylinder. In addition, the tests are performed at different times, i.e., before and after an overhaul of the turbine, which also influences the accuracy of the final result. The errors in the determination of the capacity of the LPC at low steam flows into the condenser, which are typical for cogeneration regimes and the most interesting for realization of the engineering solution considered, are especially high.Taking into account the circumstances mentioned we determined the efficiency of the updating using computational analysis based on the method of computation of quasi-stationary flows developed at the VTI in the 1970s and supplemented and advanced considerably by the presen...
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