Temperature State of the Last Cascades of Low Pressure Cylinders of Heat Turbines in Low Flow Rate Modes

Abstract

Operation of high-power turbines during the power grid regulation results in that the last cascades of low pressure section are switched over to the power consumption mode which results in additional energy losses. It is especially related to the heat turbines in which the operation modes are regulated by the rotary regulating orifice in the range of purely condensing flow rate to the flow rate that is actually close to a zero. The modes of power consumption by the last turbine cascades are attributed to low flow rate modes and are in the domain below the mode of idle running of the last cascade. Operation of the cascade with long blades in the domain of low flow-rate modes is accompanied by a high level of ventilation losses, and accordingly by the rise in steam temperature and it significantly affects its density. The suggested paper gives consideration to the approach used for the definition of power inputs in the cascades with low bushing ratio based on the use of Zutter-Traupel formula. A complicated character of a change in the steam temperature in the cascade for the domain of low flow-rate modes required to determine an averaged value of it as a function of the relative volumetric flow rate and correlate it to the steam temperature value measured behind the turbine wheel, based on the analysis of available experimental data. It allowed us to obtain the dependence of a change in the density on the pressure in the capacitor and the temperature measured at the turbine wheel output in the entire range of low flow-rate modes.