Novel cylinder switching heating system of 300 MW grade subcritical steam extraction and condensing unit

The invention relates to the technical field of unit transformation, in particular to a novel cylinder switching and heating system of a 300 MW grade subcritical steam extraction and condensing unit.The system comprises a boiler, a high-pressure cylinder and a heating network heater; when the demand for heat supply in winter is large, a low-pressure cylinder is switched to operate, a middle-low-pressure cylinder communicates with a steam heating network heater so as to provide heat for heat supply and water supply, condensate water return water of the heating network heater passes through a heating network booster pump to return to a main condensate water system after a condensate pump so as to recover heat of condensed water of the heating network heater, and the loss of the heat after entering a condenser is avoided; the condensed water of the heating network heater can be connected to the main condensed water system in front of a shaft seal heater, the shaft seal heater can be guaranteed to have enough con