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A extraction steam turbine is a turbine that extracts a portion of the steam from its intermediate stages to supply it to users, thereby providing heat in addition to generating electricity. It can be designed as a single-stage extraction type or a two-stage extraction type according to user requirements. A single-stage extraction steam turbine, also known as a single-extraction steam turbine. It consists of a high-pressure section and a low-pressure section, equivalent to a combination of a backpressure turbine and a condensing turbine. The new steam enters the high-pressure section to do work; after expanding to a certain pressure, it splits into two streams – one of which is drawn off to supply heat users, while the other enters the low-pressure section to continue expanding and doing work, before being discharged into the condenser. The designed extraction steam pressure is determined based on the requirements of the heat users, and is controlled by a pressure regulator to maintain stable extraction steam pressure. The power of a single-suction steam turbine is the sum of the powers generated by the high-pressure and low-pressure sections, and it is determined by the amount of steam supplied and the amount of steam flowing through the low-pressure section. Adjusting the steam inlet volume can yield different power levels. Therefore, to a certain extent, the thermal and electrical load requirements can be met simultaneously. A single-suction steam turbine, when the heating steam extraction amount is zero, is equivalent to a condensing steam turbine ； If all the steam entering the high-pressure cylinder is extracted and supplied to heat users, it is equivalent to a backpressure turbine. However, in actual operation, in order to cool the low-pressure cylinder and remove the heat generated by aerodynamic friction losses, a certain amount of steam must flow through the low-pressure section into the condenser; the minimum flow rate required is approximately 10% of the designed flow rate of the low-pressure cylinder. The operating conditions of a single extraction steam turbine are shown in the figure, which illustrates the relationship among the amount of fresh steam (Do), the amount of extracted steam (Ce), and electrical power (Ni) ； In the graph, Do represents the condensation volume; the ohh line denotes the condensation condition when the extraction volume is zero, while the cdd line represents the backpressure condition when the extraction volume is equal to the amount of fresh steam. Between these two lines lie the lines corresponding to constant extraction volume and constant condensation volume; they show the relationship between the total mechanical power and steam flow rate at different extraction volumes and different condensation volumes. The maximum electrical power of the steam turbine generator set at the maximum extraction rate is shown at point e in the figure; in the figure, if any two of the four values Do, De, Do, and Ni are known, the other two values can be calculated. Second-stage extraction steam turbine, also known as dual-extraction steam turbine. It can meet thermal load requirements with different parameters simultaneously. The entire steam turbine is divided into high, medium, and low-pressure sections. The new steam enters the high-pressure section to do work, expands to a certain pressure, and a portion of the steam is extracted to supply heat users ； Another portion enters the medium-pressure section to continue expanding and doing work; then a part of it is extracted for heating, while the remaining steam is discharged to the condenser through the low-pressure section. The performance curves of double-suction steam turbines are drawn based on certain typical systems and rated parameters. If the operating conditions of the turbine differ from those at which the curves were drawn, appropriate corrections should be made. In regulated extraction steam turbines, a steam distribution mechanism is provided separately for each cylinder, to control the amount of steam supplied to each cylinder individually. The steam distribution mechanisms for medium and low-pressure cylinders come in two forms: control valves and rotating diaphragms. For steam extraction units with lower power, the use of a rotating baffle facilitates the design of a single-cylinder structure ； High-pressure cylinders generally use nozzle regulation, with most regulation stages being double-row types to ensure a sufficiently large flow capacity. Double-suction steam turbines achieve high power generation efficiency when the flow rates in both the high-pressure and low-pressure cylinders are close to the design values. Due to changes in the heat load, the flow rate through each cylinder can sometimes vary significantly, resulting in lower power generation efficiency under certain operating conditions. Therefore, the regulation of extraction steam turbines should be designed based on the main thermal load, with the flow rates to each cylinder allocated reasonably to ensure high economic efficiency during long-term operation. The proper selection of the extraction pressure has a significant impact on the economic efficiency of the unit; under the condition of satisfying the heat users’ needs, the extraction pressure should be reduced as much as possible. In the early models of heating steam extraction units, the steam extraction pressure was between 0.12 and 0.25 MPa; in recent years, this lower limit has been reduced to 0.07 MPa.