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Heating Supply Reform Of Pure Condensing Turbines
Release time :
May 28,2026
Source :
Changing the original pure condensing unit to a cogeneration unit not only improves the economic efficiency of the power plant to a certain extent.
Changing the original pure condensing unit to a cogeneration unit not only improves the economic efficiency of the power plant to a certain extent, but also replaces the possible newly-built or existing scattered coal-fired or heavy oil-fired small boilers with large-capacity, high-parameter thermal power steam turbines for heating, achieving centralized heating. This can reduce the emission of air pollutants from boilers and is in line with the national environmental protection policy. With the continuous increase in fuel prices and water prices, the power generation cost of power plants has also increased accordingly. Therefore, finding new profit growth points is extremely urgent. Converting the original pure condensing unit to a cogeneration unit sacrifices a part of the power generation capacity to a certain extent, which will improve the economic efficiency of the power plant and thus alleviate the operating pressure of the power plant. The heating renovation of large-capacity pure condensing thermal power units is an inevitable trend in the future development of the thermal power market.
The design of the pure condensing unit does not consider the reserved steam extraction ports for heating; if the heating extraction steam is added, it will have an impact on the steam turbine body, flow passage, auxiliary equipment, control, and steam-water system.
The conventional heating parameters are roughly divided into the following grades:
(1) 4.0 MPa grade, above 400℃;
(2) 1.5 - 2.5 MPa, 300 - 400℃;
(3) 1.0 MPa, below 350℃;
(4) 0.3 - 0.6 MPa, below 350℃.
Extraction Method for Heating
The heating steam for thermal power generation units is divided into adjustable extraction steam (adjusting heating parameters within the turbine) and non-adjustable extraction steam (adjusting heating parameters externally).
1. Non-adjustable extraction steam
Non-adjustable extraction steam refers to extracting steam by drilling holes at corresponding positions on the turbine body or main steam pipe, reheated cold section pipe, hot section pipelines, and connecting pipes. The heating parameters change with the variation of the electrical load of the unit. The turbine itself has no regulating capability and needs to be reduced in temperature and pressure externally to meet the requirements of the heat users. To meet the unit's peak load requirements, the parameters of the extraction steam holes should be higher than the heating parameters. Generally, the principle adopted is 70% of the rated load. The parameters of the extraction steam holes can still meet the requirements of the heat users.
Theoretically, steam extraction can be conducted at any position of the turbine, but in practice, it is limited by the strength of the cylinder, the flow intensity, the position of the extraction steam, the impact of flow changes on the rotor thrust, etc.; the position of the extraction steam hole requires detailed thermal system calculation to ensure the normal, safe and stable operation of the equipment, and the position of the extraction steam opening is designed.
2. Adjustable Steam Extraction
The adjustable steam extraction refers to the method of adjusting through the internal mechanism of the turbine to meet the heating extraction steam parameters. The heating parameters within a certain operating condition are not affected by the electrical load of the unit. The heating parameters are variable values. The adjustment methods mainly include:
(1) Connecting pipe disc valve adjustment (as shown in Figure 1), used for the scheme where the heating extracting steam point is set in the middle row. It can meet adjustable extracting steam of 0.5 MPa, 0.8 - 1.0 MPa. This heating scheme is the most widely used.
(2) Seat cylinder valve adjustment (as shown in Figure 2), usually used for adjustable extraction steam with a pressure of 2 - 5 MPa. It can meet higher pressure industrial extraction steam. Due to the limitation of the unit structure, the seat cylinder valve adjustment can only be applied to the medium-pressure cylinder.
(3) Rotating diaphragm adjustment. Usually used for adjustable exhaust steam with a heating pressure of 1 - 1.5 MPa. It can meet higher pressure industrial exhaust steam.
For example, take the 30 MW steam turbine unit (produced by Jieneng) at a domestic waste incineration power plant recently upgraded by our company as an illustration (non-adjustable extraction type):
Heating Target:
Extraction pressure: 1.54 MPa (a);
Extraction temperature: 346°C;
Extraction flow rate: 35 t/h.
Heating Retrofit Scheme: Based on the unit characteristics and the power plant's heating parameter requirements, medium-pressure steam is extracted from the behind of the high-pressure steam chamber. The steam parameters meet the requirements of thermal users. The schematic thermal system diagram of the unit after retrofit is shown in the figure.
Post-renovation precautions:
(1) After the renovation, due to the addition of the extraction pipe, the "thermal capacity" of the steam turbine unit has increased. When the steam turbine unit sheds load, it is prone to a rapid increase in rotational speed. Therefore, some necessary safety measures must be taken to prevent such incidents. For example, adding extraction fast shut-off valves, extraction check valves, and safety valves on the extraction pipe can prevent steam from flowing back to the turbine flow passage in case of an accident, thereby suppressing the rapid increase in turbine speed.
(2) When the unit undergoes heating system renovation, the newly added extraction pipes and actuators, etc., should be properly considered during the specific layout, taking into account the actual situation of the power plant, and minimizing the impact on the normal operation and maintenance of the unit, or avoiding leaving potential accident hazards that could endanger the safety of the unit's operation.
(3) After the unit extracts steam for industrial use, the pressure difference corresponding to the extraction port in the turbine stage needs to be monitored. To ensure the minimum cooling flow of the unit, the pressure monitoring value of the low-pressure inlet steam needs to be increased.
References: Dongda Electric Power Design Institute
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