What is the difference between backpressure turbines and condensing turbines?

Back-pressure steam turbines do not have condensing equipment; the steam is extracted directly after being used for power generation. Common back-pressure turbines have relatively low power output, with a back-pressure of generally 1.0 MPa or 0.4 MPa, and they are usually connected to heat networks for use. Condensing steam turbines are equipped with a condenser to condense the steam that has done work; the condensed water is pressurized by a feedwater pump and sent to the boiler for reuse after passing through low- and high-pressure heaters as well as a deaerator. The system is more complex than that of backpressure units, and these turbines have higher power output, which is why they are used in all thermal power plants.

A turbine in which all steam, except for a small amount of regenerative extraction steam, enters the condenser is a condensing turbine. The exhaust steam from this type of turbine condenses into condensate water under the high vacuum conditions in the condenser. The latent heat of vaporization released during steam condensation is carried away by the cooling water (circulating water); since its temperature is already very low, it cannot be reused. Condensing steam turbines are characterized by low exhaust pressure, a large enthalpy drop of the steam within the turbine, the ability to achieve high power output, and relatively high economic efficiency. The exhaust steam from a back-pressure turbine is discharged from the turbine at a pressure higher than atmospheric pressure and supplied to heat end-users. The level of its exhaust pressure is determined by the needs of the heat users, and the amount of exhaust gas, which is also equivalent to the amount of steam supplied to the turbine, is likewise determined by the needs of the heat users. Therefore, the power of a back-pressure steam turbine is determined by the thermal load and cannot be changed independently; as a result, it cannot meet the requirements of both thermal and electrical (power) loads simultaneously. This type of unit is suitable for situations with relatively stable heat loads, and a condensing unit is provided additionally to regulate electrical loads. Another type of back-pressure unit has a relatively high exhaust pressure, which is used to supply steam to the low-pressure turbine. This type of back-pressure turbine is also known as a forward-mounted turbine.

In back-pressure steam turbines, the waste steam after doing work is directly discharged into the atmosphere, whereas in condensing turbines, specialized condensation equipment is used to condense the waste steam that has done work, so as to recover it.

The exhaust steam from a back-pressure turbine is discharged from the turbine at a pressure higher than atmospheric pressure and supplied to heat end-users. The level of its exhaust pressure is determined by the needs of the heat consumers, and the amount of exhaust steam, which is also equivalent to the amount of steam supplied to the turbine, is likewise determined by the needs of those heat consumers. The exhaust steam from this type of turbine condenses into condensate water under the high vacuum conditions in the condenser. The latent heat of vaporization released during steam condensation is carried away by the cooling water (circulating water); since its temperature is already very low, it cannot be reused.

In back-pressure steam turbines, the steam does not perform work completely before being extracted directly; the back-pressure is usually 1.0 MPa or 0.4 MPa, and such turbines are generally used in heat networks. In a condensing steam turbine, the steam does all of its work (with a back pressure at vacuum level), and specialized condensation equipment is used to condense the exhausted steam after it has done its work, so that it can be recovered.

Back-pressure turbines do not have condensers; their exhaust is released at a pressure higher than atmospheric pressure, and it is used directly for heating or industrial purposes. Double-condenser turbines, on the other hand, are equipped with condensers. With the exception of a small amount of exhaust that is used for regenerative cooling, most of the exhaust is released into the condenser under high vacuum conditions where it condenses into water. This water is then heated by a heater and sent back to the boiler via a feed pump, thus completing the steam cycle