Q&A – What is a Back Pressure Turbine and what is a Condensing Turbine?

Back Pressure Turbines: a type of steam turbine that is used in connection with industrial processes where there is a need for low or medium pressure steam. The high pressure steam enters the back pressure steam turbine and while the steam expands – part of its thermal energy is converted into mechanical energy. The mechanical energy is used to run an electric generator or mechanical equipment, such as pumps, fans, compressors etc.

The outlet steam leaves the back pressure steam turbine at “overpressure” and then the steam returns to the plant for process steam application such as heating or drying purposes.

Back Pressure Turbine

Condensing Turbines: Inside a condensing turbine – the steam expands below the atmospheric pressure and then “condenses” while heating the cooling water in a condenser.

After the steam exits the outlet of the condensing turbine, the steam’s pressure is so low; it is no longer available for providing power for industrial applications. Condensing turbines could be used in industrial power plants as condensing tails connected to back-pressure turbines. In cases of low demand for process steam the steam surplus is run through the condensing tail to generate more power.  A condensing turbine does not differ much from a back-pressure turbine in respect of its’ overall dimensions, steam values (with the exception of outlet pressure), delivery time and price.  The steam condensing equipment requires some additional “balance of plant” investments plus the availability of cooling water.  A 1 MW condensing turbine plant needs about 0.1 m3/s of cooling water.

Condensing Steam Turbine

This text is an extract from questions gathered from numerous queries of anonymous people in the Piping Engineering and Design profession. The answers or discussion of the topics were provided by James O. Pennock. Images obtained from www.coastalflange.com