Types of Steam Turbines

15 Jul

All steam turbines can be classified into two categories; extraction (condensing) steam turbine and non-condensing steam turbine also known as back pressure steam turbines.  Both of these steam turbine types have their own operating schemes and benefits which are described here in detail.

Extraction Steam Turbine

Figure 1: Extraction (condensing) steam turbine

The extraction turbine contains two outlets as shown in figure 1. The first outlet extracts the steam with intermediate pressure for the feeding of the heating process while the second outlet extracts the remaining steam with low-pressure steam for the condensation. The extraction of heat from the first outlet can be stopped to generate more output. Steam control valves at this outlet make this steam very flexible and allow adjusting the output as per demand.  The steam from the second outlet goes to the condensation chamber where cooling water brings the temperature of the steam down. The condensed water then goes back to the boiler for the regeneration of the electricity of power, therefore, it is also known as the regenerative steam turbine. The scheme of extraction turbine with cogeneration system is shown in figure 1. This turbine has following benefits and disadvantages.


  • This type of steam turbine can be used to generate a high amount of electricity.
  • It is a flexible turbine with the ability to regulate output as per changing need.


  • It is costly turbine with lots of auxiliary components
  • Heat rejection in the condensation process reduces the overall efficiency of the system.
  • It is usually used on industrial level and requires complex configuration

Figure 1: Extraction (condensing) steam turbine with cogeneration system

Back Process Steam Turbine

The non-condensing steam turbine uses high-pressure steam for the rotation of blades. This steam then leaves the turbine at the atmospheric pressure or lower pressure. The pressure of outlet steam depends on in the load, therefore, this turbine is also known as the back-pressure steam turbine. This low-pressure steam uses for processing and no steam is used for condensation. The schematic diagram of the back process steam turbine with cogeneration system is shown in figure 2. There are lots of benefits of this steam turbine but at the same time it has few disadvantages which are listed below.


  • The configuration of this steam turbine is very simple
  • It is relatively inexpensive as compared to extraction steam turbine
  • It requires very less or no cooling water
  • Its efficiency is higher as it does not reject heat in the condensation process


  • The biggest disadvantage of this type of steam turbine is that it is highly inflexible. The output of this turbine can’t be regulated as it does not allow changing the pressure and temperature of steam in the turbine, therefore, it works best with the constant load.
  • The thermal load of this turbine defines the flow of steam mass which makes it difficult to change the output value. Other methods to regulate output reduce the efficiency of the overall system.

Figure 2: Non-Condensing (Back-Pressure) Steam Turbine

37 thoughts on “Types of Steam Turbines

  1. Dear

    i want some knowledge about performance of steam turbine if operated at slight higher back pressure (1.2 kg/sq Cm) than the design (0.9 kg/sq Cm). is there any mechanical demage harm to steam turbine?

    • Dear Sana,
      more the pressure of the exhaust steam , more power you compromised.
      i.e. the power generated at 0.9ksc (exhaust pressure) is 1MW ( for eg), and if we make the exhaust pressure as 1.2ksc, this means we lost the power which we could have generated from the pressure drop of 0.3ksc (1.2-0.9).

  2. Sir i need some details, how much velocity required for rotating for this turbine anda head leangth and which types of generator used

  3. My partner and I absolutely love your blog and find many of your post’s to be just what I’m looking for. Would you offer guest writers to write content for you personally? I wouldn’t mind publishing a post or elaborating on some of the subjects you write regarding here. Again, awesome website!

  4. i am dharmendra working as an Sr. mechanical engineer in patil group . i am interested in power generation please give the details of all turbine 7 his working principal


  5. hi,

    i had a few queries with respect to the CHP process:

    1) With extraction, fuel consumption will be higher as compared to power only system. Is my assumption correct?

    2) If steam is not being extracted, then can the same amount of fuel be used to generate a higher amount of power or is it a sunk cost and power generation is limited to rated output irrespective of whether steam is being extracted or not?


    • dear sameer,

      yes with the extraction fuel consumption is higher as compared to fully condensing mode bcs in the full extraction mode we have utilized the all energy of steam means atmospheric pressure to condensing pressure (0.17 bar) which gives 15-20 % extra power.

    • Dear Sameer,
      1. The power from extraction turbine is generated as an advantage of the generated steam, though our prime use of steam is for processes. i.e. for any process if we need to generate steam ,it is advantageous to increase the capital and operation cost to generate steam of higher pressure and temperature as needed in the process. through this we can generate power as a by-product at very optimized cost.
      for eg. – if you need to construct 3 rooms for your need in your house, and suddenly you realise that you can make extra 2 rooms for optimized increased construction cost for tenants and will make income out of it .
      2. The generated power is directly proportional to the amount and pressure and temperature of the steam , but limitation is the metallurgy of the blades and casing of turbine and the rating of alternator.This means we cannot go beyond the rated capacity of turbine and alternator due to metallurgy limitations.

      Hope this will help you a bit

      • we need extraction steam for processes. If we purchase higher extraction capacity steam turbine in case we need more extraction in the future, how efficiency is affected when we use the turbine at low extraction. For example;

        steam turbine which have 160 ton/h extraction capacity, works at 130 ton/h extraction and 50 MW
        steam turbine which have 220 ton/h extraction capacity, works at 130 ton/h extraction and 50 MW

        which is more efficient in this case?

  6. Hello Sir I personally thanking you that there is lot useful stuff and basic of turbine, I am a student of Master in Engineering and want to know more about steam turbine as I want to further work on it. Actually I want to know that how much pressure and temperature required to run steam turbine and is it possible to make 2-3 Kw capacity turbine ??? Sir if you know contact me as early as possible because in this week i have to finalize my topic and have to work on it.

  7. I read a lot of interesting posts here. Probably you spend a lot of time writing, i know how to save you
    a lot of time, there is an online tool that creates high quality, SEO friendly
    posts in minutes, just search in google – laranitas free content

  8. I am diwakar singh I working in nahar group in power plan sir please give me details of formula use in calculation of 1steam velocity, 2 turbine heat rate ,3 turbine efficiency

  9. I am unable to understand the exact difference between the back pressure and extraction turbine.

    Is it correct to call an extraction type of turbine a back pressure turbine if we are not condensing steam.

    Thanks for the reply in advance.

    • hi…..I m Mani,studying diploma in mechanical engineering.
      Is any turbine like impulse-reaction turbine.. If any what’s its working principle

  10. Dear Sir 1
    I going to by condensed turbine , with capacity 25 MW h , we need to extract only 35 ton low pressure steam 3 bar and the rest will be condensate water . How much steam consumption needed for MW ? ( steam used 41 bar 370 C)
    Best regards
    Mohamed mill manager for Edfu pulp and paper mill

  11. Pingback: Steam Turbine Efficiency - Turbines Info

  12. “Its efficiency is higher as it does not reject heat in the condensation process”

    I think this statement is invalid. Absolutely, based on second law of thermodynamic, you HAVE to reject heat to obtain mechanical work. Back-pressure turbine also rejects heat. It is just not through the condensation process, but directly exhausted to the atmosphere.


    • Hey John!

      I’m not absolutely clear by what you mean by ‘function performing’…perhaps you can elaborate that.
      From my understanding, you want to know that why are we using such,different types of turbines…
      Well see , there can be different uses of steam right? It can be either condensed again into water and used again as required, or it can be used for heating purposes, or it can be sent to any plants for process requirements.
      Depending on all such various factors, it is decided by the company and the OEM/vendor for the type of turbine to be used, which will be able to satisfy the requirements of the company, be it (electric) power generation or driving an equipment or whatever else there can be…Thus the turbines can have different construction to meet up with desired ‘functionality’.
      I suggest you please read my reply on a comment below as well, to Akhil.
      Hope it helps…Please let me know.

      – Akshay Bhargava

  13. Helo sir
    Some turbine are known as condensation type knwn as extraction and bck pressure known as non condensation but in our organisation a turbine is here is called back pressure extraction turbine. Plz say about it. And clear my confusion

    • Hello Akhil.
      I’ll share my views on your query, hope it helps!
      See, in a back pressure turbine, the exhaust pressure is generally bit below the atmospheric pressure, and the turbine efficiency depends on the press. difference at inlet and exhaust as well. Here, no steam is taken at an intermediate stage for any use. Please note that the steam can be ‘tapped’ from an intermediate stage for different uses like for processes (can be sent to plants which require steam), for heating etc. Hence entire steam mass flow at inlet is obtained at outlet.
      In extraction/condensing type turbines, steam is tapped in between and a part of steam mass is sent for above mentioned uses. The remaining steam is used to drive low-pressure stage of the turbine. The steam after LP stage is then sent to a condenser, where it is converted back into water, and used as desired.
      From my understanding, as you said, “Back press. extraction” type turbine, I believe that the steam is tapped from some intermediate stage for any uses, and the rest is used for work/power output. It might not be employing any condensing units, to obtain water from steam. The steam might be simply discharged or used as desired. Hence the name.
      You can get in touch with field experts in your organisation, or contact the OEM, who will provide you with all the things that you need.
      Hope this helps.

      -Akshay Bhargava

Leave a Reply

Your email address will not be published. Required fields are marked *