Backpressure

[tool32]

I work in the electrical production field,and was wondering if anyone can explain the theory behind backpressure in a condensing turbine,and why it is so important.Thanks in advance.

 

[Metalguy]

Think of the steam flow across the last stage, and how big those blades are. It's the pressure differential that counts.

 

[poetix99]

In informal technical usage concerning turbomachinery, "back pressure" is the pressure downstream of a stage.

The turbine's exhaust pressure is often referred to as the back pressure. The term is more commonly applied to "non-condensing" machines, where the exhaust pressure is greater than local atmosphreric pressure, but is (again, informally) used for condensing machines as well

In condensing steam turbines, although the exhaust pressure is below atmoshperic pressure, it is not a COMPLETE vacuum. The value of the exhaust pressure is directly related to the amount of energy that is available from the steam to the turbine for useful power. The lower the "back pressure" (i.e. exhaust pressure), the more energy is available to the machine. It is for that reason that the "back pressure" is so important.

[It is worth mentioning that, for many reasons, a steam turbine should be operated at the conditions for which it is designed. That fact that steam energy is thermodynamically available doesn't mean that it can be utilized by the turbine. Exhaust pressure cannot be arbitrarily lowered for the sake of more power.]

If you have an hour or so, and nothing better to do, you could check thread794-33900 which features a very long, very tangential, very diverse discussion of the question vexing philosophers over the ages: "What is back-pressure?". You could, but I urge caution; you might be worse off afterward than beforehand.

 

[paragmpatel]

For the Mechanical terms Back pressure turbine is that produce Electrical powerand some steam which is extracted form the turbine isused for the process purpose. In some process like paperIndustries,Petrochemical Ind. Soda ash Ind.they have required steam for the process purpose& they have required power to run the drives.so,Back pressure machine is essencial. We can get power & Steam with the Back pressure machine.
onething the specific steam consumption is high for the Back pressure machine compare to pure condensing machine Because we are not using total enthalphy (Energy) of steam to generate the power. The reaming energy of steam giving to process purpose. Use only saturated steam for the process purpose because the saturated steam has a more enthalphy compared to the Super heated steam.
Use pure condensing machine where the dry process industries like cement Ind. They don't required steam forthe process. The specific steam consumption of steam is low compare to the back pressure machine, used all energy of steam. Refer to the Ranckile cycle.As per standard rules condensing machine has 4.1to 4.5 ton/Hour steam consumption for producing 1 MW power.
Regards,
parag.