11 replies to this topic

[CSNK]

Hi all,

 

Can anybody suggest on how to measure dryness fraction of steam in actual operation of steam turbine at the exhaust conditions where only pressure and temperature are known?

Edited by CSNK, 29 October 2018 - 05:53 AM.

[shan]

It will be 100% steam if the exhaust steam temperature is higher than the saturation temperature at the corresponding pressure.

 

It will be 0% steam if the exhaust steam temperature is lower than the saturation temperature at the corresponding pressure.

 

If the exhaust steam is at the saturation temperature at the corresponding pressure, you have to know the steam turbine inlet flow, inlet temperature, inlet pressure, turbine power, and turbine efficiency to determine the dryness of the exhaust steam.

[Bobby Strain]

Why do you need to measure the quality? There are probably special sample systems for this. Or, maybe you can find some company who can do this for you.

 

Bobby

[CSNK]

Thanks shan and bobby for the answer,

 

Hi shan, 

 

Turbine power and efficiency are not known for actual operation, only flow / p / t are known.

 

Hi bobby,

 

Actually, we wanted to know the power generated by turbine and hence quality of steam is required.

You mean to say, there is no theoretical way to calculate the turbine power with known exhaust pressure and temperature.

 

Regards,

[breizh]

Hi ,

What about the Mollier diagram for steam or the calculator attached.

 

https://www4.eere.en..._tool/propSteam

 

Hope this going to help you..

Breizh

[Bobby Strain]

Maybe it's time you told us the whole story. Steam inlet and exhaust conditions, including flow. What's on the output shaft? Speed? Anything else you have, like turbine description.

 

Bobby

[CSNK]

Hi, Breizh, 

 

This mollier diagram i have referred earlier also, but i think some thing like enthalpy or power or dryness fraction is required to know the power of the turbine. But in our case, i know only Pressure and temperature.

 

 

Hi Bobby,

 

Its condensing type turbine.

Steam inlet conditions:  - flow is 121 TPH, Pressure is 20.3 barA, and temperature is 294 Deg C.

Exhaust: Flow will be same, Pressure is 0.142 BarA, and temperature is 51 Deg C.

This turbine is delivering power to the connected compressor.

RPM of the turbine is 4595.

 

Right now due to non-availability of the dryness fraction, what i have done is calculated compressor required power based on process conditions. Taken same power for turbine and back calculated dryness fraction.

 

My intention was that how do i know power generated from turbine independently as there could be some inefficiency in turbine or inconsistency in the compressor side power calculation also. 

 

Regards,

Edited by CSNK, 30 October 2018 - 11:13 PM.

[breizh]

Hi ,

I believe you did not go through the calculator submitted otherwise you would have found one about steam turbine .

 

https://www4.eere.en...ol/equipTurbine

 

Hope this helping you .

 

Breizh

[Technical Bard]

CSNK - using P&T alone you CANNOT know the vapour fraction of the stream.  In most condensing steam turbines with subatmospheric exhaust, the steam leaving the turbine will be two-phase.

 

You need to know the adiabatic efficiency of the turbine to calculate the exhaust quality.  The other option for estimating the quality of the exhaust steam is to measure the cooling duty in the condenser (measure flow and temperature in/out of cooling water).  This can be used to estimate exhaust quality - but it's not going to be very accurate because a flow measurement on the cooling water is probably +/-1% and the temperature measurements will be +/- 1ºF.

[CSNK]

Thanks Breizh,

 

It is asking for efficiency, which we don't know and we want to calculate efficiency based on only P/T.

 

Thanks Bard,

 

We also thought of calculating condenser duty but there is very few information available on CW side.Hence, it looks as if by calculating compressor side power is the best and reasonable estimation of dryness fraction or turbine efficiency.

 

Regards,

Edited by CSNK, 01 November 2018 - 12:47 AM.

[shan]

Even if you figure out the turbine exhaust steam dryness, you are still  unable to determine the turbine mechanical efficiency by the ratio of the turbine inlet steam enthalpy and exhaust steam enthalpy because the latent heat from steam condensing may not convert the mechanical energy while condensed water droplets on the turbine blade may increase load for the turbine rotation. 

[Technical Bard]

You can't do that.  The efficiency and exhaust quality are linked - you must know one of them independently of pressure and temperature. 

 

Don't you have a turbine performance curve from the manufacturer?