steam traps on a non-condensing turbine 1

[rafal2015]

Hi, can anyone explain what the purpose of steam traps is on a non-condensing turbine where the exhaust steam is still over 100'C superheated? would that be for start-up only?

 

[dbill74]

Startup/shut down, even during normal operations getting any condensation that happens to form out of the system is needed. Better safe than sorry. There are plenty of examples of condensate induced water hammer damaging systems and in same cases killing people. Just google "condensate induced water hammer".

 

[mk3223]

It's a safety concern. To have a steam trap, so the operation won't expose to the flashing steam when draining the hot condensate as needed.

 

[rafal2015]

Thanks for your answers. What I'm trying to understand is if there is any condensate expected during normal operation. Given the high degree of superheat both on inlet and outlet of the turbine my guess was that the purpose of the traps is only to drain at start-up. I was hoping someone would be able to confirm and perhaps shed some more light on this.

 

[Compositepro]

Realy? After the responses so far you want more reassurances of some kind? Try engaging your imagination and knowledge of basic physics.

All surfaces lose heat though insulation. Water collects in low spots. Heat does not travel downward through water well, at all.

 

[rafal2015]

i don't doubt there is need for the traps for start-up or shut down. what I wonder is if there is any condensation during normal operation. given the high degree of superheat in theory there shouldn't be any

 

[crshears]

To answer the question posed in the OP, it is reasonable to believe that once everything is warmed up and operating at a point well above the saturation temperature for that pressure as per Molier charts and steam tables, condensation will not NORMALLY occur.

Unexpected water ingress from things like failed spray desuperheaters, etc., will of course throw all such suppositions out the window.

No offense, but as compositepro has alluded to, I find it odd that you even needed to ask this question, as it's such basic stuff...

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[rafal2015]

indeed, didn't get anything other than basic stuff in the replies... was hoping someone with actual practical knowledge would have something interesting to say... by the way, can't imagine why you'd ever have a desuperheater upstream of a turbine...

 

[georgeverghese]

Things always go wrong during transients, so another thing to look at to confirm that there will be no condensation on the turbine exhaust during normal ops would be to analyse this case when all of the following happen at the same time during "normal ops":

a) Some transient in feed superheated steam when the degree of superheat is lower than normal
b) Backpressure on this non condensing turbine exhaust is abnormally high due to some sudden reduction in downstream demand.
c) The turbine is operating at high isentropic efficiency.

 

[stgrme]

When starting a "cold" turbine (non-condensing or condensing type), designed for normal operation with superheated steam, there will be condensation which must be removed. As the turbine warms up, condensation will be reduced, and eventually will cease. Therefore, a reliable system for removal of this condensate must be provided for use during start-up.

According to ASME TDP-1-2013 (Prevention of Water Damage to Steam Turbines Used for Electric Power Generation: Fossil-Fueled Plants), steam traps are not a satisfactory means for removing this condensate. According to the ASME document, a “critical” drain must use a power-operated drain valve as the primary means of condensate removal. A steam trap may be used in parallel with a power-operated drain valve. I recommend that you obtain a copy of ASME TDP-1-2013 if you do not already have it. The ASME document covers the entire steam turbine cycle.

For a steam turbine which operates in the superheated region, the turbine manufacturer will recommend closing the power-operated drain valves at a certain load for any drains from the turbine itself. Typically, I would expect closure in the range of 15% to 20% load. However, you should check the manufacturer’s recommendations for your specific application.

If the installation consists of one boiler and one turbine, the boiler may not deliver the design temperature at the turbine inlet during low-load operation. The conditions at the exhaust of your non-condensing turbine should be checked to determine if the exhaust steam will still be superheated under low-load conditions.

Best of luck!

 

[rafal2015]

Thanks for your replies, I'll read through ASME TDP-1-2013 as per your advice stgrme.