5 replies to this topic

[arkae]

hi everyone..

 

i have a question.

 

Please find the sketch enclosed for Steam and Water Analysis system(SWAS).

 

In the attached drawing i have shown only a single sample point. But total there are 13 sample points.

 

The temperatures and pressures for some of the sampling points are as follows

 

1.superheated steam temperature- 568 degc and pressure- 142 barg

 

2.HP drum boiler water temperature - 340.8 and pressure - 146.5 barg

 

and so on.

 

 

A blow down header is provided which will be operated only during startup and that too only one sample point at a time will be drained.

 

The flowrate of each sample drain is 50 lph.

 

This drain header cannot be discharged directly to a concrete sump becuase concrete cannot withstand the high temperatures.

 

iam thinking of providing a Tundish(funnel drain)(indicated in attached drawing in green colour).

 

With Tundish the steam temperature can be brought down to 100degc max at atmospheric pressure.

 

 

My only doubt is that will the steam temperature will reduce suddenly to 100 degc if pressure is atmospheric.?

Attached Files

•  SWAS.pdf   106.83KB   30 downloads

[TS1979]

I think your question is about the condensate temperature instead of steam temperature. You can not sample steam that way because the way you show to sample steam is too dangerous with that high pressure. Steam may be out the pipe at choked flow condition (sonic velocity). Even if you just sample condensate, it is not a safe way to do that because of high pressure. Of course, the condensate will reduce to 100C due to evaporation. Condensate is valuable pure water and you should let the condensate back to Boiler Feed Water System instead of discharging the condensate to a sump.

 

If you just want to sample some condensate, a pot design will be better to collect the condensate in a pot and vent the steam to the atmosphere from the pot and collect the remain condensate.

[thorium90]

I would suggest you have your steam sample line go through a small exchanger using cooling water to cool down the steam to liquid, then have a regulator to reduce the pressure then a needle valve to throttle the flow. If you do not want to have a cooling water line and exchanger installed, just have the tubing coiled up and immersed in water.

 

Firstly if you just let it down to atmospheric pressure, some of your sample will flash off. This will evidently affect your readings. Therefore, you have to cool everything down and take the entire volume for your sample, not just those that did not flash off... It will definitely not be accurate if any of your steam sample flashed off. Cool it down to <40C, thats my best advice for a proper sampling regime.

Edited by thorium90, 20 June 2013 - 01:35 AM.

[arkae]

Hi
I think I couldnot explain the question exactly.

During startup, the sample cannot be analysed directly. The sample has to be drained before being analysed to remove any materials entrapped in the pipe.This drain is Discharged to the blowdown header.
My question is since the temperature and pressure is high, I want to cool down this drain before sending to sump.
Hence iam thinking of using tundish so that the pressure decreases and becomes atmospheric. I agree that steam flashes.
But if the pressure reduces to atmospheric wiill the temperature drop suddenly to 100 degc.?
Thanks for your reply in advance.

[thorium90]

Yes, when the pressure drops to atmospheric, the temperature drops to 100C too. The additional heat is removed as heat of vaporization when the remainder of the steam flashes off.

[arkae]

Thankyou very much sir for clarifying my doubt..