Use of pressure letdown for dry steam generation
Use of pressure letdown for dry steam generation
(OP)
Dear all,
I am after some general views on this..We are installing a new waste heat boiler shell next year. We can rate the new shell to a higher design pressure and would like to ensure dry stream..
We are considering raising steam at higher pressure and letting the pressure down to ensure dry steam rather than using a demister pad or steam seperator...or internal dry pipe inside the generator
Would this be a recommendated way to ensure dry steam ?
I am after some general views on this..We are installing a new waste heat boiler shell next year. We can rate the new shell to a higher design pressure and would like to ensure dry stream..
We are considering raising steam at higher pressure and letting the pressure down to ensure dry steam rather than using a demister pad or steam seperator...or internal dry pipe inside the generator
Would this be a recommendated way to ensure dry steam ?





RE: Use of pressure letdown for dry steam generation
Before considering the efficiency of a pressure letdown, may I ask whether you have checked if the TDS of the entrained water droplets may, at the end, surpass the max. allowable TDS of the steam ? I believe there are standards limiting the TDS of boiler water, and of steam, depending on pressure. See, for example, thread794-87628 and the links therein.
RE: Use of pressure letdown for dry steam generation
I think you will get better results with a steam separator, because even if you get a minor upset in the boiler (ie: foaming and carryover) the separator will remove this liquid safely, while simply reducing the pressure will only illiminate a very small amount of liquid and you will still have the potential for poor quality steam and water hammer after the boiler.
Also, the separators are static devices needing little or no maintenance, and PRV's require maintenance, replacement, etc.....
RE: Use of pressure letdown for dry steam generation
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rgs
RE: Use of pressure letdown for dry steam generation
I tend to aggre a steam seperator or internal demister or external demister does seem the way to go.. but I want peoples advice to validate it...
But i'm not sure how applicable this is to my case which uses a heat transfer fluid in a waste heat boiler.. steam generated on the shell side.. my consern with an integral superheater is i've seen lots of articles which refer to superheater damage from steam impingement and suggest that a steam demister is required upstream..
RE: Use of pressure letdown for dry steam generation
RE: Use of pressure letdown for dry steam generation
Harvey
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: Use of pressure letdown for dry steam generation
Example: take 150 psi steam at 98% quality (2% moisture) and the enthalpy is 1178.41. Expand that out to 125 psi and the quality only goes to 0.983.
RE: Use of pressure letdown for dry steam generation
rmw
RE: Use of pressure letdown for dry steam generation
Our vapour comes out quite dry (at least I don't get compaints from the users)